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Vol 11: The Classics
THE ORIGIN OF SPECIES
BY CHARLES DARWIN
WITH INTRODUCTIONS AND NOTES
VOLUME 11
P F COLLIER & SON
NEW YORK
Copyright, 1909
By P. F. Collier & Son
Designed, Printed, and Bound at
Cfte Collier Pcesg, ^eto gorb
"But with regard to the material world, we can at
least go so far as this — we can perceive that events are
brought about not by insulated interpositions of Divine
power, exerted in each particular case, but by the estab-
lishment of general laws."
Whewell: Bridgewater Treatise.
"The only distinct meaning of the word 'natural' is
stated, fixed or settled; since what is natural as much
requires and presupposes an intelligent agent to render
it so, i.e., to effect it continually or at stated times, as
what is supernatural or miraculous does to effect it for
once."
BuTLEB: Analogy of Revealed Religion.
"To conclude, therefore, let no man out of a weak con-
ceit of sobriety, or an ill-applied moderation, think or
maintain, that a man can search too far or be too well
studied in the book of God's word, or in the book of
God's works; divinity or philosophy; but rather let men
endeavour an endless progress or proficience in both."
Bacon: Advancement of Learning.
Down, Beckenham, Kent,
First Edition, November 2Jfth, 1859.
Sixth Edition, January, 1872.
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CONTENTS
PAGE
EDITOR'S INTRODUCTION 5
AN HISTORICAL SKETCH
Op the Progress of Opinion on the Origin of Species 9
INTRODUCTION 21
CHAPTER I
Variation under Domestication 25
CHAPTER II
Variation under Nature 58
CHAPTER III
Struggle for Existence 76
CHAPTER IV
Natural Selection; or the Survival op the Fittest 93
CHAPTER V
Laws op Variation 145
CHAPTER VI
Difficulties op the Theory . . . o . . 178
3
4 CONTENTS
CHAPTER VII PAGE
Miscellaneous Objections to the Theory op Natural
Selection 219
CHAPTER VIII
Instinct 262
CHAPTER IX
Hybridism 298
CHAPTER X
On the Imperfection op the Geological Record . 333
CHAPTER XI
On the Geological Succession op Organic Beings . 364
CHAPTER XII
Geographical Distribution 395
CHAPTER XIII
Geographical Distribution — continued .... 427
CHAPTER XIV
Mutual Affinities op Organic Beings: Morphology:
Embryology: Rudimentary Organs .... 450
CHAPTER XV
Recapitulation and Conclusion 499
GLOSSARY .531
INDEX 541
INTRODUCTORY NOTE
Charles Robert Darwin, horn at Shrewsbury, England, on
February 12, 1809, came of a family of remarkable intellectual
distinction which is still sustained in the present generation. His
father zvas a successful physician with remarkable powers of
observation, and his grandfather was Erasmus Darwin, the well-
knozvn author of "The Botanic Garden." He went to school at
Shrewsbury, where he failed to profit from the strict classical
curriculum there in force; nor did the regular professional
courses at Edinburgh University, where he spent two years study-
ing medicine, succeed in rousing his interest. In 1827 he was
entered at Christ's College, Cambridge, to study for the B. A.
degree, preparatory to entering the Church; but while there
his friendship with Henslow, the professor of botany, led to his
enlarging his general scientific knowledge and finally to his
joining the expedition of the "Beagle" in the capacity of natural-
ist. From this Darzmn returned after a voyage of five years
with a vast first-hand knowledge of geology and zoology, a
reputation as a successful collector, and, most i)iiportant of all,
with the germinal ideas of his theory of evolution. The next
few years were spent in working up the materials he had col-
lected; but his health gave signs of breaking, and for the rest
of his life he suffered constantly, but without complaint. With
extraordinary courage and endurance he took up a life of
seclusion and methodical regularity, and accomplished his colossal
results in spite of the most severe physical handicap. He had
married in 1839, and three years later he withdrew from London
to the little village of Down, about sixteen miles out, where he
spent the rest of his life. His custom, which was almost a
method, was to work till he was on the verge of complete collapse,
and then to take a holiday just sufficient to restore him to zvorking
condition.
As early as 1842 Darwin had thrown into rough form the out-
lines of his theory of evolution, but the enormous extent of the
investigations he engaged in for the purpose of testing it led
to a constant postponing of publication. Finally in June, 1838,
A. R. Wallace sent him a manuscript containing a statement
of an identical theory of thf origin of species, wliich had been
S
6 INTRODUCTORY NOTE
arrived at entirely independently. On the advice of Lyell, the
geologist, and Hooker, the botanist, Wallace's paper and a letter
of Darwin's of the previous year, in which he had outlined his
theory to Asa Gray, were read together on July i, 1858, and
published by the Linncean Society. In November of the follow-
ing year "The Origin of Species" was published, and the great
battle was begun between the old science and the new. This
work was followed in 1868 by his "Variation of Animals and
Plants under Domestication," that in turn by the "Descent of
Man" in 1871, and that again by "The Expression of the Emo-
tions in Man and Animals." Each of these books was the elabo-
ration or complement of a section of its predecessor. The later
years of Darwin's life were chiefly devoted to botanical research,
and resulted in a series of treatises of the highest scientific value.
He died at Down on April 19, 1882, and is buried in Westminster
Abbey.
The idea of the evolution of organisms, so far from originating
with Darwin, is a very old one. Glimpses of it appear in the
ancient Greek philosophers, especially Empedocles and Aristotle;
modern philosophy from Bacon onward shows an increasing
definiteness in its grasp of the conception; and in the age pre-
ceding Darwin's, Buffon, Erasmus Darwin, and Lamarck had
given it a fairly concrete expression. As we approach the date
of the publication of "The Origin of Species" adherence to the
doctrine not only by naturalists but by poets, such as Goethe,
becomes comparatively frequent ; and in the six years before the
joint announcement of Darwin and Wallace, Herbert Spencer
had been supporting and applying it vigorously in the field of
psychology.
To these partial anticipations, however, Darivin owed little.
When he became interested in the problem, the doctrine of the
fixity of species was still generally held ; and his solution occurred
to him mainly as the result of his ozcn observation and thinking.
Speaking of the voyage of the "Beagle," he says, "On my return
home in the autumn of 1836 I immediately began to prepare my
journal for publication, and then saw how many facts indicated
the common descent of species. ... In July (1837) I opened
my first note-book for facts in relation to the Origin of Species,
about which I had long reflected, and never ceased working for
the next twenty years. . . . Had been greatly struck from about
INTRODUCTORY NOTE 7
the vwnth of previous March on character of South American
fossils, and species on Galapagos Archipelago. These facts
(especially latter) origin of all my views." Again, "In October
(iSjS), that is fifteen months after I had begun my systematic
inquiry, I happened to read for amusement 'Malthus on Popu-
lation,' and being well prepared to appreciate the struggle for
existence which everywhere goes on from long-continued ob-
servation of the habits of animals and plants, it at once struck me
that under these circumstances favorable variations would tend
to be preserved, and unfavorable ones to be destroyed. The
result of this would be the formation of new species. Here
then I had at last got a theory by which to work."
From these statements by Darwin himself we can see how far
it is from being the case that he merely gathered the ripe fruit
of the labors of his predecessors. All progress is continuous,
and Darwin, like other men, built on the foundations laid by
others; but to say this is not to deny him originality in the only
vital sense of that word. And the importance of his contribution
— in verifying the doctrine of descent, in interpreting and apply-
ing it, and in revealing its bearings on all departments of the
investigation of nature — is proved by the fact that his work
opened a new epoch in science and philosophy. As Huxley said,
''Whatever be the ultimate verdict of posterity upon this or that
opinion which Mr. Darwin has propounded; whatever adumbra-
tions or anticipations of his doctrines may be found in the writ-
ings of his predecessors; the broad fact remains that, since the
publication and by reason of the publication of 'The Origin of
Species' the fundamental conceptions and the aims of the students
of living Nature have been completely changed."
The present year (igog) has seen the celebration of the hun-
dredth anniversary of Darwin's birth and the fiftieth anniversary
of the publication of his great work. Among the numerous ex-
pressions of honor and gratitude which the world of science has
poured upon his memory, none is more significant than the vol-
ume on "Darwin and Modern Science" which has been issued by
the press of his old University of Cambridge. In this are col-
lected nearly thirty papers by the leaders of modern science
dealing w-ith the influence of Darwin upon various fields of
thought atrd research, and zsAth the later developments and modi-
fications of his conclusions. Biology, in many different depart-
8 INTRODUCTORY NOTE
ments. Anthropology, Geology, Psychology, Philosophy, Soci-
ology, Religion, Language, History, and Astronomy are all repre-
sented, and the mere enumeration suggests the colossal nature
of his achievement and its results.
Yet the spirit of the man was almchst as wonderful as his work.
His disinterestedness, his modesty, and his absolute fairness
were not only beautiful in themselves, but remain as a proof of
the importance of character in intellectual labor. Here is his
own frank and candid sumtning up of his abilities: "My success as
a man of science, whatever this may have amounted to, has been
detertnined, as far as I can judge, by complex and diversified
mental qualities and conditions. Of these, the most important
have been — the love of science — unbounded patience in long re-
flecting over any subject — industry in obsewing and collecting
facts — and a fair share of invention as well as of common sense.
With such moderate abilities as I possess, it is truly surprising
that I should have influenced to a considerable extent the belief
of scientific men on some important paints."
AN HISTORICAL SKETCH
OF THE PROGRESS OF OPINION ON
THE ORIGIN OF SPECIES
PREVIOUSLY TO THE PUBLICATION OF
THE FIRST EDITION OF THIS WORK
I WILL here give a brief sketch of the progress of opinion on
the Origin of Species. Until recently the great majority of
naturalists believed that species were immutable productions,
and had been separately created. This view has been ably
maintained by many authors. Some few naturalists, on the
other hand, have believed that species undergo modification,
and that the existing forms of life are the descendants by
true generation of pre-existing forms. Passing over allu-
sions to the subject in the classical writers,* the first author
who in modern times has treated it in a scientific spirit was
Buffon. But as his opinions fluctuated greatly at different
periods, and as he does not enter on the causes or means of
the transformation of species, I need not here enter on
details.
*Aristotle, in his ' Physicae Auscultationes' (lib. 2, cap. 8, s. 2), after
remarking that rain does not fall in order to make the corn grow, any more
than it falls to spoil the farmer's corn when threshed out of doors, applies
the same argument to organisation; and adds (as translated by Mr. Clair
Grece, who first pointed out the passage to me), "So what hinders the dif-
ferent parts [of the body] from having this merely accidental relation in
nature? as the teeth, for example, grow by necessity, the front ones sharp,
adapted for dividing, and the grinders flat, and serviceable for masticating
the food; since they were not made for the sake of this, but it was the
result of accident. And in like manner as to the other parts in which there
appears to exist an adaptation to an end. Wheresoever, therefore, all things
together (that is all the parts of one whole) happened like as if they were
made for the sake of something, these were preserved, having been appro-
priately constituted by an internal spontaneity; and whatsoever things were
not thus constituted, perished, and still perish." We here see the principle
of natural selection shadowed forth, but how little Aristotle fully compre-
hended the principle, is shown 'by his remarks on the formation of the teeth.
10 HISTORICAL SKETCH
Lamarck was the first man whose conclusions on the
subject excited much attention. This justly-celebrated nat-
uralist first published his views in 1801 ; he much enlarged
them in 1809 in his 'Philosophic Zoologique,' and subse-
quently, in 1815, in the Introduction to his 'Hist. Nat. des
Animaux sans Vertebres.' In these works he upholds the
doctrine that species, including man, are descended from
other species. He first did the eminent service of arousing at-
tention to the probability of all change in the organic, as well
as in the inorganic world, being the result of law, and not of
miraculous interposition. Lamarck seems to have been chiefly
led to his conclusion on the gradual change of species, by the
difficulty of distinguishing species and varieties, by the almost
perfect gradation of forms in certain groups, and by the
analogy of domestic productions. With respect to the means
of modification, he attributed something to the direct action
of the physical conditions of life, something to the crossing of
already existing forms, and much to use and disuse, that is,
to the effects of habit. To this latter agency he seems to
attribute all the beautiful adaptations in nature ; — such as the
long neck of the giraffe for browsing on the branches of
trees. But he likewise believed in a law of progressive de-
velopment ; and as all the forms of life thus tend to progress,
in order to account for the existence at the present day of
simple productions, he maintains that such forms are now
spontaneously generated.*
Geoffroy Saint-Hilaire, as is stated in his 'Life,' written
by his son, suspected, as early as 1795, that what we call
species are various degenerations of the same type. It was
* I have^ taken the date of the first publication of Lamarck from Isid.
Geoffroy Saint-Hilaire's (' Hist. Nat. Generale,* torn, ii, p. 405, 1859)
excellent history of opinion on this subject. In this work a full account is
given of Buflon's conclusions on the same subject. It is curious how largely
my grandfather. Dr. Erasmus Darwin, anticipated the views and erroneous
grounds of opinion of Lamarck in his ' Zoonomia ' (vol. i. pp. 500-510), pub-
lished in 1794. According to Isid. Geoffroy there is no doubt that Goethe
was an extreme partisan of similar views, as shown in the Introduction to a
work written in 1794 and 1795, but not published till long afterwards: he
has pointedly remarked (' Goethe als Naturforscher,' von Dr. Karl Meding,
s. 34) that the future question for naturalists will be how, for instance,
cattle got their horns, and not for what they are used. It is rather a singu»
lar instance of the manner in which similar views arise at about the same
time, that Goethe in Germany, Dr. Darwin in England, and Geoffroy Saint-
Hilaire (as we shall immediately see) in France, came to the same conclu-
sion on the origin of species, in the years 1794-5.
HISTORICAL SKETCH U
not until 1828 that he published his conviction that the same
forms have not been perpetuated since the origin of all
things. Geoffroy seems to have relied chiefly on the condi-
tion of life, or the "monde amhiant" as the cause of change.
He was cautious in dravi^ing conclusions, and did not believe
that existing species are now undergoing modification; and,
as his son adds, "C'est done un probleme a reserver
entierement a I'avenir, suppose meme que I'avenir doive avoir
prise sur lui."
In 1813, Dr. W. C. Wells read before the Royal Society
'An Account of a White female, part of whose skin re-
sembles that of a Negro'; but his paper was not published
until his famous ' Two Essays upon Dew and Single Vision'
appeared in 1818. In this paper he distinctly recognises the
principle of natural selection, and this is the first recognition
which has been indicated ; but he applies it only to the races of
man, and to certain characters alone. After remarking that
negroes and mulattoes enjoy an immunity from certain trop-
ical diseases, he observes, firstly, that all animals tend to vary
in some degree, and, secondly, that agriculturists improve
their domesticated animals by selection ; and then, he adds,
but what is done in this latter case "by art, seems to be done
with equal efficacy, though more slowly, by nature, in the
formation of varieties of mankind, fitted for the country
which they inhabit. Of the accidental varieties of man,
which would occur among the first few and scattered inhab-
itants of the middle regions of Africa, some one would be
better fitted than the others to bear the diseases of the coun-
try. This race would consequently multiply, while the others
would decrease; not only from their inability to sustain the
attacks of disease, but from their incapacity of contending
with their more vigorous neighbours. The colour of this
vigorous race I take for granted, from what has been already
said, would be dark. But the same disposition to form varie-
ties still existing, a darker and a darker race would in the
course of time occur: and as the darkest would be the best
fitted for the climate, this would at length become the most
prevalent, if not the only race, in the particular country in
which it had originated." .He then extends these same views
to the white inhabitants of colder climates. I am indebted
12 HISTORICAL SKETCH
to Mr. Rowley, of the United States, for having called my
attention, through Mr. Brace, to the above passage in Dr.
Wells' work.
The Hon. and Rev. W. Herbert, afterwards Dean of Man-
chester, in the fourth volume of the ' Horticultural Trans-
actions,' 1822, and in his work of the 'Amaryllidaceae'
(^^37> PP- 19. 339) » declares that "horticultural experiments
have established, beyond the possibility of refutation, that
botanical species are only a higher and more permanent class
of varieties." He extends the same view to animals. The
Dean believes that single species of each genus were created
in an originally highly plastic condition, and that these have
produced, chiefly by intercrossing, but likewise by variation,
all our existing species.
In 1826 Professor Grant, in the concluding paragraph in
his well-known paper ('Edinburgh Philosophical Journal,'
vol. xiv. p. 283) on the Spongilla, clearly declares his belief
that species are descended from other species, and that they
become improved in the course of modification. This same
view was given in his 55th Lecture, published in the ' Lancet '
in 1834.
In 1831 Mr. Patrick Matthew published his work on 'Naval
Timber and Arboriculture/ in which he gives precisely the
same view on the origin of species as that (presently to be
alluded to) propounded by Mr. Wallace and myself in the
'Linnean Journal,' and as 'hat enlarged in the present volume.
Unfortunately the view was given by Mr. Matthew very brief-
ly in scattered passages in an Appendix to a work on a differ-
ent subject, so that it remained unnoticed until Mr. Matthew
himself drew attention to it in the 'Gardener's Chronicle,' on
April 7th, i860. The differences of Mr. Matthew's view from
mine are not of much importance : he seems to consider that
the world was nearly depopulated at successive periods, and
then re-stocked; and he gives as an alternative, that new
forms may be generated " without the presence of any mould
or germ of former aggregates." I am not sure that I under-
stand some passages ; but it seems that he attributes much
influence to the direct action of the conditions of life. He
clearly saw, however, the full force of the principle of natural
selection.
HISTORICAL SKETCH 13
The celebrated geologist and naturalist, Von Buch, in his
excellent 'Description Physique des Isles Canaries' (1836,
p. 147), clearly expresses his belief that varieties slowly be-
come changed into permanent species, which are no longer
capable of intercrossing.
Rafinesque, in his 'New Flora of North America,' pub-
lished in 1836, wrote (p. 6) as follows: — "All species might
have been varieties once, and many varieties are gradually
becoming species by assuming constant and peculiar charac-
ters;" but farther on (p. 18) he adds, "except the original
types or ancestors of the genus."
In 1843-44 Professor Haldeman ('Boston Journal of Nat.
Hist. U. States,' vol. iv. p. 468) has ably given the arguments
for and against the hypothesis of the development and modi-
fication of species : he seems to lean towards the side of
change.
The 'Vestiges of Creation' appeared in 1844. In the tenth
and much improved edition (1853) the anonymous author
says (p. 155) : — "The proposition determined on after much
consideration is, that the several series of animated beings,
from the simplest and oldest up to the highest and most re-
cent, are, under the providence of God, the results, first, of an
impulse which has been imparted to the forms of life, ad-
vancing them, in definite times, by generation, through grades
of organisation terminating in the highest dicotyledons and
vertebrata, these grades being few in number, and generally
marked by intervals of organic character, which we find to
be a practical difficulty in ascertaining affinities ; second, of
another impulse connected with the vital forces, tending, in
the course of generations, to modify organic structures in
accordance with external circumstances, as food, the nature
of the habitat, and the meteoric agencies, these being the
' adaptations ' of the natural theologian." The author ap-
parently believes that organisation progresses by sudden
leaps, but that the effects produced by the conditions of life
are gradual. He argues with much force on general grounds
that species are not immutable productions. But I cannot see
how the two supposed " impulses " account in a scientific
sense for the numerous- and beautiful co-adaptations which
we see throughout nature; I cannot see that we thus gain
14 HISTORICAL SKETCH
any insight how, for instance, a woodpecker has become
adapted to its peculiar habits of life. The work, from its
powerful and brilliant style, though displaying in the earlier
editions little accurate knowledge and a great want of
scientific caution, immediately had a very wide circulation.
In my opinion it has done excellent service in this country in
calling attention to the subject, in removing prejudice, and
in thus preparing the ground for the reception of analogous
views.
In 1846 the veteran geologist M. J. d'Omalius d'Halloy
published in an excellent though short paper (' Bulletins de
I'Acad. Roy. Bruxelles,' tom. xiii. p. 581) his opinion that
it is more probable that new species have been produced by
descent with modification than that they have been separately
created: the author first promulgated this opinion in 1831.
Professor Owen, in 1849 (' Nature of Limbs,' p. 86),
wrote as follows : — " The archetypal idea was manifested in
the flesh under diverse such modifications, upon this planet,
long prior to the existence of those animal species that
actually exemplify it. To what natural laws or secondary
causes the orderly succession and progression of such organic
phenomena may have been committed, we, as yet, are igno-
rant." In his Address to the British Association, in 1858,
he speaks (p. li.) of "the axiom of the continuous operation
of creative power^, or of the ordained becoming of living
things." Farther on (p. xc), after referring to geographical
distribution, he adds, " These phenomena shake our confi-
dence in the conclusion that the Apteryx of New Zealand
and the Red Grouse of England were distinct creations in and
for those islands respectively. Always, also, it may be well
to bear in mind that by the word * creation ' the zoologist
means ' a process he knows not what.' " He amplifies this
idea by adding that when such cases as that of the Red
Grouse are " enumerated by the zoologist as evidence of dis-
tinct creation of the bird in and for such islands, he chiefly
expresses that he knows not how the Red Grouse came to be
there, and there exclusively ; signifying also, by this mode of
expressing such ignorance, his belief that both the bird and
the islands owed their origin to a great first Creative Cause."
If we interpret these sentences given in the same Address,
HISTORICAL SKETCH 15
one by the other, it appears that this eminent philosopher felt
in 1858 his confidence shaken that the Apteryx and the Red
Grouse first appeared in their respective homes, "he knew
not how,'' or by some process "he knew not what."
This Address was delivered after the papers by Mr. Wal-
lace and myself on the Origin of Species, presently to be
referred to, had been read before the Linnean Society. When
the first edition of this work was published, I was so com-
pletely deceived, as were many others^ by such expressions as
" the continuous operation of creative power," that I included
Professor Owen with other palaeontologists as being firmly
convinced of the immutability of species; but it appears
(' Anat. of Vertebrates,' vol. iii. p. 796) that this was on my
part a preposterous error. In the last edition of this work
I inferred, and the inference still seems to me perfectly just,
from a passage beginning with the words " no doubt the type-
form," &c. (Ibid. vol. i. p. XXXV.), that Professor Owen
admitted that natural selection may have done something in
the formation of a new species; but this it appears (Ibid. vol.
iii. p. 798) is inaccurate and without evidence. I also gave
some extracts from a correspondence between Professor
Owen and the Editor of the ' London Review,' from which it
appeared manifest to the Editor as well as to myself, that
Professor Owen claimed to have promulgated the theory of
natural selection before I had done so; and I expressed my
surprise and satisfaction at this announcement; but as far
as it is possible to understand certain recently published pas-
sages (Ibid. vol. iii. p. 798) I have either partially or wholly
again fallen into error. It is consolatory to me that others
find Professor Owen's controversial writings as difficult to
understand and to reconcile with each other, as I do. As far
as the mere enunciation of the principle of natural selection
is concerned, it is quite immaterial whether or not Professor
Owen preceded me, for both of us, as shown in this historical
sketch, were long ago preceded by Dr. Wells and Mr.
Matthews.
M. Isidore Geoffroy Saint-Hilaire, in his lectures delivered
in 1850 (of which a Resume appeared in the 'Revue et Mag.
de Zoolog..' Jan. 1851), brjefly gives his reason for believing
that specific characters " sent fixes, pour chaque espece, tant
16 HISTORICAL SKETCH
qu'elle se perpetue ou milieu des memes circonstances : ils se
modifient, si les circonstances ambiantes viennent a changer."
"En resume, I'ohservation des animaux sauvages demontre
deja la variabilite limit ee des especes. Les experiences sur
les animaux sauvages devenus domestiques, et sur les ani-
maux domestiques redevenus sauvages, la demontrent plus
clairement encore. Ces memes experiences prouvent, de
plus, que les differences produites peuvent etre de valeur
generique." In his 'Hist. Nat. Generale' (tom ii. p. 340,
1859) he amplifies analogous conclusions.
From a circular lately issued it appears that Dr. Freke, in
1851 ('Dublin Medical Press,' p. 322), propounded the doc-
trine that all organic beings have descended from one pri-
mordial form. His grounds of belief and treatment of the
subject are wholly different from mine; but as Dr. Freke
has now^ (1861) published his Essay on the 'Origin of Spe-
cies by means of Organic Affinity,' the difficult attempt to
give any idea of his views would be superfluous on my part.
Mr. Herbert Spencer, in an Essay (originally published in
the 'Leader,' March, 1852, and republished in his 'Essays,' in
1858), has contrasted the theories of the Creation and the
Development of organic beings with remarkable skill and
force. He argues from the analogy of domestic productions,
from the changes which the embryos of many species under-
go, from the difficulty of distinguishing species and varie-
ties, and from the principle of general gradation, that species
have been modified; and he attributes the modification to
the change of circumstances. The author (1855) has also
treated Psychology on the principle of the necessary acquire-
ment of each mental power and capacity by gradation.
In 1852 M. Naudin, a distinguished botanist, expressly
stated, in an admirable paper on the Origin of Species
('Revue Horticole,' p. 102; since partly republished in the
'Nouvelles Archives du Museum,' tom. i. p. 171), his belief
that species are formed in an analogous manner as varieties
are imder cultivation ; and the latter process he attributes to
man's power of selection. But he does not show how selec-
tion acts under nature. He believes, like Dean Herbert, that
species, when nascent, were more plastic than at present.
He lays weight on what he calls the principle of finality;
HISTORICAL SKETCH 17
"puissance mysteriuse, indeterminee ; fatalite pour les uns;
pour les autres, volonte providentielle, dont Taction inces-
sante sur les etres vivants determine, a toutes les epoques de
I'existence du monde, la forme, le volume, et la duree de
chacun d'eux, en raison de sa destinee dans I'orde de choses
dont il fait partie. C'est cette puissance qui harmonise
chaque membre a I'ensemble, en I'appropriant a la fonction
qu'il doit remplir dans I'organisme general de la nature, fonc-
tion qui est pour lui sa raison d'etre."*
In 1853 a celebrated geologist, Count Keyserling ('Bulletin
de la Soc. Geolog.,' 2nd Ser., tom. x. p. 357), suggested that
as new diseases, supposed to have been caused by some
miasma, have arisen and spread over the world, so at certain
periods the germs of existing species may have been chem-
ically affected by circumambient molecules of a particular
nature, and thus have given rise to new forms.
In this same year, 1853, Dr. Schaaffhausen published an
excellent pamphlet ('Verhand. des Naturhist. Vereins der
Preuss. Rheinlands,' &c.), in which he maintains the devel-
opment of organic forms on the earth. He infers that many
species have kept true for long periods, whereas a few have
become modified. The distinction of species he explains by
the destruction of intermediate graduated forms. "Thus
living plants and animals are not separated from the extinct
by new creations, but are to be regarded as their descendants
through continued reproduction."
A well-known French botanist, M. Lecoq, writes in 1854
('Etudes sur Geograph. Bot.,' tom, i. p. 250), "On voit que
nos recherches sur la fixite ou la variation de I'espece, nous
conduisent directement aux idees emises, par deux hommes
justement celebres, Geoffroy Saint-Hilaire et Goethe." Some
•From references in Bronn's ' Untersuchungen iiber die Entwickelungs-
Gesetze,' it appears that the celebrated botanist and palaeontologist Unger
published, in 1852, his belief that species undergo development and modifica-
tion. D'alton, likewise, in Pander and Dalton's work on Fossil Sloths, ex-
pressed, in 1821, a similar belief. Similar views have, as is well known,
been maintained by Oken in his mystical ' Natur-Philosophie.' From_ other
references in Godron's work ' Sur I'Espece,' it seems that Bory St. Vincent,
Burdach, Poiret, and Fries, harve all admitted that new species are con-
tinually being produced.
I may add, that of the thirty-four authors named in this Historical Sketch,
who believe in the modification of species, or at least disbelieve in separate
acts of creation, twenty-seven have written on special branches of natural
history or geology.
IS HISTORICAL SKETCH
other passages scattered through M. Lecoq's large work,
make it a httle doubtful how far he extends his views on the
modification of species.
The 'Philosophy of Creation' has been treated in a mas-
terly manner by the Rev. Baden Powell, in his 'Essays on the
Unity of Worlds,' 1855. Nothing can be more striking than
the manner in which he shows that the introduction of new
species is "a regular, not a casual phenomenon," or, as Sir
John Herschel expresses it, "a natural in contradistinction to
a miraculous process."
The third volume of the 'Journal of the Linnean Society'
contains papers, read July ist, 1858, by Mr. Wallace and my-
self, in which, as stated in the introductory remarks to this
volume, the theory of Natural Selection is promulgated by
Mr. Wallace with admirable force and clearness.
Von Baer, towards whom all zoologists feel so profound a
respect, expressed about the year 1859 (see Prof. Rudolph
Wagner, 'Zoologisch-Anthropologische Untersuchungen,'
1861, s 51) his conviction, chiefly grounded on the laws of
geograpliical distribution, that forms now perfectly distinct
have descended from a single parent-form.
In June, 1859, Professor Huxley gave a lecture before the
Royal Institution on the 'Persistent Types of Animal Life.'
Referring to such cases, he remarks, "It is difficult to com-
prehend the meaning of such facts as these, if we suppose
t-hat each species of animal and plant, or each great type of
organisation, was formed and placed upon the surface of the
globe at long intervals by a distinct act of creative power;
and it is well to recollect that such an assumption is as un-
supported by tradition or revelation as it is opposed to the
general analogy of nature. If, on the other hand, we view
'Persistent Types' in relation to that hypothesis which sup-
poses the species living at any time to be the result of the
gradual modification of pre-existing species a hypothesis
which, though unproven, and sadly damaged by some of its
supporters, is yet the only one to which physiology lends any
countenance; their existence would seem to show that the
amount of modification which living beings have undergone
during geological time is but very small in relation to the
whole series of changes which they have suffered."
HISTORICAL SKETCH 19
In December, 1859, Dr. Hooker published his 'Introduction
to the Australian Flora.' In the first part of this great work
he admits the truth of the descent and modification of spe-
cies, and supports this doctrine by many original observa-
tions.
The first edition of this work was published on November
24th, 1859, and the second edition on January 7th, i860.
INTRODUCTION
When on board H.M.S. 'Beagle,' as naturalist, I was much struck
with certain facts in the distribution of the organic beings in-
habiting South America, and in the geological relations of the
present to the past inhabitants of that continent. These facts, as
will be seen in the latter chapters of this volume, seemed to throw
some light on the origin of species — that mystery of mysteries, as
it has been called by one of our greatest philosophers. On my
return home, it occurred to me, in 1837, that something might
perhaps be made out on this question by patiently accumulating
and reflecting on all sorts of facts which could possibly have any
bearing on it. After five years' work I allowed myself to specu-
late on the subject, and drew up some short notes; these I
enlarged in 1844 into a sketch of the conclusions, which then
seemed to me probable ; from that period to the present day I
have steadily pursued the same object. I hope that I may be
excused for entering on these personal details, as I give them to
show that I have not been hasty in coming to a decision.
My work is now (1859) nearly finished; but as it will take me
many more years to complete it, and as my health is far from
strong, I have been urged to publish this Abstract. I have more
especially been induced to do this, as Mr. Wallace, who is now
studying the natural history of the Malay archipelago, has arrived
at almost exactly the same general conclusions that I have on the
origin of species. In 1858 he sent me a memoir on this subject,
with a request that I would forward it to Sir Charles Lyell, who
sent it to the Linnean Society, and it is published in the third
volume of the Journal of that Society. Sir C Lyell and Dr.
Hooker, who both knew of my work — the latter having read my
sketch of 1844 — honoured me by thinking it advisable to publish,
with Mr. Wallace's excellent memoir, some brief extracts from
my manuscripts.
This Abstract, which I now publish, must necessarily be im-
perfect. I cannot here give references and authorities for my
several statements ; and I must trust to the reader reposing some
confidence in my accuracy. No doubt errors will have crept in,
though I hope I have always been cautious in trusting to good
21
22 INTRODUCTION
authorities alone. I can here give only the general conclusions at
which I have arrived, with a few facts in illustration, but which,
I hope, in most cases will suffice. No one can feel more sensible
than I do of the necessity of hereafter publishing in detail all the
facts, with references, on which my conclusions have been
grounded; and I hope in a future work to do this. For I am
well aware that scarcely a single point is discussed in this volume
on which facts cannot be adduced, often apparently leading to
conclusions directly opposite to those at which I have arrived.
A fair result can be obtained only by fully stating and balancing
the facts and arguments on both sides of each question; and this
is here impossible.
I much regret that want of space prevents my having the satis-
faction of acknowledging the generous assistance which I have
received from very many naturalists, some of them personally
unknown to me. I cannot, however, let this opportunity pass
without expressing my deep obligations to Dr. Hooker, who, for
the last fifteen years, has aided me in every possible way by his
large stores of knowledge and his excellent judgment.
In considering the Origin of Species, it is quite conceivable that
a naturalist, reflecting on the mutual affinities of organic beings,
on their embryological relations, their geographical distribution,
geological succession, and other such facts, might come to the con-
clusion that species have not been independently created, but had
descended, like varieties, from other species. Nevertheless, such
a conclusion, even if well founded, would be unsatisfactory, until
it could be shown how the innumerable species inhabiting this
world have been modified, so as to acquire that perfection of
structure and coadaptation which justly excites our admiration.
Naturalists continually refer to external conditions, such as
climate, food, etc., as the only possible cause of variation. In one
limited sense, as we shall hereafter see, this may be true ; but
it is preposterous to attribute to mere external conditions, the
structure, for instance, of the woodpecker, with its feet, tail, beak,
and tongue, so admirably adapted to catch insects under the bark
of trees. In the case of the mistletoe, which draws its nourish-
ment from certain trees, which has seeds that must be trans-
ported by certain birds, and which has flowers with separate
sexes absolutely requiring the agency of certain insects to bring
pollen from one flower to the other, it is equally preposterous to
INTRODUCTION 23
account for the structure of this parasite, with its relations to
several distinct organic beings, by the effects of external condi-
tions, or of habit, or of the volition of the plant itself.
It is, therefore, of the highest importance to gain a clear in-
sight into the means of modification and coadaptation. At the
commencement of my observations it seemed to me probable that
a careful study of domesticated animals and of cultivated plants
would offer the best chance of making out this obscure problem.
Nor have I been disappointed; in this and in all other perplexing
cases I have invariably found that our knowledge, imperfect
though it be, of variation under domestication, afforded the best
and safest clue. I may venture to express my conviction of the
high value of such studies, although they have been very com-
monly neglected by naturalists.
From these considerations, I shall devote the first chapter of
this Abstract to Variation under Domestication. We shall thus
see that a large amount of hereditary modification is at least pos-
sible; and, what is equally or more important, we shall see how
great is the power of man in accumulating by his Selection suc-
cessive slight variations. I will then pass on the variability of
species in a state of nature; but I shall, unfortunately, be
compelled to treat this subject far too briefly, as it can be treated
properly only by giving long catalogues of facts. We shall, how-
ever, be enabled to discuss what circumstances are most favour-
able to variation. In the next chapter the Struggle for Existence
amongst all organic beings throughout the world, which inevitably
follows from the high geometrical ratio of their increase, will be
considered. This is the doctrine of Malthus, applied to the whole
animal and vegetable kingdoms. As many more individuals of
each species are born than can possibly survive ; and as, conse-
quently, there is a frequently recurrent struggle for existence, it
follows that any being, if it vary however slightly in any manner
profitable to itself, under the complex and sometimes varying con-
ditions of life, will have a better chance of surviving, and thus be
naturally selected. From the strong principle of inheritance, any
selected variety will tend to propagate its new and modified form.
This fundamental subject of Natural Selection will be treated
at some length in the fourth chapter ; and we shall then see how
Natural Selection almost inevitaJ^ly causes much Extinction of the
less improved forms of life, and leads to what I have called Diver-
24 INTRODUCTION
gence of Character. In the next chapter I shall discuss the com-
plex and little known laws of variation. In the five succeeding
chapters, the most apparent and gravest difficulties in accepting
the theory will be given : namely, first, the difficulties of transi-
tions, or how a simple being or a simple organ can be changed
and perfected into a highly developed being or into an elaborately
constructed organ; secondly, the subject of Instinct, or the mental
powers of animals ; thirdly. Hybridism, or the infertility of species
and the fertility of varieties when intercrossed; and fourthly, the
imperfection of the Geological Record. In the next chapter I
shall consider the geological succession of organic beings through-
out time ; in the twelfth and thirteenth, their geographical distri-
bution throughout space ; in the fourteenth, their classification or
mutual affinities, both when mature and in an embryonic condi-
tion. In the last chapter I shall give a brief recapitulation of the
whole work, and a few concluding remarks.
No one ought to feel surprise at much remaining as yet unex-
plained in regard to the origin of species and varieties, if he make
due allowance for our profound ignorance in regard to the mutual
relations of the many beings which live around us. Who can
explain why one species ranges widely and is very numerous, and
why another allied species has a narrow range and is rare? Yet
these relations are of the highest importance, for they determine
the present welfare, and, as I believe, the future success and
modification of every inhabitant of this world. Still less do we
know of the mutual relations of the innumerable inhabitants of
the world during the many past geological epochs in its history.
Although much remains obscure, and will long remain obscure, I
can entertain no doubt, after the most deliberate study and dis-
passionate judgment of which I am capable, that the view which
most naturalists until recently entertained, and which I formerly
entertained — namely, that each species has been independently
created — is erroneous. I am fully convinced that species are not
immutable ; but that those belonging to what are called the same
genera are lineal descendants of some other and generally extinct
species, in the same manner as the acknowledged varieties of any
one species are the descendants of that species. Furthermore, I
am convinced that Natural Selection has been the most important,
but not the exclusive, means of modification.
ORIGIN OF SPECIES
CHAPTER I
Variation under Domestication
Causes of variability — Efifects of habit and the use or disuse of parts^
Correlated variation— Inheritance — Character of domestic varie-
ties — Difficulty of distinguishing between varieties and species —
Origin of domestic varieties from one or more species — Domestic
pigeons, their differences and origin — Principles of selection, an-
ciently followed, their effects — Methodical and unconscious
selection — Unknown origin of our domestic productions — Circum-
stances favourable to man's power of selection
CAUSES OF variability
WHEN we compare the individuals of the same
variety or sub-variety of our older cultivated plants
and animals, one of the first points which strikes
us is, that they generally differ more from each other than
do the individuals of any one species or variety in a state of
nature. And if we rei^ect on the vast diversity of the plants
and animals which have been cultivated, and which have
varied during all ages under the most different climates and
treatment, we are driven to conclude that this great varia-
bility is due to our domestic productions having been raised
under conditions of life not so uniform as, and somewhat
different from, those to which the parent species had been
exposed under nature. There is, also, some probability in
the view propounded by Andrew Knight, that this variability
may be partly connected with excess of food. It seems clear
that organic beings must be exposed during several genera-
tions to new conditions to cause any great amount of varia-
tion; and that, when the organisation has once begun to
vary, it generally continues varying for many generations.
No case is on record of a variable organism ceasing to vary
under cultivation. Our oldest cultivated plants, such as
2S
26 ORIGIN OF SPECIES
wheat, still yield new varieties : our oldest domesticated ani-
mals are still capable of rapid improvement or modification.
As far as I am able to judge, after long attending to the
subject, the conditions of life appear to act in two ways, —
directly on the whole organisation or on certain parts alone,
and indirectly by affecting the reproductive system. With re-
spect to the direct action, we must bear in mind that in every
case, as Professor Weismann has lately insisted, and as I have
incidentally shown in my work on 'Variation under Domesti-
cation,' there are two factors; namely, the nature of the
organism, and the nature of the conditions. The former
seems to be much the more important; for nearly similar
variations sometimes arise under, as far as we can judge,
dissimilar conditions; and, on the other hand, dissimilar
variations arise under conditions which appear to be nearly
uniform. The effects on the offspring are either definite or
indefinite. They may be considered as definite when all or
nearly all the offspring of individuals exposed to certain
conditions during several generations are modified in the
same manner. It is extremely difficult to come to any con-
clusion in regard to the extent of the changes which have
been thus definitely induced. There can, however, be little
doubt about many slight changes, — such as size from the
amount of food, colour from the nature of the food, thick-
ness of the skin and hair from climate, etc. Each of the
endless variations which we see in the plumage of our fowls
must have had some efficient cause; and if the same cause
were to act uniformly during a long series of generations on
many individuals, all probably would be modified in the
same manner. Such facts as the complex and extraordinary
out-growths which variably follow from the insertion of a
minute drop of poison by a gall-producing insect, show us
what singular modifications might result in the case of plants
from a chemical change in the nature of the sap.
Indefinite variability is a much more common result of
changed conditions than definite variability, and has prob-
ably played a more important part in the formation of our
domestic races. We see indefinite variability in the endless
slight peculiarities which distinguish the individuals of the
same species, and which cannot be accounted for by inher-
VARIATION UNDER DOMESTICATION 27
ilance from either parent or from some more remote ances-
tor. Even strongly-marked differences occasionally appear
in the young of the same litter, and in seedlings from the
same seed capsule. At long intervals of time, out of millions
of individuals reared in the same country and fed on nearly
the same food, deviations of structure so strongly pro-
nounced as to deserve to be called monstrosities arise ; but
monstrosities cannot be separated by any distinct line from
slighter variations. All such changes of structure, whether
extremely slight or strongly marked, which appear amongst
many individuals living together, may be considered as the
indefinite effects of the conditions of life on each individual
organism, in nearly the same manner as the chill afifects dif-
ferent men in an indefinite manner, according to their state
of body or constitution, causing coughs or colds, rheumatism,
or inflammation of various organs.
With respect to what I have called the indirect action of
changed conditions, namely, through the reproductive sys-
tem of being affected, we may infer that variability is thus
induced, partly from the fact of this system being extremely
sensitive to any change in the conditions, and partly
from the similarity, as Kolreuter and others have re-
marked, between the variability which follows from the
crossing of distinct species, and that which may be ob-
served with plants and animals when reared under new
or unnatural conditions. Many facts clearly show how
eminently susceptible the reproductive system is to very
slight changes in the surrounding conditions. Nothing is
more easy than to tame an animal, and few things more diffi-
cult than to get it to breed freely under confinement, even
when the male and female unite. How many animals there
are which will not breed, though kept in an almost free state
in their native country ! This is generally, but erroneously,
attributed to vitiated instincts. Many cultivated plants dis-
play the utmost vigour, and yet rarely or never seed ! In
some few cases it has been discovered that a very trifling
change, such as a little more or less water at some particular
period of growth, will determine whether or not a plant will
produce seeds. I cannot here give the details which I have
collected and elsewhere published on this curious subject;
28 ORIGIN OF SPECIES
but to show how singular the laws are which determine the
reproduction of animals under confinement, I may mention
that carnivorous animals, even from the tropics, breed in
this country pretty freely under confinement, with the excep-
tion of the plantigrades or bear family, which seldom pro-
duce young; whereas carnivorous birds, with the rarest ex-
ceptions, hardly ever lay fertile eggs. Many exotic plants
have pollen utterly worthless, in the same condition as in the
most sterile hybrids. When, on the one hand, we see domes-
ticated animals and plants, though often weak and sickly,
breeding freely under confinement; and when, on the other
hand, we see individuals, though taken young from a state of
nature perfectly tamed, long-lived and healthy (of which I
could give numerous instances), yet, having their repro-
ductive system so seriously affected by unperceived causes as
to fail to act, we need not be surprised at this system, when
it does act under confinement, acting irregularly, and pro-
ducing offspring somewhat unlike their parents. I may add,
that as some organisms breed freely under the most unnat-
ural conditions (for instance, rabbits and ferrets kept in
hutches), showing that their reproductive organs are not
easily affected ; so will some animals and plants withstand
domestication or cultivation, and vary very slightly — per-
haps hardly more than in a state of nature.
Some naturalists have maintained that all variations are
connected with the act of sexual reproduction ; but this is
certainly an error; for I have given in another work a long
list of "sporting plants," as they are called by gardeners; —
that is, of plants which have suddenly produced a single bud
with a new and sometimes widely different character from
that of the other buds on the same plant. These bud-varia-
tions, as they may be named, can be propagated by grafts,
offsets, etc., and sometimes by seed. They occur rarely
under nature, but are far from rare under culture. As a
single bud out of the many thousands, produced year after
year on the same tree under uniform conditions, has been
known suddenly to assume a new character ; and as buds on
distinct trees, growing under different conditions, have some-
times yielded nearly the same variety — for instance, buds on
peach-trees producing nectarines, and buds on common roses
VARIATION UNDER DOMESTICATION 29
producing moss-roses — we clearly see that the nature of the
condition is of subordinate importance in comparison with
the nature of the organism in determining each particular
form of variation — perhaps of not more importance than the
nature of the spark, by which a mass of combustible matter
is ignited, has in determining the nature of the flames.
EFFECTS OF HABIT AND OF THE USE OR DISUSE OF PARTS;
CORRELATED VARIATION; INHERITANCE
Changed habits produce an inherited effect, as in the pe-
riod of the flowering of plants when transported from one
climate to another. With animals the increased use or dis-
use of parts has had a more marked influence ; thus I find in
the domestic duck that the bones of the wing weigh less and
the bones of the leg more, in proportion to the whole skele-
ton, than do the same bones in the wild duck; and this
change may be safely attributed to the domestic duck flying
much less, and walking more, than its wild parents. The
great and inherited development of the udders in cows and
goats in countries where they are habitually milked, in com-
parison with these organs in other countries, is probably
another instance of the effects of use. Not one of our do-
mestic animals can be named which has not in some country
drooping ears ; and the view which has been suggested that
the drooping is due to disuse of the muscles of the ear, from
the animals being seldom much alarmed, seems probable.
Many laws regulate variation, some few of which can be
dimly seen, and will hereafter be briefly discussed. I will
here only allude to what may be called correlated variation.
Important changes in the embryo or larva will probably en-
tail changes in the mature animal. In monstrosities, the
correlations between quite distinct parts are very curious;
and many instances are given in Isidore Geoffroy St.
Plilaire's great work on this subject. Breeders believe that
long limbs are almost always accompanied by an elongated
head. Some instances of correlation are quite whimsical:
thus cats which are entirely white and have blue eyes are
generally deaf ; but it has been lately stated by Mr. Tait that
this is confined to the males. Colour and constitutional pecu-
30 ORIGIN OF SPECIES
liarities go together, of which many remarkable cases could
be given amongst animals and plants. From facts collected
by Heusinger, it appears that white sheep and pigs are in-
jured by certain plants, whilst dark-coloured individuals es-
cape : Professor Wyman has recently communicated to me
a good illustration of this fact; on asking some farmers in
Virginia how it was that all their pigs were black, they in-
formed him that the pigs ate the paint-root (Lachnanthes),
which colored their bones pink, and which caused the hoofs
of all but the black varieties to drop off; and one of the
"crackers" (i.e. Virginia squatters) added, "we select the
black members of a litter for raising, as they alone have a
good chance of living." Hairless dogs have imperfect teeth ;
long-haired and coarse-haired animals are apt to have, as is
asserted, long or many horns; pigeons with feathered feet
have skin between their outer toes ; pigeons with short beaks
have small feet, and those with long beaks large feet. Hence
if man goes on selecting, and thus augmenting, any pecu-
liarity, he will almost certainly modify unintentionally other
parts o£ the structure, owing to the mysterious laws of cor-
relation.
The results of the various, unknown, or but dimly under-
stood laws of variation are infinitely complex and diversified.
It is well worth while carefully to study the several treatises
on some of our old cultivated plants, as on the hyacinth,
potato, even the dahlia, etc.; and it is really surprising to
note the endless points of structure and constitution in which
the varieties and sub-varieties differ slightly from each
other. The whole organisation seems to have become
plastic, and departs in a slight degree from that of the
parental type.
Any variation which is not inherited is unimportant for
us. But the number and diversity of inheritable deviations
of structure, both those of slight and those of considerable
physiological importance, are endless. Dr. Prosper Lucas's
treatise, in two large volumes, is the fullest and the best on
this subject. No breeder doubts how strong is the tendency
to inheritance; that like produces like is his fundamental be-
lief: doubts have been thrown on this principle only by theo-
retical writers. When any deviation of structure often
VARIATION UNDER DOMESTICATION 31
appears, and we see it in the father and child, we cannot tell
whether it may not be due to the same cause having acted on
both; but when amongst individuals, apparently exposed to
the same conditions, any very rare deviation, due to some
extraordinary combination of circumstances, appears in the
parent — say, once amongst several million individuals — and
it reappears in the child, the mere doctrine of chances almost
compels us to attribute its reappearance to inheritance.
Every one must have heard of cases of albinism, prickly
skin, hairy bodies, etc., appearing in several members of the
same family. If strange and rare deviations of structure are
really inherited, less strange and commoner deviations may
be freely admitted to be inheritable. Perhaps the correct
way of viewing the whole subject would be, to look at the
inheritance of every character whatever as the rule, and
non-inheritance as the anomaly.
The laws governing inheritance are for the most part
unknown. No one can say why the same peculiarity in dif-
ferent individuals of the same species, or in different species,
is sometimes inherited and sometimes not so; why the child
often reverts in certain characters to its grandfather or
grandmother or more remote ancestor ; why a peculiarity is
often transmitted from one sex to both sexes, or to one sex
alone, more commonly but not exclusively to the like sex.
It is a fact of some importance to us, that peculiarities ap-
pearing in the males of our domestic breeds are often trans-
mitted, either exclusively or in a much greater degree, to
the males alone. A much more important rule, which I
think may be trusted, is that, at whatever period of life a
peculiarity first appears, it tends to reappear in the offspring
at a corresponding age, though sometimes earlier. In many
cases this could not be otherwise ; thus the inherited pecu-
liarities in the horns of cattle could appear only in the off-
spring when nearly mature; peculiarities in the silkworm
are known to appear at the corresponding caterpillar or
cocoon stage. But hereditary diseases and some other facts
make me believe that the rule has a wider extension, and
that, when there is no apparent reason why a peculiarity
should appear at any particular age, yet that it does tend to
appear in the offspring at the same period at which it first
32 ORIGIN OF SPECIES
appeared in the parent. I believe this rule to be of the
highest importance in explaining the laws of embryology.
These remarks are of course confined to the first appearance
of the peculiarity, and not to the primary cause which may
have acted on the ovules or on the male element; in nearly
the same manner as the increased length of the horns in
the offspring from a short-horned cow by a long-horned
bull, though appearing late in life, is clearly due to the male
element.
Having alluded to the subject of reversion, I may here
refer to a statement often made by naturalists — namely,
that our domestic varieties, when run wild, gradually but
invariably revert in character to their aboriginal stocks.
Hence it has been argued that no deductions can be drawn
from domestic races to species in a state of nature. I have
in vain endeavoured to discover on what decisive facts the
above statement has so often and so boldly been made.
There would be great difficulty in proving its truth: we may
safely conclude that very many of the most strongly marked
domestic varieties could not possibly live in a wild state.
In many cases we do not know what the aboriginal stock
was, and so could not tell whether or not nearly perfect re-
version had ensued. It would be necessary, in order to pre-
vent the effects of intercrossing, that only a single variety
should have been turned loose in its new home. Neverthe-
less, as our varieties certainly do occasionally revert in some
of their characters to ancestral forms, it seems to me not
improbable that if we could succeed in naturalising, or were
to cultivate, during many generations, the several races, for
instance, of the cabbage, in very poor soil (in which case,
however, some effect would have to be attributed to the
definite action of the poor soil), that they would, to a large
extent, or even wholly, revert to the wild aboriginal stock.
Whether or not the experiment would succeed, is not of
great importance for our line of argument; for by the ex-
periment itself the conditions of life are changed. If it
could be shown that our domestic varieties manifested a
strong tendency to reversion, — that is, to lose their acquired
characters, whilst kept under the same conditions, and whilst
kept in a considerable body, so that free intercrossing might
A — HC XI
CHARACTER OF DOMESTIC VARIETIES 33
check, by blending together, any slight deviations in their
structure, in such case, I grant that we could deduce nothing
from domestic varieties in regard to species. But there is
not a shadow of evidence in favour of this view: to assert
that we could not breed our cart- and race-horses, long- and
short-horned cattle, and poultry of various breeds, and escu-
lent vegetables, for an unlimited number of generations,
would be opposed to all experience.
CHARACTER OF DOMESTIC VARIETIES; DIFFICULTY OF
DISTINGUISHING BETWEEN VARIETIES AND
species; ORIGIN OF DOMESTIC
VARIETIES FROM ONE OR
MORE SPECIES
When we look to the hereditary varieties or races of otir
domestic animals and plants, and compare them with closely
allied species, we generally perceive in each domestic race,
as already remarked, less uniformity of character than in
true species. Domestic races often have a somewhat mon-
strous character ; by which I mean, that, although differing
from each other, and from other species of the same genus,
in several trifling respects, they often differ in an extreme
degree in some one part, both when compared one with an-
other, and more especially when compared with the species
under nature to which they are nearest allied. With these
exceptions (and with that of the perfect fertility of varieties
when crossed, — a subject hereafter to be discussed), domes-
tic races of the same species differ from each other in the
same manner as do the closely allied species of the same
genus in a state of nature, but the differences in most cases
are less in degree. This must be admitted as true, for the
domestic races of many animals and plants have been ranked
by some competent judges as the descendants of aboriginally
distinct species, and by other competent judges as mere
varieties. If any well-marked distinction existed between a
domestic race and a species, this source of doubt would not
so perpetually recur. It has often been stated that domestic
races do not differ from each other in characters of generic
value. It can be shown that this statement is not correct;
•B — HCXI
34 ORIGIN OF SPECIES
but naturalists differ much in determining what characters
are of generic value; all such valuations being at present
empirical. When it is explained how genera originate under
nature, it will be seen that we have no right to expect often
to find a generic amount of difference in our domesticated
races.
In attempting to estimate the amount of structural differ-
ence between allied domestic races, we are soon involved
in doubt, from not knowing whether they are descended from
one or several parent species. This point, if it could be
cleared up, would be interesting; if, for instance, it could be
shown that the greyhound, bloodhound, terrier, spaniel, and
bulldog, which we all know propagate their kind truly, were
the offspring of any single species, then such facts would
have great weight in making us doubt about the immuta-
bility of the many closely allied natural species — for in-
stance, of the many foxes — inhabiting different quarters of
the world. I do not believe, as we shall presently see, that
the whole amount of difference between the several breeds
of the dog has been produced under domestication; I believe
that a small part of the difference is due to their being
descended from distinct species. In the case of strongly
marked races of some other domesticated species, there
is presumptive or even strong evidence, that all are descended
from a single wild stock.
It has often been assumed that man has chosen for domes-
tication animals and plants having an extraordinary inherent
tendency to vary, and likewise to withstand diverse climates.
I do not dispute that these capacities have added largely to
the value of most of our domesticated productions; but how
could a savage possibly know, when he first tamed an ani-
mal, whether it would vary in succeeding generations, and
whether it would endure other climates? Has the little
variability of the ass and goose, or the small power of en-
durance of warmth by the reindeer, or of cold by the com-
mon camel, prevented their domestication? I cannot doubt
that if other animals and plants, equal in number to our
domesticated productions, and belonging to equally diverse
classes and countries, were taken from a state of nature,
and could be made to breed for an equal number of genera-
CHARACTER OP DOMESTIC VARIETIES 35
tions under domestication, they would on an average vary as
largely as the parent species of our existing domesticated
productions have varied.
In the case of most of our anciently domesticated animals
and plants, it is not possible to come to any definite con-
clusion, whether they are descended from one or several
wild species. The argument mainly relied on by those who
believe in the multiple origin of our domestic animals is,
that we find in the most ancient times, on the monuments
of Egypt, and in the lake-habitations of Switzerland, much
diversity in the breeds ; and that some of these ancient breeds
closely resemble, or are even identical with, those still ex-
isting. But this only throws far backwards the history of
civilisation, and shows that animals were domesticated at a
much earlier period than has hitherto been supposed. The
lake-inhabitants of Switzerland cultivated several kinds of
wheat and barley, the pea, the poppy for oil, and flax; and
they possessed several domesticated animals. They also
carried on commerce with other nations. All this clearly
shows, as Heer has remarked, that they had at this early
age progressed considerably in civilisation; and this again
implies a long continued previous period of less advanced
civilisation, during which the domesticated animals, kept
by different tribes in different districts, might have varied
and given rise to distinct races. Since the discovery of
flint tools in the superficial formations of many parts of
the world, all geologists believe that barbarian man existed
at an enormously remote period and we know that at the
present day there is hardly a tribe so barbarous, as not to
have domesticated at least the dog.
The origin of most of our domestic animals will prob-
ably for ever remain vague. But I may here state, that,
looking to the domestic dogs of the whole world, I have,
after a laborious collection of all known facts, come to the
conclusion that several wild species of Canidae have been
tamed, and that their blood, in some cases mingled together,
flows in the veins of our domestic breeds. In regard to
sheep and goats 1 can form no decided opinion. From facts
communicated to me by Mr., Blyth, on the habits, voice, con-
stitution, and structure of the humped Indian cattle, it is
36 ORIGIN OF SPECIES
almost certain that they are descended from a different abo-
riginal stock from our European cattle and some competent
judges believe that these latter have had two or three wild
progenitors, — whether or not these deserve to be called
species. This conclusion, as well as that of the specific dis-
tinction between the humped and common cattle, may, in-
deed, be looked upon as established by the admirable re-
searches of Professor Riitimeyer. With respect to horses,
from reasons which I cannot here give, I am doubtfully
inclined to believe, in opposition to several authors, that all
the races belong to the same species. Having kept nearly
all the English breeds of the fowl alive, having bred and
crossed them, and examined their skeletons, it appears to
me almost certain that all are the descendants of the wild
Indian fowl, Gallus bankiva; and this is the conclusion of
Mr. Blyth, and of others who have studied this bird in
India. In regard to ducks and rabbits, some breeds of which
differ much from each other, the evidence is clear that they
are all descended from the common wild duck and rabbit.
The doctrine of the origin of our several domestic races
from several aboriginal stocks, has been carried to an absurd
extreme by some authors. They believe that every race
which breeds true, let the distinctive characters be ever so
slight, has had its wild prototype. At this rate there must
have existed at least a score of species of wild cattle, as
many sheep, and several goats, in Europe alone, and several
even within Great Britain. One author believes that there
formerly existed eleven wild species of sheep peculiar to
Great Britain ! When we bear in mind that Britain has now
not one peculiar mammal, and France but few distinct from
those of Germany, and so with Hungary, Spain, etc., but
that each of these kingdoms possesses several peculiar breeds
of cattle, sheep, etc., we must admit that many domestic
breeds must have originated in Europe ; from whence other-
wise could they have been derived? So it is in India. Even
in the case of the breeds of the domestic dog throughout the
world, which I admit are descended from several wild spe-
cies, it cannot be doubted that there has been an immense
amount of inherited variation ; for who will believe that
animals closely resembling the Italian greyhound, the blood-
DOMESTIC PIGEONS 37
hound, the bull-dog, pug-dog, or Blenheim spaniel, etc. — so
unlike all wild Canidae — ever existed in a state of nature?
It has often been loosely said that all our races of dogs
have been produced by the crossing of a few aboriginal spe-
cies; but by crossing we can only get forms in some degree
intermediate between their parents; and if we account for
our several domestic races by this process, we must admit
the former existence of the most extreme forms, as the
Italian greyhound, bloodhound, bull-dog, etc., in the wild
state. Moreover, the possibility of making distinct races by
crossing has been greatly exaggerated. Many cases are on
record, showing that a race may be modified by occasional
crosses, if aided by the careful selection of the individuals
which present the desired character; but to obtain a race
intermediate between two quite distinct races, would be very
difficult. Sir J. Sebright expressly experimented with this
object and failed. The offspring from the first cross be-
tween two pure breeds is tolerably and sometimes (as I have
found with pigeons) quite uniform in character, and every-
thing seems simple enough; but when these mongrels are
crossed one with another for several generations, hardly
two of them are alike, and then the difficulty of the task
becomes manifest.
BREEDS OF THE DOMESTIC PIGEON, THEIR DIFFERENCES AND
ORIGIN
Believing that it is always best to study some special
group, I have, after deliberation, taken up domestic pigeons.
I have kept every breed which I could purchase or obtain,
and have been most kindly favoured with skins from several
quarters of the world, more especially by the Hon. W. Elliot
from India, and by the Hon. C. Murray from Persia. Many
treatises in different languages have been published on pig-
eons, and some of them are very important, as being of con-
siderable antiquity. I have associated with several eminent
fanciers, and have been permitted to join two of the London
Pigeon Clubs. The diversity of the breeds is something as-
tonishing. Compare the English carrier and the short-faced
tbimbler, and see the wonderful difference in their beaks.
38 ORIGIN OF SPECIES
entailing corresponding differences in their skulls. The
carrier, more especially the male bird, is also remarkable
from the wonderful development of the carunculated skin
about the head; and this is accompanied by greatly elongated
eyelids, very large external orifices to the nostrils, and a
wide gape of mouth. The short-faced tumbler has a beak
in outline almost like that of a finch; and the common
tumbler has the singular inherited habit of flying at a great
height in a compact flock, and tumbling in the air head over
heels. The runt is a bird of great size, with long massive
beak and large feet ; some of the sub-breeds of runts have
very long necks, others very long wings and tails, others
singularly short tails. The barb is allied to the carrier, but,
instead of a long beak, has a very short and broad one. The
pouter has a much elongated body, wings, and legs; and
its enormously developed crop, which it glories in inflating,
may well excite astonishment and even laughter. The turbit
has a short and conical beak, with a line of reversed feathers
down the breast; and it has the habit of continually expand-
ing, slightly, the upper part of the oesophagus. The Jacobin
has the feathers so much reversed along the back of the neck
that they form a hood ; and it has, proportionally to its
size, elongated wing and tail feathers. The trumpeter and
laugher, as their names express, utter a very different coo
from the other breeds. The fantail has thirty or even forty
tail-feathers, instead of twelve or fourteen — the normal
number in all the members of the great pigeon family : these
feathers are kept expanded, and are carried so erect, that in
good birds the head and tail touch : the oil-gland is quite
aborted. Several other less distinct breeds might be
specified.
