The origin of species by means of natural selection; or, The preservation of favored races in the struggle for life

Os

++
vow

we ©
J se
Se.

Sian al :

Gr, o< wer * . “—e
wibes ev SE a oe L =o eee
~ rd ~oewm ff - 7 . bd

hg aw F . . vee
22 SA — :
= -

*

PRIA

ALBERT R. MANN
LIBRARY

New York STATE COLLEGES
OF
AGRICULTURE AND HoME ECONOMICS

AT

CoRNELL UNIVERSITY

LOA

1924 052

Cornell University

Library

The original of this book is in
the Cornell University Library.

There are no known copyright restrictions in
the United States on the use of the text.

http ://archive.org/details/cu31924052394107

THE ORIGIN OF SPECIES

BY MEANS OF NATURAL SELECTION

OR THE PRESERVATION OF FAVORED
RACES IN THE STRUGGLE FOR LIFE

By CHARLES DARWIN
M.A., LL.D., F.R.S.

WITH ADDITIONS AND CORRECTIONS
FROM SIXTH AND LAST ENGLISH EDITION

TWO VOLUMES IN ONE

NEW YORK
D. APPLETON AND COMPANY

1909

Le tee
Authorized Edition.

CONTENTS.

ADDITIONS AND CORRECTIONS, TO THE SixTH Epition . Page ix

HistoricaL SKETCH ‘ - r - ri ; ; . xiii
INTRODUCTION . a i 3 . : . . . : 1
CHAPTER I.

VARIATION UNDER DOMESTICATION.

Causes of Variability—Effects of Habit and the use or disuse of
Parts—Correlated Variation—Inheritance—Character of Do-
mestic Varieties—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, anciently followed, their Effects—
Methodical and Unconscious Selection—Unknown Origin of
our Domestic Productions—Circumstances favourable to Man’s
power of Selection . . ee re ne ee ee

CHAPTER II.

VARIATION UNDER NATURE.

Variability—Individual differences—Doubtful species—Wide rang-
ing, 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 . . . . ia. Jes ess clo 8. cigs: ar eol
v

vi CONTENTS.

CHAPTER II.

STRUGGLE FOR EXISTENCE,

Its bearing on natural selection—The term used in a wide sense—
Geometrical ratio of increase—Rapid increase of naturalised
animals and plants—Nature of the checks to increase—Com-
petition universal—Effects of Climate—Protection from the
number of individuals—Complex relations of all animals and
plants throughout nature—Struggle for life most severe between
individuals 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. . Page 75

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 intercrosses between individuals of the same species—Cir-
cumstances favourable and unfavourable to the results of
Natural Selection, namely, intercrossing, isolation, number of
individuals—Slow action—Extinction caused by Natural Se-
lection—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—Ex-
plains the grouping of all organic beings—Advance in organ-
isation—Low forms preserved—Convergence of Character—
Indefinite multiplication of species—Summary . . . 97

CHAPTER V.
LAWS OF VARIATION.

Effects of changed conditions—Use and disuse, combined with
natural selection; organs of flight and of vision—Acclimatisa-

)

CONTENTS. ae

tion—Correlated variation—-Compensation and economy of
growth—False correlations—Multiple, rudimentary, and lowly
organised structures variable—Parts developed in an unusual
manner are highly variable ; specific characters more variable
than generic: secondary sexual characters variable—Species
of the same genus vary in an analogous manner—Reversions to
long-lost characters—Summary . . . . Page 164

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
perfection—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 Conditions of Existence embraced by the theory of Natu-
ralSelection. . «© «© «© «© © «© « + 207

CHAPTER VII.

MISCELLANEOUS OBJECTIONS TO THE THEORY OF NATURAL
SELECTION.

Longevity—Modifications not necessarily simultaneous—Modifica-
tions apparently of no direct service—Progressive development
—Characters of small functional importance, the most con-
stant—Supposed incompetence of natural selection to account
for the incipient stages of useful structures—Causes which in-
terfere with the acquisition through natural selection of useful
structures—Gradations of structure with changed functions—
Widely different organs in members of the same class, de-
veloped from one and the same source—Reasons for disbeliev-
ing in great and abrupt modifications » ewe 262

viii CONTENTS.

CHAPTER VIIL

INSTINCT.

Instincts comparable with habits, but different in their origin—
Instincts graduated—Aphides and ants—Instincts variable—
Domestic instincts, their origin—Natvral 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. . . . . . . ~~ Page 319

ADDITIONS AND CORRECTIONS
TO THE SIXTH EDITION.

NUMEROUS small corrections have been made in the
last and present editions on various subjects, according
as the evidence has become somewhat stronger or weaker.
The more important corrections and some add#ons in
the present volume are tabulated on the following page,
for the convenience of those interested in the subject,
and who possess the fifth edition. The second edition
was little more than a reprint of the first. . The third
edition was largely corrected and added to, and the
fourth and fifth still more largely. As copies of the
present work will be sent abroad, it may be of use if I
specify the state of the foreign editions. The third
French and second German editions were from the third
English, with some few of the additions given in the
fourth edition. A new fourth French edition has been
translated by Colonel Moulinié; of which the first half
is from the fifth English, and the latter half from the
present edition. A third German edition, under the
superintendence of Professor Victor Carus, was from the
fourth English edition; a fifth is now preparing by the
same author from the present volume. The second
American edition was from the English second, with a

ix

x

ADDITIONS AND CORRECTIONS.

few of the additions given in the third; and a third
American edition has been printed from the fifth Eng-
lish edition.
and three Russian editions from the second English
edition, and the Swedish from the fifth English edition.

The Italian is from the third, the Dutch

ae. es, Chief Additions and Corrections.
Page Page
vol. {.

100 106 | Influence of fortuitous destruction on natural se-
lection.

158 156 | On the convergence of specific forms.

220 221 | Account of the Ground-Woodpecker of La Plata
modified.

225 227 | On the modification of the eye.

230 233 | Transitions through the acceleration or retarda-
tion of the period of reproduction.

231 234 | The account of the electric organ of fishes added to.

233 287 | Analogical resemblance between the eyes of Cepha-
lopods and Vertebrates.

234 239 | Claparéde on the analogical resemblance of the
hair-claspers of the Acaride.

248 254 | The probable use of the rattle to the Rattle-snake.

248 254 | Helmholtz on the imperfection of the human eye.

255 262 |The first part of this new chapter consists of por-
tions, in a much modified state, taken from chap.
iv. of the former editions. The latter and larger
part is new, and relates chiefly to the supposed
incompetency of natural selection to account
for the incipient stages of useful structures.
There is also a discussion on the causes which
prevent in many cases the acquisition through
natural selection of useful structures. Lastly,
reasons are given for disbelieving in great and
sudden modifications. Gradations of character,
often accompanied by changes of function, are
likewise here incidentally considered.

268 333 |The statement with respect to young cuckoos
ejecting their foster-brothers confirmed.

270 334 | On the cuckoo-like habits of the Molothrus.

vol. ff.
307 9 | On fertile hybrid moths.
819 22 |The discussion on the fertility of hybrids not

having been acquired through natural selection
condensed and modified, ‘

ADDITIONS AND CORRECTIONS.

aun, ety. Chief Additions and Corrections.
Page ae
vol. it,

326 On the causes of sterility of hybrids, added to and
corrected.

377 81 | Pyrgoma found in the chalk.

402 107 | Extinct forms serving to connect existing groups.

440 148 | On earth adhering to the feet of migratory birds.

463 172 | On the wide geographical range of a species of
Galaxias, a fresh-water fish.

505 218 | Discussion on analogical resemblances, enlarged
and modified.

516 232 | Homological structure of the feet of certain mar-
supial animals.

518 236 | On serial homologies, corrected.

520 237 | Mr. KE. Ray Lankester on morphology.

§21 240 | On the asexual reproduction of Chironomus.

541 262 | On the origin of rudimentary parts, corrected.

547 262 oe on the sterility of hybrids, cor-
rected.

552 275 | Recapitulation on the absence of fossils beneath
the Cambrian system, corrected.

568 293 | Natural selection not the exclusive agency in the
modification of species, as always maintained
in this work.

572. | 297 | The belief in the separate creation of species. gen-

erally held by naturalists, until a recent period.

“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 establishment 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, 2. e., to effect it
continually or at stated times, as what is supernatural or miraculous
does to effect it for once.”

Butter: Analogy of Revealed Religion.

“To conclude, therefore, let no man out of a weak conceit 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 24th, 1859.
Siath Edition, Jan. 1872.

xii

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 witt 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 allusions to the sub-
ject in the classical writers,* the first author who in

* Aristotle, in his ‘Physica 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 different 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. hereso-
ever, therefore, all things together (that is all the parts of one
whole) happened like as if they were made for the sake of some-
thing, these were preserved, having been appropriately constituted

xiii

Xiv HISTORICAL SKETCH.

modern times has treated it in a scientific spirit was
Buffon. But as his opinions fluctuated greatly at dif-
ferent periods, and as he does not enter on the causes
or means of the transformation of species, I need not
here enter on details.

Lamarck was the first man whose conclusions on the
subject excited much attention. This justly-celebrated
naturalist first published his views in 1801; he much
enlarged them in 1809 in his ‘ Philosophie Zoologique,’
and subsequently, in 1815, in the Introduction to his
‘Hist. Nat. des Animaux sans Vertébres.’ In these
works he upholds the doctrine that all species, including
man, are descended from other species. He first did
the eminent service of arousing attention to the proba-
bility 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 produc-
tions. 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

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
comprehended the principle, is shown by his remarks on the
formation of the teeth,

HISTORICAL SKETCH. XV

branches of trees. But he likewise believed in a law of
progressive development; and as all the forms of life
thus tend to progress, in order to account for the ex-
istence at the present day of simple productions, he
maintains that such forms are now spontaneously gen-
erated*

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 not until 1828 that he published
his conviction that the same forms have not been per-
petuated since the origin of all things. Geoffroy seems
to have relied chiefly on the conditions of life, or the
“monde ambiant” as the cause of change. He was
cautious in drawing conclusions, and did not believe
that existing species are now undergoing modification;
and, as his son adds, “ C’est donc un probléme 4 réserver
entiérement & Vavenir, supposé méme que l’avenir doive
avoir prise sur lui.”

In 1813, Dr. W. C. Wells read before the Royal

* T have taken the date of the first publication of Lamarck from
Isid. Geoffroy Saint-Hilaire’s (‘ Hist. Nat. Générale,’ tom. ii. p.
405, 1859) excellent history of opinion on this subject. In this
work a full account is given of Buffon’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), published in
1794. According to Isid. Geoffroy there is no doubt that Goethe
was an extreme partisan of similar views, as shown in the Intro-
duction to a work written in 1794 and 1795, but not published till
long afterwards: he has pointedly remarked (‘Goethe als Natur-
forscher,’ 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 singular 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
conclusion on the origin of snecies, in the years 1794-5,

xvi HISTORICAL SKETCH.

Society ‘An Account of a White female, part of whose
skin resembles 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 indi-
cated; but he applies it only to the races of man, and
to certain characters alone. After remarking that ne-
groes and mulattoes enjoy an immunity from certain
tropical diseases, he observes, firstly, that all animals
tend to vary in some degree, and, secondly, that agri-
culturists improve their domesticated animals by selec-
tion; 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 inhabi-
tants of the middle regions of Africa, some one would
be better fitted than the others to bear the diseases of
the country. 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 neigh-
bours. 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 varieties 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

HISTORICAL SKETCH. XVii

climates. I am indebted to Mr. Rowley, of the United
States, for having called my attention, through Mr.
Brace, to the above passage in Dr. Well’s work.

The Hon. and Rev. W. Herbert, afterwards Dean of
Manchester, in the fourth volume of the ‘ Horticultural
Transactions,’ 1822, and in his work on the ‘ Amaryl-
lidaceee ’ (1837, 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 para-
graph in his well-known paper (‘ Edinburgh Philosophi-
cal 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 that en-
larged in the present volume. Unfortunately the view
was given by Mr. Matthew very briefly in scattered
passages in an Appendix to a work on a different sub-
ject, so that it remained unnoticed until Mr. Matthew
himself drew attention to it in the ‘ Gardener’s

Chronicle,’ on April 7th, 1860. The differences of Mr.
2

xviii HISTORICAL SKETCH.

Matthew’s view from mine are not of much importance:
he seems to consider that the world was nearly de-
populated 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 understand
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.

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 become changed into permanent
species, which are no longer capable of intercrossing.

Rafinesque, in his ‘New Flora of North America,’
published in 1836, wrote (p. 6) as follows:—“ All
species might have been varieties once, and many va-
rieties are gradually becoming species by assuming con-
stant and peculiar characters;” 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 develop-
ment and modification 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 recent, are, under the

AISTORICAL SKETCH. xix

providence of God, the results, first, of an impulse which
has been imparted to the forms of life, advancing them,
in definite times, by generation, through grades of or-
ganisation terminating in the highest dicotyledons and
vertebrata, these grades being few in number, and gen-
erally marked by intervals of organic character, which
we find to be a practical difficulty in ascertaining affini-
ties; 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 apparently be-
lieves 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 can-
not 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 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, imme-
diately had a very wide circulation. In my opinion it
has done excellent service in this country in calling at-
tention 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’Hal-
loy published in an excellent though short paper (‘ Bul-
letins de Acad. Roy. Bruxelles” tom. xiii. p. 581)

xx HISTORICAL SKETCH.

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 divers 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 ignorant.” 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 dis-
tribution, 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 distinct 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 Crea-
tive Cause.” If we interpret these sentences given
in the same Address, one by the other, it appears that
this eminent philosopher felt in 1858 his confidence

HISTORICAL SKETCH. xxi

shaken that the Apteryx and the Red Grouse first ap-
peared 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.
Wallace 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 pub-
lished, I was so completely deceived, as were many
others, by such expressions as “ the continuous operation
of creative power,” that I included Professor Owen with
other paleontologists as being firmly convinced of the
immutability of species; but it appears (‘ Anat. of Ver-
tebrates,’ 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 spe-
cies; but this it appears (Ibid. vol. iii. p. 798) is in-
accurate and without evidence. I also gave some ex-
tracts 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 announce-
ment; but as far as it is possible to understand certain
recently published passages (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

me HISTORICAL SKETCH.

enunciation of the principle of natural selection is con-
cerned, 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 de-
livered in 1850 (of which a Résumé appeared in the
‘Revue et Mag. de Zoolog.,’ Jan. 1851), briefly gives
his reason for believing that specific characters. “sont
fixés, pour chaque espéce, tant qu’elle se perpétue au
milieu des mémes circonstances: ils se modifient, si les
circonstances ambiantes viennent 4 changer.” “ En-
résumé, observation des animaux sauvages démontre
déja la variabilité limitée des espéces. Les expériences
sur les animaux sauvages, devenus domestiques, et sur
les animaux domestiques redevenus sauvages, la démon-
trent plus clairement encore. Ces mémes expériences
prouvent, de plus, que les différences produites peuvent
étre de valeur générique.” In his ‘ Hist. Nat. Générale’
(tom. ii. p. 430, 1859) he amplifies analogous conclusions.

From a circular lately issued it appears that Dr.
Freke, in 1851 (‘ Dublin Medical Press,’ p. 322), pro-
pounded the doctrine that all organic beings have de-
scended from one primordial 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 Species by means of Or-
ganic Affinity,’ the difficult attempt to give any idea of
his views would be superfluous on my part.

Mr. Herbert Spencer, in an Essay (originally pub-
lished 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

HISTORICAL SKETCH. Xxili

remarkable skill and force. He argues from the analogy
of domestic productions, from the changes which the
embryos of many species undergo, from the difficulty
of distinguishing species and varieties, 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
acquirement of each mental power and capacity by gra-
dation.

In 1852 M. Naudin, a distinguished botanist, ex-
pressly stated, in an admirable paper on the Origin of
Species (‘Revue Horticole, p. 102; since partly repub-
lished in the ‘ Nouvelles Archives du Muséum,’ tom. i.
p- 171), his belief that species are formed in an analo-
gous manner as varieties are under cultivation; and
the latter process he attributes to man’s power of selec-
tion. But he does not show how selection 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,
“puissance mystérieuse, indéterminée; fatalité pour les
uns; pour les autres, volonté providentielle, dont l’ac-
tion incessante sur les étres vivants détermine, 4 toutes
les époques de l’existence du monde, la forme, le vol-
ume, et la durée de chacun d’eux, en raison de sa des-
tinée dans Vordre de choses dont il fait partie. C’est
cette puissance qui harmonise chaque membre 4 |’en-
semble, en l’appropriant 4 la fonction qu’il doit remplir
dans l’organisme général de la nature, fonction qui est
pour lui sa raison d’étre.” *

* From references in Bronn’s ‘Untersuchungen iiber die Ent-
wickelungs-Gesetze,’ it appears that the celebrated botanist and

eae HISTORICAL SKETCH.

In 1853 a celebrated geologist, Count Keyserling
(‘ Bulletin de la Soc. Géolog.,’ 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 chemically affected by circum-
ambient 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 development of organic forms on the earth. He
infers that many species have kept true for long periods,
whereas a few have become modified. ‘he 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 contin-
ued reproduction.”

A well-known French botanist, M. Lecoq, writes in
1854 (‘Etudes sur Géograph. Bot.,’ tom. i. p. 250),
“ On voit que nos recherches sur la fixité ou la variation
de Vespéce, nous conduisent directement aux idées

palzontologist Unger published, in 1852, his belief that species
undergo development and modification. Dalton, likewise, in
Pander and Dalton’s work on Fossil Sloths, expressed, in 1821, a
similar belief. Similar views have, as is well known, been main-
tained by Oken in his mystical ‘ Natur-Philosophie.’ From other
references in Godron’s work ‘Sur l’Espéce,’ it seems that Bory
St. Vincent, Burdach, Poiret, and Fries, have all admitted that new
species are continually 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.

HISTORICAL SKETCH. p.6.4)

émises, par deux hommes justement célébres, Geoffroy
Saint-Hilaire et Goethe.” Some other passages scattered
through M. Lecoq’s large work, make it a little doubt-
ful how far he extends his views on the modification of
species.

The ‘ Philosophy of Creation’ has been treated in a
masterly 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 1st, 1858, by Mr.
Wallace and myself, in which, as stated in the intro-
ductory remarks to this volume, the theory of Natural
Selection is promulgated by Mr. Wallace with admir-
able force and clearness.

Von Baer, towards whom all zoologists feel so pro-
found 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 geographical distribution, that
forms now perfectly distinct have descended from a
single parent-form.

In June, 1859, Professor Huxley gave a lecture be-
fore the Royal Institution on the ‘ Persistent Types of
Animal Life.’ Referring to such cases, he remarks,
“Tt is difficult to comprehend the meaning of such
facts as these, if we suppose that each species of animal
and plant, or each great type of organisation, was
formed and placed upon the surface of the globe at

a HISTORICAL SKETCH,

long intervals by a distinct act of creative power; and
it is well to recollect that such an assumption is as
unsupported 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 supposes the species living at any
time to be the result of the gradual modification of
pre-existing species a hypothesis which, though un-
proven, 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.”

In December, 1859, Dr. Hooker published his ‘ Intro-
duction to the Australian Flora.’ In the first part of
this great work he admits the truth of the descent and
modification of species, and supports this doctrine by
many original observations.

The first edition of this work was published on No-
vember 24th, 1859, and the second edition on January
Tth, 1860.

ORIGIN OF SPECIES.

INTRODUCTION.

WHEN on board H.M.S. ‘ Beagle, as naturalist, I was
much struck with certain facts in the distribution of
the organic beings inhabiting South America, and in
the geological relations of the present to the’ past in-
habitants 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 mys-
tery 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 al-
lowed myself to speculate 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 proba-
ble: from that period to the present day I have steadily
pursued the same object. I hope that I may be ex-
cused for entering on these personal details, as I give
them to show that I have not been hasty in coming to a
decision.

1

oy) INTRODUCTION.

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 vol-
ume of the Journal of that society. Sir C. Lyell
and Dr. Hooker, who both knew of my work—the lat-
ter 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 manu-
scripts.

This Abstract, which I now publish, must necessarily
be imperfect. I cannot here give references and au-
thorities 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 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 refer-
ences, 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

INTRODUCTION. 3

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 satisfaction 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 con-
ceivable that a naturalist, reflecting on the mutual affini-
ties of organic beings, on their embryological relations,
their geographical distribution, geological succession,
and other such facts, might come to the conclusion
that species had not been independently created, but
had descended, like varieties, from other species. Never-
theless, 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, &c., as the only possible cause
of variation X In one limited sense, as we shall here-
after 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 nourishment from certain trées, which has

4 INTRODUCTION.

seeds that must be transported by certain birds, and
which has flowers with separate sexes absolutely re-
quiring the agency of certain insects to bring pollen
from one flower to the other, it is equally preposterous
to account for the structure of this parasite, with its
relations to several distinct organic beings, by the effects
of external conditions, or of habit, or of the volition of
the plant itself.

It is, therefore, of the highest importance to gain a
clear insight into the means of modification and co-
adaptation. At the commencement of my observations
it seemed to me probable that a careful study of domes-
ticated 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 per-
plexing cases I have invariably found that our knowl-
edge, imperfect though it be, of variation under domes-
tication, 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 commonly ne-
glected by naturalists.

From these considerations, I .shall devote the first
chapter of this Abstract to Variation under Domesti:
cation. We shall thus see that a large amount of
hereditary modification is at least possible; and, what
is equally or more important, we shall see how great
is the power of man in accumulating by his Selection
successive slight variations. I will then pass on to
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, however, be
enabled to discuss what circumstances are most favour-

INTRODUCTION. 5

able to variation. In the next chapter the Struggle for
Existence amongst all organic beings throughout the
world, which inevitably follows from the high geo-
metrical 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 rn than can possibly survive; and _
as, consequently, there is a frequently. recurring-struggle
“for existence, it follows that any being, if it vary how-
ever_slightly in_any manner profitable... toitself, under
the complex and sometimes varying conditions of life,
will have a better chance of. “surviving, and 1 thus be
naturally selected. From the strong principle of inheri-
tance, 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 in-
evitably causes much Extinction of the less improved
forms of life, and leads to what I have called Diver-
gence of Character. In the next chapter I shall discuss
the complex 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 transitions, or how a
simple being or a simple organ can be changed and per-
fected into a highly developed being or into an elab-
orately constructed organ; secondly, the subject of In-
stinct, or the mental powers of animals; thirdly, Hybrid-
ism, or the infertility of species and the fertility of
varieties when intercrossed; and fourthly, the imperfec-
tion of the Geological Record. In the next chapter I
shall consider the geological succession of organic beings

6 INTRODUCTION,

throughout time; in the twelfth and thirteenth, their
geographical distribution throughout space; in the four-
teenth, their classification or mutual affinities, both when
mature and in an embryonic condition. 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 unexplained 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 rela-
tions 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 dispassionate judgment of which I am capable, that
the view which most naturalists until recently enter-
tained, and which I formerly entertained—namely, that
each species has been independently created—is errone-
ous. I am fully convinced that: species aré ot Immuta-
ble; but that those belonging to what arfe called the
same genera are lineal descendants of somle other and
generally extinct species, in the same majnner as the
acknowledged varieties of any one species\ are the de-
scendants of that species Furthermore, I am convinced
that Natural Selection has been the most bnportant, but
not the exclusive, means of modification:

Cuap. I] VARIATION UNDER DOMESTICATION, 7

CHAPTER I.

VARIATION UNDER DOMESTICATION.

Causes of Variability—HEffects of Habit and the use or disuse of
Parts—Correlated Variation—Inheritance—Character of Do-
mestic Varieties—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, anciently followed, their Effects—
Methodical and Unconscious Selection—Unknown Origin of
our Domestic Productions—Circumstances favourable to Man’s
power of Selection.

Causes of Variability.

WHEN we compare the individuals of the same vari-
ety or sub-variety of our older cultivated plants and ani-
mals, one of the first points which strikes us is, that they
generally differ more from each other than do the in-
dividuals of any one species or variety in a state of
nature. And if we reflect 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 variability is due to our
domestic productions having been raised under condi-
tions of life not so uniform as, and somewhat differ-
ent from, those to which the parent species had been
exposed under nature. There is, also, some probability

2°

FS) VARIATION UNDER DOMESTICATION. [Cuar. L

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 ex-
posed during several generations to new conditions to
cause any great amount of variation; 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 wheat,
still yield new varieties: our oldest domesticated ani-
mals are still capable of rapid improvement or modifi-
cation.

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 respect to the direct action, we must
‘bear in mind that in every case, as Professor Weis-
mann has lately insisted, and as I have incidentally
shown in my work on ‘ Variation under Domestication,
there are two factors: namely, the nature of the organ-
ism, and the nature of the conditions. The former seems
to be much the more important; for nearly similar vari-
ations 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 defi-
nite 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 conclusion in regard to the
extent of the changes which have been thus definitely

Cuap. 1.] VARIATION UNDER DOMESTICATION. 9

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, thickness of
the skin and hair from climate, &c. Each of the endless
variations which we see in the plumage of our fowla
must have had some efficient cause; and if the same
cause were to act uniformly during a long series of gen-
erations on many individuals, all probably would be
modified in the same manner. Such facts as the com-
plex and extraordinary out-growths which invariably fol-
low from the insertion of a minute drop of poison by a
gall-producing insect, show us what singular modifica-
tions 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
probably played a more important part in the forma-
tion of our domestic races. We see indefinite vari-
ability in the endless slight peculiarities which
distinguish the individuals of the same species, and
which cannot be accounted for by inheritance from
either parent or from some more remote ancestor.
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 coun-
try and fed on nearly the same food, deviations of
structure so strongly pronounced 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

10 VARIATION UNDER DOMESTICATION. [Cuar. L

as the indefinite effects of the conditions of life on each
individual organism, in nearly the same manner as the
chill affects different men in an indefinite manner, ac-
cording 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 ac-
tion of changed conditions, namely, through the repro-
ductive system being affected, we may infer that vari-
ability 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 remarked, between the variability
which follows from the crossing of distinct species,
and that which may be observed with plants and ani-
mals when reared under new or unnatural condi-
tions. Many facts clearly show, how eminently sus-
ceptible 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
difficult than to get it to breed freely under confine-
ment, 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 coun-
try! This is generally, but erroneously, attributed to
vitiated instincts. Many cultivated plants display 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; but to show how singular the

Cuap. 1] VARIATION UNDER DOMESTICATION. 11

laws are which determine the reproduction of animals
under confinement, I may mention that carnivorous ani-
mals, even from the tropics, breed in this country pretty
freely under confinement, with the exception of the
plantigrades or bear family, which seldom produce
young; whereas carnivorous birds, with the rarest ex-
ceptions, hardly ever lay fertile eggs. Many exotic
plants have pollen utterly worthless, in the same con-
dition as in the most sterile hybrids. When, on the
one hand, we see domesticated 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 re-
productive 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 producing offspring somewhat unlike
their parents. I may add, that as some organisms breed
freely under the most unnatural 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 cultiva-
tion, and vary very slightly—perhaps hardly more than
in a state of nature.

¥ Some naturalists have maintained that all variations
aré connected with the act of sexual reproduction; bu
this is certain] 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

12 VARIATION UNDER DOMESTICATION. (Cap. I,

same plant. These bud variations, as they may be
named, can be propagated by grafts, offsets, &c., 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 con-
ditions, have sometimes yielded nearly the same variety
—for instance, buds on peach-trees producing nec-
tarines, and buds on common roses producing moss-
roses—we clearly see that the nature of the conditions
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 com-
bustible 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
period of the flowering of plants when transported from
one climate to another. With animals the increased
use or disuse of parts has had a more marked influence;
thus J 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 skeleton, 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

Cuap. 1] VARIATION UNDER DOMESTICATION. 13

in countries where they are habitually milked, in com-
parison with these organs in other countries, is proba-
bly another instance of the effects of use. Not one of
our domestic 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 entail 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. Hilaire’s great work on this
subject. Breeders believe that long limbs are almost
always accompanied by an elongated head. Some in-
stances of correlation are quite whimsical: thus cats
which are entirely white and have blue eyes are gen-
erally deaf; but it has been lately stated by Mr. Tait
that this is confined to the males. Colour and con-
stitutional peculiarities go together, of which many re-
markable cases could be given amongst animals and
plants. From facts collected by Heusinger, it appears
that white sheep and pigs are injured by certain plants,
whilst dark-coloured individuals escape: Professor Wy-
man has recently communicated to me a good illustra-
tion of this fact; on asking some farmers in Virginia
how it was that all their pigs were black, they informed
him that the pigs ate the paint-root (Lachnanthes),
which coloured their bones pink, and which caused the
hoofs of all but the black varieties to drop off; and one

14 VARIATION UNDER DOMESTICATION. [Cuap. lL

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 peculiarity,
he will almost certainly modify unintentionally other
parts of the structure, owing to the mysterious laws of
correlation.

The results of the various, unknown, or but dimly
understood 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, &c.;
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 belief: doubts have
been thrown on this principle only by theoretical
writers. When any deviation of structure often appears,

Cap. I.] VARIATION UNDER DOMESTICATION. 15

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, ap-
parently 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, &c., appearing in several members of the
same family. If strange and rare deviations of struc-
ture are really inherited, less strange and commoner
deviations may be freely admitted to be inheritable.
Perhaps the correct way of viewing the whole sub-
ject 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 different individuals of the same species, or in dif-
ferent species, is sometimes inherited and sometimes not
so; why the child often reverts in certain characters
to its grandfather or grandmother or more remote an-
cestor; why a peculiarity is often transmitted from
one sex to both sexes, or to one sex alone, more com-
monly but not exclusively to the like sex. It is a fact
of some importance to us, that peculiarities appearing
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

16 VARIATION UNDER DOMESTICATION. [Cuap. 1.

reappear in the offspring at a corresponding age, though
sometimes earlier. In many cases this could not be
otherwise; thus the inherited peculiarities in the horns
of cattle could appear only in the offspring when nearly
mature; peculiarities in the silkworm are known to ap-
pear 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 appeared in the parent. I believe this
tule to be of the highest importance in explaining the
laws of embryology. These remarks are of course con-
fined to the first appearance of the peculiarity, and not
to the primary cause which may have acted on the
oyules 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

Cuap. 1] VARIATION UNDER DOMESTICATION. 17

state. In many cases we do not know what the abo-
riginal stock was, and so could not tell whether or not
nearly perfect reversion had ensued. It would be neces-
sary, in order to prevent the effects of intercrossing,
that only a single variety should have been turned
loose in its new home. Nevertheless, as our varieties
certainly do occasionally revert in some of their charac-
ters 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 argu-
ment; for by the experiment 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 con-
siderable body, so that free intercrossing might 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 esculent vegetables, for
an unlimited number of generations, would be opposed
to all experience.

18 CHARACTER OF DOMESTIC VARIETIES. [Cxap. 1.

Character of Domestic Varieties; difficulty of dis-
tinguishing between Varieties and Species; origin
of Domestic Varieties from one or more Species.

When we look to the hereditary varieties or races of
our 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 monstrous 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 another, 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), domestic 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 character of generic value. It can be shown
that this statement is not correct; but naturalists differ

Cuar, L.] CHARACTER OF DOMESTIC VARIETIES. 19

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 do-
mesticated races.

In attempting to estimate the amount of structural
difference 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 bull-dog, 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 immutability of
the many closely allied natural species—for instance,
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 domesti-
cation; 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 domes-
ticated 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
domestication animals and plants having an extraordi-
nary 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 domes-
ticated productions: but how could a savage possibly

20 CHARACTER OF DOMESTIC VARIETIES. [Cuar. L

know, when he first tamed an animal, 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 endurance of
warmth by the reindeer, or of cold by the common
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 generations 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 conclusion, 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 existing.
But this only throws far backwards the history of
civilisation, and shows that animals were domesticated
at amuch earlier period than has hitherto beensupposed.
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

Cnap. I] CHARACTER OF DOMESTIC VARIETIES, ot

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 pres-
ent 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
probably 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
Canide have been tamed, and that their blood, in some
cases mingled together, flows in the veins of our do-
mestic breeds. In regard to sheep and goats I can form
no decided opinion. From facts communicated to me
by Mr. Blyth, on the habits, voice, constitution, and
structure of the humped Indian cattle, it is almost
certain that they are descended from a different
aboriginal 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 distinction between the humped
and common cattle, may, indeed, be looked upon as
established by the admirable researches 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

92 CHARACTER OF DOMESTIC VARIETIES. [Cuap. L

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. 4They 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, &c., but that
each of these kingdoms possesses several peculiar breeds
of cattle, sheep, &c., we must admit that many domestic
breeds must have originated in Europe; for whence
otherwise 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 species, 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 bloodhound, the
bull-dog, pug-dog, or Blenheim spaniel, &c.—so unlike
all wild Canide—ever existed in a state of nature? It

Caap. 1.] DOMESTIC PIGEONS. 23

has often been loosely said that all our races of dogs
have been produced by the crossing of a few aboriginal
species; 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,
&c., 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 between
two pure breeds is tolerably and sometimes (as I have
found with pigeons) quite uniform in character, and
everything seems simple enough; but when these mon-
grels are crossed one with another for several genera-
tions, hardly two of them are alike, and then the diffi-
culty 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 pur-
chase 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
4

24 DOMESTIC PIGEONS. (Cuar. L.

different languages have been published on pigeons,
and some of them are very important, as being of
considerable 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 astonishing. Compare the English
carrier and the short-faced tumbler, and see the
wonderful difference in their beaks, entailing corres-
ponding 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 expanding slightly, the upper part of the
cesophagus. 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

Cuar. I.) DOMESTIC PIGEONS. 95

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 develop-
ment 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
vertebree vary in number; as does the number of the
ribs, together with their relative breadth and the pre-
sence of processes. The size and shape of the apertures
in the sternum are highly variable; so is the degree
of divergence and relative size of the 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 cor-
relation with the length of beak), the size of the crop
and of the upper part of the oesophagus; the develop-
ment 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
scutelle on the toes, the development of skin between
the toes, are all points of structure 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

26 DOMESTIC PIGEONS. [Cuap. 1

some breeds the voice and disposition, differ remarkably.
Lastly, in certain breeds, the males and females have
come to differ in a slight degree from 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-in-
herited 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), in-
cluding 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 degree applicable
in other cases, I will here briefly give them. If the
several breeds are not varieties, and have not proceeded
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 possessed the characteristic
enormous crop? The supposed aboriginal 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

Cuap. I.] DOMESTIC PIGEONS. 24

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 ex-
terminated; and the common rock-pigeon, which has
the same habits with the domestic breeds, has not
been exterminated 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 «bove-
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 animals to breed freely under domesti-
cation; yet on the hypothesis of the multiple origin
of our pigeons, it must be assumed that at least seven
or eight species were so thoroughly domesticated in
ancient times by half-civilised man, as to be quite pro-
lifie under confinement.

An argument of great weight, and applicable in
several other cases, is, that the above-specified breeds,
though agreeing generally with the wild rock-pigeon
in constitution, habits, voice, colouring, and in most

28 DOMESTIC PIGEONS. [Cuap. ]

parts of their structure, yet are certainly highly abnor.
mal in other parts; we may look in vain through the
whole great family of Columbide for a beak like that
of the English carrier, or that of the short-faced tumbler,
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-civilised man succeeded in thoroughly
domesticating several species, but that he intention-
ally or by chance picked out extraordinarily abnormal
species; and further, that these very species have since
all become extinct or unknown. So many strange con-
tigencies are improbable in the highest degree.

Some facts in regard to the colouring of pigeons well
deserve 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-domestic 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. More-
over, 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 offspring
are very apt suddenly to acquire these characters,
To give one instance out of several which I have ob-
served:—I crossed some white fantails, which breed

Cap. 1] DOMESTIC PIGEONS. 29

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 aud 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 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 jreverting to an ancestor of foreign blood,
removed by! a greater number of generations. In a
breed whicli has been crossed only once, the tendency
to revert to any character derived from such a cross
will natujrally become less and less, as in each suc-
ceeding ¢seneration there will be less of the foreign
blood; brat when there has been no cross, and there
'

30 DOMESTIC PIGEONS. [Cuar. L

1s a tendency in the breed to revert to a character which
was lost during some former generation, this tendency,
for all that we can see to the contrary, may be trans-
mitted undiminished for an indefinite number of gen-
eratioms. These two distinct cases of reversion are
often confounded together by those who have written
on inheritance...

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 aninuals 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 domestic
animals, this conclusion is probably quite correct, if
applied to species closely related to \each other. But
to extend it so far as to suppose that species, aborigi-
nally as distinct as carriers, tumblers, pouters, end fan-
tails now are, should yield offspring perfeculy fertile
inter se, would be rash in the extreme. _

From these several reasons, namely,—th¢ improba-
bility of man having formerly made wl or eight
supposed species of pigeons to breed freely under do-
mestication;—these supposed species bole quite un-
known in a wild state, and their not having become
anywhere feral;—these species presenting ‘certain very
abnormal characters, as compared with all other
Columbide, though so like the rock- -pigeon in most
respects;—the occasional re-appearance of \ the blue
colour and various black marks in all the breeds, both
when kept pure and when crossed;—and lestly, the

Cuar. I] DOMESTIC PIGEONS. 31

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. Secondly, 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 variable, 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 earliest known record of pigeons is in the fifth
Aigyptian dynasty, 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

32 DOMESTIC PIGEONS. [Cuap. L

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 his-
torian, “His Majesty by crossing 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-
plaining the immense amount of variation which pigeons
have undergone, will likewise be obvious when we treat
of Selection. 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

Cuap. I] DOMESTIC PIGEONS. 33

has attended, are descended from so many aboriginally
distinct species. Ask, as I have asked, a celebrated
raiser of Hereford cattle, whether his cattle might not
have descended from Long-horns, 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. In-
numerable other examples could be given. The ex-
planation, I think, is simple: from long-continued
study they are strongly impressed with the differences
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 differences 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 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 caution, when they deride the idea of species in a
state of nature being lineal descendants of other
species?

84 SELECTION BY MAN. [Cuap. L

Principles of Selection anciently followed, and their
Liffects.

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 at-
tributed to the direct and definite 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 domesticated 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 suddenly, 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
suddenly 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 wheu 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 com-

Cuap, I. SELECTION BY MAN. 35

pare the host of agricultural, culinary, orchard, and
flower-garden races of plants, most useful to man at dif-
ferent 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 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 accumulative selection: nature gives successive varia-
tions; 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
hypothetical. 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 organisation as some-
thing plastic, which they can model almost as they
please. If I had space I could quote numerous pas-
sages to this effect from highly competent authorities.
Youatt, who was probably better acquainted with the
works of agriculturists than almost any other indi-
vidual, and who was himself 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 Somerville, speaking of what breeders
have done for sheep, says:—“ It would seem as if they

36 SELECTION BY MAN. [Caar. L

had chalked out upon a wall a form perfect in itself,
and then had given it existence.” In Saxony the im-
portance 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
ordinary cases. If selection consisted merely in sepa-
rating 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 judg-
ment 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 im-
provements; if he wants any of these qualities, he will
assuredly fail. Few would readily believe in the natural

Cuap. 1] SELECTION BY MAN. 37

capacity and years of practice requisite to become 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 pro-
duced 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 florists’ flowers,
when the flowers of the present day are compared 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 animals 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 ob-
serving 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 comparison with
the leaves and flowers of the same set of varieties.
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 differeht kinds of goose-

38 METHODICAL SELECTION. [Cuap, I,

berries 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,—perhaps
never, the case. The law of correlated variation, the
importance of which should never be overlooked, will
ensure some differences; but, as a general rule, it can-
not 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 references to works of
high antiquity, in which the full importance of the
principle is acknowledged. In rude and. barbarous
periods of English history choice animals were often
imported, and laws were passed to prevent their ex-
portation: the destruction of horses under a certain
size was ordered, and this may be compared to the
“roguing ” of plants by nurserymen. The principle of
selection I find distinctly given in an ancient Chinese
encyclopedia. Explicit rules are laid down by some
of the Roman classical writers. From passages in
Genesis, it is clear that the colour of domestic animals
was at that early period attended to. Savages now
sometimes cross tlfeir dogs with wild canine animals,

Cuap, I] UNCONSCIOUS SELECTION. 39

to improve 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 as-
sociated with Europeans. Some of these facts do not
show actual selection, but they show that the breeding
of domestic animals was carefully attended to in an-
cient times, and is now attended to by the lowest sav-
ages. 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
naturally tries to get as good dogs as he can, and after-
wards breeds from his own best dogs, but he has no
wish or expectation of permanently altering the breed.
Nevertheless we may infer that this process, continued
during centuries, would improve and modify any breed,
in the same way as Bakewell, Collins, &c., 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
5

40 UNCONSCIOUS SELECTION. [Cuap. L

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’s 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 pro-
bably 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,
though the old Spanish pointer certainly came from
Spain, Mr. Borrow has not seen, as I am informed by
him, any native dog in Spain like our pointer.

By a similar 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 Goodwood 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 ac-
counts 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 great-
ly from the rock-pigeon.

Cuap, 1] UNCONSCIOUS SELECTION. 41

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 production 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 suspicion
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 varie-
ties.”

If there exist savages so barbarous as never to think
of the inherited character of the offspring of their do-
mestic animals, yet any one animal particularly useful to
them, for any special purpose, would be carefully pre-
served during famines and other accidents, to which say-
ages 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 indi-
viduals, 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

49, UNCONSCIOUS SELECTION. (Cuar. 1,

become blended together by crossing, 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 pear 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 surprise
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 unconsciously. 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 preserved the best varieties they could anywhere
find.

_A large amount of change, thus slowly and un-
consciously accumulated, explains, ar 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

Cuap. 1] UNCONSCIOUS SELECTION. 43

centuries or thousands.-of. years to improve or modify
‘most of our plants up to their present standard of use-
ad to man, che can understand how it is that neither

‘single plant worth culture. It is not that these coun-—
“tries, so rich in species, do not by a strange chance pos-
sess the aboriginal stocks of any useful plants, but that
the native plants have not been improved by con-
tinued selection up to a standard of perfection com-
parable 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, individuals of the same
species, having slightly different constitutions 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 coun-
tries.

On the view here given of the important part which
selection by man has played, it becomes at once
obvious, how it is that our domestic races show adap-
tation 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

AA UNCONSCIOUS SELECTION. [Cuar. I

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 externally visible; and indeed he rarely cares for
what is internal. 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 de-
veloped in some slight degree in an unusual manner,
or a pouter till he saw a pigeon with a crop of some-
what unusual size;fand 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 be-
come 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 individ-
uals of other and distinct breeds, in which as many as
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 cesopha-
gus,—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 value 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

Cuar, I.] UNCONSCIOUS SELECTION. 45

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
standard 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 valuable, and will
then probably first receive a provincial name. In
gemi-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 ac-
knowledged, the principle, as I have called it, of un-
conscious selection will always tend,—perhaps more
at one period than at another, as the breed rises or falls
in fashion,—perhaps more in one district than in an-

46 CIRCUMSTANCES FAVOURABLE. [Cuap. L

other, according to the state of civilisation of the in-
habitants,—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,
favourable,,or the reverse, to man’s power of selection.
A high degree of variability is obviously favourable, as
freely giving the materials for selection to work on;
not that mere individual differences are not amply
sufficient, with extreme care, to allow of the accumula-
tion of a large amount of modification in almost any
desired direction. But as variations manifestly 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 selection. But probably the most
important element is that the animal or plant should

!

Caar.L] CIRCUMSTANCES FAVOURABLE. 47

be so highly valued by man, that the closest attention
1s paid to even the slightest deviations in its. qualities
or structure. Unless such attention be paid nothing
can be affected. 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 strawberry had always varied since it was
cultivated, but the slight varieties had been neglected.
As soon, however, as gardeners picked out individual
plants with slightly larger; earlier, or better fruit, and
raised seedlings from them, and again picked out the
best seedlings and bred from them, then (with some aid
by crossing distinct species) those many admirable varie-
ties 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 propagated 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
Jong kept up; such breeds as we do sometimes see are

48 CIRCUMSTANCES FAVOURABLE. [Caap. L

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 sur-
prisingly 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
display of distinct breeds; but the goose, under the
conditions to which it is exposed when domesticated,
seems to have a singularly inflexible organisation,
though it has varied to a slight extent, as I have else-
where 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 assert that the limit has been attained
in any one case; for almost 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 increased to
their utmost 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 in-
stance, there must be a limit to the fleetness of any

Cuar.I.] CIRCUMSTANCES FAVOURABLE. 49

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 muscular
fibres. But what concerns us is that the domestic
varieties 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. Isidore 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 characters, Eclipse was
far fleeter, and a dray-horse is incomparably stronger
than any two natural species belonging to the same
genus. So with plants, the seeds of the different varie-
ties 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 regard to the fruit of the several varieties
of the plum, and still more strongly with the melon, as
well as in many other analogous 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

50 SUMMARY OF SELECTION. [Cuap, 1

to the increased use or disuse of parts. The final re-
sult is thus rendered infinitely complex. In some cases
the intercrossing of aboriginally distinct species appears
to have played an important part in the origin of our
breeds. When several breeds have once been formed in
any country, their occasional intercrossing, with the aid
of selection, has, no doubt, largely aided in the forma-
tion of new sub-breeds; but the.importance of crossing
has been much exaggerated, both in regard 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 varia-
bility both of hybrids and of mongrels, and the steril-
ity 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 ac-
cumulative action of Selection, whether applied method-
ically and quickly, or unconsciously and slowly but
more efficiently seems to have been the predominant
Power.

Cuap. IL] VARIATION UNDER NATURE. 51

CHAPTER II.

VARIATION UNDER NATURE.

Variabilit y—Individual differences—Doubtful species— Wide rang-
ing. much diffused, and common species, vary most—Species of
thy larger genera in each country vary more frequently than
tke species of the smaller genera—Many of the species of the
la ‘ger genera resemble varieties in being very closely, but un-
eqtally, related to each other, and in having restricted ranges.

BE.oRE applying the principles arrived at in the last
chapter to organic beings in a state of nature, we must
briefly ciscuss 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 definition has satisfied all
naturalists; yet every naturalist knows vaguely what
he means when he speaks of a species. Generally the
term includes the unknown element of a distinct act of
creation. The term “variety” is almost equally
difficult to define; but here community of descent
is almost universally 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 considerable deviation of
structure, generally injurious, or not useful to the
species. Some authors use the term “ variation” in a

52 VARIATION UNDER NATURE. _ [Cuap. IL

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 Al-
pine 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
deviations of structure such as we occasionally s2e in
our domestic productions, more especially with plants,
_ are ever permanently propagated in a state of n:.ture.
Almost every part of every organic being is so leauti-
fully related to its complex conditions of life that it
seems as improbable that any part should have been
suddenly produced perfect, as that a complex 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 soxst of proboscis, and if any wild species of the
same genus had naturally 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 resembling
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 reproduction (which is not always the case),
as they occur rarely and singularly, their preservation
would depend on unusually favourable circumstances.
They would, also, during the first and succeeding gen-

Cnap. I1.] INDIVIDUAL DIFFERENCES. 53

erations 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

preservation 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.
No one supposes that all the individuals of the same
species are cast in the same actual mould. These in-
dividual differences are of the highest importance 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 manner
as man accumulates in any given direction individual
differences in his domesticated productions. These
individual differences generally affect what naturalists
consider unimportant 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, sometimes vary in the
individuals of the same species. I am convinced that
the most experienced naturalist would be surprised at
the number of the cases of variability, even in impor-
tant 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

54 INDIVIDUAL DIFFERENCES. [Cuap. II.

men who will laboriously examine internal and im-
portant organs, and compare them in many specimens
of the same species. It would never have been ex-
pected that the branching of the main nerves close to
the great central 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
Coceus, which may almost be compared to the irregular
branching of the stem of a tree. This philosophical
naturalist, I may add, has also shown that the muscles
in the larve of certain insects are far from uniform.
Authors sometimes argue in a circle when they state
that important organs never vary; for these same au-
thors practically rank those parts as important (as some
few naturalists have honestly 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 dif-
ferences, which is extremely perplexing: I refer to
those genera which have been called “ protean” or
“polymorphic,” in which the species present an in-
ordinate amount of variation. With respect 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
polymorphic genera some of the species have fixed and
definite characters. Genera which are polymorphic
in one country seem to be, with a few exceptions, poly-

Jap. II,] INDIVIDUAL DIFFERENCES. 55

morphic in other countries, 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
consequently have not been seized on and rendered
definite by natural selection, as hereafter to be ex-
plained.

Individuals of the same species often present, as is
known to every one, great differences of structure, in-
dependently of variation, as in the two sexes of various
animals, in the two or three castes of sterile females
or workers amongst insects, and in the immature and
\arval states of many of the lower animals. There
are, also, cases of dimorphism and trimorphism, both
‘vith animals and plants. Thus, Mr. Wallace, who
his lately| called attention to the subject, has shown
thiat the females of certain species of butterflies, in the
Malayan archipelago, regularly appear under two or
€Ven three conspicuously distinct forms, not connected
by' intermiediate varieties. Fritz Miiller has described
analogous [but more extraordinary cases with the males
of Certain| Brazilian Crustaceans: thus, the male of a
Tanajg regtularly occurs under two distinct forms; one
of these has strong and differently shaped pincers,
and the other has antenne much more abundantly fur-
nisheq 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 gra-
datisns, it is. probable that they were once thus con-

nested. Mr. : ‘Wallace, for instance, describes a certain
6

56 DOUBTFUL SPECIES. [Cuap.

butterfly which presents in the same island a great
range of varieties connected by intermediate links,/and
the extreme links of the chain closely resemble the two
forms of an allied dimorphic species inhabiting an-
other part of the Malay archipelago. Thus also with
ants, the several worker-castes are generally! quite
distinct; but in some cases, as we shall hereafiter see,
the castes are connected together by finely graduated
varieties. So it is, as I have myself observed, wit:h some
dimorphic plants. It certainly at first appears a highly
remarkable fact that the same female l»utterfly
should have the power of producing at fthe 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, bear-
ing three different kinds of females and thrée or even
six different kinds of males. Nevertheless these
cases are only exaggerations of the common fact
that the female produces offspring of ‘two sex/€s
which sometimes differ from each other in a wondertful
manner.

Doubtful Species.

‘

The forms which possess in some considerable degree
the character of species, but which are so closely sixnilar
to other forms, or are so closely linked to them by *nter-
mediate gradations, that naturalists do not like to
rank them as distinct species, are in several TespectS the
most important for us. We have every reason to be-
lieve 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 2an

Cnar. Ii] DOUBTFUL SPECIES. 57

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 species, and the other as the variety. But cases of
great difficulty, which I will not here enumerate, some-
times arise in deciding whether or not to rank one form
as a variety of another, even when they are closely con-
nected by intermediate 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 suppose either that
they do now somewhere exist, or may formerly 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 natural-
ists having sound judgment and wide experience seems
the only guide to follow. We must, however, in many
cases, decide by a majority of naturalists, for few well-
marked and well-known varieties can be named which
have not been ranked as species by at least some com-
petent judges.

That varieties of this doubtful nature are far from
uncommon 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 varie-
ties. 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

58 DOUBTFUL SPECIES. [Cuap. IL

as varieties, but which have all. been ranked by bota-
nists 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 difference 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 com-
mon 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
Malayan archipelago, shows that they may be classed
under four heads, namely, as variable forms, as local
forms, as geographical 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 differences are seen to be so
slight and graduated, that it is impossible to define or
describe them, though at the same time the extreme
forms are sufficiently distinct. The geographical races
or sub-species are local forms completely fixed and iso-.
lated; but as they do not differ from each other by

Cuap. II.] ‘DOUBTFUL SPECIES. 59

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 natural economy of each island as do the
local forms and sub-species; but as they are distin-
guished from each other by a greater amount of differ-
ence than that between the local forms and sub-species,
they are almost universally ranked by naturalists as
true species. Nevertheless, no certain criterion 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
eompare, 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 dis-
tinction 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 ad-
mirable work, but which would certainly be ranked as
distinct species by many entomologists. Even Treland
has a few animals, now generally regarded as varieties,
but which have been ranked as species by some Zo-
ologists. Several experienced ornithologists consider
our British red grouse as only a strongly-marked race
of a Norwegian species, whereas the greater number
rank it as an undoubted species peculiar to Great
Britain. A wide distance between the homes of two
doubtful forms leads many naturalists to rank them
as distinct species; but what distance, it has been well
asked, will suffice; if that between America and Europe

60 DOUBTFUL SPECIES. (Cuap. Il

is ample, will that between Europe and the Azores, or
Madeira, or the Canaries, or between the several islets
of these small archipelagos, be sufficient?

Mr. B. D. Walsh, a distinguished entomologist of the
United States, has described what he calls Phytophagic
varieties 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 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 differences 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 determine for another,
even if he can do so for himself, which of these Phy-
tophagic forms ought to be called species and which
varieties. Mr. Walsh ranks the forms which it may
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 in-
termediate links connecting the several forms should
now be found. The naturalist thus loses his best guide
in determining whether to rank doubtful forms as varie-
ties or species. This likewise necessarily occurs with
closely allied organisms, which inhabit distinct conti-
nents or islands. When, on the other hand, an animal

Cuap. IL] DOUBTFUL SPECIES. 61

or plant ranges over the same continent, or inhabits
many islands in the same archipelago, and pre-
sents 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 varie-
ties.

“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 distant
countries, or in two geological formations, they believe
that- two distinct species are hidden under the same
dress. The term species thus comes to be a mere use-
less abstraction, implying and assuming a separate act
of creation. It is certain that many forms, considered
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 terms has been
generally accepted, is vainly to beat the air.

Many of the cases of strongly-marked varieties or
doubtful species well deserve consideration; for several
interesting lines of argument, from geographical dis-
tribution, analogical variation, hybridism, &c., have
been brought to bear in the attempt to determine their
rank; but space does not here permit me to discuss
them. Close investigation, in many cases, will no
doubt bring naturalists to agree how to rank doubtful
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

62 DOUBTFUL SPECIES. ‘ [Cuap. IL

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 close-
ly 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 authorities
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 structure which vary in
the several species, and estimates numerically 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 development, sometimes without any assignable
reason. Such characters 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 remarks: “They are mistaken, who
repeat that the greater part of our species are clearly

Cuap, II.] DOUBTFUL SPECIES. 63

limited, and that the doubtful 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 provisional.
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. Thus Quercus robur has twenty-
eight varieties, all of which, excepting six, are clustered
round three sub-species, namely, Q. pedunculata, sessili-
flora, 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 ro-
bur. 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 believes
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 paleontol-
ogy, geographical 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 perplexed in determining what differences to
consider as specific, and what as varietal; for he knows

64 DOUBTFUL SPECIES. [Cuap. IL

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 difference in the forms which he is continu-
ally studying; and he has little general knowledge of an-
alogical variation in other groups and in other coun-
tries, by which to correct his first 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 ob-
servations be widely extended, he will in the end gen-
erally be able to make up his own mind: but he will
succeed in this at the expense of admitting much varia-
tion,—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 continu-
ous, in which case he cannot hope to find intermediate
links, he will be compelled to trust almost en-
tirely 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

Cuap. 11] DOUBTFUL SPECIES. 65

impresses the mind with the idea of an actual pas-
sage.

Hence I look at individual differences, though of
small interest to the systematist, as of the highest im-
portance for us, as being the first steps towards such
slight varieties as are barely thought worth recording
in works on natural history. 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 leading 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 exposed;
but with respect to the more important and adaptive
characters, the passage from one stage of difference to
another, 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 _variety 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
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. Wollas-
ton 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

66 DOMINANT SPECIES VARY MOST. [Cuap. IL

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 I 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 differ from
the term variety, which is given to less distinct and more
- fluctuating forms. The term variety, again, in com-
parison with mere individual differences, 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
difficulties, 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 state-
ments are fairly well established. The whole subject,
however, treated as it necessarily 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.

Cuap, 11.] DOMINANT SPECIES VARY MOST. 67

Alphonse de Candolle and others have shown that
plants 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 competition (which, as we shall hereafter
see, is an equally or more important circumstance) with
different sets of organic beings. But my tables fur-
ther 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 dif-
fused within their own country (and this is a different
consideration from wide range, and to a certain extent
from commonness), oftenest give rise to varieties suffi-
ciently 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 coun-
try, and are the most numerous in individuals,—which
oftenest produce well-marked varieties, or, as I con-
sider them, incipient species. And this, perhaps, 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
species which are already dominant will be the most
likely to yield offspring, which, though in some slight
degree modified, still inherit those advantages that
enabled their parents to become dominant over their
compatriots. In these remarks on predominance, it
should be understood that reference 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

0 SPECIES OF LARGER GENERA VARIABLE, [Caar. II.

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 numer-
ous 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 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. ¢., 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 somewhat 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 coriditions 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 re-
sult, that I am surprised that my tables show even a

Cuap, II.] SPECIES OF LARGER GENERA VARIABLE. 69

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 wherever many closely related species (i. ¢.,
species of the same genus) have been formed, many
varieties or incipient species 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 variation, circum-
stances have been favourable for variation; and hence
we might expect that the circumstances would generally
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 hav-
ing 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,

70 SPECIES OF LARGER GENERA VARIABLE. [Cuape. IL

the species of the larger genera on one side, and those
of the smaller genera on the other side, and it has in-
variably proved to be the case that a larger propor-
tion of the species on the side of the larger genera pre-
sented varieties, than on the side of the smaller genera.
Moreover, the species of the large genera which pre-
sent any varieties, invariably present a larger average
number of varieties than do the species of the small
genera. Both these results follow when another divis-
ion 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; inasmuch
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,

~Cuap. 11] SPECIES OF LARGER GENERA. " RE

that, where many species of a genus have been formed,

on an average many are still forming; and this certainly
holds good.

Many of the Species included within the Larger Genera
resemble Varieties in being very closely, but wnequally,
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 intermediate 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 analogy
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 between_the
species is often exceedingly small. { I have endeavoured
to te&t 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

72 SPECIES OF LARGER GENERA, (Cap. IT.

species greater than the average are now manufactur-
ing, 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 differ-
ence.

Moreover, the species of the larger genera are re-
lated to each other, in the same manner as the varieties
of any one species are related to each other. No nat-
uralist pretends that all the species of a genus are equal-
ly distinct from each other; they may generally be
divided into sub-genera, or sections, 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
certain forms—that is, round their parent-species.
Undoubtedly there is one most important point of dif-
ference 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 differences between varie-
ties 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 indeed 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,

Cuap. II] RESEMBLE VARIETIES. 13

and in so far resemble varieties, often have much re-
stricted ranges. For instance, Mr. H. C. Watson 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 prov-
inces into which Mr. Watson has divided Great Britain.
Now, in this same Catalogue, 53 acknowledged varie-
ties are recorded, and these range over 7.7 provinces;
whereas, the species to which these varieties belong
range over 14.3 provinces. So that the acknowledged
varieties have nearly the same restricted average 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 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 varieties.
In large genera the species are apt to be closely, but
unequally, allied together, forming little clusters round

74 RESEMBLE VARIETIES. [Cuar. IL

other species. Species very closely allied to other spe-
cies apparently have restricted ranges. In all these re-
spects the species 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
dominant species of the larger genera within each class
which on an average yield the greatest number of
varieties; and varieties, 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 divid-
ed into groups subordinate to groups.

Cuar. UL] STRUGGLE FOR EXISTENCE, 5

CHAPTER III.

STRUGGLE FOR EXISTENCE.

Its bearing on natural selection—The term used in a wide sense—
Geometrical ratio of increase—Rapid increase of naturalised
animals and plants—Nature of the checks to increase—Com-
petition universal—Effects of Climate—Protection from the
number of individuals—Complex relations of all animals and
plants throughout nature—Struggle for life most severe between
individuals 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: indeed I am not aware that this has ever
been disputed. It is immaterial for us whether a mul-
titude of doubtful forms be called species or sub-species
or varieties; what rank, for instance, the two or three
hundred doubtful forms of British plants are 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 con-

46 sii ae FOR EXISTENCE. [Cuap. IIL

ditions of life, and of one organic being to another
being, been perfected! We see these beautiful co-adap-
tations most plainly in the woodpecker and the mistle-
toe; and only a little less plainly in the humblest para-
site which clings to the hairs of a quadruped 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 adap-
tations 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 constitute 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 in-
finitely 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

Cuap. Ill] STRUGGLE FOR EXISTENCE, q7

expression often used by Mr. Herbert Spencer of the
Survival of the Fittest is more accurate, and is some-
times equally convenient. We have seen that man
by selection can certainly produce great results, 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 seé, 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
easier than to admit in words the truth of the universal
struggle for life, 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 dis-
tribution, 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 constantly destroying
life; or we forget how largely these songsters, or their
eggs, or their nestlings, are destroyed by birds and beasts

78 STRUGGLE FOR EXISTENCE. [Cuap. IIL

of prey; we do not always bear in mind, that, though
food may be now superabundant, it is not so at all sea-
sons 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
metaphorical 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. ‘T'wo canine animals, in a time of dearth, may
be truly said to struggle with each other which shall
get food and live. Buta 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 parasites grow on the same tree, it lan-
guishes and dies. But several seedling mistletoes, grow-
ing close together on the same branch, may more truly
be said to struggle with each other. As the mistletoe is
disseminated by birds, its existence depends on them;
and it may metaphorically be said to struggle with other
fruit-bearing plants, in tempting the birds to devour and
thus disseminate its seeds. In these several senses,
which pass into each other, I use for convenience’ sake
the general term of Struggle for Existence.

Cuap. IIL] GEOMETRICAL RATIO OF INCREASE. "9

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 oc-
casional year, otherwise, on the principle of geometri-
cal increase, its numbers would quickly become so in-
ordinately great that no country could support the pro-
duct. 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 1 restraint from ‘marriage. Although

“ gome species may be now increasing, more or less rapid-
ly, in numbers, all eannot 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. Linneus 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 should be a million plants. The

80 GEOMETRICAL RATIO OF INCREASE. [Cuap, IIL

elephant is reckoned the slowest breeder of all known
animals, and I have taken some pains to estimate its
probable minimum 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 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 circum-
stances 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 incredible. So it is with plants; cases could
be given of introduced 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 com-
monest over the whole plains of La Plata, clothing
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 supposes, that the fertility of

Cuap, IIL] GEOMETRICAL RATIO OF INCREASE. 81

the animals or plants has been suddenly and tem-
porarily increased in any sensible degree. The ob-
vious explanation is that the conditions of life have
been highly favourable, and that there has consequently
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 ex-
traordinarily 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 assert, 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 geometrical tendency to
increase must be checked by destruction at some period
of life. Our familiarity with the larger domestic ani-
mals tends, I think, to mislead us: we see no great de-
struction 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 an-
nually produce 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 favour-
able 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

82 GEOMETRICAL RATIO OF INCREASE. [Caap. IL

the world. One fly deposits hundreds of eggs, and
another, like the hippobosca, a single one; but this
difference does not determine how many individuals of
the two species can be supported in a district. A large
number of eggs is of some importance to those species
which depend on a fluctuating amount of food, for it
allows them rapidly to increase in number. But the
real importance 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 number 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 suffice 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 animal or plant depends only indirectly on the
number of its eggs or seeds.

In looking at Nature, it is most necessary to keep
the foregoing considerations always in mind—never te
forget that every single organic being may 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 falls either on the young
or old, during each generation or at recurrent intervals.
Lighten any check, mitigate the destruction ever so
little, and the number of the species will almost in-
stantaneously increase to any amount.

Cuap, IIL] NATURE OF THE CHECKS TO INCREASE. 83

Nature of the Checks to Increase.

The causes which check the natural tendency of
each species to increase are most obscure. Look at
the most vigorous 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 incomparably
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
considerable length, more especially in regard to the
feral animals of South America. Here I will make
only a few remarks, just to recall to the reader’s mind
some of the chief points. Eggs or very young animals
seem generally to suffer 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 seedlings suffer most from germi-
nating 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 insects. 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 species growing

84 NATURE OF THE CHECKS TO INCREASE. [Cuap. IIL

on a little plot of mown turf (three feet by four) nine
species perished, from the other species being allowed to
grow up freely.

The amount of food for each species of course gives
the extreme limit to which each can increase; but
very frequently 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 de-
struction 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,
although 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 elephant protected by its dam.

Climate plays an important part in determining the
average number 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 tremendous destruction, when
we remember that ten per cent. is an extraordinarily
severe mortality from epidemics with man. The ac-
tion of climate seems at first sight to be quite indepen-
dent 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

Cuap, I1L.] NATURE OF THE CHECKS TO INCREASE. 85

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 tempted to at-
tribute 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 suffering enormous de-
struction at some period of its life, from enemies or
from competitors for the same place and food; and
if these enemies or competitors be in the least degree
favoured by any slight change of climate, they will
increase in numbers; and as each area is already fully
stocked with inhabitants, the other species must de-
crease. 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 favoured, as
in this one being hurt. So it is when we travel north-
ward, but in a somewhat lesser degree, for the number
of species of all kinds, and therefore of competitors,
decreases northwards; hence in going northwards, or
in ascending 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 ele-
ments.

That climate acts in main part indirectly by favour-
ing other species, we clearly see in the prodigious num-

$6 NATURE OF THE CHECKS TO INCREASE. [Czap. IIL

ber of plants which in our gardens can perfectly well
endure our climate, but which never become naturalised,
for they cannot compete with our native plants nor re-
sist destruction by our native animals.

When a species, owing to highly favourable circum-
stances, increases inordinately in numbers in a small
tract, epidemics—at least, this seems generally to
occur with our game animals—often ensue; and here
we have a limiting check independent 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 facility of diffusion
amongst the crowded animals, been disproportionally
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
individuals of the same species, relatively to the num-
bers of its enemies, is absolutely necessary for its pres-
ervation. 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 super-
abundance of food at this one season, increase in num-
ber proportionally to the supply of seed, as their num-
bers are checked during the winter; but any one who
has tried, knows how troublesome it is to get seed from
a few wheat or other such plants in a garden: I have
in this case lost every single seed. This view of the
necessity 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

Cnap. III] STRUGGLE FOR EXISTENCE. 87

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 conditions of
its life were so favourable that many could exist to-
gether, 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
unexpected are the checks and relations between or-
ganic beings, which have to struggle together in the
same country. 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 hundred 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 passing from
one quite different soil to another: not only the pro-
portional 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 insectivor-

ou birds were very common in the plantations, which
8

88 STRUGGLE FOR EXISTENCE. [Cuae. IIL

were not to be seen on the heath; and the heath was
frequented by two or three distinct insectivorous birds.
Here we see how potent has been the effect of the in-
troduction of a single tree, nothing whatever else having
been done, with the exception of the land having been
enclosed, so that cattle could not enter. But how im-
portant an element enclosure is, I plainly saw near
Farnham, in Surrey. Here there are extensive heaths,
with a few clumps of old Scotch firs on the distant hill-
tops: within the last ten years large spaces have been
enclosed, 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 perpet-
ually 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 enclosed, it became
thickly clothed with vigorously growing young firs.
Yet the heath was so extremely barren and so extén-
sive that no one would ever have imagined thhat
cattle would have so closely and effectually searched! it
for food.

Here we see that cattle absolutely determine t'he

Cnap. IIL] STRUGGLE FOR EXISTENCE. 89

existence of the Scotch fir; but in several parts of the
world insects determine the existence of cattle. Per-
haps 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 number 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
some means, probably by other parasitic insects. Hence,
if certain insectivorous birds were to decrease in Para-
guay, the parasitic insects would probably increase;
and this would lessen the number of the navel-frequent-
ing flies—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 Staffordshire, the insectivorous
birds, and so onwards in ever-increasing circles of com-
plexity. 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!

90 STRUGGLE FOR EXISTENCE. [Cuap. III.

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 in-
sects, 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
experiments that humble-bees are almost indispensable
to the fertilisation of the heartsease (Violo 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 be-
came extinct or very rare in England, the heartsease
and red ¢lover would become very rare, or wholly dis-
appear. 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 hum-
ble-bees, believes that “more than two-thirds of them
are thus destroyed all over England.” Now the num-

Cuap. III.] STRUGGLE FOR EXISTENCE, . 91

ber. 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
animal in large numbers in a district might deter-
mine, through the intervention first of mice and
then of bees, the frequency 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 determining 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 beauti-
ful diversity and proportion of kinds as in the surround-
ing virgin forest. What a struggle must have gone
on during long centuries between the several kinds
of trees each annually scattering its seeds by the thou-
sand; 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

92 , STRUGGLE FOR EXISTENCE. [Cuae. IIL

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 to the ground according
to definite laws; but how simple is the problem where
each shall fall compared to that of the action and re-
action 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 some-
times 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 ex-
posed to the same dangers. In the case of varieties
of the same species, the struggle will generally be al-
most equally severe, and we sometimes see the contest
soon decided: for instance, if several varieties of wheat
be sown together, and the mixed seed be resown, some
of the varieties 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

Cuar. IIIl.] STRUGGLE FOR EXISTENCE. 92

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 ke2ping together different varieties of
the medicinal leech. It may even be doubted whether
the varieties of any of our domestic plants or animals
have so exactly the same strength, habits, and constitu-
tion, that the original proportions of a mixed stock
(crossing being prevented) could be kept up for half-a-
dozen generations, if they were allowed to struggle to-
gether, in the same manner as beings in a state of nature,
and if the seed or young were not annually preserved in
due proportion.

<.

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 constitution, and always in structure, the
struggle will generally be more severe between them, if
they come into competition with each other, than be-
tween 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 an-
other 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 climates! In Russia the small Asiatic cock-
roach has everywhere driven before it its great con-
gener. In Australia the imported hive-bee is rapidly
exterminating the small, stingless native bee. One spe-

94 STRUGGLE FOR EXISTENCE. [Cuar. ILL.

cies 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 pre-
cisely say why one species has been victorious over an-
other in the great battle of life.

A corollary of the highest importance may be de-
duced from the foregoing remarks, namely, that the
structure of every organic being is related, in the most
essential yet often hidden manner, to that of all the
other organic beings, with which it comes into compe
tition for food or residence, or from which it has t»
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 dis-
tributed and fall on unoccupied ground. In the water-
beetle, the structure of its legs, so well adapted for div-
ing, 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 re-
lation 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

Cuap. IIL] STRUGGLE FOR EXISTENCE. 95

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 vigorously 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 perfectly 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 im-
agination to give the plant the power of increasing in
number, we should have to give it some advantage over
its competitors, or over the animals which prey on it.
On the confines cf 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 co far,
that they are destroyed 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 individuals
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

96 STRUGGLE FOR EXISTENCE. [Cuar. II,

give it some advantage over a different set of competi-
tors or enemies.

It is good thus to try in imagination to give to any
one species an advantage over another. Probably in
no single instance should we know what to do. This
ought to convince 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 striv-
ing to increase in a geometrical 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 incessant, that no
fear is felt, that death is generally prompt, and that the
vigorous, the healthy, and the happy survive and
multiply.

Cuap, IV.] NATURAL, SELECTION. 9%

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 intercrosses between individuals of the same species—Cir-
cumstances favourable and unfavourable to the results of
Natural Selection, namely, intercrossing, isolation, number of
individuals—Slow action—Extinction caused by Natural Se-
lection—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—Ex-
plains the grouping of all organic beings—Advance in organ-
isation—Low forms preserved—Convergence of character—
Indefinite multiplication of speciee—Summary.

How will the struggle for existence, briefly discussed
in the last chapter, act in regard to variation? Can the
principle of selection, which we 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
occurring 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 or-
ganisation becomes in some degree plastic. But the
variability, which we almost universally meet with in

-

98 NATURAL SELECTION, [Cuae. IV.

our domestic productions, is not directly produced, as
Hooker and Asa Gray have well remarked, by man; he
can neither originate varieties, nor prevent their occur-
rence; he can preserve and accumulate such as do
occur. Unintentionally he exposes organic beings to
new and changing 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 consequently what in-
finitely 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 use-
ful to man have undoubtedly occurred, that other varia-
tions useful in some way to each being in the great and
complex battle of life, should occur in the course of
many successive generations? If such do occur, can we
doubt (remembering that many more individuals are
born than can possibly survive) that individuals having
any advantage, however slight, over others, would have
the vest chance of surviving and of procreating their
kind? On the other hand, we may feel sure that any
variation in the least degree injurious would be rigidly
destroyed. This preservation of favourable 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 per-
haps we see in certain polymorphic species, or would ul-
timately become fixed, owing to the nature of the organ-
ism and the nature of the conditions.

Cuap. IV.] NATURAL SELECTION. 99

Several writers have misapprehended or objected to
the term Natural Selection. Some have even imagined
that natural 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 selection; 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 implies 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 lit-
eral sense of the word, no doubt, natural selection is a
false term; but who ever objected to chemists speaking
if the elective affinities of the various elements?—and
{et 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 of the planets?
Kvery one knows what is meant and is implied by such
raetaphorical expressions; and they are almost necessary
for brevity. So again it is difficult to avoid personify-
ing the word Nature; but I mean by Nature, only the
aggregate 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 under-
gaving some slight physical change, for instance, of
‘limate. The proportional numbers of its inhabitants

100 NATURAL SELECTION. [Cuap. IV.

will almost immediately undergo a change, and some
species will probably become extinct. We may con-
clude, from what we have seen of the intimate and com-
plex 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 like-
wise seriously disturb the relations of some of the former
inhabitants. Let it be remembered 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 fav-
oured 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
chapter, that changes in the conditions of life give a
tendency to increased variability; and in the foregoing
cases the conditions have changed, and this would mani-
festly be favourable to natural selection, by affording a
better chance of the occurrence of profitable variations.
Unless such occur, natural selection can do nothing.
Under the term of “ variations,” it must never be forgot-
ten that mere individual differences are included. As

Cuap. IV.] NATURAL SELECTION. 101

man can produce a great result with his domestic animals
and plants by adding up in any given direction individ-
ual differences, so could natural selection, 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 im-
migration, is necessary in order that new and unoccupied
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 modifica-
tions in the structure or habits of one species would
often give it an advantage 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 defence. No country can be
named in which all the native inhabitants are now so!
perfectly adapted to each other and to the physical con-
ditions 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 naturalised
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, |

afi [ may be allowed to personify the natural preservation

102 NATURAL SELECTION. (Cuap. IV.

or survival of the fittest, 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 con-
stitutional difference, on the whole machinery of life.
Man selects only for his own good: Nature only for that
of the being which she tends. Every selected charac-
ter 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
selected 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 destroy all inferior ani-
mals, 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
slightest differences of structure or constitution may well
turn the nicely-balanced scale in the struggle for life,
and so be preserved. How fleeting are the wishes and
efforts of man! how short his time! and consequently
how poor will be his results, compared with those ac-
cumulated by Nature during whole geological periods!
Can we wonder, then, that Nature’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

Cuap. IV.] NATURAL SELECTION, 103

is daily and hourly scrutinising, throughout the world,
the slightest variations; rejecting those that are bad,
preserving and adding up all that are good; silently
and insensibly working, whenever and wherever oppor-
tunity offers, at the improvement of each organic being
in relation to its organic and inorganic 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 individual differences of the same fa-
vourable nature as before; and these must be again pre-,
served, and so onwards step by step. Seeing that individ-
ual differences of the same kind perpetually recur, this
can hardly be considered as an unwarrantable assump-
tion. But whether it is true, we can judge only by seeing
how far the hypothesis accords with and explains 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 struc-
tures, 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

9

104 NATURAL SELECTION, [Caap. IV.

of their lives would increase in countless numbers; 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 particular colour would
produce little effect: we should remember how essentia\
\t 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. Ir
plants, the down on the fruit and the colour of the flesh
are considered by botanists as characters of the most
trifling importance: yet we hear from an excellent horti-
culturist, Downing, that in the United States, smooth-
skinned fruits suffer far more from a beetle, a Curculio,
than those with down; thet purple plums suffer 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 differ-
ence 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 differ-
ences would effectually settle which variety, whether a
smooth or downy, a yellow or purple fleshed fruit, should
succeed.
In looking at many small points of difference be-
tween species, which, as far as our ignorance permits us

Cuap. IV.] NATURAL SELECTION. 105

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 correlation, when one part varies,
and the variations are accumulated through natural
selection, other modifications, often of the most unex-
pected nature, will ensue.

As we see that those variations which, under domes-
tication, appear at any particular period of life, tend to
reappear in the offspring at the same period;—for in-
stance, 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 silk-worm; in the eggs of 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 varia-
tions 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 selection, 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 concern the mature insect;
and these modifications may affect, through correlation,
the structure of the adult. So, conversely, 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 be-
come extinct.

Natural selection will modify the structure of the

106 NATURAL SELECTION. [Cuar. IV

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 se-
lected 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 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 perish; 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

Cuap. IV.] SEXUAL SELECTION. 107

manner which protected them from their enemies. Yet
many of these eggs or seeds would perhaps, if not de-
stroyed, have yielded individuals better adapted to their
conditions of life than any of those which happened to
survive. 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 whic
would in other ways be beneficial 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 develored,—yet of those which do
survive, the best adapted individuals, supposing that
there is any variability in a favourable direction, will
tend to propagate their kind in larger numbers co
the less well adapted. If the numbers be wholly kept
down by the causes just indicated, as will often have
been the case, natural selection will be powerless in
certain beneficial directions; but this is no valid objec-
tion 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 improve-
ment at the same time in the same area.

Sexual Selection.

Inasmuch as peculiarities often appear under do-
mestication in one sex and become hereditarily attached
to that sex, so no doubt it will be under nature. Thus
it is rendered possible for the two sexes to be modified

108 SEXUAL SELECTION. [Cuar. IV.

through natural selection 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 oc-
curs. This leads me to say a few words on what I have
called Sexual Selection. This form of selection de-
pends, 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 re-
or no offspring. Sexual selection is, therefore, less
rigorous than natural selection. 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 vigor, 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
indomitable 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 se-
lection of his best cocks. How low in the scale of
nature the law of battle descends, I know not; male alli-
gators have been described as fighting, bellowing, and
whirling round, like Indians in a war-dance, for the pos-
session of the females; male salmons have been observed
fighting all day long; male stag-beetles sometimes bear
wounds from the huge mandibles of other males; the
males of certain hymenopterous insects have been fre-
quently seen by that inimitable observer M. Fabre, fight-
ing for a particular female who sits by, an apparently
unconcerned beholder of the struggle, and then retires

Cuap. IV.] SEXUAL SELECTION. 109

with the conqueror. The war is, perhaps, severest be-
tween 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 meansof defence maybe given
through meansof sexual selection,as the maneof thelion,
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 peace-
ful character. All those who have attended to the sub-
ject, believe that there is the severest rivalry between the
males of many species to attract, by singing, the females.
The rock-thrush of Guiana, birds of paradise, and some
others, congregate; and successive males display with
the most elaborate care, and show off in the best manner,
their gorgeous plumage; they likewise perform strange
antics before the females, which, standing by as spec-
tators, 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, during thousands of generations, the most
melodious or beautiful males, according to their stand-
ard 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,

110 ILLUSTRATIONS OF THE ACTION OF [Cuap. IV.

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 fe-
males of any animal have the same general habits of life,
but differ in structure, colour, or ornament, such dif-
ferences have been mainly caused by sexual selection:
that is, by individual males having had, in suc-
cessive 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 dif-
ferences to this agency: for we see in our domestic ani-
mals 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 mon-
strosity.

Illustrations of the Action of Natural Selection, or the
Survival of the Fittest.

In order to make it clear how, as I believe, natural
selection 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

Cuap. IV.) NATURAL SELECTION. 111

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, 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 alternative had frequently occurred. I saw
the great importance of individual differences, and this
led me fully to discuss the results of unconscious se-
lection by man, which depends on the preservation of all
the more or less valuable individuals, and on the de-
struction of the worst. I saw, also, that the preserva-
tion 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.
Nevertheless, until reading an able and valuable article
in the ‘North British Review’ (1867), I did not ap-

112. ILLUSTRATIONS OF THE ACTION OF [Cuar. lV.

preciate how rarely single variations, whether slight or
strongly-marked, could be perpetuated. The author
takes the case of a pair of animals, producing during
their lifetime two hundred offspring, of which, from
various causes of destruction, only two on an average
survive to pro-create their kind. This is rather an ex-
treme 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 variation; 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 dis-
puted. 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 consequently flourished, nevertheless there would
be a very poor chance of this one individual perpetuating
its kind to the exclusion of the common form; but there
can hardly be a doubt, judging by what we see taking
place under domestication, 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

Cuap. IV.] NATURAL SELECTION, 113

owing to a similar organisation being similarly acted on
—of which fact numerous instances could be given with
our domestic productions. In such cases, if the varying
individual did not actually transmit to its offspring its
newly-acquired character, it would undoubtedly trans-
mit 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 tend-
ency to vary in the same manner has often been so
strong that all the individuals of the same species have
been similarly 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 sur-
vival of the fittest.

To the effects of intercrossing in eliminating varia-
tions 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. Oonsequently 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

114 ILLUSTRATIONS OF THE ACTION OF [Cuap. LV.

district, competing with and conquering the unchanged
individuals on the margins of an ever-increasing circle.
It may be worth while to give another and more com-
plex 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 instance, by glands at the base of the
stipules in some Leguminose, 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 indi-
viduals of the same species would thus get crossed; and
the act of crossing, as can be fully proved, gives rise to
vigorous seedlings which consequently would have the
best chance of flourishing and surviving. The plants
which produced flowers with the largest glands or nec-
taries, excreting most 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 insects 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
visiting 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 little pollen were carried, at first

Cuap. IV.] NATURAL SELECTION. 115

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 con-
tinued, had been rendered highly attractive to insects,
they would, unintentionally 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 likewise illustrating one step in
the separation of the sexes of plants. Some holly-trees
bear only male flowers, which have four stamens produ-
cing 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 detected.
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, never-
theless 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

116 ILLUSTRATIONS OF THE ACTION OF [Cuar. IV.

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 im-
potent; 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 advantage-
ous on the principle of the division of labour, individ-
uals with this tendency more and more increased, would
be continually favoured or selected, until at last a com-
plete separation of the sexes might be effected. It
would take up too much space to show the various steps,
through dimorphism and other means, by which the
separation of the sexes in plants of various kinds is ap-
parently 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 condition, or, as he
expresses it, are more or less diceciously polygamous.

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. Bear-
ing such facts in mind, it may be believed that under
certain circumstances. individual differences in the cur-

Cuap. IV.] NATURAL SELECTION. 117

vature or length of the proboscis, &c., too slight to be
appreciated by us, might profit a bee or other insect, so
that certain individuals would be able to obtain their
food more quickly than others; and thus the communi-
ties 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 pratense and incarnatum) do not on a
hasty glance appear to differ in length; yet the hive-bee
can easily suck the nectar out of the incarnate clover,
but not out of the common red clover, which is visited
by humble-bees alone; so that whole fields of 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 determines 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 com-
mon hive-hee, and which freely crosses with it, is able to
reach and suck the nectar of the red clover. Thus, ina
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-bees were to become rare

®

118 ON THE INTERCROSSING [Cuap. IV.

in any country, it might be a great advantage to the
plant to have a shorter or more deeply divided corolla, so
that the hive-bees should be enabled to suck its flowers.
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 struc-
ture mutually favourable to each other.

I am well aware that this doctrine of natural selec-
tion, 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 insignificant, when used in ex-
plaining the excavation of the deepest valleys or the for-
mation of long lines of inland cliffs. Natural selection
acts only by the preservation and accumulation of small
inherited modifications, each profitable to the preserved
being; and as modern geology has almost banished such
views as the excavation of a great valley by a single dilu-
vial 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 obvious that two individuals must always (with
the exception of the curious and not well understood
cases of parthenogenesis) unite for each birth; but in

Cuap, IV.] OF INDIVIDUALS. 119

the case of hermaphrodites this is far from obvious.
Nevertheless there is reason to believe that with all her-
maphrodites two individuals, either occasionally or
habitually, concur for the reproduction of their kind.
This view was long ago doubtfully suggested by Spren-
gel, Knight and Kélreuter. We shall presently see its
importance; but I must here treat the subject with ex-
treme brevity, though I have the materials prepared for
an ample discussion. All vertebrate animals, all insects,
and some other large groups of animals, pair for each
birth. Modern research has much diminished the num-
ber of supposed hermaphrodites, and of real hermaphro-
dites a large number pair; that is, two individuals regu-
larly unite for reproduction, 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 in-
dividuals ever concur in reproduction? As it is impos-
sible 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 ac-
cordance with the almost universal belief of breeders,
that with animals and plants a cross between different
varieties, or between individuals of the same variety but
of another strain, gives vigour and fertility to the off-
spring; and on the other hand, that close interbreeding
diminishes vigour and fertility; that these facts alone in-
cline me to believe that it is a general law of nature that
no organic being fertilises itself for a perpetuity of gen-
erations; but that a cross with another individual is occa-
sionally—perhaps at long intervals of time—indispen-

sable. 10

120 ON THE INTERCROSSING. [Cuap. IV.

On the belief that this is a law of nature, we can,
think, understand several large classes of facts, such a
the following, which on any other view are inexplicable,
Every hybridizer knows how unfavourable exposure ta
wet is to the fertilisation of a flower, yet what a multi.
tude of flowers have their anthers and stigmas fully ex.
posed to the weather! If an occasional cross be indis-
pensable, 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 neces:
sary are the visits of bees to many papilionaceous flowers,
that their fertility is greatly diminished if these visits be
prevented. Now, it is 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 an-
thers of one flower and then the stigma of another; but
it must not be supposed that bees would thus produce 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 invariably and completely destroys, as has been
shown by Gartner, the influence of the foreign pollen.

When the stamens of a flower suddenly spring to-
wards the pistil, or slowly move one after the other to-
wards it, the contrivance seems adapted solely to ensure

Cuap. IV.] OF INDIVIDUALS. 121

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 Kélreuter 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 effectu-
ally 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 in-
stance, in Lobelia fulgens, there is a really beautiful and
elaborate contrivance by which all the infinitely numer-
ous pollen-granules are swept out of the conjoined an-
thers 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. An-
other 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 recently Hildebrand, and others,
have shown, and as I can confirm, either the anthers
burst before the stigma is ready for fertilisation, or the
stigma is 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!

122 ON THE INTERCROSSING [Cuap. IV.

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 occasional cross
with a distinct individual being advantageous or indis-
pensable!

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
distinct variety having a prepotent effect over the
flower’s own pollen; and that this is part of the gen-
eral 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

Cuap. IV.] OF INDIVIDUALS. 123

can be considered as distinct individuals only in a lim-
ited sense. I believe this objection to be valid, but that
nature has largely provided against it by giving to trees
a strong tendency to bear flowers with separated sexes.
When the sexes are separated, 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 occasionally
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
request 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 terres-
trial species are hermaphrodites, such as the land-mol-
lusca and earth-worms; but these all pair. As yet I have
not found a single terrestrial animal which can fertilise
itself. This remarkable fact, which offers so strong a
contrast with terrestrial plants, is intelligible on the
view of an occasional cross being indispensable; for ow-
ing to the nature of the fertilising 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-

jy CIRCUMSTANCES FAVOURABLE TO THE [Caapr. IV.

rents of water offer an obvious means for an occasional
cross. As in the case of flowers, I have as yet failed,
after consultation with one of the highest authorities,
namely, Professor Huxley, to discover a single hermaph-
rodite animal with the organs of reproduction so per-
fectly enclosed that access from without, and the oc-
casional 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 spe-
cies of the same family and even of the same genus,
though agreeing closely with each other in their whole
organisation are hermaphrodites, and some unisexual.
But if, in fact, all hermaphrodites do occasionally inter-
cross, 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 occasional intercross between distinct indi-
viduals is a very general, 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 dif-
ferences are always included, will evidently be favour-
able. A large number of individuals, by giving a better
chance within any given period for the appearance of

Cuap. IV.] RESULTS OF NATURAL SELECTION. 125

profitable variations, will compensate 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 selec-
tion, 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 fa-
vourable variations be inherited by some at least of the
offspring, nothing can be effected by natural selection.
The tendency to reversion may often check or prevent
the work; but as this tendency has not prevented man
from forming by selection numerous 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 al-
lowed freely to intercross, his work will completely fail.
But when many men, without intending to alter the
breed, have a nearly common standard of perfection, and
all try to procure and breed from the best animals, im-
provement surely but slowly follows from this uncon-
scious process of selection, notwithstanding 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
individuals 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 conditions of life; and then, if the
same species undergoes modification in different dis-
tricts, the newly-formed varieties will intercross on the
confines of each, But we shall see in the sixth chapter

126 CIRCUMSTANCES FAVOURABLE TO THE [Caur. lV.

that intermediate varieties, inhabiting intermediate dis-
tricts, 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 coun-
tries; and this I find to be the case. With hermaph-
rodite 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 intercrossing would always eliminate the effects
of natural selection; for I can bring forward a consider-
able body of facts showing that within the same area,
two varieties of the same animal may long remain dis-
tinct, from haunting different stations, from breeding
at slightly different seasons, or from the individuals of
each variety preferring to pair together.

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 ani-
mals which unite for each birth; but, as already stated,
we have reason to believe that occasional intercrosses
take place with all animals and plants. Even if these

Cuar.1V.] RESULTS OF NATURAL SELECTION. 127

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-fertilisation, that
they will have a better chance of surviving and propa-
gating their kind; and thus in the long run the influ-
ence 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 con-
ditions of life, only through the principle of inherit-
ance, and through natural selection which will destroy
any individuals departing from the proper type. If
the conditions of life change and the form undergoes
modification, uniformity of character can be given to
the modified offspring, solely by natural selection pre-
serving similar favourable variations.

Isolation, also, is an important element in the modifi-
cation of species through natural selection. In a con-
fined or isolated area, if not very large, the organic and
inorganic conditions of life will generally be almost
uniform; so that natural 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 interesting 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
necessary elements for the formation of new species.
The importance of isolation is likewise great in prevent-

128 CIRCUMSTANCES FAVOURABLE TO THE [Cuar. IV.

ing, after any physical change in the conditions, such as
of climate, elevation of the land, &c., the immigration of
better adapted organisms; 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 num-
ber 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 aris-
ing.

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 assumed by me to play an all-important part
in modifying species, as if all the forms of life were
necessarily undergoing change through some innate law.
Lapse of time is only so far important, and-its impor-
tance in this respect is great, that it gives a better
chance of beneficial variations arising and of their being
selected, accumulated, and fixed. It likewise 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 re-
marks, and look at any small isolated area, such as an
oceanie island, although the number of species inhabit-
ing it is small, as we shall see in our chapter on Geo-
graphical 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

Cuar, IV.] RESULTS OF NATURAL SELECTION. 129

island at first sight seems to have been highly favourable
for the production of new species. But we may thus de-
ceive 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 individuals
of the same species there supported, but the conditions
of life are much more complex from the large number of
already existing species; and if some of these many spe-
cies become modified and improved, others will have to
be improved in a corresponding degree, or they will be
exterminated. Each new form, also, as soon as it has
been much improved, will be able to spread over the
open and continuous area, and will thus come into com-
petition with many other forms. Moreover, great areas,
though now continuous, will often, owing to former os-
cillations of level, have existed in a broken condition; so
that the good effects of isolation will generally, to a cer-
tain 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 al-

130 CIRCUMSTANCES FAVOURABLE TO THE [Cusr. IV.

ready have been victorious over many competitors, will be
those that will spread most widely, and will give rise to
the greatest 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, under-
stand some facts which will be again alluded to in our
chapter on Geographical Distribution; for instance, the
fact of the productions of the smaller continent of Aus-
tralia now yielding before those of the larger Europzo-
Asiatic area. Thus, also, it is that continental produc-
tions 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 modifica-
tion 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 tertiary
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 there 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 ex-
tent orders at present widely sundered in the natural
scale. These anomalous forms may be called living fos-
sils; they have endured to the present day, from having
inhabited a confined area, and from having been exposed
to less varied, and therefore less severe, competition.

To sum up, as far as the extreme intricacy of the

Cuap. 1V.] RESULTS OF NATURAL SELECTION. 131

subject permits, the circumstances favourable and un-
favourable for the production of new species through
natural selection. I conclude that for terrestrial produc-
tions 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 inhabitants will
have been numerous in individuals and kinds, and will
have been subjected to severe competition. When con-
verted 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 modi-
fication of the old inhabitants; and time will have been
allowed for the varieties in each to become well modified
and perfected. When, by renewed elevation, 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
slowness 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 exist-

132 EXTINCTION BY NATURAL SELECTION. [Cuar. IV.

ing 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 create new
places, ready to be filled up by better adapted forms, 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 dif-
ferences of the right nature in various parts of the or-
ganisation might occur. The result would often he
greatly retarded by free intercrossing. Many will ex-
claim that these several causes are amply sufficient to
neutralise the power of natural selection. I do not be-
lieve so. But I do believe that natural selection will gen-
erally 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 ac-
cord well with what geology tells us of the rate and man-
ner 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 com-
plexity of the coadaptations between all organic beings,
one with another and with their physical conditions of
life, which may have been effected 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

Cuap. IV.] EXTINCTION BY NATURAL SELECTION. 133

being intimately connected with natural selection.
Natural selection acts solely through the preservation of
variations in some way advantageous, which consequent-
ly endure. Owing to the high geometrical rate of in-
crease 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 in-
dividuals will run a good chance of utter extinction,
during great fluctuations in the nature of the seasons,
or from a temporary increase in the number of its ene-
mies. But we may go further than this; for, as new
forms are produced, unless we admit that specific forms
can go on indefinitely increasing in number, many old
forms must become extinct. That the number of spe-
cific forms has not indefinitely increased, geology plainly
tells us; and we shall presently attempt to show why it
it is that the number of species throughout the world
has not become immeasurably great.

We have seen that the species which are most numer-
ous 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 re-
corded 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 modi-
fied and improved descendants of the commoner species.

From theseseveral considerations I think it inevitably
follows, that as new species in the course of time are

134 DIVERGENCE OF CHARACTER. [Cuaap. 1Y.

formed through natural selection, others will become
rarer and rarer, and finally extinct. The forms which
stand in closest competition with those undergoing
modification and improvement 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 do-
mesticated productions, through the selection of im-
proved 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 bysome murderous pestilence.”

Divergence of Character.

The principle, which I have designated by this term,
is of high importance, and explains, as I believe, several
important 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 fromeach other than do good and distinct species.

