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ox THE ORIGIN OF SPEGIES.

" But with regard to tlic luatcrial world, vfc can at least go so far as tliia
— wc can perceive that events are brought about not by insulated interpo-
sitions of Divine power, exerted in each particular case, but by the estab-
lishment of general laws."

Whewkll: Bridjcwatcr Treatise.

" The only distinct moaning of the word ' natural ' is slalnl, Jixcel, or
tcllled ; since what is natural as much requires and presupposes an intelli-
gent agent to render it so, i. c., to effect it continually or at stated times,
as what is supernatural or miraculous does to effect it for once."

Butler : An(do<ji/ of Revealed Religion,

" To conclude, therefore, let no man out of a weak conceit of sobriety,
or an ill-applied moderation, think or maintain, that a man can search too
far or be too well studied in the book of God's word, or in the book of
God's works ; divinity or philosophy ; but rather let men endeavor an end-
less progress or proCcicncc in both."

Bacon : Advancement of Learning.

ON , . ^

THE ORIGIN OF SPECIES

MEANS OF NATURAL SELECTION,

PRESERVATION OF FAVORED RACES IN THE STRUGGLE
FOR LIFE.

BY

CHAELES DAEWIN, M.A., F.E.S.,

4VTII0P. OP " JOUr.NAL OF lU-;8EAKCnES DURING H. M. S. BEAOLE's VOYAGE KOUND
TOE WOnLD," ETC., ETC.

Flinil EPfTlOX, WITH ADDITIoyS ASD CORItECTIOXS.

NEAV YOEK:
i>. A PPL ETON AND COMPANY,

5 4 9 & 5 5 1 BROADWAY.
1871.

OOISTTEIS'TS

nisTORiCAL Sketch ........ paoe 9

I.VTBOnUCTION ......... 17

CHAPTER I.

VARIATION CNDE.I DOMESTICATION.

Causes of Variability— EfTocts of Habit— Correlated Variation— Inheritance— Char-
acter of Domestic Varieties — Diflftculty 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 23

CHAPTER II.

VARIATION UNDER NATCRE.

Vailability- Individual Differences— Doubtful Species— Wide-ranging, much dif-
fused, 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 . 52

CHAPTER III.

STRUGGLE FOR EXISTENCE.

its bearing on Natural Selection— The Term used in a wide Sense— Geometrical rjutio
of Increase — Rai)id Increase of Naturalized Animals and Plants — Nature of tlio
Checks to Increase— Competition universal— Effects of Climate— Protection fri)ni
the Number of Individuals— Complex Relations of all Animals and Plants through

6 CONTENTS.

out Nature— Strugiclo for Life most severe hctwccn Individuals and Varieties of
the same Species : often severe between Species of the same Genns— The Rela-
tion of Organism to Organism the most important of all Relations faoe 69

CHAPTER IV.

NATURAL PKLKCTION, OR THE SrUVIVAL OF TIIK FITTEST.

Natural Selection— its Power compared with Man's Selection — its Power on Char-
acters of trifling Importance— its Power at all Ages and on both Sexes — Sexual
Selection— On the Generality of Intercrosses bi^tween Individuals of the same
Species — Circumstances fiivorable and unfavorable to the Uesults of Natural Se-
lection, 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 Nat-
ural Selection, through Divergence of Character and Extinction, on the Descend-
ants from a Common Parent — Explains the Grouping of all Organic Beings— Ad-
vance in Organization— Low Forms preserved — Objections considered— Uniform-
ity of certain Characters due to their Unimportance and to their not having been
acted on by Natural Selection— Indefinite Multiplication of Species— Summary.

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 — Com-
pensation and Economy of Growtli — False Correlations — Multiple, Rudimentary,
and Lowly-organized Structures variable — Parts developed in an Unusual Man-
ner are highly variable: Specific Characters more variable than Generic: Second-
ary Sexual Characters variable — Species of the same Genus vary in an analogous
Manner- Reversions to long-lost Characters — Summary . . . 137

CHAPTER VI.

DIFFICULTIES OF THE TIIEORV.

Difficulties of the Theory of Descent with Modification— Transitions— Absence or
Rarity of Transitional Varieties — Transitions in Habits of Life — Diversified Elal)-
its in the same Species— Species with Habits widely diO'erent from those of their
Allies— Organs of Extreme Perfection — Modes of Traifsition — 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 .... 167

CHAPTER VII.

INSTINCT.

Instincts comjiarable with Ilabils, but different in tlu-ir Origin— Instincts graduated
— Aphides and Ants— Instincts variable— Domestic Instincts, their Origin— Nat-

CONTENTS. Y

nral lOBtincls of the Cuckoo, Ostrich, and Parasitic Bees— Slave-making Ants —
Hive-bee, its cell-making instinct— ChanKCs of In!<linct and Structure not neces-
earlly simultaneous— Difllcultics of the Theory of the Natural Selection of In-
stincts—Xeuter or Sterile Insects— Summary . . . . PAGE 201

CHAPTER VIII.

innuiDisM.

Distinction between the Sterility of First Crospoe and of Hybrids— Sterility various
in Degree, not universal, affected by close Interbreeding, removed by Domesti-
cation-Laws goveiTiing the Sterility of Hybrids- Sterility not a special Endow-
ment, but incidental on other DilTerenccB, not accumulated by Natural Selection
— Causes of the Sterility of First Crosses and of Hybrids— Parallelism between
the Effects of Changed Conditions of Life and of Crossing— Dimorphism and
Trimorphism — Fertility of Varieties when crossed and of their Mongrel Offspring
not universal— Hybrids and Mongrels compared independently of their Fertility
—Summary ......... 233

CHAPTER IX.

ON TIIK IMrEIlFECTION OF THE GEOLOGICAL KECOP.D.

On the Absence oflntcrmediatc Varieties at the Present Day — On the Nature of Ex-
tinct Intermediate Varieties ; on their Number— On the Lapse of Time, as in-
ferred from the Kjite of Denudation and of Deposition— On the Lapse of Time as
estimated by Years- On the Poorness of our Palcontological Collections— on the
Denudation of Granitic Areas— On the Interaiittence of Geological Formations —
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 Fossilifcrous Strata— Antiquity of the Habitable Earth . . 2CC

CHAPTER X.

ON THE GEOLOGICAL SUCCESSION OF ORCLVXIC BEINGS.

Ou the Slow and Successive Appearance of New Species— On their Different Rates
of Cliange— Species once lost do not reappear — Groups of Species follow the
same General Kules 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 E.\tinct Species to each other and to Living Spe-
cles- On the State of Development of Ancient Forms— On the Succession of the
eamc Types within the same Areas— Summary of preceding and present Chapter

293

CHAPTER XI.

GEOGUAmiCAL DISTRIUITION.

PrcBont Distribntlon cannot bo accounted for by Differences In Physical Conditions
— Importance of Carriers — Aflliiity of the Productions of the same Continent—

CONTENTS.

Centres of Creation— Means of Dispersal by Changes of Climate and of the Level
of the Land, and by Occasional Means— Dispersal during the Glacial Period-
Alternate Glacial Periods in the North and South . . . page 322

CHAPTER XII.

GEOGllAnilC'AL DISTRIBUTION' COUtinUcJ.

Distribution of Fresh-water Productions— On the Inhabitants of Oceanic Islands-
Absence of Batrachians and of Terrestrial Mammals— On the Relation of the In-
habitants of Islands to those of the nearest Main-land— On Colonization from the
nearest Source with subsequent Modification— Summary of the last and present
Chapter 351

CHAPTER XIII.

MUTUAL AFFINITIES OF ORGANIC BEINGS : MORPHOLOGY : EMBRYOLOGY : RUDI-
MENTARY ORGANS.

Classiflcation, Groups subordinate to Groups— Natural System— Eules and Difficulties
in Classification, explained on the Theory of Descent with Modification— Classi-
fication of Varieties- Descent always used in Classification— Analogical or Adap-
tive Characters— Affinities, General, Complex, and Radiating— Extinction sepa-
rates and defines Groups— Morphology, between members of the same Class, be-
tween 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 . . 372

CHAPTER XIV.

RECAPITULATION 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— IIow far the Theory of Natural Selection
may be extended- Efl"ects of its Adoption on the Study of Natural History— Con-
cluding Remarks ......... 412

«»

Instruction to Binder.— The Diagram to front page 114.

An Historical Sketcu of the Recent Progress of
Opinion on tue Origin of Species.

I WILL here give a brief slcetch of the progress of opinion on the Origin
of Species. Until recently, the great majority of naturalists believed that
species were immutable productions, and had been separately created. This
view has been ably maintained by many authors. Some few naturalists, on
the other hand, have believed that species undergo Tiiodification, and that
the existing forms of life arc the descendants by true generation of pre-
existing forms. Passing over allusions to the subject in the classical
writers,* the first author who in modern times has treated it in a scientific
spirit was Buffon. But, as his opinions fluctuated greatly at different
periods, and as he does not enter on the causes or means of the 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 enlarged them in 1809 in his " Philosophic Zoologique,"
and subsequently, in 1815, in the introduction to his "Hist. Nat. des Ani-
maux sans Vcrtcbres." 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 the
organic as well as in the inorganic world being the result of law, and not of
miraculous interposition. Lamarck seems to have been chiefly led to his

* Aristotle, In his " Phygictc Anecultationes " (I'l'- 2, cap. 8, s. 2), after remarking
that rain docs not fall in order to make the com grow, auy more than it falls to gpoil
the farmer's com when threshed out of doors, applies the same arf::umcnt to orfrani-
zaliou, and adds (as translated by Mr. Clair Grecc, who first pointed out the passaio
to me): "-So, what hinders the different parts [of the body] from haviuii 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 masticat-
ing the food ; since they were not made for the sake of tliiH, but it was the result of
accident. And in like manner as to the other parts in which there appears to exist
nn adaptation to an end. Wheresoever, therefore, all things together ^tllat is, all tho
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 spon-
taneity ; and whatsoever things were not thus constituted perished, and still perish."
Wo hero sec the principle of natural selection shadowed forth ; but how little
Aristotle fully comprehended the principle is shown byhia remarks on the formation
of tho teeth.

10 IIISTOKICAL SKETCH.

conclusion on the graJiuil cliangc of species by the dilTicully of distinguish-
ing species and varieties, bj- the almost perfect gradation of forms in certain
groups, and by the analogy of domestic productions. With respect to the
means of modification, he attributed something to the direct action of the
physical conditions of life, something to the crossing of already existing
forms, and much to use and disuse — that is, to the efTccts of habit. To this
latter agency he seems to attribute all the beautiful adaptations in Nature —
such as the long neck of the giraffe for browsing on the branches of trees.
But he likewise believed in a law of progressive 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 arc
now spontaneously generated.*

Geoffroy Saint-IIilaire, as is stated in his "Life," written by his son, sus-
pected, as early as IvOo, that what we call species are various degenerations
of the same type. It was not until 1828 that he puljjishcd 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 " monde
ambiant,''^ as the cause of change. lie was cautious in drawing conclusions,
and did not believe that existing species are now undergoing modification ;
and, as his son adds, " C'cst done un probleme h, reserver cntierement h
I'avenir, suppos6 meme que I'avenir doive avoir prise sur lui."

In 1813 Dr. "W. C. AVells read before the Eoyal Society "An Account
of a White Female, Part of whose Skin resembles that of a Negro;" but
his paper was not published until his famous " Two Essays upon Dew and
Single Vision " appeared, in 1818. In this paper he distinctly 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-
nniuity from certain tropical di.-cases, he observes, firstly, that all animals

* I have taken the date of tlic first publication of Lamarck from Isid. Qeofl'roy
Saint-Ililaire'8 ("Hist. Nat. Guncralc," torn. 11., p. 405, 1S50) cxrcllent history of
opinion on this subject. In this work a full account is pivcn of Buftbn's conclusious
on the pame subject. It is curious how largely my grandfather, Dr. Erasmus Dar.
win, anticipated the views and erroneous grounds of opinion of Lamarck in Iiis
"Zoononiia" (vol. i., pp. 500-510), published in ITUt. According to Isid. Geoffroy,
there is no doubt that Goethe was an extreme partisan of similar views, ns shown
in llic introduction to a work written in 1794 and 1795, but not published <\\\ long
afterward: he has pointedly remarked ("Goethe als Naturforsclicr," von Dr. Karl
Meding, s. 31) tbat the future question for naturalists will be how, for Instance, cattle
got tlielr horns, and not for wbat they are used. It is rather a singular instance of
the manner in wliieh similar views arise at about the same time, that Goethe in Ger-
many, Dr. Darwin in England, and (icoffroy Saint-Ililai re (as we shall immediately
eee) in France, came to the same conclusion on the origin of species, in the years
1794-'95.

niSTOKICAL SKETCH. H

tend to varj- iu some deforce, and, secondly, that agriculturists improve their
domesticated animals by selection ; and then, he adds, but what is done in
this latter case " by art seems to be done with equal cdicacy, though more
slowly, by Nature, in the formation of varieties of mankind, fitted for the
country which they inhabit. Of the accidental varieties of man, which
would occur among the first few and scattered inhabitants of the middle
regions of Africa, some one would be better fitted than the others to bear
the diseases of the country. This race would consequently multiply, while
the others would decrease — not only from their inability to sustain the at-
tacks 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 already said, would be dark. But, tlie 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." lie then extends
these same views to the white inhabitants of colder climates. I am in-
debted to Mr. Rowley, of the Uniteil States, for having called my attention,
through Mr. Brace, to the above passage in Dr. Wells's work.

The lion, and Kcv. W. Herbert, afterward Dean of Manclicster, in the
fourth volume of the " Horticultural Transactions," 1822, and in his work on
the " Amaryllidacere " (1S37, pp. 10, 339), declares that " horticultural exper-
iments have established, beyond the possibility of refutation, that botanical
species are only a higher and more permanent class of varieties." He ex-
tends the same view to animals. The dean believes that single species of
each genus were created in an originally highly plastic condition, and that
these have produced, chiefly by intercrossing, but likewise by variation, all
ovir existing species.

In 182G Professor Grant, in the concluding paragraph in his well-known
paper {Edinhtirgh Philosoplikal Journal, vol. xiv., p. 283) on the Spongilla,
clearly declares his belief that species are descended from other species, and
that they become improved in the course of modification. This same view
was given in his 55th Lecture, published in the Lancet in 1834.

In 1831 Mr. Patrick Matthew published his work on "Xaval Timl)er and
Arboriculture," in which he gives precisely the same view on the origin of
species as that (presently to be alluded to) propounded by ^Ir. Wallace and
myself in the Lluncan 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 adiflcrcnt sul)jeet, so that it remained
unnoticed until Mr. Matthew himself drew attention to it in the Gardcncr^a
Chronicle, on April Y, 1860. The difTcrcnecs of Mr. JIatthew's view from
mine arc not of much importance ; he seems to consider that the world was

12 HISTORICAL SKETCH.

nearly depopulated at successive periods, and then restocked ; and he gives,
as an alternative, that new forms may be generated " without the presence
of any mould or germ of former aggregates." I am not sure that I under-
stand some passages ; but it seems tliat he attributes much influence to the
direct action of the conditions of life. He clearly saw, however, the full
force of tlie principle of natural selection.

The" celebrated geologist and naturalist. Yon Buch, in his excellent "De-
scription Physique dcs lies Canaries" (1836, p. 147), clearly expresses his
belief that varieties slowly become changed into permanent species, which
arc no longer capable of intercrossing.

Rafinesquc, in his "New Flora of North America," published in 1836,
wrote (p. C) as follows : " All species might have been varieties once, and
many varieties are gradually becoming species by assuming constant and pe-
culiar characters:" but further on (p. 18) he adds, "except the original
types or ancestors of the genus."

In 1813-41 Prof. Ilaldcman {Boston Journal of Nat. ///.s/., U. States, vol.
iv., p. 463) has ably given the arguments for and against the hypothesis of
the development and modification of species ; he seems to lean toward the
side of change.

The " Ycstigcs of Creation" appeared in 1844. In the tenth and much
improved edition (1853) the anonymous author says (p. 155): "The propo-
sition 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 imparted to the forms of life, advancing them, in definite
times, by generation, through grades of organization terminating in the high-
est dicotyledons and vertebrata, these grades being few in number, and gen-
erally marked by intervals of organic character, which we find to be a prac-
tical difficulty in ascertaining affinities; second, of another impulse connected
with the vital forces, tending, in the course of generations, to modify organic
structures in accordance with external circumstances, as food, the nature of
the habitat, and the meteoric agencies, these being the ' adaptations ' of the
natural theologian." The author apparently believes thr.t organization pro-
gresses by sudden leaps, but that the eflccts produced by the conditions of
life arc gradual. lie argues with much force on general grounds that species
arc not immutable productions. But I cannot see how the two supposed
"impulses" account in a scientific sense for the numerous and beautiful co-
adaptations which wc sec throughout Nature ; I cannot see that we thus gain
any insight how, for instance, a woodpecker has become adapted to its pecu-
liar habits of life. " The work, from its powerful and brilliant style, though
di:<playing in the earlier editions little accurate knowledge and a gi-eat want
of scientific caution, immedi.itcly had a very wide circulation. In my opiu-

IIISTOEICiVL SKETCH. 13

ion it has done excellent service in this country in callinj; attention to the
subject, in removing prejudice, and in thus preparing the ground lor the re-
ception of analogous views.

In 1816 the veteran geologist, M. J. d'Omalius d'llalioy, published in au
excellent, though short paper {Bulletins dc PAcad. Jioy. JSi-uxcllcs, torn,
xiii., p. 581), his oinuion tliut it is more probable that new species have been
produced by descent with modification, than that they have been separately
created. The author first promulgated this opinion in 1831.

Trof. Owen, in 1819 ("Nature of Limbs," p. SO), wrote as follows:
" The archetypal idea was mauirested in the flesh under divers such modifi-
cations, upon this planet, long prior to the existence of those animal species
that actually exemplify it. To what natural laws or secondary causes the or-
derly succession and progression of such organic phenomena may have been
committed, we, as yet, are ignorant." In his Address to the British Asso-
ciation, in 1858, he speaks (p. li.) of "the axiom of the continuous operation
of creative pow'er; or of the ordained becoming of living things." Further on
(p. xc), after referring to geograpliical distribution, he adds : " These phe-
nomena shake our confidence in the conclusion that the Apteryx of New
Zealand and the Red Grouse of England were distinct creations, in and for
tho.^e islands respectively. Always, also, it may be well to bear in mind
that by the word 'creation' the zoologist means 'a process he knows not
what.' " lie amplifies this idea by adding that, when such eases as that of
the IJed Grouse arc " enumerated by the zoologist as evidence of distinct
creation of the bird in and for such islands, he chiefly expresses that he
knows not how the lied Grouse came to be there, and there exclusively, sig-
nifying 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."

This Address was delivered after the papers, by Mr. "Wallace and myself,
on the Origin of .'Species, presently to be referred to, had been read before
the Linnean Society. "When the first edition of this work was published, I
was so completely deceived, as were many others, by such expressions
as "the continuous operation of creative power," that I included Prof.
Owen with other paleontologists, as being firmly convinced of the immuta-
bility 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 bo perfectly just — from a passage
beginning with the words " no doubt the type-form," etc. (ibid., vol. i., p.
XXXV.), that Prof. Owen admitted that natural selection may have done

1 4 IIISTOKICAL SKETCH.

Bometliinp; in tlio foriuation of new ppccics ; but tliir:, it appears (ibiil., vol.
ii., p. 708), is inaccurate and witliout evidence. I also gave some extracts
from a correspondence between Prof. Owen and the editor of the Lon-
don licvicw, from which it appeared manifest to the editor as well as to
myself, that Prof. Owen claimed to have promulgated the theory of nat-
ural selection before I had done so ; and I expressed my surprise and satis-
faction at this announcement ; but, as far as it is possible to understand cer-
tain reccntl}--published passages (ibid., vol. iii., p. "JOS), I have, cither par-
tially or wholly, again fallen into error. It is consolatory to me that others
find Prof. 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 Prof. Owen preceded me, for both of us, as shown in tliis historical
sketch, were long ago preceded by Dr. "Wells and Mr. Matthew.

M. Isidore GcoflVoy Saint-IIilaire, in his Lectures delivered in 1850 (of
which a resume appeared iu the Hevue ctMn(/. dc ZooJog.^ January, 1851),
briefly gives his reason for believing that specific characters " sont fixes,
pour chaque esijuce, tant qu'elle se perpetue au milieu des m6mes circon-
stanccs: lis se modifient, si Icscirconstanccsambiantcs vienncnti changer."
"En r6sume, Vohservation des animaux sauvages dcmontre dejiHavariabihte
limiiie des cspeces. Les experiences sur Ics animaux sauvages dcvcnus do-
mcstiqucs, ct sur les animaux domestiques redcvenus sauvages, la demon-
trent plus claircment encore. Ccs memcs experiences prouvcnt, deplus, que
les diirercnces produites peuvent ctre de valcur gcniriqne.''^ In his " Hist.
Nat. Generalc" (tom. ii., p. 430, 1859) he amplifies analogous conclusions.

From a circular lately issued it appears that Dr. Frekc, in 1851 {Dublin
Medical Frcsa, p. 322), propounded the doctrine that all organic beings have
descended from one primordial form. His grounds of belief and treatment
of the subject are wholly diflVrent from mine; but, as Dr. Freke has now
(1801) ptiblishcd his Essay on the "Origin of Species by means of Organic
Affinity," the difficult attempt to give any idea of his views would be super-
fluous on my part.

Mr. Herbert Spencer, in an Essay (originally published in the Leader,
March, 1852, and republished in his " Essays " in 1858), has contrasted the
theories of the Creation and the Development of organic beings with re-
markable skill and force. He argues from the analogy of domestic pro-
ductions, from the changes which the embryos of many species undergo,
from the difficulty of distinguishing species and A-arictics, and from the prin-
ciple of general gradation, that species have been modified ; and he attributes
the modification to the change of circumstances. The author (1855) has
also treated Psychology on the principle of tliencce.-sary acquirement of each
mental power and capacity by gradation.

HISTORICAL SKETCH. 15

In 1852 M. Naudin, a distinguished botanist, expressly stated, in an ad-
mirable paper on the Origin of Species {Revue Horlkolc^ p. 102 ; sir.ce
partlj' republished in the "Nouvelles Archives du Museum," torn, i., p.
171), his belief that species are formed in an analogous manner as varie-
ties arc under cultivation ; and the latter process he attributes to man's
power of selection. But he does not show how selection acts under Nature.
lie believes, like Dean Herbert, that species, when nascent, were more
plastic than at present. lie lays weight on what he calls the principle of
linality, "puissance mysturieusc, indeterminee; fatalite pour les uns ; pour
les autres, volonto providentielle, dont Taction inecssante sur les etres vi-
vants determine, ii toutcs les epoqucs de Texistcncc du mondc, la forme, Ic
volume, et la durcc do chacun d'cux, en raison dc sa destiuC-e dans I'ordre
de choses dont il fait partie. C'est cette puissance qui harmonise chaquc
membrc i rensemble en I'appropriant h. la fonction qu'il doit rcmplir dans
Torganisme general de la nature, fonction qui est pour lui sa raison
d'etre"*

In 1853 a celebrated geologist. Count Keyscrling {BuV.ei'ni ilc la Soc.
Gcohg., 2d Scr., tom. x., p. SSV), suggested that as new diseases, supposed
to have been caused by some miasma, have arisen and spread over the
world, so at certain periods the germs of existing species may have been
cliemically affected by circumambient molecules of a particular nature, and
thus have given rise to new forms.

In this same year, 1853, Dr. SchaalTliauscn published an excellent pam-
phlet (" Yerhand. des Naturhist. Yereins dcr Prcus.-!. Ilhcinlands," etc.), in
which he maintains the progressive development of organic forms on the
earth. lie infers that many species have kept true for long periods,
whereas a few become modified. The distinction of species he explains
by the destruction of intermediate graduated forms. " Thus living plants
and animals are not separated from the extinct by new creations, but are to
be regaiilod as their descendants through continued reproduction."

A well-known French botanist, 51. Lccoq, writes in 185-1 ("Etudes sur

♦ From rofcrcnccs in Bronn's " Untcrsucluui^xon iibcr die Entwifkchins-'-Oe-
pptze " it nppca^^^ that the celebrated botanist and paleontologifit Unser published in
]S5'2 his belief that Bpcclcs undergo development and modillcntion. D'Alton, likc-
wi!»c, in Pander and Dalton's? work on Fosfil Slothp, cxprcc-scd, in 1821, a similar
belief. Similar views have, as is well known, been uinintained by Okcn in his mys-
tical " Niitur-PhiloKophic." From other refcrencci? in Godron's work "Siir VEi-
pc^co," it seems that Bory St. Vinecut, Burdacli, Poiret, and Fries, have all admitted
that new species are continually bciii:; produced.

I may add that, of the thirfy-foiir authors named in this lliKtnrical Skcicli, who
believe In the modification of species, or nt leasit disbelieve in sepanite acts of
creation, twenty-seven have written on special branches of natural history or
geology.

16 HISTORICAL SKETCH.

Geograph. Bot.," torn, i., p. 250), " Oa voit que nos rcchcrchcs sur la fixate
ou la variation ilc Tespece, nous conduiscnt dircctcment aux idecs emisea
par deux honiincs justcmcnt celebrcs, Geofifroy Saint-llilairc ct Goethe."
Some other passages, scattered through M. Lccoq'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 masterly manner
by the Rev. Baden Powell, in his "Essays on the Unity of Worlds," 1855.
Nothing can be more striking than the manner in which he shows that the
introduction of a new species is " a regular, not a casual phenomenon," or,
as Sir John llerschel expresses it, " a natural in contradistinction to a mi-
raculous process."

The third volume of the Journal of the Linnean Sociehj 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.

Yon Baer, toward whom all zoologists feel so profound a respect, ex-
pressed, about the year 1859 (see Prof. Rudolph Wagner, " Zoologisch-An-
thropologische Untcrsuchungen," 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, Prof. Huxley gave a lecture before the Royal Institution
on the "Persistent Types of Animal Life." Referring to such cases, he re-
marks : " 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 or-
ganization, 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 op-
posed to the general analogy of Nature. If, on the other hand, we view
' Persistent Types' in relation to that hypothesis which supposes the species
living at any time to be the result of the gradual modification of pre-
existing species — a hypothesis which, though 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 modi-
fication which living beings have undergone during geological time is but
very small in relation to the whole scries of changes which they have suf-
fered."

In December, 1859, Dr. Hooker published his " Introduction to the Aus-
tralian Flora." In the first part of this great work he admits the truth of
the descent and modiCcatiou of species, and supports this doctrine by many
original observations.

The first edition of this work was published on November 24, 1850, and
the second edition on January 7, 18G0.

ON THE ORIGIN OF SPECIES.

INTRODUCTION.

When on board H. M. S. " Beagle," as naturalist, I -was
much struck -with certain facts in the distribution of the organic
beings inhabiting South Amdrica, and in the geological rela-
tions 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 bcei\ called by one of our great-
est pliiloso^ihcrs. On my return home, it occurred to me, in
1837, that something might perhaps be made out on this ques-
tion by patiently accumulating and reflecting on all sorts of
facts which could possibly have any bearing on it. After five
years' work I allowed myself to 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 :
fiom that period to the present day I have steachly pursued
tlie same object. I hope that I may be excused from 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 nearly finished ; but as it will take me two
or three more years to complete it, and as my health is far
from strong, I have been urged to publish this Abstract. I
have more especially been induced to do this, as Mr. Wallace,
who is now studying the natural history of the Malay archi-
pelago, has arrived at almost exactly the same general conclu-
sions 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 Lycll, who sent it to the Linnean Society, and

18 INTRODUCTION.

it is published in the third vohime of the Journal of tliat So-
ciety, Sir C Lycll :uid Dr. Hooker, who both Icnew of my
work — tlic hitter having read my sketch of 1844 — honored me
by thinking it advisable to publish, with Mr. Wallace's excel-
lent memoir, some 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 accurac}'. No doubt errors Avill have
crept in, tliough I hope I have always been cautious in trust-
ing to good authorities alone. I can here give only the general
conclusions at which I have arrived, with a few facts in illustra-
tion, but which, I hope, in most cases will suffice. No one can
feel more sensible than I do of the necessity of hereafter pul>
lishing in detail all the facts, Avith references, on wliich 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 Avjiich facts cannot be adduced,
often apparently leading to conclusions directly opposite to
those at Avhich I have arrived. A fair result can be obtained
only by fully stating and balancing tlie facts and arguments
on both sides of each question ; and this is here imj^ossible.

I much regret that Avant of space prevents my having the
satisfaction of acknowledging the generous assistance Avhich I
have received from A^ery many naturalists, some of them per-
sonally unknoAvn to me. I cannot, hoAvevcr, let this 02')por-
tunity pass Avithout expressing my deep obligations to Dr.
Hooker, Avho for tlie last fifteen years has aided me in CA'ery
[wssible Avay by his large stores of knoAAdedge and liis excellent
judgment.

In considering the Origin of Species, it is quite conceivable
that a naturalist, reflecting on the mutual affinities of organic
beings, on their embryological relations, their geographical
distribution, geological succession, and other such facts, might
come to the conclusion that species had not been independently
created, l)ut had descended, like varieties, from other species.
Nevertlielcss, such a conclusion, even if Avell founded, Avould be
unsatisfactory, imtil it could be shoAvn how the innumerable
species inhabiting this Avorld haA'e been modified, so as to ac-
quin? that perfection of structure and coadaptation Avhich justly
excites our admiration. Naturalists continually refer to exter-
nal conditions, such as climate, food, etc., as the only possible
cause of variation. In one limited sense, as Ave shall hereafter

INTRODUCTION. 19

see, this may bo true ; but it is preposterous to attribute
to mere exteriuil conditions, the structure, for instance, of
the woodpecker, with its feet, tail, beak, and tonjTue, so ad-
mirably adapted to catch insects under the bark of trees. In
the case of the mistletoe, which draws its nourishment from
certain trees, M'hich has seeds that must be transported by cer-
tain birds, and which has flowers with separate sexes absolutely
requiring the ag^ency of certain insects to brin<^ pollen from one
flower to the other, it is equally preposterous to account for
the structure of this parasite, with its relations to several dis-
tinct organic beings, by the efl'ects 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 coramencem(mt of my observations it seemed to me prob-
able that a carcfyl study of domesticated animals and of culti-
vated plants would oiler the best chance of making out this
obscure problem. Nor have I been disappointed; in this and
in all other perplexing cases I have invariably found that our
knowledge, imperfect though it be, of variation under domesti-
cation, aflbrded the best and safest clew. I may venture to
express my conviction of the high value of such studies, al-
though they have been very commonly neglected by natural-
ists.

From these considerations, I shall devote the first chapter
of this Aljstract to Variation under Domestication. We shall
thus see that a large amount of hereditary modification is at
least possible ; and, what is equally or more important, we
shall see how great is the jiower of man in accumulating by
his Selection successive slight variations. I will then pass on
to the variability of species in a state of nature ; but I shall,
unfortunately, be compelled to treat this subject far too briefly,
as it can be treated properly only by giving long catalogues
of facts. We shall, however, be enabled to discuss what cir-
cumstances are most favorable to variation. In the next chap-
ter the Struggle for Existence among all organic beings
througliout the world, which inevitably follows from the high
geometrical ratio of their increase, Avill be treated of. This is
the doctrine of Malthus, applied to the whole animal and vege-
table kingdoms. As many more individuals of each species
are born than can possil)ly survive ; and as, consequently, there
is a frequently-recurring struggle for existence, it follows that
any being, if it vary however slightly in any manner profitable

20 INTRODUCTION.

to itself, under tlie complex and sometimes varying conditions
of life, uill have a better chance of survivinq-, and thus be nat-
la'cdhj sdectcd. 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 tlie 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 com2:)lcx and little-known laws of variation.
In the four succeeding chajitcrs, the most apparent and gravest
difficulties in accepting the theory will be given : namely, first,
the difficulties of transitions, or how a simple being or a simple
organ can be changed and perfected into a highly-developed
being or into an elaborately-constructed organ ; secondly, the
subject of Instinct, or the mental powers of animals ; thirdly,
Hybridism, or the infertility of species, and the fertility of va-
rieties when intercrossed ; and fourthly, the imperfection of
the Geological Record. In the next chapter I shall consider
the geological succession of organic beings throughout time ;
in the eleventh and twelfth, their geographical distribution
throughout space ; in the thirteenth, their classification or mu-
tual atlinities, both when mature and in an embrj-onic condi-
tion. In the last chapter I shall give a brief recapitulation of
the whole work, and a few concluding remarks.

No one ought to feel surprise at much remaining as yet
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. AVho can explain why one species ranges Avidely and is
very numerous, and why another allied species has a narrow
range and is rare ? Yet these relations are of the highest im-
]')ortance, for they determine the present welfare, and, as I be-
lieve, the future success and modification of every inhabitant
of tins world. Still less do we know of tlic mutual relations
of the innumerable inhabitants of the world during tlie man}"-
past geological epochs in its history. Although much remains
obscure, and Avill long remain obscure, I can entertain no
doubt, after the most deliberate study and dispassionate judg-
ment of which I am cajiable, that the view which most natu-
ralists entertain, and which I fonnerly entertained — namely,
that each species has been independently created — is erio-

INTRODUCTION. 21

neons. I am fully convinced that species arc not immutable ,
but that those belonging to what are called the same genera
are hncal descendants of some other and generally extinct spe-
cies, in the same manner as the acknowledged varieties of any
one sjiecies arc the descendants of that species. Further-
more, I am convinced that Natural Selection has been the
most important but not the exclusive means of modification.

22 VARIATION Chap. I.

GIIAPTER I.

VAEIATION UNDER DOMESTICATION.

C!aii8PS of Variability— Effects of Habit— Correlated Variation— Inheritance— Char-
acter of Domestic Varieties — Ditliculty of (liHtintruiehinj,' between Varieties and
Species — Orii^in of Dome.stic Varieties from oiie or inorc (species — Domestic
Pigeons, their Differences and Origin— Principles of Selection, anciently followed,
their Effects — Methodical and Uuconscious Selection— Unknown Orisin of our
Domestic Productions— Circumstances favorable to Man's Power of Selection.

Causes of Yariahility.

WnEN 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 generallj' differ
from each other more than do the indi^aduals of any one spe-
cies or variety in a state of nature. And if we reflect on the
vast diversity of the plants and animals which have been cul-
tivated, and which have varied during all ages under the most
different climates and treatment, Ave are driven to conclude
that this great variability is due to our domestic productions
having been raised under conditions of life not so uniform as,
and somewhat different from, those to which the parent-species
had been exposed luider nature. There is also, I think, 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 generations to new conditions to cause any appreciable
amount of variation ; and that, when the organization has once
l)cgun to vary, it generally continues varying for many gencr-
atitms. No case is on record of a variable organism ceasing
to vary imder cultivation. Our oldest cultivated plants, siicli
as wheat, still yield new varieties : our oldest domesticated
animals arc still capable of rapid improvement or modifica-
tion.

As far as I am able to judge, after long attending to the
subject, the conditions of life ajipcar to act in two ways — di-

CuAP. I. U^'DER DOMESTICATION. 03

rcctly ou the -wliole orn-anizalion or on certain parts alone, and
indirectly by affecting the reproductive system. With respect
to the direct action, Ave must bear in mind that in every case,
as Prof. Weismann has lately insisted, and as I have incident-
ally shown in my -work on " Variation under Domestication,"
there are two factors : namely, the nature of the organism, and
the nature of the conditions. The former seems to be much
the more important; for nearly similar variations sometimes
arise under, as far as we can judge, dissimilar conditions ; and,
on the other hand, dissimilar variations under conditions which
appear to be nearly uniform. The effects on the offspring are
cither defmite or indefmitc. They may be considered as defi-
nite when all or nearly all the offspring of individuals exposed
to certain conditions during several generations are modified
in the same manner. It is extremely difficult to come to any
conclusion in rcgjird 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
amoimt of food, color from the nature of the food, thickness of
the skin and hair from climate, etc. Each of the endless vari-
ations which we sec in the plumage of our fowls must hare
had some efficient cause ; and if the same cause were to act
uniformly during a long scries of generations on many indi-
viduals, all probably would be modified in the same manner.
Such facts as the complex and extraordinary outgrowths
which invariably follow from the insertion of a minute drop of
])oison by a gall-producing insect, show us what singular mod-
ifications might result in the case of plants from a chemical
change in the nature of the sap.

Indefinite variability is a much more common result of
changed conditions than definite variability, and has probably
played a more important part in the formation of our domestic
races. We see indefinite Aariability in the endless slight pe-
culiarities which distinguish the individuals of the same spe-
cies, and which cannot be accounted for by inheritance from
cither parent or from some more remote ancestor. Even
strongly-marked differences occasionally appear in the young
of the same litter, and in seedlings from the same seed-capsules.
At long intervals of time, out of millions of individuals rc^ared
in the same country and fed on nearly the same fooJ, dona-
tions of structure so strongly pronounced as to deserve to be
called monstrosities arise; but monstrosities cannot be sepa-
rated by any distinct Une from slighter variations. All such

24 VARIATION Chap. I.

changes of structure, ■whether extremely slight or strongly
marked, which appear among many individuals living together,
may be considered as the indefinite elTects of the conditions of
life on each individual organism, in nearly the' same manner as
a chill allxicts diflerent men in an indefinite manner, according
to their state of body or constitution, causing coughs or colds,
rheumatism, or inflammations of various organs.

With respect to what I have called the indirect action of
changed conditions, namely, through the reproductive system
being afTected, Ave 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 Kolreutcr and others have remarked, between the variabil-
ity which follows from the crossing of distinct species, and
that which may be observed with all plants and animals
Avhen reared under new or unnatural conclitions. Many facts
clearly show how eminently susceptible the reproductive sys-
tem 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,
oven Avhen the male and female unite. How many animals
there are Avhich Avill not breed, though kept in an almost free
state in their native country ! This is generally, but errone-
ously, 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 liave
collected and elscAvhere published on this curious subject ; but,
to show how singular the laws are Avhich determine the repro-
duction of animals under confinement, I may mention that car-
nivorous animals, even from the tropics, breed in this country
pretty freely under confinement, with the exception of the
jilantigrades or bear family, Avhich seldom produce young;
whereas carnivorous birds, with the rarest exceptions, hardly
ever lay fertile eggs. Many exotic plants have jwllen utterly
worthless, in the same condition as in the most sterile hybrids.
When, on the one hand, we sec domesticated animals and
jilants, though often weak and sickly, yet breechng freely un-
der confinement ; and when, on the other hand, we see indi-
viduals, though taken young from a state of nature, ]>erfectly
tamed, long-lived, and healthy (of which I could give numerous

Chap. I. UNDEIl DOMESTICATIOin. 25

instances), yet having their reproductive system so seriously
anccted by uiiperceived causes as to fail to act, Ave need not
he surprised at this system, when it does act under confine-
UKMit, acting irregularly, and jiroducing offspring' somewhat
imlike their parents. I may adil, that as some organisms breed
fn^ely under the most unnatural conditions (for instance, rali-
bits and ferrets kept in hutches), showing that their reproduc-
tive organs arc not 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 cer-
tainly an eiTor; for I have given in another woi'k 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-diilerent character from that of the
other buds on the same plant. These bud-variations, as they
may be named, can be propagated by grafts, offsets, etc., and
sometimes by seed. They occur rarely under nature, but far
from rarely under culture. As a single bud out of the manj^
thousands produced year after year under uniform conditions
on the same tree, has been known suddenly to assmne a new
character ; and as buds on distinct trees growing und(^r differ-
ent conditions, have sometimes yielded nearly the same variety
— for instance, buds on peach-trees producing nectarines, and
buds on common roses producing moss-roses — we clearly see
tliat the nature of the conditions is of quite subordinate impor-
tance in comparison with the nature of the organism in deter-
mining each particular form of variation — of not more impor-
tance than the nature of the spark by wliich a mass of combus-
t \h\o matter is ignited, has in determining the nature of the
flames.

Effects of Habit ; Correlated Variation / Inheritance.

Habits are inherited and have a decided influence ; as in
the period of the flowering of plants when transported from
one climate to another. In animals they have a more marktnl
effect ; for instance, I llnd in the domestic duck that the bones
of the wing weigh less and the bones of the leg more, in pro-
portion to the whole skeleton, than do the same bones in the
wild-duck ; and this change may be safely attributed to the do-
mestic duck flying mucli less, and walking more, than its Mild
]):irents. The great and inherite<l development of the udders

26 VAKIATION Chap. I.

in cows and goats in countries where they arc habitually milked,
in comparison with the state of these organs in other coimtries,
is probably another instance of the cfl'ects of use. Not one of
our domestic animals can be named which has not in some
country drooping ears ; and the view which has been suggested
that the drooping is due to the disuse of the muscles of the
ear, from the animals being seldom alarmed by danger, seems
probable.

^lany laws regulate variation, some few of which can be
dimly seen, and will hereafter be briefly discussed. I will here
only allude to what may be called correlated variation. Im-
portant changes in the embryo or larva will probably entail
changes in the mature animal. In monstrosities, the correla-
tions between quite distinct parts are very curiovis ; and many
instances are given in Isidore Geofl'roy 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. Color and coii-
stitutional peculiarities go together, of which many remarkable
cases could be given among animals and plants. From facts
collected by Heusinger, it appears that white sheep and pigs
are injured by certain plants, while dark-colored mdii-iduals es-
cape : Prof. Wyman has recently communicated to me a good
illustration of this fact ; on asking some farmers in Florida 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 off; and one of the "crackers" (i. e., Florida
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 ani-
mals are apt to have, as is asserted, long or many horns ;
pigeons with feathered feet have skin between their outer
toes; pigeons with short beaks have small feet, and those
with long beaks large feet. Hence if man goes on selecting,
and thus augmenting, any peculiarity, he will almost certainly
modify imintentionally other parts of the structure, owing to
tlie mysterigus laws of correlation.

The results of the various, unknown, or but dimly under-
stood laws of variation are infinitely complex and diversified.
It is well worth Avhile can-fiilly to study the several treatises
on some of our ol<l cultivated jilants, as on tlie ]iyaci:ith, potato.

Chap. I. UNDER DOMESTICATION. 27

even the dahlia, etc. ; and it is really surprising to note the
endless points in structure and constitution in which the varie-
ties and sub-varieties differ slig'litly from each other. The
whole organization seems to have become plastic, and tends to
depart 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 struc-
ture, both those of slight and those of considerable physiological
importance, are endless. Dr. Prosper Lucas's treatise, in two
large volumes, is the fullest and the best on this subject. No
breeder doubts how strong is the tendency to inheritance : that
like produces like is his fundamental belief : doubts have been
tlirown on this principle only by theoretical writers. When
any deviation of structure often appears, and we see it in the
father and child, we cannot tell Avhether it may not be due to
the same cause having acted on both ; but when among indir
viduals, apparently exposed to the same conditions, any very
rare deviation, due to some extraordinary combination of cir-
cumstances, appears in the parent — say, once among several
million individuals — and it reappears in the child, the mere
doctrine of chances almost compels us to attribute its re-
appearance to inheritance. Every one must have heard of
cases of albinism, prickly sldn, hairy bodies, etc., appearing in
several members of the same family. If strange and rare devia-
tions of structure are really inherited, less strange and com-
moner deviations may be freely admitted to be inheritable.
Perhaps the correct way of viemng the whole subject, Avould
be, to look at the inheritance of every character whatever as
tlie rule, and non-inheritance as the anomaly.

The hiAvs governing inheritance are for tlie most part un-
Icnown. No one can say why the same peculiarity in tlifferent
individuals of the same species, or in different species, is some-
tiiucs inherited and sometimes not so; why the child often re-
verts in certain characters to its grandfather or grandmother or
more remote ancestor ; why a peculiarity is often transmitted
fi'om 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 impor-
tance to us, that jK'culiarities appearing in the males of our
domestic breeds are ofLen transmitted, either exclusively or in
a nmch greater degree, to tlie males alone. A much more im-
portant rule, which I think may be trusted, is that, at Avhatevrr
period of life a peculiarity first appears, it tends to reappear in
the ollspring at a corresponding age, though sometimes earlier.

23 VARIATION Chap. I.

In many cases this could not be otherwise : thus the inherited
pocuharities in tlie horns of cattle could appear only in the
oflsprini^ when nearly mature ; peculiarities in the silkworm
are known to appear at the corrcsjoondinf^ caterpillar or cocoon
staple. But hereditary diseases and some other facts make mc
believe that the rule has a Avider extension, and that, when
there is no apparent reason why a peculiarity should appear at
any particular ai^e, yet that it does tend to appear in the off-
spring at the same period at which it first appeared in the par-
ent. I believe this rule to be of the hig-hest importance in
explaining- the laws of embryology. These remarks are of
course confined to the first appearance of the peculiarity, and
not to its primary cause, which may have acted on the ovules
or on the male element ; in nearly the same manner as in the
ofi'spring- from a short-horned cow by a long-horned bull, the
greater length of horn, though appearing late in life, is clearly
due to the male element.

Having alluded to the sul)ject of reversion, I may here refer
to a statement often made by naturalists — namely, that our
domestic varieties, "when rim Avild, gradually but invariably re-
vert 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 Avould be great difli-
cidiy 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
Avhat the aboriginal stock was, and so could not tell whether
or not nearly perfect reversion had ensued. It Avould be ne-
cessary, 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
i-evert in some of their characters to ancestral forms, it seems
to mc not improbable, that, if we could succeed in naturalizing,
or were to cultivate, duringmany generations, the several races,
for instance, of the cabbage, in very poor soil (in which case,
however, some effect would have to 1)C attributed to the definite
action of the poor soil), 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 imjiortance
for our line of argument ; for by the experiment itself the con-
ditions of life are chanixed. If it couUl be sliown that our do

CuAr. I. UNDER DOMESTICATION. 29

incstic 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 considerable body, so that
free intercrossin2^ mig-ht 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 we could not breed our cart and race horses, long
and short horned cattle, and poultry of various breeds, and
esculent vegetables, for an unlimited number of generations,
would be opposed to all experience.

Character of Domestic Varieties ; Difficult}/ of distinguish-
inff heticeen Varieties and Species y Origin of Domestic
Varieties from one or more /Sjjecies.

When we look to the hereditary varieties or races of our
domestic animals and plants, and compare them with closely-
alUed species, wc generally perceive in each domestic race, as
already remarked, less uniformity of character than in true
species. Domestic races often have a somewhat monstrous
character ; by which I mean that, although differing from each
other, and from f)thcr species of the same genus, in several
trifling res]iects, 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
witli 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, only in most cases in a less de-
gree, in the same manner as do closely-allied species of the
same genus in a state of natiu-e. This must be admitted as
true, for the domestic races of many animals and plants have
•been rank(!d by some competent judges as the descendants of
aboriginally distinct species, and by other competent judges as
mere varieties. If any well-marked distinction existed be-
tween a domestic race and a species, this source of doubt
would not so perpetually recur. It has often been stated that
domestic races do not diffcT from each other in characters of
generic value. It can ])e shown that this statement is not cor-
rect; but naturalists differ nuich in determining what char-
acters are of gimerio value ; all such valuations being at
present empirical. When it is explained how genera origi-
nate under nature, it will bo seen that we have no right to

so CIIAEACTEK OF Ciiap. 1.

expect often to find a generic amount of difference in our do-
mesticated races.

In attempting to estimate tlie amount of structural difler-
encc between the domestic races of the same species, we are
soon involved in doubt, from not knowing whether they have
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 grevhound, bloodhound, terrier,
spaniel, and bull-dog, which we all know propagate their kind
so 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 very closely-allied natural species —
for instance, of the many foxes — inhabiting different quarters
of the Avorld. I do not believe, as we shall presently see, that
the whole amount of difference between the several breeds of
the dog has been produced under domestication ; I believe
that some small part of the difference is due to their having
descended from distinct species. In the case of strongly-
marked races in some other domesticated species, there is
presumptive, or even strong, evidence that all are descended
from a single wild stock.

It has often been assumed that man has chosen for domes-
tication animals and plants having an extraordinary inherent
tendency to var}^, and likewise to withstand diverse climates.
I do not dispute that these capacities have added largely to
the value of most of our domesticated productions ; but how
could a savage possibly know, when he first tamed an animal,
M'hether it would vary in succeeding generations, and whether
it would endure other climates ? Has the little variability of
the ass and goose, or the small power of endurance of warmth
by the reindeer, or of cold by the common camel, prevented
their domestication ? I cannot doubt that if other animals and
plants, equal in number to our domesticated productions, and
belonging to equally diverse classes and countries, were taken
from a state of nature, and could be made to breed for an equal
number of generations under domestication, they would on an
average vary as largely as the parent-species of our existing
domesticated productions have varied.

In the case of most of our anciently-domesticated animals
and jilants, it is not possible to come to any definite conclusion,
whether they are descended from one or several wild species.
The argiunent mainly relied on by those who believe in the
multiple origin of our domestic animals is, that we find in the

Chap. I. DOMESTIC VARIETIES. 31

most ancient times, on tlie 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 ani-
mals Avere domesticated at a much earlier period than has hith-
erto l>een supposed. The lake-inhabitants of Switzerland cul-
tivated several kinds of wheat and barley, the pea, the poppy
t\)v oil, and llax ; and they possessed several domesticatcnl ani-
mals ; they had also commerce with other nations. All this
clearly shows, as Heer has remarked, that they had at this
early ag-c progressed considerably in civilization ; and this
again implies a long-continued previous period of less advanced
civilization, during which the domesticated animals, kept by
the different tribes in different districts, might have varied and
given rise to distinct races. Since the discovery of flint tools
or celts in the superficial formations in many parts of the world,
all geologists believe that barbax-ian man existed at an enor-
mously remote period ; and we know that at the present day
there is hardly a tribe so barbarous as not to have domesti-
cated at least the dog.

The origin of most of our domestic animals will probably
forever remain vague. But I may here state that, looking
to the domestic dogs of the Avholc world, I have, after a la-
borious collection of all known facts, come to the conclusion
that several wild species of Canidre have been tamed, and that
their blood, in some cases mingled together, llows in the A-eins
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 they are de-
scended 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 those
deserve to be called species or races. This conclusion, as Avell
as the specific distinction between the humped and common
cattle, may, indeed, be looked at as established by the recent
admirable researches of Prof. Kutimeyer. With respect to
horses, from reasons which I cannot here give, I am doubtfully
inclined to believe, in opposition to several authors, that all the
races belong to the saine species. Having kept nearly all the
English breeds of the fowl alive, having bred and crossed them,
and examined their skeletons, it appears to me almost certain

32 CU^AKACTER OF Chap.*.

that all are the descendants of the wild Indian fowl, Gallus
bankiva; and Ihis is tlie conclusion of Mr. Bljth, and of others
who have studied this bird in India. In reg'ard to ducks and
rabbits, some breeds of which difler much from each otiier, the
evidence is clear that they arc all descended from the common
wild duck and rabbit.

The doctrine of the origin of our several domestic races from
several aborig'inal stocks, has been carried to an absurd ex-
treme by some authors. They believe that every race which
breeds true, let the distinctive characters be ever so slight,
has had its wild protot^qDe. At this rate, there must have ex-
isted at least a score of species of wild cattle, as many sheep,
and several goats, in Europe alone, and several even within
Great Britain. One author believes that there formerly existed
in Great Britain eleven wild species of sheej? peculiar to it !
When v,e bear in mind that Britain has now hardly one pecu-
liar mammal, and France but few distinct from those of Ger-
many, and conversely, and so with Hungary, Spain, etc., but
that each of these kingdoms possesses several peculiar breeds
of cattle, sheep, etc., we must admit that many domestic breeds
have originated in Europe ; for whence have they been derived,
as these several countries could not possess so large a number
of peculiar species for parent-stocks ? So it is in India. Even
in the case of the domestic dogs of the whole world, which I
admit to have descended from several wild species, it cannot be
doubted that there has been an immense amount of inherited
variation ; for who will believe tliat animals closely resembling
the Italian greyhound, the bloodhound, the bull-dog, pug-dog,
or Blenheim spaniel, etc. — so xmlike all Avild Canida? — ever ex-
isted freely 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 Ave can
only get forms in some degree intermediate between their par-
ents ; and if we account for our several domestic races by this
process, we must admit the former existence of the most ex-
treme forms, as the Italian greyhound, bloodhound, bull-dog,
etc., in the wild state. Moreover, the possibility of making
distinct races by crossing has been greatly exaggerated. Many
cases are on record, showing that a race may be modified by
occasional crosses, if aided by the careful selection of the in-
dividuals which present the desired character; but to obtaui a
race nearly intermediate between two extronely dilTerent races
or species, would be very dillicult. Sir J. Sebright expressly

CnAP. I. DOMESTIC VARIETIES. 33

experimented for this object, and failed. The oflspriii^v from
the first cross between two pure breeds is tolerably and some-
times (as I have found with pip^eons) extremely uniform, and
every thing seems simple enouji-h ; but when these mongrels
are crossed one "with another for several generations, hardly
two of them are alike ; and then the extreme dilEculty of the
task becomes apparent. Certainly, a breed intermediate be-
tween tico very distinct breeds could not be got without ex-
treme care and long-continued selection ; nor can I find a case
on record of a permanent race having been thus formed.

Breeds of the Domestic Pigeon, their Differences and Origin.

Belie\ing that it is alwa^'S best to study some special group,
I have, after deliberation, taken up domestic pigeons. I have
kept every breed whieli I could purchase or obtain, and have
lieen most kindly fav(^red with skins from several quarters of
the world, more especially by the Hon. W. Elliot from India,
and by the Hon. C. Murray from Persia. Many treatises in
different languages have been published on pigeons, and some
of them are very important, as being of considerable antiquity.
I have associated witli several eminent fanciers, and have been
permitted to join two of the London Pigeon Clubs. The diver-
sity of the breeds is something astonishing. Compare the Eng-
lish carrier and the short-faced tumbler, and see the Avonderful
difference in tlieir beaks, entailing corresponding differences in
tlieir skulls. The carrier, more especially the male bird, is also
remarlvable from the wonderful development of the caruncu-
lated skin about the head; and this is accompanied by greatly-
elongated eyelids, very large external orifices to the nostrils,
and a wide gape of mouth. The short-faced tumbler has a
b(>ak in outline almost like that of a finch; and the common
tuin])ler has the singular inherited habit of flying at a great
height in a compact flock, and tumbling in the air head over
heels. The runt is a bird of great size, with long, massive beak
and large feet ; some of tlie sub-ljreeds of runts have very long
necks, others very long Avings and tails, others singularly short
tails. The barb is allied to the carrier, but, instead of a long
beak, has a very short and broad one. The ])outer has a much-
elongated body, wings, and legs ; and its enormously devel-
oped crop, which it glories in inllating, may well excite aston-
ishment and even laughter. The turbit has a very short and
conical beak, with a line of reversed feathers down the breast;

34 DOMESTIC PIGEONS. Chap. I.

and it has the hal)it of continually expanding slightly the up-
per part of tlie a?so2:)hagus. The Jacobin has the feathers so
much reversed along the back of the neck that the}' form a
hood ; and it has, proportionally to its size, much-elongated
wing and tail feathers. The trumpeter and laugher, as their
names express, utter a very different coo from the otlier breeds.
The fantail has thirty or even forty tail-feathers, instead of
twelve or fourteen — the normal number in all members of the
great pigeon family ; and 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 dis-
tinct breeds might be specified.

In the skeletons of the several breeds, the development of
the bones of the face in length and breadth and curvature dif-
fers enormously. The shape, as Avell 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 mouth, the proportional
length of the eyelids, of the orifice of the nostrils, of the tongue
(not always in strict correlation with the length of beak), the
size of the crop and of the upper part of the ccso})liagus ; the
development and abortion of the oil-gland ; the number of the
primary wing and caudal feathers ; the relative length of wing
and tail to each other and to the body ; the relative length of leg
and of the feet ; the number of scutcHa^ on the toes, the develop-
ment of skin between the toes, arc all points of structure -which
are variable. The period at which the perfect plumage is ac-
quired, varies, as does the state of the do^^^l with which the nest-
ling birds are clothed when hatched. The shape and size of the
eggs vary. The manner of flight, and in some breeds the voice
and disposition, differ remarkably. Lastly, in certain breeds, the
males and females have come to dilVer 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-de-
fined species. Moreover, I do not believe that any ornitliolo-
gist would place the English canicr, the short-faced tumbler,
the runt, tlic barb, pouter and fantail in the same genus;

Chat. I. DOMESTIC TIGEONS. ,35

more especially as in each of these breeds several truly-inher-
ited sub-breeds, or s2Dccies as he would have called them, could
be shown him.

Great as the differences are between the breeds of pigeons,
I am fully convinced that the common opinion of naturalists
is correct, namely, that all are descended from the rock-pigeon
(Columba livia), including under this term several geograplii-
cal races or sul>specics, Avhich 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 Ijricfly give them. If the several breeds are
not varieties, and have not proceeded from the rock-pigeon,
they must have descended from at least seven or eight abori-
ginal 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 enonnous
crop? The supposed aboriginal stocks must all have been
rock-pigeons, that is, not breeding or willingly perching on
trees. But besides Columba livia, Avith its geographical sub-
species, only two or three other species of rock-pigeons are
known ; and these have not any of the characters of the
domestic breeds. Hence the supposed aboriginal stocks must
either still exist in the countries where they were originally
domesticated, and yet be unknown to ornithologists ; and this,
considering their size, habits, and remarkable characters, seems
improbable ; or they must have become extinct in the wild
state. But birds breeding on precijiices, and good fliers, are
unlikely to be exterminated ; and the common rock-pigeon,
which has the same habits with the domestic breeds, has not
been exterminated even on several of the smaller British isiecs,
or on the shores of the Mediterranean. Hence the supposed
extermination of so many species having similar habits with
the rock-pigeon seems a very rash assumption. Moreover,
the several above-named domesticated breeds have been trans-
ported to all parts of tlie world, and, therefore, some of them
must have been carried back again into their native country;
but not one has ever become wild or feral, though the dovecot-
pigeon, which is the rock-pigeon in a very slightly altered
state, has become feral in several places. Again, all recent
experience shows that it is difficult to get any wild animal to
breed freely imder domestication : yet, on the hypothesis of tlie
multiple oritrin of our pigeons, it must be assumed that at least

36 ^ DOMESTIC PIGEONS. Chap. I.

seven or eight species were so thoroughly domesticated in
ancient times by half-civilized man, as to be quite prolific un-
der confinement.

An argument of grcat_ weight, and applicable in several
other cases, is, that the above-specified breeds, though agree-
ing generally with the wild rock-pigeon in constitution, habits,
voice, coloring, and in most parts of their structure, yet are
certainly highly abnormal in other parts ; we may look in vain
throughout the whole great family of Columbida? for a beak
liUe that of the English carrier, or that of the short-faced tum-
bler, or barb; for reversed feathers like those of the Jacobin;
for a crop like that of the pouter; for tail-feathers like those
of the fantail. Hence it must be assumed, not only that half-
civilized man succeeded in thoroughly domesticating several
species, but that he intentionally or by chance picked out ex-
traordinarily abnormal species ; and further, that these very
species have since all become extinct or unknown. So many
strange contingencies are improbable in the highest degree.

Some facts in regard to the coloring of pigeons Avell de-
serve consideration. The rock-pigeon is of a slaty-blue, with
white loins ; the Indian sub-species, C intermedia of Strick-
land, having this part bluish ; the tail has a terminal dark bar,
with the outer feathers externally edged at the base with
white ; the wings have two black bars. Some semi-domestic
breeds, and some truly wild breeds, have," besides the two
black bars, the wings checkered with black. These several
marks do not occur together in any other species of the Avhole
family. Now, in every one of the domestic breeds, taking
thoroughly well-bred birds, all the above marks, even to the
white edging of the outer tail-feathers, sometimes concur per-
fectly developed. Moreover, when birds belonging to two or
more distinct breeds are crossed, none of Avhich 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 Avhich notoriously breeds very
true ; the mongrels were dusky and mottled. I then crossed
one of the mongrel barb-fanlails with a mongrel barb-spot, and

Chap. I. DOMESTIC PIGEONS. 37

tlicy produced a bird of as beautiful a bhie color, with the
white loius, double black Aviiif^-bar, and barred and Avliite-
ed^cd tail-feathers, as any wild rock-pi2;'eon ! We can under-
stand these facts, on the well-known principle of reversion to
ancestral characters, if all the domestic breeds are descended
from the rock-])igeoii. ]}ut if we deny this, we must make
one of the two following; highly improbable suppositions :
cither, 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 with-
in a score, of generations, been crossed by the rock-pigeon :
I say within a dozen or twenty generations, for no instance
is known of crossed descendants reverting to an ancestor
of foreign' blood, removed by a greater nmnbcr of genera-
tions. In a breed which has been crossed only once, the
tendency to revert to any character derived from such a cross
will naturall}'^ become less and less, as in each succeeding
generation there will be less of the foreign blood ; but when
there has been no cross, and there is a tendency in the breed
to revert to a character which was lost during some former
generation, this tendency, for all that we can see to the contrary,
may be transmitted imdiminishcd for an indefinite nunil)er of
generations. These two distinct cases of reversion are often
confounded together by those who have Avritten on inheritance.

Lastly, the hybrids or mongrels from between all the
domestic breeds of pigeons are perfectly fertile. I can state
this from my own oljservationR, purposely made, on the most
distinct breeds. Now, it is diflicult, perhaps impossible, to
bring forward one case of the hybrid offspring of two animals
clenrbj distbict being themselves perfectly fertile. Some
authors believe that long-continu(?d domestication eliminates
this strong tendency to sterilily: from the histor}' of tlie dog,
and of some other domestic animals, there is great probability
in this hypothesis, if applied to species closely related to each
other, thougli it is imsupported by a single experiment. But
A.O extend the h^11otIlesis so far as to suppose that sjx'cies,
aboriginally as distinct as carriers, tumblers, pouters, and fan-
tails now are, should yield offspring perfectly fertile inter se^
seems to me rash in the extreme.

From these several reasons, namely, the improbability of

38 DOMESTIC PIGEONS. Chap. I.

man having formerly got seven or eight supposed species of
pigeons to breed freely under domestication ; these supposed
species being quite unknown in a ■wild state, and their be-
coming nowhere feral ; these species having very al^normal
characters in certain respects, as conijoared with all other Co-
lumbida?, thougli so like in most other respects to the rock-
pigeon ; the bkic color and various black marks occasionally
apjiearing in all the breeds, both when kept pure and when
crossed ; the mongrel offspring being perfectly fertile — from
these several reasons, taken together, we may safely conclude
that all our domestic breeds have descended from the Columba
livia Avith its geographical sub-species.

