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

SIl|P E B. Ml Slibrarg

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Charles Darwin.

WORLD'S FAMOUS BOOKS

The Origin of Species

By Means of Natural Selection

Or the Preservation of Favored
Races in the Struggle for Life

By
Charles Darwin

TWO VOLUMES IN ONE

Illustrated

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''But with regard to the material world, we can at least
go so far as this — we can perceive tliat events are brought
about not by insulated interpositions of Divine power,
exerted in each particular case, but by the establishment
of general laws." — Whewell: Bridgeivater Treatise.

''The only distinct meaning of the word * natural' is
stated, fixed or settled; since what is natural as much re-
quires and presu Piloses an intelligent agent to render it so,
i.e., ^o effect it continually or at stated times, as what is
supernatural or miraculous does to effect it for once." —
Butler: Analogy of Revealed Religion.

*' To conclude, therefore, let no man out of a weak con-
ceit of sobriety, or an ill-applied moderation, think or
maintain, that a man can search too far or be too welt
studied in the book of God's word, or in the book of God'*%
works; divinity or philosophy; but rather let me^i
endeavor an endless progress or proficience in both/^—-
Bacoj^: Advancement of Learning,

I

I

AN HISTORICAL SKETCH

OF THE PROGRESS OF OPINION ON THE ORIGIN

OF SPECIES,

PKEVIOUSLT TO THE PUBLICATIOJT OP THE FIRST EDITIOK

OF THIS WOEK.

I WILL here give a brief sketch of the progress of opin-
ion on the Origin of Species. Until recently the great
majority of naturalists believed that species were immut-
able 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 ])re exist-
ing forms. Passing over allusions to the subject in the
classical writers,* the first author who in modern times

*Aristotle, in liis " Pliysicae Auscultationes " (lib. 2, cap. 8, s. 2),
after remarking that rain does not fall in order to make tlie corn
grow, any more than it falls to spoil the farmer's corn when threshed
out of doors, applies the same argument to organization; 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,
Afif] in like manner as to other parts in which there appears to exist
an adaptation to an end. Wheresoever, therefore, all things
together (that is all the parts of one whole) happened like as if they
were made for the sake of something, these were preserved, having
been appropriately constituted by an internal spontaneity, and what-
soever things were not thus constituted, perished and still peri.'=;h."
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.

Vi HISTORICAL SKETCH.

has treated it in a scientific spirit was Buffon. Bn' as his
opinions fluctuated greatly at different periods, and as he
does not enter on the causes or means of the transforma-
tion 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 en-
larged them in 1809 in his " Philosophic Zoologique/^ and
subsequently, 1815, in the Introduction to his *'Hist. Kat.
des Animaux sans Vertebres." 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 probability of all change in tlie
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 distinguish-
ing species and varieties, by the almost perfect gradation
of forms in certain groups, and by the analogy of domestic
productions. With respect to the means of modification,
he attributed something to the direct action of the ph3'S-
ieal conditions of life, something to the crossing of
already existing forms, and much to use and disuse, that
is, to the etiects of habit. To this latter agency he seems
to attribute all the beautiful adaj^tations in nature; such
as the long ne'3k of the girafl'e for browsing on the 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 existence at the
present day of simple productions, he maintains that such
forms are now spontaneous!}' generated.*

Geoffroy Saint-Hilaire, as is stated in his ^^Life," writ-
ten by his son, suspected, as early as 1795, that what we
call species are various degenerations of the same type. It

* I have taken the date of the first publication of Lamarck from
Isidore Geoifroy Saint-Hilaire's ("Hist. Nat. Generale," torn, ii. p=
405, 1859) excellent history of opinion on this subject. In this work
a full account is given of Buffon's conclusions on the same subject.
It is curious how largely my grandfather, Dr. Erasmus DarAvin,
anticipated the views and erroneous grounds of opinion of Lamarck
in his "Zoonomia" (vol. i. pp. 500-510), published in 1704. Accord-
ing to Isid. Geoft'roy there is no doubt that Goethe was an extreme
pOFiasan ci amilax views^ as shown in the iartroduclaon fco a woa-k

BISTORIGAL SKETCH. yf\\

was not until 1828 that he published his conviction that
the same forms have not been perpetuated since the origin
of all things. Geoffroy seems to have relied chiefly on the
conditions of life, or the ^'moncle ambiant" as the cause of
change. He was cautious in drawing conclusions, aud did
not believe that existing species are now undergoing modi-
fication; and, as his son adds, "C'est done un probleme a
reserver enti^rement a Favenir, suppose meme que Tavenir
doive avoir prise sur lui/'

In 1813 Dr. W. C. Wells read before the Royal Society
"An Account of a White Female, part of whose skin
resembles that of a ISTegro ; " but his paper was not pub-
lished until his famous " Two Essays upon Dew and Single
Vision^' appeared in 1818. In this pai:)er he distinctly
recognizes the principle of natural selection, and this is the
first recognition which has been indicated; but he applies
it only to the races of man, and to certain characters alone.
After remarking that negroes and mulattoes enjoy an im-
munity from certain tropical diseases, he observes, firstly,
that all animals tend to vary in some degree, and, secondly,
that agriculturists improve their domesticated amimals by
selection; and then, he adds, but what is done in this
latter case " by art, seems to be done with equal efficacy,
though more slowly, by nature, in the formation of varie-
ties of mankind, fitted for the country which they inhabit.
Of the accidental varieties of man, which would occur
among the first few and scattered inhabitants of the middle
regions of Africa, some one would be better fitted than
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 neighbors. The color of this
vigorous race I take for granted, from what has been

written in 1794 and 1795, but not pubUslied till long afterward: lie
lias pointedly remarked ("Goethe als Naturforscher," von Dr. Karl
Meding, s. 34) that the future question for naturalists will be how, for
instance, cattle got their horns and not for what they are used. It is
rather a singular instance of the manner in which simihir views arise
at about the same time, that Goethe in Germany, Dr. Darwin in Eng-
land, and GeofEroy Saint- Hilaire (as we shall immediately see) in
France, came to the same conclusion on the origin of species, in the
years 1794-5.

Tiii ' HISTORICAL SKETCH.

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 samxC views to the white inhabitants of
colder climates. I am indebted to Mr. Rowley, of the
United States, for having called my attention, through Mr.
Brace, to the above passage of Dr. Wells' work.

The Hon. and Rev. W. Herbert, afterward Dean of
Manchester, in the fourth volume of the '^ Horticultural
Transactions," 1822, and in his work on the *' Amarylli-
dacese*' (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 con-
dition, and that these have produced, chiefly by inter-
crossing, but likewise by variation, all our existing species.

In 1826 Professor Grant, in the concluding paragraph
in his well-known paper (*'* Edinburgh Philosophical
Journal," vol. xiv, p. 283) on the Spongilla, clearly de-
clares 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 Fifty-fifth
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 enlarged
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 subject, so that it re-
mained unnoticed until Mr. Matthew himself drew atten-
tion to it in the '* Gardeners' Chronicle," on April 7,
1860. The differences of Mr. Matthew's views from mine
are not of much importance: he seems to consider that the
world was nearly depopulated at successive periods, and
then restocked; and he gives as an alternative, that uew

mSTOniCAL SKETCH. ix

forms may be generated '' without the presence of any
mold 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 prin-
ciple 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.

Eafinesque, in his '^ New Flora of North America," pub-
lished in 1836, wrote (p. 6) as follows: '''All species might
have been varieties once, and many varieties are gradually
becoming species by assuming constant and peculiar char-
acters;" but further on (p. 18) he adds, ''except the
original types or ancestors of the genus."

In 1843-44 Professor Haldeman f " 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 toward
the side of change.

The " Vestiges of Creation" appeared in 1844. In the
tenth and much improved edition (1853) the anony-
mous 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 providence
of God, the results, first, of an impulse which has been im-
parted to the forms of life, advancing them, in definite
times, by generation, through grades of organization ter-
minating in the highest dicotyledons and vertebrata, these
grades being few in number, and generally marked by in-
tervals of organic character, which we find to be a practi
cal difficulty in ascertaining affinities; second, oi another
impulse connected with the vital forces, tending, in the
course of generations, to modify organic structures in ac-
cordance Avith external circumstances, as food, the nature
of the habitat, and the meteoric agencies, these being the
' adaptations ' of the natural theologian." The author ap-
parently believes that organization progresses by sudden
leaps, but that the effects produced by the conditions of

X HISTORICAL SKETCH.

life are gradual. He argues witli much force on general
grounds that species are not immutable productions. But
I cannot see how the two supposed ^ 'impulses"^ account in a
scientific sense for the numerous and beautiful coadaptations
which we see tliroughout nature; I cannot see that we
thus gain an 3^ 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 early editions little accurate knowledge and a great
want of scientific caution, immediately had a very wide
circulation. In my opinion it has done excellent service
in this country in calling attention to the subject, in re-
moving prejudice, and in thus preparing the ground for
the reception of analogous views.

In 1846 the veteran geologist M. J. d'Omalins d^Halloy
published in an excellent though short paper (" Bulletins
de FAcad. Roy. Bruxelles," torn, xiii, p. 581) his opinion
that it is more probable that new species have been pro-
duced by descent with modification than that they have
been separately created: the author first promulgated this
opinion in 1831.

Professor Owen, in 1819 (^'ISTature of Limbs," p. 86),
wrote as follows: '* The archetypal idea was manifested
in the flesh under diverse such modifications, upon this
planet, long prior to the existence of those animal species
that actually exemplify it. To what natural laws or secon-
dary 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 xA.ssociation,
in 1858, he speaks (p. li) of ''the axiom of the continuous
operation of creative power, or of the ordained becoming
of living things.''^ Further on (p. xc), after referring to
geographical distribution, he adds, "These phenomena
shake our confidence 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' tlie 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

EISTOmCAL SKETCH. xi

how the Red Grouse came to be there, and there exclu-
sively; signifying also, by this mode of expressing such
ignorance, his belief that both the bird and the islands
owed their origin to a great first Creative Cause." If we
interpret these sentences given in the same address, one by
the other, it appears that this eminent philosopher felt in
1858 his confidence shaken that the Apteryx and the Red
Grouse first appeared in their respective homes *' he knew
not how," or by some process *'he knew not what."

Tliis 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 published, 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 palgeon-
tologists as being firmly convinced of the immutability of
species; but it appears (^'Anat. of Vertebrates," vol. iii,
p. 796) that this was on my part a preposterous error. In
the last edition of this work I inferred, and the inference
still seems to me perfectly just, from a passage beginning
with the words "no doubt the type-form," etc. (Ibid., vol.
i, p. xxxv), that Professor Owen admitted that natural
selection may have done something in the formation of a
new species ; but this it appears (Ibid., vol. iii, p. 798) is
inaccurate and without evidence. I also gave some extracts
from a correspondence between Professor Owen and the
editor of the ^' London Review," from which it appeared
manifest to the editor as well as to myself, that Professor
Owen claimed to have promulgated the theory of natural
selection before I had done so ; and I expressed my sur-
prise and satisfaction at this announcement ; but as far as
it is possible to understand certain recently published pas-
sages (Ibid., vol. iii, p. 798) I have either partially or
wholly again fallen into error. It is consolatory to me
that others find Professor Owen^s controversial writings as
difficult to understand and to reconcile with each other, as
I do. As far as the mere enunciation of the principle of
natural selection is concerned, it is quite immaterial
whether or not Professor Owen preceded me, for both of
us, as shown in this historical sketch, were long ago pre-
ceded by Dr. Wells and Mr. Matthews.

xii HISTORICAL SKETCH.

M. Isidore Geoffroy Saint-Hilaire, in his lectures deliv-
ered in 1850 (of which a Resume appeared in the *' Revue
et Mag. de Zoolog.," Jan., 1851), briefly gives his reason
for believing that specific characters ''sont fixes, pour
chaque espece, tant qu'elle se perpetue au milieu des
memes circonstauces: ils se moditient, si les circonstances
ambiantes viennent a changer." '^En resume, Vobserva-
tion des animaux sauvages demontre deja la variabilite
limit ee des especes. Les experiences sur les animaux
sauvages devenus domestiques, et sur les animaux domes-
tiques redevenus sauvages, la demontrent plus clairement
encore. Ces memes experiences prouvent, de plus, que les
differences produites peuvent etre de valeu7' generique.'*
In his ^aiist. Nat. Generale'' (tom. ii, p. 430, 1859) he
amplifies analogous conclusions.

From a circular lately issued it appears that Dr. Freke,
m 1851 {'' Dublin Medical Press," p. 332), propounded
the doctrine that all organic beings have descended from
one primordial form. His grounds of belief and treat-
ment of the subject are wholly different from mine ;
but as Dr. Freke has now (1861) published his Essay on
^he ^' Origin of Species by means of Organic Affinity,'^
the difficult attempt to give any idea of his views would
be superfluous on my part.

Mr. Herbert Spencer, in an Essay (originally 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
remarkable skill and force. He argues from the analogy
of domestic productions, from the changes which the em-
bryos of many species undergo, from the difficulty of dis-
tinguishing species and varieties, and from the principle of
general gradation, that species have been modified ; and
he attributes the modification to the change of circum-
Btances. The author (1855) has also treated Psychology
on the principle of the necessary acquirement of each
mental power and capacity by gradation.

In 1852 M. Naudin, a distinguished botanist, expressly
stated, in an admirable paper on the Origin of Species
(•'Revue Horticole," p. 1k)Z \ since partly republished in
the *']SIouvelles Archives du Museum," tom. i, p. 171), his
belief that species are formed in an analogous manner as

HISTORICAL, SKETCH. xiii

varieties are under cultivation ; and the latter process lie
attributes to man's power of selection. But he does not
show how selection acts under nature. He believes,
like Dean Herbert, that species, when nascent, were more
plastic tlian at present. He lays weight on wliat he calls
the principle of finality, " puissance mysterieuse, ind6-
terminee ; fatality pour les uns ; pour les autres volonte
providentielle, dont Taction incessante sur les ^tres vi-
vantes determine, a toutes les epoques de Fexistence du
monde, la forme, le volume, et la duree de chacun d'eux,
en raison de sa destinee dans Tordre de choses dont il fait
partie. C'est cette puissance qui harmonise chaque
membre a Fensemble, en Tappropriant a la fonction qu'il
doit remplir dans Torganisme general de la nature, fonc-
tion qui est pour lui sa raison d'etre." *

In 1853 a celebrated geologist, Count Keyserling (*^ Bul-
letin de la Soc. Geolog.," 2d Ser., tom. x, p. 357), sug-
gested 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 alfected by circumambient molecules of a
particular nature, and thus have given rise to new forms.

In this same year, 1853, Dr. Schaaffhausen published an
excellent pamphlet (^^Verhand. des Naturhist. Vereins der
Preuss. Rheinlands," etc.), in which he maintains the de-
velopment of organic forms on the earth. He infers that
many species have kept true for long periods, whereas a
fcAV have become modified. The distinction of species he
explains by the destruction of intermediate graduated

*Fiom references in Bronn's " Untersuchungen ilber die Ent-
wickeluiigs-Gesetze," it appears that the celebrated bot-anist and
palaeontologist Unger published, in 1852, his belief that species
undergo development and modification. Balton, likewise, in Pander
and Dalton's work on Fossil Sloths, expressed, in 1821, a similar
belief. Similar views have, as is well known, been maintained by
Oken in his my?;tical "Natur-Philosophie." From other references
in Godron's work "Sur I'Espece," 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-fonr
authors named in this Historical Sketch, who believe in the modi-
cation of species, or at least disbelieve in separate acts of crea-
tion, twenty-seven have written on ^)ecial branches of natural
kistory or geology.

XiT HISTORICAL SKETCH,

forms. ** Thus living plants and animals are not sepa-
rated from the extinct by new creations, but are to be
regarded as their descendants through continued repro-
duction/'

A well-known French botanist, M. Lecoq, writes in
1854 ('^Etudes sur Geograph. Bot. torn, i, p. 250), "On
voit que nos recherches sur la fixite ou la variation de
Tespece, nous conduisent directement aux idees emises
par deux hommes justement celebres, Geoffroy Saint-
Hilaire et Goethe." Some other passages scattered through
M. TiCcoq^s large work make it a little doubtful how far he
extends his views on the modification of species.

The "Philosophy of Creation '' has been treated in a
m-: ^terly manner by the Rev. Baden Powell, in his "Essays
on the Unity of Worlds," 1855. Nothing can be more
striking than the manner in which he shovv^s that the intro-
duction of new species is "a regular, not a casual phenom-
enon," 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 1, 1858, by Mr.
Wallace and myself, in which, as stated in the introductory
remarks to this volume, the theory of Natural Selection is
promulgated by Mr. Wallace with admirable force and
clearness.

Von Baer, toward whom all zoologists feel so profound a
respect, expressed about the year 1859 (see Prof. Rudolph
Wagner, " Zoologisch-Anthropologische Untersuchungen,"
1861, s. 51) his conviction, chiefly grounded on the laws of
geographical distribution, that forms now perfectly distinct
have descended from a single parent-form.

In June, 1859, Professor Huxley gave a lecture before
the Royal Institution on the " Persistent Types of Animal
Life." Referring to such cases, he remarks, " It is difficult
to comprehend the meaning of such facts as these, if we
suppose that each species of animal and plant, or each
great type of organization, was formed and placed upon the
surface of the globe at long intervals by a distinct act of
creative power; and it is well to recollect that such an
assumption is as 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 r^ation to

mSTORIOAL SKETCM. xt

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 unproven, and
sadly damaged by some of its supporters, is yet the only
one to which physiology lends any countenance; their
existence would seem to show that the amount of modifica-
tion 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 modifica-
tion of species, and supports this doctrine by many original
observations.

The first edition of this work was published on Novem-
ber 24, 1859, and the second edition on January 7, 1860.

\

CONTENTS.

PiGB.

Introduction 1

CHAPTER I.

VAmATION UNDER DOMESTICATION.

Causes of Variability — EfEects of Habit and the use or disuse
of Parts — Correlated Variation— Inberitance — Character of
Domestic Varieties — Difficulty of distinguishing between
Varieties and Species — Origin of Domestic Varieties from
one or more Species — Domestic Pigeons, their Diiferences
and Origin — Principles of Selection, anciently followed,
their Elfects — Methodical and Unconscious Selection —
Unknown Origin of our Domestic Productions — Circum-
stances favorable to Man's power of Selection 6

CHAPTER n.

VARIATION UNDER NATURE.

Variability — Individual differences — Doubtful species — Wide
ranging, much diffused, and common species, vary most —
Species of the larger genera in each country vary more
frequently than the species of the smaller genera — Many
of the species of the larger genera resemble varieties in
being very closely, but unequally, related to each other, and
in having restricted ranges 89

CHAPTER III.

STRUGGLE FOR EXISTENCE.

Its bearing on natural selection — The term used in a wide
sense — Geometrical ratio of increase — Rapid increase of
naturalized animals and plants — Nature of the checks to
increase — Competition universal — Effects of climate — Pro-
tection from the number of individuals— Complex relations
of all animals and plants throughout nature— Struggle for

xviii CONTENTS.

Pass.
life most severe between individuals and varieties of tlie
same species: often severe between species of the same
genus — The relation of organism to organism the most
important of all relations 57

CHAPTER IV.

NATURAJj SELECTION; OR THE SUBVIVAL OP 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 — Circumstances favorable and unfavorable to the
results of Natural Selection, namely, intercrossing, isolation,
number of individuals — Slow action — Extinction caused by
Natural Selection — Divergence of Character, related to the
diversity of inhabitants of any small area and to naturaliza-
tion— Action of Natural Selection, through Divergence of
Character and Extinction, on the descendants from a
common parent — Explains the grouping of all organic
beings — Advance in organization — Low forms preserved —
Convergence of character — Indefinite multiplication of
species — Summary 73

CHAPTER V.

LAWS OF VARIATION.

Effects of changed conditions — Use and disuse, combined
with natural selection; organs of flight and of vision —
Acclimatization — Correlated variation — Compensation and
economy of growth — False correlations — Multiple, rudi-
mentary and lowly organized structures variable — Parts
developed in an unusual manner ai'e highly variable;
specific characters more variable than generic; secondaiy
sexual characters variable — Species of the same genus vary
in an analogous manner — Reversions to long-lost charac-
ters— Summary 126

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 diflBculty — Natura non facit saltum — Organs of

CONTENTS, xix

Page.
small importance — Organs not in all cases absolutely per-
fect— The law of Unity of Type and of the Conditions of
Existence embraced by the theory of Natural Selection 108

CHAPTER VII.

MISCELLANEOUS OBJECTIONS TO THE THEORY OP NATURAL

SELECTION.

Longevity — Modifications not necessarily simultaneous — Modi-
fications apparently of no direct service — Progressive
development — Characters of small functional importance,
the most constant — Supposed incompetence of natural selec
tion to account for the incipient stages of useful structures
— Causes which interfere with the acquisition through
natural selection of useful structures — Gradations of struct-
ure with changed functions — Widely different organs in
members of the same class, developed from one and the
same source — Reasons for disbelieving in great and abrupt
modifications 199

CHAPTER VIIL

INSTINCT.

Instincts comparable with habits, but different in their
origin — Instincts graduated — Aphides and ants — Instincts
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 243

CHAPTER IX.

HYBRIDISM.

Distinction between the sterility of first crosses and of
hybrids — Sterility various in degree, not universal, affected
by close interbreeding, removed by domestication — Laws
governing the sterility of hybrids— Sterility not a special
endowment, but incidental on other differences, not accumu-
lated 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 univereal— Hybrids and mon-
grels compared independently of their fertility— Summary... 277

XX CONTENTS.

CHAPTER X.

OTT THE IirPERFECTION OF THE GEOLOGICAL HECOHD.

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 rale of
denudation and of deposition — On the lapse of time as esti-
mated by years — On the poorness of our palseontological col-
lections— On the intermittence of geological formations — On
the denudation of granitic areas — On the absence of inter-
mediate varieties in any one formation — On the sudden
appearance of groups of species — On their sudden appear-
ance in the lowest known fossiliferous strata — Antiquity of
the habitable earth 313

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 appearance 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 843

CHAPTER XII.

GEOGRAPHICAL DISTRIBUTIOK.

Present distribution cannot be accounted for by differences
in physical conditions — Importance of barriers — Affinity
of the productions of the same continent — Centers of crea-
tion— 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 „ 375

CHAPTER XIII.

GEOGRAPHICAL DISTRIBUTION — Continued.

Distribution of fresh-water productions — On the inhabitants
of oceanic islands — Absence of Batrachians and of terrestrial
Mammals — On the relation of the inhabitants of islands to

CONTENTS.

ixi

Paox.
tliose of the nearest mainland — On colonization from the
nearest source with subsequent modification— Summary of
the last and present chapter 405

CHAPTER XIV.

MUTUAL AFFINITIES OF ORGANIC BEINGS: MORPHOLOGY — KMEBY-

OLOGY — RUDIMENTARY ORGANS.

Classification, groups subordinate to groups — Natural system —
Rules and difficulties in classification, explained on the
theory of descent with modification — Classification of varie-
ties— Descent always used in classification — Analogical or
adaptive characters — Affinities, general, complex and radiat-
ing— Extinction separates and defines groups — Morphology,
between members of the same class, between parts of the
same individual — Embryology, laws of, explained by varia-
tions not supervening at an early age, and being inherited
at a corresponding age — Rudimentary organs, their origin
explained — Summary 428

CHAPTER XV.

RECAPITULATION AND CONCLUSION.

Recapitulation of the objections to the theory of Natural Selec-
' tion — Recapitulation of the general and special circum-
stances in its favor — Causes of the general belief in the
immutability of species — How far the theory of Natural
Selection may be extended — Effects of its adoption on
the study of Natural History — Concluding remarks 476

Glossary op Scientific Terms 507

Index ^21

ORIGIN OF SPECIES.

mTRODUOTIOK

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 inhabitants
of that continent. These facts, as will be seen in the latter
chapters of this volume, seemed to throw some light on the
origin of species — that mystery of mysteries, as it has been
called by one of our greatest philosophers. On my return
home, it occurred to me, in 1837, that something might
perhaps be made out on this question by patiently accumu-
lating and reflecting on all sorts of facts which could possi-
bly have any bearing on it. After five years' work I
allowed 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 probable: from
that period to the present day I have steadily pursued the
same object. I hope that I may be excused for entering
on these personal details, as I give them to show that I
have not been hasty in coming to a decision.

My work is now (1859) nearly finished; but as it will
take me many more years to com23lete it, and as my health
is far from strong, I have been urged to publish this ab-
stract. 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
ihird volume of the Journal of that Society. Sir C. Lyell

2 INTRODUCTION.

and Dr. Hooker, who both knew of my work — the latter
having read my sketch of 18-4-i — lionored me by thinking
it advisable to publish, with Mr. Wallace's excellent memoir,
gome brief extracts from my manuscripts.

This abstract, which I now publish, must necessarily be
imperfect. I cannot here give references and authorities
for my several statements; and I must trust to the reader
reposing some confidence in my accuracy. No doubt errors
may have crept in, though I hope I have always been cau-
tious 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 references, on which my conclusions have been
grounded; and I hope in a future work to do this. For
I am well aware that scarcely a single point is discussed in
this volume on which facts cannot be adduced, often ap-
parently leading to conclusions directly opposite to those
at which I have arrived. A fair result can be obtained
only by fully stating and balancing the facts and arguments
on both sides of each question; and this is here impossible.

I much regret that want of space prevents my having
the satisfaction of acknowledging the generous assistance
which I have received from very many naturalists, some
of them personally unknov/n to me. I cannot, however,
let this opportunity i3ass 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 conceiv-
able that a naturalist, reflecting on the mutual affinities of
organic beings, on their embryological relations, their
geographical distribution, geological succession, and other
such facts, might come to the conclusion that species had
not been independently created, but had descended, like
varieties, from other species. Nevertheless, such a con-
clusion, even if well founded, would be unsatisfactory, until
it could be shown how the innumerable s]">ecies, inhabit-
ing this world have been modified, so as to acquire that
perfection of structure and coadaptation which justly
excites our admiration. Naturalists continually refer to

INTRODUCTION, 9

external conditions, each as climate, food, etc., as the only
possible cause of variation. In one limited sense, as we
shall hereafter see, this may be true; but it is preposterous
to attribute to mere external conditions, the structure, for
instance, of the woodpecker, with its feet, tail, beak and
tongue, so admirably adapted to catch insects under the
bark of trees. In the case of the mistletoe, which draws
its nourishment from certain trees, which has seeds that
must be transported by certain birds, and which has flowers
with separate sexes absolutely requiring the agency of cer-
tain 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 coadaptation.
At the commencement of my observations it seemed to me
probable that a careful study of domesticated animals and
of cultivated plants would offer the best chance of making
out this obscure problem. Nor have I been disappointed;
in this and in all other perplexing cases I have invariably
found that our knowledge, imperfect though it be, of vari-
ation under domestication, afforded the best and safest
clue. I may venture to express my conviction of the high
value of such studies, although they have been very com-
monly neglected by naturalists.

From these considerations, I shall devote the first chap-
ter of this abstract to variation under domestication. "We
shall thus see that a large amount of hereditary modifica-
tion is at least possible; and, what is equally or more im-
portant, 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, how-
ever, be enabled to discuss what circumstances are most
favorable to variation. In the next chapter the strug-
gle for existence among all organic beings throught)ut
the world, which inevitably follows from the high geomet-
rical ratio of their increase, will be considered. This i^s

4 INTRODUCTION.

the doctrine of Malthns, applied to the whole animal and
vegetable kingdoms. As many more individuals of each
species are born than can possibly survive; and as, conse-
quently, there is a frequently recurring struggle for exist-
ence, it follows that any being, if it vary however slightly
in any manner profitable to itself, under the complex and
sometimes varying conditions of life, will have a better
chance of surviving, and thus be naturally selected. From
the strong principle of inheritance, any selected variety
will tend to propagate its new and modified form.

This fundamental subject of natural selection will be
treated at some length in the fourth chapter; and we shall
then see how natural selection almost inevitably causes
much extinction of the less improved forms of life, and
leads to what I have called divergence 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 tran-
sitions, or how a simple being or a simple organ can be
changed and perfected into a highly developed being or
into an elaborately constructed organ; secondly, the sub-
ject of instinct, or the mental powers of animals; thirdly,
hybridism, or the infertility of species and the fertility of
varieties when intercrossed; and fourthly, the imperfection
of the geological record. In the next chapter I shall con-
sider the geological succession of organic beings through-
out time; in the twelfth and thirteenth, their geogi'aphical
distribution throughout space; in the fourteenth, 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 ransre 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 modifica-

INTRODUCTION. 5

tion of every inhabitant of this world. Still less do we
know of the mutual relations of the innumerable inhab-
itants of the world during the many past geological epochs
in :.ts history. Although much remains obscnre^ 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 entertained, and which I formerly entertained —
namely, that each species has been independently created
— is erroDeous. I am fully convinced that species are not
immutable^ but that those belonging to what are called the
same genera are lineal descendants of some other and
generally extinct species, in the same manner as the
acknowledged varieties of any one species are the descend-
ants of that species. Furthermore, I am convinced that
natural selection has been the most important, but not tho
exclusive, means of modification.

VABIATIOM UNDER DOMESTICATION,

CHAPTER L

VARIATION" UNDER DOMESTICATION".

Causes of Varialjility — Effects of Habit and tlie use or disuse of
Parts — Correlated Variation — Inheritance — Character of Domes-
tic Varieties — Dilficulty 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 favorable to Man's
power of Selection.

CAUSES OF VARIABILITY.

When we compare the individuals of the same variety
or sub-variety of our older cultivated plants and animals,
one of the first points which strikes us is, that they gen-
erally differ more from each other than do the individuals
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 con-
ditions of life not so uniform as, and somewhat different
from, those to which the parent species had been exposed
under nature. There is, also, some probability in the view
propounded by Andrew Knight, that this variability may
be partly connected with excess of food. It seems clear
that organic beings must be exposed during several gener-
ations to new conditions to cause any great amount of
variation; and that, when tlie organization has once begun
to vary, it generally continues varying for many gener-
ations. No case is on record of a variable organism ceas-
ing to vary under cultivation. Our oldest cultivated
plants, such as wheat, still yield new varieties: our oldest

vauiation under domestication. 7

domesticated animals are still capable of rapid improve-
ment or modificationc

As far as I am able to judge, after long attending to the
subject, the conditions of life appear to act in two wavs —
directly on the wliole organization or on certain parts
alone^ and indirectly by aifecting the reproductive system.
With respect to the direct action, we must bear in mind
that in every case, as Professor Weismann has lately
insisted, and as I have incidently shown in my work on
'^Variation under Domestication,^^ there are two factors:
namely; the nature of the organism and the nature of the
conditionSc The former seeuis to be much the more
important, for nearly similar variations sometimes arise
under, as far as we can judge, dissimihir conditions; aud,
on the other hand, dissimilar variations arise under condi-
tions which appear to be nearly uniform. The effects on
the offspring are either definite or indefinite. They may
be considered as definite when all or nearly all the offspring
of individuals exposed to certain conditions during several
generations are modified in the same manner. It is
extremely difficult to come to any conclusion in regard to
the extent of the changes which have been thus definitely
induced. There can, however, be little doubt about many
slight changes, such as size from the amount of food,
color from the nature of the food, thickness of the skin
and hair from climate, etc. Each of the endless variations
which we see in the plumage of our fowls must have had
some efficient cause; and if the same cause were to act
uniformly during a long series of generations on many
individuals, all probably would be modified in the same
manner. Such facts as the complex and extraordinary
outgrowths which variably follow from the insei'tiou of a
minute drop of poison by a gall-producing insect, shows us
what singular modifications might result in the case ot
plants from a chemical change in the nature of the sap.

Indefinite variability is a much more common result of
changed conditions than definite variability, and has prob-
ably played a more important part in the formation of our
domestic races. We see indefinite variability in the end-
less 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

g VARIATION UNDER DOMBSTIGATIONo

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 country
and fed on nearly the same food, deviations of structure so
strongly pronounced as to deserve to be called monstros-
ities arise; but monstrosities cannot be separated by any
distinct line from slighter variations. All such changes of
itructure, whether extremely slight or strongly marked,
which appear among many individuals living together,
m-dy be considered as the indefinite effects of the condi-
tions of life on each individual organism, in nearly the
same manner as the chill effects different men in an indefi-
nite manner, according to their state of body or constitu-
tion, causing coughs or colds, rheumatism, or inflammation
of various organs.

With respect to what I have called the indirect action of
changed conditions, namely, through the reproductive
system of being affected, we may infer that variability is
thus induced, partly from the fact of this system being
extremely sensitive to any change in the conditions, and
partly from the similarity, as Kolreuter and others have
remarked, between the variability which follows from the
crossing of distinct species, and that which may be observed
with plants and animals when reared under new or unnat-
ural conditions. Many facts clearly show how eminently
susceptible the reproductive system is to very slight
changes in the surrounding conditions. Nothing is more
easy than to tame an animal, and few things more difficult
than to get it to breed freely under confinement, even when
the male and female unite. How many animals there are
which will not breed, though kept in an almost free state in
their native country I This is generally, but erroneously
attributed to vitiated instincts. Many cultivated plants
display the utmost vigor, 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
laws are which determine the reproduction of animals

VARIATION UNDER DOMESTICATION. 9

under confinement, I may mention thiit carnivorous
animals, even from the tropics, breed in tliis country
pretty freely under confinement, with the exception of the
plantigrades or bear family, which seldom produce young;
whereas carnivorous birds, with the rarest exception, hardly
ever lay fertile eggs. Many exotic plants have pollen
utterly worthless, in the same condition as in the most
sterile hybrids. When, on the one hand, we see domesti-
cated 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
reproductive 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 irregu-
larly, 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 reproduct-
ive organs are not easily affected; so will some animals and
plants withstand domestication or cultivation, and vary
very slightly — perhaps hardly more than in a state of
nature.

Some naturalists have maintained that all variations are
connected with the act of sexual reproduction; but this is
certainly an error; for I have given in anotlier work a long
list of '' sporting plants, ^^ as they are called by gardeners;
that is, of plants which have suddenly produced a single
bud with a new and sometimes widely different character
from that of the other buds on the same plant. These
bud variations, as they may be named, can be propagated
by grafts, off'sets, etc., and sometimes by seed. They
©ocur rarely under nature, but are far from rare under
culture. As a single bud out of many thousands produced
year after year on the same tree under uniform conditions,
nas been known suddenly to assume a new cha7*acter; 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 nectarines,
and buds on common roses producing moss-roses — we
cl«arly see that the nature of the conditions is of subordi-

10 VARIATION UNDER DOMESTICATION.

nate importance in comparison with the nature of the
organism in determining each particular form of varia-
tion; perhaps of not more importance than the nature of
the spark, by which a mass of combustible matter is
ignited, has in determining the nature of the flames.

EFFECTS OF HABIT AND OF THE USE OR DISUSE OF PARTS;
CORRELATED VARIATIO:?^; IIs^HERITANCE.

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;
thas I find in the domestic duck that the bones of the
wing weigh less and the bones of the leg more, in
proportion to the whole 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 in countries where they are habitually milked, in
comparison with these organs in other countries, is prob-
ably 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 sug-
gested that the drooping is due to disuse of the muscles of
the ear, from t!.e animals being seldom much alarmed,
seems probable.

Many laws regulate variation, some few of which can bo
dimly seen, and will hereafter be briefly discussed. I will
here only allude to what may he called correlated variation.
Important changes in the embryo or larva will probablv
entail changes in the mature animal. In monstrosities, the
correlations between quite distinct parts are very curious;
and many instances are given in Isidore G-eoffroy St.
Hilaire's great work on this subject. Breeders believe that
long limbs are almost always accompanied by an elongated
head. Some instances of correlation are quite whimsical;
thus cats which are entirely white and have blue eyes are
generally deaf; but it has been lately stated by Mr. Tait
that this is conflned to the males. Color and constitu-
tional pecularities go together, of which many remarkable

VARIATTOJSr UNDER DOMESTICATION. i\

cases could be given among animals and plants. From
facts collected by Heusinger, it appears that wliite sheep
and pigs are injured by certain pUints, while dark-colored
individuals escape: Professor Wyman has recently com-
municated to me a good illustration 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 colored their bones pink, and which
caused the hoofs of all but the black varieties to drop otf;
and one of the '^ crackers" (/. 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; pigeon.s
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 cer-
tainly 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, etc. ; and it is really
surprising to note the endless points of structure and con-
stitution in which the varieties and sub-varieties differ
slightly from each other. The whole organization 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 consider-
able physiological importance, are endless. Dr. Prosper
Lucas^ treatise, in two large volumes, is the fullest
and the best on this subject. No breeder doubts liow
strong is the tendency to inheritance; that like pi'o
duces like is his fundamental belief : doubts have
been thrown on this principle only by theoretical
writers. AYhen any deviation of structure often appears,
and we see it in the father and child, we cannot tell
whether it may not be due to the same cause having acted

12 VARIATION UNDER DOMESTICATION.

on both; but when among individuals, apparently exposed
to the same conditions, any very rare deviation, due to
some extraordinary combination of circumstances, appeals
in the parent — say, once among several million individu-
als— and it reappears in the child, the mere doctrine of
ciiances almost compels us to attribute its reappearance to
inheritance. Every one must have heard of crises of al-
binism, prickly skin, hairy bodies, etc., appearing in
several members of the same family. If strange and rare de-
viations of structure are really inherited, less strange and
commoner deviations may be freely admitted to be inherit-
able. Perha^DS the correct way of viewing the whole
subject would be, to look at the inheritance of every
character whatever as the rule, and non-inheritance as the
anomaly.

The laws governing inheritance are for the most part
unknown. No one can say why the same peculiarity in
different individuals of the same species, or in different
species, is sometimes inherited and sometimes not sOo why
the child often reverts in certain characteristics to its grand-
father or grandmother or more remote ancestor; why a
peculiarity is often transmitted from one sex to both sexes,
or to one sex alone, more commonly but not exclusively to
the like sex. It is a fact of some importance to us, that
peculiarities appearing in the males of our domestic breeds
are often transmitted, either exclusively or in a much
greater degree, to the males alone. A much more im-
portant rule, which I think may be trusted, is that, at
whatever period of life a peculiarity first appears, it tends
to reappear in the offspring at a corresponding age, though
sometimes earlier. In many cjises this could not be other-
wise; thus the inherited peculiarities in the horns of cattle
could appear only in the offspring when nearly mature;
peculiarities in the silk-worm are known to appear at the
corresponding caterpillar or cocoon stage. But hereditary
diseases and some other facts make me believe that the
rule has a wider extension, and that, when there is no ap-
parent reason why a peculiarity should appear at any
particular age, yet that it does tend to appear in the off-
spring at the same period at Avhich it first appeared in the
parent. I believe this rule to be of the highest importance
in explaining the laws of embryology. These remarks are

VARIATION- UNDER DOMESTICATION. I3

of course confined to the first appearance of the peculiarity,
and not to the primary cause which may have acted on the
ovules or on the male element; in nearly the same manner
as the increased length of the horns in the oifspring froa
a short-horned cow by a long-horned bull, though appear,
ing 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 endeavored to discover on what decisive facts
the above statement has so often and so boldly been made.
There would be great difficulty in proving its truth: we
may safely conclude that very many of the most strongly
marked domestic varieties could not possibly live in a wild
state. In many cases we do not know what the aboriginal
stock was, and so could not tell whether or not nearly per-
fect reversion had ensued. It would be necessary, 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 characters to ancestral forms, it
seems to me not improbable that if we could succeed in
naturalizirg, or were to cultivate, during many gener-
ations, the several races, for instance, of the cabbage, in
very poor soil — in which case, however, some effect would
have to be attributed to the definite action of the poor
soil — that they would, to a large extent, or even wholly,
revert to the wild aboriginal stock. Whether or not the
experiment would succeed is not of great importance for
our line of argument; for by the 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, while
kept under the same conditions and while 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 favor of this view: to assert that wo

14 CHARACTER OF DOMESTIC VARIE2IEB,

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.

CHARACTER OF DOMESTIC VARIETIES; DIFFICULTY OF DIS-
TIXGUISHIXG BETWEEJ^ VARIETIES AXD 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 domes-
tic race, as already remarked, less uniformity of character
than in true species. Domestic races often have a some-
what monstrous character ; by which I mean, that,
although dillering 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 com-
petent 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 per-
petually recur. It has often been stated that domestic races
do not differ fi'om each other in characters of generic value.
It can be shown that this statetnent is not correct; but
naturalists differ much in determing what characters are
of generic value; all such valuations being at present
empirical. When it is explained how genera originate
under nature, it will be seen that we have no right to
expect often to find a generic amount of difference in our
domesticated races.

CHARACTER OF DOMESTIC VARIETIES. 15

In attempting to estimate the amount of structural dif-
ference 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 the different
quarters of the world. I do not believe, as we shall pres-
ently see, that the whole amount of difference between the
several breeds of the dog has been produced under domes-
tication; I believe that a small part of the difference is due
to their being descended from distinct species. In the case
of strongly marked races of some other domesticated
species, there is presumptive or even strong evidence that
all are descended from a single wild stock.

It has often been assumed that man has chosen for do-
mestication animals and plants having an extraordinary
inherent tendency to vary, and likewise to withstand
diverse climates. I do not dispute that these capacities
have added largely to the value of most of our domesticated
productions; but how could a savage possibly know, wdien
he first tamed an animal, whether it would varv in sue-
ceeding 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 domesti-
cation? 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 jiarent
species of our existing domesticated productions have
varied.

In the case of most of our anciently domesticated animals
and plants, it is not possible to come to any definite con-
clusion, whether they are descended fi'om one or several
-ivild s^'eoi^s. The argument mainly relied on by those wlio

16 CHARACTERS OF DOMESTIC VARIETIES.

believe in the multiple origin of onr domestic animals is,
that we find in the most ancient times, on the monuments
of Egypt, and in tlie 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 backward
the history of civilization, and shows that animals were
domesticated at a much earlier period than has hitherto
been supposed. The lake-inhabitants of Switzerland cul-
tivated several kinds of wheat and barley, the pea, the
poppy for oil and flax ; and they possessed several domesti-
cated 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
civilization ; and this again implies a long continued pre-
vious period of less advanced civilization, 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 forma-
tions of many parts of the world, all geologists believe that
barbarian men exsisted at an enormously remote period ;
and we know that at the present day there is hardly a tribe
so barbarous as not to have domesticated at least the dog.
The origin of most of our domestic animals will prob-
ably forever 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 Canidse have been
tamed, and that their blood, in some cases mingled
together, flows in the veins of our domestic breeds. In
regard to sheep and goats 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 thev 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 establislied
by the admirable researches of Professor Kiitimeyer. With
respect to horses, from reasons which I cannot here give, I

CHARACTER OF DOMESTIC VARIETIES. 17

am doubtfully inclined to believe, in opposition to several
authors, that all the races belong to the same species.
Having kept nearly all the English breeds of the fowl alive,
having bred and crossed them, and examined their skele-
tons, it appears to me almost certain that all are the
descendents 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 otlier, tlie
evidence is clear that they are all descended from the
common duck and wild rabbit.

The doctrine of the origin of our several domestic races
from several aboriginal stocks, has been carried to an
absurd extreme by some authors. They believe that every
race which breeds true, let the distinctive characters be
ever so slight, has had its wild prototype. At this rate
there must have existed at least a score of species of Avild
cattle, as many sheep, and several goats, in Europe alone,
and several even within Great Britain. One author believes
that there formerly existed eleven wild species of sheep
peculiar to Great Britain! When we bear in mind that
Britain has now not one peculiar mammal, and France but
few distinct from those of Germany, and so with Hungary,
Spain, etc., but that each of these kingdoms possesses sev-
eral peculiar breeds of cattle, sheep, etc., Ave 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 S23aniel, etc. — so unlike
all wild Canidae — ever existed in a state of nature? It
has often been loosely said that all our races of dogs have
been produced by the crossing of a few aboriginal species;
but by crossing we can only get forms in some degree inter-
mediate between their parents; and if we account for our
several domestic races by this i)rocess, we must admit the
former existence of the most extreme forms, as the Italian
greyhound, bloodhound, bull-dog, etc., in the wild state.

|y DOMESTIC PIGEONS.

Moreover, the possibility of niakiug distinct races by cross-
ing 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 inter-
mediate 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
every thing seems simple enough; but when these mongrels
are crossed one with another for several generations, hardly
two of them are alike^ and then the difficulty of the task
becomes manifest.

BEEEDS OF THE DOMESTIC PIGEOJ^, THEIK DIFFEREI^CES

Aii^D ORIGIN.

Believing that it is always best to study some special
group, I have, after deliberation, taken up domestic
pigeons. I have kept every breed which I could purchase
or obtain, and have been most kindly favored with skins
from several quarters of the world, more especially by the
Hon. V/, Elliot, from India, and by the Hon. C. Murray,
from Persia. Many treatises iii 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 per-
mitted 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 won-
derful development of the carunculated skin about the
head; and tins is accompanied by greatly elongated eyelids,
very large external oriiices 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

DOMESTIC PIGEONS. 19

and large feet; some of the sub-breeds of runts "have tery
long necks, others very long wings and tails, othcs sinmj^
larl}^ short tails. The barb is allied to the carreer, 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
esophagus. The Jacobin has the feathers so much reversed
along the back of the neck that they forma hood; and it has,
proportionally to its size, elongated wing and tail feathers.
The trumpeter and laugher, as their names express, utter
a very different coo from the other breeds. The fantail
has thirty or even forty tail-feathers, instead of twelve or
fourteen — the normal number in all the members of the
great pigeon family: these feathers are kept expanded and
are carried so erect that in good birds the head and tail
touch: the oil-gland is quite aborted. Several other less
distinct breeds might be specified.

/ In the skeletons of the several breeds, the development
f of the bones of the face, in length and breadth and curva-
ture, 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 vertebra vary
in number; as does the number of the ribs, together with
their relative breadth and the presence 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 m.outh, the proportional length of the eye-
lids, of the orifice of the nostrils, of the tongue (not always
in strict correlation with the length of beak), the size of
the crop and of the upper part of the esophagus; the
development and abortion of the oil-gland; the number of
the primary wing and caudal feathers; the relative length
of the wing and tail to each other and to the body; the
relative length of the leg and foot; the number of scutellie
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

20 DOMESTIC PIGEONS,

state of the down with which the nestling birds are clothed
when hatched. The shape and size of the eggs vary. The
manner of flight, and in some breeds the voice and disposi-
tion, differ remarkabl}'. 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-inherited sub-breeds, or species,
as he would call them, could be shown him.

Great as are the differences between the breeds of the
pigeon, I am fully convinced that the common opinion of
naturalists is correct, namely, that all are descended from
the rock-pigeon (Columbia livia), including under this
term several geographical races or sub-species, which differ
from each other "in the most trifling respects. As several
of the reasons which have led me to this belief are in some
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 de-
scended 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
species of rock-pigeons are known; and these have not any
of the characters of the domestic breeds. Hence the sup-
posed aboriginal stocks must either still exist in the coun-
tries 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 flyers, are unlikely

DOMESTIC PIGEONS. 21

to be exterminated; 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 sup-
posed extermination of so many species having similar
habits with the rock-pigeon seems a very rash assumption.
Moreover, the seveial above-named domesticated breeds
have been transported to all parts of the world, and, there-
fore, 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 diffi-
cult to get wild animals to breed freely under domestica-
tion; 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-civilized man as to be quite prolific under confine-
ment.

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 constitu-
tion, habits, voice, coloring, and in most parts of their
structure, yet are certainly highly abnormal in other parts;
we may look in vain through the whole great family of Col-
umbidae 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-civilized man succeeded in
thoroughly domesticating several species, but that he in-
tentionally or by chance picked out extraordinarily abnor-
mal species; and further, that these very species have since
all become extinct or unknown. So many strange contin-
gencies are improbable in the highest degree.

Some facts in regard to the coloring of pigeons well de-
serve consideration. The rook-pigeon is of a slaty-blue,
with white loins; but the Indian sub-species, C. interme-
dia of Strickland, has this part bluish. The tail lias a ter-
minal 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,

22 JDOMESTIG PIGEONS.

have, besides the two black barS;, the wings checkered with
black. These several marks do not occur together in any
other species of the whole family. Xow, 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 observed :
I crossed some white fantails, which breed very
true, with some black barbs — and it so happens that
blue varieties of barbs are so rare that I never heard of an
instance in England; and the mongrels were black, brown
and mottled. I also crossed a barb with a spot, which is a
white bird with a red tail and red spot on the forehead,
and which notoriously breeds very true; the mongrels were
dusky and mottled. I then crossed one of tlie mongrel
barb-fantails with a mongrel barb-spot, and they produced
a bird of as beautiful a blue color, with the white loins,
double black wing-bar, and barred and white-edged tail-
feathers, as any wild rock-pigeon ! We can understand
these facts, on the well-known principle of reversion to
ancestral characters, if all the domestic breeds are de-
scended 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 colored and marked like the rock-
pigeon, although no other existing species is thus colored
and marked, so that in each separate breed there might be
a tendency to revert to the very same colors 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 descend-
ants reverting to an ancestor of foreign blood, removed by
a greater number of generations. In a : reed which has
been crossed only once the tendency to revert to any
character derived from such a cross will naturally become
less and less, as in each succeeding generation there will be
less of the foreign blood; but when there has been no cross.

DOMESTIC PIGEOI^^S, 23

and there is a tendency in the hreed to revert to a character
which was lost during some former generation, this
tendency, for all that we can see to the contrary, mav be
transmitted undiminished for an indefinite number of gen-
erations. These two distinct cases of reversion are often
confounded together by those who have written on in-
heritance.

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 tlie most
distinct breeds. Now, hardly any cases have been ascer-
tained with certainty of hybrids from two quite distinct
species of animals being perfectly fertile. Some authors
believe that long-continued domestication eliminates this
strong tendency to sterility in species. From the history
of the dog, and of some other domestic animals, this con-
clusion is probably quite correct, if applied to species
closely related to each other. But to extend it so far as to
suppose that species, aboriginally as distinct as carriers,
tumblers, pouters, and fantails now are, should yield off-
spring perfectly fertile inter se, would be rash in the
extreme.

From these several reasons, namely, the improbability
of man having formerly made seven or eight supposed
species of pigeons to breed freely under domestication — •
these supposed species being quite unknown in a wild state,
and their not having become anywhere feral — these species
presenting certain very abnormal characters, as compared
with all other Columbidae, though so like the rock-pigeon
in most res|)ects — the occasional reappearance of the blue
color and various black marks in all the breeds, both when
kept pure and when crossed — and lastly, the mongrel off-
spring 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
Columbfe livia with its geographical sub-species.

In favor of this view, I may add, firsth\ 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

24 DOMESTIC PIGEONS,

the rock-pigeon, yet that by comparing the several sub.
breeds of tliese 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 Egyptian 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
can reckon up their pedigree and race.''' Pigeons w^ere
much valued by Akber Khan, in India, about the year
1600; never less than 20,000 pigeons were taken with the
court. '* The monarchs of Iran and Turan sent him some
very rare birds;" and, continues the courtly historian,
'' His Majesty, by crossing the breed?, which method was
never practiced before, has improved them astonishingly."'
About this same period the Dutch were as eager about
pigeons as were the old Eomans. The paramount impor-
tance of these considerations in explaining the immense
amount of variation which pigeons have undergone, will
likewise be obvious when we treat of selection. We shall
then, also, sec how it is that the several breeds so often
have a somewhaj . lonstrous character. It is also a most
favorable 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 wa+ched the several kinds, well knowing
how truly they breed, I felt fully as much difficulty in

SELECTION B Y MAN. 25

believing that since they had been domesticated they had
all proceeded from a common parent, as any naturalist
could in coming to a similar conclusion in regard to the
many species of finches, or other groups of birds, in
nature. One circumstance has struck me much; namely,
that nearly all the breeders of the various domestic
animals and the cultivators of plants, with whom I
have conversed, or whose treatises I have read, are
firmly convinced that the several breeds to which each
has attended, are descended from so many aboriginally dis-
tinct species. Ask, as I have asked, a celebrated raiser ol
Hereford cattle, whether his cattle might not have de-
scended 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 Kibston-pippin or Codlin-apple, could
ever have proceeded from the seeds of the same tree. In-
numerable other examples could be given. The explana-
tion, 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 know-
ing 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?

PRINCIPLES OF SELECTIOIT A27CIENTLY FOLLOWED, AND

THEIR EFFECTS.

Let US now briefly consider the steps by which domestic
races have been produced, either from one or from seveial

26 8BLJ£GTI0N B Y MAIT,

allied species. Some effect may be attributed 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 ac-
count by such agencies for the differences between a di-ay
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 botauists,
for instance, believe that the fuller's teasel, with its hooks,
which can not be rivaled 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 when we
compare the dray-horse and race-horse, the dromedary and
camel, the various breeds of sheep fitted either for culti-
vated 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 com-
pare the game-cock, so pertinacious in battle, with other
breeds so little quarrelsome, with " everlasting layers "
which never desire to sit, and with the bantam so small and
elegant; when we compare the host of agricultural, culi-
nary, orchard and flower-garden races of plants, most useful
to man at different seasons and for different purposes, or so
beautiful in his eves, we must, I think, look further than
to mere variability. We can not suppose that all the
breeds were suddenly j^roduced 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 variations;
man adds them up in certain directions useful to him. In
this sense he may be said to have made for himself useful
breeds.

The great power of this principle of selection is not
hypothetical. It is certain that several of our eminent
breed ei's have, even within a single lifetime, modified to a
large extent their breeds of cattle and sheep. In order
fully to realize what they iiave done it is almost necessary

SELECTION B Y MAN. 27

to read several of the many treatises devoted to this sub-
ject, and to inspect the animals. Breeders habitually
speak of an animal's organization as something plastic,
which they can model almost as they please. If I had
space I could quote numerous passages to this effect from
highly competent authorities. ^Youatt, who was probably
better acquainted with the works of agriculturists than
almost any other individual, 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 mold he K
pleases,"" Lord Somerville, speakins^ of what breeders ^
nave done for sheep, says: " It would seem as if they had
chalked out upon a wall a form perfect in itself, and then
had given it existence. "" In Saxony the importance of the
principle of selection in regard to merino sheep is so fully
recognized that men follow it as a trade: the sheep are
placed on a table and are studied, like a picture by a con-
noisseur; 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 ped-
igree; 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 some-
times among closely allied sub-breeds. And when a cross
has been made, the closest selection is far more indispen-
sable even than in ordinary cases. If selection consisted
merely in separating some very distinct variety and breed-
ing from it, the principle would be so obvious as hardly to
be worth notice; but its importance consists in the great
effect produced by the accumulation in one direction,
during successive generations, of differences absolutely
inappreciable by an uneducated eye — differences which I
for one have vainly attempted to appreciate. Not one man
in a thousand has accuracy of eye and judgment sufficient
to become an eminent breeder. If gifted with these qual-
ities, and he studies his subject for years, and devotes his

28 SELECTION B Y MAN,

lifetime to it witli indomitable perseverance, he will suc-
ceed, and may make great improvements; if he wants any
of these qualities, he will assuredly fail. Few would read-
ily believe in the natural capacity and years of practice
requisite to become even a skillful pigeon-fancier,>^

The same principles are followed by horticulturi:;ts; but
the variations are here often more abrupt. No one sup-
poses that our choicest productions have been produced by
a single variation from the aboriginal stock. We have
proofs that this has not been so in several cases in which
exact records have been kept; thus, to give a very trifling
instance, the steadily increasing size of the common goose-
berry 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. -^ W^hen 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,
m fact, likewise followed; for hardly any one is so careless
as to breed from his worst animals.-

In regard to plants, there is another means of observing
the accumulated effects of selection — namely, by comparing
the diversity of flowers in the different varieties of the same
species in the flower garden; the diversity of leaves, pods,
or tubers, or whatever part is valued, in the kitchen-garden,
in comparison with the flowers of the same varieties; and
the diversity of fruit of the same species in the orchard, in
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 flow-
ers of the heartsease are, and how alike the leaves; how
much the fruit of the different kinds of gooseberries differ
in size, color, shape and hairyness, and yet the flowers pre-
sent 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 corre-
lated variation, the importance cf which should never be
overlooked, will insure: some dif erences; but, as a general
rule, it cannot be doubted that the continued selection of

VJsrcoj^ serous selection. 29

slight variations, either in the leaves, the flowers, or tlie
fruit, will produce races ditrering from eacli 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 at-
tended to of late years, and many treatises have been pub-
lished on the subject; and the result has been, in a corre-
sponding 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 wliich
the full importance of the principle is acknowledged. In
rude and barbarous periods of English history clioice ani-
mals were often imported, and laws were passed to prevent
their exportation: the destruction of horses under a certain
size was ordered, and this may be compared to the
^^roguing" of plants by nurserymen. The principle of
selection I find distinctly given in an ancient Chinese ency-
clopedia. Explicit rules are laid down by some of the
Roman classical writers. From passages in Genesis, it is
clear that the color of domestic animals was at that early
period attended to. Savages now sometimes cross their
dogs with wild canine animals, to improve the breed, and
they formerly did so, as is attested by passages in Pliny.
The savages in South Africa match their draft cattle by
color, as do some of the Esquimaux their team of dogs.
Livingstone states that good domestic breeds are highly
valued, by the negroes in the interior of Africa who have
not associated with Europeans. Some of these facts do
not show actual selection, but they show that the breeding
of domestic animals vra-s carefully attended to in ancient
times, and is now attended to by the lowes-t savages. It
would, indeed, have been a strange fact, had attention not
been paid to breeding, for the inheritance of good and bud
qualities is so obvious.

UXCOKSCIOUS SELECTION".

At the present time, eminent breeders try by methodical
selection, with a distinct object in view, to make ;i new
strain or sub-breed, sujierior 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

30 XTNCONSGIOUS SELECTION.

one tiying to possess and breed from the best individual
animals, is more important. Tims, a man who intends
keeping pointers naturally tries to get as good dogs as he can,
and afterward 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
tlie same way as Bakewell, Collins, etc., by this very same
process, only carried on more methodically, did greatly
modify, even during their lifetimes, the forms and qualities
of their cattle. Slow and insensible changes of this kind
can never be recognized unless actual measurements or care-
ful drawings of the breeds in question have been made long
ago, which may serve for comparison. In some cases, how-
ever, unchanged, or but little changed, individuals of the
same breed exist in less civilized districts, where the breed
has been less improved. There is reason to believe that
King Charles^ spaniel has been unconsciously modified to a
large extent since the time of that monarch. Some highly
competent authorities are convinced that the setter is
directly derived from the spaniel, and has probably been
slowly altered from it. It is known that the English
pointer has been greatly changed within the last century,
and in this case the change has, it is believed, been chiefly
effected by crosses with the foxhound; but what concerns
us is, that the change has been effected unconsciously and
gradually, and yet so effectually that, though the old
Spanish j)ointer certainly came from Spain, Sir. 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 race-horses have come to surpass in fleetness and size
the parent Arabs, so that the latter, by the regulations for
the Goodwood Races, are favored in the weights which they
carry. Lord Spencer and others have shown how the
cattle of England have increased in weight and in early
maturity, compared with the stock formerly kept in this
country. By comparing the accounts given in various old
treatises of the former and present state of carrier and
tumbler pigeons in Britain, India and Persia, we can trace
the stages through which they have insensibly passed, and
come to differ so greatly from the rock-pigeon.

UNCONSCIOUS SELECTION. 31

Yonatt gives an excellent illustration of the effects of a
course of selection v/hich maybe 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 the 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 upward 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 varieties."

If there exist savages so barbarous as never to think of
the inherited character of the offspring of their domestic
animals, yet any one animal particularly useful to them,
for any special pur230se, would be carefully preserved
during famines and other accidents, to which savages are
so liable, and such choice animals would thus generally
leave more oft'spring 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 bv the bar-
barians of Tierra del Fuego, by their killing and devouring
their old women, in times of dearth, as of less value than
their dogs.

In plants the same gradual process of improvement
through the occasional preservation of the best individuals,
whether or not sufficiently distinct to be ranked at their
first appearance as distinct varieties, and whether or not
two or more species or races have become blended togetlier
by crossing, may plainly be recognized in the increased size
and beauty which we now see in the varieties of the hearts-
ease, 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 hearts-
ease 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

^Z UNCONSCIOUS SELECTION.

very inferior qudity. I have seen great surprise expressed
in horticultural works at the wonderful skill of gardeners
in having produced sucli 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 uncon-
sciously. 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 onward.
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 any-
where find.

/a large amount of change, thus slowly and uncon-
sciously accumulated, explains, as 1 believe, the well-
known fact, that in a number of cases we cannot
recognize, and therefore do not know, the wild parent-
stocks of the plants which have been longest cultivated
in our flower and kitchen gardens. It it has taken
centuries or thousands of years to improve or modify most
of our plants up to their present standard of usefulness to
man, we can understand how it is that neither Australia,
the Cape of Good Hope, nor any other region inhabited by
quite uncivilized man, has afforded us a single plant worth
culture. It is not that these countries, so rich in species,
do not by a strange chance possess the aboriginal stocks of
any useful plants, but that the native plants have not been
improved by continued selection up to a standard of per-
fection comparable with that acquired by the plants in
countries anciently civilized.

In regard to tlie domestic animals kept by uncivilized
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 circum-
stanced, individuals of the same species, having slightly
different constitutions or structure, would often suc-
ceed 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

VNCONSGIOUS SELECTION. 33

remarked by some authors, have more of the character of
tnie species than the varieties kept in civilized countries..^--
/On the view here given of the important part whicli
selection by man has played, it becomes at once obvious,
how it is that our domestic races show adaptation in their
structure or in their habits to man's wants or fancies. We
can, I think, further understand the frequently abnormal
character of our domestic races, and likewise their differ-
ences being so great in external characters, and relatively
so slight in internal parts or organs. Man can hardly
select, or only with much difficulty, any deviation of
structure excepting such as is 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 developed in some slight degree in an unusual
manner, or a pouter till he saw a pigeon with a crop of
somewhat unusual size; and the more abnormal or unusual
any character was when it first appeared, the more likely
it would be to catch his attention. But to use such an ex-
pression as trying to make a fantail is, I have no doubt, in
most cases, utterly incorrect. The man who first selected
a pigeon with a slightly larger tail, never dreamed what the
descendants of that pigeon would become through long-
continued, partly unconscious and partly methodical, selec-
tion. Perhaps the parent-bird of all fantails had only
fourteen tail-feathers somewhat expanded, like the present
Java fantail, or like individuals of other and distinct
breeds, in which as many as seventeen tail-feathers have
been counted. Perhaps the first pouter-pigeon did not in-
flate its crop much more than the turbit now does
the upper part of its esophagus — a habit which is disre-
garded by all fanciers, as it is not one of the points of the^
breed.

/Nor let it be thought that some great deviation of struc-
ture would be necessary to catch the fancier's eye: he per-
ceives 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
individuals of the same species, be judged of by the value

34 CIRCUMSTANCES FA YORABLE TO SELECTION.

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 re-
jected as faults or deviations from the standard of per-
fection in each breed. The common goose has not given
rise to any marked varieties; hence the Toulouse and the
common breed, which dilfer only in color, that most fleet-
ing 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
fa^'t, a breed, like a dialect of a language, can hardly be
sai 1 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 neighborhood. But they will as
yet hardly have a distinct name, and from being only
slightly valued, their history will have been disregarded.
When farther improved by the same slow and gradual
process, they will spread more widely, and will be recog-
nized as something distinct and valuable, and will then
probably first receive a provincial name. In semi-civilized
countries, with little free communication, the spreading of
a new sub-breed would be a slow process. As soon as the
points of value are once acknowledged, the principle, as I
have called it, of unconscious selection will always tend —
perhaps more at one period than at another, as the breed
rises or falls in fashion — perhaps more in one district than
in another, according to the state of civilization of the in-
habitants— slowly to add to the characteristic features of
the breed, whatever thev mav be. But the chance v.-iil be
infinitely small of any record having been preserved of such
slow, varying and insensible changes. .^-^

CIRCUMSTAJ^CES PATORABLE TO MAI^T'S POWEE OF SELEC-
TION?'.

I will now say a few words on the circumstances, favor-
able or the reverse, to man's power of selection. A high
degree of variability is obviously favorable, as freely giving

CIRGTTMSTANCES FAVORABLE TO SELECTION. 35

the materials for selection to work on; not that mere in-
dividual differences are not amply sufficient, with extreme
care, to allow of the accumulation 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 part of Yorkshire, ^'As they generally
belong to poor people, and are mostly iyi 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 v,diere the conditions for its
propagation are favorable. 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
be so highly valued by man, that the closest attention is
paid to even the slightest deviations in its qualities or
structure. Unless such attention be paid nothing can be
effected. I have seen it gravely remarked, that it was
most fortunate that the strawberry began to vary just when
gardeners began to attend to this plant. Ko 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 varieties of the strawberry were
raised which have appeared during the last half-century.

With animals, facility in preventing crosses is an im-
portant element in the formation of new races — at least,
in a country which is already stocked with other races. In
this respect inclosure of the land plays a part. Wander-
ing 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,

36 CIRCUMSTANCES FAVORABLE TO SELECTION.

though mingled in the same aviary; and this circumstance
must have largely favored 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 noctural rambling habits, can not
be easily matched, and, although so much valued by
women and children, we rarely see a distinct breed long
kept up; such breeds as we do sometimes see are almost
alv,ays 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, etc., 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 atten-
tion 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
organization, though it has varied to a slight extent, as I
have elsewhere described.

Some authors have maintained that the amount of varia-
tion in our domestic productions is soon reached, and can
never afterward 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 im-
proved in many ways within a recent period; and this im-
plies 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 re-
marked with much truth, a limit will be at last reached.
For instance, tiiere must be a limit to the fleetness of any
terrestrial animal, as this will be determined by the fric-
tion to be overcome, the weight of the body to be carried,
and the power of contraction in the muscular fibers. But

CIRCUMSTANCES FA VORABLE TO SELECTION, 37

what concerns us is that the domestic varieties of the same
species diifer from each other in almost every character,
which man lias attended to and selected, more than do tlie
distinct species of the same genera. Isidore Geolfroy St.
Hilaire has proved this in regard to size, and so it is with
color, and probahly with the length of hair. With respect
to fleetness, which depends on many bodily character's,
Eclipse was far fleeter, and a dray-horse is comparably
stronger, than any two natural species belonging to the same
genus. So with plants, the seeds of the different varieties
of the bean or maize probably differ more in size than do
the seeds of the distinct species in any one genus in the
same two families. The same remark holds good in 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 ani-
mals and plants. Changed conditions of life are of tho
highest importance in causing variability, both by acting
directly on the organization, and indirectly by affecting the
reproductive system. It is not probable that variability is
an inherent and necessary contingent, under all circum-
stances. 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. Some-
thing, but how much we do not know, may be attributed
to the definite action of the conditions of life. Some, per-
haps a great, effect may be attributed to the increased use
or disuse of parts. The final result 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 occa-
sional intercrossing, with the aid of selection, has, no
doubt, largely aided in the formation of new sub-breeds;
but the importance of crossing has been much exaggerated,
both in regard to animals and to those plants wliich are
propagated by seed. With plants which are temporarily
propagated by cuttings, buds, etc., the importance of cross-
ing is immense; for the cultivator may here disregard the
extreme variability both of hybrids and of mongrels, and

?,8 CIRCUMSTANCES FAVORABLE TO SELECTION;

the sterility of hybirds; but plants not propagated by seed
are of little importance to ns, for their endurance is only
temporary. Over all these causes of change, the accumu-
lative action of selection, whether applied methodically
and quickly, or unconsciously and slowly, but more
efficiently, seems to have been the predominant power.

VARIATION UNDER NATURE, 39

CHAPTER II.

VARIATIOif 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 th©
larger genera resemble varieties in being very closely, but un-
equally, related to each other, and in having restricted ranges.

Before applying the principles arrived at in the last
chapter to organic beings in a state of nature, we must
briefly discuss whether these latter are subject to any
variation. To treat this subject properly, a long catalogue
of dry facts ought to be given; but these I shall reserve for
a future work. Nor shall I here discuss the various defini-
tions 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.
Generallv the term includes the unknown element of r
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, gener-
ally injurious, or not useful to the species. Some authors
use the term "variation'^ in a technical sense, as implying
a modification directly due to the physical conditions of
life; and '* variations '^ in this sense are supposed not to be
inherited; but who can say that the dwarfed condition of
shells in the brackish waters of the Baltic, or dwarfed
plants on Alpine summits, or the thicker fur of an animal
from far northward, would not in some cases bo inherited
for at least a few generations? And in this case I presume
that the form would be called a variety.

'40 INDIVIDUAL DIFFERENCES.

It may be doubted whether sudden and considerable
deviations of structure, such as we occasionally see in our
domestic productions, more especially with plants, are ever
permanently propagated in a state of nature. Almost
every part of every organic being is so beautifully related
to its complex conditions of life that it seems as improbable
that any part should have been suddenly produced perfect,
as that a complex machine should have been invented by
man in a perfect state. Under domestication monstrosi-
ties sometimes occur which resemble normal structures in
widely diiferent animals. Thus pigs have occasionally been
born with a sort 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 singly, their
preservation would depend on unusually favorable circum-
stances. They would, also, during the first and succeeding
generations cross with the ordinary form, and thus their
abnormal character would almost inevitably be lost. But
I shall have to return in a future chapter to the preserva-
tion and perpetuation of single or occasional variations.

INDIVIDUAL DIFFERENCES.

The many slight differences which appear in the offspring
from the same jiarents, 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 mold. These individual differences are of the
highest importance for us, for they are often inherited, as
must be familiar to every one; and they thus afford mate-
rials 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

INDIVIDUAL DIFFERENCES. 41

consider imimportant 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 natu-
ralist would be surprised at the number of the cases of
variability, even in important parts of structure, which he
could collect on good authority, as I have collected, during
a course of years. It should be remembered that systema-
tists are far from being pleased at finding variability in
important characters, and that there are not many men
who will laboriously examine internal and important
organs, and compare them in many specimens of the same
species. It would never have been expected 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 Coccus, which may almost be compared to
the irregular branching of the stem of a tree. This philo-
sophical naturalist, I may add, has also shown that the
muscles in tiie larvae of certain insects are far from uni-
form. Authors sometimes argue in a circle when they
state that important organs never vary; for these same
authors practically rank those parts as important (as some
few naturalists have 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 differences
which is extremely perplexing : I refer to those genera
which have been called '^protean" or *^ polymorphic," in
which species present an inordinate 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 among 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, polymorphic
in other countries, and likewise, judging from Briichiopod

42 INDIVIDUAL DIFFERENCES,

shells, at former periods of time. These facts are very
perplexing, for they seem to show that this kind of varia-
bility is independent of the conditions of life. I am in-
clined to suspect that we see, at least in some of these
polymoq:)hic 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 explained.

Individuals of the same species often present, as is
known to every one, great ditferences 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 among insects, and in the immature and larval
states of many of the lower animals. There are, also, cases
of dimorphism and trimorphism, both with animals and
plants. Thus, Mr. Wallace, who has lately called attention
to the subject, has shown that the females of certain
species of butterflies, in the Malayan Archipelago, reg-
ularly appear under two or even three conspicuously dis-
tinct forms, not connected bv intermediate varieties. Fritz
Muller has described analogous but more extraordinary
cases with the males of certain Brazilian Crustaceans: thus,
the male of a Tanais regularly occurs under two distinct
forms; one of these has strong and differently shaped
pincers, and the other has antennae much more abundantly
furnished with smelling-hairs. Although in most of these
cases, the two or three forms, both with animals and plants,
are not now connected by intermediate gradations, it is
probable that they were once thus connected. Mr. Wallace,
for instance, describes a certain butterfly which presents in
the same island a great range of varieties connected by in-
termediate links, and the extreme links of the chain closely
resemble the two forms of an allied dimorphic species in-
habiting another part of the Malay Archipelago. Thus
also with ants, the several worker-castes are generally quite
distinct; but in some cases, as we shpJl hereafter see, the
castes are connected together by finely graduated varieties.
So it is, as I have myself observed, with some dimorphic
plants. It certainly at first appears a highly remarkable
fact that the same female butterfly should have the power
of producing at the same time three distinct female forms
and a'male; and that an hermaphrodite plaait sliouM pro-

DOUBTFUL SPECIES. 43

dnce from the same seed-capsule three distinct herma-
phrodite forms, bearing three different kinds of females and
three or even six different kinds of males. Nevertheless
these cases are only exao^gerations of the common fact that
the female produces offspring of two sexes which some-
times differ from each other in a wonderful manner.

DOUBTFUL SPECIES.

The forms which possess in some considerable degree
the character of species, but which are so closely similar
to other forms, or are so closely linked to them by
intermediate gradations, that naturalists do not like to
rank them as distinct species, are in several respects the
most important for us. We have every reason to
believe that many of these doubtful and closely allied
forms have permanently retained their characters for a
long time; for as long, as far as we know, as have good
and true species. Practically, when a naturalist can
unite by means of intermediate links any two forms, he
treats the one as a variety of the other; ranking the most
common, but sometimes the one first described as the
species, and the other as the variety. But cases of great
difficulty, which I will not here enumerate, sometimes arise
in deciding whether or not to rank one form as a variety
of another, even when they are closely connected by inter-
mediate links; nor will the commonly assumed hybrid
nature of the intermediate forms alwavs remove the difti-
culty. In very man}^ cases, however, one form is ranked
as a vaiiety of another, not because the intermediate links
have actually been found, but because analogy leads the
observer to sujopose 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 naturalists having
sound judgm.ent and wide experience seems the only guide
to follow. We must, however, in many cases, decide by a
majority of naturalists, for few well-mai-ked and well-
known varieties can be named which have not been ranked
as species by at least some competent judges.

That varieties of this doubtful nature are far from

44 DOUBTFUL SPECIES,

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 num-
ber of forms have been ranked by one botanist as good
Bpecies, and by another as mere varieties. Mr. H. C.
Watson, to whom I lie under deep obligation for assistance
of all kinds, has marked for me 182 British plants, which
are generally considered as varieties, but which have all
been ranked by botanists as species; and in making this
list he has omitted many trifling varieties, but which never-
theless have been ranked by some botanists as species, and
he has entirely omitted several highly polymorphic genera.
Under genera, including the most poiymorijhic forms, Mr.
Babington gives 251 species, whereas Mr. Bentham gives
only 112 — a difference of 139 doubtful forms! Among
animals w^hich unite for each birth, and which are highly
locomotive, doubtful forms, ranked by one zoologist as a
species and by another as a variety, can rarely be found
within the same country, but are common in separated
areas. How many of the birds and insects in North
America and Europe, which differ very slightly from each
other, have been ranked by one eminent naturalist as un-
doubted species, and by another as varieties, or, as they
are often called, geogi-aphical 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 representa-
tive species. The first or variable forms vary much within
the limits of the same island. The local forms are moder-
ately 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 isolated ; but as they do not
differ from each other by strongly marked and
important characters, ** There is no possible test but
individual opinion to determine which of them shall be
considered as species and which as varieties."" Lastly,

DOUBTFUL BPEUIKS. 45

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 distinguished from each other by a
greater amount of difference than that between the local
forms and sub-species, they are almost universally ranked
by naturalists as true species. Nevertheless, no certain
criterion can possibly be given by which variable forms,
local forms, sub species and representative species can bo
recognized.

Many years ago, when comparing, and seeing others com-
pare, the birds from the closely neighboring islands of the
Galapagos Archipelago, one with another, and with those
from the American mainland, I was much struck how en-
tirely vague and arbitrary is the distinction between species
and varieties. On the islets of the little Maderia group
there are many insects which are characterized as
varieties in Mr. Wollaston's admirable work, but which
would certainly be ranked as distinct species by many en-
tomologists. Even Ireland has a few animals, now gen-
erally regarded as varieties, but which have been ranked as
species by some zoologists. Several experienced ornitholo-
gists 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 pecuhar to Great
Britain. A wide distance between the homes of two doubt-
ful forms leads many naturalists to rank them as distinct
species; but what distance, it has been well asked, will suf-
fice if that between America and Europe is ample, will that
between Europe and the Azores, or Maderia, or the Cana-
ries, or between the several islets of these small archipelagos,
be sufficient?

Mr. B. D. "Walsh, a distinguished entomologist of tlie
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 color,
size, or in the nature of their secretions. In some instances
the males alone, in other instances, both males and females.

46 DOUBTFUL SPECIES,

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 ranl<:ed
by all entomologists as good species. But no observer can
determine for another, even if he can do so for himself,
which of these Phytophagic forms ought to be called
species and which varieties. Mr. Walsh ranks the forms
which it may be supposed would freely intercross, as varie-
ties; 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 can not be expected that
intermediate links connecting the several forms should
now be found. The naturalist thus loses his best guide in
determining whether to rank doubtful forms as varieties
or species. This likewise necessarily occurs with closely
allied organisms, which inhabit distinct continents or
islands. When, on the other hand, an animal or plant
ranges over the same continent, or inhabits many islands in
the same archipelago, and presents different forms in the
different areas, there is always a good chance that inter-
mediate forms will be discovered which will link together
the extreme states; and these are then degraded to the
rank of varieties.

Some few naturalists maintain that animals never pre-
sent 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 useless abstraction, imply-
ing 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 compe-
tent 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 doubt-
ful species well deserve consideration; for several interest-
ing lines of argument, from geographical distribution,
analogical variation, hybridism, etc., have been brought to
bear in the attempt to determine their rank; but space

DOUBTFUL SPECIES. 47

does not here permit me to discuss them. Close investiga-
tion, 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 animal or plant in a state of nature be
highly useful to man, or from any cause closely attracts
his attention, varieties of it ^vill almost universally be
found recorded. These varieties, moreover, will often be
ranked by some authors as species. Look at the common
oak, how closely it has been studied; yet a German author
makes more than a dozen species out of forms, which are
almost universally considered by other botanists to be vari-
eties; 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 pub-
lished by A. de Candolle, on the oaks of the whole world.
No one ever had more ample materials for the discrimina-
tion 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 vari-
ations. 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, aud
never found connected by intermediate states. After
this discussion, the result of so much labor, he
emphatically remarks: ''They are mistaken, who
repeat that the greater part of our species are clearly
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.

48 DOUBTFUL SPECIES.

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, sessiliflora and pubescens. The
forms which connect these three sub-species are compara-
tively rare; and, as Asa Gray again remarks, if these con-
necting forms which are now rare were to become totally
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 Quer-
cus robur. Finally, De Candolle admits that out of the 300
species, which will be enumerated in his Prodromus as
belonging to the oak family, at least two-thirds are provis-
ional 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 palaeontology, geographical
botany and zoology, of anatomical structure and classific-
ation.'^

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 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 doubtful forms. His general ten-
dency 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 continually studying; and he has little general
knowledge of analogical variation in other groups and in
other countries 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 obser-
vations be widely extended he will in the end generally be

DOVBTlruL SPECIES. 49

able to make up his own mind; but he will succeed in this
at the expense of admitting much variation, and the truth
of this admission will often be disputed by other natural-
ists. When he comes to study allied forms brought from
countries not now continuous, in which case he cannot
hope to find intermediate links, he will be compelled to
trust almost entirely to analogy, and his difficulties Avill
rise to a climax.

Certainly no clear line of demarcation has as yet been
drawn between species and sub-species — that is, the forms
which in the opinion of some naturalists come very near
to, but do not quite arrive at, the rank of species; or,
again, between sub-species and well-marked varieties, or
between lesser varieties and individual differences. These
differences blend into each other by an insensible series;
and a series impresses the mind with the idea of an actual
passage.

Hence I look at individual differences, though of small
interest to the systematist, as of the highest importance
for us, as being the first steps toward 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 toward more
strongly marked and permanent varieties; and at the lat-
ter, as leading to sub-species, and then to sjoecies. 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 im-
portant 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 ex-
plained, 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 considera-
tions 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 ex-
tinct, or they may endure as varieties for very long periods,
as ha^ been shown to be the case by Ish. Wollaston with
the varieties of certain fossil land-shells in Madeira, and

50 I)OMIjS'ANT SPECIES VARY M0S7\

with plants by Gaston de Saporta. If a variety were to
flourish so as to exceed in numbers the parent species, it
would then rank as the species, and the species as the
variety; or it might come to supplant and exterminate the
parent species; or both might co-exist, and both rank as
independent species. But we shall hereafter return to this
subject.

From these remarks it will be seen that I look at the
term species as one arbitrarily given, for the sake of con-
venience, 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 comparison with mere
individual differences, is also ajoplied arbitrarily, for con-
venience sake.

WIDE-KANGII^G, MUCH DIFFUSED, AND COMMO]!f 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. 0. 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 statements 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.

Alphonso 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

BPECIE8 OF LARGER GENERA VARIABLE, 51

sets of organic beings. But my tables further show that,
in any limited country, the species which are the most
common, that is abound most in individuals, and the
species which are most widely diffused within their own
country (and this is a dili'erent consideration from wide
range, and to a certain extent from commonness), oftenest
give rise to varieties sufficiently well-marked to have been
recorded in botanical works. Hence it is the most flourish-
ing, or, as they may be called, the dominant species — those
which range widely, are the most diffused in their own
country, and are the most numerous in individuals — which
oftenest produce well-marked varieties, or, as I consider
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 inliabitants 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
predominence, 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 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 para-
sitic fungus is infinitely more numerous in individuals,
and more widely diffused. But if the conferva or parasitic
fungus exceeds its allies in the above respects, it will then
be dominant within its own class.

SPECIES OF THE LARGER GE:N-ERA IX EACH COUNTRY
YARY 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

52 8PECIE8 OF LAliGER GENERA VARIABLE.

larger genera (i. e., those iucludiug many species) being
placed on one side, and all those in the smaller genera on
the other side, the former will be found to include a some-
what larger number of the very common and much diffused
or dominant species. This might have been anticipated,
for the mere fact of many species of the same genus in-
habiting any country, shows that there is something in
the organic or inorganic conditions of that country favor-
able to the genus; and, consequently, we might have ex-
pected to have found in the larger genera, or those includ-
ing many species, a larger proportional number of dominant
species. But so many causes tend to obscure this result, that
I am surprised that my tables show even a small majority
on the side of the larger genera. I will here allude to only
two causes of obscurity. Fresh water and salt-loving
plants generally have very wide ranges and are much dif-
fused, 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 organization 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 organized 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.e., species of
the same genus) have been formed, many varieties or incip-
ient 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, circumstances have been favorable for variation;
and hence we might expect that the circumstances would
generally still be favorable to variation. On tlie other
hand, if we look at each species as a special act of creation,
there is no apparent reason why more varieties should
occur in a group having many species, than in one having
few.