Cuap.1V.] DIVERGENCE OF CHARACTER, 135

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 dif-
ference between species? That this does habitually
happen, we must infer from most of the innumerable
species throughout nature presenting well-marked dif-
ferences; whereas varieties, the supposed prototypes and
parents of future well-marked species, present slight and
ill-defined 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 dif-
fer 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 fan-
cier is, for instance, struck by a pigeon having a slightly
shorter beak; another fancier is struck by a pigeon hav-
ing a rather longer beak; and on the acknowledged
principle that “fanciers do not and will not admire a
medium standard, but like extremes,” they both go on
(as has actually occurred with the sub-breeds of the tum-
bler-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
11 :

186 DIVERGENCE OF CHARACTER, [Cuap. LV.

history, the men of one nation or district required swift-
er horses, whilst those of another required stronger
and bulkier horses. The early differences 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.
Ultimately, 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 animals with intermediate characters, being
neither very swift nor very strong, would not have been
used for breeding, and will thus have tended to dis-
appear. Here, then, we see in man’s productions the
action of what may be called the principle of divergence,
causing differences, at first barely appreciable, 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 prin-
ciple apply in nature? I believe it can and does apply
most efficiently (though it was a long time before I saw
how), from the simple circumstance that the more diver-
sified the descendants from any one species become in
structure, constitution, and habits, by so much will they
be better enabled to seize on many and widely diver-
sified 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

ae

it

D. Appleton & C? NewYork.

Cuap.IV.] DIVERGENCE OF CHARACTER. 137

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 diver-
sified 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 otherwise natural selection can affect 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 dif-
fered 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 suc-
ceed in living on the same piece of ground. And we
know that each species and each variety of grass is annu-
ally sowing almost countless seeds; and is thus striv-
ing, as it may be said, to the utmost to increase in num-~
ber. Consequently, in the course of many thousand
generations, the most distinct varieties of any one species
of grass would have the best chance of succeeding and
of increasing in numbers, and thus of supplanting the

138 DIVERGENCE OF CHARACTER. [Cuap. IV.

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 struc-
ture, is seen under many natural circumstances. In an
extremely small area, especially if freely open to immi-
gration, and where the contest between individual and
individual must be very severe, 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 (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 accompanying differences of habit
and constitution, determine that the inhabitants, which
thus jostle each other most closely, shall, as a general
tule, 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

Cap. IV.) DIVERGENCE OF CHARACTER. 139

commonly looked at as specially created and adapted
for their own country. It might also, perhaps, have
been expected that naturalised .plants would have be-
longed to a few groups more especially adapted to certain
stations in their new homes. But the case is very dif-
ferent; and Alph. de Candolle has well remarked, in his
great and admirable work, that floras gain by naturalisa-
tion, 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
belong to 162 genera. We thus see that these natural-
ised plants are of a highly diversified nature. They differ,
moreover, to a large extent, from the indigenes, for out
of the 162 naturalised genera, no less than 100 genera are
not there indigenous, and thus a large proportional addi-
tion is made to the genera nowlivingin 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 compatriots; 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
inhabitants of the same region is, in fact, the same as
that of the physiological division of labour in the organs
of the same individual body—a subject so well eluci-
dated by Milne Edwards. No physiologist doubts that a
stomach adapted to digest vegetable matter alone, or
flesh alone, draws most nutriment from these substances.

140 RESULTS OF THE ACTION OF [Cuar. IV.

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 indi-
viduals be capable of there supporting themselves. A set
of animals, with their organisation but little diversified,
could hardly compete with a set more perfectly diversified
in structure. It may be doubted, for instance, whether the
Australian marsupials, which are divided into groups dif-
fering but little from each other, and feebly represent-
ing, 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 diversifi-
cation in an early and incomplete stage of development.

The Probable Effects of the Action of Natural Selection
through Divergence of Character and Extinction, on
the Descendants of a Common Ancestor.

After the foregoing discussion, which has been much
compressed, we may assume that the modified descend-
ants of any one species will succeed so much the better
as they become more diversified in structure, and are
thus enabled to encroach 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 selection and of extinc-
tion, tends to act.

The accompanying diagram will aid us in understand-
ing 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

Crap. IV.] NATURAL SELECTION, 141

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
varyin large genera than in 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, be-
longing to a genus large in its own country. The
branching and diverging dotted lines of unequal lengths
proceeding 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 principle. of benefit derived
from divergence of character comes in; for this will
generally lead to the most different or divergent varia-
tions (represented by the outer dotted lines) being pre-
served 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 accumu-
lated 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 dia-
gram, may represent each a thousand or more genera-
tions. After a thousand generations, species (A) is sup-
posed to have produced two fairly well-marked varieties,
namely a1 and m+. These two varieties will generally

142 RESULTS OF THE ACTION OF [Cuap. IV.

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 nu-
merous than most of the other inhabitants of the same
country; they will also partake of those more general
advantages which made the genus to which the parent-
species belonged, a large genus in its own country. And
all these circumstances are favourable to the production
of new varieties.

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 a1 is supposed in the diagram to have
produced variety a7, which will, owing to the principle
of divergence, differ more from (A) than did variety a’.
Variety m+ is supposed to have produced two varieties,
namely m? and s?, 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 genera-
tions, 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
varieties or modified descendants of the common parent
(A), will generally go on increasing in number and
diverging in character. In the diagram the process is
represented up to the ten-thousandth generation, and
under a condensed and simplified form up to the four-
teen-thousandth generation.

Cuap. IV.] NATURAL SELECTION. 143

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 irregu-
lar, nor that it goes on continuously; it is far more prob-
able that each form remains for long periods unaltered,
and then again undergoes modification. Nor do I sup-
pose that the most divergent varieties are invariably pre-
served: a medium form may often long endure, and may
or may not produce more than one modified descendant;
for natural selection will always act according to the na-
ture of the places which are either unoccupied or not per-
fectly occupied by other beings; and this will depend on
infinitely complex relations. But as a general rule, the
more diversified in structure the descendants from any
one species can be rendered, the more places they will
be enabled to seize on, and the more their modified pro-
geny will increase. In our diagram the line of succession
is broken at regular intervals by small numbered letters
marking the successive forms which have become suffi-
ciently distinct to be recorded as varieties. But these
breaks are imaginary, and might have been inserted any-
where, after intervals long enough to allow the accumu-
lation of a considerable amount of divergent variation.

As all the modified descendants from a common and
widely-diffused species, belonging to a large genus, will
tend to partake of the same advantages which made their
parent successful in life, they will generally go on mul-
tiplying in number as well as diverging in character:
this is represented in the diagram by the several diver-
gent branches proceeding from (A). The modified off-
spring from the later and more highly improved
branches in the lines of descent, will, it is probable, often
take the place of, and so destroy, the earlier and less

144 RESULTS OF THE ACTION OF [Cuap. IV.

improved 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 modifica-
tion 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 diverging
in character from their original stocks, without either
having given off any fresh branches or races.

After ten thousand generations, species (A) is sup-
posed to have produced three forms, a’, f?°, and m?°,
which, from having diverged in character during the suc-
cessive generations, will have come to differ largely, but
perhaps unequally, from each other and from their com-
mon parent. If we suppose the amount of change be-
tween each horizontal line in our diagram to be exces-
sively 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 last into well-defined species. Thus the
diagram illustrates the steps by which the small differ-
ences distinguishing varieties are increased into the
larger differences distinguishing species. By continuing
the same process for a greater number of generations (as
shown in the diagram in a condensed and simplified
manner), we get eight species, marked by the letters
between a** and m**, all descended from (A). Thus, as
I believe, species are multiplied and genera are formed.

Cuap. IV.} NATURAL SELECTION, 145

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 thousand generations, either two well-
marked varieties (w!° and z?°) or two species, according
to the amount of change supposed to be represented be-
tween the horizontal lines. After fourteen thousand
generations, six new species, marked by the letters n1* to
z'*, are supposed to have been produced. In any genus,
the species which are already very different 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 dif-
ferent places in the polity of nature: hence in the dia-
gram 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 con-
tinue to transmit unaltered descendants; and this is
shown in the diagram by the dotted lines unequally pro-
longed 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 con-
stant tendency in the improved descendants of any one
species to supplant and exterminate in each stage of de-
scent their predecessors and their original progenitor.
For it should be remembered that the competition will
generally be most severe between those forms which are

146 RESULTS OF THE ACTION OF [Caup. IV.

most nearly related to each other in habits, constitution,
and structure. Hence all the intermediate forms be-
tween 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 progenitor do not come into com-
petition, both may continue to exist.

If, then, our diagram be assumed to represent a con-
siderable 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 (n1* to z1*) new species.

But we may go further than this. The original spe-
cies 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 num-
ber 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

Cuap. IV.] NATURAL SELECTION. 147

they will have taken the places of, and thus extermi-
nated not only their parents (A) and (I), but likewise
some of the original species which were most nearly re-
lated 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 trans-
mitted 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 a** and z‘* will be much greater than that be-
tween the most distinct of the original eleven species.
The new species, moreover, will be allied to each other in
a widely different manner. Of the eight descendants
from (A) the three marked a‘, g**, p**, will be nearly
related from having recently branched off from a}; 5+,
and f‘*, from having diverged at an earlier period from
a®, will be in some degree distinct from the three first;
named species; and lastly, 014, e1¢, and m*4, 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) dif-
fered largely from (A), standing nearly at the extreme
end of the original genus, the six descendants from (I)
will, owing to inheritance alone, differ considerably from
the eight descendants from (A); the two groups, more-
over, are supposed to have gone on diverging in dif-

148 RESULTS OF THE ACTION OF [Cuapr. IV.

ferent directions. The intermediate species, also (and
this is a very important consideration), which connected
the original species (A) and (I), have all become, ex-
cepting (F), extinct, and have left no descendants.
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
produced 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 downwards towards a single
point; this point represents a species, the supposed pro-
genitor of our several new 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 be-
tween the parent-species (A) and (I), now supposed to
be extinct and unknown, it will be in some degree inter-
mediate 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
parents, the new species (F**) will not be directly inter-
mediate between them, but rather between types of the
two groups; and every naturalist will be able to call such
eases before his mind.

In the diagram, each horizontal line has hitherto

Cuap. IV.)} NATURAL SELECTION. 149

been supposed to represent a thousand generations, but
each may represent 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 be-
ings, 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
extinct 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 diagram, we suppose the amount of change, repre-
sented by each successive group of diverging dotted lines
to be great, the forms marked a** to p**, those marked
b** and f1*, and those marked 014 to m1, will form three
very distinct genera. We shall also have two very dis-
tinct genera descended from (I), differing widely from
the descendants of (A). These 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
belonging 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

150 RESULTS OF THE ACTION OF [Cuap. IV.

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 common. Hence,
the struggle for the production of new and modified de-
scendants 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 varia-
tion 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 ultimately
prevail, no man can predict; for we know that many
groups formerly most extensively developed, have now
become 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 small-
er groups will become utterly extinct, and leave no modi-
fied descendants; and consequently that, of the species
living at any one period, extremely few will transmit de-
scendants to a remote futurity. I shall have to return to
this subject in the chapter on Classification, but I may
add that as, according to this view, extremely few of the
more ancient species have transmitted descendants
to the present day, and, as all the descendants of the

Cuap, IV,] NATURAL SELECTION. 151

game 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 Organisation tends to advance.

Natural Selection acts exclusively by the preserva-
tion and accumulation of variations, which are benefi-
cial under the organic and inorganic conditions to which
each creature is exposed at all periods of life. The ulti-
mate result is that each creature tends to become more
and more improved in relation to its conditions. This
improvement inevitably leads to the gradual advance-
ment of the organisation of the greater number 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
organisation. Amongst the vertebrata the degree of in-
tellect 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 sev-
eral 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 ap-
plicable and the best, namely, the amount of differenti-

ation of the parts of the same organic being, in the adult
12

152 ON THE DEGREE TO WHICH = [Caur. IV.

state as I should be inclined to add, and their specialisa-
tion for different functions; or, as Milne Edwards would
express it, the completeness of the division of physio-
logical labour. But we shall see how obscure this sub-
ject is if we look, for instance, to fishes, amongst which
some naturalists rank those as highest which, like the
sharks, approach nearest to amphibians; whilst other
naturalists rank the common bony or teleostean fishes as
the highest, inasmuch as they are most strictly fish-like,
and differ 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 intel-
lect 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 differentiation and specialisation of the sev-
eral organs in each being when adult (and this will in-
clude the advancement of the brain for intellectual pur-
poses), natural selection clearly leads towards this
standard: for all physiologists admit that the speciali-
sation of organs, inasmuch as in this 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 se-
lection. On the other hand, we can see, bearing in mind
that all organic beings are striving to increase at a high
ratio and to seize on every unoccupied or less well occu-
pied place in the economy of nature, that it is quite pos-
sible for natural selection gradually to fit a being to a

Cuap. IV.] ORGANISATION TENDS TO ADVANCE. 153

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 conven-
iently discussed in our chapter on Geological Succession.

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? Lamarck, 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 spontaneous
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 develop-
ment—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 ani-
malcule—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, unim-
proved or but little improved, and might remain 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

154 ON THE DEGREE TO WHICH [Cuap. IV.

period in nearly their present state. But to suppose
that most of the many now existing low forms have not
in the least advanced since the first dawn of life would
be extremely rash; for every naturalist who has dis-
sected some of the beings 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 mammals and fish—amongst mammalia, to
the co-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 invertebrate
classes. But mammals and fish hardly come into com-
petition 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 aérial respiration; so that warm-blooded
mammals when inhabiting the water lie under a disad-
vantage in having to come continually to the surface to
breathe. With fishes, members of the shark family
would not tend to supplant the lancelet; for the lance-
let, as I hear from Fritz Miller, has as sole companion
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 nu-
merous monkeys, and probably interfere little with each
other. Although organisation, on the whole, may have

Cuap. IV.] ORGANISATION TENDS TO ADVANCE 155

advanced and be still advancing throughout the world,
yet the scale will always present many degrees of per-
fection; for the high advancement 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 competition.
In some cases, as we shall hereafter see, lowly organised
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 favourable variations arising.

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
favourable nature may never have arisen for natural
selection to act on and accumulate. In no case, prob-
ably, has time sufficed for the utmost possible amount of
development. In some few cases there has been what
we must call retrogression of organisation. But the
main cause lies in the fact that under very simple con-
ditions 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 struc-
ture, 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

156 CONVERGENCE OF CHARACTER. ([Cuar. IV.

homologous units of any order become differentiated in
proportion as their relations to incident forces become
different ” would come into action. But as we have no
facts to guide us, speculation on the subject is almost
useless. 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 pro-
duced: variations in a single species inhabiting an iso-
lated station might be beneficial, and thus the whole
mass of individuals might be modified, or two distinct
forms might arise. But, as I remarked towards the close
of the Introduction, no one ought to feel surprise at
much remaining as yet unexplained on the origin of spe-
cies, if we make due allowance for our profound igno-
rance 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
importance of divergence of character (in which, how-
ever, he apparently believes), and that convergence, as
it may be 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 attribute to con-
vergence a close and general similarity of structure in
the modified descendants of widely distinct forms. The
shape of a crystal is determined solely by the molecular

Cuar. 1V.] CONVERGENCE OF CHARACTER. 157

forces, and it is not surprising that dissimilar substances
should sometimes assume the same form; but with or-
ganic beings we should bear in mind that the form of
each depends on an infinitude of complex relations,
namely on the variations which have arisen, these being
due to causes far too intricate to be followed out,—on
the nature of the variations which haye been preserved
or selected, and this depends on the surrounding phys-
ical conditions, and in a still higher degree on the sur-
rounding organisms with which each being has come
into competition,—and lastly, on inheritance (in itself 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 dif-
fered in a marked manner, should ever afterwards con-
verge so closely as to lead to a near approach to identity
throughout their whole organisation. If this had oc-
curred, we should meet with the same form, inde-
pendently of genetic connection, recurring in widely
separated geological formations; and the balance of evi-
dence 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 im-
portant; and as the number of species in any country
goes on increasing, the organic conditions of life must
become more and more complex. Consequently there

158 CONVERGENCE OF CHARACTER. [Caar. IV.

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 Australia, 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 in-
creased. 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 conditions; therefore, if an area be inhab-
ited by very many species, each or nearly each species
will be represented by few individuals; and such species
will be liable to extermination from accidental fluctua-
tions in the nature of the seasons or in the number of
their enemies. The process of extermination 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 exter-
minate thousands on thousands of species. Rare spe-
cies, 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 favourable variations; consequently,
the process of giving birth to new specific forms would
thus be retarded. When any species becomes very rare,
close interbreeding will help to exterminate it; authors

Cuap. IV.] SUMMARY. 159

have thought that this comes into play in accounting
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 im-
portant 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
specific forms throughout the world. Dr. Hooker has
recently shown that in the S.E. corner of Australia,
where, apparently, there are many invaders from dif-
ferent 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 aug-
mentation 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 disputed; then, considering the in-
finite complexity of the relations of all organic beings to
each other and to their conditions of life, causing an in-
finite diversity in structure, constitution, and habits, to
be advantageous to them, it would be a most extraor-

160 NATURAL SELECTION, [Cuap. IV.

dinary 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 variations 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 improve-
ment of each creature in relation to its organic and inor-
ganic conditions of life; and consequently, in most
cases, to what must be regarded as an advance in organi-
sation. 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
inherited 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 or-
dinary selection, by assuring to the most vigorous and
best adapted males the greatest number of offspring.
Sexual selection will also give characters useful to the
males alone, in their struggles or rivalry with other
males; and these characters will be transmitted 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 condi-
tions and stations, must be judged by the general tenor
and balance of evidence given in the following chapters.
But we have already seen how it entails extinction; and
how largely extinction has acted in the world’s history,
geology plainly declares.. Natural selection, also, leads

Cuap. 1V.] SUMMARY. 161

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 in-
habitants of any small spot, and to the productions
naturalised in foreign lands. Therefore, during the
modification of the descendants of any one species, and
during the incessant struggle of all species to increase
in numbers, the more diversified the descendants be-
come, the better will be their chance of success in the
battle for life. Thus the small differences distinguish-
ing varieties of the same species, steadily tend. to in-
crease, till they equal the greater differences 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 transmit to their modified offspring that
superiority which. now makes them dominant in their
own countries. Natural selection, as has just been re-
marked, leads to divergence of character and to much
extinction of the less improved and intermediate forms
of iife. 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 wonderful fact—
the wonder of which we are apt to overlook from fa-
miliarity—that all animals and all plants throughout
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 spe-
cies most closely related, species of the same genus less
closely and unequally related, forming sections and sub-

162 NATURAL SELECTION. [Cuar. IV.

genera, species of distinct genera much less closely re-
lated, 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 end-
less cycles. If species had been independently created,
no explanation would have been possible of this kind of
classification; but it is explained through inheritance
and the complex action of natural selection, entailing
extinction and divergence of character, as we have seen
illustrated in the diagram.

The affinities of all the beings of the same class have
sometimes 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 surrounding 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 flour-
ished 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

Cuap. 1V.] SUMMARY. 163

living and modified descendants. From the first growth
of the tree, many a limb and branch has decayed and
dropped off; 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 we here and
there see a thin straggling branch springing from a fork
low down in a tree, and which by some chance has been
favoured and is still alive on its summit, so we occa-
sionally see an animal like the Ornithorhynchus or
Lepidosiren, which in some small degree connects by its
affinities two large branches of life, and which has ap-
parently 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.

164 LAWS OF VARIATION. [Cuae. V.

CHAPTER V.
LAWS OF VARIATION.

Effects of changed conditions—Use and disuse, combined with
natural selection; organs of flight and of vision—Acclimatisa-
tion—Correlated variation—Compensation and economy of
growth—False correlations—Multiple, rudimentary, and lowly
organised structures variable—Parts developed in an unusual
manner are highly variable ; specific characters more variable
than generic: secondary 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 varia-
tions—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 acknowl-
edge plainly our ignorance of the cause of each par-
ticular variation. Some authors believe it to be as

~much the function of the reproductive system to pro-
duce individual differences, or slight deviations of struc-
ture, as to make the child like its parents. But the
fact of variations and monstrosities occurring much
more frequently under domestication than under na-
ture, 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 conditions of life to which each species has been
exposed during several successive generations. In the

Cap, V]. LAWS OF VARIATION. 165

first chapter I attempted to show that changed con-
ditions act in two ways, directly on the whole organi-
sation 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 organisation seems to become plastic, and we
have much fluctuating 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 become modified in the
same way.

It is very difficult to decide how far changed con-
ditions, such as of climate, food, &., have acted in a
definite manner. 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 innumerable 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-

166 LAWS OF VARIATION. [Cuar. V.

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 va-
rying organisms are interesting in as far as they present
characters analogous to those possessed by the species
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 accumula-
tive 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 difference may be due
to the warmest-clad individuals having been favoured
and preserved during many generations, 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
produced from the same species under external condi-
tions of life as different as can well be conceived; and,
on the other hand, of dissimilar varieties being produced
under apparently the same external conditions. Again,
innumerable instances are known to every naturalist, of
species keeping true, or not varying at all, although
living under the most opposite climates. Such con-
siderations 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 one sense the conditions of life may be said, not
only to cause variability, either directly or indirectly,
but likewise to include natural selection, for the con-

Cuap. V.] EFFECTS OF USE AND DISUSE. 16%

ditions determine whether this or that variety shall
survive. But when man is the selecting agent, we
clearly see that the two elements of change are dis-
tinct; variability is in some manner excited, but it is
the will of man which accumulates the variations 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
diminished them; and that such modifications are in-
herited. Under free nature, we have no standard of
comparison, by which to judge of the effects of long-
continued use or disuse, 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 sev-
eral 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 es-
cape danger, it is probable that the nearly wingless
condition of several birds, now inhabiting or which
lately inhabited several oceanic islands, tenanted by no

beast of prey, has been caused by disuse. The ostrich
13

168 EFFECTS OF USE AND DISUSE, [Cuar. V.

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 in-
creased 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 specimens 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 condition. In the
Ateuchus or sacred beetle of the Egyptians, they are
totally deficient. The evidence that accidental mutila-
tions can be inherited is at present not decisive; but
the remarkable cases observed by Brown-Séquard 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 in-
sects.

In some cases we might easily put down to disuse

Cuar. V.] EFFECTS OF USE AND DISUSE. 169

modifications of structure which are wholly, or mainly,
due to natural selection. Mr. Wollaston has discovered
the remarkable 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 species in this condition!
Several facts,—namely, that beetles in many parts of
the world are frequently blown to sea and perish; that
the beetles in Madeira, as observed by Mr. Wollaston,
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. Wollaston, that certain large groups of beetles,
elsewhere excessively numerous, which absolutely re-
quire the use of their wings, are here almost entirely
absent;—these several considerations make me believe
that the wingless condition of so many Madeira beetles
is mainly due to the action of natural selection, com-
bined probably with disuse. For during many suc-
cessive 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-feed-
ers, 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 reduced, but even enlarged. This is

170 EFFECTS OF USE AND DISUSE. ([Cuar. V.

quite compatible with the agtion 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 shipwrecked 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 per-
haps by natural selection. In South America, a bur-
rowing rodent, the tuco-tuco, or Ctenomys, is even more
subterranean in its habits 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 ap-
peared on dissection, having been inflammation of the
nictitating membrane. As frequent inflammation of
the eyes must be injurious to any animal, and as eyes
are certainly not necessary to animals having subter-
ranean habits, a reduction in their size, with the adhe-
sion of the eyelids and growth of fur over them, might
in such case be an advantage; and if so, natural selec-
tion 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

Cuap. V.] EFFECTS OF USE AND DISUSE. 171

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 animals living in darkness,
their loss may be attributed to disuse. In one of the
blind animals, namely, the cave-rat (Neotoma), two of
which were captured by Professor Silliman 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 ex-
posed for about a month to a graduated light, acquired
a dim perception 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 animals having been separately cre-
ated 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, Schiddte has remarked,
“We are accordingly prevented from considering the
entire phenomenon 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 which subsists gen-
erally between the fauna of Europe and of North
America.” On my view we must suppose that Amer-
ican animals, having in most cases ordinary powers of
vision, slowly migrated by successive generations from
the outer world into the deeper and deeper recesses

172 EFFECTS OF USE AND DISUSE. [Cuar. V.

of the Kentucky caves, as did European animals into
the caves of Europe. We have some evidence of this
gradation of habit; for, as Schiddte remarks, “ We ac-
cordingly look upon the subterranean faunas as small
ramifications which have penetrated into the earth
from the geographically limited faunas of the adja-
cent tracts, and which, as they extended themselves
into darkness, have been accommodated to surround-
ing circumstances. Animals not far remote from or-
dinary forms, prepare the transition from light to dark-
ness. Next follow those that are constructed for
twilight; and, last of all, those destined for total dark-
ness, and whose formation is quite peculiar.” ‘These
remarks of Schiddte’s, it should be understood, apply
not to the same, but to distinct species. By the time
that an animal had reached, after numberless gener-
ations, 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 antenne or
palpi, as a compensation for blindness. Notwithstand-
ing 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 continent. And
this is the case with some of the American cave-animals,
as I hear from Professor Dana; and some of the Eu-
ropean cave-insects are very closely allied to those of
the surrounding country. It weuld be difficult to give
any rational explanation of the affinities of the blind
cave-animals to the other inhabitants of the two con-
tinents on the ordinary view of their independent cre-
ation. That several of the inhabitants of the caves

Cuap. V.] ACCLIMATISATION, 173

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 is found in abundance on shady rocks far
from caves, the loss of vision in the cave-species of this
one genus has probably had no relation to its dark
habitation; for it is natural that an insect already
deprived of vision should readily become adapted to
dark caverns. Another blind genus (Anophthalmus)
offers this remarkable peculiarity, that the species, as
Mr. Murray observes, have not as yet been found any-
where 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 se-
cluded abodes. Far from feeling surprise that some
of the cave-animals should be very anomalous, as
Agassiz has remarked in regard 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
surprised that more wrecks of ancient life have not
been preserved, owing to the less severe competition to
which the scanty inhabitants of these dark abodes will
have been exposed.

Acclimatisation.

Habit is hereditary with plants, as in the period of
flowering, 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 ex-

174 ACCLIMATISATION. [Caar. V.

tremely 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, acclimatisation
must be readily effected during a long course of descent.
It is notorious that each species is adapted to the cli-
mate of its own home: species from an arctic or even
from a temperate region cannot endure a tropical
climate, or conversely. 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
reason to believe that species in a state of nature are
closely limited in their ranges by the competition of
other organic beings quite as much as, or more than, by
adaptation to particular climates. 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 tem-
peratures; that is, they become acclimatised: thus the
pines and rhododendrons, raised from seed collected by
Dr. Hooker from the same species growing at different
heights on the Himalaya, were found to possess in this
country different constitutional powers of resisting 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
other cases. In regard to animals, several authentic

Cuap. V.] ACCLIMATISATION, 175

instances could be adduced of species having largely
extended, within historical times, their range from
warmer to cooler latitudes, 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 acclima-
tised 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 because they bred readily under confinement,
and not because they were subsequently found capable
of far-extended transportation, the common and ex-
traordinary 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 proportion of other
animals now in a state of nature could easily be brought
to bear widely different climates. We must not, how-
ever, 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 con-
sidered as domestic animals, but they have been trans-
ported by man to many parts of the world, and now
have a far wider range 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 adaptation to any special cli-
mate may be looked at as a quality readily grafted on
an innate wide flexibility of constitution, common to

176 ACCLIMATISATION. [Cuar. V.

most animals. 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 cli-
mate, 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 cir-
‘cumstances, into action.

How much of the acclimatisation of species to any
peculiar climate is due to mere habit, and how much. to
the natural selection of varieties having different innate
constitutions, and how much to both means combined,
is an obscure question. That habit or custom has some
influence, I must believe, both from analogy and from
the incessant advice given in agricultural works, even
in the ancient Encyclopedias of China, to be very cau-
tious in transporting animals from one district to an-
other. 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 pre-
serve those individuals which were born with consti-
tutions best adapted to any country which they in-
habited. 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 published 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

Crap. V.] CORRELATED VARIATION. 177

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 ef-
fected, for it is now as tender as ever it was! The case,
also, of the kidney-bean has been often cited for a
similar purpose, and with much greater weight; but
until someone will sow, during 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 constitution of seedling kidney-beans never appear,
for an account has been published how much more
hardy some seedlings are than others; and of this fact
I have myself observed 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 struc-
ture; but that the effects have often been largely com-
bined with, and sometimes overmastered by, the natural
selection of innate variations.

Correlated Variation.

I mean by this expression that the whole organisa-
tion is so tied together during its growth and develop-
ment, that when slight variations in any one part occur,
and are accumulated through natural selection, other
parts become modified. This is a very important sub-
ject, most imperfectly understood, and no doubt wholly
different classes of facts may be here easily confounded

178 CORRELATED VARIATION. [Cuar. V.

together. We shall presently see that simple inheri-
tance often gives the false appearance of correlation.
One of the most obvious real cases is, that variations of
structure arising in the young or larve naturally tend
to affect the structure of the mature animal. ‘The sev-
eral parts of the body which are homologous, and which,
at an early embryonic period, are identical in structure,
and which are necessarily exposed to similar conditions,
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 believed by some anatomists to be homolo-
gous with the limbs. These tendencies, I do not doubt,
may be mastered more or 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 ren-
dered 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 au-
thors that with birds the diversity in the shape of the
pelvis causes the remarkable 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 swal-

lowing determine the position and form of several of the
most important viscera.

Cuap. V.] CORRELATED VARIATION. 179

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 complete whiteness and blue eyes with
deafness, or between the tortoise-shell colour and the
female sex; or in pigeons between their feathered feet
and skin betwixt the outer toes, or between the pres-
ence 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 homol-
ogy comes into play? With respect to this latter case
of correlation, I think it can hardly be accidental,
that the two orders of mammals which are most
abnormal in their dermal covering, 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 impor-
tance of the laws of correlation and variation, inde-
pendently of utility and therefore of natural selection,
than that of the difference between the outer and inner
flowers in some Compositous 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 accompanied with the partial or
complete abortion of the reproductive organs. But in
some of these plants, the seeds also differ in shape and
structure. These differences have sometimes been at-
tributed to the pressure of the involucra on the florets,

180 CORRELATED VARIATION. [Cuar. V.

or to their mutual pressure, and the shape of the seeds
in the ray-florets of some Composite countenances this
idea; but with the Umbellifere, 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 Composite
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 be-
come abnormally symmetrical. I may add, as an in-
stance of this fact, and as a striking case of correlation,
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 be-
coming 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 in-
sects, whose agency is highly advantageous or necessary
for the fertilisation 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 cor-
related with any difference in the corolla, can be in
any way beneficial: yet in the Umbellifere these dif-

Cuap. V.] CORRELATED VARIATION. 181

ferences are of such apparent importance—the seeds
being sometimes orthospermous in the exterior flowers
and celospermous in the central flowers,—that the
elder De Candolle founded his main divisions in the
order on such characters. Hence modifications of struc-
ture, 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 varia-
tion structures which are common to whole groups of
species, and which in truth are simply due to inheri-
tance; for an ancient progenitor may have acquired
through natural selection some one modification in
structure, and, after thousands of generations, some
other and independent modification; and tl.ese two
modifications, having been transmitted to a whole group
of descendants with diverse habits, would naturally be
thought to be in some necessary manner correlated.
Some other correlations are apparently due to the man-
ner in which natural selection can alone act. For in-
stance, Alph. de Candolle has remarked that winged
seeds are never found in fruits which do no: 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.

182 COMPENSATION AND ECONOMY OF GROWTH.

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 fatten 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 atrophied,
the fruit itself gains largely in size and quality. In
our poultry, a large tuft of feathers on the head is
generally 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 application; but many good observers,
more especially botanists, believe in its truth. I will
not, however, here give any instances, for I see hardly
any way of distinguishing between the effects, on the
one hand, of a part being largely developed 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
adjoining part.

I suspect, also, that some of the cases of compensa-
tion 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

COMPENSATION AND ECONOMY OF GROWTH. 183

economise every part of the organisation. If under
changed conditions of life a structure, before useful,
becomes less useful, its diminution will be favoured, for
it will profit the individual not to have its nutriment
wasted in building up an useless structure. I can thus
only understand a fact with which I was much struck
when examining cirripedes, and of which many analo-
gous 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 Proteo-
lepas: for the carapace in all other cirripedes consists
of the three highly-important 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 re-
duced to the merest rudiment attached to the bases of
the prehensile antenne. Now the saving of a large
and complex structure, when rendered superfluous,
would be a decided advantage to each successive in-
dividual of the species; for in the struggle for life to
which every animal is exposed, each would have a bet-
ter chance of supporting 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 becomes, through changed habits, superfluous, with-
out by any means causing some other part to be largely
developed in a corresponding degree. And, conversely,
that natural selection may perfectly well succeed in
largely developing an organ without requiring as a neces-

sary compensation the reduction of some adjoining part.
14

184 MULTIPLE AND RUDIMENTARY. [Caape. V.

Multiple, Rudimentary, and Lowly-organised Structures
are Variable.

It seems to be a rule, as remarked by Is. Geoffry St.
Hilaire, both with varieties and species, that when any
part or organ is repeated many times in the same in-
dividual (as the vertebre in snakes, and the stamens
in polyandrous flowers) 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 organisa-
tion, 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 re-
jected 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 par-
ticular shape. Natural selection, it should never be
forgotten, 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 varia-

Cuap. V.] STRUCTURES VARIABLE. 185

bility seems to result from their uselessness, and conse-

quently from natural selection having had no power to
check deviations in their structure.

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 un-
usually developed in one species or in a few species
in comparison with the same part in many closely
allied species. Thus, the wing of a bat is a most ab-
normal 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 spe-
cies had wings developed in a remarkable manner in
comparison with the other species of the same genus.
The rule applies very strongly in the case of secondary
sexual characters, when displayed in any unusual man-
ner. 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 re-

f
’

186 UNUSUALLY DEVELOPED PARTS. [Caap. V.

production. The rule applies to males and females;
but more rarely to the females, as they seldom offer
remarkable secondary sexual characters. The rule be-
ing so plainly applicable in the case of secondary 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 her-
maphrodite 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 remarkable cases; I will here give only
one, as it illustrates the rule in its largest applica-
tion. The opercular valves of sessile cirripedes (rock
barnacles) are, in every sense of the word, very im-
portant 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 homologous valves in the
different species being sometimes wholly unlike in
shape; and the amount of variation in the individuals
of the same species is so great, that it is no exaggeration
to state that the varieties of the same species differ 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,
inhabiting the same country, vary extremely little, I
have particularly attended to them; and the rule cer-
tainly seems to hold good in this class. I cannot make
out that it applies to plants, and this would have seri-

Cuap. V.] HIGHLY VARIABLE. 187

ously 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 re-
markable degree or manner in a species, the fair pre-
sumption is that it is of high importance to that species:
nevertheless it is in this case eminently liable to varia-
tion. 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 descended
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 ani-
mal 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 charac-
ter: and the breed may be said to be degenerating.
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 or-
ganisation is left in a fluctuating condition. But what
here more particularly concerns us 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

188 UNUSUALLY DEVELOPED PARTS. [CuarP. V.

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 notoriously difficult to breed nearly
perfect birds, many departing widely from the standard.
There may truly be said to be a constant struggle go-
ing on between, on the one hand, the tendency to re-
version 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
developed in an extraordinary manner in any one spe-
cies, compared with the other species of the same genus,
we may conclude that this part has undergone an
extraordinary amount of modification since the period
when the several species branched off from the com-
mon progenitor of the genus. This period will sel-
dom be remote in any extreme degree, as species rarely
endure for more than one geological period. An ex-
traordinary amount of modification implies an unusu-
ally large and long-continued amount of variability,
which has continually 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 general rule, still
expect to find more variability in such parts than in
other parts of the organisation which have remained for

Cuap. V.} HIGHLY VARIABLE, 189

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 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 descendants, 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 con-
tinued 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 char-
acter, and no one would be surprised at one of the

190 SPECIFIC CHARACTERS [Cuar. V.

blue species varying into red, or conversely; 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 example be-
cause the explanation which most naturalists would
advance is not here applicable, namely, that specific
characters are more variable than generic, because they
are taken from parts of less physiological importance
than those commonly used for classing genera. I be-
lieve 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 su-
perfluous to adduce evidence in support of the state-
ment, that ordinary specific characters are more variable
than generic; but with respect to important characters,
I 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 con-
stant throughout a large group of species, differs con-
siderably 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 spe-
cific value, often becomes variable, though its physio-
logical 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
species of the same group, the more subject it is to
anomalies in the individuals.

On the ordinary view of each species having been
independently created, why should that part of the
structure, which differs from the same part in other

Cuap. V.] MORE VARIABLE THAN GENERIC. 191

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 explana-
tion can be given. But on the view that species are
only strongly marked and fixed varieties, 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 several 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 pro-
genitor, 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 since the period when the species
branched off from a common progenitor, it is probable
that they should still often be in some degree variable,
—at least more variable than those parts of the or-
ganisation 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

192 SECONDARY SEXUAL [Caap. V.

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 fe-
males. 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 action than ordinary selection,
as it does not entail death, but only: gives fewer off-
spring to the less favoured males. Whatever 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 succeeded 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
between the two sexes of the same species are generally
displayed 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 com-
mon to very large groups of beetles, but in the
Engide, as Westwood has remarked, the number varies
greatly; and the number likewise differs in the two

Cur. V.] CHARACTERS VARIABLE. 193

sexes of the same species. Again in the fossorial
hymenoptera, the neuration of the wings is a character
of the highest importance, because common to large
groups; but in certain genera the neuration differs in
the different species, and likewise in the two sexes of
the same species. Sir J. Lubbock has recently remarked,
that several minute crustaceans offer excellent illustra-
tions of this law. “In Pontella, for instance, the sexual
characters are afforded mainly by the anterior antenne
and by the fifth pair of legs: the specific differences
also are prineipally given by these organs.” This re-
lation 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 species. Consequently, whatever part
of the structure of the common progenitor, or of its
early descendants, became variable, variations of this
part would, it is highly probable, be taken advantage of
by natural and sexual selection, in order to fit the sev-
eral species to their several places in the economy 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 possessed by all the species;—that the frequent ex-
treme variability of any part which is developed in a
species in an extraordinary 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 common to a whole group of species;

194 DISTINCT SPECIES PRESENT [Cuap. V.

—that the great variability of secondary sexual charac-
ters, and their great difference in closely allied species;
—that secondary sexual and ordinary specific differences
are generally displayed in the same parts of the organisa-
tion—are all principles closely connected together.
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 hay-
ing 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 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 distinct 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 aboriginal rock-pigeon;
these then are analogous variations in two or more
distinct races. The frequent presence of fourteen 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

Cuap. V.] ANALOGOUS VARIATIONS. 195

several races of the pigeon having inherited from a com-
mon parent the same constitution and tendency to vari-
ation, when acted on by similar unknown influences.
In the vegetable kingdom 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 varieties 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 add-
ed, namely, the common turnip. According to the or-
dinary 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 community of descent, and a consequent ten
dency to vary in a like manner, but to three separate
yet closely related acts of creation. Many similar
eases 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, name-
ly, the occasional appearance in all the breeds, of slaty-
blue birds with two black bars on the wings, white loins,
a bar at the end of the tail, with the outer feathers ex-
ternally 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 re-
version, and not of a new yet analogous variation ap-
pearing in the several breeds. We may, I think, confi-
dently come to this conclusion, because, as we have seen,

196 DISTINCT SPECIES PRESENT [Caap. V.

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 inherit-
ance.

No doubt it is a very surprising fact that characters
should reappear after having been lost for many, prob-
ably for hundreds 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 1 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 remarked, for all that we can see to the
contrary, be transmitted for almost any number of gen-
erations. 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 hun-
dred generations, but that in each successive 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

Cuap, V.} ANALOGOUS VARIATIONS. 197

tendency in each generation to produce blue plumage.
The abstract improbability of such a tendency being
transmitted through a vast number of generations, is
not greater than that of quite useless or rudimentary
organs being similarly transmitted. A mere tendency
to produce a rudiment is indeed sometimes thus in-
herited.

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 anal-
ogous 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 analogous variation
would probably be of an unimportant nature, for the
preservation of all functionally important characters
will have been determined through natural selection, in
accordance 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 reversionary 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 variations; 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

15

198 DISTINCT SPECIES PRESENT [Cuap. V.

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 analogous 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 themselves can only doubtfully be
ranked as species; and this shows, unless all these
closely allied forms be considered as independently cre-
ated species, that they have in varying assumed 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 an allied species. I have col-
lected 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 repeat that such cases certainly oc-
cur, and seem to me very remarkable.

I will, however, give one curious and complex case,
not indeed as affecting any important character, but
from occurring 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,

Cuap. V.] ANALOGOUS VARIATIONS. 199

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
actually quite lost, in dark-coloured asses. The koulan
of Pallas is said to have been seen with a double shoul-
der-stripe. Mr. Blyth has seen a specimen of the hemi-
onus 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
England of the spinal stripe in horses of the most dis-
tinct breeds, and of ail colours: transverse bars on the
legs are not rare in duns, mouse-duns, and in one in-
stance in a chestnut: a faint shoulder-stripe may some-
times 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 Belgian cart-horse with a double stripe
on each shoulder and with leg-stripes; I have myself
seen a dun Devonshire pony, and a small dun Welsh
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
15

200 DISTINCT SPECIES PRESENT [Cuap. V.

as purely-bred. The spine is always striped; the legs
are generally barred; and the shoulder-stripe, which is
sometimes double and sometimes treble, is common;
the side of the face, moreover, is sometimes striped.
The stripes are often plainest in the foal; and some-
times 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 infor-
mation 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 my-
self 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 disappeared completely.
Without here entering on further details, I may state
that I have collected cases of leg and shoulder stripes
in horses of very different 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 spe-
cies—one of which, the dun, was striped; and that the
above-described appearances are all due to ancient
crosses with the dun stock. But this view may be
safely rejected; for it is highly improbable that the

Cuap. V.] ANALOGOUS VARIATIONS. 201

heavy Belgian cart-horse, Welsh ponies, Norwegian cobs,
the lanky Kattywar race, &., inhabiting the most dis-
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
species of the horse-genus. Rollin asserts, that the com-
mon 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 excel-
lent treatise on the horse, has given a figure 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 off-
spring subsequently 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 remarkable 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 hemio-
nus; and this hybrid, though the ass only occasionally
has stripes on its 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 con-

202 DISTINCT SPECIES PRESENT [Crap. V.

vinced 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 tendency strong whenever a dun tint appears—
a tint which approaches to that of the general colouring
of the other species of the genus. The appearance of
the stripes is not accompanied by any change of form
or by any other new character. We see this tendency to
become striped most strongly displayed in hybrids from
between several of the most distinct species. Now ob-
serve 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 tendency for the blue tint and bars and marks
to reappear in the mongrels. I have stated that the
most probable hypothesis to account for the reappear-
ance of very ancient characters, is—that there is a fen-
dency in the young of each successive generation to
produce the long-lost character, and that this tendency,
from unknown causes, sometimes prevails. And we

Cuap. V.] ANALOGOUS VARIATIONS. 203

have just seen that in several species of the horse-genus
the stripes are either plainer or appear more commonly
in the young 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 gen-
erations, and I see an animal striped like a zebra, but
perhaps otherwise very differently constructed, the com-
mon parent 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 inde-
pendently 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 in-
habiting distant quarters of the world, to produce hy-
brids 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
mere mockery and deception; I would almost as soon
believe with the old and ignorant cosmogonists, that fos-
sil 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
profound. 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

204 _ DISTINCT SPECIES PRESENT [CHap. V;

producing the lesser differences between varieties of the
same species, and the greater differences between species
of the same genus. Changed conditions generally in-
duce 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 produc-
- ing 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 nourishment from the ad-
joining parts; and every part of the structure which can
be saved without detriment will be saved. Changes
of structure at an early age may affect parts subsequently
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 selection. It follows probably from this
same cause, that organic beings low in the scale are more
variable than those standing higher in the scale, and
which have their whole organisation 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 varia-

Cuar, V1] ANALOGOUS VARIATIONS. 205

ble than generic characters, or those which have long
been 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 individual; for in 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 organisa-
tion has generally been taken advantage of in giving
secondary sexual differences to the two sexes of the
same species, and specific differences to the several spe-
cies of the same genus. Any part or organ developed
to an extraordinary size or in an extraordinary man-
ner, in 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 variable
in a much higher degree than other parts; for variation
is a long-continued and slow process, and natural selec-
tion will in such cases not as yet have had time to over-
come the. tendency to further variability and to rever-
sion 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

206 LAWS OF VARIATION. [Cuar. V.

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 common 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 modifications
will add to the beautiful and harmonious diversity of
nature.

Whatever the cause may be of each slight difference
between the offspring and their parents—and a cause
for each must exist—we have reason to believe that it
is the steady accumulation of beneficial differences which
has given rise to all the more important modifications
of structure in relation to the habits of each species.

Cuap, VL] DIFFICULTIES OF THE THEORY. 207

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
perfection—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 Conditions of Existence embraced by the theory of Natu-
tal Selection.

Lone 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 staggered;
but, to the best of my judgment, the greater number
are only apparent, and those that are real are not, I
think, fatal to the 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 spe-
cies 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

208 ABSENCE OR RARITY [Caar. VL

believe that natural selection could produce, on the one
hand, an organ of trifling importance, 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 the
instinct which leads the bee to make cells, and which
has practically anticipated 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
miscellaneous objections in the following chapter; In-
stinct 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 com-
petition. 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 convenient to discuss this question in the
chapter on the Imperfection of the Geological Record;

cnap. VL] OF TRANSITIONAL VARIETIES, 209

and I will here only state that I believe the answer
mainly lies in the record being incomparably less per-
fect 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 continent, we generally meet at successive inter-
vals with closely allied or representative species, evi-
dently filling nearly the same place in the natural econ-
omy of the land. These representative species often
meet and interlock; and as the one becomes 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
absolutely 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 common 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 region,
though they must have existed there, and may be em-
bedded there in a fossil condition. But in the inter-
mediate region, having intermediate conditions of life,
why do we not now find closely-linking intermediate
varieties? This difficulty for a long time quite con-

210 ABSENCE OR RARITY (Cuar. VI

founded me. But I think it can be in large part ex-
plained.

In the first place we should be extremely cautious in
inferring, 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 inter-
mediate varieties existing in the intermediate zones.
By changes in the form of the land and of climate,
marine areas now continuous must often have existed
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 perfectly defined species have been formed on
strictly continuous 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 wander-
ing 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 generally narrow in comparison with the ter-
ritory proper to each. We see the same fact in ascend-
ing mountains, and sometimes it is quite remarkable
how abruptly, as Alph. de Candolle has 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

Onap. VI] OF TRANSITIONAL VARIETIES. O11

the physical conditions of life as the all-important ele-
ments of distribution, these facts ought to cause surprise,
as climate and height or depth graduate away insen-
sibly. 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 in-
directly related in the most important manner to other
organic beings,—we see that the range of the inhabi-
tants 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 competition; and as these species are already de-
fined objects, not blending one into another by insen-
sible 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 lessened numbers, will, dur-
ing fluctuations in the number of its enemies or of its
prey, or in the nature of the seasons, be extremely
liable to utter extermination; and thus its geo-
graphical range will come to be still more sharply de-
fined.

As allied or representative species, when inhabiting
a continuous area, are generally distributed in such a
manner that each has a wide range, with a compara-
tively 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 vary-
ing species inhabiting a very large area, we shall have

212 ABSENCE OR RARITY [Cuar. VL

to adapt two varieties to two large areas, and a third
variety to a narrow intermediate zone. The inter-
mediate variety, consequently, will exist in lesser num-
bers 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 varie-
ties intermediate between well-marked varieties in the
genus Balanus. And it would appear from information
given me by Mr. Watson, Dr. Asa Gray, and Mr. Wol-
laston, that generally, when varieties intermediate be-
tween two other forms occur, they are much rarer
numerically than the forms which they connect. Now,
if we may trust these facts and inferences, and conclude
that varieties linking two other varieties together gen-
“erally have existed in lesser numbers than the forms
which they connect, then we can understand why in-
termediate varieties should not endure for very long
periods:—why, as a general rule, they should be ex-
terminated 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 exter-
minated 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 impor-
tant 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 inter-
mediate variety, which exists in smaller numbers in

Cuar, VIL] OF TRANSITIONAL VARIETIES, 218

a narrow and intermediate zone. For forms existing
in larger numbers will have a better chance, within any
given period, of presenting further favourable varia-
tions 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 illus-
trate what I mean by supposing three varieties of sheep
to be kept, one adapted to an extensive 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 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 num-
bers, 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 pre-
sent an inextricable chaos of varying and intermediate
links: first, because new varieties are very slowly formed,
for variation is a slow process, and natural selection can

914 ABSENCE OR RARITY [Caap. VI

do nothing until favourable individual differences or
variations occur, and until a place in the natural polity
of the country can be better filled by some modification
of some one or more of its inhabitants. And such new
places will depend on slow changes of climate, or on the
occasional immigration of new inhabitants, and, prob-
ably, 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 modifications of struc-
ture in some degree permanent; and this assuredly 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 rendered sufficiently distinct to
rank as representative species. In this case, intermedi-
ate varieties between the several representative 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 ormorevarieties have been formed
in different portions of a strictly continuous area, inter-
mediate varieties will, it is probable, at first have been
formed in the intermediate zones, but they will gen-
erally have hada short duration. For these inter-
mediate varieties will, from reasons already assigned
(namely from what we know of the actual distribution

Cuap, VIL] OF TRANSITIONAL VARIETIES. 915

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 inter-
mediate varieties will be liable to accidental extermina-
tion; and during the process of further modification
through natural selection, they will almost certainly
be beaten and supplanted by the forms which they con-
nect; 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 assuredly have existed; but the very pro-
cess of natural selection constantly tends, as has been so
often remarked, to exterminate the parent-forms and
the intermediate links. Consequently 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 imperfect and
intermittent record.

On the Origin and Transitions of Organic Beings
with 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

16

216 TRANSITIONS OF ORGANIC BEINGS, [Caar. VL

adapted to its place in nature. Look at the Mustela
vison of North America, which has webbed feet, and
which resembles an otter in its fur, short legs, and form
of tail. During 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 insectivorous quadruped
could possibly have been converted into a flying bat,
the question would have been far more difficult to
answer. Yet I think such difficulties have little
weight.

Here, as on other occasions, I lie under a heavy
disadvantage, for, out of the many striking cases which
I have collected, I can only give 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 flattened, 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 squir-
rels 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 astonish-
ing 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

Cuap. VI.] TRANSITIONS OF ORGANIC BEINGS. 217

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 vege-
tation 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 exter-
minated, unless they also became modified and improved
in structure in a corresponding manner. Therefore,
I can see no difficulty, more especially under chang-
ing conditions of life, in the continued preservation of
individuals with fuller and fuller flank-membranes, each
modification being useful, each being propagated, until,
by the accumulated effects of this process of natural
selection, a perfect so-called flying squirrel was pro-
duced.

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. An ex-
tremely wide flank-membrane 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 con-
nect the Galeopithecus with the other Insectivora, yet
there is no difficulty in supposing that such links for-
merly 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 believ-
ing that the membrane connected fingers and fore-arm
of the Galeopithecus might have been greatly length-

218 TRANSITIONS OF ORGANIC BEINGS. [Cuar. VL

ened by natural selection; 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-mem-
brane 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 the 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 transi-
tion are at least possible.

Seeing that a few members of such water-breathing
classes as the Crustacea and Mollusca are adapted to
live on the land; and seeing that we have flying birds
and mammals, flying 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 by the aid of their fluttering
fins, might have been modified into perfectly winged
animals. If this had been effected, who would have

Cuar. VL] TRANSITIONS OF ORGANIC BEINGS. 219

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
particular habit, as the wings of a bird for flight, we
should bear in mind that animals displaying early tran-
sitional 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 selection. Fur-
thermore, 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 numbers 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 stage of perfection,
so as to have given them a decided advantage over other
animals in the battle for life. Hence the chance of
discovering species with transitional grades of structure
in a fossil condition will always be less, from their hav-
ing existed in lesser numbers, than in the case of species
with fully developed structures.

I will now give two or three instances both of diver-
sified and of changed habits in the individuals of the
same species. In either case it would be easy for natu-
ral selection to adapt the structure of the animal to
its changed habits, or exclusively to one of its several
habits. It is, however, difficult to decide, and im-

220 TRANSITIONS OF ORGANIC BEINGS. [Caar. VL

material for us, whether habits generally change first
and structure afterwards; or whether slight modifica-
tions of structure lead to changed habits; both probably
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 exclusively on artificial substances. Of diver-
sified habits innumerable instances could be given: I
have often watched a tyrant flycatcher (Saurophagus
sulphuratus) in South America, 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 own 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 struc-
ture 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 seizing
insects in the chinks of the bark? Yet in North
America there are woodpeckers which feed largely on

Cuap, VI.] TRANSITIONS OF ORGANIC BEINGS. 221

fruit, and others with elongated wings which chase in-
sects 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 wood-
pecker is plainly declared; yet, as I can assert, not only
from my own observations, but from those of the ac-
curate 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 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 aérial 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; nevertheless it is essentially
a petrel, but with many parts of its organisation pro-
foundly modified in relation to its new habits of life;

922 TRANSITIONS OF ORGANIC BEINGS, [Cuap. VL

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, and remains as long as four hours beneath
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 agreement. What can be plainer than that the
webbed feet of ducks and geese are formed for swim-
ming? Yet there are upland geese with webbed feet
which rarely go near the water; and no one except Au-
dubon 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 fur-
nished with membrane of the Grallatores are formed
for walking over swamps and floating plants?—the
water-hen and landrail 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 of structure.

Cuap. VI.J ORGANS OF EXTREME PERFECTION. 223

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 be-
gun to change.

He who believes in separate and innumerable acts of
creation 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 acknowledge that
every organic being is constantly endeavouring to in-
crease 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 in-
habitant, 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
woodpeckers where hardly a tree grows; that there
should be diving 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 con-
trivances for adjusting the focus to different distances,
for admitting different amounts of light, and for the
correction of spherical and chromatic aberration, could

994 ORGANS OF EXTREME PERFECTION. [Cuar. VL

have been formed by natural selection, seems, I freely
confess, absurd in the highest degree. 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 Vor popult, vor 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 certainly the case; if further, the eye
ever varies and the variations be inherited, as is like-
wise certainly the case; and if such variations should
be useful to any animal under changing 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 considered as subversive of the theory. How a nerve
comes to be sensitive to light, hardly concerns us more
than how life itself originated; but I may remark that,
as some of the lowest organisms, in which nerves can-
not be detected, are capable of perceiving light, it does
not seem impossible that certain sensitive elements
in their sarcode should become aggregated and de-
veloped 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 possible, and for the
chance of some gradations having been transmitted in

Cuap. VI] ORGANS OF EXTREME PERFECTION. 995

an unaltered or little altered condition. But the state
of the same organ in distinct classes may incidentally
throw light on the steps by which it has been perfected.

The simplest organ which can be called an eye con-
sists 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, apparently 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 dis-
tinguish light from darkness. In certain star-fishes,
small depressions in the layer of pigment which sur-
rounds the nerve are filled, as described by the author
just quoted, with transparent gelatinous matter, pro-
jecting with a convex surface, 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-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 optical contrivance. With insects it
is now known that the numerous facets on the cornea

996 ORGANS OF EXTREME PERFECTION, [Caar. VI.

of their great compound eyes form true lenses, and that
the cones include curiously modified nervous filaments.
But these organs in the Articulata are so much diver-
sified 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 difficulty ceases to
be very great in believing that natural selection 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 pos-
sessed 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 selec-
tion; 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 extremely slight and gradual. Different
kinds of modification would, also, serve for the same

Cuar. VI.] ORGANS OF EXTREME PERFECTION. 227

general purpose: as Mr. Wallace 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 regularity
of curvature will be an improvement. So the con-
traction 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 per-
fected at any stage of the construction of the instru-
ment.” Within the highest division of the animal
kingdom, namely, the Vertebrata, we can start from an
eye so simple, that it consists, as in the lancelet, 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, ac-
cording to the high authority of Virchow, the beautiful
crystalline lens is formed in the embryo by an accumu-
lation of epidermic cells, lying in a sack-like fold of
the skin; and the vitreous body is formed from embry-
onic 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

998 ORGANS OF EXTREME PERFECTION. [Cuar. VI.

highest human intellects;-and we naturally infer that
the eye has been formed by a somewhat analogous pro-
cess. But may not this inference be presumptuous?
Have we any right to assume that the Creator works by
intellectual powers like those of man? If we 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 beneath, and then suppose every part of this
layer to be continually changing slowly in density, so as
to separate into layers of different densities and thick-
nesses, placed at different distances from each other,
and with the surfaces of each 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 suppose 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 multiply them almost
infinitely, and natural selection will pick out with un-
erring 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?

Cuap, VI] MODES OF TRANSITION. 229

Modes of Transition.

If it could be demonstrated that any complex organ
existed, which could not possibly have been formed by
numerous, successive, slight modifications, my theory
would absolutely break down. But I can find out no
such case. No doubt many organs exist of which we
do not know the transitional grades, more especially if
we look to much-isolated species, round which, accord-
ing to the theory, there has been much extinction. Or
again, if we take an organ common to 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 Co-
bites the alimentary canal respires, digests, and ex-
cretes. In the Hydra, the animal may be turned in-
side out, and the exterior surface will then digest and
the stomach respire. In such cases natural selection
might specialise, if any advantage were thus gained, the
whole or part of an organ, which had previously per-
formed 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
17

930 MODES OF TRANSITION. (Cuap. VIL

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 charac-
ter of the species. It is, however, probable that the
two sorts of flowers borne by the same plant were origi-
nally differentiated 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 important means of transition: to give one
instance,—there are fish with gills or branchie 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 vascular 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 twin-
ing, by clasping a support with their sensitive tendrils,
and by the emission of aérial 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 individual. 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 obliter-
ated.

The illustration of the swimbladder in fishes is a
good one, because it shows us clearly the highly im-
portant fact that an organ originally constructed for
one purpose, namely, flotation, may be converted into

Cuap. V1] MODES OF TRANSITION. 931

one for a widely different purpose, namely, respiration.
The swimbladder has, also, been worked in as an acces-
sory to the auditory organs of certain fishes. All phys-
iologists admit that the swimbladder is homologous,
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 converted into lungs, or an organ used exclusively
for respiration.

According to this view it may be inferred that all
vertebrate animals with true lungs are descended by
ordinary generation from an ancient and unknown pro-
totype, 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, notwithstanding
the beautiful contrivance by which the glottis is closed.
In the higher Vertebrata the branchie 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 branchie might have been gradu-
ally worked in by natural selection for some distinct pur-
pose: for instance, Landois has shown that the wings of
insects are developed from the trachex; 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 impor-
tant to bear in mind the probability of conversion

from one function to another, that I will give another
17

939 MODES OF TRANSITION. [Cuar. VL

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 branchix, the whole surface of
the body and of the sack, together with the small frena,
serving for respiration. The Balanide or sessile cirri-
pedes, 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 lacune
of the sack and body, and which have been considered by
all naturalists to act as branchie. Now I think no one
will dispute that the ovigerous frena in the one family
are strictly homologous with the branchie of the other
family; indeed, they graduate into each other. There-
fore 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 respira-
tion, have been gradually converted by natural selection
into branchie, 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 cirri-
pedes, who would ever have imagined that the branchie
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
reproduction. 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

Cuar. VI] MODES OF TRANSITION. 233

early age, before they have acquired their perfect charac-
ters; and if this power became thoroughly well de-
veloped 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 ani-
mals, 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 in-
stances 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 Miil-
ler, after maturity. In all such cases,—and many could
be given,—if the age for reproduction were retarded, 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 been modified through 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 primordially acquired by
graduated steps.

234 DIFFICULTIES OF THE THEORY ([Cuap. VI.

Special Difficulties of the Theory of Natural Selection.

Although we must be extremely cautious in con-
cluding that any organ could not have been produced
by successive, small, transitional gradations, yet un-
doubtedly serious cases of difficulty 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 surprising, 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 ani-
mal 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 electrical, 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 discharge;
and, as Dr. Radcliffe insists, “in the electrical apparatus
of the torpedo during rest, there would seem to‘be a
charge in every respect like that which is met with in

Cuap. VI.] OF NATURAL SELECTION. 235
,

muscle and nerve during rest, and the discharge of the
torpedo, instead of being peculiar, may be only another
form of the discharge which depends upon the action of
muscle and 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 progeni-
tors 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 gradu-
ally 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 inheritance from a common
ancestor; and its absence in some of the members to
loss through disuse or natural selection. So that, if the
electric organs had been inherited from some one an-
cient progenitor, we might have expected that all elec-
tric 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 pos-
sessed electric organs, which their modified descend-
ants have now lost. But when we look at the subject
more closely, we find in the several fishes provided with
electric organs, that these are situated in different parts
of the body,—that they differ in construction, 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

236 DIFFICULTIES OF THE THEORY [Caap. VL

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 homologous, but only as analogous in
function. Consequently there is no reason to suppose
that they have been inherited from a common progeni-
tor; for had this been the case they would have closely
resembled each other in all respects. Thus the diffi-
culty of an organ, apparently the same, arising in several
remotely allied species, disappears, leaving only the
lesser yet still great difficulty; namely, by what gradu-
ated steps these organs have been developed in each sep-
arate group of fishes.

The luminous organs which occur in a few insects,
belonging to widely different families, and which are
situated in different parts of the body, offer, under our
present state of ignorance, a difficulty almost exactly
parallel with that of the electric crgans. Other similar
cases could be given; for instance 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 almost as re-
mote as is possible amongst flowering plants; but here
again the parts are not homologous. In all cases of
beings, far removed from each other in the scale of or-
ganisation, which are furnished with similar and pe-
culiar organs, it will be found that although the gen-
eral appearance and function of the organs may be the
same, yet fundamental differences between them can
always be detected. For instance, the eyes of cephalo-
pods or cuttle-fish and of vertebrate animals appear won-
derfully alike; and in. such widely sundered groups
no part of this resemblance can be due to inheritance

Cuap. VL] OF NATURAL SELECTION, 237

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 darkened chamber. Beyond this superficial resem-
blance, 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. The
retina is wholly different, with an actual inversion of the
elemental parts, and with a large nervous ganglion in-
cluded within the membranes of the eye. The relations
of the muscles are as different as it is possible to con-
ceive, 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 de-
veloped through the natural selection of successive
slight variations; but if this be admitted in the one
case, it is clearly possible in the other; and fundamental
differences of structure in the visual organs of two
groups might have been anticipated, in accordance with
this view of their manner of formation. As two men
have sometimes independently hit on the same inven-
tion, so in the several foregoing cases it appears that
natural selection, working for the good of each being,

238 DIFFICULTIES OF THE THEORY [Cuar. VI.

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 pro-
genitor.

Fritz Miiller, 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 impor-
tant 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 struc-
ture of the water-breathing branchiz, even to the micro-
scopical hooks by which they are cleansed. Hence it
might have been expected that in the few species be-
longing 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 advanced by me, be accounted for by inheritance
from a common progenitor. But as the vast majority
of the species in the above two families, as well as most
other crustaceans, are aquatic in their habits, it is im-
probable in the highest degree, that their common pro-
genitor should have been adapted for breathing air.

Cuap. V1] OF NATURAL SELECTION. 239

Miller 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
differences are intelligible, and might even have been
expected, on the supposition that species belonging to
distinct families had slowly become adapted to live
more and more out of water, and to breathe the air.
For these species, from belonging to distinct families,
would have differed to a certain extent, and in ac-
cordance with the principle that the nature of each
variation depends on two factors, viz., the nature of
the organism and that of the surrounding conditions,
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 arrive 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 remains 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
Claparéde, has argued in the same manner, and has
arrived at the same result. He shows that there are
parasitic mites (Acaride), belonging to distinct sub-
families and families, which are furnished with hair-
claspers. These organs must have been independent-
ly 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,—

240 DIFFICULTIES OF THE THEORY [Cuar. VL

of the hind-legs,—of the maxille or lips,—and of ap-
pendages 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 remotely allied, by organs in appearance, though
not in development, closely similar. On the other hand,
it isa common 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 butterfly, 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,—from the long
row of neatly interlocking teeth in a Nucula to the
simple ligament of a Mussel! Seeds are disseminated by
their minuteness,—by their capsule being converted into
a light balloon-like envelope,—by being embedded in
pulp or flesh, formed of the most diverse parts, and ren-
dered nutritious, 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 fur-
nished 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 diver-
sified 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

Cuap. VI.] OF NATURAL SELECTION. 241

shop, but such a view of nature is incredible. With
plants having separated sexes, and with those in which,
though hermaphrodites, the pollen does not spontane-
ously 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 in-
exhaustible number of contrivances, all for the same
purpose and effected 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 some-
times capable of neatly adapted movements through
irritability or elasticity. From such structures we may
advance till we come to such a case of extraordinary
adaptation 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 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 labellum stands
over the bucket, and is itself hollowed out into a sort
of chamber with two lateral entrances; within this
chamber there are curious fleshy ridges. The most

949 DIFFICULTIES OF THE THEORY [Cnav. VL

ingenious man, if he had not witnessed what takes place,
could never have imagined what purpose all these parts
serve. But Dr. Criiger saw crowds of large humble-
bees visiting the gigantic flowers 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 passage formed
by the spout or overflow. Dr. Criiger saw a “ continual
procession ” of bees thus crawling out of their involun-
tary 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 com-
rades into the bucket and then crawls out by the pas-
sage, the pollen-mass necessarily comes first into con-
tact 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 crawl 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

Cuap. VIL} OF NATURAL SELECTION. 243

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 inevi-
tably touch a long, tapering, sensitive projection, or, as
I have called it, the antenna. This antenna, when
touched, transmits a sensation or vibration to a certain
membrane which is instantly ruptured; 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 in-
numerable other instances, can we understand the gradu-
ated 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 modification 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

944 DIFFICULTIES OF NATURAL SELECTION. [Cuar. VI.

its successive adaptations to changed -habits and con-
ditions 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 proportion of living and known forms is
to the extinct and unknown, 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 in-
deed is shown by that old, but somewhat exaggerated,
canon in natural history of “ Natura non facit saltum.”
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 nig-
gard in innovation. Why, on the theory of Creation,
should there be so much variety and so little real nov-
elty? Why should all the parts and organs of many in-
dependent 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 struc-
ture? 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. 945

Organs of little apparent Importance, as affected by
Natural Selection.

As natural selection acts by life and death,—by the
survival 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 importance; 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 characters, 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 consti-
tutional differences or from determining the attacks
of insects, might assuredly be acted on by natural se-
lection. The tail of the giraffe looks like an artifi-
cially 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 posi-
tive 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 ene-
mies, would be able to range into new pastures and
thus gain a great advantage. It is not that the larger
quadrupeds are actually destroyed (except in some rare

246 | ORGANS OF LITTLE IMPORTANCE [Caap. VI.

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 pro-
genitor, and, after having been slowly perfected at a
former period, have been transmitted to existing
species in nearly the same state, 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 locomo-
tion the tail is in most aquatic animals, its general pres-
ence and use for many purposes in so many land animals,
which in their lungs or modified swimbladders betray
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
importance 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 conditions of life ——of so-called spon-
taneous 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 correlation,

Cuap. VI.] AFFECTED BY NATURAL SELECTION. 94"

compensation, of the pressure of one part on another,
&c.,—and finally of sexual selection, by which charac-
ters of use to one sex are often gained and then trans-
mitted 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 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 selection; 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 quadrupeds, so the spikes on
the palm may at first have been developed for this ob-
ject, 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 adaptation for wallowing in putridity; and so

it may be, or it may possibly be due to the direct action
18

948 ORGANS OF LITTLE IMPORTANCE [Cuapr. VL

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 in-
dispensable 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 struc-
ture 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 between the breeds of our domesticated ani-
mals in different countries,—more especially in the less
civilised countries where there has been but little
methodical selection. Animals kept by savages in dif-
ferent countries often have to struggle for their own
subsistence, and are exposed to a certain extent to natu-
ral selection, and individuals with slightly different
constitutions would succeed best under different cli-
mates. 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 af-
fects the growth of the hair, and that with the hair
the horns are correlated. Mountain breeds always dif-
fer 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;

Cuap. VI.] AFFECTED BY NATURAL SELECTION. 9249

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 together 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 breeds of
swine have undergone. But we are far too ignorant to
speculate on the relative importance of the several
known and unknown causes of variation; and I have
made these remarks only to show that, if we are un-
able to account for the characteristic differences of
our several domestic breeds, which nevertheless are gen-
erally admitted to have arisen through ordinary gen-
eration 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 or
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 be-
lieve that many structures have been created for the
sake of beauty, to delight man or the Creator (but this

950 UTILITARIAN DOCTRINE, HOW FAR TRUE:

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 absolutely 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, in-
dependently of any advantage thus gained. But a still
more important consideration is that the chief part
of the organisation of every living creature is due ta
inheritance; and consequently, though each being as-
suredly is well fitted for its place in nature, many struc-
tures have now no very close and direct relation to
present habits of life. Thus, we can hardly believe 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. But webbed feet no doubt were as use-
ful 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; but we may further
venture to believe that the several bones in the limbs
of the monkey, horse, and bat, were originally devel.
oped, on the principle of utility, probably through the
reduction of more numerous bones in the fin of some

Cuap. VI] BEAUTY, HOW ACQUIRED. 251

ancient fish-like progenitor of the whole class. It is
scarcely possible to decide 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 conclude 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 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 am-
monites of the Secondary period, created that man
might ages afterwards admire them in his cabinet?
Few objects are more beautiful than the minute silice-
ous ¢ases of the diatomacez: 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 productions of nature; but they have been

952 UTILITARIAN DOCTRINE, HOW FAR TRUE:

rendered conspicuous in contrast 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 habitually pro-
duce two kinds of flowers; one kind open and coloured
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 pro-
duced only such poor flowers as we see on our fir, oak,
nut and ash trees, on grasses, spinach, docks, and net-
tles, 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 berries of the
holly are beautiful objects,—will be admitted by every
one. But this beauty serves merely as a guide to birds
and beasts, in order that the fruit may be devoured
and the matured seeds disseminated: I infer that this is
the case from having as yet found no exception to the
tule 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 mag-
nificently coloured butterflies, have been rendered

Cuap, VI.] BEAUTY, HOW ACQUIRED. 253

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 apparently lies in the colours acquired
throngh sexual selection having been trasmitted to
both sexes, instead of to the males alone. How the
sense of beauty in its simplest form—that is, the re-
ception of a peculiar kind of pleasure from certain col-
ours, forms, and sounds—was first developed in the
mind of man and of the lower animals, is a very ob-
scure subject. The same sort of difficulty is presented,
if we enquire 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 modi-
fication in a species exclusively for the good of another
species; though throughout nature one species inces-
santly takes advantage of, and profits by, the structures
of others. But natural selection can and does often
produce structures for the direct injury of other ani-
mals, as we see in the fang of the adder, and in the ovi-
positor of the ichneumon, by which its eggs are de-
posited in the living bodies of other insects. If it

954 UTILITARIAN DOCTRINE, HOW FAR TRUE:

could be proved that any part of the structure of any
one species had been formed for the exclusive good of
another species, it would annihilate my theory, for such
could not have been produced through natural selection.
Although many statements may be found in works 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 ex-
pands 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
structure 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

Cuap. VIL} | BEAUTY, HOW ACQUIRED. 255

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 inhabitants of the same country with which it
comes into competition. And we see that this is the
standard of perfection attained under nature. The en-
demic productions of New Zealand, for instance, are
perfect one compared with another; but they are now
rapidly yielding before the advancing legions of plants
and animals introduced from Europe. Natural selec-
tion will not produce absolute perfection, nor do we al-
ways meet, as far as we can judge, with this high stand-
ard under nature. The correction for the aberration of
light is said by Miiller 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 wonderful powers of the human eye,
adds these remarkable words: “That which we have
discovered in the way of inexactness 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 sensa-
tions. One might say that nature has taken delight
in accumulating contradictions in order to remove all °
foundation from the theory of a pre-existing harmony
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 contrivances are less perfect. Can we consider
the sting of the bee as perfect, which, when used

256 UTILITARIAN DOCTRINE, HOW FAR TRUE:

against many kinds of enemies, cannot be withdrawn,
owing to the backward serratures, and thus inevi-
tably 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 instru-
ment, like that in so many members of the same great
order, and that it has since been modified but not per-
fected for its present purpose, with the poison origi-
nally adapted for some other object, such as to produce
galls, since intensified, we can perhaps 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 ad-
mire the truly wonderful power of scent by which the
males of many insects find their females, can we ad-
mire the production for this single purpose of thou-
sands of drones, which are utterly useless to the com-
munity 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 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
maternal 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 contrivances, by which orchids and many
other plants are fertilised through insect agency, can
we consider as equally perfect the elaboration of

Cuap. VI] SUMMARY. 257

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 Con-
ditions of Haxistence embraced by the Theory of Natu-
ral Selection.

We have in this chapter discussed some of the diffi-
culties 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 variable, and are not
linked together by a multitude of intermediate grada-
tions, partly because the process of natural selection 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 extinc-
tion of preceding and intermediate gradations. Close-
ly allied species, now living on a continuous area, must
often have been formed when the area was not con-
tinuous, and when the conditions of life did not insen-
sibly graduate away from one part to another. When
two varieties are formed in two districts of a continuous
area, an intermediate variety will often be formed, fitted
for an intermediate zone; but from reasons assigned,
the intermediate variety will usually exist in lesser
numbers than the two forms which it connects; conse-
quently the two latter, during the course of further
modification, from existing in greater numbers, will
have a great advantage over the less numerous inter-

258 SUMMARY. [Cuar. VL

mediate variety, and will thus generally succeed in
supplanting and exterminating it. .

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 in-
stance, 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 con-
geners. 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 woodpeckers, 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 con-
ditions 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 performed simultaneously very different
functions, and then having been in part or in whole
specialised for one function; and two distinct organs

Cuar. VL] SUMMARY. 259

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
fame purpose and in external appearance closely similar
may have been separately and independently formed;
but when such organs are closely examined, essential
differences in their structure can almost always be de-
tected; and this naturally follows from the principle
of natural selection. On the other hand, the common
tule throughout nature is infinite. diversity of structure
for gaining the same end; and this again naturally fol-
lows from the same great principle.

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, modifica-
tions are probably the direct result of the laws of varia-
tion or of growth, independently of any good having
been thus gained. But even such structures have often,
as we may feel assured, been subsequently taken ad-
vantage 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 fre-
quently been retained (as the tail of an aquatic animal by
its terrestrial descendants), though it has become of such
small importance 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

260 SUMMARY. [Cuap. VL

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 success 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
individuals and more diversified forms, and the com-
petition will have been severer, and thus the standard
of perfection will have been rendered higher. Natural
selection will not necessarily lead to absolute perfection;
nor, as far as we can judge by our limited faculties, can
absolute perfection be everywhere predicated.

On the theory of natural selection we can ciearly
understand 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 correct; but if we include all those of past times,
whether known or unknown, it must on this theory be
strictly true.

It is generally acknowledged that all organic beings
have 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 existence, so often in-
sisted on by the illustrious Cuvier, is fully embraced by
the principle of natural selection. For natural selection

Car. V1] SUMMARY. 261

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 in-
creased use or disuse of parts, being affected by the di-
rect action of the external conditions of life, and sub-
jected 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. —

263 MISCELLANEOUS OBJECTIONS ‘10 ‘tHE [Cuap. VL.

CHAPTER VII.

MISCELLANEOUS OBJECTIONS TO THE THEORY OF
NATURAL SELECTION.

Longevity—Modifications not necessarily simultaneous—M odifica-
tions apparently of no direct service—Progressive development
—Characters of small functional importance, the most con-
stant—Supposed incompetence of natural selection to account
for the incipient stages of useful structures—Causes which in-
terfere with the acquisition through natural selection of useful
structures—Gradations of structure with changed functions—
Widely different organs in members of the same class, de-
veloped from one and the same source—Reasons for disbeliev-
ing in great and abrupt modifications.

I witt devote this chapter to the consideration of
various miscellaneous objections which have been ad-
vanced 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 sub-
ject. Thus a distinguished German naturalist has as-
serted that the weakest part of my theory is, that I con-
sider 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

Cuar, VII.) THEORY OF NATURAL SELECTION. 263

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
mathematical accuracy, that longevity is a great advan-
tage to all species, so that he who believes in natural
selection “must arrange his genealogical tree” in such
a manner that all the descendants have longer lives than
their progenitors! Cannot 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 udvantages gained through natural selec-
tion, survive from year to year by means of its seeds or
ova? Mr. E. Ray Lankester has recently discussed this
subject, and he concludes, as far as its extreme com-
plexity 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 de-
termined 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 remarked, 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
19

964 MISCELLANEOUS OBJECTIONS TO THE [Cuar. VI.

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 modification having been effected since the
glacial period would have been of some avail against
those who believe in an innatc and necessary law of de-
velopment, but is powerless against the doctrine of natu-
ral selection or the Survival of the fittest, which implies
that when variations or individual differences of a bene-
ficial nature happen to arise, these will be preserved;
but this will be effected only under certain favourable
circumstances.

The celebrated paleontologist, Bronn, at the close of
his German translation of this work, asks, how, on the
principle of natural selection, can a variety live side by
side with the parent species? If both have become
fitted for slightly different habits of life or conditions,
they might live together; and if we lay on one side poly-
morphic 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

Cuap,. VII] THEORY OF NATURAL SELECTION, 965

from each other in single characters, but in many parts;
and he asks, how it always comes that many parts of
the organisation 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 trans-
mitted all together, they would appear to us as if they
had been simultaneously developed. The best answer,
however, to the above objection is afforded by those
domestic races which have been modified, chiefly
through man’s power of selection, for some special pur-
pose. 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 transfor-
mation,—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 at-
tributed partly to the principle of correlated growth, and
partly to so-called spontaneous variation.

A much more serious objection has been urged by
Bronn,and recently by Broca, namely, that many charac-
ters appear to be of no service whatever to their pos-

966 MISCELLANEOUS OBJECTIONS TO THE [Cuap. VIL

sessors, and therefore cannot have been influenced
through natural selection. Bronn adduces the length
of the ears and tails in the different 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 unim-
portant for the welfare of the species. He consequently
believes in an innate tendency towards progressive
and more perfect development. He specifies the ar-
rangement 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 divi-
sions in the parts of the flower, the position of the ovules,
the shape of the seed, when not of any use for dissemina-
tion, &e.

There is much force in the above objection. Never-
theless, we ought, in the first place, to be extremely
cautious in pretending to decide what structures now
are, or have formerly been, of use to each species. In
the second place, it should always be borne in mind
that when one part is modified, so will be other parts,
through certain dimly seen causes, such as an increased
or diminished flow of nutriment to a part, mutual pres-
sure, an early developed part affecting one suhsequently
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 agen-
cies may be all grouped together, for the sake of brevity,
under the expression of the laws of growth. In the

Cuap. VIL] THEORY OF NATURAL SELECTION. 267

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 con-
ditions apparently plays a quite subordinate part. Bud-
variations, such as the appearance of a moss-rose on a
common rose, or of a nectarine on a peach-tree, offer
good instances of spontaneous variations; but even in
these cases, if we bear in mind the 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 oc-
casionally 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
modifications 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 selection 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 fore-
going 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

968 MISCELLANEOUS OBJECTIONS TO THE [Cuar. VIL.

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 opes,
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 theyno 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 in-
fluenced by its length.

With respect to plants, to which on account of Nage-
li’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 special function; but they are
now known to be of the highest importance for the
fertilisation of the species through the aid of insects,
and have probably been gained through natural selec-
tion. 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 signification; but Dr. Hooker informs me
that within the same ovarium, the upper ovules alone in

Cuar, VIL] THEORY OF NATURAL SELECTION. 269

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
produce flowers of two kinds,—the one open of the
ordinary structure, the other closed and imperfect.
These two kinds of flowers sometimes differ wonder-
fully 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 benefits which
certainly are derived from this process are thus secured.
The closed and imperfect flowers are, however, mani-
festly of high importance, as they yield with the utmost
safety a large stock of seed, with the expenditure of
wonderfully 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 columne 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 perfect flowers), the sepals are reduced from
the normal number of five to three. .In one section of
the Malpighiacee the closed flowers, according to A. de
Jussieu, are still further modified, for the five stamens

270 MISCELLANEOUS OBJECTIONS TO THE [Cuar. VIL

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 ordi-
nary flowers of these species; the style is aborted; and
the ovaria are reduced from three to two. Now al-
though 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 clos-
ure of the flowers superfluous, 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
pentamerous. In many Composite and Umbellifere
(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

Cuap. VIL] THEORY OF NATURAL SELECTION. 971

abortion of the reproductive organs. It is a more
curious fact, previously referred to, that the achenes
or seeds of the circumference and centre sometimes dif-
fer greatlyin form, colour, and other characters. In Car-
thamus and some other Composite the central achenes
alone are furnished with a pappus; and in Hyoseris the
same head yields achenes of three different forms. In
certain Umbelliferee the exterior seeds, according to
Tausch, are orthospermous, and the central one ccelo-
spermous, and this is a character which was considered
by De Candolle to be in other species of the highest
systematic importance. Prof. Braun mentions a Fu-
mariaceous 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 subor-
dinate 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 condition, 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 gener-
ally of a highly important nature, affecting only some
of the flowers on the same plant, or occurring on dis-
tinct plants, which grow close together under the same
conditions. As these variations seem of no special use

972 MISCELLANEOUS OBJECTIONS TO THE [Cuap. VIL

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 tetram-
erous, pentamerous, &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
with 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 estivation is almost as frequently that
of the Rhinanthidex as of the Antirrhinidex, to which
latter tribe the genus belongs. Aug. St. Hilaire gives
the following cases: the genus Zanthoxylon belongs to
a division of the Rutacee 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 Helianthemum the capsule has been de-
scribed as unilocular or 3-locular; and in H. mutabile,
“Une lame, plus ou moins large,s’étend 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
oleeformis 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
donc dans un méme individu des loges et un style qui

Cuap. VIL] THEORY OF NATURAL SELECTION. 273

se rattachent tantét 4 un axe verticale et tantét 4 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 selec-
tion. But with respect 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 classi-
fications. The acquisition of a useless part can hard-
ly 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 in-
voked, 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 uniform-
ly for a length of time, we may infer that the result
would be almost uniform; and in this case all the in-
dividuals of the species would be modified in the same
manner.

From the fact of the above characters being unim-
portant for the welfare of the species, any slight varia-
tions which occurred in them would not have been ac-
cumulated and augmented through natural selection.
A structure which has been developed through long-

274 MISCELLANEOUS OBJECTIONS TO THE [Caar. VIL

continued selection, when it ceases to be of service to a
species, generally becomes variable, as we see with rudi-
mentary organs; for it will no longer be regulated by
this same power of selection. But when, from the na-
ture of the organism and of the conditions, modifica-
tions 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 importance to the greater number
of mammals, birds, or reptiles, whether they were clothed
with hair, feathers, or scales; yet hair has been trans-
mitted to almost all mammals, feathers to all birds, and
scales to all true reptiles. A structure, whatever it may
be, which is common to many allied forms, is ranked by
us as of high systematic importance, and consequently is
often assumed to be of high vital importance to the
species. Thus, as I am inclined to believe, morpho-
logical differences, which we consider as important—
such as the arrangement 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 varia-
tions, which sooner or later became constant through
the nature of the organism and of the surrounding con-
ditions, as well as through the intercrossing of distinct
individuals, but not through natural selection; 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
species, are the most important to the systematist; but,
as we shall hereafter see when we treat of the genetic

Cnap, VII] THEORY OF NATURAL SELECTION. 275

principle of classification, this is by no means so para-
doxical as it may at first appear.

Although we have no good evidence of the existence
in organic beings of an innate tendency towards pro-
gressive development, yet this necessarily follows, as I
have attempted to show in the fourth chapter, through
the continued action 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
secently 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. Mi-
vart 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 be-
lieve, any other writer. He likewise often assumes that
I attribute nothing to variation, independently of natu-
ral selection, whereas in the work just referred to I have
collected a greater number of well-established cases than
can be found in any other work known to me. My judg-

276 MISCELLANEOUS OBJECTIONS TO THE [Cuap. VIL

ment 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 conclu-
sions 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,
considered in the present volume. The one new point
which appears to have struck many readers is, “ that
natural selection is incompetent to account for the in-
cipient stages of useful structures.” This subject is
intimately connected with that of the gradation of cha-
racters, 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 here 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 beauti-
fully 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 preserving 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

Cuap. VIL] THEORY OF NATURAL SELECTION. 977

perish, if not fed by their owners. Before coming to
Mr. Mivart’s objections, it may be well to explain once
again how natural selection will act in all ordinary cases.
Man has modified some of his animals, without neces-
sarily having attended to special points of structure,
by simply preserving and breeding from the fleetest in-
dividuals, 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 in-
dividuals 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 dif-
ferences, 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 probable habits of life; for those indi-
viduals 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 pe-
culiarities, or with a tendency to vary again in the 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 in-
tercross, and will destroy all the inferior individuals.

278 MISCELLANEOUS OBJECTIONS TO THE [Cuapr. VIL

By this process long-continued, which exactly corre-
sponds 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
objections. One is that the increased size of the body
would obviously require an increased supply of food,
and he considers 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 overlook the fact, that in-
creased 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 his 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.

Cuap. VII.) THEORY OF NATURAL SELECTION. 279

Mr. Mivart then asks (and this is his second objec-
tion), if natural selection be so potent, and if high
browsing be so great an advantage, why has not any
other hoofed quadruped acquired a long neck and lofty
stature, besides the giraffe, and, in a 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 formerly in-
habited 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 ad-
vantage 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 competi-
tion 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
belonging 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 conjecture what

changes of structure would be favourable to its increase
20

980 MISCELLANEOUS OBJECTIONS TO THE [Cuar. VIL

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 at 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 §. America, though it is so luxuriant;
whilst 8. 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
more favourable than others for the development of so
large a quadruped as the giraffe.

In order that an animal should acquire some struc-
ture specially and largely developed, it is almost indis-
pensable 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 different man-
ner and degree; and that some species are much more
variable than others. Even if the fitting variations did
arise, it does not follow that natural selection would be
able to act on them, and produce a structure which ap-
parently would be beneficial to the species. For in-
stance, if the number of individuals existing in a country
is determined chiefly through destruction by beasts of
prey,—by external or internal parasites, &c.,—as seems
often to be the case, then natural selection will be able

Cuap, VIL] THEORY OF NATURAL SELECTION. 281

to do little, or will be greatly retarded, in modifying any
particular structure for obtaining food. Lastly, natural
selection is a slow process, and the same favourable con-
ditions 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
browsing 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, besides the general ones just indicated, have
probably interfered with the acquisition through natural
selection of structures, 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 reasons in answer, why have not seals and bats
given birth on such islands to forms fitted to live on the
Jand? But seals would necessarily be first converted
into terrestrial carnivorous 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. Grada-
tions of structure, with each stage beneficial to a chang-

989 MISCELLANEOUS OBJECTIONS TO THE [Caap. VIL

ing species, will be favoured only under certain peculiar
conditions. A strictly terrestrial animal, by occasion-
ally 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 reconversion into a terres-
trial form. Bats, as formerly shown, probably 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
purposes, 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 run-
ning 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 de-
veloped 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 conjectural, and their relative
probability cannot be weighed, it would be useless to

Cuap. VIL] THEORY OF NATURAL SELECTION. 983

give them. A definite answer to the latter question
ought not to be expected, seeing that no one can solve
the simpler problem why, of two races of savages, one
has risen higher in the scale of civilisation than the oth-
ev; and this apparently implies increased brain-power.

We will return to Mr. Mivart’s other objections. In-
sects 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 latter 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 excellent
instance of a résemblance 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 neutralise 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 per-
petuate.”

But in all the foregoing cases the insects in their
original state no doubt presented some rude and ac-
cidental resemblance to an object commonly found in
the stations frequented by them. Nor is this at all
improbable, considering the almost infinite number of

284 MISCELLANEOUS OBJECTIONS TO THE [Caap. VII.

surrounding objects and the diversity in form and colour
of the hosts of insects which exist. As some rude re-
semblance is necessary for the first start, we can under-
stand 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 origi-
nally 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 rendered the
insect at all less like the imitated object, they would be
eliminated. There would indeed be force in Mr. Mi-
vart’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 respect 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 re-
sembles “a stick grown over by a creeping moss or jun-
germannia.” So close was this resemblance, that a na-
tive Dyak maintained that the foliaceous 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 towardsits preser-
vation; and the more perfect the resemblance so much
the better for the insect. Considering the nature of the

Cuap. VII.] THEORY OF NATURAL SELECTION. 285

differences between the species in the group which in-
cludes 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 greatest peculiarities. The baleen consists of a
row, on each side, of the upper jaw, of about 300 plates
or laminz, 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, accord-
ing to Scoresby, four feet, in another three, in another
eighteen inches, and in the Balenoptera 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 augmenta-
tion within serviceable limits would be promoted by
natural selection alone. But how to obtain the begin-

986 MISCELLANEOUS OBJECTIONS TO THE [Cuap. vil.

ningof such useful development?” In answer,it may be
asked, why should not the early progenitors of the
whales with baleen have possessed 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 misconstrued into say-
ing 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 lamelle by finely graduated steps,
each of service to its possessor.

The beak of a shoveller-duck (Spatula clypeata) in
a more beautiful and complex structure than the mouth
of a whale. The upper mandible is furnished on eack
side (in the specimen examined by me) with a row or
comb formed of 188 thin, elastic lamelle, obliquely be-
velled 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 membrane 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 inch beneath the edge. At their
bases there is a short subsidiary row of obliquely trans-
verse lamelle. 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 project 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 moderately large Balenoptera rostrata, in
which species the baleen is only nine inches long; so

Cuar. VII] THEORY OF NATURAL SELECTION. 287

that if we were to make the head of the shoveller as
long as that of the Balenoptera, the lamella would be
six inches in length,—that is, two-thirds of the length
of the baleen in this species of whale. The lower man-
dible of the shoveller-duck is furnished with lamelle
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 lamelle are
frayed into fine bristly points, so that they thus curious-
ly resemble the plates of baleen. In the genus Prion, a
member of the distinct family of the Petrels, the upper
mandible alone is furnished with lamelle, 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 shovel-
ler’s beak we may proceed (as I have learnt from infor-
mation and specimens sent to me by Mr. Salvin), with-
out any great break, as far as fitness for sifting is con-
cerned, 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
lamelle 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 crush-
ing food. The edges of the lower mandible are crossed
by numerous fine ridges, which project very little. Al-
though the beak is thus very inferior as a sifter to
that of the shoveller, yet this bird, as every one knows,
coustantly uses it for this purpose. There are other

988 MISCELLANEOUS OBJECTIONS TO THE [Caar. VIL

species, as I hear from Mr. Salvin, in which the lamelle
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 re-
sembles that of the common duck; but the lamelle 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 water out at the corners.” Its
chief food, however, is grass, which it crops like the com-
mon goose. In this latter bird, the lamelle of the upper
mandible are much coarser than in the common duck,
almost confluent, about 27 in number on each side, and
terminating 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 tearing 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
lamelle 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 lamelle, might be converted
by small changes into a species like the Egyptian goose,
—this into one like the common duck,—and, lastly, into
one like the shoveller, provided with a beak almost ex-
clusively adapted for sifting the water; for this bird

Cua. VII] THEORY OF NATURAL SELECTION. 989

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 se-
curing live fish.

Returning to the whales. The Hyperoodon bidens
is destitute of true teeth in an efficient condition, but
its palate is roughened, according to Lacepéde, with
small, unequal, hard points of horn. There is, there-
fore, nothing improbable in supposing that some early
Cetacean form was provided with similar points of horn
on the palate, but rather more regularly 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 lamelle as
well-developed as those of the Egyptian goose, in which
case they would have been used both for seizing objects
and for sifting the water; then into lamelle like those
of the domestic duck; and so onwards, until they became
as well constructed as those of the shoveller, in which
case they would have served exclusively as a sifting ap-
paratus. From this stage, in which the lamelle would
be two-thirds of the length of the plates of baleen in the
Balenoptera rostrata, gradations, which may be ob-
served 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 ancient
Cetaceans, with the functions of the parts slowly chang-
ing during the progress of development, as are the grada-

990 MISCELLANEOUS OBJECTIONS TO THE [Cuar. VIL

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 ex-
istence, and that the structure of every part of its frame
must be well adapted to its conditions of life.

The Pleuronectide, 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 surface of an ordinary fish: it is of a
white colour, less developed in many ways than the
upper side, with the lateral fins often of smaller size.
But the eyes offer the most remarkable peculiarity; 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 formerly 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 habit-
ual position on one side. The lower eye would, also,
have been liable to be abraded by the sandy bottom.
That the Pleuronectide are admirably adapted by their
flattened and asymmetrical structure for their habits of
life, is manifest from several species, such as soles,
flounders, &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
Schiddte remarks, “a long series of forms exhibiting a

Cuap, VIL] THEORY OF NATURAL SELECTION. 291

gradual transition from Hippoglossus pinguis, which
does not in any considerable degree alter the shape in
which it leaves the ovum, to the soles, which are entire-
ly 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, indeed, 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 excellent observations
published in 1867 by Malm. The Pleuronectide, whilst
very young and still symmetrical, with their eyes stand-
ing on opposite sides of the head, cannot long retain a
vertical position, owing to the excessive depth of their
hodies, the small size of their lateral fins, and to their
being destitute of a swimbladder. Hence soon grow-
ing 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 between the eyes conse-
quently 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 cartilaginous and flexible, so that it readily yields to
muscular action. It is also known with the higher ani-
nals, even after early youth, that the skull yields and

992 MISCELLANEOUS OBJECTIONS TO THE [Cuar. VIL.

is altered in shape, if the skin or muscles be perma-
nently contracted through disease 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 rendered rather crooked. These fishes, how-
ever, are soon able to hold themselves in a vertical posi-
tion, and no permanent effect is thus produced. With
the Pleuronectide, 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 perma-
nent 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 increased
through the principle of inheritance. Schiddte be-
lieves, in opposition to some other naturalists, that the
Pleuronectide are not quite symmetrical even in the
embryo; and if this be so, we could understand how it
is that certain species, whilst young, habitually fall over
and rest on the left side, and other species on the right
side. Malm adds, in confirmation of the above view,
that the adult Trachypterus arcticus, which is not amem-
ber of the Pleuronectide, rests on its left side at the
bottom, and swims diagonally through the water 3 and in
this fish, the two sides of the head are said to be some-
what dissimilar. Our great authority on Fishes, Dr.
Giinther, concludes his abstract of Malm’s paper, by
remarking that “the author gives a very simple expla-

Cuar, VII.] THEORY OF NATURAL SELECTION. 293

nation of the abnormal condition of the Pleuronec-
toids.”

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 inherited 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. Traquair supposes,
of feeding with ease on the ground. Disuse, on the other
hand, will account for the less developed condition 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 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 sup-
posed 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 surround-
ing surface, or the presence of bony tubercles on the

994 MISCELLANEOUS OBJECTIONS TO THE [Caar. VIL

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 be-
fore insisted, that the inherited effects of the increased
use of parts, and perhaps of their disuse, will be strength-
ened 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 de-
gree 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
apparently owes its origin exclusively to use or habit.
The extremity of the tail in some American monkeys
has been converted 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 impossible to believe that in any num-
ber 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 off-
spring.” 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 confinement some harvest
mice (Mus messorius) which do not possess a structu-

Cuap. VII.] THEORY OF NATURAL SELECTION. 295

rally 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 climbing. I
have received an analogous account from Dr. Giinther,
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 prehen-
sile, as is the case with some members of the same order.
Why Cercopithecus, considering its habits whilst young,
hasnot 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 extreme-
ly remote period, and we can know nothing positively
about their manner of development. Mr. Mivart asks:
“Ts 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 hyper-
trophied 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 mam-
mary glands will have been at first developed within the
marsupial sack. In the case of the fish (Hippocampus)
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
development of the young, that they are nourished by

21

996 MISCELLANEOUS OBJECTIONS TO THE [Cuap. VIL

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 pos-
sible that the young might have been similarly nour-
ished? 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-nourished off-
spring, than would the individuals which secreted 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, aswe see in the Ornithorhyncus, at the
base of the mammalian series. Through what agency
the glands over a certain space became more highly
specialised than the others, I will not pretend 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 natural selection, unless the young at the same
time were able to partake of the secretion. There is no
greater difficulty in understanding how young mam-
mals 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 leav-
ing the shell they have learnt to pick up grains of food.
In such cases the most probable solution seems to be,

Cuar. VIL] THEORY OF NATURAL SELECTION. 297

that the habit was at first acquired by practice at a
more advanced 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 special provision
exist, the young one must infallibly be choked by the in-
trusion 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. Mivart then asks how did natural selec-
tion 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 be suggested in an-
swer 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
swallowing solid food.