In favor of this view, I may add, first, that C. livia, or the
rock-pigeon, has been found capable of domestication in Europe
and in India ; and that it agrees in habits and in a great num-
ber of points of structure with all the domestic breeds. Second-
ly, although an English carrier or a short-faced tumbler differs
immensely in certain characters from the rock-pigeon, yet by
comparing the several sub-breeds of these varieties, more
especially those brought from distant countries, we can make
in these two cases, and in some but not in all other cases,
an almost perfect series between the extremes of stlncture.
Thirdly, those characters which are mainly distinctive of each
breed, for instance the wattle and length of beak of the car-
rier, the shortness of that of the tumbler, and the number of
tail-feathers in the fantail, ai'C in each breed eminently variable;
and the explanation of this fact Avill be obvious Avhcn we come
to treat of Selection. Fourthly, pigeons have been Avatched
and tended Avith the utmost care, and loved by many people.
They liaA'C been domesticated for thousands of years in several
quarters of the Avorld ; the earliest knoAvn record of pigeons
is in the fifth Eg^-ptian dynasty, about 3000 B. c, as Avas
pointed out to me by Prol; Lcpsius ; 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 AA'e hear from Pliny,
immense prices Averc giAxn for pigeons ; " nay, they are come
to this pass, that they can reckon up their pedigree and race."
Pigeons Avere much A'alued by Akbar Ivlian in India, about
the j-ear IGOO; never less than 20,000 pigeons Avere taken
Avith the tourt. " The monarchs of Iran and Turan sent him
some very rare birds;" and, continues the courtly historian,
" his Majesty by crossing the breeds, Avhich method Avas ncA'cr
practised before, has improved them astonishingly." About

Chap. I. DOMESTIC PIGEONS. 39

this saino period the Dutch were as easier about pigeons as
were the old Romans. The paramount importance of these
considerations in explainini^ the immense amount of variation
Avhich pigeons have undcr2;one, will be obvious when Ave treat
of Selection. We shall then, also, see how it is that the
several breeds so often have a somewhat monstrous character.
It is also a most 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 tlie probable origin of domestic pigeons
at some, yet quite insufiieient, length ; because when I first
kept pigeons and watched the several kinds, avcU knowing how
truly they breed, I felt fully as mucli dilliculty in believing
that since they had been domesticated they had all proceeded
from a common parent, as any naturalist could in coming to
a similar conclusion in regard to the many species of finches,
or other groups of birds, in nature. One circumstance has
struck me much ; namely, that nearly all the breeders of the
various domestic animals and the cultivators of plants, v/ith
whom I have conversed, or Avhose treatises I have read, are
firmly convinced that the several breeds to Avhich each has
attended, are descended from so many aboriginally distinct
species. Ask, as I have asked, a celebrated raiser of Here-
ford cattle, whether his cattle might not have descended from
Long-horns, or both from a common parent-stock, and he Avill
laugh you to scorn, I have never met a pigeon, or })oultry,
or duck, or rabljit fancier, Avho 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 tlie several sorts, for instance a Ribston-
pippin or Codlin-apple, could ever have proceeded from the
seeds of the same tree. Innumerable other examples could
be given. The explanation, I think, is simple : from long-
continued study they are strongly impressed with the differ-
ences between the several races ; and though they well know
that each race varies slightly, for they win their prizes by
selecting such slight differences, yet they ignore all general
arguments, and refuse to sum u[) in their minds slight differ-
ences accumulated during many successive generations. May
not those naturalists who, knowing far less of the laws of
inheritance than does the breeder, and knowing no more than
be docs of the intermediate links in the long lines of descent,

40 SELECTION BY MAN. Cn.sr. I.

yet admit that many of our domestic races are descended from
the same parents — may they not learn a lesson of caution,
when tlicy deride the idea of species in a state of nature being
lineal descendants of other species ?

Princi2>les of Selection anciently foUoiccd, and their Effects.

r^et us now briefly consider the steps by which domestic
races have been produced, either from one or from several
allied species. Some elTect may be attributed to the direct
and definite action of the external conditions of life, and some
little to habit ; but he would be a bold man who would ac-
count by such agencies for the differences between a dray and
race horse, a greyhound and bloodhound, a carrier and tumbler
jiigeon. One of the most remarkable features in our domesti-
cated 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 suddenl}-, or by
one step ; many botanists, for instance, ])elieve that the fuller's
teasel, with its hooks, which cannot be rivalled by any mechan-
ical 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 tlie turnspit-tlog ; and tliis is
known to have been the case with the ancon sheep. But when
we compare the dray-horse and race-horse, the dromedary and
camel, the various breeds of sheep fitted either for cultivated
land or mountain-pasture, with the wool of one breed good for
one purpose, and that of another breed for another purpose ;
when we compare the many breeds of dogs, each good for man
in very different ways ; when we compare the game-cock, so
pertinacious in battle, with other breeds so little quarrelsome,
with "everlasting layers" which never desire to sit, and Avith
the bantam so small and elegant ; w^hen we compare the host
of agricultural, culinary, orchard, and flower-garden races of
plants, most useful to man at dillerent seasons and for differ-
ent purposes, or so beautiful in his eyes, we must, I think,
look fi'rther than to mere variability. "We cannot sup]")ose
that all the breeds were suddenly produced as perfect and as
useful as we now see them ; indeed, in many cases, we know
that this has not been their history. The key is man's ])ower
of accumulative selection: Nature gives successive variations;
man a<lds them up in certain directions useful to him. In tliig
sense he may be said to have made for himself useful breeds.

Chap. I. SELECTION BY MAN. 41

Tlie great poAVcr of tliis j^rinciple of selection is not hj-
potlietical. It is certain that several of our eminent breeders
nave, even within a single lifetime, modilied to a large extent
the breeds of cattle and sheep. In order fully to realize -what
they have done, it is almost necessary to read several of the
many treatises devoted to this subject, and to inspect the ani-
mals. Breeders habitually speak of an animal's organization
as something quite plastic, which they can model almost as
thcv 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 agricultu-
rists than almost any other individual, and who was himself a
very good judge of an animal, speaks of the principle of selec-
tion as " that Avliich enables the agriculturist, not only to mod-
ify the character of his flock, but to change it altogether. It
is the magician's wand, by means of which he may summon
into life whatever form and mould he pleases." Lord Somer-
ville, speaking of what breeders have done for sheep, says :
" It would seem as if they had chalked out upon a -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 arc studied, like a picture by
a connoisseur ; this is done three times at intervals of months,
and the sheep are each time marked and classed, so that the
very best may ultimately be selected for breeding.

What English breeders have actually eifectecl is proved by
the enormous prices given for animals with a good pedigree ;
and these have now been exported to almost every quarter of
the world. The imjirovement is by no means generally due
to crossing diilerent breeds ; all the best breeders are strongly
opposed to this practice, except sometimes among closely-al-
lied sub-breeds. And when a cross has been made, the closest
selection is far more indispensable even than in ordinary cases.
If selection consisted merely in separating some very distinct
variety, and breeding from it, the princi^Dlc would be so obvi-
ous as liardly to be worth notice ; but its imjiortance consists
in the great edec't produced by tlie accumulation in one direc-
tion, during successive generations, of diiferences absolutely
inappreciable by an imeducated e^-c — diflerences which I for
one have vainly attempted to appreciate. Not one man in a
thousand has accuracy of eye and judgment sufficient to be-
come an eminent breeder. If gifted with these qualities, and

io SELECTION BY MAN. Ca.vr. 1,

lie studies his subject for years, and devotes his lifetime to it
witli indomitable ])erscverance, he "sviU succeed, and may make
great improvements ; if he wants any of these qualities, he aa'III
assuredly fail. Few -would readily believe in the natural ca-
pacity and years of practice requisite to become even a skilful
pigeon-fancier.

The same principles are followed by horticulturists ; but the
variations are here often more abrupt. No one supposes that
our choicest productions have been produced by a single vari-
ation from the aboriginal stock. "W^e have proofs that this is
not so in some cases in Avhich exact records have been kept :
thus, to give a very trifling instance, the steadily-increasing
size of the common gooseberry may be quoted. We see an
astonishing improvement in many florists' flowers, when the
flowei'S of the present day are compared with drawings made
only twenty or thirty years ago. When a race of plants is
once pretty Avell 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
]iroper standard. With animals this kind of selection is, in
fact, also followed ; for hardly any one is so careless as to
allow his Avorst animals to breed.

In regard to plants, there is another means of observing the
accmnulated 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 compari-
son with the flowers of the same varieties ; and the diversity
of fruit of the same species in the orchard, in comparison with
the leaves and flowers of the same set of varieties. See how
different the leaves of the cabbage are, and how extremely
alike the flowers ; how unlike the flowers of the heart's-ease
are, and how alike the leaves ; how much the fruit of the dif-
ferent kinds of gooseberries differ in size, color, shape, and
hairiness, and yet the flowers present very slight differences.
It is not that tlie 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.
Tlie law of correlated variation, the importance of which should
never be overlooked, will insure some diflerences ; but, as a
general rule, I cannot doul)t that the continued selection of
slight v:iriations, either in the leaves, the flowers, or the fruit,
will produce races dillering from each other chiefly in these
characters.

Chap. I UNCONSCIOUS SELECTION. 43

It may be objected that the principle of selection has been
reduced to methodical practice ibr scarcely more than three-
quarters of a century ; it has certainly been more attended to
of late years, and many treatises have been published on the
subjc^ct ; and the result has been, in a correspondinjr degree, rapid
and important. But it is very far from true that the jjrinciple is
a modern discovery. I could give several references to the full
acknowledgment of the importance of the principle in woiks
of higli anti(iuity. In rude and barbarous periods of English
history, choice animals -were often imported, and laws were
passed to prevent their exportation : the destruction of horses
imdcr a certain size was ordered, and this may be comjiared
to tlic " roguing " of plants by nurserymen. Tlic principle of
selection 1 lind distinctly given in an ancient Chinese encyclo-
pajdia. Exjilicit 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 draught^cattle by color, as do some of the PJsqui-
maux their teams of dogs. Livingstone states that good do-
mestic breeds arc highly valued by the negroes in the interior
of Africa who have not associated with Euroj^eans. Some of
these facts do not show actual selection, but they show that
the breeding of domestic animals was carefully attended to in
ancient times, and is now attended to by the lowest savages.
It would, indeed, have been a strange fact, had attention not
been paid to breeding, for the inheritance of good and bad
qualities is so obvious.

Unconscious Selection.

At the present time, eminent breeders try by methodical
selection, with a distinct object in view, to make a new strain
or sul>breed, superior to any thing existing in the country.
But, for our purpose, a kind of Selection, which may be called
Unconscious, and which results frojn every one trying to pos-
sess and breed from the best individual animals, is more im-
portant. Thus, a man who intends keeping pointere naturally
tries to get as good dogs as he can, and afterward breeds from
his own best dogs, but he has no wish or exjiectation of per-
manently altering the breed. Nevertheless, we may infer that

(4 DNCONSCIOUS SELECTION. Ciiai-. I.

Iliis process, continued during centuries, Avould improve and
modify any I)recd, in the same "way as Bakeivell, Collins, etc.,
by this very same process, only carried on more metliodically,
did greatly modify, even during their own lifetimes, the forms
and qualities of their cattle. Slow and insensible changes of
this kind could never be recognized unless actual measure-
ments or careful drawings of the breeds in cjuestion had been
made long ago, which might serve for comparison. In some
cases, however, imchanged or but little changed individuals
of the same breed may be found in less civilized districts,
Avhere the breed has been less improved. There is reason to
believe that King Charles's spaniel has been unconsciously
modified to a large extent since the time of that monarch.
Some highly-competent authorities are convinced that the
setter is directly derived from the spaniel, and has 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 elfected
by crosses Avith the fox-hound ; but what concerns us is, that
the change has ]:)ccn elTccted unconsciously and gradually, and
yet so eifectually, that, thougli the old Spanish pointer cer-
tainly came from Spain, Mr. Boitow 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,
the whole body of English race-horses have come to surpass
in fleetness and size the parent Arab stock, so that the latter,
1)}' the regulations for the Goodwood Races, are favored in the
Aveights tlicy carry. Lord Sjicncer 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 old pigeon
treatises of carriers ami tumblers with these breeds as now
existing in Britain, India, and Persia, Ave can, I think, clearly
trace the stages through Avhich they have insensibly passed,
and come to dilfer so greatly from the rock-pigeon.

Youatt gives an excellent illustration of the effects of a
course of selection, AA-hich may be considered as unconsciously
followed, in so far that the breeders could never have expect-
ed, or even have A\ished, to produce the result Avliich ensueil —
namely, the production of tAvo distinct strains. The two Hocks
of Leicester sheep ke])t by Mr. Buckley and INIr. Burgess, as
Mr. Youatt remarks, " have been purely bred from the original
stock of Mr. Bakewell for upAvard of lifty years. There is not

Ci.vr. I. UNCONSCIOUS SELECTION. 45

a suspicion existing in the mind of any one at all acquainted
with the subject, that the owner of cither of them has deviated
in any one instance from tlie pure blood of Mr. BakewcU's
flock, and yet the difference between tlie sheep possessed by
these two f^entlemen is so f^reat that they have the appear-
ance of being quite difl'erent varieties."

If there exist savages so barbarous as never to think of
the inherited character of the offspring of their domestic ani-
mals, yet any one animal particularly useful to them, for any
special purpose, would be carefully preserved during famines
and other accidents, to Avhich savages are so liable, and such
choice animals would thus generally leave more offspring than
the inferior ones ; so that in this case there would be a kind *
of unconscious selection going on. We see the value set on
animals even by the barbarians of Tierra del Fuego, by their
killing and devouring their old women, in times of dearth, as
of less value than their dogs.

In plants the same gradual process of improvement, through
the occasional preservation of the best indi\4duals, whether or
not sufBciently distinct to be ranked at their first appearance
as distinct varieties, and whether or not two or more species
or races have become blended together by crossing, may plainly
be recognized in the increased size and beauty which we now
see in the varieties of the heart's-easo, rose, pelargonium,
dahlia, and other plants, when compared \\-ith the older varie-
ties or with their parent-stocks. No one would ever expect
to get a first-rate heart's-ease or dahlia from the seed of a wild
plant. No one would expect to raise a first-rate melting ]jear
from the seed of the wild pear, though he might succeed from
a poor seedling growing wild, if it had come from a garden-
stock. The pear, though cultivated in classical times, appears,
from Pliny's description, to have been a fruit of very inferior
quality. I have seen great surprise expressed in horticultm-al
works at the wonderful skill of gardeners, in having produced
such splendid results from such poor materials ; but the art
has been simple, and, as far as tlie final result is concerned,
lias been followed almost unconsciously. It has consisted in
always cultivating the best-known variety, sowing its seeds,
antl, when a sliglitly-better variety has chanced to appear,
selecting it, and so onward. But the gardeners of the classi-
cal period, who cultivated the best pear they could procure,
never thought Avhat splendid fruit we should eat; though wo.
owe our excellent fruit, in some small degree, to their having

to UNCONSCIOUS SELECTION. Chap. I.

naturally chosen and preserved the best varieties they could
anywhere inid.

A laro-e amount of chang'c in our cultivated plants, thus
slowly and unconsciously accumulated, explains, as I 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. If it has taken centuries or thousands
of 3'^ears 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 aiforded us
a single plant worth culture. It is not that these countries, so
rich in species, do not by a strange chance possess the abori-
ginal stocks of any useful plants, but that the native plants
have not been improved by continued selection up to a stand-
ard of perfection comparable with that given to tiie plants in
countries anciently civilized.

In regard to the 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 diifcrently circumstanced, individ-
\ials of the same species, having slightly-different constitutions
or structure, would often succeed better in the one country
than in the other; and thus by a process of "natural selec-
tion," as will hereafter be more fully explained, two sub-breeds
might be formed. This, perhaps, partly explains Avhat has
been remarked by soiiic authors, namely, that the varieties
kept by savages have more of the character of species than
the varieties kept in civilized countries.

On the view here given of the all-important part which
selection by man has played, it becomes at once ob\-ious how
it is that our domestic races show adaptation in their stnicture
or in their habits to man's wants or fancies. We can, I think,
further understand the frequently-abnormal character of our
domestic races, and likewise their differences being so great
in external characters, and relatively so slight in internal parts
or organs. Man can hardly select, or only with much dilhculty,
any deviation of structure, excepting such as is externally vis-
ible ; and indeed he rarely cares for what is internal. He can
never act l)y selection, excepting on variations which are first
given to him in some slight degree by Nature. No man would
ever try to make a fantail till he saw a pigeon with a tail de-

CiiAr. I. UNCONSCIOUS SELECTION. 47

veloped in some slis^lit degree in an unusual manner, or a
pouter till lie saw a pi<j^eon -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 expression as trying to make
a fantail, is, I have no doubt, in most cases, utterly incorrect.
The man Avho first selected a pigeon with a slightly-larger
tail, never dreamed what the descendants of that pigeon would
ht'come through long-continued, partly-unconscious and parti y-
nicthodical selection. Perhaps the parent-bird of all fantails
had only fourteen tail-feathers somewhat expanded, like the
jircsent Java fantail, or like individuals of other and distinct
breeds, in which as many as seventeen tail-feathers have been
counted. Perhaps tlie first pouter-pigeon did not inflate its
crop much more than the turbit now does the upper part of its
ccsojihagus-^a habit which is disregarded by aU fanciers, as it
is not one of the points of the breed.

Nor let it be thought that some great de\'iation 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 be set on any slight
differences in the individuals of the same species, be judged of
by the value which would now be set on them, after several
])reeds have once fairly been established. Many slight differ-
ences might, and indeed do now, arise among pigeons, which
are rejected as faults or deviations from the standard of per-
fection of each breed. The common goose has not given rise
to any marked varieties; hence the Toulouse and the common
breed, Avhich differ only in color, that most fleeting of char-
acters, have lately been exhibited as distinct at our poultry-
shows.

I think those views explain what has sometimes been
noticed — namely, that we know nothing about the origin or
history of any of our domestic breeds. But, in fact, a breed,
like a dialect of a language, can hardly be said to have a dis-
tinct 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 imjiroves them,
and the improved animals slowly spread in the immediate
neighborhood. But as yet they will hardly have a distinct
name, and, from being only slightly valued, their history will
be disregardt>d, ^^''hen further improved by the same slow

48 CIRCUMSTANCES FAVORABLE TO SELECTION. Chap. I.

and gradual process, tliey will spread more widely, and will get
recognized as sometliing 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 in a new strain are once acknowledged, the principle,
as I have called it, of unconscious selection will always tend — per-
haps 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 inhabitants — slowly
to add to the characteristic features of the breed, whatever
they may be. But the chance may be infinitely small of any
record having been jireserved of such slow, varying, and insen-
sible changes.

Circumstances favorable to Mail's Power of Selection.

I must now say a few words on the circumstances, favor-
able, or the reverse, to man's power of selection. A high de-
gree of variability is obviously favorable, as freely giving the
materials for selection to work on ; not that mere individual
differences are not amply sufficient, with extreme care, to allow
of the 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 indi-
viduals being kept ; and hence tliis comes to be of the highest
importance to success. On this principle Marshall formerly
remarked, with respect to the sheep of parts of Yorkshu-e, that,
" as they generally belong to poor people, and are mostly in
small lots, they never can l)e improved." On the other hand,
nurservmen, from raising large stocks of the same plants, arc
generally far more successful than amateurs in getting new
and valuable varieties. The keejiing of a large number of in-
dividuals of a species in any country requires that the species
should be placed under favorable conditions of life, so as to
breed freely in that countr>', A\^hcn the indi\'iduals of any
species are scanty, all the individuals, whatever their quality
may be, will generally be allowed to l)reed, and this will effect-
ually prevent selection. But probably the most important
point of all is, that the animal or plant should be so highly
useful to man, or so much valued hy him, that tlie closest at-
Irntion is paid to even the slightest dmiation in the qualities

Chap. I. CIRCUMSTANCES FAVORABLE TO SELECTION. 49

or structure of each individual. Unless such attention be paid
nothinf^ can be effected. I have seen it gravely remarked, that
it was most fortimate that tlic strawberry began to vary just
when gardeners began to attend closely to this plant. No doubt
the strawberry had always varied since it was cultivated, but
the slight varieties had been neglected. As soon, however,
as gardeners picked out individual plants with slightly larger,
earlier, or better fruit, and raised seedlings from them, and
again })ickcd out the best seedlings and bred from them, then,
there appeared (aided by some crossing with distinct species)
those many admirable varieties of the strawberry which have
been raised during the last thirty or forty years.

In the case of animals with separate sexes, facility in pre-
venting crosses is an important element of success in the for-
mation of new races — at least, in a country which is already
stocked with -other races. In this respect, enclosure of the
land plays a part. Wandering savages or the inhabitants of
open plains rarely possess more than one breed of the same
species. Pigeons can be mated for life, and this is a great
convenience to the fancier, for thus many races may be im-
proved and kept true, 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 tliey serve for food. On the
other hand, cats, from their nocturnal rambling habits, cannot
be easily matched, and, although so much valued by women
and children, we hardly ever see a distinct breed kept up ; such
breeds as we do sometimes sec are iilmost always imported
from some other country. Although I do not doubt that some
domestic animals vary less than others, yet the rarity or ab-
sence of distinct l)reeds of the cat, the donkey, peacock, goose,
etc., may be attril)uted in main part to selection not having
been l)rought into play : in cats, from tlie difhculty in pairing
them : in donkeys, from onl}'^ a few ])oing kept by poor jieople,
and little attention paid to their breeding; for recently, in cer-
tain parts of Spain and of the United States, tliis animal has
been surprisingly modified and improved by careful selection :
in peacocks, from not being very easily reared and a large
stock not kejit : in geese, from being valuable only for two
puqioses, food and featliers, and more especially from no
plccisure having lieen felt in the display of distinct breeds ; but
the goose seems to have a singularly inflexible organization.

50 SUMMARY OF VAEIATION. Chap. I.

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 g'reatly improved
in many ways within a recent period ; and this imjilies varia-
tion. It would be equally rash to assert that characters now
increased to their vitmost limit, could not, after remaining fixed
for many centuries, again vary under new conditions of hfe.
No doul)t, as Mr. Wallace has remarked with much truth, a
limit will be at last reached. For instance, there must be a
limit to the fleetness of any terrestrial animal, as this will be
determined by the friction to be overcome, the weight of body
to be carried, and the power of contraction in the muscular
fibres. But what concerns us is that the domestic varieties
of the same species differ from each other in almost every
character, Mhich man has attended to and selected, more than
do the distinct species of the same genera. Isidore Geoffroy
St.-Hilaire has proved this in regard to size, and so it is with
color, and probably Muth the length of hair. With respect to
fleetness, which depends on many bodily characteristics. Eclipse
was far fleeter, and a drajMiorse is incomparably stronger, than
any two equine species. So with plants, the seeds of the dif-
ferent varieties of the bean or maize difl'cr more in size than
do the seeds of the distinct species in any one genus of the
same two families. The same remark holds good in regard
to the fruit of the several varieties c»f the plum, and still more
so with the melon, as well as in endless other analogous cases.

To sum up on the origin of our domestic races of animals
and plants. Changed conditions of life are of the highest im-
portance in causing variability, both directly l)y acting on the
organization, and indirectly by aft'ccting the reproductive sj's-
tem. It is not probable that variability is an inherent and
necessary contingent, under all circumstances. The greater
or less force of inheritance and reversion determine Avhether
variations shall endure. Yariability is governed by many un-
known laws, more especially by that of correlation. Some-
Ihing may be attributed to the definite action of the conditions
of life, but how much, we do not know. Something must be
:iltiil)uted to use and disuse. The final result is thus rendered
inllnilely comjilex. In some cases the intercrossing of abori-
ginally distinct species, has probably played an important part
in the orijxin of oin* domestic breeds. When several breeds

Chap. I. SUMMARY OF VAEIATION. 51

have once been formed in any country, their occasional inter-
crossing-, -with the aid of selection, has, no doubt, largely aided
in forming new sub-breeds ; but the importance of crossing
has been much exaggerated, both in regard to animals and
to those plants which are propagated by seed. With plants
which are temporarily propagated by cuttings, buds, etc, the
importance of crossing is immense ; for the cultivator may
here disregard the extreme variability both of hybrids and of
mongrels, and the frequent sterility of hybrids ; but plants
not propagated by seed are of little importance to us, for their
endurance is only temporary. Over all these causes of Change
the accumulative action of Selection, whether applied method-
ically and quickly, or unconsciously and slowly, but more efB-
ciently, is by far the predominant Power.

VAEIATION UNDER NATURE. Chap. II.

CHAPTER II.

VARIATION UXDER NATURE.

Variability— Individual Differences— Doubtful Species— Wide-ranging, much dif-
fused, and Common Species, vary meet- Species of the Larger Genera in each
Country vai"y more frequently than the Species of the Smaller Genera— Many of
the Species of the Larger Genera resemble Varieties in being very closely, bat
unequally, related to each other, and in having Restricted Ranges.

Before applying the principles arrived at in the last cha|>
ter to organic beings in a state of nature, we must briefly dis-
cuss whether these latter are subject to any variation. To
treat this subject at all properlj^ a long catalogue of dry facts
ought to be given; but these I shall reserve for my future
work. Nor shall I here discuss the various definitions which
have been given of the term species. No one definition has
as yet satisfied all naturalists ; yet every naturalist knows
vaguely what he means when he speaks of a species. Gen-
erally the term includes the unknown element of a distinct
act of creation. The term "variety" is almost equally 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 devia-
tion of structure, generally injurious to or not useful to the
species. Some authors use the term "variation" in a techni-
cal sense, as implying a modification directly due to the physi-
cal conditions of life ; and " variations " in this sense are sup-
posed 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 be inher-
ited for at least some few generations ? and in this c;ise I
presume that the form would be called a variety.

It may be doubted whether sudden and great deviations of
structure such as we occasionally see in our domestic produc-

Chap. II. INDIVIDUAL DIFFERENCES. 53

tions, more especially with plants, are ever permanently prop-
agated in a state of nature. Almost every part of every
organic being is so beautifully related in 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 invente4 by man in a perfect state. Under
domestication monstrosities often occur which resemble noi
mal structures in widely-different animals. Thus pigs have
often been born with a sort of proboscis like that of tlie tapir
or elephant. Now, if any wild species of the pig-genus had
naturally possessed a proboscis, it might have been argued that
tliis in like manner had suddenly 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 would bear on the question. If mon-
strous forms of this kind ever do appear in a state of nature
and are capable of propagation (which is not always the case),
as they occur rarely and singly, their preservation would de-
pend on unusually favorable circumstances. They would, also,
during the first and succeeding generations cross with the or-
dinary form, and thus they would almost inevitably lose their
abnormal character. But I shall have to retvu^n in a future
cliapter to the preservation and perpetuation of occasional va-
riations.

Individual Differences.

Tlie many slight differences Avhich frequently appear in the
offspring from the same parents, or which may be presumed to
have thus arisen, from being frequently observed in the indi-
viduals of the same species inhabiting the same confined local-
ity, may be called indiA-idual differences. No one supposes
that all the indi\'iduals of the same species are cast in the same
actual mould. These individual differences are of the highest
importance for us, for they are often inherited, as must be fa-
miliar to every one ; and they thus afford materials for natural
selection to act on and accumulate, in the same manner as man
accumulates in any given direction individual differences in
his domesticated production.s. These individual differences
generally affect what naturalists consider unimportant parts ;
but I could show, by a long catalogue of facts, that parts which
must be called important, whether viewed under a physiolo-
gical or classificatory point of view, sometimes vary in the indi-
viduals of the same species. I am convinced that the most ex-

54 INDIVIDUAL DIFFERENCES. Chap. II.

perienced naturalist would be surprised at the number of the
oases of variability, even in important parts of structure, which
lie could collect on ^ood authority, as I have collected, during
a course of years. It should be remembered that systematists
are far from bcing^ pleased at finding variability in important
characters, and that there are not many men who wiU labori-
ously examine internal and important ort^ans, and compare
tliem in many specimens of the same species. It Avould 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, recently, Sir J. Lubbock has shown a degree of .
variability in these main nerves in Coccus, which ma}' almost
be compared to the irregular branching of the stem of a tree.
This philosophical naturalist, I may add, has also recently
sliowu that the muscles in the larva? of certain insects are far
from luiiform. 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 natu-
ralists have honestly confessed), which do not vary ; and, under
this point of view, no instance will ever be found of an impor-
tant part varying : but under any other point of view many
instances assuredly can be given.

There is one point connected with individual differences,
which is extremely perplexing : I refer to those genera which
have been called " protean " or " polymorphic," in which the
species present an inordinate amount of variation ; and about
which hardly two naturalists agree whether to rank them as
species or as varieties. We niay instance Rubus, Rosa, and
Hieracium among plants, several genera of insects, several gen-
era of Brachiopod shells, and the Ruff (Machetes pugnax)
among birds. In most polpnorphic genera some of the species
have fixed and definite characters. Genera which are poly-
morpliic in one country seem to be, with some few exceptions,
])olymorphic in other countries, and likewise, judging from
Brachiopod shells, at former periods of time. These facts are
very perplexing, for they seem to sliow that this kind of varia-
bility is independent of the conditions of life. I am inclined
to suspect that we have, at least in some of these polymorphic
gen(»ra, variations which are of no service or disservice to the
Hpccics, and which, consequently, have not been seized on and
reiiden^d delinite by natural selection, as hereafter to be ex-
j)hiined.

CiiAP. II. INDIVIDUAL DIFFERENCES. 55

Individuals of the same species often present ^cat difTcr-
eiices of structure, as in the two sexes of various animals, iuthe
two or three castes of sterile females or workers amon^^ insects,
and in the immature and larval states of many of the lower ani-
mals. Tlierc are, however, other cases, namely, of dimori)hism
and trimorphism, which might easily be, and have frecjucntly
l)een, confounded with varial^ility, but which are quite distinct.
I refer to the two or three dillerent forms which certain animals
of either sex, and certain hermaphrodite plants, habitually pre-
sent. Thus, Mr. Wallace, who has lately called special atten-
tion to the subject, has shown that the females of certain spe-
cies of butterflies, in the Malayan archipelaj^o, regularly ap-
pear under two or even three consjoicuously distinct forms, not
connected together by intermediate varieties. The winged and
frequently wingless states of so many Hemipterous insects may
probably be included as a case of dimorphism, and not of mere
variability. Fritz Muller, also, has recently described analo-
gous but more extraordinary cases with the males of certain
Brazilian Crustaceans : thus, the male of a Tanais regularly
occurs under two widely-dillerent forms, not connected by any
intermediate links ; one of these forms has much stronger and
differently-shaped pincers for seizing the female, and the other,
as if for compensation, has anlennaj much more abundantly
furnished with smelhng-hairs, so as to have a better chance of
finding the female. Again, the males of another Crustacean,
an Orchestia, occur under two distinct forms, with pincers dif-
fering much more from each other in structure, than do the
pincers of most species of the same genus. With respect to
plants, I have recently shown that in several -widely-distinct
orders, the species present two or even three forms, which arc
abruptly distinguished from each other in several important
]ioints, as in the size and color of the pollen-grains ; and these
forms, though all hermaphrotlites, differ from each other in
their reproductive power, so that for full fertility, or indeed in
some cases for any fertility, they must reciprocally impregnate
each other. Although the forms of the few dimorphic and tri-
morphic animals and plants which have been studied, are not
now connected together by intermi^diate links, it is ]irol)able
that thi^ will be found to occur in other cases ; for Mr. \\''allacc
observed a certain Ijutterlly which jiresentcd in the same island
a great range of varieties connected by intermediate links, and
the extreme links of the chain closely resembled the two forms
of an allied dimorphic species inhabiting another part of the

5G DOUBTFUL SPECIES. CnAP. II,

Malay archipelago. Tlius also with ants, the several worker-
castes are generally cjuite distinct ; but in some cases, as we
shall hereafter see, the castes are connected together by gradu-
ated varieties. It certainly at first appears a highly-remark-
able fact that the same female butterfly should have the power
of producing at the same time three distinct female forms and
a male ; that a male Crustacean should generate two male
forms and a female form, all widely different from each other ;
and that an hermaphrodite plant should produce from the same
seed-capsule three distinct hermaplu-odite forms, bearing three
different kinds of females and three or even six different kinds
of males. Nevertheless these cases are only exaggerations of
the universal fact that every female produces males and females,
Avhich in some instances differ in a wonderful manner fj-omeach
other.

Doubtful jSpecies.

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 grada-
tions, 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
in their own country for a long time ; for as long, as far as we
knoAV, as have good and true species. Practically, when a
naturalist can unite two forms together by othei*s having inter-
mediate characters, he treats the one as a variety of the other,
ranking the most common, but sometimes the one first de-
scribed, as the species, and the other as the variety. But
cases of great difliculty, which I will not here enumerate,
sometimes occur in deciding whether or not to rank one form
as a variety of another, even when they are closely connected
by intermediate links ; nor will the commonly-assumed hybrid
nature of the intermediate links always remove the difficulty.
In very many cases, however, one form is ranked as a variety
of another, not because the intermediate links have actually
been found, but because analogy leads the observer to suppose
either that they do now somewhere exist, or may formerly
have existed ; and here a wide door for tlie 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

Chap. II. DOUBTFUL SPECIES. 57

judgment and wide experience seems the only guide to follow.
itVe must, however, in many cases, decide by a majority of
naturalists, for few well-marked and well-known varieties can
be named which have not been ranked as species by at least
some competent judges.

That varieties of this doubtful nature are far from uncom-
mon cannot be disputed. Compare the several floras of Great
Britain, of France, or of the United States, drawn up by dif-
ferent botanists, and see Avhat a surprising number of forms
have been ranked by one botanist as good species, and by an-
other as mere varieties. ^Ir. H. C. Watson, to whom I lie
inider deep obligation for assistance of all kinds, has marked
fur me 18"v British plants, which are generally considered as
varieties, but which have all been ranked by botanists as spe-
cies ; and in making this list he has omitted many trifling varie-
ties, but which nevertheless have been ranked by some bota-
nists as specie's, and he has entirely omitted several bighly-poly-
morj^hic genera. Under genera, including the most polymor-
{)hic forms, Mr. Babington gives 251 species, whereas Mr.
Benthara gives only 112 — a difference of 139 doubtful forms !
Among animals which unite for each birth, and which are
highly locomotive, doubtful forms, ranked by one zoologist as
a species and by another as a variety, can rarely be found
within the same country, but are common in separated areas.
How many of those birds and insects in North America and
Europe, which differ very slightly from each other, have been
ranked by one eminent naturalist as undoubted species, and by
another as varieties, or, as they are often called, as geographical
races ! Mr. Wallace, in several valuable papers on the various
animals, especially on the Lepidoptera, inhabiting the islands of
the great Malayan archipelago, shows that they may be classed
under four heads, namely, as variable forms, as local forms,
as geographical races or sul)-species, and as true representative
species. The first or variable forms vary much within the
limits of the same island. The local forms are moderately
constant and distinct in eqch separate island; but when all
the forms from the several islands arc compared, the differ-
ences are seen to be so slight and graduated, that it is impos-
sible to define or describe them, though at the same time the
extreme forms are sufficiently distinct. The geographical
races or sul>speoies are local forms completely fixed and iso-
lated; but as they do not differ from each other by strongly-
marked and important characters, " there is no possible test but

58 DOUBTFUL SPECIES. Cuap. II.

individual opinion to determine which of them shall be consid-
ered as species and -which as varieties." Lastly, representa-
tive species fill the same place in the natural economy of each
island as do the local forms and sub-species ; but, as they are
distinp^uished from each other by a greater amount of differ-
ence than that between the local forms and sub-species, they
are almost imiversally ranked by naturalists as true species.
Nevertheless, no certain criterion can possibly be given by
which variable forms, local forms, sub-species, and representa-
tive species can be recognized.

Many years ago, when comparing, and seeing others com-
pare, the birds from the closely-neighboring islands of the
Galapagos archipelago, both one with another, and with those
from the American main-land, I was much struck how entirely
vague and arbitrary is the distinction between species and
varieties. On the islets of the little Madeira group there are
many insects Avhich are characterized as varieties in Mr. Wol-
laston's admirable work, but which would certainly be ranked
as distinct species by many entomologists. Even Ireland has
a few animals, now generally regarded as varieties, but which
have been ranked as species by some zoologists. Several
experienced ornithologists consider our British red grouse as
only a strongly-marked race of a Norwegian species, whereas
the greater number rank it as an undoubted species peculiar
to Great Britain. A wide distance between the homes of two
doubtful forms leads many naturalists to rank them as distinct
species ; but what distance, it has been Avell asked, Avill suf-
fice ; if that between America and Europe is ample, will that
lietween Europe and the Azores, or Madeira, or tlie Canaries,
or between the several islets of these small archipelagos, be
sufficient ?

Mr. B. D. Walsh, a distinguished entomologist of the United
States, has lately 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 in-
discriminately 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, either ex-
el usivel}' 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 l)()th males and females, liave been olisen'ed to be
thus alTected in a shght degree. When the diflerencos are

Chap. II. DOUBTFUL SPECIES. 59

rather more strongly marked, and when both sexes and all aj^os
are afTectcd, the forms -would be ranked by all entomolo<^ists as
species. But no observer can determine for others, 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 together,
as varieties ; and those Avhich appear to have lost this jjower,
as species. As the ditfcrences depend on the insects having
long fed on distinct plants, it cannot be expected that inter-
mediate links connecting tlie several forms should now be
found. The naturalist thus loses his best guide in determining
whether to rank such doubtful forms as varieties or sjiecies.
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 intermediate forms may be discovered which shall
link together the extreme states ; and these arc then degraded
to the rank of varieties.

Some few naturalists maintain that animals never present
varieties ; but then these same; naturalists rank the slightest
differences as of specific value; and when the same identical
form is met with in two distant countries, or in tM'o geological
formations, they believe that two distinct species are hidden
under the same dress. Tlie term species thus comes to be a
mere useless mental abstraction, implying and assuming a sepa
rate act of creation. It is certain that many forms, considered
by highly-competent judges as varieties, so completely resemble
species in character, that they have been thus ranked by other
highly-competent judges. But to discuss whether they ought
to lie called species or varieties, before any definition of these
terms has been generally accepted, is A'ainly to beat the air.

Many of the cases of strongly-marked varieties or doul)tful
species well deserve consideration ; for several interesting lines
of argument, from geographical distribution, analogical varia-
tion, hybridism, etc., have been brought to l)ear on tlie attempt
to determine their rank ; but space does not here permit me
to discuss them. Close investigation, in many cases, will bring
naturalists to an agreement how to rank doubtfid forms. Yet
it must be confessed that it is in the best-known countries that
we find the greatest number of forms of doubtful value. I
have been struck Avith the fact that, if any animal or plant in a

CO DOUBTFUL SPECIES. Chap. II.

state of nature be liigbly useful to man, or from any cause
closely attract his attention, varieties of it will almost univer-
sally 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
imiversally considered as varieties ; and in this country the
highest botanical authorities and practical men can Ix) quoted
to show that the sessile and pedunculated oaks are either good
and distinct species or mere varieties.

I may here allude to a remarkable memoir lately published
by A. de Candolle, on the oaks of the whole world. No one
ever had more ample materials for the discrimination of the
species, or could have worked on them with more zeal and
sagacity. He first gives in detail all the many points of struc-
ture which vary in the species, and estimates numerically the
relative frequency of the variations. He specifics above a
dozen characters Avliich niay be found varying even on the same
branch, sometimes according to age or development, sometimes
without any assignable reason. Such characters of course are
not 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 saj^- that he
gives the rank of species to the forms that differ by characters
never varying on the same tree, and never found connected by
intermediate states. After this discussion, the result of so
much labor, he emphatically remarks : " They are mistaken,
who repeat that the greater part of our species arc 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 Avere fovuidcd upon a few specimens,
that is to say, were provisional. Just as we come to know
them better, intermediate forms flow in, and doubts as to spe-
cific 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. peduuculata, sessilifiora, and
pubescens. The forms which connect these three sulvspecies
are comparatively rare ; and, as Asa Gray remarks, if these
connecting forms, whi(;h are now rare, were to become wholly
extinct, the three sub-species Avould hold exactly the same
relation to each other, as do the four or five provisionally-

Cnxr. II. DOUBTFUL SPECIES. 61

admitted species which closely surround the typical Qucnuis
rol)ur. Finally, De Candolle admits that, out of the three hun-
dred species, Avhicli will l^e enumerated in his Prodromus as
belonging to the oak family, at least two-thirds are provisional
species, that is, are not known strictly to fulfil the definition
above given of a true species. For it should be added that De
Candolle no longer believes that species are immutable crea-
tions, but concludes that the derivative theory of the succession
of forms is the most natural one, " and the most accordant with
tlie known facts in paleontology, geographical botany and zo-
ology, of anatomical structure and classification ; " but, he adds,
direct proof is still wanting.

When a young naturalist commences the study of a group
of organisms quite unknown to him, he is at first much per-
plexed to determine what difiercnces 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 tendency will be to make many species, for he will
become impressed, just like the pigeon or poultry fancier l)eforc
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 corrett his first impressions. As he extends the
range of his oljservations, he will meet Avith more cases of diffi-
culty ; for ho will encounter a greater number of closely-allied
forms. But if his observations be widely extended, he will in
the end generally l)e enaljled to make up his own mind which
to call varieties and wliich species ; but he will succeed in this
at the expense of admitting much variation — and the truth of
this admission will often be disputed by other naturalists.
AV'hen, moreover, he comes to study allied forms brought from
countries not now continuous, in which case he cannot hope to
find tlie intermediate links between his doubtful forms, he will
have to trust almost entirely to analog}-, and his difliculties rise
to a climax.

Certainl}^ no clear line of demarcation has as yet been drawn
between species and sub-sju^cies — that is, the forms which in
the ojjinion 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

G2 DOMINANT SPECIES VARY MOST. Chap. II.

individual differences. These differences blend into each other
in an insensible scries ; and a seiies 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 latter, as leading to sub-
species or species. The passages from one stage of difference
to another may, in some cases, be the simple result of the
long-continued action of different physical conditions ; but in
most cases they may be attributed to the gradual accumulative
'action of natural selection, as hereafter to be more fullj" ex-
plained, on fluctuating variability. • Hence a well-marked
variety may be called an incipient species ; but whether this
belief is justifiable must be judged of by the general weight
of the facts and considerations given throughout this Avork.

It need not be supposed that all varieties or incipient spe-
cies necessarily attain the rank of species. They may become
extinct, or they may endure as varieties for very long periods,
as has been shown to be the case by Mr. Wollaston with the
varieties of certain fossil land-shells in Madeira, and with plants
by Gaston de Saporta, If a variety were to flourish so as to
exceed in immbers the parent-species, it would then rank as
the species, and the species as the variety ; or it might come
1o supplant and exterminate the parent-species ; or both might
coexist, 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 tlie sake of convenience,
to a set of individuals closely resembling each other, and that
it does not essentially differ from the term variety, which is
given to less distinct and more fluctuating forms. The term
variety, again, in comparison with mere individual differences,
is also applied arbitrarily, and for mere convenience' sake.

Wide-ranging^ much-d {fused, and Commo7i Siyecics, vary

most.

Guided by theoretical considerations, I thought that some
interesting results might be obtained in regard to the nature

Chat. II. DOMINANT SPECIES VARY MOST. 63

and relations of the species which vary most, by tabulatinj^
all the varieties in several Avell-workcd floras. At first this
seemed a simple task ; but Mr. H. C. W^atson, to whom I am
much indebted for valuable advice and assistance on this sub-
ject, soon convinced me that there were many difficulties, as
did subsequently Dr. Hooker, even in strono^er terms. I shall
reserve • for my future work the discussion of these difficulties,
and the tables themselves of the proportional numbers of the
varying species. Dr. Hooker permits me to add that, after
liaviufT' carefully read my manuscript, and examined the tables,
he tliinks tliat the follo\\ing statements are fairly well estab-
lished. The whole subject, however, treated as it necessarily
here is with much brevity, is rather pcrplexin;T, and allusions
cannot be avoided to the "struggle for existence," "divergence
of character," and other cjuestions, hereafter to be discussed.

Alphonse de Candollc and others have shown that plants
which have very wide ranges generally present varieties ; and
this might have been expected, as they become exposed to
diverse physical conditions, and as they come into competition
(which, as we shall hereafter see, is an equally or more im-
portant circumstance, with different sets of organic beings. But
my ta])les further show that, in any limited country, the species
winch arc most common, that is, abound most in individuals,
and the species Avhich are most widely diifused within their
own country (and this is a different consideration from wide
range, and to a certain extent from commonness) oftenest give
rise to varieties sufficiently well marked to have been recorded
in botanical works. Hence it is the most flourishing, or, as
they may be called the dominant species — those which range
widely, are the most diffused in their own country, and arc the
most numerous in individuals — wln'ch oftenest produce well-
marked varieties, or, as I consider them, incipient species.
And this, perhaps, might have been anticipated; for, as varie-
ties, in order to become in any degree permanent, necessarily
have to struggle with the other inhabitants of the coimtry,
the species which are already dominant will be the most likely
to yield olTspring, which, though in some slight degree modi-
fied, still inlu^rit those advantages tliat enabled their parents to
become dominant over their compatriots. In these remai'ks
on predominance, it should l)e understood that reference is
marie only to those forms which come into competition Avith
each other, and more especially to the members of the same
genus or class having nearly similar habits of life. With re-

64 SPECIES OF LARGER GENERA VARIABLE. Chap. II.

spect to cominoiinoss or the number of individuals of any spe-
cies, the comparison, of course, relates only to the members of
the same group. A plant 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, not livini^^ under widely-
different conditions of Hfe. Such a plant is not the less domi-
nant in the sense here used, because some conferva inhabiting
the water or some parasitic fungus is infinitely more numerous
in individuals, and more widely diffused ; if one kind of conferva
or parasitic fungus exceeded its allies in the above respects,
it would be a dominant form within its own class.

JSjjecies of the Larger Genera in each Country vary more
frequently than the Species of the Smaller Genera.

If the plants inhabiting a country and descrilicd in any
Flora be divided into two ecjual masses, all those in the larger
genera (i. e., those including many species) being placed on
one side, and all those in the smaller genera on the other side,
a somewhat larger number of the very common and much-dif-
fused or dominant species will be found on the side of the
larger genera. This, again, might have been anticipated ; for
the mere fact of many species of the same genus inhabiting any
country, shows that there is something in the organic or inor-
ganic conditions of that country favorable to the genus ; and,
consequently, we might have expected to have found in the
larger genera, or those including many species, a large propor-
tional 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 have generally very wide ranges and are
much diffused, but this seems to be connected with the nature
of the stations inhabited by them, and has little or no relation
to the size of the genera to which the species belong. Again,
plants low in the scale of 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. Tlie
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 tliat the species of the
larger genera in each country would oftener present varieties,

CnAP. 11. SPECIES OF LARGER GENERA VARIABLE. 65

than the species of the smaller g'enera ; for wherever many
closely-related species (i. e., species of the same genus) have
been fornietl, many varieties or incipient species ought, as a
general rule, to be now forming. Where many large trees
grow, we expect to find saplings. Where many species of a
genus have been formed tkrough variation, circumstances have
been favorable for variation ; and hence we might expect thai
the circumstances would generally be still favorable to varia-
tion. On the other hand, if we look at each species as a special
act of creation, there is no apparent reason why more varieties
should occur in a group having many species, than in one
having few.

To test the truth of this anticipation, I have arranged the
j^lants 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 gCnera on
the other sid(?, and it has invariably proved to be the case that
a larger proportion of ±he 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 pre-
sent any varieties, invariably present a larger average number
of varieties than do the species of the small genera. Both these
results follow when another diWsion is made, and when all the
least genera, with from only one to four species, are absolutely
excluded from the tables. These facts are of plain significa-
tion 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 expres-
sion, the manufactory of species has been active, we ought
generally to find the manufactory still in action, more espe-
cially as we have every reason to believe the process of manu-
facluring new species to be a slow one. And this certainly
is the case, if varieties be looked at as incipient species ; for
my tables clearly show as a general rule that, wherever many
speci(^s of a genus have been formed, the species of that genus
present a nvunber of varieties, that is, of incipient species, be-
yond the average. It is not that all large genera are now
varying nuich, and are thus increasing in the lunnber of their
species, or that no small genera are now varying and increas-
ing; for if this had l)een 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, declined,

OG SPECIES OF LARGER GENERA Chap. II.

aiul disappeared. All that we -want to show is, that, where
many species of a genus have been formed, on an average
many arc still forming ; and this certainly holds good.

Many of tJic Sjiccies included iclthln the Larger Genera re-
semble Varieties in being very closely, but unequally, related
to each other, and in having liestricted Manges.

There are other relations between the species of large gen-
era and their recorded varieties which deserve notice. We
have seen that there is no infallible criterion by which to dis-
tinguish species and well-marked varieties ; and in those cases
in which intermediate links have not been found between
doubtful forms, naturalists are compelled to come to a deter-
mination by the amount of difference between them, judging by
analogy whether or not the amoimt suffices to raise one or both
to the rank of species. Hence the amount of difference is one
very important criterion in settling whether two forms should be
ranked as species or varieties. Now Fries has remarked in
regard to plants, and Westwood in regard to insects, that in
large genera the amount of difference between the sjiecies is
often exceedingly small. I have endeavored to test this nu-
merically 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, tlie 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 num-
ber of varieties or incipient species greater than the average
are now manufacturing, many of the species already manufac-
tured 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 large 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 arc 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 certain
other species. And what are varieties but groups of forms,
imequally related to each other, and clustered round certain
forms — that is, round their parent-species ? Undoubtedly there

Chap. II. RESEMBLE VARIETIES. 07

is one most important point of dilFerencc between varieties and
species ; namely, that the amount of diflerencc between varieties,
M'hen compared with each other or with their parent-species, is
much less than that betw'een the species of the same genus. But
■when WG come to discuss the principle, as I call it, of Diver-
gence of Character, we shall see how this may be explained,
and how the lesser diiferences between varieties tend to in-
crease into the greater differences between species.

There is one other point which is worth notice. Varieties
generally have much-restricted ranges : this statement is in-
deed scarcely more than a truism, for, if a variety were found
to have a wider range thaii that of its sujiposed parent-species,
their denominations would be reversed. But there is also
reason to believe that those species which are very closely
allied to other species, and in so far resemble varieties, often
have much-restricted ranges. For instance, Mr. II. C. Watson
has marked for me, in the well-sifted London Catalogue of
plants (fourth edition), G3 plants which are therein ranked as
species, but which he considers as so closely allied to other
species as to be of doubtful value : these 63 reputed species
range on an average over G.9 of the provinces into which Mr.
Watson has divided Great Britain. Now, in this same cata-
logue, 53 acknowledged varieties are recorded, and these range
over 7.7 jirovinces ; whereas, the species to Avhich these vari-
eties belong range over 14.3 provinces. So that the acknowl-
edged varieties have very nearly the same restricted average
range as have those very closely allied forms, marked for me
liy Mr. Watson as doubtful species, but which are almost uni-
versally ranked by British botanists as good and true species.

Summart/.

Finally, then, varieties caimot be distinguished from species
— except, first, by the discovery of intermediate linking forms;
and, secondly, by a certain indefinite amount of difference be-
tween them ; for two forms, if differing very little, are gener-
ally ranked as varieties, notwithstanding that they cannot be
closely connected ; but the amount of difference considered
necessary to give to any two forms the rank of species cannot
be defined. In genera having more than the average number
of species in any country, the species of these genera have
more than the average number of varieties. In large genera
the species are apt to be closely, but uncfiually, allied together.

68 SUMMARY. Chap. II.

forming little clusters round certain other species. Species
very closoly allied to other species apparently have restricted
rang'cs. In all these several 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 in-
explicable if species are independent creations.

We have, also, seen that it is the most nourishing or dom-
inant species of the larger genera within each class which on
an average 3'ield the greatest number of varieties ; and varie-
ties, as we shall hereafter see, tend to become converted into
new and distinct species. Thus the larger genera tend to be-
come larger ; and throughout Nature the forms of life which
are now dominant tend to become still more dominant by leav-
ing many modified and dominant descendants. But by steps
hereafter to be explained, the larger genera also tend to break
up into smaller genera. And thus, the forms of life through-
out the universe become divided into groups subordhiate to
groups.

Chap. III. STRUGGLE FOB EXISTENCE. 69

CHAPTER III.

STRUGGLE FOR EXISTENCE.

Its bearing on Natural Selection— The Term used In a wide Sense— Geometrical Ratio
oriucroase — Rapid Iiicreaao of Nuturalized Animals and Plants— Nature of tho
Checks to Incroase— Competition universal— EftectR of Climate — Protection from
the Number of Individuals — Complex Relations of all Animals and Plants throush-
out Nature— St ru;;srlo for Life most severe between Individuals and Varieties of
the same *Specics: often severe between Species of the same Genus — The Rela-
tion of Organism to Or^^anism the most important of all Relations.

Before entering on the subject of this chapter, I must
make a few prehminary 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 immaterial 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 the mere existence of individual variability and of some
few well-marked varieties, though necessary as the foundation
for the work, helps us but little in understanding how species
arise in Nature. How have all those exquisite adaptations of
one part of the organization to another part, and to the condi-
tions of life, and of one organic being to another being, been
perfected ? We see these beautiful coadaptations most plain-
ly in the woodpecker and the mistletoe ; and only a little less
])lainly in the hinnblest parasite which clings to the hairs of a
quadruped or feathers of a bird; in the structure of the beetle
wliich dives through the water ; in the ])lumed seed which is
wafted by the gentlest breeze ; in short, we see beautiful
adaptations everywhere and in every part of the organic
world.

Again, it may be asked, how is it that varieties, which I
have called incipient species, become ultimately converted into

70 STRUGGLE FOR EXISTENCE. Cuap. III.

good and distinct species, which in most cases obviously differ
from each oilier far more than do the varieties of the same
species? How do those groups of species, wliich 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. 0\\4ng to this struggle,
variations, however slight, and from whatever cause proceed-
ing, 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, wUl thus have a better
chance of surviving, for, of the many individuals of an}^ species
Avhich 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 expres-
sion often used by Mr. Herbert Spencer of the Survival of the
Fittest is more accurate, and is sometimes equally convenient.
'SVe have seen that man by selection can certainly produce
great results, and can adapt organic beings to his own uses,
through the accumulation of slight but useful variations, given
to him by the hand of Nature. But Natural Selection, as we
shall hereafter see, is a power incessantly ready for action, and
is as immeasurably superior to man's feeble efforts as the
works of Nature are to those of Art.

We will now discuss in a little more detail the struggle for
existence. In my future work this subject will be treated, as
it well deserves, at greater length. The elder De Candolle
and Ijyell have largely and philosophically shown that all
organic beings are exposed to severe competition. In regard
to plants, no one has treated this subject Avith more spirit and
ability than AV. Herbert, Dean of Manchester, evidently the
result of his great horticultural knowledge. Nothing is easier
than to admit in words the truth of the universal struggle for
life, or more difficult — at least I have found it so — than con-
stantly to bear this conclusion in mind. Yet unless it be
thoroughly engrained in the mind, the whole economy of
Nature, with every fact on distriljution, rarity, abundance, ex-
tinction, and variation, will be dimly seen or quite misunder-
stood. We behold the face of Nature bright Avith gladness,
Ave often sec superabundance of food ; Ave do not see, or Ave

CuAP. HI. GEOMETRICAL KATIO OF INCREASE. 71

forget, tliat the birds which arc idly singing round us mostly
live on insects or seeds, and are thus constantly destroying
life ; or we forget how largely these songsters, or their eggs,
or their nestlings, are destroyed by birds and beasts 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.

Tlie 2h'm, Stu-uggle for Existence^ used in a Large Sense.

I should premise that I use this term in a large and meta-
phorical sense, including dependence of one being on another,
and including (which is more important) not only the life of
the indi\-idual, but success in lea\'ing progeny. Two canine
animals, in a time of dearth, may be truly said to struggle with
each -other which shall get food and live. But a plant on the
edge of a desert is said to struggle for life against the drought,
though more properly it should be said to be dependent on the
moisture. A plant which annually produces a thousand seeds,
of which on an average only one 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 will
languish and die. But several seedling mistletoes, growing
close together on the same branch, may more truly be said to
struggle with each other. As the mistletoe is disseminated by
birds, its existence depends on birds ; and it may metaphori-
cally be said to struggle with other fruit-bearing plants, in
order to tempt birds to devour and thus disseminate its seeds
rather than those of other plants. In these several senses,
which pass into each other, I use for convenience' sake the
general term of struggle for existence.

Geometrical Ratio of Increase.

A struggle for existence inevitably follows from the high
rate at which all organic beings tend to increase. Every being
which during its natural lifetime produces several eggs or
seeds, must suffer destruction during some period of its life,
and during some season or occasional year, otherwise, on the
principle of geometrical increase, its numbers would quickly

72 GEOMETRICAL RATIO OF INCREASE. Chap. III.

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, cither one individual with another of the same spe-
cies, or -with the individuals of distinct species, or with the phys-
ical conditions 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 for marriage. Although some
species may be now increasing, more or less rapidly, in num-
bers, all cannot do so, for the world would not hold them.

There is no exception to the rule that every organic being
naturally increases at so high a rate, that, if not destroyed, the
earth would soon be covered by the progeny of a single pair.
Even slow-breeding man has doubled in twenty-five years, and
at this rate, in a few thousand years, there would literally not
be standing-room for his progeny. Linnasus has calculated
that if an annual plant produced only two seeds — and there is
no plant nearly so unproductive as this — and their seedlings
next year produced two, and so on, then in twenty years thei'C
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 go'es 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 seven hundred
and forty to seven hundi'ed and fifty years, there would be alive
nearly nineteen million elephants descended from the first pair.

But we have better evidence on this subject than mere
theoretical calculations, namely, the numerous recorded cases
of the astonishingly ra\nd increase of various animals in a state
of nature, "when circumstances have been favorable to them
during two or three following seasons. Still more striking is
the evidence from our domestic animals of many kinds which
liave 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 Avould have been incredible. So it is with
plants : cases could be given of introduced plants which have
b(>come common throughout whole islands in a period of less
than ten years. Several of the plants, such as the caitloon,
and a tall thistle, now most numerous over the wide plains of

CiiAP. III. GEOMETRICAL RATIO OF' INCREASE. 73

La Plata, clothing square leagues of surface almost to the ex-
clusion of all other plants, have been introduced from Europe ;
and there are plants which now range in India, as I hear from
Dr. Falconer, from Cape Comorin to tlie Himalaya, which have
been imported from xVmerica since its discovery. In such
cases, and endless instances could be given, no one supposes
that the fertility of these animals or phuits has been suddenly
and temporarily increased in any sensil)le degree. The obvious
explanation is that the conditions of lifeliave been very favor-
able, and that there has consequently been less destruction of
the old and 3'oung, and that nearly all the young have been
enabled to breed. In such cases the geometrical ratio of in-
crease, the result of which never fails to be surprising, simply
explains the extraordinarily rapid increase and wide diffusion
of naturalized productions in their new homes.

In a state of nature almost every plant produces seed, and
among animals there are very few which do not annually pair.
Hence we may confidently assert, that all plants and animals
are tending to increase at a geometrical ratio — that all would
most rapidly stock every station in which they could anjdiow
exist — and that the geometrical tendency to increase must be
checked by destruction at some period of life. Our familiarity
with the larger domestic animals tends, I think, to mislead us :
Ave see no great destruction falling on them, and we forget that
thousands are annually slaughtered for food, and that in a
state of nature an equal number would have somehow to be
disposed of.

The only difference between organisms which annually pro-
duce eggs or seeds by the thousand, and those which produce
extremely few, is, that the slow-breeders would require a few
more years to people, under favorable conditions, a Avliole dis-
trict, let it be ever so large. The condor lays a couple of eggs
and tlic 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 o<i;g, yet it is believed to be the most numerous bird in
the world. One fly deposits hundreds of eggs, and another,
like the hippolwsca, a single one; but this dillerence does not
det(^nnine how many individuals of the two species can be sup-
ported in a district. A large nmnber of eggs is of some im-
j)ortance to those species which depend on a rapidly-fluctuating
amount of food, for it allows them rapidly to increase in num-
ber. 15ut the real importance of a large number of eggs or
seeds is to make up for nuich destruction at some period of life :
4

74 NATURE OF THE CHECKS TO INCREASE. Chap. IIT,

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 i)roduccd, and yet the average stock be
fully kept up; ])ut if many eggs or young are dcstroj'ed, many
must be produced, or the species will become extinct. It
would suilicc to keep up the full number of a tree, which lived
on an average for a thousand years, if a single seed were pro-
duced once in a thousand years, supposing that this seed were
never destroyed, and Could lie insured to germinate in a fitting
place. So that, in all cases, the average number of any animal
or plant depends only indirectly on the number of its eggs or
seeds.

In looking at Nature, it is most necessary to keep the fore-
going considerations always in mind — never to forget that
everj- single organic being around us 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 hea\'y destruction in-
evitably falls either on the young or old, during each genera-
tion or at recurrent intervals. Lighten any check, mitigate
the destruction ever so little, and the number of the species
will almost instantaneously increase to any amount.

Nature of the Checks to Increase.

The causes which check the natural tendency of each spe-
cies to increase are most obscure. Look at the most vigorous
species ; by as much as it swarms in numbers, by so much will
its tendency to increase be still further increased. We know
not exactly what the checks are in even one single instance.
Nor will this surprise any one who reflects hov/ ignorant we
are on this head, even in regard to mankind, so incomparably
better known than any other animal. This subject has been
alily treated by several authors, and I shall, in my future work,
discuss some of the checks at considerable length, more es-
pecially 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 genei-ally to sufler 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, I believe that it
is the seedlings which sufier most from germinating in ground
iilrcvady thickly stocked with othcn- jilants. Seedlings, also, are
destroyed in vast numbers by various enemies ; for instance.

CiiAr. III. NATURE OF THE CHECKS TO INCREASE. 75

on a jiicco of ground three feet long and two wide, dug and
cleared, and wliere there could be no choking from other plants,
I marked all the seedlings of our native weeds as they came
up, and out of the 357 no less than 295 were destroyed, chielly
by slugs and insects. If turf which has long been mown, and
the case would be the same with turf closely browsed by quad-
rupeds, be let to grow, the more vigorous plants gradually
kill the less vigorous though fully-grown plants ; thus out of
twenty species growing on a little plot of turf (three feet by
four) nine species perished from the other species being allowed
to grow up freely.