To test the truth of this anticipation I have arranged

SPECIES OF LARGER GENERA. 53

che plants of twelve countries, and the coleopterous insects
of two districts, into two nearly equal masses, the species
of the larger genera on one side, and those of the smaller
genera on the other side, and it has invariably proved to be
the case that a larger proportion of the species on the side
of the larger genera presented varieties, than on the side of
the smaller genera. Moreover, the species of the large
genera which present any varieties, invariably present a
larger average number of varieties than do the species of
the small genera. Both these results follow when another
division is made, and when all the least genera, with from
only one to four species, are altogether excluded from the
tables. These facts are of plain signification on the view
that species are only strongly marked and permanent
varieties; for wherever many species of the same genus
have been formed, or where, if we may use the expression,
the manufactory of species has been active, we ought
generally to find the manufactory still in action, more
especially as we have every reason to believe the process of
manufacturing new species to be a slow one. And this
certainly holds true if varieties be looked at as incipient
species; for my tables clearly show, as a general rule, that,
wherever many species of a genus have been formed, the
species of that genus present a number of varieties, that is,
of incipient species, beyond the average. It is not that all
large genera are now varying much, and are thus increasing
in the number of their species, or that no small genera are
now varying and increasing; for if this had been so, it
would have been fatal to my theory; 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, that where many species of a
genus have been formed, on an average many are still
forming; and this certainly holds good.

MAN"Y OF THE SPECIES IJ^CLUDED WITHIJT THE LARGER
GENERA RESEMBLE VARIETIES IN^ BEIXG VERY CLOSELY,
BUT UNEQUALLY, RELATED TO EACH OTHER, AND IN
HAVING RESTRICTED RANGES.

There are other relations between the species of large

54 SPECIES OF LARGER GENERA.

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 com^oelled to come to a determination
by the amount of difference between them, judging by anal-
ogy whether or not the amount suffices to raise one or both to
the rank of species. Hence the amount of difference is one
very important criterion in settling whetlier 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
endeavored to test this numerically by averages, and, as far
as my imperfect results go, they confirm the view. I have
also consulted some sagacious and experienced observers,
and, after deliberation, they concur in this view. In this
respect, therefore, the species of the larger genera resemble
varieties, more than do the species of the smaller genera.
Or the case may be put in another way, and it may be said,
that in the larger genera, in which a number of varieties or
incipient species greater than the average are now manu-
facturing, many of the species already manufactured still
to a certain extent resemble varieties, for they differ from
each other by less than the usual amount of difference.

Moreover, the species of the larger genera are related to each
other, in the same manner as the varieties of any one species
are related to each other. No naturalist pretends that all
the species of a genus are equally distinct from each other;
they may generally be divided into sub-genera, or 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 differ-
ence between varieties and sj)ecies, 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

RESEMBLE VARIETIES. 55

how the lesser differences between varieties tend to increase
into the greater differences between species.

There is one other point which is worth notice. Varie-
ties generally have much restricted ranges. This state-
ment is indeed scarceh^ more than a truism, for, if a
variety were found to have a wider range than that
of its supposed parent species, their denominations
would be reversed. But there is reason to believe
that the species which are very closely allied to other
species, and in so far resemble varieties, often have much
restricted ranges. For instance, Mr. H. 0. Watson has
marked for me in the well-sifted London catalogue of
Plants (4th edition) sixty-three 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
sixty-three reputed species range on an average over 6.9
of the provinces into which Mr. Watson has divided
Great Britain. Now, in this same catalogue, fifty-
three acknowledged varieties 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 fr.om species,
— except, first, by the discovery of intermediate Imking
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 countrv,
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
plusters round other species. Species very closely allied to

o6 RESEMBLE VARIEllES.

other species apparently have restricted rauges. In all
these respects 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 inex-
plicable if species are independent creations.

We have also seen that it is the most flourishing or domi-
nant 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 con-
verted 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, tho
larger genera also tend to break up into smaller genera.
And thus, the forms of life tb^'oughout the universe be-
come divided into groups subordinate to groups.

STRUGGLE FOR EXISTENCE, 57

CHAPTER III.

STKUGGLE FOR EXISTEi^CE.

Its bearing on natural selection — The term used in a wide sense —
Geometrical ratio of increase — Eapid increase of naturalized
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 among 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 imma-
terial for us whether a multitude 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 tlie mere exist-
ence 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 organization to another part, and to tlie condi-
tions of life and of one organic being to another being,
been perfected? We see these beautiful co-adaptations
most plainly in the woodpecker and the mistletoe; and only
a little less plainly in the humblest parasite 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

58 JSTE UG GLE FOR EXISTENCE.

short, we see beautiful adaptations everywhere and iu 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 sj^ecies? 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, hoAvever slight
and from whatever cause proceeding, if they be in any
degree profitable to the individuals of a species, in their
infinitely complex relations to other organic beings and
to their physical conditions of life, will tend to the
preservation of such individuals, and will generally be
inherited by the offspring. The offspring, also, will
thus have a better chance of surviving, for, of the many
individuals of any species which are periodically born,
but a small number can survive. I have called this
principle, by which each slight variation, if useful, is
preserved, by the term natural selection, in order to
mark its relation to man^s power of selection. But the
expression often used by Mr. Herbert Spencer, of the Sur-
vival of the Fittest, is more accurate, and is sometimes
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, we shall hereafter see, is a power
incessantly ready for action, and is as immeasurably superior
to man's feeble efforts as the works of Nature are to those
of Art.

AVe 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 philosophicajly
shown that all organic beings are exposed to severe compe-
tition. In regard to plants, no one has treated this sub-
ject with more spirit and ability than W. Herbert, Dean
of Manchester, evidently the result of his great horticul-

STRUGGLE FOR EXISTENCE. 59

tural knowledge. Nothing is easier than to admit iu
words the truth of the universal struggle for life, or more
difficult — at least I found it so — than constantly to bear
this conclusion in mind. Yet unless it be thoroughly en-
grained in the mind, the whole economy of nature, with
every fact on distribution, rarity, abundance, extinction,
and variation, will be dimly seen or quite misunderstood.
We behold the face of nature bright with gladness, we
often see superabundance of food; we do not see or we
forget that the birds which are idly singing round ns
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 of prey; we do not always bear in mind, that,
though food may be now superabundant, it is not so at all
seasons of each recurring year.

THE TEEM^ STEUGGLE FOE EXISTEl^CE, USED IN" A LAEGE

SEi^SE.

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 prog-
eny. Two canine animals, in a time of dearth, may be
truly said to struggle with each other which shall get food
and live. But a plant on the edge of a desert is said to
struggle for life against the drought, though more jorop-
erly 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 languishes and dies. But several seedling mistle-
toes, growing close together on the same branch, may more
truly be said to struggle with each other. As the mistle-
toe 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

60 GEOMETRICAL RATIO OF INCREASE.

thus disseminate its seeds. In these several senses, which
pass into each other, I use for convenience sake the gen-
eral term of Struggle for Existence.

GEOMETRICAL EATIO OF INCREASE.

A struggle for existence inevitably follows from the high
rate at which all organic beings tend to increase. Every
being, which during its natural lifetime produces several
eggs or seeds, must suffer destruction during some period
of its life, and during some season or occasional year,
otherwise, on the principle of geometrical increase, its
numbers would quickly become so inordinately great that
no country could support the product. Hence, as more
individuals are produced than can possibly survive, there
must in every case be a struggle for existence, either one in-
dividual with another of the same species, or with the
individuals of disMnct species, or with the physical con-
ditions of life. It is the doctrine of Malthus applied with
manifold force to the whole animal and vegetable king-
doms; for in this case there can be no artificial increase of
food, and no prudential restraint from marriage. Although
some species may be now increasing, more or less rapidly,
in numbers, all can not 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. Linngeus has calculated that if an annual plant
produced only two seeds — and there is no plant so unpro-
ductive as this — and their seedlings next year produced
two, and so on, then in twenty years there would be a
million plants. The 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

JEOMETRIOAL RATIO OF INCItEASE, 61

740 to 750 years there would be nearly nineteen million
elephants alive descended from the first pair.

Bat we have better evidence on this subject than mere
theoretical calculations, namely, the numerous recorded
cases of the astonishingly rapid increase of various animals
in a state of nature, when circumstances have been favor-
able 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 commonest over the wide plains of La
Plata, clothing square leagues of surface almost to the ex-
clusion 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 inported from America since
its discovery. In such cases, and endless others, could be
given, no one supposes, that the fertility of the animals or
plants has been suddenly and temporarily increased in any
sensible degree. The obvious explanation is that the con-
ditions of life have been highly favorable, 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
extraordinarily and rapid increase and wide diffusion in their
new homes.

In a state of nature almost every full-grown plant an-
nually produces seed, and among animals there are very
few which do not annually pair. Hence we may confi-
dently assert that all plants and animals are tending to in-
crease 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 cheolcod by
destruction at some period of life. Our familiarity with
the larger domestic animals tends, I think, to mislead us;

62 GEOMETraCAL RATIO OF INCREASE.

we see no great destruction falling on them, but we do not
keep in mind that thousands are annually slaughtered for
food, and that in a state of nature an equal number would
have somehow to be disposed of.

The only difference between organisms which annually
produce eggs or seeds by the thousand, and those which
produce extremely few, is, that the slow breeders would re-
quire a few more years to people, under favorable condi-
tions, 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 Qgg, yet it is be-
lieved to be the most numerous bird in the world. One
fly deposits hundreds of eggs, and another, like the hippo-
bosca, 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 im-
portance 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 insured to germinate in a fitting
place; so that, in all cases, the average number of any an-
imal 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 to 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 gen-
eration or at recurrent intervals. Lighten any check, mit-
igate the destruction ever so little, and the number of the
species will almost instantaneously increase to any amount

NATURE OF THE CHECKS TO INCREASE, C3

NATURE OF THE CHECKS TO Il^CREASE.

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 seed-
lings suffer most from germinating in ground already
thickly stocked with other plants. Seedlings, also, are
destroyed in vast numbers by various enemies; for instance,
on a piece of ground three feet long and two wide, dug and
cleared, and where there could be no choking from other
plants, I marked all the seedlings of our native weeds as
they came up, and out of 357 no less than 295 were de-
stroyed, 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 grown 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 fre-
quently it is not the obtaining food, but the serving as prey
to other animals, which determines the average number of
a species. Thus, there seems to be little doubt that the
stock of partridges, grouse and hares on any large estate
depends chiefly on the destruction of vermin. If not one
head of game were shot during the next twenty years in

64 NATURE OF THE CHECKS TO INCREASE.

England, and, at the same time, if no vermin were de-
stroyed, 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 numbers of a species, and periodical seasons of ex-
treme cold or drought seem to be the most effective of all
checks. I estimated (chiefly from the 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 extraordinarially severe mortality from
epidemics with man. The action of climate seems at first
sight to be quite independent of the struggle for existence;
but in so far as climate chiefly acts in reducing food,
it brings on the most severe struggle between the indi-
viduals, whether of the same or of distinct species, which
subsist on the same kind of food. Even when climate,
for instance, extreme cold, acts directly, it will be the least
vigorous individuals, or those which have got least food
through the advancing winter, which will suffer the 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
cliange of climate being conspicious, we are tempted to
attribute the whole effect to its direct action. But this is
a false view; we forget that each species, even where it
most abounds, is constantly suffering enormous destruc-
tion at some period of its life, from enemies or from com-
petitors for the same place and food; and if these enemies
or competitors be in the least degree favored 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 decrease. When we travel southward
and see a species decreasing in numbers, we may feel sure
that the cause lies quite as much in other species being
favored, as in this one being hurt. So it is when we
travel northward, but in a somewhat lesser degree, for
the number of species of all kinds, and^ therefore of

NATURE OF THE CHECKS TO INCREASE. r,5

competitors, decreases northward, or in ascending a mount-
ain, we far oftener meet with stunted forms, due to the
directly injurious action of climate, than we do in proceed-
ing southward or in descending a mountain. When we
reach the Arctic regions, or snow-capped summits, or abso-
lute deserts, the struggle for life is almost exclusively with
the elements.

That climate acts in main part indirectly by favoring
other species we clearly see in the prodigious number of
plants which in our gardens can perfectly well endure our
climate, but which never become naturalized, for they
cannot compete with our native plants nor resist destruc-
tion by our native animals.

When a species, owing to highly favorable circumstances,
increases inordinately in numbers in a small tract, epidem-
ics— 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 among the crowded animals,
but disproportionally favored: and here comes in a sort of
struggle between the parasite and its prey.

On the other hand, in many cases, a large stock of indi-
viduals of the same species, relatively to the numbers of its
enemies, is absolutely necessary for its preservation. Thus
we can easily raise plenty of corn and rape-seed, etc., in
our fields, because the seeds are in great excess compared
with the number of birds which feed on them; nor can the
birds, though having a superabundance of food at this one
season, increase in number proportionally to the supply of
seed, as their numbers 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 preser-
vation, explains, I believe, some singular facts in nature
such as that of very rare plants being sometimes extremely
abundant, in the few spots where they do exist; and that
of some social plants being social, that is abounding in
individuals, even on the extreme verge of their range. For
in such cases, we may believe, that a plant conld exist only

66 STRUGGLE FOR EXISTENCE.

where the conditions of its life were so favorable that maay
could exist together, and thus save the species from utter
destruction. I should add that the good effects of inter-
crossing, 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 unex-
pected are the checks and relations between organic 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 inclosed twenty-
five years previously and planted with Scotch fir. The change
in the native vegetation of the planted part of the heath
was most remarkable, more than is generally seen in pass-
ing from one quite different soil to another: not only the
proportional numbers of the heath-plants were wholly
changed, but twelve species of plants (not counting grasses
and carices) flourished in the plantations, which could not
be found on the heath. The effect on the insects must
have been still greater, for six insectivorous birds were very
common in the plantations, which 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 introduction of a single tree, nothing
whatever else having been done, with the exception of the
land having been inclosed, so that cattle could not enter.
But how important an element inclosure 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
inclosed, and self-sown firs are now springing up in multi-
tudes, so close together that all cannot live. When I
ascertained that these young trees had not been sown or
pljiijted I was m much surprised R-t their numbers that I

STRUGGLE FOR EXISTENCE, 67

went to several points of view, whence I could exuniine
hundreds of acres of the uninclosed heath, and literally J
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 perpetually browsed down by the cattle.
In one sqiiare 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 inclosed, it became thickly clothed
with vigorously growing young firs. Yet the heath was so
extremelv barren and so extensive that no one would ever
have imagined that cattle would have so closely and effec-
tually searched it for food.

Here we see that cattle absolutely determine the
existence of the Scotch fir; but in several parts of the
world insects determine the existence of cattle. Perhaps
Paraguay offers the most curious instance of this; for here
neither cattle nor horses nor dogs have ever run wild,
though they swarm southward and northward in a feral
state; and Azara and Rengger have shown that this is
caused by the greater 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 Paraguay, the parasitic insects
would probably increase; and this would lessen the num-
ber of the navel-frequenting 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 insectivor-
ous birds, and so onward 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

68 STRUGGLE FOR EXIBTENVE.

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 deso-
late the world, or invent laws on the duration of the forms
of life!

I am tempted to give one more instance showing how
plants and animals, remote in the scale of nature, are
bound together by a web of complex relations. I shall
hereafter have occasion to show that the exotic Lobelia
folgens is never visited in my garden by insects, and con-
sequently, 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
fertilize them. I find from experiments that humble-bees
are almost indispensable to the fertilization of the hearts-
ease (Violo tricolor), for other bees do not visit this flower.
I have also found that the visits of bees are necessary for the
fertilization of some kinds of clover; for instance twenty
heads of Dutch clover (Trifolium repens) yielded 2,290
seeds, but twenty other heads, protected from bees, produced
not one. Again, 100 heads of red clover (T. pratense)

Eroduced 2,700 seeds, but the same number of protected
eads 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 fertilize 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 became extinct or
very rare in England, the heartsease and red clover would
become very rare, or wholly disappear. The number of
humble-bees in any district depends in a great measure
upon the number of field-mice, which destroy their combs
and nests; and Colonel Newman, who has long attended to
the habits of humble-bees, believes that *^more than two-
thirds of them are thus destroyed all over England."
Now the number of mice is largely dependent, as every
one knows, on the number of cats; and Colonel 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."

STRUOQLE FOR EXISTENCE, GO

Hence it is quite credible that the presence of a feline
animal in large numbers in a district might determine,
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, act-
ing 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 dis-
tricts. When we look at the plants and busbes clothing
an entangled bank, we are tempted to attribute their pro-
portional numbers and kinds to what we call chance. But
how false a view is this! Every one has heard that when
an American forest is cut down, a very different vegetation
springs up; but it has been observed that ancient Indian
ruins in the Southern United States, which must formerly
have been cleared of trees, now display the same beautiful
diversity and proportion of kinds as in the surrounding
virgin forests. What a struggle must have gone on during
long centuries between the several kinds of trees, each
annually scattering its seeds by the thousand; what war
between insect and insect — between insects, snails and
other animals with birds and beasts of prey — all striving to
increase, all feeding on each other, or on the trees, their
seeds and seedlings, or on the other plants which first
clothed the ground and thus checked the growth of the
trees! Throw up a handful of feathers and all fall to the
ground according to definite laws; but how simple is the
problem where each shall fall compared to that of tlie
action and reaction of the innumerable plants and animals
which have determined, in the course of centuries, the
proportional numbers and kinds of trees now growing on
the old Indian ruins!

The dependency of one organic being on another, as of a
parasite on its prey, lies generally between beings remote
in the scale of nature. This is likewise sometimes the
case with those which may be strictly said to struggle with
each other for existence, as in the case of locusts and grass-
feeding quadrupeds. But the struggle will almost invari-
ably be most severe between the individuals of the same

70 STRUGGLE FOR EXISTENCE.

species, for they frequent the same districts, require the
same food, and are exposed to the same dangers. In the
case of varieties of the same species, the struggle will
generally be almost 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 colored sweet peas, they must be each
year harvested separately, and the seed then mixed
in due proportion, otherwise the weaker kinds will
steadily decrease in number and disappear. So again
with the varieties of sheep; it has been asserted that certain
mountain varieties will starve out other mountain varieties,
so that they cannot be kept together. The same result
has followed from keeping together 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 constitution, 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 together, in the same man-
ner as beings in a state of nature, and if the seed or young
were not annually preserved in due proportion.

STRUGGLE FOE LIFE MOST SEVERE BETWEEN" liTDIVIDUALS
AND VARIETIES OF THE SAME SPECIES.

As the species of the same genus usually have, though
by no means invariabl}^ 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 between the species
of distinct genera. We see this in ther recent extension
over parts of the United States of one species of swallow
having caused the decrease of another species. The recent
increase of the missel-thrush in parts of Scotland has caused
the decrease of the song-thrush. How frequently we hear
of onQ species of rat taking the place of another species

STRUGGLE FOR EXISIiLJ^CE. 71

under the most different climates! In Russia the small
Asiatic cockroach has everywhere driven before it its great
congener. In Australia the imported hive-bee is rapidly
exterminating the small, stingless native bee. One species
of charlock has been known to supplant another species;
and so in other cases. We can dimly see why the com-
petition should be most severe between allied forms, which
fill nearly the same place in the economy of nature; but
probably in no one case could we precisely say why one
species has been victorious over another in the great battle
of life.

A corollary of the highest importance may be deduced
from the foregoing remarks, namely, that the structure of
every organic being is related, in Uie most essential yet
often hidden manner, to that of all the other organic
beings, with which it comes into competition for food or
residence, or from which it has to escape, or on which it
preys. This is obvious in the structure of the teeth and
talons of the tiger; and in that of the legs and claws of the
parasite which clings to the hair on the tiger's body. But
in the beautifully plumed seed of the dandelion, and in
the flattened and fringed legs of the water-beetle, the re-
lation seems at first confined to the elements of air and
water. Yet the advantage of the plumed seeds no doubt
stands in the closest relition to the land being already
thickly clothed with other plants, so that the seeds may
be widely distributed and fall on unoccupied ground. In
the water-beetle, the structure of its legs, so well adapted
for diving, allows it to compete with other aquatic insects,
to hunt for its own prey, and to escape serving as prey to
other animals.

The store of nutriment laid up within the seeds of many
plants seems at first sight to have no sort of relation to
other plants. But from the strong growth of young plants
produced from such seeds, as peas and beans, when sown
in the midst of long grass, it may be suspected that the
chief use of the nutriment in the seed is to favor the growth
of the seedlings, while 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,

^2 STIILGQLE FOR EXISTENCE.

dampness or dryness, for elsewhere it ranges into slightly
hotter or colder, damper or drier districts. In this case we
can clearly see that if we wish in imagination to give the
plant the power of increasing in numbers, we should have
to give it some advantage over its competitors, or over the
animals which prey on it. On the confines of its geo-
graphical range, a change of constitution with respect to
climate would clearly be an advantage to our plant; but we
have reason to believe that only a few plants or animals
range so far, that they are destroyed exclusively by the
rigor of the climate. Not until we reach the extreme con-
fines of life, in the Arctic regions or on the borders of an
utter desert, will competition cease. The land may be ex-
tremely 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, among new competitors, the conditions
of its life will generally be changed in an essential manner,
although the climate may be exactly the same as in its
former home. If its average numbers are to increase in
its new home, we should have to modify it in a different
way to what we should have had to do in its native
country; for we should have to give it some advantage
over a different set of competitors or enemies.

It is good thus to try in imagination to give 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 or-
ganic being is striving 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.

HATUBAL SELEOTION, 73

CHAPTER IV.

NATURAL SELECTION"; OR THE SURVIVAL OF THE FITTEST.

Natural Selection — its power compared with man's selection — its
power on characters of trifling importance — its power at all ages
and on both sexes — Sexual Selection — On the generality of inter-
crosses between individuals of the same species — Circumstances
favorable and unfavorable to the results of Natural Selection,
namely, intercrossing, isolation, number of individuals — Slow
action — Extinction caused by Natural Selection — Divergence of
Character, related to the diversity of inhabitants of any small
area and to naturalization — Action of Natural Selection, through
Divergence of Character and Extinction, on the descendants
from a common parent — Explains the grouping of all organic
beings — Advance in organization — Low fonns preserved — Con-
vergence of character — Indefinite multiplication of species —
Summary.

How will the struggle for existence, briefly discussed in
the last chapter, act in regard to variation? Can the prin-
ciple 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 efi&ciently. 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 domesti-
cation, it may truly be said that the whole organization
becomes in some degree plastic. But the variability, which
we almost universally meet with in our domestic produc-
tions is not directly produced, as Hooker and Asa Gray
have well remarked, by man; he can neither originate
varieties nor prevent their occurrence; he can only pre-
serve and accumulate such as do occur. Unintentionally
he exposes organic beings to new and changiug conditions
of life, and variability ensues; but similar changes of con-
ditions might and do occur under nature. Let it also be

74 NATURAL SELECTION.

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 infinitely varied diversities of structure mis'ht be of
use to each being under changing conditions of life. Can
it then be thousfht im^Drobable, seeing that variations
useful to man have undoubtedl}^ occurred, that other
variations 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 ad-
vantage, liowever slight, over others, would have the best
chance of surviving and procreating their kind? On the
other hand, we may feel sure that any variation in the least
degree injurious would be rigidh^ destroyed. This preser-
vation of favorable individual differences and variations,
and the destruction of those which are injurious, I have
called Katural Selection, or the Survival of the Fittest.
Variations neither useful nor injurious would not be affected
by natural selection, and w^ould be left either a fluctuating
element^ as perhaps we see in certain polymorphic species,
or would ultimately become fixed, owing to the nature of
the organism and the nature of the conditions.

Several writers have misapprehended or objected to the
term Natural Selection. Some have even imagined that
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 differ-
ences 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 applica-
ble to them! In the literal sense of the word, no doubt,
natural selection is a false term; but who ever objected to
chemists speaking of the elective aftinities of the various
elements? — and yet an acid cannot strictly be said to elect
the base with which it in preference combines. It has
been said that I speak of natural selection as an active

NATURAL SELECTION. 75

power or Deity; but who objects to an author speaking of
the attraction of gravity as ruling the movements of the
planets? Every one knows what is meant and is implied
by such metaphorical expressions; and they are almost
necessary for brevity. So again it is difficult to avoid per-
sonifying the word Nature; but I mean by nature, only
the 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 undergoing some
slight physical change, for instance, of climate. The pro-
portional numbers of its inhabitants will almost immedi-
ately undergo a change, and some species will probably be-
come extinct. We may conclude, from what we have seen
of the intimate and complex manner in which the inhabi-
tants of each country are bound together, that any change
in the numerical proportions of the inhabitants, independ-
ently of the change of climate itself, would seriously affect
the others. If the country were open on its borders, new
forms would certainly immigrate, and this would likewise
seriously disturb the relations of some of the former inhab-
itants. 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 man-
ner 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
favored the individuals of any species, by better adapting
them to their altered conditions, would tend to be pre-
served; 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 ten-
dency to increased variability; and in the forgoing cases
the conditions have changed, and this would manifestly be
favorable to natural selection; by affording a better chance

•J-e NATURAL SELECTION.

of the occurrence of i^rofitable variations. TJnless sucli
occur, natural selection can do nothing. Under the
term of ^^ variations," it must never be forgotten that
mere individual differences are included. As man
can produce a great result with his domestic animals and
plants by adding up in any given direction individual dif-
ferences, 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 immigration, 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 modifications 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 inhab-
itants are now so perfectly adapted to each other and to
the physical conditions under which they live, that none
of them could be still better adapted or improved; for in
all countries the natives have been so far conquered by
naturalized productions that they have allowed some for-
eigners to take firm possession of the land. And as for-
eigners 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 selec-
tion, what may not natural selection effect? Man can act
only on external and visible characters; Nature, if I may
be allowed to personify the natural preservation or survival
of the 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 constitutional 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 character is fully exercised by her,

NATURAL SELECTION. 77

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 fit-
ting 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; does
not allow the most vigorous males to struggle for the
females; he does not rigidly destroy all inferior animals,
but protects during each varying season, as far as lies in
his power, all his productions. He often begins his selec-
tion by some half -monstrous form, or at least by some mod-
ification prominent enough to catch the eye or to be
plainly useful to him. Under nature, the slightest differ-
ences 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 accumulated by Nature
during whole geological periods! Can we wonder, then,
that Nature's productions should be far ''truer" in char-
acter 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 workman-
ship?

It may metaphorically be said that natural selection
is daily and hourly scrutinizing, throughout the world, the
slightest varifitionri; rejecting those that are bad, preserv-
ing and adding up all that are good; silently and insen-
sibly working, tvhenever and ivherever opportunity 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 tliat
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 favorable
nature as before; and these must again be preserved, and

78 NATURAL SELECTION,

so onward, step by step. Seeing that individual differences
of the same kind perpetually recur, this can hardly be con-
sidered as an unwarrantable assumption. But whether it
is true, we can judge only by seeing how far the hypothe-
sis 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 structures,
which we are apt to consider as of very trifling importance,
may thus be acted on. When we see leaf-eating insects
green, and bark-feeders mottled-gray; the alpine ptarmigan
white in winter, the red grouse the color of heather, we
must believe that these tints are of service to these birds
and insectr in preserving them from danger. Grouse, if
not destroyed at some period of their lives, would increase
in countless numbers; they are known to suffer largely
from birds of prey; and hawks are guided by e3^esight to
their prey — so much so that on j^arts of the continent per-
sons are warned not to keep white pigeons, as being the
most liable to destruction. Hence natural selection might
be effective in giving the j)roper color to each kind of
grouse, and in keeping that color, when once acquired,
true and constant. Nor ought we to think that the oc-
casional destruction of an animal of any particular color
would produce little effect; we should remember how
essential it is in a flock of white sheep to destroy a lamb
with the faintest trace of black. We have seen how the
color of hogs, which feed on the ^^ paint-root" in Virginia,
determines whether they shall live or die. In plants, the
down on the fruit and the color of the flesh are considered
by botanists as characters of the most trifling importance;
yet we hear from an excellent horticulturist. Downing,
that in the United States that smooth-skinned fruits suffer
far more from a beetle, a Curcuho, than those with down;
that purple jolums suffer far more from a certain disease
than yellow plums; whereas another disease attacks yellow-
fleshed peaches far more those with other colored
flesh. If, with all the aids of art, these slight differ-
ences make a great difference in cultivating the several
varieties, assuredly, in a state of nature, where the trees

NATURAL SELECTION. 79

would have to struggle with other trees and with a host of
enemies, such differences would effectually settle which
variety, whether a smooth or downy, a yellow or a purple-
fleshed fruit, should succeed.

In looking at many small points of difference between
species, which, as far as our ignorance permits us to judge,
seem quite unimportant, we must not forget that climate,
food, etc., 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 tlie variations are
accumulated through natural selection, other modifica-
tions, often of the most unexpected nature, will ensue.

As we see that those variations which, under domesti-
cation, appear at any particular period of life, tend to
reappear in the offspring at the same period; for instance,
in the shape, size and flavor 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 color of the down
of their chickens; in the horns of our sheep and cattle
when nearly adult; so in a state of nature natural selection
will be enabled to act on and modify organic beings at any
age, by the accumulation of variations profitable at that
age, and by their inheritance at a corresponding age. If it
profit a plant to have its seeds more and more widely dis-
seminated 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 eft'ect,
through correlation, the structure of the adult. So, con-
versely, modifications in the adult may affect the structure
of the larva; but in all cases natural selection will insure
that they shall not be injurious: for if they were so., the
species would become extinct.

Natural selection will modify the structure of the young
m relation to the parent and of the parent in relation to
the young. In social animals it will adapt the structure of
each individual for the benefit of the whole community;
if the community profits by the selected change. V, hat

80 NATURAL SELECTION'.

natural selection cannot do, is to modify the structure of
one species, without giving it any advantage, for the good
of another sj^ecies; and though statements to this effect
may be found in works of natural history, I cannot find
one case whicii will bear investigation. A structure used
only once in an animaFs 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 eggs.
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 simul-
taneously 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 manner
which protected them from their enemies. Yet many of
these eggs or seeds would perhaps, if not destroyed, have
yielded individuals better adapted to their conditions of
life than any of those which happened to 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 which 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 dis-
trict be not wholly kept down by such causes — or again let
the destruction of eggs or seeds be so great that only a
hundredth or a thousandth part are developed — yet of

SEXUAL SELECTION, 81

those which do survive, the best adapted individuals, sup-
posiug that there is any variability in a favorable direction,
will tend to propagate their kind in larger numbers than
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 ben-
eficial directions; but this is no valid objection to its effi-
ciency at other times and in other ways; for we are far
from having any reason to suppose that many species ever
undergo modification and improvement at the same time
in the same area.

SEXUAL SELECTlOl^r.

Inasmuch as peculiarities often appear under domestica-
tion in one sex and become hereditarily attached to that
sex, so no doubt it will be under nature. Thus it is ren-
dered possible for the two sexes to be modified through
natural selection in relation to different habits of life, as is
sometimes the case; or for one sex to be modified in rela-
tion to the other sex, as commonly occurs. This leads me
to say a few words on what I have called sexual selection.
This form of selection depends, not on a struggle for exist-
tence in relation to other organic beings or to external
conditions, but on a struggle between the individuals of
one sex, generally the males, for the possession of the other
sex. The result is not death to the unsuccessful competi-
tor, but few or no offspring. Sexual selection is, there-
fore, 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, a son
having special weapons, confined to the male sex. A horn-
less stag or spurless cock would have a poor chance of
leaving numerous off'spring. Sexual selection, by always
allowing the victor to breed, might surely give indomitable
courage, length of spur and strength to the wing to strike
in the spurred leg, in nearly the same manner as does the
brutal cockfighter by the careful selection of his best cocks.
How low in the scale of nature the law of battle descends
I know not; male alligators have been described as fight-
ing, bellowing and whirling round, like Indians in a war-
dance, for the possession of the females; male salmons have

82 Sexual selection.

been observed fighting all day long; male stag-beetles
sometimes bear wounds from tlie huge mandibles of other
males; the males of certain hymenopterous insects have
been frequently seen by that inimitable observer M.
Fabre, fighting for a particular female who sits by, an ap-
parently unconcerned beholder of the struggle, and then
retires with the conqueror. The war is, perhaps, severest
between the males of pol3'gamous animals, and these seem
oftenest provided with special weapons. The males of
carnivorous animals are already well armed; though to
them and to others, special means of defence may be
given through means of sexual selection, as the mane of
the lion, and the hooked jaw to the male salmon; for the
shield may be as important for victory as the sword or
spear.

Among birds, the contest is often of a more peaceful
character. All those who have attended to the subject,
believe that there is the severest rivalry between the males
of many species to attact, 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 spectators, at
last choose the most attractive partner. Those who have
closely attended to birds in confinement well know that
they often take individual preferences and dislikes: thus
Sir E. Heron has described how a pied peacock was emi-
nently 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, accord-
ing 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, accord-
to their standard of beauty, might produce a marked
effect. Some well-known laws, with respect to the pumage
of male and female birds, in comparison with the plumage
of the young, can partly be explained through the action
of sexual selection on variations occurring at different
ages, and transmitted to the males alone or to both sexes
at corresponding ages; but I have not space here to enter
on this subject.

SEXUAL SELECTION. 83

Thus it is, as I believe, that when the males and females
of any animal have the same general habits of life, but
differ in structure, color, or ornament, such differences
have been mainly caused by sexual selection: that is, by
individual males having had, in successive generations,
some slight advantage over other males, in their weapons,
means of defense, or charms, which they have transmitted
to their male offspring alone. Yet, I would not wish to
attribute all sexual differences to this agency: for we see
in our domestic animals peculiarities arising and becoming
attached to the male sex, which apparently have not been
augmented through selection by man. The tuft of hair on
the breast of the wild turkey-cock cannot be of any use,
and it is doubtful whether it can be ornamental in the eyes
of the female bird; indeed, had the tuft appeared under
domestication it would have been called a monstrosity.

ILLUSTRATIONS OF THE ACTIOIT OF I^ATURAL SELECTION,
OR THE SURVIVAL OF THE FITTEST.

In order to make it clear how, as I believe, natural selec-
tion acts, I must beg permission to give one or two imagi-
nary illustrations. Let us take the case of a wolf, which
preys on various animals, securing some by craft, some by
strength, and some by fleetuess; and let us suppose that
the fleetest prey, a deer for instance, had from any change
in the country increased in numbers, or tliat other
prey had decreased in numbers, during that season of the
year when the wolf was hardest pressed for food. Under
such circumstances the swiftest and slimmest wolves 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 fleetnessof 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 tliought of mod-
ifying 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

Si ILL U8TRA TIoNS OF THE ACTION

greyliouud-like form, which pursues deer, and the other
more bulk}^, with shorter legs, which more frequently
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 ^Dreserved.
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 selection by
man, which depends on the preservation of all the more or
less valuable individuals, and on the destruction of the
worst. I saw, also, that the preservation in a state of
nature of any occasional deviation of structure, such as a
monstrosity, would be a rare event; and that, if at first
preserved, it would generally be lost by subsequent inter-
crossing with ordinary individuals. Nevertheless, until
reading an able and valuable article in the '^ North British
Review" (1867), I did not appreciate how rarely single
variations, whether slight or strongly marked, could be
perpetuated. The author takes the case of a j^air of ani-
mals, 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 extreme estimate for most of the higher
animals, but by no means so for many of the lower organ-
isms. 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. SupjDOsing
it to survive and to breed, and that half its young
inherited the favorable variation; still, as the Reviewer
goes on to show, the youug would have only a slightly
better chance of surviving and breeding; and this chance
would go on decreasing in the succeeding generations.
The justice of these remarks cannot, I think, be
disputed. If, for instance, a bird of some kind could
procure 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 perpet-
uating its kind to the exclusion of the common form; but

0^ NATURAL SELECTION. g5

there can hardly be a doubt, judging by wluit 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
owing to a similar organization being similarly acted on —
of which fact numerous instances could be given with our
domestic productions. In such cases, if the varying indi-
vidual did not actually transmit to its offspring its newly-
acquired character, it would undoubtedly transmit to them,
as long as the existing conditions remained the same, a
still stronger tendency to vary in the same manner. There
can also be little doubt that the tendency to vary in the
same manner has often been so strong that all the individ-
uals of the same species have been similarly modified with-
out 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 guille-
mots 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 scon be supplanted by the modified form,
through the survival of the fittest.

To the effects of intercrossing in eliminating variations of
all kinds, I shall have to recur; but it maybe 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. Consequently each newly-formed variety would gen-
erally be at first local, as seems to be the common rule with
varieties in a state of nature; so that similarly modified indi-
viduals would soon exist in a small body together, and
would often breed together. If the new variety were suc-
cessful in its battle for life, it would slowly spread from a
central district, competing with and conquering the ini-
changed individuals ou the margins of an ever-increasing
circle.

86 ILLUSTRATIONS OF THE ACTION

It maybe worth while to give another and more complex
illustration of the action of natural selection. Certain
plants excrete sweet juice, apparently for the sak« of elim-
inating something injurious from the sap: this is effected,
for instance, by glands at the base of the stipules in some
Leguminos^e, 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 ben-
efit the plant. Now, let us suppose that the juice or nectar
was excreted from the inside of the flowers of a certain
number of plants of any species. Insects in seeking the
nectar would get dusted with pollen, and would often
transport it from one flower to another. The flowers of
two distinct individuals of the same species would thus get
crossed; and the act of crossing, as can be fully proved,
gives rise to vigorous seedlings, which consequently would
have the best chance of flourishing and surviving. The
plants which produced flowers with the largest glands or
nectaries, 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, Avhich had their stamens and
pistils placed, in relation to the size and habits of the par-
ticular insect which visited them, so as to favor in any
degree the transportal of the pollen, would likewise be
favored. 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 fertilization,
its destruction appears to be a simple loss to the plant; yet
if a little pollen were carried, at first occasionally and then
habitually, by the pollen-devouring insects from flower to
flower, and a cross thus effected, although nine-tenths of
the pollen were destro3^ed it might still be a great gain to
the plant to be thus robbed; and the individuals which
produced more and more pollen, and had larger anthers,
would be selected.

When our plant, by the above process long continued,
had been rendered highly attractive to insects, they would,
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

OF NATURAL selection: 37

sexes of planes. Some holly-trees bear only male flowers,
which have four stamens producing a rather small quan-
tity 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 polen 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 favorable
to bees, nevertheless every female flower which I examined
had been effectually fertilized 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 ren-
dered so highly attractive to insects that pollen was regu-
larly carried from flower to flower, another process might
commence. No naturalist doubts the advantage of what
has been called the '*^ physiological division of labor;" hence
we may believe that it would be advantageous to a plant to
produce stamens alone in one flower or on one whole plant,
and pistils alone in another flower or on another plant.
In plants under culture and placed under new conditions
of life, sometimes the male organs and sometimes the
female organs become more or less impotent; now if we
suppose this to occur in ever so slight a degree under
nature, then, as pollen is already carried regularly from
flower to flower, and as a more complete separation of the
sexes of our plant would be advantageous on the principle
of the division of labor, individuals with this tendency
more and more increased, would be continually favored or
selected, until at last a complete separation of the sexes
might be effected. It would take up too much space to
show the various steps, though dimorphism_ and other
means, by which the separation of the sexes in plants of
various kinds is apparently now in progress; but I may
add that some of the species of holly in North America
are, according to Asa Gray, in an exactly intermediate
condition, or, as he expresses it, are more or less dia^ciously
polygamous.

88 ILLUSTRATIONS OF THE ACTION

Let us now turn to the nectar-feeding insects; we may
suppose the plant, of which we have been slowly increasing
the nectar by continued selection, to be a common plant;
and that certain insects depended in main part on its
nectar for food. I could give many facts showing how
anxious bees are to save time: for instance, their habit of
cutting holes and sucking the nectar at the bases of certain
flowers, which with a very little more trouble they can enter
by the mouth. Bearing such facts in mind, it may be believed
that under certain circumstances individual differences in
the curvature or length of the probocis, etc., 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 communities to
which they belonged would flourish and throw off many
swarms inheriting the same peculiarities. The tubes of
the corolla of the common red or incarnate clovers (Trifo-
lium 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 the red clover offer in vain an abun-
dant supply of precious nectar to the hive-bee. That this
nectar is much liked bv 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-bee, and which freel}^ crosses with it, is able to
reach and suck the nectar of the red clover. Thus, in a
country where this kind of clover abounded, it might be
a great advantage to the hive-bee to have a slightly longer
or differently constructed proboscis. On the other hand,
as the fertility of this clover absolutely depends on bees vis-
iting the flowers, if humble-bees were to become rare in any

OF NATURAL STCLECTION. 89

country, it might be a great advantage to the nlant to have
a shorter or more deeply diviied corolla, so that tlie hive-
bees should be enabled to suck its flowers. Thus I can un-
derstand how a flower and a bee might slowly become,
either simal'^aneously 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 flight deviations of structure mutually favorable
to each other.

I am well aware that this doctrine of natural selection,
exemplified :n the above 'maginary instances, is open to
the same objections which were first urged against Sir
Charles LyelFs noble views on " the modorn changes of
the earth, as Illustrative of geology;-*' but we now seldom
hear the agencies which we see still a: Tork, spoken of as
trifling or insignificant, when used In explaining the excava-
tion of the deepest valleys or the formation of long Lines of
inland oiiffs. Natural selection acts only by the preserva-
tion and accumulation of small inherited modifications,
each profitable to the preserved being; and as modern geol-
ogy has almost banished such views as the excavation of a
great valley by a single diluvial wave, so will natural selec-
tion banish the belief of the continued creation of new or-
ganic beings, or of any great and sudden modification in
their structure.

OlSr THE Ilfl-TEECEOSSIKG OF Iiq-DIVIDUALS.

I must here introduce a short digression. In the case of
a,nimals and plants with separated sexes, it is of course ob-
vious that two individuals must always (with the ex-
ception of the curious and not well understood cases of
parthenogenesis) unite for each birth; but in the case of
hermaphrodites this is far from obvious. Nevertheless
there is reason to believe that with all hermaphrodites two
individuals, either occasionally or habitually, concur for
the reproduction of their Kind. This view was long ago
doubtfully suggested by Sprengel Knight and Kolreuter.
We shall presently see its importance, but I must hero
treat the subject with extreme brevity, though I have the
materials prepared for an ample discussion. All vertebrate
animals, all insects and some other large groups of animals.

90 ON THE INTERCROSSINO

pair for each birth. Modern research has much diminished
the number of supposed hermaphrodites and of real herma-
phrodites 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 cer-
tainly do not habitually pair, and a vast majority of plants
are hermaphrodites. What reason, it may be asked, is
there for sujDposingin these cases that two individuals ever
concur in reproduction? As it is impossible here to enter
on details, I must trust to some general considerations
alone.

In the first place, I have collected so large a body of
facts, and made so many experiments, showing, in accord-
ance 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 vigor and fertility to the offspring; and on
the other hand, that close interbreeding diminishes vigor
and fertility; that these facts alone incline me to believe
that it is a general law of nature that no organic being
fertilizes itself for a perpetuity of generations; but that a
cross with another individual is occasionally — perhaps at
long intervals of time — indispensable.

On the belief that this is a law of nature, we can, I
think, understand several large classes of facts, such as
the following, which on any other view are inexplicable.
Every hybridizer knows how unfavorable exposure to wet
is to the fertilization of a flower, yet what a multitude of
flowers have their anthers and stigmas fully exposed to the
weather! If an occasional cross be indispensable, notwith-
standing that the plant's own anthers and pistil stand so
near each other as almost to insure self-fertilization, the
fullest freedom for the entrance of pollen from another in-
dividual will explain the above state of exposure of the
organs. Many flowers, on the other hand, have their
organs of fructification closely inclosed, as in the great
papilionaceous or pea-family; but these almost invariably
present beautiful and curious adajDtations in relation to the
visits of insects. So necessary are the visits of bees to
many papilionaceous flowers, that their fertility is greatly
diminished if these visits be prevented. JMow, it is scarcely
possible for insects to fly from flower to flower, and not to

OF INDIVIDUALS. 91

carry pollen from one to the other, to the great good of the
plant. Insects act like a camel-hair pencil, and it is suffi-
cient, to insure fertilization, just to touch with the same
brush the anthers 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 specie*
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 toward
the pistil, or slowly move one after the other toward
it, the contrivance seems adapted solely to ensure self-
fertilization; and no doubt it is useful for this end: but
the agency of insects is often required to cause the stamens
to spring forward, as Kolreuter has shown to be the case
with the barberry; and in this very genus, which seems to
have a special contrivance for self-fertilization, it is well
known that, if closely-allied forms or varieties are planted
near each other, it is hardly possible to raise pure seedlings,
60 largely do they naturally cross. In numerous other
cases, far from self-fertilization being favored, there are
special contrivances which effectually prevent the stigma
receiving pollen from its own flower, as I could show from
the works of Sprengel and others, as well as from my own
observations: for instance, in Lobelia fulgens, there is
a really beautiful and elaborate contrivance by which all
the infinitely numerous pollen-granules are swept out of
the conjoined anthers of each flower, before the stigma of
fhat individual flower is ready to receive them; and as this
flower is never visited, at least in my garden, by insects, it
never sets a seed, though by placing pollen from one flower
on the stigma of another, I raise plenty of seedlings.
Another species of Lobelia, which is visited by bees, seeds
freely in my garden. In very many other cases, though
there is no special mechanical contrivance to prevent the
stigma receiving pollen from the same flower, yet, as
Sprengel, and more recently Hildebrand and others liave
shown, and as I can confirm, either the anthers burst
before the stigma is ready for fertilization, or the stigma is
ready before the pollen of that flower is ready, so that these
^o-named dichoganiotis plants have in fact separated sexes^

92 ON TEE INTERGMOSSING

and must habitually be crossed. So it is with the recipro-
cally dimorphic and trimorDhic plants previously alluded
to. How strange are these facts! How strange that the
pollen and stigmatic surface of the sa.me flower, though
placed so close together, as if for the very purpose of self-
fertilization, should be in so many cases mutually useless
to each otlier? How simply are these facts explained on
the view of an occasional cross with a distinct individual
being advantageous or indispensable!

If several varieties of the cabbage, radish, onion and of
some other plants, be allowed to seed near each other, a
large majority of the seedling thus raised turn out, as I
founds mongrels: for instance, I raised 233 seedling cab-
bages 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 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 general law of good being derived from the intercross-
ing of distinct individuals of the same species. When dis-
tinct species are crossed the case is reversed, for a plant's
own pollen is almost always prepotent over foreign pollen;
but to this subject we shall return in a future chapter.

In the case of a large tree covered with innumerable
flowers, it may be objected that pollen could seldom be
carried from tree to tree, and at most only from flower
to flower on the same tree; and flowers on the same tree
can be considered as distinct individuals only in a limited
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 regu-
larly carried from flower to flower; and this will give
a better chance of pollen being occasionally carried from

OP mniviDUALs, 03

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 antici-
pated. On the other hand. Dr. Hooker informs me that
the rule does not hold good in Australia: but if most of
the Australian trees are dichogamous, the same result
would follow as if they bore flowers with separated sexes.
I have made these few remarks on trees simply to call
attention to the subject.

Turning for a brief space to animals: various terrestrial
species are hermaphrodites, such as the land-mollusca and
earth-worms; but these all pair. As yet 1 have not found
a single terrestrial animal which can fertilize itself. This
remarkable fact, which offers so strong a contrast with ter-
restrial plants, is intelligible on the view of an occasional
cross being indispensible; for owing to the nature of the
fertilizing element there are no means, analogous to the
action of insects and of the wind with plants, by which an
occasional cnoss could be effected with terrestrial animals
without the concurrence of two individuals. Of aquatic
animals, there are many self-fertilizing hermaphrodites;
but here the currents 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
hermaphrodite animal with the organs of rej^ reduction so
perfectly enclosed that access from without, and the occa-
sional 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 diflB-
culty; but I have been enabled, by a fortunate chance, to
prove that two individuals, though both of self-fertilizing
hermaphrodites, do sometimes cross.

It must have struck most naturalists as a strange anomaly
that, both with animals and plants, some species of the
same family and even of the same genus, though agreeing
closely with each other in their whole organization, are
hermaphrodities, and some unisexual. But if, in fact, all
hermaphrodities do occasionally intercross, the difference
between them and unisexual species is, as far as fuuction
is concerned, ver/ small.

94 CIRCUMSTANCES FAVORABLE TO THE

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 individuals
is a very general, if not universal, law of nature.

CIRCUMSTAi>rCES FAVORABLE FOR THE PRODUCTIOIS" OF
NEW FORMS THROUGH NATURAL SELECTION.

This is an extremely intricate subject. A great amount
of variability, under which term individual differences are
always included, will evidently be favorable. A large num-
ber of individuals, by giving a better chance within any
giveJi period for the appearance of 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 selection, she does not grant an indefi-
nite 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
favorable 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 allowed 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 pro-
cure and breed from the best animals, improvement surely
but slowly follows from this unconscious process of selec-
tion, notwithstanding that there is no separation of selected
individuals. Thus it v/ill 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 pre-
served. But if the area be large, its several districts will
almost certainly present different conditians of life; and

RESULTS OF JS'-ATUHAL SELECTION. 95

then, if the same species undergoes modification in differ-
ent districts, the newly formed varieties will intercross on
the confines of each. But we shall see in the sixth chap-
ter 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 countries;
and this I find to be the case. With hermaphrodite or-
ganisms which cross only occasionally, and likewise Avitli
animals which unite for each birth, but which wander lit-
tle 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 afterward
spread, so that the individuals of the new variety would
chiefly cross together. On this principle nurserymen
always prefer saving seed from a large body of plants, as
the chance of intercrossing is thus lessened.

Even with animals which unite for each birth, and which
do not propagate rapidly, we must not assume that free in-
tercrossing would always eliminate the effects of natural
selection; for I can bring forward a considerable body of
facts showing that within the same area two varieties of
the same animal may long remain distinct, from haunting
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 animals
which unite for each birth; but, as already stated, we
have reason to believe that occesional intercrosses take
place with all animals and plants. Even if these take
place only at long intervals of time, the young thus pro-
duced will gain so much in vigor and fertility over the
offspring from long-continued self-fertilization, that they
will have a better chance of surviving and propagating their
kind; and thus in the long-run the influence of crosses,
even at rare intervals, will be great. With respect to or-

96 CIRCUMSTANCES FAVORABLE TO THE

gallic beings extremely low in the scale, which do not
propagate sexually, nor conjugate, and which cannot pos-
sibly intercross, uniformity of character can be retained
by them under the same conditions of life, only through
the principle of inheritance, and through natural selection
which will destroy any individuals departing from the
proper type. If the conditions of life change and the form
undergoes modification, uniformity of character can be
given to the modified offspring, solely by natural selection
preserving similar favorable variations.

Isolation also is an important element in the modifica-
tion of species through natural selection. In a confined 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 indi-
viduals of the same species in the same manner. Inter-
crossing with the inhabitants of the surrounding districts,
will also be thus prevented. Moritz Wagner has lately pub-
lished an interesting essay on this subject, and has sho\7n
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 isola-
tion are necessary elements for the formation of new species.
The importance of isolation is likewise great in prevent-
ing, after any physical change in the conditions, such as
of climate, elevation of the land, etc., 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 import-
ance. If, however, an isolated area be very small, either
from being surrounded by barriers, or from having very
peculiar physical conditions, the total number of the in-
habitants will be small; and this will retard the production
of new species through natural selection, by decreasing the
chances of favorable variations arising.

The mere lapse of time by itself does nothing, either for
or against natural selection. I state this because it has
been erroneously asserted that the element of time has
been assumed by me to play an all-important part in modi-

HESULTS OF NATURAL SELECTION. 07

f jing species, as if all tlie forms of life were necessarily
undergoing change through some innate law. Lai)8e of
fime is only so far important, and its importance in this
respect is great, that it gives a better chance of beneficial
variations arising and of their being selected, accumulated,
and fixed. It likewise tends to increase the direct action
of the physical conditions of life, in relation to the consti-
tution of each organism.

If we turn to nature to test the truth of these remarks,
and look at any small isolated area, such as an oceanic
island, although the number of species inhabiting it is
smal], as we shall see in our chapter on Geographical Dis-
tribution; yet of these species a very large proportion are
endemic, — that is, have been produced there and nowhere
else in the world. Hence an oceanic island at first sight
seems to have been highly favorable for the production of
new species. But we may thus deceive ourselves, for to
ascertain whether a small isolated area, or a large open
area like a continent, has been most favorable for the pro-
duction of new organic forms, we ought to make the com-
parison within equal times; and this we are incapable of
doing.

Although isolation is of gi^eat importance in the produc-
tion 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 cajDable 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 favorable variations, arising from the
large number of individuals of the same species there sup-
ported, but the conditions of life are much more complex
from the large number of already existing species; and if
some of these many species 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 competi-
tion with many other forms. Moreover, great areas, though
now continuous, will often, owing to former oscillations of
level, have existed in a broken condition; so that the good
effects of isolation will generally, to a certain extent, have
concurred. Finally, I conclude that, although small

98 CIRCUMSTANCES FAVORABLE TO THE

isolated areas have been in some respects highly favorable
for the production of new species, yet that the course of
modification will generally have been more rapid on large
areas; and what is more important, that the new forms
produced on large areas, which already have been victor-
ious 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 Austra-
lia now yielding before those of the larger Europaeo- Asiatic
area. Thus, also, it is that continental productions have
everywhere become so largely naturalized on islands.
On a small island, the race for life will have been less
severe, and there will have been less modification and less
extermination. Hence, we can understand how it is that
the flora of Maderia, 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. Con-
sequently, the competition between fresh water productions
will have been less severe than elsewhere, new forms will
have been then more slowly produced, and old forms more
slowly exterminated. And it is in fresh water basins that
we find seven genera of Ganoid fishes,, remnants of a once
preponderant order: and in fresh water we find some of the
most anomalous forms now known in the world as the
Ornithorhynchus and Lepidosiren, which, like fossils, con-
nect to a certain extent orders at present widely sundered
in the natural scale. These anomalous forms may be
called living fossils; 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, com-
petition.

To sum up, as far as the extreme intricacy of the subject
permits, the circumstances favorable and unfavorable for
the production of new species through natural selection.
I conclude that for terrestrial productions a large conti-

RESULTS OF NATURAL SELECTION. 09

nental area, whicli has undergone many oscillations o^
level, will have been the most favorable for the prod net iou
of many new forms of life, fitted to endure for a long time
and to spread widely. While the area existed as a conti-
nent the inhabitants will have been numerous in individu-
als and kinds, and will have been subjected to severe com-
petition. ^ When converted by subsistance into large
separate islands there will still have existed many indi-
viduals 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 immigra-
tion will have been prevented, so that new places in the
polity of each island will have had to be filled up by the
modification of the old inhabitants; and time will have
been allowed for the varieties in each to become well modi-
fied and perfected. "When, by renewed elevation, the
islands were reconverted into a continental area, there will
again have been very severe competition; the most favored
or improved varieties will have been enabled to spread;
there will have been much extinction of the less improved
forms, and the relative proportional numbers of the various
inhabitants of the reunited continent will again have been
changed; and again there will have been a fair field for
natural selection to improve still further the inhabitants,
and thus to produce new species.

That natural selection generally acts with extreme slow-
ness I fully admit. It can act only when there are places
in the natural polity of a district which can be better occu-
pied by the modification of some of its existing inhabitants.
The occurrence of such places will often depend on physi-
cal changes, which generally take place very slowly, and
on the immigration of better adapted forms being pre-
vented. As some few of the old inhabitants become modi-
fied 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 degree from each other, it would often
be long before differences of the right nature in various
parts of the organization might occur. The result would
often be greatly retarded by free intercrossing. Many will
exclaim that these several causes are amply sufficient to

100 EXTINCTION B Y NATURAL 8ELEGIT0N.

neutralize the power of natural selection. I do not believe
so. But I do believe that natural selection will generally
act very slowly, only at long intervals of time, and only on
a few of the inhabitants of the same region. I further
believe that these slow, intermittant results accord well
with what geology tells us of the rate and manner at which
the inhabitants of the world have changed.

Slow though the process of selection may be, if feeble
man can do much by artificial selection, I can see no limit
to the amount of change, to the beauty and complexity of
the coadaptations between all organic beings, one with
another and with their physical conditions of life, which
may have been affected in the long course of time through
nature's power of selection, that is by the survival of the
fittest.

EXTI^fCTIOK CAUSED BY NATUEAL SELECTION.

This subject will be more fully discussed in our chap-
ter on Geology; but it must here be alluded to from
being intimately connected with natural selection. Nat-
ural selection acts solely through the preservation of vari-
ations in some way advantageous, which consequently en-
dure. Owing to the high geometrical rate of increase of
all organic beings, each area is already fully stocked with
inhabitants; and it follows from this, that as the favored
forms increase in number, so, generally, will the less fa-
vored decrease and become rare. Earity, as geology tells
us, is the precursor to extinction. We can see that any
form which is represented by few individuals will run a
good chance of utter extinction, during great fluctuations
in the nature or the seasons, or from a temporary increase
ir. the number of its enemies. 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 specific forms has not indefinitely increased, geology
plainly tells us; and we shall presently attempt to show
why 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 favor-

DIVERGENCE OF (JHAItACTER. iQl

able variations within any given period. We have evi-
dence of this, in the facts stated in the second chapter,
showing that it is the common and diffused or dominant
species which offer the greatest number of recorded vari-
eties. Hence, rare species will be less quickly modified or
improved within any given period; they will consequently
be beaten in the race for life by the modified and improved
descendants of the commoner species.

From these several considerations I think it inevitably
follows, that as new species in the course of time are
foniied 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 suifer 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 related
genera — which, from having nearly the same structure,
constitution and habits, generally come into the severest
competition with each other consequently, each new vari-
ety 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 extermina-
tion among our domesticated productions, through the
selection of improved forms by man. Many curious in-
stances 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 agricul-
tural writer) '^as if by some murderous pestilence.^'

DIVEEGEKCE OF CHARACTER.

The principle, which I have designated by this tenn, ia
of high importance, and explains, as I believe, several im-
portant facts. In the first place, varieties, even strongly
marked ones, though having somewhat of the chanic-
ter of species — as is shown by the hopeless doubts
in many cases how to rank them — yet certainly differ
far less from each other than do good and distinct

102 DIVERGENCE OF CHARACTER.

species. Nevertheless according to my view, varieties are
species in the process of formation, or are, as I have called
them, incipient species. How, then, does the lesser differ-
ence between varieties become augmented into the greater
difference between species? That this does habitually
happen, we must infer from most of the innumerable
species throughout nature presenting well-marked differ-
ences; 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 differ
from its parent in the very same character and in a greater
degree; but this alone would never account for so habitual
and large a degree of difference as that between the species
of the same genus.

As has always been my practice, I have sought light on
this head from our domestic productions. We shall here
find something analogous. It will be admitted that the
production of races so different as short-horn and Here-
ford cattle, race and cart horses, the several breeds of
pigeons, etc., could never have been effected by the mere
chance accumulation of similar variations during many
successive generations. In practice, a fancier is, for in-
stance, struck by a pigeon having a slightly shorter beak;
another fancier is struck by a pigeon having a rather longer
beak; and on the acknowledged principle that " fanciers
do not and will not admire a medium standard, but like
extremes,'^ they both go on (as has actually occurred with
the sub-breeds of the tumbler-pigeon) choosing and breed-
ing from birds with longer and longer beaks, or with
shorter and shorter beaks. Again, we may suppose that
at an early period of history, the men of one nation or dis-
trict required swifter horses, while those of another re-
quired 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 dis-
tinct breeds. As the differences became greater, the in-

DIYERGENGE OF CIIAllACTEH. io3

ferior animals with intermediate characters, being neither
very swift nor very strong, would not have been used for
breeding, and will thus have tended to disappear. Here,
then, we see in man's productions the action of what may be
called the 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 principle
apply in nature? I believe it can and does apply most
etficiently (though it was a long time before I saw how),
from the simple circumstance that the more diversified 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 diversified places in
the polity of nature, and so be enabled to increase in
numbers.

We can clearly discern this in the case of animals with
simple habits. Take the case of a carnivorous quadruped,
of which the number that can be supported in any country
has long ago arrived at its full average. If its natural
power of increase be allowed to act, it can succeed in in-
creasing (the country not undergoing any change in con-
ditions) 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, climb-
ing trees, frequenting water, and some perhaps becoming
less carnivorous. The more diversified in habits and
structure the descendants of our carnivorous animals
become, the more places they will be enabled to occupy.
What applies to one animal will apply throughout all time
to all animals — that is, if they vary — for otherwise natural
selection can effect nothing. So it will be with plants. It
has been experimentally proved, that if a plot of ground
be sown with one species of grass, and a similar plot be
sown with several distinct genera of grasses, a greater
number of plants and a greater weight of dry herbage can
be raised in the latter than 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

104 DIVERGENCE OF CHARACTER.

varying, and the varieties were continually selected which
differed from each other in the same manner, though in a
very slight degree, as do the distinct species and genera of
grasses, a greater number of individual plants of this
species, including its modified descendants, would succeed
in living on the same piece of ground. And we know that
each species and each variety of grass is annually sowing
almost countless seeds; and is thus striving, as it may be
said, to the utmost to increase in number. Consequently,
in the course of many thousand generations, the most dis-
tinct varieties of any one species of grass would have the
best chance of succeeding and of increasing in numbers,
and thus of supplanting the less distinct varieties; and
varieties, when rendered very distinct from each other,
take the rank of species.

The trutli of the principle that the greatest amount of
life can be supported by great diversification of structure,
is seen under many natural circumstances. In an extremely
small area, especially if freely open to immigration, and
where the contest between individual and individual must
be very severe, we always find great diversity in its inhabi-
tants. 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 j^lants
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 more food
by a rotation of plants belonging to the m^ost 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 (suppos-
ing its nature not to be in any way peculiar), and may be
said to be striving to the utmost to live there; but, it is
seen, that where they come into the closest competition, the
advantages of diversification of structure, with the accom-
panying differences of habit and constitution, determine
that the inhabitants, which thus jostle each other most
closely, shall, as a general rule, belong to what we call
different genera and orders.

The same principle is seen in the naturalization of

DIVERGENCE OF CHA RA OTER. 1 05

plants through man's agency in foreign lands. It miglit
have been expected that the plants which would suc-
ceed in becoming naturalized in any land would generally
have been closely allied to the indigenes; for these are
commonly looked at as specially created and adapted for
their own county. It might also, perhaps, have been ex-
pected that naturalized plants would have belonged to a
few groups more especially adapted to certain stations in
their new homes. But the case is very different; and
Alph. de Candolle has well remarked, in his great and
admirable work, that floras gain by naturalization, pro-
portionally 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 Xorthern United States," 260
naturalized plants are enumerated, and these belong to 1G2
genera. We thus see that these naturalized plants are of
a highly diversified nature. They differ, moreover, to a
large extent, from the indigenes, for out of the 1G2
naturalized genera, no less than 100 genera are not there
indigenous, and thus a large proportional addition is made
to the genera now living in the United States.

By considering the nature of the plants or animals which
have in any country struggled successfully with the indi-
genes, and have there become naturalized, 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 dif-
ferences, 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 labor in the organs of the
same individual body — a subject so well elucidated by
Milne Edwards. No physiologist doubts that a stomach
adapted to digest vegetable matter alone, or flesh alone,
draws most nutriment from these substances. So in the
general economy of any land, the more widely and per-
fectly the animals and plants are diversified for different
habits of life, so will a greater number of individuals be
capable of there supporting themselves- A set of animals,
with their organization but little diversified, could hardly

106 RESULT OF THE ACTION

compete with a set more perfectly diversified in structure.
It may be doubted, for instance, whether the Austrahan
marsupials, which are divided into groups differing but
little from each other, and feebly representing, as Mr.
Waterhouse and others have remarked, our carnivorous,
ruminant and rodent mammals, could successfully com-
pete with these well-developed orders. In the Australian
mammals, we see the process of diversification in an early
and incomplete stage of development.

THE PKOBABLE EFFECTS OF THE ACTION" OF NATURAL
SELECTION" THROUGH DIVERGENCE OF CHARACTER
AND EXTINCTION, ON THE DESCENDANTS OF A COM-
MON ANCESTOR.

After the foregoing discussion, which has been much
compressed, we may assume that the modified descendants
of any one species will succeed so much the better as they
become more diversified in structure, and are thus enabled
to encroach on places occupied by other beings. ]N^ow let
us see how this principle of benefit being derived from
divergence of character, combined with the principles of
natural selection and of extinction, tends to act.

The accompanying diagram will aid us in understanding
this rather perplexing subject. Let A to L represent the
species of a genus large in its own country; these species are
supposed to resemble each other in unequal degrees, as is
so generally the case in nature, and as is represented
in the diagram by the letters standing at unequal distances.
I have said a large genus, because as we saw in the second
chapter, on an average more sj^ecies vary in 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
most widely diffused, vary more than do the rare and
restricted species. Let (A) be a common, widely-diffused,
and varying species, belonging to a genus large in its own
country. The branching and diverging dotted lines of
unequal lengths 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

OF NATURAL SELECTION. lO;

after long intervals of time; nor are tliey all supposed to
endure for equal periods. Only those variations wliich arc
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
variations (represented by the outer dotted lines) being
preserved and accumulated by natural selection. AVhen a
dotted line reaches one of the horizontal lines, and is there
marked by a small numbered letter, a sufficient amount of
variation is supposed to have been accumulated to form it
into a fairly well marked variety, such as would be thought
worthy of record in a systematic work.

The intervals between the horizontal lines in tlie dia-
gram, may represent each a thousand or more generations.
After a thousand generations, species (A) is supposed to
have produced two fairly well marked varieties, namely
a^ and m^. These two varieties will generally still be
exposed to the same conditions which made their parents
variable, and the tendency to variability is in itself hered-
itary; consequently they will likewise tend to vary, and
commonly in nearly the same manner as did their parents.
Moreover, these two varieties, being only slightly modified
forms, will tend to inherit those advantages which made
their parent (A) more numerous than most of the other
inhabitants of the same country; they will also partake of
those more general advantages which made the genus to
which the parent species belonged, a large genus in its own
country. And all these circumstances are favorable to the
production of new varieties.

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 cc^ is supposed in the diagram to have pro-
duced variety a^, 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

108

RESULT OF THE ACTIOM

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OF NATURAL SELECTION,

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more modified condition, some producing two or three
varieties, and some failing to produce any. Thus the
Tttrieties or modified descendants of the common parent
(A), will generally go on increasing in number and diverg-
ing in character. In the diagram the process is repre-
sented up to the ten-thousandth generation, and under a
condensed and sim23lified form up to the fourteen-thous-
andth generation.

But I must here remark that I do not suppose that the
process aver goes on so regularly as is represented in the
diagj'am, though in itself made somewhat irregular, nor
that it goes on continuously; it is far more probable that
each form remains for long periods unaltered, and then
again undergoes modification. Nor do I suppose that the
most divergent varieties are invariably preserved: a medium
form may often long endure, and may or may not produce
more than one modified descendant; for natural selection
will always act according to the nature of the places which
are either unoccupied or not perfectly occupied by other
beings; and this will depend on infinitely complex rela-
tions. But as a general rule, the more diversified in struc-
ture the descendants from any one species can be rendered,
the more places they will be enabled to seize on, and the
more their modified progeny will increase. In our diagram
the line of succession is broken at regular intervals by small
numbered letters marking the successive forms which have
become sufficiently distinct to be recorded as varieties. But
these breaks are imaginary, and might have been inserted
anywhere, after intervals long enough to allow the accumu-
lation of a considerable amount of divergent variation.

As all the modified descendents from a common and
widely-dilfused 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 multi-
plying in number as well as diverging in character: this
is represented in the diagram by the several divergent
branches proceeding from (A). The modified offspring
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 improved branches:
this is represented in the diagram by some of the lower
branches not reaching to the upper horizontal lines, lu

OF NA TUBAL SELECTION, 1 1 1

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 tbe
amount of divergent modification may have been augmented.
This case would be represented in the diagram, if all the
lines proceeding from (A) were removed, excepting that
from «! to «!". In the same way the English racehorse
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 supposed
to have produced three forms, a^^,f^^, and m'^^, which,
from having diverged in character during the successive
generations, will have come to differ largely, but perhaps
unequally, from each other and from their common parent.
If we suppose the amount of change between each hori-
zontal line in our diagram to be excessively small, these
three forms may still be only well-marked varieties; but
we have only to suppose the steps in the process of modi-
fication to be more numerous or greater in amount, to
convert these three forms into doubtful or at least into
well-defined species. Thus the diagram illustrates the
steps by which the small differences distinguishing varieties
are increased into the larger differences distinguishing
species. By continuing the same process for a greater
number of generations (as shown in the diagram in a con-
densed 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.

In a large genus it is probable that more than one sj^e-
cies 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 between the horizontal
lines. After fourteen thousand generations, six new spe-
cies, marked by the letters n'^'^ to 2;i*, are supnosed to
have been produced. In any genus, the species which are
already very ditt'erent 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

112 RESULT OF THE ACTION

on new and widely different places in the polity of nature;
hence in the diagram I have chosen the extreme species
(A), and the nearly extreme species (I), as tliose which
have largely varied, and have given rise to new varieties
and species. The other nine species (marked by capital
letters) of our original genus, may for long but unequal
periods continue to transmit unaltered descendants; and
this is shown in the diagram by the dotted lines unequally
prolonged upward.

But during the process of modification, represented in
the diagram, another of our principles, namely that of ex-
tinction, will have played an important part. As in each
fully stocked country natural selection necessarily acts by
the selected form having some advantage in the struggle
for life over other forms, there will be a constant tendency
in the improved descendants of anyone species to supplant
and exterminate in each stage of descent their predecessors
and their original progenitor. For it should be remem-
bered that the competition will generally be most severe
between those forms which are most nearly related to each
other in habits, constitution and structure. Hence all the
intermediate forms between the earlier and later states,
that is between the less and more improved states of
the same species, as well as the original parent species
itself, will generally tend to become extinct. So it proba-
bly 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 progen-
itor do not come into competition, both may continue to
exist.

If, then, our diagram be assumed to represent a consid-
erable 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 re-
placed by six {n^^ to z^^) new species.

But we may go further than this. The original species of
our genus were supposed to resemble each other in unequal
degrees, as is so generally the case in nature; species (A) being
more nearly related to B, 0 and D than to the other spe-
cies; and species (I) more to G, H, K, L than to the others.

OF NA TURA L SELECTION'. 1 1 '/

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, four-
teen in number at the fourteen-thousandth generation, will
probably have inherited some of the same advantages;
they have also been modified and improved in a diversified
manner at each stage of descent, so as to have become
adapted to many related places in the natural economy of
their country. It seems, therefore, extremely probable tliat
they will have taken the places of, and thus exterminated,
not only their parents (A) and (I), but likewise some of
the original species which were most nearly related to their
parents. Hence very few of the original species will have
transmitted offspring to the fourteenth thousandth genera-
tion. AVe may suppose that only one (F) of the two
species (E and F) which were least closely related to the
other nine original species, has transmitted descendants to
this late stage of descent.

The new species in our diagram, descended from the
original eleven species, will now be fifteen in number.
Owing to the divergent tendency of natural selection, the
extreme amount of difference in character between species
a^* and z^^ will be much greater than that between the
most distinct of the original eleven species. The new
species, moreover, will be allied to each other in a widely
different manner. Of the eight descendants from (A) the
three marked a", q^*, 7.?^*, will be nearly related from
having recently branched off from a}^; b^^ and/^*, from hav-
ing diverged at an earlier period from a^, will be in some
degree distinct from the three first-named species; and
lastly, o^S e" and m}^, will be nearly related one to the
other, but, from having diverged at the first commence-
ment of the process of modification, will be widely differ-
ent from the other five species, and may constitute a sub-
genus or a distinct genus.

The six descendants from (I) will form two sub-genera
or genera. But as the original species (I) differed largely
from (A), standing nearly at the extreme end of the
original genus, the six descendants from (I) will, owing to
inheritance alone, differ considerably from the eight de-
scendants from (A); the two groups, moreover, are sup-

114 RESULT OF THE ACTIOlit

posed to have gone on diverging in different directions.
The intermediate species, also (and this is a very import-
ant consideration), which connected the original species
(A) and (I), have all become, except (F), extinct, and
have left no descendants. Hence the six new species de-
scended from fl), and the eight descendants from (A),
will have to be ranked as very distinct genera, or even as
distinct sob-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 desceuded 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 downward toward a single point; this point rep-
resents a species, the supposed progenitor of our several
new sub-genera and genera.

It is worth while to reflect for a moment on the charac-
ter of the new species f^*, wdiich 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 de-
scended from a form that stood between the parent-
species (A) and (I), now supposed to be extinct and un-
known, it vrill be in some degree iiitermediate in character
between the two groups descended from these two species.
But as these two groups have gone on diverging in charac-
ter from the type of their parents, the new species (f^*)
will not be directly intermediate between them, but rather
between types of the two groups; and every naturalist
will be able to call such cases before his mind.

In the diao-ram each horizontal line has hitherto 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 sub-
ject, and I think we shall then see that the diagram throws
light on the afUnities of extinct beings, which, though
generally belonging to the same orders, families or genera,
with those now living, yet are often, in some degree, inter-

OF NATURAL SELECTION. 115

mediate in character between existing groups; and we can
understand this fact, for the extinct species lived at various
remote epochs when the branching Unes 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 represented
by each successive group of diverging dotted lines to be
great, the forms marked a}^ to p^^, those marked h^^ and
/^S and those marked o^* to ?;i^*, will form three very dis-
tinct genera. We shall also have two very distinct genera
descended from (I), differing widely from the descendants of
(A). These two groups of genera will thus form two dis-
tinct families, or orders, according to the amount of diver-
gent modification supposed to be represented in the dia-
gram. And the two new families, or orders, are descended
from two species of the original genus, and these are sup-
posed to be descended from some still more ancient and
unknown form.

We have seen that in each country it is the species be-
longing to the larger genera which oftenest present varie-
ties or incipient species. This, indeed, might have been
expected; for, as natural selection acts through one form
having some advantage over other forms in the struggle for
existence, it will chiefly act on those which already have
some advantage; and the largeness of any group shows that
its species have inherited from a common ancestor some
advantage in common. Hence, the struggle for the pro-
duction of new and modified descendants will mainly lie
between the larger groups which are all trying to incroase
in number. One large group will slowly conquer another
large group, reduce its number, and thus lessen its chance
of further variation and improvement. Within the same
large group, the later and more highly perfected sub-
groups, from branching out and seizing on many new
places in the polity of nature, will constantly tend to sup-
})iant and destroy the earlier and less improved sub-gi-oups.
Small and broken groups and sub-groups will finally disap-
pear. Looking to the future, we can predict that the
groups of organic beings which are now hirge and trium-
phant, and which are least broken up, that is, which have
as yet suffered least extinction, will, for a long period, con-

116 ON THE DEGREE TO WHICH

tinue to increase. But which groups will ultimately pre*
vail, no man can predict; for we know that many groups,
formerly most extensively developed, have now become ex-
tinct. Looking still more remotely to the future, we may
predict that, owing to the continued and steady increase of
the larger groups, a multitude of smaller groups will be-
come utterly extinct, and leave no modified descendants;
and consequently that, of the species living at any one
period, extremely few will transmit descendants to a
remote futurity. I shall have to return to this subject in the
chapter on 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 same species form a class, we
can understand how it is that there exist so few classes in
each main division of the animal and vegetable kingdoms.
Although few of the most ancient species have left modi-
fied 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.

OK THE DEGREE TO WHICH ORGAN'IZATION' TEN^DS TO

ADVANCE.

Natural selection acts exclusively by the preservation and
accumulation of variations, which are beneficial under the
organic and inorganic conditions to which each creature is
exposed at all periods of life. The ultimate result is that
each creature tends to become more and more improved
in relation to its conditions. This improvement inevitably
leads to the gradual advancement of the organization of
the greater number of living beings throughout the world.
But here we enter on a very intricate subject, for natural-
ists have not defined to each other's satisfaction what is
meant by an advance in organization. Among the verte-
brata the degree of intellect and an approach in structure
to man clearly come into play. It might be thought that
the amount of change which the various parts and organs
pass through in their development from embryo to
maturity would suffice as a standard of comparison; but
there are cases, as with certain parasitic crustaceans, in

OROANIZA TlOJSr TENDS TO AD VANCE. 1 1 7

which several parts of the structure become less perfect, so
that the mature animal cannot be called liiglier tliau its
larva. Von Baer's standard seems the most widely appli-
cable and the best, namely, the amount of differentiation of
the parts of the same organic being, in the adult state, as I
should be inclined to add, and their specialization for
different functions; or, as Milne Edwards would express it,
the completeness of the division of physiological labor.
But we shall see how obscure this subject is if we look, for
instance, to fishes, among which some naturalists rank
those as highest which, like the sharks, approach nearest
to amphibians; while 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, among which the
standard of intellect is of course quite excluded; and here
some botanists rank those plants as highest which have
every organ, as sepels, petals, stamens and pistils, fully
developed in each flower; whereas other botanists, probably
with more truth, look at the plants v/hich have their
several organs much modified and reduced in number as
the highest.

If we take as the standard of high organization, the
amount of differentiation and specialization of the several
organs in each being when adult (and this will include the
advancement of the brain for intellectual purposes),
natural selection clearly leads toward this standard: for
all physiologists admit that the specialization 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 toward specialization
is within the scope of natural selection. 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 occupied place in the
economy of nature, that it is quite possible for natural
selection gradually to fit a being to a situation in which
several organs would be superfluous or useless: in such
cases there would be retrogression in the scale of organiza-
tion. Whether organization on the whole has actually ad-
vanced from the remotest geological periods to the present

118 ON THE DEGREE TO WBICB

day will be more conveniently 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 every where supplanted and exter-
minated the lower? Lamarck, who believed in an innate
and inevitable tendency toward 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 continu-
ally 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 selec-
tion, or the survival of the fittest, does not necessarily in-
clude progressive development — it only takes advantage of
such variations as arise and are beneficial to each creature
under its complex relations of life. And it may be asked
what advantage, as far as we can see, would it be to an in-
fusorian animalcule — to an intestinal worm — or even to au
earth-worm, to be highly organized. If it were no advan-
tage, these forms would be left, by natural selection, un-
improved or but little improved, and might remain for in-
definite ages in their present lowly condition. And geol-
ogy tells us that some of the lowest forms, as the infusoria
and rhizopods, have remained for an enormous period in
nearly their present state. But to suppose that most of the
many now existing low forms have not in the least ad-
vanced since the first dawn of life would be extremely
rash; for every naturalist who has dissected some of the
beings now ranked as very low in the scale, must have been
struck with their really wondrous and beautiful organiza-
tion.

Nearly the same remarks are applicable, if we look to the
different grades of organization within the same great
group; for instance, in the vertebrata, to the co-existence
of mammals and fish — among mammalia, to the co-exist-
ence of man and the ornithorhynchus — among fishes, to
the co-existence of the shark and thelancelet (Amphioxus),
which latter fish in the extreme simplicity of its structure

ORGANIZATION TENDS TO ADVANCE, 119

approaches the invertebrate classes. But mammals and
fish hardly come into competition with each other; the ad-
vancement of the whole class of mammals, or of certain
members in this class, to the highest grjide would not lead
to their taking the place of fishes. "Physiologists believe
that the brain must be bathed by warm blood to be highly
active, and this requires aerial respiration; so that warm-
blooded mammals when inhabiting the water lie under a
disadvantage in having to come continually to the surface
to breathe. With fishes, members of the shark family
would not tend to supplant the lancelet; for the lancelet,
as I hear from Fritz Miiller, has as sole companiou and
competitor on the barren sandy shore of South Brazil, an
anomalous annelid. The three lowest orders of nuun-
mals, namely, marsupials, edentata, and rodents, co-exist
in South America in the same region with nnmeroua
monkeys, and probably interfere little with each other.
Although organization, on the whole, may have advanced
and be still advanciug throughout the world, yet the scale
will always present many degrees of perfection; 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 here-
after see, lowly organized forms appear to have been pre-
served to the jDresent day, from inhabiting confined or
peculiar stations, where they have been subjected to less
severe competion, and where their scanty numbers have re-
tarded the chance of favorable variations arising.

Finally, I believe that many lowly organized forms nov
exist throughout the world, from various causes. In some
cases variations or individual differences of a favorable
nature may never have arisen for natural selection to act
on and accumulate. In no case, probably, has time suf-
ficed for the utmost possible amount of development. In
some few cases there has been what we must call retro-
gression or organization. But the main cause lies in the
fact that under very simple conditions of life a hi;: h organi-
zation would be of no service, — possibly would bo of actual
disservice, as being of a more delicate nature, and more
liable to be put out of order and injured.

Looking to the firgt dawu of life,' when all orgauio beiugd^

[20 CJO YERGENCE OF CHARACTER.

as we may believe, presented the simplest structure, how,
it has been asked, could the first step in the advancement
or differentiation of parts have arisen? Mr. Herbert
Spencer would probably answer that, as soon as simple
unicellular organism came by growth or division to be
compounded of several cells, or became attached to any
supporting surface, his law '^that homologous units of
any order become differentiated in proportion as their rela-
"tions to incident forces become different'' would come
into action. But as we have no facts to guide us, specula-
tion on the subject is almost useless. It is, however, an
error to suppose that there would be no struggle for exist-
ence, and, consequently, no natural selection, until many
forms had been produced: variations in a single species
inhabiting an isolated station might be beneficial, and
thus the whole mass of individuals might be modified, or
two distinct forms might arise. But, as I remarked toward
the close of the introduction, no one ought to feel surprise
at much remaining as yet unexplained on the origin of
species, if we make due allowance for our profound ignor-
ance on the mutual relations of the inhabitants of the
world at the present time, and still more so during past
ages.

COl!?'VBRGE]!q'CE OF CHARACTER.

Mr. H. C. Watson thinks that I have overrated the im-
portance of divergence of character (in which, however, he
apparently believes), and that convergence, as it may be
called, has likewise played a part. If two species belonging
to two distinct though allied genera, had both produced a
large number of new and divergent forms, it is conceivable
that these might approach each other so closely that they
would have all to be classed under the same genus; and
thus the descendants of two distinct genera would converge
into one. But it would in most cases be extremely rash to at-
tribute to convergence a close and general similarity of struct-
ure in the modified descendants of widely distinct forms.
The shape of a crystal is determined solely by the molecular
forces, and it is not surprising that dissimilar substances
should sometimes assume the same form; but with organic
beings we should bear in mind that the form of each de-
pends on an infinitude of complex relations, namely on the

CO VEROENCE OF CHARACTER. \ o \

variations which have arisen, these being due to causes far too
intricate to be followed out — on the nature of the variations
which have been preserved or selected, and this depends on
the surrounding physical conditions, and in a still higher de-
gree on the surrounding 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 eoually com-
plex relations. It is incredible that the descendants of two
organisms, which had originally differed in a marked man-
ner, should ever afterward converge so closely as to lead
to a near approach to identity throughout their whole
organization. If this had occurred, we should meet with
the same form, independently of genetic connection, re-
curring in widely separated geological formations; and the
balance of evidence is opposed to any such an admission.