We will now turn for a short space to the lower divi-
sions of the animal kingdom. The Echinodermata (star-
fishes, sea-urchins, &c.) are furnished with remarkable
organs, called pedicellariz, which consist, when well
developed, of a tridacytle forceps—that is, of one formed
of three serrated arms, neatly fitting together and
placed on the summit of a flexible stem, moved by mus-
cles. These forceps can seize firmly hold of any object;

298 MISCELLANEOUS OBJECTIONS TO THE [Caar. VIL.

and Alexander Agassiz has seen an Echinus or sea-urchin
rapidly passing particles of excrement 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 de-
fence.

With respect to these organs, Mr. Mivart, as on so
many previous occasions, asks: “ What would be the
utility of the first rudimentary beginnings of such struc-
tures, and how could such incipient buddings have ever
preserved the life of a single Echinus?” He adds, “ not
even the sudden development of the snapping action
could have been beneficial without the freely moveable
stalk, nor could the latter have been efficient without
the snapping jaws, yet no minute merely indefinite
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 pedi-
cellarie, one resembling those of Echinus, and the other
those of Spatangus; and such cases are always inter-
esting as affording the means of apparently sudden

Cuap, VIL] THEORY OF NATURAL SELECTION. 999

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 researches and those of Miiller, that both in star-
fishes and sea-urchins the pedicellarize must undoubted-
ly 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 pedicellariw. The
gradations extend even to the manner in which ordinary
spines and pedicellarie with their supporting calcare-
ous rods are articulated to the shell. In certain genera
of star-fishes, “the very combinations needed to show
that the pedicellarie are only modified branching
spines” may be found. Thus we have fixed spines, with
three equi-distant, serrated, moveable branches, articu-
lated to near their bases; and higher up, on the same
spine, three other moveable branches. Now when the lat-
ter 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 between the arms of the
pedicellariz and the moveable branches of a spine, is un-
mistakable. It is generally admitted that the ordinary
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 prehensible or snap-
ping apparatus. Thus every gradation, from an ordinary
fixed spine to a fixed pedicellaria, would be of service.

800 MISCELLANEOUS OBJECTIONS TO THE [Cuar. VII.

In certain genera of star-fishes these organs, instead
of being fixed or borne on an immoveable support, are
placed on the summit of a flexible and muscular, though
short, stem; and in this case they probably subserve
some additional function besides defence. In the sea-
urchins the steps can be followed by which a fixed spine
becomes articulated to the shell, and is thus rendered
moveable. I wish I had space here to give a fuller ab-
stract of Mr. Agassiz’s interesting observations on the de-
velopment of the pedicellariz. All possible gradations,
as he adds, may likewise be found between the pedi-
cellarie of the star-fishes and the hooks of the Ophiuri-
ans, another group of Echinodermata; and again be-
tween the pedicellarie of sea-urchins and the anchors of
the Holothurie, also belonging to the same great class.

Certain compound animals, or zoophytes as they have
been termed, namely the Polyzoa, are provided with
curious organs called avicularia. These differ much in
structure in the different species. In their most perfect
condition, they curiously 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 pedicellarie of the Echinoder-

Cuar, VIL] THEORY OF NATURAL SELECTION. 801

mata, which he considers as “ essentially similar,” having
been developed through natural selection in widely dis-
tinct divisions of the animal kingdom. But, as far as
structure is concerned, I can see no similarity between
tridactyle pedicellarie and avicularia. The latter re-
semble somewhat more closely the chele or pincers of
Crustaceans; and Mr. Mivart might have adduced with
equal appropriateness this resemblance as a special diffi-
culty; 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 move-
able lip or lid of the cell corresponding with the lower
and moveable mandible of the avicularium. Mr. Busk,
however, Coes not know of any gradations now existing
between a zooid and an avicularium. It is therefore
impossible to conjecture by what serviceable 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 chele 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 shuts
down either on the square summit of the broad penulti-
mate 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 promi-
nent, sometimes furnished with irregular teeth; and
against these the terminal segment shuts down. By an

302 MISCELLANEOUS OBJECTIONS TO THE [Caape. VIL

increase in the size of this projection, with its shape, as
well as that of the terminal segment, slightly modified
and improved, the pincers are rendered more and more
perfect, until we have at last an instrument as efficient
as the chele 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 examined by me the vibracula were slightly
curved and serrated along the outer margin; and all
of them on the same polyzoary often moved simul-
taneously; so that, acting like long oars, they swept a
branch rapidly across the object-glass of my micro-
scope. When a branch was placed on its face, the vibrac-
ula 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 poly-
zoary, removing what might be noxious to the delicate
inhabitants of the cells when their tentacula are pro-
truded.” The avicularia, like the vibracula, probably
serve for defence, but they also catch and kill small liv-
ing 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; some with avicularia alone, and a few with
vibracula alone.

It is not easy to imagine two objects more widely
different in appearance than a bristle or vibraculum,
and an avicularium like the head of a bird; yet they are
almost certainly homologous and have been developed
from the same common source, namely a zooid with its

Caap, VII] THEORY OF NATURAL SELECTION. 38038

cell. Hence we can understand 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 de-
termine 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 in-
cluded zooid could hardly have disappeared at once.
In many cases the vibracula have a grooved support at
the base, which seems to represent the fixed beak;
though this support in some species is quite absent.
This view of the development of the vibracula, if trust-
worthy, is interesting; for supposing that all the species
provided. 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, resembling a bird’s head or an irregular box or
hood. It is interesting 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 dif-
ferent ways and under different circumstances.

In the vegetable kingdom Mr. Mivart only alludes
to two cases, namely the structure of the flowers of

304 MISCELLANEOUS OBJECTIONS TO THE [Cuar. VIL

orchids, and the movements of climbing plants. With
respect to the former, he says, “ the explanation of their
origin is deemed thoroughly unsatisfactory—utterly al
sufficient to explain the incipient, infinitesimal begin-
nings 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 only a few
details on one alone of the most striking peculiarities of
the flowers of orchids, namely their pollinia. A pollin-
ium 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 con-
sidered; yet I may mention that at the base of the or-
chidaceous 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 con-
siderable length and highly developed, we have good
evidence in the aborted pollen-grains which can some-
times 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 be-
longing to other orders the stigma secretes a little viscid
matter. Now in certain orchids similar viscid matter

Car, VIL] THEORY OF NATURAL SELECTION. 805

is secreted, but in much larger quantities by one alone
of the three stigmas; and this stigma, perhaps in con-
sequence 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 multi-
tude 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, to a
highly complex pollinium, admirably adapted for trans-
portal by insects; nor will he deny that all the grada-
tions in the several species are admirably adapted in
relation to the general structure of each flower for its
fertilisation by different insects. In this, and in almost
every other case, the enquiry 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 beings, it is as use-
less to ask, as it is hopeless to attempt answering, such
questions.

We will now turn to climbing plants. These can be
arranged 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

306 MISCELLANEOUS OBJECTIONS TO HH [Caapr. VIL

two latter classes the stems have generally, but not
always, lost the power of twining, 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 indifferent-
ly placed in either class. But in ascending the series
from simple twiners to leaf-climbers, an important qual-
ity is added, namely sensitiveness to a touch, by which
means the foot-stalks of the leaves or flowers, or these
modified 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 gradations in function and structure between
simple twiners and tendril-bearers are in each case bene-
ficial 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 sup-
port, and forms the basis of our series, it may naturally
be asked how did plants acquire this power in. an in-
cipient degree, afterwards to be improved and increased
through natural selection. The power of twining de-
pends, firstly, on the stems whilst young being extremely
flexible (but this is a character common to many plants
which are not climbers); and, secondly, on their con-
tinually bending to all points of the compass, 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

Cuar. VIL] THEORY OF NATURAL SELECTION. 307

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 in-
herited 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 imper-
fect 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 irregular-
ly; 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; any-
how, they are not of the least use in the way of climb-
ing, 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 ex-
posed 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.

308 MISCELLANEOUS OBJECTIONS TO THE [Cuapr. VIL

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 sensitiveness, it ought to be found in a
nascent condition in many plants which have not be-
come climbers. This is the case: I observed that the
young flower-peduncles of the above Maurandia 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 ex-
posure to a hot sun, when they were gently and repeat-
edly 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 move-
ments, due to a touch or shake, in the young and grow-
ing organs of plants, can be of any functional impor-
tance to them. But plants possess, in obedience to vari-
ous stimuli, powers of movement, which are of manifest
importance to them; for instance, towards and more
rarely from the light,—in opposition to, and more rare-
ly in the direction of, the attraction of gravity. When
the nerves and muscles of an animal are excited by gal-
vanism or by the absorption of strychnine, the conse-

Cuar. VII] THEORY OF NATURAL SELICTION. 80%

quent movements may be called an incidental result, for
the nerves and muscles have not been rendered specially
sensitive to these stimuli. So with plants it appears that,
from having the power of movement in obedience to cer-
tain stimuli, they are excited in an incidental manner by
a touch, or by being shaken. Hence there is no great dif-
ficulty in admitting that in the case of leaf-climbers and
tendril-bearers, it is this tendency which has been taken
advantage of and increased through natural selection.
It is, however, probable, from reasons which I have as-
signed in my memoir, that this will have occurred only
with plants which had already acquired 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 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 pretend to decide; but
we know that certain periodical movements, 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 diffi-
culty on this head. A good opportunity has thus been
afforded for enlarging a little on gradations of structure,
often associated with changed functions,—an important

810 MISCELLANEOUS OBJECTIONS TO THE [Cuap. VIL

subject, which was not treated at sufficient length in
the former editions of this work. I will now briefly
recapitulate the foregoing cases.

With the giraffe, the continued preservation of the
individuals 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 de-
struction 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 to-
gether with inheritance will have aided in an important
manner in their co-ordination. With the many insects
which imitate various objects, there is no improbabilityin
the belief that an accidental resemblance to some com-
mon 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
resemblance at all closer; and thiswill 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 tendency to the formation of irregular little
points of horn on the palate; and it seems to be quite
within the scope of natural selection to preserve all fa-
vourable variations, until the points were converted first
into lamellated knobs or teeth, like those on the beak of
a goose,—then into short lamelle, like those of the do-
mestic ducks,—and then into lamellz, 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 lamelle are first used as
teeth, then partly as teeth, and partly as a sifting appara-
tus, and at last almost exclusively for this latter purpose.

Cuar. VII] THEORY OF NATURAL SELECTION. 311

With such structures as the above lamelle of horn or
whalebone, 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 mamme 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 concentrated
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 Kchi-
noderm, which served as a defence, became developed
through natural selection into tridactyle pedicellarie,
than in understanding 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 developed from the same
source; and with the vibracula we can understand how
the successive gradations might have been of service.
With the pollinia of orchids, the threads which origin-
ally served to tie together the pollen-grains, can be
traced cohering into caudicles; and the steps can like-
wise 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, be-
came attached to the free ends of the caudicles;—all
these gradations being of manifest benefit to the plants

22

319 MISCELLANEOUS OBJECTIONS TO THE (Caar. VIL

in question. With respect to climbing 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 species, to which it would apparently have
been advantageous? But it is unreasonable to expect a
precise answer to such questions, considering our ignor-
ance of the past history of each species, and of the condi-
tions 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-ordi-
nated 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-en-
during conditions, often of a peculiar nature, are neces-
sary for the development of a structure; and the re-
quisite conditions 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 con-
siders it as “ demonstrably insufficient ” to account for

Cuap. VII.] THEORY OF NATURAL SELECTION. 313

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 partake 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 specified. I am bound to add, that some
of the facts and arguments 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 evolu-
tion under some form. Mr. Mivart believes that species
change through “an internal force or tendency,” about
which it is not pretended that anything is known. That
species have a 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 selec-
tion by man has given rise to many well-adapted do-
mestic races, and which through the aid of natural se-
lection would equally well give rise by graduated steps
to natural races or species. The final result will gener-
ally 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
naturalists agree with him, that new species manifest
themselves “ with suddenness and by modifications ap-
pearing 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 apparently he

314 MISCELLANEOUS OBJECTIONS TO THE [Cuar. VIL

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 im-
probable in the highest degree.

Every one who believes in slow and gradual evolu-
tion, 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 domestication. Of these latter variations
several maybe attributed to reversion; and thecharacters
which thus reappear were, it is probable, in many cases
at first gained in a gradual manner. 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. Ex-
cludingsuch cases of abrupt variations, the few which re-
main would at best constitute, if found in a state of na-
ture, doubtful species, closely related to their parental
types.

My reasons for doubting whether natural species
have changed as abruptly as have occasionally domestic
races, and for entirely disbelieving that they have
changed in the wonderful manner indicated by Mr. Mi-
vart,are as follows. According to our experience, abrupt
and strongly marked variations occur in our domesti-
cated productions, singly and at rather long intervals of
time. If such occurred under nature, they would be
liable, as formerly explained, to be lost by accidental

Cuar. VII] THEORY OF NATURAL SELECTION. 315

causes of destruction and by subsequent inter-crossing;
and so it is known to be under domestication, unless ab-
rupt 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 sup-
posed 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 difficulty, as in the case of un-
conscious selection by man, is avoided on the theory of
gradual evolution, through the preservation 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 spe-
cies and even the genera of many large natural families
are so closely allied together, that it is difficult to dis-
tinguish not a few of them. On every continent in pro-
ceeding from north to south, from lowland to upland,
&e., we meet with a host of closely related or representa-
tive species; as we likewise do on certain distinct conti-
nents, 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 inhabi-
tants 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 with-
in the same areas; or if we compare the fossil species
embedded in the sub-stages of the same geclogical forma-
tion. It is indeed manifest that multitudes of species

316 MISCELLANEOUS OBJECTIONS TO THE [Cuap. VIL

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 in an
abrupt or sudden manner. Nor should it be forgotten,
when we look to the special parts of allied species, in-
stead of to distinct species, that numerous and wonder-
fully fine gradations 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 in-
cluded 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 prin-
ciple 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 varieties; yet it may be maintained that some have
been developed 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

Caar. VIL] THEORY OF NATURAL SELECTION. 317

spheroid from one facet to another, hardly deserve
consideration. One class of facts, however, namely,
the sudden appearance of new and distinct forms of
life in our geological formations supports at first sight
the belief in abrupt development. But the value of this
evidence depends entirely on the perfection of the geo-
logical record, in relation to periods remote in the his-
tory 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 de-
velopment of the wings of birds or bats, or the sudden
conversion of a Hipparion into a horse, hardly any light
is thrown by the belief in abrupt modifications on the
deficiency of connecting links in our geological forma-
tions. 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 insensibly fine steps. Embryological resemblances
of all kinds can be accounted for, as we shall hereafter
see, by the progenitors of our existing species having
varied after early youth, and having transmitted their
newly acquired characters to their offspring, at a corres-
ponding age. The embryo 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 ex-
tinct forms belonging to the same class. On this view
of the meaning of embryological resemblances, and in-
deed on any view, it is incredible that an animal should

318 MISCELLANEOUS OBJECTIONS, ETC. [Cuapr. VIL.

have undergone such momentous and abrupt transforma-
tions, as those above indicated; and yet should not bear
even a trace in its embryonic condition of any sudden
modification; every detail in its structure being de-
veloped by insensibly fine steps.

He who believes that some ancient form was trans-
formed suddenly through an internal force or tendency
into, for instance, one furnished with wings, will be al-
most compelled to assume, in opposition to all analogy,
that many individuals varied simultaneously. It can-
not 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-adapta-
tions, he will not be able to assign a shadow of an ex-
planation. He will be forced to admit that these great
and sudden transformations 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.

Cuap. VIIL] INSTINCT. 319

CHAPTER VIII.
INSTINCT.

Instincts comparable. with habits, but different in their origin—
Instincts graduated—Aphides and ants—lInstincts variable—
Domestic 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 suffi-
cient to overthrow my whole theory. I may here pre-
mise that I have nothing to do with the origin of the
mental powers, any more than I have with that of life it-
self. 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 ac-
tions are commonly embraced by this term; but every
one understands what is meant, when it is said that in-
stinct impels the cuckoo to migrate and to lay her eggs
in other birds’ nests. An action, which we ourselves re-
quire experience to enable us to perform, when per-
formed 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

320 INSTINCT. (Cuar. VITL

what purpose it, is performed, is usually said to be in-
stinctive. But I could show that none of these charac-
ters 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 meta-
physicians have compared instinct with habit. This
comparison gives, I think, an accurate notion of the
frame of mind under which an instinctive action is
performed, but not necessarily of its origin. How un-
consciously many habitual actions are performed, in-
deed not rarely in direct opposition to our conscious
will! yet they may be modified by the will or reason.
Habits easily become associated with other habits, with
certain periods of time, and states of the body. When
once acquired, they often remain constant throughout
life. Several other points of resemblance between in-
stincts and habits could be pointed out. As in repeat-
ing a well-known song, so in instincts, one action fol-
lows another by a sort of rhythm; if a person be inter-
rupted 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 cater-
pillar, which makes a very complicated hammock; for
if he took a caterpillar which had completed its ham-
mock up to, say, the sixth stage of construction, and put
it into a hammock 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 benefit from this, it

Cuap. VIIL] INSTINCT. 391

was much embarrassed, and in order to complete its
hammock, seemed forced to start from the third stage,
where it had left off, and thus tried to complete the al-
ready finished work.

If we suppose any habitual action to become in-
herited—and it can be shown that this does sometimes
happen—then the resemblance between what originally
was a habit and an instinct becomes so close as not to
be distinguished. If Mozart, instead of playing the
pianoforte at three years old with wonderfully 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
number of instincts have been acquired by habit in one
generation, and then transmitted by inheritance to suc-
ceeding generations. 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 acquired by habit.

It will be universally admitted.that instincts are as
important as corporeal structures for the welfare of each
species, under its present conditions of life. Under
changed conditions of life, it is at least possible that
slight modifications of instinct 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 se-
lection preserving and continually accumulating vari-
ations of instinct to any extent that was profitable. It
is thus, as I believe, that all the most complex and won-
derful 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

822 INSTINCT. [Cuap. VIIL

that the effects of habit are in many cases of subordinate
importance to the effects of the natural selection of what
may be called spontaneous variations of instincts;—that
is of variations produced 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
accumulation of numerous slight, yet profitable, varia-
tions. Hence, as in the case of corporeal structures, we
ought to find in nature, not the actual transitional gra-
dations by which each complex instinct has been ac-
quired—for these could be found only in the lineal an-
cestors of each species—but we ought to find in the col-
lateral lines of descent some evidence of such gradations;
or we ought at least to be able to show that gradations of
some kind are possible; and this we certainly can do. I
have been surprised to find, making allowance for the
instincts of animals having been but little observed ex-
cept in Europe and North America, and for no instinct
being known amongst extinct species, how very gener-
ally gradations, leading to the most complex instincts,
can be discovered. Changes of instinct may sometimes
be facilitated by the same species having different in-
stincts at different periods of life, or at different seasons
of the year, or when placed under different circum-
stances, &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 spe-
cies can be shown to occur in nature.

Again, as in the case of corporeal structure, and con-
formably 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

Caap. VIL] INSTINCT. 323

the strongest instances of an animal apparently perform-
ing 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 antenne; 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 antenne on the abdomen first of one
aphis and then of another; and each, as soon as it felt
the antenne, 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 cer-
tain, 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 excretion is extremely viscid, it is no doubt a
convenience to the aphides to have it removed; there-
fore 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 advantage of the instincts
of others, as each. takes advantage of the weaker bodily

324 INSTINCT. (Cuap. VIII.

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 indispensable, 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
indispensable for the action of natural selection, as
many instances as possible ought to be given; but want
of space prevents me. I can only assert that instincts
certainly do vary—for instance, 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 de-
pendence 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 collecting propolis, used a
cement of wax and turpentine, with which he had cov-
ered 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 experience,and bythe sight of fear of the same enemy
in other animals. The fear of man is slowly acquired,
as I have elsewhere shown, by the various animals which

Caar. VIII.J CHANGES OF HABIT OR INSTINCT. 325

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 ad-
duced 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 statements, 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.

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 strength-
ened by briefly considering a few cases under domesti-
cation. We shall thus be enabled to see the part which
habit and the selection of so-called spontaneous varia-
tions have played in modifying the mental qualities of
our domestic animals. It is notorious how much domes-
tic 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-

326 CHANGES OF HABIT OR INSTINCT [Cuar. VIL

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 woodcocks 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 cannot be doubted that
young pointers (I 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 cer-
tainly in some degree inherited by retrievers; and a ten-
dency to run round, instead of at, a flock of sheep, by
shepherd dogs. I cannot see that these actions, per-
formed 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 knowthat he
points to aid his master, than the white butterfly knows
why she lays her eggs on the leaf of the cabbage—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 in-
stincts; but they have been acted on by far less rigorous
selection, and have been transmitted for an incompar-
ably shorter period, under less fixed conditions of life.

Cap, VIIL] IN DOMESTICATED ANIMALS. 327

How strongly these domestic instincts, habits, and
dispositions are inherited, and how curiously they be-
come 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 grey-
hound has given to a whole family of shepherd-dogs a
tendency to hunt hares. These domestic instincts, when
thus tested by crossing, resemble natural instincts, 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 ac-
tions which have become inherited solely from long-con-
tinued and compulsory 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 witnessed, 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 selec-
tion of the best individuals in successive generations
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
23

3828 CHANGES OF HABIT OR INSTINCT [Cuap. VIIL

have thought, only the exaggerated pause of an animal
preparing to springon its prey. When the first tendency
to point was once displayed, methodical selection and
the inherited effects of compulsory training in each suc-
cessive generation would soon complete the work; and
unconscious selection is still in progress, as each man
tries to procure, without intending to improve the breed,
dogs which stand and hunt best. On the other hand,
habit alone in some cases has sufficed; hardly any ani-
mal is more difficult to tame than the young of the wild
rabbit; scarcely any animal is tamer than the young
of the tame rabbit; but I can hardly suppose that do-
mestic 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
remarkable 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 perma-
nently the minds of our domestic animals 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 coun-
tries 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

Caap. VIII] IN DOMESTICATED ANIMALS. 329

poultry, sheep, and pigs! No doubt they occasionally
do make an attack, and are then beaten; and if not cured,
they are destroyed; sc that habit and some degree of se-
lection have probably concurred in civilising by inherit-
ance 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 in-
formed 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 turkeys) from
under her, and conceal themselves in the surrounding
grass or thickets; and this is evidently done for the
instinctive purpose of allowing,as we see inwild ground-
birds, their mother to fly away. But this instinct re-
tained by our chickens has become useless under domes-
tication, 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, pe-
culiar mental habits and actions, which at first appeared
from what we must in our ignorance call an accident.
In some cases compulsory habit alone has sufficed to pro-
duce inherited mental changes; in other cases, com-
pulsory habit has done nothing, and all has been the
result of selection, pursued both methodically and un-
consciously: but in most cases habit and selection have
probably concurred.

330 SPECIAL INSTINCTS. [Caar. VILL

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 generally and
justly been ranked by naturalists as the most wonderful
of all known instincts.

Instincts of the Cuckoo.—It is supposed by some
naturalists that the more immediate cause of the in-
stinct 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 unincu-
bated, or there would be eggs and young birds of dif-
ferent ages in the same nest. If this were the case, the
process of laying and hatching might be inconveniently
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 occasionally lays her eggs in other
birds’ nests; but I have lately heard from Dr. Merrell,
of Iowa, that he once found in Ilinois ayoung cuckoo to-
gether with a young jay-in the nest of a Blue jay (Gar-
rulus cristatus); and as both were nearly full feathered,
there could be no mistake in their identification. I
could also give several instances of various birds which

Cuap, VII] INSTINCTS OF THE CUCKOO. 831

have been known occasionally to lay their eggs in other
birds’ nests. Now let us suppose that the ancient pro-
genitor of our European 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 ear-
lier 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 advantage. 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 continued pro-
cess of this nature, I believe that the strange instinct of
our cuckoo has been generated. It has, also, recently
been ascertained on sufficient evidence, by Adolf Mil-
ler, 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 instinct 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

332 INSTINCTS OF THE CUCKOO. ([Cuap. VIL

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 vora-
cious young bird receives ample food. Secondly, that
the eggs are remarkablysmall,not exceeding those of the
skylark,—a bird about one-fourth as large as the cuckoo.
That the small size of the egg is a real case of adapta-
tion 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 instinct,
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 beneficent ar-
rangement, 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 advan-
tage to this species to have laid eggs even smaller than
those now laid, so as to have deceived 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. Ram-
say remarks that two of the Australian cuckoos, when

Cuar, VII.) INSTINCTS OF THE CUCKOO. 333

they lay their eggs in an open nest, manifest a decided
preference for nests containing 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 invari-
ably displayed the above instinct, it would assuredly
have been added to those which it is assumed must all
have been acquired together. The eggs of the Austral-
ian Bronze cuckoo vary, according to Mr. Ramsay, to an
extraordinary 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 this age is in a most helpless condition, Mr.
Gould was formerly inclined to believe that the act of
ejection was performed by the foster-parents themselves.
But he has now received 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 impor-
tance for the young cuckoo, as is probably the case, to
receive as much food as possible soon after birth, I can
see no special difficulty in its having gradually acquired,
during successive generations, the blind desire, the
strength, and structure necessary for the work of ejec-
tion; for those young cuckoos which had such habits

834 INSTINCTS OF THE MOLOTHRUS. [Cuap. VIIL

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 some-
what 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 un-
hatched 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 re-
marked, a transitory sharp tooth for cutting through
the tough egg-shell. For if each part is liable to indi-
vidual 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 se-
lection.

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 interesting gradation in the perfection of their in-
stincts. 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
out the nestlings of the stranger. They either lay 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

Cuar. VIIL] INSTINCTS OF THE MOLOTHRUS. 335

parasitic, for he has seen the young of this species fol-
lowing 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
irregular untidy 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 ascer-
tained, 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 extraordinary habit of pecking
holes in the eggs, whether of their own species or of their
foster-parents, which they find in the appropriated 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 in evolution, but he
appears to have been so much struck by the imperfect
instincts of the Molothrus bonariensis that he quotes
my words, and asks, “ Must we consider these habits,
not as especially endowed or created instincts, but as
small consequences of one general law, namely, tran-
sition? ”

Various birds, as has already been remarked, occa-
sionally lay their eggs in the nests of other birds. This
habit is not very uncommon with the Gallinacee, and
throws some light on the singular instinct of the ostrich.

3836 SPECIAL INSTINCTS. [Cuar. VIIL

In this family several hen-birds unite and lay first a
few eggs in one nest aud 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 bona-
riensis, has not 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 Sphegide (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 larve, 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 selection making an occasional habit perma-
nent, 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

Cuap. VIII] SLAVE-MAKING INSTINCT. 337

by Pierre Huber, a better observer even than his cele-
brated father. This ant is absolutely dependent on its
slaves; without their aid, the species would certainly be-
come extinct in a single year. The males and fertile fe-
males do no work of any kind, and the workers or sterile
females, though most energetic and courageous in cap-
turing slaves, do no other work. They are incapable
of making their own nests, or of feeding their own
larve. When the old nest is found inconvenient, and
they have to migrate, it is the slaves which determine
the migration, 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 larve and pupe 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 saved the survivors; made some cells and tended
the larve, 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 wonder-
ful an instinct could have been perfected.

Another species, Formica sanguinea, was likewise
first discovered 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 Museum, 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 doubting the

838 SPECIAL INSTINCTS. (Caar. VIIL

existence of so extraordinary an instinct as that of mak-
ing 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 larvee and pup are exposed, the slaves work ener-
getically together with their masters 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 either 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 numer-
ous; 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 present 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. During the year 1860,
however, in the month of July, I came across a com-
munity 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

Cuar. VIIL] SLAVE-MAKING INSTINCT. 339

Scotch-fir-tree, twenty-five yards distant, which they
ascended together, probably in search of aphides or
cocci. According to Huber, who had ample opportuni-
ties 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 even-
ing; and, as Huber expressly states, their principal office
is to search for aphides. This difference 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 Eng-
land.

One day I fortunately witnessed a migration of F.
sanguinea. from one nest to another, and it was a most
interesting spectacle to behold the masters carefully
carrying their slaves in their jaws instead of being car-
ried 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 approached 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. san-
guinea. The latter ruthlessly killed their small oppo-
nents, and carried their dead bodies as food to their
nest, twenty-nine yards distant; but they were prevent-
ed from getting any pupe to rear as slaves. I then dug
up a small parcel of the pupe of F. fusca from another
nest, and put 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

340 SPECIAL INSTINCTS. [Cuar. VIII,

parcel of the pupx of another species, F. flava, with a
few of these little yellow ants still clinging to the frag-
ments 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 cour-
ageous, and I have seen it ferociously attack other ants.
In one instance I found to my surprise an independent
community of F. flava under a stone beneath a nest of
the slave-making F. sanguinea; and when I had acci-
dentally disturbed both nests, the little ants attacked
their big neighbours with surprising courage. Now I
was curious to ascertain whether F. sanguinea could dis-
tinguish the pupe 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 pupe of
FE. fusca, whereas they were much terrified when they
came across the pupz, 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 yellow ants had
crawled away, they took heart and carried off the
pupe.

One evening I visited another community of F.
sanguinea, and found a number of these ants returning
home and entering their nests, carrying the dead bodies
of F. fusca (showing that it was not a migration) and
numerous pup. 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

Cuar. VILL] SLAVE-MAKING INSTINCT. 341

individuals of F. fusca were rushing about in the great-
est agitation, and one was perched motionless 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 confir-
mation 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. rufescens. The latter does not build
its own nest, does not determine its own migrations, does
not collect food for itself or its young, and cannot even
feed itself: it is absolutely dependent on its numerous
slaves. Formica sanguinea, on the other hand, pos-
sesses much fewer slaves, and in the early part of the
summer extremely few: the masters determine when and
where a new nest shall be formed, and when they mi-
grate, the masters carry the slaves. Both in Switzerland
and England the slaves seem to have the exclusive care
of the larvee, and the masters alone go on slave-making
expeditions. In Switzerland the slaves and masters
work together, 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 collect building materials and
food for themselves, their slaves and larve. 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
pup of other species, if scattered near their nests, it is
possible that such pupe originally stored as food might

342 SPECIAL INSTINCTS. (Cuap. VIII.

bezonie developed; and the foreign ants thus uninten-
tionally 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 collecting pupe,
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 species—until an ant was formed as ab-
jectly dependent on its slaves as is the Formica rufes-
cens.

Cell-making instinct of the Hive-Bee—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 enthusiastic admiration. We hear from
mathematicians that bees have practically solved a re-
condite problem,and have made their cells of the proper
shape to hold the greatest possible amount of honey,
with the least possible consumption of precious wax in
their construction. It has been remarked that a skil-
ful 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

Cuap. VII] | CELL-MAKING INSTINCT. 343

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 in-
stincts.

I was led to investigate this subject by Mr. Water-
house, who has shown that the form of the cell stands in
close relation to the presence of adjoining cells; and the
following view may, perhaps, be considered only as a
modification of his theory. Let us look to the great
principle of gradation, 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 Mex-
ican Melipona domestica, carefully described and figured
by Pierre Huber. The Melipona itself is intermediate
in structure between the hive and humble bee, but
more nearly related to the latter; it forms a nearly
regular waxen comb of cylindrical cells, in which the
young are hatched, and, in addition, some large cells of

wax for holding honey. These latter cells are nearly
24

344 SPECIAL INSLINCTS. (Cap, VIIL

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
completed; but this is never permitted, the bees building
perfectly 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 surfaces in any one cell necessarily enter
into the construction of three adjoining cells. It is ob-
vious that the Melipona saves wax, and what is more im-
portant, 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
Melipona 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. Accordingly I 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:—

Cuap. VIIL] CELL-MAKING INSTINCT. 845

If a numter of equal spheres be described with
their centres placed in two parallel layers; with the cen-
tre of each sphere at the distance of radius X 4/ 2, or
radius X 1.41421 (or at some lesser distance), from the
ventres of the six surrounding spheres in the same
layer; and at the same distance 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 result a double layer
of hexagonal prisms united together by pyramidal bases
formed of three rhombs; and the rhombs and the sides
of the hexagoral prisms will have every angle identi-
cally the same with the best measurements which have
been made of the cells of the hive-bee. But I hear
from Prof. Wyman, who has made numerous careful
measurements, 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.

Heuce 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 that Melipona
to have the power of forming her cells truly spherical,
and of equal sizes; and this would not be very surpris-
ing, seeing that she already does so to a certain extent,
and seeing what perfectly cylindrical burrows many in-
sects 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 cylindri-
cal cells; and we must further suppose, and this is the
greatest difficulty, that she can somehow judge accu-

346 SPECIAL INSTINCTS. (Cuap. VIIL

rately at what distance to stand from her fellow-labour-
ers 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 cer-
tain extent; and then she unites the points of intersec-
tion by perfectly flat surfaces. By such modifications
of instincts which in themselves are not very wonderful,
—hardly more wonderful than those which guide a bird
to make its nest,—I believe that the hive-bee has ac-
quired, through natural selection, her inimitable archi-
tectural powers.

But this theory can be tested by experiment. Fol-
lowing 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 min-
ute circular pits in it; and as they deepened these little
pits, they made them wider and wider until they were
converted into shallow basins, appearing to the eye per-
fectly true or parts of a sphere, and of about the diam-
eter of a cell. It was most interesting to observe that,
wherever several bees had begun to excavate these basins
near together, they had begun their work at such a dis-
tance from each other, that by the time the basins had
acquired the above-stated width (7. e. about the width of
an ordinary cell), and were in depth 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 ex-
cavate, and began to build up flat walls of wax on the
lines of intersection between the basins, so that each
hexagonal prism was built upon the scalloped edge of a
smooth basin, instead of on the straight edges of a
three-sided pyramid as in the case or ordinary cells.

Cuap. VIIL] | CELL-MAKING INSTINCT. 347

I then put into the hive, instead of a thick, rectangu-
lar piece of wax, a thin and narrow, knife-edged ridge,
coloured with vermilion. The bees instantly began on
both sides to excavate little basins near to each other, in
the same way as before; but the ridge of wax was so
thin, that the bottoms of the basins, if they had been
excavated to the same depth as in the former experi-
ment, would have broken into each other from the
opposite sides. The bees, however, did not suffer this
to happen, and they stopped their excavations in due
time; so that the basins, as soon as they had been a little
deepened, came to have flat bases; and these flat bases,
formed by thin little plates of the vermilion wax left
ungnawed, were situated, as far as the eye could judge,
exactly along the planes of imaginary intersection
between the basins on the opposite sides of the ridge of
wax. Jn some parts, only small portions, in other parts,
large portions of a rhombic plate were thus left between
the opposed basins, but the work, from the unnatural
state of things, had not been neatly performed. The
bees must have worked at very nearly the same rate in
circularly gnawing away and deepening the basins on
both sides of the ridge of vermilion wax, in order to
have thus succeeded in leaving flat plates between the
basins, by stopping work at the planes of intersection.

Considering how flexible thin wax is, I do not see
that there is any difficulty in the bees, whilst at work on
the two sides of a strip of wax, perceiving when they
have gnawed the wax away to the proper thinness, and
then stopping their work. In ordinary combs it has ap-
peared to me that the bees do not always succeed in
working at exactly the same rate from the opposite
sides; for I have noticed half-completed rhombs at the

348 SPECIAL INSTINCTS. [Cuap. VIIL

base of a just commenced cell, which were slightly con-
cave on one side, where J suppose that the bees had ex-
cavated too quickly, and convex on the opposed side
where the bees had worked less quickly. In one well
marked instance, I put the comb back into the hive, and
allowed the bees to go on working for a short time, and
again examined the cell, and I found that the rhombic
plate had been completed, and had become perfectly
flat: it was absolutely impossible, from the extreme
thinness of the little plate, that they could have effected
this by gnawing away the convex side; and I suspect
that the bees in such cases stand on opposite sides and
push and bend the ductile and warm wax (which as I
have tried is easily done) into its proper intermediate
plane, and thus flatten it.

From the experiment of the ridge of vermilion wax
we can see that, if the bees were to build for themselves
a thin wall of wax, they could make their cells of
the proper shape, by standing at the proper distance
from each other, by excavating at the same rate, and by
endeavouring to make equal spherical hollows, but never
allowing the spheres to break into each other. Now
bees, as may be clearly seen by examining the edge of
a growing comb, do make a rough, circumferential wall
or rim all round the comb; and they gnaw this away
from the opposite sides, always working circularly as
they deepen each cell. They do not make the whole
three-sided pyramidal base of any one cell at the same
time, but only that one rhombic plate which stands on
the extreme growing margin, or the two plates, as the
case may be; and they never complete the upper edges
of the rhombic plates, until the hexagonal walls are
commenced. Some of these statements differ from

Cuap. VIII] CELL-MAKING INSTINCT. 349

those made by the justly celebrated elder Huber, but
I am convinced of their accuracy; and if I had
space, I would show that they are conformable with
my theory.

Huber’s statement that the very first cell is exca-
vated out of a little parallel-sided wall of wax, is not, as
far as I have seen, strictly correct; the first commence-
ment having always been a little hood of wax; but I will
not here enter on details. We see how important a part
excavation plays in the construction of the cells; but it
would be a great error to suppose that the bees cannot
build up a rough wall of wax in the proper position—
that is, along the plane of intersection between two ad-
joining spheres. I have several specimens showing
clearly that they can do this. Even in the rude circum-
ferential rim or wall of wax round a growing comb, flex-
ures may sometimes be observed, corresponding in posi-
tion to the planes of the rhombic basal plates of future
cells. But the rough wall of wax has in every case to be
finished off, by being largely gnawed away on both sides.
The manner in which the bees build is curious; they al-
ways make the first rough wall from ten to twenty times
thicker than the excessively thin finished wall of the cell,
which will ultimately be left. We shall understand how
they work, by supposing masons first to pile up a broad
ridge of cement, and then to begin cutting it away
equally on both sides near the ground, till a smooth, very
thin wall is left in the middle; the masons always piling
up the cut-away cement,and adding fresh cement on the
summit of the ridge. We shall thus have a thin wall
steadily growing upward but always crowned by a
gigantic coping. From all the cells, both those just
commenced and those completed, being thus crowned

350 SPECIAL INSTINCTS. [Cuapr. VIII.

by a strong coping of wax, the bees can cluster end
crawl over the combwithout injuring the delicate hexeg-
onal walls. These walls, as Professor Miller has lanl
ascertained for me, vary greatly in thickness; being, on
an average of twelve measurements made near the bor-
der of the comb, x4, of an inch in thickness; whereas
the basal rhomboidal plates are thicker, nearly in the
proportion of three to two, having a mean thickness,
from twenty-one measurements, of g$, of an inch. By
the above singular manner of building, strength is con-
tinually given to the comb, with the utmost ultimate
economy of wax.

It seems at first to add to the difficulty of under-
standing how the cells are made, that a multitude of bees
all work together; one bee after working a short time at
one cell going to another, so that, as Huber has stated,
a score of individuals work even at the commencement
of the first cell. I was able practically to show this
fact, by covering the edges of the hexagonal walls of a
single cell, or the extreme margin of the circumferential
rim of a growing comb, with an extremely thin layer of
melted vermilion wax; and I invariably found that the
colour was most delicately diffused by the bees—as
delicately as a painter could have done it with his brush
—by atoms of the coloured wax having been taken from
the spot on which it had been placed, and worked into
the growing edges of the cells all round. The work of
‘construction seems to be a sort of balance struck between
many bees, all instinctively standing at the same relative
distance from each other, all trying to sweep equal
spheres, and then building up, or leaving ungnawed,
the planes of intersection between these spheres. It was
really curious to note in cases of difficulty, as when two

Cuap. VIII] CELL-MAKING INSTINCT. 351

pieces of comb met at an angle, how often the bees would
pull down and rebuild in different ways the same cell,
sometimes recurring to a shape which they had at first
rejected.

When bees have a place on which they can stand in
their proper positions for working,—for instance, on a
slip of wood, placed directly under the middle of a comb
growing downwards, so that the comb has to be built
over one face of the slip—in this case the bees can lay
the foundations of one wall of a new hexagon, in its
strictly proper place, projecting beyond the other com-
pleted cells. It suffices that the bees should be enabled
to stand at their proper relative distances from each
other and from the walls of the last completed cells, and
then, by striking imaginary spheres, they can build up a
wall intermediate between two adjoining spheres; but,
as far as I have seen, they never gnaw away and finish off
the angles of a cell till a large part both of that cell and
of the adjoining cells has been built. This capacity in
bees of laying down under certain circumstances a
rough wall in its proper place between two just-com-
menced cells, is important, as it bears on a fact, which
seems at first subversive of the foregoing theory; namely,
that the cells on the extreme margin of wasp-combs are
sometimes strictly hexagonal; but I have not space here
to enter on this subject. Nor does there seem to me any
great difficulty in a single insect (as in the case of a
queen-wasp) making hexagonal cells, if she were to work
alternately on the inside and outside of two or three
cells commenced at the same time, always standing at
the proper relative distance from the parts of the cells
just begun, sweeping spheres or cylinders, and building
up intermediate planes. ,

352 SPECIAL INSTINCTS. [Cuar. VIII.

“™Euatural selection acts only by the accumulation
of slight modifications of structure or instinct, each
profitable to the individual under its conditions of life,
it may rcasonably be asked, how a long and graduated
succession of modified architectural instincts, all tending
towards the present perfect plan of construction, could
have profited the progenitors of the hive-bee? I think
the answer is not difficult: cells constructed like those
of the bee or the wasp gain in strength, and save much
in labour and space, and in the materials of which they
are constructed. With respect to the formation of wax,
it is known that bees are often hard pressed to get suffi-
cient nectar, and I am informed by Mr. Tegetmeier that
it has been experimentally proved that from twelve to
fifteen pounds of dry sugar are consumed by a hive of
bees for the secretion of a pound of wax; so that a pro-
digious quantity of fluid nectar must be collected and
consumed by the bees in a hive for the secretion of the
wax necessary for the construction of their combs.
Moreover, many bees have to remain idle for many days
during the process of secretion. A large store of honey
is indispensable to support a large stock of bees during
the winter; and the security of the hive is known
mainly to depend on a large number of bees being sup-
ported. Hence the saving of wax by largely saving
honey and the time consumed in collecting the honey
must be an important element of success to any family of
bees. Of course the success of the species may be de-
pendent on the number of its enemies, or parasites, or
on quite distinct causes, and so be altogether independ-
ent of the quantity of honey which the bees can collect.
But let us suppose that this latter circumstance deter-
mined, as it probably often has determined, whether a

Cnap, VIII] §CELL-MAKING INSTINCT. 353

hee allied to our humble-bees could exist in large num-
bers in any country; and let us further suppose that the
community lived through the winter, and. consequently
required a store of honey: there can in this case be no
doubt that it would be an advantage to our imaginary
humble-bee if a slight modification in her instincts led
her to make her waxen cells near together, so as to inter-
sect a little; for a wall in common even to two adjoining
cells would save some little labour and wax. Hence it
would continually be more and more advantageous to
our humble-bees, if they were to make their cells more
and more regular, nearer together, and aggregated into
a mass, like the cells of the Melipona; for in this case a
large part of the bounding surface of each cell would
serve to bound the adjoining cells, and much labour and
wax would be saved. Again, from the same cause, it
would be advantageous to the Melipona, if she were to
make her cells closer together,and more regular in every
way than at present; for then,as we have seen, the spheri-
cal surfaces would wholly disappear and be replaced by
plane surfaces; and the Melipona would make a comb as
perfect as that of the hive-bee. Beyond this stage of
perfection in architecture, natural selection could not
lead; for the comb of the hive-bee, as far as we can see,
is absolutely perfect in economising labour and wax.
Thus, as I believe, the most wonderful of all known
instincts, that of the hive-bee, can be explained by
natural selection having taken advantage of numerous,
successive, slight modifications of simpler instincts;
natural selection having, by slow degrees, more and
more perfectly led the bees to sweep equal spheres at a
given distance from each other in a double layer, and to
build up and excavate the wax along the planes of inter-

354 OBJECTIONS TO THE THEORY (Czar. VIII.

section; the bees, of course, no more knowing that they
swept their spheres at one particular distance from each
other, than they know what are the several angles of the
hexagonal prisms and of the basal rhombic plates; the
motive power of the process of natural selection having
been the construction of cells of due strength and of
the proper size and shape for the larve, this being
effected with the greatest possible economy of labour
and wax; that individual swarm which thus made the
best cells with least labour, and least waste of honey
in the secretion of wax, having succeeded best, and
having transmitted their newly-acquired economical
instincts to new swarms, which in their turn will have
had the best chance of succeeding in the struggle for
existence.

Objections to the Theory of Natural Selection as applied
to Instincts: Neuter and Sterile Insects.

It has been objected to the foregoing view of the ori-
gin of instincts that “ the variations of structure and of
instinct must have been simultaneous and accurately
adjusted to each other, as a modification in the one
without an immediate corresponding change in the
other would have been fatal.” The force of this objec-
tion rests entirely on the assumption that the changes in
the instincts and structure are abrupt. To take as an
illustration the case of the larger titmouse (Parus
major) alluded to in a previous chapter; this bird often
holds the seeds of the yew between its feet on a branch,
and hammers with its beak till it gets at the kernel.
Now what special difficulty would there be in natural
selection preserving all the slight individual variations
in the shape of the beak, which were better and better

Cuar. VIIL] OF NATURAL SELECTION. 355

adapted to break open the seeds, until a beak was
formed, as well constructed for this purpose as that of
the nuthatch, at the same time that habit, or compul-
sion, or spontaneous variations of taste, led the bird to
become more and more of a seed-eater? In this case the
beak is supposed to be slowly modified by natural selec-
tion, subsequently to, but in accordance with, slowly
changing habits or taste; but let the feet of the titmouse
vary and grow larger from correlation with the beak, or
from any other unknown cause, and it is not improbable
that such larger feet would lead the bird to climb more
and more until it acquired the remarkable climbing in-
stinct and power of the nuthatch. In this case a grad-
ual change of structure is supposed to lead to changed
instinctive habits. To take one more case: few in-
stincts are more remarkable than that which leads the
swift of the Eastern Islands to make its nest wholly of
inspissated saliva. Some birds build their nests of mud,
believed to be moistened with saliva; and one of the
swifts of North America makes its nest (as I have seen)
of sticks agglutinated with saliva, and even with flakes
of this substance. Is it then very improbable that the
natural selection of individual swifts, which secreted
more and more saliva, should at last produce a species
with instincts leading it to neglect other materials, and
to make its nest exclusively of inspissated saliva? And
so in other cases. It must, however, be admitted that
in many instances we cannot conjecture whether it was
instinct or structure which first varied.

No doubt many instincts of very difficult explana-
tion could be opposed to the theory of natural selec-
tion—cases, in which we cannot see how an instinct
could have originated; cases, in which no intermediate

356 OBJECTIONS TO THE THEORY [Caapr. VIIL

gradations are known to exist; cases of instincts of such
trifling importance, that they could hardly have been
ected on by natural selection; cases of instincts almost
identically the same in animals so remote in the scale of
nature, that we cannot account for their similarity by
inheritance from a common progenitor, and conse-
quently must believe that they were independently ac-
quired through natural selection. I will not here enter
on these several cases, but will confine myself to one
special difficulty, which at first appeared to me insuper-
able, and actually fatal to the whole theory. I allude
to the neuters or sterile females in insect-communi-
ties; for these neuters often differ widely in instinct and
in structure from both the males and fertile females,
and yet, from being sterile, they cannot propagate their
kind.

The subject well deserves to be discussed at great
length, but I will here take only a single case, that of
working or sterile ants. How the workers have been
rendered sterile is a difficulty; but not much greater
than that of any other striking modification of struc-
ture; for it can be shown that some insects and other
articulate animals in a state of nature occasionally be-
come sterile; and if such insects had been social, and
it had been profitable to the community that a number
should have been annually born capable of work, but in-
capable of procreation, I can see no especial difficulty in
this having been effected through natural selection.
But I must pass over this preliminary difficulty. The
great difficulty les in the working ants differing widely
from both the males and the fertile females in structure,
as in the shape of the thorax, and in being destitute of
wings and sometimes of eyes, and in instinct. As far

Cuar, Vili] OF NATURAL SELECTION. 357

as instinct alone is concerned, the wonderful difference
in this respect between the workers and the perfect
females, would have been better exemplified by the hive-
bee. Ifa working ant or other neuter insect had been
an ordinary animal, I should have unhesitatingly as-
sumed that all its characters had been slowly acquired
through natural selection; namely, by individuals hav-
ing been born with slight profitable modifications,
which were inherited by the offspring; and that these
again varied and again were selected, and so onwards.
But with the working ant we have an insect differing
greatly from its parents, yet absolutely sterile; so that it
could never have transmitted successively acquired
modifications of structure or instinct to its progeny. It
may well be asked how is it possible to reconcile this
case with the theory of natural selection?

First, let it be remembered that we have innumera-
ble instances, both in our domestic productions and in
those in a state of nature, of all sorts of differences of in-
herited structure which are correlated with certain ages,
and with either sex. We have differences correlated
not only with one sex, but with that short period when
the reproductive system is active, as in the nuptial
plumage of many birds, and in the hooked jaws of the
male salmon. We have even slight differences in the
horns of different breeds of cattle in relation to an arti-
ficially imperfect state of the male sex; for oxen of cer-
tain breeds have longer horns than the oxen of other
breeds, relatively to the length of the horns in both the
bulls and cows of these same breeds. Hence I can sce
no great difficulty in any character becoming correlated
with the sterile condition of certain members of insect-
communities: the difficulty lies in understanding how

358 OBJECTIONS TO THE THEORY ([Cuap. VIII.

such correlated modifications of structure could have
been slowly accumulated by natural selection.

This difficulty, though appearing insuperable, is
lessened, or, as I believe, disappears, when it is remem-
bered that selection may be applied to the family, as
well as to the individual, and may thus gain the desired
end. Breeders of cattle wish the flesh and fat to be
well marbled together: an animal thus characterised
has been slaughtered, but the breeder has gone with
confidence to the same stock and has succeeded. Such
faith may be placed in the power of selection, that a
breed of cattle, always yielding oxen with extraordi-
narily long horns, could, it is probable, be formed by
carefully watching which individual bulls and cows,
when matched, produced oxen with the longest horns;
and yet no ox would ever have propagated its kind.
Here is a better and real illustration: according to M.
Verlot, some varieties of the double annual Stock from
having been long and carefully selected to the right
degree, always produce a large proportion of seedlings
bearing double and quite sterile flowers; but they like-
wise yield some single and fertile plants. These latter,
by which alone the variety can be propagated, may be
compared with the fertile male and female ants, and the
double sterile plants with the neuters of the same com-
munity. As with the varieties of the stock, so with so-
cial insects, selection has been applied to the family, and
not to the individual, for the sake of gaining a service-
able end. Hence we may conclude that slight modi-
fications of structure or of instinct, correlated with
the sterile condition of certain members of the com-
munity, have proved advantageous: consequently the
fertile males and females have flourished, and trans-

Cuap. VIIL.] OF NATURAL SELECTION, 859

mitted to their fertile offspring a tendency to produce
sterile members with the same modifications. This
process must have been repeated many times, until
that prodigious amount of difference between the fer-
tile and sterile females of the same species has been pro-
duced, which we see in many social insects.

But we have not as yet touched on the acme of the
difficulty; namely, the fact-that the neuters of several
ants differ, not only from the fertile females and males,
but from each other, sometimes to an almost incredible
degree, and are thus divided into two or even three
castes. The castes, moreover, do not commonly gradu-
ate into each other, but are perfectly well defined; be-
ing as distinct from each other as are any two species of
the same genus, or rather as any two genera of the same
family. Thus in Eciton, there are working and soldier
neuters, with jaws and instincts extraordinarily ditf-
ferent: in Cryptocerus, the workers of one caste alone
carry a wonderful sort of shield on their heads, the use
of which is quite unknown: in the Mexican Myrmeco-
cystus, the workers of one caste never leave the nest;
they are fed by the workers of another caste, and they
have an enormously developed abdomen which secretes a
sort of honey, supplying the place of that excreted by
the aphides, or the domestic cattle as they may be called,
which our European ants guard and imprison.

It will indeed be thought that I have an overweening
confidence in the principle of natural selection, when I
do not admit that such wonderful and well-established
facts at once annihilate the theory. In the simpler case
of neuter insects all of one caste, which, as I believe,
have been rendered different from the fertile males and

females through natural selection, we may conclude
25

360 OBJECTIONS TO THE THEORY [Cuap. VIII.

from the analogy of ordinary variations, that the succes-
sive, slight, profitable modifications did not first arise
in all the neuters in the same nest, but in some few
alone; and that by the survival of the communities with
females which produced most neuters having the ad-
vantageous modification, all the neuters ultimately came
to be thus characterised. According to this view we
ought occasionally to find in the same nest neuter in-
sects, presenting gradations of structure; and this we
do find, even not rarely, considering how few neuter
insects out of Europe have been carefully examined.
Mr. F. Smith has shown that the neuters of several
British ants differ surprisingly from each other in size
and sometimes in colour; and that the extreme forms
can be linked together by individuals taken out of the
same nest: I have myself compared perfect gradations of
this kind. It sometimes happens that the larger or the
smaller sized workers are the most numerous; or that
both large and small are numerous, whilst those of
an intermediate size are scanty in numbers. Formica
flava has larger and smaller workers, with some few
of intermediate size; and, in this species, as Mr. F.
Smith has observed, the larger workers have simple eyes
(ocelli), which though small can be plainly distinguished,
whereas the smaller workers have their ocelli rudimen-
tary. Having carefully dissected several specimens of
these workers, I can affirm that the eyes are far more
rudimentary in the smaller workers than can be ac- |
counted for merely by their proportionally lesser size;
and I fully believe, though I dare not assert so posi-
tively, that the workers of intermediate size have their
ocelli in an exactly intermediate condition. So that
here we have two bodies of sterile workers in the same

Cuap. VII] OF NATURAL SELECTION. 361

nest, differing not only in size, but in their organs of
vision, yet connected by some few members in an inter-
mediate condition. I may digress by adding, that if the
smaller workers had been the most useful to the com-
munity, and those males and females had been continu-
ally selected, which produced more and more of the
smaller workers, until all the workers were in this con-
dition; we should then have had a species of ant with
neuters in nearly the same condition as those of Myr-
mica. For the workers of Myrmica have not even rudi-
ments of ocelli, though the male and female ants of this
genus have well-developed ocelli.

I may give one other case: so confidently did I ex-
pect occasionally to find gradations of important struc-
tures between the different castes of neuters in the same
species, that I gladly availed myself of Mr. F. Smith’s
offer of numerous specimens from the same nest of the
driver ant (Anomma) of West Africa. The reader will
perhaps best appreciate the amount of difference in
these workers, by my giving not the actual measure-
ments, but a strictly accurate illustration: the difference
was the same as if we were to see a set of workmen
building a house, of whom many were five feet four
inches high, and many sixteen feet high; but we must
in addition suppose that the larger workmen had heads
four instead of three times as big as those of the smaller
men, and jaws nearly five times as big. The jaws, more-
over, of the working ants of the several sizes differed
wonderfully in shape, and in the form and number of
the teeth. But the important fact for us is, that,
though the workers can be grouped into castes of dif-
ferent sizes, yet they graduate insensibly into each
other, as does the widely-different structure of their

362 OBJECTIONS TO NATURAu SHLECTION. [Caap. VIIL

jaws. I speak confidently on this latter point, as Sir J.
Lubbock made drawings for me, with the camera lucida,
of the jaws which I dissected from the workers of the
several sizes. Mr. Bates, in his interesting ‘ Naturalist
on the Amazons,’ has described analogous cases.

With these facts before me, I believe that natural
selection, by acting on the fertile ants or parents, could
form a species which should regularly produce neuters,
all of large size with one form of jaw, or all of small
size with widely different jaws; or lastly, and this is
the greatest difficulty, one set of workers of one size
and structure, and simultaneously another set of workers
of a different size and structure;—a graduated series
having first been formed, as in the case of the driver
ant, and then the extreme forms having been produced
in greater and greater numbers, through the survival of
the parents which generated them, until none with an
intermediate structure were produced.

An analogous explanation has been given by Mr.
Wallace, of the equally complex case, of certain Malayan
Butterflies regularly appearing under two or even three
distinct female forms; and by Fritz Miiller, of certain
Brazilian crustaceans likewise appearing under two wide-
ly distinct male forms. But this subject need not here
be discussed.

I have now explained how, as I believe, the wonder-
ful fact of two distinctly defined castes of sterile workers
existing in the same nest, both widely different from
each other and from their parents, has originated. We
can see how useful their production may have been to a
social community of ants, on the same principle that
the division of labour is useful to civilised man. Ants,
however, work by inherited instincts and by inherited

Cuap. VIL] SUMMARY. 363

organs or tools, whilst man works by acquired knowl-
edge and manufactured instruments. But I must con-
fess, that, with all my faith in natural selection, I should
never have anticipated that this principle could have
been efficient in so high a degree, had not the case of
these neuter insects led me to this conclusion. I have,
therefore, discussed this case, at some little but wholly
insufficient length,in order to showthe power of natural
selection, and likewise because this is by far the most
serious special difficulty which my theory has encoun-
tered. The case, also, is very interesting, as it proves
that with animals, as with plants, any amount of modi-
fication may be effected by the accumulation of numer-
ous, slight, spontaneous variations, which are in any way
profitable, without exercise or habit having been brought
into play. For peculiar habits confined to the workers
or sterile females, however long they might be followed,
could not possibly affect the males and fertile females,
which alone leave descendants. I am surprised that
no one has hitherto advanced this demonstrative case
of neuter insects, against the well-known doctrine of in-
herited habit, as advanced by Lamarck.

Summary.

I have endeavoured in this chapter briefly to show
that the mental qualities of our domestic animals vary,
and that the variations are inherited. Still more briefly
I have attempted to show that instincts vary slightly in
a state of nature. No one will dispute that instincts
are of the highest importance to each animal. There-
fore there is no real difficulty, under changing condi-
tions of life,in natural selection accumulating to any ex-

364 SUMMARY. [Cuap. VIIL

tent slight modifications of instinct which are in any
way useful. In many cases habit or use and disuse have
probably come into play. I do not pretend that the
facts given in this chapter strengthen in any great de-
gree my theory; but none of the cases of difficulty, to
the best of my judgment, annihilate it. On the other
hand, the fact that instincts are not always absolutely
perfect and are liable to mistakes:—that no instinct can
be shown to have been produced for the good of other
animals, though animals take advantage of the instincts
of others;—that the canon in natural history, of “ Na-
tura non facit saltum,” is applicable to instincts as well
as to corporeal structure, and is plainly explicable on
the foregoing views, but is otherwise inexplicable,
—all tend to corroborate the theory of natural selec-
tion.

This theory is also strengthened by some few other
facts in regard to instincts; as by that common case of
closely allied, but distinct species, when inhabiting dis-
tant parts of the world and living under considerably
different conditions of life, yet often retaining nearly
the same instincts. For instance, we can understand,
on the principle of inheritance, how it is that the thrush
of tropical South America lines its nest with mud, in
the same peculiar manner as does our British thrush;
howit is that the Hornbills of Africa and India have the
same extraordinary instinct of plastering up and im-
prisoning the females in a hole in a tree, with only a
small hole left in the plaster through which the males
feed them and their young when hatched; how it is that
the male wrens (Troglodytes) of North America build
“ cock-nests,” to roost in, like the males of our Kitty-
wrens,—a habit wholly unlike that of any other known

Cuap. VIII] SUMMARY. 365

bird. Finally, it may not be a logical deduction, but
to my imagination it is far more satisfactory to look at
such instincts as the young cuckoo ejecting its foster-
brothers,—ants making slaves,—the larve of ichneu-
monide feeding within the live bodies of caterpillars,—
not as specially endowed or created instincts, but as
small consequences of one general law leading to the
advancement of all organic beings,—namely, multiply,
vary, let the strongest live and the weakest die.

(7)

END OF VOLUME L

THE ORIGIN OF SPECIES
VOL. II

CONTENTS OF VOL. IL

CHAPTER IX,

HYBRIDISM.

Distinction between the sterility of first crosses and of hybrids—
Sterility various in degree, not universal, affected by close in-
terbreeding, removed by domestication—Laws governing the
sterility of hybrids—Sterility not a special endowment, but
incidental on other differences, not accumulated by natural
selection—Causes of the sterility of first crosses and of hybrids
—Parallelism between the effects of changed conditions of life
and of crossing—Dimorphism and trimorphism—Fertility of
varieties when crossed and of their mongrel offspring not uni-
versal—Hybrids and mongrels compared independently of their
fertility—Summary . . . . «. « « Pagel

CHAPTER X.

ON THE IMPERFECTION OF THE GEOLOGICAL RE@ORD.

On the absence of intermediate varieties at the present day—On
the nature of extinct intermediate varieties; on their number—
On the lapse of time, as inferred from the rate of denudation -
and of deposition—On the lapse of time as estimated by years
—On the poorness of our paleontological collections—On the
intermittence of geological formations—On the denudation of
granitic areas—On the absence of intermediate varieties in any
one formation—On the sudden appearance of groups of species
—On their sudden appearance in the lowest known fossiliferous

strata—Antiquity of the habitable earth . . . . 48
iii

av

CONTENTS,

CHAPTER XI.

ON THE GEOLOGICAL SUCCESSION OF ORGANIC BEINGS.

On the slow and successive appearance of new species—On their

different rates of change—Species once lost do no* reappear—
Groups of species follow the same general rules in their ap-
pearance and disappearance as do single species—On extinction
—On simultaneous changes in the forms of life throughout the
world—On the affinities of extinct species to each other and to
living species—On the state of development of ancient forms—
On the succession of the same types within the same areas—
Summary of preceding and present chapter » « Page 89

CHAPTER XII.

GEOGRAPHICAL DISTRIBUTION.

Present distribution cannot be accounted for by differences in

physical conditions—Importance of barriers—Affinity of the
productions of the same continent—Centres of creation—Means
of dispersal by changes of climate and of the level of the land.
and by occasional means—Dispersal during the Glacial period
—Alternate Glacial periods in the North and South . . 129

CHAPTER XIII.

GEOGRAPHICAL DISTRIBUTION—continued.

Distribution of fresh-water productions—On the inhabitants of

oceanic islands—Absence of Batrachians and of terrestrial Mam-
mals—On the relation of the inhabitants of islands to those of
the nearest mainland—On colonisation from the nearest source
with subsequent modification—Summary of the last and present
chapter . F . . . . ; . . 7 - 171

CONTENTS. v

CHAPTER XIV.

MUTUAL AFFINITIES OF ORGANIC BEINGS: MORPHOLOGY:
EMBRYOLOGY : RUDIMENTARY ORGANS.

CLASSIFICATION, groups subordinate to groups—Natural system—
Rules and difficulties in classification, explained on the theory
of descent with modification—Classification of varieties—De-
scent always used in classification—Analogical or adaptive char-
acters —Affinities, general, complex, and radiating—Extinction
separates and defines groups—Morpuovoey, between members
of the same class, between parts of the same individual—
EmsBryotogy, laws of, explained by variations not super-
vening at an early age, and being inherited at a correspond-
ing age—RubDIMENTaRY oRGANS; their origin explained—Sum-
Marys kw . « «Page 202

CHAPTER XV.

BECAPITULATION AND CONCLUSION,

Recapitulation of the objections to the theory of Natural Selection
—Recapitulation of the general and special circumstances in its
favour—Causes of the general belief in the immutability of
species—How far the theory of Natural Selection may be ex-
tended—Effects of its adoption on the study of Natural History
—Concluding remarks 3 ce ROT

Giossary or Scientiric TERMS é . . cd . 307

INDEX . . . ° . e ° e ° r ° . 323

ORIGIN OF SPECIES.

CHAPTER IX.
HYBRIDISM.

Distinction between the sterility of first crosses and of hybrids—
Sterility various in degree, not universal, affected by close in-
terbreeding, removed by domestication—Laws governing the
sterility of hybrids—Sterility not a special endowment, but
incidental on other differences, not accumulated by natural
selection—Causes of the sterility of first crosses and of hybrids
—Parallelism between the effects of changed conditions of life
and of crossing—Dimorphism and trimorphism—Fertility of
varieties when crossed and of their mongrel offspring not uni-
versal—Hybrids and mongrels compared independently of their
fertility—Summary.

Tue view commonly entertained by naturalists is
that species, when intercrossed, have been specially en-
dowed with sterility, in order to prevent their confusion.
This view certainly seems at first highly probable, for
species living together could hardly have been kept dis-
tinct had they been capable of freely crossing. The
subject is in many ways important for us, more especial-
Ay as the sterility of species when first crossed, and that

‘of their hybrid offspring, cannot have been acquired, as
shall show, by the preservation n of successive profitable ©

2 HYBRIDISM. [Cuap. IX.

degrees of sterility. It is an incidental result—of dif-

ferences in the reproductive systems. of the parent-
species.

In treating this subject, two classes of facts, to a
large extent fundamentally different, have generally
been confounded; namely, the sterility of species when
first crossed, and the sterility of the hybrids produced
from them.

Pure species have of course their organs of reproduc-
tion in a perfect condition, yet when intercrossed they
produce either few or no offspring. Hybrids, on the
other hand, have their reproductive organs functionally
impotent, as may be clearly seen in the state of the
male element in both plants and animals; though the
formative organs themselves are perfect in structure, as
far as the microscope reveals. In the first case the two
sexual elements which go to form the embryo are per-
fect; in the second case they are either not at all de-
veloped, or are imperfectly developed. This distinc-
tion is important, when the cause of the sterility, which
is common to the two cases, has to be considered. The
distinction probably has been slurred over, owing to the
sterility in both cases being looked on as a special en-
dowment, beyond the province of our reasoning
powers.

The fertility of varieties, that is of the forms known
or believed to be descended from common parents, when
crossed, and likewise the fertility of their mongrel off-
spring, is, with reference to my theory, of equal im-
portance with the sterility of species; for it seems to
make a broad and clear distinction between varieties
and species.

Degrees of Sterility—First, for the sterility of spe-

Cuap. 1X,] DEGREES OF STERILITY. 3

cies when crossed and of their hybrid offspring. It is
impossible to study the several memoirs and works of
those two conscientious and admirable observers, Kél-
reuter and Gartner, who almost devoted their lives to
this subject, without being deeply impressed with the
high generality of some degree of sterility. Kdélreuter
makes the rule universal; but then he cuts the knot,
for in ten cases in which he found two forms, considered
by most authors as distinct species, quite fertile to-
gether, he unhesitatingly ranks them as varieties. Girt-
ner, also, makes the rule equally universal; and he dis-
putes the entire fertility of Kélreuter’s ten cases. But
in these and in many other cases, Gartner is obliged
carefully to count the seeds, in order to show. that there
is any degree of sterility. He always compares the
maximum number of seeds produced by two species
when first crossed, and the maximum produced by their
hybrid offspring, with the average number produced by
both pure parent-species in a state of nature. But
causes of serious error here intervene: a plant, to be
hybridised, must be castrated, and, what is often more
important, must be secluded in order to prevent pollen
being brought to it by insects from other plants.
Nearly all the plants experimented on by Girtner were
potted, and were kept in a chamber in his house. That
these processes are often injurious to the fertility of a
plant cannot be doubted; for Gartner gives in his table
about a score of cases of plants which he castrated, and
artificially fertilised with their own pollen, and (ex-
cluding all cases such as the Leguminose, in which there
is an acknowledged difficulty in the manipulation)
half of these twenty plants had their fertility in some
degree impaired. Moreover, as Gartner repeatedly
26

4 HYBRIDISM. (Cap. IX.

crossed some forms, such as the common red and
blue pimpernels (Anagallis arvensis and ccerulea),
which the best botanists rank as varieties, and found
them absolutely sterile, we may doubt whether many
species are really so sterile, when intercrossed, as he be-
lieved.

It is certain, on the one hand, that the sterility of
various species when crossed is so different in degree
and graduates away so insensibly, and, on the other
hand, that the fertility of pure species is so easily
affected by various circumstances, that for all practical
purposes it is most difficult to say where perfect fertility
ends and sterility begins. I think no better evidence
of this can be required than that the two most ex-
perienced observers who have ever lived, namely Kél-
reuter and Gartner, arrived at diametrically opposite
conclusions in regard to some of the very same forms.
It is also most instructive to compare—but I have not
space here to enter on details—the evidence advanced
by our best botanists on the question whether certain
doubtful forms should be ranked as species or varieties,
with the evidence from fertility adduced by different
hybridisers, or by the same observer from experiments
made during different years. It can thus be shown
that neither sterility nor fertility affords any certain
distinction between species and varieties. The evidence
from this source graduates away, and is doubtful in the
same degree as is the evidence derived from other con-
stitutional and structural differences.

In regard to the sterility of hybrids in successive
generations; though Gartner was enabled to rear some
hybrids, carefully guarding them from a cross with
either pure parent, for six or seven, and in one case for

Cuar. IX] DEGREES OF STERILITY. 5

ten generations, yet he asserts positively that their fer-
tility never increases, but generally decreases greatlyand
suddenly. With respect to this decrease, it may first be
noticed that when any deviation in structure or constitu-
tion is common to both parents, this is often transmitted
in an augmented degree to the offspring; and bothsexual
elements in hybrid plants are already affected in some
degree. But I believe that their fertility has been di-
minished in nearly all these cases by an independent
cause, namely, by too close interbreeding. I have made
so many experiments and collected so many facts, show-
ing on the one hand that an occasional cross with a dis-
tinct individual or variety increases the vigour and fer-
tility of the offspring, and on the other hand that very
close interbreeding lessens their vigour and fertility,
that I cannot doubt the correctness of this conclusion.
Hybrids are seldom raised by experimentalists in great
numbers; and as the parent-species, or other allied
hybrids, generally grow in the same garden, the visits of
insects must be carefully prevented during the
flowering season: hence hybrids, if left to themselves,
will generally be fertilised during each generation by
pollen from the same flower; and this would probably
be injurious to their fertility, already lessened by their
hybrid origin. I am strengthened in this conviction
by a remarkable statement repeatedly made by Gartner,
namely, that if even the less fertile hybrids be artificially
fertilised with hybrid pollen of the same kind, their
fertility, notwithstanding the frequent ill effects from
manipulation, sometimes decidedly increases, and goes
on increasing. Now, in the process of artificial fertilisa-
tion, pollen is as often taken by chance (as I know from
my own experience) from the anthers of another flower,

6 HYBRIDISM. [Cuap. IX.

as from the anthers of the flower itself which is to be fer-
tilised; so that a cross between two flowers, though
probably often on the same plant, would be thus effected.
Moreover, whenever complicated experiments are in
progress, so careful an observer as Gartner would have
castrated his hybrids, and this would have ensured in
each generation a cross with pollen from a distinct
flower, either from the same plant or from another
plant of the same hybrid nature. And thus, the strange
fact of an increase of fertility in the successive genera-
tions of artificially fertilised hybrids, in contrast with
those spontaneously self-fertilised, may, as I believe, be
accounted for by too close interbreeding having been
avoided.

Now let us turn to the results arrived at by a third
most experienced hybridiser, namely, the Hon. and Rev.
W. Herbert. He is as emphatic in his conclusion that
some hybrids are perfectly fertile—as fertile as the pure
parent-species—as are Kélreuter and Gartner that some
degree of sterility between distinct species is a universal
law of nature. He experimented on some of the very
same species as did Gartner. The difference in their
results may, I think, be in part accounted for by
Herbert’s great horticultural skill, and by his having
hot-houses at his command. Of his many important
statements I will here give only a single one as an ex-
ample, namely, that “every ovule in a pod of Crinum
capense fertilised by C. revolutum produced a plant,
which I never saw to occur in a case of its natural fecun-
dation.” So that here we have perfect or even more
than commonly perfect fertility, in a first cross between
two distinct species.

This case of the Crinum leads me to refer to a

Cuap, [X.] DEGREES OF STERILITY. q

singular fact, namely, that-individual plants of certain
species of Lobelia, Verbascum and Passiflora, can easily
be fertilised by pollen from a distinct species, but not
by pollen from the same plant, though this pollen can
be proved to be perfectly sound by fertilising other
plants or species. In the genus Hippeastrum, in Cory-
dalis as shown by Professor Hildebrand, in various or-
chids as shown by Mr. Scott and Fritz Miiller, all the
individuals are in this peculiar condition. So that with
some species, certain abnormal individuals, and in other
species all the individuals, can actually be hybridised
much more readily than they can be fertilised by pollen
from the same individual plant! ‘To give one instance,
a bulb of Hippeastrum aulicum produced four flowers;
three were fertilised by Herbert with their own pollen,
and the fourth was subsequently fertilised by the pollen
of a compound hybrid descended from three distinct
species: the result was that “the ovaries of the three
first flowers soon ceased to grow, and after a few days
perished entirely, whereas the pod impregnated by the
pollen of the hybrid made vigorous growth and rapid
progress to maturity, and bore good seed, which vege-
tated freely.” Mr. Herbert tried similar experiments
during many years, and always with the same result.
These cases serve to show on what slight and mysterious
causes the lesser or greater fertility of a species some-
times depends.

The practical experiments of horticulturists, though
not made with scientific precision, deserve some notice.
It is notorious in how complicated a manner the species
of Pelargonium, Fuchsia, Calceolaria, Petunia, Rhodo-
dendron, &c., have been crossed, yet many of these
hybrids seed freely. For instance, Herbert asserts that

8 -HYBRIDISM. [Cuap. 1X.

a hybrid from Calceolaria integrifolia and plantaginea,
species most widely dissimilar in general habit, “ re-
produces itself as perfectly as if it had been a natural
species from the mountains of Chili.” I have taken
some pains to ascertain the degree of fertility of some
of the complex crosses of Rhododendrons, and I am
assured that many of them are perfectly fertile. Mr.
C. Noble, for instance, informs me that he raises stocks
for grafting from a hybrid between Rhod. ponticum and
catawbiense, and that this hybrid “ seeds as freely as it
is possible to imagine.” Had hybrids when fairly
treated, always gone on decreasing in fertility in each
successive generation, as Gartner believed to be the
case, the fact would have been notorious to nursery-
men. Horticulturists raise large beds of the same hy-
brid, and such alone are fairly treated, for by insect
agency the several individuals are allowed to cross freely
with each other, and the injurious influence of close
interbreeding is thus prevented. Any one may readily
convince himself of the efficiency of insect-agency by
examining the flowers of the more sterile kinds of hy-
brid Rhododendrons, which produce no pollen, for he
will find on their stigmas plenty of pollen brought from
other flowers.

In regard to animals, much fewer experiments have
been carefully tried than with plants. If our systematic:
arrangements can be trusted, that is, if the genera of
animals are as distinct from each other as are the genera
of plants, then we may infer that animals more widely
distinct in the scale of nature can be crossed more easily
than in the case of plants; but the hybrids themselves
are, I think, more sterile. It should, however, be borne
in mind that, owing to few animals breeding freely under

Cuap. IX.] DEGREES OF STERILITY. 9

confinement, few experiments have been fairly tried: for
instance, the canary-bird has been crossed with nine dis-
tinct species of finches, but, as not one of these breeds
freely in confinement, we have no right to expect that
the first crosses between them and the canary, or that
their hybrids, should be perfectly fertile. Again, with
respect to the fertility in successive generations of the
more fertile hybrid animals, I hardly know of an in-
stance in which two families of the same hybrid have
been raised at the same time from different parents, so
as to avoid the ill effects of close interbreeding. On the
contrary, brothers and sisters have usually been crossed
in each successive generation, in opposition to the con-
stantly repeated admonition of every breeder. And in
this case, it is not at all surprising that the inherent
sterility in the hybrids should have gone on increas-
ing.

Although I know of hardly any thoroughly well-
authenticated cases of perfectly fertile hybrid animals, I
have reason to believe that the hybrids from Cervulus
vaginalis and Reevesii, and from Phasianus colchicus
with P. torquatus, are perfectly fertile. M. Quatrefages
states that the hybrids from two moths (Bombyx cyn-
thia and arrindia) were proved in Paris to be fertile inter
se for eight generations. It has lately been asserted
that two such distinct species as the hare and rabbit,
when they can be got to breed together, produce off-
spring, which are highly fertile when crossed with one
of the parent-species. The hybrids from the common
and Chinese geese (A. cygnoides), species which are
so different that they are generally ranked in distinct
genera, have often bred in this country with either pure
parent, and in one single instance they have bred inter

10 HYBRIDISM. [Cuap. IX

se. This was effected by Mr. Eyton, who raised two
hybrids from the same parents, but from different
hatches; and from these two birds he raised no less than
eight hybrids (grandchildren of the pure geese) from one
nest. In India, however, these cross-bred geese must
be far more fertile; for I am assured by two eminently
capable judges, namely Mr. Blyth and Capt. Hutton,
that whole flocks of these crossed geese are kept in
various parts of the country; and as they are kept for
profit, where neither pure parent-species, exists, they
must certainly be highly or perfectly fertile.

With our domesticated animals, the various races
when crossed together are quite fertile; yet in many
cases they are descended from two or more wild species.
From this fact we must conclude either that the abo-
riginal parent-species at first produced perfectly fertile
hybrids, or that the hybrids subsequently reared under
domestication became quite fertile. This latter alter-
native, which was first propounded by Pallas, seems by
far the most probable, and can, indeed, hardly be
doubted. It is, for instance, almost certain that our
dogs are descended from several wild stocks; yet, with
perhaps the exception of certain indigenous domestic
dogs of South America, all are quite fertile together;
but analogy makes me greatly doubt, whether the sev-
eral aboriginal species would at first have freely bred
together and have produced quite fertile hybrids. So
again I have lately acquired decisive evidence that the
crossed offspring from the Indian humped and common
cattle are inter se perfectly fertile; and from the ob-
servations by Riitimeyer on their important osteological
differences, as well as from those by Mr. Blyth on their
differences in habits, voice, constitution, &c., these two

Cuap, IX.] DEGREES OF STERILITY. 11

forms must be regarded as good and distinct species.
The same remarks may be extended to the two chief
races of the pig. We must, therefore, either give up
the belief of the universal sterility of species when
crossed; or we must look at this sterility in animals, not
as an indelible characteristic, but as one capable of being
removed by domestication.

Finally, considering all the ascertained facts on the
intercrossing of plants and animals, it may be concluded
that some degree of sterility, both in first crosses and
in hybrids, is an extremely general result; but that it
cannot, under our present state of knowledge, be con-
sidered as absolutely universal.

x

Laws governing the Sterility of first Crosses and of
Hybrids.

We will now consider a little more in detail the laws
governing the sterility of first crosses and of hybrids.
Our chief object will be to see whether or not these
laws indicate that species have been specially endowed
with this quality, in order to prevent their crossing and
blending together in utter confusion. The following
conclusions are drawn up chiefly from Gartner’s ad-
mirable work on the hybridisation of plants. I have
taken much pains to ascertain how far they apply to
animals, and, considering how scanty our knowledge is
in regard to hybrid animals, I have been surprised to
find how generally the same rules apply to both king-
doms. :

It has been already remarked, that the degree of
fertility, both of first crosses and of hybrids, graduates
from zero to perfect fertility. It is surprising in how

12 LAWS GOVERNING THE STERILITY [Caapr. 1X

many curious ways this gradation can be shown; but
only the barest outline of the facts can here be given.
When pollen from a plant of one family is placed on
the stigma of a plant of a distinct family, it exerts no
more influence than so much inorganic dust. From
this absolute zero of fertility, the pollen of different spe-
cies applied to the stigma of some one species of the
same genus, yields a perfect gradation in the number
of seeds produced, up to nearly complete or even quite
complete fertility; and, as we have seen, in certain
abnormal cases, even to an excess of fertility, beyond
that which the plant’s own pollen produces. So in
hybrids themselves, there are some which never have
produced, and probably never would produce, even
with the pollen of the pure parents, a single fertile seed:
but in some of these cases a first trace of fertility may be
detected, by the pollen of one of the pure parent-species
causing the flower of the hybrid to wither earlier
than it otherwise would have done; and the early with-
ering of the flower is well known to be a sign of in-
cipient fertilisation. From this extreme degree of
sterility we have self-fertilised hybrids producing a
greater and greater number of seeds up to perfect fer-
tility.

The hybrids raised from two species which are very
difficult to cross, and which rarely produce any off-
spring, are generally very sterile; but the parallelism
between the difficulty of making a first cross, and the
sterility of the hybrids thus produced—two classes of
facts which are generally confounded together—is by
no means strict. There are many cases, in which two
pure species, as in the genus Verbascum, can be united
with unusual facility, and produce numerous hybrid-

Cuap. 1X.] OF FIRST CROSSES AND OF HYBRIDS. 13

offspring, yet these hybrids are remarkably sterile. On
the other hand, there are species which can be crossed
very rarely, or with extreme difficulty, but the hybrids,
when at last produced, are very fertile. Even within
the limits of the same genus, for instance in Dianthus,
these two opposite cases occur.

The fertility, both of first crosses and of hybrids, is
more easily affected by unfavourable conditions, than
is that of pure species. But the fertility of first crosses
is likewise innately variable; for it is not always the
same in degree when the same two species are crossed
under the same circumstances; it depends in part upon
the constitution of the individualswhich happen to have
been chosen for the experiment. So it is with hybrids,
for their degree of fertility is often found to differ
greatly in the several individuals raised from seed out
of the same capsule and exposed to the same condi-
tions.

By the term systematic affinity is meant, the general
resemblance between species in structure and constitu-
tion. Now the fertility of first crosses, and of the
hybrids produced from them, is largely governed by
their systematic affinity. This is clearly shown by hy-
brids never having been raised between species ranked
by systematists in distinct families; and on the other
hand, by very closely allied species generally uniting
with facility. But the correspondence between syste-
matic affinity and the facility of crossing is by no means
strict. A multitude of cases could be given of very
closely allied species which will not unite, or only with
extreme difficulty; and on the other hand of very dis-
tinct species which unite with the utmost facility. In
the same family there may be a genus, as Dianthus, in

14 LAWS GOVERNING THE STERILITY [Cuar. IX.

which very many species can most readily be crossed;
and another genus, as Silene, in which the most perse-
vering efforts have failed to produce between extremely
close species a single hybrid. Even within the limits
of the same genus, we meet with this same difference;
for instance, the many species of Nicotiana have been
more largely crossed than the species of almost any other
genus; but Gartner found that N. acuminata, which
is not a particularly distinct species, obstinately failed
to fertilise, cr to be fertilised by no less than eight other
species of Nicotiana. Many analogous facts could be
given.

No one has been able to point out what kind or what
amount of difference, in any recognisable character, is
sufficient to prevent two species crossing. It can be
shown that plants most widely different in habit and
general appearance, and having strongly marked differ-
ences in every part of the flower, even in the pollen, in
the fruit, and in the cotyledons, can be crossed. An-
nual and perennial plants, deciduous and evergreen trees,
plants inhabiting different stations and fitted for ex-
tremely different climates, can often be crossed with
ease.

By a reciprocal cross between two species, I mean
the case, for instance, of a female-ass being first crossed
by a stallion, and then a mare by a male-ass; these two
species may then be said to have been reciprocally
crossed. There is often the widest possible difference
in the facility of making reciprocal crosses. Such cases
are highly important, for they prove that the capacity
in any two species to cross is often completely independ-
ent of their systematic affinity, that is of any differ-
ence in their structure or constitution, excepting in

Cuap, IX.] OF FIRST CROSSES AND OF HYBRIDS. 15

their reproductive systems. he diversity of the result
in reciprocal crosses between the same two species was
long ago observed by K6lreuter. To give an instance:
Mirabilis jalapa can easily be fertilised by the pollen of
M. longiflora, and the hybrids thus produced are suffi-
ciently fertile; but Kolreuter tried more than two hun-
dred times, during eight following years, to fertilise
reciprocally M. longiflora with the pollen of M. jalapa,
and utterly failed. Several other equally striking cases
could be given. Thuret has observed the same fact
with certain sea-weeds or Fuci. Gartner, moreover,
found that this difference of facility in making recipro-
cal crosses is extremely common in a lesser degree. He
has observed it even between closely related forms (as
Matthiola annua and gilabra) which many botanists
rank only as varieties. It is also a remarkable fact, that
hybrids raised from reciprocal crosses, though of course
compounded of the very same two species,.the one spe-
cies having first been used as the father and then as
the mother, though they rarely differ in external char-
acters, yet generally differ in fertility in a small, and oc-
casionally in a high degree.

Several other singular rules could be given from:
Gartner: for instance, some species have a remarkable
power of crossing with other species; other species of
the same genus have a remarkable power of impressing
their likeness on their hybrid offspring; but these two
powers do not at all necessarily go together. There are
certain hybrids which, instead of having, as is usual,
an intermediate character between their two parents,
always closely resemble one of them; and such hybrids,
though externally so like one of their pure parent-
species, are with rare exceptions extremely sterile. So

16 LAWS GOVERNING THE STERILITY [Cuap. IX.

again amongst hybrids which are usually intermediate
in structure between their parents, exceptional and
abnormal individuals sometimes are born, which closely
resemble one of their pure parents; and these hybrids
are almost always utterly sterile, even when the other
hybrids raised from seed from the same capsule have a
considerable degree of fertility. These facts show how
completely the fertility of a hybrid may be independent
of its external resemblance to either pure parent.

Considering the several rules now given, which
govern the fertility of first crosses and of hybrids, we
see that when forms, which must be considered as good
and distinct species, are united, their fertility graduates
from zero to perfect fertility, or even to fertility under
certain conditions in excess; that their fertility, besides
being eminently susceptible to favourable and unfa-
vourable conditions, is innately variable; that it is by
no means always the same in degree in the first cross
and in the hybrids produced from this cross; that the
fertility of hybrids is not related to the degree in which
they resemble in external appearance either parent; and
lastly, that the facility of making a first cross between
any two species is not always governed by their syste-
matic affinity or degree of resemblance to each other.
This latter statement is clearly proved by the differ-
ence in the result of reciprocal crosses between the same
two species, for, according as the one species or the
other is used as the father or the mother, there is gen-
erally some difference, and occasionally the widest pos-
sible difference, in the facility of effecting an union.
The hybrids, moreover, produced from reciprocal crosses
often differ in fertility.

Now do these complex and singular rules indicate

Cuap. IX.] OF FIRST CROSSES AND OF HYBRIDS. 17

that species have been endowed with sterility simply
to prevent their becoming confounded in nature? I
think not. For why should the sterility be so extremely
different in degree, when various species are crossed,
all of which we must suppose it would be equally im-
portant to keep from blending together? Why should
the degree of sterility be innately variable in the in-
dividuals of the same species? Why should some spe-
cies cross with facility, and yet produce very sterile
hybrids; and other species cross with extreme difficulty,
and yet produce fairly fertile hybrids? Why should
there often be so great a difference in the result of a re-
ciprocal cross between the same two species? Why,
it may even be asked, has the production of hybrids
been permitted? To grant to species the special power
of producing hybrids, and then to stop their further
propagation by different degrees of sterility, not strictly
related to the facility of the first union between their
parents, seems a strange arrangement.

The foregoing rules and facts, on the other hand,
appear to me clearly to indicate that the sterility both
of first crosses and of hybrids is simply incidental or
dependent on unknown differences in their reproductive
systems; the differences being of so peculiar and lim-
ited a nature, that, in reciprocal crosses between the
same two species, the male sexual element of the one
will often freely act on the female sexual element of the
other, but not in a reversed direction. It will be ad-
visable to explain a little more fully by an example what
I mean by sterility being incidental on other differences,
and not a specially endowed quality. As the capacity
of one plant to be grafted or budded on another is un-
important for their welfare in a state of nature, I pre-

18 LAWS GOVERNING THE STERILITY [Cuap. 1X.

sume that no one will suppose that this capacity is a
specially endowed quality, but will admit that it is inci-
dental on differences in the laws of growth of the two
plants. We can sometimes see the reason why one tree
will not take on another, from differences in their rate of
growth, in the hardness of their wood, in the period of
the flow or nature of their sap, &c.; but in a multitude
of cases we can assign no reason whatever. Great di-
versity in the size of two plants, one being woody and
the other herbaceous, one being evergreen and the other
deciduous, and adaptation to widely different climates,
do not always prevent the two grafting together. As in
hybridisation, sowith grafting, the capacity is limited by
systematic affinity, for no one has been able to graft
together trees belonging to quite distinct families; and,
on the other hand, closely allied species, and varieties
of the same species, can usually, but not invariably, be
grafted with ease. But this capacity, as in hybridisation,
is by no means absolutely governed by systematic
affinity. Although many distinct genera within the
same family have been grafted together, in other cases
species of the same genus will not take on each other.
The pear can be grafted far more readily on the quince,
which is ranked as a distinct genus, than on the ap-
ple, which is a member of the same genus. Even dif-
ferent varieties of the pear take with different de-
grees of facility on the quince; so do different varie-
ties of the apricot and peach on certain varieties of the
plum.

As Gartner found that there was sometimes an
innate difference in different individuals of the same
two species in crossing; so Sageret believes this to be
the case with different individuals of the same two spe-

Cuap. 1X.] OF FIRST CROSSES AND OF HYBRIDS. 19

cies in being grafted together. As in reciprocal crosses,
the facility of effecting an union is often very far from
equal, so it sometimes is in grafting; the common goose-
berry, for instance, cannot be grafted on the currant,
whereas the currant will take, though with difficulty, on
the gooseberry.

We have seen that the sterility of hybrids, which
have their reproductive organs in an imperfect con-
dition, is a different case from the difficulty of uniting
two pure species, which have their reproductive organs
perfect; yet these two distinct classes of cases run to
a large extent parallel. Something analogous occurs
in grafting; for Thouin found that three species of
Robinia, which seeded freely on their own roots, and
which could be grafted with no great difficulty on a
fourth species, when thus grafted were rendered barren.
On the other hand, certain species of Sorbus, when
grafted on other species yielded twice as much fruit as
when on their own roots. We are reminded by this
latter fact of the extraordinary cases of Hippeastrum,
Passiflora, &c., which seed much more freely when fertil-
ised with the pollen of a distinct species, than when
fertilised with pollen from the same plant.

We thus see, that, although there is a clear and great
difference between the mere adhesion of grafted stocks,
and the union of the male and female elements in the
act of reproduction, yet that there is a rude degree of
parallelism in the results of grafting and of crossing dis-
tinct species. And as we must look at the curious and
complex laws governing the facility with which trees can
be grafted on each other as incidental on unknown differ-
ences in their vegetative systems, so I believe that the

still more complex laws governing the facility of first
27

20 CAUSES OF THE STERILITY (Cuap. IX,

crosses are incidental on unknown differences in their
reproductive systems. These differences in both cases,
follow to a certain extent, as might have been expected,
systematic affinity, by which term every kind of resem-
blance and dissimilarity between organic beings is at-
tempted to be expressed. The facts by no means seem
to indicate that the greater or lesser difficulty of either
grafting or crossing various species has been a special
endowment; although in the case of crossing, the diffi-
culty is as important for the endurance and stability of
specific forms, as in the case of grafting it is unimpor-
tant for their welfare.

Origin and Causes of the Sterility of first Crosses
and of Hybrids.

_ At one time it appeared to me de as it has to
might have been slowly acquired near the he natural
selection of slightly lessened degrees of fertility, “Which,
like any other variation, spontaneously appeared in cer-
tain individuals of one variety when crossed with those
of another variety. For it would clearly be advantage-
ous to two varieties or incipient species, if they could be’
kept from blending, on the same principle that, when
man is selecting a the same time two varieties, it is
necessary that he should keep them separate. In the
.first place, it may be remarked that species inhabiting
distinct regions are often sterile when crossed; now it
could clearly have been of no advantage to such sepa-
rated species to have been rendered mutually sterile,
and consequently this could not have been effected
through natural selection; but it may perhaps be argued,

Cuap. IX.] OF FIRST CROSSES AND OF HYBRIDS. a1

that, if a species was rendered sterile with some one com-
patriot, sterility with other species would follow as a
necessary contingency. In the second place, it is almost
as much opposed to the theory of natural selection as to
that of special creation, that in reciprocal crosses the
male element of one form should have been rendered
utterly impotent on a second form, whilst at the same
time the male element of this second form is enabled
freely to fertilise the first form; for this peculiar state
of the reproductive system could hardly have been ad-
vantageous to either species.
In considering the probability of natural selection
having come into action, in rendering species mutually
sterile, the greatest difficulty will be found to lie in the
existence of many graduated steps from slightly lessened
it would profit an Sos species, if it it were rendered
fn some slight degree sterile when crossed with its
“parent form or with some other variety; for thus fewer
~~bastardised and deteriorated offspring would be pro-
duced to ‘commingle their blood with the new species in
process of formation. But he who will take the trouble
“fo reflect on the steps by which this first degree of
sterility could be increased through natural selection
to that high degree which is common with so many
species, and which is universal with species which have
been differentiated to a generic or family rank, will
find the subject extraordinarily complex. After mature
reflection it seems to me that this could not have been
effected through natural selection. Take the case of
any two species which, when crossed, produced few and
sterile offspring; now, what is there which could favour
the survival of those individuals which happened to

22 CAUSES OF THE STERILITY [Cuap. IX,

be endowed in a slightly higher degree with mutual
infertility, and which thus approached by one small
step towards absolute sterility? Yet an advance of
this kind, if the theory of natural selection be brought to
bear, must have incessantly occurred with many species,
for a multitude are mutually quite barren. With sterile
neuter insects we have reason to believe that modifica-
tions in their structure and fertility have been slowly
accumulated by natural selection, from an advantage
having been thus indirectly given to the community to
which they belonged over other communities of the same
species; but an individual animal not belonging to a so-
cial community, if rendered slightly sterile when crossed
with some other variety, would not thus itself gain any
advantage or indirectly give any advantage to the other
individuals of the same variety, thus leading to their
preservation.