The amount of food for each species of course gives the
extreme limit to which each can increase ; but very frequently
it is not the obtaining food, but the serving as prey to other
animals, which determines the average numbers of a species.
Thus', there seems to be little doubt that the stock of par-
tridges, grouse, and hares, on any large estate depends chiefly
on the destruction of vermin. If not one head of game were
shot during the next twenty years in England, and, at the
same time, if no vermin were destroyed, tliere would, in all
prnba])ility, be less game tlian at present, although hundreds
of thousands of game animals are now annually killed. On the
other hand, in some eases, as with the elephant, none are de-
stroyed by beasts of prey; for even the tiger in India most
larely dares to attack a young elephant protected by its dam.

Climate plays an important part in determining the aver-
ige numbers of a species, and periodical seasons of extreme
cold or drought seem to be the most effective of all checks. I
estimated (chiefly from the greatly reduced numbers of nests
in the sjiring) that the winter of 1854-55 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 ex-
traordinarily 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 cliiefly
acts in reducing food, it brings on the most severe struggle
between the individuals, whether of the same or of distinct
species, which subsist on the same kind of food. Evon when
climate, for instance extreme cold, acts directly, it will be the
least vigorous, or thost; whicli have got least i'ood through the
advancing winter, which will suffer most. "When we travel
from south to north, or from a damp region to a dry, we in-
variidily sec some species gradually getting rarer and rarer,

•J 6 NATURE OF THE CHECKS TO INCPwEASE. Chap. III.

and finally disappearing- ; and the change of climate being con-
spicuous, we are tempted to attribute the whole effect to its
direct action. But tliis is a false view : we forget that each
species, even where it most abounds, is constantly suffering
enormous destruction at some period of its life, from enemies
or from competitors for the same place and food;. and if these
enemies or competitors be in the least degree favored by any
slight change of climate, they will increase in numbers, and,
as each area is aheady fully stocked with inhabitants, the other
species will decrease. "\\Tien we travel southward and see a
species decreasing in numbei"s, Ave may feel sure that the cause
lies quite as much in other species being favored, as in tliis
one being hurt. So it is when we travel northward, but in a
somewhat lesser degree, for the number of species of all kinds,
and therefore of competitors, decreases northward; hence, in
going northward, or in ascending a mountain, we far oftener
meet with stvuited forms, due to the directly injurious action
of climate, than we do in proceeding southward or in descend-
ing a mountain. When we reach the Arctic regions, or snow-
capped summits,- or absolute deserts, the struggle for life is
almost exclusively with the elements.

That climate acts in main part indirectly by favoring other
species, Ave may clearly see in the prodigious number of plants
in our gardens which can perfectly Avell endure our chmate,
l)ut which never become naturalized, for they cannot compete
with om- native plants, nor resist destmction by our native
animals.

When a species, owing to highly favorable circumstances,
increases inordinately in numbers in a small tract, epidemics —
at least this seems generally to occur with our game animals —
often ensue : and here we have a limiting check independent
of the struggle for life. But even some of these so-called
epidemics appear to be due to parasitic worms, which have
from some cause, possibly in jiart through facihty of diffusion
among the crowded animals, l)ecn disproportionally favored ;
and here comes in a sort of sti-uggle between the parasite and
its prey.

On the other hand, in many cases, a large stock of individ-
uals of the same species, relatively to the numbers of its ene-
mies, is absolutely necessary for its preservation. Thus we can
easily raise plenty of corn and rape-seed, etc., in our fields, be-
cause the seeds are in great excess compared with the mnnber
of birds which feed on them ; nor can the birds, though liavinq

Chap. III. STRUGGLE FOR EXISTENCE. 77

a superabundance of food at tliis one season, increase in num-
ber proportionally to the supply of seed, as their numbers are
checked during -winter ; but any one who has tried, knows
how troublesome it is to get seed from a few wheat or other
such plants in a garden : I have in this case lost every single
seed. This view of the necessity of a large stock of the same
species for its preservation, explains, I believe, some singular
facts in Nature, such as that of very rare plants being some-
times extremely abundant in the few spots where they do
occur; and that of some social plants being social, that is,
abounding in individuals, even on the extreme confines of their
range. For in such cases, we may believe, that a plant could
exist only where the conditions of its life were so favorable
that many could exist together, and thus save the species from
utter destruction. I should add that the good effects of fre-
quent intercrossing, and the ill eff'ects of close interbreeding,
probably come into play in some of these cases ; but on tliis
intricate subject I will not here enlarge.

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, has
interested me. In Staffordshire, on the estate of a relation,
where I had ample means of investigation, there was a large
and extremely barren heath, which had never been touched by
the hand of man ; but several hundred acres of exactly the
same nature had been enclosed twenty-five years previously
and planted with Scotch fir. The change in the native vegeta-
tion of the ])lanted part of the heath was most remarkable,
more than is generally seen in passing from one quite diiTerent
soil to another; not only the proportional numbers of the heath-
plants were wholly changed, but twelve species of j)lants (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 conmion 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 cff"cct of the introduction of a single tree, nothing

78 STEUGGLE FOIi EXISTENCE. Cuap. III.

wliatever Cise liavinji^ been clone, "vvith the cxce}7tion of the
huid having 1)ecn enclosed, so that cattle could not enter. But
how important an clement enclosure is, I plainly saw near Farn-
ham, in Surrc}'. Plcrc there are extensive heaths, with a few
clumps of old Scotch firs, on the distant hill-tops : within the
last ten j'ears larg'e spaces have been enclosed, and self-sown
firs are now sprini!:iii2^ up in multitudes, so close together that
all cannot live. When I ascertained that these young trees
had not been sown or planted, I was so much surprised at their
numbcre that I went to several points of view, whence I could
examine hundreds of acres of the unenclosed heath, and liter-
ally I could not see a single Scotch fir, except the old planted
clumps. But on looking closely between the st^ms of the
heath, I found a multitude of seedlings and little trees, which
had been perpetually browsed down by the cattle. In one
square yfu'd, at a point some himdred 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 laud was enclosed,
it became thickly clothed with vigorously-growing young firs.
Yet the heath was so extremely barren and so extensive that
no one would ever have imagined that cattle would have so
closely and effectually searched it for food.

Here we see that cattle absolutely determine the existence
of the Scotch fir ; but in several parts of the world insects
determine the existence of cattle. Perhaps Paraguay offers
the most curious instance of this ; for here neither cattle nor
horses nor dogs have ever run wild, though they swarm south-
ward and northwai'd in a feral state ; and ^Vzara and Pengger
have shown that this is caused by the greater number in Para-
guay of a certain fly, which lays its eggs in the navels of these
animals when first born. The increase of these flics, numerous
as they are, must be habitually checked by some mean?, proba-
bly l)y other parasitic insects. Hence, if certain insectivorous
birds were to decrease in Paraguay, the parasitic insects would
probably increase ; and this Avould lesson the num])er of the
navel-frequenting flies — then cattle and horses would become
f(>ral, and this would certainly greatly alter (as indeed I have
obseiTod in parts of South America) the vegetation : this again
would largely aflect the insects; and this, as Ave have just seen
in Staffordshire, the insectivorous birds, and so onward in
ever-increasing circles of complexity. We began this scries

CflAr. III. STRUGGLE FOR EXISTENCE. 79

by insectivorous birds, and -we have ended with tlieni. Not
tliat in nature the rehitions can ever be as simple as this. Bat-
tle within battle must ever be recurring' with varying' success ;
and yet in the long-run the forces are so nicely balanced, that
the lace of Nature remains uniform for long periods of time,
tliough assuredly the merest trifle would often give the victory
to one organic being over another. Nevertheless, so profound
is our ignorance, and so high our presumption, that we marvel
when we hear of the extinction of an organic being ; and, as
we do not see the cause, we invoke cataclysms to desolate the
world, or invent laws on the duration of the forms of life !

I am tempted to give one more instance showing how
plants and animals, most remote in the scale of Nature, are
bound together by a web of complex relations. I shall here-
after have occasion to show that the exotic Lobelia fulgens, in
this part of England, is never visited by insects, and conse-
fiucntly, from its peculiar structure, never sets a seed. Near-
ly 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 indispen-
sable to the fertilization of the heart's-ease (Viola 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, 20 heads of Dutch clover (Trifolium
repens) yielded 2,290 seeds, but 20 other heads protected from
bees produced not one. Again, 100 heads of red clover (T.
pratense) produced 2,700 seeds, but the same number of pro-
tected heads produced not a single seed. Humble-bees alone
visit red clover, as other bees cannot reach the nectar. It has
been suggested that moths may 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 humljle-bces became extinct or very rare in
England, ihe heart's-ease and red clover would become very
rare, or wholly disappear. The number of humble-bees in any
district depends in a great degree on the number of field-mice,
which destroy their combs and nests ; and Colonel Newman,
who has long attended lo 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 hirgely depend-
ent, as every one knows, on tlic niunber of cats : and Colonel
Newman says, " Near villages and small towns I have found

80 STRUGGLE FOK EXISTENCE. Chap. ^ly,

the nests of humble-bees more numerous than elsewhere, Mhich
I attribute to the number of cats that destroy the mice." Hence
it is quite credible that the presence of a fefine animal in large
numbers in a district might determine, through the interven-
tion first of mice and then of bees, the frequency of certain
flowers in that district !

In the case of every species, many different checks, acting
at diflerent 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 concur in determining
the average number or even the existence of the species. In
some cases it can be shown that widely-different checks act on
the same species in different districts. When we look at the
jilants and bushes clothing an entangled bank, Ave are tempted
to attribute their proportional numbers and kinds to what we
call chance. But how false a view is this ! Every one has
heard that when an American forest is cut down, a very differ-
ent vegetation springs up ; but it has been observed that an-
cient Indian ruins in the Southern United States, which must
formerly haA'e been cleared of trees, now display the same
beavitiful diversity and proportion of kinds as in the surround-
ing virgin forest. What a struggle must have gone on during
long centuries betAveen the scA'cral kinds of trees, each annual-
ly scattering its seeds by the thousand ; Avhat Avar betAvcen
insect and insect — between insects, snails, and other animals,
Avith birds and beasts of pre}^ — all striving to increase, ail
fcx'ding on each other, or on the trees, their seeds and seed-
lings, or on the other plants Avhich first clothed the groimd
and thus checked the groAvth of the trees ! ThroAV vip a handful
of feathers, and all must fall to the ground according to defi-
nite laAvs ; but Iioav simple is the jiroblem Avhere each shall fall
compared to that of the action and reaction of the innumerable
plants and animals which haA'C determined, in the course of
centuries, the proportional numbers and kinds of trees noAV
ffroAving on the old Indian ruins !

The dependency of one organic being on another, as of a
parasite on its prey, lies generally betAveen beings remote in
the scale of nature. This is likcAvise sometimes the case Avith
those Avhich may strictly be said to struggle Avith each other
for existence, as in the case of locusts and grass-feeding quad-
rupeds. But the struggle Avill almost invariably be most
severe betAveen the individuals of the same species, for they
frequent the same districts, require the same food, and are

CiiAr. 111. STRUGGLE FOlt EXISTENCE. 81

exposed to the same dangers. lu the case of vai-ietics 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 Avhich best
suit the soil or climate, or are naturally the most fertile, Avill
beat the others and so yield more seed, and will consequently
in a few years quite su^iplant the other varieties. To keep vip
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, other-
wise the weaker kinds Avill steadily decrease in number and
disappear. So, again, with the varieties of sheep : it has licen
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 varie-
ties 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 could be kept up for half
a dozen generations, if they were allowed to struggle together,
like beings in a stUte of nature, and if the seed or young were
not annually sorted.

' Struggle for Life most severe between Individuals and Vari-
eties of the same Sjyecles.

As species of the same genus have usually, though by no
means invariably, much similarity in habits and constitution,
and always in structure, the struggle will generally be more
severe between species of the same genus, when they come
into competition Avith each other, than between species of dis-
tinct genera. We see this in the recent extension over parts
of the United States of one species of swallow having caused
the decrease of another species. The recent increase of the
missel-thrush in parts of Scotland has caused the decrease of
the song-thrush. How frequently we hear of one. species of
rat taking the place of another species under the most differ-
ent climates ! In Russia the small Asiatic cockroach has every-
where driven before it its great congener. In Australia the
imported hivG^bce is rapidly exterminating the small, .stingless
native bee. One species of charlock has been known to sup-
plant another species ; and so in other cases. We can dimly

82 STRUGGLE FOR EXISTENCE. Cuap. III.

see why the competition should be most severe between allied
forms, which fill nearly the same place in the economy of Na-
ture ; but probably in no one case could "vve precisely say why
one species has been victorious over another in the great bat-
tle of life.

A corollary of the highest importance may be deduced
from the foregoing remarks, namely, that the structure of
every organic being is related, in the 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 dandehon, and in the flattened and fringed legs of the
water-beetle, the relation seems at first confined to the ele-
ments of air and Avater. Yet the advantage of plumed seeds
no doubt stands in the closest relation to the land being
already thickly clothed Avith other plants ; so that the seeds
may be widely distributed and fall on iinoccupied ground. In
the water-beetle, the structm-e of its legs, so well adapted for
diving, allows it to compete with other a'quatic insects, to
hunt for its own prey, and to escape ser\dng as prey to other
animals.

The store of nutriment laid up witliin the seeds of many
plants seems at first sight to have no sort of relation to other
jilants. 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
luitriment in the seed is to favor the growth of the young seed-
ling, 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 qviadruplc its nimibers ? We know that it can per-
fectly well withstand a little more heat or cold, dampness or
dryness, for elsewhere it ranges into slightly hotter or colder,
damper or drier districts. In this case we can clearly sec that
if we wished in imagination to give the plant the power of in-
creasing in number, we should have to give it some advantage
over its competitors, or over the aTiimals which jireyed on it.
( )n the confines of its geographical range, a change of consti-
tution Avith respect to climate would clearly be an advan-
tage to our plant ; but we have reason to believe that only a

Chap. III. STKUGGLE FOR EXISTENCE. 83

few plants or aniniiils rani]fc so far, that tbcy are destroyed by
the rigor of the climate alone. Not until we reach the extreme
confines of life, in the Arctic regions or on the borders of an
utter desert, will competition cease. The land may be ex-
tremely cold or dry, yet there will be competition between
some few species, or between the individuals of the same spe-
cies, for the Avarmest or dampest spots.

Hence, also, we can see that when a plant or animal is
placed in a new country among new competitors, tliough the
climate may be exactly the same as in its former home, yet
the conditions of its life will generally be changed in an essen-
tial manner. If we wished to increase its average numbers in
its new home, we should have to modify it in a diflerent way
to what we should have to do in its native country; for we
should have to give it some advantage over a different set of
convpetitors or enemies.

It is good thus to try in imagination to give any form
some advantage over another. Probably in no single instance
should we know what to do, so as to succeed. It will con-
A-ince us of our ignorance on the mutual relations of all organic
beings ; a conviction as necessar}', as it seems difficult to ac-
quire. All that we can do is, to keep steadily in mind that
each organic 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 jirompt, and that the vigorous, the
healthy, and the haj^py, survive and multiply.

84 NATUEAL SELECTION. Ciiap. IV.

• CHAPTER IV.

NATURAL SELECTION, OK THE SURVIVAL OF THE FITTEST.

Natural Selection— its Power compared with jMan's Selection— its Power on Char-
acters of trifling Importance— its Power at all A<;e8 and on both Soxes— Sexual
Selection— On the CJenenility of Intercrosses between Individuals of the same
Species — Circumstances favorable and unfavorable to the Results of Natural Se-
lection, namely. Intercrossing:, Isolation, Nnnibor 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 Nat-
ural Selection, through Divergence of Character and Extinction, on the Descend-
ants from a C(<mmou Parent— Explains the Grouping of all Organic Heings— Ad-
vance in Organization — Low Forms preserved — Objections considered— Uniform-
ity of certain Characters due to their Unimportance and to their not having been
acted on by Natural Selection— Indefinite Multiplication of Species — Summary.

How will the struggle for existence, briefly discussed in
tlie last chapter, act in regard to variation ? Can the principle
of selection, which we have seen is so potent in the hands of
man, apply in Nature ? I think we shall see that it can act
most effectually. Let the endless number of peculiar varia-
tions in our domestic productions, and, in a lesser degree, in
those under Nature, be borne in ^ind ; as well as the strength
of the hereditary tendency. Under domestication, it may be
tridy said that the Avliole organization becomes in some degree
plastic. But the variability, which we almost universally meet
with in our domestic productions, is not directly produced, as
Hooker and Asa Gray have well remarked, by man ; he can
neither originate varieties, nor prevent their occurrence ; he
can onlv preserve and acciunulate such as do occur; uninten-
tionally he exjioses organic beings to new and changing con-
ditions of life, and variability ensues; but similar changes of
conditions might and do occur under Nature. Let it als«> be
borne in mind how inlinitely complex and close-fitting are the
mutual relations of all organic beings to each other and to
tlieir physical conditions of life ; and consequently what in-
finitely-varied diversities of structure may be of use to each
l)cing under changing conditions of life. Can it, then, be
thought improbable, seeing that variations usefid to man have
undoubtedly occurred, that other variations useful in some way

CiiAP. IV. NATURAL SELECTION. 85

to each beinp^ in the frrcat and complex battle of life, sliouUl
sometimes occur in the course of thousands of generations?
If such do occur, can we doubt (remembering' that many more
individuals are born than can possibly survive) that individuals
having any advantage, however slight, over others, would have
the best chance of surviving and of procreating their kind ?
On the other hand, we may feel sure that any variation in the
least degree injurious would be rigidly destroyed. This pres-
ervation of favorable variations, and the destruction of injuri-
ous variations, I call Natural Selection, or the Survival of the
Fittest. Variations neither useful nor injurious would not be
affected by natural selection, and would be left either a fluc-
tuating 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
tenn Natural Selection. Some have even imagined that nat-
ural selection induces variability, whereas it imphes only the
preservation of such variations as occur and are beneficial to
the being under its conditions of life. No one objects to agri-
culturists speaking of the potent effects of man's selection ; and
in this case the individual differences given by Nature, which
man for some object selects, must of necessity first occur.
Others have objected that the term selection implies conscious
choice in the animals Avhich become modified; and it has even
been urged that, as plants have no volition, natural selection is
not applicable to them ! In the literal sense of the word, no
doubt, natural selection is a false term ; but who ever objected
to chemists speaking of the elective affinities of the various
elements ? — and yet an acid cannot strictl}^ be said to elect the
base with which it in preference combines. It has been said
that I speak of natural selection as an active power or Deity ;
but who objects to an author speaking of the attraction of
gravity as ruling the movements of the planets ? Every one
knows what is meant and is implied by such metaphorical ex-
])ressions ; and they are almost necessary for brevity. So,
again, it is difficult to avoid personifying 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 as-
certained by us. With a little familiarity such superficial ob-
jections Avill be forgotten.

We shall best understand the probable course of natural
selection by taking the case of a country undergoing some

SG NATURAL SELECTION. Chap. IV.

slii^ht iihysical chanire, for instance, of climate. The propor-
tional numbers of its inhabitants -would almost immediately
undergo a change, and some species might become extinct.
AVe may conclude, from what avc have seen of the intimate
and complex manner in which the inhabitants of each country
arc boinid together, that any change in the numerical jiropor-
tions of some of the inhabitants, independently of the change
of climate itself, would seriously affect the others. If the
country were open on its borders, new fonns would certainly
innnigrate, and this also would often seriously disturb the re-
lations of some of the former inhabitants. Let it be remem-
bered how powerful the influence of a single introduced tree
or mammal has been sliOAvn 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 Natvire Avhich would
assuredly be better fdled up, if some of the original inhabitants
were in some manner modified ; for, had the area been ojien to
immigration, these same places would have been seized by in-
truders. In such cases, slight modifications, which in any way
favored the individuals of any species, by better adajiting them
to their altered conditions, would tend to be prcsen-ed ; and
natural selection would have free scope for the Avork of im-
provement.

We have reason to believe, as stated in the first chapter,
that changes in the conditions of life cause or excite a ten-
dency to vary ; and in the foregoing case the conditions are
supposed to have changed, and this would manifestly be favor-
able to natural selection, by giving a better chance of profit-
able variations occurring; and unless such do occur, natural
selection can do nothing. Under the term of "variations," it
must never be forgotten that mere individual diflerences are
always included. As man can certainly ]noducc a great result
with his domestic animals and plants by adding up in any
given direction individual differences, so could natural selection,
but far more easily, from having incomparably longer time for
action. Nor do I believe that any great physical change, as
of climate, or any imusual degree of isolation to check immi-
gration, is actually necessary to ])roduce new and unoccujiied
places for natural selection to fill up by modifying and im])rf)v-
ing some of the A-arying inhabitants. For as all the inhabit-
ants of each country are struggling together Avith nic(^ly-bal-
anccd forces, extremely-slight modifications in the structure oi

CnAi-. IV. NATURAL SELECTION. 87

habits of one si)ecics would often give it an advantugc over
others ; and still further modifications of the same liind Avould
often still further increase the advantage, as long as the species
continued under the same conditions of life and profited by
similar means of sul)sistence and defence. No country can be
named, in which all the native inhabitants are now so perfectly
adapted to each other and to the physical 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, tliat they have allowed
foreigners to take iirin ])ossession of the land. And, as for-
eigners have thus in every country beaten some of the natives,
Ave may safely conclude that the natives might have been mod-
ified with advantage, so as to have better resisted the in-
truders.

As man can produce and certainly has produced a great
result by his methodical and unconscious means of selection,
what may not natural selection effect ? Man can act only on
external and visible characters : Nature, if I may be allowed
to j)ersonify the natural preservation or survival of the fittest,
cares nothing for appearances, except in so far as they are use-
ful 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, 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 peculiac
and fitting manner ; he feeds a long and a short beaked pigeon
on the same food ; he does not exercise a long-backed or long-
legged quadrup(^(l in any peculiar manner ; he exposes sheep
with long and short wool to the same climate. lie 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 produc-
tions. He often begins his selection by some half-monstrous
form; or at least by some modification prominent enough to
catch the eye or to be plainly useful to him. Under Nature,
the slightest differences of structure or constitution may well
turn the nicely-balanceil scale in the struggle for life, and so be
preserved. How fleet uig are the wishes and eflbrts of man!
how short his time ! and consequently how poor will be his
results, comjiared with those accumulated l)y Nature during

88 NATUKAL SELECTION. Chap. IV.

whole geological periods ! Can we wonder, then, that Nature's
productions should be far " truer " in character than man's pro-
ductions ; tliat they should be infinitely better adapted to the
most complex conditions of life, and should plainly bear the
stamp of far higher workmanship?

It may metaphorically l)e said that natural selection ig daily
and hourly scrutinizing, throughout the world, the slightest vari-
ations ; rejecting those that are bad, preserving and adding up
all that are good ; silently and insensibly working, whenever
and wherever opportunity oft'ers, 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 tlie lapse of ages, and then
so imperfect is our view into long-past geological ages, that
we see only that the forms of life are now different from what
they formerly were.

In order that any great amount of modification in any part
should be eflectcd, a variety when once formed must again,
perliaps after a long interval of time, vary or present individ-
ual difl"erences of the same favorable nature, and these must be
again preserved, and so onward step by step. Seeing that
individual differences of all kinds perpetually recur, this can
hardly be considered as an unwarrantable assumption. But
whether all this has actually taken place must be judged by
how far the h}q5othesis accords with and explains tlie general
phenomena of Nature. On the other liand, the ordinary belief
that the amount of possible variation is a strictly-limited quan-
tity is 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, avc must believe that these
tints are of service to these birds and insects in preserving them
from danger. Grouse, if not destroyed at some period of their
lives, would increase in countless numbers ; they are known to
suffer largely from bii'ds of prey ; and hawks are guided by eye-
sight to their prey — so much so, that on parts of the Continent
persons are warned not to keep white pigeons, as being the
most liable to destruction. Hence natural selection miglit be
most eflective in giving the proper color to each kind of grouse,
and in keeping that color, when once acquired, true and con

CiiM-. IV. NATURAL SELECTION. 89

stant. Nor ougbt we to think that the occasional destruction
of an animal of any particular color would produce little effect :
we should remember how essential it is in a flock of white
slicep to destroy every lamb with the faintest trace of black.
A\'e have seen how the color of the ho<^s, when fcedino: on the
" paint-root " in Florida, 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, Down-
ing, that in the United States smooth-skinned fruits sullcr far
more from a beetle, a curculio, than those Avith down ; that pur-
ple plums suffer far more from a certain disease than 3X'llow
plums ; whereas another disease attacks yellow-fleshed peaches
far more than those with other colored flesh. If, with all the
aids of art, these slight differences make a great difl'crence in
cultivating the several varieties, assuredly, in a state of nature,
where the trees would have to struggle with other trees and
with a host of enemies, such differences would effectually settle
whicli variety, whether a smooth or downy, a yellow or purple
fleshed fruit, should succeed.

In looking at many small points of difference between spe-
cies, which, as far as our ignorance permits us to judge, seem
quite unimportant, we must not forget that climate, food, etc.,
may have produced some direct eflect. It is also necessary to
bear in mind that, owing to the law of correlation, Avhen one
part varies, and the A\ariations are accumulated through natural
selection, other modifications, often of the most unexpected
nature, avUI ensue.

As we see that those variations Avhicli under domestication
appear at any particular })eriod of life, tend to rcapjwar 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 tlieir chickens; in the horns of our
sheep and cattle when nearly adult — so, in a state of nature,
natural selection Avill be enabled to act on and modify organic
beings at any age, by the accumulation of variations profitable
j-t that age, and by their inheritance at a corresponding age.
If it profit a plant to have its seeds more and more Avidely dis-
seminated by the wind, I can sec no greater difliculty in this
being effected tlirough natural selection than in the cotton-
planter increasing and improving by selection the down in the

DO SEXUAL SELECTION. CriAr. IV.

pods on his cotton-trces. Natural selection may modify and
adapt the larva of an insect to a score of continovncics, wholly
tlillcrent from tliose which concern the mature insect; and
these modilicalions may affect, throug'h correlation, the stnio
ture of the adult. So, conversely, modifications in the adult
may affect tlie 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 in
relation to the parent, and of the parent in relation to the
young. In social animals it will adapt the structure of each
indivitlual for the benefit of the Avhole community ; if this in
consequence profits by the selected change. What natural
selection cannot do, is to modify the structure of one species,
without giving it any advantage, for the good of another spe-
cies ; and, though statements to this effect may be found in
works of natural history, I cannot find one case which will
bear investigation. A structure used only once in an animal's
life, if of high importance to it, might be modified to any ex-
tent by natural selection ; for instance, the great jaws pos-
sessed by certain insects, used exclusively for opening the
cocoon — or the hard tip to the beak of nestling birds, used for
breaking th(^ eir'^. It has been asserted that, of the best short-
lieaked tumbler-pigeons, a greater number 2:)erish in the egg
than are al^le 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-
j^rown pigeon very short for the bird's own advantage, the pro-
cess of modification Avould be very slow, and there would be
simultaneously the most rigorous selection of all the young
birds within the egg, which had the most powerful and hardest
beaks, for all with weak beaks would inevitably perish ; or,
more delicate and more easily-l)rokcn shells might be se-
lected, the thickness of the shell being knoAvn to vary like
every other structure.

Sexual Selection.

Inasmuch as peculiarities often appear under domestication
in one sex and become hereditarily attached to that sex, the
same fact no doubt occurs under Nature, and if so, natural se-
lection will be able to modify one sex in its functional n'lations
to the otlier sex, or in relation to Avholly-ditrerent liabits of life
in the two sexes, as is sometimes the case with insects. And

Chap. IV. SEXUAL SELECTION. 91

this leads ine to saj a few words on what I call Sexual Selec-
tion. This depends, not on a sti'ugf^le for existence, l)ut on a
struo^g'lc between the males for possession of tlie females; the
result is not death to the inisuccessful competitor, but few or
HO oifsprino-. Sexual selection is, therefore, less rit^orous than
natural selection. Generally, the most vigorous males, those
\vhich are best fitted for their places in Nature, will leave most
progeny. But, in many cases, victory depends not on general
vigor, but on having special weapons, confined to the male
sex. A hornless stag or spurless cock would have a poor
chance of leaving numerous ollspring. Sexual selection, by
always allowing the victor to breed, might surely give indom-
itable courage, length to the spur, and strength to the wing
to strike in the spurred leg, as in the case of the brutal cock-
fighter, who knows well how to improve his breed hy the care-
ful selection of the best cocks. How low in the scale of Nature
the law of battle descends, I know not ; male alligators have
been described as fighting, bellowing, and Avhirling round, like
Indians in a war-dance, for the possession of the females ; male
salmons have been seen fighting all day long ; male stag-])eetles
sometimes bear wounds from the huge mandibles of other
mules ; tlie males of certain hymcnopterous insects have been
fivcjuently seen by that inimitable observer M. Fabre, fighting
for a particular female, Avho sits by, an apparently imcon-
cerned beholder of the struggle, and then retires with the con-
queror. The war is, perhaps, severest between the males of
l)olygamous animals, and these seem oftenest provided with
special weapons. The males of carnivorous animals arc already
well armed ; though to them and to others, special means of de-
fence may be given through means of sexual selection, as the
mane to 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 char-
acter. All those who have attended to the subject, believe
that there is the severest rivalry between the males of many
species to attract l)y singing the females. The rock-thrush of
Guiana, birds of Paradise, and some others, congregate; and
successive males display tlieir gorgeous plumage and perform
strange antics l)efore the females, whieli, standing bv as spec-
tators, at last choose the most attractive partner. 1'hose who
have closely attended to birds in confinement well know that
they often take individual preferences and dislikes: thus Sir

02 ILLUSTRATIONS OF THE ACTION OF Chap. IV.

Iv. Iloroii has described how one pied peacock was eminently
attractive to all his hen-birds. I cannot here enter on the ne-
cessary details ; but if man can in a short time jjive elegant
carriage and beauty to his bantams according to liis standard
of beauty, I can see no good reason to doubt that female
birds, by selecting, during thousands of generations, the most
melodious or beautiful males, according to their standard of
beauty, might jiroduce a marked effect. Some well-known
laws, with respect to the plumage of male and female birds, in
comparison with the plumage of the young, can be explained
through the action of sexual selection on variations occurring
at diiierent ages, and being transmitted to the males alone or
to both sexes at a corresponding age ; but I have not space
here to enter on this "subject.

Thus it is, as I believe, that when the males and females of
any animal have the same general habits of life, but diller in
structure, color, or ornament, such differences have been main-
ly caused by sexual selection ; that is, by individual males hav-
ing had, in successive generations, some slight advantage over
other males, in their weapons, means of defence, or charms ;
and having transmitted these advantages to their male off-
spring. Yet, I would not Avish to attribute all such sexual dif-
ferences to this agency : for we see peculiarities arising and
becoming attached to the male sex in our domestic animals (as
the greater development of the Avattle in male carrier-pigeons,
horn-like protuberances in certain fowls, etc.), Avhich are in no
way useful. We see analogous cases under Nature — for in-
stance, the tuft of hair on the breast of the turkej'-cock, Avliich
cannot be useful, and can hardly be ornamental ; indeed, had
the tuft appeared under domestication, it would have been
called a monstrosity.

Illustratio7is of the Action of Natural Selection, or the Sur-
vival of the Fittest.

In order to make it clear how, as I believe, natural selec-
tion acts, I must beg permission to give one or two imaginary
illustrations. Let us take the case of a wolf, which preys on
various animals, securing some by craft, some by strength, and
some by (leetness ; and let us suppose that tlie fleetest prey,
a deer for instance, had from any change in the country in-
creased in numbers, or that other prey had decreased in num-
bers, during that season of the year when the wolf was hardest

CiiAP. IV. NATUKAL SELECTION. 93

pressed for food. Under such cLrcumstances the swiftest and
slimmest wolves would have the best chance of survdving-, and
so be preserved or selected — provided always that they retained
strength to master their prey at this or at some other period
of the year, when they might bo compelled to prey on other
animals. I can see no more reason to doubt tliis, than that
man can improve the fleetness of his greyhounds by careful and
methodical selection, or by unconscious selection which results
from each man trying to keep the best dogs without any
thought of modifying the breed. I may add, that, according
to Mr. Pierce, there are two varieties of the wolf inhabiting
the Catskill Mountains in the United States, one with a light,
greyhound-like form, which pursues deer, and the other more
bulky, with shorter legs, which more 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 strong-
Ij'-marked variation having been preserved. In former editions
of this work I sometimes spoke as if this latter alternative had
frequently occurred. I saw the great importance of individual
differences, and this led me fully to discuss the results of un-
conscious selection by man, which depends on the preservation
of the better-adapted or more 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 preserved,
it would generally be lost by subsequent intercrossing with
ordinary individuals. Nevertheless, until reading an able and
valuable article in the N'orth Uritish lievieio (18G7), I did not
appreciate how rarely single variations, whether slight or
strongly-marked, could be perpetuated. The author takes the
case of a pair of animals, whicli produce during their lifetime
two hundred offspring, of which, from various causes of de-
struction, only two on an average survive to procreate their
kind. Tliis is rather an extreme estimate for most of the
higher animals, but by no means so for many of the lower
organisms. He then shows that if a single individual were
born, whicli varied in souk* maimer, giving it twice as g'ood a
chance of life as that of the other individuals, yet the chances
would be strongly against its survival. Supposing it to sur-
vive and to breed, and that half its young inherited the favor-
able variation ; still, as the Reviewer goes on to show, the
young would liavo only a slightly-better chance of survaving

3 1 ILLUSTEATIOKS OF TUE ACTION OF Cuap. IV.

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
couhl procure its food more easily by having its beak curved,
and if one Avere born with its beak strongly carved, and
wliich consequently flourished, nevertheless there would be
a very poor chance of this one individual perpetuating its kind
to the exclusion of the common form ; but there can hardly be
a doubt, judging by what we see taking place imder domesti-
cation, that this result Avould follow from the preservation dur-
ing many generations of a large number of indiWduals with
more or less curved beaks, and from the destruction of a still
larger numlier Avith the straightest beaks.

It should not, however, be overlooked that certain varia-
tions, which no one would rank as mere individual differences,
frequently recur, owing to a similar organization being simi-
larly acted on — of which fact numerous instances could be
given with our domestic productions. In such cases, if a vary-
ing individual did not actually transmit to its offspring its
newly-acquired character, it would imdoubtedly transmit, as
long as the existing conditions remained the same, a still
stronger tendency to vary in the same manner. The condi-
tions might indeed act in so energetic and definite a manner as
to lead to the same modification in all the individuals of the
species without the aid of selection. But we may suppose
that the conditions sufficed to effect only a third, or fourth, or
tenth part of the individuals ; and several such cases could be
given ; for instance, it has been estimated by Graba that in the
Faroe Islands about one-fiftli of the guillemots, Avhich all breed
together, consist of a well-marked variety ; and this Avas for-
meily ranked as a distinct species under the name of Uria
lacrymans. Now, in such cases, if the variation were of a ben-
eficial nature, the original form would soon be sup})lantcd by
the modified form, through the survival of the fittest.

With reference to the eftects of intercrossing and of com-
petition, it should be borne in mind that most animals antl plants
keep to their proper homes, and do not needlessly Avander
aljout ; Ave see this CA'cn Avith migratory birds, Avhich almost
always return to the same district. Consequently each newly-
formed variety Avould generally be at lirst local, as seems to
1)0 the common rule Avith A'arieties in a state of nature ; so that
siinilarlA'-modified individuals Avould soon exist in a small l)ody
together, and would often breed together. If the v.vw variety

Chap. IV. NATURAL SELECTION. 95

was successful in its battle for life, it would slowly spread from
a central spot, competinp^ Avitli and conf[U(>rinof the uncluuifred
individuals on the niar<>-ins of an ever-increasing circle. But
to the subject of intercrossing we shall have to return. It may
be objected by those who have not attended to natural history,
that tlie long-continued accumulation of individual differences
could not give rise to parts or organs which seem to us, and
arc often called, new. But, as we shall hereafter find, it is dif-
ficult to advance any good instance of a really new organ ;
even so complex and perfect an organ as the eye can be showa t(<
graduate downward into mere tissue sensitive to diffused light
It may be worth Avhile to give another and more complex
illustration of tlie action of natural selection. Certain plants
excrete sweet juice, apparently for the sake of eliminating
something injurious from their sap: this is effected, for in-
stance, by glands at the base of the stipules in some Legunii-
nosa^, and at the backs of the leaves of the common laurel.
This juice, though small in quantity, is greedily sought by in-
sects ; but their visits do not in any way benefit the plant.
Now, let us suppose that the juice or nectar was excreted
from the inside of the flowers of a certain number of plants of
anv species. Insects in seeking the nectar would get dusted
with pollen, and would certainly 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 cross-
ing, as Ave have good reason to believe, would produce vigor-
ous seedlings, which consequently would have the best chance
of flourishing and surviving. The plants which produced flow-
ers with the largest glands or nectaries, excreting most nectar,
would oftencst be visited by insects, and would oftenest be
crossed ; and so in the long-run would gain the upper hand and
form a local variet}'. The flowers, also, wliich had their sta-
mens and pistils placed, in relation to the size and habits of the
particular insect which visited them, so as to favor in any
dcgr(>e the transportal of the pollen, would likewise be favored.
AVe might have taken the case of insects visiting flowers for
Ihc sake of collecting pollen instead of nectar; and as pollen is
formed for the sole purpose of fertilization, its destruction ap-
pears to be a simple loss to the plant ; 3-et if a little pollen
"were canied, at first occasionally and then habitually, by the
pollen-devouring insects from flower to flower, and a cross thus
ellected, although nine-tenths of the pollen were destroyed, it
might still be a great gain to the plant; and the individuals

96 ILLUSTRATIONS OF THE ACTION OF Chap. IV.

which produced more and more pollen, and had larger anthers,
would be selected.

"When our plant, by the above process long continued, had
been rendered highly attractive to insects, they would, unin-
tentionally on their part, regularly carry pollen from flower to
flower; and that they do this cfl'ectually, I could easily show
l)y many striking facts. I will give only one, as likewise illus-
trating one step in the separation of the sexes of plants. Some
liolly-trees bear. only male flowers, which have four stamens
])roducing a rather small quantity of pollen, and a rudimentary
l)istil ; other holly-trees bear only female flowers ; these have
a full-sized pistil, and four stamens with shrivelled anthers, in
which not a grain of pollen can be detected. Having found
a female tree exactly sixty yards from a male tree, I put the
stigmas of twenty flowers, taken from difierent 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, neverthe-
less 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 rendered so highly attractive to
insects that pollen was regularly carried from flower to flower,
another process might commence. No naturalist doubts the
advantage of what has been called the " physiological division
of labor ; " hence we may believe that it would be advanta-
geous 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,
tlien, 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 di\'ision of
labor, individuals with this tendency more and more increased,
would be continually favored or selected, until at last a eoin-
phite separation of the sexes might be effected. It would
take up too much space to show the various steps, through
diinorpliism and other means, by which the separation of the
sexes in plants of various kinds is aiiparently now in progress ;

Chap. IV. NATUKAL SELECTION. 97

but I may add that .some of the species of holly in North
America are, accordiiifj to Asa Gray, in an intermediate con-
dition, or, as he cxpixvsses it, arc more or less diceciously po-
lygamous.

Let us now turn to the nectar-feeding insects. We may
suppose the plant, of which we have been slowly increasing
the nectar hy continued selection, to be a common plant ; and
that certain insects depended in main part on its nectar for
fooil. 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 they
can, with a very little more troul)le, enter by the mouth.
Bearing such facts in mind, it may be believed that, under cer-
tain circumstances, individual differences in the curvature or
length of the proboscis, etc., too slight to be appreciated by
us, might profit a bee or other insect, so that certain individ-
uals would be able to obtain their food more quickly than
others ; and thus the communities to which they belonged
would ilourish and throw off many swarms inheriting the same
peculiarities. The tulles of the corolla of the common red and
incarnate clovers (Trifolium pratense and incarnatum) do not
on a hasty glance appear to differ in length ; yet the hive-bee
ran easily suck the nectar out of the incarnate clover, but not
out of the common red clover, Avhich is visited by humble-bees
alone ; so that whole fields of the red clover in vain offer an
abundant supply of precious nectar to the hive-bee. Tliat this
nectar is much liked by the hive-bee is certain ; for I have re-
])eatedly seen, but only in the autumn, many hive-bees sucking
the (lowei-s 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
nve 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 and which freely crosses with the common hive-bee, is
able to. reach and suck the nectar of the connnon red clover.
Thus, in a country where this kind of clover abounded, it might
be a great advantage to the hive-bee to have a slightly-longer
or differently-constructed proboscis.. On the other hand, as
the fertility of this clover absolutely depends on bees visiting

98 INTEECEOSSING OF INDIVIDUALS. Chap. IV.

tlio llowiTri, if humble-bees were to become rare in any country,
it miglit be a great advantage to the plant to have a shorter
or more deeply-divided corolhi, so that the hive-bees should be
induced to suck its flowers. Thus I can understand how a
flower and a bee might slowly become, either simultaneously
or one after the other, modified and adapted to each other in
the most perfect manner, by the continued preservation of all
the individuals M'hich presented slight deviations of structure
mutually favorable to each other.

I am Avcll aware that this doctrine of natural selection,
exemplified in the above imaginary instances, is open to the
same objections which were at first urged against Sir Charles
Lycll's noble \aews on " the modern changes of the earth, as
illustrative of geology ; " but Ave now seldom hear the agencies,
still at work, spoken of as trifling or insignificant, when applied
to the excavation of the deepest valleys or to the formation of
long lines of inland cliffs. Natural selection acts only by the
preservation and accumulation of small inherited modifications,
each profitable to the preserved being ; and as modern geology-
has almost banished such views as the excavation of a great
valley by a single diluvial wave, so will natural selection, if
it be a true principle, banish the belief of the continued crea-
tion of new organic beings, or of any great and sudden modifi-
cation in their structure.

On the Infererossmff of Individuals.

I must here introduce a short digression. In the case of
animals and plants with separated sexes, it is of course obvi-
ous that two individuals must always (with the exception of
the curious and not well-understood cases of parthenogenesis)
unite for each birth ; but in the case of hermaphrodites this is
far from obvious. Nevertheless tliere is reason to believe that
with all hermaphrodites two individuals, either occasionally or
habitually, concur for the reproduction of their kind. This
vicAV was first suggested by Andrew Knight. "SVe shall pres-
enth' see its importance : but I must here treat the subject
with extreme 1)revity, thougli I have the materials prepared
for an anijile discussion. All vertebrate animals, all insects,
and some other large groups of animals, pair for each birth.
Modern research has nuich diminished the number of supjiosed
hermajihrodites, and of real hermaphrodites a large number
pair; that is, two individuals regularly unite for reproduction,

CiiAr. IV. INTERCROSSING OF INDIVIDUALS. 99

Aviiieh is all that concerns us. But still there arc many lier-
maphrodito animals wliicli certainly do not habitually pair, and
a \-ast majority of plants are hermaphrodites. What reason, it
may be asked, is there for supposing in these cases that two
individuals ever concur in reproduction? As it is impossible
here to enter on details, I nuist trust to some general consid-
erations alone.

In the first place, I have collected so large a body of facts,
showing, in accordance with the almost universal belief of
breeders, that Avith animals and plants a cross between differ-
ent 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 dose interbreeding diminishes vig-
or and fertility ; tliat these facts alone incline me to believe
that it is a general law of Nature that no organic being fertil-
izes itself for a perpetuity of generations ; but that a cross
with another individual is occasionally — perhaps at long inter-
vals of time — indispensable.

On the belief that this is a law of Nature, we can, I think,
miderstand several large classes of facts, such as the follow-
ing, which on any other view are inexplicable. Every hybrid-
izer knows how unfavorable exposure to wet is to the fertili-
zation of a flower, yet Avhat a multitude of flowers have their
anthers and stigmas fully exposed to the weather ! If an
occasional cross be indispensable, notwithstanding that the
plant's own anthers and pistil stand so near each other as
almost to insure self-fertilization, the fullest freedom for the
entrance of pollen from another individual Avill explain the
above state of exposure of the organs. Many flowers, on the
other hand, have their organs of fructification closely enclosed,
as in the great papilionaceous or pea-fainily ; but in most of
these flowers there is a curious adaptation between their struc-
ture and the manner in which bees suck the nectar; for, in
doing this, they either push the flower's own pollen on the
stigma, or bring pollen from another flower. So necessary are
the visits of bees to many ]iapiIionaceous flowers, that I have
found, by experiments published elsewhere, that their fertility
is greatly diminished if these visits be prevented. Now, it is
scarcely possible that bees should fly from flower to flower,
and not carry pollen from one to the other, to the great good,
as I believe, of the plant. IJees will act lik(^ a camel-hair pen-
cil, and it is quite sufficient just to touch the anthers of one
flower and then the stigma of another with the same brush to

100 INTEKCEOSSING OF INDIVIDUALS. Ca.vp. IV.

insure fertilization ; but it must not be supposed that bees
would thus produce a multitude of hybrids between distinct
species ; for if you brinf^ on the same brush a plant's own pol-
len and pollen from another species, the former will have such
a prepotent effect, that it will invariably and completely de-
stroy, as has been shown by Gartner, any influence from the
foreig'n pollen,

^V'hen the stamens of a flower suddenly spring toward the
pistil, or slowly move one after the other toward it, the con-
trivance seems adapted solely to insure 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 Kol-
reutcr 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, so largely do they naturally cross. In
many other cases, far from there being any aids for self-fertili-
zation, there are special contrivances, as I could show from the
writings of C C. Sprengel and from my own observations,
which effectually prevent the stigma receiving pollen from its
own flower : 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 an-
thers of each flower, before the stigma of that individual flower
is ready to receive them; and as this flower is never visited, at
least in my garden, b}^ insects, it never sets a seed, though by
placing pollen from one flower on the stigma of another, I
raised plenty of seedlings ; and while another species of Lobe-
lia growing close by, which is visited by bees, seeds freely.
In very many other cases, though there be no special mechani-
cal contrivance to prevent the stigma of a flower receiving its
own pollen, yet, as C. C. Sprengel has 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 tliat these plants have in fact separated
sexes, and nnist habitually be crossed. So it is with the recip-
rocally dimorphic and trimorphic plants pre\dously alluded to.
How strange are these facts ! How strange that the pollen
and stigmatic surface of the same flower, though placed so
close together, as if for the very purpose of self-fertilization,
should in so many cases be nuitually useless to each other!
Hov>' simjily are these facts explained on the view of an oeca-

OiAP. IV. INTERCROSSING OF INDIVIDUALS. 101

sional cross Avilli a distinct individual being advantageous or
indispensable !

If several varieties of tlie cabbage, radish, onion, and of
some otlicr plants, be allowed to seed near eacli other, a large
majority, as I have found, of the seedlings thus raised will
turn out mongrels : for instance, I raised 233 seedling cab-
Ixigcs from some jilants 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 l)y its own six sta-
mens, but by those of the many other flowers on the same plant;
and the pollen of each flower readily gets on its own stigma
without insect-agency ; for I have found that a plant carefully
protected produced the full number of pods. How, then,
comes it that sucli a vast number of the seedlings are mongrel-
ized ? • I suspect that it must arise from the pollen of a distinct
varii'tj/ having a prepotent effect over a flower's own pollen ;
and that this is part of the general law of good being derived
from the intercrossing of distinct individuals of the same spe-
cies. When distinct species are crossed the case is directly the
reverse, for a jilant's own pollen is almost always prepotent
over foreign pollen ; but to this subject Ave shall return in a
future chapter.

In the case of a large tree covered with innumerable flow-
ers, 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 tre*, and that flowers on the same tree can be con-
sidered as distinct individuals only in a limited sense. I be-
lieve this objection to be valid, but that Nature has largely pro-
vided against it by giving to trees a strong tendency to bear
flowers with separated sexes. When the sexes are separated,
although the male and female flowers may be produced on the
same tree, we can see that pollen must be regularly carried
from flower to flower; and this will give a better chance of
]i()llen being occasionally carried from tree to tree. That trees
belonging to all Ord<»rs have their sexes more often separated
than other plants, I And to be the case in this country ; and at
my request Dr. Hooker tabulated the trees of New Zealand,
and Dr. Asa Gray those of the United States, and the result
was as I anticipated. On the other hand. Dr. Hooker has re-
cently informc(l me that he flnds that the rule does not hold in
Australia ; and I have made these few remarks on the sexes of
trees simply to call attention to the subject.

102 INTERCROSSING OF INDIVIDUALS. Cii\r. IV.

Turning- for a very brief space to animals : on ilic land
there are some hcrmaplirodites, as land-moUusca and eartli-
worms ; but these all pair. As yet I have not found a single
case of a terrestrial animal Avhich fertilizes itself. Wc can un-
derstand this remarkable fact, Avhich offers so strong a contrast
Avith terrestrial plants, on the view of an occasional cross being
indispensable, by considering the medium in which terrestrial
animals live, and the nature of the fertilizing element ; for we
know of no means, analogous to the action of insects and of
the wind in the case of plants, by which an occasional cross
could be effected "with terrestrial animals, "without the concur-
rence of two individuals. Of aquatic animals, there are many
self-fertilizing hermaphrodites ; but here currents in the water
offer an obvious means for an occasional cross. And, as in the
case of flowers, I have as yet failed, after consultation Avith
one of the highest authorities, namely, Prof. Huxley, to dis-
cover a single case of an hermaphrodite anim:il with the organs
of reproduction so perfectly enclosed within the body, that ac-
cess from without and the occasional influence of a distinct in-
dividual can be shown to be physically impossible. Cirripedes
long appeared to me to present a case of very great difficulty
under this point of view ; but I have been enabled, by a
fortunate chance, elsewhere to prove that two individuals,
though both are self-fertilizing hermaphrodites, do sonietimcs
cross.

It must have struck most naturalists as a strange anomaly
that, in the case of both animals and plants, species of the same
family and even of the same genus, though agreeing closely
with each other in almost their whole organization, yet are not
rarely, some of them hermaphrodites, and some of them uni-
sexual. But if, in fact, all hermaphrodites do occasionally in-
tercross with other individuals, the difference between hermaph-
rodites and unisexual species, as far as function is concerned,
becomes very small.

From these several considerations and from the many spe-
cial facts which I have collected, but which I am not here able
to give, I am strongly inclined to suspect that, both in the
vegetable and animal kingdoms, an occasional intercross with
a distinct individual is a law of Nature. I am well aware that
there are, on this view, many cases of difficulty, some of which
I am trying to investigate. Finally, then, we may conclude
that, in many organic beings, a cross between two individuals
is an ()l)vious necessity for each l)irth ; in many others it occurs

Chai-. IV. niODUCTION OF NEW FORMS. 103

perhaps only at long' intervals ; but in none, as I suspect, can
self-fertilization go on for perpetuity.

Clrcnmstanccs favorable for the Production of Neio Forms
through Natural Selection.

Tliis is an extremely intricate subject. A great amount of
variability, under which term individual differences are always
included, will evidently be favorable. A large number of in-
dividuals, by giving a better chance for the appearance of
profitable variations within any given period, will compensate
for a lesser amount of variability in each individual, and is, I
believe, an extremely important element of success. Though
Nature grants long periods of time for the work of natural se-
lection, she does not grant an indefinite period ; for, as all or-
ganic -beings arc striving to seize on each place in the economy
of Nature, if any one species docs not become modified and im-
proved 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 nat-
ural sclecticjn. Tlie tendency to reversion may. often check or
prevent the work ; but as tliis tendency has not prevented
man from forming by selection nimierous domestic races, why
.sliould it prevail against natural selection ?

In the case of methodical selection, a breeder selects for
some definite object, and free intercrossing Avill wholly stop
his work. But when many men, without intending to alter the
breed, have a nearly common standard of perfection, and all
try to procure and breed from the best animals, much improve-
ment surely but slowly follows from this unconscious process
of selection, notwithstanding a large amount of crossing with
inferior animals. Thus it Avill be in Nature; for within a con-
Ihied area, with some place in its polity not perfectly occu]iicd,
natural selection will always tend to preserve all the individ-
uals varying in the right direction, though in different degrees,
so as better to fill up the imoccupied place. But if the area be
very large, its several districts will almost certainly present
different conditions of life ; and then, if the same species under-
g()(^s modification in different parts, the newly-formed varieties
will intercross on the confines of each district. But we shall
see in the seventh chapter that intermediate varieties, inhabit-
ing an intermediate district, whether the result of the crossing
of other varieties, or originally formed with an intermediate

104 CIRCUMSTANCES TAYOKABLE TO THE CnAr. IV.

character, will in llie lonrr-run generally be supplanted by one
of the varieties on either hand. Intercrossing will aflect those
animals most which unite for each birth and Avauder 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 hennaphrodite organisms which cross only occasionally,
and likewise with animals which unite for each l)irth,but which
wander little and can increase at a very rapid rate, a new and
iinpro\'ed variety might be quickly formed on any one spot,
and might there maintain itself in a body and afterward
spread, so that the crossing would be chiefly between the indi-
viduals of the new variety living together in the same place.
On this principle, nurserymen always prefer saving seed from
a large body of plants, as the chance of intercrossing is thus
lessened.

Even in the case of animals which breed slowly and xmite
for each birtli, Ave must not assume that the effects of natural
selection Avill always be immediately oveq:)OAvered by free inter-
crossing ; for I can bring a considerable body of facts, showing
that, Avitljin the- same area, varieties of the same animal may
long remain distinct, from haunting different stations, from
breeding at slightly-tlifferent seasons, or from varieties of the
same kind preferring to pair together.

Intercrossing plays a very important part in Nature in keep-
ing the individuals of the same species, or of the same \'ariety,
true and xmifonn in character. It will obviously thus act far
more elViciently with those animals Avhich unite for each birth ;
but as already stated we have reason to believe that occasional
intercrosses take place with all animals and with all plants.
Even if these take ]ilace only at long intcr\-als of time, the
young thus produced Avill gain so much in vigor and fertihty
over the offspring from long-continued self-fertilization, that
the}' Avill have a better chance of surviving and propagat-
ing their kind ; and thus, in the long-run, the influence of inter-
crosses, even at rare intervals, will be great. If there exist
organic beings which never intercross, uniformity of character
ran be retained among them, as long as their conditions of
life remain tho same, only through the principle of inheritance
and through natural selection destroying any which depart from
tlic proper type ; but if their conditions of life change and they
undergo modification, xmiformity of character can be given to
their modified offspring, solely b^' natural selection prescn-ing
similar favorable variations.

Cbap. IV. KESULTS OF NATURAL SELECTION. IQH

Isolation, also, is an important clement in the changes
effected tlirout^h 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 individuals of the same spe-
cies in the same manner. Intercrossing with the inhal)itants
of the surrounding districts ^vill, also, be prevented. Moritz
Wagner has lately published an interesting essay on this sub-
ject, and has shown that the service rendered by isolation in
preventing crosses between newly-formed varieties is probably
greater even than I have supposed. But from reasons already
assigned I can by no means agree with this naturalist, that
migration and isolation are necessary for the formation of new
species. The importance of isolation is likewise great in pre-
venting, 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 econ-
cmy of the district are left open for the old inhabitants to strug-
gle for and become ada])ted to. Lastly, isolation will give time
for a new variety to be slowly improved ; and this may some-
times be of importance in the productioTi of new species. If,
however, an isolated area be very small, either from being sur-
rounded by jjarriers, or from having very peculiar physical con-
ditions, the total number of the inlialiitants will be small ; and
this will retard the production of new species through natural
selection, by decreasing the chances of the appearance of favor-
able individual diflerences.

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-imjiortant part in modifying species, as if
all ^vere necessarily undergoing change through the action of
some iimate law. Lapse of time is only so fur injportant, and
its importance in this respect is great, that it gives a better
chaiKMj of beneficial variations arising, being selected, increased,
and fixed, in relation to the; slowly-clianging organic and in-
organic (•f)iiditions of life. It likewise favors the definite action
of the conditions of life.

If \\c turn to Nature to test the truth of these remarks, and
look at any small, isolated area, such as an oceanic island, al-
though the number of the dilTt^rent species inhabiting it is small,
as we shall see in our chapter on Geographical Distribution;
yet of the species a very large proportion are endemic — that is,

lOO CinCU.MSTANCES FAVORABLE TO THE Ciiap. IV,

have l.ccn produced llicre, and nowhere else in the world.
Hencn^ :m oceanic ishxnd at first sie^ht seems to have been
hig'hly 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 production of new organic forms, we
ought to make the comparison -within equal times ; and this
wc are incajiahlo of doing.

Although isolation is of great importance in the production
of new species, on the Avhole I am inclined to believe that large-
ness of area is still more important, especially for the produc-
tion of species which shall prove capable of enduring for a long
period, and of spreading Avidcly. Throughout a great and open
area, not only Avill there be a better chance of favorable varia-
tions arising from the large number of individuals of the same
species there supported, but the conditions of life are much
more complex from the large number of already existing spe-
cies ; 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 compe-
tition with many others. Moreover, great areas, though now
continuous, owing to former oscillations of level, will often
have existed in a broken condition, so that the good effects of
isolation will generally, to a certain extent, have concuiTed.
Finally, I conclude that, although small isolated areas probably
have beeii in some respects highly favorable for the production
of new species, yet that the course of modification will gener-
ally have been more rapid on large areas ; and, what is more
important, that the new forms j)roduced on large areas, which
already have been victorious over many competitors, will be
tliose that will s])rea(l most widely, will give rise to most new
varit^ties and species, and will thus play the most important
part in the changing history of the organic Avorld.

We can, perhaps, on these Aiews, imderstand some facts
wliich will be again alluded to in our chapter on Geographical
Distribution ; for instance, that the ]iroductions of the smaller
continent of Australia are now yielding before those of the
larger Europa'o- Asiatic area. Thus, also, it is that continental
pniductions 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 ex-

Chap. IV. KESULTS OF NATURAL SELECTION. iQ>j

termination. Ilcncc, perhaps, it is liiat the flora of Madeira,
accordin<^ to Oswald Heer, resembles the extinct tertiary flora
of Europe. ^Vll fresh-water basins, taken together, make a
small area compared with that of the sea or of the land ; and,
consequently, the competition between fresh-water productions
will have been less severe than elsewhere ; new forms will have
been more slowly formed, and old forms more slowly extermi-
nated. And it is in fresh water that Ave find seven genera of
Ganoid fishes, remnants of a once preponderant order : and in
ii?sh water we find some of the most anomalous forms now
known in the world, as the Ornithorhynchus and Lepidosiren,
which, like fossils, connect to a certain extent orders at present
widely separated 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 having been
exposed to less varied and therefore less severe competition.

To sum up the circumstances favorable and unfavorable for
the production of new species through natural selection, as far
as the extreme intricacy of the svibject permits. I conclude
that fur terrestrial productions a large continental area, which
has imdergone many oscillations of level, will have been the
most favorable for the production of many ncAV forms of life,
fitted to endure for a long time and to spread widely. While
the area existed as a continent, the inhabitants will have been
numerous in individuals and kinds, and Avill have been subjected
to severe competition. When converted by subsidence 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, immigration will
have been prevented, so that new places in the polity of each
island will have had to be filled up by modifications of the old
inhabitants; and time will have been allowed for the varieties
in each to become well modified and perfected. When, by
renewed elevation, the islands were reconverted into a conti-
nental area, there will again have been severe competition :
the most faxorcd or improved varieties will have been enabled
to spread : there will have been much extinction of the less
improved forms, and the relative proportional ninnbcrs of the
various inhabitants of tin; reunited continent will again have
been changed ; and, again, there will have been a fair lield for
natural selection to improve still further the inhabitants, and
thus to produce new species.

108 EXTIXCTIOX BY NATURAL SELECTION. CiiAP. IV.

That natural sc^lcction acts "vvith extreme slowness I fully
iidniit. The result depends on there beings places in the polity
of Nature, wliich can be better filled through some of the in-
habitants of the country undergoinf^ modifications of some kind.
The existence of such places will often depend on physical
changes, which are generally very slow, and on the immigra-
tion of better-adapted forms being checked. But the effects
of natural selection will probably still oftener depend on some
few of the inhabitants becoming slowly modified ; the mutual
relations of the other inhabitants being thus disturbed. Al-
though all the individuals of the same species differ more or
less from each other, differences of the right nature, better
adapted to the then existing conditions, may not soon occur.
The results will often be greatly retarded by free intercrossing.
Many will exclaim that these several causes are amply suffi-
cient to neutralize the power of natural selection. I do not
believe so. But I do believe that natural selection generally
acts very slowly in effecting changes, at long intervals of time,
and only on a few of the inhabitants of the same region. I
further believe that these slow, intermittent results of natural
selection accord perfectly 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 infinite complexity of the
coadaptations between all organic beings, one with another and
with their physical conditions of life, "which may be effected in
the long course of time by Nature's power of selection, or the
survival of the fittest.

Extinction caused by Natural Selection,

This subject will be more fully discussed in our chapter on
Geology ; but it must be here alluded to from being inti-
mately connected with natural selection. Natural selection
acts solely through the preservation of variations in some way
advantageous, which consequently endure. Owing to the high
geometrical ratio of increase of all organic beings, each area is
already stocked with the full number of its existing inhabit-
ants, and as most areas are already stocked with a great diver
sity of forms, it follows that, as each selected and favored form
increases in number, so generally will the less favored forms

CriAP. IV. EXTINCTION BY NATURAL SELECTION. 109

decrease and l^eooinc rare. Rarity, as geolo<T:y tells us, is the
precursor to e.vtinclion. We can, also, see that any form rep-
resented l>y few individuals will, during fluctuations in the sea-
sons or in the numlxir of its enemies, run a good chance of
utter extinction. But we may go further than this ; for, as
new forms are continually and slowly being produced, unless
we believe that tlie mnnber of specific forms goes on perpet-
ually and almost indetinitely increasing, many inevitably must
become extinct. That the number of speciiic forms has not
indcHnitely increased, geology tells us plainly ; and we shall
presently attempt to show why it is that the number of species
throughout the world has not become immeasurably great.

AW; have seen tliat the species which are most numerous in
individuals have the best chance of producing favorable varia-
tions within any given period. We have evidence of this, in
the facts stated in the second chapter, showing that it is the
common species which offer the greatest number of recorded
varieties, or incipitnit species. Hence, rare species will be less
quickly moditieil or improved within any given period, and
they will consequently be beaten in the race for life by the
modified descendants of the commoner species.