In the skeletons of the several breeds, the development of
the bones of the face in length and breadth and curvature
differs enormously. The shape, as well as the breadth and
length of the ramus of the lower jaw, varies in a highly
remarkable manner. The caudal and sacral vertebrae vary
in number; as does the number of the ribs, together with
their relative breadth and the presence of processes. iThe size
and shape of the apertures in the sternum are highly vari-
able; so is the degree of divergence and relative size of the
DOMESTIC PIGEONS 39
two arms of the furcula. The proportional width of the
gape of mouth, the proportional length of the eyelids, of the
orifice of the nostrils, of the tongue (not always in strict
correlation with the length of beak), the size of the crop
and of the upper part of the oesophagus; the development
and abortion of the oil-gland; the number of the primary
wing and caudal feathers; the relative length of the wing
and tail to each other and to the body; the relative length
of the leg and foot; the number of scutellae on the toes, the
development of skin between the toes, are all points of struct-
ure which are variable. The period at which the perfect
plumage is acquired varies, as does the state of the down
with which the nestling birds are clothed when hatched.
The shape and size of the eggs vary. The manner of flight,
and in some breeds the voice and disposition, differs re-
markably. Lastly, in certain breeds, the males and females
have come to differ in a slight degree in each other.
Altogether at least a score of pigeons might be chosen,
which, if shown to an ornithologist, and he were told that
they were wild birds, would certainly be ranked by him
as well-defined species. Moreover, I do not believe that any
ornithologist would in this case place the English carrier,
the short-faced tumbler, the runt, the barb, pouter, and
fantail in the same genus ; more especially as in each of
these breeds several truly inherited sub-breeds, or species, as
he would call them, could be shown him.
Great as are the differences between the breeds of the
pigeon, I am fully convinced that the common opinion of
naturalists is correct, namely, that all are descended from
the rock-pigeon (Columba livia), including under this term
several geographical races or sub-species, which differ from
each other in the most trifling respects. As several of the
reasons which have led me to this belief are in some de-
gree applicable in other cases, I will here briefly give them.
If the several breeds are not varieties, and have not pro-
ceeded from the rock-pigeon, they must have descended from
at least seven or eight aboriginal stocks; for it is impossible
to make the present domestic breeds by the crossing of any
lesser number: how, for instance, could a pouter be produced
by crossing two breeds unless one of the parent-stocks pos-
40 ORIGIN OF SPECIES
sessed the characteristic enormous crop? The supposed abo-
riginal stocks must all have been rock-pigeons, that is, they
did not breed or willingly perch on trees. But besides C.
livia, with its geographical sub-species, only two or three
other species of rock-pigeons are known and these have
not any of the characters of the domestic breeds. Hence
the supposed aboriginal stocks must either still exist in the
countries where they were originally domesticated, and yet
be unknown to ornithologists; and this, considering their
size, habits, and remarkable characters, seems improbable ;
or they must have become extinct in the wild state. But
birds breeding on precipices, and good fliers, are unlikely
to be exterminated ; and the common rock-pigeon, which has
the same habits with the domestic breeds, has not been ex-
terminated even on several of the smaller British islets, or
on the shores of the Mediterranean. Hence the supposed
extermination of so many species having similar habits with
the rock-pigeon seems a very rash assumption. Moreover,
the several above-named domesticated breeds have been
transported to all parts of the world, and, therefore, some
of them must have been carried back again into their native
country; but not one has become wild or feral, though the
dovecot-pigeon, which is the rock-pigeon in a very slightly
altered state, has become feral in several places. Again,
all recent experience shows that it is difficult to get wild ani-
mals to breed freely under domestication; yet on the hy-
pothesis of the multiple origin of our pigeons, it must be
assumed that at least seven or eight species were so thor-
oughly domesticated in ancient times by half-civilised man,
as to be quite prolific under confinement.
An argument of great weight, and applicable in several
other cases, is, that the above-specified breeds, though agree-
ing generally with the wild rock-pigeon in constitution, habits,
voice, colouring, and in most parts of their structure, yet are
certainly highly abnormal in other parts ; we may look in vain
through the whole great family of Columbidae for a beak like
that of the English carrier, or that of the short-faced tum-
bler, or barb; for reversed feathers like those of the Jacobin;
for a crop like that of the pouter; for tail-feathers like those
of the fantail. Hence it must be assumed not only that half-
DOMESTIC PIGEONS 41
civilised man succeeded in thoroughly domesticating several
species, but that he intentionally or by chance picked out
extraordinarily abnormal species; and further, that these very
species have since all become extinct or unknown. So many
strange contingencies are improbable in the highest degree.
Some facts in regard to the colouring of pigeons well de-
serve consideration. The rock-pigeon is of a slaty-blue, with
white loins ; but the Indian sub-species, C. intermedia of
Strickland, has this part bluish. The tail has a terminal dark
bar, with the outer feathers externally edged at the base with
white. The wings have two black bars. Some semi-domes-
tic breeds, and some truly wild breeds, have, besides the two
black bars, the wings chequered with black. These several
marks do not occur together in any other species of the whole
family. Now, in every one of the domestic breeds, taking
thoroughly well-bred birds, all the above marks, even to the
white edging of the outer tail-feathers, sometimes concur
perfectly developed. Moreover, when birds belonging to two
or more distinct breeds are crossed, none of which are blue
or have any of the above-specified marks, the mongrel off-
spring are very apt suddenly to acquire these characters. To
give one instance out of several which I have observed: — I
crossed some white fantails, which breed very true, with some
black barbs — and it so happens that blue varieties of barbs
are so rare that I never heard of an instance in England; and
the mongrels were black, brown, and mottled. I also crossed
a barb with a spot, which is a white bird with a red tail and
red spot on the forehead, and which notoriously breeds very
true; the mongrels were dusky and mottled. I then crossed
one of the mongrel barb-fantails with a mongrel barb-spot,
and they produced a bird of as beautiful a blue colour, with
the white loins, double black wing-bar, and barred and white-
edged tail-feathers, as any wild rock-pigeon ! We can under-
stand these facts, on the well-known principle of reversion to
ancestral characters, if all the domestic breeds are descended
from the rock-pigeon. But if we deny this, we must make
one of the two following highly improbable suppositions.
Either, first, that all the several imagined aboriginal stocks
were coloured and marked .like the rock-pigeon, although no
other existing species is thus coloured and marked, so that in
42 ORIGIN OF SPECIES
each separate breed there might be a tendency to revert to
the very same colours and markings. Or, secondly, that each
breed, even the purest, has within a dozen, or at most within
a score, of generations, been crossed by the rock-pigeon; I
say within a dozen or twenty generations, for no instance is
known of crossed descendants reverting to an ancestor of
foreign blood, removed by a greater number of generations.
In a breed which has been crossed only once, the tendency to
revert to any character derived from such a cross will nat-
urally become less and less, as in each succeeding generation
there will be less of the foreign blood; but when there has
been no cross, and there is a tendency in the breed to revert
to a character which was lost during some former genera-
tion, this tendency, for all that we can see to the contrary,
may be transmitted undiminished for an indefinite number of
generations. These two distinct cases of reversion are often
confounded together by those who have written on inheri-
tance.
Lastly, the hybrids or mongrels from between all the breeds
of the pigeon are perfectly fertile, as I can state from my
own observations, purposely made, on the most distinct breeds.
Now, hardly any cases have been ascertained with certainty
of hybrids from two quite distinct species of animals being
perfectly fertile. Some authors believe that long-continued
domestication eliminates this strong tendency to sterility in
species. From the history of the dog, and of some other do-
mestic animals, this conclusion is probably quite correct, if
applied to species closely related to each other. But to ex-
tend it so far as to suppose that species, aboriginally as dis-
tinct as carriers, tumblers, pouters, and fantails now are,
should yield offspring perfectly fertile inter se, would be
rash in the extreme.
From these several reasons, namely, — the improbability of
man having formerly made seven or eight supposed species
of pigeons to breed freely under domestication; — these sup-
posed species being quite unknown in a wild state, and their
not having become anywhere feral ; — these species presenting
certain very abnormal characters, as compared with all other
Columbid?e, though so like the rock-pigeon in most respects;
— the occasional re-appearance of the blue colour and various
DOMESTIC PIGEONS 43
black marks in all the breeds, both when kept pure and when
crossed ; — and lastly, the mongrel offspring being perfectly
fertile ; — from these several reasons, taken together, we may
safely conclude that all our domestic breeds are descended
from the rock-pigeon or Columba livia with its geographical
sub-species.
In favour of this view, I may add, firstly, that the wild C.
livia has been found capable of domestication in Europe and
"in India; and that it agrees in habits and in a great number
of points of structure with all the domestic breeds. Sec-
ondly, that, although an English carrier or a short-faced
tumbler differs immensely in certain characters from the
rock-pigeon, yet that, by comparing the several sub-breeds of
these two races, more especially those brought from distant
countries, we can make, between them and the rock-pigeon,
an almost perfect series; so we can in some other cases, but
not with all the breeds. Thirdly, those characters which are
mainly distinctive of each breed are in each eminently vari-
able, for instance the wattle and length of beak of the carrier,
the shortness of that of the tumbler, and the number of tail-
feathers in the fantail ; and the explanation of this fact will
"be obvious when we treat of Selection. Fourthly, pigeons
have been watched and tended with the utmost care, and
loved by many people. They have been domesticated for
thousands of years in several quarters of the world ; the ear-
liest known record of pigeons is in the fifth Egyptian dy-
nasty, about 3000 B.C., as was pointed out to me by Professor
Lepsius; but Mr. Birch informs me that pigeons are given
in a bill of fare in the previous dynasty. In the time of the
Romans, as we hear from Pliny, immense prices were given
for pigeons; "nay, they are come to this pass, that they can
reckon up their pedigree and race." Pigeons were much
valued by Akber Khan in India, about the year 1600; never
less than 20,000 pigeons were taken with the court. "The
monarchs of Iran and Turan sent him some very rare birds ;"
and, continues the courtly historian, "His Majesty by cross-
ing the breeds, which method was never practised before, has
improved them astonishingly." About this same period the
Dutch were as eager about .pigeons as were the old Romans.
The paramount importance of these considerations in ex-
44 ORIGIN OF SPECIES
plaining the immense amount of variation which pigeons have
undergone, vv^ill likewise be obvious when we treat of Selec-
tion. We shall then, also, see how it is that the several
breeds so often have a somewhat monstrous character. It is
also a most favourable circumstance for the production of
distinct breeds, that male and female pigeons can be easily
mated for life ; and thus different breeds can be kept together
in the same aviary.
I have discussed the probable origin of domestic pigeons at
some, yet quite insufficient, length ; because when I first kept
pigeons and watched the several kinds, well knowing how
truly they breed, I felt fully as much difficulty in believing
that since they had been domesticated they had all proceeded
from a common parent, as any naturalist could in coming to
a similar conclusion in regard to the many species of finches,
or other groups of birds, in nature. One circumstance has
struck me much; namely, that nearly all the breeders of the
various domestic animals and the cultivators of plants, with
whom I have conversed, or whose treatises I have read, are
firmly convinced that the several breeds to which each has
attended, are descended from so many aboriginally distinct
species. Ask, as I have asked, a celebrated raiser of Here-
ford cattle, whether his cattle might not have descended from
Longhorns, or both from a common parent-stock, and he will
laugh you to scorn. I have never met a pigeon, or poultry,
or duck, or rabbit fancier, who was not fully convinced that
each main breed was descended from a distinct species. Van
Mons, in his treatise on pears and apples, shows how utterly
he disbelieves that the several sorts, for instance a Ribston-
pippin or Codlin-apple, could ever have proceeded from the
seeds of the same tree. Innumerable other examples could
be given. The explanation, I think, is simple: from long-
continued study they are strongly impressed with the differ-
ences between the several races ; and though they well know
that each race varies slightly, for they win their prizes by
selecting such slight differences, yet they ignore all general
arguments, and refuse to sum up in their minds slight differ-
ences accumulated during, many successive generations. May
not those naturalists who, knowing far less of the laws of
inheritance than does the breeder, and knowing no more than
SELECTION BY MAN 45
he does of the intermediate links in the long lines of descent,
yet admit that many of our domestic races are descended
from the same parents — may they not learn a lesson of cau-
tion, when they deride the idea of species in a state of nature
being lineal descendants of other species?
PRINCIPLES OF SELECTION ANCIENTLY FOLLOWED, AND
THEIR EFFECTS
Let us now briefly consider the steps by which domestic races
have been produced, either from one or from several allied
species. Some effect may be attributed to the direct and defi-
nite action of the external conditions of life, and some to
habit; but he would be a bold man who would account by
such agencies for the differences between a dray- and race-
horse, a greyhound and bloodhound, a carrier and tumbler
pigeon. One of the most remarkable features in our domes-
ticated races is that we see in them adaptation, not indeed to
the animal's or plant's own good, but to man's use or fancy.
Some variations useful to him have probably arisen sud-
denly, or by one step; many botanists, for instance, believe
that the fuller's teasel, with its hooks, which cannot be
rivalled by any mechanical contrivance, is only a variety of
the wild Dipsacus ; and this amount of change may have sud-
denly arisen in a seedling. So it has probably been with the
turnspit dog; and this is known to have been the case with
the ancon sheep. But when we compare the dray-horse and
race-horse, the dromedary and camel, the various breeds
of sheep fitted either for cultivated land or mountain pasture,
with the wool of one breed good for one purpose, and that
of another breed for another purpose ; when we compare the
many breeds of dogs, each good for man in different ways;
when we compare the game-cock, so pertinacious in battle,
with other breeds so little quarrelsome, with "everlasting
layers" which never desire to sit, and with the bantam so
small and elegant; when we compare the host of agricultural,
culinary, orchard, and flower-garden races of plants, most
useful to man at different seasons and for different purposes,
or so beautiful in his eyes, we must, I think, look further
than to mere variability. We cannot suppose that all the
46 ORIGIN OF SPECIES
breeds were suddenly produced as perfect and as useful as we
now see them ; indeed, in many cases, we know that this has
not been their history. The key is man's power of accumu-
lative selection : nature gives successive variations ; man adds
them up in certain directions useful to him. In this sense he
may be said to have made for himself useful breeds.
The great power of this principle of selection is not hypo-
thetical. It is certain that several of our eminent breeders
have, even within a single lifetime, modified to a large extent
their breeds of cattle and sheep. In order fully to realise
what they have done, it is almost necessary to read several
of the many treatises devoted to this subject, and to inspect
the animals. Breeders habitually speak of an animal's organi-
sation as something plastic, which they can model almost as
they please. If I had space I could quote numerous passages
to this effect from highly competent authorities. Youatt,
who was probably better acquainted with the works of agri-
culturists than almost any other individual, and who was him-
self a very good judge of animals, speaks of the principle of
selection as "that which enables the agriculturist, not only to
modify the character of his flock, but to change it altogether.
It is the magician's wand, by means of which he may summon
into life whatever form and mould he pleases." Lord Somer-
ville, speaking of what breeders have done for sheep, says : —
"It would seem as if they had chalked out upon a vi^all a form
perfect in itself, and then had given it existence." In Sax-
ony the importance of the principle of selection in regard to
merino sheep is so fully recognised, that men follow it as a
trade ; the sheep are placed on a table and are studied, like a
picture by a connoisseur ; this is done three times at intervals
of months, and the sheep are each time marked and classed,
so that the very best may ultimately be selected for breeding.
What English breeders have actually effected is proved by
the enormous prices given for animals with a good pedigree ;
and these have been exported to almost every quarter of the
world. The improvement is by no means generally due to
crossing different breeds ; all the best breeders are strongly
opposed to this practice, except sometimes amongst closely
allied sub-breeds. And when a cross has been made, the
closest selection is far more indispensable even than in ordi-
SELECTION BY MAN 47
nary cases. If selection consisted merely in separating some
very distinct variety, and breeding from it, the principle would
be so obvious as hardly to be worth notice ; but its importance
consists in the great effect produced by the accumulation in
one direction, during successive generations, of differences
absolutely inappreciable by an uneducated eye — differences
which I for one have vainly attempted to appreciate. Not
one man in a thousand has accuracy of eye and judgment
sufficient to become an eminent breeder. If gifted with these
qualities, and he studies his subject for years, and devotes his
lifetime to it with indomitable perseverance, he will succeed,
and may make great improvements ; if he wants any of these
qualities, he will assuredly fail. Few would readily believe
in the natural capacity and years of practice requisite to be-
come even a skilful pigeon-fancier.
The same principles are followed by horticulturists ; but
the variations are here often more abrupt. No one supposes
that our choicest productions have been produced by a single
variation from the aboriginal stock. We have proofs that
this has not been so in several cases in which exact records
have been kept; thus, to give a very trifling instance, the
steadily increasing size of the common gooseberry may be
quoted. We see an astonishing improvement in many flor-
ists' flowers, when the flowers of the present day are com-
pared with drawings made only twenty or thirty years ago.
When a race of plants is once pretty well established, the
seed-raisers do not pick out the best plants, but merely go
.over their seed-beds, and pull up the "rogues," as they call
the plants that deviate from the proper standard. With ani-
mals this kind of selection is, in fact, likewise followed; for
hardly any one is so careless as to breed from his worst
animals.
In regard to plants, there is another means of observing
the accumulated effects of selection — namely, by comparing
the diversity of flowers in the different varieties of the same
species in the flower-garden ; the diversity of leaves, pods, or
tubers, or whatever part is valued, in the kitchen-garden, in
comparison with the flowers of the same varieties; and the
diversity of fruit of the same species in the orchard, in com-
parison with the leaves and flowers of the same set of vari-
48 ORIGIN OF SPECIES
eties. See how different the leaves of the cabbage are, and
how extremely alike the flowers; how unlike the flowers of
the heartsease are, and how alike the leaves; how much the
fruit of the different kinds of gooseberries differ in size,
colour, shape, and hairiness, and yet the flowers present very
slight differences. It is not that the varieties which differ
largely in some one point do not differ at all in other points;
this is hardly ever, — I speak after careful observation, — per-
haps never, the case. The law of correlated variation, the im-
portance of which should never be overlooked, will ensure
some differences ; but, as a general rule, it cannot be doubted
that the continued selection of slight variations, either in the
leaves, the flowers, or the fruit, will produce races differing
from each other chiefly in these characters.
It may be objected that the principle of selection has been
reduced to methodical practice for scarcely more than three-
quarters of a century; it has certainly been more attended to
of late years, and many treatises have been published on the
subject; and the result has been, in a corresponding degree,
rapid and important. But it is very far from true that the
principle is a modern discovery. I could give several refer-
ences to works of high antiquity, in which the full impor-
tance of the principle is acknowledged. In rude and bar-
barous periods of English history choice animals were often
imported, and laws were passed to prevent their exportation:
the destruction of horses under a certain size was ordered,
and this may be compared to the "roguing" of plants by nur-
serymen. The principle of selection I find distinctly given in
an ancient Chinese encyclopaedia. Explicit rules are laid
down by some of the Roman classical writers. From pas-
sages in Genesis, it is clear that the colour of domesticated
animals was at that early period attended to. Savages now
sometimes cross their dogs with wild canine animals, to im-
prove the breed, and they formerly did so, as is attested by
passages in Pliny. The savages in South Africa match their
draught cattle by colour, as do some of the Esquimaux their
teams of dogs. Livingstone states that good domestic breeds
are highly valued by the negroes in the interior of Africa
who have not associated with Europeans. Some of these
facts do not show actual selection, but they show that the
UNCONSCIOUS SELECTION 49
breeding of domestic animals was carefully attended to in
ancient times, and is now attended to by the lowest savages.
It would, indeed, have been a strange fact, had attention
not been paid to breeding, for the inheritance of good and
bad qualities is so obvious.
UNCONSCIOUS SELECTION
At the present time, eminent breeders try by methodical
selection, with a distinct object in view, to make a new strain
or sub-breed, superior to anything of the kind in the country.
But, for our purpose, a form of Selection, which may be
called Unconscious, and which results from every one trying
to possess and breed from the best individual animals, is more
important. Thus, a man who intends keeping pointers nat-
urally tries to get as good dogs as he can, and afterwards
breeds from his own best dogs, but he has no wish or expec-
tation of permanently altering the breed. Nevertheless we
may infer that this process, continueci during centuries, would
improve and modify any breed, in the same way as Bakewell,
Collins, etc., by this very same process, only carried on more
methodically, did greatly modify, even during their lifetimes,
the forms and qualities of their cattle. Slow and insensible
changes of this kind can never be recognised unless actual
measurements or careful drawings of the breeds in question
have been made long ago, which may serve for comparison.
In some cases, however, unchanged, or but little changed
individuals of the same breed exist in less civilised districts,
where the breed has been less improved. There is reason to
believe that King Charles' spaniel has been unconsciously
modified to a large extent since the time of that monarch.
Some highly competent authorities are convinced that the
setter is directly derived from the spaniel, and has probably
been slowly altered from it. It is known that the English
pointer has been greatly changed within the last century, and
in this case the change has, it is believed, been chiefly effected
by crosses with the foxhound : but what concerns us is, that
the change has been effected unconsciously and gradually, and
yet so effectually, that, thpugh the old Spanish pointer cer-
tainly came from Spain, Mr. Borrow has not seen, as I am
so ORIGIN OF SPECIES
informed by him, any native dog in Spain like our pointer.
By a simple process of selection, and by careful training,
English racehorses have come to surpass in fleetness and size
the parent Arabs, so that the latter, by the regulations for the
Goodw^ood Races, are favoured in the weights which they
carry. Lord Spencer and others have shown how the cattle
of England have increased in weight and in early maturity,
compared with the stock formerly kept in this country. By
comparing the accounts given in various old treatises of the
former and present state of carrier and tumbler pigeons in
Britain, India, and Persia, we can trace the stages through
which they have insensibly passed, and come to differ so
greatly from the rock-pigeon.
Youatt gives an excellent illustration of the effects of a
course of selection, which may be considered as unconscious,
in so far that the breeders could never have expected, or even
wished, to produce the result which ensued — namely, the pro-
duction of two distinct strains. The two flocks of Leicester
sheep kept by Mr. Buckley and Mr. Burgess, as Mr. Youatt
remarks, "have been purely bred from the original stock of
Mr. Bakewell for upwards of fifty years. There is not a sus-
picion existing in the mind of any one at all acquainted with
the subject, that the owner of either of them has deviated in
any one instance from the pure blood of Mr. Bakewell's flock,
and yet the difference between the sheep possessed by these
two gentlemen is so great that they have the appearance of
being quite different varieties."
If there exist savages so barbarous as never to think of the
inherited character of the offspring of their domestic animals,
yet any one animal particularly useful to them, for any
special purpose, would be carefully preserved during famines
and other accidents, to which savages are so liable, and such
choice animals would thus generally leave more offspring
than the inferior ones ; so that in this case there would be a
kind of unconscious selection going on. We see the value set
on animals even by the barbarians of Tierra del Fuego, by
their killing and devouring their old women, in times of
dearth, as of less value than their dogs.
In plants the same gradual process of improvement,
through the occasional preservation of the best individuals.
UNCONSCIOUS SELECTION 51
whether or not sufficiently distinct to be ranked at their first
appearance as distinct varieties, and whether or not two or
more species or races have become blended together by cross-
ing, may plainly be recognised in the increased size and beauty
which we now see in the varieties of the heartsease, rose,
pelargonium, dahlia, and other plants, when compared with
the older varieties or with their parent-stocks. No one would
ever expect to get a first-rate heartsease or dahlia from the
seed of a wild plant. No one would expect to raise a first-
rate melting p)ear from the seed of the wild pear, though he
might succeed from a poor seedling growing wild, if it had
come from a garden-stock. The pear though cultivated in
classical times, appears, from Pliny's description, to have
been a fruit of very inferior quality. I have seen great sur-
prise expressed in horticultural works at the wonderful skill
of gardeners, in having produced such splendid results from
such poor materials ; but the art has been simple, and, as far
as the final result is concerned, has been followed almost un-
consciously. It has consisted in always cultivating the best-
known variety, sowing its seeds, and, when a slightly better
variety chanced to appear, selecting it, and so onwards. But
the gardeners of the classical period, who cultivated the best
pears which they could procure, never thought what splendid
fruit we should eat ; though we owe our excellent fruit in
some small degree to their having naturally chosen and pre-
served the best varieties they could anywhere find.
A large amount of change, thus slowly and unconsciously
accumulated, explains, as I believe, the well-known fact, that
in a number of cases we cannot recognise, and therefore do
not know, the wild parent-stocks of the plants which have
been longest cultivated in our flower and kitchen gardens.
If it has taken centuries or thousands of years to improve or
modify most of our plants up to their present standard of
usefulness to man, we can understand how it is that neither
Australia, the Cape of Good Hope, nor any other region in-
habited by quite uncivilised man, has afforded us a single plant
worth culture. It is not that these countries, so rich in
species, do not by a strange chance possess the aboriginal
stocks of any useful plants, but that the native plants have not
been improved by continued selection up to a standard of
52 ORIGIN OF SPECIES
perfection comparable with that acquired by the plants in
countries anciently civilised.
In regard to the domestic animals kept by uncivilised man,
it should not be overlooked that they almost always have to
struggle for their own food, at least during certain seasons.
And in two countries very differently circumstanced, indi-
viduals of the same species, having slightly different consti-
tutions or structure, would often succeed better in the one
country than in the other ; and thus by a process of "natural
selection," as will hereafter be more fully explained, two sub-
breeds might be formed. This, perhaps, partly explains why
the varieties kept by savages, as has been remarked by some
authors, have more of the character of true species than the
varieties kept in civilised countries.
On the view here given of the important part which selec-
tion by man has played, it becomes at once obvious, how it is
that our domestic races show adaptation in their structure or
in their habits to man's wants or fancies. We can, I think,
further understand the frequently abnormal character of our
domestic races, and likewise their differences being so great
in external characters, and relatively so slight in internal
parts or organs. Man can hardly select, or only with much
difficulty, any deviation of structure excepting such as is ex-
ternally visible ; and indeed he rarely cares for what is inter-
nal. He can never act by selection, excepting on variations
which are first given to him in some slight degree by nature.
No man would ever try to make a fantail till he saw a pigeon
with a tail developed in some slight degree in an unusual
manner, or a pouter till he saw a pigeon with a crop of some-
what unusual size ; and the more abnormal or unusual any
character was when it first appeared, the more likely it would
be to catch his attention. But to use such an expression as
trying to make a fantail, is, I have no doubt, in most cases,
utterly incorrect. The man who first selected a pigeon with
a slightly larger tail, never dreamed what the descendants of
that pigeon would become through long-continued, partly
unconscious and partly methodical, selection. Perhaps the
parent-bird of all fantails had only fourteen tail-feathers
somewhat expanded, like the present Java fantail, or like in-
dividuals of other and distinct breeds, in which as many as
UNCONSCIOUS SELECTION S3'
seventeen tail-feathers have been counted. Perhaps the first
pouter-pigeon did not inflate its crop much more than the
turbit now does the upper part of its oesophagus, — a habit
which is disregarded by all fanciers, as it is not one of the
points of the breed.
Nor let it be thought that some great deviation of structure
would be necessary to catch the fancier's eye : he perceives
extremely small differences, and it is in human nature to
fancy any novelty, however slight, in one's own possession.
Nor must the value which would formerly have been set on
any slight differences in the individuals of the same species,
be judged of by the value which is now set on them, after
several breeds have fairly been established. It is known that
with pigeons many slight variations now occasionally appear,
but these are rejected as faults or deviations from the stand-
ard of perfection in each breed. The common goose has not
given rise to any marked varieties ; hence the Toulouse and
the common breed, which differ only in colour, that most
fleeting of characters, have lately been exhibited as distinct
at our poultry-shows.
These views appear to explain what has sometimes been
noticed — namely, that we know hardly anything about the
origin or history of any of our domestic breeds. But, in
fact, a breed, like a dialect of a language, can hardly be said
to have a distinct origin. A man preserves and breeds from
an individual with some slight deviation of structure, or takes
more care than usual in matching his best animals, and thus
improves them, and the improved animals slowly spread in the
immediate neighbourhood. But they will as yet hardly have
a distinct name, and from being only slightly valued, their
history will have been disregarded. When further improved
by the same slow and gradual process, they will spread more
widely, and will be recognised as something distinct and valu-
able, and will then probably first receive a provincial name.
In semi-civilised countries, with little free communication,
the spreading of a new sub-breed would be a slow process.
As soon as the points of value are once acknowledged, the
principle, as I have called it, of unconscious selection will
always tend, — perhaps more at one period than at another, as
the breed rises or falls in fashion, — perhaps more in one dis-
54 ORIGIN OF SPEaES
trict than in another, according to the state of civilisation of
the inhabitants, — slowly to add to the characteristic features
of the breed, whatever they may be. But the chance will be
infinitely small of any record having been preserved of such
slow, varying, and insensible changes.
CIRCUMSTANCES FAVOURABLE TO MAN's POWER OF SELECTION
I will now say a few words on the circumstances, favour-
able, or the reverse, to man's power of selection. A high de-
gree of variability is obviously favourable, as freely giving
the materials for selection to work on ; not that mere indi-
vidual differences are not amply sufficient, with extreme care,
to allow of the accumulation of a large amount of modifica-
tion in almost any desired direction. But as variations mani-
festly useful or pleasing to man appear only occasionally, the
chance of their appearance will be much increased by a large
number of individuals being kept. Hence, number is of the
highest importance for success. On this principle Marshall
formerly remarked, with respect to the sheep of parts of
Yorkshire, "as they generally belong to poor people, and are
mostly in small lots, they never can be improved." On the
other hand, nurserymen, from keeping large stocks of the
same plant, are generally far more successful than amateurs
in raising new and valuable varieties. A large number of
individuals of an animal or plant can be reared only where
the conditions for its propagation are favourable. When the
individuals are scanty, all will be allowed to breed, whatever
their quality may be, and this will effectually prevent selec-
tion. But probably the most important element is that the
animal or plant should be so highly valued by man, that the
closest attention is paid to even the slightest deviations in its
qualities or structure. Unless such attention be paid nothing
can be effected. I have seen it gravely remarked, that it was
most fortunate that the strawberry began to vary just when
gardeners began to attend to this plant. No doubt the straw-
berry had always varied since it was cultivated, but the slight
varieties had been neglected. As soon, however, as gar-
deners picked out individual plants with slightly larger, ear-
lier, or better fruit, and raised seedlings from them, and again
CIRCUMSTANCES FAVOURABLE TO SELECTION 55
picked out the best seedlings and bred from them, then (with
some aid by crossing distinct species) those many admirable
varieties of the strawberry were raised which have appeared
during the last half-century.
With animals, facility in preventing crosses is an important
element in the formation of new races, — at least, in a country
which is already stocked with other races. In this respect
enclosure of the land plays a part. Wandering savages or
the inhabitants of open plains rarely possess more than one
breed of the same species. Pigeons can be mated for life, and
this is a great convenience to the fancier, for thus many races
may be improved and kept true, though mingled in the same
aviary ; and this circumstance must have largely favoured the
formation of new breeds. Pigeons, I may add, can be propa-
gated in great numbers and at a very quick rate, and inferior
birds may be freely rejected, as when killed they serve for
food. On the other hand, cats, from their nocturnal rambling
habits, cannot be easily matched, and, although so much
valued by women and children, we rarely see a distinct breed
long kept up ; such breeds as we do sometimes see are almost
always imported from some other country. Although I do
not doubt that some domestic animals vary less than others,
yet the rarity or absence of distinct breeds of the cat, the
donkey, peacock, goose, &c., may be attributed in main part
to selection not having been brought into play : in cats, from
the difficulty in pairing them ; in donkeys, from only a few
being kept by poor people, and little attention paid to their
breeding; for recently in certain parts of Spain and of the
United States this animal has been surprisingly modified and
improved by careful selection ; in peacocks, from not being
very easily reared and a large stock not kept; in geese, from
being valuable only for two purposes, food and feathers, and
more especially from no pleasure having been felt in the dis-
play of distinct breeds ; but the goose, under the conditions to
which it is exposed when domesticated, seems to have a sin-
gularly inflexible organisation, though it has varied to a
slight extent, as I have elsewhere described.
Some authors have maintained that the amount of variation
in our domestic productions^ is soon reached, and can never
afterwards be exceeded. It would be somewhat rash to as-
56 ORIGIN OF SPECIES
sert that the limit has been attained in any one case ; for al-
most all our animals and plants have been greatly improved in
many ways within a recent period ; and this implies variation.
It would be equally rash to assert that characters now in-
creased to their usual limit, could not, after remaining fixed
for many centuries, again vary under new conditions of life.
No doubt, as Mr. Wallace has remarked with much truth, a
limit will be at last reached. For instance, there must be a
limit to the fleetness of any terrestrial animal, as this will
be determined by the friction to be overcome, the weight of
body to be carried, and the power of contraction in the mus-
cular fibres. But what concerns us is that the domestic vari-
eties of the same species differ from each other in almost
every character, which man has attended to and selected,
more than do the distinct species of the same genera. Isi-
dore Geoffroy St. Hilaire has proved this in regard to size,
and so it is with colour and probably with the length of hair.
With respect to fleetness, which depends on many bodily char-
acters. Eclipse was far fleeter, and a dray-horse is incom-
parably stronger than any two natural species belonging to
the same genus. So with plants, the seeds of the different
varieties of the bean or maize probably differ more in size,
than do the seeds of the distinct species in any one genus in
the same two families. The same remark holds good in re-
gard to the fruit of the several varieties of the plum, and still
more strongly with the melon, as well as in many other anal-
ogous cases.
To sum up on the origin of our domestic races of animals
and plants. Changed conditions of life are of the highest
importance in causing variability, both by acting directly on
the organisation, and indirectly by affecting the reproductive
system. It is not probable that variability is an inherent and
necessary contingent, under all circumstances. The greater
or less force of inheritance and reversion determine whether
variations shall endure. Variability is governed by many
unknown laws, of which correlated growth is probably the
most important. Something, but how much we do not know,
may be attributed to the definite action of the conditions of
life. Some, perhaps a great, effect may be attributed to the
increased use or disuse of parts. The final result is thus
CIRCUMSTANCES FAVOURABLE TO SELECTION 57
rendered infinitely complex. In some cases the intercrossing
of aboriginally distinct species appears to have played an im-
portant part in the origin of our breeds. When several
breeds have once been formed in any country, their occa-
sional intercrossing, with the aid of selection, has, no doubt,
largely aided in the formation of new sub-breeds ; but the im-
portance of crossing has been much exaggerated, both in re-
gard to animals and to those plants which are propagated by
seed. With plants which are temporarily propagated by cut-
tings, buds, &c., the importance of crossing is immense ; for
the cultivator may here disregard the extreme variability
both of hybrids and of mongrels, and the sterility of hybrids ;
but plants not propagated by seed are of little importance to
us, for their endurance is only temporary. Over all these
causes of Change, the accumulative action of Selection,
whether applied methodically and quickly, or unconsciously
and slowly but more efficiently, seems to have been the pre-
dominant Power.
CHAPTER TI
Variation Under Nature
Variability — Individual diflPerences — Doubtful species — Wide ranging,
much diffused, and common species, vary most — Species of the
larger genera in each country vary more frequently than the
species of the smaller genera — Many of the species of the larger
genera resemble varieties in being very closely, but unequally,
related to each other, and in having restricted ranges.
BEFORE applying the principles arrived at in the last
chapter to organic beings in a state of nature, we must
briefly discuss whether these latter are subject to any
variation. To treat this subject properly, a long catalogue of
dry facts ought to be given ; but these I shall reserve for a
future work. Nor shall I here discuss the various definitions
which have been given of the term species. No one defini-
tion has satisfied all naturalists;, yet every naturalist knows
vaguely what he means when he speaks of a species. Gen-
erally the term includes the unknown element of a distinct
act of creation. .The term "variety" is almost equally diffi-
cult to define ; but here community of descent is almost uni-
versally implied, though it can rarely be proved. We have
also what are called monstrosities ; but they graduate into
varieties. By a monstrosity I presume is meant some consid-
erable deviation of structure, generally injurious, or not use-
ful to the species. Some authors use the term "variation" in
a technical sense, as implying a modification directly due to
the physical conditions of life; and "variations" in this sense
are supposed not to be inherited ; but who can say that the
dwarfed condition of shells in the brackish waters of the
Baltic, or dwarfed plants on Alpine, summits, or the thicker
fur of an animal from far northwards, would not in some
cases be inherited for at least a few generations? and in this
case I presume that the form would be called a variety.
It may be doubted whether sudden and considerable devi-
58
INDIVIDUAL DIFFERENCES 59
ations of structure such as we occasionally see in our domes-
tic productions, more especially with plants, are ever perma-
nently propagated in a state of nature. Almost every part
of every organic being is so beautifully related to its complex
conditions of life that it seems as improbable that any part
should have been suddenly produced perfect, as that a com-
plex machine should have been invented by man in a perfect
state. Under domestication monstrosities sometimes occur
which resemble normal structures in widely different animals.
Thus pigs have occasionally been born with a sort of pro-
boscis, and if any wild species of the same genus had nat-
urally possessed a proboscis, it might have been argued that
this had appeared as a monstrosity; but I have as yet failed
to find, after diligent search, cases of monstrosities resem-
bling normal structures in nearly allied forms, and these alone
bear on the question. If monstrous forms of this kind ever
do appear in a state of nature and are capable of reproduc-
tion (which is not always the case), as they occur rarely and
singly, their preservation would depend on unusually favour-
able circumstances. They would, also, during the first and
succeeding generations cross with the ordinary form, and
thus their abnormal character would almost inevitably be lost.
But I shall have to return in a future chapter to the pres-
ervation and perpetuation of single or occasional variations.
INDIVIDUAL DIFFERENCES
The many slight differences which appear in the offspring
from the same parents, or which it may be presumed have
thus arisen, from being observed in the individuals of the
same species inhabiting the same confined locality, may be
called individual differences. Xo one supposes that all the
individuals of the same species are cast in the same actual
mould. These individual differences are of the highest im-
portance for us, for they are often inherited, as must be
familiar to every one; and they thus afford materials for
natural selection to act on and accumulate, in the same man-
ner as man accumulates in any given direction individual dif-
ferences in his domesticated productions. These individual
dift'erences generally affect what naturalists consider unim-
60 ORIGIN OF SPECIES
portant parts ; but I could show by a long catalogue of facts,
that parts which must be called important, whether viewed
under a physiological or classificatory point of view, some-
times vary in the individuals of the same species. I am con-
vinced that the most experienced naturalist would be sur-
prised at the number of the cases of variability, even in im-
portant parts of structure, which he could collect on good
authority, as I have collected, during a course of years. It
should be remembered that systematists are far from being
pleased at finding variability in important characters, and that
there are not many men who will laboriously examine inter-
nal and important organs, and compare them in many speci-
mens of the same species. It would never have been expected
that the branching of the main nerves close to the great cen-
tral ganglion of an insect would have been variable in the
same species; it might have been thought that changes of
this nature could have been effected only by slow degrees;
yet Sir J. Lubbock has shown a degree of variability in these
main nerves in Coccus, which may almost be compared to the
irregular branching of the stem of a tree. This philosoph-
ical naturalist, I may add, has also shown that the muscles in
the larvae of certain insects are far from uniform. Authors
sometimes argue in a circle when they state that important
organs never vary; for these same authors practically rank
those parts as important (as some few naturalists have hon-
estly confessed) which do not vary; and, under this point of
view, no instance will ever be found of an important part
varying; but under any other point of view many instances
assuredly can be given.
There is one point connected with individual differences,
which is extremely perplexing: I refer to those genera which
have been called "protean" or "polymorphic," in which the
species present an inordinate amount of variation. With re-
spect to many of these forms, hardly two naturalists agree
whether to rank them as species or as varieties. We may
instance Rubus, Rosa, and Hieracium amongst plants, several
genera of insects and of Brachiopod shells. In most poly-
morphic genera some of the species have fixed and definite
characters. Genera which are polymorphic in one country
seem to be, with a few exceptions, polymorphic in other coun-
INDIVIDUAL DIFFERENCES 61
tries, and likewise, judging from Brachiopod shells, at former
periods of time. These facts are very perplexing, for they
seem to show that this kind of variability is independent of
the conditions of life. I am inclined to suspect that we see,
at least in some of these polymorphic genera, variations which
are of no service or disservice to the species, and which con-
sequently have not been seized on and rendered definite by
natural selection, as hereafter to be explained.
Individuals of the same species often present, as is known
to every one, great differences of structure, independently
of variation, as in the two sexes of various animals, in
the two or three castes of sterile female or workers amongst
insects, and in the immature and larval states of many of
the lower animals.
There are, also, cases of dimorphism and trimorphism,
both with animals and plants. Thus, Mr. Wallace, who
has lately called attention to the subject, has shown
that the females of certain species of butterflies, in the Ma-
layan archipelago, regularly appear under two or even three
conspicuously distinct forms, not connected by intermediate
varieties. Fritz Miiller has described analogous but more
extraordinary cases with the males of certain Brazilian
Crustaceans: thus, the male of a Tanais regularly occurs
under two distinct forms ; one of these has strong and dif-
ferently shaped pincers, and the other has antennae much
more abundantly furnished with smelling-hairs. Although
in most of these cases, the two or three forms, both with
animals and plants, are not now connected by intermediate
gradations, it is probable that they were once thus connected.
Mr. Wallace, for instance, describes a certain butterfly which
presents in the same island a great range of varieties con-
nected by intermediate links, and the extreme links of the
chain closely resemble the two forms of an allied dimorphic
species inhabiting another part of the Malay archipelago.
Thus also with ants, the several worker-castes are generally
quite distinct; but in some cases, as we shall hereafter see,
the castes are connected together by finely graduated varie-
ties. So it is, as I have myself observed, with some dimor-
phic plants. It certainly at first appears a highly remarkable
fact that the same female butterfly should have the power
62 ORIGIN OF SPECIES
of producing at the same time three distinct female forms
and a male; and that an hermaphrodite plant should produce
from the same seed-capsule three distinct hermaphrodite
forms, bearing three different kinds of females and three or
even six different kinds of males. Nevertheless these cases
are only exaggerations of the common fact that the female
produces offspring of two sexes which sometimes differ from
each other in a wonderful manner.
DOUBTFUL SPECIES
The forms which possess in some considerable degree the
character of species, but which are so closely similar to other
forms, or are so closely linked to them by intermediate gra-
dations, that naturalists do not like to rank them as distinct
species, are in several respects the most important for us.
We have every reason to believe that many of these doubtful
and closely allied forms have permanently retained their
characters for a long time; for as long, as far as we know,
as have good and true species. Practically, when a naturalist
can unite by means of intermediate links any two forms, he
treats the one as a variety of the other; ranking the most
common, but sometimes the one first described, as the spe-
cies, and the other as the variety. But cases of great diffi-
culty, which I will not here enumerate, sometimes arise in
deciding whether or not to rank one form as a variety of
another, even when they are closely connected by interme-
diate links; nor will the commonly-assumed hybrid nature
of the intermediate forms always remove the difficulty. In
very many cases, however, one form is ranked as a variety
of another, not because the intermediate links have actually
been found, but because analogy leads the observer to sup-
pose either that they do now somewhere exist, or may for-
merly have existed; and here a wide door for the entry of
doubt and conjecture is opened.
Hence, in determining whether a form should be ranked
as a species or a variety, the opinion of naturalists having
sound judgment and wide experience seems the only guide to
follow. We must, however, in many cases, decide by a ma-
jority of naturalists, for few well-marked and well-known
DOUBTFUL SPECIES 63
varieties can be named which have not been ranked as spe-
cies by at least some competent judges.
That varieties of this doubtful nature are far from un-
common cannot be disputed. Compare the several floras of
Great Britain, of France, or of the United States, drawn up
by different botanists, and see what a surprising number of
forms have been ranked by one botanist as good species,
and by another as mere varieties. Mr. H. C. Watson, to
whom I lie under deep obligation for assistance of all kinds,
has marked for me 182 British plants, which are generally
considered as varieties, but which have all been ranked by
botanists as species; and in making this list he has omitted
many trifling varieties, but which nevertheless have been
ranked by some botanists as species, and he has entirely
omitted several highly polymorphic genera. Under genera,
including the most polymorphic forms, Mr. Babington gives
251 species, whereas Mr. Bentham gives only 112, — a differ-
ence of 139 doubtful forms ! Amongst animals which unite
for each birth, and which are highly locomotive, doubtful
forms, ranked by one zoologist as a species and by another
as a variety, can rarely be found within the same country,
but are common in separated areas. How many of the birds
and insects in North America and Europe, which differ very
slightly from each other, have been ranked by one eminent
naturalist as undoubted species, and by another as varieties,
or, as they are often called, geographical races ! Mr. Wallace,
in several valuable papers on the various animals, especially
on the Lepidoptera, inhabiting the islands of the great Ma-
layan archipelago, show that they may be classed under four
heads, namely, as variable forms, as local forms, as geo-
graphical races or sub-species, and as true representative
species. The first or variable forms vary much within the
limits of the same island. The local forms are moderately
constant and distinct in each separate island ; but when all
from the several islands are compared together, the differ-
ences are seen to be so slight and graduated, that it is im-
possible to define or describe them, though at the same time
the extreme forms are sufficiently distinct. The geo-
graphical races or sub-species are local forms completely
fixed and isolated; but as they do not differ from each other
64 ORIGIN OF SPECIES
by strongly marked and important characters, "there is no
possible test but individual opinion to determine which of
them shall be considered as species and which as varieties."
Lastly, representative species fill the same place in the nat-
ural economy of each island as do the local forms and sub-
species; but as they are distinguished from each other by a
greater amount of difference than that between the local
forms and sub-species, they are almost universally ranked
by naturalists as true species. Nevertheless, no certain cri-
terion can possibly be given by which variable forms, local
forms, sub-species, and representative species can be
recognised.
Many years ago, when comparing, and seeing others com-
pare, the birds from the closely neighbouring islands of the
Galapagos archipelago, one with another, and with those
from the American mainland, I was much struck how entirely
vague and arbitrary is the distinction between species and
varieties. On the islets of the little Madeira group there are
many insects which are characterised as varieties in Mr.
Wollaston's admirable work, but which would certainly be
ranked as distinct species by many entomologists. Even Ire-
land has a few animals, now generally regarded as varie-
ties, but which have been ranked as species by some zoolo-
gists. Several experienced ornithologists consider our
British red grouse as only a strongly-marked race of Nor-
wegian species, whereas the greater number rank it as an
undoubted species peculiar to Great Britain. A wide dis-
tance between the homes of two doubtful forms leads many
naturalists to rank them as distinct species; but what dis-
tance, it has been well asked, will suffice; if that between
America and Europe is ample, will that between Europe and
the Azores, or Madeira, or the Canaries, or between the sev-
eral islets of these small archipelagos, be sufficient?
Mr. B. D. Walsh, a distinguished entomologist of the
United States, has described what he calls Phytophagic vari-
eties and Phytophagic species. Most vegetable-feeding
insects live on one kind of plant or on one group of plants;
some feed indiscriminately on many kinds, but do not in
consequence vary. In several cases, however, insects found
living on different plants, have been observed by Mr. Walsh
DOUBTFUL SPECIES 65
to present in their larval or mature state, or in both states,
slight, though constant differences in colour, size, or in the
nature of their secretions. In some instances the males
alone, in other instances both males and females, have been
observed thus to differ in a slight degree. When the differ-
ences are rather more strongly marked, and when both
sexes and all ages are affected, the forms are ranked by all
entomologists as good species. But no observer can deter-
mine for another, even if he can do so for himself, which of
these Phytophagic forms ought to be called species and
which varieties. Mr. Walsh ranks the forms which it m>y
be supposed would freely intercross, as varieties ; and those
which appear to have lost this power, as species. As the
differences depend on the insects having long fed on distinct
plants, it cannot be expected that intermediate links connect-
ing the several forms should now be found. The naturalist
thus loses his best guide in determining whether to rank
doubtful forms as varieties or species. This likewise neces-
sarily occurs with closely allied organisms, which inhabit
distinct continents or islands. When, on the other hand,
an animal or plant ranges over the same continent, or in-
habits many islands in the same archipelago, and presents
different forms in the different areas, there is always a good
chance that intermediate forms will be discovered which will
link together the extreme states ; and these are then degraded
to the rank of varieties.
Some few naturalists maintain that animals never present
varieties; but then these same naturalists rank the slightest
difference as of specific value; and when the same identical
form is met with in two distinct countries, or in two geologi-
cal formations, they believe that two distinct species are hid-
den under the same dress. The term species thus comes to
be a mere useless abstraction, implying and assuming a sep-
arate act of creation. It is certain that many forms, consid-
ered by highly-competent judges to be varieties, resemble
species so completely in character, that they have been thus
ranked by other highly-competent judges. But to discuss
whether they ought to be called species or varieties, before
any definition of these terras has been generally accepted, is
vainly to beat the air.
- C — HC XI
66 ORIGIN OF SPECIES
Many of the cases of strongly-marked varieties or doubtful
species well deserve consideration; for several interesting
lines of argument, from geographical distribution, analogical
variation, hybridism, &c., have been brought to bear in the
attempt to determine their rank ; but space does not here per-
mit me to discuss them. Close investigation, in many cases,
will no doubt bring naturalists to agree how to rank doubt-
ful forms. Yet it must be confessed that it is in the best
known countries that we find the greatest number of them.
I have been struck with the fact, that if any animal or plant
in a state of nature be highly useful to man, or from any
cause closely attracts his attention, varieties of it will almost
universally be found recorded. These varieties, moreover,
will often be ranked by some authors as species. Look at the
common oak, how closely it has been studied; yet a German
author makes more than a dozen species out of forms, which
are almost universally considered by other botanists to be
varieties; and in this country the highest botanical authori-
ties and practical men can be quoted to show that the sessile
and pedunculated oaks are either good and distinct species or
mere varieties.
I may here allude to a remarkable memoir lately published
by A. de Candolle, on the oaks of the whole world. No one
ever had more ample materials for the discrimination of the
species, or could have worked on them with more zeal and
sagacity. He first gives in detail all the many points of struc-
ture which vary in the several species, and estimates numeri-
cally the relative frequency of the variations. He specifies
above a dozen characters which may be found varying even
on the same branch, sometimes according to age or develop-
ment, sometimes without any assignable reason. Such char-
acters are not of course of specific value, but they are, as Asa
Gray has remarked in commenting on this memoir, such as
generally enter into specific definitions. De Candolle then
goes on to say that he gives the rank of species to the forms
that differ by characters never varying on the same tree, and
never found connected by intermediate states. After this
discussion, the result of so much labour, he emphatically re-
marks: "They are mistaken, who repeat that the greater
part of our species are clearly limited, and that the doubtful
DOUBTFUL SPECIES 67
species are in a feeble minority. This seemed to be true, so
long as a genus was imperfectly known, and its species were
founded upon a few specimens, that is to say, were pro-
visional. Just as we come to know them better, intermediate
forms flow in, and doubts as to specific limits augment." He
also adds that it is the best known species which present the
greatest number of spontaneous varieties and sub-varieties.
The Quercus robur has twenty-eight varieties, all of which,
excepting six, are clustered round three sub-species, namely,
Q. pedunculata sessiliflora, and pubescens. The forms which
connect these three sub-species are comparatively rare; and,
as Asa Gray again remarks, if these connecting forms which
are now rare, were to become wholly extinct, the three sub-
species would hold exactly the same relation to each other, as
do the four or five provisionally admitted species which
closely surround the typical Quercus robur. Finally, De
Candolle admits that out of the 300 species, which will be
enumerated in his Prodromus as belonging to the oak family,
at least two-thirds are provisional species, that is, are not
known strictly to fulfil the definition above given of a true
species. It should be added that De Candolle no longer be-
lieves that species are immutable creations, but concludes
that the derivative theory is the most natural one, "and the
most accordant with the known facts in palaeontology, geo-
graphical botany and zoology, of anatomical structure and
classification."
When a young naturalist commences the study of a group
of organisms quite unknown to him, he is at first much per-
plexed in determining what differences to consider as specific,
and what as varietal r for he knows nothing of the amount
and kind of variation to which the group is subject; and this
shows, at least, how very generally there is some variation.
But if he confine his attention to one class within one country,
he will soon make up his mind how to rank most of the doubt-
ful forms. His general tendency will be to make many
species, for he will become impressed, just like the pigeon or
poultry fancier before alluded to, with the amount of differ-
ence in the forms which he is continually studying; and he
has little general knowledge 'of analogical variation in other
groups and in other countries, by which to correct his first
68 ORIGIN OF SPECIES
impressions. As he extends the range of his observations, he
will meet with more cases of difficulty ; for he will encounter
a greater number of closely-allied forms. But if his observa-
tions be widely extended, he will in the end generally be able
to make up his own mind ; but he will succeed in this at the
expense of admitting much variation, — and the truth of this
admission will often be disputed by other naturalists. When
he comes to study allied forms brought from countries not
now continuous, in which case he cannot hope to find inter-
mediate links, he will be compelled to trust almost entirely to
analogy, and his difficulties will rise to a climax.
Certainly no clear line of demarcation has as yet been
drawn between species and sub-species — that is, the forms
which in the opinion of some naturalists come very near to,
but do not quite arrive at, the rank of species: or, again,
between sub-species and well-marked varieties, or between
lesser varieties and individual differences. These differences
blend into each other by an insensible series; and a series
impresses the mind with the idea of an actual passage.
Hence I look at individual differences, though of small
interest to the systematist, as of the highest importance for
us, as being the first steps towards such slight varieties as
are barely thought worth recording in works on natural his-
tory. And I look at varieties which are in any degree more
distinct and permanent, as steps towards more strongly-
marked and permanent varieties; and at the latter, as lead-
ing to sub-species, and then to species. The passage from
one stage of difference to another may, in many cases, be
the simple result of the nature of the organism and of the
different physical conditions to which it has long been ex-
posed; but with respect to the more important and adaptive
characters, the passage from one stage of dift'erence to an-
other, may be safely attributed to the cumulative action of
natural selection, hereafter to be explained, and to the effects
of the increased use or disuse of parts. A well-marked vari-
ety may therefore be called an incipient species; but whether
this belief is justifiable must be judged by the weight of the
various facts and considerations to be given throughout this
work.
It need not be supposed that all varieties or incipient
DOMINANT SPECIES VARY MOST 69
species attain the rank of species. They may become extinct,
or they may endure as varieties for very long periods, as
has been shown to be the case by Mr. Wollaston with the
varieties of certain fossil land-shells in Madeira, and with
plants by Gaston de Saporta. If a variety were to flourish
so as to exceed in numbers the parent species, it would then
rank as the species, and the species as the variety; or it
might come to supplant and exterminate the parent species;
or both might co-exist, and both rank as independent species.
But we shall hereafter return to this subject.
From these remarks it will be seen that 1 look at the term
species as one arbitrarily given, for the sake of convenience,
to a set of individuals closely resembling each other, and
that it does not essentially diiTer from the term variety, which
is given to less distinct and more fluctuating forms. The
term variety, again, in comparison with mere individual dif-
ferences, is also applied arbitrarily, for convenience' sake.
WIDE-RANGING, MUCH DIFFUSED, AND COMMON SPECIES
VARY MOST
Guided by theoretical considerations, I thought that some
interesting results might be obtained in regard to the nature
and relations of the species which vary most, by tabulating
all the varieties in several well-worked floras. At first this
seemed a simple task; but Mr. H. C. Watson, to whom I am
much indebted for valuable advice and assistance on this
subject, soon convinced me that there were many difficulties,
as did subsequently Dr. Hooker, even in stronger terms. I
shall reserve for a future work the discussion of these diffi-
culties, and the tables of the proportional numbers of the
varying species. Dr. Hooker permits me to add that after
having carefully read my manuscript, and examined the
tables, he thinks that the following statements are fairly well
established. The whole subject, however, treated as it neces-
sarily here is with much brevity, is rather perplexing, and
allusions cannot be avoided to the "struggle for existence,"
"divergence of character," and other questions, hereafter to
be discussed.
Alphonse de Candolle- and others have shown that plants
70 ORIGIN OF SPECIES
which have very wide ranges generally present varieties;
and this might have been expected, as they are exposed to
diverse physical conditions, and as they come into competi-
tion (which, as we shall hereafter see, is an equally or more
important circumstance) with different sets of organic beings.
But my tables further show that, in any limited country, the
species which are the most common, that is abound most in
individuals, and the species which are most widely diffused
within their own country (and this is a different considera-
tion from wide range, and to a certain extent from com-
monness), oftenest give rise to varieties sufificiently well-
marked to have been recorded in botanical works. Hence
it is the most flourishing, or, as they may be called, the
dominant species, — those which range widely, are the most
diffused in their own country, and are the most numerous
in individuals, — which oftenest produce well-marked varie-
ties, or, as I consider them, incipient species. And this, per-
haps, might have been anticipated; for, as varieties, in order
to become in any degree permanent, necessarily have to
struggle with the other inhabitants of the country, the spe-
cies which are already dominant will be the most likely to
yield offspring, which, though in some slight degree modi-
fied, still inherit those advantages that enabled their parents
to become dominant over their compatriots. In these re-
marks on predominance, it should be understood that refer-
ence is made only to the forms which come into competition
with each other, and more especially to the members of the
same genus or class having nearly similar habits of life.
With respect to the number of individuals or commonness
of species, the comparison of course relates only to the
members of the same group. One of the higher plants may
be said to be dominant if it be more numerous in individuals
and more widely diffused than the other plants of the same
country, which live under nearly the same conditions. A
plant of this kind is not the less dominant because some
conferva inhabiting the water or some parasitic fungus is
infinitely more numerous in individuals, and more widely
diffused. But if the conferva or parasitic fungus exceeds
its allies in the above respects, it will then be dominant
within its own class.
SPECIES OF LARGER GENERA VARIABLE 71
SPECIES OF THE LARGER GENERA IN EACH COUNTRY VARY
MORE FREQUENTLY THAN THE SPECIES OF THE
SMALLER GENERA
If the plants inhabiting a country, as described in any
Flora, be divided into two equal masses, all those in the
larger genera (i.e., those including many species) being
placed on one side, and all those in the smaller genera on
the other side, the former will be found to include a some-
what larger number of the very common and much diffused
or dominant species. This might have been anticipated; for
the mere fact of many species of the same genus inhabiting
any country, shows that there is something in the organic
or inorganic conditions of that country favourable to the
genus ; and, consequently, we might have expected to have
found in the larger genera, or those including many species,
a larger proportional number of dominant species. But so
many causes tend to obscure this result, that I am surprised
that my tables show even a small majority on the side of
the larger genera. I will here allude to only two causes of
obscurity. Fresh-water and salt-loving plants generally
have very wide ranges and are much diffused, but this seems
to be connected with the nature of the stations inhabited by
them, and has little or no relation to the size of the genera
to which the species belong. Again, plants low in the scale
of organisation are generally much more widely diffused
than plants higher in the scale; and here again there is no
close relation to the size of the genera. The cause of lowly-
organised plants ranging widely will be discussed in our
chapter on Geographical Distribution.
From looking at species as only strongly-marked and well-
defined varieties, I was led to anticipate that the species of
the larger genera in each country would oftener present
varieties, than the species of the smaller genera: for wher-
ever many closely related species (i.e.. species of the same
genus) have been formed, many varieties or incipient spe-
cies ought, as a general rule, to be now forming. Where
many large trees grow, we' expect to find saplings. Where
many species of a genus have been formed through varia-
tion, circumstances have" been favourable for variation; and
72 ORIGIN OF SPECIES
hence we might expect that the circumstances would gener-
ally be still favourable to variation. On the other hand, if
we look at each species as a special act of creation, there is
no apparent reason why more varieties should occur in a
group having many species, than in one having few.
To test the truth of this anticipation I have arranged the
plants of twelve countries, and the coleopterous insects of
two districts, into two nearly equal masses, the species of
the larger genera on one side, and those of the smaller genera
on the other side, and it has invariably proved to be the case
that a larger proportion of the species on the side of the
larger genera presented varieties, than on the side of the
smaller genera. Moreover, the species of the large genera
which present any varieties, invariably present a larger
average number of varieties than do the species of the small
genera. Both these results follow when another division is
made, and when all the least genera, with from only one to
four species, are altogether excluded from the tables. These
facts are of plain signification on the view that species are
only strongly-marked and permanent varieties; for wherever
many species of the same genus have been formed, or where,
if we may use the expression, the manufactory of species
has been active, we ought generally to find the manufactory
still in action, more especially as we have every reason to
believe the process of manufacturing new species to be a
slow one. And this certainly holds true, if varieties be
looked at as incipient species; for my tables clearly show as
a general rule that, wherever many species of a genus have
been formed, the species of that genus present a number of
varieties, that is of incipient species, beyond the average.
It is not that all large genera are now varying much, and
are thus increasing in the number of their species, or that
no small genera are now varying and increasing; for if this
had been so, it would have been fatal to my theory: inas-
much as geology plainly tells us that small genera have in
the lapse of time often increased greatly in size; and that
large genera have often come to their maxima, decline, and
disappeared. All that we want to show is, that, where many
species of a genus have been formed, on an average many
are still forming; and this certainly holds good.
RESEMBLE VARIETIES 73
MANY OF THE SPECIES INCLUDED WITHIN THE LARGER
GENERA RESEMBLE VARIETIES IN BEING VERY CLOSELY,
BUT UNEQUALLY, RELATED TO EACH OTHER, AND
IN HAVING RESTRICTED RANGES
There are other relations between the species of large
genera and their recorded varieties which deserve notice. We
have seen that there is no infallible criterion by which to
distinguish species and well-marked varieties; and when in-
termediate links have not been found between doubtful
forms, naturalists are compelled to come to a determination
by the amount of difference between them, judging by anal-
ogy whether or not the amount suffices to raise one or both
to the rank of species. Hence the amount of difference is
one very important criterion in settling whether two forms
should be ranked as species or varieties. Now Fries has
remarked in regard to plants, and Westwood in regard to
insects, that in large genera the amount of difference be-
tween the species is often exceedingly small. I have en-
deavoured to test this numerically by averages, and, as far
as my imperfect results go, they confirm the view. I have
also consulted some sagacious and experienced observers,
and, after deliberation, they concur in this view. In this
respect, therefore, the species of the larger genera resemble
varieties, more than do the species of the smaller genera.
Or the case may be put in another way, and it may be said,
that in the larger genera, in which a number of varieties or
incipient species greater than the average are now manu-
facturing, many of the species already manufactured still to
a certain extent resemble varieties, for they differ from each
other by less than the usual amount of difference.