But it would be superfluous to discuss this question
in detail; for with plants we have conclusive evidence
that the sterility of crossed species must be due to some
principle, quite independent of natural selection. Both
Gartner and Kélreuter have proved that in genera in-
cluding numerous species, a series can be formed from
species which when crossed yield fewer and fewer seeds,
to species which never produce a single seed, but yet
are affected by the pollen of certain other species, for
the germen swells. It is here manifestly impossible to
select the more sterile individuals, which have already
ceased to yield seeds; so that this acme of sterility,
when the germen alone is affected, cannot have been
gained through selection; and from the laws governing
the various grades of sterility being so uniform through-
out the animal and vegetable kingdoms, we may infer

Cuap. 1X.] OF FIRST CROSSES AND OF HYBRIDS. 23

that the cause, whatever it may be, is the same or nearly
the same in all cases.

We will now look a little closer at the probable na-
ture of the differences between species which induce
sterility in first crosses and in hybrids. In the case of
first crosses, the greater or less difficulty in effecting an
union and in obtaining offspring apparently depends on
several distinct causes. There must sometimes be a
physical impossibility in the male element reaching the
ovule, as would be the case with a plant having a pistil
too long for the pollen-tubes to reach the ovarium. It
has also been observed that when the pollen of one spe-
cies is placed on the stigma of a distantly allied species,
though the pollen-tubes protrude, they do not penetrate
the stigmatic surface. Again, the male element may
reach the female element but be incapable of causing
an embryo to be developed, as seems to have been the
case with some of Thuret’s experiments on Fuci. No
explanation can be given of these facts, any more than
why certain trees cannot be grafted on others. Lastly,
an embryo may be developed, and then perish at an early
period. This latter alternative has not been sufficiently
attended to; but I believe, from observations communi-
cated to me by Mr. Hewitt, who has had great experience
in hybridising pheasants and fowls, that the early death
of the embryo is a very frequent cause of sterility in
first crosses. Mr. Salter has recently given the results
of an examination of about 500 eggs produced from
various crosses between three species of Gallus and their
hybrids; the majority of these eggs had been fertilised;
and in the majority of the fertilised eggs, the embryos
had either been partially developed and had then per-

94 CAUSES OF THE STERILITY (Cuap. 1X,

ished;* G#~had become nearly mature, but the young
chickens had been unable to break through the shell.
Of the chickens which were born, more than four-fifths
died within the first few days, or at latest weeks, “ with-
out any obvious cause, apparently from mere inability
to live;” so that from the 500 eggs only twelve chick-
ens were reared. With plants, hybridised embryos prob-
ably often perish in a like manner; at least it is known
that hybrids raised from very distinct species are some-
times weak and dwarfed, and perish at an early age;
of which fact Max Wichura has recently given some
striking cases with hybrid willows. It may be here
worth noticing that in some cases of parthenogenesis,
the embryos within the eggs of silk moths which had
not been fertilised, pass through their early stages of
development and then perish like the embryos pro-
duced by a cross between distinct species. Until becom-
ing acquainted with these facts, I was unwilling to be-
lieve in the frequent early death of hybrid embryos; for
hybrids, when once born, are generally healthy and long-
lived, as we see in the case of the common mule. Hy-
brids, however, are differently circumstanced before
and after birth: when born and living in a country
where their two parents live, they are generally placed
under suitable conditions of life. But a hybrid par-
takes of only half of the nature and constitution of its
mother; it may therefore before birth, as long as it is
nourished within its mother’s womb, or within the egg
or seed produced by the mother, be exposed to condi-
tions in some degree unsuitable, and consequently be
liable to perish at an early period; more especially as all
very young beings are eminently sensitive to injurious
or unnatural conditions of life. But after all, the cause

Cuap. 1X.] OF FIRST CROSSES AND OF HYBRIDS. 25

more probably lies in some imperfection in the original
act of impregnation, causing the embryo to be imper-
fectly developed, rather than in the conditions to which
it is subsequently exposed.

In regard to the sterility of hybrids, in which the
sexual elements are imperfectly developed, the case is
somewhat different. I have more than once alluded to
a large body of facts showing that, when animals and
plants are removed from their natural conditions, they
are extremely liable to have their reproductive systems
seriously affected. This, in fact, is the great bar to
the domestication of animals. Between the sterility
thus superinduced and that of hybrids, there are many
points of similarity. In both cases the sterility is inde-
pendent of general health, and is often accompanied
by excess of size or great luxuriance. In both cases the
sterility occurs in various degrees; in both, the male
element is the most lable to be affected; but some-
times the female more than the male. In both, the
tendency goes to a certain extent with systematic affin-
ity, for whole groups of animals and plants are rendered
impotent by the same unnatural conditions; and whole
groups of species tend to produce sterile hybrids. On
the other hand, one species in a group will sometimes
resist great changes of conditions with unimpaired fer-
tility; and certain species in a group will produce un-
usually fertile hybrids. No one can tell, till he tries,
whether any particular animal will breed under confine-
ment, or any exotic plant seed freely under culture;
nor can he tell till he tries, whether any two species
of a genus will produce more or less sterile hybrids.
Lastly, when organic beings are placed during several
generations under conditions not natural to them,

26 CAUSES OF THE STERILITY [Cuap. IX.

they are extremely liable to vary, which seems to be
partly due to their reproductive systems having been
specially affected, though in a lesser degree than
when sterility ensues. So it is with hybrids, for their
offspring in successive generations are eminently liable
to vary, as every experimentalist has observed.

Thus we see that when organic beings are placed
under new and unnatural conditions, and when hybrids
are produced by the unnatural crossing of two species,
the reproductive system, independently of the general
state of health, is affected in a very similar manner.
In the one case, the conditions of life have been dis-
turbed, though often in so slight a degree as to be in-
appreciable by us; in the other case, or that of hybrids,
the external conditions have remained the same, but
the organisation has been disturbed by two distinct
structures and constitutions, including of course the
reproductive systems, having been blended into one.
For it is scarcely possible that two organisations should
be compounded into one, without some disturbance
occurring in the development, or periodical action, or
mutual relations of the different parts and organs one
to another or to the conditions of life. When hybrids
are able to breed inter se, they transmit to their off-
spring from generation to generation the same com-
pounded organisation, and hence we need not be sur-
prised that their sterility, though in some degree varia-
ble, does not diminish; it is even apt to increase, this
being generally the result, as before explained, of too
close interbreeding. The above view of the sterility
of hybrids being caused by two constitutions being com-
pounded into one has been strongly maintained by Max
Wichura.

Cuar. 1X.] OF FIRST CROSSES AND OF HYBRIDS. oT

It must, however, be owned that we cannot under-
stand, on the above or any other view, several facts
with respect to the sterility of hybrids; for instance,
the unequal fertility of hybrids produced from recipro-
cal crosses; or the increased sterility in those hybrids
which occasionally and exceptionally resemble closely
either pure parent. Nor do I pretend that the fore-
going remarks go to the root of the matter; no explana-
tion is offered why an organism, when placed under un-
natural conditions, is rendered sterile. All that I have
attempted to show is, that in two cases, in some respects
allied, sterility is the common result,—in the one case
from the conditions of life having been disturbed, in
the other case from the organisation having been dis-
turbed bytwo organisations being compounded into one.

A similar parallelism holds good with an allied yet
very different class of facts. It is an old and almost
universal belief founded on a considerable body of evi-
dence, which I have elsewhere given, that slight changes
in the conditions of life are beneficial to all living things.
We see this acted on by farmers and gardeners in their
frequent exchanges of seed, tubers, &c., from one soil
or climate to another, and back again. During the con-
valescence of animals, great benefit is derived from al-
most any change in their habits of life. Again, both
with plants and animals, there is the clearest evidence
that a cross between individuals of the same species,
which differ to a certain extent, gives vigour and fer-
tility to the offspring; and that close interbreeding
continued during several generations between the near-
est relations, if these be kept under the same conditions
of life, almost always leads to decreased size, weakness,
or sterility.

28 STERILITY OF HYBRIDS. [Cuap. IX.

Hence it seems that, on the one hand, slight
changes in the conditions of life benefit all organic be-
ings, and on the other hand, that slight crosses, that is
crosses between the males and females of the same spe-
cies, which have been subjected to slightly different
conditions, or which have slightly varied, give vigour
and fertility to the offspring. But, as we have seen, or-
ganic beings long habituated to certain uniform condi-
tions under a state of nature, when subjected, as under
confinement, to a considerable change in their condi-
tions, very frequently are rendered more or less sterile;
and we know that a cross between two forms, that have
become widely or specifically different, produce hybrids
which are almost always in some degree sterile. I am
fully persuaded that this double parallelism is by no
means an accident or an illusion. He who is able to
explain why the elephant and a multitude of other
animals are incapable of breeding when kept under only
partial confinement in their native country, will be able
to explain the primary cause of hybrids being so gen-
erally sterile. He will at the same time be able to ex-
plain how it is that the races of some of our domesticated
animals, which have often been subjected to new and
not uniform conditions, are quite fertile together, al-
though they are descended from distinct species, which
would probably have been sterile if aboriginally crossed.
The above two parallel series of facts seem to be con-
nected together by some common but unknown bond,
which is essentially related to the principle of life; this
principle, according to Mr. Herbert Spencer, being that
life depends on, or consists in, the incessant action and
reaction of various forces, which, as throughout nature,
are always tending towards an equilibrium; and when

Cuap. IX.] DIMORPHISM AND TRIMORPHISM. 99

this tendency is slightly disturbed by any change, the
vital forces gain in power.

Reciprocal Dimorphism and Trimorphism.

This subject may be here briefly discussed, and will
be found to throw some light on hybridism. Several
plants belonging to distinct orders present two forms,
which exist in about equal numbers and which differ
in no respect except in their reproductive organs; one
form having a long pistil with short stamens, the other
a short pistil with long stamens; the two having dif-
ferently sized pollen-grains. With trimorphic plants
there are three forms likewise differing in the lengths
of their pistils and stamens, in the size and colour of
the pollen-grains, and in some other respects; and as
in each of the three forms there are two sets of stamens,
the three forms possess altogether six sets of stamens
and three kinds of pistils. These organs are so pro-
portioned in length to each other, that half the sta-
mens in two of the forms stand on a level with the
stigma of the third form. Now I have shown, and the
result has been confirmed by other observers, that,
in order to obtain full fertility with these plants,
it is necessary that the stigma of the one form should
be fertilised by pollen taken from the stamens of cor-
responding height in another form. So that with di-
morphic species two unions, which may be called legiti-
mate, are fully fertile; and two, which may be called
illegitimate, are more or less infertile. With trimor-
phic species six unions are legitimate, or fully fer-
tile,—and twelve are illegitimate, or more or less infer-
tile.

30 RECIPROCAL DIMORPHISM (Cuap. IX,

The infertility which may be observed in various
dimorphic and trimorphic plants, when they are il-
legitimately fertilised, that is by pollen taken from
stamens not corresponding in height with the pistil,
differs much in degree, up to absolute and utter steril-
ity; just in the same manner as occurs in crossing dis-
tinct species. As the degree of sterility in the latter
case depends in an eminent degree on the conditions
of life being more or less favourable, so I have found
it with illegitimate unions. It is well known that if
pollen of a distinct species be placed on the stigma of a
flower, and its own pollen be afterwards, even after a
considerable interval of time, placed on the same stigma,
its action is so strongly prepotent that it generally anni-
hilates the effect of the foreign pollen; so it is with
the pollen of the several forms of the same species, for
legitimate pollen is strongly prepotent over illegitimate
pollen, when both are placed on the same stigma. I
ascertained this by fertilising several flowers, first il-
legitimately, and twenty-four hours afterwards legiti-
mately with the pollen taken from a peculiarly coloured
variety, and all the seedlings were similarly coloured;
this shows that the legitimate pollen, though applied
_ twenty-four hours subsequently, had wholly destroyed
or prevented the action of the previously applied il-
legitimate pollen. Again, as in making reciprocal
crosses between the same two species, there is occasion-
ally a great difference in the result, so the same thing
occurs with trimorphic plants; for instance, the mid-
styled form of Lythrum salicaria was illegitimately fer-
tilised with the greatest ease by pollen from the longer
stamens of the short-styled form, and yielded many
seeds; but the latter form did not yield a single seed

Cuap. IX.] AND TRIMORPHISM. 81

when fertilised by the longer stamens of the mid-styled -
form.

In all these respects, and in others which might be
added, the forms of the same undoubted species when
illegitimately united behave in exactly the same manner
as do two distinct species when crossed. This led me
carefully to observe during four years many seedlings,
raised from several illegitimate unions. The chief re-
sult is that these illegitimate plants, as they may be
called, are not fully fertile. It is possible to raise from
dimorphic species, both long-styled and short-styled
illegitimate plants, and from trimorphic plants all three
illegitimate forms. These can then be properly united
in a legitimate manner. When this is done, there is no
apparent reason why they should not yield as many
seeds as did their parents when legitimately fertilised.
But such is not the case. They are all infertile, in
various degrees; some being so utterly and incurably
sterile that they did not yield during four seasons a
single seed or even seed-capsule. The sterility of these
illegitimate plants, when united with each other in 2
legitimate manner, may be strictly compared with that
of hybrids when crossed inter se. If, on the other hand,
a hybrid is crossed with either pure parent-species, the
sterility is usually much lessened: and so it is when
an illegitimate plant is fertilised by a legitimate plant.
In the same manner as the sterility of hybrids does not
always run parallel with the difficulty of making the
first cross between the two parent-species, so the sterility
of certain illegitimate plants was unusually great, whilst
the sterility of the union from which they were derived
was by no means great. With hybrids raised from the
same seed-capsule the degree of sterility is innately

32 RECIPROCAL DIMORPHISM [Cuap. 1X,

variable, so it is in a marked manner with illegitimate
plants. Lastly, many hybrids are profuse and persistent
flowerers, whilst other and more sterile hybrids pro-
duce few flowers, and are weak, miserable dwarfs;
exactly similar cases occur with the illegitimate off-
spring of various dimorphic and trimorphic plants.

Altogether there is the closest identity in character
and behaviour between illegitimate plants and hybrids.
It is hardly an exaggeration to maintain that illegitimate
plants are hybrids, produced within the limits of the
same species by the improper union of certain forms,
whilst ordinary hybrids are produced from an improper
union between so-called distinct species. We have also
already seen that there is the closest similarity in all re-
spects between first illegitimate unions and first crosses
between distinct species. This will perhaps be made
more fully apparent by an illustration; we may suppose
that a botanist found two well-marked varieties (and
such occur) of the long-styled form of the trimorphic
Lythrum salicaria, and that he determined to try by
crossing whether they were specifically distinct. He
would find that they yielded only about one-fifth of the
proper number of seeds, and that they behaved in all
the other above specified respects as if they had been two
distinct species. But to make the case sure, he would
raise plants from his supposed hybridised seed, and he
would find that the seedlings were miserably dwarfed
and utterly sterile, and that they behaved in all other
respects like ordinary hybrids. He might then main-
tain that he had actually proved, in accordance with
the common view, that his two varieties were as good
and as distinct species as any in the world; but he would
be completely mistaken.

Cuap. IX.] AND TRIMORPHISM. 33

The facts now given on dimorphic and trimorphic
plants are important, because they show us, first, that
the physiological test of lessened fertility, both in first
crosses and in hybrids, is no safe criterion of specific
distinction; secondly, because we may conclude that
there is some unknown bond which connects the in-
fertility of illegitimate unions with that of their illegiti-
mate offspring, and we are led to extend the same view
to first crosses and hybrids; thirdly, because we find,
and this seems to me of especial importance, that two
or three forms of the same species may exist and may
differ in no respect whatever, either in structure or in
constitution, relatively to external conditions, and yet
be sterile when united in certain ways. For we must
remember that it is the union of the sexual elements of
individuals of the same form, for instance, of two long-
styled forms, which results in sterility; whilst it is the
union of the sexual elements proper to two distinct
forms which is fertile. Hence the case appears at first
sight exactly the reverse of what occurs, in the ordinary
unions of the individuals of the same species and with
crosses between distinct species. It is, however, doubt-
ful whether this is really so; but I will not enlarge on
this obscure subject.

We may, however, infer as probable from the con-
sideration of dimorphic and trimorphic plants, that the
sterility of distinct species when crossed and of their
hybrid progeny, depends exclusively on the nature of
their sexual elements, and not on any difference in their
structure or general constitution. We are also led to
this same conclusion by considering reciprocal crosses,
in which the male of one species cannot be united, or
can be united with great difficulty, with the female of

34 FERTILITY OF VARIETIES [Cuap. IX.

a second species, whilst the converse cross can be effected
with perfect facility. That excellent observer, Gart-
ner, likewise concluded that species when crossed are
sterile owing to differences confined to their reproduc-
tive systems.

Fertility of Varieties when Crossed, and of their
‘Mongrel Offspring, not universal.

It may be urged, as an overwhelming argument, that
there must be some essential distinction between species
and varieties, inasmuch as the latter, however much
they may differ from each other in external appearance,
cross with perfect facility, and yield perfectly fertile
offspring. With some exceptions, presently to be
given, I fully admit that this is the rule. But the sub-
ject is surrounded by difficulties, for, looking to varie-
ties produced under nature, if two forms hitherto re-
puted to be varieties be found in any degree sterile to-
gether, they are at once ranked by most naturalists
as species. For instance, the blue and red pimpernel,
which are considered by most botanists as varieties, are
said by Gartner to be quite sterile when crossed, and
he subsequently ranks them as undoubted species. If
we thus argue in a circle, the fertility of all varieties
produced under nature will assuredly have to be
granted.

If we turn to varieties, produced, or supposed to have
been produced, under domestication, we are still in-
volved in some doubt. For when it is stated, for in-
stance, that certain South American indigenous domes-
tic dogs do not readily unite with European dogs, the
explanation which will occur to every one, and probably

Cuap. IX.] WHEN CROSSED. 85

the true one, is that they are descended from aborigi-
nally distinct species. Nevertheless the perfect fertil-
ity of so many domestic races, differing widely from
each other in appearance, for instance those of the
pigeon, or of the cabbage, is a remarkable fact; more es-
pecially when we reflect how many species there are,
which, though resembling each other most closely, are
utterly sterile when intercrossed. Several considera-
tions, however, render the fertility of domestic varieties
less remarkable. In the first place, it may be observed
that the amount of external difference between two
species is no sure guide to their degree of mutual steril-
ity, so that similar differences in the case of varieties
would be no sure guide. It is certain that with species
the cause lies exclusively in differences in their sexual
constitution. Now the varying conditions to which
domesticated animals and cultivated plants have been
subjected, have had so little tendency towards modify-
ing the reproductive system in a manner leading to
mutual sterility, that we have good grounds for admit-
ting the directly opposite doctrine of Pallas, namely,
that such conditions generally eliminate this tendency;
so that the domesticated descendants of species, which
in their natural state probably would have’ been in
some degree sterile when crossed, become perfectly fer-
tile together. With plants, so far is cultivation from
giving a tendency towards sterility between distinct
species, that in several well-authenticated cases already
alluded to, certain plants have been affected in an op-
posite manner, for they have become self-impotent
whilst still retaining the capacity of fertilising, and
being fertilised by, other species. If the Pallasian doc-

trine of the elimination of sterility through long-con-
28

86 FERTILITY OF VARIETIES (Cuap. 1X,

tinued domestication be admitted, and it can hardly
be rejected, it becomes in the highest degree improbable
thet similar conditions long-continued should likewise
induce this tendency; though in certain cases, with
species having a peculiar constitution, sterility might
occasionally be thus caused. Thus, as I believe, we
can understand why with domesticated animals varieties
have not been produced which are mutually sterile; and
why with plants only a few such cases, immediately to
be given, have been observed.

The real difficulty in our present subject is not, as it
appears to me, why domestic varieties have not become
mutually infertile when crossed, but why this has so
generally occurred with natural varieties, as soon as they
have been permanently modified in a sufficient degree
to take rank as species. We are far from precisely
knowing the cause; nor is this surprising, seeing how
profoundly ignorant we are in regard to the normal
and abnormal action of the reproductive system. But
we can see that species, owing to their struggle for ex-
istence with numerous competitors, will have been ex-
posed during long periods of time to more uniform
conditions, than have domestic varieties; and this may
well make a wide difference in the result. For we
know how commonly wild animals and plants, when
taken from their natural conditions and subjected to
captivity, are rendered sterile; and the reproductive
functions of organic beings which have always lived
under natural conditions would probably in like man-
ner be eminently sensitive to the influence of an un-
natural cross. Domesticated productions, on the other
hand, which, as shown by the mere fact of their domesti-
cation, were not originally highly sensitive to changes

Cuap. IX.] WHEN CROSSED. 37

in their conditions of life, and which can now generally
resist with undiminished fertility repeated changes of
conditions, might be expected to produce varieties,
which would be little liable to have their reproductive
powers injuriously affected by the act of crossing with
other varieties which had originated in a like manner.

I have as yet spoken as if the varieties of the same
species were invariably fertile when intercrossed. But
it is impossible to resist the evidence of the existence
of a certain amount of sterility in the few following
cases, which I will briefly abstract. The evidence is
at least as good as that from which we believe in the
sterility of a multitude of species. The evidence is,
also, derived from hostile witnesses, who in all other
cases consider fertility and sterility as safe criterions of
specific distinction. Gdrtner kept during several years
a dwarf kind of maize with yellow seeds, and a tall
variety with red seeds growing near each other in his
garden; and although these plants have separated sexes,
they never naturally crossed. He then fertilised thirteen
flowers of the one kind with pollen of the other; but
only a single head produced any seed, and this one head
produced only five grains. Manipulation in this case
could not have been injurious, as the plants have sepa-
rated sexes. No one, I believe, has suspected that these
varieties of maize are distinct species; and it is impor-
tant to notice that the hybrid plants thus raised were
themselves perfectly fertile; so that even Gartner did
not venture to consider the two varieties as specifically
distinct.

Girou de Buzareingues crossed three varieties of
gourd, which like the maize has separated sexes, and he
asserts that their mutual fertilisation is by so much the

88 FERTILITY OF VARIETIES [Cuap. IX

less easy as their differences are greater. How far these
experiments may be trusted, I know not; but the forms
experimented on are ranked by Sageret, who mainly
founds his classification by the test of infertility, as
varieties, and Naudin has come to the same conclusion.

The following case is far more remarkable, and seems
at first incredible; but it is the result of an astonishing
number of experiments made during many years on
nine species of Verbascum, by so good an observer and
so hostile a witness as Gartner: namely that the yellow
and white varieties when crossed produce less seed than
the similarly coloured varieties of the same species.
Moreover, he asserts that, when yellow and white varie-
ties of one species are crossed with yellow and white
varieties of a distinct species, more seed is produced
by the crosses between the similarly coloured flowers,
than between those which are differently coloured. Mr.
Scott also has experimented on the species and varieties
of Verbascum; and although unable to confirm Gart-
ner’s results on the crossing of the distinct species, he
finds that the dissimilarly coloured varieties of the
same species yield fewer seeds, in the proportion of 86
to 100, than the similarly coloured varieties. Yet these
varieties differ in no respect except in the colour of
their flowers; and one variety can sometimes be raised
from the seed of another.

Kolreuter, whose accuracy has been confirmed by
every subsequent observer, has proved the remarkable
fact, that one particular variety of the common tobacco
was more fertile than the other varieties, when crossed
with a widely distinct species. He experimented on
five forms which are commonly reputed to be varieties,
and which he tested by the severest trial, namely, by

Cuap. 1X,] WHEN CROSSED. 39

reciprocal crosses, and he found their mongrel offspring
perfectly fertile. But one of these five varieties, when
used either as the father or mother, and crossed with
the Nicotiana glutinosa, always yielded hybrids not so
sterile as those which were produced from the four
other varieties when crossed with N. glutinosa. Hence
the reproductive system of this one variety must have
been in some manner and in some degree modified.

From these facts it can no longer be maintained that
varieties when crossed are invariably quite fertile.
From the great difficulty of ascertaining the infertility
of varieties in a state of nature, for a supposed variety,
if proved to be infertile in any degree, would almost
universally be ranked as a species;—from man attend-
ing only to external characters in his domestic varieties,
and from such varieties not having been exposed for
very long periods to uniform conditions of life;—from
these several considerations we may conclude that fer-
tility does not constitute a fundamental distinction be-
tween varieties and species when crossed. The gen-
eral sterility of crossed species may safely be looked at,
not as a special acquirement or endowment, but as in-
cidental on changes of an unknown nature in their sex-
ual elements.

Hybrids and Mongrels compared, independently of thetr
fertility.

Independently of the question of fertility, the off-
spring of species and of varieties when crossed may be
compared in several other respects. Girtner, whose
strong wish it was to draw a distinct line between spe-
cies and varieties, could find very few, and, as it seems

40 HYBRIDS AND MONGRELS COMPARED. [Cuap. Dx

to me, quite unimportant differences between the so-
called hybrid offspring of species, and the so-called
mongrel offspring of varieties. And, on the other hand,
they agree most closely in many important respects.

I shall here discuss this subject with extreme brevity.
The most important distinction is, that in the first
generation mongrels are more variable than hybrids;
but Gartner admits that hybrids from species which
have long been cultivated are often variable in the
first generation; and I have myself seen striking
instances of this fact. Gartner further admits that
hybrids between very closely allied species are more
variable than those from very distinct species; and
this shows that the difference in the degree of variabil-
ity graduates away. When mongrels and the more
fertile hybrids are propagated for several generations,
an extreme amount of variability in the offspring in
both cases is notorious; but some few instances of both
hybrids and mongrels long retaining a uniform charac-
ter could be given. The variability, however, in the
successive generations of mongrels is, perhaps, greater
than in hybrids.

This greater variability in mongrels than in hybrids
does not seem at all surprising. For the parents of
mongrels are varieties, and mostly domestic varieties
(very few experiments having been tried on natural
varieties), and this implies that there has been recent
variability, which would often continue and would
augment that arising from the act of crossing. The
slight variability of hybrids in the first generation, in
contrast with that in the succeeding generations, is a
curious fact and deserves attention. For it bears on
the view which I have taken of one of the causes of

Cuap. IX.] HYBRIDS AND MONGRELS COMPARED. 4)

ordinary variability; namely, that the reproductive
system from being eminently sensitive to changed con-
ditions of life, fails under these circumstances to per-
form its proper function of producing offspring closely
similar in all respects to the parent-form. Now hy-
brids in the first generation are descended from spe-
cies (excluding those long-cultivated) which have not
had their reproductive systems in any way affected, and
they are not variable; but hybrids themselves have
their reproductive systems seriously affected, and their
descendants are highly variable.

But to return to our comparison of mongrels and
hybrids: Gartner states that mongrels are more liable
than hybrids to revert to either parent-form; but this,
if it be true, is certainly only a difference in degree.
Moreover, Gartner expressly states that hybrids from
long cultivated plants are more subject to reversion
than hybrids from species in their natural state; and
this probably explains the singular difference in the
results arrived at by different observers: thus Max
Wichura doubts whether hybrids ever revert to their
parent-forms, and he experimented on uncultivated
species of willows; whilst Naudin, on the other hand,
insists in the strongest terms on the almost universal
tendency to reversion in hybrids, and he experimented
chiefly on cultivated plants. Gartner further states
that when any two species, although most closely allied
to each other, are crossed with a third species, the
hybrids are widely different from each other; whereas
if two very distinct varieties of one species are crossed
with another species, the hybrids do not differ much.
But this conclusion, as far as I can make out, is
founded on a single experiment; and seems directly

42 HYBRIDS AND MONGRELS COMPARED. [Caap. IX.

~

ipueertea.the results of several experiments made by
Kolreuter.

Such alone are the unimportant differences which
Gartner is able to point out between hybrid and mon-
grel plants. On the other hand, the degrees and kinds
of resemblance in mongrels and in hybrids to their
respective parents, more especially in hybrids pro-
duced from nearly related species, follow according to
Gartner the same laws. When two species are crossed,
one has sometimes a prepotent power of impressing
its likeness on the hybrid. So I believe it to be with
varieties of plants; and with animals one variety cer-
tainly often has this prepotent power over another
variety. Hybrid plants produced from a reciprocal cross,
generally resemble each other closely; and so it is with
mongrel plants from a reciprocal cross. Both hybrids
and mongrels can be reduced to either pure parent-
form, by repeated crosses in successive generations with
either parent.

These several remarks are apparently applicable to
animals; but the subject is here much complicated,
partly owing to the existence of secondary sexual char-
acters; but more especially owing to prepotency in
transmitting likeness running more strongly in one sex
than in the other, both when one species is crossed with
another, and when one variety is crossed with another
variety. For instance, I think those authors are right
who maintain that the ass has a prepotent power over
the horse, so that both the mule and the hinny resemble
more closely the ass than the horse; but that the pre-
potency runs more strongly in the male than in the
female ass, so that the mule, which is the offspring of
the male ass and mare, is more like an ass, than is

Cuap. 1X.] HYBRIDS AND MONGRELS COMPARED. 43

the hinny, which is the offspring of the female ass and
stallion.

Much stress has been laid by some authors on the
supposed fact, that it is only with mongrels that the
offspring are not intermediate in character, but closely
resemble one of their parents; but this does sometimes
occur with hybrids, yet I grant much less frequently
than with mongrels. Looking to the cases which I
have collected of cross-bred animals closely resembling
one parent, the resemblances seem chiefly confined to
characters almost monstrous in their nature, and which
have suddenly appeared—such as albinism, melanism,
deficiency of tail or horns, or additional fingers and
toes; and do not relate to characters which have been
slowly acquired through selection. A tendency to sud-
den reversions to the perfect character of either parent
would, also, be much more likely to occur with mon-
grels, which are descended from varieties often sud-
denly produced and semi-monstrous in character, than
with hybrids, which are descended from species slowly
and naturally produced. On the whole, I entirely
agree with Dr. Prosper Lucas, who, after arranging an
enormous body of facts with respect to animals, comes
to the conclusion that the laws of resemblance of the
child to its parents are the same, whether the two
parents differ little or much from each other, namely,
in the union of individuals of the same variety, or of
different varieties, or of distinct species.

Independently of the question of fertility and steril-
ity, in all other respects there seems to be a general and
close similarity in the offspring of crossed species, and
of crossed varieties. If we look at species as having
been specially created, and at varieties as having been

44 SUMMARY. [Cuap. IX.

producea’sy~secondary laws, this similarity would be
an astonishing fact. But it harmonises perfectly with
the view that there is no essential distinction between

species and varieties.

Summary of Chapter.

First crosses between forms, sufficiently distinct to
be ranked as species, and their hybrids, are very gen-
erally, but not universally, sterile. The sterility is of
all degrees, and is often so slight that the most careful
experimentalists have arrived at diametrically opposite
conclusions in ranking forms by this test. The sterility
is innately variable in individuals of the same spe-
cies, and is eminently susceptible to the action of fa-
vourable and unfavourable conditions. The degree of
sterility does not strictly follow systematic affinity, but
is governed by several curious and complex laws. It is
generally different, and sometimes widely different in re-
ciprocal crosses between the same two species. It is not
always equal in degree in a first cross and in the hybrids
produced from this cross.

In the same manner as in grafting trees, the capac-
ity in one species or variety to take on another, is inci-
dental on differences, generally of an unknown nature,
in their vegetative systems, so in crossing, the greater
or less facility of one species to unite with another is in-
cidental on unknown differences in their reproductive
systems. There is no more reason to think that species
have been specially endowed with various degrees of
sterility to prevent their crossing and blending in na-
ture, than to think that trees have been specially en-
dowed with various and somewhat analogous degrees of

Cuap, IX.] SUMMARY. 45

difficulty in being grafted together in order to prevent
their inarching in our forests.

The sterility of first crosses and of their hybrid
progeny has not been acquired through natural se-
lection. In the case of first crosses it seems to depend
on several circumstances; in some instances in chief
part on the early death of the embryo. In the case of
hybrids, it apparently depends on their whole organi-
sation having been disturbed by being compounded
from two distinct forms; the sterility being closely
allied to that which so frequently affects pure species,
when exposed to new and unnatural conditions of life.
He who will explain these latter cases will be able to
explain the sterility of hybrids. This view is strongly
supported by a parallelism of another kind: namely,
that, firstly, slight changes in the conditions of life
add to the vigour and fertility of all organic beings;
and secondly, that_the crossing of forms, which have

been exposed to slightly different conditions of life”
or which have varied, favours the size, vigour, and fer-
tility. of their offspring. The facts given on the steril-
ity of the illegitimate unions of dimorphic and trimor-
phic plants and of their illegitimate progeny, perhaps
render it probable that some unknown bond in all cases
connects the degree of fertility of first unions with that
of their offspring. The consideration of these facts on
dimorphism, as well as of the results of reciprocal
crosses, clearly leads to the conclusion that the primary
cause of the sterility of crossed species is confined to
differences in their sexual elements. But why, in the
case of distinct species, the sexual elements should
so generally have become more or less modified, leading
to their mutual infertility, we do not know; but it

46 SUMMARY. (Cuapr. IX.

~

seeis to stand in some close relation to species having
been exposed for long periods of time to nearly uniform
conditions of life.

It is not surprising that the difficulty in crossing any
two species, and the sterility of their hybrid offspring,
should in most cases correspond, even if due to distinct
causes: for both depend on the amount of difference
between the species which are crossed. Nor is it sur-
prising that the facility of effecting a first cross, and
the fertility of the hybrids thus produced, and the
capacity of being grafted together—though this latter
capacity evidently depends on widely different circum-
stances—should all run, to a certain extent, parallel
with the systematic affinity of the forms subjected to
experiment; for systematic affinity includes resem-
blances of all kinds.

First crosses between forms known to be varieties, or
sufficiently alike to be considered as varieties, and their
mongrel offspring, are very generally, but not, as is so
often stated, invariably fertile. Nor is this almost
universal and perfect fertility surprising, when it is
remembered how liable we are to argue in a circle with
respect to varieties in a state of nature; and when we
remember that the greater number of varieties have
been produced under domestication by the selection of
mere external differences, and that they have not been
long exposed to uniform conditions of life. It should
also be especially kept in mind, that long-continued
domestication tends to eliminate sterility, and ic there-
fore little likely to induce this same quality. Inde-
pendently of the question of fertility, in all other re-
spects there is the closest general resemblance between
hybrids and mongrels,—in their variability, in their

Cuar. IX.] SUMMARY. 47

power of absorbing each other by repeated crosses, and
in their inheritance of characters from both parent-
forms. Finally, then, although we are as ignorant of
the precise cause of the sterility of first crosses and of
hybrids as we are why animals and plants removed
from their natural conditions become sterile, yet the
facts given in this chapter do not seem to me opposed

to the belief that species aboriginally existed as varie-
ties.

48 IMPERFECTION OF THE (Cuap. X.

CHAPTER X.
ON THE IMPERFECTION OF THE GEOLOGICAL RECORD.

On the absence of intermediate varieties at the present day—On
the nature of extinct intermediate varieties; on their number—
On the lapse of time, as inferred from the rate of denudation
and of deposition—On the lapse of time as estimated by years
—On the poorness of our palzontological collections—On the
intermittence of geological formations—On the denudation of
granitic areas—On the absence of intermediate varieties in any
one formation—On the sudden appearance of groups of species
—On their sudden appearance in the lowest known fossiliferous
strata—Antiquity of the habitable earth.

In the sixth chapter I enumerated the chief objec-
tions which might be justly urged against the views
maintained in this volume. Most of them have now
been discussed. One, namely the distinctness of spe-
cific forms, and their not being blended together by in-
numerable transitional links, is a very obvious difficulty.
I assigned reasons why such links do not commonly oc-
cur at the present day under the circumstances ap-
parently most favourable for their presence, namely, on
an extensive and continuous area with graduated phys-
ical conditions. I endeavoured to show, that the life of
each species depends in a more important manner on
the presence of other already defined organic forms,
than on climate, and, therefore, that the really govern-
ing conditions of life do not graduate away quite insen-
sibly like heat or moisture. I endeavoured, also, to

Cuap. X.] GEOLOGICAL RECORD. 49

show that intermediate varieties, from existing in lesser
numbers than the forms which they connect, will gen-
erally be beaten out and exterminated during the course
of further modification and improvement. The main
cause, however, of innumerable intermediate links not
now occurring everywhere throughout nature, depends
on the very process of natural selection, through which
new varieties continually take the places of and sup-
plant their parent-forms. But just in proportion as
this process of extermination has acted on an enormous
scale, so must the number of intermediate varieties,
which have formerly existed, be truly enormous. Why
then is not every geological formation and every stra-
tum full of such intermediate links? Geology assured-
ly does not reveal any such finely-graduated organic
chain; and this, perhaps, is the most obvious and seri-
ous objection which can be urged against the theory.
The explanation lies, as I believe, in the extreme imper-
fection of the geological record.

In the first place, it should always be borne in mind
what sort of intermediate forms must, on the theory,
have formerly existed. I have found it difficult, when
looking at any two species, to avoid picturing to my-
self forms directly intermediate between them. But
this is a wholly false view; we should always look for
forms intermediate between each species and a common
but unknown progenitor; and the progenitor will gen-
erally have differed in some respects from all its modi-
fied descendants. To give a simple illustration: the
fantail and pouter pigeons are both descended from
the rock-pigeon; if we possessed all the intermediate
varieties which have ever existed, we should have an
extremely close series between both and the rock-

50 IMPERFECTION OF THE [Coap. X.

pigeo?> but we should have no varieties directly in-

termediate between the fantail and pouter; none, for
instance, combining a tail somewhat expanded with
a crop somewhat enlarged, the characteristic features of
these two breeds. These two breeds, moreover, have
become so much modified, that, if we had no historical
or indirect evidence regarding their origin, it would not
have been possible to have determined, from a mere
comparison of their structure with that of the rock-
pigeon, C. livia, whether they had descended from this
species or from some other allied form, such as C. cenas.

So, with natural species, if we look to forms very
distinct, for instance to the horse and tapir, we have
no reason to suppose that links directly intermediate
between them ever existed, but between each and an
unknown common parent. The common parent will
have had in its whole organisation much general re-
semblance to the tapir and to the horse; but in some
points of structure may have differed considerably from
both, even perhaps more than they differ from each
other. Hence, in all such cases, we should be unable
to recognise the parent-form of any two or more spe-
cies, even if we closely compared. the structure of the
parent with that of its modified descendants, unless at
the same time we had a nearly perfect chain of the in-
termediate links.

It is just possible by the theory, that one of two
living forms might have descended from the other; for
instance, a horse from a tapir; and in this case direct
intermediate links will have existed between them.
But such a case would imply that one form had re-
mained for a very long period unaltered, whilst its de-
scendants had undergone a vast amount of change;

Cuap. X.] GEOLOGICAL RECORD. 51

and the principle of competition between organism and
organism, between child and parent, will render this a
very rare event; for in all cases the new and improved
forms of life tend to supplant the old and unimproved
forms.

By the theory of natural selection all living species
have been connected with the parent-species of each
genus, by differences not greater than we see between
the natural and domestic varieties of the same species
at the present day; and these parent-species, now gen-
erally extinct, have in their turn been similarly con-
nected with more ancient forms; and so on backwards,
always converging to the common ancestor of each
great class. So that the number of intermediate and
transitional links, between all living and extinct spe-
cies, must have been inconceivably great. But as-
suredly, if this theory be true, such have lived upon the
earth.

On the Lapse of Time, as inferred from the rate of
Deposition and extent of Denudation.

Independently of our not finding fossil remains of
such infinitely numerous connecting links, it may be
objected that time cannot have sufficed for so great an
amount of organic change, all changes having been
effected slowly. It is hardly possible for me to recall
to the reader who is not a practical geologist, the facts
leading the mind feebly to comprehend the lapse of
time. He who can read Sir Charles Lyell’s grand work
on the Principles of Geology, which the future his-
torian will recognise as having produced a revolution in

natural science, and yet does not admit how vast have
29

59 THE LAPSE OF TIME. [Cuar. X

been the past periods of time, may at once close this
volume. Not that it suffices to study the Principles of
Geology, or to read special treatises by different ob-
servers on separate formations, and to mark how each
author attempts to give an inadequate idea of the dura-
tion of each formation, or even of each stratum. We can
best gain some idea of past time by knowing the
agencies at work, and learning how deeply the surface of
the land has been denuded, and how much sediment
has been deposited. As Lyell has well remarked, the
extent and thickness of our sedimentary formations are
the result and the measure of the denudation which the
earth’s crust has elsewhere undergone. Therefore a
man should examine for himself the great piles of super-
imposed strata, and watch the rivulets bringing down
mud, and the waves wearing away the sea-cliffs, in
order to comprehend something about the duration of
past time, the monuments of which we see all around
us.

It is good to wander along the coast, when formed of
moderately hard rocks, and mark the process of degra-
dation. The tides in most cases reach the cliffs only for
a short time twice a day, and the waves eat into them
only when they are charged with sand or pebbles;
for there is good evidence that pure water effects noth-
ing in wearing away rock. At last the base of the cliff
is undermined, huge fragments fall down, and these,
remaining fixed, have to be worn away atom by atom,
until after being reduced in size they can be rolled
about by the waves, and then they are more quickly
ground into pebbles, sand, or mud. But how often
do we see along the bases of retreating cliffs rounded
boulders, all thickly clothed by marine productions,

Crap. X.] THE LAPSE OF TIME. 538

showing how little they are abraded and how seldom
they are rolled about! Moreover, if we follow for a few
miles any line of rocky cliff, which is undergoing deg-
radation, we find that it is only here and there, along
a short length or round a promontory, that the cliffs
are at the present time suffering. The appearance of
the surface and the vegetation show that elsewhere
years have elapsed since the waters washed their base.
We have, however, recently learnt from the obser-
vations of Ramsay, in the van of many excellent ob-
servers—of Jukes, Geikie, Croll, and others, that sub-
aerial degradation is a much more important agency than
coast-action, or the power of the waves. The whole
surface of the land is exposed to the chemical action
of the air and of the rain-water with its dissolved car-
boniec acid, and in colder countries to frost; the disin-
tegrated matter is carried down even gentle slopes
during heavy rain, and to a greater extent than might
be supposed, especially in arid districts, by the wind; it
is then transported by the streams and rivers, which
when rapid deepen their channels, and triturate the
fragments. On a rainy day, even in a gently undulat-
ing country, we see the effects of subaerial degradation
in the muddy rills which flow down every slope. Messrs.
Ramsay and Whitaker have shown, and the observation
is a most striking one, that the great lines of escarp-
ment in the Wealden district and those ranging across
England, which formerly were looked at as ancient sea-
coasts, cannot have been thus formed, for each line
is composed of one and the same formation, whilst our
sea-cliffs are everywhere formed by the intersection
of various formations. This being the case, we are
compelled to admit that the escarpments owe their

BA THE LAPSE OF TIME. (Cua. X.

origin in chief part to the rocks of which they are com-
posed having resisted subaerial denudation better than
the surrounding surface; this surface consequently has
been gradually lowered, with the lines of harder rock
left projecting. Nothing impresses the mind with the
vast duration of time, according to our ideas of time,
more forcibly than the conviction thus gained that sub-
aerial agencies which apparently have so little power,
and which seem to work so slowly, have produced great
results.

When thus impressed with the slow rate at which
the land is worn away through subaerial and littoral
action, it is good, in order to appreciate the past dura-
tion of time, to consider, on the one hand, the masses
of rock which have been removed over many extensive
areas, and on the other hand the thickness of our sedi-
mentary formations. I remember having been much
struck when viewing volcanic islands, which have been
worn by the waves and pared all round into perpen-
dicular cliffs of one or two thousand feet in height;
for the gentle slope of the lava-streams, due to their
formerly liquid state, showed at a glance how far the
hard, rocky beds had once extended into the open ocean.
The same story is told still more plainly by faults,—
those great cracks along which the strata have been up-
heaved on one side, or thrown down on the other, to
the height or depth of thousands of feet; for since the
crust cracked, and it makes no great difference whether
the upheaval was sudden, or, as most geologists now
believe, was slow and effected by many starts, the sur-
face of the land has been so completely planed down
that no trace of these vast dislocations is externally
visible. The Craven fault, for instance, extends for

Cuap. X,] THE LAPSE OF TIME. 55

upwards of 30 miles, and along this line the vertical
displacement of the strata varies from 600 to 3000 feet.
Professor Ramsay has published an account of a down-
throw in Anglesea of 2300 feet; and he informs me
that he fully believes that there is one in Merioneth-
shire of 12,000 feet; yet in these cases there is nothing
on the surface of the land to show such prodigious
movements; the pile of rocks on either side of the crack
having been smoothly swept away.

On the other hand, in all parts of the world the piles
of sedimentary strata are of wonderful thickness. In
the Cordillera I estimated one mass of conglomerate at
ten thousand feet; and although conglomerates have
probably been accumulated at a quicker rate than finer
sediments, yet from being formed of worn and rounded
pebbles, each of which bears the stamp of time, they
are good to show how slowly the mass must have been
heaped together. Professor Ramsay has given me the
maximum thickness, from actual measurement in most
cases, of the successive formations in different parts of
Great Britain; and this is the result:—

Feet.
Paleozoic strata (not including igneous beds)......... 57,154
Secondary strata... .. cc cece eee eee e eee cee ee enncees 13,190
Tertiary strata...... 0... cece cece es eee ee enter eeeee 2,240

—making altogether 72,584 feet; that is, very nearly
thirteen and three-quarters British miles. Some of the
formations, which are represented in England by thin
beds, are thousands of feet in thickness on the Con-
tinent. Moreover, between each successive formation,
we have, in the opinion of most geologists, blank
periods of enormous length. So that the lofty pile of
sedimentary rocks in Britain gives but an inadequate

56 THE LAPSE OF TIME. [Cuar. X

idea of the time which has elapsed during their accumu-
lation. The consideration of these various facts im-
presses the mind almost in the same manner as does the
vain endeavour to grapple with the idea of eternity.
Nevertheless this impression is partly false. Mr.
Croll, in an interesting paper, remarks that we do not
err “in forming too great a conception of the length of
“ geological periods,” but in estimating them by years.
When geologists look at large and complicated phe-
nomena, and then at the figures representing several
million years, the two produce a totally different effect
on the mind, and the figures are at once pronounced too
small. In regard to subaerial denudation, Mr. Croll
shows, by calculating the known amount of sediment
annually brought down by certain rivers, relatively to
their areas of drainage, that 1000 feet of solid rock, as
it became gradually disintegrated, would thus be re-
moved from the mean level of the whole area in the
course of six million years. This seems an astonishing
result, and some considerations lead to the suspicion
that it may be too large, but even if halved or quartered
it is still very surprising. Few of us, however, know
what a million really means: Mr. Croll gives the fol-
lowing illustration: take a narrow strip of paper, 83
feet 4 inches in length, and stretch it along the wall of
a large hall; then mark off at one end the tenth of an
inch. This tenth of an inch will represent, one hundred
years, and the entire strip a million years. But let it
be borne in mind, in relation to the subject of this work,
wnat a hundred years implies, represented as it is by a
measure utterly insignificant in a hall of the above
dimensions. Several eminent breeders, during a single
lifetime, have so largely modified some of the higher

Cuap. X.] THE LAPSE OF TIME. 57

animals which propagate their kind much more slowly
than most of the lower animals, that they have formed
what well deserves to be called a new sub-breed. Few
men have attended with due care to any one strain for
more than half a century, so that a hundred years repre-
sents the work of two breeders in succession. It is not
to be supposed that species in a state of nature ever
change so quickly as domestic animals under the guid-
ance of methodical selection. The comparison would
be in every way fairer with the effects which follow
from unconscious selection, that is the preservation of
the most useful or beautiful animals, with no intention
of modifying the breed; but by this process of uncon-
scious selection, various breeds have been sensibly
changed in the course of two or three centuries.

Species, however, probably change much more
slowly, and within the same country only a few change
at the same time. This slowness follows from all the
inhabitants of the same country being already so well
adapted to each other, that new places in the polity of
nature do not occur until after long intervals, due to the
occurrence of physical changes of some kind, or through
the immigration of new forms. Moreover variations or
individual differences of the right nature, by which
some of the inhabitants might be better fitted to their
new places under the altered circumstances, would not
always occur at once. Unfortunately we have no means
of determining, according to the standard of years, how
long a period it takes to modify a species; but to the
subject of time we must return.

58 THE POORNESS OF OUR [Cuap. X,

On the Poorness of Paleontological Collections.

Now let us turn to our richest geological museums,
and what a paltry display we behold! That our col-
lections are imperfect is admitted by every one. The
remark of that admirable paleontologist, Edward
Forbes, should never be forgotten, namely, that very
many fossil species are known and named from single
and often broken specimens, or from a few specimens
collected on some one spot. Only a small portion of
the surface of the earth has been geologically explored,
and no part with sufficient care, as the important dis:
coveries made every year in Europe prove. No organ
ism wholly soft can be preserved. Shells and bones de-
cay and disappear when left on the bottom of the sea,
where sediment is not accumulating. We probably take
a quite erroneous view, when we assume that sediment ia
being deposited over nearly the whole bed of the sea, at
a rate sufficiently quick to embed and preserve fossil re-
mains. Throughout an enormously large proportion of
the ocean, the bright blue tint of the water bespeaks its
purity. The many cases on record of a formation con-
formably covered, after an immense interval of time, by
another and later formation, without the underlying
bed having suffered in the interval any wear and tear,
seem explicable only on the view of the bottom of the
sea not rarely lying for ages in an unaltered condition.
The remains which do become embedded, if in sand or
gravel, will, when the beds are upraised, -generally be
dissolved by the percolation of rain-water charged with
carbonic acid. Some of the many kinds of animals
which live on the beach between high and low water
mark seem to be rarely preserved. For instance, the

Cuap. X.)] PALAZSONTOLOGICAL COLLECTIONS. 59

several species of the Chthamaline (a sub-family of
sessile cirripedes) coat the rocks all over the world in
infinite numbers: they are all strictly littoral, with the
exception of a single Mediterranean species, which in-
habits deep water, and this has been found fossil in
Sicily, whereas not one other species has hitherto been
found in any tertiary formation: yet it is known that
the genus Chthamalus existed during the Chalk period.
Lastly, many great deposits requiring a vast length of
time for their accumulation, are entirely destitute of
organic remains, without our being able to assign any
reason: one of the most striking instances is that of the
Flysch formation, which consists of shale and sandstone,
several thousand, occasionally even six thousand feet in
thickness, and extending for at least 300 miles from
Vienna to Switzerland; and although this great mass
has been most carefully searched, no fossils, except a
few vegetable remains, have been found.

With respect to the terrestrial productions which
lived during the Secondary and Paleozoic periods, it is
superfluous to state that our evidence is fragmentary in
an extreme degree. For instance, until recently not a
land-shell was known belonging to either of these vast
periods, with the exception of one species discovered by
Sir C. Lyell and Dr. Dawson in the carboniferous strata
of North America; but now land-shells have been found
in the lias. In regard to mammiferous remains, a
glance at the historical table published in Lyell’s
Manual will bring home the truth, how accidental and
rare is their preservation, far better than pages of detail.
Nor is their rarity surprising, when we remember how
large a proportion of the bones of tertiary mammals
have been discovered either in caves or in lacustrine

60 THE POORNESS OF OUR [CHap. X.

deposits; and that not a cave or true lacustrine bed is
known belonging to the age of our secondary or palzo-
zoic formations. :

But the imperfection in the geological record largely
results from another and more important cause than
any of the foregoing; namely, from the several forma-
tions being separated from each other by wide intervals
of time. This doctrine has been emphatically admitted
by many geologists and paleontologists, who, like E.
Forbes, entirely disbelieve in the change of species.
‘When we see the formations tabulated in written works,
or when we follow them in nature, it is difficult to
avoid believing that they are closely consecutive. But
we know, for instance, from Sir R. Murchison’s great
work on Russia, what wide gaps there are in that coun-
try between the superimposed formations; so it is in
North America, and in many other parts of the world.
The most skilful geologist, if his attention had been
confined exclusively to these large territories, would
never have suspected that, during the periods which
were blank and barren in his own country, great piles
of sediment, charged with new and peculiar forms of .
life, had elsewhere been accumulated. And if, in each
separate territory, hardly any idea can be formed of the
length of time which has elapsed between the consecu-
tive formations, we may infer that this could nowhere
be ascertained. The frequent and great changes in
the mineralogical composition of consecutive forma-
tions, generally implying great changes in the geography
of the surrounding lands, whence the sediment was
derived, accord with the belief of vast intervals of time
having elapsed between each formation.

We can, I think, see why the geological formations

Cuap. X.] PALAXONTOLOGICAL COLLECTIONS, 61

of each region are almost invariably intermittent; that
is, have not followed each other in close sequence.
Scarcely any fact struck me more when examining
many hundred miles of the South American coasts,
which have been upraised several hundred feet within
the recent period, than the absence of any recent de-
posits sufficiently extensive to last for even a short
geological period. Along the whole west coast, which is
inhabited by a peculiar marine fauna, tertiary beds are
so poorly developed, that no record of several successive
and peculiar marine faunas will probably be preserved
to a distant age. A little reflection will explain why,
along the rising coast of the western side of South
America, no extensive formations with recent or ter-
tiary remains can anywhere be found, though the supply
of sediment must for ages have been great, from the
enormous degradation of the coast-rocks and from
muddy streams entering the sea. The explanation, no
doubt, is, that the littoral and sub-littoral deposits are
continually worn away, as soon as they are brought up
by the slow and gradual rising of the land within the
grinding action of the coast-waves.

We may, I think, conclude that sediment must be
accumulated in extremely thick, solid, or extensive
masses, in order to withstand the incessant action of
the waves, when first upraised and during successive
oscillations of level as well as the subsequent subaerial
degradation. Such thick and extensive accumulations
of sediment may be formed in two ways; either in pro-
found depths of the sea, in which case the bottom will
not be inhabited by so many and such varied forms of
life, as the more shallow seas; and the mass when up-
raised will give an imperfect record of the organisms

62 THE POORNESS OF OUR (Cuap. X.

which existed in the neighbourhood during the period
of its accumulation. Or, sediment may be deposited to
any thickness and extent over a shallow bottom, if it
continue slowly to subside. In this latter case, as long
as the rate of subsidence and the supply of sediment
nearly balance each other, the sea will remain shallow
and favourable for many and varied forms, and thus
a rich fossiliferous formation, thick enough, when up-
raised, to resist a large amount of denudation, may be
formed.

I am convinced that nearly all our ancient forma-
tions, which are throughout the greater part of their
thickness rich in fossils, have thus been formed during
subsidence. Since publishing my views on this subject
in 1845, I have watched the progress of Geology, an
have been surprised to note how author after author,
in treating of this or that great formation, has come to
the conclusion that it was accumulated during subsi-
dence. I may add, that the only ancient tertiary forma-
tion on the west coast of South America, which has
been bulky enough to resist such degradation as it has
as yet suffered, but which will hardly last to a dis-
tant geological age, was deposited during a downward
oscillation of level, and thus gained considerable thick-
ness. .

All geological facts tell us plainly that each area
has undergone numerous slow oscillations of level, and
apparently these oscillations have affected wide spaces.
Consequently, formations rich in fossils and sufficiently
thick and extensive to resist subsequent degradation,
will have been formed over wide spaces during periods
of subsidence, but only where the supply of sediment
was sufficient to keep the sea shallow and to embed

Cuap, X.] PALAZONTOLOGICAL COLLECTIONS, 63

and preserve the remains before they had time to de-
cay. On the other hand, as long as the bed of the sea
remains stationary, thick deposits cannot have been ac-
cumulated in the shallow parts, which are the most
favourable to life. Still less can this have happened
during the alternate periods of elevation; or, to speak
more accurately,-the beds which were then accumu-
lated will generally have been destroyed by being
upraised and brought within the limits of the coast-
action.

These remarks apply chiefly to littoral and sub-lit-
toral deposits. In the case of an extensive and shallow
sea, such as that within a large part of the Malay Archi-
pelago, where the depth varies from 30 or 40 to 60
fathoms, a widely extended formation might be formed
‘luring a period of elevation, and yet not suffer exces-
sively from denudation during its slow upheaval; but
the thickness of the formation could not be great, for
nwing to the elevatory movement it would be less than
the depth in which it was formed; nor would the de-
posit be much consolidated, nor be capped by overlying
formations, so that it would run a good chance of being
worn away by atmospheric degradation and by the ac-
tion of the sea during subsequent oscillations of level.
It has, however, been suggested by Mr. Hopkins, that
if one part of the area, after rising and before being
denuded, subsided, the deposit formed during the ris-
ing movement, though not thick, might afterwards be-
come protected by fresh accumulations, and thus be
preserved for a long period.

Mr. Hopkins also expresses his belief that sedimen-
tary beds of considerable horizontal extent have rarely
been completely destroyed. But all geologists, except-

64 THE POORNESS OF OUR [Cuap. &

ing the few who believe that our present metamorphic
schists and plutonic rocks once formed the primordial
nucleus of the globe, will admit that these latter rocks
have been stript of their covering to an enormous ex-
tent. For it is scarcely possible that such rocks could
have been solidified and crystallized whilst uncovered;
but if the metamorphic action occurred at profound
depths of the ocean, the former protecting mantle of
rock may not have been very thick. Admitting then
that gneiss, mica-schist, granite, diorite, &c., were
once necessarily covered up, how can we account for
the naked and extensive areas of such rocks in many
parts of the world, except on the belief that they have
subsequently been completely denuded of all overlying
strata? That such extensive areas do exist cannot be
doubted: the granitic region of Parime is described by
Humboldt as being at least nineteen times as large as
Switzerland. South of the Amazon, Boué colours an
area composed of rocks of this nature as equal to that
of Spain, France, Italy, part of Germany, and the
British Islands, all conjoined. This region has not
been carefully explored, but from the concurrent testi-
mony of travellers, the granitic area is very large: thus,
Von Eschwege gives a detailed section of these rocks,
stretching from Rio de Janeiro for 260 geographical
miles inland in a straight line; and I travelled for 150
miles in another direction, and saw nothing but granitic
rocks. Numerous specimens, collected along the
whole coast from near Rio Janeiro to the mouth of the
Plata, a distance of 1100 geographical miles, were ex-
amined by me, and they all belonged to this class. In-
land, along the whole northern bank of the Plata I
saw, besides modern tertiary beds, only one small patch

Cuap. X.] PALASONTOLOGICAL COLLECTIONS. 65

of slightly metamorphosed rock, which alone could have
formed a part of the original capping of the granitic
series. Turning to a well-known region, namely, to
the United States and Canada, as shown in Professor
H. D. Rogers’s beautiful map, I have estimated the
areas by cutting out and weighing the paper, and I
find that the metamorphic (excluding “ the semi-meta-
“morphic ”) and granitic rocks exceed, in the propor-
tion of 19 to 12.5, the whole of the newer Paleozoic
formations. In many regions the metamorphic and
granitic rocks would be found much more widely ex-
tended than they appear to be, if all the sedimentary
beds were removed which rest unconformably on them,
and which could not have formed part of the original
mantle under which they were crystallized. Hence it
is probable that in some parts of the world whole forma-
tions have been completely denuded, with not a wreck
left behind.

One remark is here worth a passing notice. During
periods of elevation the area of the land and of the ad-
joining shoal parts of the sea will be increased, and new
stations will often be formed:—all circumstances favour-
able, as previously explained, for the formation of
new varieties and species; but during such periods there
will generally be a blank in the geological record. On
the other hand, during subsidence, the inhabited area
and number of inhabitants will decrease (excepting on
the shores of a continent when first broken up into an
archipelago), and consequently during subsidence,
though there will be much extinction, few new varie-
ties or species will be formed; and it is during these
very periods of subsidence, that the deposits which are
richest in fossils have been accumulated.

66 ABSENCE OF INTERMEDIATE VARIETIES [Cuar. 4.

On the Absence of Numerous Intermediate Varieties tn
any Single Formation.

From these several considerations, it cannot be
doubted that the geological record, viewed as a whole,
is extremely imperfect; but if we confine our attention
to any one formation, it becomes much more difficult to
understand why we do not therein find closely gradu-
ated varieties between the allied species which lived at
its commencement and at its close. Several cases are
on record of the same species presenting varieties in
the upper and lower parts of the same formation; thus,
Trautschold gives a number of instances with Am-
monites; and Hilgendorf has described a most curious
case of ten graduated forms of Planorbis multiformis in
the successive beds of a fresh-water formation in Swit-
zerland. Although each formation has indisputably
required a vast number of years for its deposition, sev-
eral reasons can be givenwhy each should not commonly
include a graduated series of links between the species
which lived at its commencement and close; but I
cannot assign due proportional weight to the following
considerations.

Although each formation may mark a very long
lapse of years, each probably is short compared with the
period requisite to change one species into another. I
am aware that two paleontologists, whose opinions are
worthy of much deference, namely Bronn and Wood-
ward, have concluded that the average duration of each
formation is twice or thrice as long as the average dura-
tion of specific forms. But insuperable difficulties,
as it seems to me, prevent us from coming to any just
conclusion on this head. When we see a species first

Cuap. X.] IN ANY SINGLE FORMATION. 67

appearing in the middle of any formation, it would be
rash in the extreme to infer that it had not elsewhere
previously existed. So again when we find a species
disappearing before the last layers have been deposited,
it would be equally rash to suppose that it then became
extinct. We forget how small the area of Europe is
compared with the rest of the world; nor have the sev-
eral stages of the same formation throughout Europe
been correlated with perfect accuracy.

We may safely infer that with marine animals of all
kinds there has been a large amount of migration due
to climatal and other changes; and when we see a
species first appearing in any formation, the probabil-
ity is that it only then first immigrated into that area.
It is well-known, for instance, that several species ap-
pear somewhat earlier in the paleozoic beds of North
America than in those of Europe; time having appa-
rently been required for their migration from the
American to the European seas. In examining the
latest deposits in various quarters of the world, it has
everywhere been noted, that some few still existing
species are common in the deposit, but have become
extinct in the immediately surrounding sea; or, con-
versely, that some are now abundant in the neighbour-
ing sea, but are rare or absent in this particular deposit.
It is an excellent lesson to reflect on the ascertained
amount of migration of the inhabitants of Europe dur-
ing the glacial epoch, which forms only a part of one
whole geological period; and likewise to reflect on the
changes of level, on the extreme change of climate, and
on the great lapse of time, all included within this
same glacial period. Yet it may be doubted whether,
in any quarter of the world, sedimentary deposits, in-

‘0

68 ABSENCE OF INTERMEDIATE VARIETIES ([Cuap. X.

including fossil remains, have gone on accumulating
within the same area during the whole of this period.
It is not, for instance, probable that sediment was de-
posited during the whole of the glacial period near
the mouth of the Mississippi, within that limit of depth
at which marine animals can best flourish: for we know
that great geographical changes occurred in other parts
of America during this space of time. When such
beds as were deposited in shallow water near the mouth
of the Mississippi during some part of the glacial period
shall have been upraised, organic remains will prob-
ably first appear and disappear at different levels, ow-
ing to the migrations of species and to geographical
changes. And in the distant future, a geologist, ex-
amining these beds, would be tempted to conclude that
the average duration of life of the embedded fossils had
been less than that of the glacial period, instead of hav-
ing been really far greater, that is, extending from be-
fore the glacial epoch to the present day.

In order to get a perfect gradation between two
forms in the upper and lower parts of the same forma-
tion, the deposit must have gone on continuously ac-
cumulating during a long period, sufficient for the slow
process of modification; hence the deposit must be
a very thick one; and the species undergoing change
must have lived in the same district throughout the
whole time. But we have seen that a thick formation,
fossiliferous throughout its entire thickness, can ac-
cumulate only during a period of subsidence; and to
keep the depth approximately the same, which is neces-
sary that the same marine species may live on the same
space, the supply of sediment must nearly counterbal-
ance the amount of subsidence. But this same move-

Cuap. X.] IN ANY SINGLE FORMATION. 69

ment of subsidence will tend to submerge the area
whence the sediment is derived, and thus diminish the
supply, whilst the downward movement continues. In
fact, this nearly exact balancing between the supply of
sediment and the amount of subsidence is probably a
rare contingency; for it has been observed by more than
one paleontologist, that very thick deposits are usually
barren of organic remains, except near their upper or
lower limits.

It would seem that each separate formation, like the
whole pile of formations in any country, has generally
been intermittent in its accumulation. When we see,
as is so often the case, a formation composed of beds
of widely different mineralogical composition, we may
reasonably suspect that the process of deposition has
been more or less interrupted. Nor will the closest
inspection of a formation give us any idea of the length
of time which its deposition may have consumed.
Many instances could be given of beds only a few feet
in thickness, representing formations, which are else-
where thousands of feet in thickness, and which must
have required an enormous period for their accumula-
tion; yet no one ignorant of this fact would have even
suspected the vast lapse of time represented by the
thinner formation. Many cases could be given of the
lower beds of a formation having been upraised, de-
nuded, submerged, and then re-covered by the upper
beds of the same formation,—facts, showing what wide,
yet easily overlooked, intervals have occurred in its ac-
cumulation. In other cases we have the plainest evi-
dence in great fossilised trees, still standing upright
as they grew, of many long intervals of time and changes
of level during the process of deposition, which would

70 ABSENCE OF INTERMEDIATE VARIETIES [Caar. X.

not have been suspected, had not the trees been pre-
served: thus Sir C. Lyell and Dr. Dawson found carbon-
iferous beds 1400 feet thick in Nova Scotia, with an-
cient root-bearing strata, one above the other at no
less than sixty-eight different levels. Hence, when the
same species occurs at the bottom, middle, and top of a
formation, the probability is that it has not lived on the
same spot during the whole period of deposition, but
has disappeared and reappeared, perhaps many times,
during the same geological period. Consequently if it
were to undergo a considerable amount of modification
during the deposition of any one geological formation,
a section would not include all the fine intermediate
gradations which must on our theory have existed, but
abrupt, though perhaps slight, changes of form.

It is all-important to remember that naturalists have
no golden rule by which to distinguish species and
varieties; they grant some little variability to each
species, but when they meet with a somewhat greater
amount of difference between any two forms, they rank
both as species, unless they are enabled to connect them
together by the closest intermediate gradations; and
this, from the reasons just assigned, we can seldom
hope to effect in any one geological section. Supposing
B and C to be two species, and a third, A, to be found in
an older and underlying bed; even if A were strictly
intermediate between B and C, it would simply be
ranked as a third and distinct species, unless at the
same time it could be closely connected by interme-
diate varieties with either one or both forms. Nor
should it be forgotten, as before explained, that A
might be the actual progenitor of B and C, and yet
would not necessarily be strictly intermediate between

Cuap, X.]} IN ANY SINGLE FORMATION. vel

them in all respects. So that we might obtain the
parent-species and its several modified descendants from
the lower and upper beds of the same formation, and un-
less we obtained numerous transitional gradations, we
should not recognise their blood-relationship, and
should consequently rank them as distinct species.

It is notorious on what excessively slight differences
many paleontologists have founded their species; and
they do this the more readily if the specimens come
from different sub-stages of the same formation. Some
experienced conchologists are now sinking many of the
very fine species of D’Orbigny and others into the
rank of varieties; and on this view we do find the kind
of evidence of change which on the theory we ought to
find. Look again at the later tertiary deposits, which
include many shells believed by the majority of natu-
talists to be identical with existing species; but some
excellent naturalists, as Agassiz and Pictet, maintain
that all these tertiary species are specifically distinct,
though the distinction is admitted to be very slight; so
that here, unless we believe that these eminent natu-
talists have been misled by their imaginations, and
that these late tertiary species really present no dif-
ference whatever from their living representatives, or
unless we admit, in opposition to the judgment of most
naturalists, that these tertiary species are all truly dis-
tinct from the recent, we have evidence of the frequent
occurrence of slight modifications of the kind required.
If we look to rather wider intervals of time, namely,
to distinct but consecutive stages of the same great
formation, we find that the embedded fossils, though
universally ranked as specifically different, yet are far
more closely related to each other than are the species

72 ABSENCE OF INTERMEDIATE VARIETIES (Cusp. »

found in more widely separated formations; so that
here again we have undoubted evidence of change in
the direction required by the theory; but to this latter
subject I shall return in the following chapter.

With animals and plants that propagate rapidly and
do not wander much, there is reason to suspect, as we
have formerly seen, that their varieties are generally at
first local; and that such local varieties do not spread
widely and supplant their parent-forms until they have
been modified and perfected in some considerable de-
gree. According to this view, the chance of discov-
ering in a formation in any one country all the early
stages of transition between any two forms, is small,
for the successive changes are supposed to have been
local or confined to some one spot. Most marine ani-
mals have a wide range; and we have seen that with
plants it is those which have the widest range, that
oftenest present varieties; so that, with shells and other
marine animals, it is probable that those which had
the widest range, far exceeding the limits of the known
geological formations in Europe, have oftenest given
rise, first to local varieties and ultimately to new spe-
cies; and this again would greatly lessen the chance of
our being able to trace the stages of transition in any
one geological formation.

It is a more important consideration, leading to the
same result, as lately insisted on by Dr. Falconer, name-
ly, that the period during which each species under-
went modification, though long as measured by years,
was probably short in comparison with that during
‘which it remained without undergoing any change.

It should not be forgotten, that at the present day,
with perfect specimens for examination, two forms can

Cuap. X.] IN ANY SINGLE FORMATION. 13

seldom be connected by intermediate varieties, and thus
proved to be the same species, until many specimens
are collected from many places; and with fossil species
this can rarely be done. We shall, perhaps, best per-
ceive the improbability of our being enabled to con-
nect species by numerous, fine, intermediate, fossil links,
by asking ourselves whether, for instance, geologists
at some future period will be able to prove that our
different breeds of cattle, sheep, horses, and dogs are
descended from a single stock or from several abori-
ginal stocks; or, again, whether certain sea-shells in-
habiting the shores of North America, which are
ranked by some conchologists as distinct species from
their European representatives, and by other con-
chologists as only varieties, are really varieties, or
are, as it is called, specifically distinct. This could
be effected by the future geologist only by his discover-
ing in a fossil state numerous intermediate grada-
tions; and such success is improbable in the highest de-
gree.

It has been asserted over and over again, by writers
who believe in the immutability of species, that geology
yields no linking forms. This assertion, as we shall
see in the next chapter, is certainly erroneous. As Sir
J. Lubbock has remarked, “Every species is a link
“between other allied forms.” If we take a genus
having a score of species, recent and extinct, and de-
stroy four-fifths of them, no one doubts that the re-
mainder will stand much more distinct from each other.
Tf the extreme forms in the genus happen to have been
thus destroyed, the genus itself will stand more distinct
from other allied genera. What geological research
has not revealed, is the former existence of infinitely

74. ABSENCE OF INTERMEDIATE VARIETIES [Cuap. X.

numerous gradations, as fine as existing varieties, con-
necting together nearly all existing and extinct species.
But this ought not to be expected; yet this has been
repeatedly advanced as a most serious objection against
my views.

It may be worth while to sum up the foregoing
remarks on the causes of the imperfection of the geo-
logical record under an imaginary illustration. The
Malay Archipelago is about the size of Europe from the
North Cape to the Mediterranean, and from Britain to
Russia; and therefore equals all the geological forma-
tions which have been examined with any accuracy,
excepting those of the United States of America. I
fully agree with Mr. Godwin-Austen, that the present
condition of the Malay Archipelago, with its numerous
large islands separated by wide and shallow seas, prob-
ably represents the former state of Europe, whilst
most of our formations were accumulating. The Malay
Archipelago is one of the richest regions in organic
beings; yet if all the species were to be collected which
have ever lived there, how imperfectly would they
represent the natural history of the world!

But we have every reason to believe that the ter-
restrial productions of the archipelago would be pre-
served in an extremely imperfect manner in the forma-
tions which we suppose to be there accumulating. Not
many of the strictly littoral animals, or of those which
lived on naked submarine rocks, would be embedded;
and those embedded in gravel or sand would not en-
dure to a distant epoch. Wherever sediment did not
accumulate on the bed of the sea, or where it did not
accumulate at a sufficient rate to protect organic bodies
from decay, no remains could be preserved.

Cuap. X.| IN ANY SINGLE FORMATION. 45

Formations rich in fossils of many kinds, and of
thickness sufficient to last to an age as distant in futu-
rity as the secondary formations lie in the past, would
generally be formed in the archipelago only during
periods of subsidence. These periods of subsidence
would be separated from each other by immense in-
tervals of time, during which the area would be either
stationary or rising; whilst rising, the fossiliferous for-
mations on the steeper shores would be destroyed, al-
Most as soon as accumulated, by the incessant coast-
action, as we now see on the shores of South America.
Even throughout the extensive and shallow seas with-
in the archipelago, sedimentary beds could: hardly be
accumulated of great thickness during the periods of
elevation, or become capped and protected by subse-
quent deposits, so as to have a good chance of enduring
to a very distant future. During the periods of sub-
sidence, therewould probably be much extinction of life;
during the periods of elevation, there would be much
variation, but the geological record would then be less
perfect.

It may be doubted whether the duration of any one
great period of subsidence over the whole or part of the
archipelago, together with a contemporaneous accumu-
lation of sediment, would exceed the average duration of
the same specific forms; and these contingencies are in-
dispensable for the preservation of all the transitional
gradations between any two or more species. If such
gradations were not all fully preserved, transitional
varieties would merely appear as so many new, though
closely allied species. It is also probable that each
great period of subsidence would be interrupted by os-
cillations of level, and that slight climatal changes

46 ABSENCE OF INTERMEDIATE VARIETIES [Cuap. X.

would intervene during such lengthy periods; and in
these cases the inhabitants of the archipelago would
migrate, and no closely consecutive record of their
modifications could be preserved in any one formation.

Very many of the marine inhabitants of the archi-
pelago now range thousands of miles beyond its con-
fines; and analogy plainly leads to the belief that it
would be chiefly these far-ranging species, though only
some of them, which would oftenest produce new varie-
ties; and the varieties would at first be local or con-
fined to one place, but if possessed of any decided ad-
vantage, or when further modified and improved, they
would slowly spread and supplant their parent-forms.
When such varieties returned to their ancient homes,
as they would differ from their former state in a nearly
uniform, though perhaps extremely slight degree, and
as they would be found embedded in slightly different
sub-stages of the same formation, they would, accord-
ing to the principles followed by many palzontologists,
be ranked as new and distinct species.

If then there be some degree of truth in these re-
marks, we have no right to expect to find, in our geo-
logical formations, an infinite number of those fine
transitional forms which, on our theory, have connected
all the past and present species of the same group into
one long and branching chain of life. We ought only
to look for a few links, and such assuredly we do find—
some more distantly, some more closely, related to
each other; and these links, let them be ever so close,
if found in different stages of the same formation,
would, by many paleontologists, be ranked as distinct
species. But I do not pretend that I should ever have
suspected how poor was the record in the best preserved

Cuap. X.] IN ANY SINGLE FORMATION. "7

geological sections, had not the absence of innumerable
transitional links between the species which lived at
the commencement and close of each formation, pressed
so hardly on my theory.

On the sudden Appearance of whole Groups of allied
Species.

The abrupt manner in which whole groups of spe-
cies suddenly appear in certain formations, has been
urged by several paleontologists—for instance, by Agas-
siz, Pictet, and Sedgwick—as a fatal objection to the be-
lief in the transmutation of species. If numerous spe-
cies, belonging to the same genera or families, have
really started into life at once, the fact would be fatal to
the theory of evolution through natural selection. For
the development by this means of a group of forms, all
of which are descended from some one progenitor, must
have been an extremely slow process; and the progeni-
tors must have lived long before their modified descen-
dants. But we continually overrate the perfection of
the geological record, and falsely infer, because certain
genera or families have not been found beneath a cer-
tain stage, that they did not exist before that stage.
In all cases positive paleontological evidence may be
implicitly trusted; negative evidence is worthless, as
experience has so often shown. We continually forget
how large the world is, compared with the area over
which our geological formations have been carefully
examined; we forget that groups of species may else-
where have long existed, and have slowly multiplied,
before they invaded the ancient archipelagoes of Europe
and the United States. We do not make due allowance

78 SUDDEN APPEARANCE OF [Cuar. X.

for the intervals of time which have elapsed between
our consecutive formations,—longer perhaps in many
cases than the time required for the accumulation of
each formation. These intervals will have given time
for the multiplication of species from some one parent-
form: and in the succeeding formation, such groups or
species will appear as if suddenly created.

I may here recall a remark formerly made, namely,
that it might require a long succession of ages to adapt
an organism to some new and peculiar line of life, for
instance, to fly through the air; and consequently that
the transitional forms would often long remain con-
fined to some one region; but that, when this adapta-
tion had once been effected, and a few species had thus
acquired a great advantage over other organisms, a
comparatively short time would be necessary to produce
many divergent forms, which would spread rapidly and
widely, throughout the world. Professor Pictet, in his
excellent Review of this work, in commenting on early
transitional forms, and taking birds as an illustration,
cannot see how the successive modifications of the an-
terior limbs of a supposed prototype could possibly
have been of any advantage. But look at the penguins
of the Southern Ocean; have not these birds their front
limbs in this precise intermediate state of “ neither true
“arms nor true wings”? Yet these birds hold their
place victoriously in the battle for life; for they exist
in infinite numbers and of many kinds. I do not sup-
pose that we here see the real transitional grades
through which the wings of birds have passed; but
what special difficulty is there in believing that it
might profit the modified descendants of the penguin,
first to become enabled to flap along the surface of the

Cuap. X]. GROUPS OF ALLIED SPECIES. "9

sea like the logger-headed duck, and ultimately to rise
from its surface and glide through the air?

I will now give a few examples to illustrate the
foregoing remarks, and to show how liable we are to
error in supposing that whole groups of species have
suddenly been produced. Even in so short an interval
as that between the first and second editions of Pictet’s
great work on Palzontology, published in 1844-46 and
in 1853-57, the conclusions on the first appearance and
disappearance of several groups of animals have been
considerably modified; and a third edition would re-
quire still further changes. I may recall the well-
known fact that in geological treatises, published not
many years ago, mammals were always spoken of as
having abruptly come in at the commencement of the
tertiary series. And now one of the richest known ac-
cumulations of fossil mammals belongs to the middle of
the secondary series; and true mammals have been dis-
covered in the new red sandstone at nearly the com-
mencement of this great series. Cuvier used to urge
that no monkey occurred in any tertiary stratum; but
now extinct species have been discovered in India, South
America and in Europe, as far back as the miocene
stage. Had it not been for the rare accident of the pres-
ervation of footsteps in the new red sandstone of the
United States, who would have ventured to suppose that
no less than at least thirty different bird-like animals,
some of gigantic size, existed during that period? Not
a fragment of bone has been discovered in these beds.
Not long ago, paleontologists maintained that the
whole class of birds came suddenly into existence during
the eocene period; but now we know, on the authority
of Professor Owen, that a bird certainly lived during

80 SUDDEN APPEARANCE OF [Caap. X

the deposition of the upper greensand; and still more
recently, that strange bird, the Archeopteryx, with a
long lizard-like tail, bearing a pair of feathers on each
joint, and with its wings furnished with two free claws,
has been discovered in the oolitic slates of Solenhofen.
Hardly any recent discovery shows more forcibly than
this, how little we as yet know of the former inhabitants
of the world.

I may give another instance, which, from having
passed under my own eyes, has much struck me. Ina
memoir on Fossil Sessile Cirripedes, I stated that, from
the large number of existing and extinct tertiary spe-
cies; from the extraordinary abundance of the indi-
viduals of many species all over the world, from the
Arctic regions to the equator, inhabiting various zones
of depths from the upper tidal limits to 50 fathoms;
from the perfect manner in which specimens are pre-
served in the oldest tertiary beds; from the ease with
which evena fragment of avalve can be recognised; from
all these circumstances, I inferred that, had sessile cirri-
pedes existed during the secondary periods, they would
certainly have been preserved and discovered; and as
not one species had then been discovered in beds of
this age, I concluded that this great group had been
suddenly developed at the commencement of the ter-
tiary series. This was a sore trouble to me, adding as
I then thought one more instance of the abrupt ap-
pearance of a great group of species. But my work had
hardly been published, when a skilful paleontologist,
M. Bosquet, sent me a drawing of a perfect specimen
of an unmistakable sessile cirripede, which he had him-
self extracted from the chalk of Belgium. And, as
if to make the case as striking as possible, this cirripede

Cuap. X.] GROUPS OF ALLIED SPECIES. 81

was a Chthamalus, a very common, large, and ubiqui-
tous genus, of which not one species has as yet been
found even in any tertiary stratum. Still more re-
cently, a Pyrgoma, a member of a distinct sub-family of
sessile cirripedes, has been discovered by Mr. Wood-
ward in the upper chalk; so that we now have abun-
dant evidence of the existence of this group of animals
during the secondary period.

The case most frequently insisted on by paleonto-
logists of the apparently sudden appearance of a whole
group of species, is that of the teleostean fishes, low
down, according to Agassiz, in the Chalk period. This
group includes the large majority of existing species.
But certain Jurassic and Triassic forms are now com-
monly admitted to be teleostean; and even some paleo-
zoic forms have thus been classed by one high authority.
If the teleosteans had really appeared suddenly in the
northern hemisphere at the commencement of the chalk
formation the fact would have been highly remarkable;
but it would not have formed an insuperable difficulty,
unless it could likewise have been shown that at the
same period the species were suddenly and simultane-
ously developed in other quarters of the world. It
is almost superfluous to remark that hardly any fossil-
fish are known from south of the equator; and by run-
ning through Pictet’s Palzontology it will be seen that
very few species are known from several formations
in Europe. Some few families of fish now have a con-
fined range; the teleostean fishes might formerly have
had a similarly confined range, and after having been
largely developed in some one sea, have spread widely.
Nor have we any right to suppose that the seas of the
world have always been so freely open from south to

82 GROUPS OF ALLIED SPECIES [Caap. X,

north as they are at present. Even at this day, if
the Malay Archipelago were converted into land, the
tropical parts of the Indian Ocean would form a
large and perfectly enclosed basin, in which any great
group of marine animals might be multiplied; and
here they would remain confined, until some of the
species became adapted to a cooler climate, and
were enable to double the Southern capes of Af-
rica or Australia, and thus reach other and distant
seas.

From these considerations, from our ignorance of
the geology of other countries beyond the confines of
Europe and the United States, and from the revolution
in our paleontological knowledge effected by the dis-
coveries of the last dozen years, it seems to me to be
about as rash to dogmatize on the succession of organic
forms throughout the world, as it would be for a natura-
list to land for five minutes on a barren point in Aus-
tralia, and then to discuss the number and range of its
productions.

On the sudden Appearance of Groups of allied Species
in the lowest known Fossiliferous Strata.

There is another and allied difficulty, which is much
more serious. I allude to the manner in which species
belonging to several of the main divisions of the animal
kingdom suddenly appear in the lowest known fossili-
ferous rocks. Most of the arguments which have con-
vinced me that all the existing species of the same group
are descended from a single progenitor, apply with
equal force to the earliest known species. For in-
stance, it cannot be doubted that all the Cambrian and

Cap. X.] IN LOWES1' FOSSILIFEROUS STRATA. 83

Silurian trilobites are descended from some one crusta-
cean, which must have lived long before the Cambrian
age, and which probably differed greatly from any
known animal. Some of the most ancient animals, as
the Nautilus, Lingula, &c., do not differ much from
living species; and it cannot on our theory be supposed,
that these old species were the progenitors of all the
species belonging to the same groups which have sub-
sequently appeared, for they are not in any degree in-
termediate in character.

Consequently, if the theory be true, it is indisputable
that before the lowest Cambrian stratum was deposited
long periods elapsed, as long as, or probably far longer
than, the whole interval from the Cambrian age to the
present day; and that during these vast periods the
world swarmed with living creatures. Here we en-
counter a formidable objection; for it seems doubtful
whether the earth, in a fit state for the habitation of
living creatures, has lasted long enough. Sir W.
Thompson concludes that the consolidation of the crust
can hardly have occurred less than 20 or more than
400 million years ago, but probably not less than 98 or
more than 200 million years. These very wide limits
show how doubtful the data are; and other elements
may have hereafter to be introduced into the problem.
Mr. Croll estimates that about 60 million years have
elapsed since the Cambrian period, but this, judging
from the small amount of organic change since the
commencement of the Glacial epoch, appears a very
short time for the many and great mutations of life,
which have certainly occurred since the Cambrian for-
mation; and the previous 140 million years can hardly

be considered as sufficient for the development of the
' 31

84 GROUPS OF ALLIED SPECIES (Cap. X,

varied forms of life which already existed during the
Cambrian period. It is, however, probable, as Sir Wil-
liam Thompson insists, that the world at a very early
period was subjected to more rapid and violent changes
in its physical conditions than those now occurring;
and such changes would have tended to induce changes
at a corresponding rate in the organisms which then
existed.

To the question why we do not find rich fossiliferous
deposits belonging to these assumed earliest periods
prior to the Cambrian system, I can give no satisfactory
answer. Several eminent geologists, with Sir R. Mur-
chison at their head, were until recently convinced
that we beheld in the organic remains of the lowest
Silurian stratum the first dawn of life. Other highly
competent judges, as Lyell and E. Forbes, have dis-
puted this conclusion. We should not forget that only
a small portion of the world is known with accuracy.
Not very long ago M. Barrande added another and
lower stage, abounding with new and peculiar species,
beneath the then known Silurian system; and now,
still lower down in the Lower Cambrian formation, Mr.
Hicks has found in South Wales beds rich in trilobites,
and containing various molluscs and annelids. The
presence of phosphatic nodules and bituminous matter,
even in some of the lowest azoic rocks, probably indi-
cates life at these periods; and the existence of the
Eozoon in the Laurentian formation of Canada is gener-
ally admitted. There are three great series of strata be-
neath the Silurian system in Canada, in the lowest of
which the Eozoon is found. Sir W. Logan states that
their “united thickness may possibly far surpass that
“ of all the succeeding rocks, from the base of the paleo-

Caar, X.] IN LOWEST FOSSILIFEROUS STRATA. 85

“zoic series to the present time. We are thus carried
“back to a period so remote, that the appeatance of the
“so-called Primordial fauna (of Barrande) may by some
“be considered as a comparatively modern event.” The
Eozoon belongs to the most lowly organised of all
classes of animals, but is highly organised for its class;
it existed in countless numbers, and, as Dr. Dawson has
remarked, certainly preyed on other minute organic
beings, which must have lived in great numbers. Thus
the words, which I wrote in 1859, about the existence
of living beings long before the Cambrian period, and
which are almost the same with those since used by Sir
W. Logan, have proved true. Nevertheless, the diffi-
culty of assigning any good reason for the absence of
vast piles of strata rich in fossils beneath the Cambrian
system is very great. It does not seem probable that
the most ancient beds have been quite worn away by
denudation, or that their fossils have been wholly ob-
literated by metamorphic action, for if this had heen
the case we should have found only small remnants of
the formations next succeeding them in age, and these.
would always have existed in a partially metamorphosed
condition. But the descriptions which we possess of
the Silurian deposits over immense territories in Russia
and in North America, do not support the view, that
the older a formation is, the more invariably it has
suffered extreme denudation and metamorphism.

The case at present must remain inexplicable; and
may be truly urged as a valid argument against the
views here entertained. To show that it may hereafter
receive some explanation, I will give the following hy-
pothesis. From the nature of the organic remains
which do not appear to have inhabited profound depths,

86 GROUPS OF ALLIED SPECIES [Cuap. X.

in the several formations of Europe and of the United
States; and from the amount of sediment, miles in
thickness, of which the formations are composed, we
may infer that from first to last large islands or tracts
of land, whence the sediment was derived, occurred in
the neighbourhood of the now existing continents of
Europe and North America. This same view has since
been maintained by Agassiz and others. But we do not
know what was the state of things in the intervals be-
tween the several successive formations; whether Europe
and the United States during these intervals existed as
dry land, or as a submarine surface near land, on which
sediment was not deposited, or as the bed of an open and
unfathomable sea.

Looking to the existing oceans, which are thrice as
extensive as the land, we see them studded with many
islands; but hardly one truly oceanic island (with the
exception of New Zealand, if this can be called a truly
oceanic island) is as yet known to afford even a remnant
of any paleozoic or secondary formation. Hence we
may perhaps infer, that during the paleozoic and sec-
ondary periods, neither continents nor continental is-
lands existed where our oceans now extend; for had
they existed, paleozoic and secondary formations would
in all probability have been accumulated from sediment
derived from their wear and tear; and these would have
been at least partially upheaved by the oscillations of
level, which must have intervened during these enor-
mously long periods. If then we may infer anything
from these facts, we may infer that, where our oceans
now extend, oceans have extended from the remotest
period of which we have any record; and on the other
hand, that where continents now exist, large tracts of

Cuap. X.] IN LOWEST FOSSILIFEROUS STRATA. 87

land have existed, subjected no doubt to great oscilla-
tions of level, since the Cambrian period. The col-
oured map appended to my volume on Coral Reefs, led
me to conclude that the great oceans are still mainly
areas of subsidence, the great archipelagoes still areas of
oscillations of level, and the continents areas of eleva-
tion. But we have no reason to assume that things have
thus remained from the beginning of the world. Our
continents seem to have been formed by a preponder-
ance, during many oscillations of level, of the force of
elevation; but may not the areas of preponderant move-
ment have changed in the lapse of ages? At a period
long antecedent to the Cambrian epoch, continents may
have existed where oceans are now spread out; and clear
and open oceans may have existed where our continents
now stand. Nor should we be justified in assuming
that if, for instance, the bed of the Pacific Ocean were
now converted into a continent we should there find
sedimentary formations in a recognisable condition older
than the Cambrian strata, supposing such to have been
formerly deposited; for it might well happen that strata
which had subsided some milesnearerto the centre of the
earth, and which had been pressed on by an enormous
weight of superincumbent water, might have undergone
far more metamorphic action than strata which have al-
ways remained nearer to the surface. The immense
areas in some parts of the world, for instance in South
America, of naked metamorphic rocks, which must have
been heated under great pressure, have always seemed to
me to require some special explanation; and we may per-
haps believe that we see in these large areas, the many
formations long anterior to the Cambrian epoch in a
completely metamorphosed and denuded condition.

88 IMPERFECTION OF GEOLOGICAL RECORD. [Cur X

The several difficulties here discussed, namely—that,
though we find in our geological formations many links,
between the species which now exist and which formerly
existed, we do not find infinitely numerous fine transi-
tional forms closely joining them all together;—the
sudden manner in which several groups of species first
appear in our European formations;—the almost entire
absence, as at present known, of formations rich in fos-
sils beneath the Cambrian strata,—are all undoubtedly
of the most serious nature. We see this in the fact that
the most eminent paleontologists, namely, Cuvier,
Agassiz, Barrande, Pictet, Falconer, E. Forbes, &c., and —
all our greatest geologists,as Lyell, Murchison, Sedgwick,
&c., have unanimously, often vehemently, maintained
the immutability of species. But Sir Charles Lyell
now gives the support of his high authority to the op-
posite side; and most geologists and paleontologists are
much shaken in their former belief. Those who believe
that the geological record is in any degree perfect, will
undoubtedly at once reject the theory. For my part,
following out Lyell’s metaphor, I look at the geological
record as a history of the world imperfectly kept, and
written in a changing dialect; of this history we pos-
sess the last volume alone, relating only to two or three
countries. Of this volume, only here and there a short
chapter has been preserved; and of each page, only here
and there a few lines. Each word of the slowly-changing
language, more or less different in the successive chap-
ters, may represent the forms of life, which are en-
tombed in our consecutive formations, and which falsely
appear to have been abruptly introduced. On this
view, the difficulties above discussed are greatly dimin-
ished, or even disappear.

Cuar. XL] SUCCESSION OF ORGANIC BEINGS. Faye]

CHAPTER XI.

ON THE GEOLOGICAL SUCCESSION OF ORGANIC BEINGS

On the slow and successive appearance of new species—On their
different rates of change—Species once lost do not reappear—
Groups of species follow the same general rules in their ap-
pearance and disappearance as do single species—On extinction
—On simultaneous changes in the forms of life throughout the
world—On the affinities of extinct species to each other and to
living species—On the state of development of ancient forms—
On the succession of the same types within the same areas—
Summary of preceding and present chapter.

LET us now see whether the several facts and laws
relating to the geological succession of organic beings
accord best with the common view of the immutability
of species, or with that of their slow and gradual modi-
fication, through variation and natural selection.

New species have appeared very slowly, one after
another, both on the land and in the waters. Lyell has
shown that it is hardly possible to resist the evidence on
this head in the case of the several tertiary stages; and
every year tends to fill up the blanks between the stages,
and to make the proportion between the lost and exist-
ing forms more gradual. In some of the most recent
beds, though undoubtedly of high antiquity if measured
by years, only one or two species are extinct, and only
one or two are new, having appeared there for the first
time, either locally, or, as far as we know, on the face of
the earth. The secondary formations are more broken;

90 THE GEOLOGICAL SUCCESSION [Cuap. XL

but, as Bronn has remarked, neither the appearance
nor disappearance of the many species embedded in
each formation has been simultaneous.

Species belongingto different genera and classes have
not changed at the same rate, or in the same degree.
In the older tertiary beds a few living shells may still
be found in the midst of a multitude of extinct forms.
Falconer has given a striking instance of a similar fact,
for an existing crocodile is associated with many lost
mammals and reptiles in the sub-Himalayan deposits.
The Silurian Lingula differs but little from the living
species of this genus; whereas most of the other Silurian
Molluscs and all the Crustaceans have changed greatly.
The productions of the land seem to have changed at a
quicker rate than those of the sea, of which a striking
instance has been observed in Switzerland. ‘There is
some reason to believe that organisms high in the scale,
change more quickly than those that are low: though
there are exceptions to this rule. The amount of or-
ganic change, as Pictet has remarked, is not the same in
each successive so-called formation. Yet if we compare
any but the most closely related formations, all the spe-
cies will be found to have undergone some change.
When a species has once disappeared from the face of
the earth, we have no reason to believe that the same
identical form ever reappears. The strongest apparent
exception to this latter rule is that of the so-called
“colonies” of M. Barrande, which intrude for a period
in the midst of an older formation, and then allow the
pre-existing fauna to reappear; but Lyell’s explanation,
namely, that it is a case of temporary migration from a
distinct geographical province, seems satisfactory.

These several facts accord well with our theory,

Crap. XL] OF ORGANIC BEINGS. 91

which includes no fixed law of development, causing all
the inhabitants ofan area to change abruptly, or simul-
taneously, or to an equal degree. The process of modi-
fication must be slow, and will generally effect only a
few species at the same time; for the variability of each
species is independent of that of all others. Whether
such variations or individual differences as may arise
will be accumulated through natural selection in a
greater or less degree, thus causing a greater or less
amount of permanent modification, will depend on many
complex contingencies—on the variations being of a
beneficial nature, on the freedom* of intercrossing, on
the slowly changing physical conditions of the country,
on the immigration of new colonists, and on the nature
of the other inhabitants with which the varying species
come into competition. Hence it is by no means sur-
prising that one species should retain the same identi-
cal form much longer than others; or, if changing,
should change in a less degree. We find similar rela-
tions between the existing inhabitants of distinct coun-
tries; for instance, the land-shells and coleopterous in-
sects of Madeira have come to differ considerably from
their nearest allies on the continent of Europe, whereas
the marine shells and birds have remained unaltered.
We can perhaps understand the apparently quicker rate
of change in terrestrial and in more highly organised
productions compared with marine and lower produc-
tions, by the more complex relations of the higher
beings to their organic and inorganic conditions of life,
as explained in a former chapter. When many of the
inhabitants of any area have become modified and im-
proved, we can understand, on the principle of compe-
tition, and from the all-important relations of organ-

92 THE GEOLOGICAL SUCCESSION [Caar. AL

ism to organism in the struggle for life, that any form
which did not become in some degree modified and im-
proved, would be liable to extermination. Hence we see
why all the species in the same region do at last, if we
look to long enough intervals of time, become modified,
for otherwise they would become extinct.