Mr. Watson has also objected that the continued action
of natural selection, together with divergence of character,
would tend to make an indefinite number of specific forms.
As far as mere inorganic conditions are concerned, it seems
probable that a sufficient number of species would soon
become adapted to all considerable diversities of heat,
moisture, etc.; but I fully admit that the mutual relations
of organic beings are more important; and as the number
of species in any country goes on increasing, the organic
conditions of life must become more and more complex.
Consequently there seems at first 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 naturalized.
But geology shows us, that from an early part of the ter-
tiary period the number of species of shells, and tliat from
the middle pa/t of this same period, the number of mam-
mals has not greatly or at all increased. What then^checks
an indefinite increase in the number of species? Tlio
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 inhabited by very many species, each or nearly

122 SUMMARY.

each species will be represented by few individuals; and
such species will be liable to extermination from accidental
fluctuations in the nature of the seasons or in the number
of their enemies. The process of extermination in such
cases would be rapid, whereas the production of new species
must always be slow. Imao^ine the extreme case of as manv
Species as individuals in England, and the first severe winter
or very dry summer would exterminate thousands on thou-
sands of species. Eare species, and each species will become
rare if the number of species in any country becomes in-
definitely increased, will, on the principle often explained,
present within a given period few favorable variations; con-
sequently, the process of giving birth to new specific forms
would thus be retarded. AYhen any species becomes very
rare, close interbreeding will help to exterminate it; authors
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, etc. Lastly, and this
I am inclined to think is the most important element, a
dominant species, which has already beaten many compet-
itors 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 veri/
widely, consequently they will tend to supplant and exter-
minate 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 southeast cor-
ner of Australia, where, apparently, there are many in-
vaders from different quarters of the globe, the endemic
Australian species have been greath^ reduced in number.
How much weight to attribute to these several considera-
tions 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 CHAPTEB.

If under clianging conditions of life organic beings pre-
sent 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 cannoi

SUMMARY. 1*^1

be disputed; then, considering the infinite complexity of
the relations of all organic beings to each other and to their
conditions of life, causing an infinite diversity in structure,
constitution and habits, to be advantageous to them, it
would be a most extraordinary fact if no variations had
ever occurred useful to each being's own welfare, in the
same manner as so many variations have occurred useful to
man. But if variations useful to any organic being ever
do occur, assuredly individuals thus characterized 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 ofl:'spring similarly characterized. This
principle of preservation, or the survival of the fit-
test, I have called natural selection. It leads to the im-
provement of each creature in relation to its organic and in-
organic conditions of life; and consequently, in most cases,
to what must be regarded as an advance in organization.
Nevertheless, low and sim])le forms will long endure if well
fitted for their simple conditions of life.

Natural selection, on the principle of qualities being in-
herited at corresponding ages, can miodify the egg, seed or
young as easily as the adult. Among many animals sexual
selection will have given its aid to ordinary selection by
assuring to the most vigorous and best adapted males tlie
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
lo divergence of character; for the more organic beings
diverge in structure, habits and constitution, by so mucli
the more can a large number be supported on the area, of
which we see proof by looking to tlie inhabitants of any
small spot, and to the productions naturalized in foreign
l^uds. Therefore^ during the modification of the descend-

124 SUMMARY.

ants of any one species, and during the incessant struggle of
all species to increase in numbers, the more diversified the
descendants become, the better will be their chance of suc-
cess in the battle for life. Thus the small differences dis-
tinguishing varieties of the same species, steadily tend to
increase, 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. Nat-
ural selection, as has just been remarked, leads to diverg-
ence of character and to much extinction of the less
improved and intermediate forms of life. On these prin-
ciples, 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 familiarity — 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 species most closely related,
species of the same genus less closely and unequally related,
forming sections and sub-genera, species of distinct genera
much less closely related, and genera related in different
degrees, forming sub-families, families, orders, sub-classes
and classes. The several subordinate groups in any class
cannot be ranked in a single file, but seen clustered round
points, and these round other points, and so on in almost
endless cycles. If species had been independently created,
no explanation would have been possible of this kind of class-
ification; 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

SUMMARY. 125

of extinct species. At each period of growth all the grow-
ing twigs have tried to branch out on all sides, and to over-
top and kill the surrounding twigs and branches, in tlie
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 bnds by ramifying branches may well
represent the classification of all extinct and living species
in groups subordinate to gi'oups. Of the many twigs
which flourished when the tree was a mere bush, only two
or three, now grown into great branches, yet survive and
bear the other branches; so with the species which lived
during long-past geological periods, very few have left
living and modified descendants. From the first growth
of the tree, many a limb and branch has decayed and
dropped of!;; and these fallen branches of various sizes
may represent those whole orders, families and genera
which have now no living representatives, and which are
known to us only in a fossil state. As w'e here and
there see a thin, straggling branch springing from a fork
low down in a tree, and which by some chance has been
favored and is still alive on its summit, so we occasionally
see an animal like the Ornithorhynchus or Lepidosiren,
which in some small degree connects by its aflinities two
large branches of life, and which has apparently been
saved from fatal competition by having inhabited a pro-
tected 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 witli its dead
and broken branches the crust of the earth, and covers tlie
Hurfacewith its ever-branching and beautiful ramifications.

186 LAWS OF VARIATION.

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
organized 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 variations —
BO common and multiform with organic beins's under do-
niestication, and inalesser degree with those under nature
< — were due to chance. Tliis, of course is a wholly incorrect
expression, but it serves to acknowledge plainly our igno-
rance of the cause of each particular variation. Some
authors believe it to be as much the function of the repro-
ductive S3'stem to produce individual differences, or slight
deviations of structure, as to make the child like its parents.
But the fact of variations and monstrosities occurring
much more frequently under domestication than under
nature, and the greater variability of species having wide
ranges than of those with restricted ranges, lead to the con-
clusion that variability is generally related to the conditions
of life to which each species has been exposed during sev-
eral successive generations. In the first chapter I at-
tempted to show that changed conditions act in two ways,
directly on the whole organization or on certain parts alone,
and indirectly through the reproductive system. In all cases
there are tw^o 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
organization seems to become plastic, and we have much

LAWS OF VARIATION. 127

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 individuaU
become modified in the same way.

It is very difficult to decide how far changed conditions,
such as of climate, food, etc., have acted in a definite
manner. There is reason to believe that in the course of
time the effects have been greater tlian can be j^roved by
clear evidence. But we may safely conclude that the
innumerable complex co-adaptations of structure, wliich
we see throughout nature between various organic beings,
cannot be attributed simply to such action. In tlie follow-
ing 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 colored 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 colored under a clear
atmosphere, than when living near the coast or on islands;
and Wollaston is convinced that residence near the sea
affects the colors of insects. Moquin-Tandon gives a list
of plants which, when growing near the sea-shore, have
their leaves in some degree fleshy, though not elsewhere
fleshy. These slightly varying organisms are interesting
in as far as they present characters analogous to those pos-
sessed by the species which are confined to similar condi-
tions.

When a variation is of the slightest use to any being, we
cannot tell how much to attribute to the accumulative
action of natural selection, and how much to the definite
action of the conditions of life. Thus, it is well known
to furriers that animals of the same- species have thicker
and better fur the further nortli they live; but who can
tell how much of this difference may be due to the warmest;
clad individuals having been favored 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 pro-
duced from the same species under external conditions
ot life as different as can well be conceived; and, on th«

128 EFFECTS OF USE AND DISUSE,

other hand, of dissimilar varieties being produced under
apparently the same external conditions. Again, innumer-
able instances are known to every naturalist, of species
keeping true, or not varying at all, although living under
the most opposite climates. Such considerations as these
incline me to lay less weight on the direct action of the
surrounding conditions, than on a tendency to vary, due
to causes of which we are quite ignorant.

In one sense the conditions of life may be said, not only
to cause variability, either directly or indirectly, but like-
wise to include natural selection, for the conditions
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 distinct; variability is in some
manner excited, but it is the will of man which accumu-
lates the variations in certain direction; and it is this latter
agency which answers to the survival of the fittest under
nature.

EFFECTS OF THE INCREASED USE AND DISUSE OF PARTS, AS
CONTROLLED BY NATURAL SELECTION.

From the facts alluded to in the first chapter, I think
there can be no doubt that use in our domestic animals has
strengthened and enlarged certain parts, and disuse dimin-
ished them; and that such modifications are inherited.
Under free nature we have no standard of comparison by
which to judge of the effects of long-continued use or
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 several in this state. The logger-headed
duck of South America can only flap along the surface
of the water, and has its wings in nearly the same condition
as the domestic Aylesbury duck; it is a remarkable fact
that the young birds, according to Mr. Cunningham, can
fly, while the adults have lost this power. As the larger
ground-feeding birds seldom take flight except to escape
danger, it is probable that the nearly wingless condition of
several birds, now inhabiting or which lately inhabited
several oceanic islands, tenanted by no beasts of prey, has

EFFECTS OF USE AND DISUSE. 120

been caused by disuse. The ostrich indeed inliabits con-
tinents, and is exposed to danger from which it cannot
escape by flight, but it can defend itself, by kicking its
enemies, as efticiently as many quadrupeds. We may
believe that the progenitor of the ostrich genus liad habits
like those of the bustard, and that, as the size and weight
of its body were increased during successive generations,
its legs were used more and its wings less, until they be-
came incapable of flight.

Kirby has remarked (and I have observed the same fact)
that the anterior tarsi, or feet, of many male dung-feeding
beetles are often broken off; he examined seventeen speci-
mens 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 Egyp-
tians, they are totally deficient. The evidence that acci-
dental mutilations can be inherited is at present not de-
cisive; but the remarkable cases observed by Brown-Sequard
in guinea-pigs, of the inherited effects of operations,
should make us cautious in denying this tendency. Hence,
it will perhaps be safest to look at the entire absence of the
anterior tarsi in Ateuchus, and their rudimentary con-
dition in some other genera, not as cases of inherited mu-
tilations, but as due to the effects of long continued disuse;
for as many dung-feeding beetles are generally found with
their tarsi lost, this must happen early in life; therefore
the tarsi cannot be of much importance or be much used
by these insects.

In some cases we might easily put down to disuse
modifications of structure which are wholly, or mainly duo
to natural selection. Mr. Wollaston has discovered the
remarkable fact that 200 beetles, out of the 550 species (but
more are now known) inhabiting Maderia, are so far defi-
cient 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 fre-
quently blown to sea and perish; that the beetles in Maderia,
as observed by Mr. Wollaston, lie much concealed, until
the wind lulls and the sun shines; that the proportion of

130 EFFECTS OF USE AND DISUSE,

wingless beetles is larger on the exposed Desertas than in
Maderia itself; and especially the extraordinary fact, so
strongly insisted on by Mr. Wollaston, that certain large
groups of beetles, elsewhere excessively numerous, which
absolutely require the use of their wings, are here almost
entirely absent. These several considerations make me be-
lieve that the wingless condition of so many Maderia
beetles is mainly due to the action of natural selection,
combined probably with disuse. For during many succes-
sive generations each individual beetle which flew least,
either from its wings having been ever so little less per-
fectly 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 Maderia which are not ground-feeders,
and which, as certain flower-feeding coleoptera and
lepidoptera, must habitually use their wings to gain their
subsistence, have, as Mr. Wollaston suspects, their wings
not at all reduced, but even enlarged. This is quite com-
patable with the action of natural selection. For when
a new insect first arrived on the island, the tendency of
natural selection to enlarge or to reduce the wings, would
depend on whether a greater number of individuals were
saved by successfully battling with the winds, or by giving
up the attempt and rarely or never flying. As with
mariners 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
swimmers if they had not been able to swim at all and had
stuck to the wreck.

The eyes of moles and of some burrowing rodents are
rudimentary in size, and in some cases are quite covered
by skin and fur. This state of the eyes is probably due to
gradual reduction from disuse, but aided perhaps by
natural selection. In South America, a burrowing rodent,
the tuco-tuco, or Ctenomys, is even more subterranean in
its habits 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 con-
clition^ the cause, as appeared on dissection, having been

EFFECTS OF USE AND DISUSE. 131

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
subterranean habits, a reduction in their size, with the
adhesion of the eyelids and growth of fur over them,
might in such case be an advantage; and if so, natural
selection would aid the effects of disuse.

It is well known that several animals, belonging to the
most different classes, which inhabit the caves of Carniola
and Kentucky, are blind. In some of the crabs the
foot-stalk for the eyes remains, though the eye is gone;
the stand for the telescope is there, though the telescope
with its glasses has been lost. As it is difficult to imag-
ine 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, tlie 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 imasfine conditions of life more similar
than deep limestone caverns under a nearly similar climate;
so that, in accordance with the old view of the blind ani-
mals having been separately created for the American and
European caverns, very close similarity in their organiza-
tion and affinities might have been expected. This is cer-
tainly not the case if we look at the two whole faunas; and
with respect to the insects alone, Schiodte has remarked:
" We are accordingly prevented from considering the entire
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 generally between the fauna
of Europe and of North America.'' On my view we must
suppose that American animals, having in most cases ordi-
nary powers of vision, slowly migrated by successive gener-
ations from the outer world into the deeper and deeper re-
cesses of the Kentucky caves, as did European animals into

132 EFFECTS OF USE AND DISUSE.

the caves of Europe. "We have some evidence of this gra-
dation of habit; for, as Schiodte remarks: " We accord-
ingly look upon the subterranean faunas as small ramifica-
tions which have penetrated into the earth from the geo-
graphically limited faunas of the adjacent tracts, and
which, as they extended themselves into darkness, have
been accommodated to surrounding circumstances. Ani-
mals not far remote from ordinary forms, prepare the tran-
sition from light to darkness. Next follow those that are
constructed for twilight; and, last of all, those destined for
total darkness, and whose formation is quite peculiar.^'
These remarks of Schiodte's, it should be understood,
apply not to the same, but to distinct species. By the
time that an animal had reached, after numberless
generations, the deepest recesses, disuse will on this
view have more or less perfectly obliterated its eyes,
and natural selection will often have elfected other
changes, such as an increase in the length of the
antennae or palpi, as a compensation for blindness.
Notwithstanding such modifications, we might expect still
to see in the cave-animals of America, affinities to the other
inhabitants of that continent, and in those of Europe to
the inhabitants of the European continent. And this is the
case with some of the American cave-animals, as I hear from
Professor Dana; and some of the European cave-insects are
very closely allied to those of the surrounding country. It
would be difficult to give any rational explanation of the
affinities of the blind cave-animals to the other inhabit-
ants of the two continents on the ordinary view of their
independent creation. That several of the inhabitants of the
caves of the Old and New Worlds sliould 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 prob-
ably had no relation to its dark habitation; for it is natu-
ral that an insect already deprived of vision should readily
become adapted to dark caverns. Anotlier blind genus
(Anophthalmus) offers his remarkable peculiarity, that the
species, as Mr. Murray observes, have not as yet been found
anywhere except in caves; yet those which inhabit the
several caves of Europe and America are distinct; but it is

ACCLIMATIZATION. I33

possible that the progenitors of these several species, while
they were furnished with eyes, may formerly have ranged
over both continents, and then have become extinct, ex-
cepting in their present secluded abodes. Far from feeling
surprise that some of the cave-animals should be very
anomalous, as Agassiz has remarked in regard to the bliird
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.

ACCLIMATIZATION".

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, etc., and this leads me to
say a few words on acclimatization. As it is extremely
common for distinct species belonging to the same genus
to inhabit hot and cold countries, if it be true that all the
species of the same genus are descended from a single
parent-form, acclimatization must be readily effected dur-
ing a long course of descent. It is notorious that each
species is adapted to the climate of its own home: species
from an arctic or even from a temperate region cannot
endure a tropical climate, or conversely. So again, many
succulent plants cannot endure a damp climate. But the
degree of adaptation of species to the climates under which
thev live is often overrated. We mav 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 be-
coming, to a certain extent, naturally habituated to differ-
ent temperatures; that is, they become acclimatized: thus
the pines and rhododendrons, raised from seed collected

134 ACCLIMATIZATION.

by Dr. Hooker from the same species growing at different
heights on the Ilimahiyas, 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. 0, Watson on European species of flants
brought from the Azores to England; and I could give
other cases. In regard to animals, several autbeiitic
instances could be adduced of species having h.rgely
extended, within historical times, their range f rom wiiinier
to colder latitudes, and conversely; but w^e do not posi-
tively know that these animals were strictly adapted to
their native climate, though in all ordinary casos we
assume such to be the case; nor do we know that they
have subsequently become specially acclimated 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 origin-
ally chosen by uncivilized 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 extraordinary
capacity in our domestic animals of not only withstanding
the most different climates, but of being perfectl} fertile
(a far severer test) under them, may be used as an argument
that a large proportion of other animals liow in a state of
nature could easily be brought to bear widely dilferent
climates. We must not, however, push the foregoing
argument too far, on account of the probable origin of
some of our domestic animals from several wild stocks; the
blood, for instance, of a tropical and arctic wolf may per-
haps be mingled in our domestic breeds. The rat and
mouse cannot be considered as domestic animals, but they
have been transported by man to many parts of the world,
and now have a far wider range 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 climate
may be looked at as quality readily grafted on an innate
wide flexibility of constitution, common to most animals.
On this view, the capacity of enduring the most dilferent
climates by man himself and by his domestic animals, and

A CCLIMA riZA TION. I35

the fact of the extinct elephant and rhinoceros liavin^ for-
merly endured a glacial climate, whereas the living species
are now all tropical or sub-tropical in their habits, ought
not to be looked at as anomalies, but as examples of a vtrv
common flexibility of constitution^ brought, under pecuhur
circumstances, into action.

How much of the acclimatization of species to any
peculiar climate is due to mere habit, and how much to the
natural selection of varieties having different innate con-
stitutions, and how much to both means combined, is an
obscure question. That habit or custom has some influ-
ence, I must believe, both from analogy and from tlie in-
cessant advice given in agricultural works, even in the
ancient Encyclopedias of China, to be very cautious in
transporting animals from one district to another. And
as it is not likely that man should have succeeded in select-
ing 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 selec-
tion would inevitably tend to preserve those individuals
which were born with constitutions best adapted to any
country whicli they inhabited. In treatises on many kinds
of cultivated plants, certain varieties are said to with-
stand certain climates better than others; this is strik-
ingly shown in works on fruit-trees published in the United
States, in which certain varieties are habitually recom-
mended for the northern and others for the southern states;
and as most of these varieties are of recent origin, they can
not owe their constitutional differences to habit. The case
of the Jerusalem artichoke, which is never propagated in
England by seed, and of which, consequently, new varieties
have not been produced, has even been advanced, as prov-
ing that acclimatization cannot be effected, 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 some one will sow, during a score
of generations, his kidney-beans so |early tliat 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 ia

136 CORRELATED VARIATION.

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, Ave may conclude that habit, or use and
disuse, have, in some cases, played a considerable part in
the modification of the constitution and structure; but
that the effects have often been largely combined with, and
sometimes overmastered by, the natural selection of innate
variations.

CORRELATED VARIATIOi^r.

I mean by this expression that the whole organization is
so tied together, during its growth and development, that
when slight variations in any one part occur and are accu-
mulated through natural selection, other parts become
modified. This is a very important subject, most
imperfectly understood, and no doubt wholly different
classes of facts may be here easily confounded together.
We shall presently see that simple inheritance often gives
the false appearance of correlation. One of the most
obvious real cases is, that variations of structure arising in
the young or larvae naturally tend to affect the structure of
the mature animal. The several parts which are homo-
logous, 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
homologous 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 rendered per-
manent 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 homolo-
gous parts in normal structures, as in the union of the

CORRELATED VARIATION. I37

petals into a tube. Hard parts seem to affect the form of
adjoining soft parts; it is believed by some authors that
with birds the diversity in the shape of the pelvis causes
the remarkable diversity in the shape of tlieir kidneys.
Others believe that the shape of the pelvis in the human
mother influences by pressure the shape of the head of the
child. In snakes, according to Schlegel, the form of the
body and the manner of swallowing determine the position
'and form of several of the most important viscera.
I The nature of the bond is frequently quite obscure. M. Is.
I Geoffroy St. Hilaire has forcibly remarked that certain mal-
'conformations frequently, and that others rarely, coexist
without our being able to assign any reason. What can
be more singular than the relation in cats between com-
plete whiteness and blue eyes with deafness, or between
the tortoise-shell color and the female sex; or in
pigeons, between their feathered feet and skin betwixt the
outer toes, or between the presence of more or less down on
the young pigeon when first hatched, with the future color
of its plumage; or again, the relation between the hair and
the teeth in the naked Turkish dog, though here no doubt
homology 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, etc.), are likewise on the
whole the most abnormal in their teeth, but there are so
many exceptions to this rule, as Mr. Mivart has remarked,
that it has little value.

I know of no case better adapted to show the importance
of the laws of correlation and variation, independently of
utility, and therefore of natural selection, than that of the
difference between the outer and inner flowers in some
compositous and umbelliferous plants. Everyone 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 sculpture. These differences
have sometimes been attributed to the pressure of the in-
volucra on the florets, or to their mutual pressure, and the
shape of the seeds in the ray florets of some composite

138 CORRELATED VARIATION.

lC3 l,> \

countenances this idea; but with the umbellifera3 it u
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 composita?
the seeds of the outer and inner florets difl'er, without any
difference in the corolla. Possibly these several differ-
ences may be connected with the different flow of nutri-
ment toward the central and external flowers. We know,
at least, that with irregular flowers those nearest to the
axis are most subject to peloria, that is to become abnormally
symmetrical. I may add, as an instance of this fact, and
as a striking case of correlation, that in many pelargoniums
the two upx)er petals in the central flower of the truss often
lose their patches of darker color; and when this occurb,
the adherent nectary is quite aborted, the central flower
thus becoming peloric or regular. When the color 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, Spren-
geFs idea that the ray-florets serve to attract insects, whose
agency is highly advantageous, or necessary for the fertili-
zation of tliese plants, is highly probable; and if so, nat-
ural selection may have come into play. But with respect
to the seeds, it seems impossible that their differences in
shape, which are not always correlated with any difference
in the corolla, can be in any way beneficial; yet in the um-
belliferge these differences are of such apparent importance
— the seeds being sometimes orthospermous in the exterior
flowers and co^lospermous in the central flowers — that the
elder De Candolle founded his main divisions in the order
on such characters. Hence modifications of structure,
viewed by systematists as of high value, may be wholly
due to the laws of variation and correlation, without
being, as far as we can judge, of the slightest service to the
species.

We may often falsely attribute to correlated variation
structures which are common to whole groups of species,
and which in truth are simply due to inhericance; for an
ancient progenitor may have acquired through natural

COMPENSATION AND ECONOMY OF GROWTH. 139

selection some one modification in structure, and, after
thousands of generations, some other and independent
modification; and these two modifications, huvin^^ been
transmitted to a whole group of descendants witli diverse
habits, would naturally be thought to be in some necessary
manner correlated. Some other correlations are apparently
due to the manner in which natural selection can alone
act. For instance, Alph. de Candolle has remarked that
winged seeds are never found in fruits which do not open;
I should explain this rule by the impossibihty 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.

COMPE]^SATIOK AJ^D ECONOMY OF GROWTH.

The elder Geoff roy 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 economize on the other side.'"
I think this holds true to a certain extent with our domes-
tic 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 gen-
erally accompanied by a diminished comb, and a large
beard by diminished wattles. With species in a state of
nature it can hardlv be maintained that the law is of uni-
versal application; but many good observers, more espe-
cially botanists, believe in its truth. I will not, however,
here give any instances, for I see hardly any way of distin-
guishing between the effects, on the one hand, of a part
being largely developed through natural selection and
another and adjoining part being reduced by the same pro-
cess or by disuse, and, on the other hand, the actual with-
drawal of nutriment from one part owing tc the excess of
growth in another and adjoining part.

1 40 MUL TIP LB AND R UBIMENTAR T

I suspect, also, that some of the cases of compensation
which have been advanced, and likewise some other facts,
may be merged under a more general principle, namely,
that natural selection is continually trying to econo-
mize every part of the organization. If under changed
conditions of life a structure, before useful, becomes less
useful, its diminution will be favored, for it will profit the
individual not to have its nutriment wasted in building up
a useless structure. I can thus only understand a fact with
which I was much struck when examining cirripedes, and
of which many analogous instances could be given: namely,
that when a cirripede is parasitic within another cirripede
and is thus protected, it loses more or less completely its
own shell or carapace. This is the case with the male
Ibla, and in a truly extraordinary manner with the 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 Proteole-
pas, the whole anterior part of the head is reduced to the
merest rudiment attached to the bases of the prehensile
antennae. Now the saving of a large and complex struc-
ture, when rendered superfluous, would be a decided ad-
vantage to each successive individual of the species; for in
the struggle for life to which every animal is exposed, each
would have a better chance of 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 organization, as soon as it
becomes, through changed habits, superfluous, without by
any means causing some other part to be largely devel-
oped in a corresponding degree. And conversely, that
natural selection may perfectly well succeed in largely de-
veloping an organ without requiring as a necessary com-
pensation the reduction of some adjoining part.

MULTIPLE, EUDIMEN^TARY, AND LOVTLY-ORGAKIZED STEUC-

TURES ARE VARIABLE.

It seems to be a rule, as remarked by Is. Geoffrey St.
Hilaire, both with varieties and species, that when any part
or organ is repeated many times in the same individual (as

8TRUCTURE8 VARIABLE. 141

the vertebrae in snakes, and the stamens in pol3'androu8
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 re-
marked that multiple parts are extremely liable to vary
in structure. As ''vegetable repetition/' to use Professor
Owen's expression, is a sign of low organization, the fore-
going statements accord with the common opinion of natu-
ralists, 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
organization have been but little specialized for particular
functions; and as long as the same part has to perform
diversified work, we can perhaps see why it should remain
variable, that is, why natural selection should not have
preserved or rejected each little deviation of form so care-
fully 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; while a tool
for some particular purpose must be of some particular
shape. Natural selection, it should never be forgotten,
can act solely through and for the advantage of each being.
Rudimentary parts, as is generally admitted, are apt to
be highly variable. We shall have to recur to this subject;
and I will here only add that their variability seems to re-
sult from their uselessness, and consequently from natural
selection having had no power to check deviations in their
structure.

A PART DEVELOPED 11^ ANY SPECIES IN AN EXTRAORDI-
NARY 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 bo
here introduced. I can only state my conviction that it is
a rule of high generality. I am aware of several causes of

143 UNUSVALLY DEVELOPED PARTS

error, but I hope that I have made due allowances fot
them. It should be understood that the rule by no means
applies to any part, hov/ever unusually developed, unless
it be unusually developed in one species or in a lew species
in comparison with the same part in many closely allied
species. Thus, the wing of the bat is a most abnormal
structure in the class of mammals, but the rule would not
apply here, because the whole group of bats possesses
wings; it would apply only if some one species had wings
developed in a remarkable 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 manner. The term, secondary
sexual characters, used by Hunter, relates to characters
which are attached to one sex, but are not directly con-
nected with the act of reproduction. The rule applies to
males and females; but more rarely to the females, as they
seldom offer remarkable secondary sexual characters. The
rule being 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 char-
acters is clearly shown in the case of hermaphrodite cirri-
pedes; I particularly attended to Mr. Waterhouse^s remark,
while 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 hero give only one, as it illustrates the rule in its
largest application. Tiie opercular valves of sessile cirri-
pedes (rock barnacles) are, in every sense of the word, very
important structures, and they differ extremely little even
in distinct genera; but in the several species of one genus,
Pyrgoma, these valves present a marvellous amount of
diversification; the 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, in-

EIGHLT VARIABLE. I4.5

lial3iting the same country, vary extremely little, I h:iv©
particularly attended to them; and the rule certainly seems
to hold good in this class. I cannot make out that it
appHes to plants, and this would have seriously sliaken mr
belief in its truth, had not the great variability in plants
made it particularly difficult to compare their relative de-
grees of variability.

When we see any part or organ developed in a remark-
able degree or manner in a species, the fair presumption ia
that it is of high importance to that species: nevertheless
it is in this case eminently liable to variation. AVhy
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 tlie view that
groups of species are descended from some other species,
and have been modified through natural splection, I think
we can obtain some light. First let me make some pre-
liminary remarks. If, in our domestic animals, any part
or the whole animal be neglected, and no selection be ap-
plied, that part (for instance, the comb in the Dorking
fowl) or the whole breed will cease to have a uniform
character: and the breed may be said to be degeneraung.
In rudimentary organs, and in those which have been but
little specialized 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 organization 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, etc., these being the
points now mainly attended to by Englisli 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 going on between, on tho
one hand, the tendency to reversion to a less perfect state,
as well as an innate tendency to new variations, and, on

144 UNUSUALLY DEVELOPED PARTS

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 ra^oidly
going on, much variability in the parts undergoing modi-
fication may always be expected.

Now let us turn to nature. When a part has been
developed in an extraordinary manner in any one species,
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 common progenitor of the
genus. This period will seldom be remote in any extreme
degree, as species rarely endure for more than one geolog-
ical period. An extraordinary amount of modification
implies an unusually 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 organization which have remained for
a much longer period nearly constant. And this, I am
convinced, is the case. That the struggle between nat-
ural selection on the one hand, and the tendency to rever-
sion 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 tlie 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 con-
tiuued selection of the individuals varying in the required

HIGHLY VARIABLE. I45

manner and degree, and by the continued rejection of tlioHe
tending to revert to a former and less modified condition.

SPECIFIC CHARACTERS MORE VARIABLE THAN GEXERIC

CHARACTERS.

The principle discussed under the last heading may be
applied to our present subject. It is notorious that spe-
cific characters are more variable than generic. 'Vo ex-
plain by a simple example what is meant: if in a large
genus of plants some species had blue flowers and some
had red, the color would be only a specific character, and
no one would be surprised at one of the blue species vary-
ing into red, or conversely; but if all the species had blue
flowers, the color would become a generic character, and
its variation would be a more unusual circumstance. I
have chosen this example because the explanation which
most naturalists would advance is not here applicable,
namely, that specific characters are more variable than gen-
eric, because they are taken from parts of less physiological
importance than those commonly used for classing genera.
I believe this explanation is partly, yet only indirectly,
true; I shall, however, have to return to this point in the
chapter on Classification. It would be almost superfluous
to adduce evidence in support of the statement, that ordi-
nary 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 im.portant organ or part,
which is generally very constant throughout a large group
of species, differs considerably in closely allied species, it is
often variable in the individuals of the same species. And
this fact shows that a character, which is generally of gen-
eric value, when it sinks in value and becomes only of spe-
cific value, often becomes variable, though its i)hysiol()gical
importance may remain the same. Something of the same
kind applies to monstrosities: at least Is. Gcoft'roy 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 individ-
uals.

On the ordinary view of each species having been inde-

148 SECONDARY SEXUAL CHARACTERS YARIABLK

pendently created, why should that part of the struc-
ture, which differs from the same part in other
independently created species of the same genus, be more
variable than those parts which are closely alike in the
several species? I do not see that any explanation can be
given. But on the view that species are only strongly
marked and fixed varieties, we might expect often to find
them still continuing to vary in those parts of their struc-
ture 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 char-
acters may be attributed to inheritance from a common
progenitor, for it can rarely have happened that natural selec-
tion will have modified several distinct species, fitted to
more or less widely different habits, in exactly the same
manner: and as those so-called generic characters have been
inherited from before the period when the several species
first branched off from their common progenitor, and sub-
sequently have not varied or come to differ in any degree,
or only in a slight degi'ee, 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 stili often be in
some degree variable — at least more variable than those
parts of the organization which have for a very long period
remained constant.

SECOHDART SEXUAL CHARACTERS VARIABLE.

I think it will be admitted by naturalists, without my
entering on details, that secondary sexual characters are
highly variable. It will also be admitted that species of
the same group differ from each other more widely in their
secondary sexual characters, than in other parts of their
organization: compare, for instance, the amount of differ-
ence between the males of gallinaceous birds, in which
secondary sexual characters are strongly displayed, with

SECONDARY SEXUAL CHARACTERS VARIABLE. 147

the tamount of difference between the fetnales. Tlie c;ins«^
of the original variability of these cliaracters is not mani-
fest; but we can see why they should not liave been ren-
dered as coQstant and uniform as otliers, for tliev are ac-
cumulated by sexual selection, which is less rigid in ita
action than ordinary selection, as it does not entail death,
but only gives fewer offspring to the less favored males.
Whatever the cause may be of the variability of secondary
sexual characters, as they are highly variable, sexual selec-
tion 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 organization in
which the species of the same genus differ from each other.
Of this fact I will give in illustration the two first in-
stances which happen to stand on my list; and as the dif-
ferences in these cases are of a very unusual nature, the
relation can hardly be accidental. The same number of
joints in the tarsi is a character common to very
large groups of beetles, but in the Engid^e, as West-
wood has remarked, the number varies greatly and the
number likewise differs in the two sexes of the same
species. Again in the fossorial hymenoptera, the neu ra-
tion of the wings is a character of the highest importance,
because common to large groups; but in certain genera the
neuration dift'ers in the different species, and likewise in
the two sexes of the same species. Sir J. Lubbock has
recently remarked, that several mi ante crustaceans offer
excellent illustrations of this law. *' In Pontella, for
instance, the sexual characters are afforded mainly by the
anterior antenna3 and by the fifth pair of legs: the specific
differences also are principally given by these organs."
This relation has a clear meaning on my view: I look at all
the species of the same genus as having as certainly
descended from a common progenitor, as have the two sexes
of any one 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 aud

148 DISTINCT SPECIES PRESENT

sexual selection, in order to fit the 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 pos-
sessed by all the species; that the frequent extreme varia-
bility of any part which is developed in a species in an
extraordinary manner in comparison vv^ith 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; that the great varia-
bility of secondary sexual characters and their great differ-
ence in closely allied species; that secondary sexual and
ordinary specific differences are generally displayed in the
same parts of the organization, 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 having more or less completely, according to the
lapse of time, overmastered the tendency to reversion and
to further variability, to sexual selection being less rigid
than ordinary selection, and to 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.

DISTI2q"CT SPECIES PRESENT AN"ALOGOUS VARIATIONS, SO
THAT A VARIETY OF ONE SPECIES OFTEN ASSUMES A
CHARACTER PROPER TO AN ALLIED SPECIES, OR RE-
VERTS 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-varie-
ties with reversed feathers on the head, and with feathers

ANALOGOUS VARIATIONS, I49

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
several races of the pigeon having inherited from a common
parent the same constitution and tendency to variation,
when acted on by similar unknown influences. In the
vegetable 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 bot-
anists 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 maybe added, namely, the common turnip.
According to the ordinary 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 conse-
quent tendency to vary in a like manner, but to three
separate yet closely related acts of creation. Many similar
cases of analogous variation have been observed by Naudin
in the great gourd family, and by various authors in our
cereals. Similar cases occurring wath insects under nat-
ural conditions have lately been discussed with much abil-
ity by Mr. Walsh, w^ho has grouped them under his law of
equal3le variability.

With pigeons, however, we have another case, namely,
the occasional appearance in all the breeds, of slaty-bhie
birds with two black bars on the wings, white loins, a bar
at the end of the tail, with the outer feathers externally
edsred near their basis with white. As all these marks are
characteristic of the parent rock-pigeon, I presume tiiat no
one will doubt that this is a case of reversion, and not of a
new yet analogous variation appearing in the several
breeds. We may, I think, confidently come to this con-
clusion, because, as we have seen, these colored marks are
eminently liable to appear in tlic crossed oilspring of two
distinct and differently colored breeds; and in this case
there is nothing in the external conditions of life to cause

150 DISTINCT SPECIES PRESENT

the reappearance of the slaty-bhie, with the several marks,
beyond the influence of the mere act of crossing on the
laws of inheritance.

No doubt it is a very surprising fact that characters
should reappear after having been lost for many, probably
for hundreds of generations. But when a breed has been
crossed only once by some other breed, the offspring occa-
sionally 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 pro-
portion of blood, to use a common expression, from one
ancestoi", is only one in 2048; and yet, as we see, it is gen-
erally 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 hoth 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 hundred genera-
tions, but that in each successive generation the character
iu question has been lying latent, and at last, under
unknown favorable conditions, is developed. With the
barb-i:)igeon, for instance, which very rarely produces a
blue bird, it is probable that there is a latent tendency in
each generation to produce blue plumage. The abstract
improbability of such a tendency being transmitted through
a vast number of generations, is not greater than that of
quite useless or rudimentary organs being similarly trans-
mitted. A mere tendency to produce a rudiment is indeed
•sometimes thus inherited.

As all the species of the same genus are supposed to be
descended from a common progenitor, it might be expected
that they would occasionally vary in an analogous manner;
so that the varieties of two or more species would resemble
each other, or that a variety of one species would resemble
in certain characters another and distinct species, this
other species being, according to our view, only a well-
marked and permanent variety. But characters exclusively

ANALOGOUS VARIATIONS. 15)

due to analogous variation \TOuId probably be of an unim
portant nature, for the preservation of all fiuictionallv im-
portant characters will have been determined through
natural selection, in accordance with the different hiibits
of the species. It might further be expected thut the
species of the same genus would occasionally exhibit rever-
sions 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 tlie
parent rock-pigeon was not feather-footed or turn-crowned,
we could not have told, whether such characters in our
domestic breeds were reversions or only analogous varia-
tions; but we might have inferred that the blue color was
a case of reversion from the number of the markings,
which are correlated with this tint, and whicli would not
probaby have all appeared together from simple variation.
More especially we might have inferred this from the blue
color and the several marks so often appearing wlien dif-
ferently colored 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 assum-
ing 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 forma,
which themselves can only doubtfully be ranked as species;
and this shows, unless all these closely allied forms be con-
sidered as independently created species, that they have in
varing 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
collected a long list of such cases; but here, as before, I lie
under the great disadvantage of not being able to give
them. I can only repeat that such cases certainly occur,
and seem to me very remarkable.

152 DISTINCT SPECIES PRESENT

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 tranverse bars on its legs, like those on
the legs of the zebra. It has been asserted that these are
plainest in the foal, and, from inquiries which I have
made, I believe this to be true. The stripe on the shoulder is
sometimes double, and is very variable in length and outline.
A white ass, but not an albino, has been described without
either spinal or shoulder stripe; and these stripes are some-
times very obscure, or actually quite lost, in dark-colored
asses. The koulan of Pallas is said to have been seen with a
double shoulder-stripe. Mr. Blyth has seen a specimen
of the hemionus with a distinct shoulder-stripe, though
it properly has none; and I have been informed by Colonel
Poole that the foals of this species are generally striped on the
legs and faintly on the shoulder. The quagga, though so
plainly barred like a zebra over the body, is without bars
on the legs; but Dr. Gray has figured one specimen with
very distinct zebra-like bars on the hocks.

With respect to the horse, I have collected cases in
England of the spinal stripe in horses of the most distinct
breeds and of all colors; transverse bars on the legs are not
rare in duns, mouse duns, and in one instance in a chest-
nut; a faint shoulder-stripe may sometimes be seen in
duns, and I have seen a trace in a bay horse. My son
made a careful examination and sketch for me of a dun
Belgian cart-horse with a double stripe on each shoulder
and with leg- stripes. I have myself seen a dun Devon-
shire pony, and a small dun Welsh pony has been carefully
described to me, both with three parallel stripes on each
shoulder.

In the northwest part of India the Kattywar breed of
horses is so generally striped, that, as I hear from Colonel
Poole, w^ho examined this iDreed for the Indian Govern-
ment, a horse without stripes is not considered as purely
bred. The spine is always striped, the legs are generally
barred, and the shoulder-stripe, which is sometimes double
and sometimes treble, is common; the side of the face,
moreover, is sometimes striped. The stripes are often

ANALOGOUS VARIATIONS. 153

plainest in the foal, and sometimes quite disappear in old
horses. Colonel Poole has seen both gray and bay Katty-
war horses striped when first foaled. I have also reason to
suspect, from information given me by Mr. W. \\ . Ed-
wards, that with the English race-horse the spinal stripe is
much commoner in the foal than in the full-grown animal.
I have myself recently bred a foal from a bay mare (off-
spring 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 com-
pletely. 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 color is included,
from one between brown and black to a close approach to
cream color.

I am aware that Colonel Hamilton Smith, who has writ-
ten on this subject, believes that the several breeds of the
horse are descended from several aboriginal species, one of
which, the dun, was striped; and that the above-described
appearances are all due to ancient crosses with the dun
stock. But this view may be safely rejected, for it is
higlily improbable that the heavy Belgian cart-horse,
Welsh ponies, Norwegian cobs, the lanky Kattywar race,
etc., inhabiting the most distant 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. Eollin 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 excellent
treatise on the horse, has given a figure of a similar mule.
In four colored drawings, which I have seen, of liybridu

154 DISTINCT SPECIES PRESENT

between the ass and zebra, the legs were much more plainly
barred than the rest of the body; and in one of them there
was a double shoulder-stripe. In Lord Morton's famous
hybrid, from a chestnut mare and male quagga, the hybrid
and even the pure offspring subsequently produced from
the same mare by a black Arabian Bire, 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 tliat he
knows of a second case) from the ass and the hemionus;
and this hybrid, though the ass only occasionally has stripes
on his legs and the hemionus has none and has not even a
shoulder-stripe, nevertheless had all four legs barred, and
had three short shoulder-stripes, like those on the dun
Devonshire and AVelsh ponies, and even had some zebra-
like stripes on the sides of its face. With respect to this
last fact, I was so convinced that not even a stripe of color
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
Been, 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 coloring 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 niost
strongly displayed in hybrids from between several of the
most distinct species. Now observe the case of the several
breeds of pigeons: they are descended from a pigeon (in-
cluding two or three sub-species or geographical races) of
a bluish color, 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 with-
out any other change of form or character. When the
oldest and truest breed of various colors are crossed, we see
a strong tendency for the blue tint and bars and marks

ANALOGOUS VARIATIONS, I55

to reappear in the nK)ngrels. I have stated tliat the
most probable hypothesis to account for the reappear-
ance of very ancient characters, is — that there is a
tendency in the young of each successive generation
to produce the long-lost character, and that this ten-
dency, from unknown causes, sometimes prevails. And
we have just seen that in several species of the horse
genus the stripes are either plainer or appear more com-
monly 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 con-
fidently to look back thousands on thousands of genera-
tions, and I see an animal striped like a zebra, but perhaps
otherwise very differently constructed, the common 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 independ-
ently created, will, I presume, assert that each species has
been created with a tendency to vary, both under nature
and under domestication, in this particular manner, so as
often to become striped like the other species of the genus;
and that each has been created with a strong tendency,
when crossed with species inhabiting distant quarters of
the world, to produce hybrids resembling in their stripes,
not their own parents, but other species of the genus. To
admit this view is, as it seems to me, to reject a real for an
unreal, or at least for an unknown cause. It makes the
works of God a mere mockery and deception; I would
almost as soon believe with the old and ignorant cosmo-
gonists, that fossil shells had never lived, but had been
created in stone so as to mock the shells living on the sea-
shore.

SUMMARY.

Our ignorance of the laws of variation is profound.
Not in one case out of a hundred can we pretend to assign
any reason why this or that part has varied. But when-
ever we have the means of instituting a comparison, the
same laws appear to have acted in producing the lesser dif-

/

156 SUMMARY.

ferences between varieties of the same species, and the
greater diffences between species of the same genus. Changed
conditions generally induce mere fluctuating variability,
but sometimes they cause direct and definite effects; and
these may become strongly marked in the course of time,
though we have not sufficient evidence on this head.
Habit in producing 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 man-
ner, and homologous parts tend to cohere. Modifications
in hard parts and in external parts sometimes affect softer
and internal parts. AVhen one part is largely developed, per-
haps it tends to draw nourishment from the adjoining 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, undoubtedly occur. Mutiple parts
are variable in number and in structure, perhaps arising
from such parts not having been closely specialized 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 organization more specialized.
Rudimentary organs, from bfjing useless, are not regulated by
natural selection, and hence ^u'e 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 variable than generic char-
acters, 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 vari-
able, 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
among these species, we now find, on an average, most

SUMMARY. 157

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 organization
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 species of the same genus.
Any part or organ developed to an extraordinary sizu or in
an extraordinary manner, in comparison with the same
part or organ in the allied species, must have gone tlirough
an extraordinary amount of modilication since the geims
arose; and thus we can understand why it slioukl often
still be variable in a much higher degree than other parts;
for variation is a long-continued and slow process, and
natural selection will in such cases not as yet have had
time to overcome the tendency to further variability and
to reversion to a less modified state. But when a species
with an extraordinarily developed organ has become the
parent of many modified descendants — wliich on our view
must be a very slow process^ requiring a long lapse of time
— in this case, natural selection has succeeded in giving a
fixed character to the organ, in however extraordinary a
manner it may have been developed. Species inheriting
nearly the same constitution from a 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 progeni-
tors. Although new^ and important modifications may not
arise from reversion and analogous variation, such modi-
fications will add to the beautiful and harmonious diver-
sity of nature.

Whatever the cause may be of each slight difference be-
tween 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 difi'crences which has
given rise to all the more important modifications of struc-
ture in relation to the habits of each species.

158 DIFFICULTIES OF THE TIiEOBT.

CHAPTEE 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 Natural
Selection.

Long before the reader has arrived at this part of my
work, a crowd of difficulties will have occurred to him.
Some of them are so serious that to this day I can hardly
reflect on them without being in some degree 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 ejections may be classed under the
following heads: First, why, if species have descended from
other species by fine gradations, do we not everywhere see
innumerable transitional forms? Why is not all nature in
confusion, instead of the species being, as we see them,
well defined?

Secondly, is it possible that an animal having, for
instance, the structure and habits of a bat, could have been
formed by the modification of some other animal with
widely different habits and structure? Can we believe that
natural selection could produce, on the one hand, an organ
of trifling 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? AVhat shall we say to the instinct which

DIFFICULTIES OF THE THEORY. 159

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, wherejvs,
when varieties are crossed, their fertility is uniin})aired?

The two first heads will here be discussed; some miscel-
laneous objections in the following chapter; Instinct and
Hybridism in the two succeeding chapters.

ON THE ABSENCE OR RARITY OF TRANSITIONAL VARIETIES.

As natural selection acts solely by the preservation of
profitable modifications, each new form will tend in a
fully-stocked country to take the place of, and finally to
exterminate, its own less improved parent-form and other
less-favored forms with which it comes into competition.
Thus extinction and natural selection go hand in hand.
Hence, if we look at each species as descended from some
unknown form, both the parent and all the transitional
"varieties will generally have been exterminated by the
very process of the formation and perfection of the new
form.

But, as by this theory innumerable transitional forms
must have existed, why do we not find them imbedded
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;
and I will here onlv state that I believe the anr^wer mainly
lies in the record being incomparably less perfect than is
generally supposed. The crust of the earth is a vast
museum; but the natural collections have been imperfectly
made, and only at long intervals of time.

But it may be urged that when several closely allied
species inhabit the same tenitory, we surely ougiit to find
at the present time many transitional forms. Let us take
a simple case: in traveling from north to south over a con-
tinent, we generally meet at successive intervals with
closely allied or representative species, evidently filling
nearly the same place in the natural economy of the land.
These 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

160 ABSENCE OR RARITY

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 metrop-
olis 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 transi-
tional 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 imbedded there in a
fossil condition. But in the intermediate region, having
intermediate conditions of life, why do we not now find
closely linking intermediate varieties? This difficulty for
a long time quite confounded me. But I think it can be
in large part explained.

In the first place we should be extremely cautious in in-
ferring, because an area is now continuous, that it has been
continuous during a long period. Geology would lead us
to believe that most continents have been broken up into
islands even during the later tertiary periods; and in such
islands distinct species might liave been separately formed
without the possibility of intermediate 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 continu-
ous 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
formerlv broken condition of areas now continuous, has
played an important part in the formation of new species,
more especially with freely-crossing and wandering
animals.

In looking at species as they are now distributed over a
wide area, we generally find them tolerably numerous over
a large territory, then becoming somewhat abruptly rarer
and rarer on the confines, and finally disappearing. Hence
the neutral territory between two representative species is
generally narrow in comparison with the territory proper
to each. We see the same fact in ascending mountains.

OF TRANSITIONAL VARIETIES. \{',\

and sometimes it is quite remarkable how abruptly, a-
Alph. de CandoUe has observed, a common alpine species
disappears. The same fact has been noticed by E. Forbes
in sounding the depths of the st;a \vitii the dredge.
To those who look at climate and the physical conditions
of life as the all-important elements of distribution, these
facts ought to cause surprise, as climate and height or depth
graduate away insensibly. But when we bear iii mind that
almost every species, even in its metropolis, would increase
immensely in numbers, were it not for other competing
species; that nearly all either prey on or serve as prey for
others; in short, that each organic being is either directly
or indirectly related in the most important manner to
other organic beings — we see that the range of the inhab-
itants 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 com-
petition; and as these species are already dehned objects,
not blending one into another by insensible gradations, the
range of any one species, depending as it does on the range
of others, will tend to be sharj^ly defined. Moreover, each
species on the confines of its range, where it exists in les-
sened numbers, will, during 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
geographical range will come to be still more sharply
defined.

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 comparatively narrow
neutral territory between them, in which they become
rather suddenly rarer and rarer; then, as varieties do not es-
sentially differ from species, the same rule will probably
apply to both; and if we take a varying species inhabiting a
very large area, we shall have to adai)t two varieties to two
large areas, and a third variety to a narrow intermediate zone.
The intermediate variety, consequently, will exist in lesser
numbers from inhabiting a narrow and lesser area; and
practically, as far as I can make out, this rule holds good
with varieties in a state of nature. I have met with strik-
ing instances of the rule in the case of varieties intermediate

16!8 ABSENCE OR RARITY

between well-marked varieties in the genus Balanus. And
it would appear from information given me by Mr. Watson,
Dr. Asa Gray and Mr. Wollaston, that generally, when
varieties intermediate between two other forms occur, they
are much rarer numerically than the forms which they con-
nect. Now, if we may trust these facts and inferences,
and conclude that varieties linking two other varieties to-
gether generally have existed in lesser numbers than the
forms which they connect, then we can understand why
intermediate varieties should not endure for very long
periods: why, as a general rule, they should be exter-
minated and disappear, sooner than the forms which they
originally linked together.

For any form existing in lesser numbers would, as already
remarked, run a greater chance of being exterminated
than one existing in large numbers; and in this particular
case the intermediate form would be eminently liable
to the inroads of closely allied forms existing on both
sides of it. But it is a far more important considera-
tion, that during the process of further modification,
by which two varieties are supposed to be converted
and perfected into two distinct species, the two which
exist in larger numbers, from inhabiting larger areas,
will have a great advantage over the intermediate
variety, which exists in smaller numbers in a narrow and
intermediate zone. For forms existing in larger numbers
will have a better chance, within any given period, of pre-
senting further favorable variations for natural selection to
seize on, than will the rarer forms which exist in lesser
numbers. Hence, the more common forms, in the race for
life, will tend to beat and supplant the less common forms,
for these will be more slowly modified and improved. It
is the same principle which, as I believe, accounts for the
common species in each country, as shown in the second
chapter, presenting on an average a greater number of well-
marked varieties than do the rarer species. I may 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 inhabi-
tants are all trying with equal steadiness and skill to im-
prove their stocks by selection; the chances in this case

OF TRANSITIONAL VARIETIES. lotj

will be strongly in favor of the great liolderson the mount-
ains or on the plains, improving their breeds nioro
quickly than the small holders on the intermediate narrow,
hilly tract; and consequently the improved moimiain or
plain breed will soon take the place of the less improved
hill breed; and thus the two breeds, which originallv ex-
isted in greater numbers, will come into close contact' with
each other, without the interposition of the supplanted, in-
termediate hill variety.

To sum up, I believe that species come to be tolerably
well-defined objects, and do not at any one period present
an inextricable chaos of varying and intermediate links:
first, because new varieties are veiy slowly formed, for vari-
ation is a slow process, and natural selection can do noth-
ing nntil favorable individual differences or variations
occur, and until a place in the natural polity of the coun-
try can be better filled by some modification of some one
or more of its inhabitants. And such new places will de-
pend on slow changes of climate, or on the occasional im-
migration of new inhabitants, and, probably, in a still more
important degree, on some of the old inhabitants becoming
slowly modified, with the new forms thus produced and
the old ones acting and reacting on each other. So that,
in any one region and at any one time, we ought to see
only a few species presenting slight 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 wliich
many forms, more especially among the classes which
unite for each birth and wander much, may have sepa-
rately been rendered sufficiently distinct to rank as repi-e-
sentative species. In this case, intermediate varieties be-
tween 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 extern) in-
ated, so that they will no longer be found in a living state.

Thirdly, when two or more vai-ieties have been formed
in different portions of a strictly continuous area, interme-
diate varieties will, it is probable, at first bave been formed
in the intermediate zones, but they will generally have liad

1 64 TRANSITIONS OF ORGANIC BEINGS.

a short duration. For these intermediate varieties will,
from reasons already assigned (namely from what
we know of the actual distribution of closely allied
or representative species, and likewise of acknowl-
edged varieties), exist in the intermediate zones in lesser
numbers than the varieties which they tend to connect.
From this cause alone the intermediate varieties will be
liable to accidental extermination; and during the process
of further modification through natural selection, they
will almost certainly be beaten and supplanted by the
forms which they connect; for these, from existing in
greater numbers, will, in the aggregate, present more
varieties, and thus be further improved through natural
selection and gain further advantages.

Lastly, looking not to any one time, but at all time, if
my theory be true, numberless intermediate varieties, link-
ing closely together all the species of the same group, must
assuredly have existed; but the very process 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 among fossil remains, which are preserved, as we
shall attempt to show in a future chapter, in an extremely
imperfect and intermittent record.

01^ THE OKIGIN" AND TKANSITION OF ORGAN"IO BEIi^GS
WITH PECULIAE HABITS AKD 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 sub-
sisted? It would be easy to show that there now exist
carnivorous animals presenting close intermediate grades
from strictly terrestrial to aquatic habits; and as each
exists by a struggle for life, it is clear that each must be
well adapted to its place in nature. Look at the Mustela
vision 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

TRANSITIONS OF ORQANK' D EING3. 1 1 ;;,

land animals. If a different case hiwl been taken, and it
had been asked how an insectivorous quadruped could pos-
sibly have been converted into a flying bat, tlie question
would have been far more difficult to answer. Yet I think
such difficulties luive little weight.

Here, as on other occasions, 1 he under a heavy disad-
vantage, for, out of the many striking cases wliich I liave
collected, I can give only one or two instances of transitional
habits and structures in allied species; and of diversified
habits, either constant or occasional, in the same species.
And it seems to me that nothing less than a long list of
such cases is sufficient to lessen the difficulty in any par-
ticular case like that of the bat.

Look at the family of squirrels; here we have the finest
gradation from animals with their tails only slightly flat-
tened, and from others, as Sir J. Richardson lias remarked,
with the posterior part of their bodies rather wide and with
the skin on their flanks rather full, to the so-called flying
squirrels; and flying squirrels have their limbs and even the
base of the tail united by a broad expanse of skin, which
serves as a parachute and allows them to glide through the
air to an astonishing distance from tree to tree. We can-
not doubt that each structure is of use to each kiiul of
squirrel in its own country, by enabling it to e^scape birds
or beasts of pre}^, to collect food more quickly, or,
as there is reason to believe, to lessen the danger from
occasional falls. But it does not follow from this fact that
the structure of each squirrel is the best that it is possible
to conceive under all possible conditions. Let the climate
and vegetation change, let other competing rodents or new
beasts of prey immigrate, or old ones become moditied, 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 become modified and improved
in structure in a correspondirg manner. Therefore, I can
see no difficulty, more especially under changing conditions
of life, in the continued preservation of individuals with
fuller and fuller flank-membranes, each modification being
useful, each being propagated, until, by the accumulated
effects of this process of natural selection, a perfect so-
called flying squirrel was produced.

How look at the Galeopithecus or so-called flying lemur,

10(5 TRANSITIONS OF ORGANIC BEINGS.

which was formerly ranked among bats, but is now believed
to belong to the Insectivora. An extremely wide flank-
membrane stretches from the corners of the jaw to the tail
and inckides the limbs with the elongated fingers. This
flank-membrane is furnished with an extensor muscle.
Although no graduated links of structure, fitted for
gliding through the air, now connect the Galeopi-
thecus with the other Insectivora, yet there is no dif^
ficiilty in supposing that such links formerly existed,
and that each was developed in the same manner
as with the less perfectly gUding 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 forearm of
the Galeopithecus might have been greatly lengthened 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-membrane extends
from the top of the shoulder to the tail and includes the
hind-legs, we perhaps see traces of an apparatus originally
fitted for gliding through the air rather than for flight.

If about a dozen genera of birds were to become extinct,
who would have ventured to surmise that birds might have
existed which used their wings solely as flappers, like the
logger headed duck (Micropterus of Eyton); as fins in the
water and as front-legs on the hand, 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 necessarially the best possible under all possible con-
ditions. It must not be inferred from these remarks that
any of the grades of wing-structure here alluded to, which
perhaps may all be the result of disuse, indicate the steps
by which birds actually acquired their perfect power of
flight; but they serve to show what diversified means of
transition are at least possible.

Seeing that a few members of such water-breathing
classes as the Crustacea and 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 reptilesj it is conceivable that flying-

TRANSITIONS OF ORGANIC BEINGS. 16?

fish, which now glide far through the air, slightly rising
and turning by the aid of their fluttering lins, might liave
been modified into perfectly winged animals. If this had
been effected, who would have ever imagined that in an
early transitional state they had been the inhabitants of
the open ocean, and had used their incipient organs of
flight exclusively, so far as we know, to escape being de-
voured by other fish?

When we see any structure highly perfected for any par-
ticular habit, as the wings of a bird for flight, we should
bear in mind that animals displaying early transitional
grades of the structure will selclom have survived to the
present day, for they will have been supplanted by their
successors, which were gradually rendered more perfect
through natural selection. Furthermore, we may con-
clude 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 sub-
ordinate forms. Thus, to return to our imaginary illus-
tration 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 perfec-
tion, 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 having
existed in lesser numbers, than in the case of species with
fully developed structures.

I will now give two or three instances, both of diversified
and of changed habits, in the individuals of the same
species. In either case it would be easy for natural selec-
tion 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 immaterial for us, whether
habits generally change first and structure afterward; or
whether slight modifications of structure lead to changed
habits; both probably often occurring almost simulUne-
ouslv. Of cases of changed habits it will suffice mei-eiy to
allude to that of the many British insects which now teed
on exotic plants, or exclusively on artificial hubbtancee.

168 TRANSITIONS OF ORGANIC BEINGS,

Of diversified habits innumerable instances could be given:
I have often watclied a tyrant flycatcher (Saurophagus sul-
phuratus) 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 nut-
hatch. 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 differ-
ent from those proper to their species and to the other
s.pecies of the same genus, we might expect that such in-
dividuals would occasionally give rise to new species,
having anomalous habits, and with their structure
either slightly or considerably modified from that of their
type. And such instances occur in nature. Can a more
striking instance of adaptation be given than that of
a woodpecker for climbing trees and seizing insects in the
chinks of the bark? Yet in North America there are
woodpeckers which feed largely on fruit, and others
with elongated wings which chase insects on the wing.
On the plains of La Plata, where hardly a tree grows,
there is a woodpecker (Colaptes campestris) which has two
toes before and two behind, a long-pointed tongue, pointed
tail-feathers, sufficiently stiff to support the bird in a verti-
cal position on a post, but not so stiff as in the typical wood-
peckers, 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 wood-
pecker. Even in such trifling characters as the coloring,
the harsh tone of the voice, and undulatory flight, its close
blood-relationship to our common woodpecker is plainly
declared; yet, as I can assert, not only from my own ob-
servations, but from those of the accurate Azara, in certain
large districts it does not climb trees, and it makes its
nest in holes in banks! In certain other districts, however,

TRANSITIONS OF OliGANIG BEINGS. IfiO

this same woodpecker, as Mr. Hudson states, frequents
trees, and bores boles in tbe trunk for its nest. 1 may
mention as anotber illustration of tbe varied babits of tbis
genus, tbat a Mexican Colaptes lias been described by De
Saussure as boring boles into bard wood in order to lay up a
store of acorns.

Petrels are tbe most aerial and oceanic of birds, but,
m tbe quiet sounds of Tierra del Fuego, tbe Puffinuria
berardi, in its general babits, in its astonisbing power of
diving, in its manner of swimming and of flying wben
made to take fligbt, would be mistaken by any one
for an auk or a grebe; nevertbeless it is essentially a
petrel, but witb many parts of its organization pro-
foundly modified in relation to its new babits of life;
fs^bereas tbe woodpecker of La Plata bas bad its structure
only sligbtly modified. In tbe case of tbe water-ouzel,
tbe acutest observer, by examining its dead body, would
never bave suspected its sub-aquatic babits; yet tbis bird,
wbicb is allied to tbe tbrusb family, subsists by diving —
using its wings under water, and grasping stones witb its
feet. All tbe members of tbe great order of Hymenopter-
ous insects are terrestrial, excepting tbe genus Procto-
trupes, wbicb Sir Jobn Lubbock bas discovered to be
acquatic in its babits; it often enters tbe water and dives
about by tbe use not of its legs but of its wings, and re-
mains as long as four bours beneatb tbe surface; yet it
exbibits no modification in structure in accordance witb
its abnormal babits.

He wbo believes tbat eacb being bas been created as we
now see it, must occasionally bave felt surprise wben be
has met witb an animal having babits and structure not in
asfreement. What can be plainer than that tbe webbed
feet of ducks and geese are formed for swimming? Yet
tbere are upland geese witb webbed feet wbicb rarely go
near tbe water; and no one, except Audubon, bas seen
tbe frigate-bird, wbicb bas all its four toes webbed, aligbt
on tbe surface of tbe ocean. On tbe otber band, grebes
and coots are eminently aquatic, although tbeir toes are
only bordered by membrane. Wliat seems plainer tban
tbat the long toes, not furnished witb membrane of tbo
Grallatores, are formed for walking over swamps and float-
ing plants? The water-hen and landrail are members of

170 ORGANS OF EXUiEME PEliFECTIOir.

this order, yet the first is nearly as aquatic, as the coot, and
the second is 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. The
webbed feet of the upland goose may be said to have be-
come almost rudiuientary in function, though not in struc-
ture. In the frigate-bird, the deeply scooped membrane
between the toes shows that structure has begun to change.
He who believes in separate and innumerable acts of
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 con-
stantly endeavoring to increase in numbers; and that if
any one being varies ever so little, either in habits or struc-
ture, and thus gains an advantage over some other inhab-
itant of the same country, it will seize on the place of that
inhabitant, however different that may be from its own
place. Hence it will cause him no surprise that there should
be geese and frigate-birds with webbed feet, living on the
dry land and rarely alighting on the water, that there
should be long-toed corncrakes, living in meadows instead
of in swamps; that there should be woodpeckers where
hardly a tree grows; that there should be diving thrushea
and diving Hymenoptera, and petrels with the habits of
auks.

ORGAl^S OF EXTREME PERFECTION" Ay^B COMPLICATIOIf.

To suppose that the eye wath all its inimitable contri-
vances for adjusting the focus to different distances, for
admitting different amounts of light, and for the correction
of spherical and chromatic aberration, could have been
formed by natural selection, seems, I freely confess,
absurd in the highest degree. When it was first said that
the sun stood still and the world turned round, the com-
mon sense of mankind declared the doctrine false; but the
old saying of Vox 2^opuli, vox Dei, as every philosopher
knows, can not be trusted in science. Reason tells me,
that if numerous gradations from a simple and imperfect

OHQANS of extreme perfection. 171

eye to one complex and perfect can be shown to exist, each
grade being useful to its possessor, as is certaitily the case;
if further, the eye ever varies and the variations be in-
herited, as is likewise certainly the case; and if such varia-
tions should be useful to any animal under changing con-
ditions of life, then the difficulty of believing that a per-
fect and complex eye could be formed by natural selection,
though insuperable by our imagination, should not be con-
sidered as subversive of the theorv. 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 low-
est 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 developed into nerves, endowed with this
special sensibility.

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

The simplest organ which can be called an eye consists
of an optic nerve, surrounded by pigment-cells and covered
by translucent skin, but without any lens or other refract-
ive 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 distinguish light from darkness. In
certain star-fishes, small depressions in the layer of pig-
ment which surrounds the nerve are filled, as described by
the author just quoted, with transparent gelatinous matter,
projecting with a convex surface, like tiie cornea in the
higher animals. He suggests that this serves not to form
an image, but only to concentrate the luminous rays and

172 ORGANS OF EXTREME PERFECTION.

render their perception more easy. In this concentration
of the rays we gain the first and hy far the most important
step toward 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 some-
times forming a sort of pupil, but destitute of lens or
other optical contrivance. With insects it is now known
that the numerous facets on the cornea of their great com-
pound eyes form true lenses, and that the cones include
curiously modified nervous filaments. But these organs in
the Articulata are so much diversified that Miiller formerly
made three main classes with seven subdivisions, besides a
fourth main class of aggregated simple eyes.

When we reflect on these facts, here given much too
briefly, with respect to the wide, diversified, and graduated
range of structure in the eyes of the lower animals; and
when we bear in mind how small the number of all living
forms must be in comparison with those which have
become extinct, the 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 membrane, into an optical
instrument as perfect as is possessed by any member of the
Articulata class.

He who will go thus far, ought not to hesitate to go
one step further, if he finds on finishing this volume
that large bodies of facts, otherwise inexplicable, can be
explained by the theory of modification through natural
selection; he ought to admit that a structure even as
perfect as an eagle's eye might thus be formed, although
in this case he does not know the transitional states. It
has been objected that in order to modify the eye
and still preserve it as a perfect instrument, many
changes would have to be effected simultaneously, which,
it is assumed, could not be done through natural
selection; but as I have attempted to show in my
work on the variation of ..domestic animals, it is not

ORGANS OF EXTREME PERFECTION. 173

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 general purpose: as Mr. Wallace has remarked, *' If
a len 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 curva-
ture will be an improvement. So the contraction of the
iris and the muscular movements of the eye are neither of
them essential to vision, but only improvements which
might have been added and perfected at any stage of the
construction of the instrument.''' Within the highest
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 apparatus. In fishes and reptiles, as Owen has re-
marked, " The range of gradation of dioptric structures
is very great.''' It is a significant fact that even in man,
according to the high authority of Virchow, the beautiful
crystalline lens is formed in the embryo by an accumula-
tion of epidermic cells, lying in a sack-like fold of the skin;
and the vitreous body is formed from embryonic sub-
cutaneous tissue. To arrive, however, at a just conclusion
regarding the formation of the eye, with all its marvellous
yet not absolutely perfect characters, it is indispensable
that the reason should conquer the imagination; but I
have felt the difficulty far too keenly to be surprised at
others hesitating to extend the principle of natural selec-
tion to so startling a length.

It is scarcely possible to avoid comparing the eye with
a telescope. We know that this instrument has been per-
fected by the long-continued efforts of the highest human
intellects; and we naturally infer that the eye has been
formed by a somewhat analogous process. But may not
this inference be presumptuous? Have we any right to
assume that the 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

174 MODES OF TRANSITION,

every part of this layer to be continually changing slowly
in density, so as to separate into layers of different densi-
ties and thicknesses, 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 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 pro-
duced, and then the old ones to be all destroyed. In
living bodies, variation will cause the slight alteration,
generation will multiply them almost infinitely, and natural
selection will pick out with unerring skill each improve-
ment. Let this process go on for millions of years; and
during each 5^ear on millions of individuals of many kinds;
and may we not believe that a living optical instrument
might thus be formed as superior to one of glass, as the
works of the Creator are to those of man?

MODES OF TKAKSITI03S".

If it could be demonstrated that any complex organ ex-
isted, which could not possibly have been formed by nu-
merous, 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, around which, according 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 grada-
tions of some kind. Numerous cases could be given

MO Dm OF TRANSITION. I75

among the lower animals of the same organ performing at
the same time wholly distinct functions; thus in the hirva
of the dragon-fly and in the fish Cobites the alimentary
canal respires, digests and excretes. In the Hydra, the
animal may be turned inside out, and the exterior surface
will then digest and the stomach respire. In such cases
natural selection might specialize, if any advantage were
thus gained, the whole or part of an organ, which had
previously performed two functions, for one function
alone, and thus by insensible steps greatly change its
nature, Many plants are known which regularly produce
at the same time differentlv constructed flowers: and if
such plants were to produce one kind alone, a great change
would be effected with comparative suddenness in the
character of the species. It is, however, probable that the
two sorts of flowers borne by the same plant were originally
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 branchiae that breathe the air dis-
solved in the water, at the same time that they breathe
free air in their swim-bladders, this latter organ being
divided by highly vascular partitions and having a ductus
pneumaticus for the supply of air. To give another in-
stance from the vegetable kingdom: plants climb by three
distinct means, by spirally twining, by clasping a support
with their sensitive tendrils, and by the emission of aerial
rootlets; these three means are usually found in distinct
groups, but some few species exhibit two of the means, or
even all three, combined in the same 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 oUiterated.

The illustration of the swim-bladder in tishes is a
good one, because it shows us clearly the highly
important fact that an organ originally constructed for
one purpose, namely, flotation, may be converted into

176 MODES OF TRAJSSITION,

one for a widely different purpose, namely, respiration.
The swim-bladder has, also, been worked in as an accessory
to the auditory organs of certain fishes. All physiologists
admit that the swim-bladder 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 swim-bladder has actually been converted
into lungs, or an organ used exclusively for respiration.

According to this view it may be inferred that all verte-
brate animals with true lungs are descended by ordinary
generation from an ancient and unknown prototype, which
was furnished with a floating apparatus or swim-bladder.
We can thus, as I infer from Owen's interesting descrip-
tion 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
intc the lungs, notwithstanding the beautiful contrivance
by which tho glottis is closed. In the higher Vertebrata
the branchi^ have wholly disappeared — but in the embryo
the slits on the sides of the neck and the loop-like course
of the arteries still mark their former position. But it is
conceivable that the now utterly lost branchiae might have
been gradually worked in by natural selection for some dis-
tinct purpose: for instance, Laudois has shown that tho
wings of insects are developed from the trachea; it is there-
fore highly probable that in this great class organs which
once served for respiration have been actually converted
into organs for flight.

In considering transitions of organs, it is so important to
bear in mind the probability of conversion from one func-
tion to another, that I will give another instance. Pedun-
culated cirripedes have two minute folds of skin, called by
me the ovigerous frena, which serve, through the means of
a sticky secretion, to retain the eggs until they are hatched
within the sack. These cirripedes have no branchiae, the
whole surface of the body and of the sack, together with
the small frena, serving for respiration. The Balanid^ or
sessile cirripedes, on the other hand, have no ovigerous
frena, the eggs lying loose at the bottom of the sack,
within the well-inclosed shell; but they have, in the same
relative position with the frena, large, much-folded mem-
branes, which freely communicate with the circulatory

MODES OF TRANSITION. I77

lacunae of the sack and body, and which have been consid-
ered by all naturalists to act as branchiae. Now 1 tliink no
one will dispute that the ovigerous frena in the one family
are strictly homologous with the branchiae of the other
family; indeed, they graduate into each other. Tlierefore
it need not be doubled that the two little folds of skin,
which originally served as ovigerous frena, but which, like-
wise, very slightly aided in the act of respiration, have
been gradually converted by natural selection into branchiae
simply through an increase in their size and the obliteratii^n
of their adhesive glands. If all pedunculated cirri pedes
had become extinct, and they have suffered far more extinc-
tion than have sessile cirripedes, who would ever have im-
agined that the branchiae in this latter family had origin-
ally existed as organs for preventing the ova from being
washed out of the sack?

There is anotlier possible mode of transition, namely,
through the acceleration or retardation of the period of re-
production. This has lately been insisted on by Professor
Cope and others in the United States. It is now known
that some animals are capable of reproduction at a very
early age, before they have acquired their perfect charac-
ters; and if this power became thoroughly well developed
in a species, it seems probable that the adult stage of devel-
opment would sooner or later be lost; and in this case,
especially if the larva differed much from the mature form,
the character of the species would be greatly changed and
degraded. Again, not a few animals, after arriving at
maturity, go on changing in character during nearly their
whole lives. With mammals, for instance, the form of the
skull is often much altered with age, of which Dr. Murie
has given some striking instances with seals. Every one
knows how the horns of stags become more aiul moi-e
branched, and the plumes of some birds become more finely
developed, as they grow older. Professor Cope states that
the teeth of certain lizards change much in shajie with ad-
vancing years. With crustaceans not only many trivial,
but some important parts assume a new character, as re-
corded by Fritz Miiller, 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

nS DIFFICULTIES OF TEE THBOUT

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 com-
paratively 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 be-
tween the mature and the old, were primordially acquired
by graduated steps.

SPECIAL DIFFICULTIES OF THE THEORY OF NATURAL

SELECTION.

Although we must be extremely cautious in concluding
that any organ could not have been produced by successive,
small, transitional gradations, yet undoubtedly serious
cases of difficulty occur.

One of the most series is that of neuter insects, which
are often differently constructed from either the males or
fertile females; but tliis 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 defense, and perhaps for secur-
ing prey; yet in the ra,y, as observed by Matteucci, an
analogous organ in the tail manifests but little electricity,
even when the animal is greatly irritated; so little that it
can hardly be of any use for the above purposes. More-
over, in the ray, besides the organ just referred to, there
is, as Dr. E. McDonnell 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 tor-
pedo. It is generally admitted that there exists between
these organs and ordinary muscle a close analogy, in inti-
mate 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 con-
traction is accompanied by an electrical discharge; and, as
Dr. Eadcliffe 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 muscle and

OF NATURAL SELECTION. 179

nerve diinng the rest, and the discharge of the torpedo,
instead of being peculiar, may be only another form of the
discharge which attends npon the action of muscle and
motor nerve." Beyond this we cannot at present go in tlie
way of explanation; but as we know so little about tlie uses
of these organs, and as we know notliing about the habits
and structure of the progenitors of the existing electric
fishes, it would be extremely bold to maintain that no
serviceable transitions are possible by which these organs
might have been gradually developed.

These organs appear at first to offer another and far
more serious difficulty; for they occur in about a dozen
kinds of fish, of which several are widely remote in their
affinities. When the same organ is found in several mem-
bers 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 ancient progenitor, we might have
expected that all electric fishes would have been specially
related to each other; but this is far from the case. Nor
does geology at all lead to the belief that most fishes for-
merly possessed electric organs, which their modified
descendants have now lost. But when we look at the sub-
ject 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 from dif-
ferent sources, and this is j^erhaps the most important of
all the differences. Hence in the several fishes furnished
with electric organs, these cannot be considered as hom-
ologous, but only as analogous in function. Consequently
there is no reason to suppose that they have been inherited
from a common progenitor; for had this been the case they
would have closely resembled each other in all respects.
Thus the difficulty of an organ, apparently the same, aris-
ing in several remotely allied species, disappears, leaving
only the lesser yet still great difficulty: namely, by what
graduated steps these organs have been developed in each
separate group of fishes.

180 DIFFICULTIES OF THE THEORY

The luminous organs which occur in a few insects,
belonging to widely different families, and which are sit-
uated in diiferent parts of the body, offer, under our pres-
ent state of ignorance, a difficulty almost exactly parallel
with that of the electric organs. Other similar cases could
be given; for instance in plants, the very curious contriv-
ance of a mass of pollen-grains, borne on a foot-stalk with
an adhesive gland, is apparently the same in Orchis and
Asciepias, genera almost as remote as is possible among
flowering plants; but here again the parts are not
homologous. In all cases of beings, far removed from
each other in the scale of organization, which are fur-
nished with similar and peculiar organs, it will be found
that although the general appearance and function of the
organs may be the same, yet fundamental differences
between them can always be detected. For instance, the
eyes of Gephalopods or cuttle-fish and of vertebrate ani-
mals appear wonderfully alike; and in such widely sun-
dered groups no part of this resemblance can be due
to inheritance from a common progenitor, Mr. Mivart
has advanced this case as one of special difficult}^, 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 re-
semblance, there is hardly any real similarity between the
eyes of cuttle-fish and vertebrates, as may be seen by con-
sulting 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
wnat occurs in the vertebrata. The retina is wholly dif-
ferent, with an actual inversion of the elemental parts,
and with a large nervous ganglion included within the
membranes of the eye. Tlie relations of the muscles
are as different as it is possible to conceive, and so in
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

OF NATURAL SELECTION. 181

either case could have been developed through the natural
selection of successive slight variations; but if this be ad-
mitted 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 ac-
cordance with this view of their manner of formation.
As two men have sometimes independently hit on tlie
same invention, so in the several foregoing cases it appears
that natural selection, working for the good of eacli being,
and taking advantage of all favorable variations, has pro-
duced similar organs, as far as function is concerned, in
distinct organic beings, which owe none of their structure
in common to inheritance from a common progenitor.

Fritz 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 fev/ species, possessing an air-breathing appara-
tus and fitted to live out of the water. In two of these
families, which were more especially examined by Miiller,
and which are nearly related to each other, the species
agree most closely in all important characters: namely in
their sense organs, circulating systems, in the position of
the tufts of hair within their complex stomachs, and lastly in
the whole structure of the water-breathing branchia3, even to
the microscopical hooks by which they are cleansed. Hence
it might have been expected that in the few species belong-
ing 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, while 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 improb-
able in the highest degree that their common progenitor
should have been adapted for breathing air. Miiller
was thus led carefully to examine the apparatus in the air-
breathing species; and he found it to differ in each in
several important points, as in the position of the orifices,

182 DIFFICULTIES OF THE THEORY

in the manner in which they are opened and closed, and in
some accessory details. Now such differences are intelligi-
ble, and might even have been expected, on the supposition
that species belonging to distinct families had slowly be-
come adapted to live more and more out of water, and to
breathe the air. For these species, from belonging to dis-
tinct families, would have differed to a certain extent, and
in accordance with the principle that the nature of each
variation depends on two factors, viz., the nature of the
organism and that of the surrounding 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 unintel-
ligible. This line of argument seems to have had great
weiglit in leading Fritz Mliller to accept the views main-
tained by me in this volume.

Another distinguished zoologist, the late Professor Cla-
parede, has argued in the same manner, and has arrived at
the same result. He shows that there are parasitic mites
(Acarid^), belonging to distinct sub-families and families,
which are furnishes with hair-claspers. These organs must
have been independently developed, as they could not have
been inherited from a common progenitor; and in the
several grou23S they are formed by the modification of the
fore legs, of the hind legs, of the maxillae or lips, and
of appendages 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 is a
common rule throughout nature that the same end should
be gained, even sometimes in the case of closely related be-
ings, by the most diversified means. How differently con-
structed 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

OF NATURAL SELECTION. 183

shut, but on what a number of patterns is the hinge con-
Btructed, 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 tlieir capsule
being converted into a light balloon-like envelope, by
being embedded in pulp or flesh, formed of the most
diverse parts, and rendered nutritious, as well as conspicu-
ously colored, so as to attract and be devoured by birds,
by having hooks and grapnels of many kinds and serrated
awns, so as to adhere to the fur of quadrupeds, and by
being furnished with wings and pluoes, as different in
shape as they are elegant in structure, so as to be wafted
by every breeze. I will gi^e one other Instance: for this
subject of the same end being gained by the most diversi-
fied means well deserves attention. Some authors main-
tain that organic beings have been formed in many ways
for the sake of mere variety, almost like toys in a shop,
but such a view, of nature is incredible. With plants
having separated sexes, and with those in which, though
hermaphrodites, the pollen does not spontaneously fall on
the stigma, some aid is necessary for their fertilization.
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 sim-
plest 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 droi:)s of nectar,
and is consequently visited by insects; and these carry the
pollen from the anthers to the stigma.

From this simple stage we may pass through an inex-
haustible number of contrivances, all for the same pur-
pose and effected in essentially the same manner, but en-
tailing changes in every part of the flower. The nectar
may be stored in variously shaped receiDtacles, with the
stamens and pistils modified in many ways, sometimes
forming trap-like contrivances, and sometimes capable of
neatly adapted movements through irritability or ehisticity.
From such structures we may advance till we come to
such a case of extraordinary adaptation as that lately de-
scribed by Dr. Criiger in the Coryanthes. This orchid lias
part of its labellum or lower lip hollowed out into a great
bucket, into which drops of almost pure water continually

184 DIFFICULTIES OF THE THEORY

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 cham-
ber with two lateral entrances; within this chamber there
are curious fleshy ridges. The most ingenious man, if he
had not witnessed what takes place, could never have
imagined what purpose all these parts serve. But Dr.
Criiger saw crowds of large humble-bees visiting the gigan-
tic 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
involuntary bath. The passage is narrow, and is roofed over
by the column, so that a bee, in forcing its way out, first
rubs its back against the viscid stigma and then against the
viscid glands of the pollen-masses. The pollen-masses are
thus glued to the back of the bee which first happens to
crawl out through the passage of a lately expanded flower,
and are thus carried away. Dr. Criiger sent me a flower in
spirits of wine, with a bee which he had killed before it
had quite crawled out, with a pollen-mass still fastened to
its back. When the bee, thus provided, flies to another
flower, or to the same flower a second time, and is pushed
by its comrades into the bucket and then crawls out by the
passage, the pollen-mass necessarily comes first into con-
tact with the viscid stigma, and adheres to it, and the
flower is fertilized. 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 l3ees from flyins:
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 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 Cor3^anthes, in order to gnaw
the labelhim; in doing this they inevitably touch a long,
tapering, sensitive projection, or, as 1 have called it, the

OF NATVRAL SELECTION, 185

antenna. ^ This antenna, when touched, transmits a sensa-
tion or vibration to a certain membrane which is instantly
ruptured; this sets free a spring by which tlie pollen- mass
is shot .^orth, 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 retain the pollen, thus effecting fertilization.

How, it may be asked, in the foregoing and in innumer-
able other instances, can we understand the graduated
scale of complexity and the multifarious means for gaining
the same end. The answer no doubt is, as already re-
marked, 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 its successive adaptations to changed habits and
conditions of life.

Finally then, although in many cases it is most difticult
even to conjecture by what transitions organs have ariivcd
at their present state; yet, considei'ing how small the pro-
portion of living and known forms is to the extinct and
unknown, I have been astonished how rarely an organ can
be named, toward which no transitional grade is known to
lead. It certainly is true, that new organs appearing as if
created for some special purpose rarely or never appear in
any being; as indeed is shown by that old, but somewhat
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
niggard in innovation.'' Why, on the theory of Creation,

186 ORGANS OF LITTLE IMPORTANOE .

should there be so much variety and so little real novelty?
Why should all the parts and organs of many independent
beings, each supposed to have been separately created for
its own proper place in nature, be so commonly linked to-
gether by graduated steps? Why should not Nature take
a sudden leap from structure to structure? On the theory
of natural selection, we can clearly understand why she
should not; for natural selection acts only by taking ad-
vantage of slight successive variations; she can never take
a great and sudden leap, but must advance by short and
sure, though slow steps.

ORGAIs^S OF LITTLE APPARE:N^T IMPORTAN^CE, AS AFFECTED

BY NATURAL SELECTIOii.