Moreover, the species of the larger genera are related to
each other, in the same manner as the varieties of any one
species are related to each other. No naturalist pretends
that all the species of a genus are equally distinct from each
other ; they may generally be divided into sub-genera, or sec-
tions, or lesser groups. As Fries has well remarked, little
groups of species are generally clustered like satellites
around other species. And what are varieties but groups of
forms, unequally related to each other, and clustered round
74 ORIGIN OF SPECIES
certain forms — that is, round their parent-species? Un-
doubtedly there is one most important point of difference
between varieties and species; namely, that the amount of
difference between varieties, when compared with each other
or with their parent-species, is much less than that between
the species of the same genus. But when we come to discuss
the principle, as I call it, of Divergence of Character, we
shall see how this may be explained, and how the lesser dif-
ferences between varieties tend to increase into the greater
differences between species.
There is one other point which is worth notice. Varieties
generally have much restricted ranges: this statement is in-
deed scarcely more than a truism, for, if a variety were
found to have a wider range than that of its supposed parent-
species, their denominations would be reversed. But there
is reason to believe that the species which are very closely
allied to other species, and in so far resemble varieties, often
have much restricted ranges. For instance, Mr. H. C. Wat-
son has marked for me in the well-sifted London Catalogue
of plants (4th edition) 63 plants which are therein ranked
as species, but which he considers as so closely allied to other
species as to be of doubtful value: these 63 reputed species
range on an average over 6*9 of the provinces into which
Mr. Watson has divided Great Britain. Now, in this same
Catalogue, 53 acknowledged varieties are recorded, and these
range over 'j-y provinces; whereas, the species to which these
varieties belong range over 14-3 provinces. So that the ac-
knowledged varieties have nearly the same restricted aver-
age range, as have the closely allied forms, marked for me
by Mr. Watson as doubtful species, but which are almost
universally ranked by British botanists as good and true
species.
SUMMARY
Finally, varieties cannot be distinguished from species, —
except, first, by the discovery of intermediate linking forms;
and, secondly, by a certain indefinite amount of difference
between them; for two forms, if differing very little, are
generally ranked as varieties, notwithstanding that they
cannot be closely connected; but the amount of difference
SUMMARY 75
considered necessary to give to any two forms the rank of
species cannot be defined. In genera having more than the
average number of species in any country, the species of
these genera have more than the average number of varie-
ties. In large genera the species are apt to be closely, but
unequally, allied together, forming little clusters round other
species. Species very closely allied to other species appar-
ently have restricted ranges. In all these respects the spe-
cies of large genera present a strong analogy with varieties.
And we can clearly understand these analogies, if species
once existed as varieties, and thus originated; whereas, these
analogies are utterly inexplicable if species are independent
creations.
We have, also, seen that it is the most flourishing or dom-
inant species of the larger genera within each class which on
an average yield the greatest number of varieties ; and varie-
ties, as we shall hereafter see, tend to become converted into
new and distinct species. Thus the larger genera tend to
become larger ; and throughout nature the forms of life
which are now dominant tend to become still more dominant
by leaving many modified and dominant descendants. But
by steps hereafter to be explained, the larger genera also
tend to break up into smaller genera. And thus, the forms
of life throughout the universe become divided into groups
subordinate to groups.
CHAPTER in
Struggle for Existence
Its bearing on natural selection — The term used in a wide sense —
Geometrical ratio of increase — Rapid increase of naturalized
animals and plants — Nature of the checks to increase — Competi-
tion universal — Effects of climate — Protection from the number
of individuals — Complex relations of al! animals and plants
throughout nature — Struggle for life most severe between indi-
viduals and varieties of the same species : often severe between
species of the same genus — -The relation of organism to organism
the most important of all relations.
BEFORE entering on the subject of this chapter, I must
make a few preliminary remarks, to show how the
struggle for existence bears on Natural Selection. It
has been seen in the last chapter that amongst organic beings
in a state of nature there is some individual variability : in-
deed I am not aware that this has ever been disputed. It is
immaterial for us whether a multitude of doubtful forms be
called species or sub-species or varieties; what rank, for in-
stance, the two or three hundred doubtful forms of British
plants ate entitled to hold, if the existence of any well-marked
varieties be admitted. But the mere existence of individual
variability and of some few well-marked varieties, though
necessary as the foundation for the work, helps us but little
in understanding how species arise in nature. How have all
those exquisite adaptations of one part of the organisation
to another part, and to the conditions of life, and of one
organic being to another being, been perfected? We see
these beautiful co-adaptations most plainly in the wood-
pecker and the mistletoe; and only a little less plainly
in the humblest parasite which clings to the hairs of a quad-
ruped or feathers of a bird: in the structure of the beetle
which dives through the water : in the plumed seed which is
wafted by the gentlest breeze; in short, we see beautiful
76
STRUGGLE FOR EXISTENCE 77
adaptations everywhere and in every part of the organic
world.
Again, it may be asked, how is it that varieties, which I
have called incipient species, become ultimately converted
into good and distinct species, which in most cases obviously
differ from each other far more than do the varieties of the
same species? How do those groups of species, which con-
stitute what are called distinct genera, and which differ
from each other more than do the species of the same genus,
arise? All these results, as we shall more fully see in the
next chapter, follow from the struggle for life. Owing to
this struggle, variations, however slight and from whatever
cause proceeding, if they be in any degree profitable to the
individuals of a species, in their infinitely complex relations
to other organic beings and to their physical conditions of
life, will tend to the preservation of such individuals, and
will generally be inherited by the offspring. The offspring,
also, will thus have a better chance of surviving, for, of the
many individuals of any species which are periodically born,
but a small number can survive. I have called this principle,
by which each slight variation, if useful, is preserved, by the
term Natural Selection, in order to mark its relation to
man's power of selection. But the expression often used by
Mr. Herbert Spencer of the Survival of the Fittest is more
accurate, and is sometimes equally convenient. We have
seen that man by selection can certainly produce great re-
sults, and can adapt organic beings to his own uses, through
the accumulation of slight but useful variations, given to
him by the hand of Nature. But Natural Selection, as we
shall hereafter see, is a power incessantly ready for action,
and is as immeasurably superior to man's feeble efforts, as
the works of Nature are to those of Art.
We will now discuss in a little more detail the struggle for
existence. In my future work this subject will be treated,
as it well deserves, at greater length. The elder De Candolle
and Lyell have largely and philosophically shown that all
organic beings are exposed to severe competition. In regard
to plants, no one has treated this subject with more spirit
and ability than W. Herbert, Dean of Manchester, evidently
the result of his great -horticultural knowledge. Nothing is
78 ORIGIN OF SPECIES
easier than to admit in words the truth of the universal
struggle for hfe, or more difficult — at least, I have found it
so — than constantly to bear this conclusion in mind. Yet
unless it be thoroughly engrained in the mind, the whole
economy of nature, with every fact on distribution, rarity,
abundance, extinction, and variation, will be dimly seen or
quite misunderstood. We behold the face of nature bright
with gladness, we often see superabundance of food; we do
not see, or we forget, that the birds which are idly singing
round us mostly live on insects or seeds, and are thus con-
stantly destroying life; or we forget how largely these song-
sters, or their eggs, or their nestlings, are destroyed by birds
and beasts of prey ; we do not always bear in mind, that,
though food may be now superabundant, it is not so at all
seasons of each recurring year.
THE TERM, STRUGGLE FOR EXISTENCE, USED IN
A LARGE SENSE
I should premise that I use this term in a large and meta-
phorical sense including dependence of one being on another,
and including (which is more important) not only the life
of the individual, but success in leaving progeny. Two
canine animals, in a time of dearth, may be truly said to
struggle with each other which shall get food and live. But
a plant on the edge of a desert is said to struggle for life
against the drought, though more properly it should be said
to be dependent on the moisture. A plant which annually
produces a thousand seeds, of which only one of an average
comes to maturity, may be more truly said to struggle with
the plants of the same and other kinds which already clothe
the ground. The mistletoe is dependent on the apple and a
few other trees, but can only in a far-fetched sense be said
to struggle with these trees, for, if too many of these para-
sites grow on the same tree, it languishes and dies. But
several seedling mistletoes, growing close together on the
same branch, may more truly be said to struggle with each
other. As the mistletoe is disseminated by birds, its exist-
ence depends on them ; and it may metaphorically be said to
struggle with other fruit-bearing plants, in tempting the
GEOMETRICAL RATIO OF INCREASE 79
birds to devour and thus disseminate its seeds. In these sev-
eral senses, which pass into each other, I use for conveni-
ence sake the general term of Struggle for Existence.
GEOMETRICAL RATIO OF INCREASE
A struggle for existence inevitably follows from the high
rate at which all organic beings tend to increase. Every
being, which during its natural lifetime produces several
eggs or seeds, must suffer destruction during some period of
its life, and during some season or occasional year, other-
wise, on the principle of geometrical increase, its numbers
would quickly become so inordinately great that no country
could support the product. Hence, as more individuals are
produced than can possibly survive, there must in every case
be a struggle for existence, either one individual with an-
other of the same species, or with the individuals of distinct
species, or with the physical conditions of life. It is the
doctrine of Malthus applied with manifold force to the whole
animal and vegetable kingdoms; for in this case there can
be no artificial increase of food, and no prudential restraint
from marriage. Although some species may be now increas-
ing, more or less rapidly, in numbers, all cannot do so, for
the world would not hold them.
There is no exception to the rule that every organic being
naturally increases at so high a rate, that, if not destroyed,
the earth would soon be covered by the progeny of a single
pair. Even slow-breeding man has doubled in twenty-five
years, and at this rate in less than a thousand years, there
would literally not be standing-room for his progeny. Lin-
n?eus has calculated that if an annual plant produced only
two seeds — and there is no plant so unproductive as this —
and their seedlings next year produced two, and so on, then
in twenty years there would be a million plants. The ele-
phant is reckoned the slowest breeder of all known animals,
and I have taken some pains to estimate its probable mini-
mum rate of natural increase; it will be safest to assume
that it begins breeding when thirty years old, and goes on
breeding till ninety years old, bringing forth six young in
the interval, and surviving till one hundred years old; if this
80 ORIGIN OF SPECIES
be so, after a period of from 740 to 750 years there would
be nearly nineteen million elephants alive, descended from
the first pair.
But we have better evidence on this subject than mere
theoretical calculations, namely, the numerous recorded cases
of the astonishingly rapid increase of various animals in a
state of nature, when circumstances have been favourable to
them during two or three following seasons. Still more
striking is the evidence from our domestic animals of many
kinds which have run wild in several parts of the world;
if the statements of the rate of increase of slow-breeding
cattle and horses in South America, and latterly in Australia,
had not been well authenticated, they would have been in-
credible. So it is with plants ; cases could be given of intro-
duced plants which have become common throughout whole
islands in a period of less than ten years. Several of the
plants, such as the cardoon and a tall thistle, which are
now the commonest over the wide plains of La Plata, cloth-
ing square leagues of surface almost to the exclusion of
every other plant, have been introduced from Europe ; and
there are plants which now range in India, as I hear from
Dr. Falconer, from Cape Comorin to the Himalaya, which
have been imported from America since its discovery. In
such cases, and endless others could be given, no one sup-
poses, that the fertility of the animals or plants has been
suddenly and temporarily increased in any sensible degree.
The obvious explanation is that the conditions of life have
been highly favourable, and that there has constantly been
less destruction of the old and young, and that nearly all the
young have been enabled to breed. Their geometrical ratio
of increase, the result of which never fails to be surprising,
simply explains their extraordinarily rapid increase and wide
diffusion in their new homes.
In a state of nature almost every full-grown plant annually
produces seed, and amongst animals there are very few
which do not annually pair. Hence we may confidently as-
sert, that all plants and animals are tending to increase at a
geometrical ratio, — that all would rapidly stock every station
in which they could anyhow exist, — and that this geomet-
rical tendency to increase must be checked by destruction at
GEOMETRICAL RATIO OF INCREASE 81
some period of life. Our familiarity with the larger domes-
tic animals tends, I think, to mislead us: we see no great
destruction falling on them, but we do not keep in mind that
thousands are annually slaughtered for food, and that in a
state of nature an equal number would have somehow to be
disposed of.
The only difference between organisms which annually pro-
duce eggs or seeds by the thousand, and those which produce
extremely few, is, that the slow-breeders would require a
few more years to people, under favourable conditions, a
whole district, let it be ever so large. The condor lays a
couple of eggs and the ostrich a score, and yet in the same
country the condor may be the more numerous of the two;
the Fulmar petrel lays but one egg, yet it is believed to be
the most numerous bird in the world. One fly deposits hun-
dreds of eggs, and another, like the hippobosca, a single
one ; but this difference does not determine how many indi-
viduals of the two species can be supported in a district.
A large number of eggs is of some importance to those spe-
cies which depend on a fluctuating amount of food, for it
allows them rapidly to increase in number. But the real im-
portance of a large number of eggs or seeds is to make up
for much destruction at some period of life; and this period
in the great majority of cases is an early one. If an animal
can in any way protect its own eggs or young, a small num-
ber may be produced, and yet the average stock be fully kept
up; but if many eggs or young are destroyed, many must be
produced, or the species will become extinct. It would suf-
fice to keep up the full number of a tree, which lived on an
average for a thousand years, if a single seed were produced
once in a thousand years, supposing that this seed were never
destroyed, and could be ensured to germinate in a fitting
place. So that, in all cases, the average number of any ani-
mal or plant depends only indirectly on the number of its
eggs or seeds.
In looking at Nature, it is most necessary to keep the fore-
going considerations always in mind — never to forget that
every single organic being jnay be said to be striving to the
utmost to increase in numbers; that each lives by a struggle
at some period of its life; that heavy destruction inevitably
82 ORIGIN OF SPECIES
falls either on the young or old, during each generation or
at recurrent intervals. Lighten any check, mitigate the de-
struction ever so little, and the number of the species will
almost instantaneously increase to any amount.
NATURE OF THE CHECKS TO INCREASE
The causes which check the natural tendency of each spe-
cies to increase are most obscure. Look at the most vig-
orous species; by as much as it swarms in numbers, by so
much will it tend to increase still further. We know not
exactly what the checks are even in a single instance. Nor
will this surprise any one who reflects how ignorant we are
on this head, even in regard to mankind, although so incom-
parably better known than any other animal. This subject
of the checks to increase has been ably treated by several
authors, and I hope in a future work to discuss it at con-
siderable length, more especially in regard to the feral ani-
mals of South America. Here I will make only a few re-
marks, just to recall to the reader's mind some of the chief
points. Eggs or very young animals seem generally to sufifer
most, but this is not invariably the case. With plants there
is a vast destruction of seeds, but, from some observations
which I have made, it appears that the seedings suffer most
from germinating in ground already thickly stocked with
other plants. Seedlings, also, are destroyed in vast numbers
by various enemies; for instance, on a piece of ground three
feet long and two wide, dug and cleared, and where there
could be no choking from other plants, I marked all the
seedlings of our native weeds as they came up, and out of
357 no less than 295 were destroyed, chiefly by slugs and in-
sects. If turf which has long been mown, and the case would
be the same with turf closely browsed by quadrupeds, be let
to grow, the more vigorous plants gradually kill the less
vigorous, though fully grown plants; thus out of twenty spe-
cies growing on a little plot of mown turf (three feet by
four) nine species perished, from the other species being al-
lowed to grow up freely.
The amount of food for each species of course gives the
extreme limit to which each can increase; but very fre-
NATURE OF THE CHECKS TO INCREASE 83
qtaently it is not the obtaining food, but the serving as prey-
to other animals, which determines the average numbers of
a species. Thus, there seems to be little doubt that the stock
of partridges, grouse and hares on any large estate depends
chiefly on the destruction of vermin. If not one head of
game were shot during the next twenty years in England,
and, at the same time, if no vermin were destroyed, there
would, in all probability, be less game than at present, al-
though hundreds of thousands of game animals are now
annually shot. On the other hand, in some cases, as with
the elephant, none are destroyed by beasts of prey; for even
the tiger in India most rarely dares to attack a young ele-
phant protected by its dam.
Climate plays an important part in determining the aver-
age numbers of a species, and periodical seasons of extreme
cold or drought seem to be the most effective of all checks.
I estimated (chiefly from the greatly reduced numbers of
nests in the spring) that the winter of 1854-5 destroyed four-
fifths of the birds in my own grounds ; and this is a tremen-
dous destruction, when we remember that ten per cent, is
an extraordinarily severe mortality from epidemics with
man. The action of climate seems at first sight to be quite
independent of the struggle for existence; but in so far as
climate chiefly acts in reducing food, it brings on the most
severe struggle between the individuals, whether of the same
or of distinct species, which subsist on the same kind of
food. Even when climate, for instance extreme cold, acts
directly, it will be the least vigorous individuals, or those
which have got least food through the advancing winter,
which will suffer most. When we travel from south to
north, or from a damp region to a dry, we invariably see
some species gradually getting rarer and rarer, and finally
disappearing; and the change of climate being conspicuous,
we are tem.pted to attribute the whole effect to its direct
action. But this is a false view; we forget that each species,
even where it most abounds, is constantly suft'ering enormous
destruction at some period of its life, from enemies or from
competitors for the same place and food ; and if these ene-
mies or competitors be in the least degree favoured by any
slight change of climate, they will increase in numbers; and
84 ORIGIN OF SPECIES
as each area is already fully stocked with inhabitants, the
other species must decrease. When we travel southward
and see a species decreasing in numbers, we may feel sure
that the cause lies quite as much in other species being fa-
voured, as in this one being hurt. So it is when we travel
northward, but in a somewhat lesser degree, for the number
of species of all kinds, and therefore of competitors, de-
creases northwards ; hence in going northwards, or in as-
cending a mountain, we far oftener meet with stunted forms,
due to the directly injurious action of climate, than we do in
proceeding southwards or in descending a mountain. When
we reach the Arctic regions, or snow-capped summits, or
absolute deserts, the struggle for life is almost exclusively
with the elements.
That climate acts in main part indirectly by favouring .
other species, we clearly see in the prodigious number of
plants which in our gardens can perfectly well endure our
climate, but which never became naturalised, for they can-
not compete with our native plants nor resist destruction
by our native animals.
When a species, owing to highly favoured circumstances,
increases inordinately in numbers in a small tract, epidemics
— at least, this seems generally to occur with our game ani-
mals — often ensue; and here we have a limiting check inde-
pendent of the struggle for life. But even some of these
so-called epidemics appear to be due to parasitic worms,
which have from some cause, possibly in part through fa-
cility of diffusion amongst the crowded animals, been dis-
proportionally favoured : and here comes in a sort of struggle
between the parasite and its prey.
On the other hand, in many cases, a large stock of indi-
viduals of the same species, relatively to the numbers of its
enemies, is absolutely necessary for its preservation. Thus
we can easily raise plenty of corn and rape-seed, &c., in our
fields, because the seeds are in great excess, compared with
the number of birds which feed on them; nor can the birds,
though having a superabundance of food at this one sea-
son, increase in number proportionally to the supply of
seed, as their numbers are checked during winter ; but any
one who has tried, knows how troublesome it is to get seed
STRUGGLE FOR EXISTENCE 85
from a few wheat or other such plants in a garden : I have
in this case lost every single seed. This view of the neces-
sity of a large stock of the same species for its preservation,
explains, I believe, some singular facts in nature such as that
of very rare plants being sometimes extremely abundant, in
the few spots where they do exist ; and that of some social
plants being social, that is abounding in individuals, even on
the extreme verge of their range. For in such cases, we
may believe, that a plant could exist only where the condi-
tions of its life were so favourable that many could exist
together, and thus save the species from utter destruction.
I should add that the good effects of intercrossing, and the
ill effects of close interbreeding, no doubt come into play
in many of these cases; but I will not here enlarge on this
subject.
COMPLEX RELATIONS OF ALL ANIMALS AND PLANTS
TO EACH OTHER IN THE STRUGGLE
FOR EXISTENCE
Many cases are on record showing how complex and un-
expected are the checks and relations between organic
beings, which have to struggle together in the same coun-
try. I will give only a single instance, which, though a
simple one, interested me. In Staffordshire, on the estate
of a relation, where I had ample means of investigation,
there was a large and extremely barren heath, which had
never been touched by the hand of man ; but several acres
of exactly the same nature had been enclosed twenty-five
years previously and planted with Scotch fir. The change
in the native vegetation of the planted part of the heath
was most remarkable, more than is generally seen in pass-
ing from one quite different soil to another: not only the
proportional numbers of the heath-plants were wholly
changed, but twelve species of plants (not counting grasses
and carices) flourished in the plantations, which could not
be found on the heath. The effect on the insects must have
been still greater, for six insectivorous birds were very com-
mon in the plantations, which were not to be seen on the
heath ; and the heath was frequented by two or three dis-
tinct insectivorous birds. Here we see how potent has been
86 ORIGIN OF SPECIES
the effect of the introduction of a single tree, nothing what-
ever else having been done, with the exception of the land
having been enclosed, so that cattle could not enter.
But how important an element enclosure is, I plainly saw
near Farnham, in Surrey. Here there are extensive heaths,
with a fevvT clumps of old Scotch firs on the distant hill-
tops: within the last ten years large spaces have been en-
closed, and self-sown firs are now springing up in multitudes,
so close together that all cannot live. When I ascertained
that these young trees had not been sown or planted, I was
so much surprised at their numbers that I went to several
points of view, whence I could examine hundreds of acres
of the unenclosed heath, and literally I could not see a
single Scotch fir, except the old planted clumps. But on
looking closely between the stems of the heath, I found a
multitude of seedlings and little trees which had been per-
petually browsed down by the cattle. In one square yard,
at a point some hundred yards distant from one of the old
clumps, I counted thirty-two little trees; and one of them,
with twenty-six rings of growth, had, during many years,
tried to raise its head above the stems of the heath, and
had failed. No wonder that, as soon as the land was en-
closed, it became thickly clothed with vigorously growing
young firs. Yet the heath was so extremely barren and so
extensive that no one would ever have imagined that cattle
would have so closely and effectually searched it for food.
Here we see that cattle absolutely determine the existence
of the Scotch fir; but in several parts of the world insects
determine the existence of cattle. Perhaps Paraguay offers
the most curious instance of this; for here neither cattle
nor horses nor dogs have ever run wild, though they swarm
southward and northward in a feral state; and Azara and
Rengger have shown that this is caused by the greater num-
ber in Paraguay of a certain fly, which lays its eggs in the
navels of these animals when first born. The increase of
these flies, numerous as they are, must be habitually checked
by seme means, probably by ether parasitic insects. Hence,
if certain insectivorous birds were to decrease in Paraguay,
the parasitic insects would probably increase ; and this
would lessen tlie number of the navel-frequenting flies —
STRUGGLE FOR EXISTENCE 87
then cattle and horses would become feral, and this would
certainly greatly alter (as indeed I have observed in parts
of South America) the vegetation: this again would largely
affect the insects; and this, as we have just seen in Stafford-
shire, the insectivorous birds, and so onwards in ever-in-
creasing circles of complexity. Not that under nature the
relations will ever be as simple as this. Battle within battle
must be continually recurring with varying success ; and yet
in the long-run the forces are so nicely balanced, that the
face of nature remains for long periods of time uniform,
though assuredly the merest trifle would give the victory to
one organic being over another. Nevertheless, so profound
is our ignorance, and so high our presumption, that we
marvel when we hear of the extinction of an organic being;
and as we do not see the cause, we invoke cataclysms to
desolate the world, or invent laws on the duration of the
forms of life !
I am tempted to give one more instance showing how plants
and animals, remote in the scale of nature, are bound together
by a web of complex relations. I shall hereafter have occasion
to show that the exotic Lobelia fulgens is never visited in
my garden by insects, and consequently, from its peculiar
structure, never sets a seed. Nearly all our orchidaceous
plants absolutely require the visits of insects to remove their
pollen-masses and thus to fertilise them. I find from experi-
ments that humble-bees are almost indispensable to the fer-
tilisation of the heartsease (Viola tricolor), for other bees
do not visit this flower. I have also found that the visits of
bees are necessary for the fertilisation of some kinds of
clover; for instance, 20 heads of Dutch clover (Trifolium
repens) yielded 2,290 seeds, but 20 other heads protected
from bees produced not one. Again, 100 heads of red
clover (T. pratense) produced 2,700 seeds, but the same
number of protected heads produced not a single seed.
Humble-bees alone visit red clover, as other bees cannot
reach the nectar. It has been suggested that moths may
fertilise the clovers; but I doubt whether they could do so
in the case of the red clover, from their weight not being
sufficient to depress the wing petals. Hence we may infer
as highly probable that, if the whole genus of humble-bees
88 ORIGIN OF SPECIES
became extinct or very rare in England, the heartsease and
red clover would become very rare^ or wholly disappear.
The number of humble-bees in any district depends in a
great measure upon the number of field-mice, which destroy
their combs and nests; and Col. Newman, who has long
attended to the habits of humble-bees, believes that "more
than two-thirds of them are thus destroyed all over Eng-
land." Now the number of mice is largely dependent, as
every one knows, on the number of cats ; and Col. Newman
says, "Near villages and small towns I have found the nests
of humble-bees more numerous than elsewhere, which I
attribute to the number of cats that destroy the mice."
Hence it is quite credible that the presence of a feline ani-
mal in large numbers in a district might determine, through
the intervention first of mice and then of bees, the fre-
quency of certain flowers in that district !
In the case of every species, many different checks, acting
at different periods of life, and during different seasons or
years, probably come into play; some one check or some few
being generally the most potent ; but all will concur in deter-
mining the average number or even the existence of the
species. In some cases it can be shown that widely-different
checks act on the same species in different districts. When
we look at the plants and bushes clothing an entangled bank,
we are tempted to attribute their proportional numbers and
kinds to what we call chance. But how false a view is this !
Every one has heard that when an American forest is cut
down, a very different vegetation springs up ; but it has been
observed that ancient Indian ruins in the Southern United
States, which must formerly have been cleared of trees,
now display the same beautiful diversity and proportion of
kinds as in the surrounding virgin forest. What a struggle
must have gone on during long centuries between the sev-
eral kinds of trees, each annually scattering its seeds by the
thousand; what war between insect and insect — between
insects, snails, and other animals with birds and beasts of
prey — all striving to increase, all feeding on each other, or
on the trees, their seeds and seedlings, or on the other plants
which first clothed the ground and thus checked the growth
of the trees ! Throw up a handful of feathers, and all fall
STRUGGLE FOR EXISTENCE 89
to the ground according to definite laws; but how simple is
the problem where each shall fall compared to that of the
action and reaction of the innumerable plants and animals
which have determined, in the course of centuries, the pro-
portional numbers and kinds of trees now growing on the
old Indian ruins !
The dependency of one organic being on another, as of a
parasite on its prey, lies generally between beings remote
in the scale of nature. This is likewise sometimes the case
with those which may be strictly said to struggle with each
other for existence, as in the case of locusts and grass-
feeding quadrupeds. But the struggle will almost invariably
be most severe between the individuals of the same species,
for they frequent the same districts, require the same food,
and are exposed to the same dangers. In the case of varie-
ties of the same species, the struggle will generally be almost
equally severe, and we sometimes see the contest soon de-
cided : for instance, if several varieties of wheat be sown
together, and the mixed seed be resown, some of the varie-
ties which best suit the soil or climate, or are naturally the
most fertile, will beat the others and so yield more seed,
and will consequently in a few years supplant the other
varieties. To keep up a mixed stock of even such extremely
close varieties as the variously-coloured sweet peas, they
must be each year harvested separately, and the seed then
mixed in due proportion, otherwise the weaker kinds will
steadily decrease in number and disappear. So again with
the varieties of sheep; it has been asserted that certain
mountain-varieties will starve out other mountain-varieties,
so that they cannot be kept together. The same result has
followed from keeping together dii¥erent varieties of the
medicinal leech. It may even be doubted whether the varie-
ties of any of our domestic plants or animals have so ex-
actly the same strength, habits, and constitution, that the
original proportions of a mixed stock (crossing being pre-
vented) could be kept up for half-a-dozen generations, if
they were allowed to struggle together, in the same manner
as beings in a state of nature, and if the seed or young were
not annually preserved in due proportion.
90 ORIGIN OF SPECIES
STRUGGLE FOR LIFE MOST SEVERE BETWEEN INDIVIDUALS
AND VARIETIES OF THE SAME SPECIES
As the species of the same genus usually have, though by
no means invariably, much similarity in habits and consti-
tution, and always in structure, the struggle will generally
be more severe between them, if they come into competition
with each other, than between the species of distinct genera.
We see this in the recent extension over parts of the United
States of one species of swallow having caused the decrease
of another species. The recent increase of the missel-thrush
in parts of Scotland has caused the decrease of the song-
thrush. How frequently we hear of one species of rat taking
the place of another species under the most different cli-
mates ! In Russia the small Asiatic cockroach has every-
where driven before it its great congener. In Australia
the imported hive-bee is rapidly exterminating the small,
stingless native bee. One species of charlock has been
known to supplant another species; and so in other cases.
We can dimly see why the competition should be most severe
between allied forms, which fill nearly the same place in the
economy of nature; but probably in no one case could we
precisely say why one species has been victorious over
another in the great battle of life.
A corollary of the highest importance may be deduced
from the foregoing remarks, namely, that the structure of
every organic being is related, in the mose essential yet often
hidden manner, to that of all the other organic beings, with
which it comes into competition for food or residence, or
from which it has to escape, or on which it preys. This is
obvious in the structure of the teeth and talons of the tiger;
and in that of the legs and claws of the parasite which clings
to the hair on the tiger's body. But in the beautifully plumed
seed of the dandelion, and in the flattened and fringed legs
of the water-beetle, the relation seems at first confined to
the elements of air and water. Yet the advantage of plumed
seeds no doubt stands in the closest relation to the land being
already thickly clothed with other plants ; so that the seeds
may be widely distributed and fall on unoccupied ground.
In the water-beetle, the structure of its legs, so well adapted
STRUGGLE FOR EXISTENCE 91
for diving, allows it to compete with other aquatic insects,
to hunt for its own prey, and to escape serving as prey to
other animals.
The store of nutriment laid up within the seeds of many
plants seems at first sight to have no sort of relation to
other plants. But from the strong growth of young plants
produced from such seeds, as peas and beans, when sown in
the midst of long grass, it may be suspected that the chief
use of the nutriment in the seed is to favour the growth of
the seedlings, whilst struggling with other plants growing
all around.
Look at a plant in the midst of its range, why does it not
double or quadruple its numbers? We know that it can per-
fectly well withstand a little more heat or cold, dampness or
dryness, for elsewhere it ranges into slightly hotter or colder,
damper or drier districts. In this case we can clearly see
that if we wish in imagination to give the plant the power of
increasing in number, we should have to give it some ad-
vantage over its competitors, or over the animals which prey
on it. On the confines of its geographical range, a change
of constitution with respect to climate would clearly be an
advantage to our plant ; but we have reason to believe that
only a few plants or animals range so far, that they are de-
stroyed exclusively by the rigour of the climate. Not until
we reach the extreme confines of life, in the Arctic regions
or on the borders of an utter desert, will competition cease.
The land may be extremely cold or dry, yet there will be
competition between some few species, or between the indi-
viduals of the same species, for the warmest or dampest
spots.
Hence we can see that when a plant or animal is placed
in a new country amongst new competitors, the conditions
of its life will generally be changed in an essential manner,
although the climate may be exactly the same as in its
former home. If its average numbers are to increase in its
new home, we should have to modify it in a different way to
what we should have had to do in its native country ; for we
should have to give it some advantage over a different set
of competitors or enemies. .
It is good thus to try in imagination to give to any one
92 ORIGIN OF SPECIES
species an advantage over another. Probably in no single
instance should we know what to do. This ought to con-
vince us of our ignorance on the mutual relations of all
organic beings; a conviction as necessary, as it is difficult
to acquire. All that we can do, is to keep steadily in mind
that each organic being is striving to increase in a geomet-
rical ratio ; that each at some period of its life, during some
season of the year, during each generation or at intervals,
has to struggle for life and to suffer great destruction.
When we reflect on this struggle, we may console ourselves
with the full belief, that the war of nature is not inces-
sant, that no fear is felt, that death is generally prompt,
and that the vigorous, the healthy, and the happy survive
and multiply.
CHAPTER IV
Natural Selection ; or the Survival of the Fittest
Natural Selection — its power compared with man's selection — its
power on characters of trifling importance — its power at all ages
and on both sexes — Sexual selection — On the generality of inter-
crosses between individuals of the same species — Circumstances
favourable and unfavourable to the results of Natural Selection,
namely, intercrossing, isolation, number of individuals — Slow
action — Extinction caused by Natural Selection — Divergence of
Character, related to the diversity of inhabitants of any small
area, and to naturalisation — Action of Natural Selection, through
divergence of Character and Extinction, on the descendants from
a common parent — Explains the grouping of all organic beings —
Advance in organisation — Low forms preserved — Convergence of
Character — Indefinite multiplication of species — Summary.
HOW will the struggle for existence, briefly discussed
in the last chapter, act in regard to variation? Can
the principle of selection, w^hich w^e have seen is so
potent in the hands of man, apply under nature? I think
we shall see that it can act most efficiently. Let the endless
number of slight variations and individual differences occur-
ring in our domestic productions, and, in a lesser degree, in
those under nature, be borne in mind : as well as the strength
of the hereditary tendency. Under domestication, it may be
truly said that the whole organisation becomes in some degree
plastic. But the variability, which we almost universally
meet with in our domestic productions, is not directly pro-
duced, as Hooker and Asa Gray have well remarked, by man ;
he can neither originate varieties, nor prevent their occur-
rence ; he can only preserve and accumulate such as do occur.
Unintentionally he exposes organic beings to new and chang-
ing conditions of life, and variability ensues ; but similar
changes of conditions might and do occur under nature. Let
it also be borne in mind how infinitely complex and close-
fitting are the mutual relations of all organic beings to each
other and to their physical' conditions of life; and conse-
93
94 ORIGIN OF SPECIES
quently what infinitely varied diversities of structure might
be of use to each being under changing conditions of life.
Can it, then, be thought improbable, seeing that variations
useful to man have undoubtedly occurred, that other vari-
ations useful in some way to each being in the great and com-
plex battle of life, should occur in the course of many suc-
cessive generations? If such do occur, can we doubt (re-
membering that many more individuals are born than can
possibly survive) that individuals having any advantage,
however slight, over others, would have the best chance of
surviving and of procreating their kind? On the other hand,
we may feel sure that any variation in the least degree injuri-
ous would be rigidly destroyed. This preservation of favour-
able individual differences and variations, and the destruction
of those which are injurious, I have called Natural Selection,
or the Survival of the Fittest. Variations neither useful nor
injurious would not be affected by natural selection, and
would be left either a fluctuating element, as perhaps we see
in certain polymorphic species, or would ultimately become
fixed, owing to the nature of the organism and the nature of
the conditions.
Several writers have misapprehended or objected to the
term Natural Selection. Some have even imagined that nat-
ural selection induces variability, whereas it implies only the
preservation of such variations as arise and are beneficial to
the being under its conditions of life. No one objects to
agriculturists speaking of the potent effects of man's selec-
tion; and in this case the individual differences given by
nature, which man for some object selects, must of necessity
first occur. Others have objected that the term selection im-
plies conscious choice in the animals which become modified;
and it has even been urged that, as plants have no volition,
natural selection is not applicable to them ! In the literal
sense of the word, no doubt, natural selection is a false term;
but who ever objected to chemists speaking of the elective
affinities of the various elements? — and yet an acid cannot
strictly be said to elect the base with which it in preference
combines. It has been said that I speak of natural selection
as an active power or Deity; but who objects to an author
speaking of the attraction of gravity as ruling the movements
NATURAL SELECTION 95
of the planets? Every one knows what is meant and is im-
plied by such metaphorical expressions ; and they are almost
necessary for brevity. So again it is difficult to avoid per-
sonifying the word Nature; but I mean by Nature, only the
^ggJ'^&^te action and product of many natural laws, and by
laws the sequence of events as ascertained by us. With a
little familiarity such superficial objections will be forgotten.
We shall best understand the probable course of natural
selection by taking the case of a country undergoing some
slight physical change, for instance, of climate. The propor-
tional numbers of its inhabitants will almost immediately un-
dergo a change, and some species will probably become ex-
tinct. We may conclude, from what we have seen of the in-
timate and complex manner in which the inhabitants of each
country are bound together, that any change in the numerical
proportions of the inhabitants, independently of the change
of climate itself, would seriously affect the others. If the
country were open on its borders, new forms would certainly
immigrate, and this would likewise seriously disturb the rela-
tions of some of the former inhabitants. Let it be remem-
bered how powerful the influence of a single introduced tree
or mammal has been shown to be. But in the case of an
island, or of a country partly surrounded by barriers, into
which new and better adapted forms could not freely enter,
we should then have places in the economy of nature which
would assuredly be better filled up, if some of the original
inhabitants were in some manner modified; for, had the area
been open to immigration, these same places would have been
seized on by intruders. In such cases, slight modifications,
which in any way favoured the individuals of any species,
by better adapting them to their altered conditions, would
tend to be preserved; and natural selection would have free
scope for the work of improvement.
We have good reason to believe, as shown in the first chap-
ter, that changes in the conditions of life give a tendencv to
increased variability; and in the foregoing cases the con-
ditions have changed, and this would manifestly be favour-
able to natural selection, by affording a better chance of the
occurrence of profitable variations. Unless such occur, nat-
ural selection can do nothing. Under the term of "vari-
96 ORIGIN: OF SPECIES
ations," it must never be forgotten that mere individual dif-
ferences are included. As man can produce a great result
with his domestic animals and plants by adding up in any
given direction individual differences, so could natural selec-
tion, but far more easily from having incomparably longer
time for action. Nor do I believe that any great physical
change, as of climate, or any unusual degree of isolation to
check immigration, Is necessary in order that new and un-
occupied places should be left, for natural selection to fill up
by improving some of the varying inhabitants. For as all
the inhabitants of each country are struggling together with
nicely balanced forces, extremely slight modifications in the
structure or habits of one species would often give it an ad-
vantage over others; and still further modifications of the
same kind would often still further increase the advantage,
as long as the species continued under the same conditions
of life and profited by similar means of subsistence and de-
fence. No country can be named in which all the native in-
habitants are now so perfectly adapted to each other and to
the physical conditions under which they live, that none of
them could be still better adapted or improved; for in all
countries, the natives have been so far conquered by natural-
ised productions, that they have allowed some foreigners to
take firm possession of the land. And as foreigners have
thus in every country beaten some of the natives, we may
safely conclude that the natives might have been modified
with advantage, so as to have better resisted the intruders.
As man can produce, and certainly has produced, a great
result by his methodical and unconscious means of selection,
what may not natural selection effect? Man can act only on
external and visible characters : Nature, if I may be allowed
to personify the natural preservation or survival of the fit-
test, cares nothing for appearances, except in so far as they
are useful to any being. She can act on every internal organ,
on every shade of constitutional difference, on the whole
machinery of life. Man selects only for his own good: Na-
ture only for that of the being which she tends. Every
selected character is fully exercised by her, as is implied by
the fact of their selection. Man keeps the natives of many
climates in the same country; he seldom exercises each se-
NATURAL SELECTION 97
lected character in some peculiar and fitting manner ; he feeds
a long and a short beaked pigeon on the same food ; he does
not exercise a long-backed or long-legged quadruped in any
peculiar manner; he exposes sheep with long and short wool
to the same climate. He does not allow the most vigorous
males to struggle for the females. He does not rigidly de-
stroy all inferior animals, but protects during each varying
season, as far as lies in his power, all his productions. He
often begins his selection by some half-monstrous form ; or
at least by some modification prominent enough to catch the
eye or to be plainly useful to him. Under nature, the slight-
est differences of structure or constitution may well turn the
nicely-balanced scale in the struggle for life, and so be pre-
served. How fleeting are the wishes and efforts of man !
how short his time ! and consequently how poor will be his
results, compared with those accumulated by Nature during
whole geological periods? Can we wonder, then, that Na-
ture's productions should be far "truer" in character than
man's productions ; that they should be infinitely better
adapted to the most complex conditions of life, and should
plainly bear the stamp of far higher workmanship?
It may metaphorically be said that natural selection is daily
and hourly scrutinising, throughout the world, the slightest
variations; rejecting those that are bad, preserving and add-
ing up all that are good ; silently and insensibly working,
whenever and wherever opportunity offers, at the improve-
ment of each organic being in relation to its organic and in-
organic conditions of life. We see nothing of these slow
changes in progress, until the hand of time has marked the
lapse of ages, and then so imperfect is our view into long-
past geological ages, that we see only that the forms of life
are now different from what they formerly were.
In order that any great amount of modification should be
effected in a species, a variety when once formed must again,
perhaps after a long interval of time, vary or present indi-
vidual differences of the same favourable nature as before ;
and these must be again preserved, and so onwards step by
step. Seeing that individual differences of the same kind
perpetually recur, this can hardly be considered as an unwar-
rantable assumption. But whether it is true, we can judge
rn-Hc XI
98 ORIGIN OF SPECIES
only by seeing how far the hypothesis accords with and ex-
plains the general phenomena of nature. On the other hand,
the ordinary belief that the amount of possible variation is
a strictly limited quantity is likewise a simple assumption.
Although natural selection can act only through and for
the good of each being, yet characters and structures, which
we are apt to consider as of very trifling importance, may
thus be acted on. When we see leaf-eating insects green,
and bark-feeders mottled-grey; the alpine ptarmigan white in
winter, the red-grouse the colour of heather, we must believe
that these tints are of service to these birds and insects in
preserving them from danger. Grouse, if not destroyed at
some period of their lives, would increase in countless num-
bers; they are known to suffer largely from birds of prey;
and hawks are guided by eyesight to their prey — so much so,
that on parts of the Continent persons are warned not to keep
white pigeons, as being the most liable to destruction. Hence
natural selection might be effective in giving the proper
colour to each kind of grouse, and in keeping that colour,
when once acquired, true and constant. Nor ought we to
think that the occasional destruction of an animal of any par-
ticular colour would produce little effect : we should remem-
ber how essential it is in a flock of white sheep to destroy a
lamb with the faintest trace of black. We have seen how
the colour of the hogs, which feed on the "paint-root" in
Virginia, determines whether they shall live or die. In
plants, the down on the fruit and the colour of the flesh are
considered by botanists as characters of the most trifling im-
portance : yet we hear from an excellent horticulturist. Down-
ing, that in the United States smooth-skinned fruits suffer
far more from a beetle, a Curculio, than those with down;
that purple plums suft'er far more from a certain disease than
yellow plums, whereas another disease attacks yellow-fleshed
peaches far more than those with other coloured flesh. If, '
with all the aids of art, these slight differences make a great
difference in cultivating the several varieties, assuredly, in a
state of nature, where the trees would have to struggle with
other trees and with a host of enemies, such differences would
effectually settle which variety, whether a smooth or downy,
a yellow or purple fleshed fruit, should succeed.
NATURAL SELECTION 99
In looking at many small points of difference between
species, which, as far as our ignorance permits us to judge,
seem quite unimportant, we must not forget that climate,
food, &c.. have no doubt produced some direct effect. It is
also necessary to bear in mind that, owing to the law of cor-
relation, when one part varies, and the variations are accu-
mulated through natural selection, other modifications, often
of the most unexpected nature, will ensue.
As we see that those variations which, under domestica-
tion, appear at any particular period of life, tend to reappear
in the offspring at the same period ; — for instance, in the
shape, size, and flavour of the seeds of the many varieties of
our culinary and agricultural plants ; in the caterpillar and
cocoon stages of the varieties of the silkworm ; in the eggs o£
poultry, and in the colour of the down of their chickens; in
the horns of our sheep and cattle when nearly adult ; — so in
a state of nature natural selection will be enabled to act on
and modify organic beings at any age, by the accumulation of
variations profitable at that age, and by their inheritance at
a corresponding age. If it profit a plant to have its seeds
more and more widely disseminated by the wind, I can see no
greater difficulty in this being effected through natural selec-
tion, than in the cotton-planter increasing and improving by
selection the down in the pods on his cotton-trees. Natural
selection may modify and adapt the larva of an insect to a
score of contingencies, wholly different from those which con-
cern the mature insect; and these modifications may effect,
through correlation, the structure of the adult. So, con-
versely, modifications in the adult may affect the structure
of the larva ; but in all cases natural selection will ensure that
they shall not be injurious: for if they were so, the species
would become extinct.
Natural selection will modify the structure of the young in
relation to the parent, and of the parent in relation to the
young. In social animals it will adapt the structure of each
individual for the benefit of the whole community ; if the
community profits by the selected change. What natural
selection cannot do, is to modify the structure of one species,
without giving it any advantage, for the good of another
species ; and though statements to this effect may be found in
100 ORIGIN OF SPECIES
works of natural history, I cannot find one case which will
bear investigation. A structure used only once in an ani-
mal's life, if of high importance to it, might be modified to
any extent by natural selection; for instance, the great jaws
possessed by certain insects, used exclusively for opening the
cocoon — or the hard tip to the beak of unhatched birds, used
for breaking the egg. It has been asserted, that of the best
short-beaked tumbler-pigeons a greater number perish in the
egg than are able to get out of it; so that fanciers assist in
the act of hatching. Now if nature had to make the beak of
a full-grown pigeon very short for the bird's own advantage,
the process of modification would be very slow, and there
would be simultaneously the most rigorous selection of all the
young birds within the egg, which had the most powerful and
hardest beaks, for all with weak beaks would inevitably per-
ish ; or, more delicate and more easily broken shells might be
selected, the thickness of the shell being known to vary like
every other structure.
It may be well here to remark that with all beings there
must be much fortuitous destruction, which can have little or
no influence on the course of natural selection. For instance
a vast number of eggs or seeds are annually devoured, and
these could be modified through natural selection only if they
varied in some manner which protected them from their ene-
mies. Yet many of these eggs or seeds would perhaps, if not
destroyed, have yielded individuals better adapted to their
conditions of life than any of those which happened to sur-
vive. So again a vast number of mature animals and plants,
whether or not they be the best adapted to their conditions,
must be annually destroyed by accidental causes, which would
not be in the least degree mitigated by certain changes of
structure or constitution which would in other ways be bene-
ficial to the species. But let the destruction of the adults be
ever so heavy, if the number which can exist in any district
be not wholly kept down by such causes, — or again let the
destruction of eggs or seeds be so great that only a hundredth
or a thousandth part are developed, — yet of those which do
survive, the best adapted individuals, supposing that there is
any variability in a favourable direction, will tend to propa-
gate their kind in larger numbers than the less well adapted.
SEXUAL SELECTION 101
If the numbers be wholly kept down by the causes just indi-
cated, as will often have been the case, natural selection will
be powerless in certain beneficial directions ; but this is no
valid objection to its efficiency at other times and in other
ways ; for we are far from having any reason to suppose that
many species ever undergo modification and improvement at
the same time in the same area.
SEXUAL SELECTION.
Inasmuch as peculiarities often appear under domestica-
tion in one sex and become hereditarily attached to that sex,
so no doubt it will be under nature. Thus it is rendered pos-
sible for the two sexes to be modified through natural selec-
tion in relation to different habits of life, as is sometimes the
case ; or for one sex to be modified in relation to the other
sex, as commonly occurs. This leads me to say a few words
on what I have called Sexual Selection. This form of selec-
tion depends, not on a struggle for existence in relation to
other organic beings or to external conditions, but on a
struggle between the individuals of one sex, generally the
males, for the possession of the other sex. The result is not
death to the unsuccessful competitor, but few or no offspring.
Sexual selection is, therefore, less rigorous than natural se-
lection. Generally, the most vigorous males, those which are
best fitted for their places in nature, will leave most progeny.
But in many cases, victory depends not so much on general
vigour, as on having special weapons, confined to the male
sex. A hornless stag or spurless cock would have a poor
chance of leaving numerous offspring. Sexual selection, by
always allowing the victor to breed, might surely give in-
domitable courage, length to the spur, and strength to the
wing to strike in the spurred leg, in nearly the same manner
as does the brutal cockfighter by the careful selection of his
best cocks. How low in the scale of nature the law of battle
descends, I know not; male alligators have been described as
fighting, bellowing, and whirling round, like Indians in a
war-dance, for the possession, of the females; male salmons
have been observed fighting all day long; male stag-beetles
sometimes bear wounds frjjm the huge mandibles of other
102 ORIGIN OF SPECIES
males ; the males of certain hymenopterous insects have been
frequently seen by that inimitable observer M. Fabre, fighting
for a particular female who sits by, an apparently uncon-
cerned beholder of the struggle, and then retires with the
conqueror. The war is, perhaps, severest between the males
of polygamous animals, and these seem oftenest provided
with special weapons. The males of carnivorous animals
are already well armed ; though to them and to others, special
means of defence may be given through means of sexual
selection, as the mane of the lion, and the hooked jaw to the
male salmon ; for the shield may be as important for victory,
as the sword or spear.
Amongst birds, the contest is often of a more peaceful
character. All those who have attended to the subject, be-
lieve that there is the severest rivalry betvv^en the males of
many species to attract, by singing, the females. The rock-
thrush of Guiana, birds of paradise, and some others, congre-
gate; and successive males display with the most elaborate
care, and show off in the best manner, their gorgeous plu-
mage; they likewise perform strange antics before the fe-
males, which, standing by as spectators, at last choose the most
attractive partner. Those who have closely attended to birds
in confinement well know that they often take individual
preferences and dislikes ; thus Sir R. Heron has described
how a pied peacock was eminently attractive to all his hen
birds. I cannot here enter on the necessary details; but if
man can in a short time give beauty and an elegant carriage
to his bantams, according to his standard of beauty, I can see
no good reason to doubt that female birds, by selecting, dur-
ing thousands of generations, the most melodious or beautiful
males, according to their standard of beauty, might produce a
marked effect. Some well-known laws, with respect to the
plumage of male and female birds, in comparison with the
plumage of the young, can partly be explained through the
action of sexual selection on variations occurring at different
ages, and transmitted to the males alone or to both sexes at
corresponding ages; but I have not space here to enter on
this subject.
Thus it is, as I believe, that when the males and females of
any animal have the same general habits of life, but differ in
ACTION OF NATURAL SELECTION 103
structure, colour, or ornament, such differences have been
mainly caused by sexual selection : that is, by individual males
having had, in successive generations, some slight advantage
over other males, in their weapons, means of defence, or
charms, which they have transmitted to their male offspring
alone. Yet, I would not wish to attribute all sexual differ-
ences to this agency : for we see in our domestic animals
peculiarities arising and becoming attached to the male sex,
which apparently have not been augmented through selection
by man. The tuft of hair on the breast of the wild turkey-
cock cannot be of any use, and it is doubtful whether it can
be ornamental in the eyes of the female bird; — indeed, had
the tuft appeared under domestication, it would have been
called a monstrosity.
ILLUSTRATIONS OF THE ACTION OF NATURAL SELECTION, OR
THE SURVIVAL OF THE FITTEST.
In order to make it clear how, as I believe, natural selec-
tion acts, I must beg permission to give one or two imaginary
illustrations. Let us take the case of a wolf, which preys on
various animals, securing some by craft, some by strength,
and some by fleetness ; and let us suppose that the fleetest
prey, a deer for instance, had from any change in the country
increased in numbers, or that other prey had decreased in
numbers, during that season of the year when the wolf was
hardest pressed for food. Under such circumstances the
swiftest and slimmest wolves would have the best chance of
surviving and so be preserved or selected, — provided always
that they retained strength to master their prey at this or
some other period of the year, when they were compelled to
prey on other animals. I can see no more reason to doubt
that this would be the result, than that man should be able to
improve the fleetness of his greyhounds by careful and
methodical selection, or by that kind of unconscious selection
which follows from each man trying to keep the best dogs
without any thought of modifying the breed. I may add,
that, according to Mr. Pierce, there are two varieties of the
wolf inhabiting the Catskill'Mountains, in the United States,
one with a light greyhound-like form, which pursues deer.
104 ORIGIN OF SPECIES
and the other more bulky, with shorter legs, which more fre-
quently attacks the shepherd's flocks.
It should be observed that, in the above illustration, I speak
of the slimmest individual wolves, and not of any single
strongly-marked variation having been preserved. In former
editions of this work I sometimes spoke as if this latter alter-
native had frequently occurred. I saw the great importance
of individual differences, and this led me fully to discuss the
results of unconscious selection by man, which depends on
the preservation of all the more or less valuable individuals,
and on the destruction of the worst. I saw, also, that the
preservation in a state of nature of any occasional deviation
of structure, such as a monstrosity, would be a rare event;
and that, if at first preserved, it would generally be lost by
subsequent intercrossing with ordinary individuals. Never-
theless, until reading an able and valuable article in the
'North British Review' (1867), I did not appreciate how
rarely single variations, whether slight or strongly-marked,
could be perpetuated. The author takes the case of a pair
of animals, producing daring their lifetime two hundred off-
spring, of which, from various causes of destruction, only two
on an average survive to pro-create their kind. This is
rather an extreme estimate for most of the higher animals,
but by no means so for many of the lower organisms. He
then shows that if a single individual were born, which varied
in some manner, giving it twice as good a chance of life as
that of the other individuals, yet the chances would be
strongly against its survival. Supposing it to survive and to
breed, and that half its young inherited the favourable vari-
ation ; still, as the Reviewer goes on to show, the young would
have only a slightly better chance of surviving and breeding;
and this chance would go on decreasing in the succeeding
generations. The justice of these remarks cannot, I think,
be disputed. If, for instance, a bird of some kind could pro-
cure its food more easily by having its beak curved, and if
one were born with its beak strongly curved, and which con-
sequently flourished, nevertheless there would be a very poor
chance of this one individual perpetuating its kind to the ex-
clusion of the common form ; but there can hardly be a doubt,
judging by what we see taking place under domestication,
ACTION OF NATURAL SELECTION 105
that this result would follow from the preservation during
many generations of a large number of individuals with more
or less strongly curved beaks, and from the destruction of a
still larger number with the straightest beaks.
It should not, however, be overlooked that certain rather
strongly marked variations, which no one would rank as mere
individual differences, frequently recur owing to a similar
organisation being similarly acted on — of which fact numer-
ous instances could be given with our domestic productions.
In such cases, if the varying individual did not actually trans-
mit to its offspring its newly-acquired character, it would un-
doubtedly transmit to them, as long as the existing conditions
remained the same, a still stronger tendency to vary in the
same manner. There can also be little doubt that the ten-
dency to vary in the same manner has often been so strong
that all the individuals of the same species have been simi-
larly modified without the aid of any form of selection. Or
only a third, fifth, or tenth part of the individuals may have
been thus affected, of which fact several instances could be
given. Thus Graba estimates that about one-fifth of the
guillemots in the Faroe Islands consist of a variety so well
marked, that it was formerly ranked as a distinct species
under the name of Uria lacrymans. In cases of this kind, if
the variation were of a beneficial nature, the original form
would soon be supplanted by the modified form, through the
survival of the fittest.
To the eft'ects of intercrossing in eliminating variations of all
kinds, I shall have to recur ; but it may be here remarked that
most animals and plants keep to their proper homes, and do
not needlessly wander about ; we see this even with migratory
birds, which almost always return to the same spot. Conse-
quently each newly-formed variety would generally be at
first local, as seems to be the common rule with varieties in a
state of nature; so that similarly modified individuals would
soon exist in a small body together, and would often breed
together. If the new variety were successful in its battle for
life, it would slowly spread from a central district, competing
with and conquering the unchanged individuals on the mar-
gins of an ever-increasing circle.
It may be worth while to give another and more complex
106 ORIGIN OF SPECIES
illustration of the action of natural selection. Certain plants
excrete sweet juice, apparently for the sake of eliminating
something injurious from the sap: this is effected, for in-
stance, by glands at the base of the stipules in some Legu-
minosse, and at the backs of the leaves of the common laurel.
This juice, though small in quantity, is greedily sought by
insects; but their visits do not in any way benefit the plant.
Now, let us suppose that the juice or nectar was excreted
from the inside of the flowers of a certain number of plants
of any species. Insects in seeking the nectar would get
dusted with pollen, and would often transport it from one
flower to another. The flowers of two distinct individuals
of the same species would thus get crossed; and the act of
crossing, as can be fully proved, gives rise to vigorous seed-
lings, which consequently would have the best chance of flour-
ishing and surviving. The plants which produced flowers
with the largest glands or nectaries, excreting much nectar,
would oftenest be visited by insects, and would oftenest be
crossed; and so in the long-run would gain the upper hand
and form a local variety. The flowers, also, which had their
stamens and pistils placed, in relation to the size and habits
of the particular insect which visited them, so as to favour
in any degree the transportal of the pollen, would likewise
be favoured. We might have taken the case of insects visit-
ing flowers for the sake of collecting pollen instead of nectar;
and as pollen is formed for the sole purpose of fertilisation,
its destruction appears to be a simple loss to the plant ; yet if
a Rttle pollen were carried, at first occasionally and then
habitually, by the pollen-devouring insects from flower to
flower, and a cross thus effected, although nine-tenths of the
pollen were destroyed, it might still be a great gain to the
plant to be thus robbed; and the individuals which produced
more and more pollen, and had larger anthers, would be
selected.
When our plant, by the above process long continued, had
been rendered highly attractive to insects, they would, unin-
tentionally on their part, regularly carry pollen from flower
to flower; and that they do this effectually, I could easily
show by many striking facts. I will give only one, as like-
wise illustrating one step in the separation of the sexes of
ACTION OF NATURAL SELECTION 107
plants. Some holly-trees bear only male flowers, which have
four stamens producing a rather small quantity of pollen, and
a rudimentary pistil; other holly-trees bear only female
flowers; these have a full-sized pistil, and four stamens with
shrivelled anthers, in which not a grain of pollen can be de-
tected. Having found a female tree exactly sixty yards from
a male tree, I put the stigmas of twenty flowers, taken from
different branches, under the microscope, and on all, without
exception, there were a few pollen-grains, and on some a
profusion. As the wind had set for several days from the
female to the male tree, the pollen could not thus have been
carried. The weather had been cold and boisterous, and
therefore not favourable to bees, nevertheless every female
flower which I examined had been effectually fertilised by the
bees, which had flown from tree to tree in search of nectar.
But to return to our imaginary case : as soon as the plant had
been rendered so highly attractive to insects that pollen was
regularly carried from flower to flower, another process
might commence. No naturalist doubts the advantage of
what has been called the "physiological division of labour;"
hence we may believe that it would be advantageous to a
plant to produce stamens alone in one flower or on one whole
plant, and pistils alone in another flower or on another plant.
In plants under culture and placed under new conditions of
life, sometimes the male organs and sometimes the female
organs become more or less impotent ; now if we suppose this
to occur in ever so slight a degree under nature, then, as
pollen is already carried regularly from flower to flower, and
as a more complete separation of the sexes of our plant would
be advantageous on the principle of the division of labour,
individuals with this tendency more and more increased, would
be continually favoured or selected, until at last a complete
separation of the sexes might be effected. It would take up
too much space to show the various steps, through dimorph-
ism and other means, by which the separation of the sexes in
plants of various kinds is apparently now in progress; but I
may add that some of the species of holly in North America,
are, according to Asa Gray, .in an exactly intermediate con-
dition, or, as he expresses it, are more or less dioeciously
polygamous.
108 ORIGIN OF SPECIES
Let us now turn to the nectar-feeding insects; we may
suppose the plant, of which we have been slowly increasing
the nectar by continued selection, to be a common plant; and
that certain insects depended in main part on its nectar for
food. I could give many facts showing how anxious bees are
to save time: for instance, their habit of cutting holes and
sucking the nectar at the bases of certain flowers, which with
a very little more trouble, they can enter by the mouth.
Bearing such facts in mind, it may be believed that under cer-
tain circumstances individual differences in the curvature or
length of the proboscis, &c., too slight to be appreciated by
us, might profit a bee or other insect, so that certain indi-
viduals would be able to obtain their food more quickly than
others; and thus the communities to which they belonged
would flourish and throw off many swarms inheriting the
same peculiarities. The tubes of the corolla of the common
red and incarnate clovers (Trifolium pra tense and incar-
natum) do not on a hasty glance appear to differ in length;
yet the hive-bee can easily suck the nectar out of the incar-
nate clover, but not out of the common red clover, which is
visited by humble-bees alone ; so that whole fields of the red
clover offer in vain an abundant supply of precious nectar to
the hive-bee. That this nectar is much liked by the hive-bee is
certain; for I have repeatedly seen, but only in the autumn,
many hive-bees sucking the flowers through holes bitten in
the base of the tube by humble-bees. The difference in the
length of the corolla in the two kinds of clover, which deter-
mines the visits of the hive-bee, must be very trifling; for I
have been assured that when red clover has been mown, the
flowers of the second crop are somewhat smaller, and that
these are visited by many hive-bees. I do not know whether
this statement is accurate; nor whether another published
statement can be trusted, namely, that the Ligurian bee, which
is generally considered a mere variety of the common hive-
bee, and which freely crosses with it, is able to reach and suck
the nectar of the red clover. Thus, in a country where this kind
of clover abounded, it might be a great advantage to the
hive-bee to have a slightly longer or differently constructed
proboscis. On the other hand, as the fertility of this clover
absolutely depends on bees visiting the flowers, if humble-
ON THE INTERCROSSING OF INDIVIDUALS 109
bees were to become rare in any country, it might be a great
advantage to the plant to have a shorter or more deeply di-
vided corolla, so that the hive-bees should be enabled to suck
its flow^ers. Thus I can understand how a flower and a bee
might slowly become, either simultaneously or one after the
other, modified and adapted to each other in the most perfect
manner, by the continued preservation of all the individuals
which presented slight deviations of structure mutually fa-
vourable to each other.
I am well aware that this doctrine of natural selection,
exemplified in the above imaginary instances, is open to the
same objections which were first urged against Sir Charles
Lyell's noble views on "the modern changes of the earth, as
illustrative of geology ;" but we now seldom hear the agencies
which we see still at work, spoken of as trifling or insignifi-
cant, when used in explaining the excavation of the deepest
valleys or the formation of long lines of inland cliffs. Nat-
ural selection acts only by the preservation and accumulation
of small inherited modifications, each profitable to the pre-
served being; and as modern geology has almost banished
such views as the excavation of a great valley by a single
diluvial wave, so will natural selection banish the belief of
the continued creation of new organic beings, or of any great
and sudden modification in their structure.