From the sesevcral considerations I think it inevitably fol-
lows, that, as new species in the course of time are formed
through natural selection, others will become rarer and rarer,
and finally extinct. The forms Avhich stand in closest compe-
tition with those imderg^oing modification and improvement,
will naturally suffer most. And we have seen in the chapter
nn the Struggle for Existence that it is the most closely-allied
forms — varieties of the same species, and species of the same
genus or of related genera — which, from having nearly the
same structure, constitution, and habits, generally come into
tlie severest competition with each other. Consequently, eacli
new variety or species, during the progress of its formation,
will generally press hardest on its nearest kindred, and tcTid to
exterminate them. We see tlie same process of extermination
among our domesticated productions, through the selection of
improved forms by man. Many curious instances could l)e given
showing how quickly new breeds of cattle, sheep, and other
animals, and varieties of flowers, take the place of older and
inferior kinds. In Yorkshire, it is historically known that the
ancient black cattle were displaced by the long-horns, and that
these " were swept away by the short-horns " (I quote the
words of an agricultural Avriter) "as if by some murderous pes-
tilence."

110 DIVERGENCE OF CHARACTER. Chap. IV.

Divergence of Character,

The principle, which I liavc dcsip^nated by this term, is of
high importance, and cxphiins, as I believe, several important
facts, in tlie first place, varieties, even strongly-marked ones,
though having somewhat of the character of species — as is
shown by the hopeless doubts in many cases how to rank
them — yet certainly differ from each other far less than do
good and distinct species. Nevertheless, according to my
view, varieties are species in the process of formation, or are,
as I have called them, incipient species. How, then, does the
lesser difference between varieties become augmented into the
greater difference between species ? That this does habitually
happen, we must infer from most of the innumerable species
throughout Nature presenting well-marked differences ; where-
as varieties, the supposed protot}-pes and parents of future
well-marked species, jiresent 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 produc-
tion of races so different as short-horn and Hereford cattle, race
and cart horses, the several breeds of pigeons, etc., could never
have been effected by the mere chance accumulation of varia-
tions of a similar character during many successive generations.
In ])ractice, a fancier is, for instance, struck by a pigeon having
a sliglitly shorter beak ; another fancier is struck by a pigeon
having a rather longer beak ; and, on the acknowledged prin-
ciple that " fanciers do not and will not admire a medium stand-
ard, but like extremes," they both go on (as has actually oc-
curred with the sub-breeds of the tumbler-pigeon) choosing and
l)rceding from birds with longer and longer beaks, or with
shorter and shorter beaks. Again, we may suppose that at an
early period one man preferred swifter horses ; another stronger
and more bulky horses. The early differences would be very
Blight; in the course of time, from the continued selection of
swifter horses by some breeders, and of stronger ones by others,
the differences would become greater, and would be noted as

rnxr. IV. DIVERGENCE or CHARACTER. HI

Ibnnin;^ two sub-breeds; finally, after the lapse of centuries
the sub-breods would become converted into two ■well-estab-
lished and distinct breeds. As the dilVerenccs slowly became
,e:reater, the inferior animals with intermediate characters, bein;i^
neither very swift nor very strong, would have been neglected,
and will have disappeared. Here, then, we see in man's pro-
ductions 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 eacli other and from their common pax-ent.

But 1»()W, it may be asked, can any analogous principle
apply in Nature ? t believe it can and does apply most effi-
ciently (though it Avas a long time before I saw how), from tlie
simple circumstance that the more diversified the descendants
from any one species become in structure, constitution, and
habrts, 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 an}?- country has
long ago arrived at its full average. If its natural powers of
increase be allowed to act, it can succeed in increasing (the
country not imdergoing any change in its conditions) only by
its varying descendants seizing on places at present occupied
by other animals: some of them, for instance, being enabled to
feed on new kinds of prey, either dead or alive ; some inhabit-
ing new stations, climbing trees, frequenting water, and some
[lerliaps becoming less carnivorous. The more diversified in
lialjits and structure the descendants of our carnivorous animal
lir'came, the more places they would bo enabled to occupy.
AViiat applies to one animal will apply throughout all time to
all animals — that is, if they vary — for otherwise natural selec-
tion can effect nothing. So it will be witli j^lants. It has been
experimentally proved that, if a plot of ground be sown witli
one species of grass, and a similar plot be sown with several
distinct genera of grasses, a greater number of phmts and a
greater weight of dry herbage can be raised by the latter jjro-
ccss. Tlie same has been found to hold good when one va-
riety and several mixed varieties of wlieat liave been sown on
equal spaces of ground. Hence, if any one species of grass
were to go on varying, and those varieties were continually
selected which differed from each other in at all the same man-

1 ] 2 DIVERGENCE OF CHARACTER. Chap. IV,

lUT as distiiKl species and gwiora of grasses differ from each
other, a greater miinber of individual phmts of this species of
grass, inchiding its modified descendants, ■would succeed in
living on the same piece of ground. And we well know that
each species and each variety of grass is aimually sowing al-
most countless seeds : and thus, as it may be said, is striving
its utmost to increase its numbers. Consequently, in the course
of many thousand generations, the most distinct varieties of
any one species of gTass would always have the best chance of
succeeding and of increasing in numbers, and thus of supplant-
ing the less distinct varieties ; and varieties, when rendered
very distinct from each other, take the rank of species.

The truth of the principle that the greatest amount of life
can be supported by great diversification of structure, is seen
iinder many natural circumstances. In an extremely small
area, especially if freely open to immigration, and where the
contest between indivitkial and individual must be severe, we
always find groat diversity in its inhabitants. For instance, I
found that a piece of turf, three feet by four in size, which had
been exposed for many years to exactly the same conditions,
supported twenty species of plants, and these belonged to
eighteen genera and to eight orders, which shoAvs how much
these plants differ from each other. So it is with tlie plants
and insects on small and imiform islets ; also in small ponds
of fresh water. Farmers find that they can raise most food by
a rotation of plants belonging to the most different orders :
Nature follows what may be called a simultaneous rotation.
Most of the animals and plants which live close round any
small piece of ground, could live on it (supposing it not to be
in any way peculiar in its nature), and may be said to be
striving to the utmost to live there ; but, it is seen, that where
tliey come into the closest competition with each other, the
advantages of diversification of structure, with the accom])any-
ing difVerenccs 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 plants
through man's agency in foreign lands. It might have been
expected that the plants which would succeed in becoming
naturalized in any land would generally have been closely
aUied to tlie indigenes ; for these are commonly looked at as
specially created and adapted for their own country. It might

Chap. IV. DIVERGENCE OF CnARACTER. 113

also, pcrliaps, liave been expected that naturalized plants would
have beloufred to a few groups more especially adapted to
certain stations in their new homes. But the case is very dif-
ferent ; and Alpli. dc Candolle has well remarked, in his great
and admirable work, that floras gain by naturalization, propor-
tionally with the number of the native genera and species, far
more in new genera than in new species. To give a single
instance : in tiie last edition of Dr. Asa Gray's " Manual of
the Flora of the Northern United States," 260 naturalized
plants are enumerated, and these belong to 162 genera. Wc
thus see that these naturalized plants are of a highly-diversified
nature. The}'" difler, moreover, to a large extent, from the in-
digenes, for, out of the 162 naturalized genera, no less than 100
genera arc not there indigenous, and thus a large proportional
addition is made to the genera now living in the United States.

By considering tlie nature of the plants or animals which
have struggled successfully with the indigenes of any country,
and have there become naturalized, we may gain some crude
idea in what manner some of the natives would have to be
modilied, in order to gain an advantage over the other natives ;
and we may at least safely infer that diversification of struc-
ture, amounting to new generic differences, would be profit-
able to them.

The advantage of diversification 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. Xo physiolo-
gist doubts that a stomach adapted to digest vegetable matter
alone, or llesh alone, draws most nutriment from these sub-
stances. So in the general economy of an}'' land, the more
widely and perfectly the animals and plants are diversified for
dilferent haljits of life, so will a greater number of inchviduals
be capable of there sujiporting themselves. A set of animals,
with their organization but little diversified, coulti hardly com-
pete with a set more perfectly diversified in structure. It may
be doubt(M], for instance, whether the Australian marsupials,
which are divided into groups differing but little from each
other, and feebly representing, as Mr, AVaterhouse antl others
have remarked, our carnivorous, ruminant, and rodent mam-
mals, could successfully compete with these well-pronounced
orders. In the Australian manmials, we see the process of
diversification in an early and incomplete stage of develop-
ment.

I ] t RESULTS OF THE ACTION OF Chap. IV,

Tlie Pi'ohdhle Results of the Action of Katural Selection
through Diverrjence of Character and JSxtinctiony vi the
Descendants of a Common Ancestor.

After tlie forcg'oing discussion, which has been much com-
pressed, we may assume that the modified descendants of any
one species Avill succeed by so much the better as they become
more diversified in structure, and are thus enabled to encroach
on places occupied by other beings. Now let us see how this
principle of benefit being derived from divergence of character,
combined with the principles of i>atural selection and of ex-
tinction, tends to act.

The accompanying diagram will aid us in understanding
this rather perplexing subject. Let A to L represent the spe-
cies 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
cliagram by the letters standing at unequal distances. I have
said a large genus, because Ave have seen in the second chap-
ter that, on an average, more of the species of large genera
vary than of small genera ; and the varying species of the
large genera present a greater number of varieties. We have,
also, seen that the species, which are the commonest and the
most widely-diilused, vary more than do the rare and restricted
species. Let (A) be a common, widely-diffused, and varying
species, belonging to a genus large in its own country. The
branching and diverging dotted lines of unequal lengths pro-
ceeding from (A), may represent its varying offspring. The
variations are supposed to be extremely slight, but of the most
diversified nature ; they are not supposed all to appear simul-
taneously, but often after long intervals of time ; nor are they
all supposed to endure for equal periods. Only those varia-
tions which are in some Avay profitable will be preserved or
naturally selected. And here the importance of the principle
of benefit being derived from divergence of character comes
in ; for this will generally lead to the most different or diver-
gent variations (represented by the outer dotted lines) being
preserved and accumulated by natural selection. When a dot-
ted line reaches one of the horizontal lines, and is there marked
by a small numbered letter, a sufficient ainount of variation is
supjiosed to have been accunuilated to have formed a fairly
well-marked variety, such as would l)e thought worthy of rec-
ord in a systematic work.

-xLxrv'
-A— xm

'. XII

XI

a" V

VLj""

']:*«/" i 1

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DC

iy

h'

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.•

a' ■■.

f

'.U'

■■::W '^

^, i ;

u' ■

,. '. ;.'

a"i

v/"

M*'^

\,.^«

^^e

. ■ ■ ^

a-'

it'^i'^

■.]:■:. ■?« •^

"' 1

/ -J.

l'.'

id*

■■*

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■■' ''iA'' =*

j;: .' \;,'-^, ■.;,; J ; 1 , 1

l'-

■ Ls

m

\ i^W :;■.' TT

<':,■ 2 1 ■ ^

T

ABCD EF GHIKL

/Jjippleton & C NcwYofk

iBl*JIf^^l>tltl«]ll!n)nil»7.^-,

Chap. IV. NATURAL SELECTION. 1 ] 5

The intervals between the horizontal lines in the dia^ara,
may ix'prescnt each a thousand generations, or ten thousand.
After a thousand generations, species (A) is supposed to have
produced two fairly well-marked varieties, namely a} and rn).
These two varieties will generally continue to be exposed to
the same conditions Avhich made their parents variable, and
the tendency to variability is in itself hereditary, consequently
tliey will tend to vary, and generally to vary in nearl}' the
same manner as their j)arents varied. Moreover, these two
varieties, being only slightl^'-niodilied forms, will tend to in-
herit those advantages which made their parent (A) more
numerous than most of the other inhabitants of the same coun-
try ; they will likewise partake of those more general advan-
tages v/hich made the genus to which the parent-species be-
longed a large genus in its ov,n country. And these circinn-
stanccs we know to bo favoral)le to tiic production of new
varieties.

If, then, these two varieties be variable, the most divergent
of their variations will generally be ])reserved during the next
thousand generations. And after this interval, variety 0} is
supposed in the diagram to have pi'oduccd variety a^, which
will, owing to the principle of divergence, difler more from (A)
than did variety a*. Variety «^' is supposed to have produced
two varieties, namely Wi" and s", diflering from each other, and
more considerably from their common parent (A). Wc may
continue the process by similar steps for any length of time ;
some of the varieties, after each thousand generations, produ-
cing only a single variety, but in a more and more modi lied con-
dition, some producing two or three varieties, and some failing
to produce any. Thus the varieties, or modified descendants,
proceeding from the common ])arent (A), will generally go on
increasing in numljcr, and diverging in character. In the dia-
gram tlie process is represented up to the ten-thousandth gen-
eration, and under a condensed and siniplilled form up to the
fourteen-thousandth generation,

IJut I must hen; remark that I do not suppose that the
process ever goes on so regularly as is represented in the dia-
gram, though in itself made somewhat irregular, nor that it
goes on continuously ; it is far more ])robable that each form
remains for long periods unaltered, and tlien again imdcr-
gocs modification. Nor do I suppose that the most di-
vergent varieties are invariably preserved: a medium form
may often long endure, and may or may not produce more

IIG RESULTS OF THE ACTION OF C'kap. TV.

than one modified descendant; for nalural selection Avill al-
ways act according to the nature of the places which arc either
unoccupied or not perfectly occupied by other beings ; and
this will depend on infinitely-complex relations. But, as a
general ruh>, the more diversified in structure tlic descendants
from any one species can be rendered, the more places they
will be enabled to seize on, and the more their modified pro-
geny will increase. In our diagram the line of succession is
liroken at regular intervals by small numbered letters marking
the succ(>ssivc forms which have become sufficiently distinct to
be recorded as varieties. But these breaks are imaginary, and
might have been inserted an^^vhere, after intervals long
enough to have allowed the accumulation of a considerable
amount of divergent variation.

As all the modified descendants from a common and wide-
ly-diffused species, belonging to a large genus, Avill tend to
partake of the same advantages which made their parent suc-
cessful in life, they will generally go on multiplying 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 latter 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 im-
j)i(ived branches : this is represented in the diagram by some
of the lower branches not reaching to the upper horizontal
lines. In some cases I do not doubt that the jirocess of modi-
fication will be confined to a single line of descent, and the
ntunber of the descendants Mill not be increased; althouglithe
amount of divergent modification may have been increased in
the successive generations. This case would be represented in
tlic diagram, if all the lines proceeding from (A) Avere removed,
excepting that from «* to rt'°. In the same way, for instance, the
English race-horse and English pointer have apparently both
gone on slowly diverging in character from their original stocks,
Mithout either having given oft' any fresh branches or races.

After ten thousand generations, species (A) is sujiposed to
liave produced three forms, «",/'", and wi", which, from hav-
ing diverged in character during the successive generations,
will have come to differ largely, but jicrhaps unequally, from
each other and from their common jvarcnt. If we suppose the
amount of change between each horizontid line in our diagram
to be excessively small, these three forms may still be only
w('ll-mark,Ml varieties ; but we have only to suppose the steps

Chap. IV. NATURAL SELECTION. 117

ill tiie process of modification to be more numerous or j^rcatcr
in amount, to convert these three forms into doubtful or at
last wcU-denncd species : thus the diao^ram iUustratcs the
steps by wliich the small diflerences distinguishing varieties
are increased into the larger differences distinguishing species.
By continuing the same process for a greater number of gener-
ations (as shown in the diagram in a condensed and simplified
manner), we get eight species, marked by the letters between
«" and m^\ all descended from (A). Thus, as I believe, spe-
cies are multiplied and genera are formed.

In a large genus it is probable that more than one species
would vary. In the diagram I have assumed that a second
species (I) has produced, by analogous steps, after ten thou-
sand generations, either two well-marked varieties (w'° and z'")
or two species, according to the amount of change supposed to
be'rcjircsented between the horizontal lines. After fourteen
thousand generations, six new species, marked by the letters
w'* to z'*, are supposed to have been produced. In any genus,
the species which are already very different in character from
each other will generally tend to produce the greatest num-
ber of modified descendants ; for they will have the best
chance of filling new and widely-different places in the polity
of Nature : hence in the diagram I have chosen the extreme
species (A), and the nearly extreme species (I), as those which
have largely varied, and have given rise to new varieties and
species. The other nine species (marked by capital letters)
of our original genus, may for long but unequal periods con-
tinue to transmit unaltered descendants ; -and this is shown in
tlu; 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 extinction,
will have played an important part. As in each fully-stocked
country natural selecti(jn necessarily acts by the selected form
having some advantage in the struggle for life over other forms,
there will be a constant tondcMicy in the improved descendants
of any one species to supplant and exterminate in each stage
of descent their pred(X"essors and their original progenitor.
For it should be remembered that the competition will gen-
erally be most severe between those forms which are most
nearly related to each other in habits, constitution, and struc-
ture. Hence all the intermediate forms between the earlier
and later states, that is, between the less and more improved
states of a species, as well as the original parent-species itself.

lis RESULTS OF THE ACTION OF Chap. IV.

will generally tend to l^ecome extinct. So it probably Avill
be ^vith many -whole collateral lines of descent, Avhich ^vill be
conquered by later and improved lines of descent. If, liow-
ever, the modified offspring of a species get into some distinct
country, or become quickly adapted to some cjuite new station,
in whic-h offspring and progenitor do not come into compe-
tition, both may continue to exist.

If, then, our diagram be assumed to represent a consider-
able amount of modification, species (A) and all the earlier va-
rieties Avill have become extinct, having" been replaced by eight
new species (a" to wi") ; and (I) will have been replaced
by six (?i" to 2'*) new species.

But we may go further than this. The original species
of our genus were supposed to resemble eacli other in unequal
degrees, as is so generally the case in Nature ; species (A)
being more nearly related to B, C, and D, than to the other
species ; and species (I) more to G, H, K, L, than to the
others. These two species (A) and (I) were also supposed to
be very common and widely-dilfuscd species, so that they must
originally have had some advantage over most of the other
species of the genus. Their modified descendants, fourteen in
number at the fourteen-thousandth generation, will probably
have inherited some of the same advantages : they have also
been modified and improved in a diversified manner at each
stage of descent, so as to have become adapted to many related
places .in the natural economy of their country. It seems,
therefore, extremely probable that they will have taken the
places of, and thus exterminatod, not only their parents (A)
and (I), but likewise some of the original species which were
most nearly related to their parents. Hence very few of the
original species will have transmitted offspring to the fourteen-
tliousandth generation. 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 origi-
nal eleven species, will now be lifteen in number. Owing to
the divergent tendency of natural selection, the extreme
amoimt of difference in character betAveen species «'* and 2'*
will be much greater than that between the most distinct of
the original eleven species. The new species, moreover, wiK
be allied to each other in a Avidely-differcnt manner. Of the
eight descendants from (A) the three marked a", <j^\ p^\ will

CiiAr. IV. NATUEAL SELECTION. 119

bo noavly related from liaving^ recently branched off from a'°/
J/*, and /'*, from liavin": diverged at an earlier period from a'',
\\\\\ be in some deo^ree distinct from the three first-named spe-
ties ; and lastly, o'\ e'*, and »i'*, will be nearly related one to
the other, but, from havinfj; diverf^ed at the first commence-
ment of tlie process of modification, will be widely different
from the other five species, and may constitute a sub-genus or
a distinct genus.

The six descendants from (I) will form two sub-genera or
genera. But as the original species (I) differed largely from
(A), standing nearly at the extreme end of the original genus,
llie six descendants from (I) will, owing to inheritance alone,
differ considerably from the eight descendants from (A) ; the
two groups, moreover, are supposed to have gone on diverging
in different directions. The intermediate species, also (and
this is a very important consideration), which connected the
original species (A) and (I), have all become, excepting (F),
extinct, and have left no descendants. Hence the six new spe-
cies descended from (I), and the eight descended from (A),
will have to be ranked as very distinct genera, or even as dis-
tinct sub- families.

Thus it is, as I believe, that two or more genera are pro-
duced, by descent Avith modification, from two or more species
of the same genus. And the two or more parent-species are
supposed to have descended from some one species of an ear-
lier 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 representing a
single species, the supposed progenitor of our several new sub-
genera and genera.

It is worth while to reflect for a moment on the character
of the new species f'*, which is supposed not to have diverged
much in character, but to have retained the fomi of (F), either
unaltered or altered only in a slight degree. In this case, its
allinitics to the other fourteen new species Avill be of a curious
and circuitous nature. Having descended from a form which
stood l)etwe(Mi the two parent-species (A) and (I), now sup-
posed to 1)0 extinct and imknown, it will be in some degree in-
l«-rmediate in character between the two groups descended
from these species. I5ut as these two groups have gone on
diverging in character from the type of their parents, the new
species (f'*) will not be directly intermediate between them,
but ratlier l^etween t}^es of the two groups; and every

120 RESULTS OF NATURAL SELECTION. Chap. IV.

naturalist will be able to bring some such case before his
mind.

In the diagram, each liorizonal line has hitherto been sup-
posed to represent a tliousand generations, but each may rep-
resent a million or several million generations ; it may also
represent a section of the successive strata of the earth's crust
including extinct remains. ' We shall, when we come to our
chapter on Geology, have to refer again to this subject, and I
think we shall then sec that the diagram throws light on the
affinities of extinct beings, Avhich, though generally belonging
to the same orders, or families, or genera, ■with those now liv-
ing, yet are often, in some degree, intermediate in character
between existing groups ; and we can understand this fact, for
the extinct species lived at very ancient epochs when the
branching lines of descent had diverged less.

I see no reason to limit the process of modification, as now
explained, to the formation of genera alone. If, in the diagram,
we suppose the amount of change represented by each succes-
sive group of diverging dotted lines to be great, the forms
marked a'* to^J>", those marked i'* and/"'\ and those marked
o'* to ni^*, will form three very distinct genera. We shall also
have two very distinct genera descended from (1), differing
widely from the descendcnts of (A). These two groups of
genera will thus form two distinct families, or orders, accord-
ing to the amount of divergent modification supposed to be
represented in the diagram. And the two new families, or
orders, are descended from two species of the original genus,
and these are suj^posed to be descended from some still more
ancient and unknown form.

We have seen that in each countrj^ it is the species belong-
ing to the larger genera which oftcnest present varieties or in-
cipient species. This, indeed, might have been expected ; for
as natural selection acts throvigh one form having some advan-
tage over other forms in the struggle for existence, it will
chiefly act on those which already have some advantage ; and
the largeness of any grouji shows that its species have inherited
from a connnon ancestor some advantage in common. Hence,
the struggle for the production of new and modified descend-
ants will mainly lie between the larger groups which are all
trying to increase in number. One large grouj) will slowl}'
ct)nfjuer another large group, reduce its numbers, and thus les-
sen its chance of further variation and improveuKMit. Within
the same large group, the later and more highly -perfected su]>

Caw. IV. ADVANCE OF ORGANIZATION. 121

j^roups, from hraneliiiig" out and seizinc^ on many new plar-cs in
the polity of Nature, will constantly tend to sujiplant and de-
stroy the earlier and Icss-iinp.roved svib-<^oups. Small and
broken ""roups and sul>irroups will hnally disappear, Lookinnf
to the future, Ave can ])redict that the groups of organic beings
which are now large and triumphant, and Avbich.are least
broken u]i, that is, which as yet have sulTered least extinction,
will for a long period continue to increase. But which groups
will ultimately prevail, no man can predict ; for we well know
that many groups formerly most extensively develojied, have
now become extinct. Looking still more remotely to the
future, we may predict that, owing to the continued and steady
increase of the larger groups, a multitude of smaller groups will
become utterly extinct, and leave no modified descendants;
and consequently that, of the species living at any one period,
extremely (gw will transmit descendants to a remote futurity.
I shall have to return to this subject in the chapter on Classifi-
cation, but I may add that as according to this view extremely
few of the more ancient species have transmitted descendants,
and as :ill the descendants of the same species form a class, we
can imdcrstand 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 motlified descendants,
yet, at remote geological periods, the earth may have been
almost as well jjcopled with species of many genera, families,
oiders, and classes, as at the; present day.

O71 the Degree to which Organization tends to advance.

Natural Selection exclusively acts by the preservation and
accunmlation of variations, which are beneficial under the or-
ganic and inorganic conditions of life to which each creature is
exposed at each successive period 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 bi'ings throughout the world. But
here we enter on a very intricate subject, for naturalists have
not defined to each other's satisfaction what is meant by an
advance in org-anization. Among the vertcbrata the degree of
intellect and approac-h in structure to man clearly come into
play. It might be thought that the amount of change Avhich
the various ])arts and organs pass through in their develop-
G

['^2 <JN THE DEGKEE TO WHICH Cuap. IV.

incnt from the cnil)ryo to maturity would suffice as a standard
of comparison ; but there are cases, as with certain parasitic
crustaceans, in Avhich several parts of the structure become
less perfect, so that the mature animal cannot be called higher
than its larva. Von Baers standard seems the most widely
applica])le and the Ix'st, namely, the amount of diflerentiation
of the diiferent parts of the same organic being, in the adult
state as I should be inclined to add, and their specialization
for difl'ercnt functions ; or, -as Milne Edwards would express it,
the completeness of the division of physiological labor. But we
shall sec how obscure this subject is if Ave look, for instance, to
fish, among which some naturalists rank those as highest which,
like the sliarks, 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. Still more plainly we
see 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 sepals, jietals, stamens, and pistils, fully devel-
oped in each flower ; whereas other botanists, probably with
more truth, look at the plants which have their several organs
much modified and reduced in number as the highest.

If we take, as the standard of high organization, the
amount of differentiation and speciahzation of the several or-
gans in each being when adult (and this will include the ad-
vancement of the brain for intellectual purposes), natural selec-
tion clearly leads toward highness ; for all physiologists admit
that the specialization of organs, inasmuch as they perform in
this state their functions better, is an advantage to each being;
and hence the accumulation of variations tending toward spe-
cialization is within the scope of natural selection. On the
other hand, Ave can see, bearing iu mind that all organic beings
are striving to increase at a high ratio and to seize on every
ill-occupied place in the economy of Nature, that it is quite pos-
sible for natural selection gradually to fit an organic being to
a situation in AA'hich scA^eral organs would be superfluous or
useless : in such cases there might be retrogression in the scale
of organization, AN'hcther organization on the Avhole has
actually adA'anced from the remotest geological jieriods to the
present day Avill be more conveniently discussed in om- chapter
on Geological Succession.

But it may be objected that, if all organic beings thus tend

1

C;i.\r. IV. ORGANIZATION TENDS TO ADVANCE. 123

to rise iu llie scale, liow is it that throughout tlie Avorkl a mul-
titude of the lowest forms still exist ; and how is it that in
each great class some forms are far more hiofhly developed than
otliers ? Why have not the more highly-developed forms
everywhere supplanted and exterminated the lower? Lamarck,
who lielieved iu an innate and ineWtable tendency toward per-
fection in all organic beings, seems to have felt this difficulty
so strongly, that he was led to suppose that new and simple
forms are continually being produced by spontaneous genera-
tion. Science, however, under her present aspect does not
countenance tlie belief, whatever the futiu-e may reveal, that
living creatures are now being generated. On our theory the
continued existence of lowly organisms oflcrs no difficulty ; for
natural selection, or the survival of the fittest, does not neces-
sarily include progressive development — it only takes advan-
tage of "such variations as arise and are bcnetlcial to each crea-
ture imder its complex relations of life. And it may be asked
what advantage, as far as we can see, would it be to an infu-
sorian animalcule — to an intestinal worm — or even to an earth-
worm, to be highly organized? If it were no advantage, tlu^se
forms would be left by natural selection miimproved or but
little improved; and might remain for indefmite ages in their
present little advanced condition. And geology tells us that
some of the lowest forms, as the infusoria and rizopods, 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 advanced since the first dawn of life
would be 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 organ-
zation.

Nearly the same remarks are applicable if we look to the
dilVt -rent grades of organization within each great group; for
instance, in the vertebrata, to the coexistence of manunals and
fish — among manunalia, to the coexistence of man and tlu;
ornitliorliynchus — among fishes, to the coexistence of the shark
and lancelet (Brancliiostoma), which latter fish in the extreme
8imi)licily of its structiue approaches the invertebrate classes.
But mammals and fisli hardly come into competition with each
other ; tiie advancement of tlie whole class of mammals, or of
certain memb(^rs in this class, to the highest grade would not
lead to their taking the place of, and thus exterminating, fishes.
Physiologists believe that the brain must be bathed by warm

12i ADVANCE OF ORGANIZATION. Chap. IV.

blood to be highly active, and tliis I'cquires auiial respiration ;
so that Avarm-bloodod maininals when inhabiting the water live
under some disadvantages in comparison with iishes. In this
latter class, members of the shark family would not tend to
supplant the lancelet ; for the lancelet, as I hear from Fritz
Miiller, has, as sole companion and competitor on the barren,
sandy shore of South Brazil, an anomalous annelid. The three
lowest orders of mammals, namely, marsupials, edentata, and
rodents, coexist in South America in the same region with
numerous monkeys, and probably interfere little with each
other. Altliougli oi'ganization, on the whole, may have ad-
vanced and be still advancing throughout the world, yet the
scale will always present many degrees of perfection; for the
high advancement of certain whole classes, or of certain mem-
bers of each class, does not at all necessarily lead to the ex-
tinction of those groups with Avhich they do not enter into
close competition. In some cases, as we shall hereafter see,
lowly-organized forms appear to have been preserved to the
present day from inhabiting confmed or peculiar stations, where
they have been subjected to less severe competition, and where
their scant}- numbers have retarded the chance of favorable
variations arising.

Finally, I believe that many lowly-organized forms now
exist throughout the Avorld, 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 sufficed for the
utmost possible amount of development. In some few cases
there has been Avhat we must call retrogression of organization.
But the main cause lies in the fact that under very simple con-
ditions of life a high organization would be of no service —
possibly would be of actual disservice, as being of a more
delicate nature, and more liable to be put out of order and
injured.

Looking to the first dawn of life, when all organic beings,
as w^e may believe, presented the simplest structun^, how, it
has been asked, couhl the first steps in the advancement or
differentiation of parts have arisen'? Mr. Herbert S])encer
would probably answer that as soon as simple unicellular or-
ganism came by growth or division to be coinj^ounded of sev-
eral cells, or became attached to any supporting surface, his
law " that homologous imits of any order become ilifferentiated
in proportion as their relations to incident forces become differ-

CiiAP. IV. VARIOUS OBJECTIONS. 125

eiit," would come into action. But as we have no facts to
guide us, all speculation on the subject is useless. It is, how-
ever, an en-or to suppose that there would be no struggle for
existence, and, conseciuently, no natural selection, until many
forms had been produced : variations in a single species in-
habiting an isolated station might be beneficial, and thus the
Avhole 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 ignorance on the mutual relations
of the inhabitants of the world during the past epochs in its
historj'.

Various Objectiofis considered.

I will here notice a few miscellaneous objections Avhich
nave been advanced against my views, as some of the previous
discussions may perhaps thus be made clearer; but it would
be useless to discuss all of them, as many have been made by
writers Avho have not taken the trouble to understand my views.
Thus a distinguished German naturalist has recently asserted
that the weakest part of my theory is, that I consider all or-
ganic beings as imperfect : what I have really said is, that all
are not as ]ierfect in relation to their conditions as they might
be ; and this is shown to be the case by so many native forms
in many quarters of the world yielding their places to intrud-
ing foreigners which have become naturalized. Nor can all
organic beings, even if they were at any one time perfectly
adapted to their conditions of life, remain so, when the condi-
tions slowly change, unless they likewise change; and no one
will dispute that the physical conditions of each country, as
well as the numbers and kinds of its inhabitants, are liable to
change.

It has been argued that, as none of the animals and plants
of Egypt, of which we know any thing, have clianged dining
the last 3,000 years, so pro1)ably none have been modified in
any other part of the world. The many animals which have
remained unehanged since the commencement of the glacial
jieriod would have been an incomparably stronger case, for
tliese have been exposed to great changes of climate and have
migrated over great distances ; whereas, in Egypt, during the
last 3,000 years, the conditions of life, as far as we know, have
remained abs(jlutely uniform. The fact of little or no modifi-

120 VARIOUS OBJPX'TIOXS. Chap. IV.

cation liuviu^ bjcn cficctcd sinco the f^lacial iicriocl would ha
of some avail ag'ainst those who believe iu an innate and
necessary law of development, l:)ut is powerless against the
doctrine of natural selection or the survival of the fittest, which
implies only that variations or individual differences of a favor-
able nature occasionally arise in a few s])ecies, and are then
preserved.

It has been objected, if natural selection be so powerful
an agent, why has not this or that organ been modified and
improved? Why has not the proboscis of the hive-bee been
lengthened so as to reach the nectar of tlie red-clover ? Why
has not the ostrich acquired the power of llight ? But grant-
ing that these parts and organs have varied in the right direc-
tion— granting that there has been time sufficient for the slow
work of natural selection, the effects being often checked, as
they will be by intercrossing and the tendency to reversion,
who will pretend that he knows the life-history of any one
organic being sufficiently well to say that any particular change
would be, on the whole, to its advantage ? Can we feel sure
that a long proboscis would not be a disadvantage to the bive-
bee in sucking the innumerable small flowers which it fre-
quents ? Can we feel sure that a long proboscis would not,
by correlation, almost necessarily give increased size to other
parts of the mouth, perhaps interfering with the delicate cell-
constructing Avork? In the case of the ostrich, a moment's
reflection will show what an enormous supply of food would
be necessary to supply force for this bird of the desert to move
its huge body through the air. But such ill-considered objec-
tions are hardly worth notice.

The celebrated paleontologist, Bronn, at the close of his
German translation of this work, asks, how, on the principle
of natural selection, can a variety live side by side with the
parent-species ? If both have become fitted for slightly-differ-
ent habits of life or conditions, they might live together ;
though, in the case of animals which freely cross and wander
much about, varieties seem to be almost always confined to
distinct localities. But if we put on one side polymorphic
species, in which the variability seems to be of a peculiar na-
ture, and all mere temporary variations, such as size, albinism,
etc., the more permanent varieties are generally fmmd, as far
as I can judge, inhabiting distinct stations, high land or low
land, dry or moist districts, or distinct regions. Bronn also
insists that distinct species never differ from each other only

Chap. IV. VAEIOUS OBJECTIONS. 12^

ill single cliaractcrs, ])ut in man}- parts; and he asks, how it
comes that natural selection should invariably have afrectcd
simultaneously many parts of the org'anization i' But there is
not the loast necessity for believing that all the parts have been
simultaneously modilied ; they may have been gained one after
the other, and from being transmitted together, they appeal
to us as if simultaneously formed. Correlation, however, will
account for various parts changing, when any one part changes.
We have e\'idence of this in our domestic races, which, though
they may difl'er greatly in some one selected character, always
diller to a certain extent in other characters.

Bronn, again, asks how natural selection can account for
dilTerences between species, which appear to be of no service
to these species, such as the length of the ears or tail, or the
folds of the enamel in the teeth, of the several species of hares
and mire ? With respect to plants, this subject has been
recently discussed by Niigeli in an admirable essay. He admits
that natural selection has effected much, but he urges that the
families of plants diil'er chiefly from each other in morphologi-
cal characters, which seem quite imimportant for the welfare
of the species. He consequently believes in an innate ten-
dency toward perfection or progressive development. He
specifies the arrangement of the cells in the tissues, and of the
leaves on the axis, as cases in which natural selection Avould
fail to act. To these may be added the numerical divisions
in the parts of the flower, the position of the ovniles, the shape
of the seed, when not of any use for dissemination, etc Prof.
Weismann, in discussing Niigeli's essay, accounts for such dif-
f(!rences by the nature of the varying organism under the action
of certain conditions ; and this is the same with what I have
called the direct and definite action of the conditions of lifo,
causing all or nearly all the individuals of the same species to
vary in the same manner. When we remember such cases as
the formation of the more complex galls, and certain monstros-
ities, which cannot be accounted for l)y reversion, cohesion,
etc., and sudden strongly-marked deviations of structure, such
as the ajipearance of a moss-roscj on a connnon rose, we must
admit that the organization of the individual is capable through
its own laws of growth, under certain conditions, of undergoing
great modifications, independently of the gradual accumulation
of slight inherited modifications. \'arious morphological differ-
ences probably come under this head, to which we sliall recur;
but many differences may at the present time be of high ser-

128 VABIOUS OBJECTIONS. Cuaf. IV.

vice, or may formerly have been so, although >vc arc not able
to perceive their use ; and these will have been acted on by
natural selection, A still larger number of mor}:)hological dif-
ferences may certainly be looked at as the necessary result —
through pressure, the withdrawal or excess of nutriment, an
early-formed jiart affecting a part subsequently developed, cor-
relation, etc. — of other adaptive changes, through wliich all
species must have j)assed during their long course of descent
and modilication.

No one will maintain that we as yet know the uses of all
the pai-ts of any one plant, or the functions of each cell in any
one organ. Five or six years ago, endless peculiarities of
structure in the flowers of orchids, great ridges and crests, and
the relative positions of the various parts AVould have been con
sidered as useless moiphological difl'erences ; but now we know
that they are of great service, and must have been under the
dominion of natural selection. No one at present can explain
Avhy the leaves in a spire diverge from each other at certain
angles ; but we can see that their arrangement is related to
their standing at equal distances from the leaves on all sides ;
and we may reasonably expect that the angles will hereafter
be shown to follow from some such cause, as the addition of
new leaves to the crowded spire in the bud, as inevitably as
the angles of a bee"'s cell follow from the manner in which the
insects work together.

In certain Avhole groups of ])lants the ovules stand erect,
and in others they are suspended ; and in some few plants
within the same ovarium one ovule holds the former and a sec-
ond ovule the latter position. These positions seem at first
purely moi-jihological and of no physiological signification ;
but Dr. Hooker informs me that, of the ovules within the same
ovarium, in some cases the upper ones alone and in other cases
the lower ones alone are fertilized ; and he suggests that this
probably depcn^ls on the direction in which the pollen-tubes
enter. If so, the position of the ovules, even when one is erect
and the other suspended, would follow from the selection of any
slight deviation in position which might favor their fertilization
and the production of seed.

Several plants Ix'longing to distinct orders habitually pro-
duce flowers of two kinds — the one open and of the orthnary
structure, the other closed and impM'fect. In the latter the
l)etals are almost alwaj-s reductxl to the merest rudiments ; the
pollen-grains are reduced in diameter ; five of the alternate

CnAP. IV. VARIOUS OBJECTIONS. log

stamens are ruilimcntury in Ononis columnas ; and in some spe-
(•i(^s of Viola three stamens arc in this state, two retaining their
proper fimction, but being' of very small size. In six out of
lliirtv of tlie closed flowers in an Indian violet (name unknown,
for the plants have not as yet jiroduced perfect flowers), the
sepals were reduced from the normal lunnber of live to three.
In one section of the Malpighiacea3 the closed flowers, according
to A. de Jussieu, are still further modified, for the five stamens
which stand opposite to tlie sepals are all aborted, a sixth
stamen standhig opposite to a j)etal being alone developed;
and this stamen is not present in the ordinary flowers of these
species ; the style is aborted ; and the ovaria are reduced froni
three to two. In all the foregoing plants the minute closed
flowers are of high service, for they yield with perfect seciu-ity,
!Uid with the expenditure of extremely little pollen, or other
organized matter, a large supply of seed ; while the perfect
flowers permit occasional crosses with distinct individuals.
Therefore, these changes may have been, and no doubt have
been, efTi.'cted through natural selection ; and I may add that
nearly all the gradations between the perfect and imperfect
flowers may sometimes be observed on the same plant.

With respect to modifications which necessarily follow from
other cljangcs — through the withdrawal or excess of nutriment
— througli pressiu-e and other unknown influences — there is
space here only for a few brief illustrations. 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,
ojicns first, and has five sepals and petals, and five divisions to
the ovarium ; while all the other flowers on the plant are te-
tramerous. In the British Adoxa the uppermost flower gener-
ally has two cjilyx-lobes with the other organs tetramerous,
while the surrounding flowers generally have three cal^'x-lobes
with the other organs pentamerous ; and this difference appears
to follow from the manner in which the flowers are closely
]> icked together. In many Compositic and Umbellifera?, and
in some other plants, the circumferential flowers have their
corollas much more developed tlian those of the centre; and
this is probably the result of natural selection, for all the
flowers are thus rendered nuich more conspicuous to those in-
sects which are useful or even neccs.sary for their fertilization.
In connection with the greater development of the corolla, the

130 VARIOUS OBJECTIONS. Chap. IV.

reproductive organs are frequently more or less aborted. It is
a more curious fact that the achenes or seeds of the circum-
ference and of the centre sometimes differ greatly in form,
color, and other characters. In Carthamus and some othoi
Composita^ the central achenes alone are furnished with a pap-
pus ; and in llyoseris the same head yields achenes of three
different forms. In certain Umbcllifeni:; the exterior seeds, ac-
cording to Tausch, are orthospermous, and the central one
coelospermous, and this difference has been considered by De
Candolle as of the highest systematic importance in the family.
If in such cases as the foregoing all the leaves, flowers, fruits,
etc., on the same plant had been subjected to precisely the
same external and internal conditions, all no doubt would have
presented the same morjohological characters ; and there clearly
woiild have been no need to call in the aid of the principle of
progressive development. With the minute closed flowers, as
well as ^^^tll many degraded parasitic animals, if it be assumed
that any such aid is requisite, we sliould have to call in an in-
nate tendency to retrogi-essive development.

]\Iany instances could be given of morphological characters
varying greatly in plants of the same species growing close
together, or even on the same individual plant ; and some of
these characters are considered as systematically important.
I will specify only a few cases Avhich have first occurred to me.
It is not necessary to give instances of flowers on the same
plant being indifferently tctramcrous, pentamcrous, etc. ; but
as when the parts are few, numerical variations are in all cases
comparatively rare, I may mention that, according to De Can-
dolle, the flowers of Papavcr bracteatum offer two sepals with
four petals (and this is the common type with jioj^pies), or
three se}>als with six petals. The manner in which the petals
are folded in the bud is in most groups a constant morpho-
logical character ; but Prof. Asa Gray states that with some
species of Mimulus, the aestivation is almost as frequently that
of the Rhinanthidea3 as c>f the Antirrhinidea?, to which tribe
the genus belongs. Aug. St.-Hilaire gives the following cases ;
the genus Zanthoxylon belongs to a di\-ision of the Kutacea3
with a single ovary, but in some of the species flowers may bo
found on the same plant, and even in the same panicle, with
cither one or two ovaries. In Helianthennnn the capsule has
been described as unilocular or 3-locular ; and in H. nuitabih^
" Une lame, plus ou moins large, sY'tend entre le pericarpe et
Ic placenta." In the flowers of Saponaria ollicinalis, Dr. Mas-

CiiAr. IV. VARIOUS OBJECTlOiNS. 131

tcrs also observed instances of botli mar<^inal and free central
placentation. Lastl}', St.-Hilaire foinid toward the southern
extreme of the ranfjc of Goniphia oletvforniis two forms which
he did not at first doubt were distinct species, but he subse-
quently saw them g-rowinp^ on the same bush ; and he then
adds, " A'oihl done dans uu memo individu des lof^es et un
style qui sc rattachent tantOt il un axe verticale et tantot ;l un
gynobase."

In the case of these plants, will it be said that they have
been detected in the act of progTessin<T toward a hijjher state
of development ? On the contrary', I should infer, from such
characters varying;' so f^reatly, that tliey Avere of extremely
small importance to the plants themselves, of whatever impoi--
tance they may be to us in our classifications. Although we
are quite ipiorant of the excitin<^ cause of each modification,
vet it st'cms probaljle from what we know of the relations of
varialjility to changed conditions, that under certain conditions
the one structure Avould have prevailed over the other, and
thus might have been rendered almost or quite constant.
l'>om th<? very fact of such diflerences being unimportant for
the welfare of the species, any slight dcAiations which did
occur Avould not be augmented or accumulated through natural
selection ; and they would be liable to obliteration through the
occasional intercrossing of distinct individuals. A structure
Avhich has hccn developed through long-continued selection,
when it ceases to be of service to the species, will generally
become variable, as we see with rudimentary organs ; for it
will no longer be regulated by this same power of selection ;
but on the other hand, when from the nature of the organism
and from a change in the conditions definite modifications have
been produced which are imimportant for the welfare of the
species, they may be, and apparently often have been, trans-
mitted in nearly the same state to numerous, otherwise modi-
fied descendants. Hair has been transmitted to almost all
mammals, feathers to all birds, and scales to all true reptiles.
A structure, whatever it may be, wiiich is common to many
alli(Ml forms, is ranked by us as of high systematic importance,
and consequently is often assimied by us in be of high vital
importance to tin* species. Thus, as I am inclined to believe,
morphological diilerenccs, which we consider as important —
such as the arrangement of the leaves, the divisions of the
ovarium, the position of the ovules, etc. — first appeared in
many cases as fluctuating variations, which sooner or later

132 VARIOUS OBJECTIONS. Cn^r. IV.

became almost constant tln-ough the nature of tlic organism
and of the surrounding' conditions, as Avell as through inter-
crossing ; for as these morphological charactei'S do not aflfect
the welfare of the species, any slight deviations in them would
not be acted on or accumulated through natural selection. It
is a strange result which we thus arrive at, namely, that char-
acters of slight vital importance to the species, are the most
important to the systematist; but, as we shall hereafter see
when we treat of the genetic principle of classification, this is
by no means so paradoxical as it at first appears. Finally,
whatever may be thought of this view, in none of the forego-
ing cases do the facts, as far as I can judge, afford any evi-
dence of the existence of an innate tendency toward perfecti-
bility or progressive development,

I need allude only to two other objections : a distinguished
botanist, Mr. H. C. ^\'atson, behoves that I have overrated the
importance of divergence of character (in which, however, he
apparently believes), and that convergence of character, as it
may be called, has likewise played a part, Tliis is an intricate
subject which need not be fully discussed. I will only remark
that if two species of two allied genera, both produced a num-
ber of new and divergent species, I can believe that they
might sometimes approach each other so closely that they
would for convenience' sake be classed in the same new genus,
and thus two genera would converge into one ; but from the
strength of the principle of inheritance, and from the two par-
ent-species already differing and consequently tending to vary
in a somewhat different manner, it seems hardly credible that
the two new groups would not at least form distinct sections
in the genus.

Mr. AVatson has also objected that the continued action of
natui'al selection with divergence of character will tend to
make an indefinite number of specific forms. As far as mere
inorganic conditions are concerned, it seems probable that a
sufficient mmiber 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 increas-
ing, the organic conditions of life become more and more com-
plex. Conscquentl}' there seems at first sight no limit to the
amount of prolitaljle diversification of structure, and therefore
no limit to the number of species wliich might be })roduced.
A\'e do not know that even the most prolific area is fully

CiiAr. IV. VARIOUS OBJECTIONS. I33

stocked with specific forms : at the Cape of Good Hope and in
Australia, which support such an astonishinnf number of spe-
cies, many European plants have become naturalized. But
fj^coloiry shows us, that from an early part of the long' tertiary
jicriod the numljcr of species of shells, and that from the mid-
dle part of this same period the numlxT of mammals, has not
greatly or at all increased. AVhat, tluMi, checks an indefinite
increase in the number of species? The amount of life (I do
ncjt mean the lunnbcr of specific forms) supported on any area
nuist have a limit, depending;' so larj^ely as it does on physical
conditions ; therefore, if an area be inhabited by very many
species, each or neaily each s})ecies "will be represented by few
individuals; and such species will be liable to extermination
fiom accidental lluctuations in the nature of the seasons or in
the number of their enemies. The process of extermination in
these <;!ases will be ra]>id, whereas the production of new spe-
cies must alwa3'S be slow. Imac^inc the extreme case of as
many species as individuals in England, and the first severe
winter or A-ery dry summer would exterminate thousands on
thousands of species. Kare species, and each species will be-
come rare if the number of species in any country becomes
indefinitely increased, will, on the principle often explained,
j)resent within a given period few favorable variations; conse-
<|uently, the process of giving birth to new specific forms will
thus be retarded. When 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 Ked Deer in Scotland, and of
liears in Norway, etc. Lastly, and this I am inclined to think
is the most important element, a dominant species, Avhich has
nlnMdy beaten many competitors in its own home, Avill tend to
spread and supplant many others. Alph. de Candolle has
shown that those species which spread widely tend generally to
spread vcnj widely ; and, consequently, they will tend to sup-
|)lMnt and exterminate several species in several areas, and
thus check the inordinate increase of specific forms throughout
the world. Dr. Hooker has recently shown that in the south-
east corner of Australia, where, apparently, there are manv in-
vaders from difTerent quarters of the world, the endemic Aus-
tralian species have been greatly reduced in number. ITow
nuich weight to attribute to these several considerations I do
not jiretend to assign ; but ronjointly they must limit in each
country the tendency to an indefinite augmentation of specific
fonns.

134 SUMMARY. Chap. IV.

Sum)) tart/ of Chcfpter.

If iiiulcr changing conditions of life organic beings present
individual difiercnces in all parts of their structure, and this
cannot be disputed ; if there bo, owing to the high geometrical
ratio of increase of each species, a severe struggle for life at
some age, season, or year, and tliis certainly cannot 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 extraor-
dinary fact if no variations ever occurred useful to each be-
ing's OAvn welfare, in the same inanner as so many variations
have occurred useful to man. /But if variations useful to any
organic being do ever occur, assuredly individuals thus charac-
terized will have the best chance of being preserved in the
struggle for life ; and from the strong principle of inheritance,
they will tend to produce ofi'spring similarly characterized.
This principle of preservation, or the survival of the fittest, I
have called Natural Selection^ It leads to the improvement
of each creature in relation to its organic and in organic condi-
tions of life ; and consequent]}', in most cases, to what must
be regarded as an advance in organization. Nevertheless, low
and simple forms will long endure if well fitted for their simple
conditions of life.

Natural selection, on the principle of qualities being in-
herited at corresponding ages, can modify the egg, seed, or
young, as easily as the adult. Among many animals, sexual
selection Avill give its aid to ordinary selection, by assuring to
the most vigorous and best adapted males the greatest num-
ber of offspring. Sexual selection will also give characters useful
only to the males, in their struggles with other males ; and
these characters Avill 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 conditions and stations,
must be judged of by the general tenor and balance of the evi-
dence given in the following chapters. But we already see
how it entails extinction ; and how largely extinction has acted
in the world's history, geology plainly tleclarcs. Natural selec-
tion, also, leads to divergence of character ; for the more organic
beings diverge in structure, habits, and constitution, by so much
can a greater number be supported on the same area — of which

CiiAF. IV. SUMMARY. I35

we see proof by looking to the inhabitants of any small spot
or (o naturalized productions. Therefore, durin> the modifica-
tion of the descendants of anj- one species, and dm'in<>* the in-
cessant stru^f^le of all species to increase in numbers, the more
diversified these descendants become, tlic better will be their
chance of succccdinrr in the battle for life. Thus, the small
dill'erences distin<]^uishint^ varieties of the same species, steadily
tend to increase, till they come to equal the greater diflfereuces
between species of tlie same genus, or even of distinct genera.

We have seen that it is the common, the widely-dilfused,
and widely-ranging species, belonging to the larger genera
within each class, which vary most; and these tend to transmit
((> their modified offspring that superiority which now makes
them dominant in their own countries. Natural selection, as
has just been remarked, leads to divergence of character and to
much Extinction of the less improved and intermediate forms of
life. On these principles, the nature of the affinities, and the
generally AvoU-dellned distinctions of the innumerable organic
beings in each class througliout the Avorld, may be explained.
It is a truly wonderful fact — the wonder of M'hich we are apt
to overlook from familiarity — that all animals and all plants
tliroughout all time and space should be related to each other
in natural groups subordinate to groups, in the manner
which Ave everywhere behold — namely, varieties of the same
species most closely related together ; species of the same genus
less closely and unequally related together, forming sections
and sub-genera ; species of distinct genera much less closely
related, and genera related m difierent degrees, forming sub-
families, families, orders, sub-classes, and classes. The several
subordinate groups in any class cannot be ranked in a single
lile, but seem rather to be clustered round points, and these
round other points, and so on in almost endless cycles. If
each species has been independently created, no explanation
rm be given of this great fact in the classification of all organic
beings; but it is explained through inheritance and tlie com-
plex action of natural selection, entailing extinction and diver-
gence of character, as we have seen illustrated in the diagram.

The affinities of all the beings of the same class have some-
limes been repres(Mited by a great tree. I believe this simile
largely speaks (lie trulli. The green and budding twigs may
represent existing species ; and those produced during former
years may represent the long succession of extinct species. At
each period of growth all the growing twigs have tried to

133 SUMMARY. CuAr. IV.

brancli out on all siili^s, and to overtop and kill the surrounding
t\vii>s and l)ranchcs, in the same manner as species and groups
of speeies have at all times overmastered other species in the
great battle for life. The limbs, di\'ided into great branches,
and those into lesser and lesser branches, were themselves once,
when the tree Avas small, budding twigs ; and this connec-
tioTi of the former and present Inids by ramifying branches may
well represent the classification of all extinct and living species
in groups subordinate to groups. Of the many twigs which
nourished when the tree was a mere bush, only two or three,
now grown into great branches, yet survive and bear all the
other branches ; so with the species which lived during long-
])ast geological periods, very few now have living and modified
descendants. From the first growth of the tree, many a limb
and branch has decayed and dropped off; and these lost
branches of various sizes may represent those whole orders,
families, and genera, which have now no living representatives,
and whicli are known to us only from being found in a fossil
state. As we here and there see a thin, straggling branch
sj)ringing 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 Ornithorh^mchus or Lepi-
dosiren, which in some small degree connects by its affinities
two large branches of life, and which has apparently been
saved from fatal competition by having inhabited a protected
station. As buds give rise by growth to fresh buds, and these,
if vigorous, branch out and overtop on all sides many a feebler
branch, so by generation I believe it has been Avith the great
Tree of Life, which fills with its dead and broken branches the
crust of the earth, and covers the surface with its ever-branch-
inc: and beautiful ramifications.

Cu.vr. V. LAWS OF VARIATION. IO7

ciiArxER y.

LAWS OF VAUIATIOX.

Effects of clmntrofl Coiuiillont'—T'iJo and Dis>nso, combined with Natural Selection;
Orirtiiii (if Fliirlit and of Vision— Acclimatization— Correlated Variatiou— Com-
pensation and Keonoiny of (imwtli— False C:orrclation» — Mnlti|)le, Uudinicntary,
and l.iiwly-or^'anized Stnietuies< variable— Parts developed in an Unusual Man-
ner are hij;ldy variable : ?>poeific Characters more variable ttwn Generic: Second-
ary Sexual characters variable— Species of the t^anic Genus vary in au analoguua
llauucr— Ueverbioua to long-lost Charactera — Sumaiary.

. I HAVE hitherto sometimes spoken as if the variations — so
comn'ion and multilorin with org'anic beings nnder domestication,
and in a lesser degree with those in a state of nature — had
l)een due to cliance. This, of course, is a wholly incorrect ex-
pression, but it serves to acknowledge plainly our ignorance
of the cause of each particular variation. Some authors be-
lieve it to be as much the function of the reproductive system
to produce individual difTerences, or slight deviations of struc-
tuie, 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 varia-
l>ility of species having wide ranges than of those having re-
stricted ranges, lead to the conclusion that variability is directly
related to the conditions of life to Avhich each species has been
exposed during several successive generations. In the first
cliapter I attempt(>d to show that changed conditions act in
two ways, directly on the whole organization or on certain
])ar(s alone, jind indirectly through the reproductive sj'stcm.
Jn all cases th(M-e ate two factors, the nature of the organism,
which is nuich the most important of the two, and the nature
of the conditions. The direct acticm of changed conditions,
leads to (h'Tmite or indefinite results. In the latter case the
organization seems to become plastic, and we have nnich fluc-
tuating variability. In the former case the nature of the or-
ganism is such that it yields readily, when subjected to cer-
lain conditions, and all, or nearly all the individuals become
modified in the same way.

l.iS LAWS OF VARIATION. Chap. V.

It is very difficult to decide how far clianii^cd conditions,
such as of climate, food, etc., have acted in a definite manner.
There is some reason to believe that in the course of time the
effects have been greater than can be proved to be the case by
any clear evidence. But we may safely conclude that the in-
niunerable complex coadaptations of structure which we see
throughout Nature between various organic beings, cannot be
attriljuted simply to such action. In the following cases the
conditions seem to have produced some slight definite effect :
E. Forbes asserts that shells at their southern limit, and when
living in shallow water, are more brightly colored than those
of the same species from farther north or from a greater depth;
but these statements have lately been disputed, Mr. Gould
believes that birds of the same species are more brightly col-
ored under a clear atmosjihere, than when living on islands or
near the coast ; and WoUaston is convinced that residence near
tlie sea affects the colors of insects. Moquin-Tandon gives a
li.st of plants which when growing near the sea-shore have their
leaves in some degree ileshy, though not elsewhere fleshj'.
Other similar facts could be given.

The fact of varieties of one species, when they range into
the habitations of other species, often acquiring in a slight
degree some of their characters, accords Avith the view that
species arc only well-marked and permanent varieties. Thus
the species of shells Avhich are confined to tropical and shal-
low seas are generally brighter-colored than those confined to
cold and deeper seas. The birds Avhich are confined to conti-
nents are, according to Mr. Gould, brighter-colored than those
of islands. The insect-species confined to sea-coasts, as every
collector knows, are often brassy or lurid. Plants which live
exclusively on the sea-side are very apt to have Ileshy leaves.
He who believes in the creation of each species, will have to
say that this insect, for instance, was created of a brassy color,
because it was intended to live near the sea, but that this other
insect became brassy through variation as soon as it reached
the sea-coast.

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. Tlius, it is avcU known to furriers that ani-
mals of the same species have thicker and better fur tlie far-
tlier north they live ; but who can tell liow much of this dif-
ference may be due to the warmest-clad individuals having

CiiAi-. V. EFFECTS OF USE AND DISUSE. in<)

1)ftM» favored and preserved during many generations, and how
much lo the action of tlie severe climate ? for it would appear
that climate has some direct action on the hair of our domestic
(juachupeds.

Instances could be given of similar varieties being produced
from the same species under external conditions of life as dif-
ferent as can well be conceived ; and, on the other hand, of
dissimilar varieties being produced imder apparently the same
external conditions. Again, innumerable instances are known
to ev(;ry naturalist, of species keeping true, or not varying at
all, although living und<'r the most opposite climates. Such
considerations as these incline me not to lay much weight on
the direct and definite action of the conditions of life; but I
fully admit that strong arguments of a general nature may be
advanced on the other side.

In one sense the conditions of life may be said, not only to
cause variability, but likewise to include natural selection ; for
the conditions determine whether this or that variety shall sur-
yi\i.\ ]3ut when man is the selecting agent, we clearly see
that the two elements of change are distinct ; the conditions
cause the variability; the will of man, acting either consciously
or unconsciously, accumulates the variations in certain direc-
tions, and tills answers to the survival of the fittest under
nature.

J^Jfects of Use and Disrise, as controlled hy Natural Selection.

From the facts alluded to in the first chapter, I think there
can be no doubt that use in our domestic animals strengthens
and enlarges certain parts, and disuse diminishes them ; and
that such modifications are inherited. Under free Nature, we
liave no standard of comparison, by which to judge of the
elfecls of long-continued use or disuse, for "we know not the
parent-fonns; but many animals have structures which- can be
(•xi)lain<'d by the efl'ects of disuse. As Prof. Owen has remarked,
llierc is no greater anomaly in Nature than a bird that cannot
l!y ; yet there are several in this state. The logger-headed duck
of South America can only llap along the surface of the water,
and has its wings in nearly the same condition as the domestic
Aylesbury duck. As the larger ground-feeding birds seldom
tak(> fiight except to escap<> danger, I believe that the nearly
wingless condition of several birds, which now inhabit or have
lately inhabited several oceanic islands, tenanted by no beast

140 EFFECTS OF USE AND DISL'SE. Chap. V.

of prey, lias been caused by disuse. The ostricli, indeed, in-
Imbils continents and is exposed to dann^er from -wliicli it cannot
escape by llii^^lit, but by kickinp^ it can defend itself from ene-
mies, as well as any of the smaller ciuadrupeds, "We may be-
lieve that the progenitor of the ostrich fj^enns had habits like
those of a bustard, and that, as natural selection increased in
successive g-enerations the size and weight of its body, its legs
were used more, and its wings less, until they became incapa-
ble 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 very often broken off ; he examined seventeen spe-
cimens in his own collection, and not one had even a relic left.
In the Onites apclles the tarsi are so habitually lost, that the
insect has been described as not having them. In some other
genera they are present, but in a rudimentary condition. In
the Ateuchus or sacred beetle of the Egyptians, they are totally
deficient. The evidence that accidental mutilations can be in-
herited is at present not quite decisive ; but the remarkable
case observed by Brown-Sequard of inherited epilepsy in guinea-
pigs, caused by an operation performed on the spinal cord,
should make us cautious in denying such power. Hence it
Avill ]>ei]iaps be safest to look at the entire absence of the an-
terior tarsi in Ateuchus, and their rudimentary condition in
some other genera, as due to the effects of long-continued
disuse; for, as many dung-feeding beetles are generally found
with their tarsi lost, this nnist happen earlv in life; therefore
tlie tarsi cannot be of much impoi'tance or be nnich used by
these insects.

In some cases we might easily put do"^^'n to disuse modifi-
cations of structure which are wholly, or mainly, due to natural
selection. Mr. AYollaston has discovered the remarkable fact
that ::300 beetles, out of the 550 species (but more are now
known) which inhabit Madeira, are so far deficient in wings
that they cannot fly; and that, of the twent^'-nine endemic
genera, no less than twenty-three genera have all their species
in this condition ! Several facts — namely, that beetles in many
parts of the world are frequently blown to sea and perish ;
that the beetles in Madeira, as observed by Mr. AVollaston, lie
much concealed, until the wind lulls and the sun shines ; that
the ])roportion of wingless beetles is larger on the exposed
Desertas than in Madeira itself; and especially the extraor-
dinary fact, so strongly insisted on by Mr. AVoUaston, of the

CiiAP. V. EFFECTS OF USE AND DISUSE. 141

alino.st entire abs'jnco of certain lar^jo groups of beetles, else-
where excessively numerous, and which groups have ha])its of
life almost necessitating frequent flight — tliese several con-
siderations have made me believe that the wingless condition
of so many Madeira beetles is mainly due to the action of
natural selection, but combined probably with disuse. For
during many successive generations each individual beetle
which Hew least, cither from its wings having been ever so
little less perfectly developed or from indolent habit, will have
had the best chance of surviving from not being blown out to
sea ; and, on the other hand, those beetles whicli most readily
took to flight would oftenest have been blown to sea and thus
have been destroyed.