As natural selection acts by life and death, by the sur-
vival of the fittest, and by the destruction of the less well-
fitted individuals, I have sometimes felt great difficulty in
understanding the origin or formation of parts of little
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 color of its
flesh, the color of the skin and hair of quadrupeds, which,
from being correlated with constitutional differences, or
from determining the attacks of insects, might assuredly
be acted on by natural selection. The tail of the giraffe
looks like an artificially constructed fly-flapper; and it
seems at first incredible that this could have been adapted
for its present purpose by successive slight modifications,
each better and better fitted, for so trifling an object as to
drive away flies; yet we should pause before being too
positive even in this case, for we know that the distribu-
tion and existence of cattle and other animals in South
America absolutely depend on their power of resisting the
attacks of insects: so that individuals which could by any
means defend themselves from these small enemies, would
be able to range into new pastures and thus gain a great

AFFECTED BY NATURAL SELECTION. 187

advantage. It is not that the larger quadrupeds are
actually destroyed (except in some rare cases) hy flics, but
they are incessantly harassed and their strength reduced,
so that they are more subject to disease, or not so well
enabled in a corning dearth to search for food, or to escape
from beasts of prey.

Organs now of trifling importance liave probably in
some cases been of high importance to an early progenitor,
and, after having been slowly perfected at a former period,
have been transmitted to existing species in nearly the
same 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 locomotion the tail is in most
aquatic animals, its general presence and use for many
purposes in so many land animals, which in their lungs or
modified swim-bladders betray their aquatic origin, may
perhaps be thus accounted for. A well-developed tail
having been formed in an aquatic animal, it might subse-
quently come to be worked in for all sorts of purposes, as a
fly-flapper, an organ of prehension, or as an aid in turn-
ing, 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. AVe must by
no means overlook the effects of the definite action of
changed conditions of life, of so-called spontaneous varia-
tions, 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, comprehension,
of the pressure of one part on another, etc., and finally of
sexual selection, by which characters of use to one sex are
often gained and then transmitted more or less perfectly to
the other sex, though of no use to the sex. But structures
thus indirectly gained, altliough at first of no advantage to
a species, may subsequently have been taken advantage of
by its modified descendants, under new condiiions of life
and newly acquired habits.

If green woodpeckers alone had existed, and we did not

188 ORGANS OF LITTLE IMPORTANCE

know that there were many black and pied kinds, I dare
say that we should have thought that the green color 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 color is probably in chief part due to
sexual selection. A trailing palm in the Malay Archipel-
ago climbs the loftiest trees by the aid of exquisitely con-
structed 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 defense against
browsing quadrupeds, so the spikes on the palm may at
first have been developed for this object, and subsequently
have been improved and taken advantage of by the plant,
as it underwent further modification and became a climber.
The naked skin on the head of a vulture is generally con-
sidered as a direct adaptation for wallowing in putridity;
and so it may be, or it may possibly be due to the direct
action of putrid matter; but we should be very cautious in
drawing any such inference, when we see that the skin on
the head of the clean-feeding male turkey is likewise
naked. The sutures in the skulls of young mammals
have been advanced as a beautiful adaptation for aiding
parturition, and no doubt they facilitate, or may be indis-
23ensable for this act: but as sutures occur in the skulls of
young birds and reptiles, which have only to escape from a
broken ^gg, we may infer that this structure has arisen
from the laws of growth, and has been taken advantage of
in the parturition of the higher animals.

We are profoundly ignorant of the cause of each slight
variation or individual difference; and we are immediately
made conscious of this by reflecting on the differences
between the breeds of our domesticated animals in differ-
ent countries, more especially in the less civilized coun-
tries, where there has been but little methodical selection.
Animals kept by savages in different countries often have
to sti'uggle for their own subsistence, and are exposed to a
certain extent to natural selection, and individuals with
slightly different constitutions would succeed best under

AFFECTED BY NATURAL SELECTION. 189

different climates. With cattle susceptibility to the attacks
of flies is correlated with color, as is the liability to be pois-
oned by certain plants; so that even color would be thus
subjected to the action of natural selection. Some observ-
ers are convinced that a damp climate affects the growth
of the hair, and that with the hair the horns are corre-
lated. Mountain breeds always differ from lowland
breeds; and a mountainous country would probably
affect the hind limbs from exercising them more, and
possibly even the form of the pelvis; and then by the
law of homologous variation, the front limbs and the head
would probably be affected. The shape, also, of the pelvis
might affect by pressure the shape of certain parts of the
young in the womb. The laborious breathing necessary in
high regions tends, as we have good reason to believe, to
increase the size of the chest; and again correlation would
come into play. The effects of lessened exercise, together
with abundant food, on the whole organization 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 unknow^n causes of variation; and I have made these
remarks only to show that, if we are unable to account for
the characteristic differences of our several domestic breeds,
which nevertheless are generally admitted to have arisen
through ordinary generation from one or a few parent-
stocks, we ought not to lay too much stress on our ignor-
ance of the precise cause of the slight analogous differences
between true species.

UTILITARIAN" DOCTRINE, HOW FAR TRUE: BEAUTY, HOW

ACQUIRED.

The foregoing remarks lead me to say a few words on
the protest lately made by some naturalists against the
utilitarian doctrine that every detail of structure has been
produced for the good of its possessor. They believe that
many structures have been created for the sake of beautv,
to delight man or the Creator (but this latter point is be-
yond the scope of scientific discussion), or for the sake of

190 UTILITARIAN DOCTRINE, HOW FAR TRUE:

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, independently of any advantage
thus gained. But a still more important consideration is
that the chief part of the organization of every living
creature is due to inheritance; and consequently, though
each being assuredly is well fitted for its place in nature,
many structures have now no very close and direct rela-
tion 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 can not believe
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 useful to the progenitor of
the upland goose and of the frigate-bird, as they now are
to the most aquatic of living birds. So we may believe
that the progenitor of the seal did not possess a flipper,
but a foot with five toes fitted for walking or grasping; and
we may further venture to believe that the several bones
in the limbs of the monkey, horse and bat, were originally
developed, on the principle of utility, probably through
the reduction of more numerous bones in the fin of some
ancient fish-like progenitor of the whole class. It is
scarcely possible to 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 de-

^BA VT7, HO W ACQ VIRED. 191

pends 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 en-
tirely different standard of beauty in their women. If beau-
tiful 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 siiells of
the Eocene epoch, and the gracefully sculptured ammonites
of the Secondary period, created that man might ages
afterward admire them in his cabinet? Few objects are
more beautiful than the minute siliceous cases of the
diatomacese : were these created that they might be ex-
amined 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 among the most beautiful productions of
nature; but they have been rendered conspicuous in con-
trast 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 fertilized by the
wind it never has a gaily-colored corolla. Several plants
habitually produce two kinds of flowers; one kind open and
colored so as to attract insects; the other closed, not
colored, destitute of nectar, and never visited by insects.
Hence, we may conclude that, if insects had not been de-
veloped 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 tir, oak, nut
and ash trees, on grasses, spinach, docks and nettles,
which are all fertilized 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 tlie
palate— that the gaily-colored fruit of the spindle-^yood
tree and the scarlet hemes of the holly are beautifui 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 dissem-
inated. I infer that this is the case from having as yet
found no exception to the rule that seeds are always thus

192 UTILITARIAN DOCTRINE, HOW FAR TRUE:

disseminated when imbedded within a fruit of any kind
(that is witliin a fleshy or pulpy envelope), if it be colored
of any brilliant tint, or rendered conspicuous by being
white or black.

On the other hand, I willingly admit that a great
number of male animals, as all our most gorgeous birds,
some fishes, reptiles, and mammals, and a host of
magnificently colored butterflies, have been rendered
beautiful for beauty's sake. But this has been effected
through sexual selection, that is, by the more beautiful
males having been continually preferred by the females,
and not for the delight of man. So it is with the music of
birds. We may infer from all this that a nearly similar
taste for beautiful colors and for musical sounds runs
through a large part of the animal kingdom. When the
female is as beautifully colored as the male, which is not
rarely the case with birds and butterflies, the cause ap-
parently lies in the colors acquired through sexual selec-
tion having been transmitted to both sexes, instead of to
the males alone. How the sense of beauty in its simplest
form — that is, the reception of a peculiar kind of pleasure
from certain colors, forms and sounds — -nvas 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 inquire how it is that certain flavors and odors give
pleasure, and others displeasure. Habit in all these cases
appears to have come to a certain extent into play; but
there must be some fundamental cause in the constitution
of the nervous system in each species.

Natural selection cannot possibly produce any modifica-
tion in a species exclusively for the good of another
species, though throughout nature one species 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 animals, as we
see in the fang of the adder, and in the ovipositor of the
ichneumon, by which its eggs are deposited in the living
bodies of other insects. If it could be proved that any
p3,rt of the structure of any one species had been formed
for the exclusive good of another species, it would anni-
hilate my theory, for such could not have been produced

BEAUTY, HOW ACQUIRED. 193

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 weiglit. 'it
is admitted that the rattlesnake has a poison fang for its
own defence and for the destruction of its prey; but some
authors suppose that at the same time it is furnished with
a rattle for its own injury, namely, to warn its prey. I
would almost as soon believe that the cat curls the end of
its tail when preparing to spring, in order to warn the
doomed mouse. It is a much more probable view that the
rattlesnake uses its rattle, the cobra expands its frill and
the puff-adder swells while 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 endeavor 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 pos-
sessor. If a fair balance be struck between the good and
evil caused by each part, each will be found on the whole
advantageous. After the lapse of time, under changing
conditions of life, if any part comes to be injurious, it will
be modified; or if it be not so, the being will become ex-
tinct as myriads have become extinct.

Natural selection tends only to make each organic being
^s perfect as, or slightly more perfect than the other in-
habitants of the same countrv with which it comes into com-
petition. And we see that this is the standard of perfec-
tion attained under nature. The endemic productions of
New Zealand, for instance, are perfect, one compai-ed with
another; but they are now rapidly yielding before the ad-
vancing legions of plants and animals introduced from
Europe. Natural selection will not produce absolute per-
fection, nor do we always meet, as far as we can judge,
with this high standard under nature. The correction for
the aberration of light is said by Miiller not to be perfect

I

194 UTILITARIAN DOCTRINE, HOW FAR TRUE:

even in that most perfect organ, the human eye. Hehn-
holtz, whose judgment no one will dispute, after describ-
ing 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 imper-
fection 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 sen-
sations. One might say that nature has taken delight in
accumulating contradictions in order to remove all founda-
tion 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 con-
trivances 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 against many kinds of enemies,
can not be withdrawn, owing to the backward serratures,
and thus inevitably causes the death of the insect by tear-
ing out its viscera?

If we look at the sting of the bee, as having existed in a
remote progenitor, as a boring and serrated instrument,
like that in so many members of the same great order, and
that it has since been modified but not perfected for
its present purpose, with the poison originally adapted for
some other object, such as to produce galls, since inten-
sified, 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 mem-
bers. If we admire the truly wonderful jiower of scent by
which the males of many insects find their females, can we
admire the production for this single purpose of thousands
of drones, which are utterlv useless to the communitv foj
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 undoubtedly this is for the good of the
community; and maternal love or maternal hatred, though

BEAUTY, HOW ACQUIRED. 195

the latter fortunately is most rare, is all the same to the
inexorable principles of natural selection. If we admire
the several ingenious contrivances by which orchids and
many other plants are fertilized through insect agency, can
we consider as equally perfect the elaboration of dense
clouds of pollen by our fir-trees, so that a few granules
may be wafted by chance on to the ovules?

SUMMARY: THE LAW OF UNITY OF TYPE AND OF THE CON-
DITIONS OF EXISTENCE EMBRACED BY THE THEORY OF
NATURAL SELECTION.

We have in this chapter discussed some of the difficulties
and objections which may be urged against the theory.
Many of them are serious; but I think that in the discussion
light has been thrown on several facts, which on the belief
of independent acts of creation are utterly obsure. We
have seen that species at any one period are not indefinitely
variable, and are not linked together by a multitude of
intermediate gradations, 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 pro-
cess of natural selection implies the continual supplanting
and extinction of preceding and intermediate gradations.
Closely allied sj^ecies, 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 insensibly
graduate away from one part to another. When two vari-
eties 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 inter-
mediate variety will usually exist in lesser numbers than
the two forms which it connects; consequently the two
latter, during the course of further modification, from ex-
isting in greater numbers, will have a great advantage over
the less numerous intermediate variety, and will thus gen-
erally 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 instance,
could not have been formed by natural selection from an
animal which at first only glided through the air.

1-^a BVMMAItT,

We have seen that a species under new conditions of life
may change its habits; or it may have diversified habits,
with some very unlike those of its nearest congeners.
Hence we can understand, bearing in mind that each or-
ganic 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 anyone; yet in the case of any organ, if we know
of a long series of gradations in complexity, each good for
its possessor, then under changing conditions of life, there
is no logical impossibility in the acquirement of any con-
ceivable degree of perfection through natural selection.
In the cases in which we know of no intermediate or transi-
tional 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 swim-bladder has appar-
ently 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 special-
ized for one function; and two distinct organs having per-
formed at the same time the same function, the one having
been perfected while aided by the other, must often have
largely facilitated transitions.

We liave seen that in two beings widely remote from each
other in the natural scale, organs serving for the same pur-
pose and in external appearance closely similar may have
been separately and independently formed; but when such
organs are closely examined, essential differences in their
structure can almost always be detected; and this naturally
follows from the principle of natural selection. On the
other hand, the common rule throughout nature is infinite
diversity of structure for gaining the same end; and this
again naturally follows from the same great principle.

In many cases we are far too ignorant to be enabled to
assert that a part or organ is so unimportant for the wel-
fare of a species, that modifications in its striicture could
not have been slowly accum';iated by means of natural
selection. In many other cases, modifications are probably

I

SUMMARY. 197

the direct result of the laws of variation or of growth, in-
dependently of any good having been thus gained. But
even such structures have often, as we may feel assured,
been subsequently taken advantage of, and still further
modified, for the good of species under new conditions of
life. We may, also, believe that a part formerly of hi^h
importance has frequently been retained (as the tail of an
aquatic animal by its terrestrial descendants), tliough 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 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 inhabi-
tants 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. Xatural selec-
tion 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 clearly under-
stand the full meaning of that old canon in natural history,
*' Natura non facit saltum." This canon, if we look to the
present inhabitants alone of the world, is not strictly cor-
rect; but if we include all 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 inde-
pendent of their habits of life. On my theory, unity of
type is explained by unity of descent. The expression of

198 SUMMAET.

conditions of existence, so often insisted on by the illus-
trious Cuvier, is full}^ embraced by the principle of natural
selection. For natural selection acts by either now adapt-
ing the varying parts of each being to its organic and in-
organic conditions of life; or by having adapted them
during past periods of time: the adaptations being aided in
many cases by the increased use or disuse of parts, being
affected by the direct action of the external conditions of
life, and subjected in all cases to the several laws of growth
and variation. Hence, in fact, the law of the Conditions
of Existence is the higher law; as it includes, through the
inheritance of former variations and adaptations, that of
Unity of Type.

MltiCELLANEO US OBJECTIONS. \ 99

CHAPTEK VII.

MISCELLANEOUS OBJECTIONS TO THE THEORY OF NATURAL

SELECTION.

Longevity — Modifications not necessarily simultaneous — Modifica-
tions apparently of no direct service — Progressive develop-
ment— 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 interfere
with the acquisition through natural selection of useful struct-
ures— Gradations of structure with changed functions — Widely
different organs in members of the same class, developed from
one and the same source — Reasons for disbelieving in great and
abrupt modifications.

I WILL devote this chapter to the consideration of
various miscellaneous objections which have been advanced
against my views, as some of the previous discussions may
thus be made clearer; but it would be useless to discuss all
of them, as many have been made by writers who have not
taken the trouble to understand the subject. Thus a dis-
guished German naturalist has asserted that the weakest
part of my theory is, that I consider all organic beings as
imperfect: what I have really said is, that all are not as
perfect as they might have been in relation to their condi-
tions; and this is shown to be the case by so many native
forms in many quarters of the world having yielded tiieir
places to intruding foreigners. Nor can organic beings,
even if they were at any one time perfectly adajHed to
their conditions of life, have remained so, when their con-
ditions changed, unless they themselves likewise changed;
and no one will dispute that the physical conditions of
each country, as well as the number and kinds of its inhab-
itants, have undergone many mutations.

A critic has lately insisted, with some parade of mathe-
matical accuracy, that longevity is a great advantage to all
species, so that he who believes in natural selection " must

200 MISCELLANEOUS OBJECTIONS TO THE

arrange his genealogical tree '^ in such a manner that all
the descendants have longer lives than their progenitors!
Cannot our critics conceive that a biennial plant or one of
the lower animals might range into a cold climate and
perish there every winter; and yet, owing to advantages
gained through natural selection, survive from year to
year by means of its seeds or ova? Mr. E. Ray Lankester
has recently discussed this subject, and he concludes, as
far as its extreme complexity allows him to form a judg-
ment, that longevity is generally related to the standard of
each species in the scale of organization, as well as to the
amount of expenditure in reproduction and in general
activity. And these conditions have, it is probable, been
largely determined through natural selection.

It has been argued that, as none of the animals and
plants of Egypt, of which we know anything, have changed
during the last three or four thousand years, so probably
have none in any part of the world. But, as Mr. G. H.
Lewes has 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 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 con-
ditions 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 innate and
necessary law of development, but is powerless against the
doctrine of natural selection or the survival of the fittest,
which implies that when variations or individual differences
of a beneficial nature happen to arise, these will be pre-
served ; but this will be effected only under certain favor-
able circumstances.

The celebrated palaeontologist, Bronn, at the close of his
German translation of this work, asks how, on the prin-
ciple of natural selection, can a variety live side by side

THEOR T OF NA TUBAL SELECTION, 20 i

with th© parent species? If both have become fitted for
slightly different habits of life or conditions, tbuy might
live together; and if we lay on one side pol^morpliic
species, in which the variability seems to be of a peculiar
nature, and all mere temporary variations, such as size,
albinism, etc., the more permanent varieties are generally
found, as far as lean discover, inhabiting distinct stations,
such as high land or low laud, dry or moist districts.
Moreover, in the case of animals which wander much
about and cross freely, their varieties seem to be generally
confined to distinct regions.

Bronn also insists that distinct species never differ
from each other in single characters, but in many parts;
and he asks, how it always comes that many parts of the
organization 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 vari-
ations, if slight, first in one part and then in another; and
as they would be transmitted all together, they would ap-
pear 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 purpose.
Look at the race and dray-horse, or at the greyhound and
mastiff. Their whole frames, and even their mental char-
acteristics, have been modified; but if we could trace eauli
step in the history of their transformation — and the hitter
steps can be traced — we should not see great and simulta-
neous changes, but first one part and then another slightly
modified and improved. Even when selection has been ap-
plied 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 tlie
flower, fruit, or leaves, has been greatly changed, almost
all the other parts have been slightly modified. This may
be attributed 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 ciiaracters

202 MISCELLANEOUS OBJECTIONS TO THE

appear to be of no service whatever to their possessors, and
therefore cannot have been influenced through natural
selection. Bronn adduces the length of the ears and tails
in the different species of hares and mice — the complex
folds of enamel in the teeth of many animals, and a multi-
tude of analogous cases. With respect to plants, this sub-
ject 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 morphological characters, which aj^pear to be quite
nnimportant for the welfare of the species. He conse-
quently believes in an innate tendency toward progressive
and more perfect development. He specifies the arrange-
ment of the cells in the tissues, and of the leaves on the
axis, as cases in which natural selection could not have
acted. To these may be added the numerical divisions in
the parts of the flower, the position of the ovules, the
shape of the seed, when not of any use for dissemina-
tion, etc.

There is much force in the above objection. Neverthe-
less, 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 nutri-
ment to a part, mutual pressure, an early developed part
affecting one subsequently developed, and so forth — as well
as through other causes which lead to the many mysterious
cases of correlation, which we do not in the least under-
stand. These agencies may be all grouped together,
for the sake of brevity, under the expression of
the laws of growth. In the third place, we have
to allow for the direct and definite action of
changed conditions of life, and for so-called spontaneous
variations, in which the nature of the conditions appar-
ently 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 spon-
taneous 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

THEORY OF NATURAL SELECTION. 203

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 indi-
vidual difference, as well as for more strongly marked
variations which occasionally arise; and if the unknown
cause were to act persistently, it is almost certain that all
the individuals of the species would be similarly moditied.

In the earlier editions of this work I underrated, as it
now seems probable, the frequency and importance of
modifications due to spontaneous variability. But it is im-
possible to attribute to this cause the innumerable struct-
ures 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, ex-
cited so much surprise in the minds of the older natural-
ists, can thus be explained.

It may be worth while to illustrate some of the foregoing
remarks. With respect to the assumed inutility of various
parts and organs, it is hardly necessary to observe that
even in the higher and best-known animals many struct-
ures exist, which are so highly developed that no one
doubts that they are of importance, yet their use has not
been, or has only recently been, ascertained. As Bronn
gives the length of the ears and tail in the several species
of mice as instances, though trifling ones, of differences in
structure which can be of no special use, I may mention
that, according to Dr. Schobl, the external ears of the
common mouse are supplied in an extraordinary manner
with nerves, so that they no doubt serve as tactile organs;
hence the length of the ears can hardly be quite unim})or-
tant. We shall, also, presently see that the tail is a highly
useful prehensile organ to some of the species; and its use
would be much influenced by its length.

With respect to plants, to which on account of Niigeli's
essay I shall confine myself in the following remarks, it
will be admitted that the flowers of the orchids present a
multitude of curious structures, which a few years ago
would have been considered as mere morphological differ-
ences without any special function; but they are now
known to be of the highest importance for the fertilization
of the species through the aid of insects, and have prob-

204 MISCELLANEOUS 0BJE0TI0N8 TO TBJB

ably been gained through natural selection. No one until
lately would have imagined that in dimorphic and tri-
morphic 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 some cases, and
in others the lower ones alone are fertilized; and he sug-
gests 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 the selection of any
slight deviations in position which favored their fertiliza-
tion, and the production of seed.

Several plants belonging to distinct orders habitually
produce flowers of two kinds — the one open, of the ordi-
nary structure, the other closed and imperfect. These two
kinds of flowers sometimes differ wonderfully in structure,
yet may be seen to graduate into each other on the same
plant. The ordinary and open flowers can be intercrossed;
and the benefits which certainly are derived from this pro-
cess are thus secured. The closed and imperfect flowers
are, however, manifestly of high importance, as they yield
with the utmost safety a large stock of seed, with the ex-
penditure 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 columnae five of the alternate sta-
mens are rudimentary; and in some species of Viola three
stamens are in this state, two retaining their proper func-
tion, 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 Malpighiaceae the closed
flowers, according to A. de Jussieu, are still further modi-

THEOR T OF NA TURAL SELECTION. v( )3

fied, for the five stamens whicli stand opposite to the sepals
are all aborted, a sixth stamen standing opposite to a petal
being alone developed; and tiiis stamen is not present in
the ordinary flowers of this 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, wdien rendered by the closure 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 func-
tional inactivity of parts, during the progress of the reduc-
tion 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 flrst, and
has five sepals and petals, and five divisions to the ovarium;
while all the other flowers on the plant are tetramerous.
In the British Adoxa the uppermost flower generally bas
two calyx-lobes with the other organs tetramerous, while
the surrounding flowers generally have three calyx-lobes
with the other organs pentamerous. In many CompositaB
and Umbellifera? (and in some other plants) the circum-
ferential flowers have their corollas much more developed
than those of the center; and this seems often connected
with the abortion of the reproductive organs. It is a more
curious fact, previously referred to, that the achenes
or seeds of the circumference and center sometimes differ
greatly in form, color and other characters. In Cartha-
mus and some other Compositae the central achenes alone
are furnished with a pappus; and in Hyoseris the same
head yields achenes of three different forms. In certain
irmbellifer,3e the exterior seeds, according to Tausch, are
orthospermous, and the central onecrelospermous, and this
is a character which was considered by De CandoUu to be iu
other species of the highest systematic importance. Pro-

206 MISCELLANEOUS OBJECTIONS TO THE

fessor Braun mentions a Fumariaceous genus, in which the
flowers in the lower part of the spike bear oval, ribbed,
one-seeded nutlets; and in the upper part of the spike,
lanceolate, two-valved and two-seeded siliques. In these
several cases, with the exception of that of the well-devel-
oped ray-florets, which are of service in making the flowers
conspicuous to insects, natural selection cannot, as far as
we can judge, have come into play, or only in a quite sub-
ordinate 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 struct-
ure, which are considered by botanists to be generally of a
highly important nature, affecting only some of the flowers
on the same plant, or occurring on distinct plants, which
grow close together under the same conditions. As these
variations seem of no special use to the plants, they cannot
have been influenced by natural selection. Of their cause
we are quite ignorant; we cannot even attribute them, as
in the last class of cases, to any proximate agency, such as
relative position. I will give only a few instances. It is
so common to observe on the same plant, flowers indiffer-
ently tetramerous, pentamerous, etc., that I need not give
examples; but as numerical variations are comparatively
rare when the parts are few, I may mention that, accord-
ing 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 char-
acter; but Professor Asa Gray states that with some species
of Mimulus, the aestivation is almost as frequently that of
the Rhinanthidege as of the Antirrhinideae, to which latter
tribe the genus belongs. Aug. St. Hilaire gives the fol-
lowing cases: the genus Zanthoxylon belongs to a division
of the Eutaceae 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

THEORY OF NATURAL ISELECTION. 207

Helianthemum the capsule has been described as uiiilocu-
lar or tri-locular; and in H. mutabile, " Une hime plus on
moins large, s'etend entre le pericarpe et le placenta." In
the flowers of Saponaria officinalis Dr. Masters lias
observed instances of both marginal and free central plac-
entation. Lastly, St. Hilaire found toward the southern
extreme of the range of Gomphia oleseformis two forms
which he did not at first doubt were distinct species, but
he subsequently saw them growing on tlie same bush; and
he then adds, " Voila done dans un rneme indivielu des
loges et un style qui se rattaclient tantot a un axe verticale
et tantot a un gynobase/'

We thus see that with plants many morphological
changes may be attributed to the laws of growth and the
inter-action of parts, independently of natural selection.
But with respect to Nageli's doctrine of an innate tend-
ency toward 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 progressiug
toward a higher state of development? On the contrary,
I should infer from the mere fact of the parts in questioi
differing or varying greatly on the same plant, that such
modifications were of extremely small importance to the
i:)lants themselves, of whatever importance they may gener-
ally be to us for our classifications. The acquisition of a
useless part can hardly be said to raise an organism in the
natural scale; and in the case of the imperfect, closed
flowers, above described, if any new principle has to be
invoked, it must be one of retrogression rather tlian of
progression; and so it must be with many parasitic and
degraded animals. We are ignorant of the exciting cause
of the above specified modifications; but if the unknown
cause were to act almost uniformly for a length of time,
we may infer that the result would be almost uniform; and
in this case all the individuals of the species would be
modified in the same manner.

From the fact of the above characters being unimpor-
tant for the welfare of the species, any slight vai-iations
which occurred in them would not have been accumulated
and augmented through natural selection. A structure
which has been developed througli long-continued selec-
tion, when it ceases to be of service to a species, generally

508 MISCELLANEOUS OBJECTIONS TO THE

becomes variable, as we see with rndimentar}^ organs; for
it will no longer be regulated by this same power of selec-
tion. But when, from the nature of the organism and of
the conditions, modifications have been induced which are
unimportant for the welfare of the species, they may be,
and apparently often have been, transmitted in nearly the
same state to numerous, otherwise modified, descendants.
It cannot have been of much importance to the greater
number of mammals^ birds, or reptiles, whether they v/ere
clothed with ha,ir, 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, morphological
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, etc., first appeared
in many cases as fluctuating variations, which sooner or
later became constant through the nature of the organism
and of the surrounding conditions, as well as through the
intercrossing of distinct individuals, but not through
natural selection; for as these morphological characters do
not ailect 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 S3'steniatist; but,
as we shall hereafter see when we treat of the genetic
principle of classiflcation, this is by no means so paradoxi-
cal as it may at first appear.

Although we have no good evidence of the existence
in organic beings of an innate tendency toward progressive
development, yet this necessarily follows, as I have attempt-
ed 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 organization, is
the degree to which the parts have been specialized or dif-
ferentiated; and natural selection tends toward this end,
inasmuch as the parts are thus enabled to perform their
functions more efi&ciently.

THEOn T OF NA TUBAL ISRL ECTION. 209

A distinguished zoologist, Mr. St. George Mivart, has
recently collected all the objections wliicli luive ever been
advanced by myself and others against the theory of natui-al
selection, as propounded by Mr. Wallace and myself, and
has illustrated them with admirable art and force. When
thus marshaled, 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. Wlu-n
discussing special cases, Mr. Mivart passes over the effects
of the increased use and disuse of parts, which 1 have
always maintained to be highly important, and have treated
in my "^^ Variation under Domestication " at greater length
than, as I believe, any other writer. He likewise often
assumes that I attribute nothing to variation, independently
of natural selection, whereas in the work just referred to
I have collected a greater number of well-established cases
than can be found in any other work known to me.
My judgment may not be trustworthy, but after reading
with care Mr. Mivart's book, and comparing each section
with what I have said on the same head, I never before
felt so strongly convinced of the general truth of the con-
clusions here arrived at, subject, of course, in so intricate
a subject, to much partial error.

All Mr. Miva^rt^s objections will be, or have been, con-
sidered in the present volume. The one new point wliich
appears to have struck many readers is, *' That natural
selection is incompetent to account for the incipient stages
of useful structures.^^ This subject is intimately connected
with that of the gradation of the characters, often
accompanied by a change of function, for instance, the
conversion of a swim-bladder into lungs, points which
were discussed in the last chapter under two headings.
Nevertheless, I will 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 beautifully
adapted for browsing on the higher branches of trees. It
can thus obtain food beyond the reach of the otlier Uugulata

2J0 MISCELLANEOUS OBJECTIONS TO THE

or hoofed animals inhabiting the same country; and this
mnst be a great advantage to it during dearths. The Niata
cattle in South x\merica show us how small a difference in
structure may make, during such periods, a great differ-
ence 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 of ten recurrent droughts,
browse on the twigs of trees, reeds, etc., to which food the
common cattle and horses are then driven; so that at
these times the Niatas perish, if not fed by their
owners. Before coming to Mr. Mivart's objections,
it may be Avell to explain once again how natural
selection will act in all ordinary cases. Man has
modified some of his animals, without necessarily haying
attended to special points of structure, by simply pre-
serving and breeding from the fleetest individuals, as with
the race-horse and greyhound, or as with the game-cock,
by breeding from the victorious birds. So underniature with
the nascent giraffe, the individuals which were the highest
browsers and were able during dearths to reach even an
inch or two above the others, will often have been pre-
served; 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
differences, 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, con-
sidering its probable habits of life; for those individuals'
which had some one part or several parts of their bodies
rather more elongated than usual, would generally have
survived. These will have intercrossed and left offspring,
either inheriting the same bodily peculiarities, or with a
tendency to vary again in the same manner ; while the
individuals less favored 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: natu--
ral selection will preserve and thus separate all the superior
individuals, allowing them freely to intercross, and will
destroy all the inferior individuals. By this process long-

THEOR 7 OF NA TUBAL SELECTION, o j i

continued, which exactly corresponds with wlmi I luive
called unconscious selection by man, combined, no doubt,
in a most important manner with the inherited elTects 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. ^[ivart brings forward two ob-
jections, One is that the increased size of the body woultl
obviously require an increased supply of food, and lie con-
siders it as '' very problematical wiiether the disadvantages
thence arising would not, in times of scarcity, more than
counterbalance the advantages." But as tlie giraffe does
actually exist in large numbers in Africa, and as some of the
largest antelopes in the world, taller than aji 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 wonld 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 de-
fence, by violently swinging its head armed with stump-
like horns. The preservation of each species can rarely be
determined by any one advantage, but by the union of all,
great and small.

Mr. Mivart then asks (and this is his second objection),
if natural selection be so potent, and if high browsing be
so great an advantage, why has not any other hoofed quad-
ruped 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
South Africa, which was formerly inhabited by numerous
herds of the giraffe, the answer is not difficult, and can
best be given by an illustration. In every meadow in

212 M1SGELLANE0V8 OBJECTIONS TO THE

England, in which trees grow, we see the lower branches
trimmed or planed to an exact level by the browsing of the
horses or cattle; and what advantage would it be, for in-
stance, 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
South Africa the competition for browsing on the higher
branches of the acacias and other trees must be between
giraife 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 while 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 favorable to its increase in some new country.
We can, however, see in a general manner that various
causes might have interfered with the development of a
long neck or proboscis. To reach the foliage at a consid-
erable height (without climbing, for which hoofed animals
are singularly ill-constructed) implies greatly increased
bulk of body; and we know that some areas support singu-
larly few large quadrupeds, for instance South America,
though it is so luxuriant, while South 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 favorable 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 favorable than others for the development
of so large a quadruped as the giraffe.

In order that an animal should acquire some structure
specially and largely developed, it is almost indispensable
that several other parts should be modified and coadapted.
Although every part of the body varies slightly, it does not

THEOR T OF NA TUBAL SELECTION. 2 1 3

follow that the necessary parts should always vary in thu
right direction and to the right degree. With the differ-
ent species of our domesticated animals we know that the
parts vary in a different manner 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 apparently would be beneficial to the spe-
cies. For instance, if the number of individuals existing
in a country is determined chiefly through destruction by
beasts of prey — by external or internal parasites, etc. — as
seems often to be the case, then natural selection will be
able to do little, or will be greatly retarded, in modifying
any particular structure for obtaining food. Lastly, nat-
ural selection is a slow process, and the same favorable
conditions must long endure in order that any marked
effect should thus be produced. Except by assigning such
general and vague reasons, we cannot explain why, in
many quarters of the world, hoofed quadrupeds have not
acquired much elongated necks or other means for brows-
ing on the higher branches of trees.

Objections of the same nature as the foregoing have been
advanced by many writers. In each case various causes,
besides the general ones just indicated, have probably in-
terfered with the acquisition through natural selection of
structures, which it is thought would be beneficial to cer-
tain species. One writer asks, why has not the ostrich
acquired the power of tiiglit? But a moment's reflection
will show what an enormous supply of food would be nec-
essai-y 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 in-
habited 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 land.^ 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 ]n-eyed
Qn by the reptiles or birds, which first colonize and abound

214 MISCELLANEOUS OBJECTIONS TO THE

on most oceanic islands. Gradations of structure, with each,
stage beneficial to a changing species, will be favored only
under certain peculiar conditions. A strictly terrestrial
animal, by occasionally hunting for food in shallow water,
then in streams or lakes, might at last be converted into
an animal so thoroughly acquatic as to brave the open
ocean. But seals would not find on oceanic islands the
conditions favorable to their gradual reconversion into a
terrestrial form. Bats, as formerly shown, probably ac-
quired 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 running
quickly on the ground, by the aid of their hind legs alone,
so as to compete with birds or other ground animals; and
for such a change a bat seems singularly ill-fitted. These
conjectural remarks have been made merely to show that
a transition of structure, with each step beneficial, is a
highly complex affair; and that there is nothing strange
in a transition not having occurred iu any particular case.

Lastly, more than one writer has asked why have some
animals' had their mental powers more highly developed
than others, as such development would be advantageous
to all? Why have not apes acquired the intellectual
powers of man? Various causes could be assigned; but as
they are conjectural, and their relative probability can not
be weighed, it would be useless to 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
civilization than the other; and this apparently implies in-
creased brain power.

We will return to Mr. Mivart^s other objections. Insects
often resemble for the sake of protection various objects,
such as green or decayed leaves, dead twigs, bits of lichen,
flowers, spines, excrement of birds, and living insects; but

THEORY OF NATURAL SELECTION. 215

to this latter point I shall hereafter recur. Tlie resein-
blauce is often Avonderfully close, and is not confined to
color, but extends to form, and even to the manner in
which the insects hold themselves. Tlie caterpillars which
project motionless like dead twigs from the bushes on
which they feed, olfer an excellent instance of a resem-
blance 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 neutralize each other, and
at first to form such unstable modifications that it is diffi-
cult, if not impossible, to see how such indefinite oscilla-
tions of infinitesimal beginnings can ever buikl up a suffi-
ciently appreciable resemblance to a leaf, bamboo, or other
object, for natural selection to seize upon and perpetuate."

But in all the forgoing cases the insects in their original
state no doubt presented some rude and accidental resem-
blance to an object commonly found in the stations fre-
quented by them. Nor is this at all improbable, consider-
ing the almost infinite number of surrounding objects and
the diversity in form and color of the hosts of insects
which exist. As some rude resemblance is necessary for
the first start, we can understand how it is that the larger
and higher animals do not (with the exception, as far as I
know^, of one fish) resemble for the sake of protection
special objects, but only the surface which commonly sur-
rounds them, and this chiefly in color. Assuming that an
insect originally happened to resemble in some degree a
dead twig or a decayed leaf, and that it varied slightly in
many ways, then all the variations which rendered the in-
sect at all more like any such object, and thus favored its
escape, would be preserved, while other variations would
be neglected and ultimately lost; or, if they rendered tlie
insect at all less like the imitated object, they would be
eliminated. There would indeed be force in Mr. ^livart'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 wuth

210 mSCELLANhlOUS OBJECTIONS TO THE

respect to '' the last touches of perfection in the mimicry;^'
as in the case given by Mr. Wallace, of a walking-stick in-
sect (Ceroxylus laceratus), which resembles '^a stick grown
over oy a creeping moss or jungermannia." So close was
this resemblance, that a native Dyak maintained that the
foliaceous excrescences were really moss. Insects are preyed
on by birds and ether enemies whose sight is probably
sharper than ours, and every grade in resemblance which
aided an insect to escape notice or detection, would tend
toward its preservation; and the more perfect the resem-
blance so much the better for the insect. Considering the
nature of the differences between the species in the group
which includes the above Ceroxylus, there is nothing im-
probable in this insect having varied in the irregularities
on its surface, and in these having become more or less
green-colored; for in every group the characters which
differ in the sevei-al species are the most apt to vary, whiltf
the generic characters, or those common to all the species,
are the most constant.

The Greenland whale is one of the most wonderful ani-
mals in the world, and the baleen, or whalebone, one of
its greatest peculiarities. The baleen consists of a row, on
each side of the upper jaw, of about 300 plates or laminae,
which stand close together transversely to the longer axis
of the mouth. Within the main row there are some subsid-
iary 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 ani-
mals subsist. The middle and longest lamina in ^he Green-
land whale is ten, twelve, or even fifteen feet in length;
but in the different species of Cetaceans there are grada-
tions in length; the middle lamina being in one species,
according to Scoresby, four feet, in another three, in
another eighteen inches, and in the Balasnoptera rostrata
only about nine inches in lengtli. The quality of the
whalebone also differs in the different species.

With respect to the baleen, Mr. Mivart remarks that if
it ^'had once attained such a size and development as to be
at all useful, then its preservation and augmentation within
serviceable limits would be promoted by natural selection

THEOR 7 OF NA TUBA L SELECTION. 21 7

alone. But how to obtain the beginning of 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 laniel-
lated beak of a duck? Ducks, like whales, subsist by sift-
ing the mud and water; and the family has sometimes
been called Onblatores, or sifters. I hope that I may not
be misconstrued into saying that the progenitors of whales
did actually possess mouths lamellated like the beak of a
duck. I wish only to show that this is not incredible, and
that the immense plates of baleen in the Greenland whale
might have been developed from such lamellae by finely
graduated steps, each of service to its possessor.

The beak of a shoveller-duck (Spatula clypeata) is a
more beautiful and complex structure than the mouth of a
whale. The upper mandible is furnished on each side (in
the specimen examined by me) with a row or comb formed
of 188 thin, elastio lamellae, obliquely bevelled so as to be
pointed, and placed transversely to the longer axis of the
mouth. They arise from the palate, and are attached by
flexible membrane to the sides of the mandible. Those
standing toward the middle are the longest, being about
one-third of an inch in length, and they project fourteen
one-hundreths of an inch beneath the edge. At their
bases there is a short subsidiary row of obliquely transverse
lamellae. In these several respects they resemble the plates
of baleen in the mouth of a v/hale. But toward the ex-
tremity of the beak they differ much, as they project in-
ward, instead of straight downward. The entire head of
the shoveller, though incomparably less bulky, is about one-
eighteenth of the length of the head of a moderately large
Balaenoptera rostrata, in which species the baleen is only
nine inches long; so that if we were to make the head of
the shoveller as long as that of the Balaenoptera, the lam-
ellae would be six inches in length, that is, two-thirds of
the length of the baleen in this species of whale. The
lower mandible of the shoveller-duck is furnished with
lamellae of equal length with these above, but liner; 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 lamella3 are
frayed into fine bristly points, so that they thus curiously-

218 MISCELLANEOUS OBJECTIONS TO TEE

resemble the plates of baleen. In the genus Prion, a
member of the distinct family of the Petrels, the upper
mandible alone is furnislied with lamellae, which are well
developed and project beneath the margin; so that the
beak of this bird resembles in this respect the mouth of a
whale.

From the highly developed structure of the shoveller's
beak we may proceed (as I have learned from information
and specimens sent to me by Mr. Salvin), without any great
break, as far as fitness for sifting is concerned, through
the beak of the Merganetta armata, and in some respects
through that of the Aix sponsa, to the beak of the common
duck. In this latter species the lamellae are much coarsei
than in the shoveller, and are firmlv attached to the sides
of the mandible; they are only about fifty in number oi
each side, and do not project at all beneath the margin.
They are square-topped, and are edged with translucent,
hardish tissue, as if for crushing food. The edges of the
lower mandible are crossed by numerous fine ridges, which
project very little. Although the beak is thus very inferio
as a sifter to that of a shoveller, yet this bird, as every one
knows, constantly uses it for this purpose. There are
other species, as I hear from Mr. Salvin, in which the
lamellse are considerably less developed than in the common
duck; but I do not know whether they use their beaks for
sifting the water.

Turning to another group of the same family. In the
Egyptian goose (Chenalopex) the beak closely resembles
that of the common duck; but the lamellae are not sg
numerous, nor so distinct from each other, nor do they
project so much inward; 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 common goose. In this latter
bird the lamellse of the upper mandible are much coarser
than in the common duck, almost confluent, about twenty-
seven in number on each side, and terminating upward 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 cut-

THEOn Y OF NA TURAL SELECTION. 2 \ o

ting herbage, for which purpose it is so well fitted that it
can crop grass closer than almost any ether animal. There
are other species of geese, as I hear from Mr. Bartlett, in
which the lamellae are less developed than in the common
goose.

We thus see that a member of the duck family, with a
beak constructed like that of a common goose and adapted
Bolely for grazing, or even a member with a beak having
less well-developed lamellae, might be converted by small
changes into a species like the Egyptian goose — this into
one like the common duck — and, lastly, into one like the
shoveller, provided with a beak almost exclusively adapted
for sifting the water; for this bird could hardly use any
part of its beak, except the hooked tip, for seizing or tear-
ing 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 differ-
ent purpose of securing live fish.

Keturning to the whales. The Hyperoodon bidens is
destitute of true teeth in an efficient condition, but its
palate is roughened, according to Lacepede, with small
unequal, hard points of horn. There is, therefore, noth-
ing 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 tear-
ing its food. If so, it will hardly be denied that the points
might have been converted through variation and natural
selection into lamellae as well-developed as those of the
Egyptian goose, in which case they would have been used
both for seizing objects and for sifting the water; then
into lamellae like those of the domestic duck; and so on-
ward, until they became as well constructed as those of the
ehoveller, in which case they would have served exclusively
as a sifting apparatus. From this stage, in which the
lamellae would be two-thirds of the length of the plates of
baleen in the Balaenoptera rostrata, gradations, which may
be observed in still-existing Cetaceans, lead us onward 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

220 MISCELLANEOUS OBJECTIOIiS TO THE

Cetaceans, with the functions of the parts slowly clmnging
during the progress of development, as are the gradations
in the beaks of the different existing members of the duck-
family. We should bear in mind that each species of duck
is subjected to a severe struggle for existence, and that the
structure of every part of its frame must be well adapted
to its conditions of life.

The Pleuronectid^e, 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
color, less developed in many ways than the upper side,
with the lateral fins often of smaller size. But the eyes
offer the most remarkable 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 colored.
Soon the eye proper to the lower side begins to glide
elovvly 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 while lying
in its habitual position on one side. The lower eye would,
also, have been liable to be abraded by the sandy bottom.
That the Pleuronectidae are admirably adapted by their
flattened and asymmetrical structure for their habits of
life, is manifest from several species, such as soles, flound-
ers, etc., being extremely common. The chief advantages
thus gained seem to be protection from their enemies, and
facility for feeding on the ground. The different mem-
bers, however, of the family present, as Schiodte remarks,
*^a long series of forms exhibiting a gradual transition
from Hippoglossus pinguis, which does not in any consid^
erable degree alter the shape in which it leaves the ovum,
to the soles, which are entirely thrown to one side.""*

Mr. Mivart has taken up this case, and remarks that a
sudden spontaneous transformation in the position of the
eyes is hardly conceivable, in which I quite agree with him.
He then adds: '^ If the transit was gradual, then how such
transit of one eye a minute fraction of the journey toward

TEEOR Y OF NA TUBAL SELECTION. ^'i I

the other side of the head could benefit the iiidividudl i,-,
indeed, far from clear. It seems, even, that sucli an in-
cipient transformation must rather have been iiijurious."
But he might have found an answer to this objection in
the excellent observations published in 1867 by Malm.
The Pleuronectidffi, while very young and still symmetri-
cal, with their eyes standing on opposite sides of the head,
cannot long retain a vertical position, owing to the exces-
sive depth of their bodies, the small size of their lateral
fins, and to their being destitute of a swim-bladder.
Hence, soon growing tired, they fall to the bottom on one
side. While thus at rest they often twist, as Malm ob-
served, the lower eye upward, 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 consequently becomes, as could be plainly seen, tem-
porarily 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 mus-
cular action. It is also known with the higher animals,
even after early vouth, that the skull vields and is altered
in shape, if the skin or muscles be permanently contracted
through disease or some accident. With long-eared rab-
bits, if one ear flops forward and downward, its weight
drags forward all the bones of the skull on the same side,
of which I have given a figure. Malm states that tlie
newly-hatched young of perches, salmon, and several other
symmetrical fishes, have the hal3it 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 upward;
and their skulls are thus rendered rather crooked. These
fishes, however, are soon able to hold themselves in a ver-
tical position, and no permanent effect is thus produced.
With the Pleuronectidse, on the other hand, the older they
grow the more habitually they rest on one side, owing to
the increasing flatness of their bodies, and a permanent
effect is thus produced on the form of the head, and on the
position of the eyes. Judging from analogy, tlie tendency
to distortion would no doubt be increased through the
principle of inheritance. Schiodte believes, in opposition

222 MISCELLANEOUS OBJECTIONS TO THE

to some other naturalists, that the Pleuronecticlae are not
quite symmetrical even in the embryo; and if this be so,
we could understand how it is that certain species, while
young, habitually fall over and rest on the left side, and
other species on the right side. Malm adds, in confirma-
tion of the above view, that the adult Trachypterus arcti-
cus, which is not a member of the Pleuronectid^, rests on
its left side at the bottom, and swims diagonally through
the water; and in this fish, the two sides of the head are
said to be somewhat dissimilar. Our great authority on
Fishes, Dr. Giinther, concludes his abstract of Malm^s
paper, by remarking that '^the author gives a very simple
explanation of the abnormal condition of the Pleu-
ronectoids."

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 endeavoring to look upward with both
eyes, while 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 toward the
lower surface, with the jaw bones stronger and more effect-
ive 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 Yarrel
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 colorless state of the ventral sur-
face of most fishes and of many other animals, we may
reasonably suppose that the absence of color in flat-fish on
the side, whether it be the right or left, which is under-
most, is due to the exclusion of light. But it cannot be
supposed that the peculiar speckled appearance of the
upper side of the sole, so like the sandy bed of the sea, or
the power in some species, as recently shown by Pouchet,

THEORY OF NATURAL SELECTION, 2*23

of changing their color in accordance with tlie surround-
ing surface, or the presence of bony tubercles on the u})per
side of the tnrbot, are due to the action of the liglit.
Here natural selection has probably come into play, as well
as in adapting the general shape of the body of these
fishes, and many other peculiarities, to their habits of life.
We should keep in mind, as I have before insisted, that
the inherited effects of the increased use of parts, and per-
haps of their disuse, will be strengthened by natural selec-
tion. For all spontaneous variations in the right direc-
tion will thus be preserved; as will those individuals which
inherit in the highest degree the effects of the increased
and beneficial use of any part. How much to attribute in
each particular case to the effects of use, and how much to
natural selection, it seems impossible to decide.

I may give another instance of a structure which appar-
ently owes its origin exclusively to use or habit. The
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 everv detail, remarks on this structure: "It is
impossible to believe that in any number of ages the first
slight incipieut tendency to grasp could preserve the lives
of the individuals possessing it, or favor their chance of
having and of rearing offspring. ^^ But there is no neces-
sity 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 pos-
sess a structurally prehensive 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 analo-
gous account from Dr. Giinther, who has seen a
mouse thus suspend itself. If the harvest mouse had
been more strictly arboreal, it would perhaps have
had its tail rendered structurally prehensile, as is
the case with some members of the same order. Why

25^4 MISCELLANEOUS OBJECTIONS TO THE

Cercopitheciis, considering its habits while young, has not
become thus provided, it would be difficult to say. It is,
however, possible that the long tail of this monkey may be
of more service to it as a balancing organ in making ita
prodigious leaps, than as a prehensile organ.

The mammary glands are common to the whole class of
mammals, and are indispensable for their existence; they
must, therefore, have been developed at an extremely
remote period, and v/e can know nothing positively about
their manner of development. Mr. Mivart asks: ^^Is it
conceivable that the young of any animal was ever saved,
from destruction by accidentally sucking a drop of scarcel}''
nutritious fluid from an accidentally hypertrophied cuta-
neous 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 marsu-
pial form; and if so, the mammary 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 a secretion from the cutaneous
glands of the sack. Now, with the early progenitors of
mammals, almost before they deserved to be thus desig-
nated, is it not at least possible that the young might have
been similiarly nourished? And in this case, the individu-
als which secreted a fluid, in some degree or manner the
most nutritious, so as to partake of the nature of milk,
Avould in the long run have reared a larger number of well-
nourished offspring, than would the individuals which
secreted a poorer fluid; and thus the cutaneous glands,
which are the liomologues of the mammary glands, would
have been improved or rendered more effective. It accords
with the widely extended principle of specialization, that
the glands over a certain space of the sack should have
become more highly developed than the remainder; and
they would then have formed a breast, but at first without
a nipple, as we see in the Ornithorhyncus, at the base of
the mammalian series. Through what agency the glands

THEORY OF J^ATURAL SELECTION. 225

over a certain space became more highly specialized than
the others, I will not pretend to decide, wlietlier 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 atfected
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 mammals
have instinctively learned to suck the breast, than in under-
standing how unhatched chickens have learned to break the
egg-shell by tapping against it with their specially adapted
beaks; or how a few hours after leaving the shell they have
learned to pick up grains of food. In such cases the most
probable solution seems to be, that the habit was at first
acquired by practice at a more advanced age, and after-
ward 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 oif spring. 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 wind-pipe. 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 selection remove in the
adult kangaroo (and in most other mammals, on the assump-
tion that they are descended from a marsupial form), ''this
at least perfectly innocent and harmless structure?" It
may be suggested in answer that the voice, which is cer-
tainly of high importance to many animals, could hardly
have been used with full force as long as the larynx en-
tered the nasal passage; and Prof essor 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 divisions
of the animal kingdom. The Echinoderniata (star-fishes,
sea-urchins, etc.) are furnished with remarkable organs,
called pedicellarias, which consist, when well developed, of

226 MISCELLANEOUS OBJECTIONS TO TEE

a tridactyle forceps — that is, of one formed of three ser«
rated arms, neatly fitting together and placed on the
summit of a flexible stem, moved by muscles. These for-
ceps can seize firmly hold of any object; 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 defence.

With respect to these organs, Mr. Mivart, as on so many
previous occasions, asks: '^ What would be the utility of
the first rudimentary hegimiings of such structures, and
how could such insipient buddings have ever preserved the
life of a single Echinus?" He adds, ^'^not even the sudden
development of the snapping action could have been bene-
ficial without the freely movable stalk, nor could the
latter have been efficient without the snapping jaws, yet
no minute, merely indefinite variations could simultane-
ously 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 capa-
ble 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, in-
forms 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 de-
scribed by M. Perrier as bearing two kinds of pedicellariae,
one resembling those of Echinus, and the other those of
Spatangus; and such cases are always interesting as afford-
ing the means of ajoparently sudden transitions, through
the abortion of one of the two states of an organ.

With respect to the steps by which these curious organs
have been evolved, Mr. Agassiz infers from his own re-
searches and those of Mr. Miiller, that both in star-fishes
and sea-urchins the pedicellariBe must undoubtedly be
looked at as modified spines. This may be inferred from
their manner of development in the individual, as well as

THEORY OF NATURAL SELECTION. 227

from a long and perfect series of gradations in different
species and genera, from simple granules to ordinary
spines, to perfect tridactyle pedicellariae. The gradation
extends even to the manner in whicli ordinary spines and
the pedicellariae, with their supporting calcareous rods, are
articulated to the shell. In certain genera of star-fishes,
"the very combinations needed to show that the pedicel-
lariae are only modified branching spines'' may be found.
Thus we have fixed spines, with three equi-distant, serrated,
movable branches, articulated to near their bases; and
higher up, on the same spine, three other movable
branches. Now when the latter arise from the summit of
a spine they form, in fact, a rude tridactyle pedicellariae,
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 pedicellariae and the movable
branches of a spine, is unmistakable. It is generally
admitted that the ordinary spines serve as a protection;
and if so, there can be no reason to doubt that those fur-
nished with serrated and movable branches likewise serve
for the same purpose; and they would thus serve still more
effectively as soon as by meeting together they acted as a
prehensile or snapping apparatus. Thus every gradation,
from an ordinary fixed spine to a fixed pedicellariae, would
be of service.

In certain genera of star-fishes these organs, instead of
being fixed or borne on an immovable support, are placed on
the summit of a flexible and muscular, though short, stem;
and in this case they probably subserve some additional
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 movable. I wish I had
space here to give a fuller abstract of Mr. Agassiz's inter-
esting observations on the development of the pedicellarite.
All possible gradations, as he adds, may likewise be found
between the pedicellariae of the star-fishes and the hooks
of the Ophiurians, another group of the Echinodermata;
and again between the pedicellariae of sea-urchins and the
anchors of the Holothuriae, also belonging to the same
great class.

Certain compound animals, or zoophytes, as they have

228 MISCELLANEOUS OBJECTIONS TO TEE

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 ob-
served by me, all the avicularia on the same branch often
moved simultaneously backward and forward, with the
lower jaw widely open, through an angle of about 90
degrees, in the course of five seconds; and their movement
caused the whole polyzoary to tremble. When the jaws
are touched with a needle they seize it so firmly that the
branch can thus be shaken.

Mr. Mivart adduces this case, chiefly on account of the
supposed difficulty of organs, namely the avicularia of
the Polyzoa and the pedicellariae of the Echinodermata,
which lie considers as ^^ essentially similar,^' having been
developed through natural selection in widely distinct
divisions of the animal kingdom. But, as far as struct-
ure is concerned, I can see no similarity between tridac-
tyle pedicellariae and avicularia. The latter resembles
somewhat more closely the chelae or pincers of Crusta-
ceans; and Mr. Mivart might have adduced with equal
appropriateness this resemblance as a special difficulty, or
even their resemblance to the head and beak of a bird.
The avicularia are believed by Mr. Busk, Dr. Smitt and
Dr. Nitsche — naturalists who have carefully studied this
group — to be homologous with the zooids and their cells
which compose the zoophyte, the moveable lip or lid of the
cell corresponding with the lower and movable mandible of
the avicularium. Mr. Busk, however, does not know of
any gradations now existing between a zooid and an avicu-
larium. 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 chelae of Crustaceans resemble in some degree the
avicularia of Polyzoa, both serving as pincers, it may be
worth while to show that with the former a long series of
serviceable gradations still exists. In the first and simplest
stage, the terminal segment of a limb shuts down either on
the square summit of the broad penultimate segment, or

THEORY OF NATURAL SELECTION, 229

against one whole side, and is thus enabled to catch hold
of an object, but the limb still serves as an organ of loco-
motion. We next find one corner of the broad penulti-
mate segment sliglitly prominent, sometimes furnished
with irregular teeth, and against these the terminal seg-
ment shuts down. By an increase in the size of this pro-
jection, with its sluipe, as well as that of the terminal
segment, slightly moclitied and improved, the pincers are
rendered more and more perfect, until we have at last an
instrument as efficient as the chelsB 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 ofteu moved simultaneously; so that, acting
like long oars, they swept a branch rapidly across the object-
glass of my microscope. When a branch was placed on its
face, the vibracula became entangled, and they made vio-
lent 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 m.ight be noxious to the delicate
inhabitants of the cells when their tentaciila are pro-
truded.^^ The avicularia, like the vibracula, probably
serve for defence, but they also catch and kill small living
animals, which, it is believed, are afterward 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 dif-
ferent in appearance than a bristle or vibraculum, and an
avicularium" like the head of a bird: vet thev are almost
certainly homologous and have been developed from the
same common source, namely a zooid with its 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 movable mandible is so much produced ami
is so like a bristle that the presence of the upper or lixod
beak alone serves to determine its avicularian nature. The

230 MISCELLANEOUS OBJECTIONS TO 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 trans-
formation, the other parts of the cell, with the included
zooid, could hardly have disappeared at once. In many
cases the vibracula have a grooved support at the base,
which seems to represent the fixed beak; though this sup-
port in some species is quite absent. This view of the de-
velopment of the vibracula, if trustworthy, is interesting;
for supposing that all the species provided with avicularia
had become extinct, no one with the most vivid imagina-
tion would ever have thought that the vibracula had orig-
inally 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 movable lip of the cell serves as a protec-
tion 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 different
ways and under different circumstances.

In the vegetable kingdom Mr. Mivart only alludes to two
cases, namely the structure of the flowers of orchids, and
the movements of climbing plants. With respect to the
former, he says: " The explanation of their origin is deemed
thoroughly unsatisfactory — utterly insufficient to explain
the incipient, infinitesimal beginnings of structures which
are of utility only when they are considerably developed."
As I have fully treated this subject in another work, I will
here give only a few details on one alone of the most strik-
ing peculiarities of the flowers of orchids, namely, their pol-
linia. A pollinium, when highly developed, consists of a
mass of pollen-grains, affixed to an elastic foot-stalk or
caudicle, and this to a little mass of extremely viscid
matter. The pollinia are by this means transported by in-
sects 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 consid-
ered; yet I may mention that at the base of the orchida-

THEORY OF NATURAL SELECTION. '^31

ceous series, in Cypripedium, we can see how the threads
were probably first developed. In other orchids the
threads cohere at one end of the pollen-masses; and this
forms the first or nascent trace of a caudicle. That this is
the origin of the caudicle, even when of considerable
length and highly developed, we have good evidence in the
aborted pollen-grains which can sometimes be detected em-
bedded within the central and solid parts.

Vv'ith respect to the second chief peculiarity, namely, the
little mass of viscid matter attached to the end of the cau-
dicle, a long series of gradations can be specified, each of
plain service to the plant. In most flowers belonging to
other orders the stigma secretes a little viscid matter. Now,
in certain orchids similar viscid matter is secreted, but in
much larger quantities by one alone of the three stigmas;
and this stigma, perhaps in consequence of the copious
secretion, is rendered sterile. When an insect visits a
flower of this kind, it rubs off some of the viscid matter,
and thus at the same time drags away some of the
pollen-grains. From this simple condition, which differs
but little from that of a multitude of common
flowers, there are endless gradations — to species in which
the pollen-mass terminates in a very short, free cau-
dicle— to others in which the caudicle becomes firmly at-
tached to the viscid matter, with the sterile stigma itself
much modified. In this latter case we have a polliuium
in its most highly developed and perfect condition. He
who will carefully examine the flowers of orchids for
himself will not clenv 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 the ordinary flowers, to a highly comjilex
pollinium, admirably adapted for transportal by insects ;
nor will he deny that all the gradations in the several
species are admirably adapted in relation to the general
structure of each flower for its fertilization by different
insects. In this, and in almost every other case, the in-
quiry may be pushed further backward ; and it may be
asked how did the stigma of an ordinary flower become
viscid, but as we do not biow the full history of any one
group of beings, it is as useless to ask, as it is hopeless to
attempt answering, such questions.

232 MISCELLANEOUS OBJECTIONS TO THE

We will now turn to climbing plants. These can be ar-
ranged in a long series, from those which simply twine
round a support, to those which I have called leaf-climbers,
and to those provided with tendrils. In these two latter
classes the stems have generally, but not always, lost the
power of twining, though they retain the power of revolv-
ing, which the tendrils likewise possess. The gradations
from leaf-climbers to tendril bearers are wonderfully close,
and certain plants may be differently placed in either
class. But in ascending the series from simple twiners to
leaf-climbers, an important quality is added, namely sen-
sitiveness to a touch, by which means the foot-stalks of the
leaves or flowers, or these modified and converted into ten-
drils, 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 beneficial in a high degree to the species.
For instance, it is clearly a great advantage to a twining
plant to become a leaf-climber; and it is probable that
every twiner which possessed leaves with long foot-stalks
would have been developed into a leaf-climber, if the foot-
stalks had possessed in any slight degree the requisite sen-
sitiveness to a touch.

As twining is the simplest means of ascending a support,
and forms the basis of our series, it may naturally be asked
how did plants acquire this power in an incipient degree,
afterward to be improved and increased through natural
selection. The power of twining depends, firstly, on the
stems while young being extremely flexible (but this is a
character common to many plants which are not climbers) ;
and, secondly, on their continually 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 part of a stem strikes against any object and
is stopped, the upper part still goes on bending and revolv-
ing, 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
qf revolving, and have thus become twiners, they must have

THEORY OF NATURAL SELECTION. 233

in'lependently acquired it, and cannot have inherited it from
a common progenitor. Hence, I was led to predict that
some slight tendency to a movement of this kind would
be found to be far from uncommon with plants which did
not climb; and that this had afforded the basis for natural
selection to work on and improve. When I made this pre-
diction, I knew of only one imperfect case, namelv, 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 afterward
Fritz Miiller discovered that the young stems of an Alisma
and of a Linum — plants which do not climb and are widely
separated in the natural system — revolved plainly, though
irregularly; and he states'^ that he has reason to suspect
that this occurs with some other plants. These slight
movements appear to be of no service to the plants in ques-
tion; anyhow, they are not of the least use in the way of
climbing, which is the point that concerns us. Neverthe-
less 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 utilized through natural selection, until they
had become converted into well-developed twining species.
With respect to the sensitiveness of the foot-stalks
of the leaves and flowers, and of tendrils, nearly the
same remarks are applicable as in the case of the revolv-
ing 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 toward the side which was touched.
Morren found in several species of Oxaiis that the leaves
and their foot-stalks moved, especially after exposure to a
hot sun, when they were gently and repeatedly touciied, or
when the plant was shaken. I repeated these observations
on some other species of Oxaiis with the same result; in
some of them the movement wjis 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

234 MISGELLANEOUIS OBJECTIONS TO THE

authority of Ilofmeister, 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 tliat the foot-stalks and tendrils are sensitive.

It is scarcely possible that the above slight movements,
due to a touch or shake, in the 3'Oung and growing organs
of plants, can be of any functional importance to them.
But plants i^ossess, in obedience to various stimuli, powers
of movement^ which are of manifest importance to them;
for instance, toward and more rarely from the light —
in opposition to, and more rarely in the direction of, the
attraction of gravity. When the nerves and muscles of an
a?iimal are excited by galvanism or by the absorption of
strychnine, the consequent movements may be called an
incidental result, for the nerves and muscles have not been
rendered specially sensitive to these stimuli. So with
plants it appears that, from having the power of movement
in obedience to certain stimuli, they are excited in an in-
cidental manner by a touch, or by being shaken. Hence
there is no great difficulty in admitting that in the case of
leaf-climbers and tendril-bearers, it is this tendency which
has been taken adrantage of and increased through natural
selection. It is, however, probable, from reasons which I
have assigned in my memoir, that this wdll have occurred
only with plants which had already acquired the power
of revolving, and had thus become twiners.

I have already endeavored 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, nat-
ural 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 skillful natu-
ralist, to prove that natural selection is incompetent to ac-
count for the incipient stages of useful structures; and I

THEOHY OF NATURAL SELECTION, 235

have shown, as I hope, that there is no great difliculty on
this head. A good opportunity has thus been alTorded for
enlarging a little on gradations of structure, often associ-
ated with strange functions — an important subject, which
was not treated at sufificient length in the former editions
of this work. I will now briefly recapitulate tlie foregoing
cases.

With the giraffe, the continued preservation of tlie indi-
viduals of some extinct high-reaching ruminant, whicli had
the longest necks, legs, etc., and could browse a little
above the average height, and the continued destruction of
those which could not browse so high, would have sufficed
for the production of this remarkable quadruped; but the
prolonged use of all the parts, together with inheritance,
will have aided in an important manner in their co-ordina-
tion. With the many insects which imitate various ob-
jecii^, there is no improbability in the belief that an acci-
dental resemblance to some common object was in each case
the foundation for the work of natural selection, since per-
fected through the occasional preservation of slight variations
which made the resemblance at all closer; and this will have
been carried on as long as the insect continued to vary,
and as long as a more and more perfect resemblance led to
its escape from sharp-sighted enemies. In certain species
of whales there is a 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 favor-
able variations, until the points were converted, first into
lamellated knobs or teeth, like those on the beak of a
goose — then into short lamellae, like those of the domestic
ducks — and then into lamellae, as perfect as those of the
shoveller-duck — and finally into the gigantic plates of
baleen, as in the mouth of the Greenland whale. In the
family of the ducks, the lamellae are first used as teetli,
then partly as teeth and partly as a sifting apparatus, and
at last almost exclusively for this latter purpose.

With such structures as the above lamella3 of horn or
whalebone, habit or use can have done little or nothing, as
far as we can judge, toward 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 con-

236 MISCELLANEOUS OBJECTIONS TO THJB

tinned use, together with inheritance. With respect to
the mammae of tlie higher animals, the most probable con-
jcctui-e 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, Tn which case they would have formed a mamma.
There is no more difficulty in understanding how the
branched spines of some ancient Echinoderm, which
served as a defence, became developed through natural
selection into tridactyle pedicellarice, than in understand-
ing tlie development of the pincers of crustaceans, through
slight, serviceable modifications in the ultimate and pe-
nultimate 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 originally served to tie together the pollen-
grains, can be traced cohering into caudicles; and the steps
can likewise be followed by which viscid matter, such as
that secreted by the stigmas of ordinary flowers, and still
subserving nearly but not quite the same purpose, became
attached to the free ends of the caudicles — all these grada-
tions being of manifest benefit to the plants 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 advan-
tageous? But it is unreasonable to expect a precise answer
to such questions, considering our ignorance of the past
history of each species, and of the conditions which at the
present day determine its numbers and range. In most
cases only general reasons, but in some few cases special
reasons, can be assigned. Thus to adapt a species to new
habits of life, many co-ordinated modifications are almost
indispensable, and it may often have happened that the
requisite parts did not vary in the right manner or to the
right degree. Many species must have been prevented
from increasing in numbers through destructive agencies,

THEORY OF NATURAL iSELECTloN, 237

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 struct-
nres, they could not have been acquired through natural
selection. In many cases complex and long-enduring con-
ditions, often of ^a peculiar nature, are necessary for the
development of a structure; and the requisite conditions
may seldom have concurred. The belief that any given
structure, which we think, often erroneously, would have
been beneficial to a species, v^ould have been gained under
all circumstances through natural selection, is opposed to
fvhat we can understand of its manner of action. Mr.
Mivart does not deny that natural selection has effected
something; but he considers it as " demonstrably insuf-
ficient " to account for the phenomena which I explain by
its agency. His chief arguments have now been con-
sidered, and the others will hereafter be considered. They
seem to me to partake little of the character of demonstra-
tion, and to have little weight in comparison with those in
favor 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 ad-
vanced for the same purpose in an able article lately pub-
lished in the ''Medico-Chirurgical Review."

At the present day almost all naturalists admit evolution
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 evolu-
tionists; but there is no need, as it seems to me, to invoke
anv internal force beyond the tendency to ordinary varia-
bility, which through the aid of selection, by man has given
rise to many well-adapted domestic races, and which,
through the aid of natural selection, would equally well
give rise by graduated steps to natural races or species.
The final result will generally have been, as already ex-
plained, an advance, but in some few cases a retrogression,
in organization.

Mr. Mivart is further inclined to believe, and some
naturalists agree with him, that new species manifest
themselves '* with suddenness and by modifications appear-

2:ib MISCELLANEOUS OBJECTIONS TO THE

ing at once." For instance, he supposes that the differ-
ences 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 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 improbable in the highest degree.

Every one who believes in slow and gradual evolution,
will of course admit that specific changes may have been
as abrupt and as great as any single variation which we
meet with under nature, or even under domestication.
But as species are more variable when domesticated or cul-
tivated than under their natural conditions, it is not prob-
able that such great and abrupt variations have often
occurred under nature, as are known occasionally to arise
under domestication. Of these latter variations several
may be attributed to reversion; and the characters which
thus reappear were, it is probable, in many cases at first
gained in a gradual manner. A still greater number must
be called monstrosities, such as six-fingered men, porcupine
men, Ancon sheep, Niata cattle, etc.; and as they are
widely different in character from natural species, they
throw very little light on our subject. Excluding such
cases of abrupt variations, the few which remain would at
best constitute, if found in a state of nature, doubtful
species, closely related to their parental types.

My reasons for doubting whether natural species have
changed as abruptly as hare occasionally domestic races,
and for entirely disbelieving that xhey have changed in the
wonderful manner indicated by Mr. Mivart, are as follows.
According to our experience, abrupt and strongly marked
variations occur in our domesticated 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 causes of destruction and by subse-
quent intercrossing; and so it is known to be under do-
mestication, unless abrupt variations of this kind are spec-
ially preserved and separated by the care of man. Hence,
in order that a new species should suddenly a^^pear in the
manner supposed by Mr. Mivart, it is almost necessary to

THEOR Y OF NA TURA L SF.L EOT ION, 239

believe, in opposition to all analogy, that several wonder-
fully changed individuals appeared simultaneously within
the same district. This difficulty, as in the case of uncon-
scious selection by man, is avoided on the theory of gradual
evolution, through the preservation of a large number of
individuals, which varied more of less in any favorable
direction, and of the destruction of a large number which
varied in an opposite manner.

That many species have been evolved in an extremely
gradual manner, there can hardly be a doubt. The species
and even the genera of many large natural families are so
closely allied together that it is difficult to distinguish not
a few of them. On every continent, in proceeding from
north to south, from lowland to upland, etc., we meet with
a host of closely related or representative species; as we
likewise do on certain distinct continents, which we have
reason to believe were formerly connected. But in making
these and the following remarks, I am compelled to allude to
subjects hereafter to be discussed. Look at the many out-
lying islands round a continent, and see how many of their
inhabitants can be raised only to the rank of doubtful
species. So it is if we look to past times, and compare the
species which have just passed away with those still living
within the same areas; or if we compare the fossil species
imbedded in the sub-stages of the same geological forma-
tion. It is indeed manifest that multitudes of species
are related in the closest manner to other species that still
exist, or have lately existed; and it will hardly be main-
tained 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, instead of to dis-
tinct species, that numerous and wonderfully fine grada-
tions can be traced, connecting together widely different
structures.

Many large groups of facts are intelligible only on the
principle that species have been evolved by very small steps.
For instance, the fact that the species included in the
larger genera are more closely related to each other, and
present a greater number of varieties than do the species
in the smaller genera. The former are also grouped in
little clusters, like varieties round species; and they pi-esent
other analogies with varieties, as was shown in our second

240 MISCELLANEOUS OBJECTIONS TO TEE

chapter. On this same principle we can understand liow
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 favor of
this view, such as the sudden crystallization of inorganic
substances, or the falling of a facetted 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 sup-
ports at first sight the belief in abrupt development. But
the value of this evidence depends entirely on the perfec-
tion of the geological record, in relation to periods remote
in the history of the world. If the record is as frag-
mentary as many geologists strenuously assert, there is
nothing strange in new forms appearing as if suddenly
developed.

Unless we admit transformations as prodigious as those
Advocated by Mr. Mivart, such as the sudden development-
of the wings of birds or bats, or the sudden conversion of
a Ilipparion into a horse, hardly any light is thrown by the
belief in abrupt modifications on the deficiency of connect-
ing links in our geological formations. But against the
belief in such abrupt changes, embryology enters a strong
protest. It is notorious that the wings of birds and bats,
and the legs of horses or other quadrupeds, are undis-
tinguishable at an eariy embryonic period, and that they
become differentiated by insensibly fine steps. Embryo-
logical resem Glances 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 trans-
mitted their newly-acquired characters to their offspring,
at a corresponding age. The embryo is thus left almost

1

TEEOR Y OF NA TUBAL SELECTION. 24 V

unailiocted, and serves as a record of the past condition of
the species. Hence it is that existing species during the
early stages of their development so often resemble ancient
and extinct forms belonging to the same class. On this
view of the meaning of erabryological resemblances, and
indeed on any view, it is incredible that an animal
should have undergone such momentous and abrupt trans-
formations as those above indicated, and yet should not
bear even a trace in its embryonic condition of any sudden
modification, every detail in its structure being developed
by insensibly fine steps.

He who believes that some ancient form was transformed
suddenly through an internal force or tendency into, for
instance, one furnished with wings, will be almost com-
pelled to assume, in opposition to all analogy, that many
individuals varied simultaneouslv. It cannot be denied
that such abrupt and great changes of structure are widely
different from those which most species apparently have
undergone. He will further be compelled to believe that
many structures beautifully adapted to all the other parts
of the same creature and to the surrounding conditions,
have been suddenly produced; and of such complex and
wonderful co-adaptations, he will not be able to assign a
shadow of an explanation. He will be forced to admit
that these great and sudden 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.

2U INSTINCT.

CHAPTER VIII.

IKSTI>^^CT.

Instincts comparable with habits, but different in their origin —
Instincts graduated — Aphides and ants — Instincts 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 development
will probably appear to the reader a difficulty sufficient to
overthrow my whole theory. I may here premise, that I
have nothing to«do with the origin of the mental powers,
any more than I have with that of life itself. We are con-
cerned only with the diversities of instinct and of the
other mental faculties in animals of the same class.

I will not attempt any definition of instinct. It would
be easy to show that several distinct mental actions are
commonly embraced by this term; but every one under-
stands what is meant, when it is said that instinct impels
the cuckoo to migrate and to [lay her eggs in other birds'
nests. An action, which we ourselves require experience
to enable us to perform, when performed by an animal,
more especially by a very young one, without experience,
and when performed by many individuals in the same way,
without their knowing for what purpose it is performed, is
usually said to be instinctive. But I could show that none
of these characters are universal. A little dose of judg-
ment or reason, as Pierre Ruber expresses it, often comes
into play, even with animals low in the scale of nature.

Frederick Cuvier and several of the older metaphysicians
have compared instinct with habit. This comparison
gives, I think, an accurate notion of the frame of mind

i

INSTINCT, 243

under which an instinctive action is performed, but not
necessarily of its origin. How unconsciously many habitual
actions are performed, indeed not rarely in direct oppo-
sition 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 instincts and habits could be pointed out. As in
repeating a well-known song, so in instincts, one action
follows another by a sort of rhythm; if a person be 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 caterpillar,
which makes a very complicated hammock; for if he took
a caterpillar which had completed its hammock up to, say,
the sixth stage of construction, and put it into a hammock
completed up only to the third stage, the caterpillar simply
re-performed the fourth, fifth and sixth stages of con-
struction. 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 was much embaiTassed, 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 already finished work.

If we suppose any habitual action to become inherited —
and it can be shown that this does sometimes happen —
then the resemblance between what originally was a habit
and an instinct becomes so close as not to be distinguished.
If Mozart, instead of playing the piano-forte 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 hj
habit in one generation, and then transmitted by inherit-
ance to succeeding generations. It can be clearly shown
that the most wonderful instincts with whicli 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 instiucts are as im-

244 INSTINCT,

portant 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 selection preserving
and continually accumulating variations of instinct to any
extent that was profitable. It is thus, as I believe, that all
the most complex and wonderful instincts have originated.
As modifications of corporeal structure arise from, and are
increased by, use or habit, and are diminished or lost by
disuse, so I do not doubt it has been with instincts. But
I believe that the effects of habit are in many cases of sub-
ordinate 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 accumu-
lation of numerous slight^ yet profitable, variations. Hence,
as in the case of corporeal structures, we ought to find in
nature, not the actual transitional gradations by which
each complex instinct has been acquired — for these could
be found only in the lineal ancestors of each species — but
we ought to find in the collateral lines of descent some
evidence of such gradations; or we ought at least 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, except in Europe and North America,
and for no instinct being known among extinct species, how
very generally gradations, leading to the most complex in-
stincts, can be discovered. Changes of instinct may some-
times 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 circumstances,
etc. ; in which case either the one or the other instinct
might be preserved by natural selection. And such in-
stances of diversity of instinct in the same species 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

INSTINCT. 2io

for itself; but has never, as far as we can judge, been jiro-
diiced for the exclusive good of others. One of tlie strou"--
est instances of an animal apparently perform in or an
action for the sole good of another, with which 1 uui
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 re-
moved all the ants from a group of about a dozen aphides
on a dock-plant, and prevented their attendance during
several hours. After this interval, I felt sure that the
aphides would want to excrete. I watched them for some
time through a lens, but not one excreted; I then tickled
and stroked them with a hair in the same manner, as well
as I could, as the ants do with their antennae; but not
one excreted. Afterward, 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 begun to play with its antennas on the abdomen
first of one aphis and then of another; and each, as soon us
it felt the antennae, immediately lifted up its abdomen and
excreted a limped drop of sweet juice, which was eagerly
devoured by the ant. Even the quite young aphides be-
haved in this manner, showing that the action was instinc-
tive, and not the result of experience. It is certain, from
the observations of Huber, that the aphides show no dis-
like to the ants: if the latter be not present they are at
lavSt compelled to eject their excretion. But as the excre-
tion is extremely viscid, it is no doubt a convenience to
the aphides to have it removed; therefore probably they do
not excrete solely for the good of the ants. Although
there is no evidence that any animal performs an action
for the exclusive good of another species, yet each tries to
take advantage of the instincts of others, as each takes
advantage of the weaker bodily structure of other
species. So again certain instincts can not 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 sucli variations, are indis-
pensable for the action of natural selection, as many
instances as possible ought to be given; but want of space

246 INSTINCT.

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 dependence on the situations
chosen, and on the nature and temperature of the country
inhabited, but often from causes wholly unknown to us.
Audubon has given several remarkable cases of differences
in the nests of tlie same species in the northern and south-
ern 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 w^as deficient?" But what
other natural material could bees use? They will work, as
I have seen, with wax hardened with vermilion or soft-
ened with lard. Andrew Knight observed that his bees,
instead of laboriously collecting propolis, used a cement of
■wax and turpentine, with which he had covered decor-
ticated trees. It has lately been shown that bees, instead
of searching for pollen, will gladly use a very different
Bubstance, namely, oatmeal. Fear of any particular enemy
is certainly an instinctive quality, as may be seen in nest-
ling birds, though it is strengthened by experience, and by
the 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 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.

Tliat the mental qualities of animals of the same kind,
born in a state of nature, vary much, could be shown by
many facts. Several cases could also be adduced of occa-
sional and strange habits in wild animals, which, if advan-
tageous 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.

CHANGES OF HABIT OH INSTINCT. 2V

IJ^fHERITED CHANGES OF HABIT OR INSTINCT IX DOilES-

TICATED ANIMALS.

^ The possibility, or even probability, of inherited varia-
tions of instinct in a state of nature will be strengtliened
by briefly considering a few cases under domestication.
We shall thus be enabled to see the part wliich habit and
the selection of so-called spontaneous variations have played
in modifying the mental qualities of our domestic animals.
It is notorious how much domestic animals vary in tlioir
mental qualities. With cats, for instance, one naturally
takes to catching rats, and anotlier mice, and these ten-
dencies are known to be inherited. One cat, according to
Mr. St. John, always brought home game birds, anotlier
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 minds 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 striking instances) will
sometimes point and even back other dogs the very first
time that they are taken out; retrieving is certainly in
some degree inherited by retrievers; and a tendency to run
round, instead of at, a flock of sheep, by shepherd dogs.
I cannot see that these actions, performed without experi-
ence by the young, and in nearly the same manner by each
individual, performed with eager delight by each breed,
and without the end being known — for the young pointer
can no more know that he points to aid his master, than
the white butterfly knows why she lays her eggs on the leaf,
of the cabbage — I cannot see that these actions dilTep
essentially from true instincts. If we were to beliold one
kind of wolf, when young and without any training, aa
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 instincts; but they have been acted on by far lesa

248 CHANGES OF HABIT OR INSTINCT

rigorous selections, and have been transmitted for an
incomparably shorter period, under less fixed conditions of

life.

IIow strongly these domestic instincts, habits, and
dispositions are inherited, and how curiously they
become mingled, is well shown when different breeds of
dogs are crossed. Thus it is known that a cross with a
bull-dog has affected for many generations the courage and
obstinacy of greyhounds; and a cross with a greyhound
has given to a whole family of shepherd-dogs a tendency
to hunt hares. These domestic 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 Eoy describes a dog, whose great-grandfather
was a wolf, and this dog showed a trace of its wild parent-
age only in one way, by not coming in a straight line to
his master, when called.

Domestic instincts are sometimes spoken of as actions
which have become inherited solely from long-continued
and 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 selection of the best individ-
uals in successive generations made tumblers what they
now are; and near Glasgow there are house- tumblers, as I
hear from Mr. Brent, which can not 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 prob-
ably, as many have thought, only the exaggerated pause of
an animal preparing to spring on its prey. When the first
tendency to point was once displayed, methodical selection
and the inherited effects of comj^ulsory training in each
successive generation would soon complete the work; and
unconscious selection is still in progress, as each man tries
to procure, without intending to improve the breed, dogs

IN DOMKtiTlCATKD ANIMALS. 249

which stand and hunt best. On the other liund, habit
alone in some cases has sufficed; hardly any animal is
more difficult to tame than the young of the wild rabbit;
scarcely any animal is tamer than the young of the tame
rabbit; but I can hardly suppose that domestic rabbits have
often been selected for tameness alone; so that we must
attribute at least the greater part of the inherited change
from extreme wildness to extreme tameness, to habit and
long-continued close confinement.

Natural instincts are lost under domestication: a re-
markable instance of this is seen in those breeds of fowls
which A^ery rarely or never become "broody," that is, never
wish to sit on their eggs. Familiarity alone prevents our
seeing how largely and how permanently the minds of our
domestic animals have been modified. It is scarcely pos-
sible 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 incur-
able in dogs which have been brought home as puppies from
countries such as Tierra del Fuego and Australia, where the
savages do not keep these domestic animals. How rarely, on
the other hand, do our civilized dogs, even when quite
young, require to be taught not to attack poultry, sheep and
pigs! No doubt they occasionally do make an attack, and
are then beaten; and if not cured, they are destroyed;
so that habit and some degree of selection have proba-
bly concurred in civilizing by inheritance our dogs. On
the other hand, young chickens have lost wholly by habit,
that fear of the dog and cat which no doubt was originally
* instinctive in them, for I am informed by Captain Hutton
that the young chickens of the parent stock, the Gallus
ibankiva, when reared in India under a hen, are at first ex-
cessively 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 in wild
ground-birds, their mother to fly away. But this instinct
retained by our chickens has become useless under domes-

250 SPECIAL INSTINCTS.

ticatiou, for the mother hen has almost lost by disuse the
power of flight.