ON THE INTERCROSSING OF INDIVIDUALS
I must here introduce a short digression. In the case of
animals and plants with separated sexes, it is of course obvi-
ous that two individuals must always (with the exception of
the curious and not well understood cases of parthenogene-
sis) unite for each birth; but in the case of hermaphrodites
this is far from obvious. Nevertheless there is reason to be-
lieve that with all hermaphrodites two individuals, either
occasionally or habitually, concur for the reproduction of
their kind. This view was long ago doubtfully suggested by
Sprengel, Knight and Kolreuter. We shall presently see its
importance; but I must here treat the subject with extreme
brevity, though I have the materials prepared for an ample
discussion. All vertebrate animals, all insects, and some
110 ORIGIN OF SPECIES
other large groups of animals, pair for each birth. Modern
research has much diminished the number of supposed her-
maphrodites, and of real hermaphrodites a large number
pair ; that is, two individuals regularly unite for reproduc-
tion, which is all that concerns us. But still there are many
hermaphrodite animals which certainly do not habitually pair,
and a vast majority of plants are hermaphrodites. What
reason, it may be asked, is there for supposing in these cases
that two individuals ever concur in reproduction? As it is
impossible here to enter on details, I must trust to some gen-
eral considerations alone.
In the first place, I have collected so large a body of facts,
and made so many experiments, showing, in accordance with
the almost universal belief of breeders, that with animals and
plants a cross between different varieties, or between indi-
viduals of the same variety but of another strain, gives vigour
and fertility to the offspring; and on the other hand, that
close interbreeding diminishes vigour and fertility ; that these
facts alone incline me to believe that it is a general law of
nature that no organic being fertilises itself for a perpetuity
of generations ; but that a cross with another individual is
occasionally — perhaps at long intervals of time — indispen-
sable.
On the belief that this is a law of nature, we can, I think,
understand several large classes of facts, such as the follow-
ing, which on any other view are inexplicable. Every
hybridizer knows how unfavourable exposure to wet is to
the fertilisation of a flower, yet what a multitude of flowers
have their anthers and stigmas fully exposed to the weather !
If an occasional cross be indispensable, notwithstanding that
the plant's own anthers and pistil stand so near each other
as almost to insure self-fertilisation, the fullest freedom for
the entrance of pollen from another individual will explain
the above state of exposure of the organs. Many flowers, on
the other hand, have their organs of fructification closely en-
closed, as in the great papilionaceous or pea- family ; but these
almost invariably present beautiful and curious adaptations
in relation to the visits of insects. So necessary are the visits
of bees to many papilionaceous flowers, that their fertility is
greatly diminished if these visits be prevented. Now, it is
ON THE INTERCROSSING OF INDIVIDUALS 111
scarcely possible for insects to fly from flower to flower, and
not to carry pollen from one to the other, to the great good
of the plant. Insects act like a camel-hair pencil, and it is
sufficient, to ensure fertilisation, just to touch with the same
brush the anthers of one flower and then the stigma of an-
other ; but it must not be supposed that bees would thus pro-
duce a multitude of hybrids between distinct species ; for if a
plant's own pollen and that from another species are placed
on the same stigma, the former is so prepotent that it in-
variably and completely destroys, as has been shown by Gart-
ner, the influence of the foreign pollen.
When the stamens of a flower suddenly spring towards the
pistil, or slowly move one after the other towards it, the con-
trivance seems adapted solely to ensure self-fertilisation; and
no doubt it is useful for this end : but the agency of insects is
often required to cause the stamens to spring forward, as
Kolreuter has shown to be the case with the barberry ; and in
this very genus, which seems to have a special contrivance
for self-fertilisation, it is well known that, if closely-allied
forms or varieties are planted near each other, it is hardly
possible to raise pure seedlings, so largely do they naturally
cross. In numerous other cases, far from self-fertilisation
being favoured, there are special contrivances which effec-
tually prevent the stigma receiving pollen from its own
flower, as I could show from the works of Sprengel and
others, as well as from my own observations : for instance,
in Lobelia fulgens, there is a really beautiful and elaborate
contrivance by which all the infinitely numerous pollen-
granules are swept out of the conjoined anthers of each
flower, before the stigma of that individual flower is ready to
receive them; and as this flower is never visited, at least in
my garden, by insects, it never sets a seed, though by placing
pollen from one flower on the stigma of another, I raise
plenty of seedlings. Another species of Lobelia, which Is
visited by bees, seeds freely in my garden. In very many
other cases, though there is no special mechanical contrivance
to prevent the stigma receiving pollen from the same flower,
yet, as Sprengel, and more rgccntly Hildebrand, and others,
have shown, and as I can confirm, either the anthers burst be-
fore the stigma is ready for fertilisation, or the stigma is
112 ORIGIN OF SPECIES
ready before the pollen of that flower is ready, so that these
so-named dichogamous plants have in fact separated sexes,
and must habitually be crossed. So it is with the reciprocally
dimorphic and trimorphic plants previously alluded to. How
strange are these facts ! How strange that the pollen and
stigmatic surface of the same flower, though placed so close
together, as if for the very purpose of self-fertilisation,
should be in so many cases mutually useless to each other?
How simply are these facts explained on the view of an oc-
casional cross with a distinct individual being advantageous
or indispensable !
If several varieties of the cabbage, radish, onion, and of
some other plants, be allowed to seed near each other, a large
majority of the seedlings thus raised turn out, as I have
found, mongrels : for instance, I raised 233 seedling cabbages
from some plants of different varieties growing near each
other, and of these only 78 were true to their kind, and some
even of these were not perfectly true. Yet the pistil of each
cabbage-flower is surrounded not only by its own six stamens
but by those of the many other flowers on the same plant;
and the pollen of each flower readily gets on its own stigma
without insect agency ; for I have found that plants carefully
protected from insects produce the full number of pods.
How, then, comes it that such a vast number of the seedlings
are mongrelized? It must arise from the pollen of a dis-
tinct variety having a prepotent effect over the flower's own
pollen ; and that this is part of the general law of good being
derived from the intercrossing of distinct individuals of the
same species. When distinct species are crossed the case is
reversed, for a plant's own pollen is almost always prepotent
over foreign pollen; but to this subject we shall return in a
future chapter.
In the case of a large tree covered with innumerable
flowers, it may be objected that pollen could seldom be carried
from tree to tree, and at most only from flower to flower on
the same tree; and flowers on the same tree can be consid-
ered as distinct individuals only in a limited sense. I believe
this objection to be valid, but that nature has largely pro-
vided against it by giving to trees a strong tendency to bear
flowers with separated sexes. When the sexes are separated.
ON THE INTERCROSSING OF INDIVIDUALS 113
although the male and female flowers may be produced on the
same tree, pollen must be regularly carried from flower to
flower ; and this will give a better chance of pollen being oc-
casionally carried from tree to tree. That trees belonging to
all Orders have their sexes more often separated than other
plants, I find to be the case in this country; and at my re-
quest Dr. Hooker tabulated the trees of New Zealand, and
Dr. Asa Gray those of the United States, and the result was
as I anticipated. On the other hand, Dr. Hooker informs me
that the rule does not hold good in Australia: but if most of
the Australian trees are dichogamous, the same result would
follow as if they bore flowers with separated sexes I have
made these few remarks on trees simply to call attention to
the subject.
Turning for a brief space to animals : various terrestrial
species are hermaphrodites, such as the land-mollusca and
earth-worms ; but these all pair. As yet I have not found a
single terrestrial animal which can fertilise itself. This re-
markable fact, which offers so strong a contrast with terres-
trial plants, is intelligible on the view of an occasional cross
being indispensable ; for owing to the nature of the fertilis-
ing element there are no means, analogous to the action of
insects and of the wind with plants, by which an occasional
cross could be effected with terrestrial animals without the
concurrence of two individuals. Of aquatic animals, there
are many self-fertilising hermaphrodites; but here the cur-
rents of water offer an obvious means for an occasional cross.
As in the case of flowers, I have as yet failed, after consulta-
tion with one of the highest authorities, namely, Professor
Huxley, to discover a single hermaphrodite animal with the
organs of reproduction so perfectly enclosed that access from
without, and the occasional influence of a distinct individual,
can be shown to be physically impossible. Cirripedes long
appeared to me to present, under this point of view, a case
of great difficulty; but I have been enabled, by a fortunate
chance, to prove that two individuals, though both are self-
fertilising hermaphrodites, do sometimes cross.
It must have struck most naturalists as a strange anomaly
that, both with animals and plants, some species of the same
family and even of the. same genus, though agreeing closely
114 ORIGIN OF SPECIES
with each other in their whole organisation, are hermaphro-
dites, and some unisexual. But if, in fact, all hermaphro-
dites do occasionally intercross, the difference between them
and unisexual species is, as far as function is concerned, very
small.
From these several considerations and from the many
special facts which I have collected, but which I am unable
here to give, it appears that with animals and plants an oc-
casional intercross between distinct individuals is a very gen-
eral, if not universal, law of nature.
CIRCUMSTANCES FAVOURABLE FOR THE PRODUCTION OF NEW
FORMS THROUGH NATURAL SELECTION.
This is an extremely intricate subject. A great amount of
variability, under which term individual differences are al-
ways included, will evidently be favourable. A large num-
ber of individuals, by giving a better chance within any given
period for the appearance of jgrofitable variations, will com-
pensate for a lesser amount of variability in each individual,
and is, I believe, a highly important element of success.
Though Nature grants long periods of time for the work of
natural selection, she does not grant an indefinite period ; for
as all organic beings are striving to seize on each place in
the economy of nature, if any one species does not become
modified and improved in a corresponding degree with its
competitors, it will be exterminated. Unless favourable vari-
ations be inherited by some at least of the offspring, nothing
can be effected by natural selection. The tendency to rever-
sion may often check or prevent the work ; but as this ten-
dency has not prevented man from forming by selection nu-
merous domestic races, why should it prevail against natural
selection ?
In the case of methodical selection, a breeder selects for
some definite object, and if the individuals be allowed freely
to intercross, his work will completely fail. But when many
men, without intending to alter the breed, have a nearly com-
mon standard of perfection, and all try to procure and breed
from the best animals, improvement surely but slowly follows
from this unconscious process of selection, notwithstanding
PRODUCTION OF NEW FORMS llS
that there is no separation of selected individuals. Thus it
will be under nature ; for within a confined area, with some
place in the natural polity not perfectly occupied, all the in-
dividuals varying in the right direction, though in different
degrees, will tend to be preserved. But if the area be large,
its several districts will almost certainly present different con-
ditions of life ; and then, if the same species undergoes modi-
fication in different districts, the newly-formed varieties will
intercross on the confines of each. But we shall see in the
sixth chapter that intermediate varieties, inhabiting inter-
mediate districts, will in the long run generally be supplanted
by one of the adjoining varieties. Intercrossing will chiefly
affect those animals which unite for each birth, and wander
much, and which do not breed at a very quick rate. Hence
with animals of this nature, for instance, birds, varieties will
generally be confined to separated countries ; and this I find
to be the case. With hermaphrodite organisms which cross
only occasionally, and likewise with animals which unite for
each birth, but which wander little and can increase at a
rapid rate, a new and improved variety might be quickly
formed on any one spot, and might there maintain itself in a
body and afterwards spread, so that the individuals of the
new variety would chiefly cross together. On this principle,
nurserymen always prefer saving seed from a large body of
plants, as the chance of intercrossing is thus lessened.
Even with animals which unite for each birth, and which
do not propagate rapidly, we must not assume that free in-
tercrossing would always eliminate the effects of natural
selection ; for I can bring forward a considerable body of
facts showing that within the same area, two varieties of the
same animal may long remain distinct, from haunting differ-
ent stations, from breeding at slightly different seasons, or
from the individuals of each variety preferring to pair to-
gether.
Intercrossing plays a very important part in nature by
keeping the individuals of the same species, or of the same
variety, true and uniform in character. It will obviously
thus act far more efficiently with those animals which unite
for each birth ; but, as already stated, we have reason to be-
lieve that occasional intercrosses take place with all animals
116 ORIGIN OF SPECIES
and plants. Even if these take place only at long intervals
of time, the young thus produced will gain so much in vigour
and fertility over the offspring from long-continued self-fer-
tilisation, that they v^ill have a better chance of surviving
and propagating their kind ; and thus in the long run the in-
fluence of crosses, even at rare intervals, will be great. With
respect to organic beings extremely low in the scale, which
do not propagate sexually, nor conjugate, and which cannot
possibly intercross, uniformity of character can be retained
by them under the same conditions of life, only through the
principle of inheritance, and through natural selection which
will destroy any individuals departing from the proper type.
If the conditions of life change and the form undergoes modi-
fication, uniformity of character can be given to the modified
offspring, solely by natural selection preserving similar fa-
vourable variations.
Isolation, also, is an important element in the modification
of species through natural selection. In a confined or iso-
lated area, if not very large, the organic and inorganic con-
ditions of life will generally be almost uniform ; so that nat-
ural selection will tend to modify all the varying individuals
of the same species in the same manner. Intercrossing with
the inhabitants of the surrounding districts will, also, be thus
prevented. Moritz Wagner has lately published an interest-
ing essay on this subject, and has shown that the service
rendered by isolation in preventing crosses between newly-
formed varieties is probably greater even than I supposed.
But from reasons already assigned I can by no means agree
with this naturalist, that migration and isolation are neces-
sary elements for the formation of new species. The im-
portance of isolation is likewise great in preventing, after
any physical change in the conditions such as of climate ele-
vation of the land, &c., the immigration of better adapted or-
ganisms; and thus new places in the natural economy of the
district will be left open to be filled up by the modification of
the old inhabitants. Lastly, isolation will give time for a
new variety to be improved at a slow rate ; and this may
sometimes be of much importance. If, however, an isolated
area be very small, either from being surrounded by barriers,
or from having very peculiar physical conditions, the total
PRODUCTION OF NEW FORMS 117
number of the inhabitants will be small ; and this will retard
the production of new species through natural selection, by
decreasing the chances of favourable variations arising.
The mere lapse of time by itself does nothing, either for
or against natural selection. I state this because it has been
erroneously asserted that the element of time has been as-
sumed by me to play an all-important part in modifying
species, as if all the forms of life were necessarily undergo-
ing change through some innate law. Lapse of time is only
so far important, and its importance in this respect is great,
that it gives a better chance of beneficial variations arising
and of their being selected, accumulated, and fixed. It like-
wise tends to increase the direct action of the physical
conditions of life, in relation to the constitution of each
organism.
If we turn to nature to test the truth of these remarks, and
look at any small isolated area, such as an oceanic island, al-
though the number of species inhabiting it is small, as we
shall see in our chapter on Geographical Distribution; yet
of these species a very large proportion are endemic, — that
is, have been produced there and nowhere else in the world.
Hence an oceanic island at first sight seems to have been
highly favourable for the production of new species. But
we may thus deceive ourselves, for to ascertain whether a
small isolated area, or a large open area like a continent, has
been most favourable for the production of new organic
forms, we ought to make the comparison within equal times ;
and this we are incapable of doing.
Although isolation is of great importance in the production
of new species, on the whole I am inclined to believe that
largeness of area is still more important, especially for the
production of species which shall prove capable of enduring
for a long period, and of spreading widely. Throughout a
great and open area, not only will there be a better chance of
favourable variations, arising from the large number of indi-
viduals of the same species there supported, but the conditions
of life are much more complex from the large number of al-
ready existing species ; and if some of these many species
become modified and improved, others will have to be im-
proved in a corresponding degree, or they will be extermi-
118 ORIGIN OF SPECIES
nated. Each new form, also, as soon as it has been much
improved, will be able to spread over the open and continu-
ous area, and will thus come into competition with many
other forms. Moreover, great areas, though now continuous,
will often, owing to former oscillations of level, have existed
in a broken condition; so that the good effects of isolation
will generally, to a certain extent, have concurred. Finally,
I conclude that, although small isolated areas have been in
some respects highly favourable for the production of new
species, yet that the course of modification will generally have
been more rapid on large areas ; and what is more important,
that the new forms produced on large areas, which already
have been victorious over many competitors, will be those
that will spread most widely, and will give rise to the great-
est number of new varieties and species. They will thus
play a more important part in the changing history of the
organic world.
In accordance with this view, we can, perhaps, understand
some facts which will be again alluded to in our chapter on
Geographical Distribution ; for instance, the fact of the pro-
ductions of the smaller continent of Australia now yielding
before those of the larger Europaeo-Asiatic area. Thus, also,
it is that continental productions have everywhere become so
largely naturalised on islands. On a small island, the race
for life will have been less severe, and there will have been
less modification and less extermination. Hence, we can
understand how it is that the flora of Madeira, according to
Oswald Heer, resembles to a certain extent the extinct ter-
tiary flora of Europe. All fresh-water basins, taken together,
make a small area compared with that of the sea or of the
land. Consequently, the competition between fresh-water
productions will have been less severe than elsewhere ; new
forms will have been then more slowly produced, and old
forms more slowly exterminated. And it is in fresh-water
basins that we find seven genera of Ganoid fishes, remnants
of a once preponderant order: and in fresh water we find
some of the most anomalous forms now known in the world
as the Ornithorhynchus and Lepidosiren, which, like fossils,
connect to a certain extent orders at present widely sundered
in the natural scale. These anomalous forms may be called
PRODUCTION OF NEW FORMS 119
living fossils ; they have endured to the present day, from
having inhabited a confined area, and from having been ex-
posed to less varied, and therefore less severe, competition.
To sum up, as far as the extreme intricacy of the subject
permits, the circumstances favourable and unfavourable for
the production of new species through natural selection. I
conclude that for terrestrial productions a large continental
area, which has undergone many oscillations of level, will
have been the most favourable for the production of many
new forms of life, fitted to endure for a long time and to
spread widely. Whilst the area existed as a continent, the in-
habitants will have been numerous in individuals and kinds,
and will have been subjected to severe competition. When
converted by subsidence into large separate islands, there
will still have existed many individuals of the same species
on each island ; intercrossing on the confines of the range of
each new species will have been checked; after physical
changes of any kind, immigration will have been prevented,
so that new places in the polity of each island will have had
to be filled up by the modification of the old inhabitants ; and
time will have been allowed for the varieties in each to be-
come well modified and perfected. When, by renewed eleva-
tion, the islands were reconverted into a continental area,
there will again have been very severe competition : the most
favoured or improved varieties will have been enabled to
spread: there will have been much extinction of the less im-
proved forms, and the relative proportional numbers of the
various inhabitants of the reunited continent will again have
been changed ; and again there will have been a fair field for
natural selection to improve still further the inhabitants, and
thus to produce new species.
That natural selection generally acts with extreme slow-
ness I fully admit. It can act only when there are places in
the natural polity of a district which can be better occupied
by the modification of some of its existing inhabitants. The
occurrence of such places will often depend on physical
changes, which generally take place very slowly, and on the
immigration of better adapted forms being prevented. As
some few of the old inhabitants become modified, the mutual
relations of others will "often be disturbed; and this will
120 ORIGIN OF SPECIES
create new places, ready to be filled up by better adapted
forrris ; "but all this will take place very slowly. Although all
the individuals of the same species differ in some slight de-
gree from each other, it would often be long before differ-
ences of the right nature in various parts of the organisation
might occur. The result would often be greatly retarded by
free intercrossing. Many will exclaim that these several
causes are amply sufficient to neutralise the power of nat-
ural selection. I do not believe so. But I do believe that
natural selection will generally act very slowly, only at long
intervals of time, and only on a few of the inhabitants of the
same region. I further believe that these slow, intermittent
results accord well with what geology tells us of the rate and
manner at which the inhabitants of the world have changed.
Slow though the process of selection may be, if feeble man
can do much by artificial selection, I can see no limit to the
amount of change, to the beauty and complexity of the co-
adaptations between' all organic beings, one with another
and with their physical conditions of life, which may have
been affected in the long course of time through nature's
power of selection, that is by the survival of the fittest.
EXTINCTION CAUSED BY NATURAL SELECTION
This subject will be more fully discussed in our chapter on
Geology; but it must here be alluded to from being inti-
mately connected with natural selection. Natural selection
acts solely through the preservation of variations in some
way advantageous, which consequently endure. Owing to
the high geometrical rate of increase of all organic beings,
each area is already fully stocked with inhabitants; and it
follows from this, that as the favoured forms increase in
number, so, generally, will the less favoured decrease and
become rare. Rarity, as geology tells us, is the precursor to
extinction. We can see that any form which is represented
by few individuals will run a good chance of utter extinc-
tion, during great fluctuations in the nature of the seasons,
or from a temporary increase in the number of its enemies.
But we may go further than this ; for, as new forms are pro-
duced, unless we admit that specific forms can go on indefi-
EXTINCTION CAUSED BY NATURAL SELECTION 121
nitely increasing in number, many old forms must become ex-
tinct. That the number of specific forms has not indefinitely
increased, geology plainly tells us ; and we shall presently at-
tempt to show why it is that the number of species through-
out the world has not become immeasurably great.
We have seen that the species which are most numerous
in individuals have the best chance of producing favourable
variations within any given period. We have evidence of
this, in the facts stated in the second chapter, showing that
it is the common and diffused or dominant species which
offer the greatest number of recorded varieties. Hence, rare
species will be less quickly modified or improved within any
given period; they will consequently be beaten in the race for
life by the modified and improved descendants of the com-
moner species.
From these several considerations I think it inevitably fol-
lows, that as new species in the course of time are formed
through natural selection, others will become rarer and rarer,
and finally extinct. The forms which stand in closest com-
petition with those undergoing modification and improve-
ment, will naturally suffer most. And we have seen in the
chapter on the Struggle for Existence that it is the most
closely-allied forms, — varieties of the same species, and
species of the same genus or of related genera, — which, from
having nearly the same structure, constitution, and habits,
generally come into the severest competition with each
other ; consequently, each new variety or species, during the
progress of its formation, will generally press hardest on its
nearest kindred, and tend to exterminate them. We see the
same process of extermination amongst our domesticated pro-
ductions, through the selection of improved forms by man.
Many curious instances could be given showing how quickly
new breeds of cattle, sheep, and other animals, and varieties
of flowers, take the place of older and inferior kinds. In
Yorkshire, it is historically known that the ancient black
cattle were displaced by the long-horns, and that these "were
swept away by the short-horns" (I quote the words of an
agricultural writer) "as if by some murderous pestilence."
122 ORIGIN OF SPECIES
DIVERGENCE OF CHARACTER
The principle, which I have designated by this term, is of
high importance, and explains, as I believe, several impor-
tant facts. In the first place, varieties, even strongly-marked
ones, though having somewhat of the character of species —
as is shown by the hopeless doubts in many cases how to
rank them — yet certainly differ far less from each other than
do good and distinct species. Nevertheless, according to my
view, varieties are species in the process of formation, or are,
as I have called them, incipient species. How, then, does
the lesser difference between varieties become augmented into
the greater difference between species? That this does habit-
ually happen, we must infer from most of the innumerable
species throughout nature presenting well-marked differ-
ences; whereas varieties, the supposed prototypes and par-
ents of future well-marked species, present slight and ill-de-
fined differences. Mere chance, as we may call it, might
cause one variety to differ in some character from its parents,
and the offspring of this variety again to differ from its
parent in the very same character and in a greater degree ;
but this alone would never account for so habitual and large
a degree of difference as that between the species of the same
genus.
As has always been my practice, I have sought light on this
head from our domestic productions. We shall here find
something analogous. It will be admitted that the production
of races so different as short-horn and Hereford cattle, race
and cart horses, the several breeds of pigeons, &c., could
never have been effected by the mere chance accumulation of
similar variations during many successive generations. In
practice, a fancier is, for instance, struck by a pigeon having
a slightly shorter beak ; another fancier is struck by a pigeon
having a rather longer beak ; and on the acknowledged
principle that "fanciers do not and will not admire a me-
dium standard, but like extremes," they both go on (as
has actually occurred with the sub-breeds of the tumbler-
pigeon) choosing and breeding from birds with longer and
longer beaks, or with shorter and shorter beaks. Again, we
may suppose that at an early period of history, the men of
DIVERGENCE OF CHARACTER 123
one nation or district required swifter horses, whilst those of
another required stronger and bulkier horses. The early dif-
ferences would be very slight ; but, in the course of time, from
the continued selection of swifter horses in the one case, and
of stronger ones in the other, the differences would become
greater, and would be noted as forming two sub-breeds. Ul-
timately, after the lapse of centuries, these sub-breeds would
become converted into two well-established and distinct
breeds. As the differences became greater, the inferior ani-
mals with intermediate characters, being neither very swift
nor very strong, would not have been used for breeding, and
will thus have tended to disappear. Here, then, we see in
man's productions the action of what may be called the prin-
ciple of divergence, causing differences, at first barely appre-
ciable, steadily to increase, and the breeds to diverge in
character, both from each other and from their common
parent.
But how, it may be asked, can any analogous principle
apply in nature? I believe it can and does apply most effi-
ciently (though it was a long time before I saw how), from
the simple circumstance that the more diversified the de-
scendants from any one species become in structure, consti-
tution, and habits, by so much will they be better enabled to
seize on many and widely diversified places in the polity of
nature, and so be enabled to increase in numbers.
We can clearly discern this in the case of animals with
simple habits. Take the case of a carnivorous quadruped,
of which the number that can be supported in any country has
long ago arrived at its full average. If its natural power of
increase be allowed to act, it can succeed in increasing (the
country not undergoing any change in conditions) only by
its varying descendants seizing on places at present occupied
by other animals; some of them, for instance, being enabled
to feed on new kinds of prey, either dead or alive; some
inhabiting new stations, climbing trees, frequenting water,
and some perhaps becoming less carnivorous. The more
diversified in habits and structure the descendants of our
carnivorous animals become, the more places they will be
enabled to occupy. What applies to one animal will apply
throughout all time to all animals — that is, if they vary — for
124 ORIGIN OF SPECIES
otherwise natural selection can effect nothing. So it will be
with plants. It has been experimentally proved, that if a
plot of ground be sown with one species of grass, and a similar
plot be sown with several distinct genera of grasses, a greater
number of plants and a greater weight of dry herbage can
be raised in the latter than in the former case. The same
has been found to hold good when one variety and several
mixed varieties of wheat have been sown on equal spaces of
ground. Hence, if any one species of grass were to go on
varying, and the varieties were continually selected which
differed from each other in the same manner, though in a
very slight degree, as do the distinct species and genera of
grasses, a greater number of individual plants of this species,
including its modified descendants, would succeed in living
on the same piece of ground. And we know that each
species and each variety of grass is annually sowing almost
countless seeds ; and is thus striving, as it may be said, to the
utmost to increase in number. Consequently, in the course of
many thousand generations, the most distinct varieties of
any one species of grass would have the best chance of suc-
ceeding and of increasing in numbers, and thus of supplanting
the less distinct varieties; and varieties, when rendered very
distinct from each other, take the rank of species.
The truth of the principle that the greatest amount of life
can be supported by great diversification of structure, is seen
under many natural circumstances. In an extremely small
area, especially if freely open to immigration, and where the
contest between individual and individual must be very se-
vere, we always find great diversity in its inhabitants. For
instance, I found that a piece of turf, three feet by four
in size, which had been exposed for many years to exactly
the same conditions, supported twenty species of plants, and
these belonged to eighteen genera and to eight orders, which
shows how much these plants differed from each other. So
it is with the plants and insects on small and uniform islets:
also in small ponds of fresh water. Farmers find that they
can raise most food by a rotation of plants belonging to the
most different orders ; nature follows what may be called a
simultaneous rotation. Most of the animals and plants which
live close round any small piece of ground, could live on it
DIVERGENCE OF CHARACTER 125
(supposing its nature not to be in any way peculiar), and
may be said to be striving to the utmost to live there ; but, it
is seen, that where they come into the closest competition, the
advantages of diversification of structure, with the accom-
panying differences of habit and constitution, determine that
the inhabitants, which thus jostle each other most closely,
shall, as a general rule, belong to what we call different
genera and orders.
The same principle is seen in the naturalisation of plants
through man's agency in foreign lands. It might have been
expected that the plants which would succeed in becoming
naturalised in any land would generally have been closely
allied to the indigenes; for these are commonly looked at as
specially created and adapted for their own country. It
might also, perhaps, have been expected that naturalised
plants would have belonged to a few groups more especially
adapted to certain stations in their new homes. But the
case is very different; and Alph. de Candolle has well re-
marked, in his great and admirable work, that floras gain by
naturalisation, proportionally with the number of the native
genera and species, far more in new genera than in new
species. To give a single instance : in the last edition of
Dr. Asa Gray's 'Manual of the Flora of the Northern United
States,' 260 naturalised plants are enumerated, and these be-
long to 162 genera. We thus see that these naturalised plants
are of a highly diversified nature. They differ, moreover, to
a large extent, from the indigenes, for out of the 162 natural-
ised genera, no less than 100 genera are not there indigenous,
and thus a large proportional addition is made to the genera
now living in the United States.
By considering the nature of the plants or animals which
have in any country struggled successfully with the indigenes,
and have there become naturalised, we may gain some crude
idea in what manner some of the natives would have to be
modified, in order to gain an advantage over their com-
patriots; and we may at least infer that diversification of
structure, amounting to new generic differences, would be
profitable to them.
The advantage of diversification of structure in the in-
habitants of the same region is, in fact, the same as that of
126 ORIGIN OF SPECIES
the physiological division of labor in the organs of the same
individual body — a subject so well elucidated by Milne Ed-
wards. No physiologist doubts that a stomach adapted to
digest vegetable matter alone, or flesh alone, draws most
nutriment from these substances. So in the general economy
of any land, the more widely and perfectly the animals and
plants are diversified for different habits of life, so will a
greater number of individuals be capable of there supporting
themselves. A set of animals, with their organisation but
little diversified, could hardly compete with a set more per-
fectly diversified in structure. It may be doubted, for in-
stance, whether the Australian marsupials, which are divided
into groups differing but little from each other, and feebly
representing, as Mr. Waterhouse and others have remarked,
our carnivorous, ruminant, and rodent mammals, could suc-
cessfully compete with these well-developed orders. In the
Australian mammals, we see the process of diversification
in an early and incomplete stage of development.
THE PROBABLE EFFECTS OF THE ACTION OF NATURAL SELECTION
THROUGH DIVERGENCE OF CHARACTER AND EXTINC-
TION, ON THE DESCENDANTS OF A COMMON
ANCESTOR
After the foregoing discussion, which has been much com-
pressed, we may assume that the modified descendants of any
one species will succeed so much the better as they become
more diversified in structure, and are thus enabled to en-
croach on places occupied by other beings. Now let us see
how this principle of benefit being derived from divergence
of character, combined with the principles of natural selec-
tion and of extinction, tends to act.
The accompanying diagram will aid us in understanding
this rather perplexing subject. Let A to L represent the
species of a genus large in its own country ; these species are
supposed to resemble each other in unequal degrees, as is
so generally the case in nature, and as is represented in the
diagram by the letters standing at unequal distances. I have
said a large genus, because as we saw in the second chapter,
on an average more species vary in large genera than in
EFFECTS OF NATURAL SELECTION 127
small genera; and the varying species of the large genera
present a greater number of varieties. We have, also, seen
that the species, which are the commonest and the most
widely diffused, vary more than do the rare and restricted
species. Let (A) be a common, widely-diffused, and varying
species, belonging to a genus large in its own country. The
branching and diverging dotted lines of unequal lengths pro-
ceeding from (A), may represent its varying offspring. The
variations are supposed to be extremely slight, but of the
most diversified nature; they are not supposed all to appear
simultaneously, but often after long intervals of time; nor
are they all supposed to endure for equal periods. Only those
variations which are in some way profitable will be preserved
or naturally selected. And here the importance of the prin-
ciple of benefit derived from divergence of character comes
in; for this will generally lead to the most different or di-
vergent variations (represented by the outer dotted lines)
being preserved and accumulated by natural selection. When
a dotted line reaches one of the horizontal lines, and is there
marked by a small numbered letter, a sufficient amount of
variation is supposed to have been accumulated to form it
into a fairly well-marked variety, such as would be thought
worthy of record in a systematic work.
The intervals between the horizontal lines in the diagram,
may represent each a thousand or more generations. After a
thousand generations, species (A) is supposed to have pro-
duced two fairly well-marked varieties, namely a^ and m^.
These two varieties will generally still be exposed to the
same conditions which made their parents variable, and the
tendency to variability is in itself hereditary ; consequently
they will likewise tend to vary, and commonly in nearly the
same manner as did their parents. Moreover, these two
varieties, being only slightly modified forms, will tend to
inherit those advantages which made their parent (A) more
numerous than most of the other inhabitants of the same
country; they will also partake of those more general advan-
tages which made the genus to which the parent-species
belonged, a large genus in its own country. And all
these circumstances are favorable to the production of new
varieties.
128 ORIGIN OF SPECIES
If, then, these two varieties be variable, the most divergent
of their variations will generally be preserved during the
next thousand generations. And after this interval, variety
a' is supposed in the diagram to have produced variety o',
which will, owing to the principle of divergence, differ more
from (A) than did variety d. Variety m^ is supposed to
have produced two varieties, namely m' and /_, differing from
each other, and more considerably from their common parent
(A). We may continue the process by similar steps for any
length of time; some of the varieties, after each thousand
generations, producing only a single variety, but in a more
and more modified condition, some producing two or three
varieties, and some failing to produce any. Thus the varie-
ties or modified descendants of the common parent (A), will
generally go on increasing in number and diverging in char-
acter. In the diagram the process is represented up to the
ten-thousandth generation, and under a condensed and sim-
plified form up to the fourteen-thousandth generation.
But I must here remark that I do not suppose that the
process ever goes on so regularly as is represented in the
diagram, though in itself made somewhat irregular, nor that
it goes on continuously; it is far more probable that each
form remains for long periods unaltered, and then again
undergoes modification. Nor do I suppose* that the most di-
vergent varieties are invariably preserved; a medium form
may often long endure, and may or may not produce more
than one modified descendant; for natural selection will al-
ways act according to the nature of the places which are
either unoccupied or not perfectly occupied by other beings;
and this will depend on infinitely complex relations. But as
a general rule, the more diversified in structure the descend-
ants from any one species can be rendered, the more places
they will be enabled to seize on, and the more their modified
progeny will increase. In our diagram the line of succession
is broken at regular intervals by small numbered letters mark-
ing the successive forms which have become sufficiently dis-
tinct to be recorded as varieties. But these breaks are
imaginary, and might have been inserted anywhere, after
intervals long enough to allow the accumulation of a con-
siderable amount of divergent variation.
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G H I K L
EFFECTS OF NATURAL SELECTION 129
As all the modified descendants from a common and widely-
diffused species, belonging to a large genus, will tend to par-
take of the same advantages which made their parent success-
ful in life, they will generally go on multiplying in number as
well as diverging in character; this is represented in the dia-
gram by the several divergent branches proceeding from (A).
The modified offspring from the later and more highly im-
proved branches in the lines of descent, will, it is probable,
often take the place of, and so destroy, the earlier and less im-
proved branches : this is represented in the diagram by some
of the lower branches not reaching to the upper horizontal
lines. In some cases no doubt the process of modification
will be confined to a single line of descent, and the number
of modified descendants will not be increased; although the
amount of divergent modification may have been augmented.
This case would be represented in the diagram, if all the
lines proceeding from (A) were removed, excepting that
from a^ to a". In the same way the English race-horse and
English pointer have apparently both gone on slowly diverg-
ing in character from their original stocks, without either
having given off any fresh branches or races.
After ten thousand generations, species (A) is supposed
to have produced three forms, a", f and w", which, from
having diverged in character during the successive genera-
tions, will have come to differ largely, but perhaps unequally,
from each other and from their common parent. If we sup-
pose the amount of change between each horizontal line in
our diagram to be excessively small, these three forms may
still be only well-marked varieties ; but we have only to
suppose the steps in the process of modification to be more
numerous or greater in amount, to convert these three forms
into doubtful or at least into well-defined species. Thus the
diagram illustrates the steps by which the small differences
distinguishing varieties are increased into the larger differ-
ences distinguishing species. By continuing the same process
for a greater number of generations (as shown in the dia-
gram in a condensed and simplified manner), we get eight
species, marked by the letters between o" and w", all de-
scended from (A). Thus, as I believe, species are multiplied
and genera are formed.
130 ORIGIN OF SPECIES
In a large genus it is probable that more than one species
would vary. In the diagram I have assumed that a second
species (I) has produced, by analogous steps, after ten thou-
sand generations, either two well-marked varieties {w^° and
s^°) or two species, according to the amount of change supn
posed to be represented between the horizontal lines. After
fourteen thousand generations, six new species, marked by
the letters jj." to s", are supposed to have been produced. In
any genus, the species which are already very dififerent in
character from each other, will generally tend to produce the
greatest number of modified descendants ; for these will have
the best chance of seizing on new and widely different places
in the polity of nature : hence in the diagram I have chosen
the extreme species (A), and the nearly extreme species (I),
as those which have largely varied, and have given rise to
new varieties and species. The other nine species (marked
by capital letters) of our original genus, may for long but
unequal periods continue to transmit unaltered descendants;
and this is shown in the diagram by the dotted lines unequally
prolonged upwards.
But during the process of modification, represented in the
diagram, another of our principles, namely that of extinction,
will have played an important part. As in each fully stocked
country natural selection necessarily acts by the selected
form having some advantage in the struggle for life over
other forms, there will be a constant tendency in the im-
proved descendants of any one species to supplant and ex-
terminate in each stage of descent their predecessors and
their original progenitor. For it should be remembered that
the competition will generally be most severe between those
forms which are most nearly related to each other in habits,
constitution, and structure. Hence all the intermediate forms
between the earlier and later states^ that is between the less
and more improved states of the same species, as well as
the original parent-species itself, will generally tend to become
extinct. So it probably will be with many whole collateral
lines of descent which will be conquered by later and
improved lines. If, however, the modified offspring of a
species get into some distinct country, or become quickly
adapted to some quite new station, in which offspring and
EFFECTS OF NATURAL SELECTION 131
progenitor do not come into competition, both may continue
to exist.
If, then, our diagram be assumed to represent a consider-
able amount of modification, species (A) and all the earlier
varieties will have become extinct, being replaced by eight
new species (a" to m") ; and species (I) will be replaced by
six (n" to 2") new species.
But we may go further than this. The original species
of our genus were supposed to resemble each other in unequal
degrees, as is so generally the case in nature; species (A)
being more nearly related to B, C, and D, than to the other
species; and species (I) more to G, H, K, L, than to the
others. These two species (A) and (I) were also supposed
to be very common and widely diffused species, so that they
must originally have had some advantage over most of the
other species of the genus. Their modified descendants,
fourteen in number at the fourteen-thousandth generation,
will probably have inherited some of the same advantages :
they have also been modified and improved in a diversified
manner at each stage of descent, so as to have become adapted
to many related places in the natural economy of their
country. It seems, therefore, extremely probable that they
will have taken the places of, and thus exterminated, not only
their parents (A) and (I), but likewise some of the original
species which were most nearly related to their parents.
Hence very few of the original species will have transmitted
offspring to the fourteen-thousandth generation. We may
suppose that only one, (F), of the two species (E and F)
which were least closely related to the other nine original
species, has transmitted descendants to this late stage of
descent.
The new species in our diagram descended from the original
eleven species, will now be fifteen in number. Owing to the
divergent tendency of natural selection, the extreme amount
of difference in character between species o" and 0" will be
much greater than that between the most distinct of the
original eleven species. The new species, moreover, will be
allied to each other in a v^idely different manner. Of the
eight descendants from (A) the three marked a", 9", />",
will be nearly related Irom having recently branched off
132 ORIGIN OF SPECIES
from d"; b^*, and f*, from having diverged at an earlier
period from a', v^^ill be in some degree distinct from the three
first-named species; and lastly, o", i" and w" will be nearly
related one to the other, but, from having diverged at the first
commencement of the process of modification, will be widely
different from the other five species, and may constitute a
sub-genus or a distinct genus.
The six descendants from (I) will form two sub-genera or
genera. But as the original species (I) differed largely from
(A), standing nearly at the extreme end of the original
genus, the six descendants from (I) will, owing to inherit-
ance alone, differ considerably from the eight descendants
from (A) ; the two groups, moreover, are supposed to have
gone on diverging in different directions. The intermediate
species, also (and this is a very important consideration),
which connected the original species (A) and (I), Have all
become, excepting (F), extinct, and have left no descend-
ants. Hence the six new species descended from (I), and
the eight descendants from (A), will have to be ranked as
very distinct genera, or even as distinct sub-families.
Thus it is, as I believe, that two or more genera are pro-
duced by descent with modification, from two or more species
of the same genus. And the two or more parent-species are
supposed to be descended from some one species of an earlier
genus. In our diagram, this is indicated by the broken lines,
beneath the capital letters, converging in sub-branches down-
wards towards a single point ; this point represents a species,
the supposed progenitor of our several sub-genera and
genera.
It is worth while to reflect for a moment on the character
of the new species f", which is supposed not to have diverged
much in character, but to have retained the form of (F),
either unaltered or altered only in a slight degree. In this
case, its affinities to the other fourteen new species will be of
a curious and circuitous nature. Being descended from a
form which stood between the parent-species (A) and (I),
now supposed to be extinct and unknown, it will be in some
degree intermediate in character between the two groups
descended from these two species. But as these two groups
have gone on diverging in character from the type of their
EFFECTS OF NATURAL SELECTION 133
parents, the new species (f") will not be directly interme-
diate between them, but rather between types of the two
groups; and every naturalist will be able to call such cases
before his mind.
In the diagram, each horizontal line has hitherto been sup-
posed to represent a thousand generations, but each may rep'
resent a million or more generations ; it may also represent a
section of the successive strata of the earth's crust including
extinct remains. We shall, when we come to our chapter on
Geology, have to refer again to this subject, and I think we
shall then see that the diagram throws light on the affinities
of extinct beings, which, though generally belonging to the
same orders, families, or genera, with those now living, yet
are often, in some degree, intermediate in character between
existing groups ; and we can understand this fact, for the ex-
tinct species lived at various remote epochs when the
branching lines of descent had diverged less.
I see no reason to limit the process of modification, as now
explained, to the formation of genera alone. If, in the dia-
gram, we suppose the amount of change represented by each
successive group of diverging dotted lines to be great, the
forms marked o" to /»", those marked &" and f *, and those
marked o" to m", will form three very distinct genera. We
shall also have two very distinct genera descended from (I),
differing widely from the descendants of (A). Those two
groups of genera will thus form two distinct families, or
orders, according to the amount of divergent modification
supposed to be represented in the diagram. And the two new
families, or orders, are descended from two species of the
original genus, and these are supposed to be descended from
some still more ancient and unknown form.
We have seen that in each country it is the species belong-
ing to the larger genera which oftenest present varieties or
incipient species. This, indeed, might have been expected;
for, as natural selection acts through one form having some
advantage over other forms in the struggle for existence, it
will chiefly act on those which already have some advantage;
and the largeness of any group shows that its species have
inherited from a common ancestor some advantage in com-
mon. Hence, the struggle for the production of new and
134 ORIGIN OF SPECIES
modified descendants will mainly lie between the larger
groups which are all trying to increase in number. One
large group will slowly conquer another large group, reduce
its numbers, and thus lessen its chance of further variation
and improvement. Within the same large group, the later
and more highly perfected sub-groups, from branching out
and seizing on many new places in the polity of Nature, will
constantly tend to supplant and destroy the earlier and less
improved sub-groups. Small and broken groups and sub-
groups will finally disappear. Looking to the future, we can
predict that the groups of organic beings which are now
large and triumphant, and which are least broken up, that
is, which have as yet suffered least extinction, will, for a long
period, continue to increase. But which groups will ulti-
mately prevail, no man can predict ; for we know that many
groups, formerly most extensively developed, have now be-
come extinct. Looking still more remotely to the future, we
may predict that, owing to the continued and steady increase
of the larger groups, a multitude of smaller groups will
become utterly extinct, and leave no modified descendants;
and consequently that, of the species living at any one period,
extremely few will transmit descendants to a remote futurity.
I shall have to return to this subject in the chapter on Classi-
fication, but I may add that as, according to this view, ex-
tremely few of the more ancient species have transmitted
descendants to the present day, and, as all the descendants
of the same species form a class, we can understand how it
is that there exist so few classes in each main division of
the animal and vegetable kingdoms. Although few of the
most ancient species have left modified descendants, yet, at
remote geological periods, the earth may have been almost
as well peopled with species of many genera, families, orders,
and classes, as at the present time.
ON THE DEGREE TO WHICH ORGANIZATION TENDS TO ADVANCE
Natural Selection acts exclusively by the preservation and
accumulation of variations, which are beneficial under the
organic and inorganic conditions to which each creature is
exposed at all periods of life. The ultimate result is that each
EFFECTS OF NATURAL SELECTION 13S
creature tends to become more and more improved in relation
to its conditions. This improvement inevitably leads to the
gradual advancement of the organisation of the greater num-
ber of living beings throughout the world. But here we enter
on a very intricate subject, for naturalists have not defined
to each other's satisfaction what is meant by an advance in
organization. Amongst the vertebrata the degree of intellect
and an approach in structure to man clearly come into play.
It might be thought that the amount of change which the
various parts and organs pass through in their development
from the embryo to maturity would suffice as a standard of
comparison; but there are cases, as with certain parasitic
crustaceans, in which several parts of the structure become
less perfect, so that the mature animal cannot be called higher
than its larva. Von Baer's standard seems the most widely
applicable and the best, namely, the amount of differentiation
of the parts of the same organic being, in the adult state as
I should be inclined to add, and their specialisation for dif-
ferent functions; or, as Milne Edwards would express it,
the completeness of the division of physiological labour. But
we shall see how obscure this subject is if we look, for in-
stance, to fishes, amongst which some naturalists rank those
as highest which, like the sharks, approach nearest to amphi-
bians; whilst other naturalists range the common bony or
teleostean fishes as the highest, inasmuch as they are most
strictly fish-like, and dififer most from the other vertebrate
classes. We see still more plainly the obscurity of the
subject by turning to plants, amongst which the standard of
intellect is of course quite excluded : and here some botanists
rank those plants as highest which have every organ, as
sepals, petals, stamens, and pistils, fully developed in each
flower; whereas other botanists, probably with more truth,
look at the plants which have their several organs much
modified and reduced in number as the highest.
If we take as the standard of high organisation, the amount
of dififerentiation and specialisation of the several organs in
each being when adult (and this will include the advance-
ment of the brain for intellectual purposes), natural selec-
tion clearly leads towards this standard : for all physiologists
admit that the specialisation of organs, inasmuch as in this
136 ORIGIN OF SPECIES
state they perform their functions better, is an advantage to
each being; and hence the accumulation of variations tending
towards specialisation is within the scope of natural selection.
On the other hand, we can see, bearing in mind that all or-
ganic beings are striving to increase at a high ratio and to
seize on every unoccupied or less well occupied place in the
economy of nature, that it is quite possible for natural selec-
tion gradually to fit a being to a situation in which several
organs would be superfluous or useless : in such cases there
would be retrogression in the scale of organisation. Whether
organisation on the whole has actually advanced from the
remotest geological periods to the present day will be more
conveniently discussed in our chapter on Geological Succes-
sion.
But it may be objected that if all organic beings thus tend
to rise in the scale, how is it that throughout the world a
multitude of the lowest forms still exist ; and how is it that
in each great class some forms are far more highly developed
than others ? Why have not the more highly developed forms
everywhere supplanted and exterminated the lower? La-
marck, who believed in an innate and inevitable tendency
towards perfection in all organic beings, seems to have felt
this difficulty so strongly, that he was led to suppose that new
and simple forms are continually being produced by spon-
taneous generation. Science has not as yet proved the truth
of this belief, whatever the future may reveal. On our
theory the continued existence of lowly organisms offers no
difficulty; for natural selection, or the survival of the fittest,
does not necessarily include progressive development — it
only takes advantage of such variations as arise and are
beneficial to each creature under its complex relations of life.
And it may be asked what advantage, as far as we can see,
would it be to an infusorian animalcule — to an intestinal
worm — or even to an earth-worm, to be highly organised.
If it were no advantage, these forms would be left, by natural
selection, unimproved or but little improved, and might re-
main for indefinite ages in their present lowly condition.
And geology tells us that some of the lowest forms, as the
infusoria and rhizopods, have remained for an enormous
period in nearly their present state. But to suppose that most
EFFECTS OF NATURAL SELECTION 137
of the many now existing low forms have not in the least
advanced since the first dawn of Hfe would be extremely
rash ; for every naturalist who has dissected some of the be-
ings now ranked as very low in the scale, must have been
struck with their really wondrous and beautiful organisation.
Nearly the same remarks are applicable if we look to the
different grades of organisation within the same great group;
for instance, in the vertebrata, to the co-existence of mam-
mals and fish — amongst mammalia, to the ca-existence of man
and the ornithorhynchus — amongst fishes, to the co-existence
of the shark and the lancelet (Amphioxus), which latter fish
in the extreme simplicity of its structure approaches the in-
vertebrate classes. But mammals and fish hardly come into
competition with each other; the advancement of the whole
class of mammals, or of certain members in this class, to the
highest grade would not lead to their taking the place of
fishes. Physiologists believe that the brain must be bathed
by warm blood to be highly active, and this requires aerial
respiration; so that warm-blooded mammals when inhabiting
the water lie under a disadvantage in having to come con-
tinually to the surface to breathe. With fishes, members
of the shark family would not tend to supplant the lancelet;
for the lancelet, as I hear from Fritz Miiller, has as sole com-
panion and competitor on the barren sandy shore of South
Brazil, an anomalous annelid. The three lowest orders of
mammals, namely, marsupials, edentata, and rodents, co-exist
in South America in the same region with numerous monkeys,
and probably interfere little with each other. Although or-
ganisation, on the whole, may have advanced and be stil'
advancing throughout the world, yet the scale will always
present many degrees of perfection ; for the high advance-
ment of certain whole classes, or of certain members of each
class, does not at all necessarily lead to the extinction of
those groups with which they do not enter into close competi-
tion. In some cases, as we shall hereafter see, lowly or-
ganised forms appear to have been preserved to the present
day, from inhabiting confined or peculiar stations, where
they have been subjected -to less severe competition, and
where their scanty numbers have retarded the chance of fav-
orable variations arising:
138 ORIGIN OF SPECIES
Finally, I believe that many lowly organised forms now
exist throughout the world, from various causes. In some
cases variations or individual differences of a favorable na-
ture may never have arisen for natural selection to act on and
accumulate. In no case, probably, has time sufficed for the
utmost possible amount of development. In some few cases
there has been what we must call retrogression of organisa-
tion. But the main cause lies in the fact that under very
simple conditions' of life a high organisation would be of no
service, — possibly would be of actual disservice, as being of
a more delicate nature, and more liable to be put out of order
and injured.
Looking to the first dawn of life, when all organic beings,
as we may believe, presented the simplest structure, how, it
has been asked, could the first steps in the advancement or
differentiation of parts have arisen? Mr. Herbert Spencer
would probably answer that, as soon as simple unicellular
organism came by growth or division to be compounded of
several cells, or became attached to any supporting surface,
his law "that homologous units of any order became differ-
entiated in proportion as their relations to incident forces
became different" would come into action. But as we have
no facts to guide us, speculation on the subject is almost use-
less. It is, however, an error to suppose that there would
be no struggle for existence, and, consequently, no natural
selection, until many forms had been produced: variations
in a single species inhabiting an isolated station might be
beneficial, and thus the whole mass of individuals might be
modified, or two distinct forms might arise. But, as I re-
marked towards the close of the Introduction, no one ought
to feel surprise at much remaining as yet unexplained on
the origin of species, if we make due allowance for our pro-
found ignorance on the mutual relations of the inhabitants
of the world at the present time, and still more so during
past ages.
CONVERGENCE OF CHARACTER
Mr. H. C. Watson thinks that I have overrated the im-
portance of divergence of character (in which, however, he
apparently believes), and that convergence, as it may be
CONVERGENCE OF CHARACTER 139
called, has likewise played a part. If two species, belonging
to two distinct though allied genera, had both produced a
large number of new and divergent forms, it is conceivable
that these might approach each other so closely that they
would have all to be classed under the same genus ; and thus
the descendants of two distinct genera would converge into
one. But it would in most cases be extremely rash to at-
tribute to convergence a close and general similarity of struc-
ture in the modified descendants of widely distinct forms.
The shape of a crystal is determined solely by the molecular
forces, and it is not surprising that dissimilar substances
should sometimes assume the same form; but with organic
beings we should bear in mind that the form of each depends
on an infinitude of complex relations, namely on the varia-
tions which have arisen, these being due to causes far too
intricate to be followed out, — on the nature of the variations
which have been preserved or selected, and this depends on
the surrounding physical conditions, and in a still higher
degree on the surrounding organisms with which each being
has come into competition, — and lastly, on inheritance (in it-
self a fluctuating element) from innumerable progenitors,
all of which have had their forms determined through equally
complex relations. It is incredible that the descendants of
two organisms, which had originally differed in a marked
manner, should ever afterwards converge so closely as to lead
to a near approach to identity throughout their whole organ-
isation. If this had occurred, we should meet with the same
form, independently of genetic connection, recurring in
widely separated geological formations; and the balance of
evidence is opposed to any such an admission.
Mr. Watson has also objected that the continued action
of natural selection, together with divergence of character,
would tend to make an indefinite number of specific forms.
As far as mere inorganic conditions are concerned, it seems
probable that a sufficient number of species would soon
become adapted to all considerable diversities of heat,
moisture, &c. ; but I fully admit that the mutual relations of
organic beings are more important; and as the number of
species in any country goes on increasing, the organic con-
ditions of life must become more and more complex. Conse-
140 ORIGIN OF SPECIES
quently there seems at first sight no limit to the amount of
profitable diversification of structure, and therefore no limit
to the number of species which might be produced. We do
not know that even the most prolific area is fully stocked
with specific forms : at the Cape of Good Hope and in Aus-
tralia, which support such an astonishing number of species,
many European plants have become naturalised. But geology
shows us, that from an early part of the tertiary period the
number of species of shells, and that from the middle part of
this same period the number of mammals, has not greatly or
at all increased. What then checks an indefinite increase
in the number of species? The amount of life (I do not mean
the number of specific forms) supported on an area must
have a limit, depending so largely as it does on physical con-
ditions ; therefore, if an area be inhabited by very many spe-
cies, each or nearly each species will be represented by few
individuals ; and such species will be liable to extermination
from accidental fluctuations in the nature of the seasons
or in the number of their enemies. The process of exter-
mination in such cases would be rapid, whereas the production
of new species must always be slow. Imagine the extreme
case of as many species as individuals in England, and the
first severe winter or very dry summer would exterminate
thousands on thousands of species. Rare species, and each
species will become rare if the number of species in any
country becomes indefinitely increased, will, on the principle
often explained, present within a given period few favorable
variations; consequently, the process of giving birth to new
specific forms would thus be retarded. When any species be-
comes very rare, close interbreeding will help to exterminate
it ; authors have thought that this comes into play in account-
ing for the deterioration of the Aurochs in Lithuania, of Red
Deer in Scotland, and of Bears in Norway, &c. Lastly, and
this I am inclined to think is the most important element, a
dominant species, which has already beaten many competitors
in its own home, will tend to spread and supplant many others.
Alph, de Candolle has shown that those species which spread
widely, tend generally to spread very widely; consequently,
they will tend to supplant and exterminate several species
in several areas, and thus check the inordinate increase of
SUMMARY OF CHAPTER 141
specific forms throughout the world. Dr. Hooker has re-
cently shown that in the S.E. corner of Australia, where,
apparently, there are many invaders from different quarters
of the globe, the endemic Australian species have been
greatly reduced in number. How much weight to attribute
to these several considerations I will not pretend to say ; but
conjointly they must limit in each country the tendency to
an indefinite augmentation of specific forms.
SUMMARY OF CHAPTER
If under changing conditions of life organic beings present
individual differences in almost every part of their structure,
and this cannot be disputed; if there be, owing to their
geometrical rate of increase, a severe struggle for life at
some age, season, or year, and this certainly cannot be dis-
puted; then, considering the infinite complexity of the rela-
tions of all organic beings to each other and to their condi-
tions of life, causing an infinite diversity in structure, consti-
tution, and habits, to be advantageous to them, it would be a
most extraordinary fact if no variations had ever occurred
useful to each being's own welfare, in the same manner as so
many variations have occurred useful to man. But if varia-
tions useful to any organic being ever do occur, assuredly
individuals thus characterised will have the best chance of
being preserved in the struggle for life ; and from the strong
principle of inheritance, these will tend to produce offspring
similarly characterised. This principle of preservation, or the
survival of the fittest, I have called Natural Selection. It
leads to the improvement of each creature in relation to its
organic and inorganic conditions of life; and consequently,
in most cases, to what must be regarded as an advance in
organism. Nevertheless, low and simple forms will long
endure if well fitted for their simple conditions of life.
Natural selection, on the principle of qualities being in-
herited at corresponding ages, can modify the egg, seed, or
young, as easily as the adult. Amongst many animals, sexual
selection will have given its aid to ordinary selection, by
assuring to the most vigorous and best adapted males the
greatest number of offspring. Sexual selection will also give
142 ORIGIN OF SPECIES
characters useful to the males alone, in their struggles or
rivalry with other males ; and these characters will be trans-
mitted to one sex or to both sexes, according to the form of
inheritance which prevails.
Whether natural selection has really thus acted in adapting
the various forms of life to their several conditions and sta-
tions, must be judged by the general tenor and balance of
evidence given in the following chapters. But we have al-
ready seen how it entails extinction ; and how largely ex-
tinction has acted in the world's history, geology plainly
declares. Natural selection, also, leads to divergence of
character; for the more organic beings diverge in structure,
habits, and constitution, by so much the more can a large
number be supported on the area, — of which we see proof by
looking to the inhabitants of any small spot, and to the pro-
ductions naturalised in foreign lands. Therefore, during the
modification of the descendants of any one species, and dur-
ing the incessant struggle of all species to increase in num-
bers, the more diversified the descendants become, the better
will be their chance of success in the battle for life. Thus
the small differences distinguishing varieties of the same spe-
cies, steadily tend to increase, till they equal the greater dif-
ferences between species of the same genus, or even of
distinct genera.
We have seen that it is the common, the widely-diffused
and widely-ranging species, belonging to the larger genera
within each class, which vary most; and these tend to trans-
mit to their modified offspring that superiority which now
makes them dominant in their own countries. Natural selec-
tion, as has just been remarked, leads to divergence of
character and to much extinction of the less improved and
intermediate forms of life. On these principles, the nature
of the affinities, and the generally well-defined distinctions
between the innumerable organic beings in each class
throughout the world, may be explained. It is a truly won-
derful fact — the wonder of which we are apt to overlook
from familiarity — that all animals and all plants through-
out all time and space should be related to each other in
groups, subordinate to groups, in the manner which we
everywhere behold — namely, varieties of the same species
SUMMARY OF CHAPTER 143
most closely related, species of the same genus less closely
and unequally related, forming sections and sub-genera, spe-
cies of distinct genera much less closely related, and genera
related in different degrees, forming sub-families, families,
orders, sub-classes and classes. The several subordinate
groups in any class cannot be ranked in a single file, but
seem clustered round points, and these round other points,
and so on in almost endless cycles. If species had been in-
dependently created, no explanation would have been pos-
sible of this kind of classification ; but it is explained through
inheritance and the complex action of natural selection, en-
tailing extinction and divergence of character, as we have
seen illustrated in the diagram.
The affinities of all the beings of the same class have some-
times been represented by a great tree. I believe this simile
largely speaks the truth. The green and budding twigs may
represent existing species ; and those produced during former
years may represent the long succession of extinct species.
At each period of growth all the growing twigs have tried
to branch out on all sides, and to overtop and kill the sur-
rounding twigs and branches, in the same manner as species
and groups of species have at all times overmastered other
species in the great battle for life. The limbs divided into
great branches, and these into lesser and lesser branches,
were themselves once, when the tree was young, budding
twigs ; and this connection of the former and present buds by
ramifying branches may well represent the classification of
all extinct and living species in groups subordinate to groups.
Of the many twigs which flourished when the tree was a
mere bush, only two or three, now grown into great branches,
yet survive and bear the other branches ; so with the species
which lived during long-past geological periods, very few
have left living and modified descendants. From the first
growth of the tree, many a limb and branch has decayed and
dropped oft; and these fallen branches of various sizes may
represent those whole orders, families, and genera which have
now no living representatives, and which are known to us
only in a fossil state. As w^ here and there see a thin strag-
gling branch springing from a fork low down in a tree, and
which by some chance ha^ been favoured and is still alive on
144 ORIGIN OF SPECIES
its summit, so we occasionally see an animal like the Ornitho-
rhynchus or Lepidosiren, which in some small degree con-
nects by its affinities two large branches of life, and which
has apparently been saved from fatal competition by having
inhabited a protected station. As buds give rise by growth
to fresh buds, and these, if vigorous, branch out and overtop
on all sides many a feebler branch, so by generation I believe
it has been with the great Tree of Life, which fills with
its dead and broken branches the crust of the earth, and
covers the surface with its ever-branching and beautiful
ramifications.
CHAPTER V
Laws of Variation
Effects of changed conditions — Use and disuse, combined with natural
selection ; organs of flight and of vision — Acclimatisation — Cor-
related variation — Compensation and economy of growth — False
correlations — Multiple, rudimentary, and lowly organised struc-
tures variable — Parts developed in an unusual manner are highly
variable ; specific characters more variable than generic : second-
ary sexual characters variable — Species of the same genus vary
in an analogous manner — Reversions to long-lost characters —
Summary.
I HAVE hitherto sometimes spoken as if the variations —
so common and multiform with organic beings under
domestication, and in a lesser degree with those under
nature — were due to chance. This, of course, is a wholly
incorrect expression, but it serves to acknowledge plainly
our ignorance of the cause of each particular variation.