The insects in Madeira which arc not ground-feeders, and
which, as the flower-feeding coleoptera and lepidoptera, must
habilually use their wings to gain their subsistence, have, as
Mr. Wuilaslon suspects, their wings not at all reduced, but
even elilarged. This is quite compatible with the action of
natural selection. For when a new insect first arrived on the
ishind, the tendency of natural selection to enlarge or to reduce
the wings, would depend on whether a greater number of in-
dividuals were saved by successfully battling with the winds,
or by giving up the attempt and rarely or never flying. As
wilh mariners shipwrecked near a coast, it would liave been
bcttiT for the good swimmers if they had been able to swim
still farther, whereas it would have been better for the bad
swinnners 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 arc
rudimentary in size, and in some cases are quite covered up ])y
skin and fur. Tliis state of the eyes is probably due to gradual
reduction from disuse, but aided perhaps by natural selection.
In Soutli America, a burrowing rodent, the tuco-tuco, or Ctcn-
omys, is even more subt(«rranean in its habits than the mole;
.and 1 was assured by a Spaniard, who had often caught them,
that th(»y were frequently blind; one which I kept alive was
certainly in this condition, the cause, as appeared on dissection,
having been inllammation of the nictitating membrane. As
frefjuent inflammation of the eyes nnist be injurious to any
animal, and as eyes are certaiidy not necessary to aiiimals
having su])terranean habits, a reduction in their size, with the
adhesion of the eyelids and growth of fur over them, might in

142 EFFECTS OF USE AND DISUSE. Chap. V,

such case be an advantage ; and if so, natural selection would
conslanlly aid the efl'ects of disuse.

It is well known that several animals, belonging to the
most different classes, which inhabit the caves of Carniola and
of Kentucky, are blind. In some of the crabs the foot-stalk for
tlie eye remains, though the eye is gone ; the stand for the
telescope is there, though the telescope with its glasses has
been lost. As it is difficult to imagine that eyes, though use-
less, could be in any way injurious to animals living in dark-
ness, I attribute their loss wholly to disuse. In one of the
bUnd animals, namely, the cave-rat (Ncotoma), two of which
were cajotured by Prof. Silliman at above half a mile dis-
tance fj-om the moutli 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 Prof. Silliman, after
having been exposed for about a month to a graduated light,
acquired a dim perception of objects.

It is difficult to imagine conditions of life more similar tlian
deep limestone caverns imdcr a nearly similar climate ; so that,
on the common view of the blind animals haWng been sepa-
rately created for the American and European caverns, very
close similarity in their organization and affinities might have
been expected. This is certainly not the case if we look at the
two whole faunas ; and, with respect to the insects alone,
Schiodte has remarked : " We are accordingly prevented from
considering the entire phenomenon in any other light than
something purely local, and the similarity which is exhibited
in a few forms between the INIannnoth 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 ordinary powers of
vision, slowly migrated by successive generations from the outer
world into the deeper and deeper recesses of the Kentucky
caves, as did European animals into the caves of Europe. We
have some evidence of this gradation of habit ; for, as Schiodte
remarks, " We accordingly look upon the subterranean faunas
as small ramifications which have penetrated into the earth from
the geograjihically limited faunas of the adjacent tracts, and
which, as they extended themselves into darkness, have been
accommodated to surrounding circumstances. Animals not far
remote from ordinary forms, proiwre the transition from light
to darkness. Next follow those that are constructed for twi-

Chap. V. EFFECTS OF USE AND DISUSE. I43

li^lit ; and, last of all, tlioso destined for total darkness, and
Aviiose formation is (juitc peculiar." These remarks of Schiiidte's,
it should be understood, apply not to the same, but to distinct
species. ]Jy the time that an animal had reached, after num-
berless generations, the deepest recesses, disuse will on this
view have more or less perfectly obliterated its eyes, and
natural selection will often have ell'ected other changes, such
as an increase in the length of the antenmu or palpi, as a com-
pensation for l)lindness. Notwithstanding such modifications,
we might expect still to sec in the cave-animals of America,
allinities to tlie 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
hi^ar from Prof. Dana ; and some of the European cave-insects
arc very closely allied to those of the surroimding countrv. It
woulil be most dillicult to give any rational explanation of the
allinities of the blind cave-animals to the other inhabitants 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 should l)e closely related, we might ex-
pect from the Avell-knowu relationship of most of their other
jiroductions. As a blind species of Bathyscia is found in abun-
dance on shady rocks far from caves, the loss of vision in the
cave-species of this one genus has probably had no relation to
its dark habitation ; and it is very natural that an insect al-
ready deprived of vision should readily become adapted to
dark caverns. Another blind genus (Anophthalmus) offers
this remarkable peculiarity: the several distinct species, as Mr.
MuiTay has remarked, iidiabit several distinct European caves
and likewise those of Kentucky, and the genus is found no-
v.here except in caves ; but it is possible that the progenitor
or progenitors of these several spec-ies, while furnished with
eyes, formerly may have ranged widely over both continents,
and then have become extinct, excepting in their ])resent se-
cluded abodes. Far from feeling surprise that some of the
rave-animals should be very anomalous, as Agassis has remarked
in regard to flu' blind fisli, the Amblyopsis, and as is the case
with the blind I'rotcus with refertMice to the reptiles of Europe,
1 am only surprised that more wrecks of ancient HA; have not
]>ccn preserved, owing to tin; less severe competition to which
the inhabitants of these daik abodes must have been exposed.

144 ACCLIMATIZATION. Chat. V.

Acclimatization,

Habit is hereditary with plants, as in the period of flower-
iii<T, in the amount of raui requisite for seeds to germinate, in
the time of sleep, etc., and tliis leads me to say a few words on
acclimatization. As it is extremely common for species of the
same genus to inhaljit hot and cold countries, if it be true that
all the species of the sanic g-cnus are descended from a single
parent-form, acclimatization must be readily effected during a
long course of descent. It is notorious that each species
is adapted to the climate of its own home : species from an
arctic or even from a temperate region cannot endure a tropical
climate, or conversely. So, again, many succulent plants can-
not endure a damp climate. But the degree of adaptation of
species to the climates under which they live is often overrated.
We may infer this from our frequent inability to predict
whether or not an im})ortcd 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 cli-
mates. But whether or not the adaptation be generally very
close, we have evidence, in the case of some few plants, of
their becoming, to a certain extent, naturally habituated to
diff(>rent temperatures ; that is, they become acclimatized: thus
the pines and rhododendrons, raised from seed collected by Dr.
Hooker from the same species gro^^^ng at different heights on
the Himalaya, were found in this country to possess different
constitutional powers of resisting cold. ^Ir. Thwaites informs
me that he has observed similar facts in Ceylon ; analogous
observations have been made by Mr. H. C. Watson on Euro-
pean species of plants brought from the Azores to England ;
and I could give other cases. In regard to animals, several
autlientic instances could be adduced of species within histori-
cal times having largely extended their range from warmer to
cooler latitudes, and conversely ; but we do not positively know
tliat these animals were strictly adapted to their native climate,
though in all ordinary cases we assume such to be the case ;
nor do we know that they have subsequently become specially
acclimatized to their new homes, so as to be better fitted for
lliiMU than they Avere at first.

As we may infer that our domestic animals were originally

CiiAP. V. ACCLIMATIZATION. Ii5

chosen by uncivilized nuin because they ■were useful^ and be-
cause they bred readily inider confinement, and not because
they were subsequently found cai)ablc of far-extended trans-
portation, the common and extraordinary capacity in our do-
mestic animals of not only withstandinf^ the most dillcrent
climates, but of beiii<T perfectly fertile (a far severer test) under
tliem, may be used as an argument that a large proportion of
other animals now in a state of nature could easily be brought
to bear widely-different climates. We must not, however,
push the foregoing argument too far, on account of the prob-
able origin of some of our domestic animals from several wild
stocks ; the blood, for instance, of a tropical and arctic wolf or
wild dog may perhaps be mingled in our domestic breeds.
The rat and mouse cannot be considered as domestic animals,
but they have been transported by man to many parts of the
world, and now have a far wider range 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 islands in the tor-
rid zones. Hence adaptation to an}' special climate may be
looked at as a quality readily grafted on an innate wide ilexi-
bility of constitution, common to most animals. On this view,
the ca]iacity of enduring the most different climates by man
himself and by his domestic animals, and the fact of the extinct
elephant and rhinoceros ha\nng formerly endured a glacial cli-
mate, whereas the living species are now all trojiical or sub-
tropical in their habits, ought not to be looked at as anomalies,
but as examples of a very common flexibility of constitution,
brought, under peculiar circumstances, into action.

How much of the acclimatization of species to any peculiar
climate is due to mere habit, and how much to the natural se-
lection of varieties having diilerent innate constitutions, and
how much to both means combined, is an obscure question.
Tliat habit or custom has some influence I nuist believe, both
from analogy and from the incessant advice given in agricul-
tural works, even in the ancient Encyclopicdias of China, to be
very cautious in trans])orting animals from one district to
another; for as it is not likely that man should have succeeded
in selecting so many breeds and sub-breeds with constitutions
specially fitted for their own districts, the result nuist, I think-,
be due to habit. On the other hand, natural si^lection would
inevitably tend to preserve those individuals wliich were born
with constitutions l)est adapted io any country which they in-
li ibih'd. In treatises on many kinds of cultivated plants, ccr-
7

146 CORKELATED VARIATION. Chap. V.

t:\in varieties are said to withstand certain climates better than
others ; this is verv strikingly shown in works on fruit-trees
published in the United States, in which certain varieties are
liabituallj recommended for the Northern and others for the
Southern States ; and, as most of these vari(>tics arc of recent
origin, they cannot owe their constitutional differences to hab-
it. The case of the Jerusalem artichoke, which is never propa-
gated in England by seed, and of which consequently new va-
rieties have not been produced, has even been advanced — for
it is now as tender as ever it was — as proving that acclimatiza-
tion cannot be effected ! Tlie 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 that a very large pro-
portion 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 precau-
tions, the experiment cannot be said to have been tried. Nor
let it be supposed that differences in the constitution of seed-
ling kidney-beans never appear, for an account has been pub-
lished how much more hardy some seedlings were than others;
and of this fact I have myself observed striking instances.

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

Correlated 'Variation.

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 accumulated
through natural selection, other parts become modified. This
is a very important subject, most imperfectly understood, and
no doubt totally different classes of facts may be here easily
confounded together : we shall presently see that simple in-
heritance often gives the false appearance of correlation. The
most obvious instance of real correlation is, that variations of
structure arising in the young or in the larvae naturally tend
to affect the structin-e of the mature animal ; in the same man-
ner as ;my malconfonnation in the early embryo is knoAvn

Chap. V. CORRELATED VAKIATION. I47

seriously to .ifFect the whole org'anization of the adult. The
several parts of the body which are homolof^ous, and which,
at an early embryonic period, are identical in structure, and
which are necessarily exposed to similar conditions, seem emi-
nently 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
bs 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 permanent by
selection.

Homologous parts, as has been remarked by some authors,
tend to cohere ; this is often seen in monstrous plants : and
nothing is more common than the union of homologous parts
in normal structures, as the imion of the petals of the corolla
into a tube. Hard parts seem to affect the forms of adjoining
soft parts ; it is believed by some authors that the diversity in
the shape of the pelvis in birds causes the remarkable diver-
sity in the shape of their kidneys. Others believe that the
shape of the pelvis in the human mother influences by pressure
the shape of the head of the child. In snakes, according to
Schlegol, the shape of the body and the manner of swallowing
determine the position and form of several of the most impor-
tant viscera.

The nature of the bond of correlation is frequently quite
obscure. M. Isidore Geoffroy St.-Hilaire has forcibly remarked
that certain malconformations very frequently, and that others
rarely coexist, without our being able to assign any reason.
^\''hat can be more singular than in cats the relation between
complete whiteness with blue eyes and deafness, or between
the tortoise-shell color and the female sex? or in pigeons be-
tween their feathered feet and skin betwixt the outer toes, or
b;^tween the jiresence of more or less down on the young birtl
when first hatched, with the future color of its plumage ; or,
again, the relation between the hair and teeth in the naked
Turkish dog, though here no doubt homology comes into play?
With respect to tliis latter case of correlation, I think it can
hardly be accidental, that, if we pick out the two orders of"
mammals which are most abnormal in their dermal covering,
viz., Cetacca (whales) and Edentata (amindilloes, scaly ant-

148 CORRELATED VARIATION. Cuap. V.

eaters, etc.), these are likewise the most abnormal in tlieir
teeth.

I know of no case better adapted to show the importance
of the laws of variation and correlation, independently of util-
ity and therefore of natural selection, than that before referred
to, of the difference between the outer and inner flowers in
some Conipositous and Umbelliferous plants. Every one knows
the dilTercnce in the ray and central florets of, for instiuice, th{^
daisy, and this difference is often accompanied with the partial
or complete abortion of the rejoroductive organs. But in some
of these plants, the seeds also differ in shape and sculpture.
These differences have been attributed by some authors to the
I^rcssure of the involucra on the florets, or to their mutual press-
in-e, and the shape of the seeds in the ray-florets of some Com-
positie countenances this idea; but with the Umbellifene, it
is by no means, as Dr. Hooker informs me, the species with
the densest heads Avhich most frequently differ in their inner
and outer flowers. It might have been tliought that the de-
velopment of the ray-pc^tals by drawing- nourishment from the
r(>productivc organs had caused their abortion ; but this can
hardly be the S(jle cause, for in some Compositir; the seeds of
the outer and inner florets differ without any difference in the
corolla. Possibly these several differences may be connected
Avith the diflcrent flow of nutriment toward tlie central and
external flowers : we know, at least, that, with normally iireg-
ular flowers, those nearest to the axis are most subject to
jK'loria, that is, they become S3'mmetrical. I may add, as an
instance of this, and of a striking case of correlation, that I
have recently observed in many pelargoniums, that in the cen-
tral flower of the truss the two upjier petals often lose their
])atches of darker color; and when this occurs, the adherent
nectary is qviite aborted. 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 developmoit of the corolla in the cen-
tral and exterior flowers, Sprengel's idea that the ray-florets
serve to attract insects, whose agency is highly advantageous
or necessary for the fertilteation of these plants, is highly jirob-
able ; and if so, natural selection may have come into i^lay.
]>ut, witli respect to the seeds, it seems impossible that their
diiVcrences in shape, which ai-e not ahvaj's correlated with any
difference in the corolla, can be in any way beneficial : yet in
the Umbellifere these differences arc of such apparent impor-

riiAP. V. COMPENSATION OF GKOWTII. 149

tiincc — the seeds bcinj^ sometimes orlliospermons in tlic exte-
rior llowers and ca-lospennoiis in the central ilowors — that the
elder iJe Caiidollo founded his main divisions in the order on
such char;- -ters. Hence, as before remarked, wc see that modi-
fications of structure, viewed by systematists as of hi^h value,
may be AvlK)lly due to the laws of variation and correlation,
without beiuf^, as far as we can judf^e, of the slightest service
t(^ the species.

We may often falsely attribute fo correlated variation
structures which arc common to whole groups of species, and
which in truth arc simply due to inheritance : for an ancient
progenitor may have acquired through natural selection some
one modification in structure, and, after thousands of genera-
tions, some other and independent modilication ; and these
two modiiications, liaving been transmitted to a whole group
of descendants witli diverse habits, would naturally l^e tlumght
_to be correlated in some necessary manner. Some correlations
are apparently due to the manner in wliich natural selection
acts. For instance, Al]ih. de Candollc has remarked that
winged seeds are never found in fruits wliich do not open : I
should ex})lainthis rule by the impossiljility of seeds gradually
becoming winged through natural selection, unless the ca])-
sules first opened themselves ; for in this case alone could the
seeds, which were a little better adapted to be Avafted by the
wind, gain an advantage over those less well fitted for wide
dispersal.

Compensation and Economy of Groxcth.

llie elder GeoiTroy and Goethe propounded, at about the
same period, their law of compensation or balanccment 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 domestic produc-
tions: if nourishment flows to one part or organ in excess, it
rarely flows, at least in excess, to another part; thus it is dif-
ficult to get a cow to give nuicli milk and to fatten readily.
The same varieties of tlic cabbage do not yield abundant and
luitritious foliage and a copious supply of oil-bearing seeds.
When the seeils in our fruits become atrophied, tlie fruit itself
gains largely in size and quality. In our poultry, a large tuft
of feathers on the head is generally accompanied by a dimin-
ished comb, and a large beard by diminished wattles. With

150 COMPENSATION OF GROWTU. Chap. V.

species in a state of nature it can hardly be maintained that
the law is of universal application ; but many jrood observers,
more especially botanists, believe in its truth. I will not, how-
ever, here give any instances, for I see hardly any way of dis-
tinguishing between the effects, on the one hand, of a part
being largel}' developed through natural selection and another
and adjoining part being reduced by this same process or by
disuse, and, on the other hand, the actual willidrawal of nutri-
ment from one part owing to the excess of growth in another
and adjoining part.

I suspect, also, that some cases of compensation which have
been advanced, and likewise some other facts, may be merged
inider a more general principle, namel}', that natural selection
is continually trying to economize in every part of the organ-
ization. If under changed conditions of life a structure before
useful becomes less useful, any diminution, however slight, in
its development, Avill be seized on by natural selection, for it
will ]iroiit 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 cirri-
pedes, and of which many other instances could be given :
namely, that when a cirripede is parasitic within another and
is thus protected, it loses more or less completely its own shell
or carapace. This is the case with the male Ibla, and in a
truly extraordinary manner with the Proteolepas ; for the car-
apace in all other cirripedes consists of the three highly-impor-
tant anterior segments of the head enormously developed, and
furnished with great nerves and muscles ; but in the parasitic
and protected Proteolepas, the whole anterior part of the head
i.s reduced to the merest rudiment attached to the bases of the
prehensile antenna?. Now the saving of a large and complex
structure, when rendered superfluous by the parasitic habits of
the Proteolepas, though effected by slow steps, would be a
decided advantage to each successive individual of the species ;
for in the struggle for life to which every animal is exposed,
each individual Proteolepas would have a better chance of
supporting itself, by less nutriment being wasted in develop-
ing a structure now become useless.

Thus, as I believe, natural selection will always succeed in
the long-run in reducing and saving every part of the organi-
zation, as soon as it is rendered by changed habits of life super-
fluous, without by any means causing some other part to be
largely develojicd in a corresponding degree; and, converse-

Chap. V. MULTIPLE STKUCTUKES VAKIABLE. 1.51

ly, that natural selection may perfectly well succeed in largely
developing any organ, without requiring as a necessary com-
pensation the reduction of some adjoinhig part.

Mullij)le, liudimentaryy and Loichj-organized Structures are

variable.

It seems to be a rule, as remarked by Is. Geoffroy St.-IIi-
laire, both in varieties and in species, that, when any part or
organ is repeated many times in the structure of the same
individual (as the vertebnu in snakes, and the stamens in poly-
androus ilowers), tlie number is variable; whereas the number
of the same part or organ, when it occurs in lesser num])ers, is
constant. The same author and some botanists have further
remarked that multiple parts are also very liable to variation
in structure. Inasmuch as this " vegetative repetition," to use
Prof. Owen's expression, seems to be a sign of low organiza-
tion, the foregoing remark seems connected with the very gen-
eral opinion of Jiaturalists that beings low in the scale of Na-
ture arc more variable than those which are liigher. I pre-
sume that lowncss in this case 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 diver-
sified Avork, wo can perhaps see Avhy it should remain variable,
that is, why natural selection should not have preserved or
rejected eacli little deviation of form so carefully as when the
part had to serve for one special purpose alone — 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 j^urpose
had better be of some particular shape. Natural selection, it
should never be forgotten, can act on each part of each being,
solely through and for its advantage.

Kudimentary parts, it has been stated by some authors, and
I believe with truth, are apt to be highly varialjle. AVe shall
have to recur to tlie general subject of rudimentary and aborted
organs; and I will here only add tliat tlieir variability seems
to be owing to their uselessness, and therefore to natiu-al selec-
tion having no power to check deviations in their structure.
Thus rudimentary parts are left to the free play of the various
laws of growth, to the effects of long-continued disuse, and to
tlic tendency to reversion.

152 UNUSUALLY DEVELOPED PARTS Chap. V.

A Part developed in any F^pccks in an extraordinary Degree
or Manner, in comparison with the same Part in allied
JS^)ccic^, tends to he highly variable.

Several years ago I was much struck by a rcmaik, to the
above effect, made by Mr, Waterliouse ; Prof. Owen, also,
seems to have come to a nearly similar conclusion. It is hope-
less to attempt to convince any one of the truth of the aljovc
j)roposition witliout giving the long array of facts which I have
collected, and which cannot possibly be here introduced. I can
only state my conviction that it is a rule of high generality.
I am aware of several causes of error, but I hope that I have
made due allowance for them. It should be understood that
the rule by no means applies to any part, however unusually
developed, unless it be unusually developed in comparison with
the same part in closely-allied species. Thus, the wing of the
bat is a most abnormal structure in the class of mammalia ; 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 develojoed in a remarkable manner in comparison with
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, applies to characters which are attached to
one sex, but are not directly connected Avith the act of repro-
duction. The nde applies to males and females ; but as females
more rarely offer remarkable secondary sexual characters, it ap-
plies more rarely to them. 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 Avhich fact I think there can be
little doubt. But that our rule is not confined to secondary
sexual characters is clearly shown in the case of hermaphrodite
cirripedes ; I particularly attended to ^Ir. \Vaterhouse's remark,
while investigating this order, and I am fully convinced that
the rule almost invariably holds good. I shall, in a future;
work, give a list of all the more remarkable cases ; I will lierc
only give one, as it illustrates the rule in its largest application.
The opercular valves of sessile cirripedes (rock barnacles) are,
in every sense of the word, very important structures, and they
diller extremely little even in different genera ; but in the several
species of one genus, Pyrgoma, these valves present a marvel-
lous amount of diversification ; the homologous valves in the

CnAi-. V. HIGHLY VARIABLE. I.53

different species beinp^ sometimes wlioUy unlike in shape; and
the amount of variation in the individuals of the same speciey
is so great, that it is no exaf^goration to state that the varieties
differ more from each other in the characters derived from these
important valves than do other species belonging to distinct
genera.

As birds within the same country vary in a remarkably
small degree, I have jiarticuhu-ly attended to them, and the
rule seems to me certainly to hold good in this class. I cannot
make out that it applies to plants, and this would seriously
have shaken my belief in its truth, had not the great variability
in plants mad(; it jiarticularly dillicult to compare their relative
degrees of variabilit}'.

When we see any part or organ developed in a remarkable
degree or maimer in any species, the fair presumption is, that
it is of high importance to that species ; nevertheless it is in
this case eminently liable to variation. Why should this be
so ? On the view that each species has been independently
created, with all its ])arts as we now see them, I can see no
explanation. But on the view that groups of species have
descended from other species, and have been modified through
natural selection, T think we can obtain some light. First, let
me remark that if any part in our domestic animals, or the
whole animal, be neglected and no selection be applied, that
I)art (for instance, the comb in the Dorking fowl) or the whole
bref'd will cease to have a imiforin character. The breed will
then be said to have degenerated. In rudimentary organs, and
in tijose which have been but little specialized for an}'' partic-
ular purpose, and perhaps in poljmiorphic groups, we see a
nearly parallel natural 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
concerns us is, that those points in our domestic animals, whicli
at the present time are undergoing rapid change by continued
selection, are also eminently liable to variation. Look at the
breeds of the pigeon ; see what a prodigious amount of differ-
ence there is in tht; beaks of tumblers, in the beaks and wattle
of carriers, in the carriage and tail of fantails, etc., these being
the points now mainly attiMided to by Englisli fanciers. Even
in sub-breeds, as in that of the short-faced tumbler, it is notori-
ously dillicult to breed nearly perfect birds, some fre(|uently
departing widely from the standard. There may truly be said
to be a constant struggle going on between, on the one hand,

15.4 UNUSUALLY DEVELOPED PARTS Cnxr. V.

the tendency to reversion to a less perfect state, as well as an
innate tendency to fnrtlier variability, and, on the other hand,
the power of steady selection to keep the breed true. In the
long'-run, selection gains the day, and we do not expect to faU
so far as to breed a bird as cf)arse as a common tumbler from a
good short-faced strain. Bnt as long as selection is rapidly
going on, nnich variability in the parts \mdergoing modification
may always he, expected. It further deserves notice tliat char-
acters, modified through selection by man, are sometimes trans-
mitted, from causes quite unknown to us, more to one sex than
to the other, generally to the male sex, as with the wattle of
carriers and the enlarged crop of pouters.

Now let us turn to Nature. AYlien a part has been devel-
oped 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 modifi-
cation since the period when the species branchetl off from the
connnon progenitor of the genus. This period will seldom be
remote in any extreme degree, as species rarely endure for more
than one geological period. An extraordinary amovmt 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
■];)een so great and long-continued within a period not exces-
sively remote, Ave might, as a general rule, still expect to find
more A-ariability in such parts than in otlier parts of the organi-
zation which have remained for a much longer period nearly
constant. And this, I am convinced, is the case. Tliat the
struggle between natural selection on the one hand, and the
tendency to reversion and variability on the other hand, will in
the course of time cease ; and that the most abnormally devel-
oped organs may be made constant, I see no reason to doubt.
Ilence, when an organ, however abnormal it may be, has been
transmitted in approximately the same condition to many modi-
fied descendants, as in the case of the wing of the bat, it must
have existed, according to my theory, for an immense period
in nearly the same state; and thus it comes to be no more vari-
al)le than any other structure. It is only in those cases in
wliich the modification has been comparatively recent and
extraordinarily great that we ought to find i\\o generative vari-
(ihllitij^ as it may be called, still present in a high degree. For
in this case tlie variability will seldom as yet have been fixed

Chap. V. HIGHLY VARIABLE. I55

by the continued selection of the individuals varj-ing in the
•required manner and degree, and by the continued rejection
of those tending to revert to a former and less-modified con-
dition.

Si'iecific Characters more variable than Generic Characters^

The principle included in the above remarks may be ex-
tended. It is notorious that specific characters are more va-
riable than generic. To exjilain by a simple example -what is
meant : If in a large genus of jilants some species had blue
flowers and some had red, the color Avould be only a specific
character, and no one "would be surprised at one of the blue
species varying into red, or conversely ; but if all the species
had blue ilowers, the color would become a generic character,
and its variation Avould be a more unusual circumstance. I
liave chosen this example because an explanation is not in this
case applicable, which most naturalists would advance, namely,
that specific characters are more variable than generic, because
they are taken from parts of less physiological importance than
those commonly used for classing genera. I believe this ex-
planation is partly, yet only indirectly, true ; I shall, however,
have to return to this subject in the cliapter on Classification.
It would be almost superfluous to adduce evidence in support
of the a])ove statement, that specific characters are more va-
riable than generic ; but I have repeatedly noticed in Avorks on
natural history, that, when an author has remarked with sur-
prise that some imjiortant organ or part, which is generally
very constant throughout large groups of species, has differed
considerably in closelj'-allied species, it has also been vari-
able in the individuals of some of the species. And this fact
shows that a character, Avhicli is generally of generic value,
when it sinks in value and becomes only of specific value, often
becomes variable, though its physiological importance may re-
main the same. Something of the same kind applies to mon-
strosities : at least Is. GeoflVoy St.-Hilaire seems to entertain
no doubt that the more an organ normally differs in the differ-
ent species of the same group, the more subject it is to indi-
vidual anomalies.

On the ordinary view of each species having been inde-
pendently created, why should that part of the structure,
which differs from the same part in other independently-created
species of the same genus, be more variable than those parts

156 SECONDARY SEXUAL Chap. V.

which are closely alike in the several species? I do not sec
that any explanation can be given. But on the vie'.v that spe-
cies are only stron2;ly marked and fixed varieties, Ave might ex-
pect to find them still oil en continuing to vary in those parts
of their structure which had varied witliin a moderately-recent
period, and which had thus come to diCfer, 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 charac-
ters in common I attribute to inheritance from a common pro-
genitor, for it can rarely have happened that natural selection
Avill have modified several species, fitted to more or less wide-
ly-diflerent habits, in exactly the same manner : and as these
so-called generic characters have been inherited from before
tlie period when the different species first branched off from
their common progenitor, and subsequently have not varied or
come to differ in any degree, or only in a slight degree, it is
not probaljle that tliey should vary at the present day. On the
other hand, the points in which species differ from other spe-
cies of the same genus are called specific characters ; and as
these specific characters have varied and come to differ since
tlie period when the species branched off from a common pro-
genitor, it is probable that they should still often be in some
degree variable — at least more variable than those parts of the
organization which have for a very long period remained con-
stant.

Secondary Sexual Characters variable.

In coimection with the present subject, I Avill make only
two other remarks. I think it will be admitted, without my
entering on details, that secondary sexual characters are very
variable; I think it also will be admitted that species of the
same group diller from each other more widely in their second-
ary sexual characters tlian in other parts of their organization;
(^ompare, for instance, tlie amount of difference between the
males of gallinaceous birds, in which secondary sexual charac-
ters are strongly displayed, with the amount of difference be-
tween the females; and the tnith of tliis jiroposition will be
granted. Tiie cause of the original variability of secondary
S(\xual characters is not manifest ; but we can see why these
characters should not have been rendered as constant and imi-
form as other parts of the organization; for secondary sexual
characters have been accumulated by sexual selection, which is

Chap. V. CHARACTERS VARIABLE. 157

less rigud in its action tlian ordinary selection, as it does not
entail death, bnt only gives fewer offspring to the less favored
males. Whatever tlie cause may be of the variability of sec-
ondary sexual characters, as they are highly variable, sexual se-
lection, will have had a wide scope for action, and may thus
readily have succeeded in giving to the species of the same
group a greater amount of difference in their sexual characters
tlian in other parts of their structure.

It is a remarkable fact that the secosdary sexual differ-
ences between the two sexes of the same sjiecies arc generally
displayed in the very same parts of the organization in whicli
the different species of the same genus dilfer from each other.
Of this fact I will give two instances in illustration, the first
which hap])en to stand on my list; and, as the differences in
these cases are of a very unusual nature, the relation can hard-
ly be accidental. The same number of joints in the tarsi is a
character generally common to very large gi-oups of beetles,
but in the Engid:e, as Westwood has remarked, the number
varies greatly; and the number likewise differs in the two
sexes of the same species : again, in fossorial liymenoptera, the
manner of neuration of the wings is a character of the highest
importance, because common to large groups ; but in certain
genera the ncin-ation differs in the different species, and like-
wise in the two sexes of the same species. Sir J. Lubbock
has recently remarked that several minute crustaceans offer ex-
cellent illustrations of this law. " In Pontella, for instance,
the sexual characters arc afforded mainly l)y the anterior an-
tenna) 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 of the subject : I look at all th(!
species of the same genus as ha^nng as certainly descended
from the same progenitor as have the two sexes of any one of
the species. Conseijuently, whatever part of the structure of
the common progenitor, or of its early descendants, became
A-ariable, variations of this part Avould, it is highly jiroljable, be
taken advantage of by natural and sexual selection, in order to
fit the several species to their several j)lac(\s in the economy of
Nature, and likewise to fit the two sexes of the same S]iecies to
each other, or to fit the males and females to different habits of
life, or the males to struggle with other males for the jiosses-
sion of the females.

Finally, then, I conclude that the greater variability of
specific characteis, or those which distinguish species from

158 DISTINCT SPECIES PRESENT Chap. V.

species, ihan of generic characters, or those which the species
possess in roinmon ; that the frequent extreme variability of
any part which is developed in a species in an extraordinary
manner in comparison with the same part in its congeners ;
and the slight degree of variability in a part, however extraor-
dinarily it may be developed, if it be common to a whole group
of species ; that the great variability of secondarj' sexual char-
acters, and the great amount of difference in these same char-
acters between closely-allied species ; that secondary sexual
and ordinary specific differences are generally displayed in the
same parts of the organization — are all principles closely con-
nected together. All being mainly due to the species of the
same group having descended from a common progenitor, from
whom they have inherited much in common — to parts whicli
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 com-
pletely, according to the lapse of time, overmastered the ten-
dency to reversion and to further variability — to sexual selec-
tion being less rigid than orchnary selection — and to variations
in the same parts having been accumulated by natural and
sexual selection, and having been thus adapted for secondary
sexual, and for ordinary purposes.

Distinct Species present analogous Variations ; and a Variety
of one Species often assumes some of the Characters of an
allied Species, or reverts to soyne of the Characters of an
early Progenitor.

These propositions will be most readily understood by look-
ing to our domestic races. The most distinct breeds of pigeons,
in countries most widely apart, present sub-varieties with re-
versed feathers on the head and feathers on the feet — charac-
ters 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 considered as a variation representing the nor-
mal 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
]>arent the same constitution and tendency to variation, when
acted on bv similar unknown influences. In the vegetable
kingdom we have a case of analogous variation in the enlarged

Chap. V. ANALOGOUS VARIATIONS. I59

stems, or roots as commonly called, of the Swedish turnip and
Ruta-ba^'a, })hmts wliich several botanists rank as varieties
produced by cultivation from a common parent; if this be not
so, the case will then be one of analogous variation in two so-
called distinct species ; and to these a third may be added,
namely, the common turnip. AccoriUng to the ordinary view
of each species having be(?n independently created, we should
have to attribute this similarity in the enlarged stems of these
three plants, not to the vera causa of community of descent,
and a consequent tendency to vary in a like manner, but to
three separate yet closely-related acts of creation. Many simi-
lar cases of analogous variation have been observed by Naudin
in the great gourd-family, and by various authors in oiu* cereals.
Similar cases occurring with insects under their natural con-
ditions have lately been discussed with much al)ility by Mr.
Walsh, who has grouped theni under his law of Equable Va-
riability.

With pigeons, however, we have another case, namely, the
occasional appearance in all the breeds of slaty-blue birds with
two black bars on the v/ings, white loins, a bar at the end of
the tail, with the outer feathers externally edged near their
bases with white. As all these marks are characteristic of the
parent rock-pigeon, I presume that no one will doubt that this
is a case of reversion, and not of a new yet analogous variation
appearing in the several breeds. ^Ve may, I think, confidently
come to tliis conclusion, because, as we have seen, these colored
marks are eminently liable to appear in tlie crossed oflsining
of two distinct and differently-colored breeds; and in this case
there is nothing in the external conditions of life to cause tlie
reappearance of the slaty-blue, with the several marks, beyond
the influence of the mere act of crossing on the laws of inher-
itance.

No doubt it is a very surprising fact that characters should
reappear after having lieen lost for many, probably for hun-
dreds of generations. But when a ])reed has been crossed only
once by some otlier breed, the offspring occasionally show a
tendency to revert in character to the foreign breed for many
generations — some say for a dozen or even a score of genera-
tions. After twelve general i(ms, the proportion of blood, to
use a common expression, of any one ancestor, is only 1 in
3,048 ; and yet, as we see, it is generally believed that a ten-
dency to reversion is retained by tliis very small projiortion of
foreign blood. In a breed which has not been crossed, but

IGO DISTINCT SPECIES PRESENT Chap. V.

in which both parents liave lost some character which ilieir
progenitor possessed, the tendency, Avliether stronf^ or -weak,
to reproduce the lost character might be, as was formerly re-
marked, for all that wc can sec to the contrary, transmitted
for almost any uuml:)cr of generations. When a character which
h;is been lost in a lu'ced, reappears after a gTcat immber of
generations, the most probable hypothesis is, not that the ofl-
spring suddenly takes after an ancestor removed by some hun-
dred generations, but that in each successive generation the
character in question has been lying latent, and at last, luidei
imknown favorable conditions, is developed. With the barb-
pigeon, for instance, which very rarely produces a blue bird,
it is probable that a latent tendency exists in each generation
to produce blue plumage. The possibility of chai'acters long
lying latent can be imderstood according to the hypothesis of
})angenesis, which I have given in another work. The abstract
improbability of a latent tendency being transmitted through
a vast number of generations, is not greater tlian that of quite
useless or rudimentary organs being thus transmitted. A mere
tendency to produce a nuHment is indeed sometimes inherited.
As all the species of the same genus are supposed, on our
theory, to be descended from a connnon progenitor, it might
be expected that they would occasionally vary in an analogous
manner; so that the varieties of two or more species would re-
semble each other, or that a variety of some 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 thus gained
would probably be of an unimportant nature, for the presence
of all important characters will be governed by natural selec-
tion, in accordance with tlic tlifTerent habits of the species, and
Avill not be left to the mutual action of the nature of tlie organ-
ism and of the conditions of life. It might further be expected
that the species of the same genus Avould occasionally exhil^it
reversions to long-lost ancestral characters. As, however, we
never know tlic exact character of the common ancestor of a
natural group, we could not distinguish these two cases : if,
iV)r instance, we did not know that the rock-pigeon was not
feather-footed or turn-crowned, we could not have told whether
these characters in our domestic breeds were reversions or only
analogous variations ; but wc might have inferred that the blue
color was a case of reversion from llie number of the markings,
whicli arc correlated with this tint, and which it docs not ap-

CiiAr. V. ANALOGOUS VAKIATIONS. Id

pear probable would all appear top^cthcr from simple ^•arialion.
More especially we might have infen-ed this, from the blue
color and the several marks so often appearinp^ when distinct
breeds of distinct colors are crossed. Hence, although under
Nature it must generally be left doubtful, what cases are re-
versions to a formerly-existing character, and what are ncAV
l)ut analogous variations, yet we ought, on oiu* theory, some-
times to iind the varying offspring of a species assuming
characters ((^ither from nivcrsion or from analogous variation)
which already are jirescnt in other members of the same group
and tliis undoubteclly is the case.

A considcrabl(! jjart of the difficulty in recognizing in our
systematic works a variable species, is due to its varieties
mocking, as it were, other species of the same genus. A con-
siderable catalogue, also, could be given of forms intermediate
between two other forms, which themselves can only doubt-
fully be ranked as species ; and this shows, unless all these
forms be considered as independently-created species, that the
one in varjing has assumed some of the characters of the other,
so as to produce the intermediate forms. But the best evi-
dence is afforded by parts or organs of an important and gen-
erally uniform nature occasionally varying so as to acquire, in
some degree, the character of the same part or organ in an
allied species. I have collected a long list of such cases ; but
here, as before, I lie mider the great disadvantage of not being
able to give them. I can only repeat that such cases certainly
do occur, and seem to me very remarkable.

I will, however, give one curious and complex case, not in-
deed as affecting any important character, but from occurring
in several species of the same genus, partly under domestica-
tion and partly under Nature. It is a case almost certainly of
reversion. The ass sometimes has very distinct transverse
bars on its legs, like those on the legs of the zebra : it has
been asserted that these are jilainest in the foal, and, from in-
qiiirics which I have made, I believe this to be true. The
stripe on the shoulder is sometimes double and is very variable
in length and outline. A white ass, but not an albino, has
been described without either spinal or shoulder stripe : and
these stripes are sometimes verv obscure, or actually (luitelost,
in dark-colored asses. The koulan or Pallas is said to have
been seen with a double shoulder-stripe. Mr. I31yth has seen
a specimen of the hemionus with a distinct shoulder-stripe,
tliough it properly has none ; and I have been informed by

1(32 DISTINCT SPECIES PRESENT Chap. V.

Colonel Poole tliat the foals of this species arc generally striped
on the legs, and faiiitly on the shoulder. The quagga, though
so plainly barred like a zebra over the body, is without bars
on the legs ; but ]3r. Gray has figured one specimen with very
distinct zebra-like bars on the hocks.

"With respect to the horse, I have collected cases in Eng-
land of the spinal stripe in horses of the most distinct breeds,
and of all colors : transverse bars on the legs are not rare in
duns, mouse-duns, and in one instance in a chestnut: a faint
shoulder-stripe may sometimes be seen in duns, and I have seen
a trace in a bay horse. JNIy son made a careful examination and
sketch for me of a dun Belgian cart-horse Avith a double stripe
on each shoulder and with leg-stripes ; I have myself seen a
dun Devonshire ponj^, 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, who
examined the breed for the Indian Government, a horse with-
out stripes is not considered as purely-bred. The spine is
always striped; the legs are generally barred; and the shoul-
der-stripe, which is sometimes double and sometimes treble, is
common ; the side of the face, moreover, is sometimes striped.
The stripes are often plainest in the foal ; and sometimes quite
disappear in old horses. Colonel Poole has seen both gray
and bay Kattywar horses striped Avhen first foaled. I have
also reason to suspect, from information given me by Mr. AV.
W. Edwards, that Avith the English race-horse the spinal strijie
is much commoner in the foal than in the full-grown animal.
I have myself recently bred a foal from a bay mare (offspring
of a Turcoman horse and a Flemish mare) by a bay English
race-horse ; this foal when a week old Avas marked on its hinder
quarters and on its forehead Avith numerous, A'ery narroAV, dark,
zebra-like bars, and its legs were feebly striped : all the stripes
soon disappeared completely. Without here entering on fur-
ther details, I may state that I have collected cases of leg and
shoulder stripes in horses of A'ery different breeds, in A'arious
countries from Britain to Eastern China ; and from NorAvay in
the north to the ISIalay Archipelago in the south. In all jiarts
of the Avorld these stripes occur far oftenest in duns and mouse-
duns ; by the term dun a large range of color is included, from
one between broAvn and black to a close approach to cream-
color.

CnAP. V. ANALOGOUS VAEIATIONS. 163

I am uwaro tliat Colonel Hamilton Smith, who lias written
on this subject, believes that the several breeds of the horse
are descended from several abori^^inal species — one of which,
the dun, was striped ; and that the above-described appear-
ances are all due to ancient crosses with the dun stock. But
this view may be safely rejected ; for it is highly improbable
that the heavy Belgian cart-horse, Welsh ponies, cobs, the lanky
Kattywar race, etc., inhabiting the most distant parts of the
world, should all have been crossed with one supposed aborigi-
nal stock.

Now let us turn to the effects of crossing the several species
of the horse-genus. lloUin asserts that the common mule
from the ass and horse is particularly apt to have bars on its
legs ; according to Mr. Gosse, in certain parts of the United
States about nine out of ten mules have striped legs. I once
saw a mule with its legs so much striped that any one might
have thought that it was a hybrid-zebra ; and Mr. W. C. Mar-
tin, in his excellent treatise on the horse, has given a figure of
a similar mule. In four colored draAvings, which I have seen,
of hybrids between the ass and zebra, the legs were much more
plainly barred tlian 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 mare
l)y a black Araljian sire, were much more plainly barred across
the legs than is even the pure quagga. Lastly, and this is an-
other 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 throe short shoulder-stripes, like those
on tlie dun Devonshire and Welsh ponies, and even had some
zebra-like stripes on the sides of its face. With respect to
this last fact, I was so convinced that not even a stripe of
color appears from what is commonly called chance, that I was
led solel}' 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
l)reed of horses, and was, as we have seen, answered in the
adirmative.

AVhat now arc we to say to these several facts ? We sec
several very distinct species of the horse-genus becoming, by

164 DISTINCT SPECIES PRESENT Cuap. V,

siin])le vaiiiition, slripod on tlio legs like a zebra, or stri})cd on
the sliouUler.s like an ass. In the liorsc we see this tendency
strong^ whenever a dun tint appears — a tint Avhidi approaches
to that of the general coloring' of the other species of the ge-
nus. The appearance of the stripes is not accompanied by any
cliange of form or by any other new character. AVe see this
tendency to become striped most strongly displayed in hybrids
from between several of the most distinct species. Now ob-
serve the case of the several breeds of pigeons : they are de-
scended from a pigeon (including two or three sub-species or
geographical races) of a bluish color, with certain bars and
other marlcs ; and Avhcn any breed assmnes by simple variation
a l)luish tint, these bars and other marks invariably reappear ;
but without any other change of form or character. When the
oldest and truest breeds of various colors are crossed, wc sec a
strong tendency for the blue tint and bars and marks to reap-
pear in the mongrels. I have stated that the most probable
hypothesis to account for the reappearance of xery ancient
characters, is — that there is a tendency in the young of each
successive generation to produce the long-lost character, and
that this tendency, from unknown causes, sometimes prevails.
And we have just seen that in several species of the horse-
genus the stripes arc either plainer or appear more commonly
in tlie young than in the old. Call the breeds of pigeons, some
of which have bred true for centuries, species ; and how exact-
ly parallel is the case with that of the species of the horse-
genus ! For myself, I venture confidently to look back thou-
sands on thousands of generations, and I see an animal striped
like a zebra, but perhaps other^vise very differently constructed,
the common parent of our domestic lu)rse (whether or not it be
descended from one or more wild stocks), of the ass, the hemi-
onus, quagga, and zebra.

He who believes tliat each equine sjiccies was indepen-
dently created, will, I presume, assert that each species has
been created with a tendency t(i vary, botli under Nature and
under domestication, in this particular manner, so as often to
become striped like other species of tlie genus ; and that each
has been created with a strong tendency, when crossed with
species inhabiting distant quarters of tlie world, to produce
hybrids resembling in tlieir stri})es, 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 imreal, or at least for an unknown,
cause. It makes the works of God a mere mockery and decep

CiiAr. V. ANALOGOUS VARIATIONS. 105

tioii; I would almost as soon believe ■with the old and if^no-
rant cosinof>;'oiusts, that fossil shells had never lived, but had
been created in stone so as to mock the shells living on the
sea-shore.

Suiiunari/.

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, liut whenever we
have the means of instituting a comparison, the same laws
ajipear to have acted in jiroducing the lesser dillerences be-
tween varieties of the same species, and the greater differences
between species of the same genus. Changed conditions gen-
erally induce mere fluctuating variability, but sometimes they
cause direct and definite effects ; and these may become
strpngly marked in the coiu'se of time, though we have not
sulhcient evidence on this head. Habit in producing constitu-
tional 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 way, and homologous parts tend to cohere,
ilodilications in hard parts and in external parts sometimes
affect softer and internal parts. When one part is largely
developed, perhaps it tends to draw nourishment from the ad-
joining parts ; and every part of the structure which can be
saved without detriment will be saved. Changes of structure
at an early age may aflect parts subsefjuently developed ; and
many cases of correlated variation, the nature of which we are
unable to understand, undoubtedly occur. Multiple parts are
variable in number and in structure, perhaps arising from such
])arts 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 vari-
able than those standing higher in the scale, and which have
llieir whole organization more specialized. Kudiinentary or-
gans, from being useless, are not regulated by natural selec-
tion, and hence arc varial)le. Specific characters — that is, the
characters which have come to differ since the several species
of (he same genus branched off from a common parent — are
more varia1)le than generics characters, or those which have
long becii inherited, and have not differed within this same
perioil. In these remarks we have referred to special parts or

1G6 SUMMARY. Chap. V.

org-ans bcin,;^ still variable, because they have recently viiried
and thus come lo differ; but vrc have also seen in the second
chapter that the same principle applies to the whole individual ;
for in a district Mhcre many species of any genus are found —
that is, where there has been much former variation and differ-
entiation, or where the manufactory of new specific forms has
been actively at work — in that district and among these spe-
cies, we now find, on an average, most varieties. Secondary
sexual characters are highly variable, and such characters differ
much in the species of the same group. Variability in the
same parts of the organization has generally been taken ad-
vantage of in giving secondary sexual differences to the sexes
of the same species, and specific differences to the several spe-
cies of the same genus. Any part or organ developed to an
extraordinary size or in an extraordinary manner, in compari-
son with the same part or organ in the allied species, must
have gone through an extraordinary amount of modification
since the genus arose ; and thus Ave can understand why it
should often still be variable in a much higher degree than
other parts ; for variation is a long-continued and slow process,
and natiu"al selection will in such cases not as yet have had
time to overcome the tendency to further variability and to
reversion to a less modified state. But when a species with
any extraordinarily-developed organ has become the parent of
many modified descendants — which on our Wew 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 constitu-
tion from a common parent and exposed to similar influences,
natui-ally tend to present analogous variations, or these same
species may occasionally revert to some of the characters of
their ancient progenitors. Although new and important modi-
fications may not arise from reversion and analogous variation,
such modifications will add to the beautiful and harmonious
diversity of Nature.

Whatever the cause may be of each slight difference be-
tween the offspring and their parents — and a cause for each
must exist — it is the steady accumulation, through natural se-
lection, of beneficial differences that has given rise to all those
modifications of structure which are the most important for the
welfare of each species.

Chap. VI. DIFFICULTIES OF THE TIIEOKY 1(J7

CHAPTER YI.

DIFFICULTIES OF THE TIIEOKY.

Difflcnilies of the Theory of Descent with Modification— Transitions— Ahsence or
Karlty of Transitional Varieties— Transitions in Habits of Life— Diversified Hab-
its iu the same Specios— Species with Habits widely different from those of their
Allies — Orj^iiis of Extreme Perfection— Modes of Tranh-ition— Cases of Ditflcully
— Natura nou fucit saltnm— Ort'ans of small Importance— Organs not in all Cases
absolutely perfect- The Law of XJniiy of Type aud of the Conditions of Existence
embraced by the Theory of Natural Selection.

Loxr, before havins; anivcd at this part of my ^-ork, a
crowd of dilFiculties will have occurred to the reader. Some
of them are so serious that to this day I can hardly reflect on
them without bein<i; stapffrered ; but, to the best of my judf^-
ment, the prreater number arc only «pparcnt, and those that are
real are not, I think, fatal to my theory.

These dilliculties and objections may be classed under the
followiuf^ heads : First, Avhy, if species have descended from
other species by insensibly line p;radations, do Ave not every-
where see ir.numcrable transitional fonns? 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 liavino", for instance,
the structure and habits of a bat, could have been formed by
the modification of some animal Avith Avidely-difl'erent structine
and habits ? Can Ave believe that natural selection could pro-
duce, on the one hand, organs of trifling importance, such as
the tail of a giraffe, Avhich serA'cs as a tly-fiapper, and, on the
other hand, organs of sucli wonderful structure, as the eye, of
Avhich we hardly as yet fiillv imderstand the inimitable perfec-
tion ?

Thirdly, can instincts be acquired and modified through
natural selection ? What shall Ave say to so marvellous an
instinct as that Avhich leads the bee to make cells, Avhich has
jiracticall}^ anticipated i\m discoveries of profound mathema-
ticians ?

108 ABSENCE OR EAEITY Cii-vp. VI.

Fourthl}', how can -wc account for species, Vv'hen crossed,
being sterile and jiroducins;^ sterile offsprinp-, "vvhcreas, when
varieties are crossed, their fertility is unimpaired?

Tiie tlrst two heads shall be here discussed — Instinct and
Hybridism in separate chapters.

On the Absence or Harlty of Transltio7ial 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 Avhich it comes into competition. Thus extinction and
natural selection go hand in hand. Hence, if we look at each
species as descended from some other iniknown form, both the
parent and all the transitional varieties will generally have
been exterminated by the very process of the formation and
perfection of the new form.

But, as by this theory innumerable transitional forms must
have existed, why do we not find them embedded in countless
numbers in the crust of the earth. It will be more convenient
to discuss tliis question in the chapter on the Imperfection of
the Geological liccord ; and I will here only st:ite that I be-
lieve the answer 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 imper-
fectly made, and only at long intervals of time.

But it may be lu-ged that when several closely-allied species
inhabit the same teixitory, we surely ought to find at the pres-
ent time many transitional forms. Let us take a simple case :
in travelling from north to south over a continent, we generally
meet at successive intervals with closely-allied or representa-
tive species, (Tvidently tilling neaily the same place in the nat-
ural economy of the land. These reiM-esentativc species often
meet and interlock ; and as the one l)ecomcs rarer and rarer,
the other becomes more and more fret(uent, till the one re-
places the other. But if we compare these species Avhere they
intermingle, they are generally as absolutel}" distinct from each
other in every detail of structiu'c as are specimens taken from
the metropolis inhalntcd by each. By my tlieory these allied
species are descended from a common parent ; and, during the
jHoccss of modilication, each has become adapted to the con-
ditions of lift^ of its own region, and has suj^planted and ex-

CiiAr. VI. OF TRANSITIONAL VAKIETIES. 169

IcriniiKited its ori^i'inal parent-form and all the transitional va-
rieties between its past and present states. Hence we ought
not to expect at the present time to mccft with numerous tran-
sitional varieties in each rei^ion, though they must have ex-
isted there, and may be embedded there in a fossil condition.
But in the intermediate region, having intermediate conditions
of life, why do we not now find closely-linking intermediatt^
varieties? This dilliculty for a long time quite confounded
nie. But I think it can be in large part explained.

In the lii-st jjlace, we should be extremely cautious in infer-
ring, be(\iuse an area is now continuous, that it has been con-
tinuous during a long period. Geology would lead us to be-
lieve that most continents have been broken up into islands
even during the later tertiary periods ; and in such islands
distinct species might have been separately formed without
the possibilit}' of intermediate varieties existing in the inter-
mediate zones. By changes in the form of the land and of
climate, marine areas now continuous must often have existed
within recent times in a far less continuous and uniform condi-
tion than at present. But I will pass over this way of escaj>
ing from the difficulty ; for I believe that many perfcctlj^Ie-
fmed sjiecies have been formed on strictly continuous areas ;
though I do not doubt that the formerly broken condition of
areas now continuous has played an important part in the for-
mation of new species, more especially ^vith frcelj'-crossing and
wandering animals.

In looking at species as they are now distributed over a
^vide 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 gener-
ally narrow in comparison with the territory projier to each.
^^'e see the same fact in ascending mountains, and sometimes
it is quite remarkable how abruptly, as Alph. de Candollc has
(il)served, a common alpine species disappears. The same fact
has been noticed by E. Forbes in sounding the depths of the
s(>a with the dredge. To those who look at climate and the
])]iysical conditions of life as the all-important elements of dis-
tribution, these facts ought to cause surprise, as climate and
height or depth graduate away insensibly. But when we bear
in mind that almost every species, even in its metropolis, would
increase immensely in numbeis, were it not for other com-
peting species; that nearly aH either prey on or serve as prey
s

170 ABSENCE OF RARITY Chap. VI.

for otlicrs ; in short, that cadi organic beinf^ is cither directly
or indirectly related in the most important manner to other
organic beings, \vc must see that the range of the inhabitants
of any country by no means exclusively depends on insensibly
changing pliysical conditions, but in large part on the presence
of other species, on which it lives, or by ■which it is destroyed,
or with which it comes into comjietition ; and as these species
arc already defmed objects, not blending one into another by
insensil)le gradations, the range of any one species, depending
as it does on the range of others, will tend to be sharply de-
fined. Moreover, each species on the confines of its range,
wherc it exists in lessened numbers, will, during fluctuations
in the number of its enemies or of its prey, or in the seasons,
be extremely liable to utter extermination ; and thus its geo-
graphical range Avill come to be still more sharply defined.

If I am right in believing that allied or representative spe-
cies, when inhabiting a continuous area, are generally so dis-
tributed that each has a wide range, with a comparatively
narrow neutral territory between tliem, in which they become
rather suddenly rarer and rarer ; then, as varieties do not essen-
tially differ from species, the same rule will probably apply to
both ; and if we take a varying species inhabiting a very large
area, we shall have to adapt two varieties to two large areas,
and a third variety to a narrow intermediate zone. The inter-
mediate variety, consequently, will exist in lesser numbers
from inhabiting a narrow and lesser area ; and practical!}', as
fiir as I can make out, this rule holds good with varieties in a
state of Tjature. I have met with striking instances of the
rule in the case of varieties intermediate between well-marked
varieties in the genus Balanus. And it would appear from
information given me by ]\Ir. "Watson, Dr. Asa Gray, and Mr.
Wollaston, that generally, when varieties intermediate between
two other forms occur, they arc much rarer numerically than
the forms which they connect. Now, if we may trust these
facts and inferences, and therefore conclude that varieties link-
ing two other varieties together hare generally existed in
lesser numbers than the forms which they connect, then, I think,
we can understand wh}' intermediate varieties should not en-
dure for very long periods ; Avhy, as a general rule, they should
be exterminated and disaiii)ear, sooner than the forms v>hich
they originally linked together.

"For any form existing in lesser numbers would, as already
remarked, ran a greater chance of being exterminated tlian

CuAi-. VI. OF TRANSITIOXAL VARIETIES. 171

one exist inn" in laro-c numbers; and in this particular case the
interniedi:it(! form would be cminentl}"^ liable to the inroads
of closely-allied forms existing on both sides of it. But a far
more important consideration, as I believe, is that, during the
process of further modification, by Avhich two varieties are
supposed to be converted and perfected into two distinct spe-
cies, the two which exist in larger numbers, from inhabiting
larger areas, will have a great advantage over the intermediate
variet}', which exists in smaller numbers in a narrow and inter-
mediate zone. For forms existing in larger numbers will al-
ways have a better chance, within any given period, of present-
ing further favorable variations for natural selection to seize
on, than will the rarer fcjrms which exist in lesser numbers.
Hence, the more common forms, in the race for life, will tend
to beat and supplant the less common forms, for these will be
more slowly modified and improved. It is the same principle
which, as I believe, accounts for the common species in each
country, as shown in the second chapter, presenting on an
average a greater number of well-marked varieties than do the
rarer species. I may illustrate what I mean by supposing three
varieties of sheep to be kept: one adapted to an extensive
mountainous region ; a second to a comparatively narrow, hilly
tract ; and a third to wide plains at the base ; and that the
inhabitants are all trying with equal steadiness and skill to
improve their stocks by selection ; the chances in this case will
be strongly in favor of the great holders on the mountains or
on the plains improving th.eir breeds more quicldy than the
small holders on the intermediate narrow, hilly tract; and con-
sequently the improved mountain or j^lain breed Avill soon
take the place of the less improved hill-breed ; and thus the
two breeds, which originally existed in greater numbers, will
come into close contact with each other, without the interpo-
sition of the supplanted, intermediate hill-variety.

To sum up, I believe that species come to be tolerabh' well-
dcfini^d objects, and do not at any one period present an inex-
tricable chaos of varying and intermediate links : first, because
new varieties are very slowly formed, for variation is a slow
])roccss, and natural selection can do nothing until favorable
individual diflerences or variations occur, and until a place in
the natural polity of the country can be better filled by some
modification of some one or more of its inhabitants. And such
«ncw places will depend on slow changer> of climate, or on the
occasional innnigratinn of new inhabitants, and, ]m)bably, in a

172 ABSENCE OR IJARITY Chap. VI.

still more important doffrco, on some of the old inhabitants be-
coming slowly moditied, 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 only to sec
a few species j)resenting slight modiiications of structure in
some degree permanent ; and this assuredly we do see.

Secondly, areas now continuous must often have existed
within the recent period as isolated portions, in which many
forms, more especially among the classes which unite for each
birth and wander much, may have separately been rendered
suiKciently distinct to rank as representative species. In this
case, intermediate varieties betw^een the several representative
species and their common parent, must have existed formerly
within each isolated portion of the land, but these links during
the process of natural selection will have been supplanted and
exterminated, so that they will no longer be found in a living
state.

Thirdly, wlien two or more varieties have been formed in
diflerent j)ortions of a strictly continuous area, intermediate
varieties Avill, it is probable, at first have been formed in the
intermediate zones, but they Avill generally have had 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 like-
Avise of acknowledged varieties), exist in the intermediate zones
in lesser numbers than the varieties which they tend to con-
nect. From this cause alone the intennediate varieties will
be hable to accidental extemiination ; and during the process
of further modification through natural selection, they will al-
most certainly lie beaten and supplanted by the forms which
they connect ; for these from existing in greater numbers will,
in the aggregate, present more variation, and thus be further
improved through natural selection and gain further advan-
tages.

Lastly, looking not to any one time, but to all time, if
my theory be true, numberless intermediate varieties, linking
closely together all the species of the same grouji, must assur-
edly have existed; but the very process of natural si'leetion
constantly tends, as has been so often remarked, to exterminate
the parent-forms and the intermediate links. Consequently
evidence of their former existence could be found only among
fossil remains, Avhich are preserved, as we shall in a future*
chapter attempt to show, in an extremely imperfect and inter-
mittent record.

CiiAi-. VI, OF TRANSITIONAL VARIETIES. 173

On the Origin and IW'nsifions of Orr/anlc Heings wifhjjecH'
liar Habits and /Structure.

It has been asked by the opponents of such views as I hold,
how, for instance, a land carnivorous animal could have been
converted into one with aquatic habits ; for how could tlu; ani-
mal in its transitional state have subsisted ? It would be easy
to show that within the same group carnivorous animals exist,
having' every intermediate grade between truly aquatic and
strictly terrestrial habits ; and as each exists by a struggle for
life, it is clear that each is well adapted in its habits to its
place in Nature. Look at the Mustela vison of North Amei-ica,
which has webbed feet, and which resembles an otter in its fur,
short legs, and form of tail; during summer this animal dives
for and preys on fish, but during the long winter it leaves the
frpzen waters, and iM'e3'S, like other polecats, on mice and land
animals. If a different case had been taken, and it had 1)een
asked how an insectivorous quadruped could possibly have
been converted into a flying bat, the question would have been
far more difficult to answer. Yet I think such difficulties have
little weight.

Here, as on other occasions, I lie imder a heavy disadvan-
tage, for, out of the many striking cases which I have collected,
I can give only one or two instances of transitional hal)its and
structures in closely-allied species of the same genus; and of
diversified habits, either constant or occasional, in the satiKj
species. And it seems to me that nothing less than a long
list of such cases is sufficient to lessen the difficulty in an}- ])ar-
ticidar case like that of the bat.

Ix)ok at the family of squirrels : here we have the finest gra-
dation from animals with their tails only slightly flattened, and
from others, as Hir J. IJichardson has remarked, with the pos-
terior part of their bodies rather wide and with the skin on
their flanks rather full, to the so-called flying-squirrels ; and fly-
ing-squirrels have their limbs and even the base of the tail united
l)y a broad expanse of skin, which serves as a parachute and
allows them to glide through the air to an astonishing distance
from tree to tree. We cannot doubt that each structure is of
use to each kind of squirrel in its own country, by enabling it
to escape birds or beasts of prey, or to coUect food moie
quickly, or, as there is reason to believe, by lessming the dan-
ger from occasional falls, lint it does not follow from this fact
that the structure of each sfjuirrel is the best that it is possible

l^.t TKANSITIOXS Chat. VI.

lo conceive under all natural conditions. Lot the climate and
vegetation change, let other coTnpcting rodents or new beasts
of prey immigrate, or old ones become modified, and all anal-
ogy would lead us to believe that some at least of the squirrels
would decrease in numbers or become exterminated, unless
they also became modified and improved in structure in a cor-
responding manner. Therefore, I can see no difficulty, more
especially under changing conditions of life, in the continued
preservation of individuals with fuller and fuller flunk-mem-
branes, each modification being useful, each being propagated,
until, by the accumulated efl'ects of this process of natural selec-
tion, a perfect so-called flying-squirrel was produced.