Hence, we may conclude that under domestication in-
stincts have been acquired and natural instincts have been
lost, partly by habit and partly by man selecting and
accumulating, during successive generations, peculiar
mental habits and actions, which at first appeared from
what we must in our ignorance call an accident. In some
cases compulsory habit alone has sufficed to produce in-
herited mental changes. In other cases compulsory habit
has done nothing, and all has been the result of
selection, pursued both methodically and unconsciously;
but in most cases habit and selection have probably
concurred.

SPECIAL INSTIIS'CTS.

We shall, perhaps, best understand how instincts in a
state of nature have become modified by selection by con-
sidering 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 natural-
ists as the most wonderful of all known instincts.

INSTINCTS OF THE CUCKOO.

It is supposed by some naturalists that the more imme-
diate cause of the instinct of the cuckoo is that she lays
her eggs, not daily, but at intervals of two or three days,
so that if she were to make her own nest and sit on her
own eggs, those first laid would have to be left for some
time unincubated or there would be eggs and young birds
of different ages in the same nest. If this were the case
the process of laying and hatching might be inconveni-
ently long, more especially as she migrates at a very
early period, and the first hatched young would probably
have to be fed by the male alone. But the American
cuckoo is in this predicament, for she makes her own nest
and has eggs and young successively hatched, all at the
same time. It has been both asserted and denied that

mSTINOTS OF THE CUCKOO. 251

the American cuckoo occasionally lays her eggs in other
birds'* nests; but 1 have lately heard from Dr. Merrill,
of Iowa, that he once found in Illinois a young cuckoo,
together with a young jay in the nest of a blue juy ((Jar-
rulus cristatus); and as both were nearly full fuathered,
there could be no mistake in their identification. 1 could
also give several instances of various birds which have
been known occasionally to lay their eggs in other birds'
nests. Now let us suppose that the ancient progenitor of
our 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 emigrate earlier or through
any other cause; or if the young were made more vigorous
by advantage being taken of the mistaken instinct of
another species than when reared by their own mother,
encumbered as she could hardly fail to be by having eg^s
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' nest, and thus be more
(Successful in rearing their young. By a continued jDrocess
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 Miiller, that
the cuckoo occasionally lays her eggs on the bare ground,
sits on them and feeds her young. This rare event is prob-
ably a case of reversion to the long-lost, aboriginal instinct
of nidification.

It has been objected that I have not noticed other re-
lated instincts and adaptations of structure in the cuckoo,
which are spoken of as necessarily co-ordinated. But in
all cases, speculation on an instinct known to us only in a
single species, is useless, for we have hitherto had no
facts to guide us. Until recently the instincts of the
European and of the non-parasitic American cuckoo alone
were known; now, owing to Mr. Ramsay's observations; we
have learned something about three Australian species,
which lay their eggs in other birds' nests. The cliii'f
points to be referred to are throe: first, that the comnioy

252 SPECIAL INSTINCTS,

cuckoo, with rare exceptions, lays only one Qgg in a nest,
60 that the large and voracious young bird receives ample
food. Secondly, that the eggs are remarkably small, not
exceeding those of the skylark — a bird about one-fourth as
large as the cuckoo. That the small size of the Qgg is a
real case of adaptation we may infer from the fact of the
uou-parasitic American cuckoo laying full-sized eggs.
Thirdly, that the young cuckoo, soon after birth, has the
instiuct, the strength and a properly shaped back for eject-
ing its foster-brothers, which then perish from cold and
hunger. This has been boldly called a beneficent arrange-
ment, in order that the young cuckoo may get sufficient
food, and that its foster-brothers may perish before they
nad acquired much feeling!

Turning now to the Australian species: though these
birds generally lay only one Qgg in a nest, it is not rare to find
two and even three eggs in the same nest. In the bronze
cuckoo the eggs vary greatly in size, from eight to ten
lines in length. Now, if it had been of an advantage to
this species to have laid eggs even smaller than those now
laid, so as to have 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 diffi.culty 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. Eamsav remarks that two of the Australian
cuckoos, when they lay their eggs in an open nest, mani-
fest a decided preference for nests containing eggs similar
in color to their own. The European species apparently
manifests some tendency toward a similar instinct, but not
rarely departs from it, as is shown by her laying her dull
and pale-colored 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 Australian bronze
cuckoo vary, according to Mr. Ramsay, to an extraordinary
degree in color; so that in this respect, as well as in size,
natural selection might have secured and fixed any advan-
tageous variation.

INSTINCTS OF THE MOLOTUliUS. 253

In the case of the European cuckoo, the offspriug of the
foster-parents are commonly ejected from the nest within
three daj's 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, while 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 ac-
quired, if it were of great importance for the young cuckoo,
as is probably the case, to receive as much food as possible
soon after birth, I can see no special difficulty in its having
gradually acquired, during successive generations, the blind
desire, the strength, and structure necessary for the work
of ejection; for those cuckoos which had such habits and
structure best developed would be the most securely reared.
The first step toward the acquisition of the proper instinct
might have been mere unintentional restlessness on the
part of the young bird, wdien somewhat advanced in age
and strength; the habit having been afterward improved,
and transmitted to an earlier age. I uan see no more diffi-
culty in this than in the unhatched young of other birds
acquiring the instinct to break through their own shells;
or than in young snakes acquiring in their upper jawS; as
Owen has remarked, a transitory sharp tooth for cutting
through the tough egg-shell. For if each part is liable to
individual variations at all ages, and the variations tend to
be inherited at a corresponding or earlier age — proposi-
tions 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 wdth the whole theory of natural selection.

Some species of Molothrus, a widely distinct genus of
American birds, allied to our starlings, have parasitic
habits like those of the cuckoo; and the species present an
interesting gradation in the perfection of their instincts.
The sexes of Molothrus badius are stated by an excellent
observer, Mr. Hudson, sometimes to live promiscuously
together in fiocks, and sometimes to pair. They either

254 SPECIAL INSTINCTS,

build a nest of their own or seize on one belonging to some
other bird, occtisionally throwing out the nestlings of the
stranger. They either lay their eggs in the nest thus appro-
priated, 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 occa-
sionally parasitic, for he has seen the young of this species
following old birds of a distinct kind and clamoring to be
fed by them. The parasitic habits of another species of
Molothrus, the M. bonariensis, are much more highly de-
veloped than those of the last, but are still far from per-
fect. 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 singular ill-adapted
situations, as on the leaves of a large thistle. They never,
however, as far as Mr. Hudson has ascertained, complete a
nest for themselves. They often lay so many eggs — from
fifteen to twenty — in the same foster-nest, that few or none
can possibly be hatched. They have, moreover, the extra-
ordinary 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 e>gg 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,
transition?"

Various birds, as has already been remarked, occasionally
lay their eggs in the nests of other birds. This habit is
not very uncommon with the Gallinacese, and throws some
light on the singular instinct of the ostrich. In this
family several hen birds unite and lay first a few eggfs in
one nest and then in another; and these are hatched by
the males. This instinct may probably be accounted for by
the fact of the hens laying a large number of eggs, but, as

SLAVE-MAKING INSTINCT. 255

with tliecnckoo, at intervals of two or three clays. Tlie
instinct, however, of the American ostrich, as in the case
of the Molothrus bonariensis, has not as yet been per-
fected; 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 re-
markable 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
possessess the pollen-collecting apparatus which would have
been indispensable if they had stored up food for their own
young. Some species of Sphegidse (wasp-like insects) are
likewise parasitic; and M. Fabre has lately shown good
reason for believing that, although the Tachytes nigra gen-
erally makes it own burrow and stores it with paralyzed
prey for its own larvae, yet that, when this insect finds a
burrow already made and stored by another sphex, it takes
advantage of the prize, and becomes for the occasion par-
asitic. In this case, as with that of the Molothrus or
cuckoo, I can see no difficulty in natural selection making
an occasional habit permanent, if of advantage to the
species, and if the insect whose nest and stored food are
feloniously appropriated^ be not thus exterminated.

SLAVE-MAKING I2S"STI]^CT.

This remarkable instinct was first discovered in the For-
mica (Polyerges) rufescens by Pierre Iluber, a better
observer even than his celebrated father. This ant is ab-
solutely dependent on its slaves; without their aid, the
species would certainly become extinct in a single year.
The males and fertile females do no work of any kind, and
the workers or sterile females, though most energetic and
courageous in capturing slaves, do no other work. They
are incapable of making their own nests, or of feeding
their own larvae. When the old nest is found incon-
venient, 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

o-.C SPECIAL INSTINCTS.

with pleuty of food which they like best, and with their
own larvse and pupae to stimulate them to work, they did
nothing; they could not even feed themselves, and many
perished of hunger. Huber then introduced a single slave
(F. fusca), and she instantly set to work, fed and saved
the survivors; made some cells and tended the larvae, and
put all to rights. What- can be more extraordinary than
lliese well-ascertained facts ? If we had not known of any
other slave-making ant, it would have been hopeless to
.^peculate how so wonderful an instinct could have beer*,
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 Brit-
ish 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 skeptical frame of mind, as any one may
well be excused for doubting the existence of so extraordi-
nary an instinct as that of making slaves. Hence, I will
give the observations which I made in some little detail.
I opened fourteen nests of F. sanguinea, and found a few
slaves in all. Males and fertile females of the slave species
(F. fusca) are found only in their own proper communi-
ties, and have never been observed in the nests of F. san-
guinea. Tlie slaves are black and not above half the size
of tlieir red masters, so that the contrast in their appear-
ance 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 dis-
turbed, and the larvae and pupae are exposed, the slaves
work energetically 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 numerous; but
Mr.^ Smith informs me that he has watched the nests at
various hours during May, June and August, both in Sur-

SLA VE-MAKINO INSTmCT. 057

rey 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 con-
stantly seen bringing in materials for the nest, and food of
all kinds. During the year 18G0, however, in the montli
of July, I came across a community with an unusual! v
large stock of slaves, and I observed a few slaves mingled
with their masters leaving the nest, and marching along
the same road to a tall Scotch fir-tree, twenty-five yards
distant, which they ascended together, probably in search
of aphides or cocci. According to Huber, who had ample
opportunities for observation, the slaves in Switzerland
habitually work with their masters in making the nest,
and they alone open and close the doors in the morning an' 1
evening; and, as Huber expressly states, their principle
office is to search for aphides. This difference in the usual
habits of the masters and slaves in the two countries, prob-
ably depends merely on the slaves being captured in greater
numbers in Switzerland than in England.

One day I fortunately witnessed a migration of F. san-
guina from one nest to another, and it was a most interest-
ing spectacle to behold the masters carefully carrying their
slaves in their jaws instead of being carried by them, as in
the case of F. rufescens. Another day my attention was
struck by about a score of the slave-makers haunting the
same spot, and evidently not in search of food; they
approached and were vigorously repulsed by an independ-
ent community of the slave-species (F. fusca); sometimes
as many as three of these ants clinging to the legs of the
slave-making F. sanguinea. The latter ruthlessly killed
their small opponents and carried their dead bodies as
food to their nest, twenty-nine yards distant; but they were
prevented from getting any pupse to rear as slaves. I then
dug up a small parcel of the pupa? 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 i^erhaps fancied that, after all, they had been
victorious in their late combat.

At the same time I laid on the same place a small parcel
of the pupse of another species, F. flav;i, with a few of
these little yellow ants still clinging to the fragments 0^

258 SPECIAL INSTINCTS.

their nest. This species is sometimes, though rarely,
made into slaves, as has been described by Mr. Smith.
Although so small a species, it is very courageous, and I
have seen it ferociously attack other ants. In one instance
I found to my surprise an independent community of F.
flava under a stone beneath a nest of the slave-making F.
sauguinea; and when I had accidentally disturbed both
nests, the little ants attacked their big neighbors with sur-
prising courage. JSTow I was curious to ascertain whether
F. sanguinea could distinguish the pupae of F. fusca,
wliich 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 pups
of F. fusca, wiiereas they were much terrified when they
came across the pupse, 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 pupae.

One evening 1 visited another community of F. san-
guinea, 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
pupae. I traced a long file of ants burdened with booty,
for about forty yards back, to a very thick clump of heath,
whence I saw the last individual of F. sanguinea emerge,
carrying a pupa; but I was not able to find the desolated
nest in the thick heath. The nest, however, must have
been close at hand, for two or three individuals of F. fusca
were rushing about in the greatest agitation, and one was
perched 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 confirma-
tion 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 conti-
nental F. rufescens. The latter does not build its own
nest, does not determine its own migrations, does not col-
lect 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, possesaea much

CELL-MAKINQ INSTINCT, 2.V.»

fewer slaves, and in the early part of the summer extremely
lew: the masters determine when and where a new nest
shall be formed, and when they migrate, the masters carry
the slaves. Both in Switzerland and England the slaves
seem to have the exclusive care of the larvae, and the mas-
ters alone go on slave-making expeditions. In Switzerhmd
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 larvae. So that
the masters in this countrv 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 oif the pupae of
other species, if scattered near their nests, it is possible
that such pupge originally stored as food might become
developed; and the foreign ants thus unintentionally reared
would then follow their proper instincts, and do what work
they could. If their presence proved useful to the species
which had seized them — if it were more advantageous to
this species, to capture workers than to procreate them —
the habit of collecting pupae, originally for food, might by
natural selection be strengthened and rendered permanent
for the very different 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, wliich, 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
nse to the species — until an ant was formed as abjectly
dependent on its slaves as is the Formica rufescens.

CELL-MAKIKG IN'STIJ^'CT OF THE HIYE-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

260 SPEGIAL INSTINCTS.

mathematicians that bees have practically solved a recon-
dite problem, and have made their cells of the proper
shape to hold tlie greatest possible amount of honey, with
the least possible consumption of precious wax in their
construction. It has been remarked that a sliillful work-
man with fitting tools and measures, would find it very
difficult to make cells of wax of the true form, though this
is effected by a crowd of bees working in a dark hive.
Granting whatever instincts you please, it seems at first
quite inconceivable how they can make all the necessary
angles and planes, or even perceive when they are correctly
made. But the difficulty is not nearly so great as at first
appears: all this beautiful work can be shown^ I think, to
follow from a few simple instincts.

I was led to investigate this subject by Mr. Waterhouse,
who has shown that the form of the cell stands in close re-
lation 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
beveled 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 ad-
joining cells on the opposite side. In the series between
the extreme perfection of the cells of the hive-bee and the
simplicity of those of the humble-bee we have the cells of
the Mexican Melipona domestica, carefully described and
figured by Pierre Huber. The Melipona itself is interme-
diate 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 hold-
ing honey. These latter cells are nearly spherical and of
nearly equal sizes, and are aggregated into an irregular

CELL-MAKING INSTINCT. 2CI

mass. But tlie important point to notice is, that these
cells are always made at that degree of nearness to each
other that they would have intersected or broken into each
other if the spheres had been completed; but this is never
permitted, the bees building perfectly fiat walls of wax be-
tween 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 imi-
tation 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 obvious that
the Melipona saves wax, and what is more important,
labor, by this manner of building; for the flat walls be-
tween 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.

Eeflecting on this case, it occurred to me that if the Meli-
pona had made its spheres at some given distance from
each other, and had made them of equal sizes and had
arranged them symmetrically in a double layer, the resulting
structure would have been as perfect as the comb of the
hive-bee. Accordingly I WTote to Professor Miller, of Cam-
bridge, and this geometer has kindly read over the follow-
ing statement, drawn up from his information, and tells
nie that it is strictly correct :

If a number of equal spheres be described with their
centers placed in two parallel layers; with the center of
each sphere at the distance of radius X ^/ '^, or radius
X 1.41421 (or at some lesser distance), from the centers of
the six surrounding spheres in the same layer; and at tho
same distance from the centers of the adjoining spheres in
the other and parallel layer; then, if ])lane6 of intersec-
tion 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 tliree rhombs; and
the rhombs and the sides of the hexagonal prisms will have

2e2 SPECIAL INSTINCTS.

every angle identically the same with the best measure-
ments which have been made of the cells of the hive-bee.
But I hear from Professor Wyman, who has made numer-
ous careful measurements, that the accuracy of the work-
manship of the bee has been greatly exaggerated; so much
80, that whatever the typical form of the cell may be, it is
rarely, if ever, realized.

Hence we may safely conclude that, if we could slightly
modify the instincts already possessed by the Melipona,
iind in themselves not very wonderful, this bee would make
a structure as wonderfully perfect as that of the hive-bee.
We must suppose the Melipona to have the power of form-
ing her cells truly spherical, and of equal sizes; and this
would not be very surprising, seeing that she already does
60 to a certain extent, and seeing what perfectly cylindri-
cal burrows many insects make in wood, apparently by
turning round on a fixed point. We must sujopose the
Melipona to arrange her cells in level layers, as she already
does her cylindrical cells; and we must further suppose,
and this is the greatest difficulty, that she can somehow
judge accurately at what distance to stand from her fellow-
laborers when several are making their spheres; but she is
already so far enabled to judge of distance, that she always
describes her spheres so as to intersect to a certain extent;
and then she unites the points of intersection by perfectly
fiat 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 acquired, through natural selection,
her inimitable architectural powers.

But this theory can be tested by experiment. Following
the example of Mr. Tegetmeier, I separated two combs,
and put between them a long, thick, rectangular strip of
wax: the bees instantly began to excavate minute circular
pits in it; and as they deepened these little pits, they made
them wider and wider until they were converted into
shallow basins, appearing to the eye perfectly true or parts
of a spliere, and of about the diameter 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 distance from each other that
by the time the basins had acquired the above-stated width

CELL-MAKING INSTINCT. 2G:i

{i.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 evcavate, and began to build up flat walls of wax on the
lines of intersection between the basins, so that each hexa-
gonal prism was built upon the scalloped edge of a smooth
basin, instead of on the straight edges of a three-sided
pyrauiid as in the case of ordinary cells.

I then put into the hive, instead of a thick, rectangular
piece of wax, a thin and narrow, knife-edged ridge, colored
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 experiment, 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 ver-
milion wax left ungnawed, were situated, as far as the eye
could Judge, exactly along the planes of imaginary inter-
section between the basins on the opposite side of the ridge
of wax. In some parts, only small portions, in otlier
parts, large portions of a rhombic plate were thus left be-
tween the opposed basins, but the work, from the unnat-
ural 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, while at work on the
two sides of a strip of wax, perceiving when they have
gnawed the wax away to the proper thinness, and tlien
stopping their work. In ordinary combs it has apj)earcd
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 base of a just com-
menced cell, wdiich were sHghtly concave on one side,

^^•4 8PECIAL INSTINCTS.

•where I suppose that the bees had excavated too quickly,
and convex on the opposed side wliere 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 affected 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
liave 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 proj)er distance from each other,
by excavating at the same rate, and by endeavoring 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 jdates, until the hexagonal
walls are commenced. Some of these statements differ
from those made by the justly celebrated elder Huber, but
I am convinced of their accuracy; and if I had space, I
could show that they are conformable with my theory.

Ruber's statement, that the very first cell is excavated
out of a little parallel-sided wall of wax, is not, as far as I
have seen, strictly correct; the first commencement having
alwavs 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
waxin the proper position — that is, along the plane of inter-
section between two adjoining spheres. I have several

CELL-MAKING INSTINCT. 2G5

specimens showing clearly that they can do this. Even
in the rude circumferential rim or wall of wax round a
growing comb, flexures may sometimes be observed, cor-
responding in position 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 always 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 under-
stand 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 by a strong coping
of wax, the bees can cluster and crawl over the comb with-
out injuring the delicate hexagonal walls. These walls, as
Professor Miller has kindly ascertained for me, vary greatly
in thickness; being, on an average of twelve measure-
ments made near the border of the comb, -g^ of an
inch in thickness; whereas the basal rhomboiclal j^lates are
thicker, nearly in the proportion of three to two, having a
mean thickness, from twenty-one measurements, of -^Ij ^^
an inch. By the above singular manner of building,
strength is continually given to the comb, with the utmost
ultimate economy of wax.

It seems at first to add to the difficulty of understanding
how the cells are made, that a multitude of bees all woik
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 fir.^t
cell. I was able practically to show this fact, by covering
the edges of the hexagonal walls of a sing-le cell, or the ex-
treme margin of the circumferential rim of a growing
comb, with an extremely thin layer of melted vermilion
wax; and I invariably found that the color was most deli-
cately diffused by the bees — as delicately as a painter could
have done it with his brush— by atoms of the colored wax

266 SPECIAL INSTINCTS.

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 stand-
ing at the same relative distance from each other, all trying
to sweep equal spheres, and then building up, or leaving
nno"nawed, the planes of intej'section between these spheres.
It was really curious to note in cases of difficulty, as Avhen
two pieces of comb met at an angle, how often the bees
would i^ull 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
downward, 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 completed 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 1 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 circum-
stances a rough wall in its proper place between two just
commenced 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 alter-
nately on the inside and outside of two or three cells com-
menced 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 interme-
diate planes.

As natural selection acts only by the accumulation of
slight modifications of structure or instinct, each profitable

CELL-MAKING INSTINCT. 2Gt

to the individual under its conditions of life, it may reason-
ably be asked, how along and graduated 8ucces.->ion of
modified architectural instincts, all tending toward the pres-
ent perfect plan of construction, could have profited the
progenitors of the hive-bee? I think the answer is not
difficult: ceils constructed like those of the bee or the wasp
gain in strength, and save much in labor 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 sufficient nectar, and I am informed
by Mr. Tegetmeier that it has been experimentally proved
that from twelve to fifteen pounds of dry sugar are con-
sumed by a hive of bees for the secretion of a pound of
wax; so that a prodigious 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 daring 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
supported. 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 independent
of the quantity oi* honey which the bees can collect. But
let us suppose that this latter circumstance determined, as
it probably often has determined, whether a bee allied
to our humble-bees could exist in large numbers in any
country; and let us further suppose tliat 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 intersect a little; for a wall in
common even to two adjoining cells would save some little
labor 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 ]\[eiiponaj

268 OBJEGTIONS TO THE THEOUT

for in this case a large part of the bounding surface of each
cell would serve to bound the adjoining cells, and much
labor 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 spherical surfaces would wholly disappear and be re-
placed 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 economizing labor and wax.

Thus, as I believe, the most wonderful of all known in-
stincts, 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 intersection; the bees, of course,
no more knowing that they swept their spheres at one par-
ticular 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 larvse,
this being effected with the greatest possible economy of
labor and wax; that individual swarm which thus made
the best cells with least labor, 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 origin
of instincts that ^Hhe 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.*'

OF NATURAL SELECTION. 2G0

The force of this objection rests entirely on the assuniptiou
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 iu natu-
ral selection preserving all the slight individual variations
in the shape of the beak, which were better and better
adapted to break open the seeds, until a beak was formed,
as well constructed for this purpose as that of the nut-
hatch, at the same time that habit, or compulsion, 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 selection, subse-
quently 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 instinct and power of
the nuthatch. In this case a gradual change of structure
is supposed to lead to changed instinctive habits. To take
one more case: few instincts 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 WAV?., 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, wnich 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 Ccinnot conjecture whether it was instinct or
structure which first varied.

No doubt many instincts of very difficult explanation
could be opposed to the theory of natural selection — cases,
in which we cannot see how an instinct could have origin-
ated; cases, in which no intermediate gradations are known
to exist; cases of instincts of such trifling importance, that

270 OBJECTIONS TO THE THEORt

they could hardly have been acted 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 consequently must believe that they were independ-
ently acquired through natural selection. I will not here
enteV on these several cases, but will confine myself to one
special difficulty, which at first appeared to me insuperable,
and actually fatal to the whole theory. I allude to the
neuters or sterile females in insect communities; 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 structure; for it can be
shown that some insects and other articulate animals
in a state of nature occasionally become 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 incapable of procrea-
tion, 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 lies 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 some-
times of eyes, and in instinct. As far as instinct
alone is concerned, the wonderful difference in this respect
between the workers and the j^erfect females would have
been better exemplified by the hive-bee. If a working ant
or other neuter insect had been an ordinary animal, I
should have unhesitatingly assumed that all its characters
had been slowly acquired through natural selection;
namely, by individuals having been born with slight profit-
able modifications, which were inherited by the offspring,
and that these again varied and again were selected, and so
onward. 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

OF NA TUBAL SELECTION. 2 7 1

moditications of structure or instinct to its progeny. It
may well be asked how it is possible to reconcile this case
with the theory of natural selection?

First, let it be remembered that we have innumerable in-
stances, both in our domestic productions and in those in
a state of nature, of all sorts of diiferences of inherited
structure which are correlated with certain ages and with
either sex. We have differences correlated not only with
one sex, but Avith 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. AVe have even
slight differences in the horns of different breeds of cattle
in relation to an artificially imperfect state of the male
sex, for oxen of certain 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 see no great difficulty in any character becoming cor-
related with the sterile condition of certain members of
insect communities; the difficulty lies in understanding
how 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 characterized has been slaugh-
tered, 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 yield-
ing oxen with extraordinarily long horns, could, it is prob-
able, be formed by carefully watching which individual
bulls and cows, when matched, produced oxen with the
longest horns; and yet no one ox would ever have propa-
gated 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 cai'efully selected
to the right degree, always produce a large proportion of
seedlings bearing double and quite sterile flowers, but they
likewise yield some single and fertile plants. Tliese latter,
by which alone the variety can be propagated, may be
compared with the fertile male and female ants, and the

272 OBJECTIONS TO THE THEORY

double sterile plants with the neuters of the same com-
munity. As with the varieties of the stock, so with social
insects, selection has been applied to the family, and not
to the individual, for the sake of gaining a serviceable end.
Hence, we ma}' conclude that slight modifications of
structure or of instinct, correlated with the sterile condi-
tion of certain members of the community, have proved
advantageous; consequently the fertile males and females
have flourished, and transmitted to their fertile offspring a
tendency to produce sterile members with the same modifi-
cations. This process must have been repeated many
times, until that prodigious amount of difference between
the fertile and sterile females of the same species has been
produced which we see in many social insects.

But we have not as yet touched on the acme of the dif-
ficulty; 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 graduate into each
other, but are perfectly well defined; being 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 extraordinaril}^ different: 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 Myrmecocystus, 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 from the
analogy of ordinary variations, that the successive, slight,
profitable modifications did not first arise in all the neuters

OF NATURAL SELECTION, 273

in the same nest, but in some few alone; and that bv tlie
survival of the communities with females wliich produced
most neuters having the advantageous modification, all
the neuters ultimately came to be thus characterized. Ac-
cording to this view we ought occasionally to find in tlie
same nest neuter insects, presenting gradations of struct-
ure; and this we do find, even not rarely, considering how
few neuter insects out of Europe have been carefully ex-
amined. Mr. F. Smith has shown that the neuters of
several British ants diller surprisingly from each other in
size and sometimes in color; 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, while 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 rudimentary. 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 accounted for merely by their proportionately 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 exactlv intermediate condition. So that here
we have two bodies of sterile workers in the same nest, dif-
fering not only in size, but in their organs of vision, yet
connected by some few members in an intermediate
condition. I may digress by adding, that if the smaller
workers had been the most useful to the community, and
those males and females had been continuallv selected,
which produced more and more of the smaller workers,
until all the workers were in this condition, we should
then have had a species of ant with neuters in nearly the
same condition as those of Myrmica. For the workers of
Myrmicahave not even rudiments 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 expect
occasionally to find gradations of important structures

274 OBJECTIONS TO THE THEORY

between the different castes of neuters in the same species,
that I gladly availed myself of Mr. F. Smithes 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 measurements, 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, moreover, 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 jaws. I speak
confidently on this latter point, as Sir J. Lubbock made
drawings for me, vrith 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 selec-
tion, by acting on the fertile ants or parents, could form a
species which should regularly produce neuters, all of large
size w^ith one form of jaw, or all of small size with widely
different jaws; or lastly, and this is the greatest difficult)^
one set of workers of one size and structure, and simulta-
neously 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 widely distinct
male forms. But this subject need not here be discussed.

I have now explained how, I believe, the wonderful fact

SUMMARY. 275

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 ha"e been to a social commu-
nity of ants, on the same principle that the division of
labor is useful to civilized man. Ants, however, work by
inherited instincts and by inherited organs or tools,
while man works by acquired knowledge and manufactured
instruments. But I must confess, 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 con-
clusion. I have, therefore, discussed this case, at some
little but wholly insufficient length, in order to show the
power of natural selection, and likewise because this is by
far the most serious special difficulty which my theory has
encountered. The case, also, is very interesting, as it
proves that with animals, as with plants, any amouut of
modification may be effected by the accumulation of
numerous, 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 of sterile females, however long they might be fol-
lowed, 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 endeavored 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 at-
tempted to show that instincts vary slightly in a state of
nature. No one will dispute that instincts are of the high-
est importance to each animal. Therefore, there is no real
difficulty, under changing conditions of life, in natural
selection accumulating to any extent 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

276 SUMMARY.

strengthen in any great degree 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 '' Natura 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 selection.

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 distant parts
of the world and living under considerable different con-
ditions of life, yet often retaining nearly the same instincts.
For instance, we can understand, on the principle of in-
heritance, how it is that the thrash of tropical South Amer-
ica lines its nest with mud, in the same peculiar manner as
does our British thrush; how it is that the Hornbills of
Africa and India have the same extraordinary instinct of
plastering up and imprisoning the females in a hole in a
tree, with only a small hole left in the i^laster 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 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 larvae of ichneumonidse
feeding within the live bodies of caterpillars, not as spe-
cially endowed or created instincts, but as small conse-
quences of one general law leading to the advancement of
all organic beings — namely, multiply, vary, let the strong-
est live and the weakest die.

HTBRIDI8M. 277

CHAPTER IX,

HYBRIDISM.

Distinction "beW-^pn the sterility of first crosses and of hybrids— .
Sterility various in degree, not universal, affected by close inter-
breeding, removed by domestication — Laws governing the
sterility of hybrids — Sterility not a special endowment, but inci-
dental on other differences, not accumulated by natural selec-
tion— 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 universal —
Hybrids and mongrels compared independently of their fertility
— Summary.

The view commonly entertained by naturalists is that
species, when intercrossed, have been specially endowed
with sterlility, in order to prevent their confusion. This
view certainly seems at first highly probable, for species
living together could hardly have been kept distinct had
they been capable of freely crossing. The subject is in
many ways important for us, more especially as the sterility
of species when first crossed, and that of their hybrid off-
spring, cannot have been acquired, as I shall show, by the
preservation of successive profitable degrees of sterility.
It is an incidental result of differences 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 con-
founded; 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 reproduction
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

278 BTBRIDISM.

themselves are perfect in structure, as far as the niicro-
scope reveals. In the first case the two sexual elements
which go to form the embryo are perfect; in the second
case they are either not at all developed, or are imperfectly
developed. This distinction is important, when the cause
of the sterility, which is common to the two cases, has to
be considered. The distinction 2)robably has been slurred
over, owing to the sterility in both cases being looked on
as a special endowment, beyond the province of our reason-
ing 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 importance
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 species when crossed and of
their hybrid offspring. It is impossible to study the sev-
eral memoirs and works of those two conscientious and ad-
mirable observers, Kolreuter and Gartner, who almost
devoted their lives to this subject, without being deeply
impressed with the high generality of some degree of ster-
ility. Kolreuter 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
together, he unhesitatingly ranks them as varieties. Gart-
ner, also, makes the rule equally universal; and he disputes
the entire fertility of Kolreuter'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 in-
tervene: a plant, to be hybridized, 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 Gartner

DEGREES OF STERILITY. 270

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 fertilized with their own pollen, and (excluding
all cases such as the Leguminosae, 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 crossed some forms, such
as the common red and blue pimpernels (Anagalhs arvensis
and coerulea), 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
believed.

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 experienced observers who have
ever lived, namely Kolreuter 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 dif-
ferent hybridizers, or by the same observer from experi-
ments made during different years. It can thus be shown
that neither sterility nor fertility affords any certain dis-
tinction 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 consti-
tutional and structural differences.

In regard to the sterility of hybrids in successive genera-
tions; though Gartner was enabled to rear some iiybrids,
carefully guarding them from a cross with either pure
parent, for six or seven, and in one case for ten generations,
yet he asserts positively that their fertility never increases,
but generally decreases greatly and suddonlv. With re^

280 HYBRIDISM.

spect to this decrease, it may first be noticed that when
any deviation in structure or constitution is common to
both parents, this is often transmitted in an augmented
degree to the offspring; and both sexual elements in hybrid
plants are already affected in some degree. But I believe
that their fertility has been diminished in nearly all these
cases by an independent cause, namely, by too close inter-
breeding. I have made so many experiments and collected,
so many facts, showing on the one hand that an occasional
cross with a distinct individual or variety increases the
vigor and fertility of the offspring, and on the other hand
that very close interbreeding lessens their vigor and fertil-
ity, that I can not 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 fer-
tilized during each generation by pollen from the same
flower; and this would probably be injurious to their fertil-
ity, 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 fertilized with hybrid pollen
of the same kind, their fertility, notwithstanding the fre-
quent ill effects from manipulation, sometimes decidedly
increases, and goes on increasing. Now, in the process of
artificial fertilization, pollen is as often taken by chance
(as I know from my own experience) from the anthers of
another flower, as from the anthers of the flower itself
which is to be fertilized; so that a cross between two flow-
ers, though probably often on the same plant, would be
thus effected. Moreover, whenever complicated experi-
ments are in progress, so careful an observer as Gartner
would have castrated his hybrids, and this would have in-
sured in each generation a cross with pollen from a dis-
tinct flower, either from the same jDlant or from another
plant of the same hybrid nature. And thus, the strange
fact of an increase of fertility in the successive generations
of artificAciUy fertilized hybrids, in contrast with those spon-
taneously self-fertilized, may, as I believe, be accounted
for by too close interbreeding having been avoided.

I

DEGREES OF STERILITY, 281

Now let us turn to the results arrived at by a third most
experienced hybridizer, 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 Kolreuter 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 horticul-
tural 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 example, namely, that "every ovule in a
pod of Orinum capense fertilized by C. revolutum pro-
duced a plant, which I never saw to occur in a case of its
natural fecundation." 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 Orinum leads me to refer to a singular
fact, namely, that individual plants of certain species
of Lobelia, Verbascum and Passiflora, can easily be fer-
tilized by the pollen from a distinct species, but not by
pollen from the same plant, though this pollen can be
proved to be perfectly sound by fertilizing other plants or
species. In the genus Hippeastrum, in Oorydalis as
shown by Professor Hildebrand, in various orchids 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 hybridized much more readily
than they can be fertilized by pollen from the same indi-
vidual plant! To give one instance, a bulb of Hippeas-
trum aulicum produced four flowers; three were fertilized
by Herbert with their own pollen, and the fourth was sub-
sequently fertilized 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 thepollen of the hybrid made vigorous
growth and rapid progress to maturity, and bore good seed,
which vegetated freely.'' Mr. Herbert tried simihir experi-
ments during many years, and always with the same result.
These cases serve to show on what slight and mysterious

282 jSYBEIDISM,

causes the lesser or greater fertility of a species sometimes
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, Rhododen-
dron, etc., have been crossed, yet many of these hybrids
seed freely. For instance, Herbert asserts that a hybrid
from Calceolaria integrifolia and plantaginea, species most
widely dissimilar in general habit, *' reproduces itself as
perfectly as if it had been a natural species from the
mountains of Chili. ^' I have taken some pains to ascer-
tain 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 hybrid,
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 hybrid 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 arrange-
ments can be trusted, that is, if the genera of animals are
as distinct from each others 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 confinement, few experiments have been fairly
tried: for instance, the canary-bird has been crossed with
nine distinct species of finches, but, as not one of these

DEOHBES OF STERILITY. 283

breeds freely in confinement, we have no right to eipect
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 nioro
fertile hybrid animals, I hardly know of an instance 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 constantly repeated admon-
ition of every breeder. And in this case, it is not at all
surprising that the inherent sterility in the hybrids should
have gone on increasing.

Although I know of hardly any thoroughly well-authen-
ticated 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. tor-
quatus, are perfectly fertile. M. Quatrefages states that
the hybrids from two moths (Bombyx cynthia and arrindia)
were proved in Paris to be fertile inter se for eight genera-
tions. It has lately been asserted that two such distinct
species as the hare and rabbit, when they can be got to
breed together, produce offspring, 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 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 Captain Hutton, that whole flocks
of these crossed geese are kept in various parts of the coun-
try; and as they are kept for profit, where neither pure
parent-species exists, they must certainly be highly or per-
fectly fertile.

With our domesticated animals, the various races when
crossed together are quite fertile; yet in many cases thej
^re descended from two or more wild species. From thia

284 LAWS GOVERNING THE STERILITY

fact we must conclude either that the aboriginal parent-
species at first produced perfectly fertile hybrids, or that
the hybrids subsequently reared under domestication
became quite fertile. This latter alternative, which was
first propounded by Pallas, seems by far the moso 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 in-
digenous domestic dogs of South America, all are quite
fertile together; but analogy makes me greatly doubt,
whether the several 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 intei' se perfectly fertile; and from the observa-
tions by Riitimeyer on their important osteological differ-
ences, as well as from those by Mr. Bly th on their differences
in habits, voice, constitution, etc., these two 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 inter-
crossing 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 considered as absolutely
universal.

LAWS GOVERIS'IKG THE STERILITY OF FIRST CROSSES AKD

OF HYBltlDS.

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 admirabb work on the hybridization
of plants. I have taken much pains to ascertain how far
they apply to animals, and, considering how scanty our

OF FIRST CROSSES AND OF HYBRIDS. 285

knowledge is in regard to hybrid animals, I have been aur
prised to find how generally the same rules apply to both
kingdoms.

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 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 species 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 cer-
tain 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 pro-
duced, 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 withering of the flower is
well known to be a sign of incipient fertilization. From
this extreme degree of sterility we have self-fertilized
hybrids producing a greater and greater number of seeds
up to perfect fertility.

The hybrids raised from two species which are very diffi-
cult to cross, and which rarely produce any offspring, 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 offspring, yet these hybrids are
remarkably sterile. On the other liand, there are species
which can be crossed very rarely, or with extreme ditliculty,
but the hybrids, when at last produced, are very fertile.
Even within the limits of the same genus, for instance ii>
pianthus, these two opposite cases occur.

286 LAWS GOYERNme THE STERILITY

The fertility, both of first crosses and of hybrids, is more
easily affected by unfavorable 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 cir-
cumstances; it depends in part upon the constitution of
the individuals which happen to have been chosen for the
experiment. So it is with hybrids, for their degree of fer-
tility is often found to differ greatly in the several indi-
viduals raised from seed out of the same capsule and ex-
posed to the same conditions.

By the term systematic affinity is meant, the general re-
semblance between species in structure and constitution.
Now the fertility of first crosses, and of the hybrids pro-
duced from them, if largely governed by their systematic
affinity. This is clearly shown by hybrids never having
been raised between species ranked by systematists in dis-
tinct families; and on the other hand, by very closely
allied species generally uniting with facility. But the cor-
respondence between systematic 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 distinct species which unite with the utmost facility.
In the same family there may be a genus, as Dianthus, in
which very many siDecies can most readily be crossed; and
another genus, as Silene, in which the most persevering
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 in-
stance, 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 par-
ticularly distinct species, obstinately failed to fertilize, or
to be fertilized, by no less than eight other species of Nico-
tiana. Many analogous facts could be given.

No one has been able to point out what kind or what
amount of difference, in any recognizable character, is suf-
ficient to prevent two species crossing. It can be shown
that plants most widely different in habit and general ap-
pearance, and having strongly marked differences in every
part of the flower, even in the pollen, in the fruit, and iii

OF FIRST CROSSES AND OF HYBRIDS. 287

the cotyledons, can be crossed. Annual and perennial
plants, deciduous and evergreen trees, plants inhabiting
different stations and fitted for extremely 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 independent
of their sytematic affinity, that is of any difference
in their structure or constitution, excepting in their
reproductive systems. The diversity of the result in recip-
rocal crosses between the same two species was long ago
observed by Kolreuter. To give an instance: Mirabilis
jalapa can easily be fertilized by the pollen of M. long-
iflora, and the hybrids thus produced are sufficiently fer-
tile; but Kolreuter tried more than two hundred times,
during eight following years, to fertilize reciprocally M. long-
iflora 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 reciprocal crosses is extremely common in a lesser
degree. He has observed it even between closely related
forms (as Matthiola annua and glabra) 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
species having first been used as the father and then as the
mother, though they rarely differ in external characters,
yet generally dift'er in fertility in a small, and occasionally
in a high degree.

Several other singular rules could be given from Giirt-
ner: 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 like-
ness 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

388 LAWS OOVEnNING THE STERILITY

character between their two parents, always closely resem-
ble one of them; and such hybrids, though externally so
like one of their pure parent-species, are with rare excep-
tions extremely sterile. So again among 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
sjoecies, are united, their fertility graduates from zero to
perfect fertility, or even to fertility under certain con-
ditions in excess; that their fertility, besides being emi-
nently susceptible to favorable and unfavorable 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 systematic affinity or degree of resemblance to each
other. This latter statement is clearly proved by the dif-
ference 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 generally some
dift'erence, and occasionally the widest possible dif-
ference, 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
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 differ-
ent in degree, when various species are crossed, all of which
we must sup|)ose it would be equally important to keep
frorn^ blending together? Why should the degree of
sterility be innately variable in the individuals of the same

OF FIRST CHOaSES AND OF IIYBRins. ^89

species? Why slioiild some species cross with facility und
yet produce very sterile hybrids; and other species cross
with extreme difficulty, aud yet produce fairly fertile
hybrids? Why should there often be so groat a difTer-
ence in the result of a reciprocal cross between the i^ame
two species? Why, it may even be asked, has the pro-
duction 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 limited 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 advisable to explain a little more
fully, by an example, what I mean by sterility being inci-
dental on other differences, and not a specially endowed
quality. As the capacity of one plant to be grafted or
budded on another is unimportant for their welfare in a
state of nature, I presume that no one will suppose that
this capacity is a specialli/ endowed quality, but will admit
that it is incidental 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, etc.; but in a multitude of
cases we can assign no reason whatever. Great diversity
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 hybridization, so
with 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 ca})acity,
as in hybridization, is by no means absolutely governed by

290 LAWS GOVERNING THE KTERILTTT

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 apple, which is a
member of the same genus. Even different varieties of
the pear take with different degrees of facihty on the
quince; so do different varieties 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 species
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 gooseberry,
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 condition, is a
different case from the difficulty of uniting two pure spe-
cies, 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 Eobinia, 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 re-
minded by this latter fact of the extraordinary cases of
hippeastrum, passiflora, etc., which seed much more freely
when fertilized with the pollen of a distinct species than
when fertilized with pollen from the same plant.
. We thus see that, although there is a clear and great dif-
ference 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 distinct species.
And as we must look at the curious and complex laws gov-
erning the facility with which trees can be grafted on each

OF FIRST CROSSES AND OF UYBIUDS. 201

other as incidental on unknown differences in their vege-
tative systems, so I believe that the still more complex
laws governing the facility of first crosses are inciaental on
unknown differences in their reproductive systems. These
differences in both cases follow, to a certain extent, as
might have been expected, systematic affinity, bv which
term every kind of resemblance and dissimilarity between
organic beings is attempted to be expressed. The facts by
no means seem to indicate that the greater or lesser diffi-
culty of either grafting or crossing various species has been
a special endowment; although in the case of crossing, the
difficulty is as important for the endurance and stability of
specific forms as in the case of grafting it is unimportant
for their welfare.

ORIGIN AND CAUSES OF THE STERILITY OF FIRST CROSSES

AND OF HYBRIDS.

At one time it appeared to me probable, as it has to others,
that the sterility of first crosses and of hybrids might have
been slowly acquired through the natural selection of
slightly lessened degrees of fertility, which, like any other
variation, spontaneously appeared in certain individuals of
one variety when crossed with those of another variety.
For it would clearly be advantageous to two varieties or
incipient species if they could be kept from blending, on
the same principle that, when man is selecting at the
same time two varieties, it is necessary that he should
keep them separate. In the first place, it may be re-
marked that species inhabiting distinct regions are often
sterile when crossed; now it could clearly have been of
no advantage to such separated species to have been
rendered mutually sterile, and consequently this could
not have been effected through natural selection; but
it may perhaps be argued, that, if a species was rendered
sterile with some one compatriot, sterility with other spe-
cies would follow as a necessary contingency. In tlie
second place, it is almost as much opposed to the theory of
natural selection as to that of special creation, that in re-
ciprocal crosses the male element of one form should have
been rendered utterly impotent on a second form, while at
the same time the male element of this second form is en-

292 G^ USES OF THE STERILITY

abled freely to fertilize the first form; for this peculiar
state of the reproductive system could hardly have been
advantageous 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 fertiUtyto ab-
solute sterility. It may be admitted that it would profit an
incipient species, if it were rendered in some slight degree
sterile when crossed with its parent form or with some
other variety; for thus fewer bastardized and deteriorated
offspring would be produced to commingle their blood with
the new species in process of formation. But he who will
take the trouble to reflect on the steps by which this first
degree of sterility could be increased through natural selec-
tion 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 reflec-
tion, it seems to me that this could not have been effected
through natural selection. Take the case of any two spe-
cies which, when crossed, produced few and sterile off-
spring; now, what is there which could favor the survival
of those individuals which happened to be endowed in a
slightly higher degree with mutual infertility, and which
thus approached by one small step toward absolute sterility?
Yet an advance of this kind, if the theory of natural se-
lection 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 be-
lieve that modifications in their structure and fertility
have been slowly accumulated by natural selection, from
an advantage having been thus indirectly given to the com-
munity to which they belonged over other communities of
the same species; but an individual animal not belonging
to a social 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 preser-
vation.

But it would be superfluous to discuss this question in
detail: for with plants we have conclusive evidence that

OF FIRST CROSSES AND OF HYBRIDS. ;>o

J

the sterility of crossed species mast be due to some princi-
ple, quite iiideijendeiit of natural selection. Botli Giirtner
and Kolreuter have proved that in genera includin;,Miuiner-
ous species, a series can be formed from species which wheu
crossed yield fewer and fewer seeds, to species wliich 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 effected, cannot have
been gained through selection; and from the laws govern-
ing the various grades of sterility being so uniform through-
out the animal and vegetable kingdoms, we may infer 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 nature
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 tliat
when the pollen of one species 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 inca-
pable 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 can not be grafted on others.
Lastly, an embryo may be developed, and then perish at
an early period. This latter alternative has not been suf-
ficiently attended to; but I believe, from observations com-
municated to me by Mr. Hewitt, who has had great ex-
perience in hybridizing 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 Callus and their hybrids;

294

CA USES OF THE STERILITY

the majority of these eggs had been fertilized; and iix the
majority of the fertilized eggs, the embryos had either been
partially developed and had then perished, or had become
neai'ly 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, " without any obvious cause, apparently
from mere inability to live;" so that from the 500 eggs only
twelve chickens were reared. With plants, hybridized em-
bryos probably often perish in a like manner; at least it is
known that hybrids raised from very distinct species are
sometimes weak and dwarfed, and perish at an early age;
of which fact Max Wichura has recently given some strik-
ing cases with hybrid willows. It may be here worth
noticing that in some cases of parthenogenesis, the em-
bryos within the eggs of silk moths which had not been
fertilized, pass through their early stages of development
and then perish like the embryos produced by a cross be-
tween distinct species. Until becoming acquainted with
these facts, I was unwilling to believe 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. Hybrids, however, are differently cir-
cumstanced before and after birth: when born and living
in a country where their two parents live, they are gener-
ally placed under suitable conditions of life. But a hybrid
partakes 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 Qgg or
seed produced by the mother, be exposed to conditions 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 more probably
lies in some imperfection in the original act of impregna-
tion, causing the embryo to be imperfectly 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

OF FIRST CROSSES AND OF UTBRrDS. 295

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 ani-
mals. Between the sterility thus superinduced and that of
hybrids, there are many points of similarity. In both
cases the sterility is independent 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 m.ale element is the most liable to be affected;
but sometimes the female more than the male. In both,
the tondency goes to a certain extent with systematic afii-
nity, 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 fertility; and
certain species in a group will produce unusually fertile
hybrids. No one can tell till he tries, whether any partic-
ular animal will breed under confinement, 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, 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 pro-
duced by the unnatural crossing of two species, the repro-
ductive system, independently of the general state of
health, is affected in a very similar manner. In the one
case, the conditions of hfe have been disturbed, tliough
often in so slight a degree as to be inappreciable by us; in
the other case, or that of hybrids, the external conditions
have remained the same, but the organization has been dis-
turbed by two distinct structures and constitutions, includ-
ing of course the reproductive systems, having been
blended into one. For it is scarcely ^ possible that two
organizations should be compounded into one, without

20G CA USES OF THE STERILITY

some disturbance occurring in the development, or periodi-
cal 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
offspring from generation to generation the same com-
pounded organization, and hence we need not be surprised
that their sterility, though in some degree variable, does
not diminish; it is even apt to increase, this being gener-
ally the result, as before explained, of too close interbreed-
ing. The above view of the sterility of hybrids being
caused by two constitutions being compounded into one
has been strongly maintained by Max Wichura.

It must, however, be owned that we cannot understand,
on the above or any other view, several facts with respect
to the sterility of hybrids; for instance, the unequal fer-
tility of hybrids produced from reciprocal crosses; or the
increased sterility in those hybrids which occasionally and
exceptionally resemble closely either pure parent. Nor do
I pretend that the foregoing remarks go to the root of the
matter; no explanation is offered why an organism, when
placed under unnatural 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 organization having been dis-
turbed by two organizations 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 evidence, 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, etc., from one soil or climate to another,
and back again. During the convalescence of animals,
great benefit is derived from almost 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
vigor and fertility to the offspring; and that close inter-
breeding continued during several generations between the
nearest relations, if these be kept under the same conditions
of life, almost always leads to decreased size, weakness, or
sterility.

OF FIRST CROSSES AND OF nTBRIDS. 297

Hence it seems that, on the one hand, slight changes in
the conditions of hfe benefit all organic beings, and on tlie
other hand, that slight crosses, that is, crosses between the
males and females of the same species, whicli have been
subjected to slightly different conditions, or which have
slightly varied, give vigor and fertility to the offspring.
But, as we have seen, organic beings long habituated to
certain uniform conditions under a state of nature, wiien
subjected, as under confinement, to a considerable change
in their conditions, 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 ex-
plain why the elephant, and a multidude 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 generally sterile.
He will at the same time be able to explain 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, although they are descended from
distinct species, which would probably have been sterile if
aboriginally crossed. The above two parallel seiies of facts
seem to be connected together by some common but un-
known 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 toward an equilibrium; and
when this tendency is slightly disturbed by any change,
the vital forces gain in power.

RECiPEOCAL dimorphism: a:n"d 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 jnstil

298

RECIPROCAL BIMORPmSM

with long stamens; the two having differently sized pollen-
grains. With triniorphic plants there are three forma
likewise differing in the lengths of their pistils and stamens,
in the size and color 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 proportioned in length to each other that half the
stamens 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 neces-
sary that the stigma of the one form should be fertilized
by pollen taken from the stamens of corresponding height
in another form. So that with dimorphic species two
unions, which may be called legitimate, are fully fertile;
and two, which may be called illegitimate, are more or less
infertile. With trimorphic species six unions are legiti-
mate, or fully fertile, and twelve are illegitimate, or more
or less infertile.

The infertility which may be observed in various dimor-
phic and trimorphic plants, when they are illegitimately
fertilized, that is by pollen taken from stamens not cor-
responding in height with the pistil, differs much in degree,
up to absolute and utter sterility; just in the same manner
as occurs in crossing distinct species. As the degree of
sterility in the latter case depends in an eminent degree on
the conditions of life being more or less favorable, 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 afterward, even after
a considerable interval of time, placed on the same stigma,
its action is so strongly prepotent that it generally annihi-
lates 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 fertilizing several flowers, first illegitimately, and twenty-
four hours afterward legitimately, with pollen taken
from a peculiarly colored variety, and all the seedlings
were similarly colored; this shows that the legitimate pollen,
though applied twenty-four hours subsequently, had

AND TRIMORPHISM. , 299

vvliolly destroyed or prevented the action of the previously
applied illegitimate pollen. Again, as in making recipro^
cal crosses between the same two species, there is occa-
sionally a great difference in the result, so the same thing
occurs with trimorphic plants; for instance, the mid-
styled form of Ly thrum salicaria was illegitimately fer-
tilized 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 when fer-
tilized 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 result 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-syled illegitimate plants, and
from trimorphic plants all three illegitimate forms. These
can then be properly united in a legitimate manner. AVhen
this is done, there is no apparent reason why they should
not yield as many seeds as did their parents when legiti-
mately fertilized. But such is not the case. They are all
infertile, in various degrees; some being so utterly and in-
curably 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 a legiti-
mate manner, may be strictly compared with that of
hybrids when crossed i7iter se. If, on the other hand, a
hybrid is crossed with either pure parent-species, the ster-
ility is usually much lessened: and so it is when an illegiti-
mate plant is fertilized 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 that sterility of certain illegiti-
mate plants was unusually great, while the sterility of the
union from which they were derived was by no moans
great. With hybrids raised from the same seed-capsule
the degree of sterility is innately variable, so it is in a
marked manner with illegitimate plants. Lastly, mnny
hybrids are profuse and persistent flowerers, while ot^:-r

300 RECIPROCAL DIMORPHISM

and more sterile hybrids produce few flowers, and are weak,
miserable dwarfs; exactly similar cases occur with the
illegitimate offspring of various dimorphic and trimorphic
plants.

Altogether there is the closest indentity in character and
behavior 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, while 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 respects between first
illegitimate unions and first crosses between distinct species.
This will perhaps be made more fully apparent by an illus*
tration; 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 deter-
mined to try by crossing whether they were specifically
distinct. He would find that they yielded only about one-
fifth of the proper number of seed, 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 hybridized 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 maintain
that he had actually proved, in accordance with the com-
mon view, that his two varieties were as good and as dis-
tinct species as any in the world; but he would be com-
pletely mistaken.

The facts now given ondimorj^hic and trimorphic plants
are important, because they show us, first, that the physio-
logical 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 infertility of illegitimate unions with
that of their illegitimate 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 impor-
tance, 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 con'

AND TRIMORPmSM. S,il

ditions, and yet be sterile when united in certain wiivs.
For we must remember that it is the union of the sexuai
elements of individuals of the same form, for instance, of
two long-styled forms, which results in sterility; ^vhile it
is the union of the sexual elements proper to two disiinct
forms which is fertile. Hence the case appears at iirst sic^ht
exactly the reverse of what occurs, in the ordinary unions
of the individuals of the same species and witli crosses
between distinct species. It is, however, doubtful whether
this is really so; but I will not enlarge on this obscure
subject.

We may, however, infer as probable from the considera-
tion of dimorphic and trimorphic plants, that the sterility
of distinct species when crossed and of their hybrid pro-
geny, depends exclusively on the nature of their sexual
elements, and not on any difference in their structure or
general constitution. AVe are also led to this same con-
clusion 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 a second species,
while the converse cross can be effected with perfect
facility. That excellent observer, Gartner, likewise con-
cluded that species when crossed are sterile owing to dif-
ferences confined to their reproductive systems.

FERTILITY OF VARIETIES WHEN CROSSED, AND OF THEIR
3I0NGREL OFFSPRING, NOT UNIVERSAL.

It may be urged as an overwhelming argument tliat
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 subject is surrounded by
difficulties, for, looking to varieties produced under nature,
if two forms hitherto reputed to be varieties be found in
any degree sterile together, they are at once ranked by
most naturalists as species. For instance, the blue and rod
pimpernel, which are considered by most botanists a5
varieties, are said by Gartner to be quite sterile wlien
crossed, and he consequentlv ranks them as undoubted

i^02 FERTILITY OF VARIETIES

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 involved
in some doubt. For when it is stated, for instance,
that certain South American indigenous domestic dogs do
not readily unite witli European dogs, the explanation
which will occur to every one, and probably the true one,
is tliat they are descended from aboriginally distinct
species. Nevertheless the perfect fertility of so many do-
mestic races, dillering widely from each other in appear-
ance, for instance, those of the pigeon, or of the cabbage,
is a remarkable fact; more especially when we reflect how
many species there are, which, though resembling each
other most closely, are utterly sterile when intercrossed.
Several considerations, however, render the fertility of do-
mestic 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
sterility, so that similar differences in the case of rarieties
would be no sure guide. It is certain that with species the
cause lies exclusively in differences in their sexual consti-
tution. Now the varying conditions to which domesticated
animals and cultivated plants have been subjected, have
had so little tendency toward modifying the reproductive
system in a manner leading to mutual sterility, that we
have good grounds for admitting the directly opposite doc-
trine of Pallas, namely, that such conditions generally
eliminate this tendency; so that the domesticated descend-
ants of species, which in their natural state probably would
have been in some degree sterile when crossed, become per-
fectly fertile together. With plants, so far is cultivation
from giving a tendency toward sterility between distinct
species, that in several well-authenticated cases already
alluded to, certain plants have been affected in an opposite
manner, for they have become self-impotent, while still
retaining the capacity of fertilizing, and being fertilized
by, other species. If the Pallasian doctrine of the elimi-
nation of sterility through long continued domestication be
admitted, and it can hardly be rejected, it becomes in the
highest degree improbable that similar conditions long-con-

WHEN CROSSED. 303

tinned should likewise induce this tendency; though in
certain cases, with species liaving a peculiar constitution,
sterility niiglit occasionally be thus caused. Thus, as I
believe, we can understand why, with domesticated ani-
mals, varieties have not been produced which are mutually
sterile; and why with plants only a few such cases, imme-
diately to be given, have been observed.

The real difficulty in our present subject is not, as it
appears to me, why domestic varieties have iu:)t 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 de-
gree to take rank as species. We are far from precisely
knowing the cause; nor is this surprising, seeing how
profoundly ignorant we are in I'egard to the uornud
and abnormal action of the reproductive system. But
we can see that species, owing to their struggle for exist-
ence with numerous competitors, will have been exposed
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 ora:anic beins^s vv^hich have alwavs lived under natural
conditions would probably in like manner be emi-
nently sensitive to the influence of an unnatural cross.
Domesticated productions, on the other hand, which, as
shown by the mere fact of their domestication, were not
originally highly sensitive to changes in their conditions of
life, and which can now generally resist with undimin-
ished fertility repeated changes of conditions, might be
expected to produce varieties, which would be little liable
to have their reproductive powers injuriously alTected by
the act of crossing with other varieties which had origi-
nated in a like manner.

I have as yet spoken as if the varieties of the saine species
were invariably fertile when intercrossed. But it is impos-
sible to resist the evidence of the existence of a certain
amount of sterility in the few following cases, which 1 will
briefly abstract. The evidence is at least as good as that
from/which we believe in the sterility of a multitude oi

304 FERTILITY OF VARIETIES

species. The evidence is also derived from hostile wit-
nesses, who in all other ca-^es consider fertility and sterility
as safe criterions of sioecific distinction. Gartner 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 sepa-
ated sexes, they never naturally crossed. He then fertil-
ized 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 important
to notice that the hybrid plants thus raised were them-
selves ^?e?/ec% fertile; so that even Gartner did not ven-
ture to consider the two varieties as specifically distinct.

Girou de Buzareiugues crossed three varieties of gourd,
which like the maize has separate sexes, and he asserts that
their mutual fertilization is by so much the less easy as
their dilferences 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 classifi-
cation bv the test of infertilitv, 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 num-
ber of experiments made during many years on nine species
of Verbascum, by so good an observer and so hostile a wit-
ness as Gartner: namely, that the yellow and white varie-
ties when crossed produce less seed than the similarly
colored varieties of the same species. Moreover^ he asserts
that, when yellow and white varieties of one species are
crossed with yellow and white varieties of a distinct
species, more seed is produced by the crosses between the
similarly colored flowers, than between those whicli are dif-
ferently colored. Mr. Scott also has experimented on the
species and varieties of Verbascum; and although unable
to confirm Gartner's results on the crossing of the distinct
species, he finds that the dissimilarly colored varieties of
the same species yield fewer seeds, in the proportion of
eighty-six to 100, than the similarly colored varieties. Yet
these varieties differ in no respect, except in the color of

WHEN CROStiED. 3(^5

their flowers; and one variety can sometimes be raised
from the seed of another.

Kolreuter, whose accuracy has been confirmed bv
every subsequent observer, lias proved the remurkablo
fact that one particuhir variety of the common tobacco
v/as more fertile than the other varieties, when crossed
mi\\ a widely distinct species, lie experimented on five
forms which are commonly reputed to be varieties, and
which he tested by the severest trial, namely, by reci})ro-
cal 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 Xico-
tiana 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 varie-
ties 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 attending 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 considera-
tions we may conclude that fertility does not constitute a
fundamental distinction between varieties and species when
crossed. The general sterility of crossed species may
safely be looked at, not as a special acquirement or endow-
ment, but as incidental on changes of an unknown nature
in their sexual elements.

HYBRIDS AKD MONGRELS COMPARED, INDEPENDENTLY

OF THEIR FERTILITY.

Independentlv of the question of fertility, the offspring
of species and of varieties when crossed may be comj)areci
in several other respects. Gartner, whose strong wish it
was to draw a distinct line between species and varieties,
could find very few, and, as it seems to me, quite unim-
portant differences between the so-called hybrid offspring

306 HYBRIDS AND MONGRELS COMPARED.

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 genera-
tion mongrels are more variable than hybrids; but Giirtner
admits that hybrids from species which have long been cul-
tivated 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
variability graduates away. When mongrels and the more
fertile h3'brids 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 character could be
given. The variability, however, in the successive gener-
ations 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 varie-
ties), and this implies that there has been recent variabil-
ity, which would often continue and would augment
that arising from the act of crossing. The slight
variability of hybrids in the first generation, in coatrast
with that in the succeeding generations, is a carious fact
and deserves attention. For it bears on the view which I
have taken of one of the causes of ordinary variability,
namely, that the reproductive system, from being eminently
sensitive to changed conditions of life, fails under these
circumstances to perform its proper function of producing
offspring closely similar in all respects to the parent form.
Now, hybrids in the first generation are descended from
species (excluding those long cultivated) which have not
had their reproductive systems in any way affected, and
thev are not variable; but hvbrids themselves have the re-
productive 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

HYBRIDS AND MONGRELS COMPARED, 307

than liybritis to revert to either parent form; but tliis, if it
be true, is certainly only a difference iu dci^ree. More-
over, Gartner expressly states tliat tlie hybri'ls from long
cultivated plants are more subject to reversion tluin
hybrids from species in their natural state; and this prob-
aijly explains the singular difference in the results arrived
at by different observers. Thus Max Wichura doubts
vv^hether hybrids ever revert to their parent forms, and lie
experimented on uncultivated species of willows, while
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; whei-eas
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 opposed to the
results of several experiments made by Kolreuter.

Such alone are the unimportant differences which
Gartner is able to point out between hybrid and mongrel
plants. On the other hand, the degrees and kinds of re-
semblance in mongrels and in hybrids to their respective
parents, more especially in hybrids produced 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 ani-
mals, one variety certainly 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 ^nongrels can be reduced to either pure parent
form by repeated crosses in successive generations with
either parent.

These several remarks are apparently api)licable to ani-
mals, but the subject is here much comi)licated, partly
owing to the existence of secondary sexual characters, but
more especially owing to prepotency in transmitting like-
ness running "more strongly in one sex than in the other,
both when one species is crossed with another and when

308 HYBRIDS AND MONGRELS COMPARED,

one variety is crossed with anotlier 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 hinuy resemble more closely the ass than the
horse; but that the prepotency runs more strongly in the
male than in the female ass, so that the mule, which is an
offspring of the male ass and mare, is more like an ass than
is the hinny, which is the offspring of the female ass and
stullion.

Much stress has been laid by some anthors on the sup-
posed 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 mon-
grels. Looking to the cases which I have collected of
cross-bred animals closely resembling one parent, the re-
semblances seem chiefly confined to characters almost mon-
strous in their nature, and v/hich have suddenly appeared
— such as albinism, melanism, deficiency of tail or horns,
or additional fingers and toes; and do not relate to char-
acters which have been slowly acquired through selection.
A tendency to sudden reversions to the perfect character
of either parent v/ould, also, be much more likely to occur
with mongrels, which are descended from varieties often
suddenly 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 con-
clusion that the laws of resemblance of the child to its
parents are the same, whether the two parents differ little
or much from each otlier, namely, in the union of individ-
uals of the same variety, or of different varieties, or of
distinct species.

Independently of the question of fertility and sterility,
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 vaiieties as having been produced by sec-
ondary laws, this similarity would be an astonishing fact.
But it harmonizes perfectly with the view that there is no
essential distinction between species and varieties.

SUMMARY. 30y

SUMMAKY OF CHAPTER.

first crosses between forms,, sufficiently distinct to be
ranked as species, and their hybrids, are veiy general Iv,
but not universally, sterile. The sterility is of all degrees',
imd is often so slight that the most careful experimental-
ists have arrived at diametrically opposite conclusions in
ranking forms bj this test. The sterility is innately vari-
able in individuals of the same species, and is eminentlv
susceptible to action of favorable and unfavorable condi-
tions. The degree of sterility does not strictly fallow
systematic affinity, but is governed by several curious and
complex laws. It is generally different, and sometimes
widely different in reciprocal crosses between the same two
species. It is not always equal in degree in a lirst cross
and in the hybrids produced from this cross.

In the same manner as in grafting trees, the capacity in
one species or variety to take on another, is incidentaf on
differences, generally of an unknown nature, in their vege-
tative systems, so in crossing, the greater or less facility of
one species to unite with another is incidental on unknown
differences in their reproductive systems. There is no
more reason to think that species have been specially en-
dowed with various degrees of sterility to prevent their
crossing and blending in nature, than to think that trees
have been specially endowed with various and somewhat
analogous degrees of 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 selection. In the
case of first crosses it seems to depend on several circum-
stances; in some instances in chief part on the early death
of the embryo. In the case of hybrids, it apparently de-
pends on their whole organization having been disturbed
by being compounded from two distinct forms; the ster-
ility being closely allied to that which so frequently affects
pure species, when exposed to new and unnatural con-
ditions "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, tliat, firstly, slight changes in the conditions of
life add to the vigor and fertility of all organic beings; and

310 SUMMARY.

secondly, that the crossing of forms, which have been ex-
posed to slightly different conditions of life, or which have
varied, favors the size, vigor and fertility of their offspring.
Tiie facts given on the sterility of the illegitimate unions
of dimorphic and trimorphic 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 re-
ciprocal 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 wh}^, in the
case of distinct species, the sexual elements should so gen-
erally have become more or less modified, leading to their
mutual infertility, we do not know; but it seems 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 be-
tween the species which are crossed. Nor it surprising
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 circumstances— should all run,
to a certain extent, parallel with the systematic affinity of
the forms subjected to experiment; for systematic affinity
includes resemblances 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 uni-
versal and perfect fertility surprisiug, when it is remem-
bered 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 con-
ditions of life. It should also be especially kept in mind,
that long-continued domestication tends to eliminate ster-
ility, and is therefore little likely to induce this same

SUMMARY. 311

quality. Independently of the question of fertility,
in all other respects there is the closest general resenil)lance
between hybrids and mongrels, in their variability, in tlieir
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 tlie 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 tha*.
species aboriginally existed as varieties.

oVZ

IMPERFECTION OF THE

CHAPTER X.

Cl^ THE IMPERFECTIOI^^ OF THE GEOLOGICAL RECORD.

On tlie 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 palaeontological 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 objections
which might be justly urged against the views maintained
in this volume. Most of them have now been discussed.
One, namely, the distinctness of si^ecific forms and their
not being blended together by innumerable transitional
links, is a very obvious difficulty. I assigned reasons why
such links do not commonly occur at the present day under
the circumstances apparently most favorable for their pres-
ence, namely, on an extensive and continuous area with
graduated physical conditions. I endeavored 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 governing condi-
tions of life do not graduate away quite insensibly like
heat or moisture. I endeavored, also, to shov/ that inter-
mediate varieties, from existing in lesser numbers than
the forms which they connect, will generally be beaten out
and exterminated during the course of further modifica-
tion and improvement. The main cause, however, of
innumerable intermediate links not now occurring every-
where throughout nature, depends on the very process of
natural selection, through which new varieties continually
take the places of and supplant their parent-forms. But

GEO LOGICAL RECORD. 31;^

just in proportion as this process of extermination lias
acted on an enormous scale, so must the number of inter-
mediate varieties, which have formerly existed, be truly
enormous. Why then is not every geological formation
and every stratum full of such intermediate links? Geo-
logy assuredly does not reveal any such tlnelv-graduated
organic chain; and this, perhaps, is the most obvious and
serious objection Avhich 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 myself forms
directly intermediate between them. But this is a wlu^lly
false view; we should always look for forms intermediate
between each species and a common but unknown pro-
genitor; and the progenitor will generally have dilTei-ed in
some respects from all its modified 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-pigeon; but we should have no varieties directly
intermediate 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 0. oenas.

So, with natural species, if we look to forms very dis-
tinct, 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 organization much general resemblance to the tapir
and to the horse; but in some points of structure may
have differed considerably from both, even perhaps mora

314 THE LAPSE OF TIME,

than they differ from each other. Hence, in all such
cases, we should be unable to recognize the j^arent-form of
any two or more species, even if we closely compared the
structure of the parent with that of its modified descend-
ants, unless at the same time we had a nearly perfect chain
of the intermediate 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 remained.
for a very long period unaltered, while its descend-
ants had undergone a vast amount of change; 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 snpplant 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 generally extinct, have in
their turn been similarly connected with more ancient
forms; and so on backward, always converging to the
common ancestor of each great class. So that the number
of intermediate and transitional links, between all living
and extinct species, must have been inconceivably great.
But assuredly, if this theory be true, such have lived upon
the earth.

Oif THE LAPSE OK TIME, AS INFERRED FROM THE RATE
OF DEPOSITIOi^ 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 liardly possible for me to recall to the reader who is
not a practical geologist, the facts leading the mind feebly
to comprehend the (apse of time. He who can read Sir
Charles LyelTs grand work on tlie Principles of Geology,
which the future historian will recognize as having pro-

THE LAPSE OF TIME. 31 5

diiced a revolution in natunil science, and yet does not
admit how vast have been the past periods of lime, may at
once close this volume. Not tliat it suilices to study tlie
Principles of Geolog-y, or to read special treatises by dltler-
ent observers on separate formations, and to mark liow
each author attempts to give an inadequate idea of tlie
duration of each foj-mation, or even of each stratum. Wc
can best gain some idea of past time by knowin.i? tlie agen-
cies at work; and learning how deeply the surface of^tiie
land has been denuded, and how much sediment lias 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 superimposed strata, and
watch the rivulets bringing down mud, and the waves
wearing away the sea-cliffs, in order to comprehend some-
thing 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 degrada-
tion. The tides in most cases reach the cliffs only fur 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 nothing 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 re-
treating cliffs rounded boulders, all thickly clothed
by marine productions, showing how little they are
abraded, and how seldom they are rolled about I More-
over, if we follow for a few miles any line of
rocky cliff, which is undergoing degradation, we find that
it is only here and there, along a short length or rouiul a
promontory, that the cliffs are at the present time suffering.
The appearance of the surface and the vegetation show tliat
elsewhere years have elapsed since the waters washed iheir
base.

We have, however^ recently learned from the observa-

316

TEE LAPSE OF TIME,

tious of Rainsay, in the van of many excellent observers —
of Jukes, Geikie, Croll and others, that subaerial degrada-
tion is a mucli 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, witli its dissolved carbonic acid, and in colder coun-
tries to frost; the disintegrated 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 undulating
country, we see the effects of subaerial degradation in the
muddy rills wdiich flow down every slope. Messrs. Eamsay
and Whitaker have shown, and the observation is a most
striking one, that the great lines of escarpment in the
Wealden district and those ranging across England, which
formerly were looked at as ancient sea-coasts, can not have
been thus formed, for each line is composed of one and the
same formation, while 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 origin in chief part to the rocks of which they are
composed, 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 subaerial
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 duration 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 sedimentary forma-
tions. I remember having been much struck when view-
ing volcanic islands, which have been worn by the waves
and pared all round into perpendicular 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

TEE LAPSE OF TIME. 317

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 upheaved 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 surface 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 upward of thirty miles, and

along this line the vertical displacement of the strata varies

from 600 to 3,0U0 feet. Professor Eamsay has published

an account of a downthrow in Anglesea of 2,300 feet; and

he informs me that he fully believes that there is one in

Merionethshire 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 Eamsay has given me the maximum thickness,

from actual measurement in most cases, of the successive

formations in dirfferent parts of Great Britain; and this is

the result:

Feet.

Palaeozoic strata (not including igneous beds) 57,154

Secondary strata "^o'o m

Tertiary strata w,L40

—making altogether 72,584 feet; that is, very nearly thir-
teen and three-quarters British miles. Some of the for-
mations, which are represented in England by thm beds,
are thousands of feet in thickness on the Continent. More-
over, betv/een each successive formation we have, in tlie
opinion of most geologists, blank periods of enormous
length. So that the lofty pile of sedimentary rocks in

31S THE LAPSE OF TIME.

Britain gives but an inadequate idea of the time which has
elapsed during their accumulation. The consideration of
these various "facts impresses the mind almost in the same
manner as does the vain endeavor 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 *Mn
forming too great a conception of the length of " geological
periods,'^ but in estimating them by years. When geolo-
gists look at large and complicated phenomena, and then
at the figures representing several million years, the two
produce a totally dilferent 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
1,000 feet of solid rock, as it became gradually disintegrated,
would thus be removed 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 if halved or quartered
it is still very surprising. Few of us, however, know what
a million really means: Mr. Croll gives the following illus-
tration: Take a narrow strip of paper, eighty-three feet
four 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, what
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
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 represents the
work of two breeders in succession. It is not to be sup-
posed that species in a state of nature ever change so
quickly as domestic animals under the guidance of method-
ical selection. The comparison would be in every way

THE LAPSE OF TIME. 819

fairer^ with the effects which follow from unconscious
selection, that is, the preservation of the most useful or
beautiful animals, with no intention of modifyino- the
breed; but by this process of unconscious selection, various
breeds have been sensibly changed in the course of two or
three centuries.

Species, however, probably change much more slowlv,
and within the same country only a few change at tlie sanie
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 tlie 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
circumstance, would not alwavs occur at once. Un-
fortunately 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.

ON" THE POORNESS OF PAL^ONTOLOGICAL COLLECTIONS.

Now let us turn to our richest geological museums, and
what a paltry display we behold! That our collections are
imperfect is admitted by every one. The remark of that
admirable palaeontologist, 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 eartli has been
geologically explored, and no part with sufficient care, as
the important discoveries made every year in Europe
prove. No organism wholly soft can be preserved. Shells
and bones decay and disappear when left on the bottom of
the sea, where sediment is not accumulating. AVe prob-
ably take a quite erroneous view, when we assume tluit
sediment is being deposited over nearly the whole bed of
the sea, at a rate sufficiently quick to imbed and preserve
fossil remains. Throughout an enormously large propor-
tion of the ocean, the bright blue tint of the water be-

320 THE POORNESS OF

speaks its purity. The many cases on record of a forma-
tion conformably covered, after an immense interval of
time, by another and later formation, without the under-
lying 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 /emains which do become imbedded, if in sand
or gravel, will, when the beds are upraised, generally
be dissolved by the percolation of rain water charged
with caibolic acid. Some of the many kinds of animals
which live on the beach between high and low water
mark scbni to be rarely preserved. For instance, the
several species of the Chthamalina3 (a sub-family of sessile
cirripedco) coat the rocks all over the world in intinite
numbers they are all strictly littoral, with the exception of
a single Mediterranean species, which inhabits deep water,
and this has been found fossil in Sicily, whereas not one
other species has hitherto been found in any tertiary for-
mation: yet it is known that the genus Olithamalus 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 in-
stances 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 resj^ect to the terrestrial productions which lived
during the Secondary and Palaeozoic periods, it is super-
fluous to state that our evidence is fragmentary in an
extreme degree. For instance, untill 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 marnmiferous remains, a glance at the histor-
ical table published in Lyell's Manual will bring home tlie
truth, how accidenral and rare is their preservation, f;i!-
better than pages of detail. Nor is their rarity surprisi ::,;•,
when we remember how large a proportion of the bones of

PAL^ONTOLOOICAL COLLECTIONS. 30 1

tertiary mammals have been discovered either in caves or in
lacustrine deposits; and that not a cave or true hicustrino
bed is known belonging to the age of our secondary or
palaeozoic formations.

But the imperfection in the geological record largely re-
sults from another and more important cause than any of
the foregoing; namely, from the several formations being
separated from each other by wide intervals of time. This
doctrine has been emphatically admitted by many geologists
and palaeontologists, who, like E. Forbes, entirely disbe-
lieve in the change of species. When we see the forma-
tions 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
K. Murchison's great work on Russia, what wide gaps there
are in that country between the superimposed formations;
so it is in North America, and in many other parts of the
world. The most skillful 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 sedi-
ment, charged with new and peculiar forms of life, had
elsewliere been accumulated. And if, in every separate
territory, hardly any idea can be formed of the length of
time which has elapsed between the consecutive forma-
tions, we may infer that this could nowhere be ascertained.
The frequent and great changes in the mineralogical com-
position of consecutive formations, 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 for-
mation.

We can, I think, see why the geological formations
of each region are almost invariable 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 w^-
raised several hundred feet within the recent period, than
the absence of anv recent deposits 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 sev-

322

THE POORNESS OF

eral 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 tertiary
remains can anywhere be found, though the supply of sedi-
ment must for ages have been great, from the enormous
degradation of the coast rocks and from the muddy streams
entering the sea. The explanation, no doubt, is that the
littoral and sublittoral 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

v/aves.

"We may, I think, conclude that sediment must be ac-
cumulated 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 profound 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 upraised will give an imperfect
record of the organisms which existed in the neighborhood
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 sedi-
ment nearly balance each other, the sea will remain shallow
and favorable for many and varied forms, and thus a rich
fossiliferous formation, thick enough, when upraised, to
resist a large amount of denudation, may be formed.

I am convinced that nearly all our ancient formations,
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, and 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 subsidence. I may add, that the only
ancient tertiary formation on the west coast of South
America, which has been bulky enough to resist such de-
gradation as it has as yet suffered, but which will hardly

PAL^ONTOLOGICAL COLLECTIONS, 303

last to a distant geological age, was deposited duriijfr a
downward oscillation of level, and thus gained considerable
thickness.

All geological facts tell us plainly tluit each area has
"undergone numerous slow oscillations of level, and appar-
ently these oscillations have affected wide spaces. Conse-
quently, formations rich in fossils and sumciently tliick
and extensive to resist subsequent degradation, will have
been formed over wide spaces during periods of sub-
sidence, but only where the supply of sediment was
sufficient to keep the sea shallow and to embed and
preserve the remains before they had time to decay. On
the other hand, as long as the bed of the sea remains sta-
tionary, thick deposits cannot have been accumulated in
the shallow parts, which are the most favorable to life.
Still less can this have happened during the alternate
periods of elevation; or, to speak more accurately, tiie beds
which were then accumulated will generally have been de-
stroyed by being upraised and brought within the limits of
the coast-action.

These remarks apply chiefly to littoral and sublittoral
deposits. In the case of an extensive and shallow sea, such
as that within a large part of the Malay Archipelago,
where the depth varies from thirty or forty to sixty fath-
oms, a widely extended formation migiit be formed during
a period of elevation, and yet not suffer excessively from
denudation during its slow upheaval; but the tiiickness
of the formation could not be great, for owing to the ele-
vatory movement it would be less than the depth in which
it was formed; nor would the deposit be much consoli-
dated, nor be capped by overlying formations, so that it
would run a good chance of being worn away by atmos-
pheric degradation and by the action 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, tlie
deposit formed during the rising movement, thougii not
thick, might afterward become protected by fresh accumu-
lations, and thus be preserved for a long pei'iixl.

Mr, Hopkins also expresses his belief that sedimentary
beds of considerable horizontal extent have rarely been
completely destroyed. But all geologists, excepting the

324 THE POORNESS OF

few who believe that our present metamorphic schists and
phitonic rocks once formed the primordial nucleus of the
globe, will admit that these latter rocks have been stripped
of their coverina: to an enormous extent. For it is
scarcely possible that such rocks could have been solidified
and crystallized while 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, etc., were once necessarially 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 over-
lying 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 Switzerlandc South of the Amazon, Boue colors
an area composed of rocks of this nature as equal to that
of Spain. Prance^ -^taly. part of Germany, and the British
Islands^ all conjoined. This region has not been carefully
explored, but from the concurrent testimony of travelers,
the granitic area is very large: thus Von Eschwege gives a
detailed section of these rocks, stretching from Eio de
Janeiro for 260 geographical miles inland in a straight
line; and I traveled for 150 miles in another direction, and
saw nothing but granitic rocks. Numerous specimens,
collected along the whole coast, from near Eio Janeiro to
the mouth of the Plata, a distance of 1,100 geographical
miles, were examined by me, and they all belonged to
this class. Inland, along the whole northern bank of
the Plata, I saw, besides modern tertiary beds, only one
small patch 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' beautiful map, I have estimated tlie areas by
cutting out and weighing the paper, and I find that the
metamorphic (excluding the " semi-metamorphic^') and
granite rocks exceed, in the proportion of 19 to 12.5,
the whole of the newer Palaeozoic formations. In many
regions tlie metamorphic and granite rocks would be found
much more widely extended than they appear to be, if all

PAL^ONWLOGICAL COLLECTIONS. 305

the sedimentary beds were removed whicli rest uiicoii-
formably on them, and which could not have formed part
of the original mantle nnder which they were crystallized.
Hence, it is probable that in some parts of the world wh(>le
formations have been completely denuded, witli not a wreck
left behind.

One remark is here worth a passing notice. During
periods of elevation the area of the laud and of the adjoin-
ing shoal parts of the sea will be increased and now t^ta-
tions will often be formed — all circumstances favorable, as
previously explained, for the formation of new varieties
and species; but during such periods there will general Iv
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 np into an archipelago), and
consequently during subsidence, though there will bo
much extinction, few new varieties 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.

ON" THE abse:n'ce of numerous intermediate varie-
ties IK ANY SII^GLE FORilATIOif.