Some authors believe it to be as much the function of the
reproductive system to produce individual differences, or
slight deviations of structure, as to make the child like its
parents. But the fact of variations and monstrosities oc-
curring miach more frequently under domestication than
under nature, and the greater variability of species having
wide ranges than of those with restricted ranges, lead to the
conclusion that variability is generally related to the condi-
tions of life to which each species has been exposed during
several successive generations. In the first chapter I at-
tempted to show that changed conditions act in two ways,
directly on the whole organisation or on certain parts alone,
and indirectly through the reproductive system. In all cases
there are two factors, the nature of the organism, which is
much the most important of the two, and the nature of the
conditions. The direct action of changed conditions leads
to definite or indefinite results. In the latter case the organi-
145
146 ORIGIN OF SPECIES
sation seems to become plastic, and we have much fluctu-
ating variability. In the former case the nature of the
organism is such that it yields readily, when subjected to
certain conditions, and all, or nearly all the individuals be-
come modified in the same way.
It is very difficult to decide how far changed conditions,
such as of climate, food, &c., have acted in a definite man-
ner. There is reason to believe that in the course of time
the effects have been greater than can be proved by clear
evidence. But we may safely conclude that the innumer-
able complex co-adaptations of structure, which we see
throughout nature between various organic beings, cannot
be attributed simply to such action. In the following cases
the conditions seem to have produced some slight definite
effect : E. Forbes asserts that shells at their southern limit,
and when living in shallow water, are more brightly col-
oured than those of the same species from further north or
from a greater depth ; but this certainly does not always
hold good. Mr. Gould believes that birds of the same species
are more brightly coloured under a clear atmosphere, than
when living near the coast or on islands ; and Wollaston
is convinced that residence near the sea affects the colours
of insects. Moquin-Tandon gives a list of plants which,
when growing near the sea-shore, have their leaves in
some degree fleshy, though not elsewhere fleshy. These
slightly varying organisms are interesting in as far as they
present characters analogous to those possessed by the spe-
cies which are confined to similar conditions.
When a variation is of the slightest use to any being, we
cannot tell how much to attribute to the accumulative action
of natural selection, and how much to the definite action of
the conditions of life. Thus, it is well known to furriers
that animals of the same species have thicker and better
fur the further north they live; but who can tell how much
of this difiference may be due to the warmest-clad individu-
als having been favoured and preserved during many genera-
tions, and how much to the action of the severe climate?
for it would appear that climate has some direct action on
the hair of our domestic quadrupeds.
Instances could be given of similar varieties being pro-
EFFECTS OF USE AND DISUSE 147
duced from the same species under external conditions o£
life as different as can well be conceived; and, on the other
hand, of dissimilar varieties being produced under appar-
ently the same external conditions. Again, innumerable in-
stances are known to every naturalist, of species keeping
true, or not varying at all, although living under the most
opposite climates. Such considerations as these incline me
to lay less weight on the direct action of the surrounding
conditions, than on a tendency to vary, due to causes of
which we are quite ignorant.
In some sense the conditions of life may be said, not only
to cause variability, either directly or indirectly, but like-
wise to include natural selection, for the conditions deter-
mine whether this or that variety shall survive. But when
man is the selecting agent, we clearly see that the two ele-
ments of change are distinct; variability is in some manner
excited, but it is the will of man which accumulates the va-
riations in certain directions; and it is this latter agency
which answers to the survival of the fittest under nature.
EFFECTS OF THE INCREASED USE AND DISUSE OF PARTS,
AS CONTROLLED BY NATURAL SELECTION
From the facts alluded to in the first chapter, I think there
can be no doubt that use in our domestic animals has
strengthened and enlarged certain parts, and disuse dimin-
ished them; and that such modifications are inherited.
Under free nature, we have no standard of comparison, by
which to judge of the effects of long-continued use or dis-
use, for we know not the parent-forms ; but many animals
possess structures which can be best explained by the effects
of disuse. As Professor Owen has remarked, there is no
greater anomaly in nature than a bird that cannot fly; yet
there are several in this state. The logger-headed duck
of South America can only flap along the surface of the
water, and has its wings in nearly the same condition as the
domestic Aylesbury-duck : it is a remarkable fact that the
young birds, according to Mr. Cunningham, can fly, while
the adults have lost this 'power. As the larger ground-
feeding birds seldom take flight except to escape danger.
148 ORIGIN OF SPECIES
it is probable that the nearly wingless condition of several
birds, now inhabiting or which lately inhabited several
oceanic islands, tenanted by no beasts of prey, has been
caused by disuse. The ostrich indeed inhabits continents,
and is exposed to danger from which it cannot escape by
flight, but it can defend itself by kicking its enemies, as
efficiently as many quadrupeds. We may believe that the
progenitor of the ostrich genus had habits like those of
the bustard, and that, as the size and weight of its body
were increased during successive generations, its legs were
used more, and its wings less, until they became incapable
of flight.
Kirby has remarked (and I have observed the same fact)
that the anterior tarsi, or feet, of many male dung-feeding
beetles are often broken off; he examined seventeen speci-
m.ens in his own collection, and not one had even a relic left.
In the Onites apelles the tarsi are so habitually lost, that
the insect has been described as not having them. In some
other genera they are present, but in a rudimentary condi-
tion. In the Ateuchus or sacred beetle of the Egyptians,
they are totally deficient. The evidence that accidental mu-
tilations can be inherited is at present not decisive; but the
remarkable cases observed by Brown-Sequard in guinea-
pigs, of the inherited effects of operations, should make us
cautious in denying this tendency. Hence it will perhaps
be safest to look at the entire absence of the anterior tarsi
in Ateuchus, and their rudimentary condition in some other
genera, not as cases of inherited mutilations, but as due to
the effects of long-continued disuse; for as many dung-
feeding beetles are generally found with their tarsi lost,
this must happen early in life; therefore the tarsi cannot
be of much importance or be much used by these insects.
In some cases we might easily put down to disuse modifi-
cations of structure which are wholly, or mainly, due to
natural selection. Air. Wollaston has discovered the remark-
able fact that 200 beetles, out of the 550 species (but more
are now known) inhabiting Madeira, are so far deficient
in wings that they cannot fly; and that, of the twenty-nine
endemic genera, no less than twenty-three have all their spe-
cies in this condition ! Several facts, — namely, that beetles
EFFECTS OF USE AND DISUSE 149
in many parts of the world are frequently blown to sea and
perish; that the beetles in Madeira, as observed by Mr. Wol-
laston. lie much concealed, until the wind lulls and the sun
shines ; that the proportion of wingless beetles is larger on
the exposed Desertas than in Madeira itself; and especially
the extraordinary fact, so strongly insisted on by Mr. Wol-
laston, that certain large groups of beetles, elsewhere ex-
cessively numerous, which absolutely require the use of their
wings, are here almost entirely absent; — these several con-
siderations make me believe that the wingless condition of
so many Madeira beetles is mainly due to the action of
natural selection, combined probably with disuse. For dur-
ing many successive generations each individual beetle which
flew least, either from its wings having been ever so little
less perfectly developed or from indolent habit, will have had
the best chance of surviving from not being blown out to
sea; and, on the other hand, those beetles which most readily
took to flight would oftenest have been blown to sea, and
thus destroyed.
The insects in Madeira which are not ground-feeders, and
which, as certain flower-feeding coleoptera and lepidoptera,
must habitually use their wings to gain their subsistence,
have, as Mr. Wollaston suspects, their wings not at all re-
duced, but even enlarged. This is quite compatible with
the action of natural selection. For when a new insect first
arrived on the island, the tendency of natural selection to
enlarge or to reduce the wings, would depend on whether a
greater number of individuals were saved by successfully
battling with the winds, or by giving up the attempt and
rarely or never flying. As with mariners ship-wrecked near
a coast, it would have been better for the good swimmers if
they had been able to swim still further, whereas it would
have been better for the bad swimmers if they had not been
able to swim at all and had stuck to the wreck.
The eyes of moles and of some burrowing rodents are
rudimentary in size, and in some cases are quite covered by
skin and fur. This state of the eyes is probably due to
gradual reduction from disuse, but aided perhaps by natural
selection. In South America, a burrowing rodent, the tuco-
tuco, or Ctenomys, is even more subterranean in its habits
150 ORIGIN OF SPECIES
than the mole; and I was assured by a Spaniard, who had
often caught them, that they were frequently blind. One
which I kept alive was certainly in this condition, the cause,
as appeared on dissection, having been inflammation of the
nictitating membrane. As frequent inflammations of the eyes
must be injurious to any animal, and as eyes are certainly
not necessary to animals having subterranean habits, a re-
duction in their size, with the adhesion of the eyelids and
growth of fur over them, might in such case be an advan-
tage; and if so, natural selection would aid the effects of
disuse.
It is well known that several animals, belonging to the
most different classes, which inhabit the caves of Carniola
and of Kentucky, are blind. In some of the crabs the foot-
stalk for the eye remains, though the eye is gone; — the
stand for the telescope is there, though the telescope with
its glasses has been lost. As it is difficult to imagine that
eyes, though useless, could be in any way injurious to ani-
mals living in darkness, their loss may be attributed to dis-
use. In one of the blind animals, namely, the cave-rat
(Neotoma), two of which were captured by Professor Silli-
man at above half a mile distance from the mouth of the
cave, and therefore not in the profoundest depths, the eyes
were lustrous and of large size; and these animals, as I am
informed by Professor Silliman, after having been exposed
for about a month to a graduated light, acquired a dim per-
ception of objects.
It is difficult to imagine conditions of life more similar
than deep limestone caverns under a nearly similar climate;
so that, in accordance with the old view of the blind ani-
mals having been separately created for the American and
European caverns, very close similarity in their organisation
and affinities might have been expected. This is certainly
not the case if we look at the two whole faunas; and with
respect to the insects alone, Schiodte has remarked, "We are
accordingly prevented from considering the entire phenome-
non in any other light than something purely local, and the
similarity which is exhibited in a few forms between the
Mammoth cave (in Kentucky) and the caves in Carniola,
otherwise than as a very plain expression of that analogy
EFFECTS OF USE AND DISUSE 151
which subsists generally between the fauna of Europe and
of North America." On my view we must suppose that
American animals, having in most cases ordinary powers of
vision, slowly migrated by successive generations from the
outer world into the deeper and deeper recesses of the Ken-
tucky caves, as did European animals into the caves of
Europe. We have some evidence of this gradation of habit;
for, as Schiodte remarks, "We accordingly look upon the
subterranean faunas as small ramifications which have pene-
trated into the earth from the geographically limited faunas
of the adjacent tracts, and which, as they extended them-
selves into darkness, have been accommodated to surround-
ing circumstances. Animals not far remote from ordinary
forms, prepare the transition from light to darkness. Next
follow those that are constructed for twilight; and, last of
all, those destined for total darkness, and whose formation is
quite peculiar." These remarks of Schiodte's, it should be
understood, apply not to the same, but to distinct species.
By the time that an animal had reached, after numberless
generations, the deepest recesses, disuse will on this view
have more or less perfectly obliterated its eyes, and natural
selection will often have effected other changes, such as an
increase in the length of the antennae or palpi, as a compen-
sation for blindness. Notwithstanding such modifications,
we might expect still to see in the cave-animals of America,
affinities to the other inhabitants of that continent, and in
those of Europe to the inhabitants of the European conti-
nent. And this is the case with some of the American cave-
animals, as I hear from Professor Dana ; and some of the
European cave-insects are very closely allied to those of the
surrounding country. It would be difficult to give any ra-
tional explanation of the affinities of the blind cave-animals
to the other inhabitants of the two continents on the ordi-
nary view of their independent creation. That several of
the inhabitants of the caves of the Old and New Worlds
should be closely related, we might expect from the well-
known relationship of most of their other productions. As
a blind species of Bathyscia js found in abundance on shady
rocks far from caves, the loss of vision in the cave-species
of this one genus has prpbably had no relation to its dark
152 ORIGIN OF SPECIES
habitation; for it is natural that an insect already deprive3
of vision should readily become adapted to dark caverns.
Another blind genus (Anophthalmus) offers this remark-
able peculiarity, that the species, as Mr. Murray observes,
have not as yet been found anywhere except in caves, yet
those which inhabit the several caves of Europe and America
are distinct; but it is possible that the progenitors of these
several species, whilst they were furnished with eyes, may
formerly have ranged over both continents, and then have
become extinct, excepting in their present secluded abodes.
Far from feeling surprise that some of the cave-animals
should be very anomalous, as Agassiz has remarked in re-
gard to the blind fish, the Amblyopsis, and as is the case
with the blind Proteus with reference to the reptiles of
Europe, I am only surpris'^d that more wrecks of ancient
life have not been preserved, owing to the less severe com-
petition to which the scanty inhabitants of these dark abodes
will have been exposed.
ACCLIMATISATION
Habit is hereditary with plants, as in the period of flower-
mg, in the time of sleep, in the amount of rain requisite for
seeds to germinate, &c., and this leads me to say a few
words on acclimatisation. As it is extremely common for
distinct species belonging to the same genus to inhabit hot
and cold countries, if it be true that all the species of the
same genus are descended from a single parent-form, acx:li-
matisation must be readily effected during a long course of
descent. It is notorious that each species is adapted to the
climate of its own home: species from an arctic or even from
a temperate region cannot endure a tropical climate, or con-
versely. So again, many succulent plants cannot endure a
damp climate. But the degree of adaptation of species to
the climates under which they live is often overrated. We
may infer this from our frequent inability to predict whether
or not an imported plant will endure our climate, and from
the number of plants and animals brought from different
countries which are here perfectly healthy. We have rea-
son to believe that species in a state of nature are closely
ACCLIMATISATION 153
limited in their ranges by the competition of other organic
beings quite as much as, or more than, by adaptation to par-
ticular chmates. But whether or not this adaptation is in
most cases very close, we have evidence with some few
plants, of their becoming, to a certain extent, naturally
habituated to different temperatures; that is, they become
acclimatised: thus the pines and rhododendrons, raised from
seed collected by Dr. Hooker from the same species grow-
ing at different heights on the Himalaya, were found to pos- ^
sess in this country different constitutional powers of re-
sisting cold. Mr. Thwaites informs me that he has observed
similar facts in Ceylon; analogous observations have been
made by Mr. H. C, Watson on European species of plants
brought from the Azores to England ; and I could give othei
cases. In regard to animals, several authentic instances
could be adduced of species having largely extended, within
historical times, their range from warmer to cooler lati-
tudes, and conversely; but we do not positively know that
these animals were strictly adapted to their native climate,
though in all ordinary cases we assume such to be the case;
nor do we know that they have subsequently become specially
acclimatised to their new homes, so as to be better fitted for
them than they were at first.
As we may infer that our domestic animals were originally
chosen by uncivilised man because they were useful and be-
cause they bred readily under confinement, and not because
they were subsequently found capable of far-extended trans-
portation, the common and extraordinary capacity in our
domestic animals of not only withstanding the most different
climates, but of being perfectly fertile (a far severer test)
under them, may be used as an argument that a large pro-
portion of other animals now in a state of nature could
easily be brought to bear widely different climates. We
must not, however, push the foregoing argument too far,
on account of the probable origin of some of our domestic
animals from several wild stocks; the blood, for instance,
of a tropical and arctic wolf may perhaps be mingled in our
domestic breeds. The rat and mouse cannot be considered as
domestic animals, but they have been transported by man to
many parts of the world, and now have a far wider range
154 ORIGIN OF SPECIES
than any other rodent; for they live under the cold climate
of Faroe in the north and of the Falklands in the south,
and on many an island in the torrid zones. Hence adap-
tation to any special climate may be looked at as a quality
readily grafted on an innate wide flexibility of constitution,
common to most anmials. On this view, the capacity of
enduring the most different climates by man himself and
by his domestic animals, and the fact of the extinct elephant
and rhinoceros having formerly endured a glacial climate,
whereas the living species are now all tropical or sub-tropical
in their habits, ought not to be looked at as anomalies, but
as examples of a very common flexibility of constitution,
brought, under peculiar circumstances, into action.
How much of the acclimatisation of species to any pecu-
liar climate is due to mere habit, and how much to the
natural selection of varieties having different innate consti-
tutions, and how much to both means combined, is an ob-
scure question. That habit or custom has some influence, I
must believe, both from analogy and from the incessant ad-
vice given in agricultural works, even in the ancient Ency-
clopaedias of China, to be very cautious in transporting ani-
mals from one district to another. And as it is not likely
that man should have succeeded in selecting so many breeds
and sub-breeds with constitutions specially fitted for their
own districts, the result must, I think, be due to habit. On
the other hand, natural selection would inevitably tend to
preserve those individuals which were born Avith consti-
tutions best adapted to any country which they inhabited.
In treatises on many kinds of cultivated plants, certain
varieties are said to withstand certain climates better than
others; this is strikingly shown in works on fruit-trees pub-
lished in the United States, in which certain varieties are
habitually recommended for the northern and others for the
southern States; and as most of these varieties are of recent
origin, they cannot owe their constitutional differences to
habit. The case of the Jerusalem artichoke, which is never
propagated in England by seed, and of which consequently
new varieties have not been produced, has even been ad-
vanced, as proving that acclimatisation cannot be effected,
for it is now as tender as ever it was ! The case, also, of the
CORRELATED VARIATION 155
kidney-bean has been often cited for a similar purpose, and
with much greater weight; but until someone will sow, dur-
ing a score of generations, his kidney-beans so early that a
very large proportion are destroyed by frost, and then collect
seed from the few survivors, with care to prevent accidental
crosses, and then again get seed from these seedlings, with
the same precautions, the experiment cannot be said to have
been tried. Nor let it be supposed that differences in the con-
stitution of seedling kidney-beans never appear, for an ac-
count has been published how much more hardy some seed-
lings are than others ; and of this fact I have myself ob-
served striking instances.
On the whole, we may conclude that habit, or use and
disuse, have, in some cases, played a considerable part in the
modification of the constitution and structure; but that the
effects have often been largely combined with, and some-
times overmastered by, the natural selection of innate
variations.
CORRELATED VARIATION
I mean by this expression that the whole organisation is
so tied together during its growth and development, that
when slight variations in any one part occur, and are accu-
mulated through natural selection, other parts become modi-
fied. This is a very important subject, most imperfectly
understood, and no doubt wholly different classes of facts
may be here easily confounded together. We shall presently
see that simple inheritance often gives the false appearance
of correlation. One of the most obvious real cases is, that
variations of structure arising in the young or larvae nat-
urally tend to affect the structure of the mature animal.
The several parts of the body which are homologous, and
which, at an early embryonic period, are identical in struc-
ture, and which are necessarily exposed to similar condi-
tions, seem eminently liable to vary in a like manner: we see
this in the right and left sides of the body varying in the
same manner ; in the front and hind legs, and even in the
jaws and limbs, varying together, for the lower jaw is be-
lieved by some anatomists to be homologous with the limbs.
These tendencies, I do not doubt, may be mastered more or
356 ORIGIN OF SPECIES
less completely by natural selection ; thus a family of stags
once existed with an antler only on one side ; and if this
had been of any great use to the breed, it might probably
have been rendered permanent by selection.
Homologous parts, as has been remarked by some authors,
tend to cohere ; this is often seen in monstrous plants : and
nothing is more common than the union of homologous
parts in normal structures, as in the union of the petals into
a tube. Hard parts seem to affect the form of adjoining
soft parts; it is believed by some authors that with birds
the diversity in the shape of the pelvis causes the remark-
able diversity in the shape of their kidneys. Others believe
that the shape of the pelvis in the human mother influences
by pressure the shape of the head of the child. In snakes,
according to Schlegel, the form of the body and the manner
of swallowing determine the position and form of several
of the most important viscera.
The nature of the bond is frequently quite obscure. M.
Is. Geoffroy St. Hilaire has forcibly remarked, that certain
malconformations frequently, and that others rarely, co-
exist, without our being able to assign any reason. What
can be more singular than the relation in cats between com-
plete whiteness and blue eyes with deafness, or between the
tortoise-shell colour and the female sex; or in pigeons be-
tween their feathered feet and skin betwixt the outer toes,
or between the presence of more or less down on the young
pigeon when first hatched, with the future colour of its
plumage; or, again, the relation between the hair and teeth
in the naked Turkish dog, though here no doubt homology
comes into play? With respect to this latter case of corre-
lation, I think it can hardly be accidental, that the two orders
of mammals which are most abnormal in their dermal cov-
erings, viz., Cetacea (whales) and Edentata (armadilloes,
scaly ant-eaters, &c.), are likewise on the whole the most
abnormal in their teeth ; but there are so many exceptions to
this rule, as Mr. Mivart has remarked, that it has little
value.
I know of no case better adapted to show the importance
of the laws of correlation and variation, independently of
utility and therefore of natural selection, than that of the
CORRELATED VARIATION 157
difference between the outer and inner flowers in some Com-
positous and Umbelliferous plants. Every one is familiar
with the difference between the ray and central florets of,
for instance, the daisy, and this difference is often accom-
panied with the partial or complete abortion of the repro-
ductive organs. But in some of these plants, the seeds also
differ in shape and sculpture. These differences have some-
times been attributed to the pressure of the involucra on
the florets, or to their mutual pressure, and the shape of the
seeds in the ray-florets of some Compositse countenances this
idea; but with the Umbelliferse, it is by no means, as Dr.
Hooker informs me, the species with the densest heads which
most frequently differ in their inner and outer flowers. It
might have been thought that the development of the ray-
petals by drawing nourishment from the reproductive
organs causes their abortion ; but this can hardly be the sole
cause, for in some Compositse the seeds of the outer and
inner florets differ, without any difference in the corolla.
Possibly these several differences may be connected with
the different flow of nutriment towards the central and
external flowers: we know, at least, that with irregular
flowers, those nearest to the axis are most subject to peloria,
that is to become abnormally symmetrical. I may add, as
an instance of this fact, and as a striking case of correla-
tion, that in many pelargoniums, the two upper petals in the
central flower of the truss often lose their patches of darker
colour; and when this occurs, the adherent nectary is quite
aborted ; the central flower thus becoming peloric or regular.
When the colour is absent from only one of the two upper
petals, the nectary is not quite aborted but is much shortened.
With respect to the development of the corolla, Sprengel's
idea that the ray-florets serve to attract insects, whose
agency is highly advantageous or necessary for the fertili-
sation of these plants, is highly probable; and if so, natural
selection may have come into play. But with respect to the
seeds, it seems impossible that their differences in shape,
which are not always correlated with any difference in the
corolla, can be in any way beneficial : yet in the Umbelliferse
these differences are of such apparent importance — the seeds
being sometimes orthospermous in the exterior flowers and
158 ORIGIN OF SPECIES
ccelospermous in the central flowers, — that the elder De
Candolle founded his main divisions in the order on such
characters. Hence modifications of structure, viewed by
systematists as of high value, may be wholly due to the laws
of variation and correlation, without being, as far as we
can judge, of the slightest service to the species.
We may often falsely attribute to correlated variation
structures which are common to whole groups of species,
and which in truth are simply due to inheritance; for an
ancient progenitor may have acquired through natural selec-
tion some one modification in structure, and, after thousands
of generations, some other and independent modification ;
and these two modifications, having been transmitted to a
whole group of descendants with diverse habits, would nat-
urally be thought to be in some necessary manner correlated.
Some other correlations are apparently due to the manner
in which natural selection can alone act. For instance, Alph.
de Candolle has remarked that winged seeds are never found
in fruits which do not open ; I should explain this rule by
the impossibility of seeds gradually becoming winged through
natural selection, unless the capsules were open for in this
case alone could the seeds, which were a little better adapted
to be wafted by the wind, gain an advantage over others
less well fitted for wide dispersal.
COMPENSATION AND ECONOMY OF GROWTH
The elder Geoffroy and Goethe propounded, at about the
same time, their law of compensation or balancement of
growth; or, as Goethe expressed it, "in order to spend on
one side, nature is forced to economise on the other side."
I think this holds true to a certain extent with our domestic
productions : if nourishment flows to one part or organ in
excess, it rarely flows, at least in excess, to another part;
thus it is difficult to get a cow to give much milk and to fat-
ten readily. The same varieties of the cabbage do not yield
abundant and nutritious foliage and a copious supply of oil-
bearing seeds. When the seeds in our fruits become atro-
phied, the frviit itself gains largely in size and quality. In
our poultry, a large tuft of feathers on the head is gener-
COMPENSATION AND ECONOMY OF GROWTH 159
ally accompanied by a diminished comb and a large beard
by diminished wattles. With species in a state of nature it
can hardly be maintained that the law is of universal appli-
cation; but many good observers, more especially botanists,
believe in its truth. I will not, however, here give any in-
stances, for I see hardly any way of distinguishing between
the effects, on the one hand, of a part being largely devel-
oped through natural selection and another and adjoining
part being reduced by this same process or by disuse, and,
on the other hand, the actual withdrawal of nutriment from
one part owing to the excess of growth in another and ad-
joining part.
I suspect, also, that some of the cases of compensation
which have been advanced, and likewise some other facts,
may be merged under a more general principle, namely, that
natural selection is continually trying to economise every
part of the organisation. If under changed conditions of
life a structure, before useful, becomes less useful, its dim-
inution will be favoured, for it will profit the individual not
to have its nutriment wasted in building up an useless struc-
ture. I can thus only understand a fact with which I was
much struck when examining cirripedes, and of which many
analogous instances could be given : namely, that when a
cirripede is parasitic within another cirripede and is thus
protected, it loses more or less completely its own shell or
carapace. This is the case with the male Ibla, and in a truly
extraordinary manner with the Proteolepas : for the cara-
pace in all other cirripedes consists of the three highly im-
portant anterior segments of the head enormously developed,
and furnished with great nerves and muscles ; but in the
parasitic and protected Proteolepas, the whole anterior part
of the head is reduced to the merest rudiment attached to
the bases of the prehensile antennae. Now the saving of a
large and complex structure, when rendered superfluous,
would be a decided advantage to each successive individual
of the species; for in the struggle for life to which every
animal is exposed, each would have a better chance of sup-
porting itself, by less nutriment being wasted.
Thus, as I believe, natural selection will tend in the long
run to reduce any part of. the organisation, as soon as it be-
160 ORIGIN OF SPECIES
comes, through changed habits, superfluous, withont by any
means causing some other part to be largely developed in a
corresponding degree. And, conversely, that natural selec-
tion may perfectly well succeed in largely developing an
organ without requiring as a necessary compensation the
reduction of some adjoining part.
MULTIPLE, RUDIMENTARY, AND LOWLY ORGANISED STRUC-
TURES ARE VARIABLE
It seems to be a rule, as remarked by Is. Geofifroy St.
Hilaire, both with varieties and species, that when any part
or organ is repeated many times in the same individual (as
the vertebrae in snakes, and the stamens in polyandrous flow-
ers) the number is variable; whereas the same part or organ,
when it occurs in lesser numbers, is constant. The same
author as well as some botanists have further remarked that
multiple parts are extremely liable to vary in structure. As
"vegetative repetition," to use Prof. Owen's expression, is a
sign of low organisation, the foregoing statements accord
with the common opinion of naturalists, that beings which
stand low in the scale of nature are more variable than those
which are higher. I presume that lowness here means that
the several parts of the organisation have been but little
specialised for particular functions; and as long as the same
part has to perform diversified work, we can perhaps see
why it should remain variable, that is, why natural selection
should not have preserved or rejected each little deviation
of form so carefully as when the part has to serve for some
one special purpose. In the same way that a knife which
has to cut all sorts of things may be of almost any shape ;
whilst a tool for some particular purpose must be of some
particular shape. Natural selection, it should never be for-
gotten, can act solely through and for the advantage of each
being.
Rudimentary parts, as it is generally admitted, are apt to be
highly variable. We shall have to recur to this subject; and
I will here only add that their variability seems to result from
their uselessness, and consequently from natural selection
having had no power to check deviations in their structure.
STRUCTURES VARIABLE 161
A PART DEVELOPED IN ANY SPECIES IN AN EXTRAORDINARY
DEGREE OR MANNER, IN COMPARISON WITH THE
SAME PART IN ALLIED SPECIES, TENDS TO
BE HIGHLY VARIABLE
Several years ago I was much struck by a remark, to the
above effect, made by Mr. Waterhouse. Professor Owen,
also, seems to have come to a nearly similar conclusion. It
is hopeless to attempt to convince any one of the truth of
the above proposition without giving the long array of facts
which I have collected, and which cannot possibly be here
introduced. I can only state my conviction that it is a rule
of high generality. I am aware of several causes of error,
but I hope that I have made due allowance for them.
It should be understood that the rule by no means applies to
any part, however unusually developed, unless it be unusu-
ally developed in one species or in a few species in compari-
son with the same part in many closely allied species. Thus,
the wing of a bat is a most abnormal structure in the class
of mammals, but the rule would not apply here, because the
whole group of bats possesses wings ; it would apply only if
some one species had wings developed in a remarkable man-
ner in comparison with the other species of the same genus.
The rule applies very strongly in the case of secondary sex-
ual characters, when displayed in any unusual manner. The
term, secondary sexual characters, used by Hunter, relates
to characters which are attached to one- sex, but are not
directly connected with the act of reproduction. The rule
applies to males and females ; but more rarely to the females,
as they seldom offer remarkable secondary sexual charac-
ters. The rule being so plainly applicable in the case of sec-
ondary sexual characters, may be due to the great variability
of these characters, whether or not displayed in any unusual
manner — of which fact I think there can be little doubt. But
that our rule is not confined to secondary sexual characters
is clearly shown in the case of hermaphrodite cirripedes; I
particularly attended to Mr. Waterhouse's remark, whilst
investigating this Order, and* I am fully convinced that the
rule almost always holds good. I shall, in a future work,
give a list of all the more Temarkable cases ; I will here give
F — HC XI
162 ORIGIN OF SPECIES
only one, as it illustrates the rule in its largest application.
The opercular valves of sessile cirripedes (rock barnacles)
are, in every sense of the word, very important structures,
and they differ extremely little even in distinct genera; but
in the several species of one genus, Pyrgoma, these valves
present a marvellous amount of diversification ; the homolo-
gous valves in the different species being sometimes wholly
unlike in shape; and the amount of variation in the indi-
viduals of the same species is so great, that it is no exag-
geration to state that the varieties of the same species dift'er
more from each other in the characters derived from these
important organs, than do the species belonging to other
distinct genera.
As with birds the individuals of the same species, inhabit-
ing the same country, vary extremely little, I have particu-
larly attended to them; and the rule certainly seems to hold
good in this class. I cannot make out that it applies to plants,
and this would have seriously shaken my belief in its truth,
had not the great variability in plants made it particularly
difficult to compare their relative degrees of variability.
When we see any part or organ developed in a remarkable
degree or manner in a species, the fair presumption is 'hat
it is of high importance to that species: nevertheless it is in
this case eminently liable to variation. Why should this be
so? On the view that each species has been independently
created, with all its parts as we now see them, I can see no
explanation. But on the view that groups of species are de-
scended from some other species, and have been modified
through natural selection, I think we can obtain some light.
First let me make some preliminary remarks. If, in our
domestic animals, any part or the whole animal be neglected,
and no selection be applied, that part (for instance, the comb
in the Dorking fowl) or the whole breed will cease to have
a uniform character: and the breed may be said to be degen-
erating. In rudimentary organs, and in those which have
been but little specialised for any particular purpose, and
perhaps in polymorphic groups, we see a nearly parallel case ;
for in such cases natural selection either has not or cannot
have come into full play, and thus the organisation is left in
a fluctuating condition. But what here more particularly
STRUCTURES VARIABLE 163
concerns lis is, that those points in our domestic animals,
which at the present time are undergoing rapid change by
continued selection, are also eminently liable to variation.
Look at the individuals of the same breed of the pigeon, and
see what a prodigious amount of difference there is in the
beaks of tumblers, in the beaks and wattle of carriers, in the
carriage and tail of fantails, &c., these being the points now
mainly attended to by English fanciers. Even in the same
sub-breed, as in that of the short-faced tumbler, it is notori-
ously difficult to breed nearly perfect birds, many departing
widely from the standard. There may truly be said to be a
constant struggle going on between, on the one hand, the
tendency to reversion to a less perfect state, as well as an
innate tendency to new variations, and, on the other hand,
the power of steady selection to keep the breed true. In the
long run selection gains the day, and we do not expect to
fail so completely as to breed a bird as coarse as a common
tumbler pigeon from a good short- faced strain. But as long as
selection is rapidly going on, much variability in the parts
undergoing modification may always be expected.
Now let us turn to nature. When a part has been devel-
oped in an extraordinary manner in any one species, com-
pared with the other species of the same genus, we may con-
clude that this part has undergone an extraordinary amount
of modification since the period when the several species
branched off from the common progenitor of the genus. This
period will seldom be remote in any extreme degree, as species
rarely endure for more than one geological period. An extra-
ordinary amount of modification implies an unusually large
and long-continued amount of variability, which has con-
tinually been accumulated by natural selection for the benefit
of the species. But as the variability of the extraordinarily
developed part or organ has been so great and long-continued
within a period not excessively remote, we might, as a gen-
eral rule, still expect to find more variability in such parts
than in other parts of the organisation which have remained
for a much longer period nearly constant. And this, I am
convinced, is the case. That the struggle between natural
selection on the one hand, and the tendency to reversion and
variability on the other -hand, will in the course of time
164 ORIGIN OF SPECIES
cease; and that the most abnormally developed organs may
be made constant, I see no reason to doubt. Hence, when
an organ, however abnormal it may be, has been transmitted
in approximately the same condition to many modified de-
scendants, as in the case of the wing of the bat, it must have
existed, according to our theory, for an immense period in
nearly the same state; and thus it has come not to be more
variable than any other structure. It is only in those cases
in which the modification has been comparatively recent and
extraordinarily great that we ought to find the generative
variability, as it may be called, still present in a high degree.
For in this case the variability will seldom as yet have been
fixed by the continued selection of the individuals varying
in the required manner and degree, and by the continued
rejection of those tending to revert to a former and less-
modified condition.
SPECIFIC CHARACTERS MORE VARIABLE THAN GENERIC
CHARACTERS
The principle discussed under the last heading may be
applied to our present subject. It is notorious that specific
characters are more variable than generic. To explain by a
simple example what is meant: if in a large genus of plants
some species had blue flowers and some had red, the colour
would be only a specific character, and no one would be sur-
prised at one of the blue species varying into red, or con-
versely; but if all the species had blue flowers, the colour
would become a generic character, and its variation would
be a more unusual circumstance. I have chosen this exam-
ple because the explanation which most naturalists would
advance is not here applicable, namely, that specific charac-
ters are more variable than generic, because they are taken
from parts of less physiological importance than those com-
monly used for classing genera. I believe this explanation
is partly, yet only indirectly, true; I shall, however, have to
return to this point in the chapter on Classification. It would
be almost superfluous to adduce evidence in support of the
statement, that ordinary specific characters are more variable
than generic; but with respect to important characters, I
SPECIFIC CHARACTERS HIGHLY VARIABLE 165
have repeatedly noticed in works on natural history, that
when an author remarks with surprise that some important
organ or part, which is generally very constant throughout
a large group of species, differs considerably in closely
allied species, it is often variable in the individuals of the
same species. And this fact shows that a character, which
is generally of generic value, when it sinks in value and
becomes only of specific value, often becomes variable,
though its physiological importance may remain the same
Something of the same kind applies to monstrosities: at
least Is. Geoffroy St. Hilaire apparently entertains no doubt,
that the more an organ normally differs in the different spe-
cies of the same group, the more subject it is to anomalies
in the individuals.
On the ordinary view of each species having been inde-
pendently created, why should that part of the structure,
which differs from the same part in other independently
created species of the same genus, be more variable than
those parts which are closely alike in the several species?
I do not see that any explanation can be given. But on the
view that species are only strongly marked and fixed varie-
ties, we might expect often to find them still continuing to
vary in those parts of their structure which have varied
within a moderately recent period, and which have thus
come to differ. Or to state the case in another manner: —
the points in which all the species of a genus resemble each
other, and in which they differ from allied genera, are called
generic characters; and these characters may be attributed
to inheritance from a common progenitor, for it can rarely
have happened that natural selection will have modified sev-
eral distinct species, fitted to more or less widely different
habits, in exactly the same manner: and as these so-called
generic characters have been inherited from before the
period when the several species first branched off from their
common progenitor, and subsequently have not varied or
come to differ in any degree, or only in a slight degree, it is
not probable that they should vary at the present day. On
the other hand, the points in* which species differ from other
species of the same genus are called specific characters: and
as these specific characters have varied and come to differ
166 ORIGIN OF SPECIES
since the period when the species branched off from a com-
mon progenitor, it is probable that they should still often be
in some degree variable, — at least more variable than those
parts of the organisation which have for a very long period
remained constant.
Secondary Sexual Characters Variable. — I think it will be
admitted by naturalists, without my entering on details, that
secondary sexual characters are highly variable. It will also
be admitted that species of the same group differ from each
other more widely in their secondary sexual characters, than
in other parts of their organisation : compare, for instance,
the amount of difference between the males of gallinaceous
birds, in which secondary sexual characters are strongly dis-
played, with the amount of difference between the females.
The cause of the original variability of these characters is
not manifest; but we can see why they should not have been
rendered as constant and uniform as others, for they are
accumulated by sexual selection, which is less rigid in its ac-
tion than ordinary selection, as it does not entail death, but
only gives fewer offspring to the less favoured males. What-
ever the cause may be of the variability of secondary sexual
characters, as they are highly variable, sexual selection will
have had a wide scope for action, and may thus have suc-
ceeded in giving to the species of the same group a greater
amount of difference in these than in other respects.
It is a remarkable fact, that the secondary differences be-
tween the two sexes of the same species are generally dis-
played in the very same parts of the organisation in which
the species of the same genus differ from each other. Of
this fact I will give in illustration the two first instances
which happen to stand on my list; and as the differences in
these cases are of a very unusual nature, the relation can
hardly be accidental. The same number of joints in the tarsi
is a character common to very large groups of beetles, but
in the Engidse, as Westwood has remarked, the number varies
greatly; and the number likewise differs in the two sexes of
the same species. Again in the fossorial hymenoptera, the
neuration of the wings is a character of the highest impor-
tance, because common to large groups; but in certain genera
the neuration differs in the different species, and likewise in
SPECIFIC CHARACTERS HIGHLY VARIABLE 167
the two sexes of the same species. Sir J. Lubbock has re-
cently remarked, that several minute crustaceans offer ex-
cellent illustrations of this law. "In Pontella, for instance,
the sexual characters are afforded mainly by the anterior
antennae and by the fifth pair of legs: the specific differences
also are principally given by these organs." This relation
has a clear meaning on my view: I look at all the species
of the same genus as having as certainly descended from
a common progenitor, as have the two sexes of any one spe-
cies. Consequently, whatever part of the structure of the
common progenitor, or of its early descendants, became vari-
ble, variations of this part would, it is highly probable, be
taken advantage of by natural and sexual selection, in order
to fit the several species to their several places in the econ-
omy of nature, and likewise to fit the two sexes of the same
species to each other, or to fit the males to struggle with
other males for the possession of the females.
Finally, then, I conclude that the greater variability of
specific characters, or those which distinguish species from
species, than of generic characters, or those which are pos-
sessed by all the species; — that the frequent extreme varia-
bility of any part which is developed in a species in an extra-
ordinary manner in comparison with the same part in its
congeners; and the slight degree of variability in a part,
however extraordinarily it may be developed, if it be com-
mon to a whole group of species; — that the great variability
of secondary sexual characters, and their great difference in
closely allied species; — that secondary sexual and ordinary
specific differences are generally displayed in the same parts
of the organisation, — are all principles closely connected to-
gether. All being mainly due to the species of the same
group being the descendants of a common progenitor, from
whom they have inherited much in common, — to parts which
have recently and largely varied being more likely still to go
on varying than parts which have long been inherited and
have not varied — to natural selection having more or less
completely, according to the. lapse of time, overmastered the
tendency to reversion and to further variability, — to sexual
selection being less rigid than ordinary selection, — and to
168 ORIGIN OF SPECIES
variations in the same parts having been accumulated by
natural and sexual selection, and having been thus adapted
for secondary sexual, and for ordinary purposes.
Distinct Species present analogous Variations, so that a
Variety of one Species often assumes a Character proper to
an allied Species, or reverts to some of the Characters of an
early Progenitor. — These propositions will be most readily
understood by looking to our domestic races. The most dis-
tinct breeds of the pigeon, in countries widely apart, present
sub-varieties with reversed feathers on the head, and with
feathers on the feet, — characters not possessed by the abo-
riginal rock-pigeon ; these then are analogous variations in
two or more distinct races. The frequent presence of four-
teen or even sixteen tail-feathers in the pouter may be con-
sidered as a variation representing the normal structure of
another race, the fantail. I presume that no one will doubt
that all such analogous variations are due to the several
races of the pigeon having inherited from a common parent
the same constitution and tendency to variation, when acted
on by similar unknown influences. In the vegetable king-
dom we have a case of analogous variation, in the enlarged
stems, or as commonly called roots, of the Swedish turnip
and Ruta baga, plants which several botanists rank as varie-
ties produced by cultivation from a common parent: if this
be not so, the case will then be one of analogous variation
in two so-called distinct species ; and to these a third may be
added, namely, the common turnip. According to the ordi-
nary view of each species having been independently created,
we should have to attribute this similarity in the enlarged
stems of these three plants, not to the vera causa of com-
munity of descent, and a consequent tendency to vary in a
like manner, but to three separated yet closely related acts
of creation. Many similar cases of analogous variation have
been observed by Naudin in the great gourd-family, and by
various authors in our cereals. Similar cases occurring with
insects under natural conditions have lately been discussed
with much ability by Mr. Walsh, who has grouped them
under his law of Equable Variability.
With pigeons, however, we have another case, namely,
the occasional appearance in all the breeds, of slaty-blue
SPECIFIC CHARACTERS HIGHLY VARIABLE 169
birds with two black bars on the wings, white loins, a bar
at the end of the tail, with the outer feathers externally
edged near their basis with white. As all these marks are
characteristic of the parent rock-pigeon, I presume that no
one will doubt that this is a case of reversion, and not of a
new yet analogous variation appearing in the several breeds.
We may, I think, confidently come to this conclusion, be-
cause, as we have seen, these coloured marks are eminently
liable to appear in the crossed offspring of two distinct and
differently coloured breeds; and in this case there is nothing
in the external conditions of life to cause the reappearance
of the slaty-blue, with the several marks, beyond the influ-
ence of the mere act of crossing on the laws of inheritance.
No doubt it is a very surprising fact that characters should
reappear after having been lost for many, probably for hun-
dreds of generations. But when a breed has been crossed
only once by some other breed, the offspring occasionally
show for many generations a tendency to revert in character
to the foreign breed — some say, for a dozen or even a score
of generations. After twelve generations, the proportion of
blood, to use a common expression, from one ancestor, is
only I in 2048; and yet, as we see, it is generally believed
that a tendency to reversion is retained by this remnant of
foreign blood. In a breed which has not been crossed but
in which both parents have lost some character which their
progenitor possessed, the tendency, whether strong or weak,
to reproduce the lost character might, as was formerly re-
marked, for all that we can see to the contrary, be trans-
mitted for almost any number of generations. When a
character which has been lost in a breed, reappears after a
great number of generations, the most probable hypothesis
is, not that one individual suddenly takes after an ancestor
removed by some hundred generations, but that in each suc-
cessive generation the character in question has been lying
latent, and at last, under unknown favourable conditions, is
developed. With the barb-pigeon, for instance, which very
rarely produces a blue bird, it is probable that there is a
latent tendency in each generation to produce blue plumage.
The abstract improbability of such a tendency being trans-
mitted through a vast number of generations, is not greater
170 ORIGIN OF SPECIES
than that of quite useless or rudimentary organs being simi-
larly transmitted. A mere tendency to produce a rudiment
is indeed sometimes thus inherited.
As all the species of the same genus are supposed to be
descended from a common progenitor, it might be expected
that they would occasionally vary in an analogous manner ;
so that the varieties of two or more species would resemble
each other, or that a variety of one species would resemble
in certain characters another and distinct species, — this other
species being, according to our view, only a well-marked and
permanent variety. But characters exclusively due to analo-
gous variation would probably be of an unimportant nature,
for the preservation of all functionally important characters
will have been determined through natural selection, in ac-
cordance with the different habits of the species. It might
further be expected that the species of the same genus would
occasionally exhibit reversions to long lost characters. As,
however, we do not know the common ancestor of any
natural group, we cannot distinguish between revisionary
and analogous characters. If, for instance, we did not know
that the parent rock-pigeon was not feather-footed or turn-
crowned, we could not have told, whether such characters in
our domestic breeds were reversions or only analogous varia-
tions; but we might have inferred that the blue colour was a
case of reversion from the number of the markings, which
are correlated with this tint, and which would not probably
have all appeared together from simple variation. More
especially we might have inferred this, from the blue colour
and the several marks so often appearing when differently
coloured breeds are crossed. Hence, although under nature it
must generally be left doubtful, what cases are reversions to
formerly existing characters, and what are new but analo-
gous variations, yet we ought, on our theory, sometimes to
find the varying offspring of a species assuming characters
which are already present in other members of the same
group. And this undoubtedly is the case.
The difficulty in distinguishing variable species is largely
due to the varieties mocking, as it were, other species of the
same genus. A considerable catalogue, also, could be given
of forms intermediate between two other forms, which them-
SPECIFIC CHARACTERS HIGHLY VARIABLE 171
selves can only doubtfully be ranked as species; and this
shows, unless all these closely allied forms be considered as
independently created species, that they have in varying as-
sumed some of the characters of the others. But the best
evidence of analogous variations is afforded by parts or
organs which are generally constant in character, but which
occasionally vary so as to resemble, in some degree, the
same part or organ in all species. I have collected a long
list of such cases; but here, as before, I lie under the great
disadvantage of not being able to give them. I can only re-
peat that such cases certainly occur, and seem to me very re-
markable.
I will, however, give one curious and complex case, not
indeed as affecting any important character, but from occur-
ring in several species of the same genus, partly under
domestication and partly under nature. It is a case almost
certainly of reversion. The ass sometimes has very distinct
transverse bars on its legs, like those on the legs of the
zebra: it has been asserted that these are plainest in the foal,
and, from inquiries which I have made, I believe this to be
true. The stripe on the shoulder is sometimes double, and is
very variable in length and outline. A white ass, but not an
albino, has been described without either spinal or shoulder
stripe : and these stripes are sometimes very obscure, or actu-
ally quite lost, in dark-coloured asses. The koulan of Pallas
is said to have been seen with a double shoulder-stripe. Mr.
Blyth has seen a specimen of the hemionus with a distinct
shoulder-stripe, though it properly has none ; and I have been
informed by Colonel Poole that the foals of this species are
generally striped on the legs, and faintly on the shoulder.
The quagga, though so plainly barred like a zebra over the
body, is without bars on the legs; but Dr. Gray has figured
one specimen with very distinct zebra-like bars on the hocks.
With respect to the horse, I have collected cases in Eng-
land of the spinal stripe in horses of the most distinct breeds,
and of all colours: transverse bars on the legs are not rare
in duns, mouse-duns, and in one instance in a chestnut; a
faint shoulder-stripe may sometimes be seen in duns, and I
have seen a trace in a bay horse. My son made a careful
examination and sketch for me of a dun Belsrian cart-horse
172 ORIGIN OF SPECIES
with a double stripe on each shoulder and with leg-stripes;
I have myself seen a dun Devonshire pony, and a small dun
\\'elsh pony has been carefully described to me, both with
three parallel stripes on each shoulder.
In the north-west part of India the Kattywar breed of
horses is so generally striped, that, as I hear from Colonel
Poole, who examined this breed for the Indian Government,
a horse without stripes is not considered as purely-bred.
The spine is always striped; the legs are generally barred;
and the shoulder-stripe, which is sometimes double and some-
times treble, is common; the side of the face, moreover, is
sometimes striped. The stripes are often plainest in the foal ;
and sometimes quite disappear in old horses. Colonel Poole
has seen both gray and bay Kattywar horses striped when
first foaled. I have also reason to suspect, from information
given me by Mr. W. W. Edwards, that with the English
race-horse the spinal stripe is much commoner in the foal
than in the full-grown animal. I have myself recently bred
a foal from a bay mare (offspring of a Turkoman horse and
a Flemish mare) by a bay English race-horse; this foal when
a week old was marked on its hinder quarters and on its
forehead with numerous, very narrow, dark, zebra-like bars,
and its legs were feebly striped: all the stripes soon disap-
peared completely. Without here entering on further details,
I may state that I have collected cases of leg and shoulder
stripes in horses of very dift'erent breeds in various countries
from Britain to Eastern China; and from Norway in the
north to the Malay Archipelago in the south. In all parts of
the world these stripes occur far oftenest in duns and mouse-
duns; by the term dun a large range of colour is included,
from one between brown and black to a close approach to
cream-colour.
I am aware that Colonel Hamilton Smith, who has written
on this subject, believes that the several breeds of the horse
are descended from several aboriginal species — one of which,
the dun, was striped; and that the above-described appear-
ances are all due to ancient crosses with the dun stock. But
this view may be safely rejected; for it is highly improbable
that the heavy Belgian cart-horse. Welsh ponies, Norwegian
cobs, the lanky Kattywar race, &c., inhabiting the most dis-
SPECIFIC CHARACTERS HIGHLY VARIABLE 173
tant parts of the world, should all have been crossed with
one supposed aboriginal stock.
Now let us turn to the effects of crossing the several spe-
cies of the horse-genus. Rollin asserts, that the common
mule from the ass and horse is particularly apt to have bars
on its legs; according to Mr. Gosse, in certain parts of the
United States about nine out of ten mules have striped legs.
I once saw a mule with its legs so much striped that any one
might have thought that it was a hybrid-zebra; and Mr.
W. C. Martin, in his excellent treatise on the horse, has
given a fi. ire of a similar mule. In four coloured drawings,
which I have seen, of hybrids between the ass and zebra, the
legs were much more plainly barred than the rest of the
body ; and in one of them there was a double shoulder-stripe.
In Lord Morton's famous hybrid, from a chestnut mare and
male quagga, the hybrid, and even the pure offspring subse-
quently produced from the same mare by a black Arabian
sire, were much more plainly barred across the legs than is
even the pure quagga. Lastly, and this is another most re-
markable case, a hybrid has been figured by Dr. Gray (and
he informs me that he knows of a second case) from the ass
and the hemionus ; and this hybrid, though the ass only occa-
sionally has stripes on his legs and the hemionus has none
and has not even a shoulder-stripe, nevertheless had all four
legs barred, and had three short shoulder-stripes, like those
on the dun Devonshire and Welsh ponies, and even had some
zebra-like stripes on the sides of its face. With respect to
this last fact, I was so convinced that not even a stripe of
colour appears from what is commonly called chance, that I
was led solely from the occurrence of the face-stripes on
this hybrid from the ass and hemionus to ask Colonel Poole
whether such face-stripes ever occurred in the eminently
striped Kattywar breed of horses, and was, as we have seen,
answered in the affirmative.
What now are we to say to these several facts? We see
several distinct species of the horse-genus becoming, by
simple variation, striped on the legs like a zebra, or striped
on the shoulders like an ass. In the horse we see this ten-
dency strong whenever a dun tint appears — a tint which ap-
proaches to that of the general colouring of the other species
174 ORIGIN OF SPECIES
of the genus. The appearance of the stripes is not accom-
panied by any change of form or by any other new character.
We see this tendency to become striped most strongly dis-
played in hj'brids from between several of the most distinct
species. Now observe the case of the several breeds of
pigeons: they are descended from a pigeon (including two or
three sub-species or geographical races) of a bluish colour,
with certain bars and other marks ; and when any breed
assumes by simple variation a bluish tint, these bars and
other marks invariably reappear ; but without any other
change of form or character. When the oldest and truest
breeds of various colours are crossed, we see a strong ten-
dency for the blue tint and bars and marks to reappear in
the mongrels. I have stated that the most probable hypothe-
sis to accotmt for the reappearance of very ancient charac-
ters, is — that there is a tendency in the young of each suc-
cessive generation to produce the long-lost character, and
that this tendency, from unknown causes, sometimes prevails.
And we have jus', seen that in several species of the horse-
genus the stripes are either plainer or appear more com-
monly in the youn^ than in the old. Call the breeds of
pigeons, some of which have bred true for centuries, species;
and how exactly parallel is the case with that of the species
of the horse-genus ! For myself, I venture confidently to
look back thousands on thousands of generations, and I see
an animal striped like a zebra, but perhaps otherwise very
differently constructed, the common parents of our domestic
horse (whether or not it be descended from one or more
wild stocks), of the ass, the hemionus, quagga, and zebra.
He who believes that each equine species was indepen-
dently created, will, I presume, assert that each species has
been created with a tendency to vary, both under nature and
under domestication, in this particular manner, so as often
to become striped like the other species of the genus ; and
that each has been created with a strong tendency, when
crossed with species inhabiting distant quarters of the world,
to produce hybrids resembling in their stripes, not their own
parents, but other species of the genus. To admit this view
is, as it seems to me. to reject a real for an unreal, or at
least for an unknown, cause. It makes the works of God a
SPECIFIC CHARACTERS HIGHLY VARIABLE 175
mere mockery and deception ; I would almost as soon believe
with the old and ignorant cosmogonists, that fossil shells had
never lived, but had been created in stone so as to mock the
shells living on the sea-shore.
Summary. — Our ignorance of the laws of variation is pro-
found. Not in one case out of a hundred can we pretend to
assign any reason why this or that part has varied. But
whenever we have the means of instituting a comparison, the
same laws appear to have acted in producing the lesser differ-
ences between varieties of the same species, and the greater
differences between species of the same genus. Changed
conditions generally induce mere fluctuating variability, but
sometimes they cause direct and definite effects; and these
may become strongly marked in the course of time, though
we have not sufficient evidence on this head. Habit in pro-
ducing constitutional peculiarities and use in strengthening
and disuse in weakening and diminishing organs, appear in
many cases to have been potent in their effects. Homologous
parts tend to vary in the same manner, and homologous parts
tend to cohere. Modifications in hard parts and in external
parts sometimes affect softer and internal parts. When one
part is largely developed, perhaps it tends to draw nourish-
ment from the adjoining parts; and every part of the struc-
ture v/hich can be saved without detriment will be saved.
Changes of structure at an early age may affect parts subse-
quently developed; and many cases of correlated variation,
the nature of which we are unable to understand, undoubt-
edly occur. Multiple parts are variable in number and in
structure, perhaps arising from such parts not having been
closely specialised for any particular function, so that their
modifications have not been closely checked by natural selec-
tion. It follows probably from this same cause, that organic
beings low in the scale are more variable than those stand-
ing higher in the scale, and which have their whole organi-
sation more specialised. Rudimentary organs, from being
useless, are not regulated by natural selection, and hence are
variable. Specific characters — that is, the characters which
have come to differ since the several species of the same
genus branched off from a common parent — are more vari-
able than generic characters, or those which have long been
176 ORIGIN OF SPECIES
inherited, and have not differed within this same period. In
these remarks we have referred to special parts or organs
being still variable, because they have recently varied and
thus come to differ; but we have also seen in the second
chapter that the same principle applies to the whole indi-
vidual; for m a district where many species of a genus are
found — that is, where there has been much former variation
and differentiation, or where the manufactory of new specific
forms has been actively at work — in that district and amongst
these species, we now find, on an average, most varieties.
Secondary sexual characters are highly variable, and such
characters differ much in the species of the same group.
Variability in the same parts of the organisation has gener-
ally been taken advantage of in giving secondary sexual
differences to the two sexes of the same species, and specific
differences to the several species of the same genus. Any
part or organ developed to an extraordinary size or in an
extraordinary manner, m comparison with the same part or
organ in the allied species, must have gone through an
extraordinary amount of modification since the genus arose;
and thus we can understand why it should often still be vari-
able in a much higher degree than other parts; for variation
is a long-continued and slow process, and natural selection
will in such cases not as yet have had time to overcome the
tendency to further variability and to reversion to a less
modified state. But when a species with any extraordinarily-
developed organ has become the parent of many modified
descendants — which on our view must be a very slow process,
requiring a long lapse of time — in this case, natural selection
has succeeded in giving a fixed character to the organ, in
however extraordinary a manner it may have been developed.
Species inheriting nearly the same constitution from a com-
mon parent, and exposed to similar influences, naturally tend
to present analogous variations, or these same species may
occasionally revert to some of the characters of their ancient
progenitors. Although new and important modifications may
not arise from reversion and analogous variation, such modi-
fications will add to the beautiful and harmonious diversity
of nature.
Whatever the cause may be of each slight difference be-
\
SPECIFIC CHARACTERS HIGHLY VARIABLE 177
tween the offspring and their parents — and a cause for each
must exist — we have reason to beheve that it is the steady
accumulation of beneficial differences which has given rise
to all the more important modifications of structure in rela-
tion to the habits of each species.
CHAPTER VI
Difficulties of the Theory
Difficulties of the theory of descent with modification — Absence or
rarity of transitional varieties — Transitions in habits of life —
Diversified habits in the same species — Species with habits widely
different from those of their allies — Organs of extreme perfec-
tion — Modes of transition — Cases of difficulty — Natura non facit
saltum — Organs of small importance — Organs not in all cases
absolutely perfect — The law of Unity of Type and of the Con-
ditions of Existence embraced by the theory of Natural
Selection.
LONG before the reader has arrived at this part of my
work, a crowd of difficulties will have occurred to him.
Some of them are so serious that to this day I can
hardly reflect on them without being in some degree stag-
gered ; but, to the best o^ my judgment, the greater number
are only apparent, and those that are real are not, I think,
fatal to theory.
These difficulties and objections may be classed under the
following heads: — First, why, if species have descended from
other species by fine gradations, do we not everywhere see
innumerable transitional forms ? Why is not all nature in
confusion, instead of the species being, as we see them, well
defined ?
Secondly, is it possible that an animal having, for instance,
the structure and habits of a bat, could have been formed by
the modification of some other animal with widely different
habits and structure? Can we believe that natural selection
could produce, on the one hand, an organ of trifling impor-
tance, such as the tail of a giraffe, which serves as a fly-
flapper, and, on the other hand, an organ so wonderful as the
eye?
Thirdly, can instincts be acquired and modified through
natural selection? What shall we say to tire instinct which
178
TRANSITIONAL VARIETIES 179
leads the bee to make cells, and which has practically antici-
pated the discoveries of profound mathematicians?
Fourthly, how can we account for species, when crossed,
being sterile and producing sterile offspring, whereas, when
varieties are crossed, their fertility is unimpaired?
The two first heads will here be discussed ; some miscel-
laneous objections in the following chapter; Instinct and
Hybridism in the two succeeding chapters.
On the Absence or Rarity of Transitional Varieties. — As
natural selection acts solely by the preservation of profitable
modifications, each new form will tend in a fully-stocked
country to take the place of, and finally to exterminate, its
own less improved parent-form and other less-favoured forms
with which it comes into competition. Thus extinction and
natural selection go hand in hand. Hence, if we look at
each species as descended from some unknown form, both
the parent and all the transitional varieties will generally
have been exterminated by the very process of the formation
and perfection of the new form.
But, as by this theory innumerable transitional forms must
have existed, why do we not find them embedded in countless
numbers in the crust of the earth ? It will be more con-
venient to discuss this question in the chapter on the Imper-
fection of the Geological Record; and I will here only state
that I believe the answer mainly lies in the record being in-
comparably less perfect than is generally supposed. The crust
of the earth is a vast museum ; but the natural collections
have been imperfectly made, and only at long intervals of
time.
But it may be urged that when several closely-allied
species inhabit the same territory, we surely ought to find at
the present time many transitional forms. Let us take a
simple case: in travelling from north to south over a conti-
nent, we generally meet at successive intervals with closely
allied or representative species, evidently filling nearly the
same place in the natural economy of the land. These represen-
tative species often meet and interlock; and as the one be-
comes rarer and rarer, the other becomes more and more
frequent, till the one replaces 'the other. But if we compare
these species where they intermingle, they are generally as ab-
180 ORIGIN OF SPECIES
solutely distinct from each other in every detail of structure
as are specimens taken from the metropolis inhabited by each.
By my theory these allied species are descended from a com-
mon parent ; and during the process of modification, each has
become adapted to the conditions of life of its own region,
and has supplanted and exterminated its original parent-
form and all the transitional varieties between its past and
present states. Hence we ought not to expect at the present
time to meet with numerous transitional varieties in each re-
gion, though they must have existed there, and may be em-
bedded there in a fossil condition. But in the intermediate
region, having intermediate conditions of life, why do we not
now find closely-linking intermediate varieties? This diffi-
culty for a long time quite confounded me. But I think it
can be in large part explained.
In the first place we should be extremely cautious in in-
ferring, because an area is now continuous, that it has been
continuous during a long period. Geology would lead us to
believe that most continents have been broken up into islands
even during the later tertiary periods ; and in such islands
distinct species might have been separately formed without
the possibility of intermediate varieties existing in the inter-
mediate zones. By changes in the form of the land and of
climate, marine areas now continuous must often have ex-
isted within recent times in a far less continuous and uniform
condition than at present. But I will pass over this way of
escaping from the difficulty ; for I believe that many per-
fectly defined species have been formed on strictly continu-
ous areas ; though I do not doubt that the formerly broken
condition of areas now continuous, has played an important
part in the formation of new species, more especially with
freely-crossing and wandering animals.
In looking at species as they are now distributed over a
wide area, we generally find them tolerably numerous over a
large territory, then becoming somewhat abruptly rarer and
rarer on the confines, and finally disappearing. Hence the
neutral territory between two representative species is gen-
erally narrow in comparison with the territory proper to each.
We see the same fact in ascending mountains, and sometimes
it is quite remarkable how abruptly, as Alph. de Candolle has
TRANSITIONAL VARIETIES 181
observed, a common alpine species disappears. The same
fact has been noticed by E. Forbes in sounding the depths of
the sea with the dredge. To those who look at climate and
the physical conditions of life as the all-important elements
of distribution, these facts ought to cause surprise, as cli-
mate and height or depth graduate away insensibly. But
when we bear in mind that almost every species, even in its
metropolis, would increase immensely in numbers, were it not
for other competing species ; that nearly all either prey on or
serve as prey for others ; in short, that each organic being is
either directly or indirectly related in the most important
manner to other organic beings, — we see that the range of the
inhabitants of any country by no means exclusively depends
on insensibly changing physical conditions, but in a large
part on the presence of other species, on which it lives, or by
which it is destroyed, or with which it comes into competi-
tion ; and as these species are already defined objects, not
blending one into another by insensible gradations, the range
of any one species, depending as it does on the range of
others, will tend to be sharply defined. Moreover, each
species on the confines of its range, where it exists in less-
ened numbers, will, during fluctuations in the number of its
enemies or of its prey, or in the nature of the seasons, be ex-
tremely liable to utter extermination ; and thus its geographi-
cal range will come to be still more sharply defined.