Now look at the Galeopithecus, or flying lemur, which for-
merly was ranked among bats. It has an extremely wide
flank-membrane, stretching from the corners of the jaw to the
tail, and including the limbs and the elongated fingers : the
flank-membrane is, also, furnished with an extensor muscle.
Although no graduated links of stracture, fitted for gliding
through the air, now connect the Galeopithecus with the other
LemuridcTJ, yet there is no difficulty in supposing that such links
formerly existed, and that each had been formed by the same
steps as in the case of the less perfectly gliding squurels ; and
that each grade of structure was useful to its possessor. Nor
can I see any insuperable difficulty in further belie\-ing it possi-
ble that the membrane-connected fingers .and forearm of the
Galeopithecus might be greatly lengthened by natural selec-
tion ; and this, as far as the organs of flight 'are concerned,
would convert it into a bat. In certain bats which have the
wing-mem])rane extended from the top of the shoulder to the
tail, including the hind legs, we perhaps yet see actual traces
of an apparatus originally fitted for gliding through the air
rather than for flight.

If about a dozen genera of birds had become extinct or
were unknown, 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 tins in
the water and front legs on the land, like the penguin; as
sails, like the ostrich ; and functionallj' for no purpose, like the
Apteryx? Yet the structure of each of these birds is good for
it, under the conditions of life to which it is exposed, for each
has to live by a struggle ; but it is not necessarily the best
possible under all possible conditions. It must not be inferred
from these remarks tliat any of the grades of wing-structure

Chap. VI. OF ORGANIC BEINGS. 175

here alluded to, ■\vliicli j)c*rliiips may all have resulted from dis-
use, indicate the natural stops by whicli birds have acquired
their perfect jK)wer of ilifj^ht ; but they serve, at least, to show
what diversified means of transition are possible.

Seeing that a few members of such water-breathing classes
as tlie Crustacea and Mollusca are adapted to live on the land;
and seeing that we have flying birds and mammals, lining in-
sects of the most divei-sified types, and formerly had Hying rej)-
tiles, it is conceivable that liying-flsh, Mhich now glide far
through the air, slightly rising and turning by the aid of their
fluttering llns, might liave been modified into perfectly-winged
animals. K this had Ix^en effected, who would have ever im-
agined that in an early ti-ansitional state they had been the in-
habitants of the open ocean, and had used their incipientorgans
of flight exclusively, as far as wc know, to escape being de-
voured by other fish ?

AVhen m'C see any structure liighlj' perfected for an}- par-
ticular habit, as the wings of a bird for llight, we should bear
in mind that animals displaying early transitional grades of the
structure will seldom exist at the present day, lor they will
have been supplanted by their successors, which Avere gradu-
ally rendered more perfect through natural selection. Further-
more, we may conclude that transitional states between struct-
ures fitted for very difl'erent habits of life Avilkrarely have been
developed at an early period in great numbers and under many
subordinate forms. Thus, to return to our imaginary illustra-
tion of the llying-fish, it does not seem probable that fishes
capable of true flight would have been develoi^ed under many
subordinate forms, for taking prey of many kinds in many
ways, on the land and in the water, imtil their organs of flight
had come to a high stage of perfection, so as to have given
them a decided advantage over other animals in the battle for
life. Hence the chance of discovering species with transition-
al 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 ihstances of diversified and of
changed habits in the individuals of the same species. In
either case it Avould be easy for natural selection to adapt the
structure of the animal to its changed habits, or exclusively to
one of its several habits. It is, however, dilhcult to decide, and
immaterial for us, whether habits generally change first and
structure afterward ; or Avhether slight modifications of struo

17G TRANSITIONS Chap. VI.

turc lead to clian^ed habits ; botli probably often occurring- al-
most sinuiltaneouslj. Of cases of champed habits it will sullice
merely to allude to that of the many British insects which now-
feed on exotic plants, or exclusively on artificial substances.
Of diversified habits innumerable instances could Ixi given : I
have often watched a tyrant flycatcher (Sauropha<^us sulphu-
ratus) in South America, hovering over one spot and then
proceeding to another, like a kestrel, and at other times stand-
ing 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 break-
ing them like a nuthatch. In North xVmerica 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 of a species following
habits widely different from those of their own species and of
the other species of the same genus, "we might expect that
such individuals Avould occasionally give rise to new sjiccies,
having anomalous habits, and with their structure either
slightly or considerably modified from that of their proper
type. And such*nstanc<?s do occur in Nature. Can a more
striking instance of adaptation be given than that of a wood-
pecker for climbing trees and seizing insects in the chinks of the
bark ? Yet in North America there are Avoodpcckci-s which
feed largely on fruit, and others with elongated wings which
chase insects on the wing. On the plains of La Plata, where
not a tree grows, there is a woodpecker (Colaptcs campestris)
which has two toes before and two behind, a long pointed
tongue, pointed tail-feathers, sufficiently stiff to support the
bird in a vertical position on a post, but not so stiff as in the
typical woodpeckers, and a straight, strong beak. The beak,
however, is not so straight or so strong as in the typical wood-
peckers, but it is strong enough to bore into wood. Hence this
Colaptes in all the essential parts of its structure is a Avoodptxk-
er. Even in such trifling characters as the coloring, the harsh
tone of the voice, and inidulatory flight, all plainly dcclareil its
close blood-relationship to ouj common Avoodpecker ; yet, as I
can assert, not only from my own observation, but from that
of the accurate Azara, it never climbs a tree ! I may mention,
as another illustration of the varied haliits of the tril)C, that a

f^^

CiiAP. VI. OF ORGANIC BEINGS. 177

Mexican Colaptes has been described by Do Saussurc as boring
holes into hard wood in order to hiy up a store of acorns, but
for what use is not yet known.

Petrels are the most ar-rial and oceanic of l)inls, l)ut in the
quiet sounds of Tierra del Fucf^o, the Pulhnuria berardi, in its
l^eneral habits, in its astouisliinii^ power of divinjr, its manner
of swiinminij;-, and of flying when made to take lliglit, would be
mistaken by anyone for an auk or a grebe; nevertheless it is es-
sentially a petrel, but with many parts of its organization pro-
foundly modified in relation to its new haliits of life ; Avhereas
the woodpecker of L:i Plata has had its structure only slightly
modified. In the case of the Avater-ouzcl, the acutest observer
by examining its dead body would never have suspected its
sub-aquatic hal)its; yet this binl, which is allied to the thrusli
familv, wholly subsists by diving — using its wings under
\yater, and grasjiing stones with its feet. AH the members of
the great order of Hymenopterous insects are terrestrial, ex-
cepting the genus Proctotrupes, which Sir J(jhn Lubbock has
recently discovered to be aquatic in its habits ; it often enters
the water and dives about by the use not of its legs but of its
wings, and remains as long as four hours beneath the surface ;
yet not the least modification in its structure can be detected
in accordance Anth such abnormal habits.

He who believes that eacli being has been created as we
now see it, must occasionally have felt surprise when he has
met with an animal having habits and structure not at all in
agreement. What can be jilaincr than that the webbed feet of
ducks and geese are formed for swimming ? Yet, there are up-
land geese with webbed feet which rarely or never go near the
water; and no one except Audubon has seen the frigate-bird,
which has all its four toes webbed, alight on the surface of the
ocean. On the other hand, grebes and coots are eminently
aquatic, although their toes are only bordered by membrane.
What .seems jilaincr than that the long toes, not furnished with
membrane, of the Grallatores are formed for walking over
swamps and lloating plants? The water-hen and landrail are
members of this order, yet the first is nearly as acjuatic as the
coot, and the second nearly as terrestrial as the quail or ])ar-
tridge. In such eases, and many others could be given, habits
have changc^d Avithout a corresponding change of structure.
The webbed feet of the upland goose may be said to have be-
come rudimentary in function, though not in structure. In the

178 ORGANS OF EXTREME PERFECTION Chap. VI.

frigate-bird, the dee])ly-scooped membrane between the toes
shows that structure has begun to change.

He Avho believes in separate and innumerable acts of crea-
tion 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 t^-pe ; but this seems to me only restating the fact in
ditrnified lano-uaffe. He Avho believes in the strug"-le for ex-
istcnce and in the principle of natural selection, will acknowl-
edge that every organic being is constantly endeavoring to
increase in numbers ; and that if any one varies ever so little,
either in habits or structure, and thus gains an advantage over
some other inhabitant of the country, it will seize on the j)lace
of that inhabitant, however different it 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, or most rai'ely alighting on the "water; that there should
be long-toed corncrakes, living in meadows instead of in
swamps ; that there should be woodpeckers Mhere not a tree
grows ; that there should be diving thnishes and diving Hymen-
optera, and petrels with the habits of auks.

Organs of Extreme Perfection and Complication.

To suppose that the eye with all its inimitable contrivances
for adjusting the focus to different distances, for admittmg
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.
"SVlien it was first said that the sun stood still and the world
turned round, the common-sense of mankind declared the doc-
trine false ; Imt the old saying of ] 'ox popxdi^ vox Dei, as every
j)hilosopher knows, cannot be trusted in science, lieason tells
me, that if numerous gradations from an imperfect and simple
eye to one jierfect and complex, each grade being useful to its
possessor, can be shown to exist, as is certainly the case; if
further, the eye ever slightly varies, and the variations be inher-
ited, as is likewise certainly the case ; and if such variations
should ever be useful to any animal under changing conditions of
life, then the dilliculty of believing that a jierfect and complex
eye could be formed l>y natural selection, though insuperable
by our imagination, cannot be considered real. How a nerve
comes to be S(Misitive to light, hardly concerns us more than
how life itself first originated ; but I may remark that, as some

CuAP. VI. AND COMPLICATION. I79

of the lowest organisms, in Avbich nerves cannot be detected,
are known to be sensitive to light, it does not seem impossible
that certain elements in the sarcode, of which they are mainly
composed, 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
j)arent-form, in order to see what gradations arc possible, and
for the cliance of some gradations liaving been transmitted in
an unaltered or little altered condition. But the state of the
organ even in distinct classes may incidentally throw light on
the steps hy which it has been perfected in any one species.

The simplest organ which can be called an eye consists of
an optic nerve, surrounded by pigment-cells covered by trans-
lucent skin, but without any lens or other refractive body. AVe
may, however, according to M. Jourdain, descend even a step
lower and find aggregates of pigment-cells, apparently serving
as an organ of vision, but without any nerve, 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 starfishes, small depressions in the
layer of pigment which surrounds tlie nerve are filled, as de-
scribed by the author just quoted, Avith transparent gelatinous
matter, projecting with a convex surface, like the cornea in the
higher animals. He suggests that this serves not to form an
image, but only to concentrate the luminous raj's and render
their perception more easy. In this concentration of the rays
we gain the first and by 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 concentrat-
ing ap]iaratus, and an image will be formed on it.

In the great class of tlie Articulata, we may start from an
optic nerve simply coatccl with pigment, the latter sometimes
forming a sort of pupil, but destitute of a lens or other optical
contrivance. "NVitii insects it is now known that the numer-
ous facets on the cornea of the great comjiound eyes form
true lenses, and that the cones include curiously-modified
nervous filaments. But these organs in the Articulata are so

ISO ORGANS OF EXTKEME PERFECTION Chap. VI.

mucli diversified that Milller formerly made three main chxsses
of compound eyes -with seven subdivisions, l^esidcs a fourth
main chiss of ag-j^regated simple eyes.

AVhcn we reflect on these facts, here f^ivcn too briefly, with
respect to the wide, diversified, and graduated range of struct-
in-e in the eyes of the lower animals ; and when we bear in
mind how small the number of all the forms now living must
he in comparison with those which have become extinct, the
ditliculty ceases to be very great in believing that natural se-
lection may have converted the simple apparatus of an optic
nerve, coated with pigment and invested by transparent mem-
brane, into an optical instrument as perfect as is possessed by
an}' member of the great Articulate Class.

He who will go thus far, ought not to hesitate to go one
step further, if he finds on finishing this volume that large bod-
ies of facts, otherwise inexplicable, can be explained by the
theory of descent with modification ; he ought to admit that a
structure even as perfect as an eagle's eye might be formed by
natural selection, although in tliis case he does not know the
transitional states. It has been objected that, in order to mod-
ify 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 do-
mestic animals, it is not necessary to suppose that all the modi-
fications were simultaneous, if tliey were extremely slight and
gradual. Even in the most highly-organized division of the
animal kingdom, namely, the Vcrtebrata, 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 both fishes
and reptiles, as Owen has remarked, " the range of gradations
of dioptric structures is very great." It is a significant fiict
that even in man, according to tlie high authority of Virchow,
tlic beautiful crj^stalline lens is formed in tlie embryo by an
accumulation of epidermic cells, lying in a sack-like fold of the
skin ; and tlie vitreous body is formed from embryonic subcu-
taneous tissue?. It is indeed indispensable, in order to arrive at
a just conclusion regarding the formation of the eye, with all
its marvellously perfect characters, that the reason should con-
quer the imagination ; but I have felt this difficulty far too
keenly to be surprised at any degree of hesitation in extend
ing the principle of natural selection to so startling a length.

CiiAr. VI. AND COMPLICATION. 181

It is scarcely possible to avoid comparing tlic eye with a
telescope. We know tliat tliis instrument lias been peri'eeted
by the long-continued ell'orts of the highest human intellects ;
and we natm-ally infer that the eye has been formed by a some-
what analogous process. But may not this inference be pre-
sumptuous ? Have we any right to assume that the Creator
works by intellectual powers like those of man? If we must
compare the e^'e to an ojjtical instrument, we ought in imagi-
nation to take a thick layer of transparent tissue, with spaces
tilled with fluid, and with a nerve sensitive to light beneatlt,
and then suppose every ])art of this layer to be continually
changing slowly in d(Misity, so as to separate into layers of
dillerent densities and thicknesses, placed at different distances
from each other, and with the surfaces of each layer slowly
changing in form. Further, Ave must suppose that there is a
power, r(>presented by natural selection or the survival of the
Mttest, always intently watching each sliglit alteration in the
transparent la^'ers ; and carefully preserving eaoli which, undc^'
varied circumstances, in any way or in any degree, tends to
jiroduce a distincter image. We must suppose each new state
of the instrument to be multiplied by the million; each to be
preserved until a better one is produced, and then the old ones
to be all destroj-ed. In living bodies, variation will cause the
slight alterations, generation will multiply them almost infi-
nitely, and natural selection Avill pick out Avith unerring skill
each improvement. Let this process go on for millions of
years ; and during each year on millions of individuals of many
kinds; and may we not believe that a living optical instrument
might tluis be formed as superior to one of glass, as the works
of the Creator are to those of man ?

Modes of Transition.

If it could be demonstrated that any com])lex organ existed,
which could not possibly have been formed by numerous, suc-
cessive, slight modifications, my theor}- would absolutely break
down. But I can find out no such case. No doubt manv or-
gans exist of which we do not know the transitional grades,
more especially if we look to much-isolated spt^cies, roimd
which, according to the theory, there has been nujch extinction.
Or again, if we take an organ common to all the members of
a large class, for in this latter case the organ must have been
originally fonnod at an extremely remote period, since which

1S2 MODES OF TRANSITION. Chap. VI.

all the mail)'- members of the class have been developed ; and,
iu order to discover the early transitional grades through
which the organ has passed, Ave should have to look to very
ancient ancestral forms, long since become extinct.

We should be extremely cautious in concluding that an or-
gan could not have been formed by transitional gradations of
some kind. Numerous cases could be given among the lower
animals of the same organ performing at the same time wholly
distinct functions ; thus the alimentary canal respires, digests,
and excretes, in the larva of the dragon-fly and in the fish Co-
bites. 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 advan-
tage were thus gained, the whole or part of an organ, Avhich
had previously performed two functions, for one function alone,
and thus by insensible steps greatly change its nature. Many
plants are known which regularly produce at the same time
differently-constructed flowers ; and if such plants were to pro-
duce one kind alone, a great change would in some cases be
effected in the character of the species. It can also be shown
that the pi'oduction of the two sorts of flowers by the same
plant has been effected by finely-graduated steps. Again, two
distinct organs in the same individual may simultaneously per-
form the same function, and this is a highly-imj^ortant means
of transition : to give one instance — there are fish with gills
or branchiae that breathe the air dissolved in the water, at the
same time that they breathe free air in their swim-bladders,
this latter organ being divided by highly-vascular partitions,
and having a ductus pneumaticus for the supply of air. To
give another instance from the vegetable kingdom: plants
climb l^y three distinct means, by spirally twining, by clasping
a support with their sensitive tendrils, and by the emission of
aerial rootlets ; tliese three means are usually found in distinct
groups, but some few plants exhibit two of the means, or even
all three, combined in ttie same individual. In all such cases
one of the two organs for performing the same function might
be modified and perfected so as to ])erf()rm all the work, being
aided during the progress of modification by the other organ ;
and then this other organ might be modified for some other
and quite distinct purpose, or be wholly obliterated.

The illustration of the swim-l)ladder in fishes is a good one,
becausi? it shows us clearly the higher important fact that an
organ originally constructed for one purpose, namely flotation,

CiiAr. VI. JIODES OF TRANSITION. 183

may be converted into one for a widcly-tliffercnt purpose,
namely, respiration. Tlie swim-bladder has, also, been worked
in as an accessory to the auditory org'ans of certain hsh. All
physiolog^ists 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 vertebrate
animals with true lungs have descended by ordinary generation
from an ancient and unknown prototype, which was furnished
witii a floating apparatus or swim-bladder. We can thus, as I
infer from Owen's interesting description of these parts, under-
sta,nd the strange fact that every particle of food and drink
which we swallow has to pass over the orifice of the trachi^a,
with some risk of falling into the lungs, notwithstanding the
beautiful contrivance by which the glottis is closed. In the
higlier Vertebrata the branchiaj 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 tlunr former position. But
it is conceivable that the now utterly lost branchiae might have
been gradually worked in by natural selection for some distinct
purpose : for instance, the branchiir; and dorsal scales of Anne-
lids are believed to be homologous with the wings and wing-
covcrs of insects, and it is not improbable that with our existing
insects organs, which at an ancient period served for respiration,
have actually been converted into organs of flight.

In considering transitions of organs, it is so important to
bear in mind the probability of conversion from one function to
another, that I will give another instance. Pedunculated cir-
ripcdes have two minute folds of skin, called by me the ovigerous
frena, Avhidi serve, through the means of a sticky secretion, to
retain the eggs until they are hatched within the; sack. These
cirri|)edes have no branclu;ii, the whole surface of the body and
of the sack, together with the small frena, serving for respira-
tion. Tiic 13alanid;\3 or sessih; cirripedes, on the other hand,
have no ovigerous frena, the eggs lying loose at the bottom of
the sack, within the well-enclosed shell ; but they iiave, in the
same relative position with the frena, large, much-fokU'd mem-
branes, which freely communicate with the circulatory lacunixj
of the sack and body, and which have been considered to be
branchiaj by Prof. Owen and by all other naturalists who have
treated on the sul)ject. Now I think no one will dispute that

184 DIFFICULTIES OF THE THEORY Chap. VI.

the ovigcrous frcna in the one family arc strictly homologous
■with the braiicliiiu of tlic other family; indeed, they graduate
into each other. Therefore it need not be doubted that the
two little folds of skin, -which originally served as ovigerous
frena, but -which, likewise, very slightly aid in the act of res-
piration, have been gradually con\erte(l by natural selection
into branchije, simply through an increase in their size and the
obliteration of their adhesive glands. If all pedunculated cir-
rijiedes had become extinct, and they have already suffered far
more extinction than have sessile cirripedes, who Avonld ever
have imagined that the branchioi in this latter family had
originally existed as organs for pre\'cnting the ova from being
washed out of the sack ?

iSj^ecial 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
transitional gradations, yet vmdoubtedly serious cases of difli-
culty occur, some of which will be discussed in my fiiture work.

One of the most serious is that of neuter insects, which are
often diiFcrently constructed from either the males or fertile
females; but this case will be treated of in the next chapter.
Tlie electric organs of fishes offer another case of special diffi-
culty ; for it is impossible to conceive by what steps these
Avondrous organs have been produced. As Owen has remarked,
there is much analogy between them and ordinary muscles, in
their manner of action, in the influence on them of the nervous
power and of stimulants svich as strychnine, and as some be-
lieve in their intimate structure. M^e do not even know of
-what use these organs are ; though in the Gjinnotus and Tor-
pedo they no doubt serve as powerful means of defence and
perhaps for securing prey; 3'et in the Kay an analogous organ
in the tail, even when greatly irritated, manifests, as lately
observed by Matteuccu, but little electricity — so little that it
can hardl}^ be of use for such purposes. ^Moreover, in the Kay,
besides the organ just referred to, there is, as Dr. K. ^McDonnell
has shown, another organ near the head, not known to be elec-
trical, but which appears to be the real homologue of the elec-
tric batter}' in the torpedo. Lastly, as we know nothing about
the lineal progenitors of these fishes, it must be admitted that
we are too ignorant to be enabled to aflirm that no transitions
arc possible, through which the electric organs might have
been developed.

CiiAi-. YI. OF NATURAL SELECTION. 185

Tliesc same organs at first appear to offer anotncr and far
more serious difficulty ; for they occur in about a dozen kinds
of fisli, of Avliich. several arc Avidely remote in their affinities.
Generally when the same organ is found in several niemhers
of the same class, especially if in mc^mbers having very differ-
ent habits of life, we may attribute its presence to inheritance
from a common ancestor; and its absence in some of the mem-
bers 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 Ijclief
that most fishes formerly possessed electric organs, which their
modified descendants have now lost. But when we look at
the subject more closely, wc find in the several fishes provided
with electric organs that these are situated in diiferent parts
of the body — that they differ in construction, as in the arrange-
ment of the plates, and according to Pacini, in the process or
means by which the electricity is excited — and lastly, in the
requisite nervous power being supplied through different nerves
from widely-diffi;rent sources, and this is perhaps the most im-
])ortant of all the diflerences. Hence in the several remotely-
atlied fishes furnished with electric organs, these cannot be
ccnisidered as homologous, 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 tlic greater difficulty disappears, leaving only
the lesser yet still great difliculty ; namely, by what graduated
steps these organs have arisen and been develojied in each sepa-
rate grouji of fishes.

Tiic luminous organs which occur only in a few insects,
belonging to widely-different fiunilies and orders, and v.hich
arc situated in different jiarts of the body, offer a difficidty
almost exactly jiaralhd witli tiiat of the electric organs. Other
cases could be given; for instance, in plants, the very curious
contrivance of a mass of pollen-grains, borne on a foot-stalk
with an adhesive gland, is apparently the same in Orchis and
Asclcpias — genera almost as remote as is possible among
flowering ])lants. In all such cases of two species, fiir removed
from each other in the scale of organization, being furnislied
with similar anomalous organs, it should be observed that, al-
though the general appearance and function of the organ may

180 DIFFICULTIES OF THE THEORY Ciur. VI.

1)0 iilcMitically the saiiie, yet some fundamental difference be-
tween them can always, or almost always, be detected. I am
inclined to believe that, in the same manner as two inen have
sometimes independently hit on the same invention, so natural
selection, working for tlie good of each being and taking ad-
vantage of analogous variations, has sometimes modified in
nearly the same way two organs in two distinct organic beings,
which owe but little of tlieir structure in common to inheritance
from a common progenitor.

Fritz MllUcr, in a remarkable work recently published, has
investigated a nearly parallel case, in order to test the views
advanced in this volume. Several families of crustaceans in-
clude a few species which possess an air-breathing apparatus,
and are fitted to live out of the water. In two of these fam-
ilies, 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-or-
gans, circulating system, in the position of the tufts of hair
with whicli their complex stomachs arc lined, and lastly in the
v/hole structure of the Avater-breatliing Ijranchia^, even to the
microscopical hooks by Avhich they arc cleansed. Hence it
might have been expected that the equally important air-
breathing apparatus would have been the same in the fevv^
species in both families Avhich live on the land ; and this might
Iiavc been tlie more confidently expected by those wlio believe
in distinct creations ; for why sliould this one apparatus, given
for the same special piu^ose to these species, have been made
to differ, Avhile all the other important organs are closely simi-
lar or rather identical ?

Fritz Mllller argues that this close similarity in so many
points of structure must, in accordance with the views ad-
vanced by me, be accounted for by inheritance from a common
progenitor. But as the vast majority of the species in tlie
above two families, as well as most crustaceans of all orders,
are aquatic in their habits, it is improbable in the highest degree,
that their common progenitor should have been adapted for
breathing air. Miiller was thus led carefully to examine the
apparatus in the air-breathing species; and in each he found
it to diffor in several important points, as in the position of the
orifices, in the manner in which they are opened and closed,
and in some accessory details. Now such differences are intelli-
gible, and might even have been anticipated, on the siip]iositi<-)n
that species belonging to distinct families had slowly become

Chap. VI. OF NATURAL SELECTION. 1S7

adapted to live more and more out of "water, and to breathe
the air. For these species, from beloiif^ing to distinct families,
■would difler to a certain extent, and in accordance with the
principle that the nature of each variation depends on two fac-
tors, viz., the nature of the orp^anism and that of the condi-
tions, the variability of these crustaceans assuredly would not
have been exactly the same. Consequently natural selection
would have had diiTerent materials or variations to work on, in
order tu arrive at the same functional result; and the structures
thus acquired would almost necessarily have dillered. On the
hypotliesis of 6C]>arate acts of creation the whole case remains
unintelli,Lrible. The above line of arn^mcnt, as advanced by
Fritz Miiller, seems to have had j^reat weiglit in leadino^ this
distin<^uislicd naturalist to accept the views maintained by me
in this volume.

• In the several cases just discussed, wc have seen that in
beings more or less remotely allied, the same end is gained
and the same function performed by organs in appearance,
though not in truth, closely similar. But the common rule
throughout Nature is that the same end is gained, even some-
times in the case of beings closely related to each other, by the
most diversified means. How differently constructed is the
feathered wing of a bird and the membrane-covered yying of a
l)at with all the digits largely developed ; and still more so the
four Avings of a butterfly, the two wings of a fly, and the two
wings of a beetle, together with the elytra ! 13ivalve shells
are made to open and shut, but on what a immber of ])atterns
is the hinge constructed, from the long row of neatly inter-
locking teetli in a Nucula to the simple ligament of a Mussel !
tSeeds arc disseminated by their minuteness — by their capsule
being converted into a light balloon-like envelope — by being-
embedded in pulp or flcsli, formed of tlie most diverse parts,
and rendered nutritious, as well as conspicuously colored, so as
to attract and be devoured by birds — ])y having hooks and
grapnels of many kinds and serrated awns, so as to adhere to
the fur of quadmpeds — and by being furnish(>d Avith wings and
plumes, as different in shape as elegant in structure, so as to
be wafted by every breez(\ I will give one other instance ;
for this subject of the same end being gained by the niost di-
versified 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

188 DIFFICULTIES OF THE THEOKY Chap. VI.

view of Nature is incrediljlo. Witli plants having' scjiarated
Bcxcs, and witli those in whicli, tlious-li herniaplnodites, the
pollen docs not spontaneously fall on tlie stig'ma, some aid is
necessary for their fertilization. AVith several kinds this is
cHected by the polli'U-yrains, which are lig'ht and incoherent,
Ix'ino; blown 1)y the wind through mere chance on to the stigma ;
and this is the simj)lest plan which can well be conceived.
An almost equally simple, though very different, plan occurs
in many plants in which a symmetrical flower secretes a few
drops of nectar, and is consequently visited by insects ; and
these carry the pollen from the anthers to the stigma.

From this simple stage we may pass through an inexhaust-
ible number of contrivances, all for the same purpose and
cflected in essentially the same manner, but entailing changes
in every part of the llower. The nectar may be stored in vari-
ously-shaped receptacles, with the stamens and pistils modi-
fied in many ways, sometimes forming traj)-like contrivances,
and sometimes capable of neatly-adapted movements through
irritability or elasticity. From such structures we may ad-
vance till Ave come to such a case of extraordinary adaptation
as that lately described by Dr. Crugcr in the Coryanthcs. Tliis
orchid has jiart of its labellum or lower lip hollowed out into
a great bucket, into which drops of almost pure water contin-
ually fall from two secreting horns which stand above it ; and
v.hen the bucket is half full, the water overflows by a spout
on one side. The basal part of the labellum stands over the
bucket, and is itself hollowed out into a sort of chamber with
two lateral entrances ; Avithin tliis chamber there are curious
fleshy ridges. The most ingenious man, if he had not Avit-
nessed Avhat takes ])lace, could never liaA^e imagined Avhat pur-
pose all these parts serve. But Dr. Crtiger saAV croAvds of
large humble-bees A'isiting the gigantic flowers of this orchid,
not in order to suck nectar, but to gnaAV ofi" the ridges Avithin
the chamber aboA^e the bucket ; in doing this they frequently
I)ushe(l each other into the bucket, and their wings being thus
Avetted they could not fly away, liut had to craAvl out through
the passage formed by tlie spout or OA-erflow. Dr. Crllger saw
a "continual procession" of bees thus crawling out of their in-
A'oluntary bath. The passage is narroAver, antl is roofed over
by the column, so that a bee, in forcing its Avay out, first rubs
its back against the viscid stigma and then against the viscid
glands of the pollen-masses. The jiollen-masses are thus glued
to the back of that bee Avhich first happens to craAvl out through

CiiAP. VI. OF NATURAL SELECTION. 189

the passage of a litely-cxpandcd flower, and arc thus carried
away. Dr. Cril<^('r sent ine a (lower in spirits of wine, with a
bee which he liad killed before it liad ([uite crawled ont with a
pollen-mass still fastened to its back. When the bee, thus
provided, (lies to another (lower, or to the same flower a sec-
ond time, and is jnished by its comrades into the bucket and
then crawls out by the iiassag-e, the pollen-mass necessarily
comes first into contact with the viscid stig'ma, and adheres to
it, and the (lower 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, wliicli prevents the bees from
flving away and forces them to crawl out through the spout,
and lub against the properly-placed viscid pollen-masses and
viscid stigma.

The construction of tlie (lower in another closely-allied or-
chid, namely, the Catasetum, is widely dilVerent, though serving
the same end; and is equally curious. Bees visit these flow-
ers, like those of the Coryanthes, in order to gnaw the label-
lum ; in doing this they inevitably touch a long, tapering,
sensitive projection, or, as I have called it, the antenna. This
antenna, when touched, transmits a sensation or vibration to a
certain membrane which is instantly ruptured ; this sets free
a spring by which the pollen-mass is shot forth, like an arrow,
in the right direction, and adheres by its viscid extremity'' to
the back of the bee. The pollen-mass of a male plant is thus
carried to the flower of a female plant, where it is brought into
contact with the stigma, which is A'iscid enough to break cer-
tain elastic threads, and, retaining the pollen, fertilization is
elTected.

How, it may be asked, in the foregoing and in innumerable
other instances, can we imderstand the graduated scale of
complexity and the multifarious means for gaining the same
end V The answer no doubt is, as already remarked, that when
two forms vary, which already diller from each other even in a
slight degree, tht; variability will not be of the same exact na-
ture, and conseciuently the results obtained through natural
selection for the same general ])urpose will not be the same.
We should also bear in mind that every highly-developed or-
ganism has passed through a long course of modilication; and
that each moditied structure tends to be inherited, so that it
will not readily be wholly lost, but may be modified again and
again. Hence the structure of each part of each species, for
whatever purpose used, is the sum of the many inherited

100 OEGANS OF LITTLE IMPORTANCE Chap. VL

changes, through which that species has passed during its suc-
cessive adaptations to changed habits and conditions of life.

Finally, then, although in many cases it is most difficult
even to conjecture by what transitions many organs have ar-
rived at their present state; yet, considering how small the
proportion of living and known forms is to the extinct and un-
known, 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 specially
created for some purjDOse, rarely or never appear suddenly in
any class ; as indeed is sho^\'n by that old, but somewhat ex-
aggerated, canon in natural history of " Natura non facit sal-
tum." Vio 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 inno- "
vation. Why, on the theory of Creation, should there be so
much variety and so little novelty ? "Why should all the parts
and organs of many independent beings, each supposed to
have been separately created for its proper place in Nature,
be so commonly linked together by graduated steps ? Why
should not Nature take a sudden leap from structm-e to struct-
ure ? On the theory of natural selection, we can clearly un-
derstand why she should not; for natural selection acts only
by taking advantage of slight successive variations ; she can
never take a sudden leap, but must advance by short and sure
though slow steps.

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

As natural selection acts by life and death — by the survival
of the fittest, and by the destruction of the less wcll-litted indi-
viduals— I have sometimes felt great dilllculty in understand-
ing the origin or formation of parts of little importance ; al-
most as great, though of a very different kind, as in the case
of the most perfect and complex organs.

In the fii-st 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 for-
mer chapter I have given instances of very trifling characters,
such as tlie down on fruit and the color of its ilesh, the color
of the skin and hair of quailrupeds, which, from being corre-
lated with constitutional differences or from determining the

Chap. VI. AFFECTED BY NATURAL SELECTION. 191

attacks of insects, mif^lit assuredly he acted on by natural se-
lection. Tlie tail of tiie g^iraffc looks like an artificially-con-
structed fly-flapper; and it seems at first incredible that tliis
could have been adapteil for its present purpose by successive
slight niodiiications, each better and better lifted, for so triliino;
an object as to drive away flies ; yet avc should pause before
being too positive even in this case, for we know that the dis-
tribution and existence of cattle and other animals in South
America absolutely depend on their power of resisting the at-
tacks 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 advantage. It
is not that the larger (juadrupeds are actually destroyed (exceiDt
in some rare cases) by flies, but they are incessantly harassed
and their strength reduced, so that they are more subject to
disease, or not so well enabled in a coming dearth to search
for food, or to escape from beasts of pre}'.

Organs now of trifling importance have probably in some
cases been of high imjiortance 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 ver}' slight use ; but any actually injurious
deviations in their structure will of course have been checked
by natiu'al selection. Seeing how important an organ of loco-
motion the tail is in most aquatic animals, its general prcsenco
and use for many purposes in so many land animals, which in
their lungs or modified swim-bladders betray their aquatic ori-
gin, 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 Ily-
flapper, an organ of prehension, or as an aid in turning, as with
the dog, though the aid in this latter respect nuist be slight,
for the hare, with hardly any tail, can double cjuickly eTiough.

In the second ])lace, ^ve may sometimes wrongly attribute
im]X)rtance to characters which have originated from quiti; sec-
ondary causes, independently of natural selection. We should
remember that climate, food, etc., probably have had some,
])erhaps a considerable, direct influence on the organization ;
that characters reajjpear from the law of reversion ; that ct>r-
relation is an important element of change; and finallv, that
sexual selection has often largely modified the external i-Iiarac-
ters of the higher animals, so as to give one male an advantage
in fighting witli other males, or in charming the female ; and

192 ORGA^'S OF LITTLE LMPOKTANCE Chap. VL

characters gained through sexual selection may be transmitted
to both sexes. Moreover, a modification, caused in any of tlic
above specified ways, may at first have been of no direct ad-
vantage to a species, ])ut may subsequently have been taken
advantage of by its descendants under new conditions of life
and newly-acquired luibits.

If, for instance, green woodpeckers alone had existed, and
"\ve did not know that there Avere many black and pied kinds,
I dare say that we should have thought that the green color
was a beautiful adaptation to hide 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 selec-
tion. A trailing palm in the Malay Archipelago climbs tlie
loftiest trees by the aid of exquisitely-constructed hooks clus-
tered 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 there is reason to l:)elieve, from tlie distribution of
the thorn-bearing species in Africa and South America, serves
as a defence against browsing quadrupeds, so tlie hooks on the
palm may first have been developed for this object, and subse-
quently been taken advantage of by the plant as it imderwent
further modification and became a climber. The naked skin
on the head of a vulture is generally considered as a direct
adaptation for wallowing in putridity ; and so it may be, or it
may possibly be due to tlie 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 adapta-
tion for aiding parturition, and no doubt they facilitate, or may
be indispensable for this act ; but as sutures occur in the skulls
of young birds and reptiles, Avliich have only to escape from
a broken C(i;ji:, 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 va-
riation or individual diflbrence ; and we are immediately made
conscious of this by reflecting on the diiferences in the breeds
of our domesticated animals in different countries — more espc-
ially in the less civilized countries where there has been but
littie methodical selection. Animals kept by savages in difler-

Chap. YI. AFFECTED BY NATUKAL SELECTION. 193

ent countries often have to struggle for their own subsistence,
and are exposed to a certain extent to natural selection, and
individuals witli sliglitly-dillerent constitutions would succeed
best under dilTerent climates. A good observer states tliat in
cattle susceptibility to the attacks of flies is correlated with
color, as is the liability to be poisoned by certain plants ; so
that even color would be thus subjected to the action of nat-
ural selection. Other observers are convinced that a damp
climate affects the growth of the hair, and tliat with the hair
the horns are correlated. Mountain-breeds alwaj-s differ from
lowland-breeds ; and a mountainous country would probably
affect the hind-limbs fmm exercising them more, and possibly
even the form of the jielvis ; and then, by the law of homolo-
gous variation, the fiont-liml)s and the head would probably be
affected. Tlie shape, also, of the pelvis might affect by press-
ure the shape of certain parts of the young in the womb.
The laborious breathing necessary in high regions would, we
have reason to believe, increase the size of the chest ; and
again- correlation would come into play. The effects on the
whole organization of lessened exercise, together with abun-
dant food, is probably still more important ; and this, as H. von
Nathusius has lately shown in his excellent Treatise, is appar-
ently one chief cause of the great modilication which the
breeds of swine have undergone. But Ave are far too ignorant
to speculate on the relative importance of the several known
and unknown causes of variation ; and I have made these
remarks only to show that, if Ave are unable to account for the
characteristic differences of our domestic breeds, which never-
theless are generally admitted to have arisen through ordinary
generation from one or a few parent-stocks, we ought not to
lay too much stress on our ignorance of the precise cause of
the sliglit analogous differences between species. I might
have adduced for this same purpose the dilferences between
the races of man, which are so strongly marked ; I may add
that some light can apparently be thrown on these differences,
through sexual selection of a particular kind, but without
entering on full details my reasoning Avould appear frivolous.

Uillliarian Doctrine howfac true: JJcauti/ /tow acquired.

The foregoing remarks lead me to say a few Avords on the
protest, lately made by some naturalists, against th«> utilitarian
doctrine that CA'cry detail of structure has been produced for
9

191 • UTILITARIAN DOCTRINE IIOW FAR TRUE: Chap. VI.

the good of its possessor. Tliey believe that many structures
have been created for l)eauty in the eyes of man, or, as already
discussed, for the sake of mere variety. Such doctrines, if
true, Avould be aljsolulely fatal to my theory. Yet I fully
admit that many structures are now of no direct use to their
possessors, and may never have been of an}- use to their pro-
genitors. No doubt, as recently remarked, the definite action
of changed conditions, correlated variation, and reversion, have
all produced their efTects. But the most important consider-
ation is that the chief part of the organization of every liv-
ing creature is simply due to inheritance; and consequently,
though each assuredly is well fitted for its place in Nature,
many structures now have no direct relation to existing habits
of life. Thus, we can hardly believe that the webbed feet of
the upland goose or of the frigate-bird are of special use to
these birds ; we cannot 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 to the progenitor of the upland goose and
of the frigate-bird, webbed feet no doubt were as useful as
they now are to the most aquatic of living birds. So we ma^'
believe that the progenitor of the seal did not possess a flipper,
but a foot with live toes fitted for walking or grasping; and
we may further venture to believe that the several bones in
the liml)s of the monkey, horse, and bat, which have been in-
herited from some ancient progenitor, were formerly of more
special use than they now are to these animals M'ith their
Avidely-diversificd habits, and might consequently have been
modilied through natural selection, M:>king due allowance
for the definite action of changed conditions, correlation, rever-
sion, etc., we may conclude that every detail of structure in
every living creature is either now or was formerly of use —
directly or indirectly through the comj^lex laws of growth.

With respect to the belief that organic beings have been
created beautiful for the delight of man — a view which it has
been pronounced may safely be accepted as true, and as sub-
versive of my whole theory — I may first remark that the idea
of the beauty of any object obviously d(^pends on the mind of
man, irrespective of any real quality in the a(hnircd object ; and
that the idea is not an innate and imalterable element in the
mind. We see this in men of ditlerent races admiring an en-
tirely diirerent standard of beauty in their women ; neither the

Cii-vr. VI. BEAUTY HOW ACQUU4ED. 195

Negro nor the Chinese admires the Caucasian bcau-idcal. The
idea also of picturesque beauty in scenery has arisen only within
modern times. On the view of beautiful objects havinj^ been
created for man's gratification, it ought to be shown that there
was less beauty on tlie face of the earth before man appeared
than since he canae on the stage. Were the l^cautiful volute
and cone shells of the Eocene epoch, and the gracefully-sculi>
tured ammonites of the Secondary period, created that man
might ages afterward admire them in his cabinet ? Few ob-
jects are more beautiful than the minute siliceous cases of the
diatomacea? : were these created that they might be examined
and admired xmder 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 ; and they have become
through natural selection beautiful, or rather conspicuous in
'contrast with the green leaves, that they might easily be ob-
served and visited by insects, so that their fertilization miglit
b'3 favored. 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 gayly-colored corolla. Again, several plants habitu-
ally produce two kinds of flowers : one kind open and colored
so as to attract insects; the other closed and iiot colored, desti-
tute of nectar, and never \-isited by insects. Hence we may
conclude that, if insects had never existed on the face of the
earth, the vegetation would not have been decked Avith beauti-
ful flowers, but Avould have produced only such poor flowers as
we now see on our firs, oaks, nut and ash trees, on grasses,
spinach, docks, and nettles. A similar line of argument holds
good with the many kinds of beautiful fruits ; that a ripe straw-
berry or cherry is as pleasing to the eye as to the palat<% that the
gayly-colored fruit of the spindle-wood-tree and the scarlet
berries of the holly are beautiful objects, will be admitted by
every one. But this beauty serves merely as a guide to birds
and beasts, that the fruit may be devoured and the manured
seeds thus disscminatod : I infer that this is the case from havhig
as yet found in every instance that seeds, Avhich are embedded
within a fruit of any king, tliat is witliin a fleshy or pulpy envel-
ope, if it be colored of any brilliant tint, or merely rendered
conspicuous by being white or black, are always disseminated
by being first devoured.

On the other hand, I willinglv admit that a great nuinlKT
of male animals, as all our ir.< st jrorgcous birds, some f\^he3

190 UTILITARIAN DOCTRINE HOW FAR TRUE: Chap. VI.

some maimnals, and a host of majTnificently-colored butterflies
and some other insects, have been rendered beautiful for
beauty's sake ; but this has Ijcen cfTected not for the dehf^ht
of man, but throup^'h sexual selection, that is, from the more
beautiful males liaving been continually preferred by their less
ornamented females. So it is Avith the music of birds. We
may infer from all this that a similar taste for lieautiful colors
ami for musical sounds runs throug-h a large part of the animal
kingilom. AVhen tlie female is as beautifully colored as the
male, Avhich is not rarely the case with birds and butterflies,
the cause simply lies in the colors acquired throuo-h sexual se-
lection having been transmitted to both sexes, instead of to
the males alone. In some instances, however, the acquirement
of conspicuous colors by the female may have been checked
through natural selection, on account of the danger to which
she would thus have been exposed during incubation.

Natural selection cannot possibly produce any modification
in any one species exclusively for the good of another species ;
though throughout Nature one species incessantly takes advan-
tage of, and profits by, the structure of others. But natural
selection can and does often produce structures for the direct
injury of otlicr animals, as we see in the fang of the adder, and
in the ovipositor of the ichneumon, by which its eggs are depos-
ited in the living bodies of other insects. If it could be proved
that any part of the structure of any one species had been
formed for the exclusive good of another species, it would
annihilate my theory, for such could not have been produced
through natural selection. Although many statements may
be found in Avorks on natural history to tliis eflcct, I cannot
find even one which seems to me of any weight. It is admitted
that the rattlesnake has a poison-fang for its own defence and
for the destruction of its prey ; but some authors supjiose that
at the same time this snake is furnished with a rattle for its
own injury, namely, to warn its prey to escape. I would
almost as soon believe that the cat curls the end of its tail
wlicn ])reparing to spring, in order to warn the doomed mouse.
But I have not space here to enter on this and other such cases.

Natural selection will never produce in a being any thing
injurious to itself, for natural selection acts solely by and for
the good of each. No organ will be formed, as Palcy has
remarked, for the purpose of causing pain or fordoing an injury
to its possessor. If a fivir balance be struck between the good
a-.id evil caused by each part, each will 1w found on the whole

Chap. VI. BE.VUTY HOW ACQUIKKD. 197

advantagccous. After the lapse of time, under changing con-
ditions of life, if any part comes to be injurious, it will be modi-
fied; or, if it be not so, the being will become extinct, as
myriads have become extinct.

Natural selection tends only to make each organic being as
perfect as, or sliglitly more perfect than, the other inliabitants
of the same country with which it has to struggle for existence.
And we see that this is the degree of perfection attained under
nature. Tlie endemic productions of New Zealand, for instance,
are perfect one compared with another; but tlicy are now
rapidly yielding before the advancing legions of ])lants and
animals introduced from Europe. Natural selection will nc»t
produce absolute perfection, nor do we always meet, as far as
we can judge, with tliis high standard under nature. The cor-
rection for the al)erration of light is said by !Mliller not to be
perfect even in that most perfect organ, the human eye. If our
•reason leads us to admire with enthusiasm a multitude of in-
imitable contrivances in nature, this same reason tells us, though
we may easily err on both sides, that some other contrivances
are less perfect. Can we consider the sting of the bee as per-
fect, which, when used against many attacking animals, cannot
be withdrawn, owing to the backward scrratures, and so inevi
tably causes the death of the insect by tearing out its viscera ?

if we look at the sting of the bee, as having originally ex-
isted in a remote progenitor as a boring and serrated instru-
ment, like that in so many members of the same great order,
and wliich has been modified but not perfected for its present
purjiose, with the poison originally adapted for some other
pur[)ose, such as to produce galls, subsequently intensified, mo
can ]ierhaps 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 conununity, it will
fulfil all the requirements of natural selection, though it may
cause the death of some few members. If we admire the truly
wonderful power of scent by which the males of many insects
find their females, can we admire the production for this single
purpose of thousands of drones, which are utterly useless to the
community for any other purpose, and which are ultimately
slaughtered by their industrious and sterile sisters ? It may be
ditVicult, Init 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 l)orn, or to perish herself in the combat ;
for undoubtedly this is for the good of the community ; and

108 SUMMARY. Cuap. VI.

inatcriKil love or maternal hatred, though the latter fortunately
is most rare, is all the same to the inexr)rablc principle of natu-
ral selection. If we admire the several ini^enious contrivances,
by which orchids and many other plants are fertilized through
insect agency, can we consider as equally perfect the elabora-
tion of dense clouds of pollen by our fir-trees, so that a few
granules may be wafted by a chance breeze on to the ovules ?

Summary : tJie Law of Unity of Type and oftJie Conditions
of Existence embraced by the Theory of JVcitural Se-
lection.

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 indepen-
dent acts of creation are uttercly obscure. 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 will always be
very slow, and will act, at any one time, only on a few forms ;
and partly because the very process of natural selection implies
the continual supplanting and extinction of preceding and in-
termediate gradations. Closely-allied species, now living on a
continuous area, must often have been formed when the area
was not continuous, and when the conditions of life did not in-
sensibly graduate away from one part to another. When two
varieties are formed in two districts of a continuous area, an
intermediate variety will often be formed, fitted for an interme-
diate zone ; but, from reasons assigned, the intermediate 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 existing in greater numbers, Avill have
a great advantage over the less numerous intermediate variety,
and Avill thus generally svicceed in sujiplanting and exterminat-
ing it.

AVe 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 could only glide through the air.

We have seen that a species may under new conditions of
life change its habits, or have diversified habits, Avith some very

Chap. VI. SUMMARY. 199

unlike those of its ne:u-est conveners. Hence, we can under-
stand, bearing in mind that each organic being is trying to Hvc
wliercver it can live, how it has arisen that there arc upland
geese with Avebbcd feet, ground woodpeckers, diving thrushes,
and jx'trels with the hal)its of auks.

Although the belief that an organ so perfect as the eye
could have been formed by natural selection, is more than
enouiih to sta^rger any one ; yet in the case of any organ, if we
know of a long series of gradations m complexity, each good
for its possessor, then, under changing conditions of life, there
is no logical impossibilit}'^ in the acquirement of any conceivable
degree of perfection through natural selection. In the cases
in which we know of no intermediate or transitional states, we
sliouhl be very cautious in concluding that none have existed,
for the homologies of man}' organs and their intermediate states
show what wonderful metamorphoses in function are at least
'possible. For instance, a swim-bladder has apparently been
converted into an air-breathing lung. The same organ having
performed simultaneously very diflerent functions, and then
liaving Ixicn in part or in whole specialized for one function ;
and two distinct organs having performed at the same time the
same function, the one having been perfected while aided by
the other, must often have largely-facilitated transitions.

We have seen in two beings, widely remote from each other
in the natural scale, that an organ serving in both for the same
purpose, and appearing closely similar, may have been sepa-
rately and independently formed ; but when such organs are
closely examined, essential dilTerences in their structure can
almost always be detected; and this naturally follows from the
principle of natural selection. On the other hand, the conunon
rule throughout Nature is infinite diversity of structure for
gaining the same end; and this again naturally, follows on the
same great principle.

In almost every case we are far too ignorant to be enaljled
lo assert that any part or organ is so unimportant for the wel-
fare of a species, that modifications in its structure could not
have been slowly accumulated by means of natural selection.
But Ave may confidently believe that many modifications,
wholly due to the laws of growth, and at first in no way advanta-
geous to a species, have been subsef|uently taken advantage of
by the still furtlier modified descendants of this species. We
may also believe tliat a part formerly of high importance has
often been retained (as tlie tail of an aquatic animal by its ter-
restrial descendants), though it has become of such small im-

200 SUMMAEY. CiiAr. VI.

portancc that it could not, in its present state, have been ac-
quired by natural selection — a power which acts solely through
tlic sur^-ival of tlie best-fitted individuals in the strufrgle for life.

Natural selection will produce nothing in one sjiecies foi
the exclusive good or injury of anotlier; though it may well
produce parts, organs, and excretions, highly useful or even in-
dispensable, or highly injurious to another species, but in all
cases at the same time useful to the owner, Natural selection
in each well-stocked country must act chiefly through the com-
pc^tition of the inhabitants one with another, and consequently
will produce perfection, or strength in the battle for life, only
according to the standard of that countrj^ Hence the inhab-
itants of one countr}', generally the smaller one, will often yield
to the inhabitants of another and generally larger country. For
in the larger country there will have existed more individuals,
and more diversified forms, and the competition will have been
severer, and thus the standard of perfection will have been
rendered higher. Natural selection will not nccessarilj' pro-
duce absolute perfection ; nor, as far as Ave can judge by our
limited faculties, can absolute perfection be evei-ywhcrc found.

On the theory of natural selection we can clearly inider-
stand the full meaning of that old canon in natural history,
" Natura non facit saltum." This canon, if we look only to
the jiresent inhabitants of the world, is not strictly correct ;
but if we include all those of past times, whether known or
not yet known, it must by my theory be strictly true.

It is generally acknowledged that all organic beings have
been formed on two groat laws — Unity of Type, and the Con-
ditions of Existence. B}^ imity of type is meant that funda-
mental agTcement in structure which we see in organic beings
of the same class, and which is quite independent of their
halnts of life. . On my theory, unity of type is explained by
unity of descent. The expression of conditions of existence, so
often insisted on by the illustrious Cuvier, is fully embraced by
tlie principle of natural selection. For natural selection acts
by either now adapting the varying parts of each being to its
organic and inorganic conditions of life ; or by having adapted
i\unn during long-past periods of time : the adaptations being
aided in some cases by use and disuse, being affected by the
direct action of the external conditions of life, and being in all
crises subjected to the several laws of growth. Hence, in fact,
the law of the Conditions of Existence is the higher law ; as it
iiuhidcs, thrnugli the inheritance of former adaptations, that
of Unity of Type,

Cii.i.Vll. INSTINCT. 201

CHAPTER VII.

INSTINCT,

Instincts coniparnl)lo with Ilabiis, but difTcront in their Orii^in— Inptincls £;radu.ited
— Aphides and Ants— Instincts vnriable— DomcBtic Instincts, tlicir Origin— Nat-
ural luHtincta of tlic Cuckoo. Ostrich, and Parasitic Bees— Slave-niakin:,' Ants—
Hive-bee, its cell-inakini; instinct— Changes of Instinct and Structure not neces-
sarily simultaneous- DilDculties of the Theory of the Natural tjelectiou of lu-
btincta— Neuter or Sterile Insects — Summary.

Instincts might have been worked into the previous chap-
ters ; but I thought that it would be more convenient to treat
the subject separately, especially as an instinct so wonderful as
that of the construction of the comb by the hive-bee will prob-
ably have occurred to many readers, :is a difficulty sufficit-nt to
overthrow the whole theory. I must premise that I have
notliing to do with the origin of tlic primary 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 qualities of animals Avithin the same class.

I will not attempt any definition of instinct. It would be
easy to show that several distinct mental actions are commoidy
embraced by this term ; but every one underst;uids what is
meant, when it is said that instinct impels the cuckoo to mi-
grate and to lay her eggs in other birds' nests. An action,
which we ourselves should require experience to enable us to
perform, when performed by an animal, more especially by a
very young one, without any experience, and when performed
by many individuals in the same way, without their knowing
for what purpose it is performed, is usutilly said to he instinc-
tive. But I could show that none of these cliaracters of in-
stinct are universal. A little dose, as Pierre Hubcr expresses
it, of judgmtMit or rea.son, often comes into play, even in ani-
mals low in the scale of nature.

Frederick Cuvier and several of the older m('tai)hysicians
have compared instinct with habit. This comparLsou gives, I
think, an accurate notion of the frame of mind under which
an instinctive action is performed, but not necessarily of its

202 INSTINCT. Chap. VII.

origin. How unconsciously many habitual actions are per*
fornieil, indeed not rarely in direct opposition to our conscious
Avill ! yet tlicy may be modified by the ■will or reason. Habits
easily become associated with other habits, and witli certain
periods of time and states of the body. A\'hcn 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 ])erson be in-
terrupted in a song, or in repeating any thing by rote, he is
generally forced to go back to recover the habitual train of
thought : so P. Huber found it Avas with a caterpillar, which
makes a very complicated hammock ; for if he took a cater-
pillar 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 reperformed
the fourth, fifth, and sixth stages of construction. If, however,
a cater])illar were taken out of a hammock made up, for in-
stance, 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 feeling the benefit of this, it was much embarrassed,
and, in order to complete its hammock, seemed forced to start
from the third stage, where it had left off, and thus tried to
complete the already-finished work.

If we suppose any habitual action to become inherited — and
I think it can be shown that tliis does sometimes happen —
then the resemblance between Avhat originally was a habit and
an instinct becomes so close as not to be distinguished. If
Mozart, instead of playing the jiiano-forte at three years old
with wonderfully little jiracticc, had played a tune with no
l)ractice at all, he might truly be said to have done so instinc-
tivclv. But it would be a serious error to suppose that the
greater number of instincts have been acquired by habit in one
generation, and then transmitted by inheritance to succeeding
generations. It can be clearly shown that the most wonder-
ful instincts with which we arc acquainted, namely, those of
the hive-bee and of many ants, could not possibly have been
acqtiired by habit.

It will be universally admitted that instincts are as imjior-
tant as corporeal structure for the welf:ire of each species, un-
der its present conditions of life. lender changed conditions
of life, it is at least possible that slight modifications of in-
stinct might be profitable to a species ; and if it can be shown

Chap. VII. INSTINCT. 203

that instincts do vary ever so little, then I can see no dilTiculty
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 in-
stiijcts have originated. As modifications of corporeal struct-
ure arise from, and arc increased b}'", 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 arc of
quite subordinate importance to the effects of the natural selec-
tion of what may be called spontaneous variations of instincts;
tliat is, of variations produced by tlie same unknown causes
which produce slight deviations of bodily structure.

No comj^lex instinct can possibly be produced througli nat-
ural selection, except by the slow and gradual accumulation
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 in-
stinct 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 shoAV 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- kno^vn among extinct
species, how very generall^'^ gradations, leading to the most
complex instincts, can be discovered. Changes of instinct may
sometimes be facilitated by the same species having different
instincts at different periods of life, or at different seasons of the
year, or when placed imder difi'erent circumstances, etc. ; in
which case cither the one or the other instinct might be pre-
served by natural selection. And such instances of diversity
of instinct in the same species can be shown to occur in nature.

Again, as in the case of corporeal structure, and conform-
ably to my theorj-, the instinct of each species is good for it-
self, but has never, as far as we can judge, been produced for
the exclusive good of others. One of the strongest instances
of an animal apparently performing an action for the sole good
of another, witli which I am acquainted, is that of ajihides vol-
untarily yielding, as was first observed l)y Hu})er, their sweet
excretion to ants ; that they do so voluntarily, the following
facts show : I removed all the ants from a group of about a
dozen aphides on a dock-plant, and prevented their attendance

204 INSTINCT. CiiAr. VII.

during several hours. After this interval, I felt sure that the
aphides would Avant to excrete. I watched thcni 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 tlie ants do with their antennre; 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 Hock it had discovered ; it then began to play witli
its anteun;i3 on the abdomen first of one aphis and then of an-
other; and each, as soon as it felt the antenna?, immediately
lifted up its abdomen and excreted a limpid drop of sweet
juice, which was eagerly devoured by the ant. Even the
quite young aphides behaved in this manner, showing that the
action Avas instinctive, and not the result of experience. It is
certain, from the observations of Huber, that the aphides show
no dislike to the ants : if the latter be not present they are at
last compelled to eject their excretion. But as the excretion
is extremely viscid, it is no doubt a convenience to the aphides
to have it removed ; tlierefore, 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 in-
stincts of others, as each takes advantage of the weaker bodily
structure of other species. So, again, certain instincts cannot
be considered as absolutely perfect ; but as details on this and
other such points are not indispensable, they may be here
passed over.

As some degree of variation in instincts under a state of
nature, and the inheritance of such variations, arc indispensable
for the action of natural selection, as many instances as pos-
sible ought to be here given ; but want of space prevents me.
I can only assert that instincts certainly do vary — for instance,
the migratory instinct — both in extent and direction, and in its
total loss. So it is with the nests of birds, which vary partly
in dependence on the situations chosen, and on the nature and
temperature of the country inhabited, but often from causes
Avliolly unknown to us : Audubon has given several remarkable
cases of differences in the nests of the same species in the
Northern and Southern United States. A\''hy, it has been asked,
if instinct be variable, has it not granted to the bee " the ability
to use some other material Avhen wax was deficient ? " But
what other material could bees use? They Avill work with
and use, as I have seen, wax hardened with vermilion and

Chap. VII. CHANGES OF HABIT OR INSTINCT. 205

softened" with lard. Andrew Knight observed that his bees,
instead of laboriously collecting propolis, used a cement of
wax and turpentine, with which he had covered decorticated
trees. It has lately been shown that bees, instead of search-
ing flowers for their pollen, will gladly use a very different
substance, namely, oatmeal. Fear of any particular enemy is
certainly an instinctive quality, as may be seen in nestling
birds, though it is strengthened by experience, and 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
llie large birds have been most persecuted by man. '\\'e may
safely attribute the greater Avildness of our large birds to this
cause ; for in iminhabited islands large birds are not more fear-
'ful than small ; and the magjDie, so wary in England, is tame
in Norwa}', as is the hooded crow in Egypt.

That the mental qualities of animals of the same kind,
bom in a state of nature, vary much, could be shown by
many facts. Several cases could also be given of occasional
and strange habits in wild animals, which, if advantageous to
the species, might give rise, through natural selection, to
new instincts. But 1 am well aware that these general state-
ments, without the facts in detail, Avill produce but a feeble
effect on the reader's mind. I can only repeat my assurance,
that I do not speak without good evidence.

Inherited Chanr/cs of Ilah'it or Instinct in Domesticated Animals.

The possibilit}', or even probability, of inherited varial ions
of instinct in a state of nature Avill be strengthened In' briefly
considering a few cases under domestication. Wc shall thus
b(; enabled to see the part Avhich habit and the selection of
so-called accidental or spontaneous variations have plaj-ed in
modifying the mentiil ([ualilies of our domestic animals. It is
notorious how much domestic animals vary in their mental
qualities. With cats, for instance, one naturally takes to catch-
ing rats, and another mice, and these tendencies are known
to be inherited. One cat, according to Mr. St. John, alwavs
brought home game-birds, another hares or rabbits, and another
Inmtcd on marshy ground and almost nightly caught wood-
cocks or snipes. A number of curious and authentic instancca

20G CHANGES OF HABIT OR INSTINCT Chap. VII.

could be g'iven of various shades ol' disjKjsitiou and of taste,
• and likcAvisc of the oddest tricks, associated with certain frames
of mind or periods of time, being inherited. But let us
look to the familiar case of the breeds of the dof^ : it cannot
be doubted that younj^ pointers (I have myself seen a striking
instance) "will sometimes point and even back other dogs
the very first time that they are taken out ; retrie\-ing is
certainly in some degree inherited by retrievers ; and a ten-
dency to run round, instead of at, a flock of sheep, by shep-
herd-dogs. I cannot see that these actions, performed with-
out experience by the young, and in nearly the same manner
by each indi\'idual, 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
differ essentially from true instincts. If we were to behold
one kind of wolf, when young and without any training, as
soon as it scented its prey, stand motionless like a statue,
and then slowly crawl forward with a peculiar gait ; and
another kind of wolf rushing round, instead of at, a herd
of deer, and driving them to a distant point, we should assur-
edly call these actions instinctive. Domestic instincts, as they
may be called, are certainly far less fixed than natural in-
stincts; but they have been acted on by far less rigorous selec-
lion, and have been transmitted for an incomparably shorter
period, imder less fixed conditions of life.

HoAV strongly these domestic instincts, habits, and dis-
positions, are inherited, and how curiously they become
mingled, is well shown when diflferent breeds of dogs are
crossed. Thus it is known that a cross with a bull-dog has
afiFected for many generations the courage and obstinacy of
greyhounds ; and a cross Avith a greyhound has given to a
whole famih^ of shepherd-dogs a tendency to hunt hares.
These domestic instincts, when thus tested by crossing, resem-
ble 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 Koy describes a dog,
whose great-grandfather was a wolf, and this dog showed a
trace of its wild parentage only in one way, by not com-
ing in a straight line to his master, when called.