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 graduated varieties
between the allied species which lived at its commence-
ment 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 Trautsehold gives a
number of instances with Ammonites, and Ililgendorf has
described a most curious case of ten graduated forms of
Planorbis multiformis in the successive beds of a fresh-
water formation in Switzerland. Although each formation
has indisputably required a vast number of years for its
deposition, several reasons can be given why each should
not commonly include a graduated series of links between
the species which lived at its commencement and close, but

3:>6 ABSENCE OF INTERMEDIATE VARIETIES

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 palasontolo^ists, whose opinions are worthy of
much deference, namely Bronn and Woodward, have con-
cluded that the average duration of each formation is twice
or thrice as long as the average duration 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 appearing in the middle of any forma-
tion, it would be rash in the extreme to infer that it had
not elsewhere previously existed. 80 again, when we find
a species disappearing before the last layers have been de-
posited, 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 safeW 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
apiDcaring in any formation, the probability is that it only
then first immigrated into that area. It is well-known,
for instance, that several species appear somewhat earlier
in the palaeozoic beds of North America than in those of
Europe; time having apparently been required for their
migration from the American to the European seas. In
examining the latest deposits, in various quarters of the
world, it lias everywhere been noted, that some few still
existing species are common in the deposit, but have
become extinct in the immediately surrounding sea; or,
conversely, that some are now abundant in the neighbor-
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 during
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

IN ANT SINQL E FORMA TION. 32 7

the world, sedimentary deposits, inchidincj fossil rcmaini^y
have gone on accumulating within tlie same ?\rea during
the whole of this period. It is not, for instance, pr()])ablo
that sediment was deposited during tlie whole of tlie
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 geograpliical 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 probably first appear and disappear at diiferent levels,
owing to the migrations of species and to geographical
changes. And in the distant future, a geologist, examin-
ing these beds, would be tempted to conclude that tlio
average duration of life of the 3mbedded fossils had been
less than that of tlie glacial period, instead of having been
really far greater, that is, extending from before 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 formation, the
deposit must have gone on continuously accumulating
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 accumulate oidy
during a period of subsidence; and to keej) Hie deptli
approximately the same, which is necessary that tiic
same marine species may live on the same space, the sup-
ply of sediment must nearly counterbalance the amount
of subsidence. But this same movement of subsi-
dence will tend to submerge tlie area whence the sediment
is derived, and thus diminish the supply, while tlie down-
ward movement continues. In fact, this neai-ly exact bal-
ancing between the supply of sediment and the amount of
subsidence is probably a rare contingency; for it has been
observed by more than one palaeontologist 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 tlu*

328 ABSENCE OF INTERMEDIATE VARIETIES

whole pile of formation in any country, has generally been
intermittent in its accumulation. When we see, as is so
often the case^ a formations composed of beds of widely
different mineralogical composition^ we may reasonably
suspect that the process of deposition has been more or less
interrupted, ."N'or will the closest inspection of a forma-
tion give us any idea of the length of time which its depo-
sition may have consumed. Many instances could be
given of beds, only a few feet in thickness, representing
formations which are elsewhere thousands of feet in thick-
ness, and which must have required an enormous period
for their accumulation; 3^et no one ignorant of this fact
would have even suspected the vast lapse of time repre-
sented by the thinner formatioUo Many cases could be
given of the lower beds of a formation having been up-
raised, denuded, submerged, and then recovered by the
upper beds of the same formation — facts, showing what
wide, yet easily overlooked, intervals have occurred in its
accumulation. In other cases we have the plainest evi-
dence in great fossilized trees, still standing upright as
they grew, of many long intervals of time and changes of
level during the process of deposition, which would not
have been suspected, had not the trees been preserved: thus
Sir C. Lyell and Dr= Dawson found carboniferous beds
1,400 feet thick in Nova Scotia, with ancient root bearing
strata, one above the other, at no less than sixty-eight dif-
ferent levels Hence, when the same species occurs at tlie
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 inter-
mediiite 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 wliich 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

IN AN Y SINGLE FORMA HON. 329

intermediate gradations; and this, from the reasons just
assigned, we can seldom, hope to effect in any one geolog-
ical 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, uidess at
the same time it could be closely connected by intermedi-
ate 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 them in all respects. 80
that we might obtain the parent-species and its several ,
modified descendants from the low^er^and upper beds of the
same formation, and unless we obtained numerous transi-
tional gradations, we should not recognize their blood-rela-
tionship, and should consequently rank them as distinct
species.

It is notorious on what excessively slight differences
many palaeontologists have founded their species; and they
do this the more readily if the specimens come from differ-
ent 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 chanije which
on the theory we ought to find. Look again at the later
tertiary deposits, which include many shells believed by
the majority of naturalists to be identical with existing
species; but some excellent naturalists, as Agassiz aiul
Pictet, maintain that all these tertiary species are specific-
ally distinct, though the distinction is admitted to be very
slight; so that here, unless we believe that tliese eminent
naturalists have been misled by their imaginations, and
that these late tertiary species really present no difference
whatever from their living representatives, or unless we
admit, in opposition to the judgment of most naturalists,
that these tertiary species are all truly distinct from the
recent, we have evidence of the frequent occurrence of slight
modifications of the kind required. If we look to ratlior
wider intervals of time, namely, to distinct but consecu-
tive stages of the same great formation, we find that the
embedded fossils, though universally ranked as specific-
ally different, yet are far more closely related to each other

330 ABSENCE OF INTERMEDIATE VARIETIES

than are the species found in more widely separated forma-
tions; so that here again we have undoubted evidence of
change in the direction ri>quired by the theory; but to this
latter subject I shall return in the following chapter.

AVith 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
widel}^ and supplant their parent-form until they have
been modified and perfected in some considerable degree.
According to this view, the chance of discovering in a
formation in any one country all the early stages of transi-
tion between any two forms, is small, for the successive
changes are sujjposed to have been local or confined to
some one spot. Most marine animals 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 j^robable that
those which had the widest range, far exceeding the limits
of the known geological formations in Euroj^e, have often-
est given rise, first to local varieties and ultimately to new
species; 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, namely, that
the period during which each species underwent modifica-
tion, 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
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 perceive the
improbability of our being enabled to connect species by
numerous, fine, intermediate, fossil links, by asking our-
selves 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
Btock or from several aboriginal stocks; or again, whether

/if AJNT SINGLE FORMA TION. 33 1

certain sea-shells inhabiting 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 discovering in a fossil
state numerous intermediate gradations; and such success
is improbable in the highest degree.

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 destroy four-tifths of them, no one
doubts that the remainder will stand much more distinct
from each other. If the extreme forms in the genus
happen to have been thus destroyed, the genus itself will
stand more distinct from other allied genera. What geo-
logical research has not revealed, is the former existence of
infinitely numerous gradations, as fine as existing varieties,
connecting 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 geological 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 Kussia ; and therefore
equals all the geological formations which have been
examined with any accuracy, excepting those of the United
States of America. I fully agree with Mr. God win- Austen,
that the present condition of the Malay Archipehigo, with
its numerous large islands separated by wide and shallow
seas, probably represents the former state of Europe,
while most of our formations were accumulatiusx. 'I'he
Malav 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 repre-
sent the natural history of the world !

But we have every reason to believe that the terrestrial

332 ABSENCE OF INTERMEDIATE VARIETIES

productions of the archipelago would be preserved in an
extremely imperfect manner in the formations 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 endure 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.

Formations rich in fossils of many kinds, and of thick-
ness sufficient to last to an age as distant in futurity as the
secondary formations lie in the past, would generally be
formed in the archipelago onl}^ during periods of subsi-
dence. These periods of subsidence would be separated
from each other by immense intervals of time, during
which the area would be either stationary or rising; while
rising, the fossiliferous formations on the steeper shores
would be destroyed, almost 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
Beas within the archipelago, sedimentary beds could hardly
be accumulated of great thickness during the periods of
elevation, or become capped and protected by subsequent
deposits, so as to have a good chance of enduring to a very
distant future. During the periods of subsidence, there
would 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 anyone great
period of subsidence over the whole or part of the archi-
pelago, together with a contemporaneous accumulation of
sediment, would exceed the average duration of the same
specific forms; and these contingencies are indispensable
for the pi'eservation of all the transitional gradations be-
tween 9.ny 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 probo,ble tha^ each great period of subsidence would
be interrupted by oscillations of level, and that slight cli-
matical phanges would intervene during such lengthy
periods^ and in these cases the inhabitants of the archi-

nr AKT SLNOL E FORM A TJON. 833

pelago would migrate, and no closely consecutive record of
their modifications could bo preserved in any one forma-
tion.

Very many of the marine inhabitants of the archipelago
now range thousands of miles beyond its confines; and
analogy plainly leads to the belief that it would be ciiielly
these far-ranging species, though only some of thenf.
which wo'ald oftenest produce new varieties; and the vari-
eties would at first be local or confined to one })lace, but if
possessed of any decided advantage, or when further modi-
fied and improved, they would slowly spread and suj)plant
their parent-forms. When such varieties returned to their
ancient homes, as they would diifer from their former state
in a nearly uniform, though perhaps extremely slight degree,
and as they would be found imbedded in slightly ditter-
ent sub-stages of the same formation, they would, accord-
ing to the principles followed by many palaeontologists, bo
ranked as new and distinct species.

If then there be some degree of truth in these remarks,
we have no right to expect to find, in our geological for-
mations, an infinite number of those fine transitional forms
which, on our theory, have connected all the jiast and
present species of the same group into one long and branch-
ing 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
tliem be ever so close, if found in difi'erent stages of tho
same formation, would, by many palaeontologists, bo
ranked as distinct species. But I do not pretend that I
should ev3r have suspected how poor was the record in the
best preserved geological sections, had not the absence of
innumerable transitional links between the species wliicii
lived at the commencement and close of each formation,
pressed so hardly on my theory.

OK THE SUDDEi^r APPEARANCE OF WHOLE GROUPS OP

ALLIED SPECIES.

The abrupt manner in which whole groups of species
suddenly appear in certain formations, has been urged by
several palaeontologists— for instance, by Agassiz. Pictet,
and Sedgwick— as a fatal objection to tho belief in tho

334 SUDDEN APPEAMANCE OP

transmutation of species. If numerous species, belonging
to the same genera or families, have reall}^ started into life
at once, the fact would be fatal to the tlieory of evolution
tlirough 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 progenitors must have lived long before
their modified descendants. But we continually overrate
the perfection of the geological record, and falsely infer,
because certain genera or families have not been found be-
neath a certain stage, that they did not exist before that
stage. In all cases positive palaeontological 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 elsewhere have long
existed, and have slowly multiplied, before they invaded
the ancient archipelagoes of Europe and the Unites States.
We do not make due allowance 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 apjoear 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 or-
ganism to some new and peculiar line of life, for instance,
to fly through the air; and consequently that the transi-
tional forms would often long remain confined to some one
region; but that, when this adaptation had once been
effected, and a few species had thus acquired a great ad-
vantage 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 succes-
sive modifications of the anterior limbs of a supposed pro-
totype could possibly have been of any advantage. But
look at the penguins of the Southern Ocean; have not

GROUPS OF ALLIED SPECIES, 335

these birds their front limbs in this precise intermediuto
state of "neither true arms nor true wings?" Yet tlie.so
birds hold their place victoriously in the battle for life; fur
they exist in infinite numbers and of many kinds. 1 do
not suppose that we here see the real transitional grades
through which the wings of birds have passed; but wliat
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 sea like the loggi*r-
headed duck, and ultimately to rise from its surface and
glide through the air?

I will now give a few examples to illustrate the fore-
going 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
Palaeontology, published in 1844-4G and in 1853-57, the
conclusions on the first appearance and disappearance of
several grouj^s of animals have been considerably modified;
and a third edition would require still further changes. I may
recall the well-known fact that in geological treatises, pub-
lished not many years ago, mammals were always sj^oken
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 discovered
in the new red sandstone at nearly the commencement 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 preservation of footstens
in the new red sandstone of the United States, who would
have ventured to suppose tliat 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 dis-
covered in these beds. JS^'ot long ap^o, pahTontoh-)gi.st3
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 the deposition of the upper greensand; and
still more recently, that strange bird, tlio Archeopteryx,

336 SUDDEN APPEARANCE OF

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 Solenho-
fen. Hardly any recent discovery shows more forcibly
than this how little we as yet know of the former inhab-
itants of the world.

I may give another instance, which, from having passed
under ray own eyes, has much struck me. In a memoir on
Fossil Sessile Cirripedes, I stated that, from the large num-
ber of existing and extinct tertiary species; from the ex-
traordinary abundance of tlie individuals of many species
all over the world, from the Arctic regions to tiie equator,
inhabiting various zones of depths, from the upper tidal
limits to fifty fatiioms; from the perfect manner in v^diicli
specimens are preserved in the oldest tertiary beds; from
the ease with v>^hich even a fragment of a valve can be
recognized; from all these circumstances, I inferred that,
had sessile cirripedes existed during the secondary periods,
they would certainly have been preserved and dis-
covered; and as not one species had then been discov-
ered in beds of this age, I concluded that this great
group had been suddenly developed at the commencement
of the tertiar}^ series. This ^vas a sore trouble to me,
adding, as 1 then thought, one more instance of the
abrupt appearance of a gi'eat group of species. But my
work had hardly been published, wdien a skillful pal^eon-
togist, M. Bosquut, sent me a drawing of a perfect speci-
men of an unmistakable sessile cirripede, which he had
himself extracted from the chalk of Belgium. And, as
if to make the case as striking as possible, this cirripede
was a Chthamalus, a very common, large, and ubiquitous
genus, of which not one species has as yet been found even
in any tertiary stratum. Still more recently, a Pyrgoma,
a member of a distinct subfamily of sessile cirrii^edes, has
been discovered by Mr. Woodward in the upper chalk; so
that we now have abundant evidence of the existence of
this group of animals during the secondary period.

The case most frequently insisted on by palaeontologists
of the apparently sudden appearance of a whole group of
species, is that of thet eleostean fishes, low down, according
to Agassiz, in the Chalk period. This group includes the
large majority of existing species. But certain Jurassic

GROUPS OF ALLIED SPECIES. 337

and Triassic forms are now commonly admitted to be
teieostean; and even some palseozoic forms have thus been
classed by one high authority. If the teleosteans liud
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 ])een
shown that at the same period the species were suddenly
and simultaneously 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-
running through Pictet's Palaeontology it will be seen that
very few species are known from several formations in
Europe. Some few families of fish now have a confined
range; the teieostean 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 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 inclosed basin, in
which any great group of marine animals might be multi-
plied; and here they would remain confined, until some of
the species became adapted to a cooler climate, and were
enabled to double the southern capes of Africa 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
palseontological knowledge effected by the discoveries of
the last dozen years, it seems to me to be about as rash
to dogmatize on the succession of organic foims throughout
the world, as it would be for a naturalist to land for five
minutes on a barren point in Australia, and then to discuss
the number and range of its productions.

ON THE SUDDEN- APPEARANCE OF GROUPS OF ALLIED
SPECIES IN THE LOWEST KNOWN FOSSILIFEKOUS STRATA.

There is another and allied difficulty, which is much
more serious. I allude to the manner in which species

338 GROUPS OF ALLIED SPECIES

belonging to several of the main divisions of the animal
kingdom suddenly appear in the lowest known fossiliferoiis
rocks. Most of the arguments which have convinced 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 instance, it cannot be doubted
that all the Cambrian and Silurian trilobites are descended
from some one crustacean, 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, etc., do not differ much
from living species; and it cannot on our theory be sup-
posed, that these old species were tlie progenitors of all the
species belonging to the same groups which have subse-
quently appeared, for they are not in any degree inter-
mediate 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 encounter 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 twenty or more than four hundred million years ago,
but probably not less than ninety-eight or more than two
hundred million years. These very wide limits show how
doubtful the data are; and other elements mav have here-
after to be introduced into the problem. Mr. Ci'oll esti-
mates that about sixty 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 certainlv occurred since the
Cambrian formation; and the previous one hundred and
forty million years can hardly be considered as sufficient
for the development of the varied forms of life which
already existed during tlie Cambrian period. It is, how-
ever, probable, as Sir William Thompson insists, that the
world at a very early period was subjected to more rapid

m LO WEST FOSSILIFEHO US STRA TA. 339

and violent changes in its physical conditions than tlioso
now occurring; and such changes would have tended to
induce changes at a corresponding rate in the or^'anisma
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. Murchison at their
head, were until recently convinced tiiat we beheld in tlie
organic remains of the lowest Silurian stratum the first
dawn of life. Other highly competent judges, as Lyell and
E. Forbes, have disputed this conclusion. "We shoiild not
forget than only a small portion of the world is known with
accuracy. Not very lon^ ago M. Barrande added anotiier
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, ^Ir. Hicks
has found South Wales beds rich in trilobites, and con-
taining various molluscs and annelids. The presence of
phosphatic nodules and bituminous matter, even in some
of the lowest azotic rocks, probablv indicates life at tliese
periods; and the existence of the Eozoon in the Lauren tiaii
formation of Canada is generally adinitted. There are three
great series of strata beneath the Silurian system in Can-
ada, 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 tho
base of the palaeozoic series to the present time.
We are thus carried back to a period so remote, that the
appearance 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 organized
of all classes of animals, but is highly organized 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. Tims
the words, which I wrote in 1S59, about the existence of
living beings long before the Cambrian perio<l, and which
are almost the same with those since used by Sir W. Logan,
have proved true. Nevertheless, the difficulty of assigning
any good reason for the absence of vast piles of strata rich
in fossils beneath the Cambrian system is very great. It

340 GROUPS OF ALLIED SPECIES

does not seem probable that the most ancient beds have
been quite worn away by denudation, or that their fossils
have been wholly obliterated oy metamorphic action, for
if this had been the case we should have found only small
remnants of the formations next succeeding them in age,
aud these would always have existed in a partially meta-
morpliosed condition. But the descriptions which we
possess of the silurian deposits over immense territories in
Russia and in Xorth America, do not support the view
that the older a formation is the more invariably it has
sutfored 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 hypothesis. From
the nature of the organic remains which do not appear to
have inhabited profound depths, 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 neighborhood of the now existing conti-
nents 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
between 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 ex-
tensive 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 palaeozoic
or secondary formation. Hence, we may perhaps infer,
that during the pala3ozoic and secondary periods, neither
continents nor continental islands existed where our oceans
now extend; for had they existed, palaeozoic and second-
ary formations would in all probability have been accumu-
lated from sediment derived from their wear and tear;
and these would have been at least partially upheaved by

m LO WEST FOSSILIFEIiO US STRA TA. 34 5.

the oscillations of level, which must have intervened
during these enormously long periods. If, then, wo may
infer anything from these facts, we may infer that, whoro
our oceans now extend, oceans have extended from the
remotest perioc] of which we have any record; and on
the other h^md, that where continents now exist,
large tracts of land have existed, subjected, no doubt, to
great oscillations of level, since the Cambrian period. The
colored map appended to my volume on Coral Keefs, led
me to conclude that the great oceans are still mainlv areas
of subsidence, the great archipelagoes still areas of oscilla-
tions of level, and the continents areas of elevation. i^>nt
we have no reason to assume that things have thus re-
mained from the beginning of the world. Our continents
seem to have been formed by a preponderance, during
many oscillations of level, of the force of elevation. Bu't
may not the areas of preponderant movement have
changed in the lapse of ages? At a period long antecedent
to the Cambrian epoch, continents may have existed where
oceans are nov/ spread out, and clear and open 0(,'eans
may have existed where our continents now stand. Xor
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
recognizable condition^ older than the Cambrian strata,
supposing such to have been formerly deposited; for it
might well happen that strata which had subsided some
miles nearer to the center 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 always remained nearer to the sur-
face. The immense areas in some parts of the world, for
instance in South America, of naked metamorphic rorks,
which must have been heated under great pressure, have
always seemed to me to require some special explana-
tion; and we may perhaps believe that we see in these
large areas the many formations long {interior to the Cam-
■^rian epoch in a completely metamorphosed and denuded

condition.

The several difficulties here discussed, nanu'ly, that,
though we find in our geological formations niany links
^fitween the species which n^w exist and which formerly

342 GROUPS OF ALLIED SPECIES.

existed, we do not find infinitely nnmerons fine transitional
forms closely joining them ail together. The sudden man-
ner in which several groups of species first appear in our
European formations, the almost entire absence, as at
present known, of formations rich in fossils beneath
the Cambrian strata, are all undoubtedly of the most
serious nature. We see this in the fact that the most em-
inent paleontologists, namely, Cuvier, Agassiz, Barrande,
Pictet, Falconer, E. Forbes, etc., and all our greatest geol-
ogists, as Lyell, Murchison, Sedgwick, etc., have unani-
mously, often vehemently, maintained the immutability of
species. But Sir Charles Lyell now gives the support of
his high authority to the opposite side, and most geologists
and palaeontologists are much shaken in their former belief.
Those who believe that the geological record is in any de-
gree 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 chapters,
may represent the forms of life, which are entombed in
our consecutive formations, and which falsely appear
to have been abruptly introduced. On this view the
difficulties above discussed are greatly diminished or even
disappear.

ORGANIC BEINGS. 343

CHAPTER XL

ON THE GEOLOGICAL SUCCESSION OF ORGANIC BEINGS.

On the slow and successive appearance of new species — On tlieir
different rates of change — Species once lost do not reappear —
Groups of species follow the same general rules in their appear-
ance 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 modifica-
tion, 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 tliat
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 existing 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 second-
ary formations are more broken; but, as Bronn has
remarked, neither the appearance nor disappearance of the
many species embedded in each formation nas been simul-
taneous.

Species belonging to 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
fo^ind in the midst of a multitude of extinct forms.

344 TEE OEOLOQIGAL SUCCESSION

Falconer has given a striking instance of a similar fact,
for an existing crocodile is associated with many lost
mammals and reptiles in the snb-Himalayaii 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 greatty.
The productions of the land soem 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 organic 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 species 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 expla-
nation, namely, that it is a case of temporary migration
from a distinct geographical province, seems satisfactory.
These several facts accord well with our theory, which
includes no fixed law of development, causing all the
inhabitants of an area to change abruptly, or simultane-
ously, or to an equal degree. The process of modification
must be slow, and will generally affect only a few species
at the same time; for the variability of each species is
independent of that of all others. Whether such varia-
tions or individual differences as may arise will be aocu-
mulated through natural selection in a greater or less
degree, thus causing a greater or less amount of perma-
nent modification, will depend on many complex contin-
gencies— 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 menus surprising tliat one species should
retain the same identical form much longer than others;

OF ORQANIO BEINGS. 34,5

or, if changing, should change in a less degree. We lind
similar relations between the existing inhubitunts of dis-
tinct_ countries; for instance, the land-shells and coU-opter-
ous insects of Madeira have come to ditler considerably
from their nearest allies on the continent of Europe,
whereas the marine shells and birds have remained
unaltered. We can perhaps understand the a])parently
quicker rate of change in terrestrial and in more higlilv
organized productions compared with marine and lowe'r
productions, by the more complex relations of tlie liigher
beings to their organic and inorganic conditions of life, as
explained in a former chapter. When many of the inhab-
itants of any area have become modified and imj)roved, we
can understand, on the principle of competition, and from
the all-important relations of organism to organism in the
struggle for life, that any form which did not become in
some degree modified and improved, 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, per-
haps, 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 accumulated at
wide and irregularly intei'mittent intervals of time; conse-
quently the amount of organic change exhibited by the fos-
sils embedded in consecutive formations 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 onre lost
should never reappear, even if the very same conditions 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 economy 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 dib-

346 THE OEOLOGIGAL SUCCESSION

tinct progenitors; and organisms 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 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 estab-
lished race of the domestic pigeon, for the successive varia-
tions would almost certainly be in some degree different,
and the newly-formed variety would probably inherit from
its progenitor some characteristic differences.

Groups of species, that this, genera and families, follow
the same general rules in their appearance and disappear-
ance 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. 1 am aware that there are
some apparent exceptions to this rule, but the exceptions
are surprisinglv 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 descend-
ants one from the other, and all from a common progeni-
tor. 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 abruptly
developed; and I have attempted to give an explanation of
this fact, which if true would be fatal to my views. But
such cases are certainly exceptional; the 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 varying thickness, ascending through
the successive geological formations, in which the species

OF OUQANIC BEINGS. 347

are found, the line will sometimes falsely appear to bei-in
at Its lower end, not in a sharp point, but abruptly it
then gradually thickens upward, often keepiug of equal
thickness for a space, and ultimately tliins out in the
upper beds, marking the decrease and finiil 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 p>roduction of a number of
allied forms necessarily being a slow and gradual process,
one species first giving rise to two or three varieties, 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.

OlS EXTI^N^CTIOISr.

"We have as yet only spoken incidentally of the disap-
pearance 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 inti-
mately connected together. The old notion of all the
inhabitants of the earth having been swept away by catas-
trophes at successive periods is very generally given up, even
by those geologists, as Elie de Beaumont, Murchison, Bar-
rande, etc., whose general views would naturally 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 isthmus and the consequent irruption
of a multitude of new inhabitants into an adjoining sea,
or by the final subsidence of an island, tlie process of ex-
tinction may have been rapid. Both single species and
whole groups of species last for very unequal ])eriods; some
groups, as we have seen, have endured from the earliest
known dawn of life to the present day; some have disap-
peared before the close of the palaeozoic period. Xo fixed
taw seems to determine the length of time during which

348 EXTINCTION.

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 production:
if their appearance and disappearance be represented, as
before, by a vertical line of varying thickness t'ne line is
found to taper more gradually at its upper 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 extermi-
nation of whole groups, as of ammonites, toward 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 supposed
that, as the individual has a definite length of life, so have
species a definite duration. Xo one can have marvelled
more than I have done at the extinction of species. When
I found in La Plata the tooth of a horse embedded v/ith
the remains of Mastodon, Megatherium, Toxodon and
other extinct monsters, Avhich all co-existed with still
living shells at a very late geological period, I was filled
with astonishment; for, seeing that the horse, since its in-
troduction by the Spaniards into South America, has run
Avild over the whole country and has increased in numbers
at an unparalleled rate, I asked myself what could so re-
cently have exterminated the former horse under conditions
of life apparently so favorable. But my astonishment was
groundless. Professor Owen soon perceived that the tooth,
though so like that of the existing horse, belonged 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 unfavorable in its conditions of life; but
whai 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 certain, from the analogy of all other
mammals, even of the slow- breeding elephant, and from the
history of the naturalization of the domestic horse in
South America, that under more favorable conditions it
would in a very few years have stocked the wdiole con-
tinent. But we could not have told what the unfavorable

EXTINCTION. 349

conditions were Avhicli checked its incre<ase, whether Roine
one or several contingencies, and at what pericxl of tlje
horse's life, and in what degree tliey severally acLod. If
the conditions had gone on, however slowly, becomii\g less
and less favorable, we assuredly should not have perceived
the fact, yet the fossil horse would certaiiily have become
rarer aiul rarer, and finally extinct — its place being seizx'd
on by some more successful competitor.

It is most difficult always to remember that the increase
of every creature is constantly being checked by unper-
ceived hostile agencies; and tliat these same unper-
ceived agencies are amply sufficient to cause rarity, and
fi.ually extinction. So little is this subject understood,
that I have heard surprise repeatedly expressed at such
great monsters as the Mastodon and the more ancient I)in-
osaurians having become extinct; as if mere bodily strength
gave victory in the battle of life. Mere size, on the con-
trary, 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 highlj capable judge. Dr. Fal-
coner, believes that it is chiefly insects which, from inces-
santly harassing and weakening the elepliant 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 naturalized quadrupeds in several parts of
South America.

We see in many cases in the more recent tertiary forma-
tions that rarity precedes extinction; and we know that
this has been the progress of events with those animah
which have been exterminated, either locally or wliollv,
tliroudi man's agency. I may repeat what I i)ul)lished in
1845,^namelv, that to admit that species generally become
rare before they become extinct— to feel no surpn.-e at the
rarity of a species, and yet to marvel greatly when the spe-
cies ceases to exist, is much the same as to adnnt that sick-
ness in the individual is the forerunner of deatii— 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.

350 EXTINCTION,

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 competition; and the con-
sequent extinction of the less-favored forms almost inevita-
bly follows. It is the same with our domestic productions;
wlien a new and slightly improved variety has been raised,
it at first supplants the less improved varieties in the same
neighborhood; 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
together. 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 sj^ecific forms which have been exterminated;
but we know that species have not gone on indefinitely in-
creasing, at least during the later geological epochs, so
that, looking to later times, we may believe that the pro-
duction of new forms has caused the extinction of about
the same number of old forms.

The competition will generally be most severe, as for-
merly 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 species will
generally cause the extermination of the parent-species;
and if many new forms have been developed 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 by a 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 'n
common. But whether it be species belonging to the
same or to a distinct class, wlaich have yielded their places

EXTINCTION.

361

to other modified and improved species, a few of the suf-
ferers may often be preserved for a long time, from bein^'
fitted to some peculiar line of life, or from inhabiting some
distant and isolated station, where they will have escai)L'd
severe competition. For iiistance, some species of Tri-^o-
nia, 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 extermination of
whole families or orders, as of Trilobites at the close of the
palaeozoic 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 unusually 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 correspondingly rapid manner; and the forms which
thus yield their places will commonly be allied, for they
will partake 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 moment that we un-
derstand the many complex contingencies 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 per-
ceived by us, the whole economy 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 another can be naturalized in a given coun-
try; then, and not until then, we may justly feel surprise
why we cannot account for the extintion of any particular
species or group of species.

0^») FORMS OF LIF^ CHANG INQ

<",

cD:i

02T THE FORMS OF LIFE CHAXGIlN^G ALMOST SIMULTA-
KEOUSLY THROUGHOUT THE WORLD.

Scarcely any pal^eontological discovery is more striking
than the fact tliat the forms of life change almost simul-
taneously throughout the world. Thus our European
Chalk formation can be recognized in many distant regions,
under the most different climates, where not a frag-
ment of the mineral chalk itself can be found; namely, in
North America, in equatorial South America, 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 unmistakable resemblance to
those of ihe Chalk. It is not that the same species are
met with; for in some cases not one species is identically
the same, but they belong to the same families, genera,
and sectioiis of genera, and sometimes are similarly char-
acterized in such trifling points as mere superficial sculp-
ture. Moreover, other forms, which are not found in the
Chalk of Europe, but whicli occur in the formations either
above or below, occur in the same order at these distant
points of the world. In the several successive palaeozoic
formatioiis of Russia, Western Europe, and North America,
a similar parallelism in the forms of life has been observed
by several authors; so it is, according to Lvell, with the
Fiuropean and North American tertiary deposits. Even if
the few fossil species which are common to the Did and
New Worlds were kept wholly out of view, the general
parallelism in the successive forms of life, in the palceozoic
and tertiary stages, would still be manifest, and the several
formations could be easily correlated.

These observations, however, relate to the marine inhabi-
tants 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 Mega-
therium, 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 anomalous monsters co-existed with
the Mastodon and Horse, it might at least have been in-

THROUGHOUT THE WOULD. 3r,;3

ferred that they had lived during one of the later tertiary

stages.

AVlien the marine forms of life are spoken of as having
changed simultaneously throughout the world, it must nol
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 tlie
pleistocene period (a very remote period as measured by
years, including the whole glacial epoch) were compjired
with those now existing in South America or in Australia,
the most skillful naturalist would hardly be able to Bay
whether the present or the pleistocene inhabitants of
Europe resembled most closely those of the southern hemi-
sphere. So, agai]i, 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 in-
habitants of Europe; and if this be so, it is evident that
fossiliferous beds now deposited on the sliorcs of Korth
America would hereafter be liable to be classed with some-
what older European beds. Nevertheless, looking to a
remotely future epoch, there can be little doubt that all
the more modern marine formations, namely, the upjjcr
pliocene, the pleistocene and strictly modern beds of
Europe, North and South America, and Australia, from
containing fossil remains in some degree allied, and from
not including those forms which are found only in the
older underlying deiDosits, would be correctly ranked as
simultaneous in a geological sense.

The fact of the forms of life changing simultaneously in
the above large sense, at distant parts of the world, has
greatly struck those admirable observers, ^iM. de Verneiiil
and d^Archiac. After referring to the j)ai-allelism of flic
paleozoic forms of life in various j)arts of Europe, they add,
"11, struck by this strange sequence, we turn our atten-
tion to North America, and there discover a series of ana-
logous phenomena, it will appear certain that all these
modifications of species, their extinction, and the intro-
duction of new ones, can not be owing to mere changes in
marine currents or other causes more or less local and
temporaiy, but depend on general laws which govern the

354 FORMS OF LIFE CHANGING

whole animal kingdom." M. Barrande has made forcible
remarks to precisely the same effect. It is, indeed, quite
futile to look to changes of cicrrents, climate, or other phy-
sical conditions, as the cause of these great mutations in
the forms of life throughout the world, under the most
different climates. We must, as Barrande has remarked,
look to some special law. We shall see this more clearly
wlien we treat of the present distribution of organic beings,
and find how slight is the relation between the johysical
conditions of various countries and the nature of their
inhabitants.

This great fact of the parallel succession of the forms of
lif? throughout the world, is explicable on the theory of
nainral 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 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 giviug rise in new countries to other new varieties
and species. The process of diffusion would often be very
elow, depending on climatal and geographical changes, on
strange accidents, and on the gradual acclimatization of
new species to the various climates through which they
might have to pass, but in the course of time the domi-
nant forms would generally succeed in spreading and would
ultimately prevail. The diffusion would, it is probable, be
slower with the terrestrial inhabitants of distinct conti-
nents than with the marine inhabitants of the continuous
sea. We might therefore expect to find, as we do find, a
less strict degree of parallelism in the succession 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 dominant species

THROUOHOUT THE WOULD. 355

spreading widely and varying; the new species thus pro-
duced being themselves dominant, owing to their having
had some advantage over their already dominant pan-rits,
as well as over other species, and again spreading, varying!
and producing new forms. The old forms wliich are
beaten and which yield their places to the new and victori-
'^us forms, will generally be allied in groups, from- inherit-
ing some inferiority in common; and, therefore, as new
and improved groups spread throughout the world, oKl
groups disappear from the world; and the succession of
forms everywhere 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 tliat blank
intervals of vast duration, as far as fossils are concerned,
occurred during the periods wlien the bed of the sea was
either stationary or rising, and likewise wlien sediment
was not thrown down quickly enough to imbed and pre-
serve organic remains. During these long and blank inter-
vals 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 believe tliat large
areas are affected by the same movement, it is probable
that strictly contemporaneous formations 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 depos-
ited in two regions during nearly, but not exactly, the
same period, we should find in both, from the causes
explained in the foregoing paragraphs, the same general
succession in the forms of life ; but the species would not
exactly correspond ; 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 Eurojie.
Mr. Prestwich, in his admirable .Memoirs on the eocene
deposits of England and France, is able to draw a close

356 AFFINITIES OF EXTINCT SPECIES.

general parallelism 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 tJiemselves differ in a
manner very difficult to account for considering the prox-
imity 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 obser-
vations 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 ;
nevertheless he finds a suprising 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 v*dth a
blank interval in the other — and if in both regions the
species have gone on slowly changing during the accumu-
lation of the several formations and during the long inter-
vals 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.

ox THE AFFINITIES OF EXTIXCT SPECIES TO EACH OTHER,

AND TO LIVING FORMS.

Let ns 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 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 intervals between existing
genera, families and orders, is certainly true; but as this
statement has often been is^nored or even denied, it mav
be well to make some remarks on this subject, and to give
Bome instances. If we confine our attention either to the

AFFINITIES OF EXTINCT SPECIES. 3.5 7

living or to the extinct species of the same class, tlie Buries
is far less perfect than if we combine both into one geiiorai
system. In the writings of Professor Owen we contimialiv
meet with the expression of generalized forms, as apj.lifd
to extinct animals; and in the writings of Agassiz, of
prophetic or synthetic types; and these terms irnply that
such forms are, in fact, intermediate or connecting "links.
Another distinguished paleontologist, M. Gaud7v, has
shown in the most striking manner Uiat many of the fossil
mammals discovered by him in iittica serve to break down
the intervals between existing genera. Cuvier ranked the
Ruminants and Pachyderms as two of the most distinct
orders of mammals; but so many fossil links have been dis-
entombed that Owen has had to alter the whole classifica-
tion, and has placed certain Pachyderms in the same
sub-order Avith ruminants: 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 Macrauchenia of South America connects to a certain
extent these two grand divisions. Ko one will deny that
the Hipparion is intermediate between the existing horse
and certain other ungulate forms. What a wonderful con-
necting link in the chain of mammals is the Typotherium
from South America, as the name given to it by Professor
Gervais expresses, and which cannot be placed in any ex-
isting order. The Sirenia form a very distinct group of tlie
mammals, and one of the most remarkable peculiarities in
existing dugong and lamentin is the entire absence of hind
limbs, without even a ludiment being left; but the extinct
Halitherium had, according to Professor Flower, an ossitiod
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 otht-r re-
spects allied. The cetaceans or whales are widely ditTerent
from all other mammals, but the tertiary Zouglodon and
Squalodon. which have been placed by some naturalists in
an order by themselves, are considered by Professor Huxley
to be undoubtedly cetaceans, *'aud to constitute connect-
ing links with the aquatic carnivora.'^

Even the wide interval between birds and reptiles has
been shown by the naturalist j'ust quoted to be ])ariiully

358 AFFINITIES OF EXTINCT SPECIES.

bridged over in the most unexpected manner, on the one
hand, by the ostrich and extinct Archeopter3^x, and on the
other hand by tlie Conipsognathus, one of the Dinosaurians
— that group which inchides the most gigantic of all ter-
restrial reptiles. Turning to the Invertebrata, Barrande
asserts, a higher authority could not be named, that he is
every day taught that, although palaeozoic animals can cer-
tainly be classed nnder 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, 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 directly interme-
diate in all its characters between two livinsr forms or
groups, the objection is probably valid. But in a natural
classification many fossil species certainly stand between
living species, and some extinct genera between living
genera, even between genera belonging to distinct families.
The most common case, especially with respect to very dis-
tinct groups, such as fish and reptiles, seems to be that,
supposing them to be distinguished at the present day by a
score of characters, 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 char-
acters 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 discovered having affinities directed
toward very distinct groups. Yet if we compare the older
reptiles and Batrachians, the older fish, the older cephalo-
pods, and the eocene mammals, with the recent members
of tlie 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 the reader

APFimnES OF EXTINCT SPECIES. 350

to turn to the diagram in the fourth chapter. We may
suppose that the numbered letters in itaHcs represent
genera, and the dotted lines diverging from them the spe-
cies in each genus. The diagram is much too siinple, too
few genera and too few species being given, but tliis is un-
important for us. The horizontal lines may represent suc-
cessive geological formations, and all the forms beneath
the uppermost line may be considered as extinct. The
three existing genera «i*, q^^, jj^^, will form a small
family; b^^ and/^*, a closely allied family or subfamily,
and ci*, 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 character is
a necessary contingency; it depends solely on the descend-
ants 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 slio^htlv altered conditions of
life, and yet retain throughout a vast period tne same gen-
eral 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 this
order, from the continued effects of extinction and diverg-
ence of character, has become divided into several siih-
families and families, some of which are supi)osed to have
perished at different periods, and some to have endured to
the present day.

By looking at the diagram we can see tliat 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 fa?nilies on the unpcrmost
line would be rendered less distinct from each other. If,

360 AFFINITIES OF EXTINCT SPECIES.

for instance, the genera a}, a^, a}'^, /', m', m", m^, were dis-
interred, these three families would be so closely linked
together that they probably would have to be united into
one great family, in nearly the same manner as has occurred
with ruminants and certain pachyderms. Yet he who
objected to consider as intermediate the extinct genera,
which thus link together the living genera of three fami-
lies, would be partly justified, for they are intermediate,
not directly, 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}^, etc., and Z>^*,
etc.) 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 wi^*), on the uppermost line, be supposed to
differ from each other by half-a-dozen iuiportaut char-
acters, then the families which existed at a period marked
VI would certainly have differed from 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
charactei' between their modified descendants, or between
their collateral relations.

Under nature the process will be far more complicated
than is represented in the diagram; for the groups will
have been more numerous; they will have endured 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 formations 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 thQ

AFFINITIES OF EXTINC2 SPECIES. 361

existing members of the same groups; and tliis by tlio
concurrent evidence of our best palseontologists is fre-
quently the case.

Thus, on the theory of descent witb modification, tlio
main facts with respect to the mutual aOiiiiiies of tbo
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 tiie earth's history will be intermediate
in general character between that which preceded and
that which succeeded it. Thus the species which lived
at the sixth great stage of descent in the diagram are the
modified offspring of those which lived at the fiftli stage,
and are the parents of those which became still more
modihed at the seventh stao^e; hence thev could hardlv fail
to be nearly intermediate in character between the forma
of life above and below. We must, however, allow for the
entire extinction of some preceding forms, and in any one
region for the immigration of new forms from otlier
regions, and for a large amount of modification during the
long and blank intervals between the successive formationd.
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 svstem, when this svstem was first discovered,
were at once recognized by palaeontologists as intermodiato
in character between those of the overlying carboniferous
and underlying Silurian systems. But each fauna is not
necessarily exactly intermedi ite, as unequal intervale of
time have elapsed between consecutive formations.

It is no real objection to the truth of the statement that
the fauna of each period as a whole is nearly intennediato
in character between the preceding and succeeding fauna?,
that certain genera offer exceptions to tbe 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 existence— do not accord in arrangement.
The species extreme in character are not the oldest or the
moat recent; nor are those which are intermediate m ciiar-

362

AFFINITIES OF EXTINCT SPECIES.

acter, intermediate iu age. But supposing for an instant, in
this and other such cases, that the record of the first appear-
ance and disappearance of the species was complete, which
is far from the case, we have no reason to believe that forms
successivel}^ produced necessarily endure for corresponding
lengths of time. A very ancient form may occasionally have
lasted much longer than a form elsewhere subsequently
produced, especially in the case of terrestrial productions
inhabiting separated districts. To compare small things
with great; if the principle living and extinct races of the
domestic pigeon were arranged in serial affinity, this ar-
rangement 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 organic
remains from an intermediate formation are in some degree
intermediate in character, is the fact, insisted on by all
pala3ontologists, that fossils from two consecutive forma-
tions are far more closely related to each other, than are
the fossils from two remote formations. Pictet gives as
a well-known instance, the general resemblance of the
organic remains from the several stages of the Chalk
formation, though the species are distinct in each stage.
This fact alone, from its generality, seems to have
shaken Professor Pictet in his belief in the immutability
of species. He who is acquainted with the distribution
of existing species over the globe, will not attempt to
account for the close resemblance of distinct species in
closely consecutive formations, by the physical conditions
of the ancient 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 prodig-
ious viscisitudes 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.

AFFINITIES OF EXTINCT SPECIES. 303

On the theory of descent, tlie full meanin.fr of the fosHil
remains from closely consecutive fonnutions being- closelv
related, though ranked as distinct species, is obvious. As
the accumulation of each formation has often bfeii inter-
rupted, 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 anv one
or in any two formations, all the intermediate varieties
between the species which appeared at the commencement
and close of these periods: but we ought to lind after
intervals, very long as measured by years, but only moder-
ately long as measured geologically, closely allied forms,
or, as they have been called by some authors, representa-
tive species; and these assuredly 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.

0^ THE STATE OF DEVELOPMENT OF ANCIENT COMPARED

WITH LIVING FORMS.

We have seen in the fourth chapter that the degree of
differentiation and specialization of the parts in organic
beings, when arrived at maturity, is the best standard, as
vet suggested, of their degree of perfection or highness.
We have also seen that, as the specialization of parts is an
advantage to each being, so natural selection will tend to
render the organization of each being more specialized and
perfect, and in this sense higher; not but tliat it may leave
many creatures with simple and unimproved structures
fitted for simple conditions of life, and in some cases will
even degrade or simplify the organization, 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 liave 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 tiie eocene
inhabitants of the world could be put into competition
with the existing iidiabitants, the former would be beaten
and exterminated by the latter, as would the secondary by
the eocene, and the palaeozoic by the secondary forms. iJo

364 STATE OF DEVELOPMENT OF

that by this fundamental test of victory in the battle for
life, as well as by the standard of the specialization of
organs, modern forms ought, on the theory of natural
selection, to stand higher than ancient forms. Is this
the case? A large majority of palaeontologists would
answer in the affirmative; and it seems that this answer
must be admitted as true, though difficult of pi-oof.

It is no valid objection to this conclusion, that certain
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. Carpenrer, progressed in
organization siuce even the Laurentian epoch; for some
organisms would have to remain fitted for simple condi-
tions of life, and what could be better fitted for this end
than these lowly organized Protozoa? Such objections as
the above would be fatal to my view, if it included advance
in organization 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 formation; for in this case, there would not have
been time sufficient for the development of these organ-
isms up to the standard which they had tlien reached.
When advanced up to any given point, there is no neces-
sity, on the theory of natural selection, for their further
continued process; though they will, during each succes-
sive age, have to be slightly modified, so as to hold their
places in relation to slight changes in their conditions.
The foregoing objections hinge on the question 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 organization on the whole has
advanced is in many ways excessively intricate. The geo-
logical record, at all times imperfect, does not extend far
enough back to show with unmistakable clearness that
within the known historv of the world ora,-anization has
largely advanced. Even at the present day, looking to
members of the same class, naturalists are not unanimous

n

ANCIENT AND LIVING FORMS. 3C5

which forms ought to be ranked as highest: thus, some
look at the selaceans or sharks, from their approach in
some important points of structure to reptiles, as the liigh-
est fish; others look at the teleosteans as "the highest. The
ganoids stand intermediate between the selaceans and
teleosteans; the latter at the present day are largely pre-
ponderant 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 organization. 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
believed to be " in fact more highly organized than a fish,
although upon another type?'^ In the complex struggle
for life it is quite credible that crustaceans, not very high
in their own class, might beat cephalopods, the highest
mollucs; and such crustaceans, though not highly devel-
oped, would stand very high in the scale of invertebrate
animals, if iuda*ed bv the most decisive of all trials — the
law of battle. Beside these inherent difficulties in decid-
ing which forms are the most advanced in organization,
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 bal-
ance— but we ought to compare all the members, high and
low, at two periods. At an ancient epoch the highest and low-
est molluscoidal animals, namely, cephalopods and brachio-
pods, swarmed in numbers; at the present time both groups
are greatly reduced, while others, intermediate in orgiini-
zation, have largely increased ; consequently some natu-
ralists maintain that molluscs were formerly more highly
developed than at present; but a stronger case can be made
out on the opposite side, by considering the vast reduction
of brachiopods, and the fact that our existing cephalopods,
though few in number, are more highly oj'gauized than
their ancient representatives. AVe ought also to compare
the relative proportional 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 verte-
brate animals exist, and if we knew that at some former
period only ten thousand kinds existed, we ought to look

366 STATE OF DEVELOPMENT 0^

at this increase in number in the highest class, which im-
plies a great displacement of lower forms, as a decided
advance in the organization of the world. We thus see
how hopelessly difficult it is to compare with perfect fair-
ness, under such extremely complex relations, the standard
of organization of the imperfectly- known faunas of succes-
sive periods.

We shall appreciate this difficulty more clearly by look-
ing to certain existing faunas and floras. From the extra-
ordinary 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 Zealand, a
multitude of British forms would in the course of time
become thoroughly naturalized there, and would exter-
minate many of the natives. On the other hand, from the
fact that hardly a single inhabitant of the southern hemi-
sphere has become wild in any part of Europe, we may
well doubt whether, if all the productions 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 Zealand. Yet the most skillful
naturalist, from an examination 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 em-
bryos of recent animals belonging to the same classes; and
that the geological succession of extinct forms is nearly
parallel with the embryological development of existing
forms. This view accords admirably well with our theory.
In a future chapter I shall attempt to show that the adult
differs from its embryo, owing to variations having super-
vened at a not early age, and having been inherited at a
corresponding age. This process, while it leaves the em-
bryo 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 modi-
fied condition of the species. This view may be true, and

!i

ANCIENT AND LIVING FORMS. 307

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 the vertebrata^
until beds rich in fossils are discovered far beneath tlie
lowest Cambrian strata — a discovery of which the chance
is small.

ON" THE SUCCESSION" OF THE SAME TYPES WITHIN THE
THE SAME AKEAS, DURIN^G THE LATEll TERTIARY
PERIODS.

Mr. Clift many years ago showed that the fossil mam-
mals 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 armor, like those of the arma-
dillo, found in several parts of La Plata; and Professor
Owen has shown in the most striking manner that most of
the fossil mammals, buried there in such numbers, are re-
lated 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 in-
sisted, in 1839 and 1845, on this "law of the succession of
types, ^^ — on "this wonderful relationship in the same con-
tinent between the dead and the living." Professor Owen
has subsequently extended the same generalization 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 showm 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.

Now, what does this remarkable law of the sncoession of
the same types within the same areas mean? He would be a

368 SUCCESSION OF THE

bold mau 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 continents ; and, on the
other hand through similarity of conditions, for the uni-
formity 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 Amer-
ica the law of distribution of terrestrial mammals was for-
merly different from what it now is. North America for-
merly partook strongly of the present character of the
southern half of the continent ; and the southern half was
formerly more closely allied, than it is at present, to the
northern half. In a similar manner we know, from Fal-
coner 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 relation to the distribution of marine animals.

On the theory of descent with modification, the great law
of the long enduring, but not immutable, succession 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 though in some degree modi-
fied descendants. If the inhabitants of one continent for-
merly 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 intermigration, the feebler will yield to the more
dominant 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 for-
merely lived in South America, have left behind them the
sloth, armadillo, and ant-eater, as their degenerate descend.

SAME TYPES IN THE SAME AREAS. .'^r.'j

ants. This cannot for an instant be admitted. 'J'hese
huge animals have become wholly extinct, and have left no
progeny. Bnt 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 progeni-
tors of the living species. It must not be forgotten that,
on onr 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 for-
mation, and in a succeeding formation there be six other
allied or representative genera, each with the same number
of species, then we may conclude that generally only one
species of each of the older genera has left mo(iified
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 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 species 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 pi-eserved
iu 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 hav«
passed away even during a single formation ; that, owing
to subsidence being almost necessary for the accumulation
of deposits rich in fossil species of many kinds, and tliick
enough to outlast future degradation, great intervals of
time must have elapsed between most of our successive for-
mations; that there has probably been more extinction
during the periods of subsidence, and more variati-.n
during the periods of elevation, and during the latter

370 SUMMARY OF THE

the record will have been least perfectly kept ; that each
single formation has not been continuously deposited;
that the duration of each formation is probably short com-
pared with the average duration of specific forms ; that
migration has played an important part in the first appear-
ance of new forms in any one area and formation ; that
widely ranging sj)ecies are those which have varied most
frequently, and have oftenest given rise to new species ; that
varieties have at first been local ; and lastly, although each
species must have passed through numerous transitional
stages, it is probable that the periods, during which each
underwent modification, though many and long as meas-
ured by years, have been short in comparison with the
periods during which each remained in an unchanged con-
dition. These causes, taken conjointly, will to a large
extent explain why — though we do find many links — we do
not find interminable varieties, connecting together all
extinct and existing forms by the finest graduated steps.
It should also be constantly borne in mind that any linking
variety 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 geo-
logical record, will rightly reject the whole theory. For he
may ask in vain where are the numberless transitional
links which must formerly have connected the closely
allied or representative species, found in the successive
stages of 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 forma-
tions of any one great region, as those of Europe, are con-
sidered; 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 nu-
merous 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 by supposing that where our oceaus now
extend they have extended for an enormous period^ and

PRECEDING AND PRESENT CHAPTERS. 371

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 w'idely
different aspect; and that the older continents, formed o'f
formations older than any known to iis, exist now only as
remnants in a metamorphosed condition, or lie still buried
under the ocean.

Passing from these difficulties, the other great leading
facts in palaeontology 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 ex-
tinction of old forms is the almost inevitable consequence
of the production of new forms. We can understand why,
when a species has once disappeared, it never reappears.
Groups of species increase in numbers slowly, and endure
for unequal periods of time; for the process cf modifica-
tion is necessarily slow, and depends on many complex
contingencies. 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 modified off-
spring on the face of the earth. But the utter extinction
of a whole grou]) of species has sometimes been a slow pro-
cess, from the survival of a few descendants, lingering in
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 of varieties
tend to people the world with allied, but modified, de-
scendants; and these will generally succeed in dis})hicing
the groups which are their inferiors in the struggle for
existence." Hence, after long intervals of time, the pro-
ductions of the world appear to have changed simultane-
ouslv.

We can understand how it is that all the forms of hfe,

372 SUMMARY OF CHAPTERS,

ancient and recent, make together a few grand classes.
We can understand, from the continued tendency to di-
vergence of character, why the more ancient a form is, the
more it genei'ally differs from those now living; why
ancient and extinct forms often tend to fill up gaps be-
tween existing forms, sometimes blending two groups, pre-
viously classed as distinct, into one; but more commonly
bringing them only a little closer together. 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 intermediate between existing forms; but are in-
termediate only by a long and circuitous course through
other extinct 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 gen-
eration. We can clearly see why the remains of an inter-
mediate formation are intermediate in character.

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 specialized; and this
may account for the common belief held by so many palae-
ontologists, that organization on the whole has progressed.
Extinct and ancient animals resemble to a certain extent the
embryos of the more recent animals belonging to the same
classes, and this wonderful fact receives a simple explana-
tion according to our views. The succession of the same
types of structure within the same areas during the later
geological 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
palaeontology plainly proclaim, as it seems to me, that
species have been produced by ordinary generation: old
forms having been supplanted by new and improved forms
of life, the products of Variation and the Survival of the
Fittest.

GEOGRAPHICAL DISTRIBUTION, 373

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 — Centers of creation— Means
of dispersal by changes of climate and of the level of the lan.l,
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 whicli strikes
US is, that neither the similarity nor the dissimilarity 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 divisions in geographical
distribution is that between the New and the Old Worlds;
yet if we travel over the vast American continent, from
the central parts of the United States to its extreme south-
ern point, we meet with the most diversified conditions;
humid districts, arid deserts, lofty mountains, grassy
plains, forests, m.arshes, 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 — at least so closely as tlie same species generally
require. 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 fauiia different from that of tlie sur-
rounding districts; for it is rare to find a group of organ-
isms confined to a small area, of which the conditions are
peculiar in only a slight degree. Notwithstanding thia

374 GEOGRAPHICAL DISTRIBUTION.

general parallelism in the conditions of Old and New
Worlds, liow 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 degrees, 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 dissimilar. Or, again, we may compare the
productions of South America south of latitude 35 degrees
with those north of 25 degrees, which consequently are
separated by a space of ten degrees of latitude, and are
exposed 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 ns 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 climate,
there might have been free migration for the northern
temperate forms, as there now is for the strictly arctic pro-
ductions. 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 op-
posite sides of lofty and continuous mountain-ranges, of
great deserts and even of large rivers, we find different
productions; though as mountain-chains, deserts, etc., are
not as impassable, or likely to have endured so long, as the
oceans separating continents, the differences are very in-
ferior 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, v»"ith extremely few shells, Crus-
tacea, or echinodermata in common; but Dr. Giinther has

GEOGiiAPUIGAL DISTRIBUTION: 375

recently shown that about thirty per cent, of tlie fislies are
the same on the opposite sides of the isthmus of Panama;
and this fact has led naturalists to believe tliat the istlimua
was formerly open. Westward of the shores of America,
a wide space of open ocean extends, with not an ishind as
a halting-place for emigi-ants; 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 dis-
tinct fauna. So that three marine faunas range northward
and southward in parallel lines not far from each otlier,
under corresponding climate; but from being separated
from each other by impassable barriers, either of laud or.
open sea, they are almost wholly distinct. On the other
hand, proceeding still further westward from the eastern
islands of the tropical parts of the Pacific, we encounter
no impassable barriers, and we have innumerable islands as
halting-places, or continuous coasts, until, after traveling
over a hemisphere, we come to the shores of Africa; and
over this vast space we meet with no well-defined and dis-
tinct marine faunas. Although so few marine animals are
common to the above-named three approximate faunas of
Eastern and Western America and the eastern Pacific
islands, yet many fishes range from the Pacific into the
Indian Ocean, and many shells are common to the eastern
islands of the Pacific and the eastern shores of Africa on
almost exactly opposite meridians of longitude.

A third great fact, partly included in the foregoing
statement, is the affinity of the productions of tlie same
continent or of the same sea, though the species themselves
are distinct at different points and stations. It is a law of
the widest generality, and every continent offers innum-
erable instances. Nevertheless, the naturalist, in travel-
ing, for instance, from north to south, never fails to be
struck by the manner in which successive groups of beings,
specificallv distinct, though nearly related, replace each
other. He hears from closely allied, yet distinct knids of
birds, notes nearly similar, and sees their nests simihirly con-
structed, but not quite alike, with eggs colored in nearly the
same manner. The plains near the Sti'aits of Magellan are
inhabited by one species of Rhea (American ostrich), and
northward the plains of La Plata by another species of the
same genus; and not by a true ostrich or emu, like those

376

OEOORAPHICAL DISTRIBUTION,

inhabiting Africa and Australia under the same latitude.
On these same plains of La Plata we see the 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 ol bizcacha; we look to the
waters, and we do not find the beaver or muskrat, but the
coypu and capybara, rodents of the South 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 essen-
tially 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. AVe see in
these facts some deep organic bond, throughout space and
time, over the same areas of land and water, independently
of physical conditions. The naturalist must be dull who
is not led to inquire 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 varieties, nearly
alike. The dissimilarity of the inhabitants of different
regions maybe attributed to modification through variation
and natural selection, and probably in a subordinate degree
to the definite influence of different physical conditions.
The degrees of dissimilarity 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 inhab-
itants on each other in leading to the preservation of differ-
ent 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 checking
migration; as does time for the slow process oi modifica-
tion through natural selection. Widely-ranging species,
abounding in individuals, which have already triumphed
over many competitors in their own widely-extended homes,
will have the best chance of seizing on new places, when

OEOORAPHICAL DISTRinUTION. 377

they spread out into new conntries. In tlieir new liotnes
they will be exposed to new conditions, and will froqucntlv
undergo further modification and improvement; and thus
they will become still further victorious, and will })roduce
groups of modified descendants. On this i)rimji})le of in-
heritance with modification we can understand how it is
that sections of genera, whole genera, and even famihes,
are confined to the same areas, as is so commonly and noto-
riously the case.

There is no evidence, as was remarked in the la^t
chapter, of the existence of any law of necessary develop-
ment. As the variability of each species is an in(le})endent
property, and will be taken advantage of by natural selec-
tion, only so far as it profits each iiulividual in its complex
struggle for life, so the amount of modificatioii in dilTerent
species will be r.o 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 afterward
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 bringing
organisms into new relations with each other and in a lesser
degree with the surrounding physical conditions. 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 tiie several
species of the same genus, though inhabiting the most
distant quarters of the world, must originally have jiro-
ceeded from the same source, as they are descended
from the same progenitor. In the case of those
species which have undergone, during whole cfeological
periods, little modification, there is not much ditliculty in
believing that thev have migrated from the same region;
for during the vast geographical and clin«atieal chunge8
which have supervened since ancient times, almost any
amount of migration is possible. Bnt in many other o.ises.
in which we have reason to believe that the species of a
genus have been produced within comparatively recent
times, there is great dimcultv on this head. It is hIro
obvious that the individuals of the same species. thongU

378 SINGLE CENTERS OF CREATION.

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 indentically the same should have been pro-
duced from parents specifically distinct.

SIls^GLE CEKTERS OP SUPPOSED CREATION.

We are thus brought to the question which has been
largely discussed 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 diffi-
culty in understanding how the same species could possi-
bly have migrated from some one point to the several dis-
tant and isolated points, where now found. Nevertheless
the simplicity of the view that each species was first pro-
duced within a single region captivates the mind. He who
rejects it, rejects the vera causa of ordinary generation
v»'ith subsequent migration, and calls in the agency of a
miracle. It is universally admitted, that in most cases the
area inhabited by a species 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 inex-
plicable instances of the same mammals inhabiting distant
points of the world. No geologist feels any difficulty in ,|

Great Britain possessing the same quadrupeds 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 mammal common to Europe |

and Australia or South America? The conditions of life I

are nearly the same, so that a multitude of European
animals and plants have become naturalized 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 mammals have not been able to
migrate, whereas some plants, from their varied means

SINGLE CENTERS OF CREATION. 379

of dispersal, have migrated across tlie wide and broken
interspaces. The great and striking influence of barriera
of all kinds, is intelligible oidy on the view that tlie <nvut
majority of species have been produced on one siderand
have not been able to migrate to the opposite side. Some
few families, many subfamilies, very many genera, a still
greater number of sections of genera, are confined to a
single region; and it has been observed by several natural-
ists that the most natural genera, or those genera in which
the species are most closely related to each other, are gen-
erally confined to the same country, or if they have a wide
range that their range is continuous. AVhat 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 produced
in one area alone, and having subsequently migrated from
that area as far as its powers of migration and subsistence
under past and present conditions permitted, is the most
probable. Undoubtedly many cases occur in which wo
cannot explain how the same species could have passed from
one point to the'other. But the geographical and climatical
changes which have certainly occurred within recent geo-
logical times, must have rendered discontinuous the for-
merly continuous range of many species. So that we are
reduced to consider 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
considerations, that each species has been produced within
one area, and has migrated thence as far as it could. It
would be hopelessly tedious to discuss all tlie exceptional
cases of the same species, now living at distant and sep-
arated points, nor do I for a moment protend that any
explanation could be offered of many instances, l^iit,
after some preliminary remarks, I will discuss a fi3W of the
most striking classes of facts, namely, the existence of the
same species on the summits of distant mountain rangos,
and at distant points in the Arctic and Antarctic regions;
and secondly (in the following chapter), the wide Jistri-

380 SINGLE CENTERS OF CREATION

bution of fresh water productions; and tiiirdl}^ the
occurrence of the same terrestrial species on islands and
on the nearest mainland, though separated by hundreds of
miles of open sea. If the existence of the same species at
distant and isolated points of the earth^s surface can in
many instances be explained on the view of each species
having migrated from a single birthplace, then, consider-
ing our ignorance with respect to former climatical and geo-
graphical changes, and to the various occasional means of
transport, the belief that a single birthplace is the law
seems to me incomparably 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 modiiication during their
mis^ration from some one area. If, when most of the spe-
cies inhabiting one region are different 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
strengthened; for the explanation is obvious on the principle
of 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 receive
from it in the course of time a few colonists, and their
descendants, though modified, would still be related 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 independent 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 species." And it is now well known
that he attributes this coincidence to descent with modi-
fication.

The question of single or multiple centres of creation
differs from another though allied question^ namely,
whether all individuals of the same species are descended
from a single pair, or single hermaphrodite, or whether, as
some authors suppose, from many individuals simultane-

MEANS OF iJliSFERtiAL. 381

ously created. Witli organic beings which never intercross*,
if such exist, each species must be descended from u suc-
cession of modified varieties, that liave supplanted eacii
other, but have never blended with other individuals or
varieties of the same species; so that, at each snocessivo
stage of modification, all the individuals of the same form
will be descended from a single parent. But in the groat
majority of cases, namely, with all organisms which habit-
ually 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 individuals will go on simultaneously changing, and
the whole 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 individuals
during each generation.

Before discussing the three classes of facts, which I have
selected as presenting the greatest amount of difficulty on
the theory of ^' single centers of creation/' I must say a
few words on the means of dispersal.

MEAN'S 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 impass-
able 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, j)resently 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 separates two marine faunas; sub-
merge 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 ^a^-
sibly even continents together, and thus have allowed terres-
trial productions to pass fi'om one to the other. No geolo-isi

382 MEANS OF DISPERSAL.

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
connected with Euroj^e or Africa, and Europe likewise
with America. Other authors have thus hypotlietically
bridged over every ocean, and united almost every island
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 recently
been united to some continent. This view cuts the
Gordian knot of the disjiersal of the same species to the
most distant points, and removes many a difficulty; but to
the best of my judgment we are not authorized in admit-
ting 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 ex-
tension of our continents, as to have united them within
the recent period to each other and to the several interven-
ing oceanic islands. I freely admit 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 former 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 in the marine faunas on the oi^posite sides of
almost every continent — the close relation of the tertiary
inhabitants of several lands and even seas to their present
inhabitants — the degree of affinity between the mammals
inhabiting islands with those af the nearest continent,
being in part determined (as we shall hereafter see) by the
depth of the intervening ocean — these and other such

MEANS OF DISPERSAL. 3g3

facts are opposed to the admission of sncli prodigious geo-
grapiiical revolutious within the recent period, as are
necessary on the view advanced by Forbes and admitted by
his followers. The nature and relative proportions of the
inhabitants of oceanic islands are likewise opposed to the
belief of their former continuity of continents. Nor does
the almost universally volcanic composition of such islands
favor the admission that they are the wrecks of sunken
continents; if they had originally existed as continental
mountain ranges, some at least of the islands would havo
been formed, like other mountain summits, of granite,
metamorphic schists, old fossiliferous and other rocks, in-
stead of consisting of mere piles of volcanic matter.

I must now say a few words on what are called acci-
dental 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 dissemination;
but the greater or less facilities for transport 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 in-
jurious action of sea-water. To my surprise I found
that out of eighty-seven kinds, sixty-four germinated
after an immersion of twenty-eight days, and a few
survived an immersion of 137 days. It deserves notice
that certain orders were far more injured than others: nine
LeguminosaB were tried, and, wdth one exception, they
resisted the salt-water badly; seven species of the allied
orders, Hydrophyllaceae and Polemoniacea;, were all killed
by a month's immersion. For convenience sake I chiefly
tried small seeds without the capsules or fruit; and as all
of these sunk in a few days, they could not have been
floated across wide spaces of the sea, whether or not they
were injured by salt water. Afterward I tried some larger
fruits, capsules, etc., 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
ninety-four plants with ripe fruit, and to place them on

384 MEANS OF DISPERSAL,

sea-Tvater. The majority sunk quickly, but some whicli,
while green, floated, for a very short time, when dried,
floated much longer; for instance, ripe hazel-nuts sunk
immediately, but when dried they floated for ninety days,
and afterward when planted germinated; an asparagus-
plant with ripe berries floated for twenty-three days, when
dried it floated for eighty-five days, and the seeds after-
ward germinated; the ripe seeds of Helosciadium sunk in
two days, when dried they floated for above ninety days,
and afterward germinated. Altogether, out of the ninety-
four dried plants, eighteen floated for above twenty-eight
days; and some of the eighteen floated for a very much longer :|

period. So that as |4 kinds of seeds germinated after an
immersion of twenty-eight days; and as -^f distinct species
with ripe fruit (but not all the same species as in the forego-
ing experiment) floated, after being dried, for above twenty-
eight days, we may conclude, as far as anything can be
inferred from these scanty facts, that the seeds of -^-^-^
kinds of plants of any country might be floated by sea-
currents during twenty-eight days, and would retain their
power of germination. In Johnston^s Physical Atlas, the
average rate of the several Atlantic currents is thirty-three
miles per diem (some currents running at the rate of sixty
miles per diem); on this average^ the seeds of -^ plants
belonging to one country might be floated across 924 miles
of sea to another country, and when stranded, if blown by
an inland gale to a favorable spot, would germinate.

Subsequently to my experiments, M. Martens tried sim-
ilar ones, but in a much better manner, for he placed the
seeds in a box in the actual sea, so that they were alter-
nately wet and exposed to the air like really floating
plants. He tried ninety-eight seeds, mostly difl'erent from
mine, but he chose many large fruits, and likewise seeds,
from plants which live near the sea; and this would have
favored both the average length of their flotation 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 -^f of his seeds of different kinds
floated for forty-two days, and were then capable of ger-
mination. But I do not doubt that plants exposed to the

MEANS OF UISPEIiSAL. 385

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
-^%- plants of a flora, after having been dried, could bo
floated across a space of sea 900 miles in width, and would
then germinate. The facts of the larger fruits often float-
ing longer than the small, is interesting; as plants with
large seeds or fruit which, as Alph. de Candolle has shown,
generally have restricted ranges, could hardly bo trans-
ported 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 irregu-
larly shaped stones are embedded in the roots of trees,
small parcelsof earth are frequently inclosed in their inter-
stices and behind them, so perfectly that not a particle
could be washed away during the longest transport: out of
one small portion of earth thus completely inclosed by the
roots of an oak about fifty years old, three dicotyledonous
plants germinated: I am certain of the accuracy of this
observation. Again, I can show that the carcasses of birds,
when floating on the sea, sometimes escape being immedi-
ately 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 thirty 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 thirty-five miles an hour; and some authors
have given a far higher estimate. I 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 twelve kinds of

386 MEANS OF DISPERSAL.

seeds, out of tlie excrement of small birds, and these
seemed perfect, and some of them, which were tried, ger-
minated. 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 five hundred 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 ex-
periments made in the Zoological Gardens, include seeds
capable of germination. Some seeds of the oat, wheat,
millet, canary, hemp, clover, and beet germinated 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 frequently 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 rejected the seeds in pellets or passed them in
their excrement; 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 m3^self 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 No-
vember, 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
upward as far as could be seen with a telescope. During
two or three days they slowly careered 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 com-
pletely coated with them. They then disappeared over the

MEANS OF DISPERSAL, 337

sea, as suddenly as they had appeared, and luive not since
visited the island. Now, in parts of Natul it is believed by
some farmers, though on insufficient evidence, thai injuri-
ous 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 wliich
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 in-
troducing 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 arg:illaceous earth from the foot of a 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 (Juncus bufonius) which germin-
ated and flowered. Mr. Swaysland, of Brighton, who dur-
ing the last forty years has paid close attention to our
migratory birds, informs me that he has often shot wag-
tails (Motacillae), wheatears, and whinchats (Saxicoht), 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 cliarged with seeds. For instance,
Prof essor 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 eighty-two plants sprung from it: those
consisted of twelve monocotyledons, including the common
oat, and at least one kind of grass, and of seventy dicotyle-
dons, 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 an-

388 MEANS OF DISPERSAL,

nually migrate — for instance, the millions of quails across
the Mediterranean — must occasionally transport a few
seeds imbedded 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, bones,
and the nest of a land-bird, it can hardly be doubted that
they must occasionally, as suggested by Lyell, have trans-
ported 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 main-
land, and (as remarked by Mr. H. 0. AYatson) from their
somewhat northern character, in comparison with the lati-
tude, I suspected that these islands had been partly stocked
by ice-born seeds during the Glacial epoch. At my request
Sir C. Lyell wrote to Si. Hartung to inquire whether he
had observed erratic bowlders 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 burdens 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 dis-
covered, have been in action year after year for tens of
thousands of years, it would, I think, be a marvelous 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 direction 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 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, however, 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 neighboring

MBA]}IS OF DISPERSAL. 389

island, but not from one distant continent to another.
The floras of distant continents would not bv sucli means
become mingled; but would remain as distinct as they now
are. The currents, from their course, would never \v\uit
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 thy
whole Atlantic Ocean, from Kortli America to the western
shores of Ireland and England; but_ seeds could be tnins-
ported by these rare wanderers only by one means, luimelv,
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 falling on favorable soil, and coming to
maturity! But it would be a great error to argue tliat
because a well-stocked island, like Great Britain, has not,
as far as is known (and it would be very dithcult 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 hundred
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, as to become
naturalized. But this is no valid argument against what
would be effected by occasional means of transpoit,
during the long lapse of geological time, while the island
was being upheaved, and before it had become fully stocked
with inhabitants. On almost bare land, with few or no
destructive insects or birds living there, nearly every seed
which chanced to arrive, if fitted for the climate, would
germinate and survive.

DISPERSAL DURING THE GLACIAL PERIOD.

The identity of many plants and animals, on mountain-
summits, separated from each other by hundreds of miles of
lowlands, where Alpine species could not i)ossibly exist, is
one of the most striking cases known of the same species
living at distant points, without the apparent possibility

390 DISPERSAL DURING

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 snow^ regions of the Alps or
Pyrenees, and in the extreme northern parts of Europe;
but it is far more remarkable, that the plants on the White
Mountains, in the United States of America, are all the
same with tliose of Labrador, and nearly all the same, as
we hear from Asa Gray, with those on the loftiest mount-
ains 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 expla-
nation of these facts. We have evidence of almost every
conceivable kind, organic and inorganic, that, within a
very recent geological period, central Europe and North
America suffered under an arctic climate. The ruins of a
house burned by fire do not tell their tale more plainly than
do the mountains of Scotland and Wales, with their scored
flanks, polished surfaces, and perched bowlders, of the icy
streams with which their valleys were lately filled. So
greatly has the climate of Europe changed, that in North-
ern Italy, gigantic moraines, left by old glaciers, are now
clothed by the vine and maize. Throughout a large part
of the United States, erratic bowlders and scored rocks
plainly reveal a former cold jDcriod.

The former influence of the glacial climate on the dis-
tribution 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 south-
ern zone became fitted for the inhabitants of the north,
these would take the places of the former inhabitants of
the temperate regions. Tlie latter, at the same time,
would travel further and further southward, unless they
were stopped by barriers, in which case they would perish.
The mountains would become covered with snow and ice,
and their former Alpine inhabitants would descend to the
plains. By the time that the cold had reached its maxi-
mum, we should have an arctic fauna and flora, covering

THE GLACIAL PERIOD, 391

the central parts of Europe, as far south as the Alps and
Pyrenees, and even stretching into Spain. 'IMie now
temperate regions of the United States would likewise bo
covered by arctic plants aud animals and these would be
nearly the same with those of Europe; for the present
eircumpolar ijihabitants, which we suppose to have every-
where traveled 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 pro-
ductions 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, while their breth-
ren 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 return-
ing warmth, would generally have been due south and
north. The Alpine plants, for example, of Scotland, as
remarked by Mr. H. 0. Watson, and those of the Pyrenees,
as remarked by Eamond, are more especially allied t^o tiio
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 of a
former Glacial period, seem to me to explain in so satis-
factory a manner the present distribution of the Alpine
and Arctic productions of Europe and America, tluit wiien
in other regions we find the same species on distant mount-
ain-summits, we may almost conclude, without other
evidence, that a colder climate formerly permitted their

392 DISPERSAL DURING

migration across the intervening lowlands, now become
too warm for their existence.

As the arctic forms moved first southward and after-
ward backward to the north, in unison with the changing
climate, they will not have been exposed during their long
migrations to any great diversity of temperature; and as
they all migrated in a body together, their mutual rela-
tions will not have been much disturbed. Hence, in
accordance with the principles inculcated in this volume,
these forms will not have been liable to much modification.
But with the Alpine productions, left isolated from the
moment of the returning 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 2^1'obability, 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 somewhat
different climatical influences. Their mutual relations will
thus have been in some degree disturbed; consequently
they will have been liable to modification; and they have
been modified; for if we compare the present Alpine plants
and animals of the several great European mountain
ranges, one with another, though m.any of the species
remain identically the same, some exist as varieties, some
as doubtful forms or sub-species and some as distinct 3^et
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, tlie 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 mountain slopes and on the
plains of North America and Europe are the same; and it
may be asked how I account for this degree of uniformity
in the sub-arctic and temperate forms round the worlds at

THE GLACIAL PElilOD. 303

the commencement of the real Glacial period. At the
present day, the sub-arctic and northern temperate pro-
ductions of the Old and New AVorlds are separated from
each other by the whole Atlantic Ocean and by the norih-
ern part of the Pacific. During the Glacial })eriod, when
the inhabitants of the Old and New Worlds lived further
southward then 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 con-
tinents. 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 in-
habitants of the world were specifically the same as now, and
we have good reason to believe that the climate was warmer
than at the present day. Hence, we may suppose that tliC
organisms which now live under latitude 60 degrees, lived
during the Pliocene period further north, under the Polar
Circle, in latitude 66-67 degrees; and that the present arctic
productions then lived on the broken land still nearer to the
23ole. Now, if we look at a terrestrial globe, we see under
the Polar Circle that there is almost continuous land from
western Europe through Siberia, to eastern America. And
this continuity of the circumpolar land, with the conse-
quent freedom under a more favorable climate for inter-
migration, will account for the supposed uniformity of tlie
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 con-
tinents have long remained in nearly the same relative
position, though subjected to great oscillations of level. 1
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 number of the same
plants and animals inhabited the almost continuous cir-
cumpolar land; and that these plants and animals, both in
the Old and New Worlds, begun slowly to migrate south-
ward as the climate became less warm, long before the
commencement of the Glacial period. We now see, as 1
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

394 DISPERSAL DURING

little identity, between the productions of North America
and Europe — a relationship which is highly remarkable,
considering the distance of the two areas, and their sepa^
ration by the whole Atlantic Ocean. We can further under-
stand tiie singular fact remarked on by several observers
that the productions of Europe and America during the
later tertiary stages were more closely related to each other
than they are at the present time; for during 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 impassible by cold, for intermigra-
tion of their inhabitants.

During the slowly decreasing warmth of the Pliocene
period, as soon as the species in common, which inhabited
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 migrated southward, they will
have become mingled in the one great region with the
native American productions, and would have had to com-
pete with them; and in the other great region, with those
of the Old World. Consequently we have here everything
favorable for much modification — for far more modifica-
tion 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 North America. Hence,
it has come, that when we compare the now living produc-
tions 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 for-
merly supposed), but we find in every great class many
forms, which some naturalists rank as geographical races,
and others as distinct species; and a host of closely allied
or representative forms which are ranked by all naturalists
as specifically distinct.

As on the land, so in the waters of the sea, a slow south-
ern migration of a marine fauna, which, daring the Pliocene
or even a somewhat earlier period, was nearly uniform along
the continuous shores of the Polar Circle, v/ill account, on
the theory of modification, for many closely allied forms
now living in marine areas completely sundered. Thus^ I

TBE GLACIAL PERIOD. 395

think, we can understand 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 crus-
taceans (as described in Dana's admirafjle work), some fish
and other marine animals, inhabiting the Mediterranean
and the seas of Jajmn — these two areas being now com-
pletely 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 cor-
respondence 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.

ALTERN"ATE GLACIAL PERIODS IIT THE KORTH AXD SOUTH.

But we must return to our more immediate subject. I
am convinced that Forbes' view may be largely extended.
In Europe we meet with the plainest evidence of the Glacial
period, from the western shores of Britain to the Ural
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 Leb-
anon, according to Dr. Hooker, perpetual snow formerly
covered the central axis, and fed glaciers which rolled
4,000 feet down the valleys. The same observer has
recently found great moraines at a low level on the Atlas
range in North Africa. Along the Himalaya, at jioints
900 miles apart, glaciers have left the marks of tht'ir
former low descent; and in Sikkim, Dr. Hooker saw maize
growing on ancient and gigantic moraines. Southward of
the Asiatic continent, on the opposite side of the equator,
we know, from the excellent researches of Dr. J. Ilaast
and Dr. Hector, that in New Zealand immense glaciers
formerly descended to a low level; and the same plants

396 ALTERNATE GLACIAL PERIODS

found by Dr. Hooker on widely separated mountains m
this island tell the same story of a former cold period.
From facts communicated to me by the Eev. W. B.
Clarke, it appears also that there are traces of former gla-
cial 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 latitude thirty-six and
thirty-seven degrees, and on the shores of the Pacific,
Avhere the climate is now so different, as far south as lati-
tude forty-six degrees. Erratic bowlders 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 Chili I
examined a vast mound of detritus with great bowlders,
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 latitude thirteen to thirty degrees south, at about the
height of 12,000 feet, deeply-furrowed rocks, resembling
those with which he was familiar in l^orway, and likewise
great masses of detritus, inchiding grooved pebbles. Along
this whole space of the Cordillera true glaciers do not now
exist even at much more considerable heights. Further
south, on both sides of the continent, from latitude forty-
one degrees to the southernmost extremity, we have the
clearest evidence of former glacial action, in numerous
immense bowlders transported far from their parent
source.

From these several facts, namely, from the glacial action
having extended all round tlie 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 gla-
ciers 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 tempera-
ture 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

m THE NORTH AND SO UTH. 397

condition 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 toward the same
end; but the most powerful appears to be the indirect in-
fluence of the eccentricity of the orbit upon oceanic cur-
rents. According to Mr. Croll, cold periods reguhirly recur
every ten or fifteen thousand years; and tliese at long in-
tervals are extremely severe, owing to certain contingen-
cies, 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 altera-
tions of climate, for about 160,000 years. With respect to
more ancient glacial periods, several geologists arc con-
vinced, 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 hemisphere is actually raised, with the
winters rendered much milder, chiefly through changes in
the direction of the ocean currents. So converselv it will
be with the northern hemisphere, while the southern passes
through a glacial period. This conclusion throws so much
light on geographical distribution that I am strongly in-
clined to trust in it; but I will first give the facts which
demand an explanation.

In South America, Dr. Hooker has showm that besides
many closely allied species, between forty and fifty of the
flowering plants of Tierra del Fuego, forming no inconsid-
erable part of its scanty flora, are common to North
America and Europe, enormously remote as these areas in
opposite liemispheres 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 (iardner
which do not exist in the low intervcTiing hot countries.
On the Silla of Caraccas the illustrious Humboldt long ago
found species belonging to genera characteristic of the
Cordillera.

In Africa, several forms characteristic of Europe, and

398 ALTERNATE GLACIAL PERIODS

some few representatives of the flora of the Cape of
Grood Hope, occur on the mountains of Abyssinia. At
the Cape of Good Hope a very few European species,
believed not to have been introduced by man, and on the
mountains several representative European forms are found
which have not been discovered in the intertropical 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 neighboring Cameroou Mount-
ains, in the Gulf of Guinea, are closely related to those on
the mountains of Abvssinia, and likewise to those of tem-
perate Europe. It now also appears, as I hear from Dr.
Hooker, that some of these same temperate plants have
been discovered by the Rev. E. T. Lowe on the mountains
of the Cape Verde Islands. This extension of the same tem-
perate 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 re-
corded 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 identi-
cally the same or representing each other, and at the same
time representing plants of Europe not found in the inter-
vening hot lowlands. A list of the genera of plants col-
lected on the loftier peaks of Java, raises a picture of a
collection made on a hillock in Europe. Still more strik-
ing is the fact that peculiar Australian forms are repre-
sented by certain 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 inter-
mediate torrid regions. In the admirable ^^Introduction
to the Flora of New Zealand, ^^ by Dr. Hooker, analogous
and striking facts are given in regard to the plants of that

IW THE NORTH AND SO UTE, 300

large island. Hence, we see that certain plants growing on
the more lofty mountains 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 re-
marked, " in receding from polar toward equatorial lati-
tudes, the Alpine or mountain flora really become less and
less Arctic.'' Besides these identical and closely allied
forms, many species inhabiting the same widely sundered
areas, belong to genera not now found in the intermediate
tropical lowlands.

These brief remarks apply to plants alone; but some few
analogous facts could be given in regard to terrestrial
animals. In marine productions, similar cases likewise
occur; as an example, I may quote a statement by the
highest authority. Professor Dana, that '' it is certainly a
wonderful fact that New Zealand should have a closer re-
semblance 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, etc., of northern forms of fish. Dr.
Hooker informs me that twenty-five species of Algse 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 tem-
perate 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 ap-
pears almost certain that at some former period, no doubt
during the most severe part of a Glacial period, the low-
lands of these great continents were everywhere tenanted
under the equator by a considerable number of temperate
forms. At this period the equatorial climate at the level
of the sea was probably about the same with that now ex-
perienced 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 tlie
equator must have been clothed with a mingled tropical
and temperate vegetation, like that described by Ilojkor as
growing luxuriantly at the height of from four to five

400 ALTERNATE GLACIAL PERIODS

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 Fernando
Po, in the Gulf of Guinea, Mr. Mann found temperate
European forms begiuing to appear ab the height 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 temper-
ate.''