In members of the same class the average amount of
change, during long and equal periods of time, may,
perhaps, be nearly the same; but as the accumulation
of enduring formations, rich in fossils, depends on great
masses of sediment being deposited on subsiding areas,
our formations have been almost necessarily accumu-
lated at wide and irregularly intermittent intervals of
time; consequently the amount of organic change ex-
hibited by the fossils embedded in consecutive forma-
tions is not equal. Each formation, on this view, does
not mark a new and complete act of creation, but only
an occasional scene, taken almost at hazard, in an ever
slowly changing drama.

We can clearly understand why a species when once
lost should never reappear, even if the very same con-
ditions of life, organic and inorganic, should recur.
For though the offspring of one species might be
adapted (and no doubt this has occurred in innumerable
instances) to fill the place of another species in the econ-
omy of nature, and thus supplant it; yet the two forms |
—the old and the new—would not be identically the
same; for both would almost certainly inherit different
characters from their distinct progenitors; and organ-
isms already differing would vary in a different manner.
For instance, it is possible, if all our fantail pigeons
were destroyed, that fanciers might make a new breed
hardly distinguishable from the present breed; but if

Cuap. XI] OF ORGANIC BEINGS. 93

the parent rock-pigeon were likewise destroyed, and
under nature we have every reason to believe that
parent-forms are generally supplanted and exterminated
by their improved offspring, it is incredible that a fantail,
identical with the existing breed, could be raised from
any other species of pigeon, or even from any other well-
established race of the domestic pigeon, for the successive
variations would almost certainly be in some degree dif-
ferent, and the newly-formed variety would probably in-
herit from its progenitor some characteristic differences.

Groups of species, that is, genera and families, fol-
low the same general rules in their appearance and dis-
appearance as do single species, changing more or less
quickly, and in a greater or lesser degree. A group,
when it has once disappeared, never reappears; that is,
its existence, as long as it lasts, is continuous. I am
aware that there are some apparent exceptions to this
rule, but the exceptions are surprisingly few, so few that
E. Forbes, Pictet, and Woodward (though all strongly
opposed to such views as I maintain) admit its truth;
and the rule strictly accords with the theory. For all
the species of the same group, however long it may
have lasted, are the modified descendants one from the
other, and all from a common progenitor. In the genus
Lingula, for instance, the species which have successively
appeared at all ages must have been connected by an
unbroken series of generations, from the lowest Silurian
stratum to the present day.

We have seen in the last chapter that whole groups
of species sometimes falsely appear to have been abrupt-
ly developed; and I have attempted to give an explana-
tion of this fact, which if true would be fatal to my
views. But such cases are certainly exceptional; the

94 EXTINCTION. [Caap. XL

general rule being a gradual increase in number, until
the group reaches its maximum, and then, sooner or
later, a gradual decrease. If the number of the species
included within a genus, or the number of the genera
within a family, be represented by a vertical line of vary-
ing thickness, ascending through the successive geologi-
cal formations, in which the species are found, the line
will sometimes falsely appear to begin at its lower end,
not in a sharp point, but abruptly; it then gradually
thickens upwards, often keeping of equal thickness for,
a space, and ultimately thins out in the upper beds,
marking the decrease and final extinction of the species.
This gradual increase in number of the species of a
group is strictly conformable with the theory, for the
species of the same genus, and the genera of the same
family, can increase only slowly and progressively; the
process of modification and the production of a number
of allied forms necessarily being a slow and gradual pro-
cess,—one species first giving rise to two or three varie-
ties, these being slowly converted into species, which in
their turn produce by equally slow steps other varieties
and species, and so on, like the branching of a great tree
from a single stem, till the group becomes large.

On Extinction.

We have as yet only spoken incidentally of the dis-
appearance of species and of groups of species. On the
theory of natural selection, the extinction of old forms
and the production of new and improved forms are
intimately connected together. The old notion of all
the inhabitants of the earth having been swept away by
catastrophes at successive periods is very generally given
up, even by those geologists, as Elie-de Beaumont, Mur-

Cuap. XI.] EXTINCTION. 95

chison, Barrande, &c., whose general views would natu-
rally lead them to this conclusion. On the contrary,
we have every reason to believe, from the study of the
tertiary formations, that species and groups of species
gradually disappear, one after another, first from one
spot, then from another, and finally from the world. In
some few cases however, as by the breaking of an isth-
mus and the consequent irruption of a multitude of new
inhabitants into an adjoining sea, or by the final subsi-
dence of an island, the process of extinction may have
been rapid. Both single species and whole groups of
species last for very unequal periods; some groups, as
we have seen, have endured from the earliest known
dawn of life to the present day; some have disappeared
before the close of the paleozoic period. No fixed law
seems to determine the length of time during which
any single species or any single genus endures. There
is reason to believe that the extinction of a whole group
of species is generally a slower process than their pro-
duction: if their appearance and disappearance be rep-
resented, as before, by a vertical line of varying thick-
ness the line is found to taper more gradually at its up-
per end, which marks the progress of extermination,
than at its lower end, which marks the first appearance
and the early increase in number of the species. In
some cases, however, the extermination of whole groups,
as of ammonites, towards the close of the secondary
period, has been wonderfully sudden.

The extinction of ‘species has been involved in the
most gratuitous mystery. Some authors have even sup-
posed that, as the individual has a definite length of
life, so have species a definite duration. No one can
have marvelled more than I have done at the extinction

96 EXTINCTION. [Cuap. XI.

of species. When I found in La Plata the tooth of a
horse embedded with the remains of Mastodon, Mega-
therium, Toxodon, and other extinct monsters, which
all co-existed with still living shells at a very late geo-
logical period, I was filled with astonishment; for, see-
ing that the horse, since its introduction by the Span-
iards into South America, has run wild over the whole
country and has increased in numbers at an unparal-
leled rate, I asked myself what could so recently have
exterminated the former horse under conditions of life
apparently so favourable. But my astonishment was
groundless. Professor Owen soon perceived that the
tooth, though so like that of the existing horse, be-
longed to an extinct species. Had this horse been still
living, but in some degree rare, no naturalist would
have felt the least surprise at its rarity; for rarity is the
attribute of a vast number of species of all classes, in all
countries. If we ask ourselves why this or that species
is rare, we answer that something is unfavourable in its
conditions of life; but what that something is we can
hardly ever tell. On the supposition of the fossil horse
still existing as a rare species, we might have felt cer-
tain, from the analogy of all other mammals, even of
the slow-breeding elephant, and from the history of the
naturalisation of the domestic horse in South America,
that under more favourable conditions it would in a
very few years have stocked the whole continent. But
we could not have told what the unfavourable condi-
tions were which checked its increase, whether some one
or several contingencies, and at what period of the
horse’s life, and in what degree they severally acted. If
the conditions had gone on, however slowly, becoming
less and less favourable, we assuredly should not have

Cuap. X1.] EXTINCTION. 97

perceived the fact, yet the fossil horse would certainly
have become rarer and rarer, and finally extinct;—its
place beingseized on bysome more successful competitor.
It is most difficult always to remember that the in-
crease of every creature is constantly being checked
by unperceived hostile agencies; and that these same
unperceived agencies are amplysufficient to cause rarity,
and finally extinction. So little is this subject under-
stood, that I have heard surprise repeatedly expressed
at such great monsters as the Mastodon and the more
ancient Dinosaurians having become extinct; as if mere
bodily strength gave victory in the battle of life. Mere
size, on the contrary, would in some cases determine, as
has been remarked by Owen, quicker extermination
from the greater amount of requisite food. Before
man inhabited India or Africa, some cause must have
checked the continued increase of the existing elephant.
A highly capable judge, Dr. Falconer, believes that it is
chiefly insects which, from incessantly harassing and
weakening the elephant in India, check its increase; and
this was Bruce’s conclusion with respect to the African
elephant in Abyssinia. It is certain that insects and
blood-sucking bats determine the existence of the larger
naturalised quadrupeds in several parts of S. America.
We see in many cases in the more recent tertiary for-
mations, that rarity precedes extinction; and we know
that this has been the progress of events with those
animals which have been 2xterminated, either locally or
wholly, through man’s agency. I may repeat what I
published in 1845, namely, that to admit that species
generally become rare before they become extinct—to
feel no surprise at the rarity of a species, and yet to mar-
vel greatly when the species ceases to exist, is much the

98 EXTINCTION, [Cuap. XL.

same as to admit that sickness in the individual is the
forerunner of death—to feel no surprise at sickness,
but, when the sick man dies, to wonder and to suspect
that he died by some deed of violence.

The theory of natural selection is grounded on the
belief that each new variety and ultimately each new
species, is produced and maintained by having some
advantage over those with which it comes into competi-
tion; and the consequent extinction of the less-fa-
voured forms almost inevitably follows. It is the same
with our domestic productions; when a new and slightly
improved variety has been raised, it at first supplants
the less improved varieties in the same neighbourhood;
when much improved it is transported far and near, like
our short-horn cattle, and takes the place of other
breeds in other countries. Thus the appearance of new
forms and the disappearance of old forms, both those
naturally and those artificially produced, are bound to-
gether. In flourishing groups, the number of new spe-
cific forms which have been produced within a given
time has at some periods probably been greater than the
number of the old specific forms which have been ex-
terminated; but we know that species have not gone on
indefinitely increasing, at least during the later geo-
logical epochs, so that, looking to later times, we may
believe that the production of new forms has caused the
extinction of about the same number of old forms.

The competition will generally be most severe, as
formerly explained and illustrated by examples, between
the forms which are most like each other in all respects.
Hence the improved and modified descendants of a spe-
cies will generally cause the extermination of the parent-
species; and if many new forms have been developed

Cuap. XI.] EXTINCTION. 99

from any one species, the nearest allies of that species,
i.e. the species of the same genus, will be the most liable
to extermination. Thus, as I believe, a number of new
species descended from one species, that is a new genus,
comes to supplant an old genus, belonging to the same
family. But it must often have happened that a new
species belonging to some one group has seized on the
place occupied bya species belonging to a distinct group,
and thus have caused its extermination. If many allied
forms be developed from the successful intruder, many
will have to yield their places; and it will generally be
the allied forms, which will suffer from some inherited
inferiority in common. But whether it be species be-
longing to the same or to a distinct class, which have
yielded their places to other modified and improved spe-
cies, a few of the sufferers may often be preserved for
a long time, from being fitted to some peculiar line of
life, or from inhabiting some distant and isolated station,
where they will have escaped severe competition. For
instance, some species of Trigonia, a great genus of shells
in the secondary formations, survive in the Australian
seas; and a few members of the great and almost extinct
group of Ganoid fishes still inhabit our fresh waters.
Therefore the utter extinction of a group is generally, as
we have seen, a slower process than its production.

With respect to the apparently sudden extermina-
tion of whole families or orders, as of Trilobites at the
close of the paleozoic period and of Ammonites at the
close of the secondary period, we must remember what
has been already said on the probable wide intervals of
time between our consecutive formations; and in these
intervals there may have been much slow extermination.

Moreover, when, by sudden immigration or by unusu-
32

LOO FORMS OF LIFE CHANGING [Cuar. XI.

ally rapid development, many species of a new group
have taken possession of an area, many of the older
species will have been exterminated in a correspond-
ingly rapid manner; and the forms which thus yield
their places will commonly be allied, for they will par-
take of the same inferiority in common.

Thus, as it seems to me, the manner in which single
species and whole groups of species become extinct
accords well with the theory of natural selection. We
need not marvel at extinction; if we must marvel, let
it be at our own presumption in imagining for a mo-
ment that we understand the many complex contin-
gencies on which the existence of each species depends.
If we forget for an instant that each species tends to
increase inordinately, and that some check is always
in action, yet seldom perceived by us, the whole econ-
omy of nature will be utterly obscured. Whenever we
can precisely say why this species is more abundant in
individuals than that; why this species and not an-
other can be naturalised in a given country; then, and
not until then, we may justly feel surprise why we can-
not account for the extinction of any particular spe-
cies or group of species.

On the Forms of Life changing almost simultaneously
throughout the World.

Searcely any paleontological discovery is more
striking than the fact that the forms of life change
almost simultaneously throughout the world. Thus our
European Chalk formation can be recognised in many
distant regions, under the most different climates, where
not a fragment of the mineral chalk itself can be found;
namely in North America, in equatorial South America,

Cuap. XI] THROUGHOUT THE WORLD. 101

in Tierra del Fuego, at the Cape of Good Hope, and in
the peninsula of India. For at these distant points,
the organic remains in certain beds present an unmis-
takeable resemblance to those of the Chalk. It is not
that the same species are met with; for in some cases
not one species is identically the same, but they be-
long to the same families, genera, and sections of genera,
and sometimes are similarly characterised in such trifling
points as mere superficial sculpture. Moreover, other
forms, which are not found in the Chalk of Europe,
but which occur in the formations either above or be-
low, occur in the same order at these distant points
of the world. In the several successive paleozoic for-
mations of Russia, Western Europe, and North America,
a similar parallelism in the forms of life has been ob-
served by several authors; so it is, according to Lyell,
with the European and North American tertiary de-
posits. Even if the few fossil species which are com-
mon to the Old and New Worlds were kept wholly out
of view, the general parallelism in the successive forms
of life, in the paleozoic and tertiary stages, would still
be manifest, and the several formations could be easily
correlated.

These observations, however, relate to the marine
inhabitants of the world: we have not sufficient data
to judge whether the productions of the land and of
fresh water at distant points change in the same parallel
manner. We may doubt whether they have thus
changed: if the Megatherium, Mylodon, Macrauchenia,
and Toxodon had been brought to Europe from La Plata,
without any information in regard to their geological
position, no one would have suspected that they had co-
existed with sea-shells all still living; but as these

102 FORMS OF LIFE CHANGING — [Cuar. XI.

anomalous monsters co-existed with the Mastodon and
Horse, it might at least have been inferred that they
had lived during one of the later tertiary stages.

When the marine forms of life are spoken of as
having changed simultaneously throughout the world,
it must not be supposed that this expression relates to
the same year, or to the same century, or even that it
has a very strict geological sense; for if all the marine
animals now living in Europe, and all those that lived
in Europe during the pleistocene period (a very remote
period as measured by years, including the whole gla-
cial epoch) were compared with those now existing in
South America or in Australia, the most skilful natu-
ralist would hardly be able to say whether the present
or the pleistocene inhabitants of Europe resembled most
closely those of the southern hemisphere. So, again,
several highly competent observers maintain that the
existing productions of the United States are more
closely related to those which lived in Europe during
certain late tertiary stages, than to the present inhabi-
tants of Europe; and if this be so, it is evident that fos-
siliferous beds now deposited on the shores of North
America would hereafter be liable to be classed with
somewhat older European beds. Nevertheless, looking
to a remotely future epoch, there can he little doubt
that all the more modern marine formations, namely,
the upper pliocene, the pleistocene and strictly modern
beds of Europe, North and South America, and Aus-
tralia, from containing fossil remains in some degree
allied, and from not including those forms which are
found only in the older underlying deposits, would be
correctly ranked as simultaneous in a geological sense.

The fact of the forms of life changing simultaneous-

Cuap. X1.] THROUGHOUT THE WORLD. 103

ly, in the above large sense, at distant parts of the world,
has greatly struck these admirable observers, MM. de
Verneuil and d’Archiac. After referring to the parallel-
ism of the paleozoic forms of life in various parts of
Europe, they add, “If, struck by this strange sequence,
we turn our attention to North America, and there
discover a series of analogous phenomena, it will appear
certain that all these modifications of species, their
extinction, and the introduction of new ones, cannot
be owing to mere changes in marine currents or other
causes more or less local and temporary, but depend on
general laws which govern the whole animal kingdom.”
M. Barrande has made forcible remarks to precisely
the same effect. It is, indeed, quite futile to look to
changes of currents, climate, or other physical con-
ditions, as the cause of these great mutations in the
forms of life throughout the world, under the most dif-
ferent climates. We must, as Barrande has remarked,
look to some special law. We shall see this more clearly
when we treat of the present distribution of organic
beings, and find how slight is the relation between the
physical conditions of various countries and the nature
of their inhabitants.

This great fact of the parallel succession of the forms
of life throughout the world, is explicable on the theory
of natural selection. New species are formed by having
some advantage over older forms; and the forms, which
are already dominant, or have some advantage over
the other forms in their own country, give birth to the
greatest number of new varieties or incipient species.
We have distinct evidence on this head, in the plants
which are dominant, that is, which are commonest and
most widely diffused, producing the greatest number of

104 FORMS OF LIFE CHANGING (Cuap. XL

new varieties. It is also natural that the dominant,
varying, and far-spreading species, which have already
invaded to a certain extent the territories of other
species, should be those which would have the best
chance of spreading still further, and of giving rise in
new countries to other new varieties and species. The
process of diffusion would often be very slow, depending
on climatal and geographical changes, on strange acci-
dents, and on the gradual acclimatisation of new species
to the various climates through which they might have
to pass, but in the course of time the dominant forms
would generally succeed in spreading and would ulti-
mately prevail. The diffusion would, it is probable, be
slower with the terrestrial inhabitants of distinct conti-
nents than with the marine inhabitants of the continu-
ous sea. We might therefore expect to find, as we do
find, a less strict degree of parallelism in the succesion of
the productions of the land than with those of the sea.
Thus, as it seems to me, the parallel, and, taken in a
large sense, simultaneous, succession of the same forms
of life throughout the world, accords well with the
principle of new species having been formed by domi-
nant species spreading widely and varying; the new
species thus produced being themselves dominant, ow-
ing to their having had some advantage over their al-
ready dominant parents, as well as over other species,
and again spreading, varying, and producing new forms.
The old forms which are beaten and which yield their
places to the new and victorious forms, will generally
be allied in groups, from inheriting some inferiority in
common; and therefore, as new and improved groups
spread throughout the world, old groups disappear from
the world; and the succession of forms everywhere

Cuap. XI.} THROUGHOUT THE WORLD. 105

tends to correspond both in their first appearance and
final disappearance.

There is one other remark connected with this subject
worth making. I have given my reasons for believing
that most of our great formations, rich in fossils, were
deposited during periods of subsidence; and that blank
intervals of vast duration, as far as fossils are concerned,
occurred during the periods when the bed of the sea
was either stationary or rising, and likewise when sedi-
ment was not thrown down quickly enough to embed
and preserve organic remains. During these long and
blank intervals I suppose that the inhabitants of each
region underwent a considerable amount of modification
and extinction, and that there was much migration from
other parts of the world. As we have reason to be-
lieve that large areas are affected by the same move-
ment, it is probable that strictly contemporaneous for-
mations have often been accumulated over very wide
spaces in the same quarter of the world; but we are
very far from having any right to conclude that this
has invariably been the case, and that large areas have
invariably been affected by the same movements. When
two formations have been deposited in two regions dur-
ing nearly, but not exactly, the same period, we should
find in both, from the causes explained in the fore-
going paragraphs, the same general succession in the
forms of life; but the species would not exactly cor-
respond; for there will have been a little more time
in the one region than in the other for modification,
extinction, and immigration.

I suspect that cases of this nature occur in Europe.
Mr. Prestwich, in his admirable Memoirs on the eocene
deposits of England and France, is able to draw a close

106 AFFINITIES OF EXTINCT SPECIES, [Cuar. XL

““Peeiaiarailelism between the successive stages in
the two countries; but when he compares certain stages
in England with those in France, although he finds in
both a curious accordance in the numbers of the species
belonging to the same genera, yet the species them-
selves differ in a manner very difficult to account for,
considering the proximity of the two areas,—unless,
indeed, it be assumed that an isthmus separated two
seas inhabited by distinct, but contemporaneous, faunas.
Lyell has made similar observations on some of the
later tertiary formations. Barrande, also, shows that
there is a striking general parallelism in the successive
Silurian deposits of Bohemia and Scandinavia; never-
theless he finds a surprising amount of difference in
the species. If the several formations in these regions
have not been deposited during the same exact periods,
—a formation in one region often corresponding with a
blank interval in the other,—and if in both regions the
species have gone on slowly changing during the accu-
mulation of the several formations and during the long
intervals of time between them; in this case the several
formations in the two regions could be arranged in the
same order, in accordance with the general succession
of the forms of life, and the order would falsely appear
to be strictly parallel; nevertheless the species would

not be all the same in the apparently corresponding
stages in the two regions.

On the Affinities of Extinct Species to each other, and
to Living Forms.

Let us now look to the mutual affinities of extinct
and living species. All fall into a few grand classes;
and this fact is at once explained on the principle of

Cap. XL] AFFINITIES OF EXTINCT SPECIES. 107

descent. The more ancient any form is, the more, as
a general rule, it differs from living forms. But, as
Buckland long ago remarked, extinct species can all be
classed either in still existing groups, or between them.
That the’ extinct forms of life help to fill up the in-
tervals between existing genera, families, and orders,
is certainly true; but as this statement has often been
ignored or even denied, it may be well to make some
remarks on this subject, and to give some instances.
If we confine our attention either to the living or to the
extinct species of the same class, the series is far less
perfect than if we combine both into one general sys-
tem. In the writings of Professor Owen we continu-
ally meet with the expression of generalised forms, as
appled to extinct animals; and in the writings of
Agassiz, of prophetic or synthetic types; and these
terms imply that such forms are in fact intermediate or
connecting links. Another distinguished palzontolo-
gist, M. Gaudry, has shown in the most striking manner
that many of the fossil mammals discovered by him in
Attica serve to break down the intervals between exist-
ing genera. Cuvier ranked the Ruminants and Pachy-
derms as two of the most distinct orders of mammals:
but so many fossil links have been disentombed that
Owen has had to alter the whole classification, and has
placed certain pachyderms in the same sub-order with
Tuminants; for example, he dissolves by gradations the
apparently wide interval between the pig and the camel.
The Ungulata or hoofed quadrupeds are now divided
into the even-toed or odd-toed divisions; but the Mac-
rauchenia of 8. America connects to a certain extent
these two grand divisions. No one will deny that the
Hipparion is intermediate between the existing horse

108 AFFINITIES OF EXTINCT SPECIES. [Cuap. XI,

and certain older ungulate forms. What a wonderful
connecting link in the chain of mammals is the Typo-
therium from S. America, as the name given to it by
Professor Gervais expresses, and which cannot be placed
in any existing order. The Sirenia form a very dis-
tinct group of mammals, and one of the most remark-
able peculiarities in the existing dugong and lamentin
is the entire absence of hind limbs without even a rudi-
ment being left; but the extinct Halitherium had, ac-
cording to Professor Flower, an ossified thigh-bone
“ articulated to a well-defined acetabulum in the pelvis,”
and it thus makes some approach to ordinary hoofed
quadrupeds, to which the Sirenia are in other respects
allied. The cetaceans or whales are widely different
from all other mammals, but the tertiary Zeuglodon
and Squalodon, which have been placed by some natu-
ralists in an order by themselves, are considered by Pro-
fessor Huxley to be undoubtedly cetaceans, “and to
constitute connecting links with the aquatic carnivora.”

Even the wide interval between birds and reptiles
has been shown by the naturalist just quoted to be
partially bridged over in the most unexpected manner,
on the one hand, by the ostrich and extinct Archeo-
pteryx, and on the other hand, by the Compsognathus,
one of the Dinosaurians—that group which includes
the most gigantic of all terrestrial reptiles. Turning to
the Invertebrata, Barrande asserts, and a higher author-
ity could not be named, that he is every day taught that,
although palwozoic animals can certainly be classed
under existing groups, yet that at this ancient period
the groups were not so distinctly separated from each
other as they now are.

Some writers have objected to any extinct species,

Cuar. XI.) AFFINITIES OF EXTINCT SPECIES. 104

or group of species, being considered as intermediate
between any two living species, or groups of species.
If by this term it is meant that an extinct form is di-
rectly intermediate in all its characters between two
living forms or groups, the objection is probably valid.
But in a natural classification many fossil species cer-
tainly stand between living species, and some extinct
genera between living genera, even between genera be-
longing to distinct families. The most common case,
especially with respect to very distinct groups, such as
fish and reptiles, seems to be, that, supposing them to be
distinguished at the present day by a score of charac-
ters, the ancient members are separated by a somewhat
lesser ‘number of characters; so that the two groups
formerly made a somewhat nearer approach to each
other than they now do.

It is a common belief that the more ancient a form
is, by so much the more it tends to connect by some of
its characters groups now widely separated from each
other. This remark no doubt must be restricted to
those groups which have undergone much change in
the course of geological ages; and it would be difficult
to prove the truth of the proposition, for every now and
then even a living animal,-as the Lepidosiren, is dis-
covered having affinities directed towards very distinct
groups. Yet if we compare the older Reptiles and
Batrachians, the older Fish, the older Cephalopods, and
the eocene Mammals, with the more recent members of
the same classes, we must admit that there is truth in
the remark.

Let us see how far these several facts and inferences
accord with the theory of descent with modification.
As the subject is somewhat complex, I must request

110 AFFINITIES OF EXTINCT SPECIES. [Caar. XL

the reader to turn to the diagram in the fourth chapter.
We may suppose that the numbered letters in italics
represent genera; and the dotted lines diverging from
them the species in each genus. The diagram is much
too simple, too few genera and too few species be-
ing given, but this is unimportant for us. The hori-
zontal lines may represent successive geological forma-
tions, and all the forms beneath the uppermost line may
be considered as extinct. The three existing genera a’*,
q'*, p'*, will form a small family; b** and f** a closely
allied family or sub-family; and o*, e'*, m**, a third
family. These three families, together with the many
extinct genera on the several lines of descent diverging
from the parent-form (A) will form an order, for all
will have inherited something in common from their
ancient progenitor. On the principle of the continued
tendency to divergence of character, which was formerly
illustrated by this diagram, the more recent any form
is, the more it will generally differ from its ancient
progenitor. Hence we can understand the rule that
the most ancient fossils differ most from existing forms.
We must not, however, assume that divergence of char-
acter is a necessary contingency; it depends solely on
the descendants from a species being thus enabled to
seize on many and different places in the economy of
nature. Therefore it is quite possible, as we have seen
in the case of some Silurian forms, that a species might
go on being slightly modified in relation to its slightly
altered conditions of life, and yet retain throughout a
vast period the same general characteristics. This is
represented in the diagram by the letter F**.

All the many forms, extinct and recent, descended
from (A), make, as before remarked, one order; and

Cuap. XI.] AFFINITIES OF EXTINCT SPECIES. 111

this order, from the continued effects of extinction and
divergence of character, has become divided into several
sub-families and families, some of which are supposed
to have perished at different periods, and some to have
endured to the present day.

By looking at the diagram we can see that if many
of the extinct forms supposed to be imbedded in the
successive formations, were discovered at several points
low down in the series, the three existing families on
the uppermost line would be rendered less distinct from
each other. If, for instance, the genera at, a®, a,
78, m3, m®, m®, were disinterred, these three families
would be so closely linked together that they probably
would have to be united into one great family, in near-
ly the same manner as has occurred with ruminants
and certain pachyderms. Yet he who objected to con-
sider as intermediate the extinct genera, which thus
link together the living genera of three families, would
be partly justified, for they are intermediate, not direct-
ly, but only by a long and circuitous course through
many widely. different forms. If many extinct forms
were to be discovered above one of the middle hori-
zontal lines or geological formations—for instance,
above No. VI.—but none from beneath this line, then
only two of the families (those on the left hand, a‘, &c.,
and ', &c.) would have to be united into one; and there
would remain two families, which would be less distinct
from each other than they were before the discovery of
the fossils. So again if the three families formed of
eight genera (a** to m**), on the uppermost line, be sup-
posed to differ from each other by half-a-dozen impor-
tant characters, then the families which existed at the
period marked VI. would certainly have differed from

112 AFFINITIES OF EXTINCT SPECIES. [Cuap. XL

each other by a less number of characters; for they
would at this early stage of descent have diverged in a
less degree from their common progenitor. Thus it
comes that ancient and extinct genera are often in a
greater or less degree intermediate in character between
their modified descendants, or between their collateral
relations.

Under nature the process will be far more compli-
cated than is represented in the diagram; for the groups
will have been more numerous; they will have en-
lured for extremely unequal lengths of time, and will
have been modified in various degrees. As we possess
only the last volume of the geological record, and that
in a very broken condition, we have no right to expect,
except in rare cases, to fill up the wide intervals in the
natural system, and thus to unite distinct families or
orders. All that we have a right to expect is, that those
groups which have, within known geological periods,
undergone much modification, should in the older for-
mations make some slight approach to each other; so that
the older members should differ less from each other in
some of their characters than do the existing members of
the same groups; and this by the concurrent evidence of
our best paleontologists is frequently the case.

Thus, on the theory of descent with modification,
the main facts with respect to the mutual affinities of
the extinct forms of life to each other and to living
forms, are explained in a satisfactory manner. And
they are wholly inexplicable on any other view.

On this same theory, it is evident that the fauna
during any one great period in the earth’s history will
be intermediate in general character between that which
preceded and that which succeeded it. Thus the spe-

Cua. XL] AFFINITIES OF EXTINCT SPECIES. 113

cies which lived at the sixth great stage of descent in
the diagram are the modified offspring of those which
lived at the fifth stage, and are the parents of those
which became still more modified at the seventh stage;
hence they could hardly fail to be nearly intermediate in
character between the forme of life above and below.
We must, however, allow for the entire extinction of some
preceding forms, and in any one region for the immi-
gration of new forms from other regions, and for a
large amount of modification during the long and blank
intervals between the successive formations. Subject
to these allowances, the fauna of each geological period
undoubtedly is intermediate in character, between the
preceding and succeeding faunas. I need give only one
instance, namely, the manner in which the fossils of the
Devonian system, when this system was first discovered,
were at once recognised by paleontologists as inter-
mediate in character between those of the overlying
carboniferous, and underlying Silurian systems. But
each fauna is not necessarily exactly intermediate, as
unequal intervals of time have elapsed between conse-
cutive formations.

It is no real objection to the truth of the statement
that the fauna of each period as a whole is nearly inter-
mediate in character between the preceding and suc-
ceeding faunas, that certain genera offer exceptions to
the rule. For instance, the species of mastodons and
elephants, when arranged by Dr. Falconer in two series,
—in the first place according to their mutual affinities,
and in the second place according to their periods of ex-
istence,—do not accord in arrangement. The species
extreme in character are not the oldest or the most
recent; nor are those which are intermediate in charac-

114 AFFINITIES OF EXTINCT SPECIES. [Cuap. XI.

ter, intermediate in age. But supposing for an instant,
in this and other such cases, that the record of the first
appearance and disappearance of the species was com-
plete, which is far from the case, we have no reason to
believe that forms successively produced necessarily en-
dure for corresponding lengths of time. A very an-
cient form may occasionally have lasted much longer
than a form elsewhere subsequently produced, especially
in the case of terrestrial productions inhabiting sepa-
rated districts. To compare small things with great;
if the principal living and extinct races of the domestic
pigeon were arranged in serial affinity, this arrange-
ment would not closely accord with the order in time
of their production, and even less with the order of
their disappearance; for the parent rock-pigeon still
lives; and many varieties between the rock-pigeon and
the carrier have become extinct; and carriers which are
extreme in the important character of length of beak
originated earlier than short-beaked tumblers, which
are at the opposite end of the series in this respect.
Closely connected with the statement, that the or-
ganic remains from an intermediate formation are in
some degree intermediate in character, is the fact, in-
sisted on by all paleontologists, that fossils from two
consecutive formations are far more closely related to
each other, than are the fossils from two remote forma-
tions. Pictet gives as a well-known instance, the gen-
eral resemblance of the organic remains from the sev-
eral stages of the Chalk formation, though the species
are distinct in each stage. This fact alone, from ‘ts
generality, seems to have shaken Professor Pictet in his
belief in the immutability of species. He who is ac-
quainted with the distribution of existing species over

Cuap, X[I.] AFFINITIES OF EXTINCT SPECIES. 115

the globe, will not attempt to account for the close re-
semblance of distinct species in closely consecutive for-
mations, by the physical conditions of the arcient areas
having remained nearly the same. Let it be remembered
that the forms of life, at least those inhabiting the sea,
have changed almost simultaneously throughout the
world, and therefore under the most different climates
and conditions. Consider the prodigious vicissitudes of
climate during the pleistocene period, which includes
the whole glacial epoch, and note how little the specific
forms of the inhabitants of the sea have been affected.

On the theory of descent, the full meaning of the
fossil remains from closely consecutive formations be-
ing closely related, though ranked as distinct species, is
obvious. As the accumulation of each formation has
often been interrupted, and as long blank intervals have
intervened between successive formations, we ought not
to expect to find, as I attempted to show in the last
chapter, in any one or in any two formations, all the in-
termediate varieties between the species which appeared
at the-commencement and close of these periods: but
we ought to find after intervals, very long as measured
by years, but only moderately long as measured geologi-
cally, closely allied forms, or, as they have been called
by some authors, representative species; and these as-
suredly we do find. We find, in short, such evidence of
the slow and scarcely sensible mutations of specific
forms, as we have the right to expect.

33

116 STATE OF DEVELOPMENT OF [Cuar. XL

On the State of Development of Ancient compared with
Living Forms.

We have seen in the fourth chapter that the degree
of differentiation and specialisation of the parts in or-
ganic beings, when arrived at maturity, is the best
standard, as yet suggested, of their degree of perfection
or highness. We have also seen that, as the speciali-
sation of parts is an advantage to each being, so natural
selection will tend to render the organisation of each
being more specialised and perfect, and in this sense
higher; not but that it may leave many creatures with
simple and unimproved structures fitted for simple con-
ditions of life, and in some cases will even degrade or
simplify the organisation, yet leaving such degraded
beings better fitted for their new walks of life. In
another and more general manner, new species become
superior to their predecessors; for they have to beat in
the struggle for life all the older forms, with which they
come into close competition. We may therefore con-
clude that if under a nearly similar climate the eocene
inhabitants of the world could be put into competition
with the existing inhabitants, the former would be beaten
and exterminated by the latter, as would the secondary
by the eocene, and the paleozoic by the secondary forms.
So that by this fundamental test of victory in the battle
for life, as well as by the standard of the specialisation
of organs, modern forms ought, on the theory of natu-
ral selection, to stand higher than ancient forms. Is
this the case? A large majority of paleontologists
would answer in the affirmative; and it seems that this
answer must be admitted as true, though difficult of
proof.

Cuar. XI.) ANCIENT AND LIVING FORMS. 117

It is no valid objection to this conclusion, that cer-
tain Brachiopods have been but slightly modified from
an extremely remote geological epoch; and that certain
land and fresh-water shells have remained nearly the
same, from the time when, as far as is known, they
first appeared. It is not an insuperable difficulty that
Foraminifera have not, as insisted on by Dr. Carpenter,
progressed in organisation since even the Laurentian
epoch; for some organisms would have to remain fitted
for simple conditions of life, and what could be better
fitted for this end than these lowly organised Protozoa? -
Such objections as the above would be fatal to my view,
if it included advance in organisation as a necessary
contingent. They would likewise be fatal, if the above
Foraminifera, for instance, could be proved to have
first come into existence during the Laurentian epoch,
or the above Brachiopods during the Cambrian forma-
tion; for in this case, there would not have been time
sufficient for the development of these organisms up to
the standard which they had then reached. When
advanced up to any given point, there is no necessity,
on the theory of natural selection, for their further
continued progress; though they will, during each suc-
cessive age, have to be slightly modified, so as to hold
their places in relation to slight changes in their con-
ditions. The foregoing objections hinge on the ques-
tion whether we really know how old the world is, and
at what period the various forms of life first appeared;
and this may well be disputed.

The problem whether organisation on the whole has
advanced is in many ways excessively intricate. The
geological record, at all times imperfect, does not ex-
tend far enough back, to shew with unmistakeable clear-

118 STATE OF DEVELOPMENT OF [Cuar. XE

ness that within the known history of the world or-
ganisation has largely advanced. Even at the present
day, looking to members of the same class, naturalists
are not unanimous which forms ought to be ranked as
highest: thus, some look at the selaceans or sharks,
from their approach in some important points of struc-
ture to reptiles, as the highest fish; others look at the
teleosteans as the highest. The ganoids stand inter-
mediate between the selaceans and teleosteans; the latter
at the present day are largely preponderant in. number;
but formerly selaceans and ganoids alone existed; and
in this case, according to the standard of highness
chosen, so will it be said that fishes have advanced or
retrograded in organisation. To attempt to compare
members of distinct types in the scale of highness seems
hopeless; who will decide whether a cuttle-fish be higher
than a bee—that insect which the great Von Baer be-
lieved to be “in fact more highly organised than a fish,
although upon another type”? In the complex strug-
gle for life it is quite credible that crustaceans, not
very high in their own class, might beat cephalopods,
the highest molluscs; and such crustaceans, though not
highly developed, would stand very high in the scale of
invertebrate animals, if judged by the most decisive of
all trials—the law of battle. Besides these inherent
difficulties in deciding which forms are the most ad-
vanced in organisation, we ought not solely to compare
the highest members of a class at any two periods—
though undoubtedly this is one and perhaps the most
important element in striking a balance—but we ought
to compare all the members, high and low, at the two
periods. At an ancient epoch the highest and lowest
molluseoidal animals, namely, cephalopods and brachio-

Caap. XI] ANCIENT AND LIVING FORMS. 119

pods, swarmed in numbers; at the present time both
groups are greatly reduced, whilst others, intermediate
in organisation, have largely increased; consequently
some naturalists maintain that molluscs were formerly
more highly developed than at present; but a stronger
case can be made out on the opposite side, by consider-
ing the vast reduction of brachiopods, and the fact that
our existing cephalopods, though few in number, are
more highly organised than their ancient representa-
tives. We ought also to compare the relative propor-
tional numbers at any two periods of the high and low
classes throughout the world: if, for instance, at the
present day fifty thousand kinds of vertebrate animals
exist, and if we knew that at some former period only
ten thousand kinds existed, we ought to look at this in-
crease in number in the highest class, which implies a
great displacement of lower forms, as a decided advance
in the organisation of the world. We thus see how
hopelessly difficult it is to compare with perfect fair-
ness under such extremely ccmplex relations, the stand-
ard of organisation of the imperfectly-known faunas of
successive periods.

We shall appreciate this difficulty more clearly, by
looking to certain existing faunas and floras. From the
extraordinary manner in which European productions
have recently spread over New Zealand, and have seized
on places which must have been previously occupied by
the indigenes, we must believe, that if all the animals
and plants of Great Britain were set free in New Zea-
land, a multitude of British forms would in the course
of time become thoroughly naturalised there, and would
exterminate many of the natives. On the other hand,
from the fact that hardly a single inhabitant of the

120 STATE OF DEVELOPMENT OF [Caap. XL

southern hemisphere has become wild in any part of
Europe, we may well doubt whether, if all the produc-
tions of New Zealand were set free in Great Britain, any
considerable number would be enabled to seize on places
now occupied by our native plants and animals. Under
this point of view, the productions of Great Britain
stand much higher in the scale than those of New Zea-
land. Yet the most skilful naturalist, from an exami-
nation of the species of the two countries, could not have
foreseen this result.

Agassiz and several other highly competent judges
insist that ancient animals resemble to a certain extent
the embryos of recent animals belonging to the same
classes; and that the geological succession of extinct
forms is nearly parallel with the embryological de-
velopment of existing forms. This view accords ad-
mirably well with our theory. In a future chapter I
shall attempt to show that the adult differs from its
embryo, owing to variations having supervened at a not
early age, and having been inherited at a corresponding
age. This process, whilst it leaves the embryo almost
unaltered, continually adds, in the course of successive
generations, more and more difference to the adult.
Thus the embryo comes to be left as a sort, of picture,
preserved by nature, of the former and less modified
condition of the species. This view may be true, and
yet may never be capable of proof. Seeing, for instance,
that the oldest known mammals, reptiles, and fishes
strictly belong to their proper classes, though some of
these old forms are in a slight degree less distinct from
each other than are the typical members of the same
groups at the present day, it would be vain to look for
animals having the common embryological character of

Cuap. XI.] ANCIENT AND LIVING FORMS. 121

the Vertebrata, until beds rich in fossils are discovered
far beneath the lowest Cambrian strata—a discovery of
which the chance is small.

On the Succession of the same Types within the same
Areas, during the later Tertiary periods.

Mr. Clift many years ago showed that the fossil
.mammals from the Australian caves were closely allied
to the living marsupials of that continent. In South
America a similar relationship is manifest, even to an
uneducated eye, in the gigantic pieces of armour, like
those of the armadillo, found in several parts of La
Plata; and Professor Owen has shown in the most strik-
ing manner that most of the fossil mammals, buried
there in such numbers, are related to South American
types. This relationship is even more clearly seen in
the wonderful collection of fossil bones made by MM.
Lund and Clausen in the caves of Brazil. I was so
much impressed with these facts that I strongly insisted,
in 1839 and 1845, on this “law of the succession of
types,”—on “this wonderful relationship in the same
continent between the dead and the living.” Professor
Owen has subsequently extended the same generalisation
to the mammals of the Old World. We see the same
law. in this author’s restorations of the extinct and
gigantic birds of New Zealand. We see it also in the
birds of the caves of Brazil. Mr. Woodward has shown
that the same law holds good with sea-shells, but, from
the wide distribution of most molluscs, it is not well
displayed by them. Other cases could be added, as the
relation between the extinct and living land-shells of
Madeira; and between the extinct and living brackish
water-shells of the Aralo-Caspian Sea.

129 SUCCESSION OF THE [Cuap. XI.

Now what does this remarkable law of the succession
of the same types within the same areas mean? He
would be a bold man who, after comparing the present
climate of Australia and of parts of South America,
under the same latitude, would attempt to account, on
the one hand through dissimilar physical conditions, for
the dissimilarity of the inhabitants of these two con-
tinents; and, on the other hand through similarity of
conditions, for the uniformity of the same types in each
continent during the later tertiary periods. Nor can it
be pretended that it is an immutable law that marsupials
should have been chiefly or solely produced in Australia;
or that Edentata and other American types should have
been solely produced in South America. For we know
that Europe in ancient times was peopled by numerous
marsupials; and I have shown in the publications above
alluded to, that in America the law of distribution of
terrestrial mammals was formerly different from what it
now is. North America formerly partook strongly of
the present character of the southern half of the con-
tinent; and the southern half was formerly more closely
allied, than it is at present, to the northern half. Ina
similar manner we know, from Falconer and Cautley’s
discoveries, that Northern India was formerly more
closely related in its mammals to Africa than it is at the
present time. Analogous facts could be given in rela-
tion to the distribution of marine animals.

On the theory of descent with modification, the
great law of the long enduring, but not immutable, suc-
cession of the same types within the same areas, is at
once explained; for the inhabitants of each quarter of
the world will obviously tend to leave in that quarter,
during the next succeeding period of time, closely allied

Cuap, XI.] SAME TYPES IN THE SAME AREAS. 123

though in some degree modified descendants. If the
inhabitants of one continent formerly differed greatly
from those of another continent, so will their modified
descendants still differ in nearly the same manner and
degree. But after very long intervals of time, and
after great geographical changes, permitting much in-
termigration, the feebler will yield to the more domi-
nant forms, and there will be nothing immutable in the
distribution of organic beings.

It may be asked in ridicule, whether I suppose that
the megatherium and other allied huge monsters, which
formerly lived in South America, have left behind them
the sloth, armadillo, and anteater, as their degenerate
descendants. This cannot for an instant be admitted.
These huge animals have become wholly extinct, and
have left no progeny. But in the caves of Brazil, there
are many extinct species which are closely allied in size
and in all other characters to the species still living in
South America; and some of these fossils may have been
the actual progenitors of the living species. It must
not be forgotten that, on our theory, all the species of the
same genus are the descendants of some one species; so
that, if six genera, each having eight species, be found in
one geological formation, and in ‘a succeeding forma-
tion there be six other allied or representative genera
each with the same number of species, then we may con-
clude that generally only one species of each of the older
genera has left modified descendants, which constitute
the new genera containing the several species; the other
seven species of each old genus having died out and left
no progeny. Or, and this will be a far commoner case,
two or three species in two or three alone of the six
older genera will be the parents of the new genera: the

124 SUMMARY OF THE (Cuap, XL

other species and the other old genera having become
utterly extinct. In failing orders, with the genera and
species decreasing in numbers as is the case with the
Edentata of South America, still fewer genera and spe-
cies will leave modified blood-descendants.

Summary of the preceding and present Chapters.

I have attempted to show that the geological record
is extremely imperfect; that only a small portion of the
globe has been geologically explored with care; that
only certain classes of organic beings have been largely
preserved in a fossil state; that the number both of
specimens and of species, preserved in our museums, is
absolutely as nothing compared with the number of
generations which must have passed away even during a
single formation; that, owing to subsidence being al-
most necessary for the accumulation of deposits rich in -
fossil species of many kinds, and thick enough to outlast
future degradation, great intervals of time must have
elapsed between most of our successive formations; that
there has probably been more extinction during the
periods of subsidence, and more variation during the
periods of elevation, and during-the latter the record
will have been less perfectly kept; that each single for-
mation has not been continuously deposited; that the
duration of each formation is probably short compared
with the average duration of specific forms; that mi-
gration has played an important part in the first ap-
pearance of new forms in any one area and formation;
that widely ranging species are those which have varied
most frequently, and have oftenest given rise to new
species; that varieties have at first been local; and lastly,

\
SS

Cuar. XL] PRECEDING AND PRESENT CHAPTERS. 125

although each species must have passed through ninner-
ous transitional stages, it is probable that the periots,
during which each underwent modification, though
many and long as measured by years, have been short
in comparison with the periods during which each re-
mained in an unchanged condition. These causes,
taken conjointly, will to a large extent explain why—
though we do find many links—we do not find inter-
minable varieties, connecting together all extinct and
existing forms by the finest graduated steps. It should
_also_be constantly borne in mind that any linking va-
riety between two forms, which might be found, would
“be-ranked, unless the whole chain could be perfectly
restored, as a new and distinct species; for it is not pre-
tended that we have any sure criterion by which species
and varieties can be discriminated.
~~ He who rejects this view of the imperfection of the
geological record, will rightly reject the whole theory.
For he may ask in vain where are the numberless tran-
sitional links which must formerly have connected the
closely allied or representative species, found in the
successive stages pf the same great formation? He
may disbelieve in the immense intervals of time which
must have elapsed between our consecutive formations;
he may overlook how important a part migration has
played, when the formations of any one great region,
as those of Europe, are considered; he may urge the
apparent, but often falsely apparent, sudden coming in
of whole groups of species. He may ask where are the
remains of those infinitely numerous organisms which
must have existed long before the Cambrian system
was deposited? We now know that at least one animal
did then exist; but I can answer this last question only

126 SUMMARY OF THE [Cuap. XI,

by supposing that where our oceans now extend they
have extended for an enormous period, and where our
oscillating continents now stand they have stood since
the commencement of the Cambrian system; but that,
long before that epoch, the world presented a widely
different aspect; and that the older continents formed
of formations older than any known to us, exist now
only as remnants in a metamorphosed condition, or lie
still buried under the ocean.

Passing from these difficulties, the other great lead-
ing facts in paleontology agree admirably with the
theory of descent with modification through variation
and natural selection. We can thus understand how
it is that new species come in slowly and successively;
how species of different classes do not necessarily change
together, or at the same rate, or in the same degree;
yet in the long run that all undergo modification to
some extent. The extinction of old forms is the almost
inevitable consequence of the production of new forms.
We can understand why, when a species has once dis-
appeared, it never reappears. Groups of species in-
crease in numbers slowly, and endure for unequal
periods of time; for the process of modification is neces-
sarily slow, and depends on many complex contingen-
cies. The dominant species belonging to large and
dominant groups tend to leave many modified descend-
ants, which form new sub-groups and groups. As these
are formed, the species of the less vigorous groups, from
their inferiority inherited from a common progenitor,
tend to become extinct together, and to leave no modi-
fied offspring on the face of the earth. But the utter
extinction of a whole group of species has sometimes
been a slow process, from the survival of a few descend-

Cua, XI] PRECEDING AND PRESENT CHAPTERS. 197

ants, lingering im protected and isolated situations.
When a group has once wholly disappeared, it does not
reappear; for the link of generation has been broken.

We can understand how it is that dominant forms:
which spread widely and yield ‘the greatest. number ber of
varieties tend to people the world with allied, but modi-
fied, descendants; and these will generally y succeed in
displacing the groups which are their inferiors in the
struggle for existence. Hence, after long intervals of
time, the productions of the world appear_. to have
changed : ‘simultaneously. ae

We can understand how it is that all the forms of
life, ancient and recent, make together a few grand
classes. We can understand, from the continued ten-
‘lency to divergence of character, why the more ancient
a form is, the more it generally differs from those now
living; why ancient and extinct forms often tend to
fill up gaps between existing forms, sometimes blending
two groups, previously classed as distinct, into one; but
more commonly bringing them only a little closer to-
gether. The more ancient a form is, the more often
it stands in some degree intermediate between groups
now distinct; for the more ancient a form is, the more
nearly it will be related to, and consequently resemble,
the common progenitor of groups, since become widely
divergent. Extinct forms are seldom directly inter-
mediate between existing forms; but are intermediate
only by a long and circuitous course through other ex-
tinct and different forms. We can clearly see why the
organic remains of closely consecutive formations are
closely allied; for they are closely linked together by
generation. We can clearly see why the remains of an
intermediate formation are intermediate in character.

128 SUMMARY OF CHAPTERS. [Cuap. XI

The inhabitants of the world at each successive
period in its history have beaten their predecessors in
the race for life, and are, in so far, higher in the scale,
and their structure has generally become more special-
ised; and this may account for the common belief held
by so many paleontologists, that organisation on the
whole has progressed. Extinct and ancient animals re-
semble to a certain extent the embryos of the more re-
cent animals belonging to the same classes, and this
wonderful fact receives a simple explanation according
to our views. The succession of the same types of
structure within the same areas during the later geologi-
cal periods ceases to be mysterious, and is intelligible
on the principle of inheritance.

If then the geological record be as imperfect as many
believe, and it may at least be asserted that the record
cannot be proved to be much more perfect, the main
objections to the theory of natural selection are greatly
diminished or disappear. On the other hand, all the
chief laws of paleontology plainly proclaim, as it seems
to me, that species have been produced by ordinary gen-
eration: old forms having been supplanted by new and
improved forms of life, the products of Variation and
the Survival of the Fittest.

Cuap. XII.) GEOGRAPHICAL DISTRIBUTION. 129

CHAPTER XII.
GEOGRAPHICAL DISTRIBUTION.

Present distribution cannot be accounted for by differences in
physical conditions—Importance of barriers—Affinity of the
productions of the same continent—Centres of creation—Means
of dispersal by changes of climate and of the level of the land,
and by occasional means—Dispersal during the Glacial period
—Alternate Glacial periods in the North and South.

In considering the distribution of organic beings
over the face of the globe, the first great fact which
strikes us is, that neither the similarity nor the dissimi-
larity of the inhabitants of various regions can be wholly
accounted for by climatal and other physical conditions.
Of late, almost every author who has studied the subject
has come to this conclusion. The case of America
alone would almost suffice to prove its truth; for if we
exclude the arctic and northern temperate parts, all
authors agree that one of the most fundamental divi-
sions in geographical distribution is that between the
New and Old Worlds; yet if we travel over the vast
American continent, from the central parts of the
United States to its extreme southern point, we meet
with the most diversified conditions; humid districts,
arid deserts, lofty mountains, grassy plains, forests,
marshes, lakes, and great rivers, under almost every
temperature. There is hardly a climate or condition
in the Old World which cannot be paralleled in the New

130 GEOGRAPHICAL DISTRIBUTION. [Cuapr. XIL
—at least as closely as the same species generally re-
quire. No doubt small areas can be pointed out in the
Old World hotter than any in the New World; but
these are not inhabited by a fauna different from that of
the surrounding districts; for it is rare to find a group
of organisms confined to a small area, of which the con-
ditions are peculiar in only a slight degree. Notwith-
standing this general parallelism in the conditions of
the Old and New Worlds, how widely different are their
living productions!

In the southern hemisphere, if we compare large
tracts of land in Australia, South Africa, and western
South America, between latitudes 25° and 35°, we shall
find parts extremely similar in all their conditions, yet
it would not be possible to point out three faunas and
floras more utterly dissimiler. Or, again, we may com-
pare the productions of South America south of lat. 35°
with those north of 25°, which consequently are sepa-
rated by a space of ten degrees of latitude, and are ex-
posed to considerably different conditions; yet they are
incomparably more closely related to each other than
they are to the productions of Australia or Africa under
nearly the same climate. Analogous facts could be
* given with respect to the inhabitants of the sea.

A second great fact which strikes us in our general
review is, that barriers of any kind, or obstacles to free
migration, are related in a close and important manner
to the differences between the productions of various
regions. We see this in the great difference in nearly
all the terrestrial productions of the New and Old
Worlds, excepting in the northern parts, where the land
almost joins, and where, under a slightly different cli-
mate, there might have been free migration for the

Cuap. XII]. GEOGRAPHICAL DISTRIBUTION. 131

northern temperate forms, as there now is for the strict-
ly arctic productions. We see the same fact in the
great difference between the inhabitants of Australia,
Africa, and South America under the same latitude;
for these countries are almost as much isolated from
each other as is possible. On each continent, also, we
see the same fact; for on the opposite sides of lofty
and continuous mountain-ranges, of great deserts and
even of large rivers, we find different productions;
though as mountain-chains, deserts, &c., are not as
impassable, or likely to have endured so long, as the
oceans separating continents, the differences are very
inferior in degree to those characteristic of distinct con-
tinents.

Turning to the sea, we find the same law. The
marine inhabitants of the eastern and western shores
of South America are very distinct, with extremely few
shells, crustacea, or echinodermata in common; but Dr.
Giinther has recently shown that about thirty per cent.
of the fishes are the same on the opposite sides of the
isthmus of Panama; and this fact has led naturalists
to believe that the isthmus was formerly open. West-
ward of the shores of America, a wide space of open
ocean extends, with not an island as a halting-place for
emigrants; here we have a barrier of another kind, and
as soon as this is passed we meet in the eastern islands
of the Pacific with another and totally distinct fauna.
So that three marine faunas range far northward and
southward in parallel lines not far from each other,
under corresponding climates; but from being sepa-
rated from each other by impassable barriers, either of
land or open sea, they are almost wholly distinct. On

the other hand, proceeding still farther westward from
34

132 GHOGRAPHIGAL DISTRIBUTION. [Caap. XII.

the eastern islands of the tropical parts of the Pacific,
we encounter no impassable barriers, and we have in-
numerable islands as halting-places, or continuous
coasts, until, after travelling over a hemisphere, we
come to the shores of Africa; and over this vast space
we meet with no well-defined and distinct marine fau-
nas. Although so few marine animals are common
to the above-named three approximate faunas of Kast-
ern and Western America and the Eastern Pacific is-
lands, yet many fishes range from the Pacific into the
Indian Ocean, and many shells are common to the east-
ern islands of the Pacific and the eastern shores of
Africa on almost exactly opposite meridians of longi-
tude.

A third great fact, partly included in the foregoing
statement, is the affinity of the productions of the same
continent or of the same sea, though the species them-
selves are distinct at different points and stations. It
is a law of the widest generality, and every continent
offers innumerable instances. Nevertheless the natural-
ist, in travelling, for instance, from north to south,
never fails to be struck by the manner in which suc-
cessive groups of beings, specifically distinct, though
nearly related, replace each other. He hears from ¢lose-
ly allied, yet distinct kinds of birds, notes nearly similar,
and sees their nests similarly constructed, but not quite
alike, with eggs coloured in nearly the same manner.
The plains near the Straits of Magellan are inhabited
by one species of Rhea (American ostrich) and north-
ward the plains of La Plata by another species of the
same genus; and not by a true ostrich or emu, like those
inhabiting Africa and Australia under the same lati-
tude. On these same plains of La Plata we see the

Cnar. XIL.] GEOGRAPHICAL DISTRIBUTION. 133

agouti and bizcacha, animals having nearly the same
habits as our hares and rabbits, and belonging to the
same order of Rodents, but they plainly display an
American type of structure. We ascend the lofty peaks
of the Cordillera, and we find an alpine species of bizca-
cha; we look to the waters, and we do not find the
beaver or musk-rat, but the coypu and capybara, ro-
dents of the 8. American type. Innumerable other
instances could be given. If we look to the islands off
the American shore, however much they may differ in
geological structure, the inhabitants are essentially
American, though they may be all peculiar species. We
may look back to past ages, as shown in the last chapter,
and we find American types then prevailing on the
American continent and in the American seas. We
see in these facts some deep organic bond, through-
out space and time, over the same areas of land and
water, independently of physical conditions. The natu-
ralist must be dull who is not led to enquire what this
bond is.

The bond is simply inheritance, that cause which
alone, as far as we positively know, produces organisms
quite like each other, or, as we see in the case of varie-
ties, nearly alike. The dissimilarity of the inhabitants
of different regions may be attributed to modification
through variation and natural selection, and probably
in a subordinate degree to the definite influence of dif-
ferent physical conditions. The degrees of dissimilar-
ity will depend on the migration of the more dominant
forms of life from one region into another having been
more or less effectually prevented, at periods more or
less remote;—on the nature and number of the former
immigrants;—and on the action of the inhabitants on

134 GEOGRAPHICAL DISTRIBUTION. [Caap. XII.

each other in leading to the preservation of different
modifications; the relation of organism to organism in
the struggle for life being, as I have already often re-
marked, the most important of all relations. Thus the
high importance of barriers comes into play by check-
ing migration; as does time for the slow process of
modification through natural selection. Widely-rang-
ing species, abounding in individuals, which have al-
ready triumphed over many competitors in their own
widely-extended homes, will have the best chance of
seizing on new places, when they spread into new coun-
tries. In their new homes they will be exposed to new
conditions, and will frequently undergo. further modi-
fication and improvement; and thus they will become still
further victorious, and will produce groups of modified
descendants. On this principle of inheritance with
modification we can understand how it is that sec-
tions of genera, whole genera, and even families, are
confined to the same areas, as is so commonly and notori-
ously the case.

There is no evidence, as was remarked in the last
chapter, of the existence of any law of necessary de-
velopment. As the variability of each species is an
independent property, and will be taken advantage of
by natural selection, only so far as it profits each in-
dividual in its complex struggle for life, so the amount
of modification in different species will be no uniform
quantity. If a number of species, after having long
competed with each other in their old home, were to
migrate in a body into a new and afterwards isolated
country, they would be little liable to modification; for
neither migration nor isolation in themselves effect any-
thing. These principles come into play only by bring-

Cuap, XII] SINGLE CENTRES OF CREATION. 135

ing organisms into new relations with each other and in
a lesser degree with the surrounding physical condi-
tions. As we have seen in the last chapter that some
forms have retained nearly the same character from an
enormously remote geological period, so certain species
have migrated over vast spaces, and have not become
greatly or at all modified.

According to these views, it is obvious that the sev-
eral species of the same genus, though inhabiting the
most distant quarters of the world, must originally have
proceeded from the same source, as they are descended
from the same progenitor. In the case of those species
which have undergone during whole geological periods
little modification, there is not much difficulty in be-
lieving that they have migrated from the same region;
for during the vast geographical and climatal changes
which have supervened since ancient times, almost any
amount of migration is possible. But in many other
cases, in which we have reason to believe that the spe-
cies of a genus have been produced within comparative-
ly recent times, there is great difficulty on this head.
It is also obvious that the individuals of the same spe-
cies, though now inhabiting distant and isolated regions,
must have proceeded from one spot, where their parents
were first produced: for, as has been explained, it is
incredible that individuals identically the same should
have been produced from parents specifically dis-
tinct.

Single Centres of supposed Creation.—We are thus
brought to the question which has been largely dis-
cussed by naturalists, namely, whether species have
been created at one or more points of the earth’s sur-
face. Undoubtedly there are many cases of extreme

136 SINGLE CENTRES OF CREATION. [Cuap. XIL

difficulty in understanding how the same species could
possibly have migrated from some one point to the sev-
eral distant and isolated points, where now found.
Nevertheless the simplicity of the view that each spe-
cies was first produced within a single region captivates
the mind. He who rejects it, rejects the vera causa of
ordinary generation with subsequent migration, and
calls in the agency of a miracle. It is universally ad-
mitted, that in most cases the area inhabited by a spe-
cles is continuous; and that when a plant or animal
inhabits two points so distant from each other, or with
an interval of such a nature, that the space could not
have been easily passed over by migration, the fact is
given as something remarkable and exceptional. The
incapacity of migrating across a wide sea is more clear
in the case of terrestrial mammals than perhaps with
any other organic beings; and, accordingly, we find no
inexplicable instances of the same mammals inhabit-
ing distant points of the world. No geologist feels any
difficulty in Great Britain possessing the same quad-
rupeds with the rest of Europe, for they were no doubt
once united. But if the same species can be produced
at two separate points, why do we not find a single mam-
mal common to Europe and Australia or South Amer.
ica? The conditions of life are nearly the same, so that
a multitude of European animals and plants have be-
come naturalised in America and Australia; and some
of the aboriginal plants are identically the same
at these distant points of the northern and southern
hemispheres? The answer, as I believe, is, that mam-
mals have not been able to migrate, whereas some plants,
from their varied ‘means of dispersal, have migrated
across the wide and broken interspaces. The great

Cuap. XIL] SINGLE CENTRES OF CREATION. 137

and striking influence of barriers of all kinds, is intelli-
gible only on the view that the great majority of species
have been produced on one side, and have not been able
to migrate to the opposite side. Some few families,
many sub-families, very many genera, and a still greater
number of sections of genera, are confined to a single
region; and it has been observed by several naturalists
that the most natural genera, or those genera in which
the species are most closely related to each other, are
generally confined to the same country, or if they have
a wide range that their range is continuous. What a
strange anomaly it would be, if a directly opposite rule
were to prevail, when we go down one step lower in the
series, namely, to the individuals of the same species,
and these had not been, at least at first, confined to some
one region!

Hence it seems to me, as it has to many other natu-
ralists, that the view of each species having been pro-
duced in one area alone, and having subsequently mi-
grated from that area as far as its powers of migration
and subsistence under past and present conditions per-
mitted, is the most probable. Undoubtedly many cases
occur, in which we cannot explain how the same species
could have passed from one point to the other. But
the geographical and climatal changes which have cer-
tainly occurred within recent geological times, must
have rendered discontinuous the formerly continuous
range of many species. So that we are reduced to con-
sider whether the exceptions to continuity of range are
so numerous and of so grave a nature, that we ought to
give up the belief, rendered probable by general con-
siderations, that each species has been produced within
one aree and has migrated thence as far as it could,

138 SINGLE CENTRES OF CREATION. [Cuap. XID

It would be hopelessly tedious to discuss all the excep-
tional cases of the same species, now living at distant
and separated points, nor do I for a moment pretend that
any explanation could be offered of many instances.
But, after some preliminary remarks, I will discuss a
few of the most striking classes of facts; namely, the
existence of the same species on the summits of distant
mountain ranges, and at distant points in the arctic and
antarctic regions; and secondly (in the following chap-
ter), the wide distribution of freshwater productions;
and thirdly, the occurrence of the same terrestrial species
on islands and on the nearest mainland, though sepa-
rated by hundreds of miles of open sea. If the exist-
ence of the same species at distant and isolated points
of the earth’s surface, can in manyinstances be explained
on the view of each species having migrated from a
single birthplace; then, considering our ignorance with
respect to former climatal and geographical changes and
to the various occasional means of transport, the belief
that a single birthplace is the law, seems to me incom-
parably the safest.

In discussing this subject, we shall be enabled at the
same time to consider a point equally important for us,
namely, whether the several species of a genus which
must on our theory all be descended from a common
progenitor, can have migrated, undergoing modifica-
tion during their migration, from some one area. If,
when most of the species inhabiting one region are dif-
ferent from those of another region, though closely
allied to them, it can be shown that migration from the
one region to the other has probably occurred at some
former period, our general view will be much strength-
ened; for the explanation is obvious on the principle of

Crap. XIL] SINGLE CENTRES OF CREATION, 1389

descent with modification. A volcanic island, for in-
stance, upheaved and formed at the distance of a few
hundreds of miles from a continent, would probably re-
ceive from it in the course of time a few colonists, and
their descendants, though modified, would still be re-
lated by inheritance to the inhabitants of that continent.
Cases of this nature are common, and are, as we shall
hereafter see, inexplicable on the theory of independ-
ent creation. This view of the relation of the species of
one region to those of another, does not differ much
from that advanced by Mr. Wallace, who concludes that
“every species has come into existence coincident both
in space and time with a pre-existing closely allied spe-
cies.” And it is now well known that he attributes this
coincidence to descent with modification.

The question of single or multiple centres of crea-
tion differs from another though allied question,—
namely, whether all the individuals of the same species
are descended from a single pair, or single hermaphrodite,
or whether, as some authors suppose, from many individ-
uals simultaneously created. With organic beings which
never intercross, if such exist, each species must be de-
scended from a succession of modified varieties, that
have supplanted each other, but have never blended
with other individuals or varieties of the same species;
so that, at each successive stage of modification, all the
individuals of the same form will be descended from a
single parent. But in the great majority of cases, name-
ly, with all organisms which habitually unite for each
birth, or which occasionally intercross, the individuals
of the same species inhabiting the same area will be kept
nearly uniform by intercrossing; so that many individ-
uals will go on simultaneously changing, and the whole

140 MEANS OF DISPERSAL. (Caap. XII.

amount of modification at each stage will not be due to
descent from a single parent. To illustrate what I
mean: our English race-horses differ from the horses of
every other breed; but they do not owe their difference
and superiority to descent from any single pair, but to
continued care in the selecting and training of many in-
dividuals during each generation.

Before discussing the three classes of facts, which I
have selected as presenting the greatest amount of diffi-
culty on the theory of “single centres of creation,” I
must say a few words on the means of dispersal.

Means of Dispersal.

Sir C. Lyell ‘and other authors have ably treated
this subject. I can give here only the briefest abstract
of the more important facts. Change of climate must
have had a powerful influence on migration. A region
now impassable to certain organisms from the nature of
its climate, might have been a high road for migration,
when the climate was different. I shall, however, pres-
ently have to discuss this branch of the subject in some
detail. Changes of level in the land must also have
been highly influential: a narrow isthmus now sepa-
rates two marine faunas; submerge it, or let it formerly
have been submerged, and the two faunas will now
blend together, or may formerly have blended. Where
the sea now extends, land may at a former period have
connected islands or possibly even continents together,
and thus have allowed terrestrial productions to pass
from one to the other. No geologist disputes that
great mutations of level have occurred within the period
of existing organisms. Edward Forbes insisted that all
the islands in the Atlantic must have been recently

Cuap. XII] MEANS OF DISPERSAL. 141

connected with Europe or Africa, and Europe likewise
with America. Other authors have thus hypothetically
bridged over every ocean, and united almost every is-
land with some mainland. If indeed the arguments
used by Forbes are to be trusted, it must be admitted
that scarcely a single island exists which has not re-
cently been united to some continent. This view cuts
the Gordian knot of the dispersal of the same species to
the more distant points, and removes many a difficulty;
but to the best of my judgment we are not authorised in
admitting such enormous geographical changes within
the period of existing species. It seems to me that we
have abundant evidence of great oscillations in the level
of the land or sea; but not of such vast changes in the
position and extension of our continents, as to have
united them within the recent period to each other and
to the several intervening oceanic islands. I freely'ad-
mit the former existence of many islands, now buried
beneath the sea, which may have served as halting-places
for plants and for many animals during their migration.
In the coral-producing oceans such sunken islands are
now marked by rings of coral or atolls standing over
them. Whenever it is fully admitted, as it will some
day be, that each species has proceeded from a single
birthplace, and when in the course of time we know
something definite about the means of distribution, we
shall be enabled to speculate with security on the for-
mer extension of the land. But I do not believe that it
will ever be proved that within the recent period most
of our continents which now stand quite separate have
been continuously, or almost continuously united with
each other, and with the many existing oceanic islands.
Several facts in distribution,—such as the great difference

149 MEANS OF DISPERSAL. [Caar. XIL

in the marine faunas on the opposite sides of almost
every continent,—the close relation of the tertiary in-
habitants of several lands and even seas to their present
inhabitants,—the degree of affinity between the mam-
mals inhabiting islands with those of the nearest conti-
nent, being in part determined (as we shall hereafter
see) by the depth of the intervening ocean,—these and
other such facts are opposed to the admission of such
prodigious geographical revolutions within the recent
period, as are necessary on the view advanced by Forbes
and admitted by his followers. The nature and rela-
tive proportions of the inhabitants of oceanic islands are
likewise opposed to the belief of their former continu-
ity with continents. Nor does the almost universally
volcanic composition of such islands favour the admis-
sion that they are the wrecks of sunken continents;—if
they had originally existed as continental mountain
tanges, some at least of the islands would have been
formed, like other mountain summits, of granite, meta-
morphic schists, old fossiliferous and other rocks, instead
of consisting of mere piles of volcanic matter.

I must now say a few words on what are called
accidental means, but which more properly should be
called occasional means of distribution. I shall here
confine myself to plants. In botanical works, this or
that plant is often stated to be ill adapted for wide dis-
semination; but the greater or less facilities for trans-
port across the sea may be said to be almost wholly
unknown. Until I tried, with Mr. Berkeley’s aid, a few
experiments, it was not even known how far seeds could
resist the injurious action of sea-water. To my sur-
prise I found that out of 87 kinds, 64 germinated after
an immersion of 28 days, and a few survived an immer-

Cuap. XIL] MEANS OF DISPERSAL. 142

sion of 137 days. It deserves notice that certain orders
were far more injured than others: nine Leguminose
were tried, and, with one exception, they resisted the
salt-water badly; seven species of the allied orders, Hy-
drophyllacee and Polemoniacew, were all killed by a
month’s immersion. For convenience’ sake I chiefly
tried small seeds without the capsule or fruit; and as
all of these sank in a few days they could not have been
floated across wide spaces of the sea, whether or not they
were injured by the salt-water. Afterwards'I tried some
larger fruits, capsules, &., and some of these floated for
a long time. It is well known what a difference there
is in the buoyancy of green and seasoned timber; and it
occurred to me that floods would often wash into the
sea dried plants or branches with seed-capsules or fruit
attached to them. Hence I was led to dry the stems
and branches of 94 plants with ripe fruit, and to place
them on sea-water. The majority sank rapidly, but
some which, whilst green, floated for a short time, when
dried floated much longer; for instance, ripe hazel-
nuts sank immediately, but when dried they floated for
90 days, and afterwards when planted germinated; an
asparagus-plant with ripe berries floated for 23 days,
when dried it floated for 85 days, and the seeds after-
wards germinated; the ripe seeds of Helosciadium sank
in two days, when dried they floated for above 90 days,
and afterwards germinated. Altogether, out of the 94
dried plants, 18 floated for above 28 days; and some of
the 18 floated for a very much longer period. So that
as $4 kinds of seeds germinated after an immersion of
28 days; and as 48 distinct species with ripe fruit (but
not all the same species as in the foregoing experiment)
floated, after being dried, for above 28 days, we may

144 MEANS OF DISPERSAL. [Cuap. XIL

conclude, as far as anything can be inferred from these
scanty facts, that the seeds of 744, kinds of plants of any
country might be floated by sea-currents during 28 days,
and would retain their power of germination. In
Johnston’s Physical Atlas, the average rate of the sev-
eral Atlantic currents is 33 miles per diem (some cur-
rents running at the rate of 60 miles per diem); on this
average, the seeds of 4; plants belonging to one coun-
try might be floated across 924 miles of sea to another
country, and when stranded, if blown by an inland gale
to a favourable spot, would germinate.

Subsequently to my experiments, M. Martens tried
similar ones, but in a much better manner, for he placed
the seeds in a box in the actual sea, so that they were
alternately wet and exposed to the air like really float-
ing plants. He tried 98 seeds, mostly different from
mine; but he chose many large fruits and likewise seeds
from plants which live near the sea; and this would
have favoured both the average length of their flota-
tion and their resistance to the injurious action of the
salt-water. On the other hand, he did not previously
dry the plants or branches with the fruit; and this, as
we have seen, would have caused some of them to have
floated much longer. The result was that 48 of his
seeds of different kinds floated for 42 days, and were
then capable of germination. But I do not doubt that
plants exposed to the waves would float for a less time
than those protected from violent movement as in our
experiments. Therefore it would perhaps be safer to
assume that the seeds of about 31°, plants of a flora,
after having been dried, could be floated across a space
of sea 900 miles in width, and would then germinate.
The fact of the larger fruits often floating longer than

Cuar.XIL] MEANS OF DISPERSAL. 145

the small, is interesting; as plants with large seeds or
fruit which, as Alph. de Candolle has shown, generally
have restricted ranges, could hardly be transported by
any other means.

Seeds may be occasionally transported in another
manner. Drift timber is thrown up on most islands,
even on those in the midst of the widest oceans; and
the natives of the coral-islands in the Pacific procure
stones for their tools, solely from the roots of drifted
trees, these stones being a valuable royal tax. I find
that when irregularly shaped stones are embedded in
the roots of trees, small parcels of earth are frequently
enclosed in their interstices and behind them,—so per-
fectly that not a particle could be washed away during
the longest transport: out of one small portion of earth
thus completely enclosed by the roots of an oak about 50
years old, three dicotyledonous plants germinated: I am
certain of the accuracy of this observation. Again, I
can show that the carcases of birds, when floating on the
sea, sometimes escape being immediately devoured: and
many kinds of seeds in the crops of floating birds long
retain their vitality: peas and vetches, for instance, are
killed by even a few days’ immersion in sea-water; but
some taken out of the crop of a pigeon, which had floated
on artificial sea-water for 30 days, to my surprise nearly
all germinated.

Living birds can hardly fail to be highly effective
agents in the transportation of seeds. I could give
many facts showing how frequently birds of many kinds
are blown by gales to vast distances across the ocean.
We may safely assume that under such circumstances
their rate of flight would often be 35 miles an hour;
and some authors have given a far higher estimate. I

146 MEANS OF DISPERSAL. (Cuap. XII,

have never seen an instance of nutritious seeds passing
through the intestines of a bird; but hard seeds of fruit
pass uninjured through even the digestive organs of a
turkey. In the course of two months, I picked up in
my garden 12 kinds of seeds, out of the excrement of
small birds, and these seemed perfect, and some of
them, which were tried, germinated. But the following
fact is more important: the crops of birds do not secrete
gastric juice, and do not, as I know by trial, injure in
the least the germination of seeds; now, after a bird
has found and devoured a large supply of food, it is
positively asserted that all the grains do not pass into
the gizzard for twelve or even eighteen hours. A bird in
this interval might easily be blown to the distance of
500 miles, and hawks are known to look out for tired
birds, and the contents of their torn crops might thus
readily get scattered. Some hawks and owls bolt their
prey whole, and, after an interval of from twelve to
twenty hours, disgorge pellets, which, as I know from
experiments made in the Zoological Gardens, include
seeds capable of germination. Some seeds of the oat,
wheat, millet, canary, hemp, clover, and beet germi-
nated after having been from twelve to twenty-one hours
in the stomachs of different birds of prey; and two
seeds of beet grew after having been thus retained for
two days and fourteen hours. Fresh-water fish, I find,
eat seeds of many land and water plants; fish are fre-
quently devoured by birds, and thus the seeds might
be transported from place to place. I forced many
kinds of seeds into the stomachs of dead fish, and then
gave their bodies to fishing-eagles, storks, and pelicans;
these birds, after an interval of many hours, either re-
jected the seeds in pellets or passed them in their excre-

Cuap, XIL] MEANS OF DISPERSAL. 147

ment; and several of these seeds retained the power of
germination. Certain seeds, however, were always
killed by this process.

Locusts are sometimes blown to great distances from
the land; I myself caught one 370 miles from the coast
of Africa, and have heard of others caught at greater
distances. The Rev. R. T. Lowe informed Sir C. Lyell
that in November 1844 swarms of locusts visited the
island of Madeira. They were in countless numbers, as
thick as the flakes of snow in the heaviest snowstorm.
and extended upwards as far as could be seen with a
telescope. During two or three days they slowly ca-
reered round and round in an immense ellipse, at least
five or six miles in diameter, and at night alighted on
the taller trees, which were completely coated with
them. They then disappeared over the sea, as suddenly
as they had appeared, and have not since visited the
island. Now, in parts of Natal it is believed by some
farmers, though on insufficient evidence, that injurious
seeds are introduced into their grass-land in the dung
left by the great flights of locusts which often visit that
country. In consequence of this belief Mr. Weale sent
me in a letter a small packet of the dried pellets, out of
which I extracted under the microscope several seeds,
and raised from them seven grass plants, belonging to
two species, of two genera. Hence a swarm of locusts,
such as that which visited Madeira, might readily be the
means of introducing several kinds of plants into an
island lying far from the mainland.

Although the beaks and feet of birds are generally
clean, earth sometimes adheres to them: in one case I
removed sixty-one grains, and in another case twenty-
two grains of dry argillaceous earth from the foot of a

35

148 MEANS OF DISPERSAL. (Cuap. XI.

partridge, and in the earth there was a pebble as large as
the seed of a vetch. Here is a better case: the leg of a
woodcock was sent to me by a friend, with a little cake
of dry earth attached to the shank, weighing only nine
grains; and this contained a seed of the toad-rush (Jun-
cus bufonius) which germinated and flowered. Mr.
Swaysland, of Brighton, who during the last forty years
has paid close attention to our migratory birds, informs
me that he has often shot wagtails (Motacille), wheat-
ears, and whinchats (Saxicole), on their first arrival on
our shores, before they had alighted; and he has several
times noticed little cakes of earth attached to their feet.
Many facts could be given showing how generally soil
is charged with seeds. For instance, Prof. Newton sent
me the leg of a red-legged partridge (Caccabis rufa)
which had been wounded and could not fly, with a ball
of hard earth adhering to it, and weighing six and a half
ounces. The earth had been kept for three years, but
when broken, watered and placed under a bell glass, no
less than 82 plants sprung from it: these consisted of
12 monocotyledons, including the common oat, and at
least one kind of grass, and of 70 dicotyledons, which
consisted, judging from the young leaves, of at least
three distinct species. With such facts before us, can
we doubt that the many birds which are annually
blown by gales across great spaces of ocean, and
which annually migrate—for instance, the millions of
quails across the Mediterranean—must occasionally
transport a few seeds embedded in dirt adhering to
their feet or beaks? But I shall have to recur to this
subject.

As icebergs are known to be sometimes loaded with
earth and stones, and have even carried brushwood,

Cuap, XIL] MEANS OF DISPERSAL. 149

bones, and the nest of a land-bird, it can hardly be
doubted that they must occasionally, as suggested by
Lyell, have transported seeds from one part to another
of the arctic and antarctic regions; and during the
Glacial period from one part of the now temperate
regions to another. In the Azores, from the large
number of plants common to Europe, in comparison
with the species on the other islands of the Atlantic,
which stand nearer to the mainland, and (as remarked
by Mr. H. C. Watson) from their somewhat northern
character in comparison with the latitude, I suspected
that these islands had been partly stocked by ice-borne
seeds, during the Glacial epoch. At my request Sir C.
Lyell wrote to M. Hartung to inquire whether he had
observed erratic boulders on these islands, and he
answered that he had found large fragments of granite
and other rocks, which do not occur in the archipelago.
Hence we may safely infer that icebergs formerly
landed their rocky burthens on the shores of these
mid-ocean islands, and it is at least possible that they
may have brought thither some few seeds of northern
plants.

Considering that these several means of transport,
and that other means, which without doubt remain to
be discovered, have been in action year after year for
tens of thousands of years, it would, I think, be a mar-
vellous fact if many plants had not thus become widely
transported. These means of transport are sometimes
called accidental, but this is not strictly correct: the
currents of the sea are not accidental, nor is the direc-
tion of prevalent gales of wind. It should be observed
that scarcely any means of transport would carry seeds
for very great distances: for seeds do not retain their

150 MEANS OF DISPERSAL. [Cuar. XII,

vitality when exposed for a great length of time to the
action of sea-water; nor could they be long carried in
the crops or intestines of birds. These means, how-
ever, would suffice for occasional transport across tracts
of sea some hundred miles in breadth, or from island
to island, or from a continent to a neighbouring island,
but not from one distant continent to another. The
floras of distant continents would not by such means
become mingled; but would remain as distinct as they
now are. The currents, from their course, would never
bring seeds from North America to Britain, though
they might and do bring seeds from the West Indies
to our western shores, where, if not killed by their very
long immersion in salt water, they could not endure our
climate. Almost every year, one or two land-birds are
blown across the whole Atlantic Ocean, from North
America to the western shores of Ireland and England;
but seeds could be transported by these rare wanderers
only by one means, namely, by dirt adhering to their
feet or beaks, which is in itself a rare accident. Even in
this case, how small would be the chance of a seed fall-
ing on favourable soil, and coming to maturity! But it
would be a great error to argue that because a well-
stocked island, like Great Britain, has not, as far as
is known (and it would be very difficult to prove this),
received within the last few centuries, through occa-
sional means of transport, immigrants from Europe or
any other continent, that a poorly-stocked island,
though standing more remote from the mainland, would
not receive colonists by similar means. Out of a hun-
dred kinds of seeds or animals transported to an island,
even if far less well-stocked than Britain, perhaps not
more than one would be so well fitted to its new home,

Cua. XIL.] THE Q@LACIAL PERIOD, 151

as to become naturalised. But this is no valid argu-
ment against what would be effected by occasional
means of transport, during the long lapse of geologi-
cal time, whilst the island was being upheaved, and
before it had become fully stocked with inhabitants.
On almost bare land, with few or no destructive in-
sects or birds living there, nearly every seed which
chanced to arrive, if fitted for the climate, would ger-
minate and survive.

Dispersal during the Glacial Period.

The identity of many plants and animals, on moun-
tain-summits, separated from each other by hundreds
of miles of lowlands, where Alpine species could not
possibly exist, is one of the most striking cases known
of the same species living at distant points, without the
apparent possibility of their having migrated from one
point to the other. It is indeed a remarkable fact to
see so many plants of the same species living on the
snowy regions of the Alps or Pyrenees, and in the ex-
treme northern parts of Europe; but it is far more re-
markable, that the plants on the White Mountains, in
the United States of America, are all the same with
those of Labrador, and nearly all the same, as we hear
from Asa Gray, with those on the loftiest mountains
of Europe. Even as long ago as 1747, such facts led
Gmelin to conclude that the same species must have
been independently created at many distinct points;
and we might have remained in this same belief, had
not Agassiz and others called vivid attention to the
Glacial period, which, as we shall immediately see,
affords a simple explanation of these facts. We have
evidence of almost every conceivable kind, organic and

152 DISPERSAL DURING [Cuap. XII.

inorganic, that, within a very recent geological period,
central Europe and North America suffered under an
arctic climate. The ruins of a house burnt by fire do
not tell their tale more plainly than do the mountains
of Scotland and Wales, with their scored flanks, pol-
ished surfaces, and perched boulders, of the icy streams
with which their valleys were lately filled. So greatly
has the climate of Europe changed, that in Northern
Italy, gigantic moraines, left by old glaciers, are now
clothed by the vine and maize. Throughout a large
part of the United States, erratic boulders and scored
rocks plainly reveal a former cold period.

The former influence of the glacial climate on the
distribution of the inhabitants of Europe, as explained
by Edward Forbes, is substantially as follows. But we
shall follow the changes more readily, by supposing a
new glacial period slowly to come on, and then pass
away, as formerly occurred. As the cold came on, and
as each more southern zone became fitted for the in-
habitants of the north, these would take the places of
the former inhabitants of the temperate regions. The
latter, at the same time, would travel further and fur-
ther southward, unless they were stopped by barriers,
in which case they would perish. The mountains
would become covered with snow and ice, and their for-
mer Alpine inhabitants would descend to the plains.
By the time that the cold had reached its maximum, we
should have an arctic fauna and flora, covering the
central parts of Europe, as far south as the Alps and
Pyrenees, and even stretching into Spain. The now
temperate regions of the United States would likewise
be covered by arctic plants and animals and these would
be nearly the same with those of Europe; for the

Cuar, XII] THE GLACIAL PERIOD. 153

present circumpolar inhabitants, which we suppose to
have everywhere travelled southward, are remarkably
uniform round the world.

As the warmth returned, the arctic forms would
retreat northward, closely followed up in their retreat
by the productions of the more temperate regions. And
as the snow melted from the bases of the mountains,
the arctic forms would seize on the cleared and thawed
ground, always ascending, as the warmth increased and
the snow still further disappeared, higher and higher,
whilst their brethren were pursuing their northern
journey. Hence, when the warmth had fully returned,
the same species, which had lately lived together on the
European and North American lowlands, would again
be found in the arctic regions of the Old and New
Worlds, and on many isolated mountain-summits far
distant from each other.

Thus we can understand the identity of many plants
at points so immensely remote as the mountains of the
United States and those of Europe. We can thus also
understand the fact that the Alpine plants of each
mountain-range are more especially related to the arctic
forms living due north or nearly due north of them:
for the first migration when the cold came on, and the
re-migration on the returning warmth, would generally
have been due south and north. The Alpine plants,
for example, of Scotland, as remarked by Mr. H. C.
Watson, and those of the Pyrenees, as remarked by
Ramond, are more especially allied to the plants of
northern Scandinavia; those of the United States to
Labrador; those of the mountains of Siberia to the
arctic regions of that country. These views, grounded
as they are on the perfectly well-ascertained occurrence

154 DISPERSAL DURING [Cuar. XIL

of a former Glacial period, seem to me to explain in so
satisfactory a manner the present distribution of the
Alpine and Arctic productions of Europe and America,
that when in other regions we find the same species
on distant mountain-summits, we may almost conclude,
without other evidence, that a colder climate formerly
permitted their migration across the intervening low-
lands, now become too warm for their existence.

As the arctic forms moved first southward and after-
wards backwards to the north, in unison with the chang-
ing climate, they will not have been exposed during
their long migrations to any great diversity of tem-
perature; and as they all migrated in a body together,
their mutual relations will not have been much dis-
turbed. Hence, in accordance with the principles in-
culcated in this volume, these forms will not have been
liable to much modification. But with the Alpine pro-
ductions, left isolated from the moment of the return-
ing warmth, first at the bases and ultimately on the
summits of the mountains, the case will have been
somewhat different; for it is not likely that all the same
arctic species will have been left on mountain-ranges
far distant from each other, and have survived there
ever since; they will also in all probability, have become
mingled with ancient Alpine species, which must have
existed on the mountains before the commencement of
the Glacial epoch, and which during the coldest period
will have been temporarily driven down to the plains;
they will, also, have been subsequently exposed to some-
what different climatal influences. Their mutual rela-
tions will thus have been in some degree disturbed; con-
sequently they will have been liable to modification; and
they have been modified; for if we compare the present

Cuap. XII} THE GLACIAL PERIOD. 155

Alpine plants and animals of the several great Euro-
pean mountain-ranges one with another, though many
of the species remain identically the same, some exist
as varieties, some as doubtful forms or sub-species, and
some as distinct yet closely allied species representing
each other on the several ranges.

In the foregoing illustration I have assumed that at
the commencement of our imaginary Glacial period,
the arctic productions were as uniform round the polar
regions as they are at the present day. But it is also
necessary to assume that many sub-arctic and some few
temperate forms were the same round the world, for
some of the species which now exist on the lower moun-
tain-slopes and on the plains of North America and
Europe are the same; and it may be asked how I ac-
count for this degree of uniformity in the sub-arctic
and temperate forms round the world, at the commence-
ment of the real Glacial period. At the present day, the
sub-aretic and northern temperate productions of the
Old and New Worlds are separated from each other by
the whole Atlantic Ocean and by the northern part of
the Pacific. During the Glacial period, when the in-
habitants of the Old and New Worlds lived farther
southwards than they do at present, they must have been
still more completely separated from each other by
wider spaces of ocean; so that it may well be asked how
the same species could then or previously have entered
the two continents. The explanation, I believe, lies in
the nature of the climate before the commencement of
the Glacial period. At this, the newer Pliocene period,
the majority of the inhabitants of the world were specifi-
cally the same as now, and we have good reason to be-
lieve that the climate was warmer than at the present

156 DISPERSAL DURING [Cuar, XII

day. Hence we may suppose that the organisms which
now live under latitude 60°, lived during the Pliocene
period farther north under the Polar Circle, in latitude
66°-67°; and that the present arctic productions then
lived on the broken land still nearer to the pole. Now,
if we look at a terrestrial globe, we see under the Polar
Circle that there is almost continuous land from wes-
tern Europe, through Siberia, to eastern America. And
this continuity of the circumpolar land, with the con-
sequent freedom under a more favourable climate for in-
termigration, will account for the supposed uniformity of
the sub-arctic and temperate productions of the Old and
New Worlds, at a period anterior to the Glacial epoch.
Believing, from reasons before alluded to, that our
continents have longremained in nearlythe same relative
position, though subjected to great oscillations of level,
I am strongly inclined to extend the above view, and
to infer that during some still earlier and still warmer
period, such as the older Pliocene period, a large num-
ber of the same plants and animals inhabited the al-
most continuous circumpolar land; and that these plants
and animals, both in the Old and New Worlds, began
slowly to migrate southwards as the climate became
less warm, long before the commencement of the Glacial
period. We now see, as I believe, their descendants,
mostly in a modified condition, in the central parts of
Europe and the United States. On this view we can
understand the relationship with very little identity,
between the productions of North America and Europe,
—a relationship which is highly remarkable, consider-
ing the distance of the two areas, and their separation
by the whole Atlantic Ocean. We can further under-
stand the singular fact remarked on by several observers

Cuar. X11] THE GLACIAL PERIOD. 157

that the productions of Europe and America during
the later tertiary stages were more closely related to
cach other than they are at the present time; for dur-
ing these warmer periods the northern parts of the Old
and New Worlds will have been almost continuously
united by land, serving as a bridge, since rendered
impassable by cold, for the intermigration of their in-
habitants.

During the slowly decreasing warmth of the Plio-
cene period, as soon as the species in common, which in-
habited the New and Old Worlds, migrated south of
the Polar Circle, they will have been completely cut off
from each other. This separation, as far as the more
temperate productions are concerned, must have taken
place long ages ago. As the plants and animals mi-
grated southward, they will have become mingled in the
one great region with the native American productions,
and would have had to compete with them; and in the
other great region, with those of the Old World. Con-
sequently we have here everything favourable for much
modification,—for far more modification than with the
Alpine productions, left isolated, within a much more
recent period, on the several mountain-ranges and on
the arctic lands of Europe and N. America. Hence it
has come, that when we compare the now living pro-
ductions of the temperate regions of the New and Old
Worlds, we find very few identical species (though Asa
Gray has lately shown that more plants are identical
than was formerly supposed), but we find in every great
class many forms, which some naturalists rank as geo-
graphical races, and others as distinct species; and a
host of closely allied or representative forms which are
ranked by all naturalists as specifically distinct.

158 ALTERNATE GLACIAL PERIODS [Cuap. XIL

~weesorthe land, so in the waters of the sea, a slow
southern migration of a marine fauna, which, during
the Pliocene or even a somewhat earlier period, was
nearly uniform along the continuous shores of the Polar
Circle, will account, on the theory of modification, for
many closely allied forms now living in marine areas
completely sundered. Thus, I think, we can -under-
stand the presence of some closely allied, still existing
and extinct tertiary forms, on the eastern and western
shores of temperate North America; and the still more
striking fact of many closely allied crustaceans (as de-
scribed in Dana’s admirable work), some fish and other
marine animals, inhabiting the Mediterranean and the
seas of Japan,—these two areas being now completely
separated by the breadth of a whole continent and by
wide spaces of ocean.

These cases of close relationship in species either
now or formerly inhabiting the seas on the eastern and
western shores of North America, the Mediterranean
and Japan, and the temperate lands of North America
and Europe, are inexplicable on the theory of creation.
We cannot maintain that such species have been created
alike, in correspondence with the nearly similar physical
conditions of the areas; for if we compare, for instance,
certain parts of South America with parts of South
Africa or Australia, we see countries closely similar in
all their physical conditions, with their inhabitants
utterly dissimilar.

Alternate Glacial Periods in the North and South.

But we must return to our more immediate subject.
I am convinced that Forbes’s view may be largely ex-

Cuap, X11.) IN THE NORTH AND SOUTH. 159

tended. In Europe we meet with the plainest evi-
dence of the Glacial period, from the western shores
of Britain to the Oural range, and southward to the
Pyrenees. We may infer from the frozen mammals
and nature of the mountain vegetation, that Siberia was
similarly affected. In the Lebanon, according to Dr.
Hooker, perpetual snow formerly covered the central
axis, and fed glaciers which rolled 400 feet down the
valleys. The same observer has recently found great
moraines at a low level on the Atlas range in N. Africa.
Along the Himalaya, at points 900 miles apart, glaciers
have left the marks of their former low descent; and
in Sikkim, Dr. Hooker saw maize growing on ancient
and gigantic moraines. Southward of the Asiatic con-
tinent, on the opposite side of the equator, we know,
from the excellent researches of Dr. J. Haast and Dr.
Hector, that in New Zealand immense glaciers formerly
descended to a low level; and the same plants found
by Dr. Hooker on widely separated mountains in this
island tell the same story of a former cold period.
From facts communicated to me by the Rev. W. B.
Clarke, it appears also that there are traces of former
glacial action on the mountains of the south-eastern
corner of Australia.

Looking to America; in the northern half, ice-borne
fragments of rock have been observed on the eastern
side of the continent, as far south.as lat. 36°-37°, and
on the shores of the Pacific, where the climate is now
so different, as far south as lat. 46°. Erratic boulders
have, also, been noticed on the Rocky Mountains. In
the Cordillera of South America, nearly under the
equator, glaciers once extended far below their present
level. In Central Chile I examined a vast mound of

160 ALTERNATE GLACIAL PERIODS [Cuap. XIL

detritus with great boulders, crossing the Portillo valley,
which there can hardly be a doubt once formed a huge
moraine; and Mr. D. Forbes informs me that he found
in various parts of the Cordillera, from lat. 13° to 30° S.,
at about the height of 12,000 feet, deeply-furrowed
rocks, resembling those with which he was familiar in
Norway, and likewise great masses of detritus, including
grooved pebbles. Along this whole space of the Cor-
dillera true glaciers do not now exist even at much
more considerable heights. Farther south on both sides
of the continent, from lat. 41° to the southernmost ex-
tremity, we have the clearest evidence of former glacial
action, in numerous immense boulders transported far
from their parent source.