As allied or representative species, when inhabiting a con-
tinuous area, are generally distributed in such a manner that
each has a wide range, with a comparatively narrow neutral
territory between them, in which they become rather suddenly
rarer and rarer; then, as varieties do not essentially differ
from species, the same rule will probably apply to both; and
if we take a varying species inhabiting a very large area, we
shall have to adapt two varieties to two large areas, and a
third variety to a narrow intermediate zone. The intermedi-
ate variety, consequently, will exist in lesser numbers from
inhabiting a narrow and lesser area ; and practically, as far as
I can make out, this rule holds good with varieties in a state
of nature. I have met with .striking instances of the rule in
the case of varieties intermediate between well-marked vari-
eties in the genus Balanus.. And it would appear from infor-
182 ORIGIN OF SPECIES
mation given me by Mr. Watson, Dr. Asa Gray, and Mr.
Wollaston, that generally, when varieties intermediate be-
tween two other forms occur, they are much rarer numeri-
cally than the forms which they connect. Now, if we may
trust these facts and inferences, and conclude that varieties
linking two other varieties together generally have existed
in lesser numbers than the forms which they connect, then
we can understand why intermediate varieties should not en-
dure for very long periods : — why, as a general rule, they
should be exterminated and disappear, sooner than the forms
which they originally linked together.
For any form existing in lesser numbers would, as already
remarked, run a greater chance of being exterminated than
one existing in large numbers ; and in this particular case the
intermediate form would be eminently liable to the inroads of
closely-allied forms existing on both sides of it. But it is a
far more important consideration, that during the process of
further modification, by which two varieties are supposed to
be converted and perfected into two distinct species, the two
which exist in larger numbers, from inhabiting larger areas,
will have a great advantage over the intermediate variety,
which exists in smaller numbers in a narrow and intermedi-
ate zone. For forms existing in larger numbers will have a
better chance, within any given period, of presenting further
favourable variations for natural selection to seize on, than
will the rarer forms which exist in lesser numbers. Hence,
the more common forms, in the race for life, will tend to beat
and supplant the less common forms, for these will be more
slowly modified and improved. It is the same principle
which, as I believe, accounts for the common species in each
country, as shown in the second chapter, presenting on an
average a greater number of well-marked varieties than do
the rarer species. I may illustrate what I mean by supposing
three varieties of sheep to be kept, one adapted to an exten-
sive mountainous region ; a second to a comparatively narrow,
hilly tract; and a third to the wide plains at the base; and
that the inhabitants are all trying with equal steadiness and
skill to improve their stocks by selection ; the chances in this
case will be strongly in favour of the great holders on the
mountains or on the plains, improving their breeds more
TRANSITIONAL VARIETIES 183
quickly than the small holders on the intermediate narrow,
hilly tract; and consequently the improved mountain or plain
breed will soon take the place of the less improved hill breed ;
and thus the two breeds, which originally existed in greater
numbers, will come into close contact with each other, with-
out the interposition of the supplanted, intermediate hill
variety.
To sum up, I believe that species come to be tolerably well-
defined objects, and do not at any one period present an inex-
tricable chaos of varying and intermediate links : first, be-
cause new varieties are very slowly formed, for variation is
a slow process, and natural selection can do nothing until
favourable individual differences or variations occur, and un-
til a place in the natural polity of the country can be better
filled by some modification of some one or more of its inhabit-
ants. And such new places will depend on slow changes of
climate, or on the occasional immigration of new inhabitants,
and, probably, in a still more important degree, on some of
the old inhabitants becoming slowly modified, with the new
forms thus produced and the old ones acting and reacting on
each other. So that, in any one region and at any one time,
we ought to see only a few species presenting slight modifi-
cations of structure in some degree permanent ; and this as-
suredly we do see.
Secondly, areas now continuous must often have existed
within the recent period as isolated portions, in which many
forms, more especially amongst the classes which unite for
each birth and wander much, may have separately been ren-
dered sufficiently distinct to rank as representative species.
In this case, intermediate varieties between the several repre-
sentative species and their common parent, must formerly
have existed within each isolated portion of the land, but
these links during the process of natural selection will have
been supplanted and exterminated, so that they will no longer
be found in a living state.
Thirdly, when two or more varieties have been formed in
different portions of a strictly continuous area, intermediate
varieties will, it is probable, at first have been formed in the
intermediate zones, but they will generally have had a short
duration. For these intermediate varieties will, from reasons
184 ORIGIN OF SPECIES
already assigned (namely from what we know of the actual
distribution of closely allied or representative species, and
likewise of acknowledged varieties), exist in the intermediate
zones in lesser numbers than the varieties which they tend to
connect. From this cause alone the intermediate varieties
will be liable to accidental extermination ; and during the
process of further modification through natural selection,
they will almost certainly be beaten and supplanted by the
forms which they connect; for these from existing in greater
numbers will, in the aggregate, present more varieties, and
thus be further improved through natural selection and gain
further advantages.
Lastly, looking not to any one time, but to all time, if my
theory be true, numberless intermediate varieties, linking
closely together all the species of the same group, must as-
suredly have existed; but the very process of natural selec-
tion constantly tends, as has been so often remarked, to ex-
terminate the parent-forms and the intermediate links. Con-
sequently evidence of their former existence could be found
only amongst fossil remains, which are preserved, as we shall
attempt to show in a future chapter, in an extremely imper-
fect and intermittent record.
On the Origin and Transitions of Organic Beings zvith
peculiar Habits and Structure. — It has been asked by the
opponents of such views as I hold, how, for instance, could
a land carnivorous animal have been converted into one with
aquatic habits ; for how could the animal in its transitional
state have subsisted? It would be easy to show that there
now exist carnivorous animals presenting close intermediate
grades from strictly terrestrial to aquatic habits ; and as each
exists by a struggle for life, it is clear that each must be well
adapted to its place in nature. Look at the Mustela vison
of North America, which has webbed feet, and which re-
sembles an otter in its fur, short legs, and form of tail. Dur-
ing the summer this animal dives for and preys on fish, but
during the long winter it leaves the frozen waters, and preys,
like other pole-cats, on mice and land animals. If a different
case had been taken, and it had been asked how an insectiv-
orous quadruped could possibly have been converted into
a flying bat^ the question would have been far more
TRANSITIONS OF ORGANIC BEINGS 185
difficult to answer. Yet I think such difficulties have little
weight.
Here, as on other occasions, I lie under a heavy disadvan-
tage, for, out of the many striking cases which I have col-
lected, I can give only one or two instances of transitional
habits and structures in allied species ; and of diversified
habits, either constant or occasional, in the same species.
And it seems to me that nothing less than a long list of such
cases is sufficient to lessen the difficulty in any particular
case like that of the bat.
Look at the family of squirrels ; here we have the finest
gradation from animals with their tails only slightly flat-
tened, and from others, as Sir J. Richardson has remarked,
with the posterior part of their bodies rather wide and with
the skin on their flanks rather full, to the so-called flying
squirrels; and flying squirrels have their limbs and even the
base of the tail united by a broad expanse of skin, which
serves as a parachute and allows them to glide through the
air to an astonishing distance from tree to tree. We cannot
doubt that each structure is of use to each kind of squirrel in
its own country^ by enabling it to escape birds or beasts of
prey, to collect food more quickly, or, as there is reason to
believe, to lessen the danger from occasional falls. But it
does not follow from this fact that the structure of each
squirrel is the best that it is possible to conceive under all
possible conditions. Let the climate and vegetation change,
let other competing rodents or new beasts of prey immigrate,
or old ones become modified, and all analogy would lead us to
believe that some at least of the squirrels would decrease in
numbers or become exterminated, unless they also became
modified and improved in structure in a corresponding man-
ner. Therefore, I can see no difficulty, more especially under
changing conditions of life, in the continued preservation of
individuals with fuller and fuller flank-membranes, each modi-
fication being useful, each being propagated, until, by the ac-
cumulated effects of this process of natural selection, a per-
fect so-called flying squirrel was produced.
Now look at the Galeopithecus or so-called flying lemur,
which formerly was ranked amongst bats, but is now believed
to belong to the Insectivora. As extremely wide flank-mem-
186 ORIGIN OF SPECIES
brane stretches from the corners of the jaw to the tail, and
includes the limbs with the elongated fingers. This flank-
membrane is furnished with an extensor muscle. Although
no graduated links of structure, fitted for gliding through the
air, now connect the Galeopithecus with the other Insec-
tivora, yet there is no difficulty to supposing that such links
formerly existed, and that each was developed in the same
manner as with the less perfectly gliding squirrels ; each
grade of structure having been useful to its possessor. Nor
can I see any insuperable difficulty in further believing that
the membrane connected fingers and fore-arm of the Galeopi-
thecus might have been greatly lengthened by natural selec-
tion ; and this, as far as the organs of flight are concerned,
would have converted the animal into a bat. In certain bats
in which the wing-membrane extends from the top of the
shoulder to the tail and includes the hind-legs, we perhaps
see traces of an apparatus originally fitted for gliding through
the air rather than for flight.
If about a dozen genera of birds were to become extinct,
who would have ventured to surmise that birds might have
existed which used their wings solely as flappers, like the
logger-headed duck (Micropterus of Eyton) ; as fins in the
water and as front-legs on the land, like the penguin ; as
sails, like the ostrich ; and functionally for no purpose, like
Apteryx? Yet the structure of each of these birds is
good for it, under the conditions of life to which it is exposed,
for each has to live by a struggle ; but it is not necessarily
the best possible under all possible conditions. It must not
be inferred from these remarks that any of the grades of
wing-structure here alluded to, which perhaps may all be the
result of disuse, indicate the steps by which birds actually
acquired their perfect power of flight; but they serve to show
what diversified means of transition are at least possible.
Seeing that a few members of such water-breathing classes
as the Crustacea and MoUusca are adapted to live on the
land ; and seeing that we have flying birds and mammals, fly-
ing insects of the most diversified types, and formerly had
flying reptiles, it is conceivable that flying-fish, which now
glide far through the air, slightly rising and turning b^ the
aid of their fluttering fins, might have been modified into per-
TRANSITIONS OF ORGANIC BEINGS 187
fectly winged animals. If this had been efifected, who would
have ever imagined that in an early transitional state they
had been the inhabitants of the open ocean, and had used
their incipient organs of flight exclusively, as far as we know,
to escape being devoured by other fish?
When we see any structure highly perfected for any par-
ticular habit, as the wings of a bird for flight, we should bear
in mind that animals displaying early transitional grades of
the structure will seldom have survived to the present day,
for they will have been supplanted by their successors, which
were gradually rendered more perfect through natural selec-
tion. Furthermore, we may conclude that transitional states
between structures fitted for very different habits of life will
rarely have been developed at an early period in great num-
bers and under many subordinate forms. Thus, to return to our
imaginary illustration of the flying-fish, it does not seem
probable that fishes capable of true flight would have been
developed under many subordinate forms, for taking prey of
many kinds in many ways, on the land and in the water, until
their organs of flight had come to a high state of perfection,
so as to have given them a decided advantage over other ani-
mals in the battle for life. Hence the chance of discovering
species with transitional grades of structure in a fossil con-
dition will always be less, from their having existed in lesser
numbers, than in the case of species with fully developed
structures.
I will now give two or three instances both of diversified
and of changed habits in the individuals of the same species.
In either case it would be easy for natural selection to adapt
the structure of the animal to its changed habits, or exclu-
sively to one of its several habits. It is, however, difficult
to decide, and immaterial for us, whether habits generally
change first and structure afterwards; or whether slight
modifications of structure lead to changed habits ; both prob-
ably often occurring almost simultaneously. Of cases of
changed habits it will suffice merely to allude to that of the
many British insects which now feed on exotic plants, or ex-
clusively on artificial substances. Of diversified habits innu-
merable instances could be given : I have often watched a
tyrant flycatcher (Sauropha'gus sulphuratus) in South Amer-
188 ORIGIN OF SPECIES
ica, hovering over one spot and then proceeding to another,
like a kestrel, and at other times standing stationary on the
margin of water, and then dashing into it like a kingfisher
at a fish. In our ov^n country the larger titmouse (Parus
major) may be seen climbing branches, almost like a creeper;
it sometimes, like a shrike, kills small birds by blows on the
head ; and I have many times seen and heard it hammering
the seeds of the yew on a branch, and thus breaking them
like a nuthatch. In North America the black bear was seen
by Hearne swimming for hours with widely open mouth, thus
catching, almost like a whale, insects in the water.
As we sometimes see individuals following habits different
from those proper to their species and to the other species of
the same genus, we might expect that such individuals would
occasionally give rise to new species, having anomalous
habits, and with their structure either slightly or considerably
modified from that of their type. And such instances occur
in nature. Can a more striking instance of adaptation be
given than that of a woodpecker for climbing trees and seiz-
ing insects in the chinks of the bark ? Yet in North America
there are woodpeckers which feed largely on fruit, and others
with elongated wings which chase insects on the wing. On
the plains of La Plata, where hardly a tree grows, there is a
woodpecker (Colaptes campestris) which has two toes before
and two behind, a long pointed tongue, pointed tail-feathers,
sufficiently stiff to support the bird in a vertical position on
a post, but not so stiff as in the typical woodpeckers, and a
straight strong beak. The beak, however, is not so straight
or so strong as in the typical woodpeckers, but it is strong
enough to bore into wood. Hence this Colaptes in all the
essential parts of its structure is a woodpecker. Even in
such trifling characters as the colouring, the harsh tone of
the voice, and undulatory flight, its close blood-relationship
to our common woodpecker is plainly declared: yet, as I can
assert, not only from my own observations, but from those
of the accurate Azara, in certain large districts it does not
climb trees, and it makes its nest in holes in banks ! In cer-
tain other districts, however, this same woodpecker, as Mr.
Hudson states, frequents trees, and bores holes in the trunk
for its nest. I may mention as another illustration of the
TRANSITIONS OF ORGANIC BEINGS 189
varied habits of this genus, that a Mexican Colaptes has been
described by De Saussure as boring holes into hard wood in
order to lay up a store of acorns.
Petrels are the most aerial and oceanic of birds, but in the
quiet sounds of Tierra del Fuego, the Puffinuria berardi, in
its general habits, in its astonishing power of diving, in its
manner of swimming and of flying when made to take flight,
would be mistaken by any one for an auk or a grebe; never-
theless it is essentially a petrel, but with many parts of its
organisation profoundly modified in relation to its new habits
of life; whereas the woodpecker of La Plata has had its
structure only slightly modified. In the case of the water-
ouzel, the acutest observer by examining its dead body would
never have suspected its sub-aquatic habits ; yet this bird,
which is allied to the thrush family, subsists by diving — using
its wings under water, and grasping stones with its feet. All
the members of the great order of Hymenopterous insects
are terrestrial, excepting the genus Proctotrupes, which Sir
John Lubbock has discovered to be aquatic in its habits ; it
often enters the water and dives about by the use not of its
legs but of its wings, : :id remains as long as four hours be-
neath the surface ; yet it exhibits no modification in structure
in accordance with its abnormal habits.
He who believes that each being has been created as we
now see it, must occasionally have felt surprise when he has
met with an animal having habits and structure not in agree-
ment. What can be plainer than that the webbed feet of
ducks and geese are formed for swimming? Yet there are up-
land geese with webbed feet which rarely go near the water;
and no one except Audubon has seen the frigate-bird, which
has all its four toes webbed, alight on the surface of the
ocean. On the other hand, grebes and coots are eminently
aquatic, although their toes are only bordered by membrane.
What seems plainer than that the long toes, not furnished
with membrane of the Grallatores are formed for walking
over swamps and floating plants ? — the water-hen and land-
rail are members of this order, yet the first is nearly as
aquatic as the coot, and the second nearly as terrestrial as
the quail or partridge. In such cases, and many others could
be given, habits have changed without a corresponding change
190 ORIGIN OF SPECIES
of structure. The webbed feet of -the upland goose may be
said to have become almost rudimentary in function, though
not in structure. In the frigate-bird, the deeply scooped
membrane between the toes shows that structure has begun
to change.
He who believes in separate and innumerable acts of cre-
ation may say, that in these cases it has pleased the Creator
to cause a being of one type to take the place of one belonging
to another type ; but this seems to me only re-stating the fact
in dignified language. He who believes in the struggle for
existence and in the principle of natural selection, will ac-
knowledge that every organic being is constantly endeavour-
ing to increase in numbers ; and that if any one being varies
ever so little, either in habits or structure, and thus gains an
advantage over some other inhabitant of the same country, it
will seize on the place of that inhabitant, however different
that may be from its own place. Hence it will cause him no
surprise that there should be geese and frigate-birds with
webbed feet, living on the dry land and rarely alighting on
the water, that there should be long-toed corncrakes, living in
meadows instead of in swamps; that there should be wood-
peckers where hardly a tree grows ; that there should be div-
ing thrushes and diving Hymenoptera, and petrels with the
habits of auks.
ORGANS OF EXTREME PERFECTION AND COMPLICATION.
To suppose that the eye with all its inimitable contrivances
for adjusting the focus to different distances, for admitting
different amounts of light, and for the correction of spherical
and chromatic aberration, could have been formed by natural
selection, seems, I freely confess, absurd in the highest de-
gree. When it was first said that the sun stood still and the
world turned round, the common sense of mankind declared
the doctrine false ; but the old saying of Vox populi, vox Dei,
as every philosopher knows, cannot be trusted in science.
Reason tells me, that if numerous gradations from a simple
and imperfect eye to one complex and perfect can be shown
to exist, each grade being useful to its possessor, as is cer-
tainly the case ; if further, the eye ever varies and the vari-
ORGANS OF EXTREME PERFECTION 191
ations be inherited, as is likewise certainly the case ; and if
such variations should be useful to any animal under chang-
ing conditions of life, then the difficulty of believing that a
perfect and complex eye could be formed by natural selection,
though insuperable by our imagination, should not be consid-
ered as subversive of the theory. How a nerve comes to be
sensitive to light, hardly concerns us more than how life it-
self originated ; but I may remark that, as some of the lowest
organisms, in which nerves cannot be detected, are capable of
perceiving light, it does not seem impossible that certain sen-
sitive elements in their sarcode should become aggregated
and developed into nerves, endowed with this special sensi-
bility.
In searching for the gradations through which an organ in
any species has been perfected, we ought to look exclusively
to its lineal progenitors; but this is scarcely ever possible,
and we are forced to look to other species and genera of the
same group, that is to the collateral descendants from the
same parent-form, in order to see what gradations are pos-
sible, and for the chance of some gradations having been
transmitted in an unaltered or little altered condition. But
the state of the same organ in distinct classes may incident-
ally throw light on the steps by which it has been perfected.
The simplest organ which can be called an eye consists of
an optic nerve, surrounded by pigment-cells and covered by
translucent skin, but without any lens or other refractive
body. We may, however, according to M. Jourdain, descend
even a step lower and find aggregates of pigment-cells, appar-
ently serving as organs of vision, without any nerves, and
resting merely on sarcodic tissue. Eyes of the above simple
nature are not capable of distinct vision, and serve only to
distinguish light from darkness. In certain star-fishes, small
depressions in the layer of pigment which surrounds the
nerve are filled, as described by the author just quoted, with
transparent gelatinous matter, projecting with a convex sur-
face, like the cornea in the higher animals. He suggests that
this serves not to form an image, but only to concentrate the
luminous rays and render their perception more easy. In
this concentration of the rays we gain the first and by far the
most important step towards the formation of a true, picture-
192 ORIGIN OF SPECIES
forming eye ; for we have only to place the naked extremity
of the optic nerve, which in some of the lower animals lies
deeply buried in the body, and in some near the surface, at
the right distance from the concentrating apparatus, and an
image will be formed on it.
In the great class of the Articulata, we may start from an
optic nerve simply coated with pigment, the latter sometimes
forming a sort of pupil, but destitute of a lens or other opti-
cal contrivance. With insects it is now known that the nu-
merous facets on the cornea of their great compound eyes
form true lenses, and that the cones include curiously modi-
fied nervous filaments. But these organs in the Articulata
are so much diversified that Miiller formerly made three main
classes with seven subdivisions, besides a fourth main class
of aggregated simple eyes.
When we reflect on these facts, here given much too briefly,
with respect to the wide, diversified, and graduated range of
structure in the eyes of the lower animals ; and when we bear
in mind how small the number of all living forms must be in
comparison with those which have become extinct, the diffi-
culty ceases to be very great in believing that natural selec-
tion may have converted the simple apparatus of an optic
nerve, coated with pigment and invested by transparent mem-
brane, into an optical instrument as perfect as is possessed
by any member of the Articulate Class.
He who will go thus far, ought not to hesitate to go one
step further, if he finds on finishing this volume that large
bodies of facts, otherwise inexplicable, can be explained by
the theory of modification through natural selection ; he ought
to admit that a structure even as perfect as an eagle's eye
might thus be formed, although in this case he does not know
the transitional states. It has been objected that in order to
modify the eye and still preserve it as a perfect instrument,
many changes would have to be effected simultaneously,
which, it is assumed, could not be done through natural
selection ; but as I have attempted to show in my work on the
variation of domestic animals, it is not necessary to suppose
that the modifications were all simultaneous, if they were ex-
tremely slight and gradual. Different kinds of modification
would, also, serve for the same general purpose : as Mr. Wal-
ORGANS OF EXTREME PERFECTION 193
face has remarked, "if a lens has too short or too long a
focus, it may be amended either by an alteration of curvature,
or an alteration of density; if the curvature be irregular, and
the rays do not converge to a point, then any increased regu-
larity of curvature v^ill be an improvement. So the contrac-
tion of the iris and the muscular movements of the eye are
neither of them essential to vision, but only improvements
which might have been added and perfected at any stage of
the construction of the instrument." Within the highest di-
vision of the animal kingdom, namely, the Vertebrata, we can
start from an eye so simple, that it consists, as in the lance-
let, of a little sack of transparent skin, furnished with a
nerve and lined with pigment, but destitute of any other ap-
paratus. In fishes and reptiles, as Owen has remarked, "the
range of gradations of dioptric structures is very great." It
is a significant fact that even in man, according to the high
authority of Virchow, the beautiful crystalline lens is formed
in the embryo by an accumulation of epidermic cells, lying in
a sack-like fold of the skin ; and the vitreous body is formed
from embryonic sub-cutaneous tissue. To arrive, however,
at a just conclusion regarding the formation of the eye, with
all its marvellous yet not absolutely perfect characters, it is
indispensable that the reason should conquer the imagination ;
but I have felt the difficulty far too keenly to be surprised at
others hesitating to extend the principle of natural selection
to so startling a length.
It is scarcely possible to avoid comparing the eye with a
telescope. We know that this instrument has been perfected
by the long-continued efforts of the highest human intellects ;
and we naturally infer that the eye has been formed by a
somewhat analogous process. But may not this inference be
presumptuous? Have we any right to assume that the Cre-
ator works by intellectual powers like those of man? If wq
must compare the eye to an optical instrument, we ought in
imagination to take a thick layer of transparent tissue, with
spaces filled with fluid, and with a nerve sensitive to light be-
neath, and then suppose every part of this layer to be con-
tinually changing slowly in density, so as to separate into
layers of different densities and thicknesses, placed at differ-
ent distances from each other, and with the surfaces of each
G — HC XI
194 ORIGIN OF SPECIES
layer slowly changing in form. Further we must suppose
that there is a power, represented by natural selection or the
survival of the fittest, always intently watching each slight
alteration in the transparent layers ; and carefully preserving
each which, under varied circumstances, in any way or in any
degree, tends to produce a distincter image. We must sup-
pose each new state of the instrument to be multiplied by the
million ; each to be preserved until a better one is produced,
and then the old ones to be all destroyed. In living bodies,
variation will cause the slight alterations, generation will mul-
tiply them almost infinitely, and natural selection will pick
out with unerring skill each improvement. Let this process
go on for millions of years ; and during each year on millions
of individuals of many kinds ; and may we not believe that a
living optical instrument might thus be formed as superior
to one of glass, as the works of the Creator are to those of
man?
MODES OF TRANSITION.
If it could be demonstrated that any complex organ ex-
isted, which could not possibly have been formed by numer-
ous, successive, slight modifications, my theory would abso-
lutely break down. But I can find out no such case. No
doubt many organs exist of which we do not know the tran-
sitional grades, more especially if we look to much-isolated
species, round which, according to the theory, there has been
much extinction. Or again, if we take an organ common to
I all the members of a class, for in this latter case the organ
must have been originally formed at a remote period, since
which all the many members of the class have been developed ;
and in order to discover the early transitional grades through
which the organ has passed, we should have to look to very
ancient ancestral forms, long since become extinct.
We should be extremely cautious in concluding that an
organ could not have been formed by transitional gradations
of some kind. Numerous cases could be given amongst the
lower animals of the same organ performing at the same time
wholly distinct functions; thus in the larva of the dragon-fly
and in the fish Cobites the alimentary canal respires, digests,
and excretes. In the Hydra, the animal may be turned in-
MODES OF TRANSITION 195
side out, and the exterior surface will then digest and the
stomach respire. In such cases natural selection might spe-
cialise, if any advantage were thus gained, the whole or part
of an organ, which had previously performed two functions,
for one function alone, and thus by insensible steps greatly
change its nature. Many plants are known which regularly
produce at the same time differently constructed flowers ; and
if such plants were to produce one kind alone, a great change
would be effected with comparative suddenness in the char-
acter of the species. It is, however, probable that the two
sorts of flowers borne by the same plant were originally dif-
ferentiated by finely graduated steps, which may still be
followed in some few cases.
Again, two distinct organs, or the same organ under two
very different forms, may simultaneously perform in the same
individual the same function, and this is an extremely im-
portant means of transition : to give one instance, — there are
fish with gills or branchiae that breathe the air dissolved in
the water, at the same time that they breathe free air in their
swimbladders, this latter organ being divided by highly vas-
cular partitions and having a ductus pneumaticus for the
supply of air. To give another instance from the vegetable
kingdom; plants climb by three distinct means, by spirally
twining, by clasping a support with their sensitive tendrils,
and by the emission of aerial rootlets ; these three means are
usually found in distinct groups, but some few species exhibit
two of the means, or even all three, combined in the same in-
dividual. In all such cases one of the two organs might
readily be modified and perfected so as to perform all the
work, being aided during the progress of modification by the
other organ; and then this other organ might be modified
for some other and quite distinct purpose, or be wholly
obliterated.
The illustration of the swimbladder in fishes is a good one,
because it shows us clearly the highly important fact that an
organ originally constructed for one purpose, namely, flota-
tion, may be converted into one for a widely different pur-
pose, namely, respiration. The swimbladder has, also, been
worked in as an accessory to the auditory organs of certain
fishes. All physiologists admit that the swimbladder is homol-
196 ORIGIN OF SPECIES
ogous, or "ideally similar" in position and structure with the
lungs of the higher vertebrate animals : hence there is no
reason to doubt that the swimbladder has actually been con-
verted into lungs, or an organ used exclusively for respi-
ration.
According to this view it may be inferred that all verte-
brate animals with true lungs are descended by ordinary gen-
eration from an ancient and unknown prototype, which was
furnished with a floating apparatus or swimbladder. We can
thus, as I infer from Owen's interesting description of these
parts, understand the strange fact that every particle of food
and drink which we swallow has to pass over the orifice of
the trachea, with some risk of falling into the lungs, notwith-
standing the beautiful contrivance by which the glottis is
closed. In the higher Vertebrata the branchiae have wholly
disappeared — but in the embryo the slits on the sides of the
neck and the loop-like course of the arteries still mark their
former position. But it is conceivable that the now utterly
lost branchiae might have been gradually worked in by nat-
ural selection for some distinct purpose : for instance, Lan-
dois has shown that the wings of insects are developed from
the tracheae ; it is therefore highly probable that in this great
class organs which once served for respiration have been
actually converted intO' organs for flight.
In considering transitions of organs, it is so important to
bear in mind the probability of conversion from one function
to another, that I will give another instance. Pedunculated
cirripedes have two minute folds of skin, called by me the
ovigerous frena, which serve, through the means of a sticky
secretion, to retain the eggs until they are hatched within the
sack. These cirripedes have no branchiae, the whole surface
of the body and of the sack, together with the small frena,
serving for respiration. The Balanidae or sessile cirripedes,
on the other hand, have no ovigerous frena, the eggs lying
loose at the bottom of the sack, within the well-enclosed shell ;
but they have, in the same relative position with the frena,
large, much-folded membranes, which freely communicate
with the circulatory lacunae of the sack and body, and which
have been considered by all naturalists to act as branchiae.
Now I think no one will dispute that the ovigerous frena in
MODES OF TRANSITION 197
the one family are strictly homologous with the branchiae of
the other family ; indeed, they graduate into each other.
Therefore it need not be doubted that the two little folds of
skin, which originally served as ovigerous frena, but which,
likewise, very slightly aided in the act of respiration, have
been gradually converted by natural selection into branchiae,
simply through an increase in their size and the obliteration
of their adhesive glands. If all pedunculated cirripedes had
become extinct, and they have suffered far more extinction
than have sessile cirripedes, who would ever have imagined
that the branchiae in this latter family had originally existed
as organs for preventing the ova from being washed out of
the sack ?
There is another possible mode of transition, namely,
through the acceleration or retardation of the period of re-
production. This has lately been insisted on by Prof. Cope
and others in the United States. It is now known that some
animals are capable of reproduction at a very early age, be-
fore they have acquired their perfect characters ; and if this
power became thoroughly well developed in a species, it seems
probable that the adult stage of development would sooner or
later be lost; and in this case, especially if the larva differed
much from the mature form, the character of the species
would be greatly changed and degraded. Again, not a few
animals, after arriving at maturity, go on changing in char-
acter during nearly their whole lives. With mammals, for
instance, the form of the skull is often much altered with age,
of which Dr. Murie has given some striking instances with
seals ; every one knows how the horns of stags become more
and more branched, and the plumes of some birds become
more finely developed, as they grow older. Prof. Cope states
that the teeth of certain lizards change much in shape with
advancing years ; with crustaceans not only many trivial, but
some important parts assume a new character, as recorded
by Fritz Miiller, after maturity. In all such cases, — and
many could be given, — if the age for reproduction were re-
tarded, the character of the species, at least in its adult state,
would be modified ; nor is it improbable that the previous and
earlier stages of development' would in some cases be hurried
through and finally lost. Whether species have often or ever
198 ORIGIN OF SPECIES
been modified throug-h this comparatively sudden mode of
transition, I can form no opinion ; but if this has occurred, it
is probable that the differences between the young and the
mature, and between the mature and the old, were primor-
dially acquired by graduated steps.
SPECIAL DIFFICULTIES OF THE THEORY OF NATURAL SELECTION
Although we must be extremely cautious in concluding that
any organ could not have been produced by successive, small
transitional gradations, yet undoubtedly serious cases of dif-
ficulty occur.
One of the most serious is that of neuter insects, which are
often differently constructed from either the males or fertile
females; but this case will be treated of in the next chapter.
The electric organs of fishes offer another case of special
difficulty ; for it is impossible to conceive by what steps these
wondrous organs have been produced. But this is not sur-
prising, for we do not even know of what use they are. In
the Gymnotus and Torpedo they no doubt serve as powerful
means of defence, and perhaps for securing prey; yet in the
Ray, as observed by Matteucci, an analogous organ in the
tail manifests but little electricity, even when the animal is
greatly irritated; so little, that it can hardly be of any use
for the above purposes. Moreover, in the Ray, besides the
organ just referred to, there is, as Dr. R. M'Donnell has
shown, another organ near the head, not known to be elec-
trical, but which appears to be the real homologue of the
electric battery in the Torpedo. It is generally admitted that
there exists between these organs and ordinary muscle a close
analogy, in intimate structure, in the distribution of the
nerves, and in the manner in which they are acted on by
various reagents. It should, also, be especially observed that
muscular contraction is accompanied by an electrical dis-
charge; and, as Dr. Radcliffe insists, "in the electrical ap-
paratus of the torpedo during rest, there would seem to be a
charge in every respect like that which is met with in muscle
and nerve during rest, and the discharge of the torpedo, in-
stead of being peculiar, may be only another form of the dis-
charge which attends upon the action of muscle and
DIFFICULTIES OF THE THEORY 199
motor nerve." Beyond this we cannot at present go in the
way of explanation; but as we know so little about the uses
of these organs, and as we know nothing about the habits
and structure of the progenitors of the existing electric fishes,
it would be extremely bold to maintain that no serviceable
transitions are possible by which these organs might have
been gradually developed.
These organs appear at first to offer another and far more
serious difficulty ; for they occur in about a dozen kinds of
fish, of which several are widely remote in their affinities.
When the same organ is found in several members of the
same class, especially if in members having very different
habits of life, we may generally attribute its presence to in-
heritance from a common ancestor ; and in its absence in
some of the members to loss through disuse or natural selec-'
tion. So that, if the electric organs had been inherited from
some one ancient progenitor, we might have expected that
all electric fishes would have been specially related to each
other; but this is far from the case. Nor does geology at all
lead to the belief that most fishes formerly possessed electric
organs, which their modified descendants have now lost. But
when we look at the subject more closely, we find in the sev-
eral fishes provided with electric organs, that those are situ-
ated in different parts of the body, — that they differ in con-
struction, as in the arrangement of the plates, and, according
to Pacini, in the process or means by which the electricity is
excited — and lastly, in being supplied with nerves proceeding
from different sources, and this is perhaps the most important
of all the differences. Hence in the several fishes furnished
with electric organs, these cannot be considered as homol-
ogous, but only as analogous in function. Consequently there
is no reason to suppose that they have been inherited from a
common progenitor ; for had this been the case they would
have closely resembled each other in all respects. Thus the
difficulty of an organ, apparently the same, arising in several
remotely allied species, disappears, leaving only the lesser yet
still great difficulty ; namely, by what graduated steps these
organs have been developed in each separate group of fishes.
The luminous organs which occur in a few insects, belong-
ing to widely different families, and which are situated in
200 ORIGIN OF SPECIES
different parts of the body, offer, under our present state of
ignorance, a difficulty almost exactly parallel with that of the
electric organs. Other similar cases could be given ; for in-
stance in plants, the very curious contrivance of a mass of
pollen-grains, borne on a foot-stalk with an adhesive gland,
is apparently the same in Orchis and Asclepias, — genera al-
most as remote as is possible amongst flowering plants; but
here again the parts are not homologous. In all cases of be-
ings, far removed from each other in the scale of organisa-
tion, which are furnished with similar and peculiar organs,
it will be found that although the general appearance and
function of the organs may be the same, yet fundamental dif-
ferences between them can always be detected. For instance,
the eyes of cephalopods or cuttle-fish and of vertebrate ani-
mals appear wonderfully alike; and in such widely sundered
groups no part of this resemblance can be due to inheritance
from a common progenitor. Mr. Mivart has advanced this
case as one of special difficulty, but I am unable to see the
force of his argument. An organ for vision must be formed
of transparent tissue, and must include some sort of lens for
throwing an image at the back of a dark:ned chamber. Be-
yond this superficial resemblance, there is hardly any real
similarity between the eyes of cuttle-fish and vertebrates, as
may be seen by consulting Hensen's admirable memoir on
these organs in the Cephalopoda. It is impossible for me
here to enter on details, but I may specify a few of the points
of difference. The crystalline lens in the higher cuttle-fish
consists of two parts, placed one behind the other like two
lenses, both having a very different structure and disposition
to what occurs in the vertebrata. T'.e retina is wholly dif-
ferent, with an actual inversion of the elemental parts, and
with a large nervous ganglion included within the mem-
branes of the eye. The relations of the muscles are as dif-
ferent as it is possible to conceive, and so in other points.
Hence it is not a little difficult to decide how far even the
same terms ought to be employed in describing the eyes of
the Cephalopoda and Vertebrata. It is, of course, open to
any one to deny that the eye in either case could have been
developed through the natural selection of successive slight
variations; but if this be admitted in the one case, it is clearly
DIFFICULTIES OF THE THEORY 201
possible in the other; and fundamental differences of struc-
ture in the visual organs of two groups might have been an-
ticipated, in accordance with this view of their manner of
formation. As two men have sometimes independently hit
on the same invention, so in the several foregoing cases it
appears that natural selection, working for the good of each
being, and taking advantage of all favourable variations, has
produced similar organs, as far as function is concerned, in
distinct organic beings, which owe none of their structure in
common to inheritance from a common progenitor.
Fritz MiJller, in order to test the conclusions arrived at in
this volume, has followed out with much care a nearly similar
line of argument. Several families of crustaceans include a
few species, possessing an air-breathing apparatus and fitted
to live out of the water. In two of these families, which were
more especially examined by Miiller, and which are nearly
related to each other, the species agree most closely in all
important characters; namely in their sense organs, circulat-
ing system, in the position of the tufts of hair within their
complex stomachs, and lastly in the whole structure of the
water-breathing branchiae, even to the microscopical hooks by
which they are cleansed. Hence it might have been expected
that in the few species belonging to both families which live
on the land, the equally-important air-breathing apparatus
would have been the same ; for why should this one apparatus,
given for the same purpose, have been made to differ, whilst
all the other important organs were closely similar or rather
identical.
Fritz Miiller argues that this close similarity in so many
points of structure must, in accordance with the views ad-
vanced by me, be accounted for by inheritance from a com-
mon progenitor. But as that vast majority of the species in
the above two families, as well as most other crustaceans,
are aquatic in their habits, it is improbable in the highest
degree, that their common progenitor should have been
adapted for breathing air. Miiller was thus led carefully to
examine the apparatus in the air-breathing species ; and he
found it to differ in each in several important points, as in
the position of the orifices, in the manner in which they are
opened and closed, and in some accessory details. Now such
202 ORIGIN OF SPECIES
differences are intelligible, and might even have been ex-
pected, on the supposition that species belonging to distinct
families had slowly become adapted to live more and more
out of M^ater, and to breathe the air. For these species, from
belonging to distinct families, would have differed to a cer-
tain extent, and in accordance with the principle that the
nature of each variation depends on two factors, viz., the
nature of the organism and that of the surrounding condi-
tions, their variability assuredly would not have been exactly
the same. Consequently natural selection would have had
different materials or variations to work on, in order to ar-
rive at the same functional result; and the structures thus
acquired would almost necessarily have differed. On the
hypothesis of separate acts of creation the whole case re-
mains unintelligible. This line of argument seems to have
had great weight in leading Fritz Miiller to accept the views
maintained by me in this volume.
Another distinguished zoologist, the late Professor Clapa-
rede, has argued in the same manner, and has arrived at
the same result. He shows that there are parasitic mites
(Acaridse), belonging to distinct sub-families and families,
which are furnished with hair-claspers. These organs must
have been independently developed, as they could not have
been inherited from a common progenitor ; and in the several
groups they are formed by the modification of the fore-legs,
— of the hind-legs, — of the maxillae or lips, — and of append-
ages on the under side of the hind part of the body.
In the foregoing cases, we see the same end gained and the
same function performed, in beings not at all or only re-
motely allied, by organs in appearance, though not in de- ,
velopment, closely similar. On the other hand, it is a com-
mon rule throughout nature that the same end should be
gained, even sometimes in the case of closely-related beings,
by the most diversified means. How differently constructed
is the feathered wing of a bird and the membrane-covered
wing of a bat ; and still more so the four wings of a butter-
fly, the two wings of a fly, and the two wings with the elytra
of a beetle. Bivalve shells are made to open and shut, but
on what a number of patterns is the hinge constructed, —
DIFFICULTIES OF THE THEORY 203
from the long row of neatly interlocking teeth in a Nucula
to the simple ligament of a Mussel ! Seeds are disseminated
&y their minuteness, — by their capsule being converted into a
fight balloon-like envelope, — by being embedded in pulp or
flesh, formed of the most diverse parts, and rendered nutri-
tious, as well as conspicuously coloured, so as to attract and
be devoured by birds, — by having hooks and grapnels of
many kinds and serrated awns, so as to adhere to the fur of
quadrupeds, — and by being furnished with wings and plumes,
as different in shape as they are elegant in structure, so as to
be wafted by every breeze. I will give one other instance ;
for this subject of the same end being gained by the most
diversified means well deserves attention. Some authors
maintain that organic beings have been formed in many ways
for the sake of mere variety, almost like toys in a shop, but
such a view of nature is incredible. With plants having
separated sexes, and with those in which, though hermaphro-
dites, the pollen does not spontaneously fall on the stigma,
some aid is necessary for their fertilisation. With several
kinds this is effected by the pollen-grains, which are light
and incoherent, being blown by the wind through mere chance
on to the stigma; and this is the simplest plan which can
well be conceived. An almost equally simple, though very
different, plan occurs in many plants in which a symmetrical
flower secretes a few drops of nectar, and is consequently
visited by insects; and these carry the pollen from the anthers
to the stigma.
From this simple stage we may pass through an inex-
haustible number of contrivances, all for the same purpose
and eft'ected in essentially the same manner, but entailing
changes in every part of the flower. The nectar may be
stored in variously shaped receptacles, with the stamens and
pistils modified in many ways, sometimes forming trap-like
contrivances, and sometimes capable of neatly adapted move-
ments through irritability or elasticity. From such structures
we may advance till we come to such a case of extraordinary
adaptions as that lately described by Dr. Criiger in the
Coryanthes. This orchid has part of its labellum or lower
lip hollowed out into a great bucket, into which drops of
almost pure water continually fall from two secreting horns
204 ORIGIN OF SPECIES
which stand above it; and when the bucket is half full, the
water overflows by a spout on one side. The basal part of
the labellnm stands over the bucket, and is itself hollowed
out into a sort of chamber with two lateral entrances ; with-
in this chamber there are curious fleshy ridges. The most
ingenious man, if he had not witnessed what takes place,
could never have imagined what purpose all these parts serve.
But Dr. Criigcr saw crowds of large humble-bees visiting the
gigantic fiowers of this orchid, not in order to suck nectar,
but to gnaw off the ridges within the chamber above the
bucket; in doing this they frequently pushed each other into
the bucket, and their wings being thus wetted they could not
fly away, but were compelled to crawl out through the pas-
sage formed by the spout or overflow. Dr. Criiger saw a
"continual procession" of bees thus crawling out of their
involuntary bath. The passage is narrow, and is roofed over
by the column, so that a bee, in forcing its way out, first rubs
its back against the viscid stigma and then against the viscid
glands of the pollen-masses. The pollen-masses are thus
glued to the back of the bee which first happens to crawl out
through the passage of a lately expanded flower, and are
thus carried away. Dr. Criiger sent me a flower in spirits of
wine, with a bee which he had killed before it had quite
crawled out with a pollen-mass still fastened to its back.
When the bee, thus provided, flies to another flower, or to
the same flower a second time, and is pushed by its comrades
into the bucket and then crawls out by the passage, the
pollen-mass necessarily comes first into contact with the
viscid stigma, and adheres to it, and the flower is fertilised.
Now at last we see the full use of every part of the flower,
of the water-secreting horns, of the bucket half full of water,
which prevents the bees from flying away, and forces them
to crawi out through the spout, and rub against the properly
placed viscid pollen-masses and the viscid stigma.
The construction of the flower in another closely allied
orchid, namely the Catasetum, is widely different, though
serving the same end; and is equally curious. Bees visit
these flowers, like those of the Coryanthes, in order to gnaw
the labellum; in doing this they inevitably touch a long,
tapering, sensitive projection, or, as I have called it, the
DIFFICULTIES OF THE THEORY 205
antenna. This antenna, when touched, transmits a sensation
or vibration to a certain membrane which is instantly rup-
tured ; this sets free a spring by which the pollen-mass is shot
forth, like an arrow, in the right direction, and adheres by
its viscid extremity to the back of the bee. The pollen-mass
of the male plant (for the sexes are separate in this orchid)
is thus carried to the flower of the female plant, where it is
brought into contact with the stigma, which is viscid enough
to break certain elastic threads, and retaining the pollen,
fertilisation is effected.
How, it may be asked, in the foregoing and in innumer-
able other instances, can we understand the graduated scale of
complexity and the multifarious means for gaining the same
end. The answer no doubt is, as already remarked, that when
two forms vary, which already differ from each other in some
slight degree, the variability will not be of the same exact
nature, and consequently the results obtained through natural
selection for the same general purpose will not be the same.
We should also bear in mind that every highly developed
organism has passed through many changes; and that each
modified structure tends to be inherited, so that each modifi-
cation will not readily be quite lost, but may be again and
again further altered. Hence the structure of each part of
each species, for whatever purpose it may serve, is the sum
of many inherited changes, through which the species has
passed during its successive adaptations to changed habits
and conditions of life.
Finally then, although in many cases it is most difficult
even to conjecture by what transitions organs have arrived
at their present state ; yet, considering how small the propor-
tion of living and known forms is to the extinct and un-
known, I have been astonished how rarely an organ can be
named, towards which no transitional grade is known to lead.
It certainly is true, that new organs appearing as if created
for some special purpose, rarely or never appear in any
being; — as indeed is shown by that old, but somewhat exag-
gerated, canon in natural history of "Natura non facit sal-
tum." We meet with this admission in the writings of almost
every experienced naturalist ; or as Milne Edwards has well
expressed it, Nature is prodigal in variety, but niggard in
206 ORIGIN OF SPECIES
innovation. Why, on the theory of Creation, should there
be so much variety and so little real novelty ? Why should
all the parts and organs of many independent beings, each
supposed to have been separately created for its proper place
in nature, be so commonly linked together by graduated
steps? Why should not Nature take a sudden leap from
structure to structure? On the theory of natural selection,
we can clearly understand why she should not; for natural
selection acts only by taking advantage of slight successive
variations; she can never take a great and sudden leap, but
must advance by short and sure, though slow steps.
ORGANS OF LITTLE APPARENT IMPORTANCE, AS AFFECTED
BY NATURAL SELECTION
As natural selection acts by life and death, — by the sur-
vival of the fittest, and by the destruction of the less well-
fitted individuals, — I have sometimes felt great difficulty in
understanding the origin or formation of parts of little im-
portance; almost as great, though of a very different kind,
as in the case of the most perfect and complex organs.
In the first place, we are much too ignorant in regard to
the whole economy of any one organic being, to say what
slight modifications would be of importance or not. In a
former chapter I have given instances of very trifling char-
acters, such as the down on fruit and the colour of its flesh,
the colour of the skin and hair of quadrupeds, which, from
being correlated with constitutional differences or from de-
termining the attacks of insects, might assuredly be acted on
by natural selection. The tail of the giraffe looks like an
artificially constructed fly-flapper; and it seems at first in-
credible that this could have been adapted for its present
purpose by successive slight modifications, each better and
better fitted, for so trifling an object as to drive away flies ;
yet we should pause before being too positive even in this
case, for we know that the distribution and existence of
cattle and other animals in South America absolutely depend
on their power of resisting the attacks of insects: so that
individuals which could by any means defend themselves
from these small enemies, would be able to range into new
ORGANS AFFECTED 207
pastures and thus gain a great advantage. It is not that the
larger quadrupeds are actually destroyed (except in some
rare cases) by flies, but they are incessantly harassed and
their strength reduced, so that they are more subject to
disease, or not so well enabled in a coming dearth to search
for food, or to escape from beasts of prey.
Organs now of trifling importance have probably in some
cases been of high importance to an early progenitor, and,
after having been slowly perfected at a former period, have
been transmitted to existing species in nearly the same date,
although now of very slight use; but any actually injurious
deviations in their Structure would of course have been
checked by natural selection. Seeing how important an
organ of locomotion the tail is in most aquatic animals, its
general presence and use for many purposes in so many land
animals, which in their lungs or modified swimbladders be-
tray their aquatic origin, may perhaps be thus accounted
for. A well-developed tail having been formed in an aquatic
animal, it might subsequently come to be worked in for all
sorts of purposes, — as a fly-flapper, an organ of prehension,
or as an aid in turning, as in the case of the dog, though the
aid in this latter respect must be slight, for the hare, with
hardly any tail, can double still more quickly.
In the second place, we may easily err in attributing im-
portance to characters, and in believing that they have been
developed through natural selection. We must by no means
overlook the effects of the definite action of changed condi-
tions of life, — of so-called spontaneous variations, which
seem to depend in a quite subordinate degree on the nature
of the conditions, — of the tendency to reversion to long-lost
characters, — of the complex laws of growth, such as of cor-
relation, compensation, of the pressure of one part on an-
other, etc., — and finally of sexual selection, by which charac-
ters of use to one sex are often gained and then transmitted
more or less perfectly to the other sex, though of no use
to this sex. But structures thus indirectly gained, although
at first of no advantage to a species, may subsequently have
been taken advantage of by its modified descendants, under
new conditions of life and newly acquired habits.
If green woodpeckers alone had existed, and we did not
208 ORIGIN OF SPECIES
know that there were many black and pied kinds, I dare say
that we should have thought that the green colour was a
beautiful adaptation to conceal this tree-frequenting bird
from its enemies; and consequently that it was a character
of importance, and had been acquired through natural selec-
tion; as it is, the colour is probably in chief part due to
sexual selection. A trailing palm in the Malay Archipelago
climbs the loftiest trees by the aid of exquisitely constructed
hooks clustered around the ends of the branches, and this
contrivance, no doubt, is of the highest service to the plant;
but as we see nearly similar hooks on many trees which are
not climbers, and which, as there is reason to believe from
the distribution of the thorn-bearing species in Africa and
South America, serve as a defence against browsing quadru-
peds, so the spikes on the palm may at first have been de-
veloped for this object, and subsequently have been improved
and taken advantage of by the plant, as it underwent further
modification and became a climber. The naked skin on the
head of a vulture is generally considered as a direct adapta-
tion for wallowing in putridity; and so it may be, or it may
possibly be due to the direct action of putrid matter; but we
should be very cautious in drawing any such inference, when
we see that the skin on the head of the clean-feeding male
Turkey is likewise naked. The sutures in the skulls of young
mammals have been advanced as a beautiful adaptation for
aiding parturition, and no doubt they facilitate, or may be
indispensable for this act; but as sutures occur in the skulls
of young birds and reptiles, which have only to escape from
a broken egg, we may infer that this structure has arisen
from the laws of growth, and has been taken advantage of in
the parturition of the higher animals.
We are profoundly ignorant of the cause of each slight
variation or individual difference ; and we are immediately
made conscious of this by reflecting on the differences be-
tween the breeds of our domesticated animals in different
countries, — more especially in the less civilised countries
where there has been but little methodical selection. Animals
kept by savages in different countries often have to struggle
for their own subsistence, and are exposed to a certain extent
to natural selection, and individuals with slightly different
UTILITARIAN DOCTRINE 209
constitutions would succeed best under different climates.
With cattle susceptibility to the attacks of flies is correlated
with colour, as is the liability to be poisoned by certain
plants; so that even colour would be thus subjected to the
action of natural selection. Some observers are convinced
that a damp climate affects the growth of the hair, and that
with the hair the horns are correlated. Mountain breeds al-
ways differ from lowland breeds ; and a mountainous country
would probably affect the hind limbs from exercising them
more, and possibly even the form of the pelvis; and then
by the law of homologous variation, the front limbs and the
head would probably be affected. The shape, also, of the
pelvis might affect by pressure the shape of certain parts of
the young in the womb. The laborious breathing necessary
in high regions tends, as we have good reason to believe,
to increase the size of the chest; and again correlation
would come into play. The effects of lessened exercise to-
gether with abundant food on the whole organisation is
probably still more important; and this, as H. von Nathusius
has lately shown in his excellent Treatise, is apparently one
chief cause of the great modification which the breed of
swine have undergone. But we are far too ignorant to specu-
late on the relative importance of the several known and un-
known causes of variation; and I have made these remarks
only to show that, if we are unable to account for the char-
acteristic differences of our several domestic breeds, which
nevertheless are generally admitted to have arisen through
ordinary generation from one or a few parent-stocks, we
ought not to lay too much stress on our ignorance of the pre-
cise cause of the slight analogous differences between true
species.
UTILITARIAN DOCTRINE, HOW FAR TRUE! BEAUTY HOW
ACQUIRED
The foregoing remarks lead me to say a few words on the
protest lately made by some naturalists, against the utilitarian
doctrine that every detail of structure has been produced for
the good of its possessor. They believe that many structures
have been created for the sake of beauty, to delight man or
210 ORIGIN OF SPECIES
the Creator (but this latter point is beyond the scope of
scientific discussion), or for the sake of mere variety, a view
already discussed. Such doctrines, if true, would be abso-
lutely fatal to my theory. I fully admit that many structures
are now of no direct use to their possessors, and may never
have been of any use to their progenitors; but this does not
prove that they were formed solely for beauty or variety.
No doubt the definite action of changed conditions, and the
various causes of modifications, lately specified, have all
produced an effect, probably a great effect, independently of
any advantage thus gained. But a still more important con-
sideration is that the chief part of the organisation of every
living creature is due to inheritance; and consequently,
though each being assuredly is well fitted for its place in
nature, many structures have now no very close and direct
relation to present habits of life. Thus, we can hardly be-
lieve that the webbed feet of the upland goose or of the
frigate-bird are of special use to these birds; we cannot be-
lieve that the similar bones in the arm of the monkey, in the
fore-leg of the horse, in the wing of the bat, and in the
flipper of the seal, are of special use to these animals. We
may safely attribute these structures to inheritance. Bwt
webbed feet no doubt were as useful to the progenitor of
the upland goose and of the frigate-bird, as they now are to
the most aquatic of living birds. So we may believe that the
progenitor of the seal did not possess a flipper, but a foot
with five toes fitted for walking or grasping; and we may
further venture to believe that the several bones in the limbs
of the monkey, horse, and bat, were originally developed,
on the principle of utility, probably through the reduction of
more numerous bones in the fin of some ancient fish-like
progenitor of the whole class. It is scarcely possible to de-
cide how much allowance ought to be made for such causes
of change, as the definite action of external conditions, so-
called spontaneous variations, and the complex laws of
growth ; but with these important exceptions, we may con-
clude that the structure of every living creature either now
is, or was formerly, of some direct or indirect use to its
possessor.
With respect to the belief that organic beings have been
UTILITARIAN DOCTRINE 211
created beautiful for the delight of man, — a belief which it
has been pronounced is subversive of my whole theory, — I
may first remark that the sense of beauty obviously depends
on the nature of the mind, irrespective of any real quality
in the admired object; and that the idea of what is beautiful,
is not innate or unalterable. We see this, for instance, in
the men of different races admiring an entirely different
standard of beauty in their women. If beautiful objects had
been created solely for man's gratification, it ought to be
shown that before man appeared, there was less beauty on
the face of the earth than since he came on the stage. Were
the beautiful volute and cone shells of the Eocene epoch, and
the gracefully sculptured ammonites of the Secondary period,
created that man might ages afterwards admire them in his
cabinet? Few objects are more beautiful than the minute
siliceous cases of the diatomaceae: were these created that
they might be examined and admired under the higher
powers of the microscope? The beauty in this latter case,
and in many others, is apparently wholly due to symmetry of
growth. Flowers rank amongst the most beautiful produc-
tions of nature ; but they have been rendered conspfcuous in
contact with the green leaves, and in consequence at the
same time beautiful, so that they may be easily observed by
insects. I have come to this conclusion from finding it an
invariable rule that when a flower is fertilised by the wind
it never has a gaily-coloured corolla. Several plants habitu-
ally produce two kinds of flowers ; one kind open and col-
oured so as to attract insects ; the other closed, not coloured,
destitute of nectar, and never visited by insects. Hence we
may conclude that, if insects had not been developed on the
face of the earth, our plants would not have been decked with
beautiful flowers, but would have produced only such poor
flowers as we see on our fir, oak, nut and ash trees, on
grasses, spinach, docks, and nettles, which are all fertilised
through the agency of the wind. A similar line of argument
holds good with fruits; that a ripe strawberry or cherry
is as pleasing to the eye as to the palate — that the gaily-
coloured fruit of the spindle-wood tree and the scarlet ber-
ries of the holly are beautiful objects, — will be admitted by
every one. But this beauty serves merely as a guide to birds
212 ORIGIN OF SPECIES
and beasts, in order that the fruit may be devotired and the
manured seeds disseminated: I infer that this is the case
from having as yet found no exception to the rule that seeds
are always thus disseminated when embedded within a fruit
of any kind (that is within a fleshy or pulpy envelope), if it
be coloured of any brilliant tint, or rendered conspicuous by
being white or black.
On the other hand, I willingly admit that a great number
of male animals, as all our most gorgeous birds, some fishes,
reptiles, and mammals, and a host of magnificently coloured
butterflies, have been rendered beautiful for beauty's sake;
but this has been effected through sexual selection, that is, by
the more beautiful males having been continually preferred
by the females, and not for the delight of man. So it is with
the music of birds. We may infer from all this that a nearly
similar taste for beautiful colours and for musical sounds
runs through a large part of the animal kingdom. When
the female is as beautifully coloured as the male, which is
not rarely the case with birds and butterflies, the cause ap-
parently lies in the colours acquired through sexual selection
having been transmitted to both sexes, instead of to the
males alone. How the sense of beauty in its simplest form —
that is, the reception of a peculiar kind of pleasure from
certain colours, forms, and sounds — was first developed in
the mind of man and of the lower animals, is a very obscure
subject. The same sort of difficulty is presented, if we en-
quire how it is that certain flavours and odours give pleasure,
and others displeasure. Habit in all these cases appears to
have come to a certain extent into play; but there must be
some fundamental cause in the constitution of the nervous
system in each species.
Natural selection cannot possibly produce any modifica-
tion in a species exclusively for the good of another species ;
though throughout nature one species incessantly takes ad-
vantage of, and profits by, the structures of others. But
natural selection can and does often produce structures for
the direct injury of other animals, as we see in the fang of
the adder, and in the ovipositor of the ichneumon, by which
its eggs are deposited in the living bodies of other insects.
If it could be proved that any part of the structure of any
UTILITARIAN DOCTRINE 213
one species had been formed for the exclusive good of an-
other species, it would annihilate my theory, for such could
not have been produced through natural selection. Although
many statements may be found in v^^orks on natural history
to this effect, I cannot find even one which seems to me of
any weight. It is admitted that the rattlesnake has a poison-
fang for its own defence, and for the destruction of its prey;
but some authors suppose that at the same time it is furnished
with a rattle for its own injury, namely, to warn its prey.
I would almost as soon believe that the cat curls the end
of its tail when preparing to spring, in order to warn the
doomed mouse. It is a much more probable view that the
rattlesnake uses its rattle, the cobra expands its frill, and
the puff-adder swells whilst hissing so loudly and harshly,
in order to alarm the many birds and beasts which are known
to attack even the most venomous species. Snakes act on the
same principle which makes the hen ruffle her feathers and
expand her wings when a dog approaches her chickens ; but
I have not space here to enlarge on the many ways by which
animals endeavour to frighten away their enemies.
Natural selection will never produce in a being any struc-
ture more injurious than beneficial to that being, for natural
selection acts solely by and for the good of each. 'No organ
will be formed, as Paley has remarked, for the purpose of
causing pain or for doing an injury to its possessor. If a fair
balance be struck between the good and evil caused by each
part, each will be found on the whole advantageous. After
the lapse of time, under changing conditions of life, if any
part comes to be injurious, it will be modified; or if it be not
so, the being will become extinct as myriads have become
extinct.
Natural selection tends only to make each organic being
as perfect as, or slightly more perfect than, the other inhabi-
tants of the same country with which it comes into competi-
tion. And we see that this is the standard of perfection
attained under nature. The endemic productions of New Zea-
land, for instance, are perfect one compared with another;
but they are now rapidly yielding before the advancing le-
gions of plants and animals introduced from Europe. Natural
selection will not produce absolute perfection, nor do we
214 ORIGIN OF SPECIES
always meet, as far as we can judge, with this high standard
under nature. The correction for the aberration of Hght
is said by Mtiller not to be perfect even in that most perfect
organ, the human eye. Helmholtz, whose judgment no one
will dispute, after describing in the strongest terms the won-
derful power of the human eye, adds these remarkable
words: "That which we have discovered in the way of in-
exactness and imperfection in the optical machine and in
the image on the retina, is as nothing in comparison with
the incongruities which we have just come across in the
domain of the sensations. One might say that nature has
taken delight in accumulating contradictions in order to re-
move all foundations from the theory of a pre-existing har-
mony between the external and internal worlds." If our
reason leads us to admire with enthusiasm a multitude of
inimitable contrivances in nature, this same reason tells us,
though we may easily err on both sides, that some other con-
trivances are less perfect. Can we consider the sting of the
bee as perfect, which, when used against many kinds of
enemies, cannot be withdrawn, owing to the backward serra-
tures, and thus inevitably causes the death of the insect by
tearing out its viscera?
If we look at the sting of the bee, as having existed in a
remote progenitor, as a boring and serrated instrument, like
that in so many members of the same great order, and that
it has since been modified, but not perfected for its present
purpose, with the poison originally adapted for some other
object, such as to produce galls, since intensified, we can per-
haps understand how it is that the use of the sting should so
often cause the insect's own death: for if on the whole the
power of stinging be useful to the social community, it will
fulfil all the requirements of natural selection, though it
may cause the death of some few members. If we admire
the truly wonderful power of scent by which the males of
many insects find their females, can we admire the produc-
tion for this single purpose of thousands of drones, which
are utterly useless to the community for any other purpose,
and which are ultimately slaughtered by their industrious and
sterile sisters? It may be difficult, but we ought to admire
the savage instinctive hatred of the queen-bee, which urges
SUMMARY 215
her to destroy the young queens, her daughters, as soon as
they are born, or to perish herself in the combat; for un-
doubtedly this is for the good of the community ; and mater-
nal love or maternal hatred, though the latter fortunately is
most rare, is all the same to the inexorable principle of
natural selection. If we admire the several ingenious contri-
vances, by which orchids and many other plants are fertilised
through insect agency, can we consider as equally perfect
the elaboration of dense clouds of pollen by our fir-trees, so
that a few granules may be wafted by chance on to the ovules ?
summary: the law of unity of type and of the
conditions of existence embraced by the
theory of natural selection
We have in this chapter discussed some of the difficulties
and objections which may be urged against the theory.