Domestic instmcts are sometimes spoken of as actions
which have bec^.me inherited solelv fi"om long - continued

CiiAP. VII. IN DOMESTICATED ANIMALS. 207

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 light tendency to this strange
habit, and tlie 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 cannot fly eighteen inches high without
going head over heels. It may be doubted whether any
one would have thought of training a dog to point, had not
some one dog naturally shown a tendency in this line ; and
this is known occasionally to happen, as I once saw, in
a pure terrier : the act of pointing is probably, as many
have thought, only the exaggerated pause of an animal
preparing to sjiring on its prey. When the first tendency
to point was once displayed, methodical selection and the
inherited effects of compulsory training in each successive
generation would soon complete the work ; and unconscious
selection is still in progress, as each man tries to procure,
without intending to improve the breed, dogs which will
stand and hunt best. On the other hand, habit alone in some
cases has sufficed ; hardly any animal is more diflicult, in most
cases, to tame than the young of the Avild rabbit ; scarcely any
animal is tamer than tlic young of the tame rabbit; bull
can hardly suppose* that domestic rabbits have often been
selected for tameness alone; so that we must attribute at
least the greater part of the inherited change from extreme
wildness to extreme tameness, to habit and long-continued
close confinement.

Natural instincts are lost under domestication : a remark-
able instance of this is seen in those breeds of fowls which
very rarely or never become " broo<ly," that is, never wish
to sit on tlieir eggs. Familiarity alone prevents our seeing
how largely and how permanently tlie minds of our domestic
animals have been modified. It is scarcely possible to doubt
that the love of man has become instinctive in tlie dog.
All wolves, foxe.s, jackals, and species of the cat genus, when
kept tame, an; most eager to attack poultry, sheep, and pigs;
and this tendency has been found incural)le in dogs which
liave been l)rought home as jiuppies from coimtries, such
as Tierra del Fuego and Australia, where the savages do

208 SPECIAL INSTINCTS. Chap. VII.

not keep lliese 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, with some de-
gree of selection, has probably concmred in civilizing by in-
heritance our dogs. On the other hand, young chickens
have lost, wholly by habit, that fear of the dog and cat
which no doubt was originally instinctive in them •, for I
am informed by Captain Hutton that the young chickens of
the parent-stock, the Gallus bankiva, when reared in India
imder a hen, are at first excessively wild. So it is with
young pheasants reared in England under a hen. It is not
that chickens have lost all fear, but fear only of dogs and
cats, for if the hen gives the danger-chuckle, they will nm
(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
tliis instinct retained by our chickens has become useless
imder domestication, 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 accumu-
lating, 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 inherited mental changes ; in
othf^r cases compulsory habit has done nothing, and all has
been the result of selection, pursued both methodically and
imconsciously : but in most cases habit and selection have
probably acted together.

Special J/isti?ii't^'i.

We shall, perhaps, best understand how instincts in a slate
of nature have become modified by selection, by considering a
few cases. I will select only three, out of tliose Avhich I sliall
have to discuss in my future work — 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 gcner-

Chap. VII. INSTINCTS OF THE CUCKOO. 209

ally and justly been ranked by naturalists as the most wonder-
ful of all known instincts.

Instincts of the Cuckoo. — It is supposed by some natu-
ralists that the more immediate cause of the instinct of the
cuckoo is that she lays her ep^gs, 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 eg'p;s, those first laid would have to be left
for some time unincubatcd, or there would be eggs and young
birds of different ages in tlie same nest. If this Avere the case,
tlie process of laying and hatching might be inconveniently
long, more especially as she migrates at a very early period ;
and the first hatched young would prol:)abl3' have to be fed by
the male alone. But the American cuckoo is in this predica-
ment ; for she makes her own nest, and has eggs and young
successively hatched, all at the same time. It has been both
asserted and denied that the American cuckoo occasionally
lays her eggs in other birds' nests ; but I have lately heard
from Dr. Merrcll, of Iowa, that he once found in Illinois a
young cuckoo together with a young jay in the nest of a Blue
jay (Garrulus cristatus) ; and as both were nearly fully feath-
ered, there could be no mistake in their identification. I could
also give several instances of various birds which have been
known occasionally to lay their eggs in other birds' nests.
Now let us suppose that the ancient progenitor of our Euro-
pean cuckoo had the habits of the American cuckoo, and that
she occasionally laid an e^^ in another bird's nest. If the old
bird profited by this occasional habit through being enabled to
migrate earlier or through any other cause ; or if the yoimg
were made more vigorous by advantage being taken of the
mistaken instinct of another species, than when reared by their
own mother, encumbered as she could hardly fail to be by
having eggs and young of different ages at the same time ;
then the old birds or the fostered young would gain an advan-
tage. And analogy would lead us to believe that the young
thus roared would be apt to follow by inheritance the occasion-
al and aberrant habit of their mother, and in their turn would
be apt to lay their eggs in other birds' nests, and thus be more
successful in rearing their young. By a continued process of
this nature, I believe that the strange instinct of our cuckoo
has been generated. It has, also, recently been ascertained
that the cuckoo occasionally lays her eggs on the bare ground,
sits on them and feeds her young ; this rare and strange event
evidently is a case of reversion to the long-lost aboriginal in-
stinct of nidification.

210 SPECIAL INSTINCTS. Chap. VII.

It has been objected that I liave not noticed other related
instincts and adaptations in the cuckoo, which are falsely
spoken of as necessarily coordinated. But in all cases, specu-
lation on an instinct known only in a single species is useless,
for we have no facts to guide us. Until quite recently the in-
stincts of the European and of the non-parasitic American
cuckoo alone Avere known ; now, owing to Mr. E. Ramsaj^'s
observations, we know something about three Australian spe-
cies, which lay their eggs in other birds' nests. The chief
points are three : first, that the cuckoo, with rare exceptions,
lays only one egg in a nest, so that the large and voracious
young l)ird may receive ample food. Secondly, that the eggs
are of remarkably small size, not exceeding those of the sky-
lark— a bird about one-fourth as large as the cuckoo. That
the small size of the egg is a real case of adaptation we may
infer from the fact of the non-parasitic American cuckoo laying
full-sized eggs. Thirdl}"-, that the young cuckoo, soon after
birth, has the instinct, the strength, and a properly-shaped
back, for ejecting its foster-brothers, which then perish from
cold and hunger. This, it has been boldly maintained, is a
beneficent arrangement, in order that the young cuckoo may
get sufficient food, and that its foster-brothers may perish be-
fore they have acquired much feeling.

Turning now to the Australian species ; though these birds
generally lay only one egg in a nest, it is not rare to find two
and even three eggs in the same nest. In the Bronze cuckoo
the eggs vary greatly in size, from eight to ten lines in length.
Now if it had been of any 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
tliere is a relation between size and the period of incubation),
then there is no difficulty in believing that a race or species
might have been formed which would have laid smaller and
smaller eggs ; for these would have been more safely hatched
and reared. ^Ir. Ramsay remarks that two of the Australian
cuckoos, Avhen they lay their eggs in an open nest, manifest a
decided preference for nests containing eggs similar in color to
their own. Tlie Eurojiean sjiecies certainly 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-Avarbler with bright greenish-blue eggs.
Had our cuckoo invariably displaj-ed the above instinct, it

Cii.vr. VII. INSTINCTS OF THE CUCKOO. oji

would assuredly have been added to those Mhich it is assumed
must all have been acquired together. The eg-gs of the Aus-
tralian ]3ronze cuckoo vary, according to Mr. Ixanisay, to an
extraordinary degree in color; so that in this respect, as well
as in size, natural selection assuredly might have secured and
iixed any advantageous variation.

With reference to the young European cuckoo ejecting its
foster-brothers — it must first be remarked that Mr. Gould, who
has paid particular attention to this subject, is convinced that
the belief is an error : he asserts that the young foster-birds
are generally ejected during the first three days, when the
yoimg cuckoo is quite powerless ; he maintains that the young
cuckoo exerts, l)y its hunger-cries, or by some other means,
such a fascination over its foster-parents, that it alone receives
food, so that the others are starved to death, and are then
tljrown out, like the egg-shells or the excrement, by the old
birds. He admits, however, that the 3'^oung cuckoo Avheu
giown older and stronger may have the power, and perhaps the
instinct, of ejecting its foster-brothers, if they hapj)en to escape
starvation during the first few days after birth. Mr. Ramsay
has arrived at the same conclusion regarding the Australian
species : he states that the young cuckoo is at first a little
helpless fat creature, but, " as it grows rapidly, it soon fills up
the greater part of the nest, and its unfortunate companions,
either smothered by its weight, or starved to death through its
greediness, are thrown out by their parents." Nevertlieless
there is so much evidence, both ancient and recent, that the
young Eurojican cuckoo does eject its foster-brothers, that this
can hardly be doubted. Now, if it were of great importance
to the young cuckoo to receive as much food as possible soon
after birth, I can sec no special difficulty in its gradually
acrjuiring, during successive generations, the habit (perhaps
through mere unintentional restlessness), the strength, and the
structure, best fitted for ejecthig its foster-brothers; for those
young cuckoos which had such habits and structure would be
the best fed and most securely reared. I can sec no more
difficulty in this, than in young birds acquiring the instinct and
the temporary hard tips to their beaks for breaking through
their own shells — or than in young snakes having 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 any age, and the variations
tend to be inherited at a corresponding age — propositions

212 SPECIAL IXSTLNOTS. Ciiai-. VII.

which caiiiioL be disputed — then the instincts and structure of
the youns-;' could be slowly modified as well as those of the
adult; antl both cases must stand or fidl with the whole theory
of natural selection.

The occasional habit of birds laying their eggs in other
birds' nests, either of the same or of distinct species, is not
very uncommon with the Gallinaceas ; and this perhaps explains
the origin of a singular instinct in the nearest allied group,
that of ostriches. For several hen-ostriches unite and lay first
a few eggs in one nest and then in another; and these arc
hatched by the males. This instinct may probably be accounted
for by the ftict of the hens lajang a large number of eggs, but,
as in the case of the cuckoo, at intervals of two or three days.
The instinct, however, of the American ostrich has not as yet
been perfected ; for a surprising number of eggs lie strewed
over the plains, so that in one day's hunting I picked up no
less than twenty lost and wasted eggs.

T\Iany bees are parasitic, and regularly lay their eggs in the
nests of other kinds of bees. This case is more remarkable
than that of the cuckoo ; for these bees have not only had their
instincts but their structure modified in accordance with their
parasitic habits ; for they do not possess the pollen-collecting
apparatus which Avould have been indispensable if they had
stored food for tlieir own yoimg. Some species, likewise, of
Sphegida) (wasp-like insects) are parasitic in the same manner
on other species ; and M. Fabre has lately shown good reason
for believing that, although the Tachytes nigra generally makes
its OAvn burrow and stores it with paralyzed prey for its own
larv;e, yet that, when this insect finds a burrow already made
and stored by another sphex, it takes advantage of the prize,
and becomes for the occasion parasitic. In this case, as Avith
the supposed case of the cuckoo, I can see no difficulty in nat-
ural selection making an occasional habit permanent, if of ad-
vantage to the species, and if the insect, whose nest and stored
food are thus feloniously appropriated, be not thus extermi-
nated.

Slave-male hip Instinct. — This remarkable instinct Avas first
discovered in the Formica (Polyerges) rufesccns by Pien-o
Huber, a better oliserv-er even than his celebrated father. This
ant is absolutely dependent on its slaves ; Avithout their aid,
the species Avould certainly become extinct in a single year.
The males and fertile females do no Avork of any kind, and the
Avorkers or sterile females, though most energetic and coura-

Chap. VII. SLAVE-MAKIXG INSTINCT. 213

{2:eous in capturinp^ slaves, do no otlier work. They are inca-
paljle of makiiii^ their own nests, or of feeding their own larv'a3.
When the old nest is found inconvenient, and they have to
migrate, it is the slaves which determine the migration, and
actually carry their masters in their jaws. So utterly helpless
are the masters, that when Hubcr shut up thirty of them with-
out a slave, but with plenty of the food Avhich they like best,
and with tlieir own larvie and pupa3 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 larv.T, and put all to
rights. What can be more extraordinary than these avcII-
ascertaincd facts ? If we had not known of any other slave-
making ant, it would have been hopeless to speculate how So
wonderful an instinct could have been perfected.

Another species, Formica sanguinea, Avas likewise first dis-
covered by P. Huber to be a slave-making ant. This species
is found in the southern parts of England, and its habits have
been attended to by Mr. F. Smith, of the British Museum, to
whom I am nnich indebted for information on this and other
subjects. Although fully trusting to the statements of Hulxu'
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 truth of so extraordinary and odious an instinct as that (jf
making slaves. Hence I will give the observations wliicli I
made, in some little detail. I oj^ened fourteen nests of F. san-
guinea, and found a few slaves in all. Males and fertile fe-
males of the slave sj)ecics (F. fusca) are found only in their
own proper communities, and have never been observed in the
nests of F. sanguinea. The slaves are black and not above
half the size of their red masters, so that the contrast in their
appearance is great. W^hen 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 larva^ and pup:c 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 nujuths of June and July, on
three successive years, I have 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 numljcr, I thought that they might behave differently wlien

214 SPECIAL INSTINCTS. Chap. VII.

more numerous ; but Mr. Smith informs me that he has watched
the nests at various liours during' May, June, and Aui^ust, both
in Surrey and Hamjishire, and lias never seen tlie slaves,
thougli present in large nundjers in August, either leave or
enter the nest. Hence he considers them as strictly house-
hold slaves. The masters, on the other hand, maybe constant-
ly seen bringing' in materials for the nest, and food of all kinds.
During the ^-ear 18G0, however, in the month of July, I came
across a community with an unusually large stock of slaves,
and I observed a few slaves mingled with their masters leaving
the nest, and marching along the same road to a tall Scotch-fir-
tree, twenty-five yards distant, which they ascended together,
prol)ably in search of aphides or cocci. According to Huber,
who had ample opportimitics for observation, the slaves in
Switzerland habitually Avork with their masters in making the
nest, and they alone open and close the doors in the morning
and evening; and, as Pluber expressly states, their jmncipal
office is to search for aphides. This difference in the usual
habits of the masters and slaves in the two coinitries probably
depends merely on the slaves being captured in greater num-
bers in Switzerland than in England.

One day I fortunately witnessed a migration of F. sanguinea
from one nest to another, and it Avas a most interesting spec-
tacle 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 b}^ an independent community of the slave-species
(F. fusca) ; sometimes as many as tliree of these ants cUnging
to the legs of the slave-making F. sanguinea. The latter ruth-
lessly 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 pupre 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 perhaps fancied that, after all, tliC}' had been vic-
torious in their late combat.

At the same time I laid on the same place a small parcel
of the ]nipre of another species, F. flava, with a few of these
little yellow ants still clinging to the fragments of their nest.
Tliis species is sometimes, though rarely, made into slaves, as

Chap. VII. SLAVE-MAKING INSTINCT. 215

has been described by Mr. Smith. Although so small a species,
it is very com'ageoiis, and I have seen it ferociously attack other
ants. In one instance I found to my surprise an independent
connnunity of F. llava under a stone beneath a nest of the
slave-making F. sanguinea ; and when I had accidentally dis-
turbed both n«'sts, tlie little ants attacked their big neighbors
with surprising courage. Now I was curious to ascertain wheth-
er F. sanguinea could distinguish the pupae of F. fusca, which
they habitually make into slaves, from those of the little and
furious F, llava, 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 pupre of F. fusca, whereas
they were much terrified when they came across the pupa?, or
even the earth from the nest, of F. flava, and cjuickly 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 pupaj.

One evening I visited another community of F. sanguinea,
and found a number of these ants returning home and entering
their nests, carrying the dead bodies of F. fusca (showing that
it was not a migration) and numerous pupa?. I traced a long
file of ants burdened Avith 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, h^wnver,
must have been close at hand, for two or three individuals of
F. fusca were rushing al^out 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
liome.

Such are the facts, though tliey did not need confirmation
by me, in regard to the wonderful instinct of making slaves.
Let it be observed what a contrast the instinctive habits of F.
sanguinea jiresent with those of the Continental F. rufescens.
The latter does not build its own nest, does not determine its
own migrations, does not collect food for itself or its young,
and cannot even feed itself: it is absolutely dependent on its
numerous slaves. Formica sanguinea, on the other hand, pos-
sesses much fewer slaves, a!id in the early part of the summer
extremely few : the mastcTS 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 lurviu, and the masters alono

•216 SPECLiL INSTINCTS. Chap. VII.

go on slave-making expeditions. In Switzerland the slaves
and masters Avork together, making and bringing materials for
the nest; both, l)iit cliiefly 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 Ijuilding-materials and food for themselves, their
slaves and larva^. So that the masters in this country receive
much less service from their slaves than they do in Switzerland.

By what steps the instinct of F. sanguinea originated I
will not pretend to conjecture. But as ants, which are not
slave-makers, Avill, as I have seen, carry off pupoe of other spe-
cies, if scattered near their nests, it is possible that such pupaj
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 pres-
ence proved useful to the species which had seized them — if it
Avere more advantageous to tliis species to capture workers
than to procreate them — the habit of collecting pupa? originally
for food might by natural selection be strengthened and ren-
dered i^ermanent 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, which, as
we have seen, is less aided by its slaves tlian the same species
in Switzerland, natural selection might increase and modify the
instinf"*^ — always supposing each modification to be of use to
th(; species — until an ant Avas fcn-med as abjectly dependent on
its slaves as is the Formica rufcscens.

Cell-making Instinct of the IIivc-J3ee. — I will not here
enter on minute details on this subject, but Avill merely give an
outline of the conclusions at Avhich I have arrived. He must
be a dull man Avho can examine the exquisite structure of a
comb, so beautifully adapted to its end, without enthusiastic
admiration. We hear from mathematicians that bees have
jiractically solved a recondite ]irobk'm, and have made their
cells of the proper shape to hold the greatest possible amount
of hone}', with the least possible consumption of precious Avax
in their construction. It has been remarked that a skilful Avork-
man Avith fitting tools and measures, Avould find it very difficult
to make cells of Avax of the true form, though this is jierfectly
elTected by a croAvd of bees Avorking in a dark hive. Granting
whatever instincts you please, it seems at first quite inconceiv-
able how they can make all the necessary angles and planes,
or even perceive Avhen they are correctly made. But the dilli-

OiiAP. VII. CELL-MAKING INSTINCT. 217

culty is not nearly so great as it at first appears : all this beau-
tiful work can be shown, I think, to follow from a few simple
instincts.

I was led to investigate this subject by INIr. Waterhoiisc,
who hasshown that the form of the cell stands in close relation
to the presence of adjoining cells ; and the following view may,
perhaps, be considered only as a modilicalion of his theory :
let us look to the great priucijile of gradation, and see Avhether
Nature does not reveal to us licr method of woik. At one end
of a .short series we have huiuble-l)ees, which use their old
cocoons to hold honey, soinctiTucs adding to them short tubes
of wax, and liUewi.s<; making separate and very iiTCgular rounded
cells of wax. At the other end (if the series Ave have the cells
of the hive-bee, jilaced in a doiil)le la^-er: each cell, as is well
known, is an hexagonal prism, with the basal edges of its six
sides bevelled so as to lit on to a pj-ramid, formed 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 simpli-
city of those of the humble-bee, we have the cells of the Mexi-
can ^lelipona domestica, carefully described and figured by
Pierre Iluber. llie I\Ielipona itself is intermediate in structure
between the hive and humble bee, but more nearly related to
the latter; it forms a nearly regular waxen comb of cylindrical
cells, in which the young are hatched, and, in addition, some
large cells of wax for holding honey. These latter cells ai'e
nearly spherical and of nearly equal sizes, and are aggregated
into an irregular mass. Ikit the important point to notice is,
that these cells are always made at that degree of nearness to
each other, that they v>ould have intersected or broken into
each other, if the spheres had been completed ; but this is never
permitted, the bees building pel-fectly Hat walls of wax between
the spheres which thus tend to intersect. Hence each cell con-
sists of an outer spherical portion, and of two, three, or more
perfectly 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 arc
united into a p}Tamid ; and this pyramid, as Huber has re-
marked, is manifestlv a gross imitation of the three-sid(Ml jiyram-
'dal baseji of th(> cell of the liivc'liee. As in the fells of the
10

218 SPECIAL INSTINCTS. Chap. VII.

hive-bee, so licre, the three plane surfaces in anyone cell neces-
sarily enter into the construction of three adjoining cells. It
is obvious that the Meli])ona saves wax, and, what is more im-
portant, lal)or, by this manner of buildinjr; for the Hat walls
between the adjoining cells are not double, but are of the Siune
thickness as the outer spherical portions, and yet each flat por-
tion forms a part of two cells.

Rc^flecting 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 erjnal sizes, and had arranged
them s^-nnnetrically in a double layer, the resulting structure
would probably have been as perfect as the comb of the hive-
bee. Accordingly, I wrote to Prof. Miller, of Cambridge, and
this geometer has kindly read over the following statement,
drawn up from his information, and tells me that it is strictly
correct :

If a number of equal spheres be described with their centres
placed in two parallel layers, with the centre of each sphere at
the distance of radius X 1^ 2, or radius X 1.414:'21 (or at some
lesser distance), from the centres of the six surrounding spheres
in the same layer; and at the same distance from the centres
of the adjoining spheres in the other and parallel layer ; then,
if planes of intersection between the several spheres in both
layers be formed, there will result a double layer of hexagonal
prisms united together by pyramidal bases formed of three
rhombs ; and the rhombs and the sides of the hexagonal prisms
will have every angle identically the same with the best meas-
urements Avhich have been made of the cells of the hive-bee.
But I hear from Prof. Wyman, who has made numerous care-
ful measurements, that the accuracy of the workmanship of the
bee has been greatly exaggerated ; so much so, that, as he adds,
whatever the typical form of the cell may be, it is rarely, if
ever, realized.

Hence, we may safely conclude that, if Ave could slightly
modify the instincts already possessed by the Melipona, and in
themselves not very wonderful, this bee would make a structure
as wonderfully perfect as that of the hive-bee. "We must sup-
pose the Melipona to have the power of forming her cells truly
spherical, and of equal sizes ; and this would not be very sur-
prising, seeing that she already does so to a certain extent, and
seeing what perfectly cvlindrical burrows in wood many insects
can make, apparently by turning round on a fixed jioint. AVc
must suppose the Melipona (o arrange her cells in level layers,

Chap. VII. CELL-MAKING INSTINCT. 219

as she already does her cylindrical cells ; and wc uiiist further
suppose, and this is the greatest difliculty, that she can some-
how 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 alwa3-s
describes her spheres so as to intersect largely ; and then she
unites tlie points of intersection by perfectly flat surfaces.
We have further to suppose, but this is no difficulty, that after
hexagonal ])risnis have been formed by the intersection of ad-
joining spheres in the same layer, she can jirolong the hexagon
to any length requisite to hold the stock of hone}*; in the same
way as the rude humble-bee adds cylinders of wax to the circu-
lar mouths of her old cocoons, ]5y such modifications of in-
stincts, in themselves not very wonderful — hardly more wonder-
ful than those which guide a bird to make its nest — I believe
tluit 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 jierfectly true or parts of a sphere, and of about the
diameter of a cell. It was most interesting to me 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 tlie time the basins had acquired the above-
stated width (i. e., about the width of an ordinary cell), and
were in d<^pth about one-sixth of the diameter of the sphere of
M'hiih they formed a part, the rims of the Ixisins intersected or
broke into each other. As soon as this occurred, the bees
ceased to excavate, and began to build up flat walls of wax on
the lines of intersection between the basins, so that each hex-
agonal prism was built upon the scalloped edge of a smooth
l)asin, instead of on the straight edges of a three-sided pyramid
as in the case of ordinary cells.

I then put into the hive, instead of a thick, rectangular
\)\cce of wax, a thin and narrow, knife-edged ridge, colored
with vermilion. The bees instantlv began on both sides to ex-
cavate little basins near to each other, in the same way as be-
fore; 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 tlio

220 SPECIAL INSTINCTS. Cuap. VII.

former experiment, would liavc broken into eacli otlier from
the opposite sides. The bees, liowcver, did not sufl'er 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 bottoms with flat sides ; and these flat sides,
formed by little thin plates of the vermilion wax left un-
p^nawed, were situated, as far as the eye could judge, exactly
along the planes of imaginary intersection between the basins
on tiie opposite sides of the ridge of wax. In some parts, only
small portions, in other parts, large portions of a rhombic jilate
had been left between the opposed basins ; but the work, from
the mmatural 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 vennilion wax, in order to have thus suc-
ceeded in leaving flat plates between the basins, by stopping
work at the jilanes of intersection.

Considering how flexible thin wax is, I do not see that
there is any dilficulty 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 then stopping their work.
In ordinarv combs it has appeared 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-commenced cell, which were slightly concave
on one side, where I suppose that the bees had excavated too
quickly, and convex on the opposed side where the bees had
■worked less quickly. In one well-marked instance, I jiut the
coml) back into the hive, and allowed the bees to go on work-
ing for a sliort time, and again examined the cell, and I found
that the rhombic plate had been completed, and had become
pcrfectli/ JJat : i^ was absolutely impossil)le, from the extreme
thinness of the little plate, that they could have effected this
by gnawing away the convex side ; and I suspect that the bees
in such cases stand on opposite sides and push and bend the
ductile and warm -wax (which, as I have tried, is easily done)
into its ])roper intermediate plane, and thus flatten it.

From the experiment of the ridge of vermilion wax we can
Bee that, if the bees were to build for themselves a thin wall
of wax, they could make their cells of the proper shape, by
standing at the proper distance from each other, by excavat-
ing at the same rate, and by endeavoring to make equal spheri-
cal hollows, but never allowing the s])hcres to break into each

CuAP. VII. CELL-MAKING INSTINCT. 221

other. Now bees, as may be clearly seen hy examining' the
od^e of a ^rowinp^ comb, do make a roug'li, circumferential
^vall or rim all round the com)) ; and they g'liaw this away from
the op])()sitc sides, always workinj]^ 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 tliat one rhom-
bic plate Avhich stands on the extreme growing marg-in, or the
two plates, as the case may be ; and th(>y never complete the
upper edges of the rhoml)ic plates, until the hexagonal walls
are comnifmced. Some of these statements dilTer from those
made by the justly-celebrated elder Uuber, but I am convinced
of their accuracy ; and, if I had space, I could show that they
are conformable with my theory.

Huber's statement, that the very first cell is excavated ouJ
of a little parallel-sided wall of wax, is not, as far as I liavo
seen, strictly correct ; the first commencement ha^'ing always
bben a little hood of wax ; but I will not here enter on these
details. We see how important a part excavation plays in the
construction of the cells ; but it would be a gn^at error to sup-
pose that the bees cannot l)uild up a rough Avail of M'ax in the
proper position — that is, along the plane of intersection be-
tween two adjoining si)heres. I have several specimens show-
ing clearly that they can do this. Even in the rude circum-
ferential rim or wall of wax round a growing comb, flexures
may sometimes be observed, corresponding 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 ofl", l)y 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.
\\^o shall understand how they work, by supposing masons first
to pile up a broad ridge of cement, and then to Ix^gin cutting
it away erjually on l)()th 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 sum-
mit of tilt; ridge. "We shall thus have a thin wall steadily
growing upward but always crowned by a gigantic coping.
From all tlu; cells, both those just commenced and those com-
pleted, Ijcing tluis crowned by a strong coping of wax, the
bees can cluster and crawl over the comb without injuring the
delicate hexagonal walls. These walls, as Prof. Miller has
kindly ascertained for me, vary greatly in thickness ; being,

222 SPECIAL INSTINCTS. Cuap. VII.

on an average of twelve measurements made near tlie border
of tlic comb, Tp^ of an inch in thickness ; whereas the basal
rhomboidal plates are thicker nearly in the proportion of three
to two, having a mean tliickness, from twenty-one measure
mcnts, of -rAs of an inch, liy the above singular maimer of
building, strength is continually given to the coml), 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 work to-
gether ; one bee after Avorking a sliort time at one cell going
to another, so that, as Hubcr has stated, a score of individuals
work even at the commencement of the first cell. I was able
practicall}'" to show this fact, by covering the edges of tlie hex-
agonal walls of a single cell, or the extreme margin of the cir-
cumferential rim of a growing comb, with an extremely thin
layer of melted vermilion wax ; and I invariably found that the
color was most delicately difiused by tlie bees — as delicately
as a painter could have done with his brush — by atoms of the
colored wax having been taken from the spot on which it had
been placed, and Avorked into the growing edges of the cells
all round. The Avork of construction seems to be a sort of
balance struck between many bees, all instinctively standing
at the same relative distance from each other, all trying to
SAveep equal spheres, and tlien building up, or leaving un-
gnaAved, the planes of intersection betAveen these spheres. It
was really curious to note in cases of difficulty, as Avhen two
pieces of comb met at an angle, hoAV often the bees Avould pull
down and rebuild in different ways the same cell, sometimes
recurring to a shaj^e which they had at first rejected.

When bees haA'e a place on Avhich they can starid in their
proper positions for Avorking — for instance, on a slip of Avood,
placed directly under the middle of a comb groAving doAvnAvard
so that the comb has to be built OA'er one face of the slip — in
this case the bees can lay the foundations of one Avail of a ncAV
hexagon, in its strictly proper place, projecting beyond the
other com])leted cells. It suffices that the bees should be en-
al)led to stand at their proper relative distances from each
other and from the A\-alls of the last completed cells, and then,
by striking imaginary spheres, they can build up a Avail inter-
mediate betAveen tAvo adjoining s])heres ; but, as far as I have
seen, they ncAxr gnaw aA\-ay 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 doAvn under ccr-

CiiAP. VII. rELL-MAKINO INSTLXCT. 223

tain circumsluuccs a rough wall in its proper place l>elwccn two
just-commenced cells, is important, as it bears on a fact, which
seems at first quite subversive of the foregoing theory ; namely,
that the cells on the extreme margin of Avasp-combs are some-
times strictly hexagonal ; but I have not space here to enter
on this subject Nor does there seem to me any great difii-
culty in a single insect (as in the case of a queen-wasp) making
hexagonal cells, if she were to work alternately on the inside
and outside of two or three cells commenced at the same time,
always standing at the proper relative distance from the parts
of the cells just Ix^guji, sweeping spheres or cylinders, and
building up intermediate planes.

As natural selection acts only by the accumulation of slight
modificiitions of structure or instinct, each profitable to the
individual under its conditions of life, it may reasonably be
asked, how a long and graduated succession of motlified archi-
tectural instincts, all tending toward the prcsent perfect plan
of construction, could have profited the progenitoi-s of the hive-
bee ? I think the answer is not diflicult: cells 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 experi-
mentally proved that from twelve to fifteen poimds of dry
sugar arc consumed by a liive of bees for the secretion of each
pound of wax; so that a prodigious quantity of fluid nectar
nmst be collected and consumed by the bees in a hive for the
secretion of the wax necessary for the construction of their
combs. Moreover, many bees have to remain idle for many
days during the jirocess of secretion. A large store of honey
is indispensable to support a largt; 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 col-
lecting the honey must be an important element of success to
any family of bees. Of course, the success of the species ma\-
be dependent on the number of its enemies, or parasites, or on
(juite distinct caiuses, and so be altogether independent of the
quantity of honey which the bees could collect. But let us
suppose that this latter circumstance determined, as it proba-
bly often has determined, whether a bee allied to our liumble-
bces could exist in large nuinbere in any country ; and let us

224 SPECIAL INSTINCTS. Chap. VII,

further suppose lliat tlie community lived tlirou;^h 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 imagi-
nary humble-bee, if a slight modification in her instincts led
her to make her waxen cells near together, so as to intci*sect ;•-
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 to-
gether, and aggregated into a mass, like the cells of the Jleli-
])ona ; 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 Avould bo saved. Again, from the same cause,
it Avould 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 sjiherical sm-
faces would wholly disappear and be replaced by plane sur-
faces ; and the Melipona Avould make a comb as perfect as that
of the hive-bee. Beyond this stage of perfection in architect-
ure, 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 v.'onderful of all known in-
stincts, that of the hive-bee, can be explained by natural selec-
tion having taken advantsige of numerous, successive, sUght
modifications of simpler instincts; natural selection having, by
slow degrees, more and more perfectly led the bees to sweej)
etjual 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 particular distance from each
other, than they know what are the several angles of the
hexagonal prisms and of tlie basal rhombic plates ; the motive
jiower of tlie process of natural selection having been the con-
struction of cells of due strength and of the proper size and
shape for tlie larv.o?, this being etlected Avith the greatest pos-
sible economy of labor and Avax ; that individual swarm which
thus made tlie best cells with least lalior, and least waste of
honey in tlie secretion of wax, having succeeded best, and liav-
ing transmitted by inheritance their newly-acquired economical
instincts to new swarms, which in their turn will have had tho
best chance of succeeding in the struggle for existence.

CiiAi-. VII. OBJECTIONS TO NATDKAL SELECTION. 225

Objectiojis to the Tlicory of Natural Selection as cq^plied to
Instincts y' Axuter and Sterile Insects.

It has been objected to the foregoing view of the origin of
instincts that " the variations of structure and of instinct must
have been simultaneous and accurately adjusted to each other,
as a modification in the one without an immediate corre-
sponding change in the other Avould have been fatal." The
force of this olijection rests entirely on the assumption that the
changes in both instinct and structure are abrupt. To take as
an illustration the case of the larger titmouse (Parus major) al-
luded to in the last chapter : this l)ird often holds the seeds of
the yew between its feet on a branch, and hannners away till
it gets into the kernel. Now what special diiliculty would
there be in natural selection preserving all the slight individ-
ual variations in the shape of the beak, Avhich were better and
better adapted to break ojien 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 sponta-
neous 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, subsequently to, but in accordance
with, slowly-changing habits or taste ; but let the feet of the
titmouse vary and grow larger from correlation with tlie beak,
or from any other imknown 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
jwwer of the nuthatch. In this case a gradual change of struct-
ure 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. iSoine birds build their nests
of nnid, 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 selec-
tion of individual swifts, wliich secreted more and more saliva,
should at last produce a species with instincts leading it to
neglect other matc^rials^ and to make its nest exclusively of
inspissated saliva? And so in other cases. It must, however,
be admitted tliat in many instances we cannot conjecture
whetlier it was instinct or structure which first varied.

No doubt many instincts of very dillicult explanation could

226 OBJECTIONS TO THE THEOICY CriAP. VII.

be 0])poscJ to tlic theory of natunil selection — cases, in -which
Ave cannot sec how an instinct could ])ossibly liave originated;
cases, in ■which no intermediate gradations arc known to exist ;
cases of instinct of such trifling importance, that they could
hardly have been acted on by natural selection ; cases of in-
stincts 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 independently acciuircd through natural
selection. I will not here enter on these several cases, but
will confine myself to one special difficulty, which at first ap-
jieared to me insuperable, and actuall}' 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 Avill here take only a single case, that of working or
sterile ants. Hoav the workers have been rendered sterile is a
difriculty : but not much greater than that of any other strik-
ing modification of structure ; for it can be shown that some
insects and other articulate animals in a state of nature occa-
sionally become sterile ; and if such insects had been social,
and it had been profitable to the community that a numl^er
should have been annually born capable of work, but incapable
of procreation, I can see no especial difficulty in this having
been efT(M'ted through natural selection. But I must pass over
this preliminary difficulty. The great difiiculty 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 sometimes of eyes, and in in-
stinct. As far as instinct alone is concerned, the Avonderful
difference in this respect between the Avorkers and the perfect
females, would have been better exemplified by the hive-bee.
If a working ant or other neuter insect had been an ordinary
animal, 1 should have mihesitatingly assumed that all its char-
acters had been slowly acquired through natural selection ;
namely, by individuals having been born with slight profitable
modifications, which were inherited by -the offspring; and that
these again varied and again were selected, and so onward.
But with the Avorking ant we have an insect differing greatly
from its parents, yet. absolutely sterile ; so that it could never
have transmitted successively-acquired modifications of struct-

Chap. VII. OF NATURAL SELECTION. 227

lire or instinct to its proc^ony. It may well be asked how is
it possible to reconcile this case with the theory of natural
selection ?

First, let it be remembered that wc have innumeral)le in-
stances, both in our domestic productions and in those in a
state of nature, of all sorts of differences of inherited structure
which are correlated with certain ages, and with either sex.
We have differences correlated not only Avith one sex, but
with that short period when the reproductive system is active,
as in the nuptial plumage of many birds, and in the hooked
jaws of the male salmon. We have even slight differences in
the horns of diQ'erent breeds of cattle in relation to an artifi-
cially imperfect state of the male sex ; for oxen of certain
breeds have longer horns than tlie oxen of other breeds, rela-
tively to the h'ugth of the horns in both the bulls and cows of
these same breeds. Hence I can see no great difficulty in any
character becoming correlated 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.

Tliis dilficulty, though ajipearing insuperable, is lessened,
' or, as I believe, disajjpears, when it is remembered that selec-
tion may l)e applied to the family, as well as to the individual,
and may thus gain the desired end. Thus, breeders of cattle
wish the flesh and fat to be well marbled together ; the animal
has been slaughtered, but the breeder has gone witli confidence
to the same stock and has succeeded. Such faith may be
placed in the power of selection, that probably a breed of
cattle, always yielding oxen Avith extraordinarily long horns,
could be slowly formed by carefully Avatching Avhich individual
bulls and cows, Avhen matched, produced oxen Avith the longest
horns ; and yet no one ox Avould ever have propagated its
kind. Here is a better and real illustration : according to M.
Vcrlot, some varieties of the double annual stock of various
colors, from having been long carefully selected to the right
degree, always produce by seed a large projinrtion of plants
l)earing double andf|nite sterile floAvers ; so that, if the A'ariety
had not likewise yielded others, it Avould at once have become
extinct; but it always yields some single and fertile plants,
Avhich differ from ordinary single A'arieties only in their power
of producing the two forms. Thus the fertile plants producing
single flowers may be compared Avith the males and females of
an ant-comnumity, and the sterile double-flowered plants, Aviiich

228 OBJECTIONS TO THE THEOKY Chap. VII.

arc rcg'ularly produced in l:ir^e numbers, with tlu; iiKiny st4?rilo
neuters of the same coininunity. Thus I l>elieve it has been
"vvith social insects : a slij^ht modification of structure, or of in-
stinct, correlated with tlic sterile condition of certain members
of the conmiunity, has been advantageous to the community:
consequently the fertile males and females of tlie same cona-
munity flourished, and transmitted to their fertile ofl'sprinfr^ a
tendency to produce sterile members having the same modifi-
cation. And I believe that this process has been repeated,
luitil that prodigious amount of difference between the fertile
and sterile females of the same species has been produced,
which wo see m so many social insects.

But we have not as yet touched on the climax of the difE-
culty : 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. Tiie castes, moreover,
do not generally 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, wnth jaws and instincts extraordinarily difi'ercnt : in
Cryptocerus, the workers of one caste alone carry a wonderful
sort of shield on their heads, the use of which is quite imknown :
in the Mexican JMyrmecocystus, 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 se-
cretes 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 con-
fidence in the principle of natural selection, when I do not ad-
mit that such wonderful and Avell-established facts at once an-
jiiliilate 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 in the same nest, but in some few alone ;
and that by the survival of the communities with females which
])r()(lure most neuters having the advantageous modification, all
the neuters ultimately come to be thus characterized. Accord-
ing to this view, Ave ought occasionally to find in the same nest

CuAr. YII. OF NATURAL SELECTION. 229

neuter insects, presenting gradations of structure ; and this we
do find, even frcquenth'-, considering liow few neuter insects
out of Europe have been carefully examined, ^[r. F. JSinith
lias shown that the neuters of several British ants differ sur-
])risingly from each other in size, and sometimes in color ; and
that the extreme forms can be linked together by individuals
taken out of the sanu; nest ; I have myself compared j^erfect
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 interme-
diate 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 workere
have simj)lc eyes (ocelli), which though small can be plainly
distinguished, whereas the smaller workers have their ocelli
rudimentary. IlaWng carefully dissected several specimens ot
these workers, I can affirm that the eyes are far more rudimen-
tary in the smaller workers than can be accounted for merely
by their proportionally lesser size ; and I fully believe, though
I dare not assert so positively, that the workers of intermediate
size have their ocelli in an exactly intermediate condition. So
that here we have two bodies of sterile workers in the same
nest, differing not only in size, but in their organs of vision, yet
conn(^cted by some few members in an intermediate condition.
I may digress by adding, that if the smaller Avorkers had been
the most useful to the community, and those males and females
had been continually selected, which produced more and more
of the smaller workers, until all the workers were in this condi-
tion, we should then have had a species of ant with neuters
nearly in the same condition with those of Mynnica. For the
workers of Mynnica have not even rudiments of ocelli, though
the male and female ants of this genus have Avcll-develoi)ed
ocelli.

I may give one other case : so confidently did I expect to find
gradations in important points of structure between the differ-
ent castes of neuters in the same species, that I glaiUy availed
myself of Mr. F. Smith's offer of numerous specimens from the
same? nest of tlie driver-ant (Aiiomma) of West Africa. The
reader will peihajis best a]i])reciate the amount of difference in
these workers, by my giving not the actual measurements, but
a strictly aecurate illustration : the difference was the same as
if we were to sec a set of workmen building a house, of whom
many were five feet four inches high, and many sixteen feet

230 OBJECTIONS TO THE TIIEOPwY Chap. VII.

high ; but wc must suppose that the larger workmen had heads
four instead of three times as l:)ig 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 f(^r us is, that, though the workers can be grouped into castes
of different 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 draw-
ings for me, with the camera lucida, of the jaws which I dis-
sected from the workers of the several sizes. Mr. Bates, in his
most interesting "Naturalist on the Amazons," has described
analogous cases.

With these facts before me, I believe that natural selection,
by acting on the fertile ants or parents, could form a species
which should regularly produce neuters, either all of large size
with one form of jaw, or all of small size M-ith jaws having a
Avidely-different structure; or lastl}^, and this is the clima.x of
dilliculty, one set of workers of one size and structure, and at
the same time 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 com[)lcx 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, as I believe, the wonderful fact
of two distinctly-defined castes of sterile workers existing in
the same nest, both widely different from each other and from
their parents, has originated. We can see how useful their
production niay have been to a social comnnmity of ants, on
the same, principle that the division of labor is useful to civil-
ized man. Ants, however, work by inherited instincts and by
inherited organs or tools, while man works by acquired knowl-
edge and manufactured instruments. But I must confess, that,
Avith all my faith in natural selection, I should never have an-
ticipated tiiat this principle could have been efficient in so high
a degree, had not the case of these neuter insects convinced me

Chap. VII. OF NATURAL SELECTION. 231

of the fact. I have, therefore, discussed this case, at some little
but wholly insuniciout length, in order to show tlio power of nat-
ural selection, and likewise because this is by far the most serious
special dillieulty which my theory has encountered. The case,
also, is very intercstinir, as it proves that with animals, as with
plants, any amount of modification may be cUc'cted ])y the ac-
cumulation o( numerous, slight, spontaneous variations, which
are in any way jirolitable, without exercise or hal)it havini^
been brouf^ht into play. For peculiar hal^its confined to the
workers or sterile females, however long they mif^ht be fol-
lowed, could not possibly affect the males and fertUe female,
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 inherited habit, as advanced
by Lamarck.

iSummari/.

I have endeavored in this chapter briefly to show that the
mental qualities of our domestic animals vary, and that the vari-
ations are inlierited. Still more briefly I have attempted to show
that instincts A'ary slightly in a state of nature. No one will
dispute that instincts are of the highest importance to each
animal. Therefore there is no real diiliculty, under changing
conditions of life, in natural selection accumulating to any ex-
tent slight modifications of instinct which are in any way use-
ful. In some cases habit or use, and disuse, have proliably come
into play. I do not pretend that the facts given in this chapter
strengthen in any great degree my theory ; but none of the
cases of diiliculty, to the best of my judgment, annihilate it.
On the other hand, the fact that instincts are not always ab-
solutely perfect, and are liable to'mistakes ; that no instinct
can be shown to have been produced for the good of other
animals, tliough animals take advantage of the instincts of
others; that tlie canon in natural history of " Natura non facit
saltuin,"isap]ili(able to instincts as well as to corporeal struct-
ure, 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 considerably diffcM-ent conditions of
lifCj yet often retaining nearly the same instincts. For instance,

232 SUMMARy. Chap. VII.

we can understand, on the principle of inheritance, how it is
that the thrush of tropical South America hues its nest -with
mud, in the same peculiar manner as docs our British thrush :
how it is that the liornbills 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
plaster throug-h Avhich the males feed them and the young
Avhen 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 lnrva3 of ichneumonidas feeding within the
live bodies of caterj:)illars — not as specially endowed or created
instincts, but as small consequences of one general laAV, lead-
ing to the advancement of all organic beings — namely, multi-
ply, vary, let the strongest live and the weakest die.

Ci:\v. Vlil. lIYBiaDISM. 23J

CHAPTER VIII.

IIYBKIDISM.

Distinction Ijctwpon the Stcrilifir of First CropfCF and of Hybrids— Slorilil.v various
in JX'iXTCf, nut uiiivtM>jil. all'i'ctcd l)y cIojji! Interbrccdincr, removed by Domesti-
cation—Lawf LTovi'miiiL,' llie Sterility of Hybrids— Sterility not a special Endow-
ment, bat incidental on oilier DilTerences, not accnmiilated by Natural Selection
— Causes of the Sterility f)f First Crosses and of Hybrids— i'urallilisrn between
llie Ell'ectrt of Clianjred Conditions of Life and of Crossin;,'— Diinnrnldsm and

, Triuiorpliism — Fertility of Varieties when crossed and of their Monjirel Ollsprinij
not universal— Hybrids and Mongrels compared independently of tlicir Fertility
—Summary.

The view generally entertained by naturalists is that
species, when intercrossed, have been specially endowed witli
sterility, in order to prevent their confusion. This view cer-
tainly seems at first hifi;hly pro])able, for s])ecies within the
same country 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 tlieir hybrid offspring, cannot
have been acquired by the continued preservation of successive,
]irolit:d)lc degrees of sterility. It is, as I hope to show, inci-
dental on differences in tlie reproductive system of the jiarciit-
spceics, and is not cither a specially acquired or endoAVcd
quality.

In treating this subject, two classes of facts, to a large ex-
tent fundamentally different, have generally been confounded
together ; namely, the sterility of two species when first crossed,
antl 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 offs])ring. Hybrids, on the other hand, have their
reproductive organs functionally impotent, as may ])e dearly
seen in the; statt; of the malt; element in both ])hints and ani-
mals ; though the formative; organs themselves are perfect in
structure, as far as the microscope reveals. In the first case
the two sexual elements which go to form the embryo are per-

234 DEGKEES OF STERILITY. Chap. YIII.

feet ; 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 probably has been
slurred over, owiniii; to the sterility in botli cases being' looked
on as. a special endowment, Ijoyond the province of our reason-
ing powers.

The fertility of vaiietics, that is of the forms known or be-
lieved to have descended from common parents, when inter-
crossed, and likewise the fertility of their mongrel offspring, is,
with reference to my theory, of equal importance with the
sterility of species ; for it seems to make a broad and clear dis-
tinction between varieties and species.

Defjrees of Sterility. — First, for the sterility of species when
crossed and of their hybrid offspring. It is impossible to study
the several memoirs and works of those two conscientious and
admirable observers, Kolrcuter and Gartner, who almost de-
voted their lives to this subject, without being deeply im-
pressed with the high generality of some degree of steriUty.
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 un-
hesitatingly ranks them as varieties. Gartner, also, makes the
rule equally universal ; and he disputes the entire fertility of
Kolrcuter'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 off-
spring, with the average number produced by both pure par-
ent-species in a state of nature, lint a serious cause of error
seems to me to be here introduced : a plant, to be hybridized,
nuist be castrated, and Avhat is often more imjiortant, must be
secluded in order to prevent pollen being brought to it by in-
sects from other plants. Nearly all the plants experimented
on by Gartner 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 Giirtner gives in his table
about a score of cases of plants Avhich he castrated, and arti-
ficially fertilized with their own pollen, and (excluding all cases
such as the Leguminosa', in which there is an acknowledged
difliculty in the manipidation) half of these twenty plants had
their fertility in some degree impaired. Moreover, as Giirlncr

Chap. VIII. DEGREES OF STERILITY. 235

ropcalcdly cnissed some forms, such as the common red and
blue pimpernels (Anagallis arvensis and ccerulea), wliicli the
best botanists rank as varieties, and found them absolutely
sterile, -sve may doubt whether many species are really so ster-
ile, when intercrossed, as he believed.

It is certain, on the one hand, that the sterility of various
species "when crossed is so dilferent in deg'ree and graduates
away so insensibly, and, on the other hand, that the fertility
of pure sjiecies is so easily aflected by various circumstances,
that for all practical purposes it is most difficult to say where
perfect fertility ends and sterility begins. I think no better
evidence of this can be required than that the two most ex-
perienced observers who have ever lived, namely, Kolrcuter
and Gartner, should luivc arrived at diametrically opposite con-
clusions in regard to the very same species. It is also most
instructive to compare — but I have not space here to enter on
details — the evidence advanced by our best botanists on the
question whether certain doubtful forms should be ranked as
species or varieties, with the evidence from fertility adduced
by different hybridizers, or by the same author, from ex])eri-
ments made during different years. It can thus be shown that
neither sterility nor fertility alfords any clear distinction ];c-
tween species and varieties; but tliat the evidence from this
source graduates away, and is doubtful in the same degree as
is the evidence derived from other constitutional and structural
differences.

In regard to the sterility of hybrids in successive generations;
though Giirtner was enabled to rear some hybrids, carefully
guarding them from a cross with either pure parent, for six or
seven, and in one case for ten generations, yet he asserts posi-
tively that their fertility never increased, but generally de-
creased greatly and suddenly. With respect 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 oiTspring; and both sexual ele-
ments in hyljritl ])lants are already allected in some degree.
15ut I believe in nearly all these cases, that the fertility has
been diminished by an independent cause, namely, by too close
interbreeding. I have collected so large a body of facts, show-
ing on the one liand 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 clc>8e interbreeding
lessons their vigor and fcrtihty, that I must admit the correct-

23G DEGREES OF STERILITY. Cu.vp. VIII.

ness of this almost universal belief among breeders. Hybrids
are seldom raised b}-- experimentalists in great numl)ers ; and
as the parent-species, or other allied hybrids, generally grow
in the same garden, the visits of insects must be carefully pre-
vented during the ilowering season: hence hyljrids will gener-
ally have to be fertilized during each generation by their own
individual pollen ; and this would probably be injurious to their
fertility, already lessened by their hybrid origin. I am strength-
ened in this conviction by a remarkable statement repeatedly
made by Giirtner, namely, that if even the less fertile hybrids
be artilicially fertilized with hybrid pollen of the same kind,
tlieir fertility, notwithstanding the frequent ill elFects from
manipulation, sometimes decidedly increases, and goes on in-
creasing. Now, in the process of ai'tilicial fertilization, pollen
is as often taken by chance (as I know from my own experi-
vncc) from the anthers of another tlower, as from the anthers
of the tlower itself which is to be fertilized ; so that a cross be-
tween two flowers, though probably often on the same plant,
would be thus etfected. Moreover, whenever complicated ex-
jieriments are in jirogress, so careful an observer as Gartner
would have castrated his hybrids, and this wovdd have insured
in each generation a cross with pollen from a distinct tlower,
either from the same plant or from another plant of the same
hj'brid nature. And thus the strange fact of an increase of
fertility in the successive generations of art tficicdhf -fertilized
hylirids, in contrast Avith those spontaneously self-fertilized,
may, as I believe, be accounted for by too close interbreeding
having been avoided.

Now let us turn to the results arrived at l)y a third most
experienced hybridizer, namely, the Hon. and Rev. W. Herbert.
He is as emphatic in his conclusion that some hybrids are per-
fectly fertile — as fertile as the pure parent-species — as are Kiil-
rcuter and Gartner that some degree of sterility between dis-
tinct species is a imiversal law of Nature. He experimented
on some of the very same species as did Gartner, The diflVr-
ence in their results may, I think, be in part accounted for by
Herliert's great horticultural skill, and by his having hot-houses
at his command. Of his many important statements I will here
give only a single one as an examjile, namcdy, that " every
ovule in a pod of Crinum capense fertilized by C. revolutuni
])roduced a plant, which I never saw to occur in a case of its
natural fecundation." So that here wc have perfect, or even
more than commonly perfect, fertility in a first cross between
two distinct species.

Chap. VIII. DEGREES OF STEKILITY. 237

This case of tlie Crinum leads me to refer to a singular fact,
namely, that individual plants of certain species of Lobelia,
Vcrbascuni, and Passillora, can easily be fertilized by pollen
from a distinct species, but not by pollen from the same; plant,
though this pollen can be proved to l)e perfectly sound by fer-
tilizing other plants or species. In the genus llippeastrum, in
Corydalis as shown by Prof. Hildebrand, in various orchids as
shown by Mr. Scott and Fritz Mliller, all the individuals are in
this })eculiar 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 jiollen from the same individual plant ! To
give one instance, a bulb of llippeastrum aulicum produced four
flowers ; three were ferlilizod by Herbert with their own pollen,
and the fourth was subsequently fertilized by the pollen of a
compound hybrid descended from three distinct species: the
result was, that " the ovaries of the first three flowers soon
ceased to grow, and after a few days perished entirely, whereas
the pod impregnated by the pollen of the hybrid made vigorous
growth and rapid progress to maturity, and bore good seed,
which vegetated freely." Mr. Herbert tried similar experi-
ments during many y(iars, and always with the same result.
With those plants in which certain individuals alone fail to be
fertilized by their own pollen, though thej^ appear cjuite healthy
and although both ovules and pollen are perfectly good with
reference to other species, yet they must be in some way in an
unnatural condition. Tliese cases serve to show on what slight
and mysterious causes the lesser or greater fertility of a species
sometimes depends.

The practical experiments of horticulturists, though not
made with scientific ])recision, deserve some notice. It is no-
torious in how complicated a manner the species of Pelargo-
nium, Fuchsia, Calceolaria, Petunia, Rhododendron, etc., have
been crossed, yet many of these hybrids seed freely. For in-
stance, Herbert asserts that a hybrid from Calceolaria integri-
folia and jilanlaginea, species most widely dissimilar in general
habit, "reproduced itself as perfectly as if it had been a natu-
ral species from the mountains of Chili." I have taken some
pains to ascertain the degree of fertility of some of the complex
crosses of Khod(jdendrons, and I am assured that many of thcrn
are perfectly fertile. Mr. C. Noble, for instance, informs mc
that he raises stocks for grafting from a hvbrid between Rhod.
Poiifieiiin and Catawbiense, and that this hybrid "seeds as

238 DEGREES OF STEKILITY. Chat. VIII.

freely as it is possible to imac^ine." Had liybrids, when fairly
treated, always p^ono on decreasing in fertility in each succes-
sive generation, as Gartner believed to be the case, the fact
would have been notorious to nursery-men. Horticulturists
raise large beds of the same hybrids, and such alone are fairly
treated, for by insect-agency the several individuals of the
same hybrid variety are allowed to freely cross with each other,
and the injurious influence of close interbreeding is thus ]irc-
vented. Any one may readily convince himself of the eih-
ciency of insect-agency by examining the lloAvers of the more
sterile kinds of hybrid Rhododendrons, which produce no pol-
len, 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 jilants. If our systematic arrange-
ments can be trusted, that is, if the genera of animals are as
distinct from each other as are the genera of plants, then we
may infer that animals more widely separated in the scale of
Nature can be more easily crossed than in the case of plants ;
l)ut the hybrids themselves are, I think, more sterile. 1 doubt
whether any case of a perfectly-fertile hybrid animal can be
considered as thoroughly well authenticated. It should, how-
ever, 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 Avith nine
other finches, but, as not one of these nine species breeds
freely in confinement, we have no right to expect that the first
crosses between them and the canary, or that their Inbrids,
should be perfectly fertile. Again, with resjiect to the fertility
in successive generations of the more fertile hybrid animals,
1 hardly know of an instance in which two fiimilies of the same
hyl>rid have been raised at the same time from difierent par-
ents, so as to avoid the ill-effects of close interbreeding. On
the contrary, brothers and sisters have usually been crossed
in each STiccessive generation, in opposition to the constantly-
repeated admonition of every breeder. And in this case, it is
not at all surprising that the inherent sterility in the hybrids
should have gone on increasing. If we were to act thus, and
pair brothers and sisters in the case of any pure animal, which
from any cause had the least tendency to sterility, the breed
would assuredly be lost in a few generations.

Although I do not know of any thoroughly well-autlienli-
catcd cases of perfectly-fertile liybrid animals, I have reason to

Chap. Vlll. DEGREES OF STERILITY. 239

believe that tlio liyl)ri(ls from Cervulus vaginalis and Rccvesii,
and from Pliasianus colchicus with P. toniuatus, arc perfectly
fertile. It has lately been asserted in France, that two such
distinct species as the hare and the raljbit, Avhen they can be
|Tot to breed together, produce offspring, which are highly fer-
tile when crossed with one of the parent-species. The hybrids
from the common and Chinese geese (A. cygnoides), species
which are so dillerent that they are generally ranked in dis-
tinct genera, have often bred in this country with either pure
parent, and, in one single instance, they have bred inter se. This
was eifected by Mr. Eyton, who raised two hybrids from the
same parents, but from difVerent 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 emi-
nently-capable judges, namely, Mr. Blyth and Captain Hutton,
that whole flocks of these crossed geese are kept in various
parts of the country ; and as they are kept for profit, where
neither pure parent-species exists, they must certainly be high-
ly or perfectly fertile.

Tlie various races of each kind of domesticated animals are
quite fertile when crossed together ; yet in many cases they
are descended from two or more wild species. From this fact
wc must conclude either that the aboriginal parent-species
produced at first perfectly fertile hybrids, or that the hybrids
subsequently reared under domestication became quite fertile.
This latter alternative, which was first propounded by Pallas,
seems tlie most probable, and can, indeed, hardly be doubted.
It is, for instance, almost certain that our dogs are descended
from several wild stocks ; yet, witli perhaps the exception of
certain indigenous domestic dogs of South America, all are
quite fertile together; and anahigy makes me greatly doubt
whether the several aljoriginal species would at first have
freely bred together, and have produced quite fertile hybrids.
So, again, I have lately acquired decisive evidence tliat the
crossed offspring from the Indian humped and common cattle
are inter se perfectly fcrtih^; and from the observations by
Ililtimeyer on their important osteijlogical differences, as well
as from tliose by Mr. IJlytli on their differences in habits, voice,
constitution, etc., these two forms must be regarded as good
and distinct species as any in the world. According to this
view of the origin of many domestic animals, we must either
give up tlie belief of the almost universal sterility of distinct

240 LAWS GOVERNING THE STERILITY Chap. VIII.

species of animals when crossed ; or we must look at sterility,
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 univ'crsal.

Laics f/overnlng the Sterility of First Grosses and of Hybrids.

We will now consider a little more in detail the circum-
stances and rules governing the sterility of first crosses and of
hybrids. Our chief object will be to see whether or not the
rules indicate that species have specially been endowed with
this quality, in order to prevent their crossing and blending to-
gether in utter confusion. The following rules and conclusions
are chiefly drawn \\\) from Gartner's admirable work on the
hybridization of plants. I have taken much pains to ascertain
how far the rules apply to animals, and, considering how scanty
our knowledge is in regard to hybrid animals, I have been sur-
prised to find how generally the same rules apply to both king-
doms.

It has been already remarked, that the degree of fertilitj'',
both of first crosses and of hybrids, graduates from zero to per-
fect 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 ])lant 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 dilferent species of
the same genus applied to the stigma of some one of the
species, 3-ields a jierfect gradation in the number of seeds pro-
duced, up to nearly comj)lete or even quite comi)lete fertility ;
and, as we have seen, in certain abnormal cases, even to an
excess of fertility, beyond tiiat which the plant's own pollen
j^roduces. So in hybrids themselves, there are some which
never have produced, and probably never would produce, even
with the pollen of the pure parents, a single fertile seed : but
in some of these cases a first trace of fertility mvcy be detected,
by the jiollen of one of the pure parent-sjiecies 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

Chap. VIII. OF FIRST CROSSES AND OF HYBRIDS. 241

to be a sign of incipient fertilization. From this extreme degree
of sterility wc have self-fertilized hybrids jiroduting a greater
and greater number of seeds up to perfect fertility,

Hyljrids from two species which are very difiicult to cross,
and which rarely produce any offspring, are generally very
sterile ; but the parallelism between the dilliculty of making a
first cross, and the sterility of the hybrids thus jiroduced — two
classes of facts which are generall}- confounded together — is by
no means strict. There are many cases, in Avhich two pure
species, :is in the genus Yerbascum, can be united with un-
usual facility, and produce numerous hybrid-offspring, yet these
hybrids are remarkabh' sterile. On the other hand, there are
sp(M-ies which can be crossed very rarelv, or with extreme diflli-
culty, but the hybrids, ■when at last produced, are very fertile.
Even within the limits of the same genus, for instance in Dian-
thus, these two opj^osite cases occur.

• The fertility, both of first crosses and of hybrids, is more
easily affected by unfavorable conditions, than is the fertility
of pure species. But the degree of fertility is likewise innately
variable ; for it is not always the same when the same two
species arc crossed under the same circumstances, but 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 fertility is often found to differ greatly in
the several individuals raised from seed out of the same ca})sule
and exposed to the same conditions.

By the term systematic affinity is meant, the resemblance
between species in structure and in constitution, more espe-
cially in the structure of parts which are of high physiological
importance and which differ little in the allied sjiecies. Now
the fertility of fust crosses between species, and of the hybrids
protluced from them, is largely governed by their systematic
affmity. This is clearly shown by hybrids never having lieen
raised l)etween species ranked by systematists in distinct fami-
lies ; and, on the other hand, by very closely-allied species gener-
ally uniting Mith facility. But the correspondence between
systematic affmit}- and the facility of crossing is by no means
strict, A nudtitude of cases could be given of very closely-
allied species which Avill not imite, or only with extreme diffi-
culty ; 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 species can most
readilv be crossed ; and another genus, as ISilcne, in which the
II

242 LAWS GOVERNING THE STERILITY Chap. VIIL

most persevering efforts have failed to produce between ex-
tremely-close species a single hybrid. Even within the limits
of the same genus, wc 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 Giirt-
ner found that N. acuminata, which is not a particularly dis-
tinct species, obstinately failed to fertilize, or to be fertilized
by, no less than eight other species of Nicotiana. Many analo-
gous facts could be given.