From these several facts, namely from the glacial
action having extended all round the northern and
southern hemispheres—from the period having been in
a geological sense recent in both hemispheres—from its
having lasted in both during a great length of time, as
may be inferred from the amount of work effected—
and lastly from glaciers having recently descended to a
low level along the whole line of the Cordillera, it at
one time appeared to me that we could not avoid the
conclusion that the temperature of the whole world
had been simultaneously lowered during the Glacial
period. But now Mr. Croll, in a series of admirable
memoirs, has attempted to show that a glacial con-
dition of climate is the result of various physical causes,
brought into operation by an increase in the eccentricity
of the earth’s orbit. All these causes tend towards the
same end; but the most powerful appears to be the in-
direct influence of the eccentricity of the orbit upon
oceanic currents. According to Mr. Croll, cold periods

Caar. XI] IN THE NORTH AND SOUTH. 161
‘

regularly recur every ten or fifteen thousand years; and
these at long intervals are extremely severe, owing to cer-
tain contingencies, of which the most important, as Sir
C. Lyell has shown, is the relative position of the land
and water. Mr. Croll believes that the last great Glacial
period occurred about 240,000 years ago, and endured
with slight alterations of climate for about 160,000 years.
With respect to more ancient Glacial periods, several
geologists are convinced from direct evidence that such
occurred during the Miocene and Eocene formations,
not to mention still more ancient formations. But the
most important result for us, arrived at by Mr. Croll,
is that whenever the northern hemisphere passes through
a cold period the temperature of the southern hemi-
sphere is actually raised, with the winters rendered much
milder, chiefly through changes in the direction of the
ocean-currents. So conversely it will be with the north-
ern hemisphere, whilst the southern passes through a
Glacial period. This conclusion throws so much light
on geographical distribution that I am strongly inclined
to trust in it; but I will first give the facts, which
demand an explanation.

In South America, Dr. Hooker has shown that be-
sides many closely allied species, between forty and
fifty of the flowering plants of Tierra del Fuego, form-
ing no inconsiderable part of its scanty flora, are com-
mon to North America and Europe, enormously remote
as these areas in opposite hemispheres are from each
other. On the lofty mountains of equatorial America
a host of peculiar species belonging to European genera
occur. On the Organ mountains of Brazil, some few
temperate European, some Antarctic, and some Andean
genera were found by Gardner, which do not exist

162 ALTERNATE GLACIAL PERIODS [Cuap. XII,

\

in the low intervening hot countries. On the Silla of
Caraccas, the illustrious Humboldt long ago found
species belonging to genera characteristic of the Cordil-
lera.

In Africa, several forms characteristic of Europe and
some few representatives of the flora of the Cape of
Good Hope occur on the mountains of Abyssinia. At
the Cape of Good Hope a very few European species, be-
lieved not to have been introduced by man, and on the
mountains several representative European forms are
found, which have not been discovered in the inter-
tropical parts of Africa. Dr. Hooker has also lately
shown that several of the plants living on the upper parts
of the lofty island of Fernando Po and on the neigh-
bouring Cameroon mountains,.in the Gulf of Guinea,
are closely related to those on the mountains of Abys-
sinia, and likewise to those of temperate Europe. It
now also appears, as I hear from Dr. Hooker, that some
of these same temperate plants have been discovered
by the Rev. R. T. Lowe on the mountains of the Cape
Verde islands. This extension of the same temper-
ate forms, almost under the equator, across the whole
continent of Africa and to the mountains of the Cape
Verde archipelago, is one of the most astonishing facts
ever recorded in the distribution of plants.

On the Himalaya, and on the isolated mountain-
ranges of the peninsula of India, on the heights of
Ceylon, and on the volcanic cones of Java, many plants
occur, either identically the same or representing each
other, and at the same time representing plants of
Europe, not found in the intervening hot lowlands.
A list of the genera of plants collected on the loftier
peaks of Java, raises a picture of a collection made on

Cua. XI] IN THE NORTH AND SOUTH. 163

a hillock in Europe! Still more striking is the fact
that peculiar Australian forms are represented by cer-
tain plants growing on the summits of the mountains
of Borneo. Some of these Australian forms, as I hear
from Dr. Hooker, extend along the heights of the
peninsula of Malacca, and are thinly scattered on the
one hand over India, and on the other hand as far north
as Japan.

On the southern mountains of Australia, Dr. F.
Miiller has discovered several European species; other
species, not introduced by man, occur on the lowlands;
and a long list can be given, as I am informed by Dr.
Hooker, of European genera, found in Australia, but
not in the intermediate torrid regions. In the admir-.
able ‘ Introduction to the Flora of New Zealand, by Dr.
Hooker, analogous and striking facts are given in re-
gard to the plants of that large island. Hence we see
that certain plants growing on the more lofty moun-
tains of the tropics in all parts of the world, and on the
temperate plains of the north and south, are either the
same species or varieties of the same species. It should,
however, be observed that these plants are not strictly
arctic forms; for, as Mr. H. C. Watson has remarked,
“in receding from polar towards equatorial latitudes,
the Alpine or mountain floras really become less and
less Arctic.” Besides these identical and closely allied
forms, many species inhabiting the same widely sun-
dered areas, belong to genera not now found in the inter-
mediate tropical lowlands.

These brief remarks apply to plants alone; but some
few analogous facts could be given in regard to terres-
trial: animals. In marine productions, similar cases

likewise occur; as an example, I may quote a statement
36

164 ALTERNATE GLACIAL PERIODS [Cuap. XII.

by the highest authority, Prof. Dana, that “it is cer-
tainly a wonderful fact that New Zealand should have
a closer resemblance in its crustacea to Great Britain,
its antipode, than to any other part of the world.” Sir
J. Richardson, also, speaks of the reappearance on the
shores of New Zealand, Tasmania, &c., of northern
forms of fish. Dr. Hooker informs me that twenty-five
species of Algw are common to New Zealand and to
Europe, but have not been found in the intermediate
tropical seas.

From the foregoing facts, namely, the presence of
temperate forms on’ the highlands across the whole of
equatorial Africa, and along the Peninsula of India, to
Ceylon and the Malay Archipelago, and in a less well-
marked manner across the wide expanse of tropical
South America, it appears almost certain that at some
former period, no doubt during the most severe part of
a Glacial period, the lowlands of these great continents
were everywhere tenanted under the equator by a con-
siderable number of temperate forms. At this period
the equatorial climate at the level of the sea was prob-
ably about the same with that now experienced at
the height of from five to six thousand feet under the
same latitude, or perhaps even rather cooler. During
this, the coldest period, the lowlands under the equator
must have been clothed with a mingled tropical and
temperate vegetation, like that described by Hooker as
growing luxuriantly at the height of from four to five
thousand feet on the lower slopes of the Himalaya, but
with perhaps a still greater preponderance of temperate
forms. So again in the mountainous island of Fer-
nando Po, in the Gulf of Guinea, Mr. Mann found tem-
perate European forms beginning to appear at the height

Cuar. XIL] IN THE NORTH AND SOUTH. 165

of about five thousand feet. On the mountains of
Panama, at the height of only two thousand: feet, Dr.
Seemann found the vegetation like that of Mexico,
“with forms of the torrid zone harmoniously blended
with those of the temperate.”

Now let us see whether Mr. Croll’s conclusion that
when the northern hemisphere suffered from the ex-
treme cold of the great Glacial period, the southern
hemisphere was actually warmer, throws any clear light
on the present apparently inexplicable distribution of
various organisms in the temperate parts of both hemi-
spheres, and on the mountains of the tropics. The
Glacial period, as measured by years, must have been
very long; and when we remember over what. vast
spaces some naturalised plants and animals have spread
within a few centuries, this period will have been ample
for any amount of migration. As the cold became more
and more intense, we know that Arctic forms invaded
the temperate regions; and, from the facts just given,
there can hardly be a doubt that some of the more vigor-
ous, dominant, and widest-spreading temperate forms in-
vaded the equatorial lowlands. The inhabitants of
these hot lowlands would at the same time have migrated
to the tropical and subtropical regions of the south, for
the southern hemisphere was at this period warmer.
On the decline of the Glacial period, as both hemi-
spheres gradually recovered their former temperatures,
the northern temperate forms living on the lowlands
under the equator, would have been driven to their
former homes or have been destroyed, being replaced
by the equatorial forms returning from the south.
Some, however, of the northern temperate forms would
almost certainly have ascended any adjoining high land,

166 ALTERNATE GLACIAL PERIODS [Cuap. XII

where, if sufficiently lofty, they would have long sur-
vived like the Arctic forms on the mountains of Europe.
They might have survived, even if the climate was not
perfectly fitted for them, for the change of temperature
must have been very slow, and plants undoubtedly pos-
sess a certain capacity for acclimatisation, as shown by
their transmitting to their offspring different consti-
tutional powers of resisting heat and cold.

In the regular course of events the southern hemi-
sphere would in its turn be subjected to a severe Glacial
period, with the northern hemisphere rendered warmer;
and then the southern temperate forms would invade
the equatorial lowlands. The northern forms which
had before been left on the mountains would now de-
scend and mingle with the southern forms. These
latter, when the warmth returned, would return to their
former homes, leaving some few species on the moun-
tains, and carrying southward with them some of the
northern temperate forms which had descended from
their mountain fastnesses. Thus, we should have some
few species identically the same in the northern and
southern temperate zones and on the mountains of the
intermediate tropical regions.’ But the species left dur-
ing a long time on these mountains, or in opposite
hemispheres, would have to compete with many new
forms and would be exposed to somewhat different
physical conditions; hence they would be eminently
liable to modification, and would generally now exist
as varieties or as representative species; and this is the
case. We must, also, bear in mind the occurrence in
both hemispheres of former Glacial periods; for these
will account, in accordance with the same principles, for
the many quite distinct species inhabiting the same

Cua. XIL] IN THE NORTH AND SOUTH. 167

widely separated areas, and belonging to genera not now
found in the intermediate torrid zones.

It is a remarkable fact strongly insisted on by
Hooker in regard to America, and by Alph. de Can-
dolle in regard to Australia, that many more identical or
slightly modified species have migrated from the north
to the south, than in a reversed direction. We see,
however, a few southern forms on the mountains of
Borneo and Abyssinia. I suspect that this preponder-
ant migration from the north to the south is due to the
greater extent of land’in the north, and to the northern
forms having existed in their own homes in greater
numbers, and having consequently been advanced
through natural selection and competition to a higher
stage of perfection, or dominating power, than the
southern forms. And thus, when the two sets became
commingled in the equatorial regions, during the alter-
nations of the Glacial periods, the northern forms were
the more powerful and were able to hold their places
on the mountains, and afterwards to migrate southward
with the southern forms; but not so the southern in
regard to the northern forms. In the same manner at
the present day, we see that very many European pro-
ductions cover the ground in La Plata, New Zealand,
and to a lesser degree in Australia, and have beaten
the natives; whereas extremely few southern forms have
become naturalised in any part of the northern hemi-
sphere, though hides, wool, and other objects likely to
carry seeds have been largely imported into Europe
during the last two or three centuries from La Plata
and during the last forty or fifty years from Australia.
The Neilgherrie mountains in India, however, offer a
partial exception; for here, as I hear from Dr. Hooker,

168 ALTERNATE GLACIAL PERIODS [Cuap. XIL

Australian forms are rapidly sowing themselves and be-
coming naturalised. Before the last great Glacial
period, no doubt the intertropical mountains were
stocked with endemic Alpine forms; but these have al-
most everywhere yielded to the more dominant forms
generated in the larger areas and more efficient work-
shops of the north. In many islands the native pro-
ductions are nearly equalled, or even outnumbered,
by those which have become naturalised; and this is
the first stage towards their extinction. Mountains are
islands on the land, and their inhabitants have yielded
to those produced within the larger areas of the north,
just in the same way as the inhabitants of real islands
have everywhere yielded and are still yielding to con-
tinental forms naturalised through man’s agency.

The same principles apply to the distribution of ter-
restrial animals and of marine productions, in the north-
ern and southern temperate zones, and on the inter-
tropical mountains. When, during the height of the
Glacial period, the ocean-currents were widely differ-
ent to what they now are, some of the inhabitants of
the temperate seas might have reached the equator; of
these a few would perhaps at once be able to migrate
southward, by keeping to the cooler currents, whilst
others might remain and survive in the colder depths
until the southern hemisphere was in its turn subjected
to a glacial climate and permitted their further progress;
in nearly the same manner as, according to Forbes, iso-
lated spaces inhabited by Arctic productions exist to
the present day in the deeper parts of the northern
temperate seas.

I am far from supposing that all the difficulties in
regard to the distribution and affinities of the identical

Cuar, XIL] IN THE NORTH AND SOUTH. 169

and allied species, which now live so widely separated
in the north and south, and sometimes on the inter-
mediate mountain-ranges, are removed on the views
above given. The exact lines of migration cannot be
indicated. We cannot say why certain species and not
others have migrated; why certain species have been
modified and have given rise to new forms, whilst others
have remained unaltered. We cannot hope to explain
such facts, until we can say why one species and not
another becomes naturalised by man’s agency in a
foreign land; why one species ranges twice or thrice as
far, and is twice or thrice as common, as another species
within their own homes.

Various special difficulties also remain to be solved;
for instance, the occurrence, as shown by Dr. Hooker, of
the same plants at points so enormously remote as Ker-
guelen Land, New Zealand, and Fuegia; but icebergs,
as suggested by Lyell, may have been concerned in their
dispersal. The existence at these and other distant
points of the southern hemisphere, of species, which,
though distinct, belong to genera exclusively confined
to the south, is a more remarkable case. Some of these
species are so distinct, that we cannot suppose that there
has been time since the commencement of the last Gla-
cial period for their migration and subsequent modi-
fication to the necessary degree. The facts seem to
indicate that distinct species belonging to the same
genera have migrated in radiating lines from a common
centre; and I am inclined to look in the southern, as in
the northern hemisphere, to a former and warmer
period, before the commencement of the last Glacial
period, when the Antarctic lands, now covered with ice,
supported a highly peculiar and isolated flora. It may

170 ALTERNATE GLACIAL PERIODS, [Cuar. XII

be suspected that before this flora was exterminated
during the last Glacial epoch, a few forms had been al-
ready widely dispersed to various points of the southern
hemisphere by occasional means of transport, and by the
aid as halting-places, of now sunken islands. Thus the
southern shores of America, Australia, and New Zealand
may have become slightly tinted by the same peculiar
forms of life.

Sir C. Lyell in a striking passage has speculated, in
language almost identical with mine, on the effects of
great alterations of climate throughout the world on
geographical distribution. And we have now seen that
Mr. Croll’s conclusion that successive Glacial periods in
the one hemisphere coincide with warmer periods in the
opposite hemisphere, together with the admission of the
slow modification of species, explains a multitude of facts
in the distribution of the same and of the allied forms
of life in all parts of the globe. The living waters have
flowed during one period from the north and during
another from the south, and in both cases have reached
the equator; but the stream of life has flowed with
greater force from the north than in the opposite direc-
tion, and has consequently more freely inundated the
south. As the tide leaves its drift in horizontal lines,
rising higher on the shores where the tide rises highest,
so have the living waters left their living drift on our
mountain summits, in a line gently rising from the
Arctic lowlands to a great altitude under the equator.
The various beings thus left stranded may be compared
with savage races of man, driven up and surviving in
the mountain fastnesses of almost every land, which
serve as a record, full of interest to us, of the former
inhabitants of the surrounding lowlands.

Cuar. XIII] FRESH-WATER PRODUCTIONS. 171

CHAPTER XIII.
GEOGRAPHICAL DISTRIBUTION—continued.

Distribution of fresh-water productions—On the inhabitants of
oceanic islands—Absence of Batrachians and of terrestrial Mam-
mals—On the relation of the inhabitants of islands to those of
the nearest mainland—On colonisation from the nearest source
with subsequent modification—Summary of the last and present
chapter.

Fresh-water Productions.

As lakes and river-systems are separated from each
other by barriers of land, it might have been thought
that fresh-water productions would not have ranged
widely within the same country, and as the sea is ap-
parently a still more formidable barrier, that they would
never have extended to distant countries. But the
case is exactly the reverse. Not only have many fresh-
water species, belonging to different classes, an enor-
mous range, but allied species prevail in a remarkable
manner throughout the world. When first collecting
in the fresh waters of Brazil, I well remember feeling
much surprise at the similarity of the fresh-water in-
sects, shells, &c., and at the dissimilarity of the sur-
rounding terrestrial beings, compared with those of
Britain.

But the wide ranging power of fresh-water produc-
tions can, I think, in most cases be explained by their
having become fitted, in a manner highly useful to

172 FRESH-WATER PRODUCTIONS. [Cuap. XTIL

them, for short and frequent migrations from pond to
pond, or from stream to stream, within their own coun-
tries; and liability to wide dispersal would follow from
this capacity as an almost necessary consequence. We
can here consider only a few cases; of these, some of the
most difficult to explain are presented by fish. It was
formerly believed that the same fresh-water species
never existed on two continents distant from each other.
But Dr. Giinther has lately shown that the Galaxias
attenuatus inhabits Tasmania, New Zealand, the Falk-
land Islands, and the mainland of South America. This
is a wonderful case, and probably indicates dispersal
from an Antarctic centre during a former warm period.
This case, however, is rendered in some degree less
surprising by the species of this genus having the
power of crossing by some unknown means considerable
spaces of open ocean: thus there is one species common
to New Zealand and to the Auckland Islands, though
separated by a distance of about 230 miles. On the same
continent fresh-water fish often range widely, and as if
capriciously; for in two adjoining river-systems some of
the species may be the same, and some wholly different.

It is probable that they are occasionally transported
by what may be called accidental means. Thus fishes
still alive are not very rarely dropped at distant points
by whirlwinds; and it is known that the ova retain
their vitality for a considerable time after removal from
the water. Their dispersal may, however, be mainly
attributed to changes in the level of the land within the
recent period, causing rivers to flow into each other.
Instances, also, could be given of this having occurred
during floods, without any change of level. The wide
difference of the fish on the opposite sides of most

Caar. XII] FRESH-WATER PRODUCTIONS. 173

mountain-ranges, which are continuous, and which con-
sequently must from an early period have completely
prevented the inosculation of the river-systems on the
two sides, leads to the same conclusion. Some fresh-
water fish belong to very ancient forms, and in such
cases there will have been ample time for great geo-
graphical changes, and consequently time and means for
much migration. Moreover, Dr. Giinther has recently
been led by several considerations to infer that with
fishes the same forms have a long endurance. Salt-
water fish can with care be slowly accustomed to live in
fresh water; and, according to Valenciennes, there is
hardly a single group of which all the members are con-
fined to fresh water, so that a marine species belonging
to a fresh-water group might travel far along the shores
of the sea, and could, it is probable, become adapted
without much difficulty to the fresh waters of a distant
land.

Some species of fresh-water shells have very wide
ranges, and allied species which, on our theory, are de-
scended from a common parent, and must have pro-
ceeded from a single source, prevail throughout the
world. Their distribution at first perplexed me much,
as their ova are not likely to be transported by birds;
and the ova, as well as the adults, are immediately
killed by sea-water. I could not even understand how
some naturalised species have spread rapidly through-
out the same country. But two facts, which I have ob-
served—and many others no doubt will be discovered—
throw some light on this subject. When ducks sudden-
ly emerge from a pond covered with duck-weed, I have
twice seen these little plants adhering to their backs;
and it has happened to me, in removing a little duck-

174 FRESH-WATER PRODUCTIONS. [Caap. XIIL

weed from one aquarium to another, that I have unin-
tentionally stocked the one with fresh-water shells from
the other. But another agency is perhaps more effec-
tual: I suspended the feet of a duck in an aquarium,
where many ova of fresh-water shells were hatching;
and I found that numbers of the extremely minute and
just-hatched shells crawled on the feet, and clung to
them so firmly that when taken out of the water they
could not be jarred off, though at a somewhat more ad-
vanced age they would voluntarily drop off. These
just-hatched molluscs, though aquatic in their nature,
survived on the duck’s feet, in damp air, from twelve to
twenty hours; and in this length of time a duck or
heron might fly at least six or seven hundred miles, and
if blown across the sea to an oceanic island, or to any
other distant point, would be sure to alight on a pool
or rivulet. Sir Charles Lyell informs me that a Dytis-
cus has been caught with an Ancylus (a fresh-water
shell like a limpet) firmly adhering to it; and a water-
beetle of the same family, a Colymbetes, once flew on
board the ‘ Beagle,’ when forty-five miles distant from
the nearest land: how much farther it might have been
blown by a favouring gale no one can tell.

With respect to plants, it has long been known what
enormous ranges many fresh-water, and even marsh
species, have, both over continents and to the most re-
mote oceanic islands. This is strikingly illustrated, ac-
cording to Alph. de Candolle, in those large groups of
terrestrial plants, which have very few aquatic members;
for the latter seem immediately to acquire, as if in con-
sequence, a wide range. I think favourable means of
dispersal explain this fact. I have before mentioned
that earth occasionally adheres in some quantity to the

Cuar, XIIL.] FRESH~WATER PRODUCTIONS. 175

feet and beaks of birds. Wading birds, which frequent
the muddy edges of ponds, if suddenly flushed, would be
the most likely to have muddy feet. Birds of this order
wander more than those of any other; and they are
occasionally found on the most remote and barren
islands of the open ocean; they would not be likely to
alight on the surface of the sea, so that any dirt on their
feet would not be washed off; and when gaining the
land, they would be sure to fly to their natural fresh-
water haunts. I do not believe that botanists are aware
how charged the mud of ponds is with seeds; I have
tried several little experiments, but’ will here give only
the most striking case: I took in February three table-
spoonfuls of mud from three different points, be-
neath water, on the edge of a little pond: this mud
when dried weighed only 62 ounces; I kept it covered
up in my study for six months, pulling up and counting
each plant as it grew; the plants were of many kinds,
and were altogether 537 in number; and yet the viscid
mud was all contained in a breakfast cup! Considering
these facts, I think it would be an inexplicable cir-
cumstance if water-birds did not transport the seeds
of fresh-water plants to unstocked ponds and streams,
situated at very distant points. The same agency may
have come into play with the eggs of some of the smaller
fresh-water animals.

Other and unknown agencies probably have also
played a part. I have stated that fresh-water fish eat
some kinds of seeds, though they reject many other
kinds after having swallowed them; even small fish
swallow seeds of moderate size, as of the yellow water-
lily and Potamogeton. Herons and other birds, cen-
tury after century, have gone on daily devouring fish;

176 FRESH-WATER PRODUCTIONS. [Cuar. XIEL

they then take flight and go to other waters, or are
blown across the sea; and we have seen that seeds retain
their power of germination, when rejected many hours
afterwards in pellets or in the excrement. When I saw
the great size of the seeds of that fine water-lily, the Ne-
lumbium, and remembered Alph. de Candolle’s remarks
on the distribution of this plant,I thought that themeans
of its dispersal must remain inexplicable; but Audubon
states that he found the seeds of the great southern
water-lily (probably, according to Dr. Hooker, the Ne-
lumbium luteum) in a heron’s stomach. Now this bird
must often have flown with its stomach thus well
stocked to distant ponds, and then getting a hearty
meal of fish, analogy makes me believe that it would
have rejected the seeds in a pellet in a fit state for
germination.

In considering these several means of distribution, it
should be remembered that when a pond or stream is
first formed, for instance, on a rising islet, it will be
unoccupied; and a single seed or egg will have a good
chance of succeeding. Although there will always be a
struggle for life between the inhabitants of the same
pond, however few in kind, yet as the number even in a
well-stocked pond is small in comparison with the num-
ber of species inhabiting an equal area of land, the
competition between them will probably be less severe
than between terrestrial species; consequently an in-
truder from the waters of a foreign country would have
a better chance of seizing on a new place, than in the
case of terrestrial colonists. We should also remember
that many fresh-water productions are low in the scale
of nature, and we have reason to believe that such be-
ings become modified more slowly than the high; and

Cuap. XII] INHABITANTS OF OCEANIC ISLANDS 177

this will give time for the migration of aquatic species.
We should not forget the probability of many fresh-
water forms having formerly ranged continuously over
immense areas, and then having become extinct at in-
termediate points. But the wide distribution of fresh-
water plants and of the lower animals, whether retain-
ing the same identical form or in some degree modified,
apparently depends in main part on the wide dis-
persal of their seeds and eggs by animals, more es-
pecially by fresh-water birds, which have great powers

of flight, and naturally travel from one piece of water to
another.

On the Inhabitants of Oceanic Islands.

We now come to the last of the three classes of facts,
which I have selected as presenting the greatest amount
of difficulty with respect to distribution, on the view
that not only all the individuals of the same species
have migrated from some one area, but that allied
species, although now inhabiting the most distant
points, have proceeded from a single area,—the birth-
place of their early progenitors. I have already given
my reasons for disbelieving in continental extensions
within the period of existing species, on so enormous a
scale that all the many islands of the several oceans
were thus stocked with their present terrestrial inhabi-
tants. This view removes many difficulties, but it does
not accord with all the facts in regard to the produc-
tions of islands. In the following remarks I shall not
confine myself to the mere question of dispersal, but
shall consider some other cases bearing on the truth of
the two theories of independent creation and of descent
with modification.

{78 INHABITANTS OF OCEANIC ISLANDS. [Cuap. XIIL

The species of all kinds which inhabit oceanic is-
lands are few in number compared with those on equal
continental areas: Alph. de Candolle admits this for
plants, and Wollaston for insects. New Zealand, for
instance, with its lofty mountains and diversified sta-
tions, extending over 780 miles of latitude, together
with the outlying islands of Auckland, Campbell and
Chatham, contain altogether only 960 kinds of flower-
ing plants; if we compare this moderate number with
the species which swarm over equal areas in South-
Western Australia or at the Cape of Good Hope, we
must admit that some cause, independently of different
physical conditions, has given rise to so great a differ-
ence in number. Even the uniform county of Cam-
bridge has 847 plants, and the little island of Angle-
sea 764, but a few ferns and a few introduced plants
are included in these numbers, and the comparison in
some other respects is not quite fair. We have evi-
dence that the barren island of Ascension aboriginally
possessed less than half-a-dozen flowering plants; yet
many species have now become naturalised on it, as
they have in New Zealand and on every other oceanic
island which can be named. In St. Helena there is
reason to believe that the naturalised plants and ani-
mals have nearly or quite exterminated many native
productions. He who admits the doctrine of the creation
of each separate species, will have to admit that a suffi-
cient number of the best adapted plants and animals
were not created for oceanic islands; for man has unin-
tentionally stocked them far more fully and perfectly
than did nature.

Although in oceanic islands the species are few in
number, the proportion of endemic kinds (i. e. those

Cuap. XIII.) INHABITANTS OF OCEANIU ISLANDS. 179

found nowhere else in the world) is often extremely
large. If we compare, for instance, the number of
endemic land-shells in Madeira, or of endemic birds in
the Galapagos Archipelago, with the number found on
any continent, and then compare the area of the island
with that of the continent, we shall see that this is true.
This fact might have been theoretically expected, for,
as already explained, species occasionally arriving after
long intervals of time in the new and isolated district,
and having to compete with new associates, would be
eminently liable to modification, and would often pro-
duce groups of modified descendants. But it by no
means follows that, because in an island nearly all the
species of one class are peculiar, those of another class,-
or of another section of the same class, are peculiar;
and this difference stems to depend partly on the spe-
cies which are not modified having immigrated in a
body, so that their mutual relations have not been much
disturbed; and partly on the frequent arrival of un-
modified immigrants from the mother-country, with
which the insular forms have intercrossed. It should
be borne in mind that the offsprizig of such crosses
would certainly gain in vigour; so that even an occasional
cross would produce more effect than might have been
anticipated. I will give a few illustrations of the fore-
going remarks: in the Galapagos Islands there are 26
land-birds; of these 21 (or perhaps 23) are peculiar,
whereas of the 11 marine birds only 2 are pecyliar; and
it is obvious that marine birds could arrive at these is-
lands much more easily and frequently than land-birds.
Bermuda, on the other hand, which lies at about the
same distance from North America as the Galapagos

Islands do from South America, and which has a very
37

180 INHABITANTS OF OCEANIC ISLANDS. [Caap. XIIT.

peculiar soil, does not possess a single endemic land-
bird; and we know from Mr. J. M. Jones’s admirable
account of Bermuda, that very many North American
birds occasionally or even frequently visit this island.
Almost every year, as I am informed by Mr. E. V.
Harcourt, many European and African birds are
blown to Madeira; this island is inhabited by 99 kinds
of which one alone is peculiar, though very closely
related to a European form; and three or four other
species are confined to this island and to the Canaries.
So that the islands of Bermuda and Madeira have
been stocked from the neighbouring continents with
birds, which for long ages have there struggled to-
gether, and have become mutually co-adapted. Hence
when settled in their new homes, each kind will have
been kept by the others to its proper place and habits,
and will consequently have been but little liable to
modification. Any tendency to modification will also
have been checked by intercrossing with the un-
modified immigrants, often arriving from the mother-
country. Madeira again is inhabited by a wonder-
ful number of peculiar land-shells, whereas not one
species of sea-shell is peculiar to its shores: now, though
we do not know how sea-shells are dispersed, yet we
can see that their eggs or larve, perhaps attached
to seaweed or floating timber, or to the feet of wading-
birds, might be transported across three or four hun-
dred miles of open sea far more easily than land-shells.
The different orders of insects inhabiting Madeira pre-
sent nearly parallel cases.

Oceanic islands are sometimes deficient in animals of
certain whole classes, and their places are occupied by
other classes; thus in the Galapagos Islands reptiles,

Cuar. XII.] INHABITANTS OF OCEANIC ISLANDS. 181

and in New Zealand gigantic wingless birds, take, or
recently took, the place of mammals. Although New
Zealand is here spoken of as an oceanic island, it is in
some degree doubtful whether it should be so ranked;
it is of large size, and is not separated from Australia
by a profoundly deep sea; from its geological charac-
ter and the direction of its mountain-ranges, the Rev.
W. B. Clarke has lately maintained that this island,
as well as New Caledonia, should be considered as ap-
purtenances of Australia. Turning to plants, Dr.
Hooker has shown that in the Galapagos Islands the
proportional numbers of the different orders are very
different from what they are elsewhere. All such dif-
ferences in number, and the absence of certain whole
groups of animals and plants, are generally accounted
for by supposed differences in the physical conditions
of the islands; but this explanation is not a little
doubtful. Facility of immigration seems to have
been fully as important as the nature of the condi-
tions.

Many remarkable little facts could be given with
respect to the inhabitants of oceanic islands. For in-
stance, in certain islands not tenanted by a single mam-
mal, some of the endemic plants have beautifully hooked
seeds; yet few relations are more manifest than that
hooks serve for the transportal of seeds in the wool or
fur of quadrupeds. But a hooked seed might be
carried to an island by other means; and the plant then
becoming modified would form an endemic species, still
retaining its hooks, which would form a useless append-
age like the shrivelled wings under the soldered wing-
covers of many insular beetles. Again, islands often
possess trees or bushes belonging to orders which else-

182 ABSENCE OF TERRESTRIAL [Cuap. XIIL

where include only herbaceous species; now trees, as
Alph. de Candolle has shown, generally have, what-
ever the cause may be, confined ranges. Hence trees
would be little likely to reach distant oceanic islands;
and an herbaceous plant, which had no chance of suc-
cessfully competing with the many fully developed trees .
growing on a continent, might, when established on an
island, gain an advantage over other herbaceous plants
by growing taller and taller and overtopping them.
In this case, natural selection would tend to add to the
stature of the plant, to whatever order it belonged,
and thus first convert it into a bush and then into a
tree.

Absence of Batrachians and Terrestrial Mammals on
Oceanic Islands.

With respect to the absence of whole orders of ani-
mals on oceanic islands, Bory St. Vincent long ago
remarked that Batrachians (frogs, toads, newts) are
never found on any of the many islands with which the
great oceans are studded. I have taken pains to verify
this assertion, and have found it true, with the ex-
ception of New Zealand, New Caledonia, the Andaman
Islands, and perhaps the Salomon Islands and the Sey-
chelles. But I have already remarked that it is doubt-
ful whether New Zealand and New Caledonia ought
to be classed as oceanic islands; and this is still more
doubtful with respect to the Andaman and Salomon
groups and the Seychelles. This general absence of
frogs, toads, and newts on so many true oceanic islands
cannot be accounted for by their physical conditions:
indeed it seems that islands are peculiarly fitted for
these animals; for frogs have been introduced into Ma-

Cuap, XIII.] MAMMALS ON OCEANIC ISLANDS. 183

deira, the Azores, and Mauritius, and have multiplied
so as to become a nuisance. But as these animals and
their spawn are immediately killed (with the excep-
tion, as far as known, of one Indian species) by sea-
water, there would be great difficulty in their trans-
portal across the sea, and therefore we can see why
they do not exist on strictly oceanic islands. But
why, on the theory of creation, they should not have
been created there, it would be very difficult to ex-
plain.

Mammals offer another and similar case. I have
carefully searched the oldest voyages, and have not
found a single instance, free from doubt, of a terrestrial
mammal (excluding domesticated animals kept by the
natives) inhabiting an island situated above 300 miles
from a continent or great continental island; and many
islands situated at a much less distance are equally
barren. The Falkland Islands, which are inhabited by
a wolf-like fox, come nearest to an exception; but this

. group cannot be considered as oceanic, as it lies on a
bank in connection with the mainland at the distance
of about 280 miles; moreover, icebergs formerly brought
boulders to its western shores, and they may have for-
merly transported foxes, as now frequently happens in
the arctic regions. Yet it cannot be said that small
islands will not support at least small mammals, for
they occur in many parts of the world on very small
islands, when lying close to a continent; and hardly an
island can be named on which our smaller quadrupeds
have not become naturalised and greatly multiplied.
Tt cannot be said, on the ordinary view of creation, that
there has not been time for the creation of mammals;
many volcanic islands are sufficiently ancient, as shown

184 ABSENCE OF TERRESTRIAL [Cuap. XIIL

by the stupendous degradation which they have suffered,
and by their tertiary strata: there has also been time
for the production of endemic species belonging to
other classes; and on continents it is known that
new species of mammals appear and disappear at a
quicker rate than other and lower animals. Although
terrestrial mammals do not occur on oceanic islands,
aerial mammals do occur on almost every island.
New Zealand possesses two bats found nowhere else
in the world: Norfolk Island, the Viti Archipelago, the
Bonin Islands, the Caroline and Marianne Archipela-
goes, and Mauritius, all possess their peculiar bats.
Why, it may be asked, has the supposed creative force
produced bats and no other mammals on remote is-
lands? On my view this question can easily be an-
swered; for no terrestrial mammal can be transported
across a wide space of sea, but bats can fly across.
Bats have been seen wandering by day far over the
Atlantic Ocean; and two North American species
either regularly or occasionally visit Bermuda, at,
the distance of 600 miles from the mainland. I hear
from Mr. Tomes, who has specially studied this
family, that many species have enormous ranges,
and are found on continents and on far distant is-
lands. Hence we have only to suppose that such
wandering species have been modified in their new
homes in relation to their new position, and we can
understand the presence of endemic bats on oceanic
islands, with the absence of all other terrestrial mam-
mals.

Another interesting relation exists, namely between
the depth of the sea separating islands ftom each other
or from the nearest continent, and the degree of affinity

Caap. XIII]. MAMMALS ON OCEANIC ISLANDS. 185

of their mammalian inhabitants. Mr. Windsor Earl
has made some striking observations on this head, since
greatly extended by Mr. Wallace’s admirable researches,
in regard to the great Malay Archipelago, which is
traversed near Celebes by a space of deep ocean, and
this separates two widely distinct mammalian faunas.
On either side the islands stand on a moderately shal-
low submarine bank, and these islands are inhabited by
the same or by closely allied quadrupeds. I have not as
yet had time to follow up this subject in all quarters of
the world; but as far as I have gone, the relation holds
good. For instance, Britain is separated by a shallow
channel from Europe, and the mammals are the same
on both sides; and so it is with all the islands near the
shores of Australia. The West Indian Islands, on the
other hand, stand on a deeply submerged bank, nearly
1000 fathoms in depth, and here we find American
forms, but the species and even the genera are quite
distinct. As the amount of modification which animals
of all kinds undergo partly depends on the lapse of
time, and as the islands which are separated from each
other or from the mainland by shallow channels, are
more likely to have been continuously united within a
recent period than the islands separated by deeper chan-
nels, we can understand how it is that a relation exists
between the depth of the sea separating two mammalian
faunas, and the degree of their affinity,—a relation
which is quite inexplicable on the theory of independ-
ent acts of creation.

The foregoing statements in regard to the inhabi-
tants of oceanic islands,—namely, the fewness of the
species, with a large proportion consisting of endemic
forms—the members of certain groups, but not those of

186 ABSENCE OF TERRESTRIAL ([Cuap. XIII.

other groups in the same class, having been modified—
the absence of certain whole orders, as of batrachians
and of terrestrial mammals, notwithstanding the pres-
ence of aerial bats,—the singular proportions of certain
orders of plants,—herbaceous forms having been de-
veloped into trees, &c.,—seem to me to accord better
with the belief in the efficiency of occasional means of
transport, carried on during a long course of time, than
with the belief in the former connection of all oceanic
islands with the nearest continent; for on this latter
view it is probable that the various classes would have
immigrated more uniformly, and from the species hav-
ing entered in a body their mutual relations would not
have been much disturbed, and consequently they would
either have not been modified, or all the species in a
more equable manner.

I do not deny that there are many and serious diffi-
culties in understanding how many of the inhabitants
of the more remote islands, whether still retaining the
same specific form or subsequently modified, have
reached their present homes. But the probability of
other islands having once existed as halting-places, of
which not a wreck now remains, must not be overlooked.
I will specify one difficult case. Almost all oceanic
islands, even the most isolated and smallest, are in-
habited by land-shells, generally by endemic species,
but sometimes by species found elsewhere,—striking
instances of which have been given by Dr. A. A. Gould
in relation to the Pacific. Now it is notorious that
land-shells are easily killed by sea-water; their eggs,
at least such as I have tried, sink in it and are killed.
Yet there must be some unknown, but occasionally effi-
cient means for their transportal. Would the just-

Cuap. XIII.] MAMMALS ON OCEANIC ISLANDS. 187

hatched young sometimes adhere to the feet of birds
roosting on the ground, and thus get transported? It
occurred to me that land-shells, when hybernating and
having a membranous diaphragm over the mouth of
the shell, might be floated in chinks of drifted timber
across moderately wide arms of the sea. And I find
that several species in this state withstand uninjured
an immersion in sea-water during seven days: one shell,
the Helix pomatia, after having been thus treated and
again hybernating was put into sea-water for twenty
days, and perfectly recovered. During this length of
time the shell might have been carried by a marine
current of average swiftness, to a distance of 660 geo-
graphical miles. As this Helix has a thick calcareous
operculum, I removed it, and when it had formed a
new membranous one, I again immersed it for four-
teen days in sea-water, and again it recovered and
crawled away. Baron Aucapitaine has since tried simi-
lar experiments: he placed 100 land-shells, belonging
to ten species, in a box pierced with holes, and im-
mersed it for a fortnight in the sea. Out of the hun-
dred shells, twenty-seven recovered. The presence of
an operculum seems to have been of importance, as
out of twelve specimens of Cyclostoma elegans, which
is thus furnished, eleven revived. It is remarkable,
seeing how well the Helix pomatia resisted with me the
salt-water, that not one of fifty-four specimens be-
longing to four other species of Helix tried by Aucapi-
taine, recovered. It is, however, not at all probable
that land-shells have often been thus transported; the
feet of birds offer a more probable method.

188 RELATIONS OF THE INHABITANTS OF [Cuap. XIII

On the Relations of the Inhabitants of Islands to those of
the nearest Mainland.

The most striking and important fact for us is the
affinity of the species which inhabit islands to those of
the nearest mainland, without being actually the same.
Numerous instances could be given. The Galapagos
Archipelago, situated under the equator, lies at the
distance of between 500 and 600 miles from the shores
of South America. Here almost every product of the
land and of the water bears the unmistakable stamp of
the American continent. There are twenty-six land-
birds; of these, twenty-one, or perhaps twenty-three are
ranked as distinct species, and would commonly be
assumed to have been here created; yet the close affinity
of most of these birds to American species is manifest
in every character, in their habits, gestures, and tones
of voice. So it is with the other animals, and with a
large proportion of the plants, as shown by Dr. Hooker
in his admirable Flora of this archipelago. The natu-
ralist, looking at the inhabitants of these volcanic is-
lands in the Pacific, distant several hundred miles from
the continent, feels that he is standing on American
land. Why should this be so? why should the species
which are supposed to have been created in the Gala-
pagos Archipelago, and nowhere else, bear so plainly
the stamp of affinity to those created in America? There
is nothing in the conditions of life, in the geological
nature of the islands, in their height or climate, or in
the proportions in which the several classes are asso-
ciated together, which closely resembles the conditions
of the South American coast: in fact, there is a con-
siderable dissimilarity in all these respects. On the

Cuap, XIII] ISLANDS TO THOSE OF THE MAINLAND. 189

other hand, there is a considerable degree of resem-
blance in the volcanic nature of the soil, in the climate,
height, and size of the islands, between the Galapagos
and Cape Verde Archipelagoes: but what an entire and
absolute difference in their inhabitants! The inhabi-
tants of the Cape Verde Islands are related to those of
Africa, like those of the Galapagos to America. Facts
such as these, admit of no sort of explanation on the
ordinary view of independent creation; whereas on the
view here maintained, it is obvious that the Galapagos
Islands would be likely to receive colonists from Amer-
ica, whether by occasional means of transport or (though
I do not -believe in this doctrine) by formerly continu-
ous land, and the Cape Verde Islands from Africa;
such colonists would be liable to- modification,—the
principle of inheritance still betraying their original
birthplace.

Many analogous facts could be given: indeed it is an
almost universal rule that the endemic productions of
islands are related to those of the nearest continent, or
of the nearest large island. The exceptions are few,
and most of them can be explained. Thus although
Kerguelen Land stands nearer to Africa than to Amer-
ica, the plants are related, and that very closely, as we
know from Dr. Hooker’s account, to those of America:
but on the view that this island has been mainly stocked
by seeds brought with earth and stones on icebergs,
drifted by the prevailing currents, this anomaly dis-
appears. New Zealand in its endemic planes is much *
more closely related to Australia, the nearest mainland,
than to any other region: and this is what might have
been expected; but it is also plainly related to South
America, which, although the next nearest continent, is

190 RELATIONS OF THE INHABITANTS OF (Caap. XIIL

so enormously remote, that the fact becomes an anom-
aly. But this difficulty partially disappears on the
view that New Zealand, South America, and the other
southern lands have been stocked in part from a nearly
intermediate though distant point, namely from the ant-
arctic islands, when they were clothed with vegetation,
during a warmer tertiary period, before the commence-
ment of the last Glacial period. The affinity, which
though feeble, I am assured by Dr. Hooker is real, be-
tween the flora of the south-western corner of Australia
and of the Cape of Good Hope, is a far more remarkable
case; but this affinity is confined to the plants, and will,
no doubt, some day be explained. 5

The same law which has determined the relation-
ship between the inhabitants of islands and the nearest
mainland, is sometimes displayed on a small scale, but
in a most interesting manner, within the limits of the
same archipelago. Thus each separate island of the
Galapagos Archipelago is tenanted, and the fact is a
marvellous one, by many distinct species; but these
species are related to each other in a very much closer
manner than to the inhabitants of the American con-
tinent, or of any other quarter of the world. This is
what might have been expected, for islands situated so
near to each other would almost necessarily receive
immigrants from the same original source, and from
each other. But how is it that many of the immigrants
have been differently modified, though only in a small
degree, in islands situated within sight of each other,
having the same geological nature, the same height,
climate, &c.? This long appeared to me a great diffi-
culty: but it arises in chief part from the deeply-seated
error of considering the physical conditions of a country

Cuap, XIII] ISLANDS TO THOSE OF THE MAINLAND. 191

as the most important; whereas it cannot be disputed
that the nature of the other species with which each has
to compete, is at least as important, and generally a far
more important element of success. Now if we look to
the species which inhabit the Galapagos Archipelago,
and are likewise found in other parts of the world, we
find that they differ considerably in the several islands.
This difference might indeed have been expected if the
islands had been stocked by occasional means of trans-
port—a seed, for instance, of one plant having been
brought to one island, and that of another plant to
another island, though all proceeding from the same
general source. Hence, when in former times an im-
migrant first settled on one of the islands, or when it
subsequently spread from one to another, it would un-
doubtedly be exposed to different conditions in the
different islands, for it would have to compete with a
different set of organisms; a plant, for instance, would
find the ground best fitted for it occupied by somewhat
different species in the different islands, and would be
exposed to the attacks of somewhat different enemies.
If then it varied, natural selection would probably fa-
vour different varieties in the different islands. Some
species, however, might spread and yet retain the same
character throughout the group, just as we see some
species spreading widely throughout a continent and
remaining the same.

The really surprising fact in this case of the Gala-
pagos Archipelago, and in a lesser degree in some an-
alogous cases, is that each new species after being formed
in any one island, did not spread quickly to the other is-
lands. But the islands, though in sight of each other,
are separated by deep arms of the sea, in most cases

192 RELATIONS OF THE INHABITANTS OF [Cuar. XIII

wider than the British Channel, and there is no reason
to suppose that they have at any former period been
continuously united. The currents of the sea are rapid
and sweep between the islands, and gales of wind are
extraordinarily rare; so that the islands are far more
effectually separated from each other than they appear
on a map. Nevertheless some of the species, both of
those found in other parts of the world and of those
confined to the archipelago, are common to the. several
islands; and we may infer from their present manner
of distribution, that they have spread from one island
to the others. But we often take, I think, an erroneous
view of the probability of closely-allied species invading
each other’s territory, when put into free interconi-
munication. Undoubtedly, if one species has any ad.
vantage over another, it will in a very brief time wholly
or in part supplant it; but if both are equally well fitted
for their own places, both will probably hold their sepa-
rate places for almost any length of time. Beingsfamil-
iar with the fact that many species, naturalised through
man’s agency, have spread with astonishing rapidity
over wide areas, we are apt to infer that most species
would thus spread; but we should remember that the
species which become naturalised in new countries are
not generally closely allied to the aboriginal inhahi-
tants, but are very distinct forms, belonging in a large
proportion of cases, as shown by Alph. de Candolle, to
distinct genera. In the Galapagos Archipelago, many
even of the birds, though so well adapted for flying
from island to island, differ on the different islands;
thus there are three closely-allied species of mocking-
thrush, each confined to its own island. Now let us
suppose the mocking-thrush of Chatham Island to be

Cuap. XIII.] ISLANDS TO THOSE OF THE MAINLAND. 193

blown to Charles Island, which has its,own mocking-
thrush; why should it succeed in establishing itself
there? We may safely infer that Charles Island is
well stocked with its own species, for annually more
eggs are laid and young birds hatched, than can possibly
be reared; and we may infer that the mocking-thrush
peculiar to Charles’s Island is at least as well fitted for
its home as is the species peculiar to Chatham Island.
Sir C. Lyell and Mr. Wollaston have communicated to
me a remarkable fact bearing on this subject; namely,
that Madeira and the adjoining islet of Porto Santo
possess many distinct but representative species of land-
shells, some of which live in crevices of stone; and
although large quantities of stone are annually trans-
ported from Porto Santo to Madeira, yet this latter
island has not become colonised by the Porto Santo
species; nevertheless both islands have been colonised
by European land-shells, which no doubt had some
advantage over the indigenous species. From these
considerations I think we need not greatly marvel at
the endemic species which inhabit the several islands of
the Galapagos Archipelago, not having all spread from
island to island. On the same continent, also, pre-
occupation has probably played an important part in
checking the commingling of the species which inhabit
different districts with nearly the same physical condi-
tions. Thus, the south-east and south-west corners of
Australia have nearly the same physical conditions, and
are united by continuous land, yet they are inhabited
by a vast number of distinct mammals, birds, and plants;
so it is, according to Mr. Bates, with the butterflies and
other animals inhabiting the great, open, and continu-
ous valley of the Amazons.

{94 RELATIONS OF THE INHABITANTS OF [Cuap. XIIL

The same principle which governs the general char-
acter of the inhabitants of oceanic islands, namely, the
relation to the source whence colonists could have been
most easily derived, together with their subsequent
modification, is of the widest application throughout
nature. We see this on every mountain-summit, in
every lake and marsh. For Alpine species, excepting
in as far as the same species have become widely
spread during the Glacial epoch, are related to those
of the surrounding lowlands; thus we have in South
America, Alpine humming-birds, Alpine rodents, Al-
pine plants, &c., all strictly belonging to American
forms; and it is obvious that a mountain, as it became
slowly upheaved, would be colonised from the surround-
ing lowlands. So it is with the inhabitants of lakes
and marshes, excepting in so far as great facility of
transport has allowed the same forms to prevail through-
out large portions of the world. We see this same prin-
ciple in the character of most of the blind animals in-
habiting the caves of America and of Europe. Other
analogous facts could be given. It will, I believe, be
found universally true, that wherever in two regions,
let them be ever so distant, many closely allied or
representative species occur, there will likewise be found
some identical species; and wherever many closely-al-
lied species occur, there will be found many forms which
some naturalists rank as distinct species, and others as
mere varieties; these doubtful forms showing us the
steps in the progress of modification.

The relation between the power and extent of mi-
gration in certain species, either at the present or at
some former period, and the existence at remote points
of the world of closely-allied species, is shown in an-

Cuar. XIIL] ISLANDS TO THOSE OF THE MAINLAND. 195

other and more general way. Mr. Gould remarked
to me long ago, that in those genera of birds which
range over the world, many of the species have very:
wide ranges. I can hardly doubt that this rule is gen-
erally true, though difficult of proof. Amongst mam-
mals, we see it strikingly displayed in Bats, and in a
lesser degree in the Felide and Canide. We see the
same rule in the distribution of butterflies and beetles.
So it is with most of the inhabitants of fresh water,
for many of the genera in the most distinct classes range
over the world, and many of the species have enormous
ranges. It is not meant that all, but that some of the
species have very wide ranges in the genera which range
very widely. Nor is it meant that the species in
such genera have on an average a very wide range; for
this will largely depend on how far the process of modi-
fication has gone; for instance, two varieties of the
same species inhabit America and Europe, and thus
the species has an immense range; but, if variation
were to be carried a little further, the two varieties
would be ranked as distinct species, and their range
would be greatly reduced. Still less is it meant, that
species which have the capacity of crossing barriers and
ranging widely, as in the case of certain powerfully-
winged birds, will necessarily range widely; for we
should never forget that to range widely implies not
only the power of crossing barriers, but the more im-
portant power of being victorious in distant lands
in the struggle for life with foreign associates. But
according to the view that all the species of a genus,
though distributed to the most remote points of
the world, are descended from a single progenitor,

we ought to find, and I believe as a general rule we
38

19¢ RELATIONS OF THE INHABITANTS OF [Cuap. XIII

do find, that some at least of the species range very
widely.

We should bear in mind that many genera in all
classes are of ancient origin, and the species in this
case will have had ample time for dispersal and sub-
sequent modification. There is also reason to believe
from geological evidence, that within each great class
the lower organisms change at a slower rate than the
higher; consequently they will have had a better chance
of ranging widely and of still retaining the same spe-
cific character. This fact, together with that of the
seeds and eggs of most lowly organised forms being very
minute and better fitted for distant transportal, prob-
ably accounts for a law which has long been observed,
and which has lately been discussed by Alph. de Can-
dolle in regard to plants, namely, that the lower
any group of organisms stands the more widely it
ranges.

The relations just discussed,—namely, lower organ-
isms ranging more widely than the higher,—some of
the species of widely-ranging genera themselves ranging
widely,—such facts, as alpine, lacustrine, and marsh
productions being generally related to those which live
on the surrounding low lands and dry lands,—the
striking relationship between the inhabitants of islands
and those of the nearest mainland—the still closer re-
lationship of the distinct inhabitants of the islands in
the same archipelago—are inexplicable on the ordinary
view of the independent creation of each species, but
are explicable if we admit colonisation from the nearest
or readiest source, together with the subsequent adap-
tation of the colonists to their new homes.

Crap, XIIL] ISLANDS TO THOSE OF THE MAINLAND. 197

Summary of the last and present Chapters.

In these chapters I have endeavoured to show, that
if we make due allowance for our ignorance of the full
effects of changes of climate and of the level of the
land, which have certainly occurred within the recent
period, and of other changes which have probably oc-
curred,—if we remember how ignorant we are with
respect to the many curious means of occasional trans-
port,—if we bear in mind, and this is a very important
consideration, how often a species may have ranged
continuously over a wide area, and then have become
extinct in the intermediate tracts,—the difficulty is not
insuperable in believing that all the individuals of the
same species, wherever found, are descended from com-
mon parents. And we are led to this conclusion, which
has been arrived at by many naturalists under the desig-
nation of single centres of creation, by various gen-
eral considerations, more especially from the impor-
tance of barriers of all kinds, and from the analogical
distribution of sub-genera, genera, and families.

With respect to distinct species belonging to the
same genus, which on our theory have spread from one
parent-source; if we make the same allowances as be-
fore for our ignorance, and remember that some forms
of life have changed very slowly, enormous periods
of time having been thus granted for their migration,
the difficulties are far from insuperable; though in this
case, as in that of the individuals of the same species,
they are often great.

As exemplifying the effects of climatal changes on
distribution, I have attempted to show how important
a part the last Glacial period has played, which affected

198 SUMMARY OF THE [Cuar, XIII

even the equatorial regions, and which, during the al-
ternations of the cold in the north and south, allowed
the productions of opposite hemispheres to mingle, and
left some of them stranded on the mountain-summits
in all parts of the world. As showing how diversified
are the means of occasional transport, I have discussed
at some little length the means of dispersal of fresh-
water productions.

If the difficulties be not insuperable in admitting
that in the long course of time all the individuals of
the same species, and likewise of the several species
belonging to the same genus, have proceeded from some
one source; then all the grand leading facts of geo-
graphical distribution are explicable on the theory
of migration, together with subseyuent modification and
the multiplication of new forms. We can thus under-
stand the high importance of barriers, whether of land
or water, in not only separating, but in apparently form-
ing the several zoological and botanical provinces. We
can thus understand the concentration of related species
within the same areas; and how it is that under dif-
ferent latitudes, for instance in South America, the in-
habitants of the plains and mountains, of the forests,
marshes, and deserts, are linked together in so mysterious
a manner, and are likewise linked to the extinct beings
which formerly inhabited the same continent. Bear-
ing in mind that the mutual relation of organism to
organism is of the highest importance, we can see why
two areas having nearly the same physical conditions
should often be inhabited by very different forms of life;
for according to the length of time which has elapsed
since the colonists entered one of the regions, or both;
according to the nature of the communication which

Cuap. XIII.) LAST AND PRESENT CHAPTERS. 199

allowed certain forms and not others to enter, either
in greater or lesser numbers; according or not, as
those which entered happened to come into more or less
direct competition with each other and with the
aborigines; and according as the immigrants were
capable of varying more or less rapidly, there would
ensue in the two or more regions, independently of
their physical conditions, infinitely diversified con-
ditions of life——there would be an almost endless
amount of organic action and reaction,—and we
should find some groups of beings greatly, and some
only slightly modified,—some developed in great force,
some existing in scanty numbers—and this we do find
in the several great geographical provinces of the world.

On these same principles we can understand, as I
have endeavoured to show, why oceanic islands should
have few inhabitants, but that of these, a large propor-
tion should be endemic or peculiar; and why, in rela-
tion to the means of migration, one group of beings
should have all its species peculiar, and another group,
even within the same class, should have all its species
the same with those in an adjoining quarter of the
world. We can see why whole groups of organisms, as
batrachians and terrestrial mammals, should be absent
from oceanic islands, whilst the most isolated islands
should possess their own peculiar species of aerial mam-
mals or bats. We can see why, in islands, there should
be some relation between the presence of mammals, in
a more or less modified condition, and the depth of the
sea between such islands and the mainland. We can
clearly see why all the inhabitants of an archipelago,
though specifically distinct on the several islets, should
be closely related to each other; and should likewise

200 SUMMARY OF THE [Cuap, XIII,

be related, but less closely, to those of the nearest con-
tinent, or other source whence immigrants might
have been derived. We can see why, if there exist very
closely allied or representative species in two areas,
however distant from each other, some identical species
will almost always there be found.

As the late Edward Forbes often insisted, there is a
striking parallelism in the laws of life throughout time
and space; the laws governing the succession of forms
in past times being nearly the same with those govern-
ing at the present time the differences in different areas.
We see this in many facts. The endurance of each spe-
cies and group of species is continuous in time; for
the apparent exceptions to the rule are so few, that
they may fairly be attributed to our not having as yet
discovered in an intermediate deposit certain forms
which are absent in it, but which occur both above and
below: so in space, it certainly is the general rule that
the area inhabited by a single species, or by a group of
species, is continuous, and the exceptions, which are not
rare, may, as I have attempted to show, be accounted for
by former migrations under different circumstances, or
through occasional means of transport, or by the species
having become extinct in the intermediate tracts.
Both in time and space species and groups of species
have their points of maximum development. Groups of
species, living during the same period of time, or liv-
ing within the same area, are often characterised by
trifling features in common, as of sculpture or colour.
In looking to the long succession of past ages, as in
looking to distant provinces throughout the world, we
find that species in certain classes differ little from each
other, whilst those in another class, or only in a different

Cuar. XII] LAST AND PRESENT CHAPTERS, 201

section of the same order, differ greatly from each other.
In both time and space the lowly organised members
of each class generally change less than the highly
organised; but there are in both cases marked excep-
tions to the rule. According to our theory, these sev-
eral relations throughout time and space are intelli-
gible; for whether we look to the allied forms of life
which have changed during successive ages, or to those
which have changed after having migrated into distant
quarters, in both cases they are connected by the same
bond of ordinary generation; in both cases the laws of
variation have been the same, and modifications
have been accumulated by the same means of natural
selection.

202 CLASSIFICATION. [Cuar. XIV,

CHAPTER XIV.

MUTUAL AFFINITIES OF ORGANIC BEINGS: MOR-
PHOLOGY: EMBRYOLOGY: RUDIMENTARY ORGANS.

CLASSIFICATION, groups subordinate to groups—Natural system—
Rules and difficulties in classification, explained on the theory
of descent with modification—Classification of varieties—De-
scent always used in classification—Analogical or adaptive char-
acters—A ffinities, general, complex, and radiating—Extinction
separates and defines groups—MorPHoLoey, between members
of the same class, between parts of the same individual—Em-
BRYOLOGY, laws of, explained by variations not supervening
at an early age, and being inherited at a corresponding age—
RuDIMENTARY ORGANS; their origin explained—Summary.

Classification.

From the most remote period in the history of the
world organic beings have been found to resemble each
other in descending degrees, so that they can be classed
in groups under groups. This classification is not arbi-
trary like the grouping of the stars in constellations. The
existence of groups would have been of simple signifi-
cance, if one group had been exclusively fitted to in-
habit the land and another the water; one to feed on
flesh, another on vegetable matter, and so on; but the
case is widely different, for it is notorious how com-
monly members of even the same sub-group have dif-
ferent habits. In the second and fourth chapters, on
Variation and on Natural Selection, I have attempted

Cua, XIV,] CLASSIFICATION. 203

to show that within each country it is the widely rang-
ing, the much diffused and common, that is the domi-
nant species, belonging to the larger genera in each
class, which vary most. The varieties, or incipient spe-
cies, thus produced, ultimately become converted into
new and distinct species; and these, on the principle
of inheritance, tend to produce other new and domi-
nant species. Consequently the groups which are now
large, and which generally include many dominant spe-
cies, tend to go on increasing in size. I further at-
tempted to show that from the varying descendants
of each species trying to occupy as many and as differ-
ent places as possible in the economy of nature, they
constantly tend to diverge in character. This latter
conclusion is supported by observing the great diversity
of forms which, in any small area, come into the closest
competition, and by certain facts in naturalisation.

I attempted also to show that there is a steady tend-
ency in the forms which are increasing in number
and diverging in character, to supplant and exterminate
the preceding, less divergent and less improved forms.
I request the reader to turn to the diagram illustrating
the action, as formerly explained, of these several prin-
ciples; and he will see that the inevitable result is, that
the modified descendants proceeding from one progeni-
tor become broken up into groups subordinate to groups.
In the diagram each letter on the uppermost line may
represent a genus including several species, and the
whole of the genera along this upper line form together
one class, for all are descended from one ancient parent,
and, consequently, have inherited something in com-
mon. But the three genera on the left hand have,
on this same principle, much in common, and form a

204 CLASSIFICATION. [Cuap. XIV.

sub-family, distinct from that containing the next two
genera on the right hand, which diverged from a com-
mon parent at the fifth stage of descent. These five
genera have also much in common, though less than
when grouped in sub-families; and they form a family
distinct from that containing the three genera still far-
ther to the right hand, which diverged at an earlier
period. And all these genera, descended from (A),
form an order distinct from the genera descended from
(I). So that we here have manyspecies descended from a
single progenitor grouped into genera; and the genera
into sub-families, families, and orders, all under one
great class. The grand fact of the natural subordina-
tion of organic beings in groups under groups, which,
from its familiarity, does not always sufficiently strike
us, is in my judgment thus explained. No doubt or-
ganic beings, like all other objects, can be classed in
many ways, either artificially by single characters, or
more naturally by a number of characters. We know,
for instance, that minerals and the elemental substances
can be thus arranged. In this case there is of course no
relation to genealogical succession, and no cause can at
present be assigned for their falling into groups. But
with organic beings the case is different, and the view
above given accords with their natural arrangement in
group under group; and no other explanation has ever
been attempted.

Naturalists, as we have seen, try to arrange the spe-
cies, genera, and families in each class, on what is called
the Natural System. But what is meant by this sys-
tem? Some authors look at it merely as a scheme for
arranging together those living objects which are most
alike, and for separating those which are most unlike;

Cuap. XIV.) CLASSIFICATION. 205

or as an artificial method of enunciating, as briefly as
possible, general propositions,—that is, by one sentence
to give the characters common, for instance, to all mam-
mals, by another those common to all carnivora, by
another those common to the dog-genus, and then,
by adding a single sentence, a full description is given
of each kind of dog. The ingenuity and utility of this
system are indisputable. But many naturalists think
that something more is meant by the Natural System;
they believe that it reveals the plan of the Creator;
but unless it be specified whether order in time or space,
or both, or what else is meant by the plan of the Creator,
it seems to me that nothing is thus added to our knowl-
edge. Expressions such as that famous one by Lin-
neus, which we often meet with in a more or less con-
cealed form, namely, that the characters do not make
the genus, but that the genus gives the characters, seem
to imply that some deeper bond is included in our classi-
fications than mere resemblance. I believe that this
is the case, and that community of descent—the one
known cause of close similarity in organic beings—is
the bond, which though observed by various degrees of
modification, is partially revealed to us by our classifica-
tions.

Let us now consider the rules followed in classifica-
tion, and the difficulties which are encountered on the
view that classification either gives some unknown plan
of creation, or is simply a scheme for enunciating gen-
eral propositions and of placing together the forrns most
like each other. It might have been thought (and
was in ancient times thought) that those parts of the
structure which determined the habits of life, and the
general place of each being in the economy of nature,

206 CLASSIFICATION. [Cuar. XIV.

would be of very high importance in classification.
Nothing can be more false. No one regards the ex-
ternal similarity of a mouse to a shrew, of a dugong to
a whale, of a whale to a fish, as of any importance.
These resemblances, though so intimately connected
with the whole life of the being, are ranked as merely
“adaptive or analogical characters;” but to the con-
sideration of these resemblances we shall recur. It
may even be given as a general rule, that the less any
part of the organisation is concerned with special habits,
the more important it becomes for classification. As
an instance: Owen, in speaking of the dugong, says,
“The generative organs, being those which are most
remotely related to the habits and food of an animal,
I have always regarded as affording very clear indica-
tions of its true affinities. We are least likely in the
modifications of these organs to mistake a merely adap-
tive for an essential character.” With plants how
remarkable it is that the organs of vegetation, on which
their nutrition and life depend, are of little significa-
tion; whereas the organs of reproduction, with their prod-
uct the seed and embryo, are of paramount importance!
So again in formerly discussing certain morphological
characters which are not functionally important, we
have seen that they are often of the highest service in
classification. This depends on their constancy through-
out many allied groups; and their constancy chiefly
depends on any slight deviations not having been pre-
served and accumulated by natural selection, which
acts only on serviceable characters.

That the mere physiological importance of an organ
does not determine its classificatory value, is almost
proved by the fact that in allied groups, in which the

Cuar, XIV] CLASSIFICATION. 207

Same organ, as we have every reason to suppose, has
nearly the same physiological value, its classificatory
value is widely different. No naturalist can’ have
worked long at any group without being struck with
this fact; and it has been fully acknowledged in the
writings of almost every author. It will suffice to quote
the highest authority, Robert Brown, who, in speaking
of certain organs in the Proteacee, says their generic
importance, “like that of all their parts, not only in
this, but, as I apprehend, in every natural family,
is very unequal, and in some cases seems to be entirely
lost.” Again, in another work he says, the genera
of the Connaracee “ differ in having one or more ovaria,
in the existence or absence of albumen, in the imbricate
or valvular estivation. Any one of these characters
singly is frequently of more than generic importance,
though here even when all taken together they appear
insufficient to separate Cnestis from Connarus.” To
give an example amongst insects: in one great division
of the Hymenoptera, the antennz, as Westwood has re-
marked, are most constant in structure; in another
division they differ much, and the differences are of
quite subordinate value in classification; yet no one will
say that the antenne in these two divisions of the
same order are of unequal physiological importance.
Any number of instances could be given of the varying
importance for classification of the same important or-
gan within the same group of beings.

Again, no one will say that rudimentary or atrophied
organs are of high physiological or vital importance;
yet, undoubtedly, organs in this condition are often of
much value in classification. No one will dispute that
the rudimentary teeth in the upper jaws of young rumi-

208 CLASSIFICATION. [Cuap. XIV.

nants, and certain rudimentary bones of the leg, are
highly serviceable in exhibiting the close affinity be-

tween ruminants and pachyderms. Robert Brown has: ° »

strongly insisted on the fact that the position of the
rudimentary florets is of the highest importance in the
classification of the grasses.

Numerous instances could be given of characters
derived from parts which must be considered of very
trifling physiological importance, but which are univer-
sally admitted as highly serviceable in the definition of
whole groups. For instance, whether or not there is an
open passage from the nostrils to the mouth, the only
character, according to Owen, which absolutely dis-
tinguishes fishes and reptiles—the inflection of the angle
of the lower jaw in Marsupials—the manner in which
the wings of insects are folded—mere colour in cer-
tain Algee—mere pubescence on parts of the flower in
grasses—the nature of the dermal covering, as hair or
feathers, in the Vertebrata. If the Ornithorhynchus
had been covered with feathers instead of hair, this ex-
ternal and trifling character would have been consid-
ered by naturalists as an important aid in determin-
ing the degree of affinity of this strange creature to
birds.

The importance, for classification, of trifling charac-
ters, mainly depends on their being correlated with many
other characters of more or less importance. The value
indeed of an aggregate of characters is very evident in
natural history. Hence, as has often been remarked, a
species may depart from its allies in several characters,
both of high physiological importance, and of almost
universal prevalence, and yet leave us in no doubt where
it should be ranked. Hence, also, it has been found

Cuap. XIV.] CLASSIFICATION. 209

that a classification founded on any single character,
however important that may be, has always failed; for
no part of the organisation is invariably constant.
The importance of an aggregate of characters, even
when none are important, alone explains the aphorism
enunciated by Linnzus, namely, that the characters do
not give the genus, but the genus gives the characters;
for this seems founded on the appreciation of many
trifling points of resemblance, too slight to be defined.
Certain plants, belonging to the Malpighiaces, bear
perfect and degraded flowers; in the latter, as A. de
Jussieu has remarked, “the greater number of the char-
acters proper to the species, to the genus, to the family,
to the class, disappear, and thus laugh at our classifi-
cation.” When Aspicarpa produced in France, during
several years, only these degraded flowers, departing
so wonderfully in a number of the most important
points of structure from the proper type of the order,
yet M. Richard sagaciously saw, as Jussieu observes,
that this genus should still be retained amongst the
Malpighiacee. This case well illustrates the spirit of
our classifications.

Practically, when naturalists are at work, they do
not trouble themselves about the physiological value
of the characters which they use in defining a group
or in allocating any particular species. If they find
a character nearly uniform, and common to a great
number of forms, and not common to others, they use
it as one of high value; if common to some lesser num-
ber, they use it as of subordinate value. This principle
has been broadly confessed by some naturalists to be the
true one; and by none more clearly than by that ex-
cellent botanist, Aug. St. Hilaire. If several trifling

210 CLASSIFICATION, [Cuap, Xiv,

characters are always found in combination, though no
apparent bond of connection can be discovered between
them, especial value is set on them. As in most groups
of animals, important organs, such as those for pro-
pelling the blood, or for aerating it, or those for prop-
agating the race, are found nearly uniform, they are
considered as highly serviceable in classification; but in
some groups all these, the most important vital organs,
are found to offer characters of quite subordinate value.
Thus, as Fritz Miiller has lately remarked, in the same
group of crustaceans, Cypridina is furnished with a
heart, whilst in two closely allied genera, namely Cypris
and Cytherea, there is no such organ; one species of
Cypridina has well-developed branchie, whilst another
species is destitute of them.

We can see why characters derived from the embryo
should be of equal importance with those derived from
the adult, for a natural classification of course includes
all ages. But it is by no means obvious, on the ordi-
nary view, why the structure of the embryo should be
more important for this purpose than that of the adult,
which alone plays its full part in the economy of nature.
Yet it has been strongly urged by those great natural-
ists, Milne Edwards and Agassiz, that embryological
characters are the most important of all; and this doc-
trine has very generally been admitted as true. Never-
theless, their importance has sometimes been exagger-
ated, owing to the adaptive characters of larve not
having been excluded; in order to show this, Fritz
Miiller arranged by the aid of such characters alone the
great class of crustaceans, and the arrangement did not
prove a natural one. But there can be no doubt that
embryonic, excluding larval characters, are of the high-

Cuap, XIV.] CLASSIFICATION. 211

est value for classification, not only with animals but
with plants. Thus the main divisions of flowering
plants are founded on differences in the embryo,—on the
number and position of the cotyledons, and on the
mode of development of the plumule and radicle. We
shall immediately see why these characters possess so
high a value in classification, namely, from the natural
system being genealogical in its arrangement.

Our classifications are often plainly influenced by
chains of affinities. Nothing can be easier than to de-
fine a number of characters common to all birds; but
with crustaceans, any such definition has hitherto been
found impossible. There are crustaceans at the oppo-
site ends of the series, which have hardly a character in
common; yet the species at both ends, from being plain-
ly allied to others, and these to others, and so onwards,
can be recognised as unequivocally belonging to this,
and to no other class of the Articulata.

Geographical distribution has often been used,
though perhaps not quite logically, in classification,
more especially in very large groups of closely allied
forms. Temminck insists on the utility or even neces-
sity of this practice in certain groups of birds; and it
has been followed byseveral entomologists and botanists.

Finally, with respect to the comparative value of the
various groups of species, such as orders, sub-orders,
families, sub-families, and genera, they seem to be, at
least at present, almost arbitrary. Several of the best
botanists, such as Mr. Bentham and others, have strong-
ly insisted on their arbitrary value. Instances could be
given amongst plants and insects, of a group first ranked
by practised naturalists as only a genus, and then raised

to the rank of a sub-family or family; and this has
39

919 CLASSIFICATION. [Cuar. XIV.

been done, not because further research has detected
important structural differences, at first overlooked, but
because numerous allied species with slightly differ-
ent grades of difference, have been subsequently dis-
covered.

All the foregoing rules and aids and difficulties in
classification may be explained, if I do not greatly
deceive myself, on the view that the Natural System is
founded on descent with modification;—that the char-
acters which naturalists consider as showing true affin-
ity between any two or more species, are those which
have been inherited from a common parent, all true
classification being genealogical;—that community of
descent is the hidden bond which naturalists have been
unconsciously seeking, and not some unknown plan of
creation, or the enunciation of general propositions,
and the mere putting together and separating objects
more or less alike.

But I must explain my meaning more fully. I be-
lieve that the arrangement of the groups within each
class, in due subordination and relation to each other,
must be strictly genealogical in order to be natural;
but that the amount of difference in the several branches
or groups, though allied in the same degree in blood to
their common progenitor, may differ greatly, being due
to the different degrees of modification which they have
undergone; and this is expressed by the forms being
ranked under different genera, families, sections, or
orders. The reader will best understand what is meant,
if he will take the trouble to refer to the diagram in the
fourth chapter. We will suppose the letters A to L to
represent allied genera existing during the Silurian
epoch, and descended from some still earlier form. In

Cuap, XIV.] CLASSIFICATION. 213

three of these genera (A, F, and I),a species has transmit-
ted modified descendants to the present day, represented
by the fifteen genera (a!* to 24*) on the uppermost hori-
zontal line. Now all these modified descendants from
a single species, are related in blood or descent in the
same degree; they may metaphorically be called cousins
to the same millionth degree; yet they differ widely
and in different degrees from each other. The forms
descended from A, now broken up into two or three
families, constitute a distinct order from those de-
scended from I, also broken up into two families. Nor
can the existing species, descended from A, be ranked
in the same genus with the parent A; or those from I,
with the parent J. But the existing genus F’* may be
supposed to have been but slightly modified; and it
will then rank with the parent-genus F; just as
some few still living organisms belong to Silurian
genera. So that the comparative value of the differ-
ences between these organic beings, which are all re-
lated to each other in the same degree in blood, has come
to be widely different. Nevertheless their genealogical
arrangement remains strictly true, not only at the pres-
ent time, but at each successive period of descent. All
the modified descendants from A will have inherited
something in common from their common parent, as
will all the descendants from I; so will it be with each
subordinate branch of descendants, at each successive
stage. If, however, we suppose any descendant of A,
or of I, to have become so much modified as to have
lost all traces of its parentage, in this case, its place in
the natural system will be lost, as seems to have occurred
with some few existing organisms. All the descendants
of the genus F, along its whole line of descent, are

214 CLASSIFICATION. [Cuar. XIV.

supposed to have been but little modified, and they form
a single genus. But this genus, though much isolated,
will still occupy its proper intermediate position. The
representation of the groups, as here given in the dia-
gram on a flat surface, is much too simple. The
branches ought to have diverged in all directions. If
the names of the groups had been simply written down
in a linear series, the representation would have been
still less natural; and it is notoriously not possible to
represent in a series, on a flat surface, the affinities
which we discover in nature amongst the beings of the
same group. Thus, the natural system is genealogical
in its arrangement, like a pedigree: but the amount of
modification which the different groups have under-
gone has to be expressed by ranking them under dif-
ferent so-called genera, sub-families, families, sections,
orders, and classes.

It may be worth while to illustrate this view of
classification, by taking the case of languages. If we
possessed a perfect pedigree of mankind, a genealogical
arrangement of the races of man would afford the best
classification of the various languages now spoken
throughout the world; and if all extinct languages, and
all intermediate and slowly changing dialects, were to
be included, such an arrangement would be the only
possible one. Yet it might be that some ancient lan-
guages had altered very little and had given rise to few
new languages, whilst others had altered much owing to
the spreading, isolation, and state of civilisation of the
several co-descended races, and had thus given rise to
many new dialects and languages. The various degrees
of difference between the languages of the same stock,
would have to be expressed by groups subordinate to

Cuar, XIV.] CLASSIFICATION. 915

groups; but the proper or even the only possible ar-
Tangement would still be genealogical; and this would
be strictly natural, as it would connect together all lan-
guages, extinct and recent, by the closest affinities, and
would give the filiation and origin of each tongue.

In confirmation of this view, let us glance at the
classification of varieties, which are known or believed
to be descended from a single species. These are
grouped under the species, with the sub-varieties under
the varieties; and in some cases, as with the domestic
pigeon, with several other grades of difference. Nearly
the same rules are followed as in classifying species.
Authors have insisted on the necessity of arranging
varieties on a natural instead of an artificial system; we
are cautioned, for instance, not to class two varieties of
the pine-apple together, merely because their fruit,
though the most important part, happens to be nearly
identical; no one puts the Swedish and common turnip
together, though the esculent and thickened stems are
so similar. Whatever part is found to be most con-
stant, is used in classing varieties: thus the great agri-
culturist Marshall says the horns are very useful for
this purpose with cattle, because they are less variable
than the shape or colour of the body, &c.; whereas with
sheep the horns are much less serviceable, because less
constant. In classing varieties, I apprehend that if we
had a real pedigree, a genealogical classification would
be universally preferred; and it has been attempted in
some cases. For we might feel sure, whether there had
been more or less modification, that the principle of
inheritance would keep the forms together which were
allied in the greatest number of points. In tumbler
pigeons, though some of the sub-varieties differ in the

916 OLASSIFICATION. (Car. XIV,

important character of the length of the beak, yet all
are kept together from having the common habit of
tumbling; but the short-faced breed has nearly or quite
lost his habit: nevertheless, without any thought on
the subject, these tumblers are kept in the same group,
because allied in blood and alike in some other respects.

With species in a state of nature, every naturalist has
in fact brought descent into his classification; for he
includes in his lowest grade, that of species, the two
sexes; and how enormously these sometimes differ in
the most important characters, is known to every natu-
ralist: scarcely a single fact can be predicated in com-
mon of the adult males and hermaphrodites of certain
cirripedes, and yet no one dreams of separating them.
As soon as the three Orchidean forms, Monachanthus,
Myanthus, and Catasetum, which had previously been
ranked as three distinct genera, were known to be some-
times produced on the same plant, they were imme-
diately considered as varieties; and now I have been
able to show that they are the male, female, and herma-
phrodite forms of the same species. The naturalist in-
cludes as one species the various larval stages of the
same individual, however much they may differ from
each other and from the adult, as well as the so-called
alternate generations of Steenstrup, which can only in
a technical sense be considered as the same individual.
He includes monsters and varieties, not from their
partial resemblance to the parent-form, but because
they are descended from it.

As descent has universally been used in classing to-
gether the individuals of the same species, though the
males and females and larve are sometimes extremely
different; and as it has been used in classing varieties

Cuap. XIV.) CLASSIFICATION, 217

which have undergone a certain, and sometimes a con-
siderable amount of modification, may not this same
element of descent have been unconsciously used in
grouping species under genera, and genera under higher
groups, all under the so-called natural system? I be-
lieve it hasbeen unconsciously used; and thus only
can I understand the several rules and guides which
have been followed by our best systematists. As we
have no written pedigrees, we are forced to trace com-
munity of descent by resemblances of any kind. There-
fore we chose those characters which are the least likely
to have been modified, in relation to the conditions
of life to which each species has been recently exposed.
Rudimentary structures on this view are as.good as, or
even sometimes better than, other parts of the organisa-
tion. We care not how trifling a character may be—let it
be the mere inflection of the angle of the jaw, the man-
ner in which an insect’s wing is folded, whether the
skin be covered by hair or feathers—if it prevail
throughout many and different species, especially those
having very different habits of life, it assumes high
value; for we can account for its presence in so many
forms with such different habits, only by inheritance
from a common parent. We may err in this respect in
regard to single points of structure, but when several
characters, let them be ever so trifling, concur through-
out a large group of beings having different habits, we
may feel almost sure, on the theory of descent, that
these characters have been inherited from a common
ancestor; and we know that such aggregated characters
have especial value in classification.

We can understand why a species or a group of
species may depart from its allies, in several of its most

218 CLASSIFICATION. [Cuap. XIV.

important characteristics, and yet be safely classed with
them. This may be safely done, and is often done, as
long as a sufficient number of characters, let them be
ever so unimportant, betrays the hidden bond of com-
munity of descent. Let two forms have not a single
character in common, yet, if these extreme forms are
connected together by a chain of intermediate groups,
we may at once infer their community of descent, and
we put them all into the same class. As we find organs.
of high physiological importance—those which serve to
preserve life under the most diverse conditions of exist-
ence—are generally the most constant, we attach especial
value to them; but if these same organs, in another
group or section of a group, are found to differ much,
we at once value them less in our classification. We
shall presently see why embryological characters are of
such high classificatory importance. Geographical dis-
tribution may sometimes be brought usefully into play
in classing large genera, because all the species of the
same genus, inhabiting any distinct and isolated region,
are in all probability descended from the same parents.
Analogical Resemblances——We can understand, on
the above views, the very important distinction between
real affinities and analogical or adaptive resemblances.
Lamarck first called attention to this subject, and he
has been ably followed by Macleay and others. The
resemblance in the shape of the body and in the fin-like
anterior limbs between dugongs and whales, and be-
tween these two orders of mammals and fishes, are ana-
logical. So is the resemblance between a mouse and a
shrew-mouse (Sorex), which belong to different orders;
and the still closer resemblance, insisted on by Mr. Mi-
vart, between the mouse and a small marsupial animal

Cuap. XIV.] ANALOGICAL RESEMBLANCES. 219

(Antechinus) of Australia. These latter resemblances
may be accounted for, as it seems to me, by adaptation
for similarly active movements through thickets and
herbage, together with concealment from enemies.

Amongst insects there are innumerable similar in-
stances; thus Linneus, misled by external appearances,
actually classed an homopterous insect as a moth. We
see something of the same kind even with our domestic
varieties, as in the strikingly similar shape of the body
in the improved breeds of the Chinese and common pig,
which are descended from distinct species; and in the
similarly thickened stems of the common and specifically
distinct Swedish turnip. The resemblance between the
greyhound and the racehorse is hardly more fanciful
than the analogies which have been drawn by some
authors between widely different animals.

On the view of characters being of real importance
for classification, only in so far as they reveal descent,
we can clearly understand why analogical or adaptive
characters, although of the utmost importance to the
welfare of the being, are almost valueless to the system-
atist. For animals, belonging to two most distinct lines
of descent, may have become adapted to similar condi-
tions, and thus have assumed a close external resem-
blance; but such resemblances will not reveal—will
rather tend to conceal their blood-relationship. We
can thus also understand the apparent paradox, that
the very same characters are analogical when one group
is compared with another, but give true affinities when
the members of the same group are compared together:
thus, the shape of the body and fin-like limbs are only
analogical when whales are compared with fishes,
being adaptations in both classes for swimming through

/
:

220 CLASSIFICATION. [Cuar. XIV.

f

the water; but between the several members of the
whale family, the shape of the body and the fin-like
limbs offer characters exhibiting true affinity; for as
these parts are so nearly similar throughout the
whole family, we cannot doubt that they have
been inherited from a common ancestor. So it is with
fishes.

Numerous cases could be given of striking resem-
blances in quite distinct beings between single parts or
organs, which have been adapted for the same functions.
A good instance is afforded by the close resemblance of
the jaws of the dog and Tasmanian wolf or Thylacinus,
—animals which are widely sundered in the natural
system. But this resemblance is confined to general ap-
pearance, as in the prominence of the canines, and in the
cutting shape of the molar teeth. For the teeth really
differ much: thus the dog has on each side of the upper
jaw four pre-molars and only two molars; whilst the
Thylacinus has three pre-molars and four molars. The
molars also differ much in the two animals in relative
size and structure. The adult dentition is preceded by
a widely different milk dentition. Any one may of
course deny that the teeth in either case have been
adapted for tearing flesh, through the natural selection
of successive variations; but if this be admitted in the
one case, it is unintelligible to me that it should be
denied in the other. I am glad to find that so high an
authority as Professor Flower has come to this same
conclusion. ;

The extraordinary cases given in a former chapter,
of widely different fishes possessing electric organs,—of
widely different insects possessing luminous organs,—
and of orchids and asclepiads having pollen-masses with

Cuap. XIV.] ANALOGICAL RESEMBLANCES. 921

viscid discs, come under this same head of analogical
resemblances. But these cases are sowonderful that they
were introduced as difficulties or objections to our
theory. In all such cases some fundamental difference
in the growth cr development of the parts, and gen-
erally in their matured structure, can be detected. The
end gained is the same, but the means, though appear-
ing superficially to be the same, are essentially different.
The principle formerly alluded to under the term of
analogical variation has probably in these cases often
come into play; that is, the members of the same class,
although only distantly allied, have inherited so much
in common in their constitution, that they are apt to
vary under similar exciting causes in a similar manner;
and this would obviously aid in the acquirement through
natural selection of parts or organs, strikingly like each
other, independently of their direct inheritance from a
common progenitor.

As species belonging to distinct classes have often
been adapted by successive slight modifications to live
under nearly similar circumstances,—to inhabit, for in-
stance, the three elements of land, air,and water,—we can
perhaps understand how it is that a numerical paral-
lelism has sometimes been observed between the sub-
groups of distinct classes. A naturalist, struck with a
parallelism of this nature, by arbitrarily raising or sink-
ing the value of the groups in several classes (and all
our experience shows that their valuation is as yet arbi-
trary), could easily extend the parallelism over a wide
range; and thus the septenary, quinary, quarternary and
ternary classifications have probably arisen.

There is another and curious class of cases in which
close external resemblance does not depend on adapta-

999 CLASSIFICATION. [Cnap. XIV,

tion to similar habits of life, but has been gained for
the sake of protection. I allude to the wonderful man-
ner in which certain butterflies imitate, as first de-
scribed by Mr. Bates, other and quite distinct species.
This excellent observer has shown that in some districts
of S. America, where, for instance, an Ithomia abounds
in gaudy swarms, another butterfly, namely, a Leptalis,
is often found mingled in the same flock; and the latter
so closely resembles the Ithomia in every shade and
stripe of colour and even in the shape of its wings, that
Mr. Bates, with his eyes sharpened by collecting during
eleven years, was, though always on his guard, continu-
ally deceived. When the mockers and the mocked are
caught and compared, they are found to be very differ-
ent in essential structure, and to belong not only to dis-
tinct genera, but often to distinct families. Had this
mimicry occurred in only one or two instances, it might
have been passed over as a strange coincidence. But, if
we proceed from a district where one Leptalis imitates
an Ithomia, another mocking and mocked species be-
longing to the same two genera, equally close in their
resemblance, may be found. Altogether no less than
ten genera are enumerated, which include species that
imitate other butterflies. The mockers and mocked
always inhabit the same region; we never find an imi-
tator living remote from the form which it imitates.
The mockers are almost invariably rare insects; the
mocked in almost every case abound in swarms. In
the same district in which a species of Leptalis closely
imitates an Ithomia, there are sometimes other Lepi-
doptera mimicking the same Ithomia: so that in the
same place, species of three genera of butterflies and
even a moth are found all closely resembling a butter-

Cuap, XIV.] ANALOGICAL RESEMBLANCES, 223

fly belonging to a fourth genus. It deserves especial
notice that many of the mimicking forms of the Lep-
talis, as well as of the mimicked forms, can be shown
by a graduated series to be merely varieties of the same
species; whilst others are undoubtedly distinct species.
But why, it may be asked, are certain forms treated
as the mimicked and others as the mimickers? Mr.
Bates satisfactorily answers this question, by showing
that the form which is imitated keeps the usual dress
of the group to which it belongs, whilst the counterfeit-
ers have changed their dress and do not resemble their
nearest allies.

We are next led to inquire what reason can be as-
signed for certain butterflies and moths so often assum-
ing the dress of another and quite distinct form; why,
to the perplexity of naturalists, has nature condescended
to the tricks of the stage? Mr. Bates has, no doubt,
hit on the true explanation. The mocked forms, which
always abound in numbers, must habitually escape de-
struction to a large extent, otherwise they could not
exist in such swarms; and a large amount of evidence
has now been collected, showing that they are distaste-
ful to birds and other insect-devouring animals. The
mocking forms, on the other hand, that inhabit the
same district, are comparatively rare, and belong to
rare groups; hence they must suffer habitually from
some danger, for otherwise, from the number of eggs
laid by all butterflies, they would in three or four gen-
erations swarm over the whole country. Now if a
member of one of these persecuted and rare groups were
to assume a dress so like that of a well-protected species
that it continually deceived the practised eyes of an
entomologist, it would often deceive predaceous birds

224 CLASSIFICATION. [Cuap. XIV.

and insects, and thus often escape destruction. Mr.
Bates may almost be said to have actually witnessed
the process by which the mimickers have come so closely
to resemble the mimicked; for he found that some of
the forms of Leptalis which mimic so many other butter-
flies, varied in an extreme degree. In one district sev-
eral varieties occurred, and of these one alone resembled
to a certain extent, the common Ithomia of the same
district. In another district there were two or three
varieties, one of which was much commoner than the
others, and this closely mocked another form of Ithomia.
From facts of this nature, Mr. Bates concludes that the
Leptalis first varies; and when a variety happens to
resemble in some degree any common butterfly inhabit-
ing the same district, this variety, from its resem-
blance to a flourishing and little-persecuted kind,
has a better chance of escaping destruction from
predaceous birds and insects, and is consequently oftener
preserved;—“ the less perfect degrees of resem-
blance being generation efter generation eliminated,
and only the others left to propagate their kind.” So
that here we have an excellent illustration of natural
selection.

Messrs. Wallace and Trimen have likewise described
several equally striking cases of imitation in the Lepi-
doptera of the Malay Archipelago and Africa, and with
some other insects. Mr. Wallace has also detected one
such case with birds, but we have none with the larger
quadrupeds. The much greater frequeney of imitation
with insects than with other animals, is probably the
consequence of their small size; insects cannot defend
themselves, excepting indeed the kinds furnished with
a string, and I have never heard of an instance of

Cuar. XIV.] ANALOGICAL RESEMBLANCES. 995

such kinds ‘mocking other insects, though they are
mocked; insects cannot easily escape by flight from
the larger animals which prey on them; there-
fore, speaking metaphorically, they are reduced,
like most weak creatures, to trickery and dissimula-
tion.

It should be observed that the process of imitation
probably never commenced between forms widely dis-
similar in colour. But starting with species already
somewhat like each other, the closest resemblance, if
beneficial, could readily be gained by the above means;
and if the imitated form was subsequently and gradu-
ally modified through any agency, the imitating form
would be led along the same track, and thus be altered
to almost any extent, so that it might ultimately assume
an appearance or colouring wholly unlike that of the
other members of the family to which it belonged.
There is, however, some difficulty on this head, for it
is necessary to suppose in some cases that ancient mem-
bers belonging to several distinct groups, before they
had diverged to their present extent, accidentally re-
sembled a member of another and protected group in
a sufficient degree to afford some slight protection; this
having given the basis for the subsequent acquisition of
the most perfect resemblance.

On the Nature of the Affinities connecting Organic
Beings.—As the modified descendants of dominant spe-
cies, belonging to the larger genera, tend to inherit
the advantages which made the groups to which they
belong large and their parents dominant, they are al-
most sure to spread widely, and to seize on more and
more places in the economy of nature. The larger and
more dominant groups within each class thus tend to

926 AFFINITIES CONNECTING (Cuap. XIV.

go on increasing in size; and they consequently sup-
plant many smaller and feebler groups. Thus we can
account for the fact that all organisms, recent and ex-
tinct, are included under a few great orders, and under
still fewer classes. As showing how few the higher
groups are in number, and how widely they are spread
throughout the world, the fact is striking that the dis-
covery of Australia has not added an insect belonging
to a new class; and that in the vegetable kingdom, as
I learn from Dr. Hooker, it has added only two or three
families of small size.

In the chapter on Geological Succession I attempted
to show, on the principle of each group having generally
diverged much in character during the long-continued
process of modification, how it is that the more ancient
forms of life often present characters in some degree
intermediate between existing groups. As some few of
the old and intermediate forms have transmitted to
the present day descendants but little modified, these
constitute our so-called osculant or aberrant species.
The more aberrant any form is, the greater must be the
number of connecting forms which have been exter-
minated and utterly lost. And we have some evidence
of aberrant groups having suffered severely from ex-
tinction, for they are almost always represented by
extremely few species; and such species as do occur
are generally very distinct from each other, which again
implies extinction. The genera Ornithorhynchus and
Lepidosiren, for example, would not have been less aber-
rant had each been represented by a dozen species, in-
stead of as at present by a single one, or by two or three.
We can, I think, account for this fact only by looking
at aberrant groups as forms which have been con-

Cuar, XIV,] ORGANIC BEINGS, 227

quered by more successful competitors, with a few mem-
bers still preserved under unusually favourable con-
ditions,

Mr. Waterhouse has remarked that, when a member
belonging to one group of animals exhibits an affinity to
a quite distinct group, this affinity in most cases is
general and not special; thus, according to Mr. Water-
house, of all Rodents, the bizcacha is most nearly related
to Marsupials; but in the points in which it approaches
this order, its relations are general, that is, not to any one
marsupial species more than to another. As these points
of affinity are believed to be real and not merely adap-
tive, they must be due in accordance with our view
to inheritance from a common progenitor. Therefore
we must suppose either that all Rodents, including the
bizeacha, branched off from some ancient Marsupial,
which will naturally have been more or less intermediate
in character with respect to all existing Marsupials; or
that both Rodents and Marsupials branched off from a
common progenitor, and that both groups have since
undergone much modification in divergent directions.
On either view we must suppose that the bizcacha has
retained, by inheritance, more of the characters of its
ancient progenitor than have other Rodents; and there-
fore it will not be specially related to any one existing
Marsupial, but indirectly to all or nearly all Marsupials,
from having partially retained the character of their
common progenitor, or of some early member of the
group. On the other hand, of all Marsupials, as Mr.
Waterhouse has remarked, the Phascolomys resembles
most nearly, not any one species, but the general order
of Rodents. In this case, however, it may be strongly

suspected that the resemblance is only analogical, owing
40

998 AFFINITIES CONNECTING — [Cuap. XiV.

to the Phascolomys having become adapted to habits
like those of a Rodent. The elder De Candolle has
made nearly similar observations on the general nature
of the affinities of distinct families of plants.

On the principle of the multiplication and gradual
divergence in character of the species descended from a
common progenitor, together with their retention by
inheritance of some characters in common, we can un-
derstand the excessively complex and radiating affini-
ties by which all the members of the same family or
higher group are connected together. For the common
progenitor of a whole family, now broken up by ex-
tinction into distinct groups and sub-groups, will have
transmitted some of its characters, modified in various
ways and degrees, to all the species; and they will con-
sequently be related to each other by circuitous lines
of affinity of various lengths (as may be seen in the dia-
gram so often referred to), mounting up through many
predecessors. As it is difficult to show the blood-re-
lationship between the numerous kindred of any an-
cient and noble family even by the aid of a genealogical
tree, and almost impossible to do so without this aid,
we can understand the extraordinary difficulty which
naturalists have experienced in describing, without the
aid of a diagram, the various affinities which they per-
ceive between the many living and extinct members of
the same great natural class.