Many of them are serious ; but I think that in the discussion
light has been thrown on several facts, which on the belief
of independent acts of creation are utterly obscure. We have
seen that species at any one period are not indefinitely vari-
able, and are not linked together by a multitude of interme-
diate gradations, partly because the process of natural selec-
tion is always very slow, and at any one time acts only on a
few forms; and partly because the very process of natural
selection implies the continual supplanting and extinction
of preceding and intermediate gradations. Closely allied
species, now living on a continuous area, must often have
been formed when the area was not continuous, and when the
conditions of life did not insensibly graduate away from one
part to another. When two varieties are formed in two dis-
tricts of a continuous area, an intermediate variety will often
be formed, fitted for an intermediate zone; but from
reasons assigned, the intermediate variety will usuallv exist
in lesser numbers than the two forms which it connects ; con-
sequently the two latter, during the course of further modi-
fication, from existing in greater numbers, will have a great
advantage over the less numerous intermediate variety, and
will thus generally succeed in supplanting and extermi-
nating it.
216 ORIGIN OF SPECIES
We have seen in this chapter how cautious we should be
in concluding that the most different habits of life could not
graduate into each other; that a bat, for instance, could not
have been formed by natural selection from an animal which
at first only glided through the air.
We have seen that a species under new conditions of life
may change its habits ; or it may have diversified habits, with
some very unlike those of its nearest congeners. Hence we
can understand, bearing in mind that each organic being is
trying to live wherever it can live, how it has arisen that
there are upland geese with webbed feet, ground woodpeck-
ers, diving thrushes, and petrels with the habits of auks.
Although the belief that an organ so perfect as the eye
could have been formed by natural selection, is enough to
stagger any one ; yet in the case of any organ, if we know of
a long series of gradations in complexity, each good for its
possessor, then, under changing conditions of life, there is
no logical impossibility in the acquirement of any conceivable
degree of perfection through natural selection. In the cases
in which we know of no intermediate or transitional states,
we should be extremely cautious in concluding that none can
have existed, for the metamorphoses of many organs show
what wonderful changes in function are at least possible.
For instance, a swimbladder has apparently been converted
into an air-breathing lung. The same organ having per-
formed simultaneously very different functions, and then
having been in part or in whole specialised for one function ;
and two distinct organs having performed at the same time
the same function, the one having been perfected whilst aided
by the other, must often have largely facilitated transitions.
We have seen that in two beings widely remote from each
other in the natural scale, organs serving for the same pur-
pose and in external appearance closely similar may have
been separately and independently formed; but when svi^h
organs are closely examined, essential differences in their
structure can almost always be detected; and this naturally
follows from the principle of natural selection. On the
other hand, the common rule throughout nature is infinite
diversity of structure for gaining the same end; and this
again naturally follows from the same great principle.
SUMMARY 217
In many cases we are far too ignorant to be enabled to
assert that a part or organ is so unimportant for the welfare
of a species, that modifications in its structure could not
have been slowly accumulated by means of natural selection.
In many other cases, modifications are probably the direct
result of the laws of variation or of growth, independently
of any good having been thus gained. But even such struc-
tures have often, as we may feel assured, been subsequently
taken advantage of, and still further modified, for the good
of species under new conditions of life. We may, also, be-
lieve that a part formerly of high importance has frequently
been retained (as the tail of an aquatic animal by its terres-
trial descendants), though it has become of such small im-
portance that it could not, in its present state, have been
acquired by means of natural selection.
Natural selection can produce nothing in one species for
the exclusive good or injury of another; though it may well
produce parts, organs, and excretions highly useful or even
indispensable, or again highly injurious to another species,
but in all cases at the same time useful to the possessor. In
each well-stocked country natural selection acts through the
competition of the inhabitants, and consequently leads to suc-
cess in the battle for life, only in accordance with the
standard of that particular country. Hence the inhabitants
of one country, generally the smaller one, often yield to the
inhabitants of another and generally the larger country.
For in the larger country there will have existed more indi-
viduals and more diversified forms, and the competition will
have been severer, and thus the standard of perfection will
have been rendered higher. Natural selection will not neces-
sarily lead to absolute perfection ; nor, as far as we can judge
by our limited faculties, can absolute perfection be every-
where predicated.
On the theory of natural selection we can clearly under-
stand the full meaning of that old canon in natural history,
"Natura non facit saltum." This canon, if we look to the
present inhabitants alone of the world, is not strictly cor-
rect; but if we include all thjose of past times, whether known
or unknown, it must on this theory be strictly true.
It is generally acknowJedged that all organic beings have
218 ORIGIN OF SPECIES
been formed on two great laws — Unity of Type, and the
Conditions of Existence. By unity of type is meant that
fundamental agreement in structure which we see in organic
beings of the same class, and which is quite independent of
their habits of life. On my theory, unity of type is explained
by unity of descent. The expression of conditions of exist-
ence, so often insisted on by the illustrious Cuvier, is fully
embraced by the principle of natural selection. For natural
selection acts by either now adapting the varying parts of
each being to its organic and inorganic conditions of life;
or by having adapted them during past periods of time: the
adaptations being aided in many cases by the increased use
or disuse of parts, being affected by the direct action of the
external conditions of life, and subjected in all cases to the
several laws of growth and variation. Hence, in fact, the
law of the Conditions of Existence is the higher law; as it
includes, through the inheritance of former variations and
adaptations, that of Unity of Type.
CHAPTER VII
Miscellaneous Objections to the Theory of Natural
Selection
Longevity — Modifications not necessarily simultaneous — Modifications
apparently of no direct service — Progressive development —
Characters of small functional importance, the most constant —
Supposed incompetence of natural selection to account for the
incipient stages of useful structures — Causes which interfere with
the acquisition through natural selection of useful structures —
Gradations of structure with changed functions — Widely different
organs in members of the same class, developed from one and
the same source — Reasons for disbelieving in great and abrupt
modifications.
I WILL devote this chapter to the consideration of various
niis,cellaneous objections which have been advanced
against my views, as some of the previous discus-
sions may thus be made clearer; but it would be useless
to discuss all of them, as many have been made by writers
who have not taken the trouble to understand the subject.
Thus a distinguished German naturalist has asserted that
the weakest part of my theory is, that I consider all organic
beings as imperfect : what I have really said is, that all are
not as perfect as they might have been in relation to their
conditions ; and this is shown to be the case by so many
native forms in many quarters of the world having yielded
their places to intruding foreigners. Nor can organic beings,
even if they were at any one time perfectly adapted to their
conditions of life, have remained so, when their conditions
changed, unless they themselves likewise changed ; and no
one will dispute that the physical conditions of each country,
as well as the numbers and kinds of its inhabitants, have
undergone many mutations.
A critic has lately insisted, with some parade of mathe-
matical accuracy, that longevity is a great advantage to all
species, so that he who believes in natural selection "must
219
220 ORIGIN OF SPECIES
arrange his genealogical tree" in such a manner that all the
descendants have longer lives than their progenitors ! Can-
not our critic conceive that a biennial plant or one of the
lower animals might range into a cold climate and perish
there every winter ; and yet, owing to advantages gained
through natural selection, survive from year to year, by
means of its seeds or ova? Mr. E. Ray Lankester has re-
cently discussed this subject, and he concludes, as far as its
extreme complexity allows him to form a judgment, that
longevity is generally related to the standard of each species
in the scale of organisation, as well as to the amount of ex-
penditure in reproduction and in general activity. And these
conditions have, it is probable, been largely determined
through natural selection.
It has been argued that, as none of the animals and plants
of Egypt, of which we know anything, have changed during
the last three or four thousand years, so probably have none
in any part of the world. But, as Mr. G. H. Lewes has re-
marked, this line of argument proves too much, for the
ancient domestic races figured on the Egyptian monuments,
or embalmed, are closely similar or even identical with those
now living; yet all naturalists admit that such races have
been produced through the modification of their original
types. The many animals which have remained unchanged
since the commencement of the glacial period, would have
been an incomparably stronger case, for these have been
exposed to great changes of climate and have migrated over
great distances; whereas, in Egypt, during the last several
thousand years, the conditions of life, as far as we know, have
remained absolutely uniform. The fact of little or no modifi-
cation having been effected since the glacial period would have
been of some avail against those who believe in an innate and
necessary law of development, but is powerless against the
doctrine of natural selection or the survival of the fittest,
which implies that when variations or individual differences
of a beneficial nature happen to arise, these will be preserved;
but this will be effected only under certain favourable cir-
cumstances.
The celebrated palseontologist, Bronn, at the close of his
German translation of this work, asks, how, on the principle
THEORY OF NATURAL SELECTION 221
of natural selection, can a variety live side by side with the
parent species? If both have become fitted for slightly dif-
ferent habits of life or conditions, they might live together;
and if we lay on one side polymorphic species, in which the
variability seems to be of a peculiar nature, and all mere
temporary variations, such as size, albinism, &c., the more
permanent varieties are generally found, as far as I can
discover, inhabiting distinct stations, — such as high land or
low land, dry or moist districts. Moreover, in the case of
animals which wander much about and cross freely, their
varieties seem to be generally confined to distinct regions.
Bronn also insists that distinct species never differ from
each other in single characters, but in many parts ; and he
asks, how it always comes that many parts of the organisa-
tion should have been modified at the same time through
variation and natural selection? But there is no necessity
for supposing that all the parts of any being have been
simultaneously modified. The most striking modifications,
excellently adapted for some purpose, might, as was formerly
remarked, be acquired by successive variations, if slight,
first in one part and then in another ; and as they would be
transmitted all together, they would appear to us as if they
had been simultaneously developed. The best answer, how-
ever, to the above objection is afforded by those domestic
races which have been modified, chiefly through man's power
of selection, for some special purpose. Look at the race
and dray horse, or at the grey-hound and mastiff. Their
whole frames and even their mental characteristics have been
modified ; but if we could trace each step in the history of
their transformation, — and the latter steps can be traced, —
we should not see great and simultaneous changes, but first
one part and then another slightly modified and improved.
Even when selection has been applied by man to some one
character alone, — of which our cultivated plants offer the
best instances, — it will invariably be found that although
this one part, whether it be the flower, fruit, or leaves, has
been greatly changed, almost all the other parts have been
slightly modified. This may. be attributed partly to the prin-
ciple of correlated growth, and partly to so-called spon-
taneous variation.
222 ORIGIN OF SPECIES
A much more serious objection has been urged by Bronn,
and recently by Broca, namely, that many characters appear
to be of no service whatever to their possessors, and therefore
cannot have been influenced through natural selection.
Bronn adduces the length of the ears and tails in the dif-
ferent species of hares and mice, — the complex folds of
enamel in the teeth of many animals, and a multitude of
analogous cases. With respect to plants, this subject has
been discussed by Nageli in an admirable essay. He admits
that natural selection has effected much, but he insists that
the families of plants differ chiefly from each other in mor-
phological characters, which appear to be quite unimportant
for the welfare of the species. He consequently believes in
an innate tendency towards progressive and more perfect
development. He specifies the arrangement of the cells in
the tissues, and of the leaves on the axis, as cases in which
natural selection could not have acted. To these may be
added the numerical divisions in the parts of the flower, the
position of the ovules, the shape of the seed, when not of any
use for dissemination, &c.
There is much force in the above objection. Nevertheless,
we ought, in the first place, to be extremely cautious in
pretending to decide what structures now are, or have for-
merly been, of use to each species. In the second place, it
should always be borne in mind that when one part is modi-
fied, so will be other parts, through certain dimly seen causes,
such as an increased or diminished flow of nutriment to a
part, mutual pressure, an early developed part affecting one
subsequently developed, and so forth, — as well as through
other causes which lead to the many mysterious cases of
correlation, which we do not in the least understand. These
agencies may be all grouped together, for the sake of brevity,
under the expression of the laws of growth. In the third
place, we have to allow for the direct and definite action of
changed conditions of life, and for so-called spontaneous
variations, in which the nature of the conditions apparently
plays a quite subordinate part. Bud-variations, such as the
appearance of a moss-rose on a common rose, or of a nec-
tarine on a peach-tree, offer good instances of spontaneous
variations; but even in these cases, if we bear in mind the
THEORY OF NATURAL SELECTION 223
power of a minute drop of poison in producing complex galls,
we ought not to feel too sure that the above variations are
not the effect of some local change in the nature of the sap,
due to some change in the conditions. There must be some
efficient cause for each slight individual difference, as well
as for more strongly marked variations which occasionally
arise ; and if the unknown cause were to act persistently, it
is almost certain that all the individuals of the species would
be similarly modified.
In the earlier editions of this work I under-rated, as it now
seems probable, the frequency and importance of modifica-
tions due to spontaneous variability. But it is impossible to
attribute to this cause the innumerable structures which are
so well adapted to the habits of life of each species. I can
no more believe in this, than that the well-adapted form of a
race-horse or greyhound, which before the principle of selec-
tion by man was well understood, excited so much surprise in
the minds of the older naturalists, can thus be explained.
It may be worth while to illustrate some of the foregoing
remarks. With respect to the assumed inutility of various
parts and organs, it is hardly necessary to observe that even
in the higher and best-known animals many structures exist,
which are so highly developed that no one doubts that they
are of importance, yet their use has not been, or has only
recently been, ascertained. As Bronn gives the length of
the ears and tail in the several species of mice as instances,
though trifling ones, of differences in structure which can
be of no special use, I may mention that, according to Dr.
Schobl, the external ears of the common mouse are supplied
in an extraordinary manner with nerves, so that they no
doubt serve as tactile organs ; hence the length of the ears
can hardly be quite unimportant. We shall, also, presently
see that the tail is a highly useful prehensile organ to some
of the species ; and its use would be much influenced by its
length.
With respect to plants, to which on account of Nageli's
essay I shall confine myself in the following remarks, it will
be admitted that the flowers of orchids present a multitude of
curious structures, which a few years ago would have been
considered as mere morphological differences without any
224 ORIGIN OF SPECIES
special function ; but they are now known to be of the highest
importance for the fertihsation of the species through the
aid of insects, and have probably been gained through natural
selection. No one until lately would have imagined that in
dimorphic and trimorphic plants the different lengths of the
stamens and pistils, and their arrangement, could have been
of any service, but now we know this to be the case.
In certain whole groups of plants the ovules stand erect,
and in others they are suspended; and within the same
ovarium of some few plants, one ovule holds the former and
a second ovule the latter position. These positions seem at
first purely morphological, or of no physiological significa-
tion; but Dr. Hooker informs me that within the same
ovarium, the upper ovules alone in some cases, and in other
cases the lower ones alone are fertilised ; and he suggests that
this probably depends on the direction in which the pollen-
tubes enter the ovarium. If so, the position of the ovules,
even when one is erect and the other suspended within the
same ovarium, would follow from the selection of any slight
deviations in position which favoured their fertilisation, and
the production of seed.
Several plants belonging to distinct orders habitually pro-
duce flowers of two kinds, — the one open of the ordinary
structure, the other closed and imperfect. These two kinds
of flowers sometimes differ wonderfully in structure, yet may
be seen to graduate into each other on the same plant. The
ordinary and open flowers can be intercrossed; and the bene-
fits which certainly are derived from this process are thus
secured. The closed and imperfect flowers are, however,
manifestly of high importance, as they yield with the utmost
safety a large stock of seed, with the expenditure of won-
derfully little pollen. The two kinds of flowers often differ
much, as just stated, in structure. The petals in the imperfect
flowers almost always consist of mere rudiments, and the
pollen-grains are reduced in diameter. In Ononis columnae
five of the alternate stamens are rudimentary ; and in some
species of Viola three stamens are in this state, two retaining
their proper function, but being of very small size. In six
out of thirty of the closed flowers in an Indian violet (name
unknown, for the plants have never produced with me per-
THEORY OF NATURAL SELECTION 225
feet flowers), the sepals are reduced from the normal num-
ber of five to three. In one section of the Malpighiacese the
closed flowers, according to A. de Jussieu, are still further
modified, for the five stamens which stand opposite to the
sepals are all aborted, a sixth stamen standing opposite to
a petal being alone developed ; and this stamen is not present
in the ordinary flowers of these species; the style is aborted;
and the ovaria are reduced from three to two. Now although
natural selection may well have had the power to prevent
some of the flowers from expanding, and to reduce the amount
of pollen, when rendered by the closure of the flowers super-
fluous, yet hardly any of the above special modifications can
have been thus determined, but must have followed from
the laws of growth, including the functional inactivity of
parts, during the progress of the reduction of the pollen and
the closure of the flowers.
It is so necessary to appreciate the important effects of
the laws of growth, that I will give some additional cases of
another kind, namely of differences in the same part or organ,
due to differences in relative position on the same plant.
In the Spanish chestnut, and in certain fir-trees, the angles of
divergence of the leaves differ, according to Schacht, in
the nearly horizontal and in the upright branches. In the
common rue and some other plants, one flower, usually the
central or terminal one, opens first, and has five sepals and
petals, and five divisions to the ovarium ; whilst all the other
flowers on the plant are tetramerous. In the British Adoxa
the uppermost flower generally has two calyx-lobes with the
other organs tetramerous, whilst the surrounding flowers
generally have three calyx-lobes with the other organs pen-
tamerous. In many Compositae and Umbelliferae (and in
some other plants) the circumferential flowers have their
corollas much more developed than those of the centre ;
and this seems often connected with the abortion of the re-
productive organs. It is a more curious fact, previously
referred to, that the achenes or seeds of the circumference
and centre sometimes differ greatly in form, colour, and
other characters. In Carthamus and some other Compositae
the central achenes alone are furnished with a pappus ; and
in Hyoseris the same head yields achenes of three different
H — HC XI
226 ORIGIN OF SPECIES
forms. In certain Umbelliferae the exterior seeds, according
to Tausch, are orthospermous, and the central one ccelosper-
mous, and this is a character which was considered by De
Candolle to be in other species of the highest systematic im-
portance. Prof. Braun mentions a Fumariaceous genus in
which the flowers in the lower part of the spike bear oval,
ribbed, one-seeded nutlets ; and in the upper part of the spike,
lanceolate, two-valved, and two-seeded siliques. In these
several cases, with the exception of that of the well developed
ray-florets, which are of service in making the flowers con-
spicuous to insects, natural selection cannot, as far as we can
judge, have come into play, or only in a quite subordinate
manner. All these modifications follow from the relative
position and inter-action of the parts ; and it can hardly be
doubted that if all the flowers and leaves on the same plant
had been subjected to the same external and internal con-
dition, as are the flowers and leaves in certain positions, all
would have been modified in the same manner.
In numerous other cases we find modifications of structure,
which are considered by botanists to be generally of a highly
important nature, affecting only some of the flowers on the
same plant, or occurring on distinct plants, which grow close
together under the same conditions. As these variations
seem of no special use to the plants, they cannot have been
influenced by natural selection. Of their cause we are quite
ignorant; we cannot even attribute them, as in the last class
of cases, to any proximate agency, such as relative position.
I will give only a few instances. It is so common to observe
on the same plant, flowers indifferently tetramerous, pentam-
erous, &c., that I need not give examples ; but as numerical
variations are comparatively rare when the parts are few, I
may mention that, according to De Candolle, the flowers of
Papaver bracteatum offer either two sepals with four petals
(which is the common type Avith poppies), or three sepals
with six petals. The manner in which the petals are folded
in the bud is in most groups a very constant morphological
character ; but Professor Asa Gray states that with some
species of Mimulus. the aestivation is almost as frequently
that of the Rhinanthidese as of the Antirrhinidese, to which
latter tribe the genus belongs. Aug. St. Hilaire gives the
THEORY OF NATURAL SELECTION 227
following cases : the genus Zanthoxylon belongs to a division
of the Rutaceae with a single ovary, but in some species
flowers may be found on the same plant, and even in the
same panicle, with either one or two ovaries. In Helian-
themum the capsule has been described as unilocular or
3-locular; and in H. mutabile, "Une lame, plus ou moins
large, s'etend entre le pericarpe et le placenta." In the
flowers of Saponaria officinalis. Dr. Masters has observed
instances of both marginal and free central placentation.
Lastly, St. Hilaire found towards the southern extreme of
the range of Gomphia oleaeformis two forms which he did
not at first doubt were distinct species, but he subsequently
saw them growing on the same bush ; and he then adds,
"Voila done dans un meme individu des loges et un style qui
se rattachent tantot a un axe verticale et tantot a un
gynobase."
We thus see that with plants many morphological changes
may be attributed to the laws of growth and the inter-action
of parts, independently of natural selection. But with re-
spect to Nageli's doctrine of an innate tendency towards
perfection or progressive development, can it be said in the
case of these strongly pronounced variations, that the plants
have been caught in the act of progressing towards a higher
state of development? On the contrary, I should infer from
the mere fact of the parts in question differing or varying
greatly on the same plant, that such modifications were of
extremely small importance to the plants themselves, of
whatever importance they may generally be to us for our clas-
sifications. The acquisition of a useless part can hardly be said
to raise an organism in the natural scale ; and in the case of the
imperfect, closed flowers above described, if any new principle
has to be invoked, it must be one of retrogression rather than
of progression; and so it must be with many parasitic and
degraded animals. We are ignorant of the exciting cause of
the above specified modifications; but if the unknown cause
were to act almost uniformly for a length of time, we may
infer that the result would be almost uniform; and in this
case all the individuals of the species would be modified in
the same manner.
From the fact of the above characters being unimportant
228 ORIGIN OF SPECIES
for the welfare of the species, any slight variations which oc-
curred in them would not have been accumulated and aug-
mented through natural selection. A structure which has been
developed through long-continued selection, when it ceases to
be of service to a species, generally becomes variable, as we
see with rudimentary organs ; for it will no longer be regu-
lated by this same power of selection. But when, from the
nature of the organism and of the conditions, modifications
have been induced which are unimportant for the welfare of
the species, they may be, and apparently often have been,
transmitted in nearly the same state to numerous, otherwise
modified, descendants. It cannot have been of much impor-
tance to the greater number of mammals, birds, or reptiles,
whether they were clothed with hair, feathers, or scales ; yet
hair has been transmitted to almost all mammals, feathers
to all birds, and scales to all true reptiles. A structure, what-
ever it may be, which is common to many allied forms, is
ranked by us as of high systematic importance, and conse-
quently is often assumed to be of high vital importance to the
species. Thus, as I am inclined to believe, morphological
dififerences, which we consider as important — such as the ar-
rangement of the leaves, the divisions of the flower or of the
ovarium, the position of the ovules, &c. — first appeared in
many cases as fluctuating variations, which sooner or later
became constant through the nature of the organism and of
the surrounding conditions, as well as through the inter-
crossing of distinct individuals, but not through natural selec-
tion; for as these morphological characters do not affect the
welfare of the species, any slight deviations in them could
not have been governed or accumulated through this latter
agency. It is a strange result which we thus arrive at,
namely that characters of slight vital importance to the spe-
cies, are the most important to the systematist; but, as we
shall hereafter see when we treat of the genetic principle of
classification, this is by no means so paradoxical as it may
at first appear.
Although we have no good evidence of the existence in
organic beings of an innate tendency towards progressive
development, yet this necessarily follows, as I have attempted
to show in the fourth chapter, through the continued action
THEORY OF NATURAL SELECTION 229
of natural selection. For the best definition which has ever
been given of a high standard of organisation is the degree
to which the parts have been specialised or differentiated;
and natural selection tends towards this end, inasmuch as
the parts are thus enabled to perform their functions more
efficiently.
A distinguished zoologist, Mr. St. George Mivart, has
recently collected all the objections which have ever been
advanced by myself and others against the theory of natural
selection, as propounded by Mr. Wallace and myself, and has
illustrated them with admirable art and force. When thus
marshalled, they make a formidable array; and as it forms
no part of Mr. Mivart's plan to give the various facts and
considerations opposed to his conclusions, no slight effort
of reason and memory is left to the reader, who may wish
to weigh the evidence on both sides. When discussing special
cases, Mr. Mivart passes over the effects of the increased
use and disuse of parts, which I have always maintained to
be highly important, and have treated in my 'Variation under
Domestication' at greater length than, as I believe, any other
writer. He likewise often assumes that I attribute nothing
to variation, independently of natural selection, whereas in
the work just referred to I have collected a greater number ot
well-established cases than can be found in any other work
known to me. My judgment may not be trustworthy, but
after reading with care Mr. Mivart's book, and comparing
each section with what I have said on the same head, I never
before felt so strongly convinced of the general truth of the
conclusions here arrived at, subject, of course, in so intricate
a subject, to much partial error.
All Mr. Mivart's objections will be, or have been, con-
sidered in the present volume. The one new point which
appears to have struck many readers is, "that natural selec-
tion is incompetent to account for the incipient stages of
useful structures." This subject is intimately connected with
that of the gradation of characters, often accompanied by
a change of function, — for instance, the conversion of a
swim-bladder into lungs, — points which were discussed in the
last chapter under two headings. Nevertheless, I will her©
230 ORIGIN OF SPECIES
consider in some detail several of the cases advanced by Mr.
Mivart, selecting those which are the most illustrative, as
want of space prevents me from considering all.
The giraffe, by its lofty stature^ much elongated neck,
fore legs, head and tongue, has its whole frame beautifully
adapted for browsing on the higher branches of trees. It can
thus obtain food beyond the reach of the other Ungulata or
hoofed animals inhabiting the same country; and this must
be a great advantage to it during dearths. The Niata cattle
in S. America show us how small a difference in structure
may make, during such periods, a great difference in preserv-
ing an animal's life. These cattle can browse as well as
others on grass, but from the projection of the lower jaw
they cannot, during the often recurrent droughts, browse on
the twigs of trees, reeds, &c., to which food the common
cattle and horses are then driven ; so that at these times the
Niatas perish, if not fed by their owners. Before coming
to Mr. Mivart's objections, it may be well to explain once
agam how natural selection will act in all ordinary cases.
Man has modified some of his animals, without necessarily
having attended to special points of structure, by simply pre-
serving and breeding from the fleetest individuals, as with
the race-horse and greyhound, or as with the game-cock, by
breeding from the victorious birds. So under nature with
the nascent giraffe, the individuals which were the highest
browsers and were able during dearths to reach even an inch
or two above the others, will often have been preserved;
for they will have roamed over the whole country in search
of food. That the individuals of the same species often
differ slightly in the relative lengths of all their parts may
be seen in many works of natural history, in which careful
measurements are given. These slight proportional differ-
ences, due to the laws of growth and variation, are not of the
slightest use or importance to most species. But it will have
been otherwise with the nascent giraffe, considering its prob-
able habits of life; for those individuals which had some one
part or several parts of their bodies rather more elongated
than usual, would generally have survived. These will have
intercrossed and left offspring, either inheriting the same
bodily peculiarities, or with a tendency to vary again in the
THEORY OF NATURAL SELECTION 231
same manner; whilst the individuals, less favoured in the
same respects, will have been, the most liable to perish.
We here see that there is no need to separate single pairs,
as man does, when he methodically improves a breed ; natural
selection will preserve and thus separate all the superior
individuals, allowing them freely to intercross, and will de-
stroy all the inferior individuals. By this process long-
continued, which exactly corresponds with what I have called
unconscious selection by man, combined no doubt in a most
important manner with the inherited effects of the increased
use of parts, it seems to me almost certain that an ordinary
hoofed quadruped might be converted into a giraffe.
To this conclusion Mr. Mivart brings forward two objec-
tions. One is that the increased size of the body would
obviously require an increased supply of food, and he con-
siders it as "very problematical whether the disadvantages
thence arising would not, in times of scarcity, more than
counterbalance the advantages." But as the giraffe does
actually exist in large numbers in S. Africa, and as some of
the largest antelopes in the world, taller than an ox, abound
there, why should we doubt that, as far as size is concerned,
intermediate gradations could formerly have existed there,
subjected as now to severe dearths? Assuredly the being
able to reach, at each stage of increased size, to a supply of
food, left untouched by the other hoofed quadrupeds of the
country, would have been of some advantage to the nascent
giraffe. Nor must we overlooV; the fact, that increased bulk
would act as a protection against almost all beasts of prey
excepting the lion; and against this animal, its tall neck, —
and the taller the better, — would, as Mr. Chauncey Wright
has remarked, serve as a watch-tower. It is from this cause,
as Sir S Baker remarks, that no animal is more difficult to
stalk than the giraffe. This animal also uses its long neck
as a means of offence or defence, by violently swinging its
head armed with stump-like horns. The preservation of
each species can rarely be determined by any one advantage
but by the union of all, great and small.
Mr. Mivart then asks (and this is his second objection),
if natural selection be so potent, and if high browsing be so
great an advantage, why has not any other hoofed quadruped
232 ORIGIN OF SPECIES
acquired a long neck and lofty stature, besides the giraffe,
and, in lesser degree, the camel, guanaco, and macrauchenia ?
Or, again, why has not any member of the group acquired a
long proboscis? With respect to S. Africa, which was for-
merly inhabited by numerous herds of the giraffe, the answer
is not difficult, and can best be given by an illustration. In
every meadow in England in which trees grow, we see the
lower branches trimmed or planed to an exact level by the
browsing of the horses or cattle ; and what advantage would
it be, for instance, to sheep, if kept there, to acquire slightly
longer necks? In every district some one kind of animal
will almost certainly be able to browse higher than the
others; and it is almost equally certain that this one kind
alone could have its neck elongated for this purpose, through
natural selection and the effects of increased use. In S.
Africa the competition for browsing on the higher branches
of the acacias and other trees must be between giraffe and
giraffe, and not with the other ungulate animals.
Why, in other quarters of the world, various animals be-
longing to this same order have not acquired either an
elongated neck or a proboscis, cannot be distinctly answered;
but it is as unreasonable to expect a distinct answer to such
a question, as why some event in the history of mankind did
not occur in one country, whilst it did in another. We are
ignorant with respect to the conditions which determine the
numbers and range of each species ; and we cannot even con-
jecture what changes of structure would be favourable to
its increase in some new country. We can, however, see in a
general manner that various causes might have interfered
with the development of a long neck or proboscis. To reach
the foliage of a considerable height (without climbing, for
which hoofed animals are singularly ill-constructed) implies
greatly increased bulk of body ; and we know that some areas
support singularly few large quadrupeds, for instance S.
America, though it is so luxuriant ; whilst S. Africa abounds
with them to an unparalleled degree. Why this should be
so, we do not know ; nor why the later tertiary periods should
have been much more favourable for their existence than the
present time. Whatever the causes may have been, we can
see that certain districts and times would have been much
THEORY OF NATURAL SELECTION 233
more favourable than others for the development of so large
a quadruped as the giraffe.
In order that an animal should acquire some structure
specially and largely developed, it is almost indispensable
that several other parts should be modified and co-adapted.
Although every part of the body varies slightly, it does not
follow that the necessary parts should always vary in the
right direction and to the right degree. With the different
species of our domesticated animals we know that the parts
vary in a dift'erent manner and degree ; and that some species
are much more variable than others. Even if the fitting vari-
ations did arise, it does not follow that natural selection
would be able to act on them, and produce a structure which
apparently would be beneficial to the species. For instance,
if the number of individuals existing in a country is deter-
mined chiefly through destruction by beasts of prey, — by ex-
ternal or internal parasites, etc., — as seems often to be the
case, then natural selection will be able to do little, or will be
greatly retarded, in modifying any particular structure for ob-
taining food. Lastly, natural selection is a slow process, and
the same favourable conditions must long endure in order
that any marked effect should thus be produced. Except by
assigning such general and vague reasons, we cannot explain
why, in many quarters of the world, hoofed quadrupeds have
not acquired much elongated necks or other means for brows-
ing on the higher branches of trees.
Objections of the same nature as the foregoing have been
advanced by many writers. In each case various causes, be-
sides the general ones just indicated, have probably inter-
fered with the acquisition through natural selection of struc-
tures, which it is thought would be beneficial to certain
species. One writer asks, why has not the ostrich acquired
the power of flight? But a moment's reflection will show
what an enormous supply of food would be necessary to give
to this bird of the desert force to move its huge body through
the air. Oceanic islands are inhabited by bats and seals, but
by no terrestrial mammals ; yet as some of these bats are
peculiar species, they must have long inhabited their present
homes. Therefore Sir C. Lyell asks, and assigns certain rea-
sons in answer, why have not seals and bats given birth on
234 ORIGIN OF SPECIES
such islands to forms fitted to live on the land? But seals
would necessarily be first converted into terrestrial carnivor-
ous animals of considerable size, and bats into terrestrial
insectivorous animals ; for the former there would be no
prey; for the bats ground-insects would serve as food, but
these would already be largely preyed on by the reptiles or
birds, which first colonise and abound on most oceanic islands.
Gradations of structure, with each stage beneficial to a chang-
ing species, will be favoured only under certain peculiar con-
ditions. A strictly terrestrial animal, by occasionally hunting
for food in shallow water, then in streams or lakes, might at
last be converted into an animal so thoroughly aquatic as to
brave the open ocean. But seals would not find on oceanic
islands the conditions favourable to their gradual reconver-
sion into a terrestrial form. Bats, as formerly shown, prob-
ably acquired their wings by at first gliding through the air
from tree to tree, like the so-called flying squirrels, for the
sake of escaping from their enemies, or for avoiding falls ;
but when the power of true flight had once been acquired, it
would never be reconverted back, at least for the above pur-
poses, into the less efficient power of gliding through the air.
Bats might, indeed, like many birds, have had their wings
greatly reduced in. size, or completely lost, through disuse;
but in this case it would be necessary that they should first
have acquired the power of running quickly on the ground,
by the aid of their hind legs alone, so as to compete with
birds or other ground animals ; and for such a change a bat
seems singularly ill-fitted. These conjectural remarks have
been made merely to show that a transition of structure, with
each step beneficial, is a highly complex affair ; and that there
is nothing strange in a transition not having occurred in any
particular case.
Lastly, more than one writer has asked, why have some
animals had their mental powers more highly developed than
others, as such development would be advantageous to all ?
Why have not apes acquired the intellectual powers of man?
Various causes could be assigned; but as they are conjec-
tural, and their relative probability cannot be weighed, it
would be useless to give them. A definite answer to the lat-
ter question ought not to be expected, seeing that no one can
THEORY OF NATURAL SELECTION 235
solve the simpler problem why, of two races of savages, one
has risen higher in the scale of civilisation than the other ;
and this apparently implies increased brain-power.
We will return to Mr. Mivart's other objections. Insects
often resemble for the sake of protection various objects, such
as green or decayed leaves, dead twigs, bits of lichen, flowers,
spines, excrement of birds, and living insects ; but to this lat-
ter point I shall hereafter recur. The resemblance is often
wonderfully close, and is not confined to colour, but extends
to form, and even to the manner in which the insects hold
themselves. The caterpillars which project motionless like
dead twigs from the bushes on which they feed, offer an ex-
cellent instance of a resemblance of this kind. The cases of
the imitation of such objects as the excrement of birds, are
rare and exceptional. On this head, Mr. Mivart remarks,
"As, according to Mr, Darwin's theory, there is a constant
tendency to indefinite variation, and as the minute incipient
variations will be in all directions, they must tend to neutral-
ise each other, and at first to form such unstable modifications
that it is difficult, if not impossible, to see how such indefinite
oscillations of infinitesimal beginnings can ever build up a
sufficiently appreciable resemblance to a leaf, bamboo, or other
object, for Natural Selection to seize upon and perpetuate."
But in all the foregoing cases the insects in their original
state no doubt presented some rude and accidental resem-
blance to an object commonly found in the stations frequented
by them. Nor is this at all improbable, considering the al-
most infinite number of surrounding objects and the diver-
sity in form and colour of the hosts of insects which exist.
As some rude resemblance is necessary for the first start, we
can understand how it is that the larger and higher animals
do not (with the exception, as far as I know, of one fish")
resemble for the sake of protection special objects, but only
the surface which commonly surrounds them, and this chiefly
in colour. Assuming that an insect originally happened to
resemble in some degree a dead twig or a decayed leaf, and
that it varied slightly in many ways, then all the variations
which rendered the insect at all more like any such object,
and thus favoured its escape) would be preserved, whilst other
variations would be neglected and ultimately lost ; or, if they
236 ORIGIN OF SPECIES
rendered the insect at all less like the imitated object, they
would be eliminated. There would indeed be force in Mr.
Mivart's objection, if we were to attempt to account for the
above resemblances, independently of natural selection,
through mere fluctuating variability; but as the case stands
there is none.
Nor can I see any force in Mr. Mivart's difficulty with re-
spect to "the last touches of perfection in the mimicry;" as
in the case given by Mr. Wallace, of a walking-stick insect
(Ceroxylus laceratus), which resembles "a stick grown over
by a creeping moss or jungermannia." So close was this
resemblance, that a native Dyak maintained that the foli-
aceous excrescences were really moss. Insects are preyed on
by birds and other enemies, whose sight is probably sharper
than ours, and every grade in resemblance which aided an
insect to escape notice or detection, would tend towards its
preservation; and the more perfect the resemblance so much
the better for the insect. Considering the nature of the dif-
ferences between the species in the group which includes the
above Ceroxylus, there is nothing improbable in this insect
having varied in the irregularities on its surface, and in these
having become more or less green-coloured; for in every
group the characters which differ in the several species are
the most apt to vary, whilst the generic characters, or those
common to all the species, are the most constant.
The Greenland whale is one of the most wonderful animals
in the world, and the baleen, or whale-bone, one of its great-
est peculiarities. The baleen consists of a row, on each side,
of the upper jaw, of about 300 plates or laminae, which stand
close together transversely to the longer axis of the mouth.
Within the main row there are some subsidiary rows. The
extremities and inner margins of all the plates are frayed
into stiff bristles, which clothe the whole gigantic palate, and
serve to strain or sift the water, and thus to secure the
minute prey on which these great animals subsist. The
middle and longest lamina in the Greenland whale is ten,
twelve, or even fifteen feet in length ; but in the different
species of Cetaceans there are gradations in length ; the
middle lamina being in one species, according to Scoresby,
THEORY OF NATURAL SELECTION 237
four feet, in another three, in another eighteen inches, and in
the Balsenoptera rostrata only about nine inches in length.
The quality of the whale-bone also differs in the different
species.
With respect to the baleen, Mr. Mivart remarks that if it
"had once attained such a size and development as to be at
all useful, then its preservation and augmentation within
serviceable limits would be promoted by natural selection
alone. But how to obtain the beginning of such useful de-
velopment?" In answer, it may be asked, why should not
the early progenitors of the whales with baleen have pos-
sessed a mouth constructed something like the lamellated
beak of a duck? Ducks, like whales, subsist by sifting the
mud and water; and the family has sometimes been called
Criblatores, or sifters. I hope that I may not be miscon-
strued into saying that the progenitors of whales did actually
possess mouths lamellated like the beak of a duck. I wish
only to show that this is not incredible, and that the immense
plates of baleen in the Greenland whale might have been
developed from such lamellae by finely graduated steps, each
of service to its possessor.
The beak of a shoveller-duck (Spatula clypeata) is a more
beautiful and complex structure than the mouth of a whale.
The upper mandible is furnished on each side (in the speci-
men examined by me) with a row or comb formed of i88
thin, elastic lamellae, obliquely bevelled so as to be pointed,
and placed transversely to the longer axis of the mouth.
They arise from the palate, and are attached by flexible mem-
brane to the sides of the mandible. Those standing towards
the middle are the longest, being about one-third of an inch
in length, and they project "14 of an iuch beneath the edge.
At their bases there is a short subsidiary row of obliquely
transverse lamellae. In these several respects they resemble
the plates of baleen in the mouth of a whale. But towards
the extremity of the beak they differ much, as they pro-
ject inwards, instead of straight downwards. The entire
head of the shoveller, though incomparably less bulky, is
about one-eighteenth of the length of the head of a mod-
erately large Balaenoptera rostrata, in which species the
baleen is only nine inches long; so that if we were to make
238 ORIGIN OF SPECIES
the head of the shoveller as long as that of the Balaenoptera,
the lamellae would be six inches in length, — that is, two-thirds
of the length of the baleen in this species of whale. The
lower mandible of the shoveller-duck is furnished with
lamellae of equal length with those above, but finer; and in
being thus furnished it differs conspicuously from the lower
jaw of a whale, which is destitute of baleen. On the other
hand, the extremities of these lower lamellae are frayed into
fine bristly points, so that they thus curiously resemble the
plates of baleen. In the genus Prion, a member of the dis-
tinct family of the Petrels, the upper mandible alone is fur-
nished with lamellae, which are well developed and project
beneath the margin; so that the beak of this bird resembles
in this respect the mouth of a whale.
From the highly developed structure of the shoveller's
beak we may proceed (as I have learnt from information and
specimens sent to me by Mr. Salvin), without any great
break, as far as fitness for sifting is concerned, through the
beak of the Merganetta armata, and in some respects through
that of the Aix sponsa, to the beak of the common duck-
In this latter species, the lamellae are much coarser than
in the shoveller, and are firmly attached to the sides of the
mandible ; they are only about 50 in number on each side, and
do not project at all beneath the margin. They are square-
topped, and are edged with translucent hardish tissue, as if
for crushing food. The edges of the lower mandible are
crossed by numerous fine ridges, which project very little.
Although the beak is thus very inferior as a sifter to that
of the shoveller, yet this bird, as every one knows, constantly
uses it for this purpose. There are other species, as I hear
from Mr. Salvin, in which the lamellae are considerably less
developed than in the common duck ; but I do not know
whether they use their beaks for sifting the water.
Turning to another group of the same family. In the
Egyptian goose (Chenalopex) the beak closely resembles that
of the common duck; but the lamellae are not so numerous,
nor so distinct from each other, nor do they project so much
inwards ; yet this goose, as I am informed by Mr. E. Bartlett,
"uses its bill like a duck by throwing the waters out at the
corners." Its chief food, however, is grass, which it crops
THEORY OF NATURAL SELECTION 239
like the common goose. In this latter bird, the lamellae of the
upper mandible are much coarser than in the common duck,
almost conflaent, about 27 in number on each side, and ter-
minating upwards in teeth-like knobs. The palate is also
covered with hard rounded knobs. The edges of the lower
mandible are serrated with teeth much more prominent,
coarser, and sharper than in the duck. The common goose
does not sift the water, but uses its beak exclusively for tear-
ing or cutting herbage, for which purpose it is so well fitted,
that it can crop grass closer than almost any other animal.
There are other species of geese, as I hear from Mr. Bartlett,
in which the lamellae are less developed than in the common
goose.
We thus see that a member of the duck family, with a beak
constructed like that of the common goose and adapted solely
for grazing, or even a member with a beak having less well-
developed lamellae, might be converted by small changes into
a species like the Egyptian goose, — this into one like the com-
mon duck, — and, lastly, into one like the shoveller, provided
with a beak almost exclusively adapted for sifting the water;
for this bird could hardly use any part of its beak, except
the hooked tip, for seizing or tearing solid food. The beak
of a goose, as I may add, might also be converted by small
changes into one provided with prominent, recurved teeth,
like those of the Merganser (a member of the same family),
serving for the widely different purpose of securing live fish.
Returning to the whales. The Hyperoodon bidens is desti-
tute of true teeth in an efficient condition, but its palate is
roughened, according to Lacepede, with small, unequal, hard
points of horn. There is, therefore, nothing improbable in
supposing that some early Cetacean form was provided with
similar points of horn on the palate, but rather more regu-
larly placed, and which, like the knobs on the beak of the
goose, aided it in seizing or tearing its food. If so, it will
hardly be denied that the points might have been converted
through variation and natural selection into lamellae as well-
developed as those of the Egyptian goose, in which case they
would have been used both for seizing objects and for sift-
ing the water; then into lamellae like those of the domestic
duck; and so onwards, until they became as well constructed
240 ORIGIN OF SPECIES
as those of the shoveller, in which case they would have
served exclusively as a sifting apparatus. From this stage,
in which the lamellae would be two-thirds of the length of
the plates of baleen in the Balsenoptera rostrata, gradations,
which may be observed in still-existing Cetaceans, lead us
onwards to the enormous plates of baleen in the Greenland
whale. Nor is there the least reason to doubt that each step
in this scale might have been as serviceable to certain an-
cient Cetaceans, with the functions of the parts slowly chang-
ing during the progress of development, as are the grada-
tions in the beaks of the different existing members of the
duck family. We should bear in mind that each species of
duck is subjected to a severe struggle for existence, and that
the structure of every part of its frame must be well adapted
to its conditions of life.
The Pleuronectidae, or Flat-fish, are remarkable for their
asymmetrical bodies. They rest on one side, — in the greater
number of species on the left, but in some on the right side;
and occasionally reversed adult specimens occur. The lower,
or resting-surface, resembles at first sight the ventral sur-
face of an ordinary fish: it is of a white color, less developed
in many ways than the upper side, with the lateral fins often
of smaller size. But the eyes offer the most remarkable pecu-
liarity; for they are both placed on the upper side of the
head. During early youth, however, they stand opposite to
each other, and the whole body is then symmetrical, with
both sides equally coloured. Soon the eye proper to the
lower side begins to glide slowly round the head to the upper
side; but does not pass right through the skull, as was for-
merly thought to be the case. It is obvious that unless the
lower eye did thus travel round, it could not be used by the
fish whilst lying in its habitual position on one side. The
lower eye would, also, have been liable to be abraded by the
sandy bottom. That the Pleuronectidae are admirably adapted
by their flattened and asymmetrical structure for their habits
of life, is manifest from several species, such as soles, floun-
ders, &c., being extremely common. The chief advantages
thus gained seem to be protection from their enemies, and
facility for feeding on the ground. The different members,
however, of the family present, as Schiodte remarks, "a long
THEORY OF NATURAL SELECTION 241
series of forms exhibiting a gradual transition from Hippo-
glossus pinguis, which does not in any considerable degree
alter the shape in which it leaves the ovum, to the soles,
which are entirely thrown to one side."
Mr. Mivart has taken up this case, and remarks that a
sudden spontaneous transformation in the position of the
eyes is hardly conceivable, in which I quite agree with him.
He then adds: "if the transit was gradual, then how such
transit of one eye a minute fraction of the journey towards
the other side of the head could benefit the individual is, in-
deed, far from clear. It seems, even, that such an incipient
transformation must rather have been injurious." But he
might have found an answer to this objection in the excel-
lent observations published in 1867 by Malm. The Pleuro-
nectidae, whilst very young and still symmetrical, with their
eyes standing on opposite sides of the head, cannot long re-
tain a vertical position, owing to the excessive depth of their
bodies, the small size of their lateral fins, and to their being
destitute of a swimbladder. Hence soon growing tired, they
fall to the bottom on one side. Whilst thus at rest they often
twist, as Malm observed, the lower eye upwards, to see above
them; and they do this so vigorously that the eye is pressed
hard against the upper part of the orbit. The forehead be-
tween the eyes consequently becomes, as could be plainly
seen, temporarily contracted in breadth. On one occasion
Malm saw a young fish raise and depress the lower eye
through an angular distance of about seventy degrees.
We should remember that the skull at this early age is car-
tilaginous and flexible, so that it readily yields to muscular
action. It is also known with the higher animals, even after
early youth, that the skull yields and is altered in shape, if
the skin or muscles be permanently contracted through dis-
ease or some accident. With long-eared rabbits, if one ear
lops forwards and downwards, its weight drags forward all
the bones of the skull on the same side, of which I have given
a figure. Malm states that the newly hatched young of
perches, salmon, and several other symmetrical fishes, have
the habit of occasionally resting on one side at the bottom;
and he has observed that they often then strain their lower
eyes so as to look upwards; and their skulls are thus ren-
242 ORIGIN OF SPECIES
dered rather crooked. These fishes, however, are soon able
to hold themselves in a vertical position, and no permanent
effect is thus produced. With the Pleuronectidae, on the
other hand, the older they grow the more habitually they
rest on one side, owing to the increasing flatness of their
bodies, and a permanent effect is thus produced on the form
of the head, and on the position of the eyes. Judging from
analogy, the tendency to distortion would no doubt be in-
creased through the principle of inheritance. Schiodte be-
lieves, in opposition to some other naturalists, that the Pleu-
ronectidoe are not quite symmetrical even in the embryo ; and
if this be so, we could understand how it is that certain spe-
cies, whilst young, habitually fall over and rest on the left
side, and other species on the right side. Malm adds, in con-
firmation of the above view, that the adult Trachypterus arc-
ticus, which is not a member of the Pleuronectidae, rests on
its left side at the bottom, and swims diagonally through the
water; and in this fish, the two sides of the head are said to
be somewhat dissimilar. Our great authority on Fishes, Dr.
Giinther, concludes his abstract of Malm's paper, by remark-
ing that "the author gives a very simple explanation of the
abnormal condition of the Pleuronectoids."
We thus see that the first stages of the transit of the eye
from one side of the head to the other, which Mr. Mivart
considers would be injurious, may be attributed to the habit,
no doubt beneficial to the individual and to the species, of
endeavouring to look upwards with both eyes, whilst resting
on one side at the bottom. We may also attribute to the in-
herited effects of use the fact of the mouth in several kinds
of flat-fish being bent towards the lower surface, with the
jaw bones stronger and more effective on this, the eyeless
side of the head, than on the other, for the sake, as Dr. Tra-
quair supposes, of feeding with ease on the ground. Disuse,
on the other hand, will account for the less developed con-
dition of the whole inferior half of the body, including the
lateral fins; though Yarrell thinks that the reduced size of
these fins is advantageous to the fish, as "there is so much
less room for their action, than with the larger fins above."
Perhaps the lesser number of teeth in the proportion of four
to seven in the upper halves of the two jaws of the plaice, to
THEORY OF NATURAL SELECTION 243
twenty-five to thirty in the lower halves, may likewise be
accounted for by disuse. From the colourless state of the
ventral surface of most fishes and of many other animals, we
may reasonably suppose that the absence of colour in flat-
fish on the side, whether it be the right or left, which is
undermost, is due to the exclusion of light. But it cannot
be supposed that the peculiar speckled appearance of the
upper side of the sole, so like the sandy bed of the sea, or
the power in some species, as recently shown by Pouchet, of
changing their colour in accordance with the surrounding
surface, or the presence of bony tubercles on the upper side
of the turbot, are due to the action of the light. Here natural
selection has probably come into play, as well as in adapting
the general shape of the body of these fishes, and many other
peculiarities, to their habits of life. We should keep in mind,
as I have before insisted, that the inherited effects of the
increased use of parts, and perhaps of their disuse, will be
strengthened by natural selection. For all spontaneous varia-
tions in the right direction will thus be preserved; as will
those individuals which inherit in the highest degree the
effects of the increased and beneficial use of any part. How
much to attribute in each particular case to the effects of use,
and how much to natural selection, it seems impossible to
decide.
I may give another instance of a structure which appar-
ently owes its origin exclusively to use or habit. The ex-
tremity of the tail in some American monkeys has been con-
verted into a wonderfully perfect prehensile organ, and
serves as a fifth hand. A reviewer who agrees with Mr.
Mivart in every detail, remarks on this structure: "It is im-
possible to believe that in any number of ages the first slight
incipient tendency to grasp could preserve the lives of the
individuals possessing it, or favour their chance of having
and of rearing offspring." But there is no necessity for any
such belief. Habit, and this almost implies that some benefit
great or small is thus derived, would in all probability suffice
for the work. Brehm saw the young of an African monkey
(Cercopithecus) clinging to the under surface of their mother
by their hands, and at the same time they hooked their little
tails round that of their mother. Professor Henslow kept in
244 ORIGIN OF SPECIES
confinement some harvest mice (Mus messorius) which do
not possess a structurally prehensile tail ; but he frequently
observed that they curled their tails round the branches of a
bush placed in the cage, and thus aided themselves in climb-
ing. I have received an analogous account from Dr. Giin-
ther, who has seen a mouse thus suspend itself. If the har-
vest mouse had been more strictly arboreal, it would perhaps
have had its tail rendered structurally prehensile, as is the
case with some members of the same order. Why Cercopi-
thecus, considering its habits whilst young, has not become
thus provided, it would be difficult to say. It is, however,
possible that the long tail of this monkey may be of more
service to it as a balancing organ in making its prodigious
leaps, than as a prehensile organ.
The mammary glands are common to the whole class of
mammals, and are indispensable for their existence; they
must, therefore, have been developed at an extremely remote
period, and we can know nothing positively about their man-
ner of development. Mr. Mivart asks: "Is it conceivable
that the young of any animal was ever saved from destruction
by accidentally sucking a drop of scarcely nutritious fluid
from an accidentally hypertrophied cutaneous gland of its
mother? And even if one was so, what chance was there of
the perpetuation of such a variation?" But the case is not
here put fairly. It is admitted by most evolutionists that
mammals are descended from a marsupial form; and if so,
the mammary glands will have been at first developed within
the marsupial sack. In the case of the fish (Hippicampus)
the eggs are hatched, and the young are reared for a time,
within a sack of this nature ; and an American naturalist,
Mr. Lockwood, believes from what he has seen of the devel-
opment of the young, that they are nourished by a secretion
from the cutaneous glands of the sack. Now with the early
progenitors of mammals, almost before they deserved to be
thus designated, is it not at least possible that the young
might have been similarly nourished? And in this case, the
individuals which secreted a fluid, in some degree or manner
the most nutritious, so as to partake of the nature of milk,
would in the long run have reared a larger number of well-
THEORY OF NATURAL SELECTION 245
nourished offspring, than would the individuals which se-
creted a poorer fluid; and thus the cutaneous glands, which
are the homologues of the mammary glands, would have been
improved or rendered more effective. It accords with the
widely extended principle of specialisation, that the glands
over a certain space of the sack should have become more
highly developed than the remainder; and they would then
have formed a breast, but at first without a nipple, as we see
in the Ornithorhyncus, at the base of the mammalian series.
Through what agency the glands over a certain space be-
came more highly specialised than the others, I will not pre-
tend to decide, whether in part through compensation of
growth, the effects of use, or of natural selection.
The development of the mammary glands would have been
of no service, and could not have been effected through nat-
ural selection, unless the young at the same time were able
to partake of the secretion. There is no greater difficulty in
understanding how young mammals have instinctively learnt
to suck the breast, than in understanding how unhatched
chickens have learnt to break the egg-shell by tapping against
it with their specially adapted beaks ; or how a few hours
after leaving the shell they have learnt to pick up grains of
food. In such cases the most probable solution seems to be.
that the habit was at first acquired by practice at a more ad-
vanced age, and afterwards transmitted to the offspring at an
earlier age. But the young kangaroo is said not to suck,
only to cling to the nipple of its mother, who has the power
of injecting milk into the mouth of her helpless, half-formed
offspring. On this head Mr. Mivart remarks : "Did no spe-
cial provision exist, the young one must infallibly be choked
by the intrusion of the milk into the windpipe. But there is
a special provision. The larynx is so elongated that it rises
up into the posterior end of the nasal passage, and is thus
enabled to give free entrance to the air for the lungs, while
the milk passes harmlessly on each side of this elongated
larynx, and so safely attains the gullet behind it." Mr. Mi-
vart then asks how did natural selection remove in the adult
kangaroo (and in most other mammals, on the assumption
that they are descended from a marsupial form), "this at
least perfectly innocent and harmless structure?" It may
246 ORIGIN OF SPECIES
be suggested in answer that the voice, which is certainly of
high importance to many animals, could hardly have been
used with full force as long as the larynx entered the nasal
passage ; and Professor Flower has suggested to me that this
structure would have greatly interfered with an animal swal-
lowing solid food.
We will now turn for a short space to the lower divisions
of the animal kingdom. The Echinodermata (star-fishes,
sea-urchins, &c.) are furnished with remarkable organs,
called pedicellariae, which consist, when well developed, of a
tridactyle forceps — that is, of one formed of three serrated
arms, neatly fitting together and placed on the summit of a
flexible stem, move'd by muscles. These forceps can seize
firmly hold of any object; and Alexander Agassiz has seen
an Echinus or sea-urchin rapidly passing particles of excre-
ment from forceps to forceps down certain lines of its body,
in order that its shell should not be fouled. But there is no
doubt that besides removing dirt of all kinds, they subserve
other functions ; and one of these apparently is defence.
With respect to these organs, Mr. Mivart, as on so many
previous occasions, asks : "What would be the utility of the
-first riidimeTitary beginnings of such structures, and how
could such incipient buddings have ever preserved the life of
a single Echinus?" He adds, "not even the sudden develop-
ment of the snapping action could have been beneficial with-
out the freely moveable stalk, nor could the latter have been
efficient without the snapping jaws, yet no minute merely in-
definite variations could simultaneously evolve these complex
co-ordinations of structure ; to deny this seems to do no less
than to affirm a startling paradox." Paradoxical as this may
appear to Mr. Mivart, tridactyle forcepses, immovably fixed
at the base, but capable of a snapping action, certainly exist
on some star-fishes; and this is intelligible if they serve, at
least in part, as a means of defence. Mr. Agassiz, to whose
great kindness I am indebted for much information on the
subject, informs me that there are other star-fishes, in which
one of the three arms of the forceps is reduced to a support
for the other two; and again, other genera in which the third
arm is completely lost. In Echinoneus, the shell is described
by M. Perrier as bearing two kinds of pedicellariae, one re-
THEORY OF NATURAL SELECTION 247
sembling those of Echinus, and the other those of Spatan-
gus; and such cases are always interesting as affording the
means of apparently sudden transitions, through the abortion
of one of the two states of an organ.
With respect to the steps by which these curious organs
have been evolved, Mr. Agassiz infers' from his own re-
searches and those of Miiller, that both in star-fishes and sea-
urchins the pedicellariae must undoubtedly be looked at as
modified spines. This may be inferred from their manner of
development in the individual, as well as from a long and
perfect series of gradations in different species and genera,
from simple granules to ordinary spines, to perfect tridactyle
pedicellariae. The gradation extends even to the manner in
which ordinary spines and the pedicellarise with their sup-
porting calcareous rods are articulated to the shell. In cer-
tain genera of star-fishes, "the very combinations needed to
show that the pedicellarise are only modified branching spines"
may be found. Thus we have fixed spines, with three equi-
distant, serrated, moveable branches, articulated to near their
bases ; and higher up, on the same spine, three other move-
able branches. Now when the latter arise from the summit
of a spine they form in fact a rude tridactyle pedicellaria,
and such may be seen on the same spine together with the
three lower branches. In this case the identity in nature be-
tween the arms of the pedicellariae and the moveable branches
of a spine, is unmistakable. It is generally admitted that the or-
dinary spines serve as a protection ; and if so, there can be
no reason to doubt that those furnished with serrated and
moveable branches likewise serve for the same purpose ; and
they would thus serve still more effectively as soon as by
meeting together they acted as a prehensile or snapping ap-
paratus. Thus every gradation, from an ordinary fixed spine
to a fixed pedicellaria, would be of service.
In certain genera of star-fishes these organs, instead of
being fixed or borne on an immovable support, are placed on
the summit of a flexible and muscular, though short, stem ;
and in this case they probably subserve some additional func-
tion besides defence. In the -sea-urchins the steps can be fol-
lowed by which a fixed spine becomes articulated to the shell,
and is thus rendered moveable. I wish I had space here to
248 ORIGIN OF SPECIES
give a fuller abstract of Mr. Agassiz's interesting observa-
tions on the development of the pedicellariae. All possible
gradations, as he adds, may likewise be found between the
pedicellariae of the star-fishes and the hooks of the Ophiuri-
ans, another group of the Echinodermata ; and again between
the pedicellariae of sea-urchins and the anchors of the Holo-
thuriae, also belonging to the same great class.
Certain compound animals, or zoophytes as they have been
termed, namely the Polyzoa, are provided with curious or-
gans called avicularia. These differ much in structure in the
different species. In their most perfect condition, they curi-
ously resemble the head and beak of a vulture in miniature,
seated on a neck and capable of movement, as is likewise the
lower jaw or mandible. In one species observed by me all the
avicularia on the same branch often moved simultaneously
backwards and forwards, with the lower jaw widely open,
through an angle of about 90°, in the course of five seconds;
and their movement caused the whole polyzoary to tremble.
When the jaws are touched with a needle they seize it so
firmly that the branch can thus be shaken.
Mr. Mivart adduces this case, chiefly on account of the
supposed difficulty of organs, namely the avicularia of the
Polyzoa and the pedicellariae of the Echinodermata, which
he considers as "essentially similar," having been developed
through natural selection in widely distinct divisions of the
animal kingdom. But, as far as structure is concerned, I can
see no similarity between tridactyle pedicellariae and avicu-
laria. The latter resemble somewhat more closely the chelae
or pincers of Crustaceans; and Mr. Mivart might have ad-
duced with equal appropriateness this resemblance as a special
difficulty ; or even their resemblance to the head and beak of
a bird. The avicularia are believed by Mr. Busk, Dr. Smitt,
and Dr. Nitsche — naturalists who have carefully studied this
group — to be homologous with the zooids and their cells
which compose the zoophyte; the moveable lip or lid of the
cell corresponding with the lower and moveable mandible of
the avicularium. Mr. Busk, however, does not know of any
gradations now existing between a zooid and an avicularium.
It is therefore impossible to conjecture by what serviceable
THEORY OF NATURAL SELECTION 249
gradations the one could have been converted into the other:
but it by no means follows from this that such gradations
have not existed.
As the chelae of Crustaceans resemble in some degree the
avicularia of Polyzoa, both serving as pincers, it may be
worth while to show that with the former a long series of
serviceable gradations still exists. In the first and simplest
stage, the terminal segment of a limb shut down either on
the square summit of the broad penultimate segment or
against one whole side ; and is thus enabled to catch hold of
an object ; but the limb still serves as an organ of locomotion.
We next find one corner of the broad penultimate segment
slightly prominent, sometimes furnished with irregular teeth ;
and against these the terminal segment shuts down. By an
increase in the size of this projection, with its shape, as well
as that of the terminal segment, slightly modified and im-
proved, the pincers are rendered more and more perfect un-
til we have at last an instrument as efficient as the chelae of
a lobster; and all these gradations can be actually traced.
Besides the avicularia, the Polyzoa possess curious organs
called vibracula. These generally consist of long bristles,
capable of movement and easily excited. In one species ex-
amined by me the vibracula were slightly curved and ser-
rated along the outer margin ; and all of them on the same
polyzoary often moved simultaneously ; so that, acting like
long oars, they swept a branch rapidly across the object-
glass of my microscope. When a branch was placed on its
face, the vibracula became entangled, and they made violent
efforts to free themselves. They are supposed to serve as a
defence, and may be seen, as Mr. Busk remarks, "to sweep
slowly and carefully over the surface of the polyzoary, re-
moving what might be noxious to the delicate inhabitants of
the cells when their tentacula are protruded." The avicu-
laria, like the vibracula, probably serve for defence, but they
also catch and kill small living animals, which it is believed
are afterwards swept by the currents within reach of the
tentacula of the zooids. Some species are provided with
avicularia and vibracula; same with avicularia alone, and a
few with vibracula alone.