Now let us see whether Mr. CrolFs conclusion that when
the northern hemisphere suffered from the extreme cold of
the great Glacial period, the southern hemisphere was
actually warmer, throws any clear light on the present ap-
parently inexplicable distribution of various organisms in
the temperate parts of both hemispheres, and on the
mountains of the tropics. The Glacial period, as measured
by years, must have been very long; and when we remem-
ber over what vast spaces some naturalized plants and ani-
mals 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 vigorous, dominant and widest-spreading temperate
forms invaded 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 hemispheres gradu-
ally recovered their former temperature, the northern tem-
perate 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 return-
ing from the south. Some, however, of the northern
temperate forms would almost certainly have ascended any
adjoining high land, where, if sufficiently lofty, they would
have long survived 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 tem-
perature must have been very slow, and plants undoubtedly
possess a cerfeain capacity for acclimatization, as shown by

IN THE NOIITS AND 80 UTH. 4( jl

their transmitting to their offspring different constitutional
powers of resisting heat and cold.

In the regular course of events the southern hemisphere
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 descend and mingle with the
southern forms. These latter, when the warmth returned,
would return to their former homes, leaving some few
species on the mountains, 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 mount-
ains of the intermediate tropical regions. But the species
left during a long time on these mountains, or in opi^osite
hemispheres, would have to compete with many new forms
and would be exposed to somewhat different ph3"sical con-
ditions; hence, they would be eminently liable to modifica-
tion, and would generally now exist as varieties or as rep-
resentative 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 in-
habiting the same 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 Candolle 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 sus-
pect that this preponderant 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 alterna-
tions of the Glacial periods, the northern forms were tho

402 ALTERNATE GLACIAL PERIODS

more powerful and were able to hold their places on the
mountains, and afterward 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 productions cover the
ground in La Plata, New Zealand, and to a lesser degree
in Australia, and have beaten the natives; whereas
extremely few soathern forms have become naturalized in
any part of the northern hemisphere, though hides, wool,
and other objects likely to carry seeds have been largely
imported into Europe during the last two or three cen-
turies from La Plata and during the last forty or fifty years
from Australia. The K"eilgherrie Mountains in India,
however, ofler a partial exception; for here, as I hear from
Dr. Hooker, Australian forms are rapidly sowing them-
selves and becoming naturalized. Before the last great
Glacial period, no doubt the intertropical mountains were
stocked with endemic Alpine forms; but these have almost
everywhere yielded to the more dominant forms generated
in the larger areas and more efficient workshops of the
north. In many islands the native productions are nearly
equalled, or even outnumbered, by those which have
become naturalized; and this is the first stage toward 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 continental forms naturalized through
man^s agency.

The same principles apply to the distribution of terres-
trial animals and of marine productions, in the northern
and southern temperate zones, and on the intertropical
mountains. When, during the height of the Glacial
period, the ocean-currents were widely different to what
they now are, some of the inhabitants of the temperate seas
might have reached the equator; of these a few would per-
haps at once be able to migrate southward, by keeping to
the cooler currents, while others might remain and sur-
vive 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, isolated spaces inhabited by Arctio

7iV THE NORTU AND SOUTH, 403

productions exist to the present day in the deeper parts of
the northern temperate seas.

I am far from siipposinoj that all the difficulties in
regard to the distribution and affinities of the identical and
allied species, which now live so widely separated in the
north and south, and sometimes on the intermediate mount-
ain-ranges, are removed on the views above given. The
exact lines of migration cannot be indicated. We cannot
say why certain species and not otliers have migrated; why
certain species have been modified and have given rise to
new forms, while others have remained unaltered. We
cannot hope to explain such facts, until we can say why
one species and not another becomes naturalized 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 Kerguelen
Land, ISTew 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 remark-
able case. Some of these species are so distinct, that we
cannot suppose that there has been time since the com-
mencement of the last Glacial period for their migration
and subsequent modification 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 center; 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 be
suspected that before this flora was exterminated during the
last Glacial epoch, a few forms had been already widely dis-
persed to various points of the southern hemisiDhere by oc-
casional means of transport, and by the aid, as lial ting-
places, of now sunken islands. Thus the soutliern shores
of America, Australia, and New Zealand may have become
slightly tinted by the same peculiar forms of life.

404

ALTERNATE GLACIAL PERIODS.

Sir C. Lyell in a striking passage lias speculated, in lan-
guage almost identical with mine, on the effects of great
alterations of climate throughout the world on geograph-
ical distribution. And we have now seen that Mr. CrolFs
conclusion that successive Glacial periods in the one hemi-
sphere coincide with warmer periods in the opposite hemi-
sphere, together with the admission of the slow modifica-
tion of species, explains a multitude of facts in the distri-
bution 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 direction, 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 surviv-
ing in the mountain fastnesses of almost every land, which
serves as a record, full of interest to us, of tlae former in-
habitants of the surrounding lowlands.

FBESE-WATER PRODUCTIONS. 406

CHAPTER XIII.

GEOGRAPHICAL DISTRIBUTION — COntinuecL

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 mainlaind — On colonization from the nearest source
with subsequent modification— Summary of the last and present
chapter.

FRESH-WATER PRODUCTION'S.

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 apparently 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, belong-
ing to different classes, an enormous range, but allied
species prevail in a remarkable manner throughout the
world. When first collecting in the fresh waters of Brazil,
I w^ell remember feeling much surprise at the similarity of
the fresh-water insects, shells, etc., and at the dissimilarity
of the surrounding terrestrial beings, compared with those

of Britain.

But the wade ranging power of fresh-water productions
can, I think, in most cases be explained by their having
become fitted, in a manner highly useful to them, for short
and frequent migrations from pond to pond, or from
stream to stream, within their own countries; 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

406 FBESII- WA TER PROD XICTI0N8.

distant from each other. But Dr. Giinther has lately
shown that the Galaxias attenuatus inhabits Tasmania,
New Zealand, the Falkland Islands and the mainland of
South America. This is a wonderful case, and probably
indicates dispersal from an Antarctic center 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 con-
siderable 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 attribu-
ted 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 differences of the
fish on the opposite sides of most mountain-ranges, which
are continuous and consequently must, from an early
period, have completely prevented the inosculation of the
river, systems on the two sides, leads to the same conclu-
sion. Some fresh-water fish belong to very ancient forms,
and in such cases there will have been ample time for
great geographical 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.

FRESE-WATER PRODUCTIONS. 407

Some species of fresh-water shells have very wide ranges,
and allied species which, on our theory, are descended from
a common parent, and must have proceeded 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 naturalized species have spread
rapidly throughout the same country. But two facts,
which I have observed — and many others no doubt will be
discovered — throw some light on this subject. When ducks
suddenly 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-weed
from one aquarium to another, that I have unintentionally
stocked the one with fresh-water shells from the other.
But another agency is perhaps more effectual: 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 advanced 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 dytiscus 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 favoring 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 remote oceanic
islands. This is strikingly illustrated, according to Alph.
de Candolle, in those large groups of terrestrial plants,
which have very few aquatic members; for the latter seem

408 :fbesh-water PEdDUCTiomr

immediately to acquire, as if in consequence, a wide
range. I think favorable means of dispersal explain
this fact. I have before mentioned that earth occa-
tionally adheres in some quantity to the feet and beaks
of birds. Wading birds, wiiich 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; 1 have tried several little experiments, but will
here give only the most striking case: I took in February
three tablespoonfuls of mud from three different points,
beneath water, on the edge of a little pond; this mud when
dried weighed only six and three-fourth 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! Consider-
ing these facts, I think it v/ould 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, century after century, have gone on daily
devouring fish; 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 afterward in pellets or in the excrement.
"When I saw the great size of the seeds of that fine water-
lily, the Nelumbium, and remembered A.lph.de Oandolle's
remarks on the distribution of this plant, I thought that

INHABITANTS OF OCEANIC ISLANDS. 409

the means 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 Nelumt
bium luteum) in a heron^s stomach. Now this bird mus-
often have flown with its stomach thus well stocked to dis-
tant ponds, and, then getting a hearty meal of fish,
analogy makes me believe that it would have rejected the
seeds in the 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 e,gg will have a good chance of succeed-
ing. Although there will always be a struggle for life be-
tween 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 tlie number of species inhabiting an
equal area of land, the competition between them will proba-
bly be less severe than between terrestrial species; conse-
quently an intruder 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 re-
member that many fresh-water productions are low in the
scale of nature, and we have reason to believe that such
beings become modified more slowly than the high;
and 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 intermediate
points. But the wide distribution of fresh-water plants,
and of the lower animals, whether retaining the same
identical form, or in some degree modified, apparently
depends in main part on the wide dispersal of their seeds
and eggs by animals, more especially by fresh-water birds,
which have great powers of flight, and naturally travel
from one piece of water to another.

OK THE IIs^HABITAKTS OF OCEANIC ISLANDS.

We now come to the last of the three classes of facts,
which 1 have selected as presenting the greatest amount
of difficulty with respect to distribution, on the view that
not only all the individuals of the »am© speci«s have

410 INHABITANTS OF OCEANIC ISLANDS.

migrated from some one area, but that allied species,
although now inhabiting the most distant points, have pro-
ceeded from a single area, the birthplace of their early pro-
genitors. I have already given my reasons for disbeliev-
ing 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 j^resent
terrestrial inhabitants. This view removes many difficul-
ties, but it does not accord with all the facts in regard to
the productions of islands. In the following remarks I
shall not confine myself to the mere question of dispersal,
bat shall consider some other cases bearing on the truth of
the two theories of independent creation and of descent
with modification.

The species of all kinds which inhabit oceanic islands
are few in number compared with those on equal continen-
tal areas: Alph. de Candolle admits this for plants, and
WoUaston for insects, ^""ew Zealand, for instance, with
its lofty mountains and diversified stations, extending over
780 miles of latitude, together with the outlying islands of
Auckland, Campbell and Chatham, contain altogether
only 960 kinds of flowering plants; if we compare this moder-
ate number with the species which swarm over equal areas
in Southwestern 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 difference
in number. Even the uniform county of Cambridge has
847 plants, and the little island of Anglesea 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. AYe have evidence that the barren island
of Ascension aboriginally possessed less than half a dozen
flowering plants; yet many species have now become
naturalized 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 naturalized plants
and animals 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 sufficient
number of the best adapted plants and animals were not
created for oceanic islands; for man has unintentionally
stocked them far more fully and perfectly than did nature.

INHABITANT^ OF OCEANIC ISLANDS, 411

Although in oceanic islands the species are few in
number, the proportion of endemic kinds {i. e. those
found nowhere else in the world) is often extremely large.
If we compare, for instance, the number of endemic land-
sliells in Madeira, or of endemic birds in the Galapagos
Archipelago, with the number foun"d 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 produce 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 seems to depend partly on the
species 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 unmodified
immigrants from the mother-country, with Avhich the
insular forms have intercrossed. It should be borne in
mind that the offspring of such crosses would certainly
gain in vigor; so that even an occasional cross would pro-
duce more effect than might have been anticipated. I will
give a few illustrations of the foregoing remarks: in the
Galapagos Islands there are twenty-six land birds; of these,
twenty-one (or perhaps twenty-three) are peculiar, whereas
of the eleven marine birds only two are peculiar; and it is
obvious that marine birds could arrive at these islands
much more easily and frequently than land birds. Ber-
muda, 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 peculiar soil,
does not possess a single endemic land bird; and we know
from Mr. J. M. Jones' 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. Y. Harcourt, many European and
African birds are blown to Madeira; this island is inhabited
by ninety-nine kinds, of whicli one alone is peculiar, though
very closely related to a European form; and three or four

412 INHABITANTS OF OCEANIC ISLANDS.

other species are confined to this island and to the Canaries.
So that the Islands of Bermuda and Madeira have been
stocked from the neighboring continents with birds, which
for long ages have there struggled together, 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 unmodified 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 larvge, perhaps attaclied to sea-weed or float-
ing timber, or to the feet of wading birds, might be trans-
ported across three or four hundred miles of open sea far
more easily than land-shells. The different orders of
insects inhabiting Madeira present 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, 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 character and the direction of its mount-
ain ranges, the Rev. W. B. Clarke has lately maintained
that this island, as well as New Caledonia, should be con-
Bidered as appurtenances of Australia. Turning to plants,
Dr. Hooker has shown that in the Galapagos Islands the
proportional numbers of the different orders are very dif-
ferent from what they are elsewhere. All such differences
in number, and the absence of certain Avhole groups of
animals and plants, are generally accounted for by sup-
posed 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
nacure of the conditions.

Many remarkable little facts could be given with respect
to tha inhabitants oi oceanic islands. For instance, in

INEABITANTS OF OCEANIC ISLANDS, 413

certain islands not tenanted by a single mammal, 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 bo 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 appendage, like the shrivelled wings under
the soldered wing-covers of many insular beetles. Again,
islands often possess trees or bushes belonging to orders
which elsewhere include only herbaceous species; now
trees, as Alph. de Caudolle has shown, generally have,
whatever 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 successfully
competing witii 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.

ABSEiSrCE OE BATRACHIAi^'S A.^T> TERRESTRIAL MAXiMALS

o:n^ oceanic islands.

With respect to the absence of whole orders of animals
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 exception of New Zealand,
New Caledonia, the Andaman Islands, and perhaps the
Solomon Islands and the Seychelles. But I have already
remarked that it is doubtful whetlier New Zealand and
New Caledonia ought to be classed as oceanic islands; and
this is still more doubtful with respect to the Andaman and
Solomon groups and the Seychelles. This general absence
of frogs, toads and newts on so many true oceanic islands
can not be accounted for by their physical conditions: in-
deed it seems that islands are peculiarly fitted for these
animals; for frogs have been introduced into Madeira, the

414 ABSENCE OF TERRESTRIAL

Azores and Mauritius, and have multiplied so as to become
a nuisance. But as these animals and their spawn are im-
mediatel}^ killed (with the exception, as far as known, of
one Indian species) by sea-water, there would be great
difficulty in their transportal 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
explain.

Mammals offer another and similar case. I have care-
fully 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) in-
habiting an island situated about 300 miles from a conti-
nent 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 near-
est to an exception; but this group cannot be considered
as oceanic, as it lies on a bank in connection with the
mainland at a distance of about 280 miles; moreover, ice-
bergs formerly brought bowlders to its western shores, and
they may have formerly transported foxes, as now fre-
quently happens in the arctic regions. Yet it cannot be
said that small islands will not support at least small mam-
mals, 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 naturalized and greatly multiplied. It
cannot be said, on the ordinary view of creation, that there
has not been time for the creation of mammals; many vol-
canic islands are sufficiently ancient, as shown by the
stupendous degradation which they have suffered, and by
their tertiary strata: there has also been time for the pro-
duction of endemic species belonging to other classes; and
on continents it is known that new species of ma.mmals ap-
pear and disappear at a quicker rate than other cind 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 Archi-
pelagoes, and Mauritius, all possess their peculiar bats.

MAMMALS ON OCEANIC ISLANDS. 415

Why, it may be asked, has the supposed creative force
produced bats and no other mammals on remote islands?
On my view this question can easily be answered; for no
terrestrial mammal can be transported across a wide space
of sea, but bats can fly across. Bats have been seen wan-
dering by day far over the Atlantic Ocean; and two North
American species, either regularly or occasionalh^, visit Ber-
muda, 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 islands. 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 ter-
restrial mammals.

Another interesting relation exists, namely, between
the depth of the sea separating islands from each other,
or from the nearest continent, and the degree of affinity
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 shallovv submarine bank,
and these islands are inhabited by the same or by closely
allied quadrupeds. I have not as 3^et 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 one thousand 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 cliannels, are more
likely to have been continuously united within a recent
period than the islands separated by deeper channels, we

416 ABSENCE OF TERRESTRIAL

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 inex-
plicable on the theory of independent acts of creation.

The foregoing statements in regard to the inhabitants of
oceanic islands, namely, the fewness of the species, with a
large proportion consisting of endemic forms — the mem-
bers of certain groups, but not those of other groups in the
same class, having been modified — the absence of certain
whole orders, as of batrachians and of terrestrial mammals,
notwithstanding the presence of aerial bats, the singular
proportions of certain orders of plants, herbaceous forms
having been developed into trees, etc., 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 immi-
grated more uniformly, and from the species having
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 equa-
ble manner.

I do not deny that there are many and serious difficul-
ties in understanding how many of the inhabitants of the
more remote islands, whether still retaining the same spe-
cific 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 diffi-
cult case. Almost all oceanic islands, even the most
isolated and smallest, are inhabited by land-shells, gener-
ally 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 efficient means for their transportal.
Would the just-hatched young sometimes adhere to the
feet of birds roosting on the ground and thus get trans-
ported? It occurred to me that land-shells, when hyber-

I:

MAMMALS ON OCEANIC ISLANDS, 417

nating and having a membranous diaphragm over the
mouth of the shell, might be floated in chinks of drifted
timber across modenitely wide arms of the sea. And i find
that several species in this state withstand uninjured an im-
mersion in sea-water during seven days. One shell, the Helix
pomatia, after having been thus treated, and again hyber-
nating, 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 geographical 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 fourteen days in sea-water, and again it recovered and
crawled away. Baron Aucapitaine has since tried similar
experiments. He placed 100 land-shells, belonging to ten
species, in a box pierced with holes, and immersed it for a
fortnight in the sea. Out of the hundred 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 re-
vived. It is remarkable, seeing how well the Helix pomatia
resisted with me the salt-water, that not one of fifty-four
specimens belonging to four other species of Helix tried by
Aucapitaine 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.

O^ THE RELi.TIO:\g OF THE IXHABITAXTS OE ISLANDS TO
THOSE OE THE NEAEEST MAINLAND.

The most striking and important fact for ns 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 Arch-
ipelago, 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 Amer-
ican 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

418 RELATIONS OF THE INHABITANTS OF

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 naturalist, looking at the inhabitants of
these volcanic islands in the Pacific, distant several hun-
dred miles from the continent, feels that he is standing on
American land. Whv should this be so? AVhv should the
species which are supposed to have been created in the
Galapagos 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 associated together, which closely resembles the
conditions of the South American coast. In fact,
there is a considerable dissimilarity in all these resj^ects.
On the 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 Archipelagos: but what an entire and abso-
lute difference in their inhabitants! The inhabitants 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 in-
dependent creation; whereas, on the view here maintained,
it is obvious that the Galapagos Islands would be likely to
receive colonists from America, whether by occasional
means of transport or (though I do not believe in this doc-
trine) by formerly continuous 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 Kergue-
len Land stands nearer to Africa than to America, 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

ISLANDS TO THOSE OF THE MAINLAND. 419

brought with earth and stones on icebergs, drifted by the
prevailing currents, this anomaly disappears. Xew Zealand
in its endemic planes is much more closely related to Aus-
tralia, 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 so enormously remote, that the
fact becomes an anomaly. But this difficulty partially dis-
appears 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 antarctic islands, when they were clothed with
vegetation, during a warmer tertiary period, before the
commencement of the last Glacial period. The affinity,
which, though feeble, I am assured by Dr. Hooker is real,
between 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.

The same law which has determined the relationship be-
t-ween the inhabitants of islands and the nearest mainland,
is sometimes displayed on a small scale, but in a most in-
teresting manner, within the limits of the same archi-
pelago. Thus each separate island of the Galapagos
Archipelago is tenanted, and the fact is a marvelous
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 continent, 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
some original source, and from each other. But how is it
that many of the immigrants have been differently modi-
fied, though only in a small degree, in islands situated
within sight of each other, having the same geolog-
ical nature, the same height, climate, etc. ? This long
appeared to me a great difficulty: but it arises in chief
part from the deeply-seated error of considering the phys-
ical conditions of a country as the most important;
whereas it cannot be disputed that the nature of the
other species with which eacli has to compete, is at
least as important, and generally a far more import-

420

RELATIONS OF THE INHABITANTS OF

ant 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 have been stocked
by occasional means of transport — 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 immigrant first settled on one of the islands, or
when it subsequently spread from one to another, it would
undoubtedly be exposed to different conditions in the dif-
ferent islands, for it would have to compete with a differ-
ent 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 favor 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 Galapagos
Archipelago, and in a lesser degree in some analogous
cases, is that each new species after being formed in any
one island, did not spread cjuickly to the other islands.
But the islands, though in sight of each other, are sepa-
rated by deep arms of the sea, in most cases 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 deep 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 m.ay infer from the present
minner 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 inter-
communication. Undoubtedly, if one species has any

ISLANDS TO THOSE OF THE MAINLAND. 4^1

advantage 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
separate places for almost any length of time. Being
familiar Avith the fact that many species, naturalized
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 naturalized in new countries
are not generally closely allied to the aboriginal inhabi-
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
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 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 possesses many distinct but representative
species of land-shells, some of which live in crevices of
stone; and although large quantities of stone are annually
transported from Porto Santo to Madeira, yet this latter
island has not become colonized by the Porto Santo
species; nevertheless, both islands have been colonized 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 Archi-
pelago not having all spread from island to island. On
the same continent, also, preoccupation has probably
played an important part in checking the commingling of
tha species which inhabit different districts with nearly the

422 RELATIONS OF THE INEABITANTS OF

same physical conditions. 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 continuous valley of the Amazons.

The same principle which governs the general clnaracter
of the inhabitants of oceanic islands, namely, the relation
to the source whence colonists could have been most
easily derived, together with their subsequent modifica-
tion, 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, Alpine plants, etc., all strictly belonging
to American forms; and it is obvious that a mountain, as
it became slowly upheaved, would be colonized from the
surrounding 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 the same princi-
ple in the character of most of the blind animals inhabiting
the caves of America and of Europe. Other analogous
facts could be given. It will, I believe, be found uni-
versally 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-allied 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 migra-
tion 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 another 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.

ISLANDS TO THOSE OF THE MAINLAND. 423

I can hardly doubt that this rule is generally true, though
difficult of proof. Among mammals, we see it strikingly
displayed in bats, and in a lesser degree in the Felidai and
Canidae. We see the same rule in the distribution of butter-
flies 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 modifica-
tion 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 dis-
tinct 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 important power of being victorious in distant lands
in the struggle for life with foreign associates. But accord-
ing to the view that all the species of a genus, though dis-
tributed 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 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 tlie species in this case will
have had ample time for dispersal and subsequent modifi-
cation. 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 specific character. This fact, together
with that of the seeds and eggs of most lowly organized
forms being very minute and better fitted for distant trans-
portal, probably accounts for a law which has long been
observed, and which has lately been discussed by Alph. de
Candolle in regard to plants, namely, that the lower any
group of organisms stands the more widely it ranges.

424 SUMMART.

The relations just discussed — namely, lower organisms
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 surround-
ing low lands and dry lands — the striking relationship
between the inhabitants of islands and those of the nearest
mainland — the still closer relationship of the distinct in-
habitants of the islands in the same archipelago — are inex-
plicable on the ordinary view of the independent creation
of each species, but are explicable if we admit colonization
from the nearest or readiest source, together with the sub-
sequent adaptation of the colonists to their new homes.

SUMMARY OF THE LAST AXD PRESEXT CHAPTERS.

In these chapters I have endeavored 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 occun-ed — if we re-
member how ignorant we are with respect to the many
curious means of occasional transport — 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 common parents. And we are led to this
conclusion, which has been arrived at by many naturalists
under the designation of single centers of creation, by
various general considerations, more especially from the
importance of barriers of all kinds, and from the ana-
logical distribution of subgenera, 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 before 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.

SUMMARY. 425

As exemplifying the effects of climatical changes on dis-
tribution, I have attempted to show liow important a pai*t
the hist Glacial period has played, which affected even the
equatorial regions, and which, during the alternations of
the cold in the north and the south, allowed the produc-
tions 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 oc-
casional 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 tiie 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 geographical distribution
are explicable on the theory of migration, together with
subsequent modification and the multiplication of new
forms. We can thus understand the high imjoortance of
barriers, whether of land or water, in not only separating
but in apparently forming the several zoological and
botanical provinces. We can thus understand the con-
centration of related species within the same areas; and
how it is that under different latitudes, for instance, in
South America, the inhabitants of the plains and mount-
ains, of the forests, marshes and deserts, are linked
together in so mysterious a manner, and are likewise
linked to the extinct beings which formerly inliabited
the same continent. Bearing in mind that the mutual
relation of organism to organism is of the highest im-
portance, 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 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 con-
ditions, infinitely diversified conditions of life; there would

426 SUMMARY.

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 gpographical provinces of the world.

On these same principles we can understand, as I have
endeavored to show, whv oceanic islands should have few
inhabitants, but that of these, a large proportion should be
endemic or peculiar; and why, in relation 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 mam-
mals, should be absent from oceanic islands, while the
most isolated islands should possess their own peculiar
species of aerial mammals 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 be
related, but less closely, to those of the nearest continent,
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 thei'e
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 governing at
the present time the differences in different areas. We
see this in many facts. The endurance of each species
and group of species is continuous in time; for the appar-
ent 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 cer-
tainly is the general rule that the area inhabited by a
single species, or by a group of species, is continuous, and

SUMMARY, 427

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 living within the same area, are often
characterized by trifling features in common, as of sculpt-
ure or color. 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, while those in another class, or only in a
different section of the same order, differ greatly from
each other. In both time and space the lowly organized
members of each class generally change less than the
highly organized; but there are in both cases marked
exceptions to the rule. According to our theory, these
several relations throughout time and space are intelligible;
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 tliey 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.

^S CLASSIFICATION.

CHAPTER XIV.

MUTUAL AFFI^^ITIES OF ORGANIC BEINGS: MORPHOLOGY —
EMBRYOLOGY — RUDIMENTARY ORGANS.

Classification, groups subordinate to groups — Xatural system — Rules
and ditficulties in classification, explained on the theory of
descent with modification — Classification of varieties — Descent
always used in classification — Analogical or adaptive characters —
Affinities, general, complex and radiating — Extinction separates
and defines groups — Morphology, between members of the same
class, between parts of the same individual — Embryology, 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 arbitrary like the
grouping of the stars in constellations. The existence of
groups would have been of simple significance, if one group
had been exclusively fitted to inhabit 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 commonly members of even the same sub-
group have different habits. In the second and fourth
chapters, on Variation and on Natural Selection, I have
attempted to show that within each country it is the widely
ranging, the much diffused and common, that is the
dominant species, belonging to the larger genera in each
class, which vary most. The varieties, or incipient species,
thus produced, ultimately become converted into new and
distinct species; and tliese, on the principle of inheritance,
tend to produce other new and dominant species. Conse-

CLASSIFICATION. 409

qiiently the groups -which are now large, and which gen-
erally include many dominant species, tend to go on in-
creasing in size. I further attempted to show that from
the varying descendants of each species trying to occupy
as many and as different 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 naturalization.
I attempted also to show that there is a steady tendency
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 principles; and he will
see that the inevitable result is, that the modified descend-
ants proceeding from one progenitor become broken up into
groups subordinate to grouj)s. 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 common. But the three genera on the left
hand have, on this same principle, much in common, and
form a subfamily, 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 subfamilies; and they form a family distinct from that
containing the three genera still further 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 many species
descended from a single progenitor grouped into genera;
and the genera into subfamilies, families and orders, all
under one great class. The grand fact of the natural sub-
ordination 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
organic beings, like all other objects, can be classed in many
ways, either artificially by single characters, or more natu-
rally by a number of characters. We know, for instance.

430 GLAbSlFIGATION.

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 species,
genera and families in each class, on what is called the
Natural System. But what is meant by this system?
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; or as an
artificial method of enunciating, as briefly as possible, gen-
eral propositions — that is, by one sentence to give the char-
acters common, for instance, to all mammals, 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 in-
genuity 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 knowledge. Expressions such as that famous one
by Linnaeus, which we often meet with in a more or less
concealed 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 classifica-
tions 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 classifications.

Let us now consider the rules followed in classification,
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 general propositions
and of placing together the forms most like each other.
It might have been thought (and was in ancient times
thought) that those parts of the structure which deter-

CLASSIFICATION. 431

mined the habits of life, and the general place of each
being in the economy of nature, would be of very high im-
portance in classification. Nothing can be more false.
No one regards the external 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 inti-
mately connected with the whole life of the being, are
ranked as merely '^adaptive or analogical characters;'^ but
to the consideration of these resemblances we shall recur.
It may even be given as a general rule, that the less any
part of the organization 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 indications of its true at!in-
ities. We are least likely in the modifications of these
organs to mistake a merely adaptive for an essential char-
acter.^' With plants how remarkable it is that the organs
of vegetation, on which their nutrition and life depend,
are of little signification; whereas the organs of reproduc-
tion, with their product the seed and embryo, are of para-
mount importance! So again, in formerly discussing cer-
tain 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
throughout many allied groups; and their constancy
chiefly depends on any slight deviations not having been
preserved 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
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 acknovvledged in the writings of almost every
author. It will suffice to quote the highest autliority,
Robert Brown, who, in speaking of certain organs in the
Proteace^e, says their generic importance, ^Mike that of all
their parts, not only in this, but, as I apprehend in every

iS2 CLASSIFICATION,

natural family, is very unequal, and in some cases seems to
be entirely lost." Again, in another work he says, the
genera of the Connaraceae " differ in having one or more
ovaria, in the existence or absence of albumen, in the im-
bricate or valvular sestivation. Any one of these charac-
tei-s singly is frequently of more than generic importance,
though liere even, when all taken together, they appear in-
sufficient to separate Cnestis from Connarus/' To give an
example among insects: in one great division of the Hy-
menoptera, the antennas, as Westwood has remarked, 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 antennse in
these two divisions of the same order are of unequal physi-
ological importance. Any number of instances could be
given of the varying importance for classification of the
same important organ 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 rudi-
mentary teeth in the upper jaws of young ruminants, and
certain rudimentary bones of the leg, are highly serviceable
in exhibiting the close affinity between 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 physi-
ological importance, but which are universally 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 distinguishes 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
color in certain Algae — mere pubescence on parts of the
flower in grasses — the nature of the dermal covering, as
hair or feathers, in the Vertebrata. If the Ornithorhyn-
chus had been covered with feathers instead of hair, this
external and trifling character would have been considered
by naturalists as an important aid in determining the de-
gree of affinity of this strange creature to birds.

CLASSIFICATION. 433

The importance, for classification, of trifling characters,
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 his-
tory. 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 preva-
lence, and yet leave us in no doubt where it should
be ranked. Hence, also, it has been found that a
classification founded on any single character, however
important that may be, has always failed; for no part of
the organization is invariably constant. The importance
of an aggregate of characters, even when none are impor-
tanc, alone explains the aphorism enunciated by Linnaeus,
namely, that the characters do not give the genus, but the
genus gives the character; for this seems founded on the
appreciation of many trifling points of resemblance, too
slight to be defined. Certain plants, belonging to the
Malpighiaceee, bear perfect and degraded flowers; in the
latter, as A. de Jussieu has remarked, " The greater num-
ber of the characters proper to the species, to the genus,
to the family, to the class, disappear, and thus laugh at
our classification." When Aspicarpa produced in France,
during several years, only these degraded flowers, depart-
ing so wonderfully in a number of the most important
points of structure from the proper tyj^e of the order, yet
M. Richard sagaciously saw, as Jussieu observes, that this
genus should still be retained among the Malpighiacea?.
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 allo-
cating 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 number, they use it as of
subordinate value. This principle has been broadly con-
fessed by some naturalists to be the true one; and by none
more clearly than by that excellent botanist, Aug. Sfc.
Hilaire. If several trifling characters are always found in
combination, though no apparent bond of connection cau
be discovered between them, especial value is set ou them

434 CLASSIFICATION.

As in most groups of animals, important organs, such as
those for propelling the blood, or for aerating it, or those
for propagating the race, are found nearly uniform, the}^
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, while in
two closely allied genera, namely Cypris and Cytherea,
there is no such organ; one species of Cypridina has well-
developed branchiae, while 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 ordinary
view, why the structure of the embryo should be more im-
portant 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 naturalists, Milne
Edwards and Agassiz, that embryological characters are
the most imjDortant of all; and this doctrine has very gen-
erally been admitted as true. Nevertheless, their impor-
tance has sometimes been exaggerated, owing to the adap-
tive characters of larv93 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 ar-
rangement did not prove a natural one. But there can bo
no doubt that embryonic, excluding larval characters, are
of the highest 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 im-
mediately 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 define a
number of characters common to all birds; but witli
crustaceans, any such definition has hitherto been found
impossible. There are crustaceans at the opposite ends of

CLASSIFICATION. 435

tlie series, wliich have hardly a character in common; yet
the species at both ends, from being plainly allied to others,
and these to others, and so onward, can be recognized as
unequivocally belonging to this, and to no other class of
the Ai'ticiilata.

Gaosrraphical distribution has often been used, though
periiaps not quite logically, in classification, more espec-
luUy in very larcre groups of closely allied forms. Tem-
rniiic'i insists on the utility or even necessity of this
practice in certain groups of birds; and it has been fol-
lowed by several entomologists and botanists.

Finally, with respect to the comparative value of the
various groups of species, such as orders, suborders, fam-
ilies, subfamilies, and genera, they seem to be, at least at
present, almost arbitrary. Several of the best botanists,
such as Mr. Bentham and others, have strongly insisted on
their arbitrary value. Instances could be given among
plants and insects, of a group first ranked by practiced
naturalists as only a genus, and then raised to the rank of
a subfamily or family; and this has been done, not be-
cause further research has detected important structural
ditferences, at first overlooked, but because numerous allied
species, with slightly diSerent grades of deference, have
been subsequently discovered.

All the foregoing rules and aids and difEculties in clas-
sification 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 characters which
naturalists consider as showing true affinity between any
two or more species, are those which have been inherited
from a common parent, all true classification being genea-
logical — ^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 believe
that the arrangement of the groups within each class, in
due subordination and relation to each other, must bo
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

438 CLASSIFICATION.

common progenitor, may differ greatly, being due to
the different degrees of modification whicli 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
three of these genera (A, F and I), a species has trans-
mitted modified descendants to the present day, repre-
sented by the fifteen genera {a^^ to z'^^) on the uppermost
horizontal line. N"ow, 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 dif-
ferent degrees from each other. The forms descended
from A, now broken up into two or three families, consti-
tute a distinct order from those desceuded 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 parent I. But the existing
genus F^* may be supposed to have been but slightly mod-
ified, 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 differences between
these organic beings, which are all related 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 present time, but at each suc-
cessive 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;
SQ will it be with each subordinate branch of descendants
at each successive stage. If, however, we suppose any de-
scendant 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 svstem 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 supposed to have been but little modi-
fied, and they form a single genus. But this genus.

CLASSIFICATION, 4*57

thongli much isolated, will still occupy its proper interme-
diate position. The representation of the groups, as here
given in the diagram 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 sim2:)ly 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 among 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 dif-
erent groups have undergone has to be expressed by rank-
ing them under different so-called genera^ subfamilies,
families, sections, orders and classes.

It may be worth while to illustrate this view of classifi-
cation, 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 sjDoken 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 languages had altered very little and
had given rise to few new languages, while others had
altered much owing to the spreading, isolation and state of
civilization of the several co-descended races, and had thus
given rise to many new dialects and languages. The
vanous degrees of difference between the languages of the
same stock would have to be expressed by groups sub-
ordinate to groups; but the proper or even the only possi-
ble arrangement would still be genealogical; and this
would be strictly natural, as it would connect together all
languages, 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 classifi-
cation of varieties, which are known oi believed to be des-
cended from a single species. These are grouped under
the species, with the subvarieties under the varieties; and
in some cases, as with the domestic pigeon, with several
other grades of difference. Nearly the same rules are fol-
lowed as in classifying species. Authors have insisted on
the necessity of arranging varieties on a natural instead of

438 CLASSIFICATION.

an artificial system; we are cautioned, for instance, not to
class two varieties of the pine apple together, mereh'' be-
cause their fruit, though the most important part, happens
to be nearly identical; no one puts the Swedish and com-
mon turnip together, though the esculent and thickened
stems are so similar. Whatever part is found to be most
constant, 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 color of the body, etc. ; whereas with sheep the
horns are much less serviceable, because less constant. In
classing varieties, I apprehend that if we had a real pedi-
gree, a genealogical classification would be universally pre-
ferred; and it has been attempted in some cases. For we
might feel sure, whether there had been more or less modi-
fication, 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 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 this 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 tlie most important
characters is known to every naturalist: scarcely a single
fact can be predicated in common of the adult males and
hermaphrodites of certain cirripedes, and yet no one
dreams of separating them. As soon as the three Orchi-
dean forms, Monachanthus, Myanthus, and Catasetum,
which had previously been ranked as three distinct genera,
were known to be sometimes produced on the same plant,
they were immediately considered as varieties; and now I
have been able to show that they are the male, female, and
hermaphrodite forms of the same species. The naturalist
includes 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 gen-
erations of Steenstrup, which can only in a technical sense

GLA8SIFIGATI0N. 439

be considered as the same individual. He includes mon-
sters and varieties, not from their partial resemblance to
the parent-form, but because they are descended from it.

As descent has universall}' been used in classing to-
gether the individuals of the same species, though the
males and females and larvee are sometimes extremely
different; and as it has been used in classing varieties
which have undergone a certain, and sometimes a consid-
erable 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 believe it has been
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 community of descent by resemblances
of any kind. Therefore, we choose 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 organ-
ization. We care not how trifling a character may be — let
it be the mere inflection of the angle of the jaw, the manner
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 throughout 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 allien, in several of its most important
characteristics, and yet be safely classed with them. This
may be safely done, and is often done, as long as a suffi-
cient number of characters, let them be ever so unimpor-
tant, betrays the hidden bond of community of descent.

440 ANALOGICAL RESEMBLANCES,

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 com-
munity of descent, and we put them all into the same
class. As we find organs of high physiological impor-
tance— those which serve to preserve life under the most
diverse conditions of existence — 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 onr
classification. We shall presently see why embryo! ogical
characters are of such high classificatory importance.
Geographical distribution may sometimes be brought use-
fully 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 RESEMBLAIJTCES.

We can understand, on the above views, the very impor-
tant distinction between real affinities and analogical or
adaptive resemblances. Lamarck first called attention to
this subject, and he has been ably followed by Macleayand
others. The resemblance in the shape of the body and in
the fin-like anterior limbs between dugongs and whales, and
between these two orders of mam.mals 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. Mivart,
between the mouse and a small marsupial animal (Antech-
inus) 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.

Among insects there are innumerable similar instances;
thus Linnaeus, misled by external ai^pearances, actually
classed an homopterous insect as a moth. We see some-
thing of the same kind even with our domestic varieties,
as in the strikingly similar shape of the body in the im-
proved breeds of the Chinese and common pig, which are
descended from distinct species; and in the similarly thick-

ANALOGICAL RESEMBLANCES. 441

ened stems of the common and specifically distinct Swedish
turnip. The resemblance between the greyhound and the
race-horse 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 systematist. For animals,
belonging to two most distinct lines of descent, may have
become adapted to similar conditions, and thus have as-
Bumed a close external resemblance; 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 to-
gether: 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
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 ances-
tor. So it is with fishes.

Numerous cases could be given of striking resemblances
in quite distinct beings between single parts or organs^
wiiich 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 appearance,
as in the prominence of the canines, and in the cut-
ting 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; while
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

442 ANALOGICAL RESEMBLANCES,

that tlie 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 viscid
discs, come under this same head of analogical resem-
blances. But these cases are so wonderful that they were
introduced as difficulties or objections to our theory. In
all such cases some fundamental difference in the growth
or development of the parts, and generally in their matured
structure, can be detected. The end gained is the same,
but the means, though appearing superficially to be the
same, are essentially different. The principle formerly
alluded to under the term of ajialogical variation has prob-
ably in these cases often come into play; that is, the mem-
bers 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 ac-
quirement 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 instance, the
three elements of land, air and water — we can perhaps
understand how it is that a numerical parallelism has
S{ metimes been observed between the subgroups of distinct
classes. A naturalist, struck with a parallelism of this
nature, by arbitrarily raising or sinking the value of the
groups in several classes (and all our experience shows that
their valuation is as 3^et arbitrary), could easily extend the
parallelism over a wide range; and thus the septenary,
quinary, quaternary and ternary classifications have prob-
ably arisen.

There is another and curious class of cases in which
close external resem.blance does not depend on adaptation

ANALOGICAL REBEMBLANCES. 443

to similar habits of life, but has been gained for the sake
of protection. I allude to the wonderful manner in which
certain butterflies imitate, as first described by Mr. Bates,
other and quite distinct species. This excellent observer
has shown that in some districts of South America, where,
for instance, an Ithomia abounds in gaudy swarms, an*
other 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 color, 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, continually deceived. When the mockers and
the mocked are caught and compared, they are found to
be very different in essential structure, and to belong not
only to distinct 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 imi-
tates 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 in-
habit the same region; we never find an imitator living
remote from the form which it imitates. The mockers are
almost invariably rare insects; the mocked in almost every
case abounds in swarms. In the same district in which a
species of Leptalis closely imitates an Ithomia, there are
sometimes other Lepidoptera mimicking the same Ithomia:
so that in the same place, species of three genera of butter-
flies and even a moth are found all closely resembling a
butterfly belonging to a fourth genus. It deserves especial
notice that many of the mimicking forms of the
Leptalis, as well as of the mimicked forms, can be shown
by a graduated series to be merely varieties of the same
species; while 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 satis-
factorily answer this question by showing tliat the form
which is imitated keeps the usual dress of the group to
which it belongs, while the counterfeiters have changed
their dress and do not resemble their nearest alJies.

444 ANALOGICAL RESEMBLANCES.

"We are next led to inquire wliat reason can be assigned
for certain butterflies and moths so often assuming tne
dress of another and quite distinct form; why, to the per-
plexity 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 destruction 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 distasteful to birds and
other insect-devouring animals. The mocking forms, on
the other hand, that inhabit the same district, are com-
paratively rare, and belong to rare groups; hence, tliey
must suffer habitually from some danger, for otherwise,
from the number of eggs laid by all butterflies, they would
in three or four generations swarm over the whole country.
Now if a member of one of these j)ersecuted and rare groups
were to assume a dress so like that of a well-protected
species that it continually deceived the practiced eyes of an
entomologist, it would often deceive predaceous birds 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 lie found that some of the forms of
Leptalis which mimic so many other butterflies, varied in
an extreme degree. In one district several varieties oc-
curred, 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 inhabiting the same district,
this varietv, from its resemblance to a flourishino^ and little
persecuted kind, has a better chance of escaping destruc-
tion from predaceous birds and insects, and is consequently
oftener preserved; " the less perfect degrees of resemblance
being generation after generation eliminated, and only the
others left to propagate their kind." So that here we have
an excellent ilhistration of natural selection.

Messrs. Wallace and Trimen have likewise described

ANALOGICAL RESEMBLANCES. 445

severiil equally striking cases of imitation in the Lepidop-
tera of the Malay Arcliipelago 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 frequency of imitation with insects than
with other animals, is probably the consequence of their
small size; insects cannot defend themselves, excepting in-
deed the kinds furnished with a sting, and I have never
heard of an instance of 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 dissimulation.

It should be observed that the process of imitation prob-
ably never commenced between forms widely dissimilar in
color. 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 gradually 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 ulti-
mately assume an appearance or coloring wholly unlike
that of the other members of the family to which it be-
longed. There is, however, some difficulty on this head,
for it is necessary to suppose in some cases that ancient
members belonging to several distinct groups, before they
had diverged to their present extent, accidentally resem-
bled a member of another and protected group in a suffi-
cient degree to afford some slight protection, this having
given the basis for the subsequent acquisition of the most
perfect resemblance.

OK THE NATURE OF THE AFFINITIES CONNECTING

ORGANIC BEINGS.

As the modified descendants of dominant species, belong-
ing to the larger genera, tend to inherit the advantages
which made the groups to which they belong large and
their parents dominant, they are almost 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 go on increasing in

446 AFFimTIES CONNECTING

size, and they consequently supplant many smaller and
feebler groups. Thus, we can account for the fact that
all organisms, recent and extinct, 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 discovery of Australia has not added an insect
belonging to a new class, and that in the vegetable king-
dom, 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 inter-
mediate 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 exterminated and utterly lost.
And we have evidence of aberrant groups having suffered
severely from extinction, for they are almost always repre-
sented 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
aberrant 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 conquered by
more successful competitors, with a few members still
preserved under unusually favorable conditions.

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. Waterhouse, 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 adaptive, they must

OROANIC BEINGS, 447

be due in accordance with our view to inheritance from a
common progenitor. Therefore, we must suppose eitiier
that all Rodents, including the bizcacha, branched off from
some ancient Marsupial, which will naturally have been
more or less intermediate in character with respect to all
existing Mursupials; 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 char-
acters of its ancient progenitor than have other Rodents;
and therefore it will not be specially related to any one
existing Marsupial, but indirectly to all or nearly all Mar-
supials, 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 sus-
pected that the resemblance is only analogical, owing 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 diver-
gence in character of the species descended from a com-
mon progenitor, together with their retention by inherit-
ance of some characters in common, we can understand
the excessively complex and radiating affinities 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 np by extinction into distinct
groups and subgroups, will have transmitted some of its
characters, modified in various ways and degrees, to all the
species; and they will consequently be related to each
other by circuitous lines of affinity of various lengths (as
may be seen in the diagram so often referred to), mounting
np through many predecessors. As it is difficulty to show
the blood relationship between the numerous kindred of
any ancient and noble family, even by tlie aid of a genea-
logical tree, and almost impossible to do so without this
aid, we can understand the extraordinary difficulty which

448 AFFINITIES CONNECTING

naturalists have experienced in describing, without the aid
of a diagram, the various affinities which they perceive
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
mavthus 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 forms of
life have been utterly lost, through which the early pro-
genitors of birds were formerly connected with the early
progenitors of the other and at that time less differentiatecl
vertebrate classes. There has been much less extinction
of the forms of life which once connected fishes with
Batrachians. There has been still less within some whole
classes, for instance the Crustacea, for here the most won-
derfully diverse forms are still linked together by a long
and only partially broken chain of affinities. Extinction
has only defined the groups: it had 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 im-
possible to give definitions by which each group could be
distinguished, still a natural 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 repre-
sent eleven Silurian 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 distin-
guished from their more immediate parents and descend-
ants. Yet the arrangement in the diagram would still
hold good and would be natural; for, on the principle of
inheritance, all the forms descended, for instance, from A,
would have something in common. In a tree we can dis-
tinguish this or that branch, though at the actual fork the
two unite and blond 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, and thus give a general idea of the

ORQANIG BEINOa. 449

value of the differences 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
making so perfect a collection: nevertheless, in certain
classes, we are tending toward this end; and Milne Ed-
wards 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 belong.
Finally, we have seen that natural selection, which fol-
lows from the struggle for existence, and which almost
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 or-
ganic beings, namely, their subordination in group under
group. We use the element of descent in classing the
mdividuals of both sexes and of all ages under one species,
although they may have but few characters in common; we
use descent in classing acknowledged varieties, however
different they may be from their parents; and I believe
that this element of descent is the hidden bond of con-
nection which naturalists 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, etc., we can under-
stand the rules which we are compelled to follow in
our classification. We can understand why we value
certain resemblances far more than others ; why wc
use rudimentary and useless organs, or others of trifling
physiological importance; why, in finding the relations
between one group and another, we summarily reject ana-
logical or adaptive characters, and yet use these same char-
acters within the limits of the same group. AVe 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 together
by the most complex and radiating lines of affinities. Wo
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 creation, we may hope to make
sure but slow progress.

450 MORPHOLOGY.

Professor Hackel in his '^ Generelle Morphologie " and
in other works, has recently brought his great knowledge
and abilities to bear on what he calls phylogeny, or the
lines of descent of all organic beings. In drawing up the
several series he trusts chiefly to embryological 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, in-
dependently of their habits of life, resemble each other in
the general plan of their organization. This resemblance
is often expressed by the term "unity of type;" or by say-
ing that the several parts and organs in the different
species of the class are homologous. The whole subject is
included under the general term of Morphology. 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 digging, the leg of the horse,
the paddle of the poi'jDoise, 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 mar-
supials— should all be constructed on the same extraor-
dinary 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 furnished
with two claws. Notwithstanding this similarity of pat-
tern, it is obvious that the hind feet of these several
animals are used for as widely different purposes as it is
possible to conceive. The case is rendered all the more.

MOnPHOLOGT. 451

striking by tlie 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 ancestor?"

Geoifroy St. Hilaire has strongly insisted on the high
importance of relative position or connection in homolo-
gous 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 forearm, 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 modifications of an upper
lip, mandibles, and two pairs of maxillae. 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 ex-
plain 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 admitted by
Owen in his most interesting work on the '* Nature of
Limbs." On the ordinary view of the independent 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 uniform 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
being profitabxo in p/^-^e way to the modified form, but
often affecting ly correlation other parts of the organizar-
tion. In changes of this nature, there will be little or no
tendency to alter the original pattern, or to transpose the

452 MOBPn')LOGT.

parts. The bones of a limb might be shortened and flat-
tened to any extent, becoming 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 aU these modifica-
tions would not tend to alter the framework of the bones
or the relative 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
constructed 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 maxillae, these parts
being perhaps very simple in form; and then natural selec-
tion will account for the definite diversity in the structure
and functions of the mouths of insects. Nevertheless, it is
conceivable that the g^^neral pattern of an organ might
become so much obscured as to be finally lost, by the
reduction and ultimately by the complete abortion of cer-
tain parts, by the fusion of other parts, and by the doubling
or multiplication of others, variations which we know to be
within the limits of possibility. In the paddles of the
gigantic extinct :ea-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 sub-
ject; namely, serial homologies, or the comparison of the
different parts or organs in the same individual, and not
of the same parts or organs in different members of the
same class. Most physiologists believe that the bones of
the skull are homologous — that is, correspond in number
and in relative connection — with the elemental parts of a
certain number of vertebrae. The anterior and posterior
limbs in all the higher vertebrate classes are plainly homo-
logous. 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 pistils, as well as their intimate structure, are
intelligible on the view that they consist of metamorphosed

MORPHOLOGY. 453

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, during
the early or embryonic stages of development in flowers, as
well as in crustaceans and many other animals, 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
inclosed in a box composed of such numerous and such ex-
traordinarily shaped pieces of bone, apparently represent-
ing vertebras? As Owen has remarked, the benefit derived
from the yielding of the separate pieces in the act of par-
turition 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 differ-
ent purposes, namely, flying and walking? Why should
one crustacean, which has an extremely complex mouth
formed of many parts, 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 pur-
poses, be all constructed on the same pattern?

On the theory of natural selection, we can, to a certain
extent, answer these questions. We need not here con-
sider 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 investigation. It is, however,
probable that some serial structures are the result of cells
multiplying by division, entailing tlie multiplication of the
t)arts 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 remarked, of all low or little specialized forms; tlierc-
fore the unknown progenitor of the Vertebrata probably
possessed many vertebrae; the unknown progenitor of the
Articulata, many segments; and the unknown progenitor
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.

454 MORFBOLOGY.

but in form. Consequently such parts, being already pres-
ent in considerable numbers, and being highly variable,
would naturally afford the materials for adaptation to the
most different purposes; yet they would generally retain,
through the force of inheritance, plain traces of their orig-
inal 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, would tend from the first to be similar; the parts
being at an early stage of growth alike, and being subjected
to nearly the same conditions. Such parts, whether more
or less modified, unless their common origin became wholly
obscured, would be serially homologous.

In the great class of molluscs, though the parts in dis-
tinct 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 indi-
vidual. 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. Kay 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 animals, owing to their de-
scent from a common progenitor with subsequent modifica-
tion, homogejious; and the resemblances which cannot thus
be accounted for, he proposes to call homoplastic. For
instance, he believes that the hearts of birds and mammals
are as a whole homogenous — that is, have been derived
from a common progenitor; but that the four cavities of the
heart in the two classes are homoplastic — that is, have been
independently developed. Mr. Lankester also adduces the
close resem.blance of the parts on the right and left sides of
the body, and in the successive segments of the same indi-
vidual animal; and here we have parts commonly called
homologous which bear no relation to the descent of dis-

Development AND embeyolo(^y. 455

tinct species from a common progenitor. Homoplastic
structures are the same with those which I have classed,
though in a very imperfect manner, as analogous modifica-
tions 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 modifications, having been preserved
for the same general purpose or function, of which many
instances have been given.

Naturalists frequently speak of the skull as formed of
metamorphosed vertebrae; the jaws of crabs as metamor-
phosed legs; the stamens and pistils in flowers as metamor-
phosed 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, etc., as having been metamor-
phosed, not one from the other, as they now exist, but
from some common and simpler element. Most natural-
ists, 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 — vertebrae in the
one case and legs in the other — have actually been con-
verted into skulls or jaws. Yet so strong is the rppearance
of this having occurred that naturalists can hardly avoid
employing language having this plain signification. Ac-
cording 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 really been metamorphosed from true though er-
tremely simple legs, is in part explained.

DEVELOPMEJS'T A]S"D EMBEYOLOGY.

This is one of the most important subjects in the vhole
round of natural history. The metamorphoses of insects,
with v/hich every one is familiar, are generally effected
abruptly by a few stages; but the transformations are in
reality numerous and gradual, tliough concealed. A cer-
tain ephemerous insect (Chloeon) during its development,
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 metamorphosis performed in

466 DEVELOl'MENT AND EMBR YOLOQ T.

a primary aud gradual manner. Many insects, and espec-
ially certain crustaceans, show ns 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 astonishing fact that a delicate branching coralline, stud-
ded with polypi, and attached to a submarine rock, sliould
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 swimming animal-
cules, which attach themselves to rocks and become devel-
oped into branching corallines; and so on in an endless
cycle. The belief in the essential identity of the process
of alternate generation and of ordinary metamorphosis has
been greatly strengthened by Wagner^s discovery of the
larva or maggot of a fly, namely the Cecidomyia, produc-
ing asexually other larv^, and these others, which finally
are developed into mature males and females, propagating
their kind in the ordinary manner by eggs.

It may be worth notice that when Wagner's remarkable
discovery was first announced, I was asked how was it pos-
sible to account for, the larva3 of this fly having acquired
the power of asexual reproduction. As long as the case
remained nnique no answer could be given. But already
Grimm has shown that another fly, a Chironomus, repro-
duces itself in nearly the same manner, and he believes
that this occurs frequently in the order. It is the pupa,
and not the larva, of the Chironomus which has this
power; and Grimm further shows that this case, to a cer-
tain extent, ^* unites that of the Cecidomyia with the
parthenogenesis of the Ooccidae;'' the term parthenogen-
esis implying that the mature females of the Coccidae are
capable of producing fertile eggs without the concourse of
the male. Certain animals 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
parthenogenetic reproduction by gradual steps to an earlier
and earlier age — Chironomus showing us an almost exactly
intermediate stage, viz., that of the pupa — and we can
perhaps account for the marvelous case of the Cecidomyia.

It has already been stated that various parts in the same
individual, which are exactly alike during an early embry-

DEVELOPMENT AND EMBR YOLOG Y, 457

onic period, become widely different and serve for widely
different pur^^oses 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 can not be
given than the statement by Von Baer that ** the embryos
of mammalia, of birds, lizards and snakes, probably also
of chelonia, are in the 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 dis-
tinguish the embryos only by their size. In my possession
are two little embryos in spirit, whose names I have
omitted to attach, ttu] c,i 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 similar-
ity in the mode of f orm.at:on of the head and trunk in these
animals. The extremitico, however, are still absent in
these embryos. But even if they had existed in the earliest
stage of their development 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 aiise
from the same fundamental form.^^ The larvge 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 animals.
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^ tliough rarel}^
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, are pinnate or divided like the
ordinary leaves of the leguminos£e.

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 conditions of exist-
ence. We can not, for instance, suppose that in the eai-

^8 DEVELOPMENT AND EMBRYOLOGY.

bryos of the vertebrata the peculiar loop-like courses of the
arteries near the branchial slits are related to similar con-
ditions— in the young mammal which is nourished in the
womb of its mother, in the Qgg 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 believe that the similar bones in the hand of a
man, vring of a bat, and fin of porpoise, are related to
similar conditions of life. No one supposes that the stripes
on the whelp of a lion, or the spots on the young black-
bird, are of any use to these animals.

The case, however, is different when an animal, during
any part of its embryonic career, is active, and has to pro-
vide for itself. The period of activity may couia on
earlier or later in life; but whenever it comes on, the
adaptation of the larva to its conditions of life is just as per-
fect and as beautiful as in the adult animal. In how im-
portant a manner this has acted, has recently been
well shown by Sir J. Lubbock in his remarks on the
close similarity of the larvae of some insects belonging
to very different orders, and on the dissimilarity of the
larvae of other insects within the same order, according
to their habits of life. Owing to such adaptations the
similarity of the larvae of allied animals is sometimes
greatly obscured; es23ecially when there is a division of
labor during the different stages of development, as
when the same larva has during one stage to search for
food, and during another stage has to search for a place of
attachment. Cases can even be given of the larvae of allied
species, or groups of species, differing more from each
other than do the adults. In most cases, however, the
larvae, though active, still obey, more or less closely, the
law of common embryonic resemblance. Cirripedes afford
a good instance of this; even the illustrious Cuvier 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 larvae in all their stages barely distinguishable.

The embryo in the course of development generally rises
in organization. I use this expression, though I am aware
that it is hardly possible to define clearly what is meant by

DEVELOPMENT AND EMBRYOLOGY. 4r.O

organization being higher or lower. But no one probubly
will dispute that the butterfly is higher than the cater-
pillar. In some cases, however, the mature animal must
be considered as lower in the scale than the larva, as with
certain parasitic crustaceans. To refer once again to cirri-
pedes: the larvae in the first stage have three pairs uf loco-
motive organs, a simple single eye, and a probosci formed
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 beauti-
fully constructed natatory legs, a pair of magnificent com-
pound eyes, and extremely complex antennae; but they
have a closed and imperfect mouth, and cannot feed: their
function at this stage is, to search out by their well-devel-
oped organs of sense, and to reach by their active powers
of 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 con-
verted into prehensile organs; they again obtain a well-
constructed mouth; but they have no antennae, and their
two eyes are now reconverted into a minute, single, simple
eye-spot. In this last and complete state, cirripedes may
be considered as either more highly or more lowly organized
than they were in the larval condition. But in some genera
the larvae become developed into hermaphodites having
the ordinary structure, and into what I have called com-
plomental m^Jes; 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 struc-
ture 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 porpoise, 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 certain members of other
groups this is the case, and the embryo does not at any
period differ widely from the adult: thus Owen has re-
marked in regard to cuttle-fish, '^ there is no metamor-

460 DEVELOPMENT AND EMBR YOLOG T.

pilosis; the cepbalopodic character is manifested long be-
fore the parts of the embryo are completed/^ Land-shells
and fresh-water crustaceans are born having their proper
forms, while the marine members of the same two great
classes pass through considerable atid often great changes
during their development. Spiders, again, barely undergo
any metamorphosis. The larvae 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 development 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 remarkable
discovery that certain shrimp-like crustaceans (allied to
Penoeus) 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 member is as yet
known to be first developed under the nauplius-form,
though many appear as zoeas; nevertheless Miiller assigns
reasons for his belief, that if there had been no suppression
of development, all these crustaceans would have appeared
as nauplii.

How, then, can we explain these several facts in embry-
ology— namely, the very general, though not universal,
difference in structure between the embrvo and the adult:
the various parts in the same individual embryo, which
ultimately become very unlike, and serve for diverse pur-
poses, being at an early period of growth alike; the com-
mon, but not invariable, resemblance between the embryos
or larvae of the most distinct species in the same class; the
embryo often retaining, while within the egg or womb,
structures which are of no service to it, either at that or at
a later period of life; on the other hand, larvae which have
to provide for their own w^ants, being perfectly adapted to
the surrounding conditions; and lastly, the fact of certain
larvae standing higher in the scale of organization than the
mature animal into which they are developed? I believe
that all these facts crai be explained as follows.

DEVELOPMENT AND EMBRYOLOGY. 461

It is commonly assumed, perhaps from Dionstrosities
affecting the embr}^© 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, can not positively tell, until some time after
birth, what will be the merits and demerits of their young
animals. We see this plainly in our own children; we
can not 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 par-
ents before the act of generation. It deserves notice that
it is of no importance 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 obtained
its food by having a much-curved beak whether or not
while young it possessed a beak of this shape, as long as it
was fed by its parents.

1 have stated in the first chapter, that at whatever age a
variation first appears in the parent, it tends to reappear
at a corresponding age in the offspring. Certain vari-
ations 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 corresponding 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 varia-
tions (taking the word in the largest sense) which
have supervened at an earlier age in the child than in the
parent.

These two principles, namely, that slight variations gen-
erally appear at a not very early period of life, and are in-
herited at a corresponding not early period, explain, as I
believe, all the above specified leading facts in embryology.
But first let us look to a few analogous cases in our domes-

462 DEVELOPMENT AND EMBR YOLOG T.

tic varieties. Some aiithoi*s who have written on dogs
maintain that the greyhound and bull-dog, though so dif-
ferent, are really closely allied 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 tiiat they differed just as much as their parents,
and this, judging by the eye, seemed almost to be the case;
but on actually measuring 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 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 com-

fared the young within twelve hours after being hatched,
carefully measured the proportions (but wdll 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. N"ow, some of these birds,
when mature, differ in so extraordinary 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 distinguished, the proportional dif-
ferences 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 remarkable 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 stage.

These facts are explained by the above two principles.
Fanciers select their dogs, horses, pigeons, etc., for breed-
ing, when nearly grown up. They are indifferent whether
the desired qualities are acquired earlier or later in life, if

DEVELOPMENT AND EMBR 70L0G 7. 463

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 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 inherited 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 extend this view to widely
distinct structures and to whole classes. The fore limbs,
for instance, which once served as legs to a remote progen-
itor, may have become, through a long course of modifica-
tion, 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
mature, when it was compelled to use its full powers to
gain its own living; and the effects thus produced will have
been transmitted to the offspring at a corresponding 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 mav have
supervened at a very early period of life, or the steps may
have been inherited at an earlier age than that at which

464 DEVELOPMENT AND EMBR YOLOG Y,

they first occurred. In either of these cases, the young or
embryo will closely resemble the mature 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. AVith respect to the final
cause of the young in such groups not passing through
any metamorphosis, we can see that this Avould follow
from the folio whig 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 in-
dispensable 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 undergo any metamorphosis, while marine
members of the same groups pass through various trans-
formations, Fritz Miiller has suggested that the process of
slowly modifying and adapting an animal to live on the
land or in fresh water, instead of in the sea, would be
greatly simplified by its not passing 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 changed habits of life, would commonly be found
unoccupied or ill-occupied by other organisms. In this
case the gradual acquirement at an earlier and earlier age
of the adult structure would be favored 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 ani-
mal to follow habits of life slightly different from those of
the parent-form, and consequently to be constructed on a
slightly different plan, or if it profited a larva already dif-
ferent from its parent to change still further, then, on the
principle of inheritance at corresponding ages, the young
or the larva? might be rendered by natural selection more
and more diff'erent from their parents to any conceivable
extent. Differences in the larva might, also, become corre-
lated 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 ani-

DEVELOPMENT AND EMBHYOLOQT, 465

mals. The adult might also become fitted for sites or
habits, in which organs of locomotion or of the senses, etc.,
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 corresponding
ages, animals might come to pass through stages of devel-
opment, perfectly distinct from the primordial condition
of their adult progenitors. Most of our best authorities
are now convinced that the various larval and j^upal stages
of insects have thus been acquired through adaptation, and
not through inheritance from some ancient form. The
curions case of Sitaris — a beetle which passes through cer-
tain unusual stages of development — will illustrate how
this might occnr. The first larval form is described by M.
Fabre, as an active, minute insect, furnished with six legs,
two long antennae, and four eyes. These larvae 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 larvae spring on them, and after-
ward crawl on to the females while paired with the males.
As soon as the female bee deposits her eggs on the surface
of the honey stored in the cells, the larvae of the Sitaris
leap on the eggs and devour them. Afterward they
undergo a complete change; their eyes disappear; their legs
and antennae become rudimentary, and they feed on honey;
so that they now more closely resemble the ordinary larvae
of insects; nltimately they undergo a further transforma-
tion, 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 embrvonic 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 Crus-
tacea, forms wonderfully distinct from each other, namely,
suctorial parasites, cirripedes, entomostraca, and even the

46(3

DEVELOP MENT AND EMBRYOLOGY,

malacostraca, appear at first as larvae under the nanplius-
form; and as these larv^ live and feed in the open
sea, and are not adapted for any peculiar habits of
life, and from other reasons assigned by Fritz Miiller, it
is probable that at some very remote period an independ-
ent adult animal, resembling the Kauplius, existed, and
subsequently produced, along several 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 descendants of some ancient progenitor,
which was furnished in its adult state with branchiae, 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; descent being the
hidden bond of connection which naturalists 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 embryo is even more
important for classification than that of the adult. In
two or more groups of animals, however 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 embryonic 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 have been so greatly modified
through adaptation to new habits of life as to be no longer
recognizable. Even in groups, in wliich the adults have
been modified to an extreme degree, community of origin
is often revealed by the structure of the larvae; we have
seen, for instance, that cirripedes, though externally so like
shell-fish, are at once known by their larvae to belong to
the great class of crustaceans. As the embryo often shows

DEVELOPMENT AND EMBRYOLOGY. 467

us more or less plainly the structure of the less modified
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, how-
ever, 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 inherited 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 larvae state to some special line of life, and transmitted
the same larval state to a whole group of descendants; for
such larval will not resemble any still more ancient form
in its adult state.

Thus, as it seems to me, the leading facts in embryology,
which are second to none in importance, are explained on
the principle of variations in the many descendants from
some one ancient progenitor, having appeared at a not
very early period of life, and having been inherited at a
corresponding period. Embryology rises greatly in inter-
est, 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 mamma-
lia, for instance, the males possess rudimentary mammae;
in snakes one lobe of the lungs is rudimentary; in birds
the "bastard-wing'^ may safely be considered as a rudir
mentary digit, and in some species the wliole wing is so fa-

IQS BUDIMENTAEY, ATROPHIED,

rudimentary that it cannot be used for fliglit. Wliat can
be more curious thau 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?

Eudimentary organs plainly declare their origin and
meanins: in various wavs. There are beetles belonsrins: to
closely allied species, or even to the same identical species,
vv'hich have either full- sized and perfect wings, or mere
rudiments of membi-ane, which not rarelv lie under wincr-
covers firmly soldered together; and in these cases it is im-
possible to doubt, that the rudiments represent wings.
Eudimentary organs sometimes retain their potentiality:
this occasionally occurs with the mammte of male mammals,
which have been known to become 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 be-
come well developed and yield milk. In regard to plants,
the petals are sometimes rudimentary, and sometimes well
developed in the individuals of the same species. In cer-
tain plants having 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 hybrid offspring was much increased in size; and this
clearly shows that the rudimentary and perfect pistils are
essentially alike in nature. An animal may possess vari-
ous 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
organization has no reference to the future life of the
animal; nor has it any adaptation to its embiwonic con-
dition; it has solely reference to ancestral adaptations, it
repeats a phase in the development of its progenitors."

AND ABORTED ORGANS. 469

An organ, serving for two purposes, may become rudi-
mentary or utterly aborted for one, even the more impor-
tant 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 ovarium. The pistil
consists of a stigma supported on a style; but in some Com-
positay, the male florets, which of course cannot be fecun-
dated, have a rudimentary pistil, for it is not crowned with
a stigma; but the style remains well developed and is
clothed in the usual manner with hairs, which serve to
brush the pollen out of the surrounding and conjoined
anthers. Again, an organ may become rudimentary for
its proper purpose, and be used for a distinct one: in cer-
tain fishes the swim-bladder seems to be rudimentarv 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,
unless we have reason to suppose that they were formerly
more highly developed, ought not to be considered as
rudimentary. They may be in a nascent condition, and in
progress toward 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 formerl}^ when still
less developed, have been of even less use than at present,
they cannot formerly have been produced through varia-
tion and natural selection, which acts solely by the preser-
vation of useful modifications. They have been partially
retained by the power of inheritance, and relate to a
former state of things. It is, however, often difficult to
distinguish between rudimentary and nascent organs; for
we can judge only b}^ analogy whether a part is capable of
further development, in which case alone it deserves to be
called nascent. Organs in this condition will always be
somewhat rare; for beings thus provided will commonly
have been supplanted by their successors with the same
organ in a more perfect state, and consequently will have
become long ago extinct. The wing of the penofuin 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

470 RUDIMENTARY, ATROPHIED,

the case; it is more probably a reduced organ, modified
for a new function: the wing of the Apter3^x, on the other
liand, is quite useless, and is truly rudimentary. Owen
considers the simple filamentary limbs of the Lepidosiren
as the "beginnings of organs which attain full functional
development in higher vertebrates; " but, according to tlie
view lately advocated by Dr. Giinther, they are probably
remnants, consisting of the persistent axis of a fin, with
the lateral rays or branches aborted. 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 certain cirripedes, which have ceased to
give attachment to the ova and are feebly developed, are
nascent branchiae.

Rudimentary organs in the individuals of the same
species are very liable to vary in the degree of their devel-
opment and in other respects. In closely allied s^Decies,
also, the extent to which the same organ has been reduced
occasionally differs much. This latter fact is well exem-
plified in the state of the wings of female moths belonging
to the same family. Rudimentary organs may be utterly
aborted; and this implies, that in certain animals or
plants, parts are entirely absent which analogy would
lead us to expect to find in them, and which are occasion-
ally found in monstrous individuals. Thus in most of the
Scrophulariaceae the fifth stamen is utterly aborted; yet we
may conclude that a fifth stamen once existed, for a rudi-
ment of it is found in many species of the family, and this
rudiment occasionally 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
understand the relations of the parts, more useful than the
discovery of rudiments. This is well shown in the draw-
ings 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 afterward wholly disappear.
It is also, I believe, a universal rule, that a rudimentary
part is of greater size in the embryo relatively to the ad-
joining parts, than in the adult; so that the organ at this

AND ABORTED ORGANS. 47I

early age is less rudimentary, or even cannot be said to be
ill 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 rudi-
mentary organs. In reflecting on them, every one must be
struck with astonishment; for the same reasoning 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 " 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 re-
tained ''to complete the scheme of nature,'* why, as Pro-
fessor Weismann asks, have they not been retained by other
snakes, which do not possess even a vestige of these same
bones? What would be 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 sum? 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 sup-
pose that the minute papilla, which often represents the
pistil in male flowers, and which is formed of mere cellalir
tissue, can thus act? (Jan 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 knowu to ap-
pear on the stumps, and I could as soon believe that these
vestiges of nails are developed in order to excrete horny
matter, as that the rudimentary nails on the fiti 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 car.
understand to a large extent the laws governing theit
imperfect developmenU We have plenty of cases of rudi-

472 RUDIMENTARY, ATROPHIED,

mentary organs in our domestic productious, as the stump
of a tail in tailless breeds, the vestige of an ear in
earless breeds of sheep — the reappearance of minute dang-
ling 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 rudi-
ments 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 produced; 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 reduced 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 conditions, 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 rudimentary.

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-
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 selec-
tion. All this ascrees well with what we see under nature.
Moreover, at whatever period of life either disuse 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 inheritance at corresponding ages
will t^nd to reproduce tki organ in its reduoed stat^ »t tJie

AND ABORTED ORGANS. 473

same mature age, but will seldom affect it in the embryo.
Thus we can understand 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, the
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 difBculty. After an organ
has ceased being used, and has become in consequence
much reduced, how can it be still further reduced in size
until the merest vestige is left; and how can it be finally
quite obliterated? It is scarcely possible that disuse can
go on producing any further effect after the organ has
once been rendered functionless. Some additional ex-
planation is here requisite w^hich I cannot give. If, for
instance, it could be proved that every part of the organ-
ization tends to vary in a greater degree toward diminution
than toward augmentation of size, then we should be able
to understand how an organ which has become useless
would be rendered, independently of the effects of disuse,
rudimentary and would at last be wholly suppressed; for
the variations toward 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 possessor,
are saved as far as is possible, will perhaps come into play
in rendering a useless part rudimentary. But this prin-
ciple will almost necessarially 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 flowei
the pistil of the female flower, and formed merely of cellu-
lar tissue, could be further reduced or absorbed for the
sake of economizing nutriment.

Finally, as rudimentary organs, by whatever steps they
may have been degraded into their present useless condi-
tion, are the record of a former state of things, and have
been retained solely through the power of inheritance — we
can understand, on the genealogical view of classification,
how it is that systematists, in placing organisms in theii^

474 ISUMMART.

proper places in the natural system, have often found rudi-
mentary parts as useful as, or even sometimes more useful
than, parts of high physiological importance. Rudimentary
organs may be compared with the letters in a word, still
retained in the spelling, but become useless in the pro-
nunciation, 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 condition, or quite aborted, far from presenting
a strange difficulty, as they assuredly d9 on the old doctrine
of creation, might even have been anticipated in accordance
with the views here explained.

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 relationships
by which all living and extinct organisms are united by
complex, radiating, and circuituous 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 constant and prevalent,
whether of high or of the most trifling importance, or, as
with rudimentary organs of no importance — the wide
opposition in value between analogical or adaptive charac-
ters, and characters of true affinity; and other such rules;
— all naturally follow if we admit the common parentage
of allied forms, together 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 element of descent has been universally used in rank-
ing together 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.

SUMMARY. 475

On tliis same view of descent with modification, most
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 embryology; 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 resem-
blance of the homologous parts or organs in allied though
distinct species, though fitted in the adult state for habUs
as different as is possible. Larvae are active embryos,
which have been specially modified in a greater or less
degree in relation to their habits of life, with their modifi-
cations 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
in mind how strong is the force of inheritance — the occur-
rence of rudimentary organs might even have been antici-
pated. The importance of embryological characters and
of rudimentary organs in classification is intelligible, on
the view that a natural arrangement must be genealogical.

Finally, the several classes of facts which have been con-
sidered in this chapter, seem to me to proclaim so plainly,
that the innumerable species, genera and families, with
which this world is peopled, are all descended, each
within its own class or group, from common parents, and
have all been modified in the course of descent, that 1
should without hesitation adopt this view, even if it were
unsupported by other facts or arguments.

476

EEOAPITULATION,

CHAPTER XV.

RECAPITULATIOI^ AND CONCLUSION".

Recapitulation of the objections to the theory of Natural Selection —
Recapitulation of the general and special circumstances in its
favor — Causes of the general belief in the immutability of
species — How far the theory of Natural Selection may be
extended — 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 en-
deavored 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 perfected, 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 insuper-
ably great, can not be considered real if we admit the fol-
lowing propositions, namely, that all parts of the organi-
zation and instincts offer, at least, individual differences —
that there is a struggle for existence leading to the preser-
vation of profitable deviations of structure or instinct — •
and, lastly, that gradations in the state of perfection of
each organ may have existed, each good of its kind. The
truth of these propositions can not, I think, be disputed.

It is, no doubt, extremely difficult even to conjecture
by what gradations many structures have been perfected,
more especially among broken and failing groups of
organic beings, which have suffered much extinction; but
we see so many strange gradations in nature, that we ought

RECAPITULATION. 47t

to be extremely cautious in saying that any organ or in-
stinct, 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 opjoosed 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 recapitulation 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 reproductive systems of the in-
tercrossed 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 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 respect 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 Gart-
ner and Kolreuter. Most of the varieties which have been
experimented on have been produced 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-spe-
cies if intercrossed, we ought not to expect that domesti-
cation would likewise induce sterility in their modified
descendants when crossed. This elimination of sterility
apparently follows from the same cause which allows on/

478 RECAPITULATION.

domestic animals to breed freely under diversifiea circum-
stances; and this again apparently follows from their
having been gradually 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 conditions of
life give vigor 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 in-
creased size and vigor. This is chiefly owing to the forms
which are crossed having been exposed to somewhat dif-
ferent conditions of life ; for I have ascertained by a labori-
ous series of experiments that if all the individuals of the
same variety be subjected during several generations to the
came 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 survive, are
rendered sterile, though retaining perfect health. This
does not occur, or only in a very slight degree, 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 distinct organizations. 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 wiiy two distinct species,
when crossed, as well as their h3'brid offspring, are gener-
ally rendered more or less sterile, while two domesticated
varieties when crossed and their mongrel offspring are per-
fec-ily fertile.

liECAFITULATION. 479

Turning to geographical distribution, the difficulties en-
countered on the theory of descent with modification
are serious enough. All the individuals of the same
species, and all the species of the same genus, or even
liigher 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 traveled from some one point
to all the others. We are often wholly unable even to con-
jecture how this could have been effected. Yet, as we have
reason to believe that some species have retained the same
specific form for very long periods of time, immensely long
as measured by years, too mnch stress ought not to be laid
on the occasional wide diffusion 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 ex-
tinction of the species in the intermediate regions. It can
not be denied that we are as yet very ignorant as to the full
extent of the various climatical 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 distribution 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 pro-
cess of modification has necessarily been slow, all the
means of migration will have been possible during a very
long period; and consequently 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 inter-
minable number of intermediate forms must have existed,
linking together all the species in each group by gradations
as fineas 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 dis-
cover directly connecting links between them, but only be-

480 RECAPITULATION.

tween 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 oc-
cupied 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 becoming 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 modifications are slowly
eifected. I have also shown that the intermediate varieties
which probably at first existed in the intermediate zones,
would be liable to be supplanted by the allied forms on
either hand; for the latter, from existing in greater num-
bers, 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 infinitude of
connecting links, between the living and extinct inhabi-
tants of the world, and at each successive period be-
tween the extinct and still older species, why is not
every geological formation charged with such links? Why
does not every collection of fossil remains afford plain evi-
dence of the gradation and mutation of the forms of life?
Although geological research has undoubtedly revealed the
former existence of many links, bringing numerous forms
of life much closer together, it does not yield the infinitely
many fine gradations between past and present species re-
quired 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 geological stages? Although we now know
that organic beings appeared on this globe, at a period in-
calculably remote, long before the lowest bed of the Cam-
brian system was deposited, why do we not find beneath
this system great piles of strata stored with the remains of
the progenitors of the Cambrian fossils? For on the
theory, such strata must somewhere have been deposited at

RECAPITULATION. 481

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 imperfect
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 characters directly interme-
diate between its modified offspring, any more than the
rock-pigeon is directly intermediate in crop and tail be-
tween its descendants, the pouter and fantail pigeons.
We should not be able to recognize a species as the parent
of another and modified species, if we were to examini7ie
the two ever so closely, unless we possessed most of the
intermediate links; and owing to the imperfection of the
geological recoid, we have no just right to expect to find
so many links. If two or three, or even more linking
forms were discovered, they would simply be ranked by
many naturalists as so many new species, more especially if
found in different geological substages, let their dif-
ferences 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 geo-
logically 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 spe-
cies have undergone modification, though long as meas-
ured by years, have probably been short in comparison
with the periods during which they retained 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 discov-
ery 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 geolog-

482 RECAPITULATION,

ical formation, tliey appear as if suddenly created there,
and will V simply classed as new species. Most forma-
tions have been intermittent in their accumnlation, and
their duration has Drobably been shorter than the avera^ie
duration of specific forms. Successive formations are m
m.ost cases separated from each other by blank intervals of
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 be-
neath 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 enormous
period in nearly their present relative positions, 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 sufficient 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 philoso-
phers are not as yet willing to admit that we know enough
of the constitution 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 that
species have all changed; and they have changed in the
manner required by the theory, for they have changed
slowly and in a graduated manner. We clearly see this in
the fossil remains from consecutive formations 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

UEGAPITULA TION, 483

difficulties whicli may be justly urged against tlie theory;
and I have now briefly recapitulated tlie answers and ex-
planations 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. Bat it deserves especial notice
that the more important objections relate to questions on
• which we are confessedly ignorant; nor do we know how
ignorant we are. We do not know all tlie possible transi-
tional gradations between the simplest and the most per-
fect organs; it cannot be pretended that we know all the
varied means of Distribution during the long lapse of
years, or that we know how imperfect is the Geological
Record. Serious as these several objections are, in my
judgment they are by no means sufficient to overthrow the
theory of descent with subsequent 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 varia-
tions as spontaneous. Variability is governed by many com-
plex laws, by correlated growth, compensation, the increased
use and disuse of parts, and the definite action of the sur-
rounding conditions. There is much difficulty in ascer-
taining how largely our domestic productions have been
modified; but we may safely infer that the amount has
been large, and that modifications 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 domesti-
cation for a very long period ; nor do we know that it
ever ceases, for new varieties are still occasionally pro-
duced by our oldest domesticated productions.

Variability is not actually caused by man ; the only
unintentionally exposes organic beings to new conditions
of life and then nature acts on the organization 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

484 RECAPITULATION.

his own benefit or pleasure. He may do this methodically,
or he may do it nnconscionsly by preserving the individ-
nals 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 suc-
cessive generation, individual differences so slight as to be
inappreciable except by an educated eye. This unconscious
process of selection has been the great agency in the for-
mation 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 inextri-
cable doubts whether many of them are varieties or aborig-
inally distinct species.

There is no reason why the principles which have acted
so efficiently under domestication should not have acted
under nature. In the survival of favored individuals and
races, during the constantly recurrent Struggle for Exist-
ence, 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
naturalized 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
which shall decrease; or finally become extinct. As the
individuals 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 almost
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 conditions, 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 possession

BEGAPITULATION. 485

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 special weapons or means
of defense or charms ; and a slight advantage will lead
to victory.

As geology plainly proclaims that each land has under-
gone great physical changes, we might have expected to
find that organic beings have varied under nature, in the
^ same way as they have varied under domestication. And
if there has been any variability under nature, it would be
an unaccountable fact if natural 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 differences in his domestic productions;
and every one admits that species present individual differ-
ences. But, beside such differences, all naturalists admit
that natural varieties exist, which are considered
sufficiently distinct 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 subspecies and species. On
separate continents, and on different parts of the same con-
tinent, when divided by barriers of any kind, and on outlying
islands, what a multitude of forms exist, which some
experienced naturalists rank as varieties, others as geo-
graphical races or subspecies, 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 individual
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 select variationsuseful
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, acting during long ages and rigidly
scrutinizing the whole constitution, structure and habits
of each creature, favoring the good and rejecting the bad?

486

RECAFITULA TION,

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 further
than this, seems to be in the highest degree probable. I
have already recapitulated, as fairly as I could, the opposed
difficulties and objections: now let us turn to the special
facts and arguments in favor 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 to have
been produced by special acts of creation, and varieties
which are acknowledged to have been produced by second-
ary 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 varieties; for where the manufactory
of species has been active, we might expect, as a general
rule, to find it still in action; and this is tlie case if varie-
ties be incipient species. I^Toreover, the species of the
larger genera, which afford the greater number of varieties
or incipient species, retain to a certain degree the character
of varieties; for they differ from each other by a less
amount of difference than do the species of smaller genera.
The closely allied species also of a 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 tlmt 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, tliere
will be a constant tendency in natural selection to preserve
the most divergent offspring of any one species. Hence,
during a long- continued course of modification, the
slight differences characteristic of varieties of the same
species, tend to be augmented into the greater differences

UECAPrrULATION. 487

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 dis-
tinct 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 character,
together with the inevitable contingency of much extinc-
tion, explains the arrangement of all the forms of life in
groups subordinate to groups, all within a few 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 inexplicable on the theory
of creation.