Extinction, as we have seen in the fourth chapter,
has played an important part in defining and widening
the intervals between the several groups in each class.
We may thus account for the distinctness of whole classes
from each other—for instance, of birds from all other
vertebrate animals—by the belief that many ancient

Cuap. XIV] ORGANIC BEINGS. 229

forms of life have been utterly lost, through which the
early progenitors of birds were formerly connected with
the early progenitors of the other and at that time less
differentiated vertebrate classes. There has been much
less extinction of the forms of life which once connected
fishes with batrachians. There has been still less with-
in some whole classes, for instance the Crustacea, for
here the most wonderfully diverse forms are still linked
together by a long and only partially broken chain of
affinities. Extinction has only defined the groups: it
has by no means made them; for if every form which
has ever lived on this earth were suddenly to reappear,
though it would be quite impossible to give definitions
by which each group could be distinguished, still a natu-
ral classification, or at least a natural arrangement,
would be possible. We shall see this by turning to the
diagram; the letters, A to L, may represent eleven Si-
lurian genera, some of which have produced large groups
of modified descendants, with every link in each branch
and sub-branch still alive; and the links not greater
than those between existing varieties. In this case it
would be quite impossible to give definitions by which
the several members of the several groups could be dis-
tinguished from their more immediate parents and de-
scendants. Yet the arrangement in the diagram would
still hold good and would be natural; for, on the prin-
ciple of inheritance, all the forms descended, for in-
stance, from A, would have something in common.
In a tree we can distinguish this or that branch, though
at the actual fork the two unite and blend together.
We could not, as I have said, define the several groups;
but we could pick out types, or forms, representing most

of the characters of each group, whether large or small,

230 AFFINITIES CONNECTING — [Cuar. XIV,

and thus give a general idea of the value of the differ-
ences between them. This is what we should be driven
to, if we were ever to succeed in collecting all the forms
in any one class which have lived throughout all time
and space. Assuredly we shall never succeed in mak-
ing so perfect a collection: nevertheless, in certain
classes, we are tending towards this end; and Milne
Edwards has lately insisted, in an able paper, on the high
importance of looking to types, whether or not we can
separate and define the groups to which such types be-
long.

Finally, we have seen that natural selection, which
follows from the struggle for existence, and which al-
most inevitably leads to extinction and divergence of
character in the descendants from any one parent-species,
explains that great and universal feature in the affinities
of all organic beings, namely, their subordination in
group under group. We use the element of descent in
classing the individuals of both sexes and of all ages
under one species, although they may have but few char-
acters in common; we use descent in classing acknowl-
edged varieties, however different they may be from
their parents; and I believe that this element of de-
scent is the hidden bond of connection which natur-
alists have sought under the term of the Natural System.
On this idea of the natural system being, in so far as it
has been perfected, genealogical in its arrangement, with
the grades of difference expressed by the terms genera,
families, orders, &c., we can understand the rules which
we are compelled to follow in our classification. We
can understand why we value certain resemblances far
more than others; why we use rudimentary and useless
organs, or others of trifling physiological importance;

Caap. XIV] ORGANIC BEINGS. 231

why, in finding the relations between one group and
another, we summarily reject analogical or adaptive
characters, and yet use these same characters within
the limits of the same group. We can clearly see
how it is that all living and extinct forms can be
grouped together within a few great classes; and how
the several members of each class are connected to-
gether by the most complex and radiating lines of
affinities. We shall never, probably, disentangle the
inextricable web of the affinities between the members
of any one class; but when we have a distinct object
in view, and do not look to some unknown plan of crea-
tion, we may hope to make sure but slow pro-
gress.

Professor Hickel in his ‘Generelle Morphologie’
and in other works, has recently brought his great
knowledge and abilities to bear on what he calls phylo-
geny, or the lines of descent of all organic beings. In
drawing up the several series he trusts chiefly to em-
bryological characters, but receives aid from homologous
and rudimentary organs, as well as from the successive
periods at which the various forms of life are believed
to have first appeared in our geological formations. He
has thus boldly made a great beginning, and shows us
how classification will in the future be treated.

Morphology.

We have seen that the members of the same class,
independently of their habits of life, resemble each other
in the general plan of their organisation. This resem-
blance is often expressed by the term “unity of type; ”
or by saying that the several parts and organs in the
different species of the class are homologous. The whole

932 MORPHOLOGY. [Cuap. XIV.

subject is included under the general term of Morphol-
ogy. This is one of the most interesting departments
of natural history, and may almost be said to be its very
soul. What can be more curious than that the hand
of a man, formed for grasping, that of a mole for dig-
ging, the leg of the horse, the paddle of the porpoise,
and the wing of the bat, should all be constructed on the
same pattern, and should include similar bones, in the
same relative positions? How curious it is, to give a
subordinate though striking instance, that the hind-feet
of the kangaroo, which are so well fitted for bounding
over the open plains,—those of the climbing, leaf-eating
koala, equally well fitted for grasping the branches of
trees,—those of the ground-dwelling, insect or root eat-
ing, bandicoots,—and those of some other Australian
marsupials,—should all be constructed on the same ex-
traordinary type, namely with the bones of the second
and third digits extremely slender and enveloped within
the same skin, so that they appear like a single toe fur-
nished with two claws. Notwithstanding this similar-
ity of pattern, it is obvious that the hind feet of these
several animals are used for as widely different pur-
poses as it is possible to conceive. The case is ren-
dered all the more striking by the American opossums,
which follow nearly the same habits of life as some of
their Australian relatives, having feet constructed on
the ordinary plan. Professor Flower, from whom
these statements are taken, remarks in conclusion: “We
may call this conformity to type, without getting much
nearer to an explanation of the phenomenon;” and
he then adds “but is it not powerfully suggestive of
true relationship, of inheritance from a common an-
cestor? ”

Cuap, XIV.] MORPHOLOGY. 233

Geoffroy St. Hilaire has strongly insisted on the high
unportance of relative position or connexion in homo-
logous parts; they may differ to almost any extent in
form and size, and yet remain connected together in the
same invariable order. We never find, for instance, the
bones of the arm and fore-arm, or of the thigh and leg,
transposed. Hence the same names can be given to the
homologous bones in widely different animals. We see
the same great law in the construction of the mouths of
insects: what can be more different than the immensely
long spiral proboscis of a sphinx-moth, the curious folded
one of a bee or bug, and the great jaws of a beetle?—
yet all these organs, serving for such widely different
purposes, are formed by infinitely numerous modifica-
tions of an upper lip, mandibles, and two pairs of max-
ille. The same law governs the construction of the
mouths and limbs of crustaceans. So it is with the
flowers of plants.

Nothing can be more hopeless than to attempt to
explain this similarity of pattern in members of the
same class, by utility or by the doctrine of final causes.
The hopelessness of the attempt has been expressly ad-
mitted by Owen in his most interesting work on the
‘Nature of Limbs.’ On the ordinary view of the in-
dependent creation of each being, we can only say that
so it is;—that it has pleased the Creator to construct
all the animals and plants in each great class on a uni-
form plan; but this is not a scientific explanation.

The explanation is to a large extent simple on the
theory of the selection of successive slight modifications,
—each modification being profitable in some way to the
modified form, but often affecting by correlation other
parts of the organisation. In changes of this nature,

234 MORPHOLOGY. [Cuap. XIV.

there will be little or no tendency to alter the original
pattern, or to transpose the parts. The bones of a limb
might be shortened and flattened to any extent, becom-
ing at the same time enveloped in thick membrane, so
as to serve as a fin; or a webbed hand might have all
its bones, or certain bones, lengthened to any extent,
with the membrane connecting them increased, so as
to serve as a wing; yet all these modifications would
not tend to alter the framework of the bones or the rela-
tive connection of the parts. If we suppose that an
early progenitor—the archetype as it may be called—
of all mammals, birds, and reptiles, had its limbs con-
structed on the existing general pattern, for whatever
purpose they served, we can at once perceive the plain
signification of the homologous construction of the limbs
throughout the class. So with the mouths of insects,
we have only to suppose that their common progenitor
had an upper lip, mandibles, and two pairs of maxille,
these parts being perhaps very simple in form; and
then natural selection will account for the infinite di-
versity in the structure and functions of the mouths
of insects. Nevertheless, it is conceivable that the gen-
eral pattern of an organ might become so much obscured
as to be finally lost, by the reduction and ultimately
by the complete abortion of certain parts, by the
fusion of other parts, and by the doubling or multi-
plication of others,—variations which we know to be
within the limits of possibility. In the paddles of the
gigantic extinct sea-lizards, and in the mouths
of certain suctorial crustaceans, the general pattern
seems thus to have become partially obscured.

There is another and equally curious branch of our
subject; namely, serial homologies, or the comparison

Cua. XIV.] MORPHOLOGY. 235

of the differant parts or organs in the same individual,
and not of the same parts or organs in different mem-
bers of the same class. Most physiologists believe that
the bones of the skull are. homologous—that is, cor-
respond in number and in relative connexion—with
the elemental parts of a certain number of vertebra.
The anterior and posterior limbs in all the higher verte-
brate classes are plainly homologous. So it is with
the wonderfully complex jaws and legs of crustaceans.
it is familiar to almost every one, that in a flower the
relative position of the sepals, petals, stamens, and pis-
tils, as well as their intimate structure, are intelligible
on the view that they consist of metamorphosed leaves,
arranged in a spire. In monstrous plants, we often get
direct evidence of the possibility of one organ being
transformed into another; and we can actually see, dur-
ing the early or embryonic stages of development in
flowers, as well as in crustaceans and many other ani-
mals, that organs, which when mature become extremely
different are at first exactly alike.

How inexplicable are the cases of serial homologies
on the ordinary view of creation! Why should the
brain be enclosed in a box composed of such numerous
and such extraordinarily shaped pieces of bone, appa-
rently representing vertebre? As Owen has remarked,
the benefit derived from the yielding of the separate
pieces in the act of parturition by mammals, will by
no means explain the same construction in the skulls
of birds and reptiles. Why should similar bones have
been created to form the wing and the leg of a bat, used
as they are for such totally different purposes, namely
flying and walking? Why should one crustacean, which
has an extremely complex mouth formed of many parts,

236 MORPHOLOGY. [Cuar. XIV,

consequently always have fewer legs; or conversely, those
with many legs have simpler mouths? Why should
the sepals, petals, stamens, and pistils, in each flower,
though fitted for such distinct purposes, be all con-
structed on the same pattern?

On the theory of natural selection, we can, to a cer-
tain extent, answer these questions. We need not here
consider how the bodies of some animals first became
divided into a series of segments, or how they became
divided into right and left sides, with corresponding
organs, for such questions are almost beyond investiga-
tion. It is, however, probable that some serial struc-
tures are the result of cells multiplying by division,
entailing the multiplication of the parts developed from
such cells. It must suffice for our purpose to bear in
mind that an indefinite repetition of the same part or
organ is the common characteristic, as Owen has re-
marked, of all low or little specialised forms; therefore
the unknown progenitor of the Vertebrata probably pos-
sessed many vertebre; the unknown progenitor of the
Articulata, many segments; and the unknown progeni-
tor of flowering plants, many leaves arranged in one
or more spires. We have also formerly seen that parts
many times repeated are eminently liable to vary, not
only in number, but in form. Consequently such parts,
being already present in considerable numbers, and
being highly variable, would naturally afford the ma-
terials for adaptation to the most different purposes;
yet they would generally retain, through the force of
inheritance, plain traces of their original or fundamental
resemblance. They would retain this resemblance all
the more, as the variations, which afforded the basis for
their subsequent modification through natural selection,

Cuap. XIV,] MORPHOLOGY, 237

would tend from the first to be similar; the parts be-
ing at an early stage of growth alike, and being sub-
jected to nearly the same conditions. Such parts,
whether more or less modified, unless their common
origin became wholly obscured, would be serially homo-
logous.

In the great class of molluscs, though the parts in
distinct species can be shown to be homologous, only a
few serial homologies, such as the valves of Chitons,
can be indicated; that is, we are seldom enabled to say
that one part is homologous with another part in the
same individual. And we can understand this fact;
for in molluscs, even in the lowest members of the class,
we do not find nearly so much indefinite repetition of
any one part as we find in the other great classes of the
animal and vegetable kingdoms.

But morphology is a much more complex subject
than it at first appears, as has lately been well shown
in a remarkable paper by Mr. E. Ray Lankester, who
has drawn an important distinction between certain
classes of cases which have all been equally ranked by
naturalists as homologous. He proposes to call the
structures which resemble each other in distinct ani-
mals, owing to their descent from a common progenitor
with subsequent modification, homogenous ; and the re-
semblances which cannot thus be accounted for, he pro-
poses to call homoplastic. Yor instance, he believes that
the hearts of birds and mammals are as a whole homo-
genous,—that is, have been derived from a common pro-
genitor; but that the four cavities of the heart in the
two classes are homoplastic,—that is, have been inde-
pendently developed. Mr. Lankester also adduccs the
close resemblance of the parts on the right and left sides

238 MORPHOLOGY. [Cuar, XIV.

of the body, and in the successive segments of the same
individual animal; and here we have parts commonly
called homologous, which bear no relation to the descent
of distinct species from a common progenitor. Homo-
plastic structures are the same with those which I have
classed, though in a very imperfect manner, as analo-
gous modifications or resemblances. Their formation
may be attributed in part to distinct organisms, or to
distinct parts of the same organism, having varied in an
analogous manner; and in part to similar modifica-
tions, having been preserved for the same general pur-
pose or function,—of which many instances have been
given.

Naturalists frequently speak of the skull as formed
of metamorphosed vertebra; the jaws of crabs as meta-
morphosed legs; the stamens and pistils in flowers as
metamorposed leaves; but it would in most cases be
more correct, as Professor Huxley has remarked, to speak
of both skull and vertebra, jaws and legs, &c., as hav-
ing been metamorphosed, not one from the other, as they
now exist, but from some common and simpler element.
Most naturalists, however, use such language only in
a metaphorical sense; they are far from meaning that
during a long course of descent, primordial organs of any
kind—vertebre in the one case and legs in the other—
have actually been converted into skulls or jaws. Yet
so strong is the appearance of this having occurred, that
naturalists can hardly avoid employing language
having this plain signification. According to the views
here maintained, such language may be used literally;
and the wonderful fact of the jaws, for instance, of a
crab retaining numerous characters which they probably
would have retained through inheritance, if they had

Cuar. XIV]. DEVELOPMENT AND EMBRYOLOGY. 239

really been metamorphosed from true through extremely
simple legs, is in part explained.

Development and Embryology.

This is one of the most important subjects in the
whole round of history. The metamorphoses of insects,
with which every one is familiar, are generally effected
abruptly by a few stages; but the transformations are
in reality numerous and gradual, though concealed.
A certain ephemerous insect (Chléeon) during its devel-
opment, moults, as shown by Sir J. Lubbock, above
twenty times, and each time undergoes a certain amount
of change; and in this case we see the act of metamor-
phosis performed in a primary and gradual manner.
Many insects, and especially certain crustaceans, show
us what wonderful changes of structure can be effected
during development. Such changes, however, reach
their acme in the so-called alternate generations of
some of the lower animals. It is, for instance, an as-
tonishing fact that a delicate branching coralline, stud-
ded with polypi and attached to a submarine rock,
should produce, first by budding and then by transverse
division, a host of huge floating jelly-fishes; and that
these should produce eggs, from which are hatched swim-
ming animalcules, which attach themselves to rocks
and become developed into branching corallines; and so
on in an endless cycle. The belief in the essential iden-
tity. of the process of alternate generation and of ordi-
nary metamorphosis has been greatly strengthened by
Wagner’s discovery of the larva or maggot of a fly, name-
ly the Cecidomyia, producing asexually other larve,
and these others, which finally are developed into ma-

940 DEVELOPMENT AND EMBRYOLOGY. [Cuar. XIV,

ture males and females, propagating their kind in the
ordinary manner by eggs.

It may be worth notice that when Wagner’s remark-
able discovery was first announced, I was asked how
was it possible to account for the larve of this fly hav-
ing acquired the power of asexual reproduction. As
long as the case remained unique no answer could be
given. But already Grimm has shown that another fly.
a Chironomus, reproduces itself in nearly the same man-
ner, and he believes that this occurs frequently in the
Order. It is the pupa, and not the larva, of the Chiro-
nomus which has this power; and Grimm further shows
that this case, to a certain extent, “ unites that of the
Cecidomyia with the parthenogenesis of the Coccide; ”
—the term parthenogenesis implying that the mature
females of the Coccide are capable of producing fertile
eggs without the concourse of the males. Certain ani-
mals belonging to several classes are now known to have
the power of ordinary reproduction at an unusually
early age; and we have only to accelerate parthenoge-
netic production by gradual steps to an earlier and ear-
lier age,—Chironomus showing us an almost exactly in-
termediate stage, viz., that of the pupa—and we can
perhaps account for the marvellous case of the Cecido-
myia.

It has already been stated that various parts in the
same individual which are exactly alike during an early
embryonic period, become widely different and serve
for widely different purposes in the adult state. So
again it has been shown that generally the embryos of
the most distinct species belonging to the same class
are closely similar, but become, when fully developed,
widely dissimilar. A better proof of this latter fact

Car, XIV.] DEVELOPMENT AND EMBRYOLOGY. 941

cannot be given than the statement by Von Baer that
“the embryos of mammalia, of birds, lizards, and
“snakes, probably also of chelonia are in their earliest
“states exceedingly like one another, both as a whole
“and in the mode of development of their parts; so
“much so, in fact, that we can often distinguish the
“embryos only by their size. In my possession are two
“little embryos in spirit, whose names I have omitted
“to attach, and at present I am quite unable to say to
“what class they belong. They may be lizards or small
“birds, or very young mammalia, so complete is
“the similarity in the mode of formation of the head
“and trunk in these animals. The extremities, how-
“ever, are still absent in these embryos. But even
“if they had existed in the earliest stage of their de-
“velopment we should learn nothing, for the feet of
“lizards and mammals, the wings and feet of birds,
“no less than the hands and feet of man, all arise from
“the same fundamental form.” The larve of most
crustaceans, at corresponding stages of development,
closely resemble each other, however different the adults
may become; and so it is with very many other ani-
mals. A trace of the law of embryonic resemblance
occasionally lasts till a rather late age: thus birds of
the same genus, and of allied genera, often resemble
each other in their immature plumage; as we see in the
spotted feathers in the young of the thrush group. In
the cat tribe, most of the species when adult are striped
or spotted in lines; and stripes or spots can be plainly
distinguished in the whelp of the lion and the puma.
We occasionally though rarely see something of the
same kind in plants; thus the first leaves of the ulex or
furze, and the first leaves of the phyllodineous acacias,

942 DEVELOPMENT AND EMBRYOLOGY. [Caapr. XIV.

are pinnate or divided like the ordinary leaves of the
leguminosee.

The points of structure, in which the embryos of
widely different animals within the same class resemble
each other, often have no direct relation to their con-
ditions of existence. We cannot, for instance, sup-
pose that in the embryos of the vertebrata the peculiar
loop-like courses of the arteries near the branchial slits
are related to similar conditions,—in the young mam-
mal which is nourished in the womb of its mother, in
the egg of the bird which is hatched in a nest, and in
the spawn of a frog under water. We have no more
reason to believe in such a relation, than we have to be-
lieve that the similar bones in the hand of a man, wing
of a bat, and fin of a porpoise, are related to similar con-
ditions of life. No one supposes that the stripes on the
whelp of a lion, or the spots on the young blackbird,
are of any use to these animals.

The case, however, is different when an animal dur-
ing any part of its embryonic career is active, and has to
provide for itself. The period of activity may come on
earlier or later in life; but whenever it comes on, the
adaptation of the larva to its conditions of life is just as
perfect and as beautiful as in the adult animal. In how
important a manner this has acted, has recently been
well shown by Sir J. Lubbock in his remarks on the
close similarity of the larve of some insects belonging to
very different orders, and on the dissimilarity of the
larvee of other insects within the same order, according
to their habits of life. Owing to such adaptations, the
similarity of the larve of allied animals is sometimes
greatly obscured; especially when there is a division of
labour during the different stages of development, as

Cuar, XIV.] DEVELOPMENT AND EMBRYOLOGY. 943

when the same larva has during one stage to search for
food, and during another stage has to search for a place
of attachment. Clases can even be given of the larve of
allied species, or groups of species, differing more from
each other than do the adults. In most cases, however,
the larve, though active, still obey, more or less closely,
the law of common embryonic resemblance. Cirripedes
afford a good instance of this; even the illustrious Cu-
vier did not perceive that a barnacle was a crustacean:
but a glance at the larva shows this in an unmistakable
manner. So again the two main divisions of cirripedes,
the pedunculated and sessile, though differing widely in
external appearance, have larve in all their stages barely
distinguishable.

The embryo in the course of development generally
rises in organisation; I use this expression, though I am
aware that it is hardly possible to define clearly what is
meant by the organisation being higher or lower. But
no one probably will dispute that the butterfly is higher
than the caterpillar. In some cases, however, the ma-
ture animal must be considered as lower in the scale
than the larva, as with certain parasitic crustaceans.
To refer once again to cirripedes: the larve in the first
stage have three pairs of locomotive organs, a simple
single eye, and a probosciformed mouth, with which
they feed largely, for they increase much in size. In
the second stage, answering to the chrysalis stage of
butterflies, they have six pairs of beautifully constructed
natatory legs, a pair of magnificent compound eyes, and
extremely complex antenne; but they have a closed
and imperfect mouth, and cannot feed: their function at
this stage is, to search out by their well-developed or-

gans of sense, and to reach by their active powers of
41

944 DEVELOPMENT AND EMBRYOLOGY. [Cuap. XIV,

swimming, a proper place on which to become attached
and to undergo their final metamorphosis. When this
is completed they are fixed for life: their legs are now
converted into prehensile organs; they again obtain a
well-constructed mouth; but they have no antenne, and
their two eyes are now reconverted into a minute, single,
simple eye-spot. In this last and complete state, cirri-
pedes may be considered as either more highly or more
lowly organised than they were in the larval condition.
But in some genera the larvee become developed into
hermaphrodites having the ordinary structure, and into
what I have called complemental males; and in the
latter the development has assuredly been retrograde,
for the male is a mere sack, which lives for a short time
and is destitute of mouth, stomach, and every other
organ of importance, excepting those for reproduction.
We are so much accustomed to see a difference in
structure between the embryo and the adult, that we are
tempted to look at this difference as in some necessary
manner contingent on growth. But there is no reason
why, for instance, the wing of a bat, or the fin of a por-
poise, should not have been sketched out with all their
parts in proper proportion, as soon as any part became
visible. In some whole groups of animals and in cer-
tain members of other groups this is the case, and the
embryo does not at any period differ widely from the
adult: thus Owen has remarked in regard to cuttle-fish,
“there is no metamorphosis; the cephalopodic char-
acter is manifested long before the parts of the embryo
are completed.” lLand-shells and fresh-water crusta-
ceans are born having their proper forms, whilst the
marine members of the same two great classes pass
through considerable and often great changes during

Cuar. XIV.] DEVELOPMENT AND EMBRYOLOGY. 945

their development. Spiders, again, barely undergo any
metamorphosis. The larve of most insects pass through
a worm-like stage, whether they are active and adapted
to diversified habits, or are inactive from being placed
in the midst of proper nutriment or from being fed by
their parents; but in some few cases, as in that of Aphis,
if we look to the admirable drawings of the develop-
ment of this insect, by Professor Huxley, we see hardly
any trace of the vermiform stage.

Sometimes it is only the earlier developmental stages
which fail. Thus Fritz Miiller has made the remark-
able discovery that certain shrimp-like crustaceans (al-
lied to Penceus) first appear under the simple nauplius-
form, and after passing through two or more zoea-stages,
and then through the mysis-stage, finally acquire their
mature structure: now in the whole great malacostracan
order, to which these crustaceans belong, no other mem-
ber is as yet known to be first developed under the nau-
plius-form, though many appear as zoeas; nevertheless
Miiller assigns reasons for his belief, that if there had
been no suppression of development, all these crusta-
ceans would have appeared as nauplii.

How, then, can we explain these several facts in
embryology,—namely, the very general, though not uni-
versal, difference in structure between the embryo and
the adult;—the various parts in the same individual
embryo, which ultimately become very unlike and serve
for diverse purposes, being at an early period of growth
alike;—the common, but not invariable, resemblance
between the embryos or larve of the most distinct spe-
cies in the same class;—the embryo often retaining
whilst within the egg or womb, structures which are
of no service to it, either at that or at a later period of

946 DEVELOPMENT AND EMBRYOLOGY. [Cuar. XIV.

life; on the other hand larve, which have to provide
for their own wants, being perfectly adapted to the sur-
rounding conditions;—and lastly the fact of certain
larvee standing higher in the scale of organisation than
the mature animal into which they are developed? I
believe that all these facts can be explained, as follows.

It is commonly assumed, perhaps from monstrosities
affecting the embryo at a very early period, that slight
variations or individual differences necessarily appear
at an equally early period. We have little evidence on
this head, but what we have certainly points the other
way; for it is notorious that breeders of cattle, horses,
and various fancy animals, cannot positively tell, until
some time after birth, what will be the merits or de-
merits of their young animals. We see this plainly in
our own children; we cannot tell whether a child will
be tall or short, or what its precise features will be.
The question is not, at what period of life each variation
may have been caused, but at what period the effects
are displayed. The cause may have acted, and I believe
often has acted, on one or both parents before the act of
generation. It deserves notice that it is of no import-
ance to a very young animal, as long as it remains in
its mother’s womb or in the egg, or as long as it is
nourished and protected by its parent, whether most of
its characters are acquired a little earlier or later in life.
It would not signify, for instance, to a bird which ob-
tained its food by having a much-curved beak whether
or not whilst young it possessed a beak of this shape,
as long as it was fed by its parents.

I have stated in the first chapter, that at whatever
age a variation first appears in the parent, it tends to
re-appear at a corresponding age in the offspring. Cer-

Car. X1V.] DEVELOPMENT AND EMBRYOLOGY. 247

tain variations can only appear at corresponding ages;
for instance, peculiarities in the caterpillar, cocoon,
or imago states of the silk-moth: or, again, in the full-
grown horns of cattle. But variations, which, for all
that we can see might have first appeared either earlier
or later in life, likewise tend to reappear at a corre-
sponding age in the offspring and parent. I am
far from meaning that this is invariably the case and
I could give several exceptional cases of variations
(taking the word in the largest sense) which have su-
pervened at an earlier age in the child than in the
parent.

These two principles, namely, that slight variations
generally appear at a not very early period of life, and
are inherited at a corresponding not early period, ex-
plain, as I believe, all the above specified leading facts
in embryology. But first let us look to a few analo-
gous cases in our domestic varieties. Some authors
who have written on Dogs, maintain that the greyhound
and bulldog, though so different, are really closely al-
lied varieties, descended from the same wild stock; hence
I was curious to see how far their puppies differed from
each other: I was told by breeders that they differed
just as much as their parents, and this, judging by the
eye, seemed almost to be the case; but on actually meas-
uring the old dogs and their six-days-old puppies, I
found that the puppies had not acquired nearly their
full amount of proportional difference. So, again, I
was told that the foals of cart and race-horses—breeds
which have been almost wholly formed by selection
under domestication—differed as much as the full-grown
animals; but having had careful measurements made
of the dams and of three-days-old colts of race and

948 DEVELOPMENT AND EMBRYOLOGY. [Cuapr. XIV.

heavy cart-horses, I find that this is by no means the
case.

As we have conclusive evidence that the breeds of
the Pigeon are descended from a single wild species, I
compared the young within twelve hours after being
hatched; I carefully measured the proportions (but will
not here give the details) of the beak, width of mouth,
length of nostril and of eyelid, size of feet and length
of leg, in the wild parent-species, in pouters, fantails,
runts, barbs, dragons, carriers, and tumblers. Now
some of these birds, when mature, differ’ in so extraordi-
nary a manner in the length and form of beak, and in
other characters, that they would certainly have been
ranked as distinct genera if found in a state of nature.
But when the nestling birds of these several breeds were
placed in a row, though most of them could just be dis-
tinguished, the proportional differences in the above
specified points were incomparably less than in the full-
grown birds. Some characteristic points of difference
——for instance, that of the width of mouth—could hardly
be detected in the young. But there was one remark-
able exception to this rule, for the young of the short-
faced tumbler differed from the young of the wild rock-
pigeon and of the other breeds, in almost exactly the
same proportions as in the adult state.

These facts are explained by the above two principles.
Fanciers select their dogs, horses, pigeons, &c., for breed-
ing, when nearly grown up: they are indifferent whether
the desired qualities are acquired earlier or later in
life, if the full-grown animal possesses them. And
the cases just given, more especially that of the pigeons,
show that the characteristic differences which have been
accumulated by man’s selection, and which give value to

Cuar. XIV.] DEVELOPMENT AND EMBRYOLOGY. 249

his breeds, do not generally appear at a very early period
of life, and are inherited at a corresponding not early
period. But the case of the short-faced tumbler, which
when twelve hours old possessed its proper characters,
proves that this is not the universal rule; for here the
characteristic differences must either have appeared at
an earlier period than usual, or, if not so, the differences
must have been inherited, not at a corresponding, but at
an earlier age.

Now let us apply these two principles to species in a
state of nature. Let us take a group of birds, descended
from some ancient form and modified through natural
selection for different habits. Then, from the many
slight successive variations having supervened in the
several species at a not early age, and having been in-
ierited at a corresponding age, the young will have been
but little modified, and they will still resemble each
other much more closely than do the adults,—just as we
have seen with the breeds of the pigeon. We may ex-
tend this view to widely distinct structures and to whole
classes. The fore-limbs, for instance, which once, served
as legs to a remote progenitor, may have become, through
a long course of modification, adapted in one descendant
to act as hands, in another as paddles, in another as
wings; but on the above two principles the fore-limbs
will not have been much modified in the embryos of
these several forms; although in each form the fore-
limb will differ greatly in the adult state. Whatever
influence long-continued use or disuse may have had in
modifying the limbs or other parts of any species, this
will chiefly or solely have affected it when nearly ma-
ture, when it was compelled to use its full powers to
gain its own living; and the effects thus produced will

250 DEVELOPMENT AND EMBRYOLOGY. [Cuap. XIV.

have been transmitted to the offspring at a correspond-
ing nearly mature age. Thus the young will not be
modified, or will be modified only in a slight degree,
through the effects of the increased use or disuse of
parts.

With some animals the successive variations may
have supervened at a very early period of life, or the
steps may have been inherited at an earlier age than
that at which they first occurred. In either of these
cases, the young or embryo will closely resemble the ma-
ture parent-form, as we have seen with the short-faced
tumbler. And this is the rule of development in certain
whole groups, or in certain sub-groups alone, as with
cuttle-fish, land-shells, fresh-water crustaceans, spiders,
and some members of the great class of insects. With
respect to the final cause of the young in such groups
not passing through any metamorphosis, we can see
that this would follow from the following contingencies;
namely, from the young having to provide at a very
early age for their own wants, and from their following
the same habits of life with their parents; for in this
case, it would be indispensable for their existence that
they should be modified in the same manner as their
parents. Again, with respect to the singular fact that
many terrestrial and fresh-water animals do not under-
go any metamorphosis, whilst marine members of the
same groups pass through various transformations, Fritz
Miller has suggested that the process of slowly modify-
ing and adapting an animal to live on the land or in
fresh water, instead gf in the sea, would be greatly sim-
plified by its not ee through any larval stage; for it
is not probable that places well adapted for both the
larval and mature stages, under such new and greatly

Car. XIV.] DEVELOPMENT AND EMBRYOLOGY. 951

changed habits of life, would commonly be found unoc-
cupied or ill-occupied by other organisms. In this case
the gradual acquirement at an earlier and earlier age
of the adult structure would be favoured by natural selec-
tion; and all traces of former metamorphoses would
finally be lost.

if, on the other hand, it profited the young of an
animal to follow habits of life slightly different from
those of the parent-form, and consequently to be con-
structed on a slightly different plar, or if it profited a
larva already different from its parent to change still
further, then, on the principle of inheritance at corre-
sponding ages, the young or the larve might be ren-
dered by natural selection more and more different from
their parents to any conceivable extent. Differences in
the larva might, also, become correlated with successive
stages of its development; so that the larva, in the first
stage, might come to differ greatly from the larva in the
second stage, as is the case with many animals. The
adult might also become fitted for sites or habits, in
which organs of locomotion or of the senses, &c., would
be useless; and in this case the metamorphosis would
be retrograde.

From the remarks just made we can see how by
changes of structure in the young, in conformity with
changed habits of life, together with inheritance at cor-
responding ages, animals might come to pass through
stages of development, perfectly distinct from the pri-
mordial condition of their adult progenitors. Most of
our best authorities are now convinced that the various
larval and pupal stages of insects have thus been acquired
through adaptation, and not through inheritance from
some ancient form. The curious case of Sitaris—a

952 DEVELOPMENT AND EMBRYOLOGY. [Cuar. XIV.

beetle which passes through certain unusual stages of
development—will illustrate how this might occur. The
first larval form is described by M. Fabre, as an active,
minute insect, furnished with six legs, two long anten-
ne, and four eyes. These larve are hatched in the
nests of bees; and when the male-bees- emerge from
their burrows, in the spring, which they do before the
females, the larve spring on them, and afterwards crawl
on to the females whilst paired with the males. As
soon as the female bee deposits her eggs on the surface
of the honey stored in the cells, the larve of the Sitaris
leap on the eggs and devour them. Afterwards they
undergo a complete change; their eyes disappear; their
legs and antennx become rudimentary, and they feed on
honey; so that they now more closely resemble the ordi-
nary larve of insects; ultimately they undergo a further
transformation, and finally emerge as the perfect beetle.
Now, if an insect, undergoing transformations like those
of the Sitaris, were to become the progenitor of a whole
new class of insects, the course of development of the
new class would be widely different from that of our
existing insects; and the first larval stage certainly
would not represent the former condition of any adult
and ancient form.

On the other hand it is highly probable that with
many animals the embryonic or larval stages show us,
more or less completely, the condition of the progenitor
of the whole group in its adult state. In the great class
of the Crustacea, forms wonderfully distinct from each
other, namely, suctorial parasites, cirripedes, entomo-
straca, and even the malacostraca, appear at first as
larve under the nauplius-form; and as these larve live
and feed in the open sea, and are not adapted for any

Cuar. XIV.] DEVELOPMENT AND EMBRYOLOGY. 953

peculiar habits of life, and from other reasons assigned
by Fritz Miiller, it is probable that at some very remote
period an independent adult animal, resembling the
Nauplius, existed, and subsequently produced, along sev-
eral divergent lines of descent, the above-named great
Crustacean groups. So.again it is probable, from what
we know of the embryos of mammals, birds, fishes, and
reptiles, that these animals are the modified descen-
dants of some ancient progenitor, which was furnished
in its adult state with branchie, a swim-bladder, four
fin-like limbs, and a long tail, all fitted for an aquatic
life.

As all the organic beings, extinct and recent, which
have ever lived, can be arranged within a few great
classes; and as all within each class have, according to
our theory, been connected together by fine gradations,
the best, and, if our collections were nearly perfect, the
only possible arrangement, would be genealogical; de-
scent being the hidden bond of connexion which natural-
ists have been seeking under the term of the Natural
System. On this view we can understand how it is that,
in the eyes of most naturalists, the structure of the em-
bryo is even more important for classification than that
of the adult. In two or more groups of animals, how-
ever much they may differ from each other in structure
and habits in their adult condition, if they pass through
closely similar embryonic stages, we may feel assured
that they all are descended from one parent-form, and
are therefore closely related. Thus, community in em-
bryonic structure reveals community of descent; but
dissimilarity in embryonic development does not prove
discommunity of descent, for in one of two groups the
developmental stages may have been suppressed, or may

954 DEVELOPMENT AND EMBRYOLOGY. [Cuap. XIV.

have been so greatly modified through adaptation to
new habits of life, as to be no longer recognisable. Even
in groups, in which the adults have been modified to
an extreme degree, community of origin is often re-
vealed by the structure of the larve; we have seen, for
instance, that cirripedes, though externally so like shell-
fish, are at once known by their larve to belong to the
great class of crustaceans. As the embryo often shows
us more or less plainly the structure of the less modi-
fied and ancient progenitor of the group, we can see
why ancient and extinct forms so often resemble in their
adult state the embryos of existing species of the same
class. Agassiz believes this to be a universal law of
nature; and we may hope hereafter to see the law proved
true. It can, however, be proved true only in those
cases in which the ancient state of the progenitor of
the group has not been wholly obliterated, either by
successive variations having supervened at a very early
period of growth, or by such variations having been in-
herited at an earlier age than that at which they first
appeared. It should also be borne in mind, that the
law may be true, but yet, owing to the geological record
not extending far enough back in time, may remain for
a long period, or for ever, incapable of demonstration.
The law will not strictly hold good in those cases in
which an ancient form became adapted in its larval state
to some special line of life, and transmitted the same
larval state to a whole group of descendants; for such
larve will not resemble any still more ancient form in
its adult state.

Thus, as it seems to me, the leading facts in embry-
ology, which are second to none in importance, are ex-
plained on the principle of variations in the many de-

Cuar.XIV.] RUDIMENTARY ORGANS. 255

scendants from some one ancient progenitor, having ap-
peared at a not very early period of life, and having been
inherited at a corresponding period. Embryology rises
greatly in interest, when we look at the embryo as a
picture, more or less obscured, of the progenitor, either

in its adult or larval state, of all the members of the
same great class.

Rudimentary, Atrophied, and Aborted Organs.

Organs or parts in this strange condition, bearing the
plain stamp of inutility, are extremely common, or even
general, throughout nature. It would be impossible to
name one of the higher animals in which some part or
other is not in a rudimentary condition. In the mam-
malia, for instance, the males possess rudimentary mam-
mz; in snakes one lobe of the lungs is rudimentary;
in birds the “ bastard-wing ” may safely be considered
as a rudimentary digit, and in some species the whole
wing is so far rudimentary that it cannot be used for
flight. What can be more curious than the presence
of teeth in foetal whales, which when grown up have
not a tooth in their heads; or the teeth, which never
cut through the gums, in the upper jaws of unborn
calves?

Rudimentary organs plainly declare their origin and
meaning in various ways. There are beetles belonging
to closely allied species, or even to the same identical
species, which have either full-sized and perfect wings,
or mere rudiments of membrane, which not rarely lie
under wing-covers firmly soldered together; and in these
cases it is impossible to doubt, that the rudiments repre-
sent wings. Rudimentary organs sometimes retain their
potentiality: this occasionally occurs with the mam-

956 RUDIMENTARY, ATROPHIED. ([Cuap. XIV.

me of male mammals, which have been known to be-
come well developed and to secrete milk. So again in
the udders in the genus Bos, there are normally four
developed and two rudimentary teats; but the latter in
our domestic cows sometimes become well developed
and yield milk. In regard to plants the petals are some-
times rudimentary, and sometimes well-developed in the
individuals of the same species. In certain plants hav-
ing separated sexes Kolreuter found that by crossing
a species, in which the male flowers included a rudiment
of a pistil, with an hermaphrodite species, having of
course a well-developed pistil, the rudiment in the hy-
brid offspring was much increased in size; and this clear-
ly shows that the rudimentary and perfect pistils are es-
sentially alike in nature. An animal may possess various
parts in a perfect state, and yet they may in one sense
be rudimentary, for they are useless: thus the tadpole
of the common Salamander or Water-newt, as Mr. G. H.
Lewes remarks, “has gills, and passes its existence in
“the water; but the Salamandra atra, which lives high
“up among the mountains, brings forth its young full-
“formed. This animal never lives in the water. Yet
“if we open a gravid female, we find tadpoles inside her
“with exquisitely feathered gills; and when placed in
“water they swim about like the tadpoles of the
“water-newt. Obviously this aquatic organisation has
“no reference to the future life of the animal, nor
“has it any adaptation to its embryonic condition; it
“has solely reference to ancestral adaptations, it
“repeats a phase in the development of its progeni-
“ tors.”

An organ, serving for two purposes, may become
rudimentary or utterly aborted for one, even the more

Cuar. XIV.] AND ABORTED ORGANS. 257

Important purpose, and remain perfectly efficient for
the other. Thus in plants, the office of the pistil is to
allow the pollen-tubes to reach the ovules within the
ovarlum. The pistil consists of a stigma supported on
a style; but in some Composite, the male florets, which
of course cannot be fecundated, have a rudimentary
pistil, for it is not crowned with a stigma; but the style
remains well developed and is clothed in the usual man-
ner with hairs, which serve to brush the pollen out of
the surrounding and conjoined anthers. Again, an or-
gan may become rudimentary for its proper purpose,
and be used for a distinct one: in certain fishes the
swim-bladder seems to be rudimentary for its proper
function of giving buoyancy, but has become converted
into a nascent breathing organ or lung. Many similar
instances could be given.

Useful organs, however little they may be developed,
untess we have reason to suppose that they were for-
merly more highly developed, ought not to be consid-
ered as rudimentary. They may be in a nascent condi-
tion, and in progress towards further development.
Rudimentary organs, on the other hand, are either quite
useless, such as teeth which never cut through the gums,
or almost useless, such as the wings of an ostrich, which
serve merely as sails. As organs in this condition would
formerly, when still less developed, have been of even
less use than at present, they cannot formerly have been
produced through variation and natural selection, which
acts solely by the preservation of useful modifications.
They have been partially retained by the power of in-
heritance, and relate to a former state of things. It is,
however, often difficult to distinguish between rudimen-
tary and nascent organs; for we can judge only by analogy

958 RUDIMENTARY, ATROPHIED, ([Cuapr. XIV,

whether a part is capable of further development, in
which case alone it deserves to be called nascent. Or-
gans in this condition will always be somewhat rare;
for beings thus provided will commonly have been sup-
planted by their successors with the same organ in a
more perfect state, and consequently will have become
long ago extinct. The wing of the penguin is of high
service, acting as a fin; it may, therefore, represent the
nascent state of the wing: not that I believe this to be
the case; it is more probably a reduced organ, modi-
fied for a new function: the wing of the Apteryx, on the
other hand, is quite useless, and is truly rudimentary.
Owen considers the simple filamentary limbs of the Lepi-
dosiren as the “beginnings of organs which attain full
functional development in higher vertebrates; ” but, ac-
cording to the view lately advocated by Dr. Giinther,
they are probably remnants, consisting of the persist-
ent axis of a fin, with the lateral rays or branches abort-
ed. The mammary glands of the Ornithorhynchus may
be considered, in comparison with the udders of a cow,
as in a nascent condition. The ovigerous frena of cer-
tain cirripedes, which have ceased to give attachment
to the ova and are feebly developed, are nascent bran-
chie.

Rudimentary organs in the individuals of the same
species are very liable to vary in the degree of their
development and in other respects. In closely allied
species, also, the extent to which the same organ has
been reduced occasionally differs much. This latter fact
is well exemplified in the state of the wings of female
moths belonging to the same family. Rudimentary or-
gans may be utterly aborted; and this implies, that in
certain animals or plants, parts are entirely absent which

Cua. X1V.] AND ABORTED ORGANS. 959

analogy would lead us to expect to find in them, and
which are occasionally found in monstrous individuals.
Thus in most of the Scrophulariacee the fifth stamen
1s utterly aborted; yet we may conclude that a fifth
stamen once existed, for a rudiment of it is found in
many species of the family, and this rudiment occasion-
ally becomes perfectly developed, as may sometimes
be seen in the common snap-dragon. In tracing the
homologies of any part-in different members of the same
class, nothing is more common, or, in order fully to un-
derstand the relations of the parts, more useful than
the discovery of rudiments. This is well shown in the
drawings given by Owen of the leg-bones of the horse,
ox, and rhinoceros. .

It is an important fact that rudimentary organs, such
as teeth in the upper jaws of whales and ruminants, can
often be detected in the embryo, but afterwards wholly
disappear. It is also, I believe, a universal rule, that
a rudimentary part is of greater size in the embryo rela-
tively to the adjoining parts, than in the adult; so that
the organ at this early age is less rudimentary, or even
cannot be said to be in any degree rudimentary. Hence
rudimentary organs in the adult are often said to have
retained their embryonic condition.

I have now given the leading facts with respect to
rudimentary organs. In reflecting on them, every one
must be struck with astonishment; for the same reason-
ing power which tells us that most parts and organs are
exquisitely adapted for certain purposes, tells us with
equal plainness that these rudimentary or atrophied
organs are imperfect and useless. In works on natural
history, rudimentary organs are generally said to have

been created “for the sake of symmetry,” or in order
42

960 RUDIMENTARY, ATROPHIED, [Cuap. XIV.

“to complete the scheme of nature.” But this is not an
explanation, merely a re-statement of the fact. Nor
is it consistent with itself; thus the boa-constrictor has
rudiments of hind-limbs and of a pelvis, and if it be
said that these bones have been retained “ to complete
the scheme of nature,” why, as Professor Weismann
asks, have they not been retained by other snakes, which
do not possess even a vestige of these same bones? What
would be the thought of an astronomer who maintained
that the satellites revolve in elliptic courses round their
planets “for the sake of symmetry,” because the planets
thus revolve round the sun? An eminent physiologist
accounts for the presence of rudimentary organs, by
supposing that they serve to excrete matter in excess,
or matter injurious to the system; but can we suppose
that the minute papilla, which often represents the
pistil in male flowers, and which is formed of mere
cellular tissue, can thus act? Can we suppose that
rudimentary teeth, which are subsequently absorbed,
are beneficial to the rapidly growing embryonic calf by
removing matter so precious as phosphate of lime?
When a man’s fingers have been amputated, imperfect
nails have been known to appear on the stumps, and I
could as soon believe that these vestiges of nails are de-
veloped in order to excrete horny matter, as that the
rudimentary nails on the fin of the manatee have been
developed for this same purpose.

On the view of descent with modification, the origin
of rudimentary organs is comparatively simple; and we
can understand to a large extent the laws governing
their imperfect development. We have plenty of cases
of rudimentary organs in our domestic productions,—as
the stump of a tail in tailless breeds,—the vestige of an

Cuap, XIV] AND ABORTED ORGANS. 261

Say in earless breeds of sheep,—the reappearance of
minute dangling horns in hornless breeds of cattle,
more especially, according to Youatt, in young animals,
—and the state of the whole flower in the cauliflower.
We often see rudiments of various parts in monsters;
but I doubt whether any of these cases throw light on
the origin of rudimentary organs in a state of nature,
further than by showing that rudiments can be pro-
duced; for the balance of evidence clearly indicates that
species under nature do not undergo great and abrupt
changes. But we learn from the study of our domestic
productions that the disuse of parts leads to their re-
duced size; and that the result is inherited.

It appears probable that disuse has been the main
agent in rendering organs rudimentary. It would at
first lead by slow steps to the more and more complete
reduction of a part, until at last it became rudimentary,
—as in the case of the eyes of animals inhabiting dark
caverns, and of the wings of birds inhabiting oceanic
islands, which have seldom been forced by beasts of prey
to take flight, and have ultimately lost the power of
flying. Again, an organ, useful under certain condi-
tions, might become injurious under others, as with the
wings of beetles living on small and exposed islands; and
in this case natural selection will have aided in reducing
the organ, until it was rendered harmless and rudi-
mentary.

Any change in structure and function, which can be
effected by small stages, is within the power of natural
selection; so that an organ rendered, through changed
habits of life, useless or injurious for one purpose, might
be modified and used for another purpose. An organ
might, also, be retained for one alone of its former func-

262 RUDIMENTARY, ATROPHIED, [Cuar. XIV

tions. Organs, originally formed by the aid of natural
selection, when rendered useless may well be variable,
for their variations can no longer be checked by natural
selection. All this agrees well with what we see under
nature. Moreover, at whatever period of life either dis-
use or selection reduces an organ, and this will generally
be when the being has come to maturity and has to
exert its full powers of action, the principle of inherit-
ance at corresponding ages will tend to reproduce the
organ in its reduced state at the same mature age, but
will seldom effect it in the embryo. Thus we can un-
derstand the greater size of rudimentary organs in the
embryo relatively to the adjoining parts, and their
lesser relative size in the adult. If, for instance, tha
digit of an adult animal was used less and less during
many generations, owing to some change of habits, or if
an organ or gland was less and less functionally exercised,
we may infer that it would become reduced in size in the
adult descendants of this animal, but would retain nearly
its original standard of development in the embryo.
There remains, however, this difficulty. After an
organ has ceased being used, and has become in con-
sequence much reduced, how can it be still further re-
duced in size until the merest vestige is left; and how
can it be finally quite obliterated? It is scarcely pos-
sible that disuse can go on producing any further effect
after the organ has once been rendered functionless.
Some additional explanation is here requisite which I
cannot give. If, for instance, it could be proved that
every part of the organisation tends to vary in a greater
degree towards diminution than towards augmentation
of size, then we should be able to understand how an
organ which has become useless would be rendered, in

Cuap. XIV.) AND AbORTED ORGANS. 263

dependently of the effects of disuse, tudimentary and
would at last be wholly suppressed; for the variations
towards diminished size would no longer be checked by
natural selection. The principle of the economy of
growth, explained in a former chapter, by which the
materials forming any part, if not useful to the pos-
Sessor, are saved as far as possible, will perhaps come
into play in rendering a useless part rudimentary. But
this principle will almost necessarily be confined to the
earlier stages of the process of reduction; for we cannot
suppose that a minute papilla, for instance, representing
in a male flower the pistil of the female flower, and
formed merely of cellular tissue, could be further re-
duced or absorbed for the sake of economising nutriment.

Finally, as rudimentary organs, by whatever steps
they may have been degraded into their present useless
condition, are the record of a former state of things, and
have been retained solely through the power of inherit-
ance,—we can understand, on the genealogical view of
classification, how it is that systematists, in placing
organisms in their proper places in the natural system,
have often found rudimentary parts as useful as, or even
sometimes more useful than, parts of high physiologi-
cal importance. Rudimentary organs may be compared
with the letters in a word, still retained in the spelling,
but become useless in the pronunciation, but which serve
as a clue for its derivation. On the view of descent
with modification, we may conclude that the existence
of organs in a rudimentary, imperfect, and useless condi-
tion, or quite aborted, far from presenting a strange
difficulty, as they assuredly do on the old doctrine of
creation, might even have been anticipated in accordance
with the views here explained.

264 SUMMARY. [Cuar. X

et
et:

Summary.

In this chapter I have attempted to show, that the
arrangement of all organic beings throughout all time
in groups under groups—that the nature of the relation-
ships by which all living and extinct organisms are
united by complex, radiating, and circuitous lines of
affinities into a few grand classes,—the rules followed
and the difficulties encountered by naturalists in their
classifications,—the value set upon characters, if con-
stant and prevalent, whether of high or of the most tri-
fling importance, or, as with rudimentary organs, of no
importance,—the wide opposition in value between an-
alogical or adaptive characters, and characters of true
affinity; and other such rules;—all naturally follow if
we admit the common parentage of allied forms, to-
gether with their modification through variation and
natural selection, with the contingencies of extinction
and divergence of character. In considering this view
of classification, it should be borne in mind that the ele-
ment of descent has been universally used in ranking to-
gether the sexes, ages, dimorphic forms, and acknowl-
edged varieties of the same species, however much they
may differ from each other in structure. If we extend
the use of this element of descent,—the one certainly
known cause of similarity in organic beings,—we shall
understand what is meant by the Natural System: it is
genealogical in its attempted arrangement, with the
grades of acquired difference marked by the
terms, varieties, species, genera, families, orders, and
classes.

On this same view of descent with modification, most

Cuap, XIV,] SUMMARY. 265

of the great facts in Morphology become intelligible,—
whether we look to the same pattern displayed by the
different species of the same class in their homologous
organs, to whatever purpose applied; or to the serial and
lateral homologies in each individual animal and
plant. ,

On the principle of successive slight variations, not
necessarily or generally supervening at a very early
period of life, and being inherited at a corresponding
period, we can understand the leading facts in Embry-
ology; namely, the close resemblance in the individual
embryo of the parts which are homologous, and which
when matured become widely different in structure and
function; and the resemblance of the homologous parts
or organs in allied though distinct species, though fitted
in the adult state for habits as different as is possible.
Larve are active embryos, which have been specially
modified in a greater or less degree in relation to their
habits of life, with their modifications inherited at a
corresponding early age. On these same principles,—
and bearing in mind that when organs are reduced in
size, either from disuse or through natural selection, it
will generally be at that period of life when the being
has to provide for its own wants, and bearing in mind
how strong is the force of inheritance—the occurrence
of rudimentary organs might even have been anticipated.
The importance of embryological characters and of rudi-
mentary organs in classification is intelligible, on the
view that a natural arrangement must be genealogical.

Finally, the several classes of facts which have been
considered in this chapter, seem to me to proclaim so
plainly, that the innumerable species, genera and fami-
lies, with which this world is peopled, are all descended,

266 SUMMARY. [Cuap. XIV,

each within its own class or group, from common
parents, and have all been modified in the course of de-
scent, that I should without hesitation adopt this view,
even if it were unsupported by other facts or arguments.

Cuar XV. RECAPITULATION, 267

(

CHAPTER XV.
RECAPITULATION AND CONCLUSION.

Recapitulation of the objections to the theory of Natural Selection
—Recapitulation of the general and special circumstances in its
favour—Causes of the general belief in the immutability of
species—How far the theory of Natural Selection may be ex-
tended—Effects of its adoption on the study of Natural History
—Concluding Remarks.

As this whole volume is one long argument, it may
be convenient to the reader to have the leading facts
and inferences briefly recapitulated.

That many and serious objections may be advanced
against the theory of descent with modification through
variation and natural selection, I do not deny. I have
endeavoured to give to them their full force. Nothing
at first can appear more difficult to believe than that
the more complex organs and instincts have been per-
fected, not by means superior to, though analogous with,
human reason, but by the accumulation of innumerable
slight variations, each good for the individual possessor.
Nevertheless, this difficulty, though appearing to our
imagination insuperably great, cannot be considered
real if we admit the following propositions, namely,
that all parts of the organisation and instincts offer, at
least, individual differences—that there is a struggle for
existence leading to the preservation of profitable devia-
tions of structure or instinct—and, lastly, that grada-

268, a RECAPITULATION. [Cuar. XV.
/

tions in the state of perfection of each organ may have

existed, each good of its kind. The truth of these

propositions cannot, I think, be disputed.

Tt is, no doubt, extremely difficult even to conjecture
by what gradations many structures have been perfected,
more especially amongst broken and failing groups of
organic beings, which have suffered much - extinction,
but we see so many strange gradations in nature, that
we ought to be extremely cautious in saying that any
organ or instinct, or any whole structure, could not have
arrived at its present state by many graduated steps.
There are, it must be admitted, cases of special difficulty
opposed to the theory of natural selection; and one of
the most curious of these is the existence in the same
community of two or three defined castes of workers or
sterile female ants; but I have attempted to show how
these difficulties can be mastered.

With respect to the almost universal sterility of
species when first crossed, which forms so remarkable a
contrast with the almost universal fertility of varieties
when crossed, I must refer the reader to the recapitula-
tion of the facts given at the end of the ninth chapter,
which seem to me conclusively to show that this sterility
is no more a special endowment than is the incapacity of
two distinct kinds of trees to be grafted together; but
__that it is incidental on differences confined _to the repro-
ductive systems of the intercrossed species. We see the
truth of this conclusion in the vast difference in the
results of crossing the same two species reciprocally,— _
that is, when one species is first used as the father and

then as the mother. Analogy from the consideration of

dimorphic and trimorphic plants clearly leads to the
same conclusion, for when the forms are illegitimately

Cuap. XV.] RECAPITULATION. 269

united, they yield few or no seed, and their offspring are
more or less sterile; and these forms belong to the same
undoubted species, and differ from each other in no re-
spect except in their reproductive organs and functions.

Although the fertility of varieties when intercrossed
and of their mongrel offspring has been asserted by so
many authors to be universal, this cannot be considered
as quite correct after the facts given on the high
authority of Gartner and Kélreuter. Most of the varie-
ties which have been experimented on have been pro-
duced under domestication; and as domestication (I do
not mean mere confinement) almost certainly tends to
eliminate that sterility which, judging from analogy,
would have affected the parent-species if intercrossed, we
ought not to expect that domestication would likewise
induce sterility in their modified descendants when
crossed. This elimination of sterility apparently follows
from the same cause which allows our domestic animals
to breed freely under diversified circumstances; and this
again apparently follows from their having been gradu-
ally accustomed to frequent changes in their conditions
of life.

A double and parallel series of facts seems to throw
much light on the sterility of species, when first crossed,
and of their hybrid offspring. On the one side, there is
good reason to believe that slight changes in the con-
ditions of life give vigour and fertility to all organic
beings. We know also that a cross between the distinct
individuals of the same variety, and between distinct
varieties, increases the number of their offspring, and
certainly gives to them increased size and vigour. This
is chiefly owing to the forms which are crossed having
been exposed to somewhat different conditions of life;

270 RECAPITULATION. [Cuap. XV,

for I have ascertained by a laborious series of experi-
ments that if all the individuals of the same variety
be subjected during several generations to the same
conditions, the good derived from crossing is often much
diminished or wholly disappears. This is one side of
the case. On the other side, we know that species which
have long been exposed to nearly uniform conditions,
when they are subjected under confinement to new and
greatly changed conditions, either perish, or if they sur-
vive, are rendered sterile, though retaining perfect
health. This does not occur, or only in a very slight de-
gree, with our domesticated productions, which have
long been exposed to fluctuating conditions. Hence
when we find that hybrids produced by a cross between
two distinct species are few in number, owing to their
perishing soon after conception or at a very early age,
or if surviving that they are rendered more or less sterile,
it’seems highly probable that this result is due to their
having been in fact subjected to a great change in their
conditions of life, from being compounded of two dis-
tinct organisations. He who will explain in a definite
manner why, for instance, an elephant or a fox will not
breed under confinement in its native country, whilst
the domestic pig or dog will breed freely under the most
diversified conditions, will at the same time be able to
give a definite answer to the question why two distinct
species, when crossed, as well as their hybrid offspring,
are generally rendered more or less sterile, whilst two
domesticated varieties when crossed and their mongrel
offspring are perfectly fertile.

Turning to geographical distribution, the difficulties
encountered on the theory of descent with modification
are serious enough. All the individuals of the same

Cuar, XV.] RECAPITULATION. 271

species, and all the species of the same genus, or even
higher group, are descended from common parents; and
therefore, in however distant and isolated parts of the
world they may now be found, they must in the course
of successive generations have travelled from some one
point to all the others. We are often wholly unable even
to conjecture how this could have been effected. Yet,
as we have reason to believe that some species have re-
tained the same specific form for very long periods of
time, immensely long as measured by years, too much
stress ought not to be laid on the occasional wide diffu-
sion of the same species; for during very long periods
there will always have been a good chance for wide
migration by many means. A broken or interrupted
range may often be accounted for by the extinction of
the species in the intermediate regions. It cannot be
denied that we are as yet very ignorant as to the full
extent of the various climatal and geographical changes
which have affected the earth during modern periods;
and such changes will often have facilitated migration.
As an example, I have attempted to show how potent
has been the influence of the Glacial period on the dis-
tribution of the same and of allied species throughout
the world. We are as yet profoundly ignorant of the
many occasional means of transport. With respect to
distinct species of the same genus inhabiting distant
and isolated regions, as the process of modification has
necessarily been slow, all the means of migration will
have been possible during a very long period; and con-
sequently the difficulty of the wide diffusion of the
species of the same genus is in some degree lessened.

As according to the theory of natural selection an
interminable number of intermediate forms must have

279 RECAPITULATION. [Cuap. XV.

existed, linking together all the species in each group by
gradations as fine as are our existing varieties, it may be
asked, Why do we not see these linking forms all around
us? Why are not all organic beings blended together
in an inextricable chaos? With respect to existing forms,
we should remember that we have no right to expect
(excepting in rare cases) to discover directly connecting
links between them, but only between each and some
extinct and supplanted form. Even on a wide area,
which has during a long period remained continuous,
and of which the climatic and other conditions of life
change insensibly in proceeding from a district occupied
by one species into another district occupied by a closely
allied species, we have no just right to expect often to
find intermediate varieties in the intermediate zones.
For we have reason to believe that only a few species
of a genus ever undergo change; the other species be-
coming utterly extinct and leaving no modified progeny.
Of the species which do change, only a few within the
same country change at the same time; and all modi-
fications are slowly effected. I have also shown that the
intermediate varieties which probably at first existed
in the intermediate zones, would be liable to be sup-
planted by the allied forms on either hand; for the lat-
ter, from existing in greater numbers, would generally
be modified and improved at a quicker rate than the
intermediate varieties, which existed in lesser numbers;
so that the intermediate varieties would, in the long
run, be supplanted and exterminated.

On this doctrine of the extermination of an infini-
tude of connecting links, between the living and extinct
inhabitants of the world, and at each successive period
between the extinct and still older species, why is not

Cuap, XV.) RECAPITULATION. 273

every geological formation charged with such links?
W hy does not every collection of fossil remains afford
plain evidence of the gradation and mutation of the
forms of life? Although geological research has un-
doubtedly revealed the former existence of many links,
bringing numerous forms of life much closer together, it
does not yield the infinitely many fine gradations be-
tween past and present species required on the theory;
and this is the most obvious of the many objections which
may be urged against it. Why, again, do whole groups
of allied species appear, though this appearance is often
false, to have come in suddenly on the successive geologi-
cal stages? Although we now know that organic be-
ings appeared on this globe, at a period incalculably re-
mote, long before the lowest bed of the Cambrian system
was deposited, why do we not find beneath this system
great piles of strata stored with the remains of the pro-
genitors of the Cambrian fossils? For on the theory,
such strata must somewhere have been deposited at
these ancient and utterly unknown epochs of the world’s
history.

I can answer these questions and objections only on
the supposition that the geological record is far more im-
perfect than most geologists believe. The number of
specimens in all our museums is absolutely as nothing
compared with the countless generations of countless
species which have certainly existed. The parent-form
of any two or more species would not be in all its char-
acters directly intermediate between its modified off-
spring, any more than the rock-pigeon is directly inter-
mediate in crop and tail between its descendants, the
pouter and fantail pigeons. We should not be able to
recognise a species as the parent of another and modi-

274 RECAPITULATION. [CHap. XV.

fied species, if we were to examine the two ever so close-
ly, unless we possessed most of the intermediate links;
and owing to the imperfection of the geological record,
we have no just right to expect to find so many links.
If two or three, or even more linking forms were dis-
covered, they would simply be ranked by many natu-
ralists as so many new species, more especially if found
in different geological sub-stages, let their differences
be ever so slight. Numerous existing doubtful forms
could be named which are probably varieties; but who
will pretend that in future ages so many fossil links
will be discovered, that naturalists will be able to decide
whether or not these doubtful forms ought to be called
varieties? Only a small portion of the world has been
geologically explored. Only organic beings of certain
classes can be preserved in a fossil condition, at least
in any great number. Many species when once formed
never undergo any further change but become extinct
without leaving modified descendants; and the periods,
during which species have undergone modification,
though long as measured by years, have probably been
short in comparison with the periods during which
they retain the same form. It is the dominant and
widely ranging species which vary most frequently and
vary most, and varieties are often at first local—both
causes rendering the discovery of intermediate links in
any one formation less likely. Local varieties will not
spread into other and distant regions until they are
considerably modified and improved; and when they
have spread, and are discovered in a geological forma-
tion, they appear as if suddenly created there, and will
be simply classed as new species. Most formations have
been intermittent in their accumulation ;and their dura-

bau XV,] RECAPITULATION. 275
|

fon has probably been shorter than the average dura-
ton of specific forms. Successive formations are in
ot cas¢s separated from each other by blank intervals
ol,time of great length; for fossiliferous formations thick
enough to resist future degradation can as a general rule
be accumulated only where much sediment is deposited
on the subsiding bed of the sea. During the alternate
periods of elevation and of stationary level the record
will generally be blank. During these latter periods
there will probably be more variability in the forms of
life; during periods of subsidence, more extinction.

- With respect to the absence of strata rich in fossils
beneath the Cambrian formation, I can recur only to
the hypothesis given in the tenth chapter; namely, that
though our continents and oceans have endured for an
encrmous period in nearly their present relative posi-
tions, we have no reason to assume that this has always
been the case; consequently formations much older than
any now known may lie buried beneath the great oceans.
With respect to the lapse of time not having been suffi-
cient since our planet was consolidated for the assumed
amount of organic change, and this objection, as urged
by Sir William Thompson, is probably one of the gravest -
as yet advanced, I can only say, firstly, that we do not
know at what rate species change as measured by years,
and secondly, that many philosophers are not as yet
willing to admit that we know enough of the constitu-
tion of the universe and of the interior of our globe to
speculate with safety on its past duration.

That the geological record is imperfect all will admit;
but that it is imperfect to the degree required by our
theory, few will be inclined to admit. If we look to
long enough intervals of time, geology plainly declares

43

276 eens (Cuar. XV:

that species have all changed; and the have changed
in the manner required by the theory, for. they a
changed slowly and in a graduated manner. W.> clearl
see this in the fossil remains from consecutive foriations
invariably being much more closely related to each other,
than are the fossils from widely separated formations.

Such is the sum of the several chief objections and
difficulties which may be justly urged against the theory;
and I have now briefly recapitulated the answers and
explanations which, as far as I can see, may be given.
I have felt these difficulties far too heavily during many
years to doubt their weight. But it deserves especial
notice that the more important objections relate to ques-
tions on which we are confessedly ignorant; nor do
we know how ignorant we are. We do not know all
the possible transitional gradations between the simplest
and the most perfect organs; it cannot be pretended
that we know all the varied means of Distribution dur-
ing the long lapse of years, or that we know how im-
perfect is the Geological Record. Serious as these sev-
eral objections are, in my judgment they are by no means
sufficient to overthrow the theory of descent with sub-
sequent modification.

Now let us turn to the other side of the argument.
Under domestication we see much variability, caused, or
at least excited, by changed conditions of life; but often
in so obscure a manner, that we are tempted to consider
the variations as spontaneous. Variability is governed
by many complex laws,—by correlated growth, compen-
sation, the increased use and disuse of parts, and the
definite action of the surrounding conditions. There is
much difficulty in ascertaining how largely our domestic

Cuap, avi] RECAPITULATION. QT7

productions have been modified; but we may safely in-
fer that the amount has been large, and that modifica-
tions can be inherited for long periods. As long as the
conditions of life remain the same, we have reason to
believe that a modification, which has already been
inherited for many generations, may continue to be
inherited for an almost infinite number of generations.
On the other hand, we have evidence that variability
when it has once come into play, does not cease under
domestication for a very long period; nor do we know
that it ever ceases, for new varieties are still occasionally
produced by our oldest domesticated productions.

Variability is not actually caused by man; he only
unintentionally exposes organic beings to new condi-
tions of life, and then nature acts on the organisation
and causes it to vary. But man can and does select the
variations given to him by nature, and thus accumulates
them in any desired manner. He thus adapts animals
and plants for his own benefit or pleasure. He may
do this methodically, or he may do it unconsciously by
preserving the individuals most useful or pleasing to
him without any intention of altering the breed. It is
certain that he can largely influence the character of a
breed by selecting, in each successive generation, indi-
vidual differences so slight as to be inappreciable except
by an educated eye. This unconscious process of selec-
tion has been the great agency in the formation of the
most distinct and useful domestic breeds. That many
breeds produced by man have to a large extent the
character of natural species, is shown by the inextric-.
able doubts whether many of them are varieties or
aboriginally distinct species.

There is no reason why the principles which have

278 RECAPITULATION. [Cuar. XV

acted so efficiently under domestication should not have
acted under nature. In the survival of favoured indi-
viduals and races, during the constantly-recurrent
Struggle for Existence, we see a powerful and ever-
acting form of Selection. The struggle for existence
inevitably follows from the high geometrical ratio of
increase which is common to all organic beings. This
high rate of increase is proved by calculation,—by the
rapid increase of many animals and plants during a
succession of peculiar seasons, and when naturalised in
new countries. More individuals are born than can
possibly survive. A grain in the balance may determine
which individuals shall live and which shall die,—which
variety or species shall increase in number, and whicl.
shall decrease, or finally become extinct. As the indi-
viduals of the same species come in all respects into the
closest competition with each other, the struggle will
generally be most severe between them; it will be al-
most equally severe between the varieties of the same
species, and next in severity between the species of the
same genus. On the other hand the struggle will often
be severe between beings remote in the scale of nature.
The slightest advantage in certain individuals, at any
age or during any season, over those with which they
come into competition, or better adaptation in however
slight a degree to the surrounding physical conditiors,
will, in the long run, turn the balance.

With animals having separated sexes, there will be
in most cases a struggle between the males for the pos-
session of the females. The most vigorous males, or
those which have most successfully struggled with their
conditions of life, will generally leave most progeny.
But success will often depend on the males having spe-

Cuar. XV.] RECAPITULATION, 279

cial weapons, or means of defence, or charms; and a
‘light advantage will lead to victory. \

As geology plainly proclaims that each ‘land has
undergone great physical changes, we might | have ex-
pected to find that organic beings have varied under
nature, in the same way as they have varied under do-
mestication. And if there has been any variability
under nature, it would be an unaccountable fact if natu-
ral selection had not come into play. It has often been
asserted, but the assertion is incapable of proof, that the
amount of variation under nature is a strictly limited
quantity. Man, though acting on external characters
alone and often capriciously, can produce within a short
period a great result by adding up mere individual dif-
ferences in his domestic productions; and every one ad-
mits that species present individual differences. But,
besides such differences, all naturalists admit that natu-
ral varieties exist, which are considered sufficiently dis-
tinct to be worthy of record in systematic works. No
one has drawn any clear distinction between. individual
differences and slight varieties; or between more plainly
marked varieties and sub-species, and species. , On sepa-
rate continents, and on different parts of the same conti-
nent when divided by barriers of any kind, and on out-
lying islands, what a multitude of forms exist, which
some experienced naturalists rank as varieties, others. as
geographical races or sub-species, and others as distinct,
though closely allied species!

If then, animals and plants do vary, let it be ever so
slightly or slowly, why should not variations or indi-
vidual differences, which are in any way beneficial, be
preserved and accumulated through natural selection, or
the survival of the fittest? If man can by patience

280 / RECAPITULATION. [Cuap. XV.

,
i

select variations useful to him, why, under changing
and complex conditions of life, should not variations
useful to nature’s living products often arise, and be
preserved or selected? What limit can be put to this
power, act.ng during long ages and rigidly scrutinising
the whole constitution, structure, and habits of each
creature,—fawouring the good and rejecting the bad? I
can see no limit to this power, in slowly and beautifully
adapting each form to the most complex relations of life.
The theory of natural selection, even if we look no far-
ther than this, seems to be in the highest degree prob-
able. I have already recapitulated, as fairly as I could,
the opposed difficulties and objections: now let us turn
to the special facts and argumentsin favour of the theory.

On the view that species are only strongly marked
and permanent varieties, and that each species first
existed as a variety, we can see why it is that no line
of demarcation can be drawn between species, commonly
supposed t) have been produced by special acts of crea-
tion, and varieties which are acknowledged to have been
produced ly secondary laws. On this same view we can
understand how it is that in a region where many species
of a genus have been produced, and where they now
flourish, these same species should present many varie-
ties; for where the manufactory of species has been ac-
tive, we might expect, as a general rule, to find it still in
action; and this is the case if varieties be incipient spe-
cies. Moreover, the species of the larger genera, which
afford the greater number of varieties or incipient spe-
cies, retain to a certain degree the character of varieties;
for they differ from each other by a less amount of differ-
ence than do the species of smaller genera. The closely

Cuar. XV.) RECAPITULATION. 281
allied species also of the larger genera apparently have
restricted ranges, and in their affinities they are clustered
in little groups round other species—in both respects
resembling varieties. These are strange relations on
the view that each species was independently created,
but are intelligible if each existed first as a variety.

As each species tends by its geometrical rate of repro-
duction to increase inordinately in number; and as the
modified descendants of each species will be enabled to
increase by as much as they become more diversified in
habits and structure, so as to be able to seize on many
and widely different places in the economy of nature,
there will be a constant tendency in natural selection
to preserve the most divergent offspring of any one spe-
cies. Hence, during a long-continued course of modi-
fication, the slight differences characteristic of varie-
ties of the same species, tend to be augmented into the
greater differences characteristic of the species of the
same genus. New and improved varieties will inevitably
supplant and exterminate the older, less improved, and
intermediate varieties; and thus species are rendered to
a large extent defined and distinct objects. Dominant
species belonging to the larger groups within each class
tend to give birth to new and dominant forms; so that
each large group tends to become still larger, and at the
same time more divergent in character. But as all
groups cannot thus go on increasing in size, for the
world would not hold them, the more dominant groups
beat the less dominant. This tendency in the large
groups to go on increasing in size and diverging in char-
acter, together with the inevitable contingency of much
extinction, explains the arrangement of all the forms of
life in groups subordinate to groups, all within a few

282 RECAPITULATION. [Cuap. XV.

great classes, which has prevailed throughout all time.
This grand fact of the grouping of all organic beings
under what is called the Natural System, is utterly in-
explicable on the theory of creation.

As natural selection acts solely by accumulating
slight, successive, favourable variations, it can produce
no great or sudden modifications; it can act only by short
and slow steps. Hence, the canon of “ Natura non facit
saltum,” which every fresh addition to our knowledge
tends to confirm, is on this theory intelligible. We can
see why throughout nature the same general end is
gained by an almost infinite diversity of means, for
every peculiarity when once acquired is long inherited,
and structures already modified in many different ways
have to be adapted for the same general purpose. We
can, in short, see why nature is prodigal in variety,
though niggard in innovation. But why this should be
a law of nature if each species has been independently
created no man can explain.

Many other facts are, as it seems to me, explicable on
this theory. How strange it is that a bird, under the
form of a woodpecker, should prey on insects on the
ground; that upland geese which rarely or never swim,
should possess webbed feet; that a thrush-like bird
should dive and feed on sub-aquatic insects; and that a
petrel should have the habits and structure fitting it for
the life of an auk! and so in endless other cases. But
on the view of each species constantly trying to increase
im number, with natural selection always ready to adapt
the slowly varying descendants of each to any unoccu-
pied or ill-occupied place in nature, these facts cease to
be strange, or might even have been anticipated.

We can to a certain extent understand how it is that

Cuar. XV] RECAPITULATION. 283

there is so much beauty throughout nature; for this
may be largely attributed to the agency of selection.
That beauty, according to our sense of it, is not univer-
sal, must be admitted by every one who will look at some
venomous snakes, at some fishes, and at certain hideous
bats with a distorted resemblance to the human face.
Sexual selection has given the most brilliant colours,
elegant patterns, and other ornaments to the males, and
sometimes to both sexes of many birds, butterflies, and
other animals. With birds it has often rendered the
voice of the male musical to the female, as well as to
our ears. Flowers and fruit have been rendered con-
spicuous by brilliant colours in contrast with the green
foliage, in order that the flowers may be readily seen,
visited and fertilised by insects, and the seeds dissem-
inated by birds. How it comes that certain colours,
sounds, and forms should give pleasure to man and the
lower animals,—that is, how the sense of beauty in its
simplest form was first acquired,—we do not know any
more than how certain odours and flavours were first
rendered agreeable.

As natural selection acts by competition, it adapts
and improves the inhabitants of each country only in
relation to their co-inhabitants; so that we need feel no
surprise at the species of any one country, although on
the ordinary view supposed to have been created and
specially adapted for that country, being beaten and
supplanted by the naturalised productions from another
land. Nor ought we to marvel if all the contrivances
in nature be not, as far as we can judge, absolutely per-
fect, as in the case even of the human eye; or if some
of them be abhorrent to our ideas of fitness. We need
got marvel at the sting of the bee. when used against

284 RECAPITULATION. [Cuap. XV.

an enemy, causing the bee’s own death; at drones be-
ing produced in such great numbers for one single act,
and being then slaughtered by their sterile sisters; at
the astonishing waste of pollen by our fir-trees; at the
instinctive hatred of the queen-bee for her own fertile
daughters; at the ichneumonide feeding within the liv-
ing bodies of caterpillars; or at other such cases. The
wonder indeed is, on the theory of natural selection,
that more cases of the want of absolute perfection have
not been detected.

The complex and little known laws governing the
production of varieties are the same, as far as we can
judge, with the laws which have governed the produc-
tion of distinct species. In both cases physical condi-
tions seem to have produced some direct and definite
effect, but how much we cannot say. Thus, when varie-
ties enter any new station, they occasionally assume some
of the characters proper to the species of that station.
With both varieties and species, use and disuse seem to
have produced a considerable effect; for it is impossible
to resist this conclusion when we look, for instance, at
the logger-headed duck, which has wings incapable of
flight, in nearly the same condition as in the domestic
duck; or when we look at the burrowing tucu-tucu,
which is occasionally blind, and then at certain moles,
which are habitually blind and have their eyes covered
with skin; or when we look at the blind animals in-
habiting the dark caves of America and Europe. With
varieties and species, correlated variation seems to have
played an important part, so that when one part has
been modified other parts have been necessarily modi-
fied. With both varieties and species, reversions to long-
1ost characters occasionally occur. How inexplicable on

Cuar. XV] RECAPITULATION. 285

the theory of creation is the occasional appearance of
stripes on the shoulders and legs of the several species of
the horse-genus and of their hybrids! How simply is
this fact explained if we believe that these species are all
descended from a striped progenitor, in the same man-
ner as the several domestic breeds of the pigeon are de-
scended from the blue and barred rock-pigeon!

On the ordinary view of each species having been
independently created, why should specific characters,
or those by which the species of the same genus differ
from each other, be more variable than generic char-
acters in which they all agree? Why, for instance,
should the colour of a flower be more likely to vary in
any one species of a genus, if the other species possess
differently coloured flowers, than if all possessed the
same coloured flowers? If species are only well-marked
varieties, of which the characters have become in a high
degree permanent, we can understand this fact; for they
have already varied since they branched off from a
common progenitor in certain characters, by which they
have come to be specifically distinct from each other;
therefore these same characters would be more likely
again to vary than the generic characters which have
been inherited without change for an immense period.
It is inexplicable on the theory of creation why a part
developed in a very unusual manner in one species alone
of a genus, and therefore, as we may naturally infer,
of great importance to that species, should be eminently
liable to variation; but, on our view, this part has under-
gone, since the several species branched off from a
common progenitor, an unusual amount of variability
and modification, and therefore we might expect the
part generally to be still variable. But a part may be

286 RECAPITULATION. [Cuap. XV.

developed in the most unusual manner, like the wing
of a bat, and yet not be more variable than any other
structure, if the part be common to many subordinate
forms, that is, if it has been inherited for a very long
period; for in this case it will have been rendered con-
stant by long-continued natural selection.

Glancing at instincts, marvellous as some are, they
offer no greater difficulty than do corporeal structures
on the theory of the natural selection of successive,
slight, but profitable modifications. We can thus under-
stand why nature moves by graduated steps in endowing
different animals of the same class with their several
instincts. I have attempted to show how much light’
the principle of gradation throws on the admirable archi-
tectural powers of the hive-bee. Habit no doubt often
comes into play in modifying instincts; but it certainly
is not indispensable, as we see in the case of neuter in-
sects, which leave no progeny to inherit the effects of
long-continued habit. On the view of all the species of
the same genus having descended from a common parent,
and having inherited much in common, we can under-
stand how it is that allied species, when placed under
widely different conditions of life, yet follow nearly the
same instincts; why the thrushes of tropical and tem-
perate South America, for instance, line their nests with
mud like our British species. On the view of instincts
having been slowly acquired through natural selection,
we need not marvel at some instincts being not perfect
and liable to mistakes, and at many instincts causing
other animals to suffer.

If species be only well-marked and permanent varie-
ties, we can at once see why their crossed offspring should
follow the same complex laws in their degrees and kinds

Cuap. XV] RECAPITULATION. 287

of Tesemblance to their parents,—in being absorbed
into each other by successive crosses, and in other such
points,—as do the crossed offspring of acknowledged
varieties, This similarity would be a strange fact, if
species had been independently created and varieties
had been produced through secondary laws.

If we admit that the geological record is imperfect
to an extreme degree, then the facts, which the record
does give, strongly support the theory of descent with
modification. New species have come on the stage slow-
ly and at successive intervals; and the amount of change,
after equal intervals of time, is widely different in dif-
ferent groups. The extinction of species and of whole
groups of species which has played so conspicuous a
part in the history of the organic world,almost inevitably
follows from the principle of natural selection; for old
forms are supplanted by new and improved forms.
Neither single species nor groups of species reappear
when the chain of ordinary generation is once broken.
The gradual diffusion of dominant forms, with the slow
modification of their descendants, causes the forms of
life, after long intervals of time, to appear as if they had
changed simultaneously throughout the world. The fact
of the fossil remains of each formation being in some
degree intermediate in character between the fossils in
the formations above and below, is simply explained by
their intermediate position in the chain of descent. The
grand fact that all extinct beings can be classed with
all recent beings, naturally follows from the living and
the extinct being the offspring of common parents. As
species have generally diverged in character during their
‘long course of descent and modification, we can under-
stand why it is that the more ancient forms, or early

288 RECAPITULATION. , [Cmap. XV.
f

progenitors of each group, so often occupy a position
in some degree intermediate between existing groups.
Recent forms are generally looked upon as being, on the
whole, higher in the scale of organisation than ancient
forms; and they must be higher, in so far as the later
and more improved forms have conquered the older and
less improved forms in the struggle for life; they have
also generally had their organs more specialised for dif-
ferent functions. This fact is perfectly compatible with
numerous beings still retaining simple and but little
improved structures, fitted for simple conditions of life;
it is likewise compatible with some forms having retro-
graded in organisation, by having become at each stage
of descent better fitted for new and degraded habits of
life. Lastly, the wonderful law of the long endurance
of allied forms on the same continent,—of marsupials
in Australia, of edentata in America, and other such
cases,—is intelligible, for within the same country the
existing and the extinct will be closely allied by descent.

Looking to geographical distribution, if we admit
that there has been during the long course of ages much
migration from one part of the world to another, owing
to former climatal and geographical changes and to the
many occasional and unknown means of dispersal, then
we can understand, on the theory of descent with modi-
fication, most of the great leading facts in Distribution.
We can see why there should be so striking a parallelism
in the distribution of organic beings throughout space,
and in their geological succession throughout time; for
in both cases the beings have been connected by the
bond of ordinary generation, and the means of modifica-
tion have been the same. We see the full meaning of
the wonderful fact, which has struck every traveller

Cuar. XV,] RECAPITULATION. 289

namely, that on the same continent, under the most
diverse conditions, under heat and cold, on mountain
and lowland, on deserts and marshes, most of the inhabit-
ants within each great class are plainly related; for they
are the descendants of the same progenitors and early
colonists. On this same principle of former migration,
combined in most cases with modification, we can under-
stand, by the aid of the Glacial period, the identity of
some few plants, and the close alliance of many others,
on the most distant mountains, and in the northern and
southern temperate zones; and likewise the close alli-
ance of some of the inhabitants of the sea in the north-
ern and southern temperate latitudes, though separated
by the whole intertropical ocean. Although two coun-
tries may present physical conditions as closely similar as
the same species ever require, we need feel no surprise at
their inhabitants being widely different, if they have
been for a long period completely sundered from each
other; for as the relation of organism to organism is the
most important of all relations, and as the two countries
will have received colonists at various periods and in
different proportions, from some other country or from
each other, the course of modification in the two areas
will inevitably have been different.

On this view of migration, with subsequent modifica-
tion, we see why oceanic islands are inhabited by only
few species, but of these, why many are peculiar or
endemic forms. We clearly see why species belonging
to those groups of animals which cannot cross wide
spaces of the ocean, as frogs and terrestrial mammals, do
not inhabit oceanic islands; and why, on the other hand,
new and peculiar species of bats, animals which can
traverse the ocean, are often found on islands far dis-

290 RECAPITULATION. [Cuar. XV

tant from any continent. Such cases as the presence of
peculiar species of bats on oceanic islands and the ab-
sence of all other terrestrial mammals, are facts utterly
inexplicable on the theory of independent acts of crea-
tion.

The existence of closely allied or representative spe-
cies in any two areas, implies, on the theory of descent
with modification, that the same parent-forms formerly
inhabited both areas; and we almost invariably find that
wherever many closely allied species inhabit two areas,
some identical species are still common to both. Where-
ever many closely allied yet distinct species occur, doubt-
ful forms and varieties belonging to the same groups
likewise occur. It is a rule of high generality that the
inhabitants of each area are related to the inhabitants of
the nearest source whence immigrants might have been
derived. We see this in the striking relation of nearly
all the plants and animals of the Galapagos archipelago,
of Juan Fernandez, and of the other American islands,
to the plants and animals of the neighbouring American
mainland; and of those of the Cape de Verde archi-
pelago, and of the other African islands to the African
mainland. It must be admitted that these facts receive
no explanation on the theory of creation.

The fact, as we have seen, that all past and present
organic beings can be arranged within a few great classes,
in groups subordinate to groups, and with the extinct
groups often falling in between the recent groups, is
intelligible on the theory of natural selection with its
contingencies of extinction and divergence of character.
On these same principles we see how it is, that the mu-
tual affinities of the forms within each class are so com-
plex and circuitous. We see why certain characters

Cuap. XV,] RECAPITULATION, 291

are far more serviceable than others for classification ;—
why adaptive characters, though of paramount import-
eos to the beings, are of hardly any importance in
classification; why characters derived from rudimentary
parts, though of no service to the beings, are often of
high classificatory value; and why embryological char-
acters are often the most valuable of all. The real
affinities of all organic beings, in contradistinction to
their adaptive resemblances, are due to inheritance or
community of descent. The Natural System is a gene-
alogical arrangement, with the acquired grades of dif-
ference, marked by the terms, varieties, species, genera,
families, &¢.; and we have to discover the lines of de-
scent by the most permanent characters whatever they
may be and of however slight vital importance.

The similar framework of bones in the hand of a
man, wing of a bat, fin of the porpoise, and leg of the
horse,—the same number of vertebre forming the neck
of the giraffe and of the elephant,—and innumerable
other such facts, at once explain themselves on the theory
of descent with slow and slight successive modifications.
The similarity of pattern in the wing and in the leg of
a bat, though used for such different purpose,—in the
jaws and legs of a crab,—in the petals, stamens, and pis-
tils of a flower, is likewise, to a large extent, intelligible
on the view of the gradual modification of parts or or-
gans, which were aboriginally alike in an early progeni-
tor in each of these classes. On the principle of succes-
sive variations not always supervening at an early age,
and being inherited at a corresponding not early period
of life, we clearly see why. the embryos of mammals,
birds, reptiles, and fishes should be so closely similar, and

so unlike the adult forms. We may cease marvelling at
44

992 RECAPITULATION. ~ [Cuap. XV.

the embryo of an air-breathing mammal or bird having
branchial slits and arteries running in loops, like those
of a fish which has to breathe the air dissolved in water
by the aid of well-developed branchiz.

Disuse, aided sometimes by natural selection, will
often have reduced organs when rendered useless under
changed habits or conditions of life; and we can under-
stand on this view the meaning of rudimentary organs.
But disuse and selection will generally act on each crea-
ture, when it has come to maturity and has to play its
full part in the struggle for existence, and will thus have
little power on an organ during early life; hence the
organ will not be reduced or rendered rudimentary at
this early age. The calf, for instance, has inherited
teeth, which never cut through the gums of the upper
jaw, from an early progenitor having well-developed
teeth; and we may believe, that the teeth in the mature
animal were formerly reduced by disuse, owing to the
tongue and palate, or lips, having become excellently
fitted through natural selection to browse without their
aid; whereas in the calf, the teeth have been left un-
affected, and on the principle of inheritance at corre-
sponding ages have been inherited from a remote period
to the present day. On the view of each organism with
all its separate parts having been specially created, how
utterly inexplicable is it that organs bearing the plain
stamp of inutility, such as the teeth in the embryonic
calf or the shrivelled wings under the soldered wing-
covers of many beetles, should so frequently occur.
Nature may be said to have taken pains to reveal her
scheme of modification, by means of rudimentary organs,
of embryological and homologous structures, but we are
too blind to understand her meaning.

Cuap, XV.] CONCLUSION. 293

I have now recapitulated the facts and considerations
which have thoroughly convinced me that species have
been modified, during a long course of descent. This
has been effected chiefly through the natural selection
of numerous successive, slight, favourable variations;
aided in an important manner by the inherited effects of
the use and disuse of parts; and in an unimportant man-
ner, that is in relation to adaptive structures, whether
past or present, by the direct action of external condi-
tions, and by variations which seem to us in our ignor-
ance to arise spontaneously. It appears that I formerly
underrated the frequency and value of these latter forms
of variation, as leading to permanent modifications of
structure independently of natural selection. But as my
conclusions have lately been much misrepresented, and
it has been stated that I attribute the modification of
species exclusively to natural selection, I may be per-
mitted to remark that in the first edition of this work,
and subsequently, I placed in a most conspicuous posi-
tion—namely, at the close of the Introduction—the
following words: “I am convinced that natural selection
has been the main but not the exclusive means of modi-
fication.” This has been of no avail. Great is the power
of steady misrepresentation; but the history of science
shows that fortunately this power does not long endure.

It can hardly be supposed that a false theory would
explain, in so satisfactory a manner as does the theory
of natural selection, the several large classes of facts
above specified. It has recently been objected that this
is an unsafe method of arguing; but it is a method used
in judging of the common events of life, and has often
been used by the greatest natural philosophers. The
undulatory theory of light has thus been arrived at; and

294 CONCLUSION. | [Cuap. XV.
|

the belief in the revolution of the earth on its own axis
was until lately supported by hardly any direct evidence.
It is no valid objection that science as yet throws no
light on the far higher problem of the essence or origin
of life. Who can explain what is the essence of the
attraction of gravity? No one now objects to following
out the results consequent on this unknown element
of attraction; nowithstanding that Leibnitz formerly ac-
cused Newton of introducing “occult qualities and
miracles into philosophy.”

I see no good reason why the views given in this vol-
ume should shock the religious feelings of any one. It
is satisfactory, as showing how transient such impres-
sions are, to remember that the greatest discovery ever
made by man, namely, the law of the attraction of grav-
ity, was also attacked by Leibnitz, “as subversive of
natural, and inferentially of revealed, religion.” A cele-
brated author and divine has written to me that “he has
“ gradually learnt to see that it is just as noble a concep-
“tion of the Deity to believe that He created a few ori-
“ ginal forms capable of self-development into other and
“ needful forms, as to believe that He required a fresh act
“of creation to supply the voids caused by the action of
“ His laws.”

Why, it may be asked, until recently did nearly all
the most eminent living naturalists and geologists dis-
believe in the mutability of species. It cannot be as-
serted that organic beings in a state of nature are sub-
ject to no variation; it cannot be proved that the
amount of variation in the course of long ages is a lim-
ited quantity; no clear distinction has been, or can be,
drawn between species and well-marked varieties. It
cannot be maintained that species when intercrossed are

Cuap. XV,] CONCLUSION. 295

mvariably sterile, and varieties invariably fertile; or
that sterility isa special endowment and sign of creation.
The belief that species were immutable productions was
almost unavoidable as long as the history of the world
was thought to be of short duration; and now that we
have acquired some idea of the lapse of time, we are too
apt to assume, without proof, that the geological record
is so perfect that it would have afforded us plain evidence
of the mutation of species, if they had undergone mu-
tation.

But the chief cause of our natural unwillingness to
admit that one species has given birth to clear and dis-
tinct species, is that we are always slow in admitting
great changes of which we do not see the steps. The
difficulty is the same as that felt by so many geologists,
when Lyell first insisted that long lines of inland cliffs
had been formed, and great valleys excavated, by the
agencies which we see still at work. The mind cannot
possibly grasp the full meaning of the term of even a
million years; it cannot add up and perceive the full
effects of many slight variations, accumulated during an
almost infinite number of generations.

Although I am fully convinced of the truth of the
views given in this volume under the form of an abstract,
I by no means expect to convince experienced naturalists
whose minds are stocked with a multitude of facts all
viewed, during a long course of years, from a point of
view directly opposite to mine. It is so easy to hide
our ignorance under such expressions as the “ plan of
creation,” “unity of design,” &c., and to think that we
give an explanation when we only re-state a fact. Any
one whose disposition leads him to attach more weight
to unexplained difficulties than to the explanation of a

296 CONCLUSION. [Cuar. XV.

certain number of facts will certainly reject the theory.
A few naturalists, endowed with much flexibility of
mind, and who have already begun to doubt the immu-
tability of species, may be influenced by this volume;
but I look with confidence to the future,—to young and
rising naturalists, who will be able to view both sides of
the question with impartiality. Whoever is led to be-
lieve that species are mutable will do good service by
conscientiously expressing his conviction; for thus only
can the load of prejudice by which this subject is over-
whelmed be removed.

Several eminent naturalists have of late published
their belief that a multitude of reputed species in each
genus are not real species; but that other species are
real, that is, have been independently created. This
seems to me a strange conclusion to arrive at. They
admit that a multitude of forms, which till lately they
themselves thought were special creations, and which
are still thus looked at by the majority of naturalists,
and which consequently have all the external character-
istic features of true species,—they admit that these
have been produced by variation, but they refuse to
extend the same view to other and slightly different
forms. Nevertheless they do not pretend that they can
define, or even conjecture, which are the created forms
of life, and which are those produced by secondary laws.
They admit variation as a vera causa in one case, they
arbitrarily reject it in another, without assigning any
distinction in the two cases. The day will come when
this will be given as a curious illustration of the blind-
ness of preconceived opinion. These authors seem no
more startled at a miraculous act of creation than at an
ordinary birth. But do they really believe that at innu-

Cuap, XV} CONCLUSION. 297

merable periods in the earth’s history certain elemental
atoms have been commanded suddenly to flash into liv-
Ing tissues? Do they believe that at each supposed act
of creation one individual or many were produced?
Were all the infinitely numerous kinds of animals and
plants created as eggs or seed, or as full grown? and in
the case of mammals, were they created bearing the
false marks of nourishment from the mother’s womb?
Undoubtedly some of these same questions cannot be
answered by those who believe in the appearance or
creation of only a few forms of life, or of some one form
alone. It has been maintained by several authors that
it is as easy to believe in the creation of a million beings
as of one; but Maupertuis’ philosophical axiom “ of least
action” leads the mind more willingly to admit the
smaller number; and certainly we ought not to believe
that innumerable beings within each great class have
been created with plain, but deceptive, marks of descent
from a single parent.

As a record of a former state of things, I have re-
tained in the foregoing paragraphs, and elsewhere, sev-
eral sentences which imply that naturalists believe in the
separate creation of each species; and I have been much
censured for having thus expressed myself. But un-
doubtedly this was the general belief when the first edi-
tion of the present work appeared. I formerly spoke
to very many naturalists on the subject of evolution,
and never once met with any sympathetic agreement.
It is probable that some did then believe in evolution,
but they were either silent, or expressed themselves so
ambiguously that it was not easy to understand their
meaning. Now things are wholly changed, and almost
every naturalist admits the great principle of evolution.

298 CONCLUSION. [Cuap. XV.

There are, however, some who still think that species
have suddenly given birth, through quite unexplained
means, to new and totally different forms: but, as I
have attempted to show, weighty evidence can be op-
posed to the admission of great and abrupt modifications.
Under a scientific point of view, and as leading to fur-
ther investigation, but little advantage is gained by be-
lieving that new forms are suddenly developed in an in-
explicable manner from old and widely different forms,
over the old belief in the creation of species from the
dust of the earth.