It is not easy to imagirTe two objects more widely different
250 ORIGIN OF SPECIES
in appearance than a bristle or vibraculum, and an avicu-
larium like the head of a bird ; yet they are almost certainly
homologous and have been developed from the same common
source, namely a zooid v^^ith its cell. Hence we can under-
stand how^ it is that these organs graduate in some cases, as
I am informed by Mr. Busk, into each other. Thus with the
avicularia of several species of Lepralia, the moveable
mandible is so much produced and is so like a bristle,
that the presence of the upper or fixed beak alone serves
to determine its avicularian nature. The vibracula may
have been directly developed from the lips of the cells,
without having passed through the avicularian stage; but
it seems more probable that they have passed through this
stage, as during the early stages of the transformation, the
other parts of the cell with the included zooid could hardly
have disappeared at once. In many cases the vibracula have
a grooved support at the base, which seems to represent thv.
fixed beak ; though this support in some species is quite ab-
sent. This view of the development of the vibracula, if trust-
worthy, is interesting; for supposing that all the species pro-
vided with avicularia had become extinct, no one with the
most vivid imagination would ever have thought that the
vibracula had originally existed as part of an organ, resem-
bling a bird's head or an irregular box or hood. It is inter-
esting to see two such widely different organs developed from
a common origin ; and as the moveable lip of the cell serves
as a protection to the zooid, there is no difficulty in believing
that all the gradations, by which the lip became converted
first into the lower mandible of an avicularium and then into
an elongated bristle, likewise served as a protection in differ-
ent ways and under different circumstances.
In the vegetable kingdom Mr. Mivart only alludes to two
cases, namely the structure of the flowers of orchids, and the
movements of climbing plants. With respect to the former,
he says, "the explanation of their origin is deemed thoroughly
unsatisfactory — utterly insufficient to explain the incipient,
infinitesimal beginnings of structures which are of utility
only when they are considerably developed." As I have
fully treated this subject in another work, I will here give
THEORY OF NATURAL SELECTION 251
only a few details on one alone of the most striking pecu-
liarities of the flowers of orchids, namely their poUinia. A
pollinium when highly developed consists of a mass of pollen-
grains, affixed to an elastic foot-stalk or caudicle, and this
to a little mass of extremely viscid matter. The pollinia are
by this means transported by insects from one flower to the
stigma of another. In some orchids there is no caudicle to
the pollen-masses, and the grains are merely tied together by
fine threads ; but as these are not confined to orchids, they
need not here be considered; yet I may mention that at the
base of the orchidaceous series, in Cypripedium, we can see
how the threads were probably first developed. In other
orchids the threads cohere at one end of the pollen-masses ;
and this forms the first or nascent trace of a caudicle. That
this is the origin of the caudicle, even when of considerable
length and highly developed, we have good evidence in the
aborted pollen-grains which can sometimes be detected
embedded within the central and solid parts.
With respect to the second chief peculiarity, namely the
little mass of viscid matter attached to the end of the caudicle,
a long series of gradations can be specified, each of plain
service to the plant. In most flowers belonging to other
orders the stigma secretes a little viscid matter. Now in cer-
tain orchids similar viscid matter is secreted, but in much
larger quantities by one alone of the three stigmas ; and this
stigma, perhaps in consequence of the copious secretion, is
rendered sterile. When an insect visits a flower of this kind,
it rubs off some of the viscid matter and thus at the same
time drags away some of the pollen-grains. From this
simple condition, which differs but little from that of a mul-
titude of common flowers, there are endless gradations, — to
species in which the pollen-mass terminates in a very short,
free caudicle, — to others in which the caudicle becomes firmly
attached to the viscid matter, with the sterile stigma itself
much modified. In this latter case we have a pollinium in its
most highly developed and perfect condition. He who will
carefully examine the flowers of orchids for himself will not
deny the existence of the above series of gradations — from a
mass of pollen-grains merely tied together by threads, with
the stigma differing but-little from that of an ordinary flower.
252 ORIGIN OF SPECIES
to a highly complex polHnium, admirably adapted for trans-
portal by insects; nor will he deny that all the gradations in
the several species are admirably adapted in relation to the
general structure of each flower for its fertilisation by differ-
ent insects. In this, and in almost every other case, the en-
quiry may be pushed further backwards ; and it may be asked
how did the stigma of an ordinary flower become viscid, but
as we do not know the full history of any one group of be-
ings, it is as useless to ask, as it is hopeless to attempt
answering, such questions.
We will now turn to climbing plants. These can be ar-
ranged in a long series, from those which simply twine round
a support, to those which I have called leaf-climbers, and to
those provided with tendrils. In these two latter classes the
stems have generally, but not always, lost the power of twin-
ing, though they retain the power of revolving, which the
tendrils likewise possess. The gradations from leaf-climbers
to tendril-bearers are wonderfully close, and certain plants
may be indifferently placed in either class. But in ascending
the series from simple twiners to leaf-climbers, an important
quality is added, namely sensitiveness to a touch, by which
means the foot-stalks of the leaves or flowers, or these modi-
fied and converted into tendrils, are excited to bend round
and clasp the touching object. He who will read my memoir
on these plants will, I think, admit that all the many grada-
tions in function and structure between simple twiners and
tendril-bearers are in each case beneficial in a high degree to
the species. For instance, it is clearly a great advantage to
a twining plant to become a leaf-climber; and it is probable
that every twiner which possessed leaves with long foot-
stalks would have been developed into a leaf-climber, if the
foot-stalks had possessed in any slight degree the requisite
sensitiveness to a touch.
As twining is the simplest means of ascending a support,
and forms the basis of our series, it may naturally be asked
how did plants acquire this power in an incipient degree,
afterwards to be improved and increased through natural se-
lection. The power of twining depends, firstly, on the stems
whilst young being extremely flexible (but this is a character
common to many plants which are not climbers) ; and, sec-
THEORY OF NATURAL SELECTION 253
ondly, on their continually bending to all points of the com-
pass, one after the other in succession, in the same order. By
this movement the stems are inclined to all sides, and are
made to move round and round. As soon as the lower part
of a stem strikes against any object and is stopped, the upper
part still goes on bending and revolving, and thus necessarily
twines round and up the support. The revolving movement
ceases after the early growth of each shoot. As in many
widely separated families of plants, single species and single
genera possess the power of revolving, and have thus become
twiners, they must have independently acquired it, and cannot
have inherited it from a common progenitor. Hence I was
led to predict that some slight tendency to a movement of this
kind would be found to be far from uncommon with plants
which did not climb; and that this had afforded the basis for
natural selection to work on and improve. When I made
this prediction, I knew of only one imperfect case, namely of
the young flower-peduncles of a Maurandia which revolved
slightly and irregularly, like the stems of twining plants, but
without making any use of this habit. Soon afterwards
Fritz Miiller discovered that the young stems of an Alisma
and of a Linum, — plants which do not climb and are widely
separated in the natural system, — revolved plainly, though
irregularly ; and he states that he has reason to suspect that
this occurs with some other plants. These slight movements
appear to be of no service to the plants in question; anyhow,
they are not of the least use in the way of climbing, which
is the point that concerns us. Nevertheless we can see that
if the stems of these plants had been flexible, and if under the
conditions to which they are exposed it had profited them to
ascend to a height, then the habit of slightly and irregularly
revolving might have been increased and utilised through
natural selection, until they had become converted into well-
developed twining species.
With respect to the sensitiveness of the foot-stalks of the
leaves and flowers, and of tendrils, nearly the same remarks
are applicable as in the case of the revolving movements of
twining plants. As a vast number of species, belonging to
widely distinct groups, are endowed with this kind of sensi-
tiveness, it ought to be foynd in a nascent condition in many
254 ORIGIN OF SPECIES
plants which have not become climbers. This is the case : I
observed that the young flower-peduncles of the above Mau-
randia curved themselves a little towards the side which was
touched. Morren found in several species of Oxalis that the
leaves and their foot-stalks moved, especially after exposure
to a hot sun, when they were gently and repeatedly touched,
or when the plant was shaken. I repeated these observations
on some other species of Oxalis with the same result ; in
some of them the movement was distinct, but was best seen
in the young leaves ; in others it was extremely slight. It is
a more important fact that according to the high authority
of Hofmeister, the young shoots and leaves of all plants move
after being shaken ; and with climbing plants it is, as we
know, only during the early stages of growth that the foot-
stalks and tendrils are sensitive.
It is scarcely possible that the above slight movements, due
to a touch or shake, in the young and growing organs of
plants, can be of any functional importance to them. But
plants possess, in obedience to various stimuli, powers of
movement, which are of manifest importance to them; for
instance, towards and more rarely from the light, — in oppo-
sition to, and more rarely in the direction of, the attraction
of gravity. When the nerves and muscles of an animal are
excited by galvanism or by the absorption of strychnine, the
consequent movements may be called an incidental result, for
the nerves and muscles have not been rendered specially sen-
sitive to these stimuli. So with plants it appears that, from
having the power of movement in obedience to certain stim-
uli, they are excited in an incidental manner by a touch, or
by being shaken. Hence there is no great difficulty in ad-
mitting that in the case of leaf-climbers and tendril-bearers,
it is this tendency which has been taken advantage of and in-
creased through natural selection. It is, however, probable,
from reasons which I have assigned in my memoir, that this
will have occurred only with plants which had already ac-
quired the power of revolving, and had thus become twiners.
I have already endeavoured to explain how plants became
twiners, namely, by the increase of a tendency to slight and
irregular revolving movements, which were at first of no use
to them ; this movement, as well as that due to a touch or
THEORY OF NATURAL SELECTION 255
shake, being the incidental result of the power of moving,
gained for other and beneficial purposes. Whether, during
the gradual development of climbing plants, natural selection
has been aided by the inherited effects of use, I will not pre-
tend to decide; but we know that certain periodical move-
ments, for instance the so-called sleep of plants, are governed
by habit.
I have now considered enough, perhaps more than enough,
of the cases, selected with care by a skilful naturalist, to
prove that natural selection is incompetent to account for the
incipient stages of useful structures; and I have shown, as I
hope, that there is no great difficulty on this head. A good
opportunity has thus been afforded for enlarging a little on
gradations of structure, often associated with changed func-
tions, — an important subject, which was not treated at suf-
ficient length in the former editions of this work. I will now
briefly recapitulate the foregoing cases.
With the giraffe, the continued preservation of the indi-
viduals of some extinct high-reaching ruminant, which had
the longest necks, legs, &c., and could browse a little above
the average height, and the continued destruction of those
which could not browse so high, would have sufficed for the
production of this remarkable quadruped; but the prolonged
use of all the parts together with inheritance will have aided
in an important manner in their co-ordination. With the
many insects which imitate various objects, there is no im-
probability in the belief that an accidental resemblance to
some common object was in each case the foundation for the
work of natural selection, since perfected through the occa-
sional preservation of slight variations which made the re-
semblance at all closer ; and this will have been carried on
as long as the insect continued to vary, and as long as a more
and more perfect resemblance led to its escape from sharp-
sighted enemies. In certain species of whales there is a ten-
dency to the formation of irregular little points of horn on
the palate ; and it seems to be quite within the scope of nat-
ural selection to preserve all .favourable variations, until the
points were converted first into lamellated knobs or teeth,
like those on the beak of a goose, — then into short lamellae,
256 ORIGIN OF SPECIES
like those of the domestic ducks — and then into lamellae, as
perfect as those of the shoveller-duck, — and finally into the
gigantic plates of baleen, as in the mouth of the Greenland
whale. In the family of the ducks, the lamellae are first used
as teeth, then partly as teeth and partly as a sifting ap-
paratus, and at last almost exclusively for this latter purpose.
With such structures as the above lamellae of horn or whale-
bone, habit or use can have done little or nothing, as far as
we can judge, towards their development. On the other
hand, the transportal of the lower eye of a flat-fish to the
upper side of the head, and the formation of a prehensile tail,
may be attributed almost wholly to continued use, together
with inheritance. With respect to the mammae of the higher
animals, the most probable conjecture is that primordially
the cutaneous glands over the whole surface of a marsupial
sack secreted a nutritious fluid ; and that these glands were
improved in function through natural selection, and concen-
trated into a confined area, in which case they would have
formed a mamma. There is no more difficulty in under-
standing how the branched spines of some ancient Echino-
derm, which served as a defence, became developed through
natural selection into tridactyle pedicellariae, than in under-
standing the development of the pincers of crustaceans,
through slight, serviceable modifications in the ultimate and
penultimate segments of a limb, which was at first used solely
for locomotion. In the avicularia and vibracula of the
Polyzoa we have organs widely different in appearance de-
veloped from the same source ; and with the virbracula we
can understand how the successive gradations might have
been of service. With the pollinia of orchids, the threads
which originally served to tie together the pollen-grains, can
be traced cohering into caudicles ; and the steps dan likewise
be followed by which viscid matter, such as that secreted by
the stigmas of ordinary flowers, and still subserving nearly
but not quite the same purpose, became attached to the free
ends of the caudicles; — all these gradations being of mani-
fest benefit to the plants in question. With respect to climb-
ing plants, I need not repeat what has been so lately said.
It has often been asked, if natural selection be so potent,
why has not this or that structure been gained by certain
THEORY OF NATURAL SELECTION 257
species, to which it would apparently have been advantage-
ous? But it is unreasonable to expect a precise answer to
such questions, considering our ignorance of the past history
of each species, and of the conditions which at the present
day determine its numbers and range. In most cases only
general reasons, but in some few cases special reasons, can
be assigned. Thus to adapt a species to new habits of life,
many co-ordinated modifications are almost indispensable,
and it may often have happened that the requisite parts did
not vary in the right manner or to the right degree. Many
species must have been prevented from increasing in numbers
through destructive agencies, which stood in no relation to
certain structures, which we imagine would have been gained
through natural selection from appearing to us advantageous
to the species. In this case, as the struggle for life did not
depend on such structures, they could not have been acquired
through natural selection. In many cases complex and long-
enduring conditions, often of a peculiar nature, are necessary
for the development of a structure; and the requisite con-
ditions may seldom have concurred. The belief that any
given structure, which we think, often erroneously, would
have been beneficial to a species, would have been gained
under all circumstances through natural selection, is opposed
to what we can understand of its manner of action. Mr.
Mivart does not deny that natural selection has effected
something; but he considers it as "demonstrably insufficient"
to account for the phenomena which I explain by its agency.
His chief arguments have now been considered, and the
others will hereafter be considered. They seem to me to par-
take little of the character of demonstration, and to have
little weight in comparison with those in favour of the power
of natural selection, aided by the other agencies often speci-
fied. I am bound to add, that some of the facts and argu-
ments here used by me, have been advanced for the same
purpose in an able article lately published in the 'Medico-
Chirurgical Review.'
At the present day almost all naturalists admit evolution
under some form. Mr. Miyart believes that species change
through "an internal force or tendency," about which it is
not pretended that anything is known. That species have a
258 ORIGIN OF SPECIES
capacity for change will be admitted by all evolutionists; but
there is no need, as it seems to me, to invoke any internal
force beyond the tendency to ordinary variability, which
through the aid of selection by man has given rise to many
well-adapted domestic races, and which through the aid of
natural selection would equally well give rise by graduated
steps to natural races or species.. The final result will gen-
erally have been, as already explained, an advance, but in
some few cases a retrogression, in organisation.
Mr. Mivart is further inclined to believe, and some nat-
uralists agree with him, that new species manifest themselves
"with suddenness and by modifications appearing at once."
For instance, he supposes that the differences between the
extinct three-toed Hipparion and the horse arose suddenly.
He thinks it difficult to believe that the wing of a bird "was
developed in any other way than by a comparatively sudden
modification of a marked and important kind;" and appa-
rently he would extend the same view to the wings of bats
and pterodactyles. This conclusion, which implies great
breaks or discontinuity in the series, appears to me improb-
able in the highest degree.
Every one who believes in slow and gradual evolution, will
of course admit that specific changes may have been as abrupt
and as great as any single variation which we meet with
under nature, or even under domestication. But as species
are more variable when domesticated or cultivated than under
their natural conditions, it is not probable that such
great and abrupt variations have often occurred under
nature, as are known occasionally to arise under domestica-
tion. Of these latter variations several may be attributed to
reversion; and the characters which thus reappear were, it
is probable, in many cases at first gained in a gradual man-
ner. A still greater number must be called monstrosities,
such as six-fingered men, porcupine men, Ancon sheep, Niata
cattle, &c. ; and as they are widely different in character from
natural species, they throw very little light on our subject.
Excluding such cases of abrupt variations, the few which re-
main would at best constitute, if found in a state of nature,
doubtful species, closely related to their parental types.
My reasons for doubting whether natural species have
THEORY OF NATURAL SELECTION 259
changed as abruptly as have occasionally domestic races, and
for entirely disbelieving that they have changed in the won-
derful manner indicated by Mr. Mivart, are as follows. Ac-
cording to our experience, abrupt and strongly marked vari-
ations occur in our domesticated productions, singly and at
rather long intervals of time. If such occurred under na-
ture, they would be liable, as formerly explained, to be lost
by accidental causes of destruction and by subsequent inter-
crossing; and so it is known to be under domestication, un-
less abrupt variations of this kind are specially preserved and
separated by the care of man. Hence in order that a new
species should suddenly appear in the manner supposed by
Mr. Mivart, it is almost necessary to believe, in opposition to
all analogy, that several wonderfully changed individuals
appeared simultaneously within the same district. This dif-
ficulty, as in the case of unconscious selection by man, is
avoided on the theory of gradual evolution, through the pres-
ervation of a large number of individuals, which varied more
or less in any favourable direction, and of the destruction of
a large number which varied in an opposite manner.
That many species have been evolved in an extremely
gradual manner, there can hardly be a doubt. The species
and even the genera of many large natural families are so
closely allied together, that it is difficult to distinguish not a
few of them. On every continent in proceeding from north
to south, from lowland to upland, &c., we meet with a host
of closely related or representative species; as we likewise
do on certain distinct continents, which we have reason to
believe were formerly connected. But in making these and
the following remarks, I am compelled to allude to subjects
hereafter to be discussed. Look at the many outlying islands
round a continent, and see how many of their inhabitants can
be raised only to the rank of doubtful species. So it is if we
look to past times, and compare the species which have just
passed away with those still living within the same areas; or
if we compare the fossil species embedded in the sub-stages
of the same geological formation. It is indeed manifest that
multitudes of species are related in the closest manner to
other species that still exist, or have lately existed; and it will
hardly be maintained that such species have been developed
260 ORIGIN OF SPECIES
in an abrupt or sudden manner. Nor should it be forgotten,
when we look to the special parts of allied species, instead of
to distinct species, that numerous and wonderfully fine grada-
tions can be traced, connecting together widely different
structures.
Many large groups of facts are intelligible only on the
principle that species have been evolved by very small steps.
For instance, the fact that the species included in the larger
genera are more closely related to each other, and present a
greater number of varieties than do' the species in the smaller
genera. The former are also' grouped in little clusters, like
varieties round species ; and they present other analogies with
varieties, as was shown in our second chapter. On this same
principle we can understand how it is that specific characters
are more variable than generic characters ; and how the parts
which are developed in an extraordinary degree or manner
are more variable than other parts of the same species.
Many analogous facts, all pointing in the same direction,
could be added.
Although very many species have almost certainly been
produced by steps not greater than those separating fine vari-
eties ; yet it may be maintained that some have been devel-
oped in a different and abrupt manner. Such an admission,
however, ought not to be made without strong evidence being
assigned. The vague and in some respects false analogies,
as they have been shown to be by Mr. Chauncey Wright,
which have been advanced in favour of this view, such as the
sudden crystallisation of inorganic substances, or the falling
of a facetted spheroid from one facet to another, hardly de-
serve consideration. One class of facts, however, namely, the
sudden appearance of new and distinct forms of life in our geo-
logical formations supports at first sight the belief in abrupt
development. But the value of this evidence depends entirely
on the perfection of the geological record, in relation to
periods remote in the history of the world. If the record is
as fragmentary as many geologists strenuously assert, there
is nothing strange in new forms appearing as if suddenly
developed.
Unless we admit transformations as prodigious as those
advocated by Mr. Mivart, such as the sudden development of
THEORY OF NATURAL SELECTION 261
the wings of birds or bats, or the sudden conversion of a
Hipparion into a horse, hardly any light is thrown by the be-
lief in abrupt modifications on the deficiency of connecting
links in our geological formations. But against the belief in
such abrupt changes, embryology enters a strong protest. It
is notorious that the wings of birds and bats, and the legs of
horses or other quadrupeds, are undistinguishable at an early
embryonic period, and that they become differentiated by in-
sensibly fine steps. Embryological resemblances of all kinds
can be accounted for, as we shall hereafter see, by the pro-
genitors of our existing species having varied after early
youth, and having transmitted their newly acquired char-
acters to their offspring, at a corresponding age. The em-
bryo is thus left almost unaffected, and serves as a record of
the past condition of the species. Hence it is that existing
species during the early stages of their development so often
resemble ancient and extinct forms belonging to the same
class. On this view of the meaning of embryological resem-
blances, and indeed on any view, it is incredible that an ani-
mal should have undergone such momentous and abrupt trans-
formations, as those above indicated ; and yet should not bear
even a trace in its embryonic condition of any sudden modi-
fication ; every detail in its structure being developed by in-
sensibly fine steps.
He who believes that some ancient form was transformed
suddenly through an internal force or tendency into, for in-
stance, one furnished with wings, will be almost compelled
to assume, in opposition to all analogy, that many individuals
varied simultaneously. It cannot be denied that such abrupt
and great changes of structure are widely different from
those which most species apparently have undergone. He
will further be compelled to believe that many structures
beautifully adapted to all the other parts of the same creature
and to the surrounding conditions, have been suddenly pro-
duced; and of such complex and wonderful co-adaptations,
he will not be able to assign a shadow of an explanation.
He will be forced to admit that these great and sudden trans-
formations have left no trace of their action on the embryo.
To admit all this is, as it seems to me, to enter into the
realms of miracle, and to leave those of Science.
CHAPTER VIII
Instinct
Instincts comparable with habits, but different in their origin — In-
stincts graduated — Aphides and ants — Instincts variable — Do-
mestic instincts, their origin — Natural instincts of the cuckoo,
molothrus, ostrich, and parasitic bees — Slave-making ants — Hive-
bee, its cell-making instinct — Changes of instinct and structure
not necessarily simultaneous — Difficulties of the theory of the
Natural Selection of instincts — Neuter or sterile insects —
Summary.
MANY instincts are so wonderful that their develop-
ment will probably appear to the reader a difficulty
sufficient to overthrow my whole theory. I may
here premise, that I have nothing to do with the origin of
the mental powers, any more than I have with that of life
itself. We are concerned only with the diversities of instinct
and of the other mental faculties in animals of the same class.
I will not attempt any definition of instinct. It would be
easy to show that several distinct mental actions are com-
monly embraced by this term ; but every one understands
what is meant, when it is said that instinct impels the cuckoo
to migrate and to lay her eggs in other birds' nests. An ac-
tion, which we ourselves require experience to enable us to
perform, when performed by an animal, more especially by a
very young one, without experience, and when performed by
many individuals in the same way, without their knowing
for what purpose it is performed, is usually said to be in-
stinctive. But I could show that none of these characters
are universal. A little dose of judgment or reason, as Pierre
Huber expresses it, often comes into play, even with animals
low in the scale of nature.
Frederick Cuvier and several of the older metaphysicians
have compared instinct with habit. This comparison gives,
I think, an accurate notion of the frame of mind under
262
INSTINCT 263
which an instinctive action is performed, but not necessarily
of its origin. How unconsciously many habitual actions are
performed, indeed not rarely in direct opposition to our con-
scious will ! yet they may be modified by the will or reason.
Habits easily become associated with other habits, with cer-
tain periods of time, and states of the body. When once
acquired, they often remain constant throughout life. Sev-
eral other points of resemblance between instincts and habits
could be pointed out. As in repeating a well-known song, so
in instincts, one action follows another by a sort of rhythm;
if a person be interrupted in a song, or in repeating anything
by rote, he is generally forced to go back to recover the
habitual train of thought; so P. Huber found it was with a
caterpillar, which makes a very complicated hammock; for if
he took a caterpillar which had completed its hammock up to,
say, the sixth stage of construction, and put it into a ham-
mock completed up only to the third stage, the caterpillar
simply re-performed the fourth, fifth, and sixth stages of
construction. If, however, a caterpillar were taken out of a
hammock made up, for instance, to the third stage, and were
put into one finished up to the sixth stage, so that much of
its work was already done for it, far from deriving any bene-
fit from this, it was much embarrassed, and in order to com-
plete its hammock, seemed forced to start from the third
stage, where it had left off, and thus tried to complete the
already finished work.
If we suppose any habitual action to become inherited — and
it can be shown that this does sometimes happen — then the
resemblance between what originally was a habit and an in-
stinct becomes so close as not to be distinguished. If Mozart,
instead of playing the pianoforte at three years old With won-
derfully little practice, had played a tune with no practice at
all, he might truly be said to have done so instinctively. But
it would be a serious error to suppose that the greater num-
ber of instincts have been acquired by habit in one genera-
tion, and then transmitted by inheritance to succeeding gen-
erations. It can be clearly shown that the most wonderful
instincts with which we are acquainted, namely, those of the
hive-bee and of many ants, could not possibly have been ac-
quired by habit.
264 ORIGIN OF SPECIES
It will be universally admitted that instincts are as im-
portant as corporeal structures for the welfare of each spe-
cies, under its present conditions of life. Under changed con-
ditions of life, it is at least possible that slight modifications
of mstinct might be profitable to a species; and if it can be
shown that instincts do vary ever so little, then I can see no
difficulty in natural selection preserving and continually accu-
mulating variations of instinct to any extent that was profit-
able. It is thus, as I believe, that all the most complex and
wonderful instincts have originated. As modifications of
corporeal structure arise from, and are increased by, use or
habit, and are diminished or lost by disuse, so I do not doubt
it has been with instincts. But I believe that the effects of
habit are m many cases of subordinate importance to the
effects of the natural selection of what may be called spon-
taneous variations of instincts; — that is of variations pro-
duced by the same unknown causes which produce slight
deviations of bodily structure.
No complex instinct can possibly be produced through
natural selection, except by the slow and gradual accumula-
tion of numerous slight, yet profitable, variations. Hence, as
in the cases of corporeal structures, we ought to find in
nature, not the actual transitional gradations by which each
complex instinct has been acquired — for these could be found
only in the lineal ancestors of each species — but we ought to
find in the collateral lines of descent some evidence of such
gradations; or we ought at least be able to show that grada-
tions of some kind are possible ; and this we certainly can do.
I have been surprised to find, making allowance for the in-
stincts of animals having been but little observed except in
Europe and North America, and for no instinct being known
amongst extinct species, how very generally gradations, lead-
ing to the most complex instincts, can be discovered. Changes
of instinct may sometimes be facilitated by the same species
having different instincts at different periods of life, or at
different seasons of the year, or when placed under different
circumstances, &c. ; in which case either the one or the other
instinct might be preserved by natural selection. And such
instances of diversity of instinct in the same species can be
shown to occur in nature.
INSTINCT 265
Again, as in the case of corporeal structure, and conform-
ably to my theory, the instinct of each species is good for
itself, but has never, as far as we can judge, been produced
for the exclusive good of others. One of the strongest in-
stances of an animal apparently performing an action for the
sole good of another, with which I am acquainted, is that of
aphides voluntarily yielding, as was first observed by Huber,
their sweet excretion to ants : that they do so voluntarily, the
following facts show. I removed all the ants from a group
of about a dozen aphides on a dock-plant, and prevented their
attendance during several hours. After this interval, I felt
sure that the aphides would want to excrete. I watched them
for some time through a lens, but not one excreted; I then
tickled and stroked them with a hair in the same manner, as
well as I could, as the ants do with their antennae ; but not one
excreted. Afterwards I allowed an ant to visit them, and it
immediately seemed, by its eager way of running about, to be
well aware what a rich flock it had discovered; it then began
to play with its antennae on the abdomen first of one aphis and
then of another ; and each, as soon as it felt the antennae,
immediately lifted up its abdomen and excreted a limpid drop
of sweet juice, which was eagerly devoured by the ant. Even
the quite young aphides behaved in this manner, showing that
the action was instinctive, and not the result of experience.
It is certain, from the observations of Huber, that the aphides
show no dislike to the ants: if the latter be not present they
are at last compelled to eject their excretion. But as the ex-
cretion is extremely viscid, it is no doubt a convenience to
the aphides to have it removed ; therefore probably they do
not excrete solely for the good of the ants. Although there
is no evidence that any animal performs an action for the
exclusive good of another species, yet each tries to take ad-
vantage of the instincts of others, as each takes advantage
of the weaker bodily structure of other species. So again
certain instincts cannot be considered as absolutely perfect;
but as details on this and other such points are not indis-
pensable, they may be here passed over.
As some degree of variation in instincts under a state of
nature, and the inheritance of such variations, are indis-
pensable for the action of natural selection, as many instances
266 ORIGIN OF SPECIES
as possible ought to be given; but want of space prevents me.
I can only assert that instincts certainly do vary — for in-
stance, the migratory instinct, both in extent and direction,
and in Its total loss. So it is with the nests of birds, which
vary partly in dependence on the situations chosen, and on
the nature and temperature of the country inhabited, but
often from causes wholly unknown to us: Audubon has given
several remarkable cases of differences in the nests of the
same species in the northern and southern United States.
Why, it has been asked, if instinct be variable, has it not
granted to the bee "the ability to use some other material
when wax was deficient"? But what other natural material
could bees use? They will work, as I have seen, with wax
hardened with vermilion or softened with lard. Andrew
Knight observed that his bees, instead of laboriously collect-
ing propolis, used a cement of wax and turpentine, with
which he had covered decorticated trees. It has lately been
shown that bees, instead of searching for pollen, will gladly
use a very different substance, namely oatmeal. Fear of any
particular enemy is certainly an instinctive quality, as may
be seen in nestling birds, though it is strengthened by experi-
ence, and by the sight of fear of the same enemy in other
animals. The fear of man is slowly acquired, as I have else-
where shown, by the various animals which inhabit desert
islands; and we see an instance of this even in England, in
the greater wildness of all our large birds in comparison with
our small birds; for the large birds have been most persecuted
by man. We may safely attribute the greater wildness of our
large birds to this cause ; for in uninhabited islands large birds
are not more fearful than small ; and the magpie, so wary in
England, is tame in Norway, as is the hooded crow in Egypt.
That the mental qualities of animals of the same kind, born
in a state of nature, vary much, could be shown by many
facts. Several cases could also be adduced of occasional and
strange habits in wild animals, which, if advantageous to the
species, might have given rise, through natural selection, to
new instincts. But I am well aware that these general state-
ments, without the facts in detail, will produce but a feeble
effect on the reader's mind. I can only repeat my assurance,
that I do not speak without good evidence.
CHANGES OF HABIT OR INSTINCT 267
INHERITED CHANGES OF HABIT OR INSTINCT IN
DOMESTICATED ANIMALS
The possibility, or even probability, of inherited variations
of instinct in a state of nature will be strengthened by briefly
considering a few cases under domestication. We shall thus
be enabled to see the part which habit and the selection of so-
called spontaneous variations have played in modifying the
mental qualities of our domestic animals. It is notorious
how much domestic animals vary in their mental qualities.
With cats, for instance, one naturally takes to catching rats,
and another mice, and these tendencies are known to be in-
herited. One cat, according to Mr. St. John, always brought
home game-birds, another hares or rabbits, and another
hunted on marshy ground and almost nightly caught wood-
cocks or snipes. A number of curious and authentic instances
could be given of various shades of disposition and of taste,
and likewise of the oddest tricks, associated with certain
frames of mind or periods of time, being inherited. But let
us look to the familiar case of the breeds of the dogs : it can-
not be doubted that young pointers (T have myself seen a
striking instance) will sometimes point and even back other
dogs the very first time that they are taken out; retrieving
is certainly in some degree inherited by retrievers ; and a ten-
dency to run round, instead of at, a flock of sheep, by shep-
herd dogs. I cannot see that these actions, performed without
experience by the young, and in nearly the same manner by
each individual, performed with eager delight by each breed,
and without the end being known — for the young pointer can
no more know that he points to aid his master, than the white
butterfly knows why she lays her eggs on the leaf of the cab-
bage — I cannot see that these actions differ essentially from
true instincts. If we were to behold one kind of wolf, when
young and without any training, as soon as it scented its prey,
stand motionless like a statue, and then slowly crawl forward
with a peculiar gait; and another kind of wolf rushing round,
instead of at, a herd of deer, and driving them to a distant
point, we should assuredly call these actions instinctive.
Domestic instincts, as they may be called, are certainly far
less fixed than natural jnstincts ; but they have been acted on
268 ORIGIN OF SPECIES
by far less rigorous selection, and have been transmitted for
an incomparably shorter period, under less fixed conditions
of life.
How strongly these domestic instincts, habits, and disposi-
tions are inherited, and how curiously they become mingled,
is well shown when different breeds of dogs are crossed.
Thus it is known that a cross with a bull-dog has affected for
many generations the courage and obstinacy of greyhounds;
and a cross with a greyhound has given to a whole family of
shepherd-dogs a tendency to hunt hares. These domestic in-
stincts, when thus tested by crossing, resemble natural in-
stincts, which in a like manner become curiously blended
together, and for a long period exhibit traces of the instincts
of either parent : for example, Le Roy describes a dog, whose
great-grandfather was a wolf, and this dog showed a trace
of its wild parentage only in one way, by not coming in a
straight line to his master, when called.
Domestic instincts are sometimes spoken of as actions which
have become inherited solely from long-continued and com-
pulsory habit; but this is not true. No one would ever have
thought of teaching, or probably could have taught, the
tumbler-pigeon to tumble, — an action which, as I have wit-
nessed, is performed by young birds, that have never seen a
pigeon tumble. We may believe that some one pigeon showed
a slight tendency to this strange habit, and that the long-
continued selection of the best individuals in successive gen-
erations made tumblers what they now are; and near Glasgow
there are house-tumblers, as I hear from Mr. Brent, which
cannot fly eighteen inches high without going head over
heels. It may be doubted whether any one would have
thought of training a dog to point, had not some one dog
naturally shown a tendency in this line; and this is known
occasionally to happen, as I once saw, in a pure terrier: the
act of pointing is probably, as many have thought, only the
exaggerated pause of an animal preparing to spring on its
prey. When the first tendency to point was once displayed,
methodical selection and the inherited effects of compulsory
training in each successive generation would soon complete
the work; and unconscious selection is still in progress, as
each man tries to procure, without intending to improve the
CHANGES OF HABIT OR INSTINCT 269
breed, dogs which stand and hunt best. On the other hand,
habit alone in some cases has sufficed; hardly any animal is
more difficult to tame than the young of the wild rabbit ;
scarcely any animal is tamer than the young of the tame rab-
bit; but I can hardly suppose that domestic rabbits have often
been selected for tameness alone ; so that we must attribute at
least the greater part of the inherited change from extreme
wildness to extreme tameness, to habit and long-continued
close confinement.
Natural instincts are lost under domestication : a remark-
able instance of this is seen in those breeds of fowls which
very rarely or never become "broody," that is, never wish to
sit on their eggs. Familiarity alone prevents our seeing how
largely and how permanently the minds of our domestic ani-
mals have been modified. It is scarcely possible to doubt that
the love of man has become instinctive in the dog. All wolves,
foxes, jackals, and species of the cat genus, when kept tame,
are most eager to attack poultry, sheep, and pigs ; and this
tendency has been found incurable in dogs which have been
brought home as puppies from countries such as Tierra del
Fuego and Australia, where the savages do not keep these
domestic animals. How rarely, on the other hand, do our
civilised dogs, even when quite young, require to be taught
not to attack poultry, sheep, and pigs ! No doubt they occa-
sionally do make an attack, and are then beaten ; and if not
cured, they are destroyed; so that habit and some degree of
selection have probably concurred in civilising by inheritance
our dogs. On the other hand, young chickens have lost,
wholly by habit, that fear of the dog and cat which no doubt
was originally instinctive in them; for I am informed by
Captain Hutton that the young chickens of the parent-stock,
the Gallus bankiva, when reared in India under a hen, are at
first excessively wild. So it is with young pheasants reared
in England under a hen. It is not that chickens have lost all
fear, but fear only of dogs and cats, for if the hen gives the
danger-chuckle, they will run (more especially young tur-
keys) from under her, and conceal themselves in the sur-
rounding grass or thickets ; and this is evidently done for the
instinctive purpose of allowing, as we see in wild ground-
birds, their mother to fly away. But this instinct retained by
270 ORIGIN OF SPECIES
our chickens has become useless under domestication, for the
mother-hen has almost lost by disuse the power of flight.
Hence, we may conclude, that under domestication instincts
have been acquired, and natural instincts have been lost,
partly by habit, and partly by man selecting and accumulating,
during successive generations, peculiar mental habits and ac-
tions, which at first appeared from what we must in our
ignorance call an accident. In some cases compulsory habit
alone has sufficed to produce inherited mental changes; in
other cases, compulsory habit has done nothing, and all has
been the result of selection, pursued both methodically and
unconsciously: but in most cases habit and selection have
probably concurred.
SPECIAL INSTINCTS
We shall, perhaps, best understand how instincts in a state
of nature have become modified by selection, by considering
a few cases. I will select only three, — namely, the instinct
which leads the cuckoo to lay her eggs in other birds' nests;
the slave-making instinct of certain ants ; and the cell-making
power of the hive-bee. These two latter instincts have gener-
ally and justly been ranked by naturalists as the most won-
derful of all known instincts.
Instincts of the Cuckoo. — It is supposed by some naturalists
that the more immediate cause of the instinct of the cuckoo
is, that she lays her eggs, not daily, but at intervals of two
or three days; so that, if she were to make her own nest and
sit on her own eggs, those first laid would have to be left for
some time unincubated, or there would be eggs and young
birds of different ages in the same nest. If this were the
case, the process of laying and hatching might be inconveni-
ently long, more especially as she migrates at a very early
period; and the first hatched young would probably have to
be fed by the male alone. But the American cuckoo is in this
predicament; for she makes her own nest, and has eggs and
young successively hatched, all at the same time. It has been
both asserted and denied that the American cuckoo occasion-
ally lays her eggs in other birds' nests; but I have lately heard
from Dr. Merrell, of Iowa, that he once found in Illinois a
young cuckoo together with a young jay in the nest of a Blue
INSTINCTS OF THE CUCKOO 271
jay (Garrulus cristatus) ; and as both were nearly full feath-
ered, there could be no mistake in their identification. I could
also give several instances of various birds which have been
known occasionally to lay their eggs in other birds' nests.
Now let us suppose that the ancient progenitor of our Euro-
pean cuckoo had the habits of the American cuckoo, and that
she occasionally laid an egg in another bird's nest. If the
old bird profited by this occasional habit through being enabled
to migrate earlier or through any other cause ; or if the young
were made more vigorous by advantage being taken of the
mistaken instinct of another species than when reared by their
own mother, encumbered as she could hardly fail to be by
having eggs and young of different ages at the same time;
then the old birds or the fostered young would gain an ad-
vantage. And analogy would lead us to believe, that the
young thus reared would be apt to follow by inheritance the
occasional and aberrant habit of their mother, and in their
turn would be apt to lay their eggs in other birds' nests, and
thus be more successful in rearing their young. By a con-
tinued process of this nature, I believe that the strange in-
stinct of our cuckoo has been generated. It has, also, re-
cently been ascertained on sufficient evidence, by Adolf
Miiller, that the cuckoo occasionally lays her eggs on the bare
ground, sits on them, and feeds her young. This rare event is
probably a case of reversion to the long-lost, aboriginal in-
stinct of nidification.
It has been objected that I have not noticed other related
instincts and adaptations of structure in the cuckoo, which
are spoken of as necessarily co-ordinated. But in all cases,
speculation on an instinct known to us only in a single species,
is useless, for we have hitherto had no facts to guide us.
Until recently the instincts of the European and of the non-
parasitic American cuckoo alone were known; now, owing to
Mr. Ramsay's observations, we have learnt something about
three Australian species, which lay their eggs in other birds'
nests. The chief points to be referred to are three: first, that
the common cuckoo, with rare exceptions, lays only one egg
in a nest, so that the large- and voracious young bird receives
ample food. Secondly, that the eggs are remarkably small,
not exceeding those of -the skylark, — a bird about one- fourth
272 ORIGIN OF SPECIES
as large as the cuckoo. That the small size of the egg is a
real case of adaptation we may infer from the fact of
the non-parasitic American cuckoo laying full-sized eggs.
Thirdly, that the young cuckoo, soon after birth, has the in-
stinct, the strength, and a properly shaped back for ejecting
its foster-brothers, which then perish from cold and hunger.
This has been boldly called a beneficial arrangement, in order
that the young cuckoo may get sufficient food, and that its
foster-brothers may perish before they had acquired much
feeling !
Turning now to the Australian species ; though these birds
generally lay only one egg in a nest, it is not rare to find two
and even three eggs in the same nest. In the Bronze cuckoo
the eggs vary greatly in size, from eight to ten lines in length.
Now if it had been of an advantage to this species to have
laid eggs even smaller than those now laid, so as to have de-
ceived certain foster-parents, or, as is more probable, to have
been hatched within a shorter period (for it is asserted that
there is a relation between the size of eggs and the period of
their incubation), then there is no difficulty in believing that
a race or species might have been formed which would have
laid smaller and smaller eggs; for these would have been
more safely hatched and reared. Mr. Ramsay remarks that
two of the Australian cuckoos, when they lay their eggs in
an open nest, manifest a decided preference for nests con-
taining eggs similar in colour to their own. The European
species apparently manifests some tendency towards a similar
instinct, but not rarely departs from it, as is shown by her
laying her dull and pale-coloured eggs in the nest of the
Hedge-warbler with bright greenish-blue eggs. Had our
cuckoo invariably displayed the above instinct, it would as-
suredly have been added to those which it is assumed must
all have been acquired together. The eggs of the Australian
Bronze cuckoo vary, according to Mr. Ramsay, to an ex-
traordinary degree in colour; so that in this respect, as well
as in size, natural selection might have secured and fixed any
advantageous variation.
In the case of the European cuckoo, the offspring of the
foster-parents are commonly ejected from the nest within
three days after the cuckoo is hatched; and as the latter at
INSTINCTS OF THE MOLOTHRUS 273
this age is in a most helpless condition, Mr. Gould was for-
merly inclined to believe that the act of ejection was per-
formed by the foster-parents themselves. But he has now re-
ceived a trustworthy account of a young cuckoo which was
actually seen, whilst still blind and not able even to hold up
its own head, in the act of ejecting its foster-brothers. One
of these was replaced in the nest by the observer, and was
again thrown out. With respect to the means by which this
strange and odious instinct was acquired, if it were of great
importance for the young cuckoo, as is probably the case, to
receive as much food as possible soon after birth, I can see
no special difificulty in its having gradually acquired, during
successive generations, the blind desire, the strength, and
structure necessary for the work of ejection; for those young
cuckoos which had such habits and structure best developed
would be the most securely reared. The first step towards
the acquisition of the proper instinct might have been mere
unintentional restlessness on the part of the young bird, when
somewhat advanced in age and strength; the habit having
been afterwards improved, and transmitted to an earlier age.
I can see no more difficulty in this, than in the unhatched
young of other birds acquiring the instinct to break through
their own shells ; — or than in young snakes acquiring in their
upper jaws, as Owen has remarked, a transitory sharp tooth
for cutting through the tough egg-shell. For if each part is
liable to individual variations at all ages, and the variations
tend to be inherited at a corresponding or earlier age, — propo-
sitions which cannot be disputed, — then the instincts and
structure of the young could be slowly modified as surely as
those of the adult ; and both cases must stand or fall together
with the whole theory of natural selection.
Some* species of Molothrus, a widely distinct genus of
American birds, allied to our starlings, have parasitic habits
like those of the cuckoo ; and the species present an interest-
ing gradation in the perfection of their instincts. The sexes
of Molothrus badius are stated by an excellent observer, Mr.
Hudson, sometimes to live promiscuously together in flocks,
and sometimes to pair. They either build a nest of their own,
or seize on one belonging to some other bird, occasionally
throwing OMt the nestlings of the stranger. They either lay
274 ORIGIN OF SPECIES
their eggs in the nest thus appropriated, or oddly enough build
one for themselves on the top of it. They usually sit on their
own eggs and rear their own young; but Mr. Hudson says it
is probable that they are occasionally parasitic, for he has
seen the young of this species following old birds of a distinct
kind and clamouring to be fed by them. The parasitic habits
of another species of Molothrus, the M. bonariensis, are much
more highly developed than those of the last, but are still far
from perfect. This bird, as far as it is known, invariably
lays its eggs in the nests of strangers ; but it is remarkable
that several together sometimes commence to build an irregu-
lar untid)' nest of their own, placed in singularly ill-adapted
situations, as on the leaves of a large thistle. They never,
however, as far as Mr. Hudson has ascertained, complete a
nest for themselves. They often lay so many eggs — from
fifteen to twenty — in the same foster-nest, that few or none
can possibly be hatched. They have, moreover, the extraordi-
nary habit of pecking holes in the eggs, whether of their own
species or of their foster-parents, which they find in the ap-
propriated nests. They drop also many eggs on the bare
ground, which are thus wasted. A third species, the M. pecoris
of North America, has acquired instincts as perfect as those
of the cuckoo, for it never lays more than one egg in a foster-
nest, so that the young bird is securely reared. Mr. Hudson is
a strong disbeliever m evolution, but he appears to have been
£0 much struck by the imperfect instincts of the Molothrus
bonariensis that he quotes my words, and asks, "Must we con-
sider these habit-s, not as especially endowed or created in-
stincts, but as small consequences of one general law, namely,
transition?"
Various birds, as has already been remarked, occasionally
lay their eggs in the nests of other birds. This habit is not
very uncommon with the Gallinaceae, and throws some light
on the singular instinct of the ostrich. In this family several
hen-birds unite and lay first a few eggs in one nest and then
in another; and these are hatched by the males. This instinct
may probably be accounted for by the fact of the hens laying
a large number of eggs, but, as with the cuckoo, at intervals
of two or three days. The instinct, however, of the American
ostrich, as in the case of the Molothrus bonariensis, has not
SLAVE-MAKING INSTINCT 275
as yet been perfected ; for a surprising number of eggs lie
strewed over the plains, so that in one day's hunting I picked
up no less than twenty lost and wasted eggs.
Many bees are parasitic, and regularly lay their eggs in the
nests of other kinds of bees. This case is more remarkable
than that of the cuckoo; for these bees have not only had
their instincts but their structure modified in accordance with
their parasitic habits ; for they do not possess the pollen-
collecting apparatus which would have been indispensable if
they had stored up food for their own young. Some species
of Sphegidae (wasp-like insects) are likewise parasitic; and
M. Fabre has lately shown good reason for believing that,
although the Tachytes nigra generally makes Its own burrow
and stores it with paralysed prey for its own larvae, yet that,
when this insect finds a burrow already made and stored by
another sphex, it takes advantage of the prize, and becomes
for the occasion parasitic. In this case, as with that of the
Molothrus or cuckoo, I can see no difficulty in natural selec-
tion making an occasional habit permanent, if of advantage
to the species, and if the insect whose nest and stored food
are feloniously appropriated, be not thus exterminated.
Slave-making instinct. — This remarkable instinct was first
discovered in the Formica (Polyerges) rufescens by Pierre
Huber, a better observer even than his celebrated father. This
ant is absolutely dependent on its slaves; without their aid,
the species would certainly become extinct in a single year.
The males and fertile females do no work of any kind, and
the workers or sterile females, though most energetic and
courageous in capturing slaves, do no other work. They are
incapable of making their own nests, or of feeding their own
larvae. When the old nest is found inconvenient, and they
have to migrate, it is the slaves which determine the migra-
tion, and actually carry their masters in their jaws. So
utterly helpless are the masters, that when Huber shut up
thirty of them without a slave, but with plenty of the food
which they like best, and with their own larvae and pupae to
stimulate them to work, they did nothing; they could not
even feed themselves, and many perished of hunger. Huber
then introduced a single slave (F. fusca), and she instantly
set to work, fed and sayed the survivors; made some cells
276 ORIGIN OF. SPECIES
and tended the larvse, and put all to rights. What can be
more extraordinary than these well-ascertained facts? If
we had not known of any other slave-making ant, it would
have been hopeless to speculate how so wonderful an mstinct
could have been perfected.
Another species, Formica sanguinea, was likewise first dis-
covered by P Huber to be a slave-making ant. This species
is found in the southern parts of England, and its habits
have been attended to by Mr. F. Smith, of the British Mu-
seum, to whom I am much indebted for information on this
and other subjects. Although fully trusting to the statements
of Huber and Mr Smith, I tried to approach the subject in a
sceptical frame of mind, as any one may well be excused for
doubtmg the existence of so extraordinary an instinct as
that of making slaves. Hence, I will give the observations
which I made in some little detail. I opened fourteen nests
of F. sanguinea, and found a few slaves in all. Males and
fertile females of the slave species (F. fusca) are found
only in their own proper communities, and have never been
observed in the nests of F. sanguinea. The slaves are black
and not above half the size of their red masters, so that the
contrast in their appearance is great. When the nest is
slightly disturbed, the slaves occasionally come out, and like
their masters are much agitated and defend the nest: when
the nest is much disturbed, and the larvae and pupae are ex-
posed, the slaves work energetically together with their mas-
ters in carrying them away to a place of safety. Hence, it
is clear, that the slaves feel quite at home. During the
months of June and July, on three successive years, I watched
for many hours several nests in Surrey and Sussex, and
never saw a slave cither leave or enter a nest. As, during
these months, the slaves are very few in number, I thought
that they might behave differently when more numerous ; but
Mr. Smith informs me that he has watched the nests at
various hours during May, June, and August, both in Surrey
and Hampshire, and has never seen the slaves, though pres-
ent in large numbers in August, either leave or enter the
nest Hence he considers them as strictly household slaves.
The masters, on the other hand, may be constantly seen
bringing in materials for the nest, and food of all kinds.
SLAVE-MAKING INSTINCT 277
During the year i860, however, in the month of July, I came
across a community with an unusually large stock of slaves,
and I observed a few slaves mingled with their masters
leaving the nest, and marching along the same road to a tall
Scotch-fir tree, twenty-five yards distant, which they ascended
together, probably in search of aphides or cocci. According
to Huber, who had ample opportunities for observation, the
slaves in Switzerland habitually work with their masters in
making the nest, and they alone open and close the doors in
the morning and evening ; and, as Huber expressly ' states,
their principal office is to search for aphides. This differ-
ence in the usual habits of the masters and slaves in the two
countries, probably depends merely on the slaves being cap-
tured in greater numbers in Switzerland than in England.
One day I fortunately witnessed a migration of F. san-
guinea from one nest to another, and it was a most interest-
ing spectacle to behold the masters carefully carrying their
slaves in their jaws instead of being carried by them, as in
the case of F. rufescens. Another day my attention was
struck by about a score of the slave-makers haunting the
same spot, and evidently not in search of food ; they ap-
proached and were vigorously repulsed by an independent
community of the slave-species (F. fusca) ; sometimes as
many as three of these ants clinging to the legs of the slave-
making F. sanguinea. The latter ruthlessly killed their small
opponents, and carried their dead bodies as food to their
nest, twenty-nine yards distant; but they were prevented
from getting any pupae to rear as slaves. I then dug up a
small parcel of the pupae of F. fusca from another nest, and
pur them down on a bare spot near the place of combat;
they were eagerly seized and carried off by the tyrants, who
perhaps fancied that, after all, they had been victorious in
their late combat.
At the same time I laid on the same place a small parcel
of the pupae of another species, F. flava, with a few of these
little yellow ants still clinging to the fragments of their
nest. This species is sometimes, though rarely, made into
slaves, as has been described by Mr. Smith. Although so
small a species, it is very courageous, and I have seen it
ferociously attack other ants. In one instance I fomid to my
278 ORIGIN OF SPECIES
surprise an independent community of F. flava under a stone
beneath a nest of the slave-making F. sanguinea; and when
I had accidentally disturbed both nests, the little ants at-
tacked their big neighbours with surprising courage. Now
I was curious to ascertain whether F. sanguinea could dis-
tinguish the pupae of F. fusca, which they habitually make
into slaves, from those of the little and furious F. flava,
which they rarely capture, and it was evident that they did
at once distinguish them ; for we have seen that they eagerly
and instantly seized the pupae of F. fusca, whereas they were
much terrified when they came across the pupae, or even the
earth from the nest, of F. flava, and quickly ran away ; but
in about a quarter of an hour, shortly after all the little yel-
low ants had crawled away, they took heart and carried off
the pupae.
One evening I visited another community of F. sanguinea,
and found a number of these ants returning home and enter-
ing their nests, carrying the dead bodies of F. fusca (show-
ing that it was not a migration) and numerous pupae. I
traced a long file of ants burthened with booty, for about
forty yards back, to a very thick clump of heath, whence I
saw the last individual of F. sanguinea emerge, carrying a
pupa ; but I was not able to find the desolated nest in the
thick heath. The nest, however, must have been close at
hand, for two or three individuals of F. fusca were rushing
about in the greatest agitation, and one was perched motion-
less with its own pupa in its mouth on the top of a spray
of heath, an image of despair over its ravaged home.
Such are the facts, though they did not need confirmation
by me, in regard to the wonderful instinct of making slaves.
Let it be observed what a contrast the instinctive habits of
F. sanguinea present with those of the continental F. rufes-
cens. The latter does not build its own nest, does not deter-
mine its own migrations, does not collect food for itself or
its young, and cannot even feed itself: it is absolutely depen-
dent on its numerous slaves. Formica sanguinea, on the
other hand, possesses much fewer slaves, and in the early
part of the summer extremely few: the masters determine
when and Avhere a new nest shall be formed, and when they
migrate, the masters carry the slaves. Both in Switzerland
CELL-MAKING INSTINCT 279
and England the slaves seem to have the exclusive care of
the larvae, and the masters alone go on slave-making expe-
ditions. In Switzerland the slaves and masters work to-
gether, making and bringing materials for the nest; both,
but chiefly the slaves, tend, and milk, as it may be called,
their aphides; and thus both collect food for the community.
In England the masters alone usually leave the nest to col-
lect building materials and food for themselves, their slaves
and larvae. So that the masters in this country receive much
less service from their slaves than they do in Switzerland.
By what steps the instinct of F. sanguinea originated I
will not pretend to conjecture. But as ants which are not
slave-makers will, as I have seen, carry off the pupae of
other species, if scattered near their nests, it is possible that
such pupae originally stored as food might become developed ;
and the foreign ants thus unintentionally reared would then
follow their proper instincts, and do what work they could.
If their presence proved useful to the species which had
seized them — if it were more advantageous to this species
to capture workers than to procreate them — the habit of col-
lecting pupje, originally for food, might by natural selection
be strengthened and rendered permanent for the very dif-
ferent purpose of raising slaves. When the instinct was
once acquired, if carried out to a much less extent even
than in our British F. sanguinea, which, as we have seen, is
less aided by its slaves than the same species in Switzerland,
natural selection might increase and modify the instinct —
always supposing each modification to be of use to the spe-
cies — until an ant was formed as abjectly dependent on its
slaves as is the Formica rufescens.
Cell-rdaking instinct of the Hivc-Bcc. — I will not here
enter on minute details on this subject, but will merely give
an outline of the conclusions at which I have arrived. He
must be a dull man who can examine the exquisite structure
of a comb, so beautifully adapted to its end, without enthusi-
astic admiration. We hear from mathematicians that bees
have practically solved a recondite problem, and have made
their cells of the proper shape to hold the greatest possible
amount of honey, with tht least possible consumption of
precious wax in their construction. It has been remarked
280 ORIGIN OF SPECIES
that a skilful workman with fitting tools and measures,
would find it very difficult to make cells of wax of the true
form, though this is effected by a crowd of bees working
in a dark hive. Granting whatever instincts you please, it
seems at first quite inconceivable how they can make all
the necessary angles and planes, or even perceive when they
are correctly made. But the difficulty is not nearly so great
as it at first appears: all this beautiful work can be shown,
I think, to follow from a few simple instincts.
I was led to investigate this subject by Mr. Waterhouse,
who has shown that the form of the cell stands in close
relation to the presence of adjoining cells; and the follow-
ing view may, perhaps, be considered only as a modification
of his theory. Let us look to the great principle of grada-
tion, and see whether Nature does not reveal to us her
method of work. At one end of a short series we have
humble-bees, which use their old cocoons to hold honey,
sometimes adding to them short tubes of wax, and likewise
making separate and very irregular rounded cells of wax.
At the other end of the series we have the cells of the hive-
bee, placed in a double layer : each cell, as is well known,
is an hexagonal prism, with the basal edges of its six sides
bevelled so as to join an inverted pyramid, of three rhombs.
These rhombs have certain angles, and the three which form
the pyramidal base of a single cell on one side of the comb
enter into the composition of the bases of three adjoining
cells on the opposite side. In the series between the extreme
perfection of the cells of the hive-bee and the simplicity of
those of the humble-bee we have the cells of the Mexican
Melipona domestica, carefully described and figured by Pierre
Huber. The Melipona itself is intermediate in structure be-
tween the hive and humble-bee, but more nearly related to
the latter ; it forms a nearly regular waxen comb of cylin-
drical cells, in which the young are hatched, and, in addi-
tion, some large cells of wax for holding honey. These
latter cells are nearly spherical and of nearly equal sizes, and
are aggregated into an irregular mass. But the important
point to notice is, that these cells are always made at that
degree of nearness to each other that they would have inter-
sected or broken into each other if the spheres had been
CELL- MAKING INSTINCT 281
completed ; but this is never permitted, the bees building per-
fectly flat walls of wax between the spheres which thus
tend to intersect. Hence, each cell consists of an outer
spherical portion, and of two, three, or more flat surfaces,
according as the cell adjoins two, three, or more other cells.
When one cell rests on three other cells, which, from the
spheres being nearly of the same size, is very frequently
and necessarily the case, the three flat surfaces are united
into a pyramid ; and this pyramid, as Huber has remarked,
is manifestly a gross imitation of the three-sided pyramidal
base of the cell of the hive-bee. As in the cells of the hive-
bee, so here, the three plane stirfaces in any one cell neces-
sarily enter into the construction of three adjoining cells.
It is obvious that the Melipona saves wax, and what is more
important, labour, by this manner of building; for the flat
walls between the adjoining cells are not double, but are
of the same thickness as the outer spherical portions, and
yet each flat portion forms a part of two cells.
Reflecting on this case, it occurred to me that if the Meli-
pona had made its spheres at some given distance from each
other, and had made them of equal sizes and had arranged
them symmetrically in a double layer, the resulting structure
would have been as perfect as the comb of the hive-bee. Ac-
cordingly 1 wrote to Professor Miller of Cambridge, and
this geometer has kindly read over the following statement,
drawn up from his information, and tells me that it is
strictly correct : —
If a number of equal spheres be described with their
centres placed in two parallel layers ; with the centre of each
sphere at the distance of radius >/ y'2, or radius X ^ '41421
(or at some lesser distance), from the centres of the six
surrounding spheres in the same layer ; and at the same dis-
tance from the centres of the adjoining spheres in the other
and parallel layer; then, if planes of intersection between
the several spheres in both layers be formed, there will re-
sult a double layei ot hexagonal prisms united together by
pyramidal bases formed of three rhombs; and the rhombs
and the sides of the hexagohal prisms will have every angle
identically the same with the best measurements which have
been made of the cells of the hive-bee. But I hear from
282 ORIGIN OF SPECIES
Prof. Wyman, who has made numerous careful measure-
ments, that the accuracy of the workmanship of the bee has
been greatly exaggerated ; so much so, that whatever the
typical form of the cell may be, it is rarely, if ever, realised.
Hence we may safely conclude that, if we could slightly
modify the instincts already possessed by the Melipona, and
in themselves not very wonderful, this bee would make a
structure as wonderfully perfect as that of the hive-bee. We
must suppose the Melipona to have the power of forming
her cells truly spherical, and of equal sizes ; and this would
not be very surprising, seeing that she already does so to a
certain extent, and seeing what perfectly cylindrical bur-
rows many insects make in wood, apparently by turning
round on a fixed point. We must suppose the Melipona to
arrange her cells in level layers, as she already does her
cylindrical cells; and we must further suppose, and this is
the greatest difficulty, that she can somehow judge accu-
rately at what distance to stand from her fellow-labourers
when several are making their spheres ; but she is already
so far enabled to judge of distance, that she always describes
her spheres so as to intersect to a certain extent ; and then
she unites the points of intersection by perfectly flat sur-
faces. By such modifications of instincts which in them-
selves are not very wonderful — hardly more wonderful than
those which guide a bird to make its nest, — I believe that
the hive-bee has acquired, through natural selection, her
inimitable architectural powers
But this theory can be tested by experiment. Following
the example of Mr. Tegetmeier, I separated two combs,
and put between them a long, thick, rectangular strip of
wax: the bees instantly began to excavate minute circular
pits in it; and as they deepened these little pits, they made
them wider and wider until they were converted into shal-
low basins, appearing to the eye perfectly true or parts of
a sphere, and of about the diameter of a cell. It was most
interesting to observe that, wherever several bees had be-
gun to excavate these basins near together, they had begun
their work at such a distance from each other, that by the
time the basins had acquired the above-stated width (/. e.
about the width of an ordinary cell), and were in depth
CELL-MAKING INSTINCT 283
about one-sixth of the diameter of the sphere of which they
formed a part, the rims of the basins intersected or broke
into each other. As soon as this occurred, the bees ceased to
excavate, and began to build up flat walls of wax on the
lines of intersection between the basins, so that each hex-
agonal prism was built upon the scalloped edge of a smooth
basin, instead of on the straight edges of a three-sided pyra-
mid as in the case of ordinary cells.