As natural selection acts solely by accumulating slight,
successive, favorable 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 con-
firm, 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 dilferent 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, shoukl prey on insects on the ground;
that upland geese, which rarely or never swim, would
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
eacli species constantly trying to increase in number, with

488 BEGAPirULATION.

natural selection always ready to adapt the slowly varying
descendants of each to any unoccupied or ill-occupied place
la nature, these facts cease to bs strange, or might even
have been anticipated.

We can to a certain extent understand how it is that
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 universal, 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 colors, elegant patterns, and
other ornaments to the males, and sometimes to b^th 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 conspicuous by brilliant colors in contrast
with the green foliage, in order that the flowers may be
easily seen, visited and fertilized by insects, and the seeds
disseminated by birds. How it comes that certain colors,
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 odors and flavors 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
naturalized productions from another land. Nor ought
we to marvel if all the contrivances in nature be not, as
far as we can judge, absolutely perfect, as in the case even
of the human eye; or if some of them be abhorrent to our
ideas of fitness. We need not marvel at the stins: of the
bee, when used against an enemy, causing the bee's own
death; at drones being 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 ichueumonidee feeding within the

RECAPITULATION. 489

living 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
detect3d.

The complex and little known laws governing the pro-
duction of varieties are the same, as far as we can judge,
with the laws which have governed the production of dis-
tinct species. In both cases physical conditions seem to
have produced some direct and definite effect, but how
much we cannot say. Thus, when varieties 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 con-
siderable 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 inhabiting 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 haa
been modified other parts have been necessarially modified.
With both varieties and species, reversions to long-lost
characters occasionally occur. How inexplicable on the
theory of creation is the occasional aj)pearance 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 de-
scended from a striped progenitor, in the same manner as
the several domestic breeds of the pigeon are descended
from the blue and barred rock-pigeon!

On the ordiuary view of each species having been inde-
pendently created, why should specific characters, or those
by which the species of the same genus differ from each
other, be more variable than generic characters in which
they all agree? Why, for instance, should the color of a
flower be more likely to vary in any one species of a genus,
if the other species possess differently colored flowers, than
if all possessed the same colored flowers? If species are
only well-marked varieties, of which the characters have

490

REGAPITULA TIOIT.

become in a higli degree permanent, we can understand
this fact; for tliey liave already varied since they branched
off from a common progenitor in certain characters, by
which they have come to be specifically distinct from each
otl^er; 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 de-
veloped 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 undergone,
since the several species branched off from a common pro-
genitor, an unusual amount of variability and modification,
and therefore we might expect the part generally to be
still variable. But a part may be 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 com-
mon to many subordinate forms, that is, if it has been in-
herited for a very long period; for in this case it will have
been rendered constant by long-continued natural selection.
Glancing at instincts, marvelous 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 understand 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 architectural powers of
the hive-bee. Habit no doubt often comes into play iu
modifying instincts; but it certainly is not indispensable,
as we see in the case of neuter insects, 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 understand 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 temperate South America, for instancCj
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

RECAPITULATION. 491

being not perfect and liable to mistakes, and at many
instincts causing other animals to suffer.

If species be only well-marked and permanent varieties,
we can at once see why their crossed offspring should
follow the same complex laws in their degrees and kinds of
resemblance 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 in-
dependently 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 slowly and at succes-
sive intervals; and the amount of change after equal
intervals of time, is widely different in different 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 prin-
ciple 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 dom-
inant forms, with the slow modification of their descend-
ants, causes the forms of life, after long intervals of time,
to appear as if they had changed simultaneously through-
out 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 beingg
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 understand why it is that the more ancient forms, or
early 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 organization than ancient
forms; and they must be higher, in so far as the later and

492 REGAPITULATIOm

more improved forms have conquered the older and less
improved forms in the struggle for life; they have also
generally had their organs more specialized for different
functions. This fact is perfectly compatible with numer-
ous beings still retaining simple and but little improved
structures, fitted for simple conditions of life; it is likewise
compatible with some forms having retrograded in organi-
zation, 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 migra-
tion from one part of the world to another, owing to
former climatical 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 modification
have been the same. We see the full meaning of the
wonderful fact, which has struck every traveler, namely,
that on the same continent, under the most diverse con-
ditions, under heat and cold, on mountain and lowland,
on deserts and marshes, most of the inhabitants within
each great class are plainly related; for they are the descend-
ants of the same progenitors and early colonists. On this
same principle of former migration, combined in most
cases with modification, we can understand, by the aid of
the Glacial period, the identity of some few plants, and the
close alliance of many others, on the most distant mount-
ains, and in the northern and southern temperate zones;
and likewise the close alliance of some of the inhabitants
of the sea in the northern and southern temperate lati-
tudes, though separated by the whole intertropical ocean.
Although two countries may present physical conditions as

RECAPITULATION. , 493

closely similar as the same species ever require, we need
feel no surprise at tlieir inhabitants being widely different,
if they have been for a long period completely sundered
from each other; for as the relation of organi to organ-
ism is the most important of all relations, an 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 distant from any con-
tinent. Such cases as the presence of peculiar species of
bats on oceanic islands and the absence of all other terres-
trial mammals, are facts utterly inexplicable on the theory
of independent acts of creation.

The existence of closely allied representative species in
any two areas, implies, on the theory of descent with
modification, that the same parent-forms formerly inhab-
ited both areas: and we almost invariably find that wher-
ever many closely allied species inhabit two areas, some
identical species are still common to both. Wherever
many closely allied yet distinct species occur, doubtful
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 neighboring American mainland; and of
those of the Cape de Verde Archipelago, and of the other
African islands to the African mainland. It must be ad-
mitted that these facts receive no explanation on the
theory of creation.

The fact, as we have seen, that all past and present

494

RECAPITULA TION.

organic beings can be arranged within a few great classes, in
groups subordinate to groups, and with the extinct groups
often falli^^? in between the recent groups, is intelligible
on the th^ of natural selection with its contingencies of
extinction and divergence of character. On these same
principles we see how it is that the mutual affinities
of the forms within each class are so complex and
circuitous. We see why certain characters are far more
serviceable than others for classification; why adaptive
characters, though of paramount importance to the beings
are of hardly any importance in classification; why charac-
ters derived from rudimentary parts, though of no service
to the beings, are often of high classificatory value; and
why embryological characters are often the most valuable
of all. The real affinities of all organic beings, in contra-
distinction to their adaptive resemblances, are due to inher-
itance or community of descent. The Natural System is a
genealogical arrangement, with the acquired grades of dif-
ference, marked by the terms, varieties, species, genera,
families, etc. ; and we have to discover the lines of descent
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 porjDoise, and leg of the horse —
the same number of vertebrae 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 simi-
larity 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 pistils of a flower, is like-
wise, to a large extent, intelligible on the view of the grad-
ual modification of parts or organs, which were aboriginally
alike in an early progenitor in each of these classes. On
the principle of successive variations not always superven-
ing 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 mav cease
marveling at 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 branchiEe.

CONCLUSION', 405

Disuse, aided sometimes by natural selection, will often
have reduced organs when rendered useless under changed
habits or conditions of life; and we can understand on this
view the meaning of rudimentary organs. But disuse and
selection will generally act on each creature, when it has
come to maturity and has to play its full part in the strug-
gle 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 procenitor 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 unaffected,
and on the principle of inheritance at corresponding 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 inexplica-
ble is it that organs bearing the plain stamp of inutility,
such as the teeth in the embryonic calf or the shriveled
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 embrj^ological and homologous
structures, but we are too blind to understand her
meaning.

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, favorable variations ; aided in an impor-
tant manner by the inherited effects of the use and disuse
of parts; and in an unimportant manner, that is, in relation
to adaptive structures, whether past or present, by the
direct action of external conditions, and by variations
which seem to us in our ignorance to arise spontaneously.
It appears that I formerly underrated the frequency and
value of these latter forms of variation, as leading to per-
manent modifications of structure independently of natural
selection. But as my conclusions have lately been much

496 CONCLUSION,

misrepresented, and it has been stated that I attribute the
modification of species exclusively to natural selection, I
may be permitted to remark that in the first edition of this
work, and subsequently, I placed in a most conspicuous
position — 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 suj^posed 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; bnt 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 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 ; notwithstanding
that Leibnitz formerly accused Newton of introducing
''occult qualities and miracles into philosophy."

I see no good reasons why the views given in this volume
should shock the religious feelings of any one. It is satis-
factory, as showing how transient such impressions are, to
remember that the greatest discovery ever made by man,
namely, the law of the attraction of gravity, was also
attacked by Leibnitz, ''as subversive of natural, and infer-
entially of revealed, religion." A celebrated author and
divine has written to me that " he has gradually learned to
see that it is just as noble a conception of the Deity to
believe that He created a few original 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 disbelieve in

CONCLTISION. 497

fcfie tnatability of species? It cannot be asserted that
organic beings in a state of nature are subject to no varia-
tion; it cannot be proved that the amount of variation in
the course of long ages is a limited quantity; no clear dis-
tinction has been, or can be, drawn between species and
well-marked varieties. It cannot be maintained that
species when intercrossed are invariably sterile and varieties
invariably fertile; or that sterility is a special endowment
and sign of creation. The belief that species were immut-
able 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 mutation.

But the chief cause of our natural unwillingness to admit
that one species has given birth to other and distinct 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 still see 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, dur-
ing a long course of years, from a point of view directly op-
posite to mine. It is so easy to hide our ignorance under
such expressions as the "plan of creation,^' "unity of de-
sign,-'' etc., and to think that we give an explanation when
we only restate a fact. Any one whose disposition leads
him to attach more weight to unexplained difficulties than
to the explanation of a 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 immutability of species, may be influenced by this vol-
ame; but I look with confidence to the future, to young

498 CONCLUSIOir.

and rising naturalists, who will be able to view botli sides
of the question with impartiality. Whoever is led to be-
lieve that species are mutable will do good service by con«
scientiously expressing his conviction ; for thus only can the
load of prejudice by which this subject is overwhelmed 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 multi-
tude 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 characteristic 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 as-
signing any distinction in the two cases. The day will
come when this will be given as a curious illustration of
the blindness 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
innumerable periods in the earth^s history certain ele-
mental atoms have been commanded suddenly to flash into
living 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 m^ain-
tained 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

CONCLUSION". 499

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 retained
in the foregoing paragraphs, and elsewhere, several sen-
tences which imply that naturalists believe in the separate
creation of each species; and I have been much censured
for having thus expressed myself. But undoubtedly this
was the general belief when the first edition of the preseut
work appeared. I formerly spoke to very many natural-
ists 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 ex-
pressed themselves so ambiguously that it was not easy to
understand their meaning. Now^ things are wholly
changed, and almost every naturalist admits the great prin-
ciple of evolution. 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 opposed to the admission of great and abrupt modifica-
tions. Under a scieutific point of view, and as leading to
further investigation, but little advantage is gained by be=
lieving that new forms are suddenly developed in an inex-
plicable manner from old and widely different forms, over
the old belief in the creation of species from the dust of
the earth.

It mav 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 favor of com-=
munity 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 subordinate to groupSo
Fossil remains sometimes tend to fill up very wide inter-
vals between existing orders.

Organs in a rudimentary condition plainly show that an
early progenitor had the organ in a fully developed condi-
tion, and this in some cases implies an enormous amount
of modification in the descendants. Throughout whole

500 CONCLUSION,

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 de-
scent 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 five progenitors, and
plants from an equal or lesser number.

x^nalogy would lead me one step further, 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 celkilar structure, their
laws of growth, and their liability to injurious influences.
We see tiiis even in so triflinsf 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
reproduction seems to be essentially similar. With all, as
far as is at present known, the germinal vesicle is the
same; so that all organisms start from a common origin=
If we look even to the two main divisions — namely, to the
animal and vegetable kingdoms — certain low forms are so
far intermediate in character that naturalists have disputed
to which kingdom they should be referred. As Professor
Asa Gray has remarked, ^^ the spores and other reproduce
tive bodies of many of the lower algae may claim to have
first a characteristically animal, and then an unequivocally
vegetable existence." Therefore, on the principle of
natural selection with divergence of character, 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 ad?nit that all the
organic beings which have ever lived on this earth may be
descended from some one primordial form. But this infer°
ence is chiefly grounded on analogy, and it is immaterial
whether or not it be accepted. No doubt it is possible, as
Mr. G. H. Lewes has urged, that at the first commence-
ment 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 Yerte-

CONCLUSION, 501

brata, Articulata, etc., we have distinct evidence in their
embryological, homologous^ and rudimentary structures,
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 labors as at j^res-
ent; but they will not be incessantly haunt 3d by the
shadowy doubt whether this or that form be a true species.
This, I feel sure and I speak after experience, 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 defina-
ble, 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
differences, 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 rank of
species.

Hereafter we shall be compelled to acknowledge that
the only distinction between species and well-marked varie-
ties is, that the latter are known, or believed to be con-
nected at the present day by intermediate gradations,
whereas species were formerly thus connected. Hence,
without rejecting the consideration of the present existence
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 acknowledged to be
merely varieties may hereafter be thought worthy of
specific names; and in this case scientific and common lan-
guage 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 freed from the
vain search for the undiscovered and undiscoverable
essence of the term species.

502 CONCLUSION.

The other and more general departments of natural his-
tory will rise greatl}' in interest. The terms used by nat-
uralists, of affinity, relationship, community of type,
paternity, morphology, adaptive characters, rudimentary
and aborted organs, etc., will cease to be metaphorical, and
will have a plain signification. When we no longer look
at an organic being as a savage looks at a ship, as some-
thing 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 summing up of the labor, the
experience, the reason, and even the blunders of numerous
w^orkmen; when we thus view each organic being, how far
more interesting — I 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 correlation,
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 infin-
itude 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 classifying will no doubt become
simpler when we have a definite object in view. We pos-
sess no pedigree or armorial bearings; and we have to dis-
cover and trace the many diverging lines of descent in our
natural genealogies, by characters of any kind which have
long been inherited. Eudimentary 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 forming a picture of the ancient forms of life.
Embryology will often reveal to us the structure, in some
degree obscured, 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

CONCLUSION. 503

parent, and have migrated from some one birth-place; anu
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, we shall surely be enabled to trace in an admir-
able manner the former migrations of the inhabitants of
the whole world. Even at present, by comparing tlie
differences between the inhabitants of the sea on the
opposite sides of a continent, and the nature of the various
inhabitants 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 fossilifer-
ous formation will be recognized as having depended on
an unusual occurrence of favorable circumstances, and the
blank intervals between the successive stages as having
been of vast duration. But we shall be able to gauge with
some security the duration of these intervals by a compari-
son of the preceding and succeeding organic forms. We
must be cautious in attempting to correlate as strictly
contemporaneous two formations, which do not include
many identical species, by the general succession of the
forms of life. As species are produced and exterminated
by slowly acting and still existing causes, and not by
miraculous acts of creation; and as the most important of
all causes of organic change is one which is almost inde-
pendent of altered and perhaps suddenly altered physical
conditions, namely, the mutual relation of organism, to
organism — the improvement of one organism entailing the
improvement or the extermination of others; it follows,
that the amount of organic change in the fossils of con-
secutive formations probably serves as a fair measure of
the relative, though not actual lapse of time. A number
of species, however, keeping in a body might remain for a
long period unchanged, while 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.

604 OONCLUSIOm

In the future T see open fields for far more important
researches. Phychologj 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 independently
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 in-
habitants 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 descendants of some few beings which lived
long before the first bed of the Cambrian system was de-
posited, they seem to me to become ennobled. Judging from
the past, we may safely infer that not one living species will
transmit its unaltered likeness to a distinct futurity.
And of the species now living very few will transmit
progeny of any kind to a far distant futurity; for the
manner in which all organic beings are grouped, shows
that the greater number of species in each genus, and all
the species in many genera, have left no descendants,
but have become utterly extinct. We can so far take a
prophetic 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 Cambrian epoch, we may
feel certain that the ordinary succession by generation has
never once been broken, and that no cataclysm has deso-
lated 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 toward perfection.

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

CONCLUSION. 505

elaborately con strnc-ted forms, so different from eacli 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 repro-
duction; Inheritance which is almost implied by reproduc-
tion; Variability from the indirect and direct action of the
conditions of life, and from use and disuse: a Ratio of In-
crease so high as to lead to a Struggle for Life, and as a
consequence to Natural Selection, entailing Divergence of
Character and the Extinction of less improved forms.
Thus, from the war of nature, from famine and death, the
most exalted object which we are capable of conceiving,
namely, the production of the higher animals, directly fol-
lows. There is grandeur in this view of life, with its sev-
eral powers, having been originally breathed by the Creator
into a few forms or into one; and that, while this planet
has gone circling 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.

i

GLOSSARY

OF THE

PRINCIPAL SCIENTIFIC TERMS USED IN THE

PRESENT VOLUME.*

Abekkant. — Forms or groups of animals or plants wliicli 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
to a focus at slightly different distances — this is called spherical
aberi'ation; at the same time the colored rays are separated by
the prismatic action of the lens and likewise brought to a focus
at different distances — this is chromatic aherrati(/)i.

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 coloring matters
characteristic of the species have not been produced in the
skin and its appendages. Albinism is the state of being an
Albino.

Alg^. — A class of plants including the ordinary sea- weeds and the
filamentous fresh- water weeds.

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 different
from its parent, but from which the parent-form is reproduced
by a process of budding, or by the division of the substance of
the first product of the egg.

Ammonites. — A group of fossil, spiral, chambered shells, allied to
the existing pearly Nautilus, but having the partitions between
the chambers waved in complicated patterns at their junction
with the outer wall of the shell.

♦I am Indebted to the kindness of Mr. W. S. Dallas for this Glossary,
which has been given because several readers have complained to me that
Bome of the terms used were unintelligible to them. Mr. Dallas has
endeavcared to give th« explanations of the tenns In as popular a form an
possible.

508 GLOSSARY.

Analogy. — That resemblance of structures wliicli depends upon
similarity of function, as in tlie wings of insects and birds.
Such structures are said to be be analogmis, and to be analog'ies
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
exhibits 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 earth-worms,
and the leeches.

Antenna. — Jointed organs appended to the head in Insects, Crusta-
cea and Centipedes, and not belonging to the mouth.

Anthers. — The summits of the stamens of flowers, in which the
pollen or fertilizing dust is produced.

Aplacentalia, Aplacentata or Aplacental Mammals. See Mam-
malia.

Archetypal. — Of or belonging to the Archetype, or ideal primitive
form upon which all the beings of a group seem to be organ-
ized.

Articui^ata. — A great division of the Animal Kingdom character-
ized 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.

Balantjs. — The genus including the common Acorn-shells which
live in abundance on the rocks of the sea-coast.

Batrachians. — A class of animals allied to the Reptiles, but under-
going a peculiar metamorphosis, in which the young animal is
generally aquatic and breathes by gills. {Examples, Frogs,
Toads and Newts.)

Bowlders. — Large transported blocks of stone generally imbedded
in clays or gravels.

Brachiopoda. — 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 tbe valves,
and furnished with fringed arms, by the action of which food is
carried to the mouth.

Branchi.<51. — Gills or organs for respiration in water.

Branchial. — Pertaining to gills or branchiae.

Cambrian System. — A series of very ancient Palaeozoic rocks,
between the Laurentian and the Silurian. Until recently these
were regarded as the oldest fossiliferous rocks.

Canid^.— The Dog-family, including the Dog, Wolf, Fox. Jackal,
etc.

Carapace. — The shell enveloping the anterior part of the body in

•\

GLOSSARY. 509

Crustaceans generally; applied also to the hard shelly pieces of
the Cirripedes.

Carboniferous. — This term is applied to the great formation which
includes, among other rocks, the coal-measures. It belongs to
the oldest, or Palaeozoic, system of formations.

Caudal. — Of or belonging to the tail.

Cephalopods. — The highest class of the Mollusca, or soft- bodied
animals, characterized by having the mouth surrounded by a
greater or less number of fleshy arms or tentacles, which, in
most living species, are furnished with sucking-cups. {Exam-
ples, Cuttle-fish, Nautilus.)

Cetacea. — An order of Mammalia, including the Whales, Dolphins,
etc., having the form of the body fish-like, the skin naked, and
only the fore limbs developed.

Chelonia. — An order of Reptiles including the Turtles, Tortoises,
etc.

Cirripedes. — An order of Crustaceans including the Barnacles and
Acorn-shells. Their young resemble those of many other Crus-
taceans in form; but when mature they are always attached 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.

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 fre-
quently enveloped during the second or resting-stage (pupa) of
their existence. The term "cocoon-stage" is here used as
equivalent to " pupa-stage."

CcELOSPERMOUS. — A term applied to those fruits of the Umbelliferae
which have the seed hollowed on the inner face.

COLEOPTERA. — 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.

CoLUiviN. — A peculiar organ in the flowers of Orchids, in which
the stamens, style and stigma (or the reproductive parts) are
united.

Composite or Compositous Plants. — Plants in which the inflores-
cence consists of numerous small flowers (florets) brought
together into a dense head, the base of which is inclosed by a
common envelope. (Examples, the Daisy, Dandelions, etc.)

Conferva. — The filamentous weeds of fresh water.

Conglomerate. — 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
colored, leaf -like organs (petals), which may be united by their
edges either in the basal part or throughout.

Correlation. — The normal coincidence of one phenomenon, characr
ter, etc., with another.

510 GLOSSARY.

Corymb. — A biincli of flowers in which those springing from the
lower part of the flower-stalks are supported on long stalks so as
to be nearly on a level with the upper ones.

Cotyledons. — 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
calcareous matter, breathing by means of gills. {Examples,
Crab, Lobster, Shrimp, etc.)

CuRCULio. — The old generic term for the Beetles known as Weevils,
characterized by their four jointed feet, and by the head being
produced into a sort of beak, upon the sides of which the
antennaD are inserted.

Cutaneous. — Of or belonging to the skin.

Degradation. — The wearing down of land by the action of the sea
or of meteoric agencies.

Denudation. — The wearing away of the surface of the land by
water.

Devonian System or Formation. — A series of Palaeozoic rocks,
including the Old Red Sandstone.

Dicotyledons or Dicotyledonous Plants. — A class of plants
characterized 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.

Differentiation. — The separation or discrimination of parts or
organs which in simpler forms of life are more or less united.

Dimorphic. — Having tv/o distinct forms. — Dimorphism is the condi-
dition of the appearance of the same species under two dissimilar
forms.

Dicecious. — Having the organs of the sexes upon distinct indi-
viduals.

DiORiTE. —A peculiar form of Greenstone.

Dorsal. — Of or belonging to the back.

Edentata. — A peculiar order of Quadrupeds, characterized by the

absence of at least the middle incisor (front) teeth in both jaws.

{Examples, the Sloths and Armadillos.)
Elytra. — The hardened fore- wings of Beetles, serving as sheaths

for the membranous hind-wings, which constitute the true

organs of flight.
Embryo. — The young animal undergoing development within the

egg or womb.
Embryology. — The study of the development of the embryo.
Endemic. — Peculiar to a given locality.
Entomostraca. — 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.
Eocene. — The earliest of the three divisions of the Tertiary epoch

of geologists. Rocks of this age contain a small proportion of

shells identical with species now living.

GLOSSARY. 511

Ephemerous Insects. — Insects allied to the May-fly.

Fauna. — The totality of the animals naturally inhabiting a certain
country or region, or which have lived during a given geological
period.

FeliDxE. — The Cat-family.

Feral. — Having become wild from a state of cultivation or domesti-
cation.

Flora. — The totality of the plants growing naturally in a country,
or during a given geological period.

Florets. — Flowers imperfectly developed in some respects, and col-
lected into a dense spike or head, as in the Grasses, the Dande-
lion, etc.

Fcetal. — Of or belonging to the foetus, or embryo in course of
development.

Foraminifera. — A class of animals of very low organization 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.

Fossiliferous. — Containing fossils.

Fossorial. — 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 (pi. Frena). — A small band or fold of skin.

Fungi (sing. Fungus). — A class of cellular plants, of which Mush-
rooms, Toadstools and Moulds, are familiar examples.

FuRCULA. — The forked bone formed by the union of the collar-bones
in many birds, such as the common Fowl.

Gallinaceous Birds. — An order of Birds of which the common
Fowl, Turkey and Pheasant, are well-known examples.

Gallus. — The genus of birds which includes the common Fowl.

Ganglion. — A swelling or knot from which nerves are given off as
from a center.

Ganoid Fishes. — Fishes covered with peculiar enameled bony
scales. Most of them are extinct.

Germinal Vesicle. — A minute vesicle in the eggs of animals, from
which the development of the embryo proceeds.

Glacial Period. — A period of great cold and of enormous extension
of ice upon the surface of the earth. It is believed that glacial
periods have occurred repeatedly during the geological 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.

Gland. — An organ which secretes or separates some peculiar product
from the blood or sap of animals or plants.

Glottis. — The opening of the windpipe into the oesophagus or
gullet.

Gneiss. — A rock approaching granite in composition, but more or less

512 GLOSSARY,

laminated, and really produced by tlie alteration of a sedimentary

deposit after its consolidation.
Grallatores. — The so-called Wading-birds (Storks, Cranes, Snipes,

etc.), 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.

Habitat, — The locality in which a plant or animal naturally lives.

Hemiptera. — An order or sub-order of Insects, characterized 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.

Homology. — 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 indi-
vidual, 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, etc., is composed. The latter is
called serial hmrkology. The parts which stand in such a relation
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.

Homoptera. — 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 Ctcadce,
Frog-hoppers, and Ajjhides, are well-known examples.

Hybrid. — The offspring of the union of two distinct species.

Hymenoptera. — 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.

Hypertrophied. — Excessively developed.

ICHNEUMONiD^. — A family of Hymenopterous insects, the members
of which lay their eggs in the bodies or eggs of other insects.

Imago. — The perfect (generally winged) reproductive state of an
insect.

Indigens. — The aboriginal animal or vegetable inhabitants of a
country or region.

Inflorescence. — The mode of arrangement of the flowers of plants.

Infusoria. — A class of microscopic Animalcules, so called from their
having originally been observed in infusions of vegetable
matters. They consist of a gelatinous material inclosed in a
delicate membrane, the whole or part of which is furnished with
short vibrating hairs (called cilia), by means of which the
animalcules swim through the water or convey the minute parti-
cles of their food to the orifice of the mouth.

GLOSSARY. 513

Insectivorous. — 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
animals, and serving in place of vessels for the circulation of the
fluids of the body.

Lamellated. — Furnished with lamellae or little plates.

Larva (pi. Larv^). — The first condition of an insect at its issuing
from the egg, when it is usually iu the form of a grub, cater-
pillar or maggot.

Larynx. — The upper part of the windpipe opening into the gullet.

Laurentian. — A group of greatly altered and very ancient rocks,
which is greatly developed along the course of the St. Lawrence,
whence the name. It is in these that the earliest known traces
of organic bodies have been found.

Legumtnos^. — 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 inclosed in a
sheath formed by two other petals. The fruit is a pod (or
legume).

Lemurid^e. — 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.

Lepidoptera. — An order of Insects, characterized by the possession
of a spiral proboscis, and of four large more or less scaly wings.
It includes the well-known Butterflies and Moths.

Littoral. — Inhabiting the sea-shore.

Loess. — A marly deposit of recent (Post-Tertiary) date, which occu-
pies a great part of the valley of the Rhine.

Malacostraca. — The higher division of the Crustacea, including
the ordinary Crabs, Lobsters, Shrimps, etc., together with the
Wood-lice and Sand-hoppers.

Mammalia. — The highest class of animals, including the ordinary
hairy quadrupeds, the Whales and Man, and characterized by
the production of living young which are nourished after birth
by milk from the teats {Mammce, 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 vascular
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 Mono-
tremes {Ornithorhynchus).

Mammiferous. — Having mammge or teats (see Mammalia).

Mandibles in Insects. — The first or uppermost pair of jaws, which

514 GLOSSARY.

are generally solid, horny, biting organs. In Birds tlie term is
applied to both jaws with their horny coverings. In Quadrupeds
the mandible is properly the lower jaw.

Marsupials. — 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, etc. (see Mammalia).

Maxilla 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.

Melanism. — The opposite of albinism; an undue development of
coloring material in the skin and its appendages,

Metamorpiiic Rocks. — Sedimentary rocks which have undergone
alteration, generally by the action of heat, subsequently to their
deposition and consolidation.

Mollusca. — 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 centers, pre-
sent no definite general arrangement. They 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.

Monocotyledons, or Monocotyledonous Plants. — Plants in
which the seed sends up only a single seed-leaf (or cotyledon);
characterized by the absence of consecutive layers of wood in 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. {Examples, Grasses, Lilies, Orchids,
Palms, etc.)

Moraines. — The accumulations of fragments of rock brought down
by glaciers.

Morphology. — The law of form or structure independent of func-
tion.

Mysis-stage. — A stage in the development of certain Crustaceans
(Prawns), in which they closely resemble the adults of a genus
{Mysis) belonging to a slightly lower group.

Nascent. — Commencing development.

Natatory. — Adapted for the purpose of swimming.

Nauplius-form. — 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 dis-
tinct genus under the name of Nauplius.

Neuration. — The arrangement of the veins or nervures in the
wings of Insects.

Nictitating Membrane. — A semi-transparent membrane, which
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, etc., from the surface of the eye.

GLOSSARY, 615

Neuters. —Imperfectly developed females of certain social insects
(such as Ants and Bees), which perform all the labors of the
community. Hence they are also called workers.

Ocelli. — The simple eyes or stemmata of Insects, usually situated
on the crown of the head between the great compound eyes.

CEsoPHAGUS.— The gullet.

Oolitic. — 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 Cirri-
pedes are those which close the aperture of the shell.

Orbit. — The bony cavity for the reception of the eye.

Organism. — An organized being, whether plant or animal.

Orthospermous. — A term applied to those fruits of the Umbelliferae
which have the seed straight.

Osculant. — Forms or groups apparently intermediate between and
connecting other groups are said to be osculant.

Ova. — Eggs.

Ovarium 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.

O VIGEROUS . — Egg-beari ng.

Ovules (of plants). — The seeds in the earliest condition.

Pachyderms. — A group of Mammalia, so called from their thick

skins, and including the Elephant, Rhinocerous, Hippopotamus,

etc.
Paleozoic. — The oldest system of fossiliferous rocks.
Palpi. — Jointed appendages to some of the organs of the mouth in

Insects and Crustacea,
Papilionace^. — Anorder of Plants (see Leguminos^). — 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

expense of, another organism.
Parthenogenesis. — The production of living organisms fromunim-

pregnated eggs or seeds.
Pedunculated, — Supported upon a stem or stalk. The peduncu-
lated oak has its acorns borne upon a footstool.
Peloria 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.
Petals. — The leaves of the corolla, or second circle of organs in a

flower. They are usually of delicate texture and brightly colored.
Phyllodineous, — Having flattened, leaf-like twigs or leaf-stalks

instead of true leaves.

516

GLOSSARY.

Pigment. — Ttie coloring material produced generally in tlie super-
ficial parts of animals. Tlie cells secreting it are called pigment-
cells.

Pinnate. — Bearing leaflets on each side of a central stalk.

Pistils. — The female organs of a flower, which occupy a position in
the center 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.

Plastic. — Readily capable of change.

Pleistocene Period. — Ths latest portion of the Tertiary epoch.

Plumule (in plants). — The minute bud between the seed-leaves of
newly-germinated plants.

Plutonic Rocks. — Rocks supposed to have been produced by
igneous action in the depths of the earth.

Pollen. — 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.

POLYANDROUS (flowers). — Flowers having many stamens.

Polygamous Plants. — Plants in which some flowers are unisexual
and others hermaphrodite. The unisexual (male and female)
flowers, may be on the same or on different plants.

Polymorphic. — Presenting many forms.

PoLYZOARY. — The common structure formed by the cells of the
Polyzoa, such as the well known Sea-mats.

Prehensile. — Capable of grasping.

Prepotent. — Having a 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, etc.

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, Foramini-
fera and Sponges, with some other forms, belong to this division.

Pupa (pi. Pup^) — The second stage in the development of an
Insect, from which it emerges in the perfect (winged) reproduc-
tive form. In most insects the pupal stage is passed in perfect
repose. The chrysalis is the pupal state of Butterflies.

Ramus. — One half of the lower jaw in the Mammalia. The portion
which rises to articulate with the skull is called the ascending
ramus.

GLOSSARY. 517

Radicle. — The minute root of an embryo plant.

Range. — 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.

Retrogression. — Backw^ard development. When an animal, as it
approaches maturity, becomes less perfectly organized than
might be expected from its early stages and known relationships,
it is said to undergo a retrog^xide deiielopment or metamorpliods.

Rhizopods. — A class of lowly organized 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 locomo-
tion and the prehension of food. The most important order is
that of the Foraminifera.

Rodents. — The gnawing Mammalia, such as the Rats, Rabbits and
Squirrels. They are especially characterized by the possession
of a single pair of chisel-like cutting teeth in each jaw, between
which and the grinding teeth there is a great gap.

RuBUS. — The Bramble Genus.

Rudimentary. — 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 vertebrae to which the sides of the pelvis in

vertebrate animals are attached.
Sarcode. — The gelatinous material of which the bodies of the lowest

animals (Protozoa) are composed.
Scutell^. — The horny plates with which the feet of birds are

generally more or less covered, especially in front.
Sedimentary Formations. — Rocks deposited as sediments from

water.
Segments. — The tranverse rings of which the body of an articulate

animal or Annelid is composed.
Sepals. — The leaves or segments of the calyx, or outermost envelope

of an ordinary flower. They are usually green, but sometimes

brightly colored.
Serratures. — Teeth like those of a saw.
Sessile. — Not supported on a stem or footstalk.
Silurian System. — A very ancient system of fossiliferous rocks

belonging to the earlier part of the Palseozoic series.
Specialization. — The setting apart of a particular organ for the

performance of a particular function.
Spinal Chord, — The central portion of the nervous system in the

Vertebrata, which descends from the brain through the arches

of the vertebrae, and gives off nearly all the nerves to the various

organs of the body.

518 GLOSS ART.

Stamens. — Tlie 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.

Stigma. — The apical portion of the pistil in flowering plants.

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 a
column from the ovary and supports the stigma at its summit.

Subcutaneous. — Situated beneath the skin.

Suctorial. — Adapted for sucking.

Sutures (in the skull). — The lines of junction of the bones of which
the skull is composed.

Tarsus (pi. Tarsi). — The jointed feet of articulate animals, such as
Insects.

Teleostean Fishes. — 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 preceeding the
establishment of the present order of things.

Trachea. — The windpipe or passage for the admission of air to the
lungs.

Tridactyle. — Three-fingered, or composed of three movable parts
attached to a common base.

Trilobites. — A peculiar group of extinct Crustaceans, somewhat
resembling the Wood-lice in external form, and, like some of
them, capable of rolling themselves up into a ball. Their
remains are found only in the Palaeozoic rocks, and most abund-
antly in those of Silurian age.

Trimorphic. — Presenting three distinct forms.

Umbellifer^. — 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 (umbel) nearly to the same level.
(Examples, Parsley and Carrot.)

Ungulata. — Hoofed quadrupeds.

Unicellular. — Consisting of a single cell.

Vascular. — Containing blood-vessels.

Vermiform. — Like a worm.

Vertebrata; or Vertebrate Animals. — The highest division of
the animal kingdom, so called from the presence in most cases of
a backbone composed of numerous joints or vertebrce, which con-
stitutes the center of the skeleton and at the same time supports
and protects the central parts of the nervous system.

GLOSSARY. 519

Whorls. — The circles or spiral lines in which the parts of plants are

arranged upon the axis of growth.
Workers. — See Neuters.

ZOEA-STAGE. — The earliest stage in the development of many of the
higher Crustacea, so called from the name of Zoea applied to
these young animals when they were supposed to constitute a
peculiar genus.

ZOOIDS. — In many of the lower animals (such as the Corals, Medusae,
etc.) reproduction takes place in two ways, namely, by means of
eggs and by a process of budding vnth 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 between two
sexual reproductions; and these forms, which are apparently
individual animals, have been called zooids.

INDEX.

Abberant groups, 447.
Abyssinia, plants of, 401.
Acclimatization, 133.
Adoxa, 205.
Affinities of extinct species,

of organic beings, 445.

Agassiz, on Amblyopsis, 133.
, on groups of species

356.

sud-

denly appearing, 343.
— , on prophetic forms, 357.
-, on embryological succession,

366.

— , on tlie Glacial period, 389.
— , on embryological charac-
ters, 434.

on the latest tertiary forms.

329.

— , on parallelism of embryo-
logical development and geo-
logical succession, 466.
— , Alex., on pedicellarise, 226.

Algse of New Zealand, 399,

Alligators, males, fighting, 81.

Alternate generations, 456.

Amblyopsis, blind fish, 133.

America, North, productions al-
lied to those of Europe, 393.

' , , bowlders and glaciers

of, 395.

^ , South, no modern forma-
tions on west coast, 322.

Ammonites, sudden extinction of,
351.

Anagallis, sterility of, 279.

Analogy of variations, 150.

Andaman Islands inhabited by a
toad, 413.

Ancylus, 407.

Animals, not domesticated from

being variable, 15.
, dome«tic, descended from

several stocks, 16.

acclimatization of, 134.

Animals of Australia, 106.

with thicker fur in cold cli-
mates, 127.

, blind, in caves, 131.

extinct, of Australia, 367.

Anomma, 273.

Antarctic islands, ancient flora of,
419.

Antechinus, 440.

Ants attending aphides, 245.

, slave-making instinct, 255.

, neuters, structure of, 272.

Apes, not having acquired intel-
lectual powers, 214.

Aphides, attended by ants, 245.

Aphis, development of, 460.

Apteryx, 166.

Arab horses, 30.

Aralo-Caspian Sea, 367.

Archeopteryx, 335.

Archiac, M. de, on the succession
of species, 353.

Artichoke, Jerusalem, 135,

Ascension, plants of, 410.

Asclepias, pollen of, 180.

Asparagus, 383.

Aspicarpa, 433.

Asses, striped, 152.

, improved by selection, 86.

Ateuchus, 129.

Aucapitaine, on land-shells, 417.

Audubon, on habits of frigate-
bird, 16©.

522

INDEX.

Audubon, on variation in birds'

nests, 246,

, on heron eating seeds, 409.

Australia, animals of, 106.

, dogs of, 249.

, extinct animals of, 367.

, European plants in, 398,

, glaciers of, 395.

Azara, on flies destroying cattle,

67.
Azores, flora of, 388.

Babington, Mr., on Britisb plants,

44.
Baer, Von, standard of Higbness,

116.
, comparison of bee and fisb,

364.
-, embryonic similarity of the

Vertebrata, 458.
Baker, Sir S., on the giraffe, 211.
Balancement of growth, 139.
Baleen, 216.

Barberry, flowers of, 91.
Barrande, M., on Silurian colo

nies, 344.
, on the succession of species,

354.
, on parallelism of palaeozoic

formations, 356.
, on affinities of ancient

species, 357.
Barriers, importance of, 373.
Bates, Mr., on mimetic butterflies,

443, 444.
Batrachians on islands, 413.
Bats, how structure acquired, 166.

, distribution of, 415.

Bear, catching water-insects, 168.
Beauty, how acquired, 189, 488.
Bee, sting of, 194.

= ■, queen, killing rivals, 194.

, Australian, extermination

of, 70.
Bees, fertilizing flowers, 68.
■= , hive, not sucking the red

clover, 88.
, hive, cell-making instinct,

259.

, Ligurian, 88.

' , variation in habits, 246.

Bees, parasitic, 255.

, humble, cells of, 260.

Beetles, wingless, in Madeira, 130.

with deficient tarsi, 129.

Bentham, Mr., on British plants,

44.

, on classification, 435.

Berkeley, Mr., on seeds in salt

water, 383.
Bermuda, birds of, 412.
Birds acquiring fear, 246.

, beauty of, 191.

• annuallv cross the Atlantic,

389.

, color of, on continents, 127.

, footsteps, and remains of,

in secondary rocks, 335.
, fossil, in caves of Brazil,

367.
, of Madeira, Burmuda and

Galapagos, 412, 413.
, song of males, 82.

— , transporting seeds, 387.
-, waders, 408.

, wingless, 128, 166,

Bizcacha, 376.

, affinities of, 447.

Bladder for swimming, in fish,

175.
Blindness of cave animals, 130.
Blyth, Mr., on distinctness of

Indian cattle, 16.

, on striped hemionus, 138.

, on crossed geese, 284.

Borrow, Mr., on the Spanish

pointer, 30.
Bory St. Vincent, on Batrachians,

413.
Bosquet, M., on fossil Chtha-

malus, 336.
Bowlders, erratic, on the Azores,

388.
Branchise, 176, 177.

, of crustaceans, 181.

, Braun, Prof., on the seeds

of Fumariacese, 206.
Brent, Mr., on house-tumblers,

248.
Britain, mammals of, 415.
Broca, Prof., on Natural Selec-
tion, 201.

INDEX.

523

Bronn, Prof., on duration of
specific forms, 326.

, various objections by, 201.

Brown, Robert, on classification,
432.

, Sequard, on inherited muti-
lations, 129.

Busk, Mr., on the Polyzoa, 228.

Butterflies, mimetic, 443, 444,
445.

Buzareingues, on sterility of varie-
ties, 304.

Cabbage, varieties of, crossed, 9.

Calceolaria, 282.

Canary-birds, sterility of hybrids,
282.

Cape de Verde Islands, produc-
tions of, 418.

, plants of, on mountains,

398.

Cape of Good Hope, plants of,
121, 410.

Carpenter, Dr., on foraminifera,
364.

Carthamus, 205.

Catasetum, 184, 438.

Cats, with blue eyes, deaf, 10.

, variation in habits of, 247.

curling tail when going to

spring, 193.

Cattle destroying fir-trees, 67.

destroyed by flies in Para-
guay, 67.

breeds of, locally extinct,

101.

— , fertility of Indian and Euro-
pean breeds, 283.
-, Indian, 16, 283.

Cave, inhabitants of, blind, 130.

Cecidomyia, 456.

Celts, proving antiquity of man,

16.
Centers of Creation, 378.
Cephalopodse, structures of eyes,

180.

, development of, 460.

Cercopithecus, tail of, 223.
Ceroxylus laceratus, 216.
Cervulus, 283.
Cetacea, teeth and hair, 137.

Cetacea, development of the
whalebone, 216.

Cetaceans, 216.

Ceylon, plants of, 399.

Chalk formation, 352.

Characters, divergence of, 101.

, sexual, variable, 141, 146.

, adaptive or analogical, 440,

Charlock, 71.

Checks to increase, 63.

, mutual, 65.

Chelae of Crustaceans, 228.

Chickens, instinctive tameness of,
249.

Chironomus, its asexual reproduc-
tion, 456.

ChthamalinaD, 320.

Chthamalus, cretacean species of,
336.

Circumstances favorable to selec-
tion of domestic products, 35,

to natural selection, 94.

Cirripedes capable of crossing, 93.

, carapace aborted, 140.

, their ovigerous frena, 177.

, fossil, 336.

, larvae of, 458.

Claparede, Prof., on the hair-
claspers of the Acaridse, 182.

Clarke, Rev. W. B., on old
glaciers in Australia, 396.

Classification, 428.

Clift, Mr., on the succession of
types, 367.

Climate, effects of, in checking
increase of beings, 64.

, adaptation of, to organisms,

133.

Climbing plants, 175.

, development of, 231.

Clover visited by bees, 88.

Cobites, intestine of, 175.

Cockroach, 71.

Collections, palaeontological, poor,
319.

Color, influenced by climate, 127.

, in relation to attack by flies,

189.

Columba livia, parent of domes-
tic pigeons, 20.

Colymbetes, 407.

524

INDEX.

Compensation of growtli, 139.
Compositae, flowers and seeds of,

187.
• , outer and inner florets of,

205.

■ , male flowers of, 469,

Conclusion, general, 495.
Conditions, slight changes in,

favorable to fertility, 296.
Convergence of genera, 120.
Coot, 169.
Cope, Prof., on the acceleration

or retardation of the period of

reproduction, 177.
Coral-islands, seeds drifted to,

385.
reefs, indicating movements

of earth, 385.
Corn crake, 170.
Correlated variation in domestic

productions, 10.
Coryanthes, 183.
Creation, single centers of, 378.
Crinum, 281.

Croll, Mr., on subaerial denuda-
tion, 316, 318.
, on the age of our oldest for-
mations, 338.
, on alternate Glacial periods

in the North and South, 396.
Crosses, reciprocal, 287.
Crossing of domestic animals,

importance in altering breeds,

18.

, advantages of, 90.

, unfavorable to selection, 94.

Criiger, Dr., on Coryanthes, 183.
Crustacea of New Zealand, 399.
Crustacean, blind, 131.

air-breathers, 181.

Crustaceans, their chelae, 228.
Cryptocerus, 272.
Ctenomys, blind, 130.
Cuckoo, instinct of, 242, 250.
Cunningham, Mr., on the flight

of the logger-headed duck, 128.
Currants, grafts of, 290.
Currents of sea, rate of, 384.
Cuvier, on conditions of existence,

242.
— — , Fred. , on instinct, 242.

Cuvier, on fossil monkeys, 335.
Cyclostoma, resisting salt water,
*417.

Dana, Prof., on blind cave-ani-
mals, 132.

, on relations of crustaceans

of Japan, 395.

, on crustaceans of New

Zealand, 399.

Dawson, Dr., on eozoon, 339.

De Candolle, Aug. Pyr., on strug-
gle for existence, 58.

, on umbelliferffi, 138.

, on general aflinities, 447.

De Candolle, Alph., on the varia-
bilitv of oaks, 47.

, on low plants, widely dis-
persed, 423.

, on widely-ranging plants

being variable, 50.

, on naturalization, 105.

, on winged seeds, 139,

, on Alpine species suddenly

becoming rare, 160.

, on distribution of plants

with large seeds, 385.

, on vegetation of Australia,

401.

, on fresh-water plants, 407.

on insular plants, 410.^

Degradation of rocks, 315.
Denudation, rate of, 316.

of oldest rocks, 339.

of granite areas, 324.

Development of ancient formS;

363.
Devonian system, 361.
Dianthus, fertility of crosses, 285
Dimorphism in plants, 42, 297.
Dirt on feet of birds, 887.
Dispersal, means of, 381.

■ during Glacial period, 389.

Distribution, geographical, 373.

, means of, 381.

Disuse, effect of, under nature,

128.
Diversification of means for same

general purpose, 182.
Division, physiological, of labor^

105.

INDEX.

525

Divergence of character, 101.
Dog, resemblance of jaw to that

of the Thylacinus, 441.
Dogs, hairless, with imperfect

teeth, 11.
' descended from several wild

stocks, 17.

, domestic instincts of, 248.

, inherited civilization of,

248.

, fertility of breeds together,

283.

, of crosses, 302.

, proportions of body in dif-
ferent breeds, when young,
461.

Domestication, variation under, 6.

Double flowers, 271.

Downing, Mr, on fruit-trees in
America, 78.

Dragon flies, intestines of, 175.

Drift-timber, 885.

Driver-ant, 274.

Drones killed by other bees, 194.

Duck, domestic, wings of, re-
duced, 10.

, beak of, 217.

, logger headed, 166.

Duckweed, 407.

Dugong, affinities of, 431.

Dung-beetles with deficient tarsi,
129.

Dytiscus, 407.

Earl, Mr. W., on the Malay

Archipelago. 415.

Ears, drooping, in domestic ani-
mals, 10.

, rudimentary, 473.

Earth, seeds in roots of trees, 885.

charged with seeds, 387.

Echinodermata,their pedicellariae,
225.

Eciton, 272.

Economy of organization, 139.

Edentata, teeth and hair, 137.

, fossil species of, 492!

Edwards, Milne, on physiological
division of labor, 105.

— — , on gradations of structure,
185.

Edwards, on embryological char-
acters, 434.

Eggs, young birds escaping from,
80.

Egypt, productions of, not modi-
fied, 200.

Electric organs, 178.

Elephant, rate of increase, 60.
, of Glacial period, 135.

Embryology, 455.
Eozoon Canadense, 339.
Epilepsy inherited, 128.
Existence, struggle for, 57.

, condition of, 198.

Extinction, as bearing on natural
selection, 115.

, of domestic varieties. 111.

,347.

Eye, structure of, 171.

Eye, correction for aberration,

194,
Eyes, reduced, in moles, 130.

Fabre, M., on hymenoptera fight-
ing, 82.

— — , on parasitic sphex, 255.

, on Sitaris, 465.

Falconer, Dr., on naturalization
of plants in India, 61.

on elephants and mastodons,

861.

and Cautley, on mammals of

sub-Himalayan beds, 368.

Falkland Islands, wolf of, 414.

Faults, 317.

Faunas, marine, 374.

Fear, instinctive, in birds, 249.

Feet of birds, young molluscs ad-
hering to, 407.

Fertilization variously effected,
183, 191.

Fertility of hybrids, 280.

, from slight changes in con-
ditions, 296.

of crossed varieties, 301.

Fir-trees destroyed by cattle, 67.

, pollen of, 195.

Fish, flying, 166.

, teleostean, sudden appear*

ance of, 836.

, eating seeds, 886, 408.

526

INDEX,

Fish, fresh-water, distribution of,

406.
Fishes, ganoid, now confined to

fresh water, 98.

, electric organs of, 178.

, ganoid, living in fresh

water, 351.
, of southern hemisphere,

399.
Flat-fish, their structure, 220.
Flight, powers of, how acquired,

166.
Flint-tools, proving antiquity of

man, 16.
Flower, Prof., on the Larnyx,

225.

, on Halitherium, 357.

, on the resemblance between

the jaws of the dog and Thyla-

cinus, 441.
Flower, Prof., on the homology

of the feet of certain mar-
supials, 451.
Flowers, structure of, in relation

to crossing, 86.
, of compositae and umbelli-

ferse, 137, 205.

, beauty of, 191.

, double, 271.

Flysch formation, destitute of or-
ganic remains, 320.
Forbes, Mr. D., on glacial action

in the Andes, 396.

, E., on colors of shells, 127.

, on abrupt range of shells in

depth, 161.
, on poorness of palseonto-

logical collections, 319.
• , on continuous succession of

genera, 346.
, on continental extensions,

382, 383.
, on distribution during Gla-
cial period, 390.
, on parallelism in time and

space, 426.
Forests, changes in, in America,

69.
Formation, Devonian, 361.

, Cambrian, 339.

, intermittent, 328.

Formations, thickness of, tM

Britain, 317.
Formica, rufescens, 255.

, sanguinea, 256.

, flava, neuter of, 273. j

Forms, lowly organized, long en

during, 118.
Frena, ovigerous, of cirripedes,

176.
Fresh-water productions, dis-
persal of, 405.
Fries, on species in large genera

being closely allied to other

species, 54.
Frigate-bird, 169.
Frogs on islands, 413.
Fruit-trees, gradual improvement

of, 31.

in United States, 48.

, varieties of, acclimatized in

United States, 135.
Fuci, crossed, 287, 298.
Fur, thicker in cold climates, 127.
Furze, 457.

Galapagos Archipelago, birds of,
411.

productions of, 417, 419.

Galaxias, its wide range, 406.

Galeopithecus, 165.

Game, increase of, checked by
vermin, 65.

Gartner, on sterility of hybrids,
279, 280, 284.

, on reciprocal crosses, 286.

, on crossed maize and ver-

bascum, 304.

, on comparison of hybrids

and mongrels, 306, 307.

Gaudry, Prof., on intermediate
genera of fossil mammals in
Attica, 357.

Geese, fertility when crossed, 283.

, upland, 169.

Geikie. Mr. , on subaerial denuda-
tion, 316.

Genealogy, important in classifi-
cation, 435.

Generations, alternate, 456.

Geographical distribution, 378.

Geography, ancient, 503.

INDEX,

627

Geoffrey St. Hilaire, on balance-
ment, 139.

, on homologous organs, 451.

, Isidore, on variability of re-
peated parts, 140.

, or correlation, in monstrosi-
ties, 10,

. , on correlation, 137.

, on variable parts being

often monstrous, 145.

Geology, future progress of, 502.

, imperfection of the record,

503.

Gervais, Prof., on Typotherium,
357.

Giraffe, tail of, 186.

, structure of, 209.

Glacial period, 389.

, affecting the North and

South, 395.

Glands, mammary, 224.

Gmelin, on distribution, 390.

Godwin- Austen, Mr., on the
Malay Archipelago, 331.

Goethe, on compensation of
growth, 139.

Gomphia, 207.

Gooseberry, grafts of, 290.

Gould, Dr. Aug. A., on land-
shells, 416.

, Mr., on colors of birds, 127.

, on instincts of cuckoo, 253.

, on distribution of genera of

birds, 422.

Gourds, crossed, 304.

Graba, on the Uria lacrymas, 85.

Grafting, capacity of, 289, 290.

Granite, areas of denuded, 324.

Grasses, varieties of, 103.

Gray, Dr. Asa, on the variability
of oaks, 47.

' , on man not causing varia-
bility, 73.

■■ , on sexes of the holly, 87.

— — , on trees of the United
States, 93.

, on naturalized plants in the

United States, 105.

, on aestivation, 206.

, on rarity of intermediate va-
rieties, 162.

Gray, on Alpine plants, 390.
, Dr. J. E., on striped mule,

152.
Grebe, 169.
Grimm, on asexual reproduction,

456.
Groups, aberrant, 446.
Grouse, colors of, 78.

, red, a doubtful species, 45.

Growth, compensation of, 139.
Giinther, Dr., on flat-fish, 222.

, on prehensile tails, 223.

, on the fishes of Panama,

374.

— , on the range of fresh- water
fishes, 406.
-, on the limbs of Lepidosiren,

470.

Haast, Dr., on glaciers of New
Zealand, 395.

Habit, effect of, under domes-
tication, 10.

, effect of, under nature, 129.

Habit, diversified, of same species,
167.

Hackel, Prof., on classification
and the lines of descent, 450.

Hair and teeth, correlated, 137.

Halitherium, 357.

Harcourt, Mr. E. V., on the birds
of Madeira, 411.

Hartung, M., on bowlders in the
Azores, 388.

Hazel-nuts, 384.

Hearne, on habits of bears, 168.

Heath, changes in vegetation, 66.

Hector, Dr., on glaciers of Nevr
Zealand, 395.

Heer, Oswald, on ancient culti-
vated plants, 16.

, on plants of Madeira, 98.

Helianthemum, 207.

Helix pomatia, 417.

, resisting salt water, 417.

Helmholtz, M., on the imperfea
tion of the human eye, 194.

Helosciadium, 384.

Hemionus, striped, 154.

Henseu, Dr., on the eyea of
Cephalopods, 180.

528

INDEX.

Herbert W., on stmiggle for'exist-
ence, 58.

, on sterility of hybrids, 281.

Hermaphrodites crossing, 90.

Heron eating seed, 409.

Heron, Sir R., on peacocks, 82.

Heusinger, on white animals poi-
soned by certain plants, 11.

Hewitt, Mr., on sterility of first
crosses, 293.

Hildebrand, Prof., on the self-
sterility of Corydalis, 281.

Hilgendorf , on intermediate varie-
ties, 325.

Himalaya, glaciers of, 395.

, plants of, 398.

Hippeastrum, 281.

Hippocampus, 224.

Hofmeister, Prof., on the move-
ments of plants, 234.

Holly-trees, sexes of, 87.

Hooker, Dr., on trees of New
Zealand, 93.

' , on acclimatization of Hima-
layan trees, 134.

Hooker, Dr., on flowers of um-
belliferse, 138.

, on the position of ovules,

204.

, on glaciers of Himalaya,

395.

, on algse of New Zealand,

399.

, on vegetation at the base of

the Hymalaya, 399.

, on plants of Tierra del

Fuego, 397.

, on Australian plants, 398,

'419.

■- , on relations of flora of

America, 401.

• , on flora of the Antarctic

lands, 403, 418.

, on the plants of the Gala-
pagos, 412, 417.

. on glaciers of the Lebanon,

395.

, on man not causing varia-
bility, 73,

, on plants of mountains of

Fernando, Po, 398.

Hooks on palms, 188.

on seeds, on islands, 413.

Hopkins, Mr., on denudation,

323.
Hornbill, remarkable instinct of,

276.
Horns, rudimentary, 472.
Horse, fossil, in La Plata, 348.
, proportions of, when young,

462.
Horses destroyed by flies in Para.

guay, 67.

, striped, 152.

Horticulturists, selection applied

by, 28.
Huber, on cells of bees, 264.
, P., on reason blended with

instinct, 242.
, on habitual nature of in-
stincts, 243.

, on slave-making ants, 255.

-, on Melipona domestica, 260.

Hudson, Mr., on the Ground-
Woodpecker of La Plata, 168.

, on the Molothrus, 253.

Humble-bees, cells of, 260.

Hunter, J., on secondary sexual
characters, 142.

Hutton, Captain, on crossed
geese, 283.

Huxley, Prof. , on structure ^ of
hermaphrodites, 93.

, on the affinities of the

Sirenia, 357.

, on forms connecting birds

and reptiles, 357.

, on homologous organs, 455.

, on the development oi

aphis, 460.

Hybrids and mongrels compared.
305.

Hybridism, 277.

Hydra, structure of, 175.

Hymenoptera, fighting, 82.

Hymenopterous insect, diving,
169.

Hyoseris, 205.

Ibla, 140.

Icebergs transporting seeds, 387.

Increase, rate of, 60.

INDEX.

529

Individuals, numbers favorable to

selection, 94.
, many, whether simulta-
neously cieated, 380.
Inheritance, laws of, 12.
- — , at corresponding ages, 12.
Insects, color of, fitted for their

stations, 78.

, sea-side, colors of, 127.

, blind, in caves.. 131.

' . luminous, 180.

■ — --, their resemblance to certain

objects, 214.

, neuter, 272.

Instinct, 242.

. not varying simultaneously

with structure, 270,
Instincts, domestic, 247.
Intercrossing, advantages of, 90,

296.
Islands, oceanic, 409.
Isolation favorable to selection,

96.

Japan, productions of, 395.

Java, plants of, 398.

Jones, Mr. J. M., on the birds of
Bermuda, 411.

Jourdain, M., on the eye-spots of
star fishes, 171.

Jukes, Prof., on subaerial denu-
dation, 316.

Jussieu, on classification, 433.

Kentucky, caves of, 101.

Kerguelen-land, flora of, 403, 418.

Kidney-bean, acclimatization of,
135.

Kidneys of birds, 137.'

Kirby, on tarsi deficient in bee-
tles, 129.

Knight, Andrew, on cause of
variation, 6.

Kolreuter, on intercrossing, 89.

, on the barberry, 91.

, on sterility of hybrids, 278,

281.

— , on crossed varieties of nico-
tiana, 305.
-, on crossing male and herma-

phrodite flowers, 468.

Kolreuter. on reciprocal crosses,

287.

Lamarck, on adaptive characters,

440.
Lancelet, 118.

, eyes of, 173.

Landois, on the development of

the wings of insects, 176.
Land-shells, distribution of, 416.

, of Madeira, naturalized, 421.

, resisting salt water, 417.

Languages, classification of, 437.
Lankester, Mr. E. Ray, on Longe-
vity, 200.

, on homologies, 454.

Lapse, great, of time, 314.

Larvge, 457, 458, 459.

Laurel, nectar secreted by the

leaves, 86.
Laurentian formation, 339.
Laws of variation, 126.
Leech, varieties of, 70.
Leguminosae, nectar secreted by

glands, 86c
Leibnitz' attack on Newton, 496.
Lepidosiren, 98, 358.
, limbs in a nascent condition,

470.
Lewes, Mr. G. H., on species not

having changed in Egypt, 200.
, on the Salamandra atra,

468.

, on many forms of life hav-
ing been at first evolved, 500.

Life, struggle for, 58.

Lingula, Silurian, 338.

Linnaeus, aphorism of, 430.

Lion, mane of, 82.

, young of, striped, 457.

Lobelia fulgens, 68, 91.

, sterility of crosses, 281.

Lockwood, Mr. , on the ova of the
Hippocampus, 224.

Locusts transporting seeds, 386.

Logan, Sir W., on Laurentian
formation, 339.

Lowness of structure connected
with variabilitv, 140.

, related to wide distribution,

423.

530

INDEX,

Lowe, Rev, R. T., on locusts
visiting Madeira, 386.

Lubbock, Sir J., on the nerves of
coccus, 41.

, on secondary sexual charac-
ters, 147.
-, on a diving bymenopterous

insect, 169.
— , on affinities, 331.

-, on metamorphoses, 455, 458.

Lucas, Dr. P., on inheritance, 11
, on resemblance of child to

parent, 308.
Lund and Clausen, on fossils of

Brazil, 367.
Lyell, Sir C, on the struggle for

existence, 58.
, on modern changes of the

earth, 89.
, on terrestrial animals not

having been developed on isl-
ands, 213.
-,on a carboniferous land-shell.

320.

— , on strata beneath Silurian
system, 386.

— , on the imperfection of the
geological record, 342.
— , on the appearance of

species, 342.

— , on Barrande's colonies, 344.

— , on tertiary formations of

Europe and North America, 352.

on parallelism of tertiary

formations, 356.
— , on transport of seeds by
icebergs, 388.
-, on great alterations of cli-

mate, 404.
— , on the distribution of fresh-
water shells, 407.
-, on land-shells of Madeira,

421.
Lyell and Dawson, on fossilized

trees in Nova Scotia, 328.
Lythrum salicaria, trimorphic,

300.

Macleay, on analogical characters,

440.
Macrauchenia, 857.

M'Donnell, Dr., on electric organs,

178.
Madeira, plants of, 98.

, beetles of, wingless, 129.

, fossil land-shells of, 367.

, birds of, 411.

Magpie tame in Norway, 246.

Males fighting, 81.

Maize, crossed, 304.

Malay Archipelago compared with

Europe, 331.

, mammals of, 415.

Malm, on flat-fish, 221.
Malpighiacesp, small imperfect

flowers of, 204.

, 433.

Mammae, their development, 224.

, rudimentary, 467.

Mammals, fossil, in secondary

formation, 335.

, insular, 414.

Man, origin of, 504.

Manatee, rudimentary nails of,

471.
Marsupials of Australia, 106.

, structure of their feet, 450.

Marsupials, fossil species of, 367.
Martens, M., experiment on seeds,

384.
Martin, Mr. W. C, on striped

mules, 153.
Masters, Dr., on Saponaria, 207.
Matteucci, on the electric organs

of rays, 178.
Matthiola, reciprocal crosses of,

287.
Maurandia, 232.
Means of dispersal, 381.
Melipona domestica. 260.
Merrill, Dr., on the American

cuckoo, 251.
Metamorphism of oldest rocks,

339.
Mice destroying bees, 68.

, acclimatization of, 134.

, tails of, 223.

Miller, Prof. , on the cells of bees,

261, 265.
Mirabilis, crosses of, 287.
Missel-thrush, 70.
Mistletoe, complex relations of, 3.

INDEX,

631

Mivart, Mr., on the relation of
hair and teeth, 137.

, on the eyes of cephalopods,

180.

, various objections to Natu-
ral Selection, 209.

on abrupt modifications,

237.

, on the resemblance of the

mouse and antechinus, 440.

Mocking-thrush of the Galapagos,
421.

Modification of species not abrupt,
499.

Moles, blind, 130.

Molothrus, habits of, 253.

Mongrels, fertility and sterility of,
301.

and hybrids compared, 305.

Monkeys, fossil, 355.

Monachanthus, 438.

Mons, Van, on the origin of fruit
trees, 25.

Monstrosities, 39.

Moquin - Tandon, on sea - side
plants, 127.

Morphology, 450.

Morren, on the leaves of Oxalis,
233.

Moths, hybrid, 283.

Mozart, musical powers of, 243.

Mud. seeds in, 408.

Mules, striped, 153.

Muller, Adolph, on the instincts
of the cuckoo, 251.

Muller, Dr. Ferdinand, on Alpine
Australian plants, 398.

Miiller, Fritz, on dimorphic crus-
taceans, 42, 274.

, on the lancelet, 119.

, on air-breathing crusta-
ceans, 181.

" , on the self- sterility of

orchids, 281.

, on embryology in relation

to classification, 434.

— ^ — , on the metamorphoses of
crustaceans, 460, 466.

, on terrestrial and fresh-
water organisms not under-
going any metamorphosis, 464.

Mtiller, Fritz, on climbing plants,
233.

Multiplication of species not in-
definite, 121.

Murchison, Sir R., on the forma
tions of Russia, 321.

, on azoic formations, 339.

, on extinction, 347.

Murie, Dr., on the modification of

the skull in old age, 177.
Murray, Mr. A., on cave-insects,

132.
Mustela, vision, 164.
Myanthus, 438.
Myrmecocystus, 272.
Myrmica, eyes of, 273.

Nageli, on morphological charac-
ters, 202.
Nails, rudimentary, 471.
Nathusius, Von, on pigs, 189.
Natural history, future progress

of, 502.

, selection, 73.

■ , system, 430.

Naturalization of forms distinct

from the indigenous species,

105.
Naturalization in New Zealand,

193.
Naudin, on analogous variations

in gourds, 149.

, on hybrid gourds, 304.

Naudin, on reversion, 307.
Nautilus, Silurian, 338.
Nectar of plants, 86.
Nectaries, how formed, 86.
Nelumbium luteum, 409.
Nests, variations in, 246, 269, 275.
Neuter insects, 272, 273.
Newman, Col., on humble-bees,

68.
New Zealand, productions of, not

perfect, 193.

, naturalized products of, 866.

, fossil birds of, 367.

, glaciers of, 395.

, crustaceans of, 399.

, algae of 399.

, number of plants of, 410.

, flora of, 419.

532

INDEX.

Ne-wton, Sir I. , attacked for irre-

ligion, 496.
, Prof. , on earth attaclied to

a partridge's foot, 387o
Nicotiana, crossed varieties of,

305.
, certain species very sterile,

286.
Nitsclie, Dr., on the Polyzoa,

228.
Noble, Mr., on fertility of Rhodo-
dendron, 282.
Nodules, phosphatic, in azoic

rocks, 339.

Oaks, variability of, 47.

Onites, appelles, 129=

Ononis, small imperfect flowers

of, 204.
Orchids, fertilization of, 183.
, the development of their

flowers, 230.
-, forms of, 438.

Orchis, pollen of, 180.

Organization, tendency to ad-
vance, 116.

Organs of extreme perfection, 170,

, electric, of fishes, 178.

, of little importance, 186.

, homologous, 451.

, rudiments of, and nascent,

467.

Ornithorhynchus, 98, 432=

, mammae of, 224.

Ostrich not capable of flight, 213.

, habit of laying eggs to-
gether, 255.
-, American, two species of,

375.

Otter, habits of, how acquired,

164.
Ouzel, water, 169.
Owen, Prof., on birds not flying,

128.
, on vegetative repetition,

141.

— , on variability of unusually
developed parts, 141.
— , on the eyes of fishes., 173=
-, on the swim-bladder of

fishes, 176.

Owen, Prof, on fossil horse of La
Plata. 348.

, on generalized form, 357.

, on relation of ruminants

and pachyderms, 357.

, on fossil birds of New Zea-
land. 367.

, on succession of types, 367

, on affinities of the dugong,

431.

, on homologous organs, 451.

, on the metamorphosis of ce-

phalopods, 459.

Pacific Ocean, faunas of, 375.

Pacini, on electic organs, 179.

Paley, on no organ formed to give
pain, 193.

Pallas, on the fertility of the
domesticated descendants of
wild stocks, 284,

Palm with hooks, 188.

Papaper bracteatum, 206.

Paraguay, cattle destroyed by
flies, 67.

Parasites, 253.

Partridge, with ball of earth at-
tached to foot, 287.

Parts greatly developed, variable,
141.

Parus major, 168.

Passiflora, 281.

Peaches in United States, 78.

Pear, grafts of, 290.

Pedicellariae, 226.

Pelagornium, flowers of, 138.

, sterility of, 282.

Pelvis of women, 137.

Peloria, 138.

Period, glacial, 389.

Petrels, habits of, 169.

Phasianus, fertility of hybrids,
283.

Pheasant, young, wild, 249.

Pictet, Prof., on groups of spe-
cies suddenly appearing, 333o

J on rate of organic change,

344=

= on continuous succession of

genera, 346.

INDEX.

633

Pictet, Prof., on close alliance of
fossils in consecutiveformations,
362.

, on change in latest tertiary

forms, 329.
-, on early transitional links.

334.
Pierce, Mr. , on varieties of wolves,

83.
Pigeons with feathered feet and

skin between toes, 11.
, breeds described, and origin

of, 18.

breeds of, how produced.

33, 35.

— , tumbler, not being able to
get out of egg, 80.
— , reverting to blue color, 151.
— , instinct of tumbling, 248.
-, young of, 462,

Pigs, black, not affected by the
paint-root, 11.

, modified by want of exer-
cise, 189.

Pistil, rudimentary, 468.

Plants, poisonous, not affecting
certain colored animals, 11.

, selection, applied to, 31.

■, gradual improvement of, 31.

, not improved in barbarous

countries, 32.
-, dimorphic, 42, 297.

, destroyed by insects, 63.

, in midst of range, have to

struggle with other plants, 71.

, nectar of, 86.

■ , fleshy, on sea-shores, 127.

, climbing, 175, 232.

fresh-water, distribution of,

407.
, low in scale, widely dis

tributed, 423.
Pleuronectidae,

their

220
Plumage, laws of

sexes of birds, 82.
Plums in the United States.
Pointer dog, origin of, 3C.

, habits of, 248.

Poison not affecting certain

colored animals, 11.

Poison, similar effect of, on ani-
mals and plants, 500.

Pollen of fir-trees, 195.

transported by various

means, 183, 191.

Pollinia, their development, 230.

Polyzoa, their avicularia, 228.

Poole, Col., on striped hemionus,
154.

Potemogeton, 408.

Pouchet, on the colors of flat-fish,
222.

Prestwich, Mr., on English and
French eocene formations, 355.

Proctotrupes, 169.

Proteolepas, 140.

Proteus, 133.

Psychology, future progress of,

504.
I Pyrgoma, found in the chalky
■ 336.

Quagga, striped, 154.

Quatref ages, M. , on hybrid moths,

283.
Quercus, variability of, 48.
Quince, grafts of, 290.

Rabbits, disposition of young,
249.

Races, domestic, characters of, 14.

Race-horses, Arab, 30.

, English, 381.

Radcliffe, Dr., the electrical or-
gans of the torpedo, 178.

Ramond, on plants of Pyrenees,
391.

Ramsay, Prof. , on subaerial denu-
dation, 316.

, on thickness of the British

formations, 317.
-, on faults, 317.

structure,
changes in

78.

Ramsay, Mr., on instincts of

cuckoo, 252.
Ratio of increase, 60.
Rats supplanting each other, 70.
, acclimatization of, 134.

, blind, in cave, 131.

Rattle-snake, 192.
Reason and instinct. 242.
Recapitulation, general, 476.

534

INDEX.

Reciprocity of crosses, 287.

Record, geological, imperfect, 312.

Rengger, on Hies destroying cat-
tle, 67.

Reproduction, rate of, 60.

Resemblance, protective, of in-
sects, 215.

to parents in mongrels and

livbrids, 306.

Reversion, law of inheritance, 13.

, in pigeons, to blue color,

151.

Rhododendron, sterility of, 282.

Richard, Prof., on Aspicarps, 433.

Richardson, Sir J., on structure
of squirrels, 165.

, on fishes of the southern

hemisphere, 399.

Robinia, grafts of, 290.

Rodents, blind, 130.

Rogers, Prof., Map of N. America,
324.

Rudimentary organs, 467.

Rudiments important for classi-
fication, 432.

Rutimeyer, on Indian cattle, 16,
284.

Salamandre atra, 468.
Saliva used in nests, 269.
Salvin, Mr., on the beaks of

ducks, 218.
Sageret, on grafts, 290.
Salmons, males fighting, and

hooked jaws of, 81.
Salt water, how far injurious to

seeds, 383.
not destructive to land-shells,

417.
Salter, Mr., on early death of

hybrid embryos, 293.
Saurophagus sulphuratus, 168.
Schacht, Prof., on Phyllotaxy,

205.
Schiodte, on blind insects, 131.

, on flat-fish, 220.

Schlegel, on snakes, 137.
Schobl, Dr., on the ears of mice,

203.
Scott, J., Mr., on the self-sterility

of orchids, 281.

Scott, J., Mr., on the crossing of
varieties of verbascum, 304.

Sea- water, how far injurious to
seeds, 383.

not destructive to land-shells,

417.

Seabright, Sir J., on crossed ani-
mals, 18.

Sedgwick, Prof., on groups of
species suddenly appearing, 333.

Seedlings destroyed by insects, 63.

Seeds, nutriment in, 71.

, winged, 139.

, means of dissemination, 183,

191, 385.

, power of resisting salt

water, 383.
-, in crops and intestines of

birds, 386.
— , eaten by fish, 386, 408.
— , in mud, 408.

-, hooked, on islands, 413.

Selection of domestic products,
25.

, principle not of recent ori-
gin, 29.
-, unconscious, 29.

, natural, 73.

, sexual, 81.

, objections to term, 74.

natural, has not induced

sterility, 291.

Sexes, relations of, 81.

Sexual characters variable, 146.

, selection, 81.

Sheep, Merino, their selection, 27.

, two sub-breeds, uninten-
tionally produced, 31.
-, mountain varieties of, 70.

Shells, colors of, 127.
-, hinges of, 182.

, littoral, seldom embedded,

319.
Shells, fresh- water, long retain

the same forms, 364.
, fresh-water, dispersal of,

406.

, of Madeira, 412.

, land, distribution of, 412.

land, resisting salt water,

417.

INDEX,

535

Slirew mouse, 440.

Sileue, infertility of crosses, 286.

Silliman, Prof., on blind rat,

131.
Sirenia, their affinities, 357.
Sitaris, metamorphosis of, 465.
Skulls of young mammals, 188,

453.
Slave-making instinct, 255.
Smith, Col. Hamilton, on striped

horses, 153.
, Mr. Fred., on slave-making

ants, 256.

■ , on neuter ants, 273.

Smith, Dr. , on the Polyzoa, 228.
Snake with tooth for cutting

through egg-shell, 253.
Somerville, Lord, on selection of

sheep, 27.
Sorbus, grafts of, 290.
Sorex, 440.

Spaniel, King Charles' breed, 30.
Specialization of organs, 117.
Species, polymorphic, 41.

, dominant, 51.

, common, variable, 50.

in large genera variable, 52.

, groups of, suddenly appear-
ing, 333, 337.
beneath Silurian formations,

339.

successively appearing, 343.

changing simultaneously

throughout the world, 352.
Spencer, Lord, on increase in size

of cattle, 30.
, Herbert, Mr., on the first

steps in diffentiation, 120.
■ , on the tendency to an

equilibrium in all forces, 297.
Sphex, parasitic, 255.
Spiders, development of, 460.
Sports in plants, 9.
Sprengel, C. C, on crossing, 89.

, on ray-florets, 138.

Squalodon, 357.

Squirrels, gradations in structure,

165.
Staffordshire, heath, changes in,

66.
Stag-beetles, fighting, 81.

Star fishes, eyes of, 171.

, their pedicellariae, 227.

Sterility from changed conditions
of life, 8.

of hybrids, 279.

, laws of. 284.

, causes of, 291.

, from unfavorable condi-

tions, 295.
not induced through natural

selection, 292.
St. Helena, productions of, 410.
St. Hilaire, Aug., on variability

of certain plants, 206.

, on classification, 433.

St. John, Mr., on habits of cats,

247.
Sting of bee, 194.
Stocks, aboriginal, of domestic

animals, 17.
Strata, thickness of, in Britain,

317.
Stripes on horses, 152.
Structure, degrees of utility of,

189.
Struggle for existence, 57.
Succession, geological, 343.

of types in same areas, 367.

Swallow, one species supplanting

another, 70.
Swaysland, Mr., on earth adher-
ing to the feet of migratory

birds, 387.
Swifts, nests of, 269.
Swim-bladder, 175.
Switzerland, lake inhabitations

of, 16.
System, natural, 430.

Tail of giraffe, 186.

of aquatic animals, 187.

, prehensible, 223.

, rudimentary, 571.

Tanais, dimorphic, 42.

Tarsi, deficient, 129.

Tausch, Dr., on umbelliferae, 205.

Teeth and hair correlated, 137.

, rudimentary, in embryonic

calf, 467, 495.
Tegetmeier, Mr., on cells of bees,

262, 267.

536

INDEX.

Temminck, on distribution aiding

classification, 435,
Tendrils, their development, 232.
Thompson, Sir W., on the age of

the habitable world, 338.
, on the consolidation of the

crust of the earth, 482.
Thouin, on grafts, 290.
Thrush, aquatic species of, 169.
, mocking, of the Galapagos,

421.

, young of, spotted, 457.

nest of, 276.

Thuret, M., on crossed fuci, 287.

Thwaites, Mr. , on acclimatization,
134.

Thylacinus, 441.

Tierra del Fuego, dogs of, 249.

, plants of, 403.

Timber-drift, 385.

Time, lapse of, 314.

, by itself not causing modi-
cation, 95.

Titmouse, 168.

Toads on islands, 413.

Tobacco, crossed varieties of, 305.

Tomes, Mr., on the distribution
of bats, 415.

Transitions in varieties rare, 159.

Traquair, Dr., on flat-fish, 222.

Trautschold, on intermediate
varieties, 325.

Trees on islands belong to pecul-
iar orders, 413.

with separated sexes, 92.

Trifolium pratense, 68, 88.

— — incarnatum, 88.

Trigonia, 351.

Trilobites, 338.

, sudden extinction of, 351.

Trimen, Mr., on imitating-insects,
444.

Trimorphism in plants, 42, 297.

Troglodytes, 276.

Tuco-tuco-blind, 130.

Tumbler pigeons, habits of, he-
reditary, 248.

Tumbler, young of, 462.

Turkey-cock, tuft of hair on
breast, 83.

, naked skin on head, 188.

Turkey-cock, young of, instinct-
ively wild, 249.

Turnip and cabbage, analogous
variations of, 149.

Type, unity of, 197, 198.

Types, succession of, in same
areas, 367.

Typotherium, 357.

Udders enlarged by use, 10.

, rudimentary, 468.

Ulex, young leaves of, 457.

Umbelliferae, flowers and seeds
of, 138,

, outer and inner florets of,

205.

Unity of type, 197, 198,

Uria lacrymans, 85.

Use, effects of, under domestica-
tion, 10.

, effects of, in a state of

nature, 128.

Utility, how far important in the
construction of each part, 189.

Valenciennes, on fresh- water fish,

406.
Variability of mongrels and

hybrids, 305.
Variation, under domestication, 7.
caused by reproductive sys

tem being affected by conditions

of Hfe, 8.

under nature, 39.

, laws of, 126.

-, correlated, 10, 136, 189.

Variations api^ear at correspond-
ing ages, 12, 79.

analogous in distinct spe-
cies, 148.

Varieties, natural, 37.

, struggle between, 70.

, domestic, extinction of, 101.

, transitional, rarity of, 159.

, when crossed, fertile, 301.

Varieties, when crossed, sterile,
303.

, classification of, 437.

Verbascum, sterility of, 281.

, varieties of, crossed, 304.

Verlot, M., on doubl** stocks, 271.

INDEX,

537

Verneuil, M. de, on the succes-
sion of species, 353.

Vibracula of the Polyzoa, 229.

Viola, small imperfect flowers of,
204.

, tricolor, 68.

Virchow, on the structure of the
crystalline lens, 173.

Virginia, pigs of, 78.

Volcanic islands, denudation of,
316.

Vulture, naked skin on head, 188.

Wading-birds, 408.

Wagner, Dr., on Cecidomyia, 456.

Wagner, Moritz, on the import
ance of isolation, 96.

Wallace, Mr., on origin of spe-
cies, 1.

, on the limit of variation

under domestication, 36.

, on dimorphic lepidoptera,

43, 274.

, on races in the Malay Archi-
pelago, 44.

, on the improvement of the

eye, 173.

, on the walking-stick insect,

216.

, on laws of geographical dis-
tribution, 380.

, on the Malay Archipelago,

415.

, on mimetic animals, 444.

Walsh, Mr. B. D., on phytopha-
gic forms, 45.

, on equal variability, 149.

Water, fresh, productions of, 405.

Water-hen, 169.

Waterhouse, Mr., on Australian
marsupials, 106.

, on greatly developed parts

being variable, 141.

, on the cells of bees, 260.

, on general affinities, 446.

Water- ouzel, 169.

Watson, Mr. H. C, on range of
varieties of British plants, 44,
55.

, on acclimatization, 134.

, on flora of Azores, 388.

Watson, Mr. II. C, on rarity of
intermediate varieties, 162.

, on Alpine plants, 391.

, on convergence, 120.

, on the indefinite multipli

cation of species, 121.

Weale, Mr., on locusts transport-
ing seeds, 387.

Web of feet in water-birds, 170.

Weismann, Prof., on the causes
of variability, 7.

, on rudimentary organs, 471,

West Indian Islands, mammals of,
415.

Westwood, on species in large
genera being closely allied to
oihers, 54.

— —- on the tarsi of Engidse, 147.
-• - - , on the antennae of hymenop-
terous insects, 432.

Whales, 216.

Wheat, varieties of, 103.

White Mountains, flora of, 390.

Whittaker, Mr., on lines of es-
carpment, 316.

Wichura, Max, on hybrids, 294,
296, 307.

Wings, reduction of size, 130.

of insects homologous with

branchiae, 176.

, rudimentary, in insects,

467.

Wolf, crossed with dog, 248.

of Falkland Isles, 414.

WoUaston, Mr., on varieties of
insects, 45.

, on fossil varieties of sheila

in Madeira, 49.

Wollaston, Mr., on colors of in-
sects on sea-shore, 127.

, on wingless beetles, 129.

, on rarity of intermediate

varieties, 162.

, on insular insects, 410.

, on land-shells of Madeira

naturalized, 421.

Wolves, varieties of, 83.

Woodcock with earth attached to
leg, 387.

Woodpecker, habits of, 168.

, green color of, 187.

538

INDEX.

Woodward, Mr., on the duration

of specific forms, 326.

, on Pyrgoma, 336.

, on the continuous succession

of genera, 346.
-, on the succession of types.

367.

World, species changing simul-
taneously throughout, 352.

Wright, Mr. Chauncey, on the
giraffe, 211.

, on abrupt modifications,

240.

Wrens, nest of, 276.

Wyman, Prof., on correlation of

color and effects of poison, 11.
, on the cells of the bee, 262.

Youatt, Mr., on selection, 27.

--, on sub breeds of sheep, 31.

, on rudimentary horns in

young cattle, 472.

Zanthoxylon, 206.
Zebra, stripes on, 152.
Zeuglodon, 357.

THE END.

i