It may be asked how far I extend the doctrine of the
modification of species. The question is difficult to
answer, because the more distinct the forms are which
we consider, by so much the arguments in favour of
community of descent become fewer in number and
less in force. But some arguments of the greatest weight
extend very far. All the members of whole classes
are connected together by a chain of affinities, and all
can be classed on the same principle, in groups sub-
ordinate to groups. Fossil remains sometimes tend
to fill up very wide intervals between existing
orders.

Organs in a rudimentary condition plainly show that
an early progenitor had the organ in a fully developed
condition; and this in some cases implies an enormous
amount of modification in the descendants. Through-
out whole classes various structures are formed on the
same pattern, and at a very early age the embryos closely
resemble each other. Therefore I cannot doubt that the
theory of descent with modification embraces all the
members of the same great class or kingdom. I believe
that animals are descended from at most only four or

Cuar. XV. CONCLUSION. 299

five progenitors, and plants from an equal or lesser
number,

Analogy would lead me one step farther, namely, to
the belief that all animals and plants are descended from
Some one prototype. But analogy may be a deceitful
guide. Nevertheless all living things have much in
common, in their chemical composition, their cellular
structure, their laws of growth, and their liability to in-
jurious influences. We see this even in so trifling a
fact as that the same poison often similarly affects plants
and animals; or that the poison secreted by the gall-
fly produces monstrous growths on the wild rose or oak-
tree. With all organic beings, excepting perhaps some
of the very lowest, sexual production seems to be es-
sentially similar. With all, as far as is at present known,
the germinal vesicle is the same; so that all organ-
isms start from a common origin. If we look even to
‘he two main divisions—namely, to the animal and
vegetable kingdoms—certain low forms are so far inter-
mediate in character that naturalists have disputed to
which kingdom they should be referred. As Professor
Asa Gray has remarked, “the spores and other repro-,
“ductive bodies of many of the lower alge may claim
“to have first a characteristically animal, and then an
“ unequivocally vegetable existence.” Therefore, on the
principle of natural selection with divergence of char-
acter, it does not seem incredible that, from some such
low and intermediate form, both animals and plants
may have been developed; and, if we admit this, we
must likewise admit that all the organic beings which
have ever lived on this earth may be descended from
some one primordial form. But this inference is chiefly
grounded on analogy, and it is immaterial whether or

300 CONCLUSION. [Cuap. XV,

not it be accepted. No doubt it is possible, as Mr. G.
H. Lewes has urged, that at the first commencement of
life many different forms were evolved; but if so, we
may conclude that only a very few have left modified
descendants. For, as I have recently remarked in regard
to the members of each great kingdom, such as the Ver-
tebrata, Articulata, &c., we have distinct evidence in
their embryological, homologous, and rudimentary struc-
tures, that within each kingdom all the members are
descended from a single progenitor.

When the views advanced by me in this volume, and
by Mr. Wallace, or when analogous views on the origin
of species are generally admitted, we can dimly foresee
that there will be a considerable revolution in natural
history. Systematists will be able to pursue their la-
bours as at present; but they will not be incessantly
haunted by the shadowy doubt whether this or that form
be a true species. This, I feel sure and I speak after ex-
perience, will be no slight relief. The endless disputes
whether or not some fifty species of British brambles
are good species will cease. Systematists will have only
to decide (not that this will be easy) whether any form
be sufficiently constant and distinct from other forms.
to be capable of definition; and if definable, whether
the differences be sufficiently important to deserve a
specific name. This latter point will become a far more
essential consideration than it is at present; for differ-
ences, however slight, between any two forms, if not
blended by intermediate gradations, are looked at by
most naturalists as sufficient to raise both forms to the
tank of species.

Hereafter we shall be compelled to acknowledge that
the only distinction between species and well-marked

Cuap. XV.] CONCLUSION. 301

Varieties is, that the latter are known, or believed, to be
connected at the present day by intermediate gradations,
whereas species were formerly thus connected. Hence,
Without rejecting the consideration of the present exist-
ence of intermediate gradations between any two forms,
we shall be led to weigh more carefully and to value
higher the actual amount of difference between them.
It is quite possible that forms now generally acknowl-
edged to be merely varieties may hereafter be thought
worthy of specific names; and in this case scientific and
common language will come into accordance. In short,
we shall have to treat species in the same manner as
those naturalists treat genera, who admit that genera
are merely artificial combinations made for convenience.
This may not be a cheering prospect; but we shall at
least be free from the vain search for the undiscovered
and undiscoverable essence of the term species.

The other and more general departments of natural
history will rise greatly in interest. The terms used
by naturalists, of affinity, relationship, community of
type, paternity, morphology, adaptive characters, rudi-
mentary and aborted organs, &c., will cease to be meta-
phorical, and will have a plain signification. When we
no longer look at an organic being as a savage looks at
a ship, as something wholly beyond his comprehension;
when we regard every production of nature as one which
has had a long history; when we contemplate every
complex structure and instinct as the summing up of
many contrivances, each useful to the possessor, in the
same way as any great mechanical invention is the sum-
ming up of the labour, the experience, the reason, and
even the blunders of numerous workmen; when we thus
view each organic being, how far more interesting—I

802 CONCLUSION. [Cuap. XV.

speak from experience—does the study of natural history
become!

A grand and almost untrodden field of inquiry will
be opened, on the causes and laws of variation, on cor-
relation, on the effects of use and disuse, on the direct
action of external conditions, and so forth. The study
of domestic productions will rise immensely in value.
A new variety raised by man will be a more important
and interesting subject for study than one more species
added to the infinitude of already recorded species.
Our classifications will come to be, as far as they can
be so made, genealogies; and will then truly give what
may be called the plan of creation. The rules for classi-
fying will no doubt become simpler when we have a defi-
nite object in view. We possess no pedigrees or armorial
bearings; and we have to discover and trace the many
diverging lines of descent in our natural genealogies, by
characters of any kind which have long been inherited.
Rudimentary organs will speak infallibly with respect
to the nature of long-lost structures. Species and groups
of species which are called aberrant, and which may
fancifully be called living fossils, will aid us in form-
ing a picture of the ancient forms of life. Embryology
will often reveal to us the structure, in some degree ob-
scured, of the prototypes of each great class.

When we can feel assured that all the individuals
of the same species, and all the closely allied species
of most genera, have within a not very remote period
descended from one parent, and have migrated from
some one birth-place; and when we better know the
many means of migration, then, by the light which
geology now throws, and will continue to throw, on
former changes of climate and of the level of the land,

Cuar. XV] CONCLSION. 303

we shall surely be enabled to trace in an admirable
manner the former migrations of the inhabitants of the
whole world. Even at present, by comparing the differ-
ences between the inhabitants of the sea on the opposite
sides of a continent, and the nature of the various in-
habitants on that continent in relation to their apparent
means of immigration, some light can be thrown on
ancient geography.

The noble science of Geology loses glory from the
extreme imperfection of the record. The crust of the
earth with its imbedded remains must not be looked at
as a well-filled museum, but as a poor collection made at
hazard and at rare intervals. The accumulation of each
great fossiliferous formation will be recognised as having
depended on an unusual concurrence of favourable cir-
cumstances, and the blank intervals between the suc-
cessive stages as having been of vast duration. But we
shall be able to gauge with some security the duration
of these intervals by a comparison of the preceding and
succeeding organic forms. We must be cautious in at-
tempting to correlate as strictly contemporaneous two
formations, which do not include many identical species,
by the general succession of the forms of life. As spe-
jes are produced and exterminated by slowly acting
and still existing causes, and not by miraculous acts of
creatNon; and as the most important of all causes of
organic\ change is oné which is almost independent of
altered fs perhaps suddenly altered physical conditions,

namely, {the mutual relation of organism to organism,—
the imp:#4ovement of one organism entailing the improve-
ment o°3t'tausted ination of others; it follows, that the
amov‘2> Damely, the prece in the fossils of consecutive

forntly follows. There is gi.as a fair measure of the

304 CONCLUSION. [Cuap. XV.

relative though not actual lapse of time. A number
of species, however, keeping in a body might remain for
a long period unchanged, whilst within the same period
several of these species by migrating into new countries
and coming into competition with foreign associates,
might become modified; so that we must not overrate
the accuracy of organic change as a measure of time.

In the future I see open fields for far more important
researches. Psychology will be securely based on the
foundation already well laid by Mr. Herbert Spencer,
that of the necessary acquirement of each mental power
and capacity by gradation. Much light will be thrown
on the origin of man and his history.

Authors of the highest eminence seem to be fully
satisfied with the view that each species has been in-
dependently created. To my mind it accords better
with what we know of the laws impressed on matter by
the Creator, that the production and extinction of the
past and present inhabitants of the world should have
been due to secondary causes, like those determining the
birth and death of the individual. When I view all
beings not as special creations, but as the lineal descend-

ants of some few beings which lived long before the first _ |.

bed of the Cambrian system was deposited, they sce
to me to become ennobled. Judging from the past, A
may safely infer that not one living species will tr Ai
its unaltered likeness to a distant futurity. Andfec of the
species now living very few will transmit pro Fpery of
any kind to a far distant futurity; for the maWtroyer in
which all organic beings are grouped, shows tw tit the
greater number of species in each ~the hyuu whi] the
species in many genera, have Icitinue to throw, o. hit
have become utterly extira of the level of the land, q

Cua XV] CONCLUSION. 305

Propaetic glance into futurity as to foretell that it will
be the common and widely-spread species, belonging to
the larger and dominant groups within each class, which
will ultimately prevail and procreate new and dominant
species. As all the living forms of life are the lineal
descendants of those which lived long before the Cam-
brian epoch, we may feel certain that the ordinary suc-
cession by generation has never once been broken, and
that no cataclysm has desolated the whole world. Hence
we may look with some confidence to a secure future
of great length. And as natural selection works solely
by and for the good of each being, all corporeal and
mental endowments will tend to progress towards per-
fection.

It is interesting to contemplate a tangled bank,
clothed with many plants of many kinds, with birds
singing on the bushes, with various insects flitting about,
and with worms crawling through the damp earth, and
to reflect that these elaborately constructed forms, so
different from each other, and dependent upon each
other in so complex a manner, have all been produced
by laws acting around us. These laws, taken in the
largest sense, being Growth with Reproduction; Inherit-
ance which is almost implied by reproduction; Varia-
bility from the indirect and direct action of the condi-
tions of life, and from use and disuse: a Ratio of In-
crease so high as to lead to a Struggle for Life, and as

consequence to Natural Selection, entailing Divergence
f Character and the Extinction of less-improved forms.
Thus, from the war of nature, from famine and death,
he most exalted object which we are capable of con-
ceiving, namely, the production of the higher animals,
directly follows. There is grandeur in this view of life,

306 CONCLUSION. [Cuap.: XV,

with its several powers, having been originally breathed
by the Creator into a few forms or into one; and that,
whilst this planet has gone cycling on according to the
fixed law of gravity, from so simple a beginning endless
forms most beautiful and most wonderful have been, and
are being evolved.

GLOSSARY

OF THE

PRINCIPAL SCIENTIFIC TERMS USED IN THE
PRESENT VOLUME.*

ABERRANT.—Forms or groups of animals or plants which deviate
in important characters from their nearest allies, so as not to
be easily included in the same group with them, are said to be
aberrant.

ABERRATION (in Optics).—In the refraction of light by a convex lens
the rays passing through different parts of the lens are brought
toa focus at slightly different distances,—this is called spherical
aberration ; at the same time the coloured rays are separated
by the prismatic action of the lens and likewise brought to a
focus at different distances,—this is chromatic aberration.

ABNORMAL.—Contrary to the general rule.

ABORTED.—An organ is said to be aborted, when its development
has been arrested at a very early stage.

ALBINISM.—Albinos are animals in which the usual colouring
matters characteristic of the species have not been produced in
the skin and its appendages. Albinism is the state of being
an albino.

Axe#,—A class of plants including the ordinary sea-weeds and the
filamentous fresh-water weeds.

*Tam indebted to the kindness of Mr. W.S. Dallas for this
Glossary, which has been given because several readers have com-
plained to me that some of the ‘erms used were unintelligible to
them. Mr. Dallas has endeavoured to give the explanations of the
terms in as popular a form as possible.

45

308 GLOSSARY.

ALTERNATION OF GENERATIONS.—This term is applied to a peculiar
mode of reproduction which prevails among many of the lower
animals, in which the egg produces a living form quite differ-
ent from its parent, but from which the parent-form is repro-
duced by a process of budding, or by the division of the
substance of the first product of the egg.

AmMonitTEs,—A group of fossil, spiral, chambered shells, allied to
the existing pearly Nautilus, but having the partitions be-
tween the chambers waved in complicated patterns at their
junction with the outer wall of the shell.

ANnaLocy.—That resemblance of structures which depends upon
similarity of function, as in the wings of insects and birds.
Such structures are said to be analogous, and to be analogues
of each other.

ANIMALCULE.—A minute animal: generally applied to those visible
only by the microscope.

ANNELIDS.—A class of worms in which the surface of the body ex-
hibits a more or less distinct division into rings or segments,
generally provided with appendages for locomotion and with
gills. It includes the ordinary marine worms, the earthworms,
and the leeches.

AnTEenn#&.—Jointed organs appended to the head in Insects, Crus-
tacea and Centipedes, and not belonging to the mouth.

ANTHERS.—The summits of the stamens of flowers, in which the
pollen or fertilising dust is produced.

APLACENTALIA, APLACENTATA or Aplacental Mammals, See Mam-
malia.

ARcHETYPAL.—Of or belonging to the Archetype, or ideal primi-
tive form upon which all the beings of a group seem to be
organised.

ArticuLata.—A great division of the Animal Kingdom character-
ised generally by having the surface of the body divided into
rings called segments, a greater or less number of which are
furnished with jointed legs (such as Insects, Crustaceans and
Centipedes).

ASYMMETRICAL.—Having the two sides unlike.

ATROPHIED.—Arrested in development at a very early stage.

BaLanus.—The genus including the common Acorn-shells which
live in abundance on the rocks of the sea-coast.
Batracuians.—A class of animals allied to the Reptiles, but

GLOSSARY. 309

undergoing a peculiar metamorphosis, in which the young
animal is generally aquatic and breathes by gills. (Ezamples,

z Frogs, Toads, and Newts.)

BouLprxs.—Large transported blocks of stone generally imbedded
in clays or gravels.

Bracniopopa.—A class of marine Mollusca, or soft-bodied animals,
furnished with a bivalve shell, attached to submarine objects
by a stalk which passes through an aperture in one of the

“ valves, and furnished with fringed arms, by the action of
which food is carried to the mouth.

Brancui#,—Gills or organs for respiration in water.

BrancutaL.—Pertaining to gills or branchiz.

CampBrian System.—A Series of very ancient Paleozoic rocks,
between the Laurentian and the Silurian. Until recently
these were regarded as the oldest fossiliferous rocks.

Canip£,—The Dog-family, including the Dog, Wolf, Fox, Jackal, &c.

Carapace.—The shell enveloping the anterior part of the body in
Crustaceans generally; applied also to the hard shelly pieces
of the Cirripedes.

CaRponireRous.—This term is applied to the great formation
which includes, among other rocks, the coal-measures. It be-
longs to the oldest, or Paleozoic, system of formations.

CaupaL.—Of or belonging to the tail.

CrpHaLopops.—The highest class of the Mollusca, or soft-bodied
animals, characterised by having the mouth surrounded by a
greater of less number of fleshy arms or tentacles, which, in
most living species, are furnished with sucking-cups. (Hz-
amples, Cuttle-fish, Nautilus.)

Ceracea.—An order of Mammalia, including the Whales, Dolphins,
&c., having the form of the body fish-like, the skin naked, and
only the fore-limbs developed.

CuELonta.—An order of Reptiles including the Turtles, Tortoises,
&e.

Crrgivepes.—An order of Crustaceans including the Barnacles and
Acorn-shells. Their young resemble those of many other
Crustaceans in form; but when mature they are always at-
tached to other objects, either directly or by means of a stalk,
and their bodies are enclosed by a calcareous shell composed of
several pieces, two of which can open to give issue to a bunch
of curled, jointed tentacles, which represent the limbs.

310 GLOSSARY.

Coccus.—The genus of Insects including the Cochineal. In these
the male is a minute, winged fly, and the female generally a
motionless, berry-like mass.

Cocoon.—A case usually of silky material, in which insects are
frequently enveloped during the second or resting-stage (pupa)
of their existence. The term “cocoon-stage” is here used as
equivalent to “ pupa-stage.” :

Ca Lospermous.—A term applied to those fruits of the Umbellif-
ere which have the seed hollowed on the inner face. :

CoLzoprera.—Beetles, an order of Insects, having a biting mouth
and the first pair of wings more or less horny, forming sheaths
for the second pair, and usually meeting in a straight line
down the middle of the back.

CoLumy.—A peculiar organ in the flowers of Orchids, in which
the stamens, style and stigma (or the reproductive parts) are
united.

Composrrz or Composrrous PLants.—Plants in which the inflores-
cence consists of numerous small flowers (florets) brought to-
gether into a dense head, the base of which is enclosed by a
common envelope. (Examples, the Daisy, Dandelion, &c.)

ConFERvV#.—The filamentous weeds of fresh water.

ConeLomMERATE.—A rock made up of fragments of rock or pebbles,
cemented together by some other material.

CoroLLa.—The second envelope of a flower usually composed of
coloured, leaf-like organs (petals), which may be united by
their edges either in the basal part or throughout.

CorRELATION.—The normal coincidence of one phendmenon, char-
acter, &c., with another.

Coryms.—A bunch of flowers in which those springing from the
lower part of the flower stalk are supported on long stalks so
as to be nearly on a level with the upper ones.

CotyLepons.—The first or seed-leaves of plants.

CrustacEans.—A class of articulated animals, having the skin of
the body generally more or less hardened by the deposition of
caleareous matter, breathing by means of gills. (Hzamples,
Crab, Lobster, Shrimp, &c.)

Curcutio.—The old generic term for the Beetles known as Wee-
vils, characterised by their four-jointed feet, and by the head
being produced into a sort of beak, upon the sides of which
the antenne are inserted.

Cutaneous.—Of or belonging to the skin,

GLOSSARY. 311

Drerapation.—The wearing down of land by the action of the sea
or of meteoric agencies,

Denupatioy.—The wearing away of the surface of the land by
water,

Devonian System or formation.—A series of Paleozoic rocks, in-
cluding the Old Red Sandstone.

DicotyLepons or DicoryLeponous Puants.—A class of plants
characterised by having two seed-leaves, by the formation of
new wood between the bark and the old wood (exogenous
growth) and by the reticulation of the veins of the leaves.
The parts of the flowers are generally in multiples of five.

Dirrerentiation.—The separation or discrimination of parts or
organs which in simpler forms of life are more or less
united,

Dimorpuic.—Having two distinct forms.—Dimorphism is the con-
dition of the appearance of the same species under two dis-
similar forms,

Draciovs.—Having the organs of the sexes upon distinct indi-
viduals.

Diorirz.—A peculiar form of Greenstone.

Dorsau.—Of or belonging to the back.

Epeytata.—A peculiar order of Quadrupeds, characterised by the
absence of at least the middle incisor (front) teeth in both
jaws. (Examples, the Sloths and Armadillos.)

E.yrra.—The hardened fore-wings of Beetles, serving as sheaths
for the membranous hind-wings, which constitute the true
organs of flight.

Empryo.—The young animal undergoing development within the
egg or womb.

EmpryoLocy.—The study of the development of the embryo.

Enpemic.—Peculiar to a given locality.

Enromostraca.—A division of the class Crustacea, having all the
segments of the body usually distinct, gills attached to the
feet or organs of the mouth, and the feet fringed with fine
hairs. They are generally of small size.

Eocrenz.—The earliest of the three divisions of the Tertiary epock
of geologists. Rocks of this age contain a small proportion of
shells identical with species now living.

Epuemerovs Insects,—Insects allied to the May-fly.

312 GLOSSARY.

Fauna.—The totality of the animals naturally inhabiting a cer-
tain country or region, or which have lived during a given
geological period.

Fe.iva.—The Cat-family.

Ferau.—Having become wild from a state of cultivation or domes-
tication.

Fiora.—The totality of the plants growing naturally in a country,
or during a given geological period.

FLorets.—Flowers imperfectly developed in some respects, and
collected into a dense spike or head, as in the Grasses, the
Dandelion, &c,

Fartau.—Of or belonging to the fcetus, or embryo in course of de-
velopment.

ForaMINIFERA.—A class of animals of very low organisation, and
generally of small size, having a jelly-like body, from the sur-
face of which delicate filaments can be given off and retracted
for the prehension of external objects, and having a calcareous
or sandy shell, usually divided into chambers, and perforated
with small apertures.

Fossitirerous.—Containing fossils.

Fossor1aL.—Having a faculty of digging. The Fossorial Hymen-
optera are a group of Wasp-like Insects, which burrow in
sandy soil to make nests for their young.

Frenum (pl. Frena).—A small band or fold of skin.

Funai (sing. Funeus).—A class of cellular plants, of which Mush-
rooms, Toadstools, and Moulds, are familiar examples,

Furcuta.—The forked bone formed by the union of the collar-
bones in many birds, such as the common Fowl.

Gatuinacrous Brrps.—An order of Birds of which the common
Fowl, Turkey, and Pheasant, are well-known examples.

Gauttus.—The genus of birds which includes the common Fowl.

GanoLion.—A swelling or knot from which nerves are given off as
from a centre.

Ganorp FisHes.—Fishes covered with peculiar enamelled bony
scales. Most of them are extinct.

GrrMinaL VESICLE.—A minute vesicle in the eggs of animals, from
which development of the embryo proceeds.

GuaciaL PEriop.—A period of great cold and of enormous exten-
sion of ice upon the surface of the earth. It is believed that
glacial periods have occurred repeatedly during the geological

GLOSSARY. 313

history of the earth, but the term is generally applied to the
close of the Tertiary epoch, when nearly the whole of Europe
was subjected to an arctic climate. '

GLanp.—An organ which secretes or separates some peculiar prod-
uct from the blood or sap of animals or plants.

Gorris.—The opening of the windpipe into the oesophagus or
gullet.

Gnetss.—A rock approaching granite in composition, but more or
less laminated, and really produced by the alteration of a sedi-
mentary deposit after its consolidation.

GRALLATORES.—The so-called Wading-birds (Storks, Cranes, Snipes,
&e.), which are generally furnished with long legs, bare of
feathers above the heel, and have no membranes between the
toes.

Granite.—A rock consisting essentially of crystals of felspar and
mica in a mass of quartz.

Hasitat.—The locality in which a plant or animal naturally lives.

Hemrptera.—An order or sub-order of Insects, characterised by
the possession of a jointed beak or rostrum, and by having the
fore-wings horny in the basal portion and membranous at the
extremity, where they cross each other. This group includes
the various species of Bugs.

HERMAPHRODITE.—Possessing the organs of both sexes,

Homotoey.—That relation between parts which results from their
development from corresponding embryonic parts, either in
different animals, as in the case of the arm of man, the fore-
leg of a quadruped, and the wing of a bird; or in the same in-
dividual, as in the case of the fore and hind legs in quadrupeds,
and the segments or rings and their appendages of which the
body of a worm, a centipede, &c., is composed. The latter is ©
called serial homology. The parts which stand in such a rela-
tion to each other are said to be homologous, and one such part
or organ is called the homologue of the other. In different
plants the parts of the flower are homologous, and in general
these parts are regarded as homologous with leaves.

Homortera.—An order or sub-order of Insects having (like the
Hemiptera) a jointed beak, but in which the fore-wings are
either wholly membranous or wholly leathery. The Cicade,
Frog-hoppers, and Aphides, are well-known examples.

Hysrip.—The offspring of the union of two distinct species.

314 GLOSSARY.

Hymenoprera.—An order of insects possessing biting jaws and
usually four membranous wings in which there are a few veins,
Bees and Wasps are familiar examples of this group.

HA ypPerRtTROPHIED.—Excessively developed.

Icuneumonip&,—A family of Hymenopterous insects, the mem-
bers of which lay their eggs in the bodies or eggs of other
insects.

Imaco.—The perfect (generally winged) reproductive state of an
insect.

Invicens.—The aboriginal animal or vegetable inhabitants of a
country or region.

InFLORESCENCE.—The mode of arrangement of the flowers of plants.

Inrusor1a.—A class of microscopic Animalcules, so called from
their having originally been observed in infusions of vegetable
matters. They consist of a gelatinous material enclosed in ¥
delicate membrane, the whole or part of which is furnisher\
with short vibrating hairs (called cilia), by means of which the
animalcules swim through the water or convey the minute par.
ticles of their food to the orifice of the mouth.

4NSECTIVOROUS.— Feeding on Insects.

INVERTEBRATA, or INVERTEBRATE ANIMALS.—Those animals which
do not possess a backbone or spinal column.

Lacuna.—Spaces left among the tissues in some of the lower ani-
mals, and serving in place of vessels for the circulation of the
fluids of the body.

LamELLATED.—Furnished with lamella or little plates.

Larva (pl. Larva).—The first condition of an insect at its issuing
from the egg, when it is usually in the form of a grub, cater-
pillar, or maggot.

Larynx.—The upper part of the windpipe opening into the gullet.

LavREvtian.—aA group of greatly altered and very ancient rocks,
which is greatly developed along the course of the St. Lau-
rence, whence thename. It is in these that the earliest known
traces of organic bodies have been found.

Leaumtnos#.—An order of plants represented by the common Peas
and Beans, having an irregular flower in which one petal stands
up like a wing, and the stamens and pistil are enclosed in a
sheath formed by two other petals, The fruit is a pod (or
legume).

GLOSSARY. 315

Lenuripa,—A group of four-handed animals, distinct from the
Monkeys and approaching the Insectivorous Quadrupeds in
some of their characters and habits. Its members have the
nostrils curved or twisted, and a claw instead of a nail upon
the first finger of the hind hands.

LePmorrera.—An order of Insects, characterised by the posses-
sion of a spiral proboscis, and of four large more or less
sealy wings. It includes the well-known Butterflies and
Moths.

Lirrora..—Inhabiting the seashore.

Lozss.—A marly deposit of recent (Post-Tertiary) date, which
occupies a great part of the valley of the Rhine.

Mauacosrraca.—The higher division of the Crustacea, including
the ordinary Crabs, Lobsters, Shrimps, &c., together with the
Woodlice and Sand-hoppers.

Mamatia.—tThe highest class of animals, including the ordinary
hairy quadrupeds, the Whales, and Man, and characterised by
the production of living young which are nourished after birth
by milk from the teats (Mamme, Mammary glands) of the
mother. A striking difference in embryonic development has
led to the division of this class into two great groups; in one
of these, when the embryo has attained a certain stage, a vas-
cular connection, called the placenta, is formed between the
embryo and the mother; in the other this is wanting, and the
young are produced in a very incomplete state. The former,
including the greater part of the class, are called Placental
mammals ; the latter, or Aplacental mammals, include the
Marsupials and Monotremes (Ornithorhynchus).

Mammirerous. Having mamma or teats (see MAMMALIA).

ManpiB.es, in Insects.—The first or uppermost pair of jaws, which
are generally solid, horny, biting organs. In Birds the term is
applied to both jaws with their horny coverings. In Quadru-
peds the mandible is properly the lower jaw.

Marsuprats.—An order of Mammalia in which the young are born
in a very incomplete state of development, and carried by the
mother, while sucking, in a ventral pouch (marsupium), such
as the Kangaroos, Opossums, &c. (see MAMMALIA).

MaxILL@, in Insects.—The second or lower pair of jaws, which are
composed of several joints and furnished with peculiar jointed

appendages called palpi, or feelers,

816 GLOSSARY,

MELANISM.—The opposite of albinism; an undue development of
colouring material in the skin and its appendages.

Mertamorpuic Rocxs.—Sedimentary rocks which have undergone
alteration, generally by the action of heat, subsequently to
their deposition and consolidation.

Mo.uiusca.—One of the great divisions of the Animal Kingdom,
including those animals which have a soft body, usually
furnished with a shell, and in which the nervous ganglia, or
centres, present no definite general arrangement. ‘hey are
generally known under the denomination of “ shell-fish ;” the
cuttle-fish, and the common snails, whelks, oysters, mussels,
and cockles, may serve as examples of them.

MonocoTyLepons, or MonocoryLeponous Puants.— Plants in
which the seed sends up only a single seed-leaf (or cotyledon) ;
characterised by the absence of consecutive layers of wood ip
the stem (endogenous growth), by the veins of the leaves being
generally straight, and by the parts of the flowers being gener-
ally in multiples of three. (Hxzamples, Grasses, Lilies, Orchids,
Palms, &c.)

Moraines.—The accumulations of fragments of rock brought down
by glaciers,

Morpuotocy.—The law of form or structure independent of
function.

Mysis-stace.—A stage in the development of certain Crustaceans
(Prawns), in which they closely resemble the adults of a genus
(Mysvs) belonging to a slightly lower group.

Nascent.—Commencing development.

Natatory.—Adapted for the purpose of swimming.

Nauptius-rorm.—The earliest stage in the development of many
Crustacea, especially belonging to the lower groups. In this
stage the animal has a short body, with indistinct indications
of a division into segments, and three pairs of fringed limbs.
This form of the common fresh-water Cyclops was described
as a distinct genus under the name of Nauplius.

NeEvuration.—The arrangement of the veins or nervures in the
wings of Insects.

Neurers.—Imperfectly developed females of certain social insects
(such as Ants and Bees), which perform all the labours of the
community. Hence they are also called workers.

Nictirating MemBrane.—A semi-transparent membrane, which

GLOSSARY. 317

can be drawn across the eye in Birds and Reptiles, either to
moderate the effects of a strong light or to sweep particles of
dust, &c., from the surface of the eye,

OcELLI.—The simple eyes or stemmata of Insects, usually situated
on the crown of the head between the great compound eyes.

Csorzacus.—The gullet.

Oouitic.—A great series of secondary rocks, so called from the
texture of some of its members, which appear to be made up
of a mass of small egg-like calcareous bodies,

OPERCULUM.—A calcareous plate employed by many Mollusca to
close the aperture of their shell. The opercular valves of Cir-
ripedes are those which close the aperture of the shell.

Onsit,—The bony cavity for the reception of the eye.

OneanisM.—An organised being, whether plant or animal.

OxtTHosPeRMoUS.—A term applied to those fruits of the Umbel-
liferee which have the seed straight.

OscuLant.—Forms or groups apparently intermediate between and
connectmg other groups are said to be osculant.

Ova.—Eggs.

Ovazium or Ovary (in plants).—The lower part of the pistil or
female organ of the flower, containing the ovules or incipient
seeds; by growth after the other organs of the flower have
fallen, it usually becomes converted into the fruit.

OvicERovs,—Egg-bearing.

Ovutes (of plants).—The seeds in the earliest condition.

Pacuyperms.—A group of Mammalia, so called from their thick
skins, and including the Elephant, Rhinoceros, Hippopotamus,
&e.

Pa.zozorc.—The oldest system of fossiliferous rocks.

Patp1.—Jointed appendages to some of the organs of the mouth in
Insects and Crustacea.

Papitionacea&.—An order of Plants (see Leauminos&).—The
flowers of these plants are called papilionaceous, or butterfly-
like, from the fancied resemblance of the expanded superior
petals to the wings of a butterfly.

Parasite.—An animal or plant living upon or in, and at the ex-
pense of, another organism.

PARTHENOGENESIS.—The production of living organisms from un-

impregnated eggs or seeds.

8318 GLOSSARY.

PEDUNCULATED.—Supported upon a stem or stalk. The peduncu-
lated oak has its acorns borne upon a footstalk.

Pe.oria or PeLorisM.—The appearance of regularity of structure
in the flowers of plants which normally bear irregular flowers.

PeLvis.—The bony arch to which the hind limbs of vertebrate
animals are articulated.

Perats.—The leaves of the corolla, or second circle of organs in
a flower. They are usually of delicate texture and brightly
coloured,

PuHyYLLopineous.—Having flattened, leaf-like twigs or leafstalks
instead of true leaves.

Piament.—The colouring material produced generally in the super-
ficial parts of animals. The cells secreting it are called pig-
ment-cells,

PinnaTEe.—Bearing leaflets on each side of a central stalk.

Pistits.—The female organs of a flower, which occupy a position
in the centre of the other floral organs, The pistil is generally
divisible into the ovary or germen, the style and the stigma.

PLAcENTALIA, PLacentata, or Placental Mammals.—See Mam-
MALIA.

PLANTIGRADES.—Quadrupeds which walk upon the whole sole of
the foot, like the Bears.

Puastic.—Readily capable of change.

PLEIstoceNE Periop.—The latest portion of the Tertiary epoch.

PLUMULE (in plants).—The minute bud between the seed-leaves of
newly-germinated plants.

Piutoyic Rocxs.—Rocks supposed to have been produced by igne-
ous action in the depths of the earth.

Po.tten.—The male element in flowering plants; usually a fine
dust produced by the anthers, which, by contact with the
stigma effects the fecundation of the seeds. This impregnation
is brought about by means of tubes (pollen-tubes) which issue
from the pollen-grains adhering to the stigma, and penetrate
through the tissues until they reach the ovary.

Po.yanprovs (flowers).—Flowers having many stamens,

Potyeamous Piants.—Plants in which some flowers are tisexual
and others hermaphrodite. The unisexual (male and female)
flowers, may be on the same or on different plants.

PotymorpPuHic.—Presenting many forms.

Potyzoary.—The common structure formed by the cells of the
Polyzoa, such as the well-known Sea-mats.

GLOSSARY. 319

PREHENSILE,—Capable of grasping.

PReporent.—Having @ superiority of power.

PRIMARIES.—The feathers forming the tip of the wing of a bird,
and inserted upon that part which represents the hand of
man.

Processes.— Projecting portions of bones, usually for the attach-
ment of muscles, ligaments, &c.

PropoLis.—A resinous material collected by the Hive-Bees from
the opening buds of various trees.

Protean.—Exceedingly variable.

Protozoa.—The lowest great division of the Animal Kingdom.
These animals are composed of a gelatinous material, and
show scarcely any trace of distinct organs. The Infusoria,
Foraminifera, and Sponges, with some other forms, belong to
this division.

Pura (pl. Pupa).—The second stage in the development of an
Insect, from which it emerges in the perfect (winged) repro-
ductive form. In most insects the pupal stage is passed in
perfect repose. The chrysalis is the pupal state of butterflies,

RapicLE.—The minute root of an embryo plant.

Ramus.—One half of the lower jaw in the Mammalia. The portion
which rises to articulate with the skull is called the ascending
ramus,

RancE.—The extent of country over which a plant or animal is
naturally spread. Range in time expresses the distribution of
a species or group through the fossiliferous beds of the earth’s
crust.

Retina.—The delicate inner coat of the eye, formed by nervous
filaments spreading from the optic nerve, and serving for the
perception of the impressions produced by light.

Retrocression.—Backward development. When an animal, as it
approaches maturity, becomes less perfectly organised than
might be expected from its early stages and known relation-
ships, it is said to undergo a retrograde development or meta- -
morphosis.

Ruizopops.—A class of lowly organised animals (Protozoa), having
a gelatinous body. the surface of which can be protruded in
the form of root-like processes or filaments, which serve for
locomotion and the prehension of food. The most important
order is that of the Foraminifera.

320 GLOSSARY.

Ropents.—The gnawing Mammalia, such as the Rats, Rabbits,
and Squirrels. They are especially characterised by the pos-
session of a single pair of chisel-like cutting teeth in each
jaw, between which and the grinding teeth there is a great
gap.

Rusus.—The Bramble Genus.

Rupimentary.—Very imperfectly developed.

Ruminants.—The group of Quadrupeds which ruminate or chew
the cud, such as oxen, sheep, and deer. They have divided
hoofs, and are destitute of front teeth in the upper jaw.

SacraL.—Belonging to the sacrum, or the bone composed usually
of two or more united vertebrx to which the sides of the pelvis
in vertebrate animals are attached.

Sarcope.—The gelatinous material of which the bodies of the
lowest animals (Protozoa) are composed.

ScurELL2.—The horny plates with which the feet of birds are gen-
erally more or less covered, especially in front.

SEDIMENTARY Formations.—Rocks deposited as sediments from
water.

Secmznts.—The transverse rings of which the body of an articulate
animal or Annelid is composed.

Sepats.—The leaves or segments of the calyx, or outermost enve-
lope of an ordinary flower. They are usually green, but some-
times brightly coloured.

SERRATURES.—Teeth like those of a saw.

SEssILE.—Not supported on a stem or footstalk.

Siturian System.—A very ancient system of fossiliferous rocks
belonging to the earlier part of the Paleozoic series.

SPECIALISATION.—The setting apart of a particular organ for the
performance of a particular function.

SpmvaL Cuorp.—The central portion of the nervous system in the
Vertebrata, which descends from the brain through the arches
of the vertebre, and gives off nearly all the nerves to the va-
rious organs of the body.

Stamens.—The male organs of flowering plants, standing in a circle
within the petals. They usually consist of a filament and an
anther, the anther being the essential part in which the pollen,
or fecundating dust, is formed. ;

SterNum.—The breast-bone.

St1¢ma.—The apical portion of the pistil in flowering plants.

GLOSSARY. 391

STIPULES.—Small leafy organs placed at the base of the footstalks

of the leaves in many plants.

STYLE.—The middle portion of the perfect pistil, which rises like
& column from the ovary and supports the stigma at its
summit.

Suscuraygovs.—Situated beneath the skin.

Suctortan.— Adapted for sucking.

Surores (in the skull).—The lines of junction of the bones of which
the skull is composed.

Tarsus (pl. Tarsr).—The jointed feet of articulate animals, such
as Insects.

TELEosTEAN Fisnxs.—Fishes of the kind familiar to us in the
present day, having the skeleton usually completely ossified
and the scales horny.

TENTACULA or TenTacLEs.—Delicate fleshy organs of prehension
or touch possessed by many of the lower animals.

TERTIARY.—The latest geological epoch, immediately preceding
the establishment of the present order of things.

TRacHEs.—The windpipe or passage for the admission of air to
the lungs.

TripactYLe.—Three-fingered, or composed of three movable parts
attached to a common base.

TerLopiTes.—A peculiar group of extinct Crustaceans, somewhat
resembling the Woodlice in external form, and, like some of
them, capable of rolling themselves up into a ball. Their
remains are found only in the Paleozoic rocks, and most
abundantly in those of Silurian age.

TrimorpPHic.—Presenting three distinct forms.

UmBe.iirera.—An order of plants in which the flowers, which
contain five stamens and a pistil with two styles, are supported
upon footstalks which spring from the top of the flower stem
and spread out like the wires of an umbrella, so as to bring all
the flowers in the same head (wmbel) nearly to the same level,
(Examples, Parsley and Carrot).

UnevuLata.—Hoofed quadrupeds.

UnIcELLULAR.—Consisting of a single cell.

VascuLar.—Containing blood-vessels.
VERMIFORM.—Like a worm.

399 GLOSSARY.

VERTEBRATA: Or VERTEBRATE ANIMALS.—The highest division of
the animal kingdom, so called from the presence in most
cases of a backbone composed of nunierous joints or vertebra,
which constitutes the centre of the skeleton and at the same
time supports and protects the central parts of the nervous
system.

Wuor.s.—The circles or spiral lines in which the parts of plants
are arranged upon the axis of growth.
WorkERS.—See neuters,

Zoka-stace.—The earliest stage in the development of many of
the higher Crustacea, so called from the name of Zoéa applied
to these young animals when they were supposed to constitute
a peculiar genus,

Zooips.—In many of the lower animals (such as the Corals, Meduse,
&c.) reproduction takes place in two ways, namely, by means of
eggs and by a process of budding with or without separation
from the parent of the product of the latter, which is often
very different from that of the egg. The individuality of the
species is represented by the whole of the form produced be-
tween two sexual reproductions; and these forms, which are
apparently individual animals, have been called zootds.

INDEX.

ABERRANT.

BALANCEMENT.

A.

ABEERANT groups, ii. 227.

Abyssinia, plants of, ii. 167.

Acclimatisation, i. 173.

Adoxa, i. 270.

Affinities of extinct species, ii. 106.

—— of organic beings, ii. 225.

Agassiz, on eet he ore i, 178.

——, on groups of species suddenly
appearing, li. 88.

——,, on prophetic formas, ii. 107.

——, on embryological succession,
ii. 120,

—, on the Glacial period, ii. 151.

——, on embryological characters,
iL. 210.

a on the latest tertiary forms, ii.

—, on parallelism of embryologi-
cal development and geological
succession, ii. 254.

—, Alex., on pedicellaria, i. 298.

Algez of New Zealand, ii. 164.

Alligators, males, fighting, i. 108.

Alternate generations, ii. 239.

Amblyopsis, blind fish, i. 173.

America, North, productions allied
to those of Europe, ii. 156.

——, —, boulders and glaciers of,
ii. 159.

—, South, no modern formations
on west coast, ii. 61.

Ammonites, sudden extinction of,
ii. 99.

Anagallis, sterility of, ii. 4.

Analogy of variations, i. 197.

Ancylus, ii. 174:

Andaman Islands inhabited by a
toad, ii. 182. ;

Animals, not domesticated from
being variable, i. 19.

——, domestic, descended from seve-
ral stocks, i. 21. :

—., — , acclimatisation of, i. 175.

—— of Australia, i. 140. a

— with thicker fur in cold cli-
mates, i. 166.

—, blind, in caves, i. 172.

—., extinct, of Australia, ii. 121.

Anomma, i. 361.

46

Antarctic islands, ancient flora of,
ii. 190.

Antechinus, ii. 219.

Ants attending aphides, i. 323.

——, slave-inaking instinct, i. 336.

——,, heuters, structure of, i. 359.

Apes, not having acquired intel-
ectual powers, 1. 282.

Aphides, attended by ants, i. 323.

Aphis, development of, ii. 245.

Apteryx, i. 218.

Arab horses, i. 40.

Aralo-Caspian Sea, ii. 121.

Archeopteryx, ii. 80.

Archiac, M. de, on the succession of
species, ii. 103.

Artichoke, Jerusalem, i. 176.

Ascension, plants of, ii. 178.

Asclepias, pollen of, i. 236.

Asparagus, ii. 143.

Aspicarpa, ii. 209.

Asses, striped, i. 198.

——., improved by selection, i. 48.

Ateuchus, i. 168.

Aucapitaine, on land-shells, ii. 187.

Audubon, on habits of frigate-bird,
i, 222.

——,, on variation in birds’ nests, i.
324.

—, on heron eating seeds, ii. 176.

Australia, animals of, i. 140.

—, dogs of, i. 328.

—, extinct animals of, ii. 121.

——,, European plants in, ii. 163.

— , glaciers of, ii. 159.

Azara, on flies destroying cattle, i.
89.

Azores, flora of, ii. 149.
B.

Babington, Mr., on British plants,
i. 58.

Baer, Von, standard of Highness, i.
151.

—, comparison of bee and fish, ii.

18.

—, embryonic similarity of the

Vertebrata, ii. 241.

Baker, Sir S., on the giraffe. i. 278.
Balancement of growth, i. 182.

323

BALEEN,

324

INDEX.

CATS,

Baleen, i. 285.

Barberry, flowers of, i. 121.

Barrande, M., on Silurian colonies,
ii. 90.

——, on the succession of species,
ii. 103.

-—, on parallelism of paleozoic
formations, ii. 106. ;
-—, on affinities of ancient species,

ii. 108.
Barriers, importance of, ii. 180.
Bates, Mr., on mimetic butterflies,
ii. 222, 293, 204,
Batrachians on islands, ii. 182.
Bats, how structure acquired, i.
218.
—, distribution of, ii. 184.
Bear, catching water-insects, i. 220.
Beauty, how acquired, i. 249; ii.
83.

Bee, sting of, i. 255.
—., queen, killing rivals, i. 256.
-——., Australian, extermination of,

i. 93.

Bees fertilising flowers, i. 90.

—, hive, not sucking the red
clover, i. 117.

— , Ligurian, i. 117.

—,, hive, cell-making instinct, i.
342,

—, variation in habits, i. 324.

—, parasitic, i. 336.

—,, humble, cells of, i. 343.

Beetles, wingless, in Madeira, i. 169.

— with deficient tarsi, i. 168.

Bentham, Mr., on British plants, i.
58.

——, on classification, ii. 211.

Berkeley, Mr., on seeds in salt
water, ii. 142.

Bermuda, birds of, ii. 180.

Birds acquiring fear, i. 325.

—, beauty of, i. 252.

—— annually cross the Atlantic, ii.
150.

—, colour of, on continents, i.

—, footsteps and remains of, in
secondary rocks, ii. 79.

——,, fossil, in caves of Brazil, ii.
121,

—, of Madeira, Bermuda, and
Galapagos, ii. 179, 180.

—, song of males, i. 109.

—— transporting seeds, ii. 148,

——,, waders, ii. 175.

——, wingless, i. 167, 218.

Bizcacha, ii. 183.

affinities of, ii. 227.

Bladder for swimming, in fish, i. 280,

Blindness of cave animals, i. 170.

Blyth, Mr., on distinctness of Indian
cattle, i. 21.

, on striped hemionus, i. 199.

——,, on crossed geese, ii. 10.

Borrow, Mr., on the Spanish pointer,
i. 40

i. 40.
Bory St. Vincent, on Batrachians,
ii. 182.

Bosquet, M., on fossil Chthamalus,
ii. 80.

Boulders, erratic, on the Azores, ii.
149,

Branchie, i. 231, 282.

—— of crustaceans, i. 238.

Braun, Prof., on the seeds of Fuma-
riacee, i. 271.

Brent, Mr., on house-tumblers, i
326.

Britain, mammals of, ii. 185.

Broca, Prof., on Natural Selection,
i, 265.

Bronn, Prof., on duration of specific
formas, ii. 66.

——, various objections by, i. 265.

Brown, Robert, on classification, ii.
207.

——, Séquard, on inherited muti-
lations, i. 168.

Busk, Mr., on the Polyzoa, i. 301.

Butterflies, mimetic, ii, 222, 293,
224,

Buzarcingues, on sterility of varie-
ties, ii. 38.

c.

Cabbage, varieties of, crossed, i, 122

Calceolaria, ii. 7, 8.

Canary-birds, sterility of hybrids:
ii. 9 :

Cape de Verde islands, productions
of,” ii. 189.
Taal plants of, on mountains, ii
2.

Cape of Good Hope, plants of, i,
158; ii. 178.
Ramet, Dr., on foraminifera, ii,

Carthamus, i. 271.

Catasetum, i, 243; ii, 216.

Cats, with blue eyes, deaf, i. 18.

, Variation in habits of, i. 325.

—— curling tail when going to
spring, i. 254,

CATTLE,

—

INDEX.

CUCKOO,

325

Cattle destroying fir-trees, i. 88.
Ted by flies in Paraguay,

—, breeds of, locally extinct, i. 184.

——, fertility of Indian and Euro-
pean breeds, ii. 10.

——, Indian, i. 21; ii. 10.

Cave, inhabitants of, blind, i. 170.

Cecidomyia, ii. 239.

eae proving antiquity of man,
i. 21.

Centres of Creation, ii. 185.
Sephalopote structures of eyes, i.

—, development of, ii. 244.

Cercopithecus, tail of, i, 294,

Ceroxylus laceratus, i, 284.

Cervulus, ii. 9.

Cetacea, teeth and hair, 1. 179.

—, development of the whale-
bone, i. 285.

Cetaceans, i. 285.

Ceylon, plants of, ii. 164.

Chalk formation, ii. 100.

Characters, divergence of, i. 184.

——,, sexual, variable, i. 185, 191.

——, adaptive or analogical, ii, 218.

Charlock, i. 94.

Checks, to increase, i. 83.

— —, mutual, i. 86.

Chele of Crustaceans, i. 300.

Chickens, instinctive tameness of,
i. 829,

Chironomus, its asexual reproduc-
tion, ii. 240.

Chthamaling, ii. 59.

Chthamalus, cretacean species of,
ii. 81.

Circumstances favourable to selec-
tion of domestic products, i. 46.
—— —— to natural selection, i. 124.
Cirripedes capable of crossing, i. 124.

——, carapace aborted, i. 184
——, their ovigerous frena, i. 232.
—, fossil, ii. 80.

— , larve of, ii. 243. 2
Claparéde, Prof., on the hair-clasp-
ers of the Acaride, i. 239. .
Clarke, Rev. W. B., on old glaciers

in Australia, ii. 159.
Classification, ii. 202, |
Clift, Mr., on the succession of types,
ij. 121. ; ot
Climate, effects of, in checking in-
crease of beings, 1. q ,
adaptation of, to organisms, 1.

¥

Climbing plants, i. 230.

——.,, development of, i. 308.

Clover visited by bees, i. 117.

Cobites, intestine of, i. 229.

Cockroach, i. 93.

Collections, paleontological, poor,
ii. 58.

Colour, influenced by climate, i. 165.

——, in relation to attack by flies,

i, 248,

Columba livia, parent of domestic

igeons, i. 26.

Colymbetes, ii. 174.

Compensation of growth, i. 182.

aaa flowers and seeds of, i.
179.

——, outer and inner florets of, i.
270.

——, male flowers of, ii. 257.

Conclusion, general, ii. 293.

Conditions, light changes in, fa-
vourable to fertility, ii. 27.

Convergence of genera, i. 156.

Coot, i. 222.

Cope, Prof., on the acceleration or
retardation of the period of repro-
duction, i, 232.

Coral-islands, seeds drifted to, ii.
145.

—— reefs, indicating movements of
earth, ii. 145.

Corn-crake, i. 223.

Correlated variation in domestic
productions, i. 13.

Coryanthes, i. 241.

Creation, single centres of, ii. 135.

Crinum, ii. 6.

Croll, Mr., on subaerial denudation,
ii. 58, 56.

——, on the age of our oldest for-
mations, ii. 83.

—, on alternate Glacial periods
in the North and South, ii. 160.

Crosses, reciprocal, ii. 14.

Crossing of domestic animals, im-
portance in altering breeds, i. 23.

—, advantages of, i. 119, 120.

——, unfavourable to selection, i
125.

Crtger, Dr., on Coryanthes, i. 241.

Crustacea of New Zealand, ii. 164.

Crustacean, blind, i. 171.

—— air-breathers, i. 238.

Crustaceans, their chele, i. 300.

Cryptocerus, i. 359.

Ctenomys, blind, i. 170.

Cuckoo, instinct of, i. 819, 330.

CUNNINGHAM,

826

INDEX.

EDWARDS,

Cunningham, Mr., on the flight of
the logger-headed duck, i. 167.

Currants, grafts of, ii. 19.

Currents of sea, rate of, ii. 144.

Cuvier, on conditions of existence,
i. 320.

Cuvier, on fossil monkeys, ii. 79.

red., on instinct, 1.320.

Cyclostoma, resisting salt water, ii.
187.

> y

D.

Dana, Prof., on blind cave-animals,
i. 172.

——, on relations of crustaceans of
Japan, ii, 158.

——, on crustaceans of New Zea-
land, ii. 164.

Dawson, Dr., on eozoon, ii. 85.

De Candolle, Aug. Pyr., on struggle
for existence, i. 77.

—, on umbellifera, i. 181.

——, on general affinities, ii. 228.

——, Alph., on the variability of
oaks, i. 62.

—. on low plants, widely dis-
persed, ii. 196.

——, on widely-ranging plants be-
ing variable, i. 67.

——, on naturalisation, i. 189.

——,, on winged seeds, i. 181.

——, on_ Alpine species suddenly
becoming rare, i. 210.

—, on distribution of plants with
large seeds, ii. 145.

——, on vegetation of Australia, ii.
167.

——,, on fresh-water plants, ii. 174.

——, on insular plants, ii. 178.

Degradation of rocks, ii. 52.

Denudation, rate of, ii. 54.

—— of oldest rocks, ii. 85.

— of granitic areas, ii. 64.

Development of ancient forms, ii.
116.

Devonian system, ii. 113.

Dianthus, fertility of crosses, ii. 13.

Dimorphism in plants, i. 55; ii. 29.

Dirt on feet of birds, ii. 148.

Dispersal, means of, ii. 140.

—— during Glacial period, ii. 151.

Distribution, srecear ical, ii. 129,

——, means of, ii. 140,

ee effect of, under nature, i.
16

Divergence of character, i. 184,

Diversification of means for same
general purpose, i. 240.

Division, physiological, of labour,

1.139. 3

Dog, resemblance of jaw to that of
nal Thylacinus, ii. 220.

Dogs, hairless, with imperfect tecth,
i, 14.

—— descended from several wild
stocks, i, 22.

——, domestic instincts of, i. 327.

——,, inherited civilisation of, i. 327,

——,, fertility of breeds together, ii.
10,

——, — of crosses, ii. 35.

——., proportions of body in differ-
ent breeds, when young, ii. 247.
Domestication, variation under, i. 7.

Double flowers, i. 358.

Downing, Mr., on fruit-trees in
America, i. 104.

Dragon flies, intestines of, i. 229.

Drift-timber, ii. 145,

Driver-ant, i. 361.

Drones killed by other bees, i. 256.

Duck, domestic, wings of, reduced,
i. 12,

—, beak of, i. 285.

——, logger-headed, i. 218,

Duck weed, ii. 173.

Dugong, affinities of, ii. 206.

Dung-beetles with deficient tarsi, i.
168.

Dytiseus, ii. 174.

‘Ez
Earl, Mr. W., on the Malay Archi-
pel ‘0, li. 185.
Ears, drooping, in domestic ani-

mals, i. 13.
——, rudimentary, ii. 261.
aarp seeds in roots of trees, ii.
—— charged with seeds, ii. 148.
Beh nodeemetey their pedicel aris,
i. 297, :
Kciton, i. 359.
Economy of organisation, i. 182.
Edentata, teeth and hair, i. 179.
——, fossil species of, ii. 288.
Edwards, Milne, on physiological
division of labour, i. 189,
er on gradations of. structure, i.

——, on embryological characters,
ii. 210,

EGas,
————

INDEX.

FRIGATE-BIRD.

327

Ege, young birds escaping from, i.
Egy Bh productions of, not modified,

Electric organs, i. 234.

Elephant, rate of increase, i. 80.

=—) of Glacial period, i. 176.

Embryology, ii. 239,

Eozoon Canadense, ii. 84.

Epilepsy inherited, i. 167.

Existence, struggle for, i. 75.

—— condition of, i. 261.

Extinction, as bearing on natural
selection, i. 150.

— of Momsstie varieties, i. 145.

—, ii. 94.

Eye, structure of, i, 225.

——,, correction for aberration, i. 255.

Eyes, reduction in moles, i. 170.

F.

Fabre, M., on hymenoptera fight-
ing, i. 108.

——, on parasitic sphex, i. 336.

—,, on Sitaris, ii. 252.

Falconer, Dr., on naturalisation of
plants in India, i. 80.

—, on elephants and mastodons,
ii, 118, :

— and Cautley, on mammals of
sub-Himalayan beds, ii. 122.

Falkland Islands, wolf of, ii. 183.

Faults, ii. 54.

Faunas, marine, ii. 181.

Fear, instinctive, in birds, i. 829.

Feet of birds, young molluses ad-
hering to, ii. 174.

Fertilisation variously effected, i.
941, 252.

Fertility of hybrids, ii. 6. — .

——, from slight changes in condi-
tions, ii 28. ,

_— of crossed varieties, ii. 34.

fir-trees destroyed by cattle, i. 88.

—, pollen of, 1. 257.

Fish, flying, i. 218.

—,, teleostean, sudden appearance
of, ii. 81. a

—, eating seeds, ii. 146, 175.

—, fresh-water, distribution of,
ii. 172.

Fishes, ganoid, now confined to
fresh water, i.130. |

—, electric organs of, i. 234.

ll.

—, ganoid, living in fresh water,-
ii. 99.

Fishes, of southern hemisphere, ii

Flat-fish, their structure, i. 290.
Flight, powers of, how acquired, i.
218.

Flint-tools, proving antiquity of
man, i. 21.

Flower, Prof., on the Larynx, i. 297.

——, on Halitherium, ii. 108.

—, on the resemblance between
the jaws of the dog and Thyla-
cinus, ii. 220.

——, on the homology of the feet of
certain marsupials, ii. 232.

Flowers, structure of, in relation to
crossing, i. 114.

—, of composite and umbelli-
fere, i. 179, 270.

—, beauty of, i. 252.

——, double, i. 358,

Flysch formation, destitute of or-
ganic remains, ii. 59.

Forbes, Mr. D., on glacial action in
the Andes, ii. 160.

—, E., on colours of shells, i. 165.

——, on abrupt range of shells in

‘ depth, i. 210.

——, on poorness of paleontological
collections, ii. 58.

—, on continuous succession of
genera, ii. 93.

——, on continental extensions, ii.
140, 141.

—, on distribution during Glacial
period, ii. 152.

—, on parallelism in time and
space, ii. 200. ;

Forests, changes in, in America, i.
91

Formation, Devonian, ii. 113.

Cambrian, ii. 84.

Formations, thickness of, in Britain,
ii. 55.

——., intermittent, ii. 69.

Formica, rufescens, i. 836.

——, sanguinea, i. 338.

—, flava. neuter of, i. 860.

Forms, lowly organised, long en-
during, i. 154

Frena, ovigerous, of cirripedes, i.
282.

Fresh-water productions, dispersal
of, ii. 171.

Fries, on species in large genera
being closely allied to other spe-
cies, 1. 71.

Frigate-bird, i, 222,

FROGS,

328

INDEX.

HABIT.

Frogs on islands, ii. 182.

¥ruit-trees, gradual improvement
of, i. 42. .

—- in United States, i. 104.

—, varieties of, acclimatised in
United States, i. 176.

Fuci, crossed, ii. 15, 23. ‘

Fur, thicker in cold climates, i. 166.

Furze, ii. 241.

G.

Galapagos Archipelago, birds of,
ii. 179.

— , productions of, ii. 188, 190.

Galaxias, its wide range, ii. 172.

Galeopithecus, i. 217.

Game, incfease of, checked by ver-
min, i. 86.

Gartner, on sterility of hybrids, ii.
3, 4, 11

——, on reciprocal crosses, ii. 15.

—, on crossed maize and verbas-
cum, ii. 37.

——, on comparison of hybrids and
mongrels, ii. 40, 41, 42.

Gaudry, Prof., on intermediate ge-
nera of fossil mammals in Attica,
ii. 107.

Geese, fertility when crossed, ii. 9,
10

——, upland, i. 222.

Geikie, Mr., on subaerial denuda-
tion, fi. 63.

Genealogy, important in classifica-
tion, ii, 212.

Generations, alternate, ii. 239.

Geoffroy St. Hilaire, on balance-
ment, i. 182.

——, on homologous organs, ii. 233.

—, Isidore, on variability of re-
peated parts, i. 184.

—, or correlation, in monstrosi-
ties, i. 13.

—, on correlation, i. 179.

——, on variable parts being often
monstrous, i. 190.

Geographical distribution, ii. 129.

Geo, aply, ancient, ii. 803.

Geology, future progress of, ii. 302.

——, imperfection of the record, ii.

Gervais, Prof., on Typotherium, ii.
108.

Giraffe, tail of, i. 245.
——, structure of, i. 276.
Glacial period, ii. 151.

Glacial period, affecting the North
and South, il. 158.

Glands, mammary, i. 295.

Gmelin, on distribution, ii. 151.

Godwin-Austen, Mr., on the Malay
Archipelago, ii. 74.

Goethe, on compensation of growth,
i. 182.

Gomphia, i. 272.

Gooseberry, grafts of, ii. 19.

Gould, Dr. Aug. A., on land-shells,
ii. 186.

—,, Mr., on colours of birds, i. 165.

——,, on instincts of cuckoo, i. 833.

——, on distribution of genera of
birds, ii. 195.

Gourds, crossed, ii. 38.

Graba, on the Uria lacrymas, i. 113.

Grafting, capacity of, ii. 18, 19, 20.

Granite, areas of denuded, ii. 64.

Grasses, varieties of, i. 137.

Gray, Dr. Asa, on the variability of
oaks, i. 62.

—, on man not causing variabil-
ity, i. 98.

——,, on sexes of the holly, i. 116.

—, on trees of the United States,
i. 128.

——, on naturalised plants in the
United States, i. 189.

——,'on estivation, i. 272.

——, on Alpine plants, ii. 151.

——, on rarity of intermediate va-
rieties, i. 212.

a Dr. J. E., on striped mule, i

99.
Grebe, i. 221.
ooo on asexual reproduction, ii

Groups, aberrant, ii. 227.
Grouse, colours of, i. 104.
——, red, a doubtful species, i. 59.
Growth, compensation of, i. 182.
Gunther, Dr., on flat-fish, i. 292.
——,, on prehensile tails, i. 295.
—, on the fishes of Panama, ii.
131.
—, on the range of fresh-water
fishes, ii. 172.
——, on the limbs of Lepidosiren,
ii. 258.
H.

Haast, Dr., on gleciers of New Zea-
land, ii. 159.

Habit, effect of, under domestica
tion, i. 12,

HABIT.

ee ee

INDEX.

HUXLEY.

329

Habit, effect of, under nature, i. 168.

ee civetsitied of same species,

Hackel, Prof., on classification and
the lines of descent, ii. 281,

Hair and teeth, correlated, i. 179.

Halitherium, ii. 108.

Harcourt, Mr. E. V.; on the birds of
Madeira, ii. 180.

Hartung, M., on boulders in the
Azores, ii. 149.

Hazel-nuts, ii. 143.

Hearne, on habits of bears, i. 220.

ea changes in vegetation, i.

Hector, Dr., on glaciers of New Zea-
land, ii. 159.

Heer, Oswald, on ancient cultivated
plants, i. 20.

——, on plants of Madeira, i. 180.

Helianthemum, i. 272.

Helix pomatia, ii. 187.

——, resisting salt water, ii. 187.

Helmholtz, M., on the imperfection
of the human eye, i. 255.

Helosciadium, ii. 143.

Hemionus, striped, i. 202.

Hensen, Dr., on the eyes of Cepha-
lopods, i. 237.

Herbert, W., on struggle for exist-
ence, 1. 77.

——, on sterility of hybrids, ii. 6.

Hermaphrodites crossing, i. 119.

Heron eating seed, ii. 176.

Heron, Sir R., on peacocks, i. 109.

Heusinger,
soned by certain plants, i. 18.

Hewitt, Mr., on sterility of first
crosses, ii. 23.

Hildebrand, Prof., on the self-ste-
rility of Corydalis, ii. 7.

Hilgendorf, on intermediate varie-
ties, ii. 66.

Himalaya, glaciers of, ii. 159.

—, plants of, ii. 162.

Hippeastrum, ii. 7.

Hippocampus, i. 295.

Hofmeister, Prof, on the move-
ments of plants, i. 308.

Holly-trees, sexes of, i. 115.

Hooker, Dr., on trees of New Zea-
land, i. 123. .

~—, on acclimatisation of Hima-
layan trees, i. 174. : ;

——,on flowers of umbellifere, i.
180.

—, on the position of ovules, i. 268.

on white animals poi-.

Hooker, Dr., on glaciers of Himala-
ya, ii. 159.

——, on alge of New Zealand, ii.
164.

——, on vegetation at the base of
the Himalaya, ii. 164.

—,, on plants of Tierra del Fuego,
ii. 161.

——, on Australian plants, ii. 163,
190.

——, on relations of flora of Amer-
ida, ii, 167.

—, on flora of the Antarctic lands,
ii. 169, 189.

—, on the plants of the Gala-
pagos, ii. 181, 188.

——, on glaciers of the Lebanon,
ii. 159.

——, on man not causing variabil-
ity, i. 97.

, on plants of mountains of

Fernando Po, ii. 162.

Hooks on palms, i. 247.

—— on seeds, on islands, ii. 181.

Hopkins, Mr., on denudation, ii. 63.

Hornbill, remarkable instinct of, i.
364.

Horns, rudimentary, ii. 261.

Horse, fossil, in La Plata, ii. 96.

——, proportions of, when young,
ii. 247.

Horses destroyed by flies in Para-
guay, i. 89.

——. striped, i. 199.

Horticulturists, selection applied by,

re

Huber, on cells of bees, i. 349.

P., on reason blended with
instinct, i. 320,

——,, on habitual nature of instincts,
i. 320.

—, on slave-making ants, i. 336.

——, on Melipona domestica, i. 343.

Hudson, Mr., on the Ground-Wood-
pecker of La Plata, i. 221.

——, on the Molothrus, i. 334.

Humble-bees, cells of, 1. 348.

Hunter, J., on secondary sexual
characters, i. 185.

Hutton, Captain, on crossed geese,
ii. 10.

Huxley, Prof., on structure of her-
maphrodites, i. 124.

——, on the affinities of the Sirenia,
ii. 108.

—,on forms connecting birds and
reptiles, ii. 108.

HUXLEY.

330

INDEX.

LOBELIA FULGENS,

Huxley, Prof., on homologous or-
gang, ii. 238. :
——, on the development of aphis,

ii. 245.
Hybrids and mongrels compared, ii.
39

Hybridism, ii. 1.

Hydra, structure of, i. 229.
Hymenoptera, fighting, i. 108.
Hymenopterous insect, diving, i. 222.
Hyoseris, i. 271.

1

Ibla, i. 183.

Icebergs transporting seeds, ii. 148.

Increase, rate of, i. 79.

Individuals, numbers favourable to
selection, i. 124.

——, many, whether simultaneously
created, ii. 189.

Inheritance, laws of, i. 15.

——, at corresponding ages, i. 15,
10

Insects, colour of, fitted for their
stations, i. 103.

——, sea-side, colours of, i. 165.

——, blind, in caves, i. 171.

——, luminous, i. 236.

—, their resemblance to certain
objects, i. 283.

—, neuter, i. 359.

Instinct, i. 319.

—, not varying simultaneously
with structure, 1. 357.

Instincts, domestic, i. 325.

Intercrossing, advantages of, i. 149,
ii. 27.

Islands, oceanic, ii. 177.

Isolation favourable to selection, i.
127.

J.

Japan, productions of, ii. 158.

Java, plants of, ii. 162.

Jones, Mr. J. M., on the birds of
Bermuda, ii. 180.

Jourdain, M., on the eye-spots of
star-fishes, 1. 225.

Jukes, Prof., on subaerial denuda-
tion, ii. 53.

Jussieu, on classification, ii. 209.

K.

Kentucky, caves of, i. 172.
Kerguelen-land, flora of, ii. 169, 189.

Kidney-bean, acclimatisation of, i.

ue
Kidneys of birds, i. 178.
Kirby, on tarsi deficient in beetles,
i. 168.

Knight, Andrew, on cause of varia-
tion, i. 8.

Kélreuter, on Intercrossing, i. 119.

—, on the hapa i. 121.

——, on sterility of hybrids, ii. 3, 4.

——, on reciprocal crosses, ii. 15.

——, on crossed varieties of nico-
tiana, ii. 38.

——, on crossing male and herma-
phrodite flowers, ii. 256.

L.
Lamarck, on adaptive characters, ii.

218,

Lancelet, i. 154.

——, eyes of, i. 227.

Landois, on the development of the
wings of insects, i. 281.

Land-shells, distribution of, ii. 186.

——, of Madeira, naturalised, ii.
193.

——, resisting salt water, ii. 187.

Languages, classification of, ii. 214.

Lankester, Mr. E. Ray, on Longe-
vity, i. 263.

——, on homologies, ii. 237.

Lapse, great, of time, ii. 51.

Larve, li. 241, 242, 248.

Laurel, nectar secreted by the leaves,
i, 114.

‘Laurentian formation, ii. 84.

Laws of variation, i. 164.

Leech, varieties of, i. 93.

sep bap nectar secreted by
glands, i. 114.

Leibnitz’ attack on Newton, ii. 294.

Lepidosiren, i. 180; ii. 109.

——, limbs in a nascent condition
ii. 258.

Lewes, Mr. G. H., on species not
having changed in Egypt, i. 263.

——,, on the Salamandra atra, ii. 256.

——, on many forms of life
been at first evolved, ii. 300.

Life, struggle for, i. 77.

Lingula, Silurian, ii. 83.

Linnzus, aphorism of, ii. 205.

Lion, mane o 1. 105.

——, young of, striped, ii. 241.

Lobelia filvens,4. 60, 191.

——,, sterility of crosses, ii. 7.

aving

LOCK Woop. INDEX. MIVART. 331
Lockwood, Mr., on the ova of the
Hippocampus, i. 295. M.

Locusts transporting seeds, ii. 147.

Logan, Sir W., on Laurentian for-
mation, ii. 84,

Lowe, Rev. R. T.,on locusts visiting
Madeira, ii. 14’

Lowness of structure connected with
variability, i. 184.

mre related to wide distribution, ii.

Lubbock, Sir J., on the nerves of
coceus, i. 54,

—, on secondary sexual charac-
ters, i. 1938.

—, on a diving hymenopterous
insect, i. 222. ties .

——, on affinities, ii, 73.

——, on_metamorphoses, ii. 239, 242.

Lucas, Dr. P., on inheritance, i. 14.

—, on resemblance of child to
parent, ii. 43.

Lund and Clausen, on fossils of
Brazil, ii. 121.

Lyell, Sir C., on the struggle for
existence, i. 77.

—, on modern changes of the
earth, i. 118.

——, on terrestrial animals not hav-
ing been developed on islands, i.
281. ;

—, on a carboniferous land-shell.
ii. 59.

—, on strata beneath Silurian sys-
tem, ii. 84.

—, on the imperfection of the geo-
logical record, ii. 88. .
——, on the appearance of species,

ii. 88.

——, on Barrande’s colonies, ii. 90.

—, on tertiary formations of
Europe and North America, ii.
101.

——, on parallelism of tertiary for-
mations, ii. 106. .
——, on transport of seeds by ice-

bergs, ii. 148. . :

——, on great alterations of climate,
ii. 170.

——,, on the distribution of fresh-
water shells, ii. 174. oe

——, on land-shells of Madeira, ii.

193.
Lyell and Dawson, on fossilized trees
in Nova Scotia, ii. 70. oo hs
Lythrum salicaria, trimorphic, ii.
82.

Macleay, on analogical characters, ’
ii. 218.

Macrauchenia, ii. 107.

M‘Donnell, Dr., on electric organs.
i, 284.

Madeira, plants of, i. 180.

——,, beetles of, wingless, i. 169.

—, fossil land-shells of, ii. 121.

——, birds of, ii. 180.

Megple tame in Norway, i. 825.

Males fighting, i. 108.

Maize, crossed, ii. 37.

Malay Archipelago compared with
Europe, ii. 74.

—, mammals of, ii. 185.

Malm, on flat-fish, i. 291.

Malpighiacez, small imperfect flow-
ers of, i, 269.

—, ii. 209. :

Mamma, their development, i. 295.

—, rudimentary, ii. 255.

Mammals, fossil, in secondary for-
mation, ii. 79.

—, insular, ii. 183.

Man, origin of, ii. 304.

Manatee, rudimentary nails of, ii.

260.
Marsupials of Australia, i. 140.
——, structure of their feet, ii. 282.
—,, fossil species of, ii. 121.
Martens, M., experiment on seede,
ii, 144.

ii, 144,

Martin, Mr. W. C., on striped mules,
i, 201.

Masters, Dr., on Saponaria, i. 272.

Matteucci, on the electric organs of
rays, i. 284.

-Matthiola, reciprocal crosses of, ii.
15.

Maurandia, i. 307.

Means of dispersal, ii. 140.

Melipona domestica, i. 343.

Merrell, Dr., on the American
cuckoo, i. 380.

Metamorphism of oldest rocks, ii. 85.

Mice destroying bees, i. 90.

——, acclimatisation of, i. 175.

—, tails of, i. 294, :

Miller, Prof., on the cells of bees, i.
344, 850.

Mirabilis, crosses of, ii. 15.

Missel-thrush, i. 98.

Mistletoe, complex relations of, i. 3.

Mivart, Mr., on the relation of hair
and teeth, i. 179.

MIVART,

332

INDEX.

ONITES.

Mivart, Mr., on the eyes of cephalo-
pods, i. 237,

——, various objections to Natural
Selection, i. 275. ; ;

——, on abrupt modifications, i. 313.

—, on the resemblance of the
mouse and antechinus, ii. 218.

Mocking-thrush of the Galapagos,
ii. 193.

Modification of species not abrupt,
ii. 298.

Moles, blind, i. 170.

Molothrus, habits of, i. 334.

Mongrels, fertility and sterility of,
iL, 84.

— and ye compared, ii. 39.

Monkeys, fossil, ii. 79.

Monachanthus, 1i. 216.

Mons, Van, on the origin of fruit-
trees, i. 33.

Monstrosities, i. 51.

Moquin-Tandon, on sea-side plants,
i. 166.

Morphology, ii. 231.

Morren, on the leaves of Oxalis, i.
308.

Moths, hybrid, ii. 9.

Mozart, musical powers of, i. 321.

Mud, seeds in, ii. 175.

Mules, striped, i. 201.

Miller, Adolf, on the instincts of the
cuckoo, i. 331.

Miller, Dr. Ferdinand, on Alpine
Australian plants, ii. 163.

Miller, Fritz, on dimorphic crusta-
ceans, i. 55, 362.

—, on the lancelet, i. 154.

——, on air-breathing crustaceans,
i. 238.

——,, on climbing plants, i. 307.

aie the self-sterility of orchids,
ll. f.

—, on embryology in relation to
classification, ii. 210.

——, on the metamorphoses of crus-
taceans, ii. 245, 253.

——, on terrestrial and fresh-water
organisms not undergoing any
metamorphosis, ii. 250.

Multiplication of species not indefi-
nite, i. 157.

Murchison, Sir R., on the forma-
tions of Russia, ii. 60.

——,, on azoic formations, ii. 84.

—-, on extinction, ii. 94.

Murie. Dr., on the modification of
the skull in on age, i. 233,

Murray, Mr. A., on cave-insects,
i. 178.

Mustela vision, i. 216.

Myanthus, ii. 216.

Myrmecocystus, i. 359.

Myrmica, eyes of, i. 361.

N.

Nageli, on morphological characters,
i. 266.

Nails, rudimentary, ii. 260.

Nathusius, Von, on pigs, i. 249.

Natural history, future progress of,
ii. 301. 2

— selection, i. 97.

—— system, il. 204.

Naturalisation of forms distinct
trom the indigenous species, i. 138.

Naturalisation in New Zealand, i.
255.

Naudin, on analogous variations in
gourds, i. 195.

——,, on hybrid gourds, ii. 38.

—, on reversion, ii. 41.

Nautilus, Silurian. ii. 83.

Nectar of plants, i. 114.

Nectaries, how formed, i. 114.

Nelumbium luteum, ii. 176.

Nests, variations in, i. 324, 355, 364.

Neuter insects, i. 859, 360.

Newman, Col., on humble-bees, i. 90.

New Zealand, productions of, not
perfect, i. 255.

——, naturalised products of, ii. 119.

——,, fossil birds of, ii. 121.

——, glaciers of, ii. 159.

——, crustaceans of, ii. 164.

, alge of, ii. 164.

——, number of plants of, ii. 178.

—, flora of, ii. 189.

Newton, Sir 1. attacked for irre-
ligion, ii. 294.

——, Prof., on earth attached to a
partridge’s foot, ji. 148.

Nicotiana, crossed varieties of, ii. 39.

=a certain species very sterile, ii.

Nitsche, Dr., on the Polyzoa, i. 301.

Noble, Mr., on fertility of Rhodo-
dendron, ii. 8. :

Nodules, phosphatic, in azoic rocks,
lL. 84,

O.

Oaks, variability of, i. 62.
Onites, appelles, i. 168.

ONONIS,

INDEX.

PLANTS,

333

viene small imperfect flowers of,

1 .

Orchids, fertilisation of, i. 241.

—, the development of their
tlowers, i. 303.

——,, forms of, ii. 216.

Orchis, pollen of, i. 236.

UypatrestOn, tendency to advance,
1, .

Organs of extreme perfection, i. 223.
——, electric, of iehen, i, 234.

—— of little importance, i. 245.
—, homologous, ii. 233.

a rudiments of, and nascent, ii.
Ornithorhynchus, i. 180; ii. 208.
——, Mamme of, i. 296.

Ostrich not enele of flight, i. 281.
re pabit of laying eggs together,

i.
——, American, two species of, ii.
182,

Otter, habits of, how acquired, i.
216.

Ouzel, water, i. 222.

eee Prof., on birds not flying, i.
ial.

—, on vegetative repetition, i.
184,

——, on variability of unusually
developed parts, i. 185.

—,, on the eyes of fishes, i. 227.

——,, on the swim-bladder of fishes,
i. 281.

—, on fossil horse of La Plata, ii.
96.

——, on generalized form, ii. 107.

—, on relation of ruminants and
pachydermas, ii. 107.

——, on fossil birds of New Zea-
land, ii. 121. .

—,, on succession of types, ii. 121.

—,, on affinities of the dugong, ii.
206.

—, on homologous organs, ii. 233.

——, on the metamorphosis of ce-
phalopods, ii. 244.

P.

Pacific Ocean, faunas of, ii, 131.
Pacini, on electric organs, i. 235. |
Paley, on no organ formed to give
ain, i. 254.
Paas, on the fertility of the domes-
ticated descendants of wild stocks,
ii. 10.

Palm with hooks, i. 247.

Papaper bracteatum, i. 272.

Paraguay, cattle destroyed by flies,
i, 89.

Parasites, i. 834.

Partridge, with ball of earth at-
tached to foot, ii. 148.

Die realy developed, variable,
i. 185.

Parus major, i. 220.

Passiflora, ii. 7.

Peaches in United States, i. 104.

Pear, grafts of, ii. 18.

Pedicellaria, i. 298.

Pelagornium, flowers of, i. 180.

—, sterility of, ii. 7.

Pelvis of women, i. 178,

Peloria, i. 180.

Period, glacial, ii. 151.

Petrels, habits of, i. 221.

Phasianus, fertility of hybrids, ii. 9.

Pheasant, young, wild, i. 829.

Pictet, Prof., on groups of species
suddenly appearing, ii. 77.

——, on rate of organic change, ii. 90.

——, on continuous succession of
genera, ii. 93.

——, on change in latest tertiary
forms, ii. 71.

——, on close alliance of fossils in
consecutive formations, ii. 114.
——, on early transitional links, ii.

8.

Pierce, Mr., on varieties of wolves,
i. 111,
Pigeons with feathered feet and skin
tween toes, i. 14.
——, breeds described, and origin
of, i. 28.
—, breeds of, how produced, i. 44,

47.
——, tumbler, not being able to get
out of egg, i. 106. )
——, reverting to blue colour, i. 197.
——, instinct of tumbling, i. 327.
—, young of, ii. 248.

Pigs, black, not affected by the
paint-root, i. 13. ;
——,, modified by want of exercise,

i, 249.
Pistil, rudimentary, ii. 256.
Plants, poisonous, not affecting cer-
tain coloured animals, i. 13.
—,, selection, applied to, i. 41.
——, gradual improverhent of, i. 42.
——, not improved in barbarous
countries, i. 43.

PLANTS,

334

INDEX.

°ALT WATER,

Plants, dimorphic, i. 55; ii. 29.

——,, destroyed by insects, i. 83.

—, in midst of range, have to
struggle with other plants, i. 95.

——, nectar of, i. 114, :

— , fleshy, on sea-shores, i. 166.

——, climbing, i. 230, 305. Ps

—, fresh-water, distribution of, ii.
174.

— , low in scale, widely distri-
buted, ii. 196. ;

Pleuronectide, their structure, i.
290.

Plumage, laws of change in sexes
of birds, i. 109.

Plums in the United States, i. 104.

Pointer dog, origin of, i. 40.

— , habits of, 1. 327.

Poison not affecting certain coloured
animals, i. 13.

—, similar effect of, on animals
and plants, ii. 299.

Pollen of fir-trees, i. 257.

—— transported by various means,
i. 241, 252,

Pollinia, their development, i. 304.

Polyzoa, their avicularia, i. 301.

Poole, Col., on striped hemionus, i.
202.

Potemogeton, ii. 175.

Pouchet, on the colours of flat-fish,
i. 293.

Prestwich, Mr., on English and
French eocene formations, ii. 105.

Proctotrupes, i. 222.

Proteolepas, 1. 183.

Proteus, i. 173.

Psychology, future progress of, ii.
304.

Pyrgoma, found in the chalk, ii. 81.

Q.

Quagga, striped, i. 201.
Gnacatices Me on hybrid moths,
9

ii. 9.
Quercus, variability of, i. 62.
Quince, grafts of, il. 18.

R.

Rabbits, disposition of young, i. 328-

Races, domestic, characters of, i. 18.

Race-horses, Arab, i. 40.

——., English, ii. 140.

Radclitfe, Dr., the electrical organs
of the torpedo, i. 234.

Ramond, on plants of Pyrenees, ii.

Ramsay, Prof., on subaerial denu-
dation, ii. 53.

—,, on thickness of the British
formations, ii. 55, 56.

| —_—, on faults, ii. 55.

Ramsay, Mr., on instincts of cuckoo,
i. 883,

Ratio of increase, i. 79.

Rats pase each other, i. 93.

——,, acclimatisation of, i. 175.

——, blind, in cave, i. 171

Rattle-snake, i. 254.

Reason and instinct, i. 319.

Recapitulation, general, ii. 267.

Reciprocity of crosses, ii. 14.

Record, geological, imperfect, ii. 48.

Rengger, on flies destroying cattle,
i. 89.

Reproduction, rate of, i. 79.
Resemblance, protective, of insects,
i. 288.

—— to parents in mongrels and
hybrids, ii. 41.

Reversion, law of inheritance, i.
16.

——, in pigeons, to blue colour, i.
198

Rhododendron, sterility of, ii. 7, 8.

Richard, Prof., on Aspicarps, ii. 209.

Richardson, Sir J., on structure of
squirrels, i. 216.

——, on fishes of the southern hemi-

ete ii, 164.

Robinia, grafts of, ii. 19.

Rodents, blind, i. 170.

HOES Prof., Map of N. America,
ii 65.

Rudimentary organs, ii. 255.

Rudiments important for classifica-
tion, ii. 207.

Bart on Indian cattle, i. 21;
ii. 10.

8.

Salamandra atra, ii. 256.

Saliva used in nests, i. 355.

Salvin, Mr., on the beaks of ducks,
i, 287.

Sageret. on grafts, ii. 18.

Salmons, males fighting, and hooked
jaws of, i. 108.

Salt water, how far injurious to
seeds, ii. 142.

—— not destructive to land-shells,
ii. 187.

SALTER.

INDEX,

STAR-FISHES,

335

Salter, Mr., on earl
embryos, ii. 23.
wna gus sulphuratus, i. 220.
Senne t, Prof, on Phyllotaxy, i.

Schiddte, on blind insects, i. 172.

a mn Salman os 290.
chlegel, on snakes, i. 178.

Schabl, -

268.

y death of hybrid

Dr., on the ears of mice, i.

oe » Mr., on the self-sterility of

orchids, ii. 7,

—,, on the crossing of varieties of

__ Verbascum, ii. 38,

Sea-water, how far injurious to
seeds, ii. 142.

—— not destructive to land-shells,
il. 187,

Sepa Sir J., on crossed animals,

1

Sedgwick, Prof., on groups of spe-
cies suddenly appearing, ii. 77.

a destroyed by insects, i.

Seeds, nutriment in, i. 94.

—, winged, i. 181.

—, means of dissemination, i.
240, 252; ii. 146,

—, power of resisting salt water,
ii. 148.

—, in crops and intestines ot
birds, ii..146.

——,, eaten by fish, ii. 146, 176.

—, in mud, ii. 175.

——, hooked, on islands, ii. 181.

Selection of domestic products, i. 34.

—, principle not of recent origin,
i, 39.

—,, unconscious, i. 39.

——, natural, i. 97.

—,, sexual, i. 107.

——,, objections to term, i. 99.

natural, has not induced steri-
lity, ii. 20.

Sexes, relations of, i. 108.

Sexual characters variable, i. 191.

—— selection, i. 107. aoe

Sheep, Merino, their selection, i. 36.

two sub-breeds, unintention-

ally produced, i. 41.

mountain varieties of, i. 93.

Shells, colours of, i. 165.

—, hinges of, i. 240. 7

—, littoral, seldom embedded, ii.
58.

—, fresh - water, long retain the
same forms, ii. 117.

Shells, fresh-water, dispersal of, ii.
173

——, of Madeira, ii. 180.

——,, land, distribution of, ii. 180.

—, land, resisting salt water, ii.
187.

Shrew-mouse, ii. 218.

Silene, infertility of crosses, ii. 14.

Silliman, Prof., on blind rat, i. 171.

Sirenia, their affinities, ii. 108.

Sitaris, metamorphosis of, ii. 252.

Skulls of young mammals, i. 248;
ii. 235.

Slave-making instinct, i. 336.

Smith, Col. Hamilton, on striped
horses, i. 200.

—, Mr. Fred., on slave-making
ants, i. 337.

——,, on neuter ants, i. 360.

Smitt, Dr., on the Polyzoa, i. 301.

Snake with tooth for cutting through
egg-shell, i. 334.

Somerville, Lord, on selection of
sheep, i. 35.

Sorbus, grafts of, ii. 19.

Sorex, li. 218.

Spaniel, King Charles’s breed, i. 40.

Specialisation of organs, i. 152.

Species, polymorphic, i. 54.

—., dominant, i. 67.

——, common, variable, i. 66.

—— in large genera variable, i. 69.

— ct es of suddenly appear-

il. 77,

a hence Silurian formations,
ii. 84.

—— successively appearing, ii. 89.

— _changi simultaneously
throughout the world, ii. 100.

Spencer, Lord, on increase in size of
cattle, i. 40.

——., Herbert, Mr., on the first steps
in differentiation, i. 155.

——, on the tendency to an equili-
brium in all forces, ii. 29.

Sphex, parasitic, i. 336.

Spiders, development of, ii. 245.

Sports in plants, i. 11.

Sprengel, C. C., on crossing, i. 119.

——, on ray-florets, i. 180.

Squalodon, ii. 108.

Squirrels, gradations in structure, i.
21

Staffordshire, heath, changes in, i

8r.
Stag-beetles, fighting, i. 108.
Bae takes, eyes of, i. "05.

STAR-FISHES,

336

INDEX.

UDDERS,

Star-Fishes, their pedicellarie, i. 299.

Sterility from changed conditions
of life, i. 10.

—— of hybrids, ii. 3.

— —, laws of, ii. 11.

——_ — ,, causes of, ii. 20.

— , from unfavourable conditions,
ii. 26.

— not induced through natural
selection, ii, 21.

St. Helena, productions of, ii. 178.

st. Hilaire, Aug., on variability of
certain plants, i. 272.

——, on classification, ii. 209.

St. John, Mr., on habits of cats, i.
B25.

Sting of bee, i. 256.

Stocks, aboriginal, of domestic ani-
mals, i. 22.

Strata, thickness of, in Britain, ii. 55.

Stripes on horses, i. 199.

Structure, degreesof utility of, i. 249.

Struggle for existence, i. 75.

Succession, geological, ii. 89.

—— of types in same areas, ii 121.

Swallow, one species supplanting
another, i. 98.

Swaysland, Mr., on earth adherin;
to the feet of migratory birds, il.
148,

Swifts, nests of, i. 355.

Swim-bladder, i. 230.

Switzerland, lake habitations of, i.
20.

System, natural, ii. 204.

T.

Tail of giraffe, i. 245.

-—— of aquatic animals, i. 246.

——,, prehensile, i. 294.

——, rudimentary, ii. 260.

Tanais, dimorphic, i. 55.

Tarsi, deticient, i. 168,

Tausch, Dr., on umbellifera, i. 271.

Teeth and hair correlated, i. 179.

——, rudimentary, in embryonic,
calf, ii, 255, 292:

Tegetmeier, Mr., on cells of bees, i.
346, 352.

Termminck, on distribution aiding
classification, ii. 211.

Tendrils, their deyelopment, i. 305.

bar i re Sir W., on the age of
the habitable world, ii. 83.

—— on the consolidation of the
crust of the earth, ii. 275.

Thouin, on grafts, ii. 19.

‘Thrush, aquatic species of, i. 222.

——, mocking, of the Galapagos, ii.
192.

—-, young of, spotted, ii. 241.

—, teat of i. 364.

‘Thuret, M., on crossed fuci, ii. 15.

‘Thwaites, Mr. on acclimatisation,
i. 174.

Thylacinus, ii. 220.

Tierra del Fuego, dogs of, i. 328.

——, plants of, ii. 169.

Timber-drift, li. 145.

Time, lapse of, ii. 51.

—— by itself not causing modifica-
tion, i. 126.

Titmouse, i. 220.

Toads on islands, ii. 182.

‘Tobacco, crossed varieties of, ii. 38.

Tomes, Mr., on the distribution ot
bats, ii. 184.

Transitions in varieties rare, i. 208.

Traquair, Dr., on flat-fish, i. 293.

Trautschold, on intermediate varie-
ties, ii. 66.

Trees on islands belong to peculiar
orders, ii. 182.

— with separated sexes, i. 123.

Trifolium pratense, i. 90,117.

—— incarnatum, i. 117.

Trigonia, ii. 99.

Trilobites, ii. 83.

——,, sudden extinction of, ii. 99.

Trimen, Mr., on imitating-insects,
li, 224,

Trimorphism in plants, i. 55; ii. 29,

Troglodytes, i. 264.

Tuco-tuco, blind, i. 170.

Tumbler pigeons, habits of, heredi-
tary, i. bor.

—~, young of, ii. 248.

Turkey-cock, tuft of hair on breast,
i. 110.

, naked skin on head, i. 248.

——. young of, instinctively wild,
i. 829.

Turnip and cabbage, analogous
variations of, i. 195.

Type, unity of, i. 260, 261.

Types, succession of, in same areag
ii. 121.

Typotherium, ii. 108.

U.

Udders enlarged by use, i. 12.
——, rudimentary, ii. 256.

ULEX,

INDEX,

WHALES,

337

Ulex, young leaves of, ii. 241.

Umbelliferee, flowers and seeds of,
i. 180.

——, outer and inner florets of, i. 270.

Unity of type, i. 260, 261.

Uria lacrymans, i. 113.

U oo of, under domestication,
i. 12.

——, effects of, in a state of nature,

i. 167.

Utility, how far important in the
construction of each part, i. 249.

Vv.

Valenciennes, on fresh-water fish,

& ii. ue by
ariability of mongrels and hy-
pad, i

Variation under domestication, i. 8.

caused by reproductive system
being affected by conditions of
life, 1. 10.

— under nature, i. 51.

——,, laws of, i. 164.

—, correlated, i. 18, 177, 248.

Variations appear at corresponding
ages, i. 16, 105.

— analogous in distinct species,
i. 193.

Varieties, natural, i. 50.

——,, struggle between, i. 93.

—, domestic, extinction of, i. 184.

——,, transitional, rarity of, i. 208.

— , when crossed, fertile, ii. 34.

Varieties, when crossed, sterile, ii.37.

—,, classification of, il. 215.

Verbascum, sterility of, ii. 7.

—, varieties of crossed, ii. 38.

Verlot, M., on double stocks, i. 358.

Verneuil,-M. de, on the succession
of species, ii. 103.

Vibracula of the Polyzoa, i. 301.

Viola, small imperfect flowers of,
i, 269.

——., tricolor, i. 90.

Virchow, on the structure of the
crystalline lens, i. 227.

Virginia, pigs of, i. 104, 7

Voleanic islands, denudation of, ii.

54,
Vulture, naked skin on head, i. 247.

WwW.

Wading-birds, ii. 175. oo.
Wagner, Dr., on Cecidomyia, ii. 239.

Wagner, Moritz, on the importance
of isolation, i. 127.

Wallace, Mr., on origin of species,
i. 2.

——,, on the limit of variation under
domestication, i. 48.

——, on dimorphic lepidoptera, i,
55, 362.

——, on races in the Malay Archi-
pelago, i. 58.

——, on the improvement of the
eye, i. 227,

—, on the walking-stick insect, i.
284,

——, on laws of geographical dis-
tribution, ii. 139.

ae on the Malay Archipelago, ii.
185.

, On mimetic animals, ii. 224.

Walsh, Mr. B. D., on phytophagic
forms, i. 60.

—, on equal variability, i. 195.

Water, fresh, productions of, ii. 171.

Water-hen, i. 222,

Waterhouse, Mr., on Australian
marsupials, i. 140.

——, on greatly developed parts
being variable, i. 185.

——,, on the cells of bees, i. 343.

——, on general affinities, ii. 227.

Water-ouzel, i. 222.

Watson, Mr. H. C., on range of
ae of British plants, i. 57,

3.

——, on acclimatisation, i. 134.

——, on flora of Azores, ii. 149.

——, on Alpine plants, li. 153.

——, on rarity of intermediate va-
rieties, i. 212.

——, on convergence, i. 156.

——, on the indefinite multiplica-
tion of species, i. 157.

Weale, Mr., on locusts transporting
seeds, ii. 147.

Web of feet in water-birds, i. 223.

Weismann, Prof., on the causes of
variability, i. 8.

——,, on rudimentary organs, ii. 260.

West Indian Islands, mammals of,
ii. 185,

Westwood, on species in large gen-
era being closely allied to others,
17,

as on the tarsi of Engide, i. 192.
——, on the antenne of hymeno-
terous insects, ii. 207.

ales, i. 285.

WHEAT.

338

INDEX.

ZEUGLODON.

Wheat, varieties of, i. 137.

White Mountains, flora of, ii. 151.

Whittaker, Mr., on lines of escarp-
ment, ii. 53. -

Wiehura, Max, on hybrids, ii. 24,
a7, 41.

Wings, reduction of size, i. 169.

— of insects homologous with
branchiz, i. 281. gi

—, rudimentary, in insects, ii.
255.

Wolf crossed with dog, i. 327.

. —— of Falkland Isles, ii. 183.

Wollaston, Mr., on varieties of in-
sects, i. 59.

——, on fossil varieties of shells in
Madeira, i. 65.

——, on colours of insects on sea-
shore, i. 165.

——,, on wingless beetles, i. 169.

—,, on rarity of intermediate va-
rieties, i, 212.

—, on insular insects, ii. 178.

——, on land-shells of Madeira nat-
uralised, ii. 193.

Wolves, varieties of, i. 111.

Woodcock with earth attached to
leg, ii. 148.

Woodpecker, habits of, i, 220.

—, green colour of, i, 247.

Woodward, Mr., on the duration of
specific forms, ii. 66.

——, on Pyrgoma, ii. 81.

——, on the continuous succession
of genera, ii. 93.

——, on the succession of types, ii.
121.

World, species changing simultane-
ously throughout, ii. 100.

Wrens, nest of, i. 364.

Wright, Mr. Chauncey, on the gi-
ratfe, i. 278.

—, on abrupt modifications, i.

Wyman, Prof., on correlation of
colour and effects of poison, i. 13.
——,, on the cells of' the bee, i. 345.

Xs
Youatt, Mr., on selection, i. 35.
——, on sub-breeds of sheep, i. 41.

—, on rudimentary horns in
young cattle, ii. 261.

Z.
Zanthoxylon, i. 272.

Zebra, stripes on, i. 199.
Zeuglodon, ii. 108,

(7%)

THE END.

wi eerrey

ar

fe to-

vee

erie
es)