No one has been able to point out what kind, or what
amount, of difference in any recognizalile character is suflicient
to prevent two species crossing. It can be shown that plants
most Avidely different in habit and general appearance, and
having strongly-marked differences in every part of the flower,
even in the pollen, in the fruit, and in the cotyledons, can be
crossed. Annual and perennial plants, deciduous and ever-
green trees, plants inhabiting difl'erent 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 stallion-horse being first crossed with a fe-
male-ass, and then a male-ass with a mare : 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 tliat the capacity in any two species to cross is often
completely independent of their systematic affinity, or of any
difference in their whole organization, except in their rej^ro-
ductive systems. The diversity of result in reciprocal crosses
between the same two species was long ago observed by Kiil-
reuter. To give an instance : Mirabilis jalapa can easily be
fertilized by the pollen of M. longiflora, and the hybrids thus
25roduced are suiliciontly fertile ; but Kolreuter tried more than
two hundred times, during eight following j-ears, to fertilize
reciprocally M, longiflora v»itli the pollen of ^I. 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 l)etween closely-re-
lated forms (as Matthiola annua and glabra) which many bota-
nists rank only as varieties. It is also a remarkable fact, that
hybrids raised from reciprocal crosses, though of course com-
pounded of the very same two species, fhe one species having

Chap. VIII. OF FIRST CIJOSSES AND OF HYBRIDS. 243

first been used as the ftithcr and tlien as the mot her, though
thev rarely ditFer in external characters, yet generally difier in
fertility in a small, and oeeasionally in a high degree.

Several other singular rules could be given iVom Gartner ;
for instance, some species have a remarkable power of crossing
with other species ; other species of tlie same genus have a re-
markablt; power of impressing their likeness on their hybrid
ollspring ; but these two powers do not at all necessarily go
together. There are certain hybrids which, instead of having,
as is usual, an intermediate character between their two par-
(mts, always closely resemble one of them ; and such hybrids,
tliougli externally so like one of their pure parent-species, are
witli rare exceptions extremely sterile. So again among hy-
brids which arc usuall}' intermediate in structure between their
jiarents, exceptional and abnormal individuals sometimes are
l)orn, Avhich closely resemble one of their pure parents; and
these hybrids are almost always utterly sterile, even Avhen the
other hybrids raised from seed from tlie same capsule have a
considerable degree of fertility. These facts .show how com-
pletely fertility in the hybrid is independent of its external
lesemblance to either pure parent.

Considering the several rules now given, Avhich govern the
fertility of first crosses and of hybrids, we see that when forms,
wliich must be considered as good and distinct species, are
united, tlieir fertility graduates from zero to perfect fertility.
<ir even to fertility iinder certain conditions in excess ; that
their fertility, besides being eminently susceptible to favorable
and imfavorable conditions is innately variable ; that it is by
no means always the same in degree in the first cross and in
th(> hybrids produced from this cross ; that the fertility of hy-
brids is not related to the degree in which the}' resemljle in
external appearance either parent ; and, lastly, that the facili-
ty of making a first cross between any two species is not al-
ways governed by their systematic aiHnity or degree of re-
semblance to each other. This latter statement is clearly
proved by the dillerencc in the result of reciprocal crosses be-
tween the same two species, for, according as the one species
or the other is used as the father or the mother, there is gen-
erally some difieriMice, and occasionally the widest possible dif-
ference, in the facility of effecting a union. Tlie hybrids, more-
over, produ(<'d from reciprocal crosses often dilTer in fertility.

Now do these complex and singular rules indicate that .spe-
cies have b(>en endowed with sterility simply to prevent their

244 LAWS GOVERNING THE STERILITY Chap. VIIL

becoming confounded in nature ? I think not. For why
should the sterility be so extremely difTerent in degree, Avhen
various species are crossed, all of Avhicli we must suppose it
would l)e equally important to keej") from blending together?
Why should the degree of sterility lie innately variable in the
individuals of the same species ? Why should some species
cross with facility, and yet produce very sterile hybrids ; and
odier species cross with extreme dilliculty, and yet produce
fairly fertile hybrids ? Why should there often be so great a
diflerence in the result of a reciprocal cross between the same
two species ? Why, it may even be asked, has the production
of hybrids been permitted ? To grant to species the special
power of producing hybrids, and then to stop their further
l)ro]iagation by dilferent 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 simplv 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 ster-
ility being incidental on other differences, and not a specially-
endowed quality. As the capacity of one plant to be grafted
or budded on another is so unimportant for its Avelfare in a
state of nature, I prcsmne that no one will suppc^se 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 na-
ture of their sap, etc. ; but in a multitj^de of cases we can as-
sign no reason whatever. Great diAersity in the size of two
plants, one being Avoody and the other herbaceous, one being
evergreen and the other deciduous, and adaptation to widely-
different climates, do not alwaA'S prevent the two grafting to-
gether. As in hybridization, so with grafting, the capacity is
limited by systematic alhniU', for no one has been able to graft
trees together belonging to ((uite distinct families: and, on the
other hand, closely-allied species, and varieties of the same

CiiAi-. Vin. OF FIRST CROSSPIS AND OF HYBRIDS. o|5

species, can usually, but not iuvariabl}', be grafted with case,
liut this capacity, as in hybridization, is by no means absolute-
ly jToverned by systematic allinity. Althoup^'h many distinct
genera within the same family have been grafted together, in
otiier cases species of the same genus will not take on each
other. The j)ear can be grafted far more readily on the
rpiince, which is ranked as a distinct genus, than on the apple,
wliich is a member of the same genus. Even dilferent varieties
of the pear take with different degrees of facility on the
quince ; so do dilTerent varieties of the apricot and peach on
certain varieties of the plum.

As Gartner found that there was sometimes an innate dif-
ference in dilferent individuals of the same two species in
crossing ; so Sageret behoves this to be the case with different
individuals of the same two species in being grafted together.
As in recipi-ocal crosses, the facility of effecting a union is
often very far from equal, so it sometimes is in grafting; the
couimon gooseberry, for instance, cannot be grafted on tlie cur-
rant, Avhereas the currant will take, though with difficulty on
the gooseberry.

AVe have seen that the sterility of hybrids, which have
their reproductive organs in an imperfect condition, is a differ-
ent case from the dilHculty of uniting two pure species, which
have their reproductive organs perfect ; yet these two distinct
cases run to a certain extent parallel. Something analogous
occurs in grafting ; for Thouin found that three species of llo-
bini;i, which seeded freely on their own roots, and which could
bo grafted with no great difficulty on another species, when
thus grafted were rendered barren. On the otiier hand, cer-
tain species of Sorbus, when grafted on other species, yielded
twice as much fruit as Avhen on their own roots. AVe are re-
minded by this latter fact of the extraordinary cases of Ilip-
jieastrum, Passillora, etc., which seed much more freely wIkmi
fertilized with the ])ollen of a distinct species, than wIk.mi fer-
tilized with }K)llen from tlie same plant.

Wc thus see, that, althougli 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 reproduc-
tion, yet that there is a rude degree of parallelism in the re-
sults of grafting and of crossing distinct species. And as wc
must look at the curious and complex laws governing the
facility with which tre(\s can be grafted on each other as inci-
dental on unknown differences in their vegetative SA'stcms, so

246 CAUSES OF TIJE STEUILITY Cu\r. VIII.

I believe that the still more complex laws governing!: the facili-
ty of first crosses are incidental on unknown dillerences in
their reproductive systems. These dilTcrences, in both cases,
follow to a certain extent, as might have been expected, sys-
tematic allinity, by Avhieh every kind of resemblance and dis-
similarity between organic beings is attempted to be ex-
jiressed. The facts by no means seem to me to indicate that
the greater or lesser dilFiculty of either grafting or crossing va-
rious species has been a special endowment ; although in the
Ciise of crossing, the difficulty is as important for the endur-
ance and stabiUty of specific forms, as in the case of grafting it
is unimportant for their Avelfare.

Origin and Causes of the Ster'tUty of First Crosses and of
JLjbrids.

At one time it appeared to me probable, as it has to others,
that the sterility of iirst crosses and of hybrids might have
been slowly acquired through the natural selection of slightly-
lessened degrees of fertility, which s]iontaneously appeared,
like any other variation, in certain indivitluals of one variety
"when crossed with 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 Iirst place, it may be
remarked that distinct regions are ofteii inhabited by groups
of species and by single species, which, when brought together
and crossed, are found to be more or less sterile ; now it could
clearly have been of no advantage to such sejiarated species to
have been rendered mutually sterile, and consequently this
could not have been effected through natiu-al selection ; but it
may perhaps be argued that, if a species were rendered sterile
with some one compatriot, sterility with other species would
follow as a necessary contingency. In the second place it is
almost as much opposed to the theory of natural selection as
to that of special creation, that in reciprocal crosses the male
element of one form should be rendered utterly impotent on a
second form, Avhile at the same time the male element of this
second form is enabled freely to fertilize the Iirst form ; for this
peculiar state of the reproductive system could not possibly be
advantageous to either species.

In considering the probability of natiual selection having

CuAr. VIII. OF FIRST CROSSES AND OF IIYBKIDS. 247

come into action, in rendering species mutually sterile, one
frrcat clifTiculty will he found to lie in the existence of many
graduated steps from slin^litly-lesscned fertility to absolute
sterility. It may be admitted, on the principle above ex-
plained, that it would \n-oi\t an incipient species if it were
rendered in some slight degree sterile when crossed with its
j)ar(>nt-form or with some other variety ; for thus fewer bas-
tartUzed and deteriorated odspiing would be produced to com-
mingle their blood with the new species in jirocess of forma-
tion. But he who will take the trouble to rellcct on the steps
by which this first degree of steriUty could be increased through
natural selection to that high degree which is common with so
many species, and which is iniiversol with species which have
been diflerentiated to a generic or family rank, will find the
subject extraordinarily complex. After mature rellection it
seems to me that this could not have been effected through
natural selection ; for it could have been of no direct advantiigc
to an individual animal to breed badly with another indi\-idual
of a dilVcrent variety, and thus to leave few offspring ; conse-
quently such individuals could not have been preserved or se-
lected. Or take the case of two species which, in their present
state when crossed, produce few and sterile oflspring ; now,
what is there which coidd favor the survival of those individuals
which ha})pe!ied to be endowed in slightly-higher degree Avith
nnitual infertility, and which thus approached by one small step
toward absolute sterility ? Yet an advance of this kind, if the
theory of natural selection be brought to bear, must have in-
cessantly occurred with many species, for a multitude are mutu-
ally quite barren. With sterile neuter insects we have reason
to believe that modifications in their structure and fertility have
been slowly accumulated by natural selection, from an advan-
tage having been thus indirectly given to the conununity to
which they belonged over other communities of the same spe-
cies ; but an individual animal not belonging to a social com-
numity, if rendered slightly sterile when crossed with some
other variety, would not thus itself gain any advantage or in-
directly give any advantage to the other individnals of the
same variety, thus leading to their preservation. From these
considerations I infer, as far as animals are concerncil, that the
various degrees of lessened fertility which occur with species
when crossed cannot have been slowly accumulated by means
of natural s(>l(>ction.

With plants, it is possible that the case may be somewhat

248 CAUSES OF THE STERILITY Chap. VIII.

(lifTcront. With many kinds, insects constantly ciirry pollen
from neigliboriniT plants to the stif^mas of each flower ; and
"with some species this is effected by the •wind. Now, if the
pollen of a variet}', when deposited on the stij]^ia of the same va-
riety, should become by spontaneous variation in ever so slig'ht a
degree prepotent over the pollen of other varieties, this would
certainly be an advantage to the variety ; for its own pollen
would thus obliterate the efl\3cts of the pollen of other varieties,
and prevent deterioration of character. And the more pre-
])(^tcnt the variety's own pollen could be rendered through nat-
ural selection, the greater the advantage would be. We know
from the researches of Giirtncr that, with s^xjcies which are
mutually sterile, the pollen of each is always prepotent on its
own stigma over that of the other species ; but we do not
know whether this prepotency is a consequence of the mutual
sterility, or the sterility a consequence of the prepotency. If
the latter view be correct, as the prepotency became stronger
through natural selection, from being advantageous to a spe-
cies in process of formation, so the sterility consequent on pre-
potency would at the same time be augmented; and the final
result would be various degrees of sterility, such as occurs with
existing species. This view might be extended to animals, if
the female before each birth received several males, so that the
sexual element of the prepotent male of her own variety ob-
literated the effects of the access of previous males belonging
to other varieties, but we have no reason to believe, at least
with terrestrial animals, that this is the case ; as most males
and females pair for each birth, and some few for life.

On the whole we may conclude, that with animals the ster-
ility of crossed species has not been slowly augmented, through
natural selection ; and as this sterility follows the same general
laws in the vegetable as in the animal kingdom, it is improba-
ble, though apparently possible, that with plants crossed spe-
cies should have been rendered sterile by a different process.
From this consideration, and remembering that species Avhich
have never coexisted in the same countiy, and Avhich therefore
could not have received any advantage from having been ren-
dei'ed mutually infertile, yet are generally sterile when cix)ssed ;
and bearing in mind that in reciprocal crosses between the
same two species there is sometimes the widest difference in
their sterility, we must give up the belief that natural selection
has come into play. We are thus driven to our former prop-
osition, namely, that the sterility of first crosses, and indi-

Chap. VIII. UF FIRST CROSSES AND OF HYBRIDS. 249

rcctly of hybrids, is simply incidental on unknow n ditFcrcnccs
in tli(^ reproductive sx'slems of the parent-species.

We may now try and look a little closer at tlic probable
nature of these dilVerenies, Avhicli induce sterility in first crosses
and in hybrids. I*iire species and hybrids difl'er, as already re-
marked, in the state of their reproductive or<z;ans ; but from
what Avill presently follow on reciprocally dimorphic and tri-
inorphic plants, it would ajipear as if some unknown bond or
law existed, which causes the young from a union not fully
fertile to be themselves more or less infertile.

In the case of first crosses between pure species, the greater
or less difiiculty in eflecting a union antl in obtaining offspring
aj^parently depends on several distinct causes. There must
sometimes be a ])hysical impossibilit}^ in the male element reach-
ing the ovule, as would be the case with a plant having a pistil
too long for tlie pollen-tubes to reach the ovarium. It has also
been observed that when 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 caimot be grafted on others. Lastly, an embryo
may be developed, and then perish at an early jieriod. This
latter alternative has not been sufHciently attended to ; but I
believe, fj-om observations communicated to me by Mr. Hewitt,
who has had great exjierience in hybridizing pheasants and
fowls, that the early death of the emliryo 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 b(itween three species of Gallus and their hy-
brids; the majority of these eggs had been fertilized; and in
the majority of the fertilized eggs, the embryos either had been
partially develojK'd and had then aborted, or had become nearly
mature, but the young chickens had been imable to break
through the shell. Of the chickens which were born, more than
four-fifths died within the first few days, or at latest weeks, " with-
out any obvious cause, apparently from mere inability to live;"
so that from the oOO eggs only twelve chickens were reared.
The early death of hybrid embryos jiroliably occurs in like
manner Avith plants; at least it is known that hybrids raised
from very distinct species arc sometimes weak and dwarfed,

250 CAUSES OF THE STERILITY Ciixr. VIII

and perish at an early aa;o ; of ■vvliicli fact Max Wirliura has
recently given some striking' cases with hybrid -willows. It
may be here worth noticing that in some cases of partheno-
genesis, embryos jiroduccd from the eggs of silk-motlis, which
liad not been fertilized, passed through their early stages of
development and then perished like the embryos produced by
a cross between two distinct species. Until becoming ac-
quainted with these facts, I was unwilling to believe in the fre-
fjuent early death of hybrid embryos ; for hj-brids, wlien once
born, are generally healthy and long-lived, as we see in the
case of the common mule. Hybrids, liowever, are differently
circumstanced before and after birth : when born and living in
a country where their two parents live, they are generally
placed under suitable conditions of life. But a hj-brid partakes
of only half of the nature and constitution of its mother, and
therefore before birth, as long as it is nourished within its
mother's womb, or within the egg or seed produced by the
mother, it may be exposed to conditions in some degree unsuit-
able, and consequently be liable to perish at an early period;
more especially as all very 3-oung beings are eminently sensitive
to injurious or uTuiatural conditions of life. But, after all, the
cause more jirobal)!}' lies in some imperfection in the original
act of impregnation, causing the embryo to be imperfectly
developed, rather than in the conditions to which it is subse-
quently exposed.

In regard to the sterility of hyl)rids, in whicli the sexual ele-
ments are imperfectly dcveloi)cd, the case is dilferent. I have
more than once alluded to a large body of facts, which I have
collected, showing that, when animals and plants are removed
from tlieir natin-al conditions, they are extremely liable to have
their reproductive svstems seriously affected. This, in fact, is
the great bar to the domestication of animals. Between the
sterility thus sujicrinduced 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 vari-
ous degrees ; in both, the male element is the most liable to
be affected ; but sometimes the female more than the male. In
both, the tendency goes to a certain extent with S3-stematic
affinity, for whole groups of animals and jilants are rendered
impotent by the same unnatural conditions; and whole groups
of species lend to produce sterik^ hvbrids. On the other hand,
one species in a grouji will sometimes resist great changes of

Chap. VIII. OF FIRST CROSSES AND OF HYBRIDS. 251

conditions with unimpaired fertility; and certain species in a
p^roiip will produce unusually fertile hybrids. No one can tell,
till he tries, whether any particular 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. Lastl}^ 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 arc eminently liable to vary, as every
experimentalist has observed.

Thus we s(>e that when organic beings are placed under new
and unnatural conditions, and when hybrids are produced by
the unnatural crossing of two species, the reproductive system,
independently of the general state of health, is affected by
sterility in a very similar manner. In the one case, tlie condi-
tions of life have been disturbed, though ofteit in so slight a
degree as to be inappreciable by vis ; in the other case, or that
of hybrids, the external conditions have remained the same,
but the organization has been disturbed by two different struct-
ures and constitutions having been blended into one. For it
is scarcely possible that two organizations should be com-
pounded into one, without some disturbance occurring in the de-
velopment, or periodical action, or mutual relations of the differ-
ent parts and organs one to another or to the conditions of life.
When hyl)rids are able to breed inter se, they transmit to their
offsj)ring from generation to generation the same compounded
organization, and hence we need not be surprised that their
sterility, thougli in some degree variable, does not diminish; it
is even a]it to increase, this being generally the result, as l)eforc
explained, of too close interbreeding. The above view of the
sterility of hybrids being caused by two different constitutions
being conlounded into one, has lately been strongly maintained
l)y Max Wichura ; but it must be owned that the sterility (as
will be immediately ex])lained) which affects the offspring of
dimorphic and trimorpliic plants, when individuals l)elonging
to the same form are united, makes this view rather doulitful.
It should, however, be borne in mind that the sterilitv of these
plants has been acfpiired for a special purpose, and may differ
in origin from that of hybrids.

It must be owned that we cannot understand, on the above

252 STERILITY OF HYBRIDS. Chap. VIII.

or any other view, scvenil facts with respect to the sterility of
hybrids ; for instance, the unequal fertility of hybrids produced
from reciprocal crosses; or the increased sterility in those hy-
brids Avhich occasionally and exceptionally reseniljle closely
cither pure parent. Nor do I pretend that the foroi^oing re-
marks go to the root of the matter ; no explanation is oflered
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
disturljed, in the other case from the organization or constitu-
tion having been disturbed by two organizations being com-
pounded into one.

A similar parallelism apparently extends to an allied yet
very different class of facts. It is an old and almost universal
belief, founded on a considerable body of evidence, that slight
changes in the conditions of life are beneficial to all living
things. We sec this acted on by fiirmcrs 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 cliange in
the habits of life. Again, both with plants and animals, there
is abundant evidence that a cross between indiWduals of the
same species, which difltr to a certain extent, gives vigor and
fertility to the oflspring; and that close interbreeding con-
tinued during several generations between the nearest rela-
tions, especially if these be kept under the same conditions of
life, almost always induces weakness and sterility.

Hence it seems that, on the one hand, slight clianges in the
conditions of life benefit all organic beings, and, on the other
hand, that slight crosses, that is, crosses between the males and
females of the same species, which have varied and become
slightly different, give vigor and fertility to the offspring. But
we have seen that greater changes, or changes of a jiarticular
nature, often render organic beings in some degree sterile ;
and that greater crosses, tliat is, crosses between males and
females which have become widely or specifically different,
produce hybrids which are generally sterile in some degree.
I cannot persuade myself that this parallelism is an accident
or an illusion. Both series of facts seem to be connected to-
gether by some common but unknown bond, which is essen-
tially related to the principle of life ; this principle apparently
being that life, as Mr. Herbert Spencer has remarked, depends

Chap. VIII. DIMORPHISM AND TRIMOKPIllSM. 253

on, or consists in, the incessant action and reaction of various
forces, which, as throui^liout Nature, are always tending toward
an e(iuilihriuiii ; and when this tendency is slip^htly disturbed
by any change, tlie vital forces apparently gain in power.

Meciprocal Dimorphism and Trimorpliism.

This subject may he here briefly discussed, and will l)e
found to throw some light on hybridism. Several plants belong-
ing to distinct orders present two forms, which exist in al)out
equal numbers, and whicli differ in no respect except in tlieir
re])roductive organs ; one form having a long pistil with short
stamens, tlie other a short ])istil with long stamens; botli with
dilVerently-sized pollen-grains. With trimorphic plants there
are three forms likewise difl'ering in the lengths of their pistils
and stamens, in the size and color of the pollen-grains, and in
some otlier respects ; and as in each of the three forms there
are two sets of stamens, there arc altogether six sets of stamens,
and three kinds of pistils. These organs are so proportioned
in length to each other, that, in any two of the forms, half the
stamens in each stand on a level with the stigma of the third
fonn. Now I have shown, and the result has been confirmed
Ijy other observers, that, in order to obtain full fertility Avith
these ])lants, it is necessary that the stigma of the one form
should be fertilized by pollen taken from the stamens of corre-
sponding height in the other form. So that with dimorphic
species two unions, wliich may be called legitimate, arc fully
fertile ; and two, which may be called illegitimate, are more
or less infertile. AVith tnmorj>hic species six imions are legiti-
mate or fully fertile, and twelve are illegitimate or more or
less infertile.

The infertility which may be observed in various dimorphic
and trimorphic ])lants, when they are illegitimately fertilized,
that is, by ]io]Um) taken from stamens not coi'responding in
height villi the pistil, dilTers much in degree, up to absolute
and utter sttM-ility ; just in the same manner as occurs in cross-
ing 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 witli iUegitimate
imions. It is well known that if pollen of a distinct species
be placed on the stigma of a flower, and its own ]iollen be
afterward, even after a considerable interval of time, placed on
the same stigma, its action is so strongly prepotent that it

g.54 RECIPKOCAL DIMORPHISM Cuap. VIII.

generally amiiliilatcs 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 botii 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 wholly destroyed or pre-
vented the action of the previously-applied illegitimate pollen.
Again, as in making reciprocal crosses between the same two
species, there is occasionally a great difference in the result, so
the same thing occurs Avith trimorphic plants ; for instance,
the mid-styled form of Lythrum salicaria Avas illegitimately
fertilized with the greatest case by pollen from the longer sta-
mens of the short-styled form, and yielded many seeds ; but
the latter form did not yield a single seed when fertilized by
the longer stamens of the mid-styled form.

In all these respects and in others which might have been
adduced, the forms of the same imdoubted species when ille-
gitimately united behave in exactly the same manner as do two
distinct S[)ecics wheii crossed. This led me carefully to ob-
serve during four years many seedlings, raised from several
illegitimate unions. The chief result is that these illegitimate
])lants, as they may be called, are not fully fertile. It is possi-
ble to raise from dimorphic species both long-styled and short-
styled illegitimate plants, and from trimorphic plants all three
illegitimate forms ; these can then be properly united in a le-
gitimate maimer. When this is done, there is no apparent
reason why they should not yield as many seeds as did their
parents when legitimately fertilized. But such is not the case ;
they are all infertile, but in various degrees; some being so
utterly and incurably sterile that they did not yield during
four seasons a single seed or even seed-capsule. The sterility
of these illegitimate plants, when united with each other in a
legitimate manner, may be strictly compared with that of hy-
brids when crossed inter sc. When on the other* hand a hybrid
is crossed with either pure parent-species, the sterility is usu-
ally much lessened : and so it is when an illegitimate plant is
fertilized by a legitimate plant. In the same manner as the
sterility of hybrids does not always run parallel with the difii-
culty of making the first cross between the two j^arent-species,
so the sterility of certain illegitimate plants was usually great,

f'liAr. VIII. AND TRIMORPIIISM. 205

while tlic sterility of the union from which they were derived
was hy no means f^n\it. ^Vith liybrids raised from the same
seed-capsule the deforce of sterility is innately variable, so it
is in a marked manner with illefritimate plants. Lastly, many
hybrids arc profuse and persistent flowcrers, while other and
more sterile hybrids produce few flowers, and arc weak, miser-
able dwarfs ; exactly similar cases occur with the illegitimate
oflspring of various dimordhic and trimorphic plants.

Altogether there is the closest identity in character and be-
havior between illegitimate plants and hybrids. It is hardly
an exaggeration to maintain that the former are hybrids, but
jjroduced within the limits of the same species by the imjiroper
imion 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
l)e+wcen distinct species. This will perhaps be made more
fully ajiparcnt by an illustration : we may suppose that a bot-
anist found two well-marked varieties (and such occur) of the
loiig-stjled form of the trimorphic Lythrum salicaria, and that
he determined to try by crossing whether they Mere specifi-
cally 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 dis-
tinct 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 common view, that his two varieties were as good
and as distinct species as any in the world ; but he would be
completely mistaken.

The facts now given on dimorphic and trimorphic plants
an» important, because they show us, first, that the ])hysi()logi-
cal test of lessened fertility, both in first crosses and in hyl)ri(ls,
is no safe critericm of specific distinction ; secondly, because we
may conclude that there is some unknown bond which connects
(li(> infertility of illegitimate unions with that of their illegiti-
mate oflspring, and we an* led to extend the same view to lirst
crosses and hybrids ; thirdly, because we find, and this seems
to me of especial importance, that two or three forms of the
same species may exist and may differ in no respect, except in
their reproductive organs, and yet be sterile when united in

256 FERTILITY OF VARIETIES Chap. VIII.

certain -ways. With dimorpliic plants, tlie unions between the
two distinct forms arc alone quite fertile, and jmxluce quite
fertile ofl'spring-, while unions between individuals belonging
to the same form are more or less sterile ; so that the result is
exactly the reverse of what occurs with distinct sj)ecies. With
dimorphic plants the resultant sterility is quite indejiendent of
any difference in general structure or constitution, for it arises
from the union of individuals belonging not only to the same
species, but to the same form. It must, therefore, depend on
the nature of the sexual elements, which are so adapted to each
other, that the male and female elements occurring in the same
form do not suit each other, Avhile those occurring in the two
distinct forms are mutually suited to each other. From these
considerations, it seems proljable that the sterility of distinct
species when crossed, and of their hybrid progeny, dejiends ex-
clusively on the nature of their sexual elements, and not on
any general difference in structure or constitution. We are,
indeed, led to this same conclusion by considering reciprocal
crosses, in which the male of one species cannot be imited, or
can be imited with great dilhculty, with the female of a sec-
ond species, while the converse cross can be effected with per-
fect facility ; for this difference in the facility of making recip-
rocal crosses and in the fertility of their offspring must be at-
tributed cither to the male or to the female element in the first
species having been differentiated, with reference to the sexual
elements of the second species in a higher degree than in the
converse case. That excellent observer, Gartner, likewise
came to this same conclusion, namely, that species when
crossed are sterile owing to differences confined to their repro-
ductive systems.

Fertility of Varieties tchen crossed, and of their Mongrel

Offqyring.

It may be urged, as an overwhelming argument, that there
must be some essential distinction between species and varie-
ties, inasmuch as the latter, however nuich tliey may differ
from each other in external ajipearance, cross with perfect facil-
it>-, and yield perfectly fertile offspring. Witli some excep-
tions, presently to be given, I fully admit that this is the rule.
But the subject is surrounded by difliculties, for, looking to va-
rieties, produced under nature, if two forms hitherto reputed to
be varieties be found in any degree sterile together, they are

Chap. VIII. WHEN CROSSED. 257

.it onre ranked l)v ina.sl naturalists as species. For instance,
the l)lue and red ijiiiipi'rnel, wliich are considered by most bot-
anists as varieties, are said l)y Giirtncr not to be quite fertile
when crossed, and he consequently ranks them as undoubted
species. If we thus art»-uo in a circle, the fertility of all varie-
ties produced under nature will assuredly have to be granted.

If we turn to varieties, produced, or supposed to have been
j)roduced, under domestication, we arc still involved in doubt.
For when it is stated, for instance, that the German Spitz dog
crosses more easily with the fox than do other dogs, or that
(v-rtain South American indigenous domestic dogs do not
rcadilv unite with European dogs, the explanation which will
o^'cur to every one, and jirobably the true one, is, that these
dogs are descended from aboriginally distinct species. Never-
theless the perfect fertility of so many domestic varieties, dif-
fering widely from each other in appearance, for instance those
of -the pigeon, or of the cabbage, is a remarkable fact; more
especially when we reflect how many species there arc, which,
though resembling each other most closely, are utterly sterile
wiien intercrossed. Several considerations, how'ever, render
the fertility of domestic varieties less remarkable. In the first
])hice, it may be observed that the amount of external dill'er-
cnce between two species is no suni guide to their degree of
mutual sterility, so that similar differences in the case of vari-
eties would be no sure guide. It is almost certain that with
species the cause lies exclusively in differences in their sexual
constitution. Now the conditions to which domesticated ani-
mals and cultivated plants have been subjected, have had so
little tendency tow^ard modifying the reproductive system in a
manner leading to mutual sterility, that we have good grounds
for admitting the directly opposite doctrine of Pallas, namely,
that such conditions generally eliminate this tendency; so that
the domesticated descendants of species, which in their natural
state would have becMi in some degree sterile when crossed,
become ])(;rfectly fertile together. With plants, so far is cul-
tivation from giving a tendency toward sterility between dis-
tinct species, that in several well-authenticated cases already
alluded to, certain ])lants have been affected in an opposite
mann(^r, for they^ have become self-impotent, while still retain-
ing the ea|)a(itv of fertilizing and being fertilized by, other
species. If the Pallasian doctrine of the elimination of sterility
through long-continued domestication be admitted, and it can
hardly be rejected, it becomes in the highest degree improl>

258 FERTILITV OF VARIETIES Chap. VIII.

tiblc tliat similar circumstances should both induce and elimi-
nate the same tendency ; though in certain cases, with species
liaving a peculiar constitution, sterility might occasionally be
thus induced. Tims, as I believe, we can understand why with
domesticated animals varieties have not been produced which
arc mutually sterile ; and why with plants only a few such
cases, immediately to l)e given, have been observed.

The real difficulty in our present subject is not, as it ap-
pears to me, why domestic varieties have not become mutually
infertile when crossed, but why this has so generally occun-ed
Avith natural varieties as soon as they have been modified in a
sufficient and permanent degree to take rank as species. "We
are far from precisely knowing the cause ; nor is this surpris-
ing, seeing hovv' profoundly ignorant we are in regard to the
normal action of the reproductive system. But we can see that
species, owing to their struggle for existence with numerous
competitors, must have been exposed to more uniform condi-
tions during long periods of time, than have been domestic
varieties ; and this may well make a wide difference in the re-
sult. For we know how commonly wild animals and plants,
when taken from their natural conditions and subjected to cap-
tivity, are rendered sterile ; and the reproductive functions of
organic beings, which have always lived and been slowly mod-
ilied under natural conditions, would probably in like manner
be eminently 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
winch can now generally resist with undiminished fertility
repeated changes of conditions, might be expected to produce
varieties, Avhich would be little liable to have their reproduc-
tive powers injuriously affected by the act of crossing with
other varieties which had originated in a like manner.

I have as yet spoken as if the varieties of the same species
were invariably fertile when intercrossed. But it is impossible
to resist the evidence of the existence of a certain amount of
sterility in the few following cases, which I will briefly abstract.
Tiie evidence is at least as good as that from which we believe
in the sterility of a multitude of s]iecies. The evidence is, also,
derived from hostile Avitncsses, who in all other cases consider
fertility and sterility as safe critej-ions of specific distinction.
Giirtner kept during several years a dwarf kind of maize with
yellow seeds, and a tall variety with red seeds growing ncai

Chap. VIII. WHEN CROSSED. 059

each oilier in his r.arclcn ; and although these j)lants liavc
separated sexes, they never naturally crossed. lie then fertil-
ized thirteen flowers of the one with the pollen of the other;
but only a sing-le head jiroduced any seed, and this one head
produced onl}' live j^rains. Manipulation in this case could not
have l)een injurious, as the plants have separated sexes. No
one, I believe, has suspected that these varieties of maize arc
distinct species; and it is important to notice that the hybrid
plants thus raised were themselves j^erfecthj fertile ; so that
even Gartner did not venture to consider the two varieties as
specilically distinct.

Girou do Buzareingues crossed three varieties of gourd,
which, like the maize, has separated sexes, and he asserts that
their mutual fertilization is by so much the less easy as their
differences are greater. How far these experiments may be
trusted, I know not ; but the forms experimented on are
rapked by Sageret, who mainly founds his classification by the
test of infertility, as varieties; and Naudin has come to the
same conclusion.

The following case is far more remarkable, and seems at
fh-st quite incredible ; but it is the result of an astonishing
number of experiments made during many years on nine spe-
cies of Verbascmn, by so good an observer and so hostile a
witness as Gartner; namely, that the yellow and white varie-
ties when crossed i)roduce less seed than the similarly-colored
varic;ties of the same species. Moreover, he asserts that, when
yellow and white varieties of one species are crossed with yel-
\o\v and white varieties of a distinct species, more seed is pro-
duced by the crosses between the similarly-colored flowers
than between those which are diflerently colored. ]\lr. Scott,
also, has experimented on the species and varieties of Verbas-
cum ; and, although unable to ctrnfinn 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 8G to 100, than the similarly-colored varieties,
^'et these varieties difl'er in no respect, except in the color of
their flowers; and one variety can sometimes be raised from
the seed of another.

Kolrcuter, whose accuracy has been confirmed by every
subscijucnt observer, has proved th(» remarkal)le fact that one
particular variety of the connnon tobacco was more fertile than
the other variiMies, when cro.ssed with a widely-distinct species.
He experimented on live fonns, which are commonly reputed

o(;,j HYBRIDS AND MONGRELS COMPARED. Chap. VIII.

to be varieties, and which he tested by the severest trial,
namel}', by reciprocal crosses, and he found their mongrel ofl-
sprinf^ perfectly fertile. But one of these five varieties, when
used either as the father or mother, and crossed with the Nico-
tiana glutinosa, always yielded hybrids not so sterile as those
which were produced from the four other varieties when crossed
with Nicotiana glutinosa. Hence the reproductive system of
this one variety must have been in some manner and in some
degree modified.

From these facts it cannot be maintained that varieties
when crossed are invariably (luitc fertile : from the great diffi-
culty of ascei'taining the infertility of varieties in a state of
nature, for a supposed variety, if proved to be infertile in any
degree, would almost universally be ranked as a species ; from
man attending only to external characters in liis domestic va-
rieties, and from such varieties not having been exposed for a
very long period to uniform conditions of life. From these sev-
eral considerations we may conclude that fertility does not con-
stitute 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 endowment,
but as incidental on changes of an vmknown nature in their
sexual elements.

Hybrids and 3fonr/rels compared^ independently of their
Fertility.

Independently of the quest i(m of fertility, the offspring of
species when crossed, and of varieties when crossed, may be
compared in several other respects. Giirtuer, whose strong
wish it was to draw a distinct line between species and varie-
ties, could find very few, and, as it seems to me, quite unim-
portant differences between the so-called hybrid offspring of
species, and the so-called mongrel offspring of varieties. And,
on the other hand, they agree most closely in many im2:)ortant
respects.

I shall here discuss this subject with extreme brevity. The
most important chstinction is, that in the first generation mon-
grels are more variable than hybrids ; but Gartner admits that
hybrids from species which have long been cultivated are often
variable in the first generation; and 1 have myself seen striking
instances of this fact. Gartner further admits that liybrida
between very closely-allied species are more variable than

Cii4.r. VIII. IIVIJRIDS AND MONGRELS COMPARED. ogi

those from very distinct species ; and this shows that the dif-
ference in the degree of variability graduates away. When
mongrels and the more fertile liybrids are propagated for sev-
eral generations, an extreme amount of variability in the off-
spring in both cases is notorious ; but some few instances of
botli hybrids and mongrels long retaining a imifonn character
could be given. The variability, however, in the successive
generations of mongrels is, perhaps, p^eater than in hybrids.

This greater variability in mongrels than in hybrids docs
not seem at all surprising. For the parents of mongrels are
varieties, and mostly domestic varieties (very few ex])eriments
having been tried on natural varieties), and this imjjlies that
there lias been recent variability, Avhich would often continue
and be added to that arising from the act of crossing. The
slight variability of hybrids in the first generation, in contrast
with the succeeding generations, is a curious fixct, and deserves
attention. For it bears on the view which I have taken of one
of the causes of ordinary variability ; namely, that the repro-
ductive systeni from being eminently sensitive to changed con-
ditions of life, fails under these circumstances to perform its
proper function of producing offspring identical in all respects
with the parent-form. Now, hybrids in the first generation
are descended from sjiecies (excluding those long cultivated)
which have not had their reproductive systems in any way
allected, and they are not variable ; but hybrids themselves
have their reproductive systems seriously affected, and their
descendants are highly variable.

Biit to return to our comparison of mongrels and hybrids :
Gfirtner states that mongrels are more liable than hybrids to
revert to cither parent-form ; but this, if it be true, is certainly
only a difference in degree. Mort>over, Gartner expressly states
that hylirids from long-cultivated plants are more subject to
reversion than hybrids from species in their natural state; and
this probably explains the singular difference in the results
arrived at by dilferent obser\'ers : thus, Max Wichura doubts
whether hybrids ever revert to their parent-forms, and he ex-
perimented on uncultivated species of willows ; while Naudin,
on the other hand, insists in the strongest terms on the almost
universal tendencv to reversion in hybrids, and he experiment-
ed chiedy on cultivated plants. Gartner further stiites that
when any two species, although most closely allied to each
other, are crossed with a third species, the hybrids arc widely
different from each other; Avhereas, if two vtM-y distinct varie-

262 HYBRIDS AND MONGRELS COMPARED. Chap. VIII.

ties of one species are crossed with another species, the hybrids
do not diiler much. But this conclusion, as far as I can make
out, is founded on a sinp^le experiment; and seems directly
opposed to tlie results of several experiments made by Kol-
reuter.

Such alone arc the imimportant dilTercnces which Gartner
is able to point out between hybrid and moiig'rel plants. On
the other hand, the dco-recs and kinds of resemblance in mon-
g^rels and in hybrids to their respective parents, more especially
in hybrids produced from nearly related species, follow accord-
ing to Giirtncr the same laws. When two species are crossed,
one has sometimes a prepotent power of impressing its likeness
on the hybrid ; and so I believe it to be with varieties of plants.
With animals 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 mongrels can be reduced to either pure parent-form, by
repeated crosses in successive generations Avith cither parent.

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

Much stress has been laid by some authors on the supposed
fact, that it is only Avith mongrels that the offspring are not
intermediate in character, but closely resemble one of their
parents ; but this does sometimes occur Avitli hybrids, yet I
grant much less frequently Avith them than Avitli mongrels.
Looking to the cases Avliich I have collected of cross-bred ani-
mals closely resembling one parent, the resemblances seem
cliiefly confined to characters almost monstrous in their nature,
and Avhich have suddcidy appeared — such as albinism, melanism,
deficiency of tail or horns, or additional fingers and toes; and
do not relate to characters Avhich have been sloAvly ac(|uired

Chap. VIU. SUMMARY. 263

through selection. Consequently, sudden reversions to the
perfect character of either parent would be much more likely
to occur with mono-rels, Avhicli are descended from varieties
often sudd(Mily produced and semi-monstrous in character, than
with hvbrids, which are descended from species slowly and
naturally produced. On the whole, I entirely agree witli Dr.
Prosper Lucas, who, after arranging an enormous body of facts
with respect to animals, comes to the conclusion that the laws
of resemblance of the child to its parents are the same, whether
the two parents dilTer little or nmch from each other, namely
in the imion of individuals 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 simi-
larity in the offspring of crossed species, and of crossed vari-
eties. If we look at species as having been specially created,
an'd at varieties as having been produced by secondary laws,
this similarity would be an astonishing fact. But it harmo-
nizes perfectly with the view that there is no essential dis-
tinction l^etwcen species and varieties.

Summary of Chapter.

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

In the same manner as in grafting trees, the capacity of one
species or variety to take on another, is incidental on differ-
ences, generally of an unknown nature, in their vegetative sys-
tems, so in crossing, the greater or less facility of one species
to unite with another is incidental on imknown differences in
their reproductive systems. There is no more reaiion to think
that species have been specially endowed with various degrees

2G4 6UMMAEY. Chap. VIH.

of sterility to prevent their crossing and blending in nature,
than to think that trees have been specially endowed with vari-
ous and somewhat analogous degrees of ditliculty in being
grafted together in order to prevent their inarching in our
forests.

Tlie sterility of first crosses and of their hylirid progeny lias
not, as far as we can judge, been acquired through natural se-
lection. In the case of first crosses it seems to depend on
several circumstances ; in some instances in chief part on the
early death of the embryo. In the case of liybrids, it perhajis
depends on tlieir whole organization having been disturbed by
lieing compounded from two distinct forms ; tlie sterility being
closely allied to that Avhich so frequently aii'ects pure species,
when exposed to unnatural conditions of life. This view is
supported by a parallelism of another kind : namely, that, first,
the crossing of forms only slightly diiferentiated favors the
vigor and fertility of their offspring, while close interbreeding
is injurious ; and secondly, that slight changes in the conditions
of life apparently add to the vigor and fertility of all organic
beings, while greater changes are often injurious. But the
facts given on the sterility of the illegitimate unions of dimor-
phic and trimorphic plants and of their illegitimate progeny,
render it probable that some unknown bond in all cases con-
nects the degree of fertility of first unions with that of their
offspring. The consideration of these facts on dimorphism, as
well as the results of reciprocal crosses, clearly leads to the
conclusion that the primary cause of tlie sterility is confined to
differences in the sexual elements. But why, in the case of
species, the sexual elements should so generally liave become
more or less modified, leading to their mutual infertility, we do
not know%

It is not surprising that the diniculty in crossing any two
species, and the sterility of their hybrid-offspring, should in
most cases correspond, even if due to distinct causes ; for both
depend on the amount of difference between the species which
are crossed. Nor is it surprising that the facility of effecting
a first cross, and the fertility of tlie 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 system-
atic afiinity of the forms subjected to experiment ; for system-
atic airiiiity includes resemblances of all kinds.

First crosses between forms known to be varieties, or snffi-

CuAP. VIII. SUMMARY. 205

cicntly alike to be considered as varieties, and their mongrel
ofl'spring, are very generally, but not, as is so often stated,
invariably fertile. Nor is this almost universal and perfect
fertility surprising, Avhen we remember liow 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 jiroduced under domestication by the selection of
mere external difl'crences, and that they have not been long
exposed to uniform conditions of life. It should also be espe-
cially kept in mind, that long-continued domestication tends to
eliminate sterility, and is therefore little likely to induce this
same cjuality. Independently of the question of fertility, in all
other respects there is the closest general resemblance between
hybrids and mongrels, in their variability, in their power of
absorbing each other by repeated crosses, and in their inheri-
tance of characters from both parent-forms. Finally, then,
although we are profoundly ignorant of the precise cause of
the sterility of first crosses and of h^'brids, the facts given in
this chapter do not seem to me opposed to the belief that vari-
eties and species are not fundamentally different.

12

2GG IMPEKFECTIO^' OF THE Chap. IX.

CHAPTER IX.

ON TIIK EMPKRFECTIOX OF THE GEOLOGICAIi EECOED.

On the Absence of Intermediate Varieties at the Present Day— On the Nature of Ex-
tinct Intermediate Variotii's : on their Number— On the Lapse of Time, as in-
ferred from the Ilate of Denudation and of Deposition — On the Lapse of Time as
estimated V)y Years — On the Poorness of our Paleontologieal Collections — on the
Denudation of Granitic Areas— On the Intermittence of Geolo'jrical Formations —
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 Uubitablc Earth.

In the sixth chapter I enumerated tlie chief objections
which iTiio;lit be justly urged against the views maintained in
this A-olume. Most of them have now been discussed. One,
namely, the distinctness of specific forms, and their not being
blended together by innumerable transitional links, is a very
obvious dilliculty. I assigned reasons why such links do not
commonly occur at the present day, under the circumstances
apparently most favorable for their presence, namely, on an
extensive and continuous area with graduated physical condi-
tions. I endeavored to show that the life of each species
depends in a more important manner on the presence of other
alrcady-deiined organic forms, than on climate ; and, therefore,
that the really governing conditions of life do not graduate
away quite insensibly like heat or moisture. I endeavored,
also, to show that intermediate varieties, from existing in lesser
numbers than the forms which they connect, will generally be
beaten out and exterminated during the course of further
modification and improvement. The main cause, however, of
innumerable intermediate links not now occurring everywhere
throughout Nature depends on the very process of natural
selection, through which new varieties continually take the
places of and exterminate their parent-forms. But just in pro-
portion as this process of extermination has acted on an enor-
mous scale, so must tlie number of intermediate varieties,
which have formerly existed, be truly enormotis. ^V^ly, then,

CuAP. IX. GEOLOGICAL RECORD. 267

is not every pfColor;ical formation and every stratum full of
such iiitermcdiate links V GeolojTy assuredly does not reveal
any such tinclv-^radiiated organic; chain; and this, perhaps, is
the most obvious and serious objection which can be urf^ed
ar^ainst the theor3^ The explanation lies, as I believe, in the
extreme imperfection of the geological record.

In the first place, it should always be borne in mind what
sort of intermediate forms must, on the tiieory, have formerly
existed. I have found it diilicult, when looking at any two
species, to avoid picturing to myself forms directbj intermedi-
ate between them. But this is a wholly false view ; we should
alwa3's look for forms intermediate between each species and
a common but unknown progenitor ; and the progenitor will
generally have ditlered in some respects from all its modified
descendants. To give a simple illustration: the fantail and
pouter pigeons have 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 jiouter ; 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 re-
garding their origin, it would not have been possible to have
determined, from a mere comparison of their structure with
tliat of the rock-pigeon, C. livia, whether they had descended
irom this species or from some other allied species, such as C.
oenas.

So with natural species, if we look to forms very distinct,
for instance to the horse and tapir, we have no reason to sup>-
pose that links ever existed directly intermediate between
them, but between each and an unknown connnon parent. The
common parent will have had in its whole; organization much
general resemblance to the tapir and to the horse ; but in some
])oints of structure may have difTcMcd considerably from both,
even perhaps more than they differ from each other. Hence,
in all such cases, we should be unable to recognize the parent-
form of any two or more s])ecies, 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 jierfect chain of
the intermediate links.

It is just possible by the theory that one of two living

208 THE LAPSE OF TIME. Chap. IX,

forms might have ilescended from the other; lor instance, a
horse from a tapir ; and in this case direct intermediate links
will have existed between them. But such a case "would im-
ply that one form had remained for a very long period unal-
tered, while its descendants 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 supplant the old and unimproved forms.

By the theory of natural selection all living species have
been connected with the parent-species of each genus, by dif-
ferences not greater than we see between the varieties of the
same species at the present day ; and these parent-species,
now generally extinct, have in their turn been similarly con-
nected with more ancient species ; and so on backward, always
converging to the common ancestor of each great class. So
that the number of intermediate and transitional links, be-
tween all living and extinct species, must have been incon-
ceivably great. But assuredly, if this theory be true, such
have lived upon the earth.

On the Lapse of Time, as inferred from the Mate of Deposi-
tion and Extent of Denudation.

Ind(^pendently of our not hnding fossil remains of such in-
finitely numerous connecting links, it may be objected that
time cannot have sufficed for so great an amount of organic
change, all changes having been etlected very sIomIv. It is
hardh' possible for me even to recall to the reader, who is not
a practical geologist, the facts leading the mind feebly to com-
prehend the lapse of time. He who can read Sir Cliarles
Ly ell's grand Avork on the Principles of Geology, which the
future historian will recognize as having produced a revolu-
tion in natural science, 3'et does not admit how vast have been
the past periods of time, may at once close this volume. Not
that it suffices to study the Princij^les of Geology, or to read
special treatises by d liferent observers on separate formations,
and to mark how each author attempts to give an inadequate
idea of the duration of each formation or even of each stratum.
We can best gain some idea of jiast time by knowing the agen-
cies at work, and learning how nuich of the surface of the land
has l)cen denuded, and how nnich sediment has been deposited.
As I.yell has well remarked, the extent and thickness of our

CiiAP. IX. THE LAl'SK OF T1MI<:. 2G9

sciliincntiiry formations arc the result and the measure of the
rlrnudation which the eartli's crust lias elsewhere under<roue.
Therefore a man should examine for himself the great piles of
superimposed strata, and watch the rivulets brini^ini^ down
niuil, and the waves wearing away the sca-clills, in order to
comprehend something about the duration of past time, the
monuments of which we sec all around us.

It is good to wander along the coast, when formed of raod-
eratcly-hard rocks, and mark the process of degradation. The
tides in most cases reach the cliffs only for a short time twice a
day, and the waves cat into them, only when they are charged
with sand or pel)bles ; for there is good evidence that pure
water elfects 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 iii size they can be rolled about by the
waves, and then they are more quickly ground into pebbles,
sand, or mud. But how often do we see along the bases of
retreating cliffs rounded bowlders, all thickly clothed by marine;
productions, showing how little they are abraded, and how
seldom they are rolled about ! Moreover, if we follow for a
few miles any line (jf rocky cliff, which is undergoing degrada-
tion, we find that it is only here and there, along a sliort length
or round a promontory, that the clifl's arc at the present time
suffering. The appearance of the surface and the vegetation,
show that elsewhere yeai'S have elapsed since the Avaters
washed their base.

We have, however, recently learned from the observations
of Ramsay, in the van of" excellent observers, of Jukes, Geikie,
Croll, and others, that subaerial degradation is a much more
imi)ortant agency than coast-action, or the power of the waves.
Tiie whole surface of the land is exposed to the chemical ac-
tion of the air and of the rain-water with its dissolved carbonic
acid, and in colder countries 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 dis-
tricts, by the wind ; it is then transported by the streams and
rivers, which when rapid deepen their chainicls, and triturate
the fragments. On a rainy day, even in a gently-undulating
country, we see the effects of subaerial degradation in the mud-
dy rills Avhich flow down each slope. Messrs. Kamsay and
Whitaker have shown, and the observation is a most striking
one, that the great lines of escarpment in the Wcaldon district

270 '^^iE LAPSE OF TIME. CiiAr. IX.

and those ranging across England, which formerly were looked
at by every one Jis ancient sea-coasts, cannot have been thus
formed, for each line is composed of one and the s;une forma-
tion, while our j^resent sea-clifls are eveiywhere formed by the
intersection of various formations. This being tlic case, we
are compcllcil to admit that the escaq^ments owe their origin
in chief part to the rocks of Avhich they are composed having
resisted subacrial denudation better than the surrounding sur-
face ; this surface consequently has l^een gradually lowered,
with the lines of harder rock left projecting. Nothing im-
presses the mind with the vast duration of time, according to
our ideas of time, more forcibly tlian the conviction thus gained
that subaiirial agencies, which apparently have so little power,
and which seem to work so slowly, have produced such great
results.

When thus impressed with the slow rate at Vv'liich tlie 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 mass of rock which has been removed over
many extensive areas, and on the other hand the tliickness of
our sedimentary formations. I remember haAnng been much
struck M'hen viewing volcanic islands, which have been worn
by the waves and pared all around 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 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 very slow and
eflected 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 dis-
placement of tlie strata varies from 600 to 3,000 feet. Prof,
liamsay has published an account of a downtlirow in Anglesea
of 2,300 feet; and lie informs me tliat he fully believes that
tliere is one in ]M(>rionethshire of 12,000 feet; yet in these
cas(>s there is nothing on the sm-face of the land to show such
prodigious movements ; tlie jiile of rocks on cither side of the
crack having been smoothly SAvej)t away.

Chap. IX. THE LAPSE OF TIME. 271

Oil the other Imnd, in all parts of the world the piles of
Kcdimentary strata arc of wonderful thickness. In the Cordil-
lera I estimated one mass of cono:lomcrate at ten thousand
feet ; and althou_Q;h conf2;lomerates have probably been accu-
nuilated at a quicker rate than liner sediments, yet from being
formed of worn and rounded pebbles, each of which bears the
stamp of time, they are f:^ood to show how slowly tlic mass
must have been heaped to<j;'ether. Prof. Ramsay has <;iven me
the niaxiir.um thickness, from actual measurement in most
cases, of the successive formations in dijf'ercnt parts of Great
Britain; and this is the result:

Feet.

Paleozoic BtratA (not including? igneous beds) 57,154

Secondary strata 13.100

Tertiary strata 2,240

— makinfi;' altogether 72,584 feet ; that is, very nearly thirteen
and three-(iuarters British miles. Some of the formations,
Avhich are represented in England by thin beds, are thousands
of feet in thickness on the Continent. Moreover, between each
successive formation, we have, in the o])inion of most geolo-
gists, enormously long blank periods. So that the lofty pile
of sedimentary rocks in 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 eteniity.

Nevertheless this impression is partly false. Mr. Croll, in
a most interesting paper, remarks that we do not err " in form-
ing too great a conception of the length of geological periods,"
but in estimating them by years. When geologists look at
large and complicated phenomena, and then at the figures rep-
resenting several million years, the two produce a totally dif-
ferent effect on the mind, and the figures are at once pro-
nounced to be too small. But in regard to denudation, Mr.
Croll shows, by calculating the known amount of sediment an-
nually brought down by certain rivers, relatively to the areas
of drainage, that 1,000 feet of rock, disintegrated through sub-
ai'rial agenci(>s, would thus be removed from the mean level of
the whoh* area in the course of six million vears. This seems
an astonishing result, and some considerations lead to the sus-
picion that it may be much too large, but even if halved or
(juartered it is still very surprising. Few of us, however, know
what a million really means: Mr. Croll gives the following

272 Tilt: LAPSE OF TIME. Cuap. IX.

illustration : take a narrow strip of paper, 83 feet 4 inclies in
length, and stretch it along the Avail 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 dimen-
sions. Several eminent breeders, during a single lifetime, have
so largely modified some of the higher animals, Avhich propa-
gate their kind much more slowly than most of the lower ani-
mals, that they have formed Avliat Avell deserve to be called
new sub-breeds. Few men have attended AA-ith due care to
any one strain for more than half a century, so that a hundred
years represent the Avork of two breeders in succession. It is
not to be supposed that species in a state of nature ever
change so quickly as domestic animals under the guidance of
methodical selection. The comparison Avould be in every AA'ay
fairer Avitli the results Avhich follow from unconscious selection,
that is, the preservation of the most useful or beautiful animals,
Avith no intention of modifying the breed ; but by this process
of unconscious selection, various breeds haA"e been sensibly
changed in the course of two or three centuries.

Species, however, probably change much more slowly, and
within the same country only a few change at the same time.
This slowness follows from all the inhabitants of the same
country being already so avcU adapted to each other that ncAV
places in the polity of Nature do not occiir until after long in-
tervals, Avhen changes of some kind in the physical conditions
or through immigration haA^e occurred; and indiA^idual differ-
ences or variations of the right nature, by Avliich some of the
inhabitants might be better fitted to their new places under
the altered circumstances, might not at once occur. According
to the standard of years Ave have no means of determining
how long a period it takes to modify a species. Mr. Croll,
judging from the amount of heat-energy in the sun and from
the date Avhich he assigns to the last glacial epoch, estimates
that only sixty million years lia\'e elapsed since the deposi-
tion of the first Cambrian formation. This appears a A'ery
short period for so many and such great mutations in the forms
of life as have certainly since occurred. It is admitted that
many of the elements in the calculation are more or less doubt-
ful, and Sir "W. Thomson giA'Cs a Avide margin to the possible
age of the habitable Avorld. But, as Ave have seen, Ave cannot

Chap. IX. PALEONTOLOGICAL COLLECTIONS. 273

comprehend what tlio firrures 00,000,000 really imply ; and
during this, or perhaps a lonfrcr roll of years, the land and the
waters have everywhere teemed with livinj^ creatures, all ex-
posed to the struggle for life and undergoing change.

On the Poorness of oitr Paleontological Collections.

Now let us turn to our richest geological museums, and
what a paltry display we behold ! That our collections arc
very imperfect is admitted by every one. The remark of that
admira1:)lc paleontologist, Edward Forbes, should not be for-
gotten, namely, that numbers of our fossil species are known
and named from single and often broken specimens, or from a
few specimens collected on some one spot. Only a small portion
of the surface of the earth has been geologically explored, and
no part with sufficient care, as the important discoveries made
eVery year in Europe prove. No organism wholly soft can be
preserved. Shells and bones Avill decay and disappear when
left on the bottom of the sea, where sediment is not accumu-
lating. I believe we often take an erroneous view, when we
tacitly admit to ourselves that sediment is being deposited
over nearly the whole bed of the sea, at a rate sufficiently
quick to embed and preserve fossil remains. Throughout an
enormously large proportion of the ocean, the bright blue tint
of the water bespeaks its purity. The many cases on record
of a formation conformably covered, after an immense interval
of time, by another and later formation, Avithout tlic underly-
ing bed having suffered in the interval any wear and tear, seem
explicable only on the view of the l)ottom of the sea not rarely
lying for ages in an unaltered condition. The remains Avhich
do become embedded, if in sand or gravel, will when the beds
are upraised generally be dissolved by the percolation of rain-
water chargetl with carbonic acid. Some of the many kinds
of animals which live on the beach between high and low
water mark seem to be rarely jireserved. For instance, the
several species of the Chthamalin;!:? (a sub-family of sessile
cirripcdes) coat the rocks all over the world in infinite
numbers: they are all slridly littoral, with the exception of a
single Medit(;rranean species, which inhabits deep water, and
this has been f(jund fossil in Sicily, whereas not one other
species has hitherto been found in any tertiary formation : yet
it is not known that the genus Chthamalus existeil during the
T^halk period. Lastly, many great deposits requiring a vast

274 THE .POORNESS OF OUR Chap. IX,

length of time for llicir Jiccuinuliilion, are entirely destitute of
organic remains, witliout our being able to assign any reason :
one of tlic most striking instances is that of the Flysch forma-
tion, -wliich 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, al-
though this great mass has been most carefully searched, no
fossils, except a fcAv vegetable remains, have been found.

"With respect to the terrestrial productions which lived
during the Secondary and Paleozoic periods, it is superfluous
to state that our evidence from fossil-remahis is fragmentary
in an extreme degree. For instance, not a land-shell until quite
recently was known belonging to cither of these vast periods,
with the exception of one species discovered by Sir C. Lyell
and Dr. DaAvsou in the carboniferous strata of North Amei'ica,
of which shell above a hundred specimens have now been col-
lected. In regard to mammiferous remains, a single glance at the
historical table published inLyell's Manual will bring home the
Iruth, how acciilental and rare is tlicir preservation, far better
than pages of detail. Nor is their rarity surprising, when we
remember how large a proportion of the bones of tertiary mam-
mals have been discovered either in caves or in lacustrine
deposits; and that not a cave or true lacustrine bed is known
belonging to the age of oiu- secondary or paleozoic formations.

But the imperfection in the geological record largely results
from another and more important cause than any of the forego-
ing ; namely, from the several formations being separated from
each other l^y wide intervals of time. This doctrine has been
most emphatically admitted by many geologists and paleon-
tologists, who, like E. Forbes, entirely disbelieve in the change
of species. When we see tiie formations tabulated in written
works, or when we follow them in Nature, it is diihcult to
avoid believing that they arc closely consecutive. But we
know, for instance, from Sir R. Murchison's great work on Rus-
sia, what wide gaps there are in that country between the
superimposed formations ; Sf) it is in North America, and in
many otlier parts of the world. The most skilful geologist, if
his attention had been confined exclusively to tliese large ter-
ritories, Avould never have suspected that, during the periods
which were blank and barren in his own country, great piles
of sediment, charged Avith new and peculiar forms of life, had
elsewhere been accumulated. And if, in each separate territory,
hardly any idea can be formed of the length of time which has-

CiiAP. IX. PALEONTOLOGICAL COLLECTIONS. 075

elapsed lictwoL'u Iho consecutive formations, we may infer that
this could nowhere be ascertained. The frequent and great
changes in the miiieralogieal composition of consecutive forma-
tions, generall}^ implying great changes in the geography of
the surronnding lands, whence the sediment has been derived,
accords with tlie belief of vast intervals of time having elapsed
between each formation.

But we can, I thinlc, see wliy the geological formations of
each region are almost invariably intermittent; that is, have
not followed each other in close sequence. Scarcely any fact
struck me more when examining many hundred miles of the
South American coasts, which have been uj)raised several hun-
dred feet Avithin the recent period, than the absence of any
recent deposits sufliciently extensive to last for even a short
geological period. Along the whole west coast, Avhich is in-
liabited by a peculiar marine fauna, tertiary beds are so poorly
cTeveloped, that no 'record of several successive and peculiar
marine faunas will probably be preserved to a distant age. A
little refl(^ction will explain Avhy, 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 sediment must for ages have been great, from the
enormous degradation of the coast-rocks and from muddy
streams entering the sea. The exjilanation, no doubt, is, that
the littoral and sub-littoral deposits are continually worn away
as soon as they nro, lirought up by the slow and gradual rising
of the land witliin the grinding action of the coast-waves.

We niay, I think, conclude that sediment must be accumu-
lated in extremely thick, solid, or extensive masses, in order
to withstand the incessant action of tlie waves, wlien lirst up-
raised and during successive oscillations of level, as well as
the subsequent subaerial degradation. Such thick and exten-
sive accumulations of sediment may be formed in two waj-s;
either in profound depths of the sea, in which case the bottom
will not be inhabited by so many and such varied f(jrms of life
as the more shallow seas; and the* mass Avhen upraised will
give an imperfect record of the organisms which existed
tliroughout the world during the period of its accunuilation;
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 hmg as the rate of subsidence and the suj>
ply of sediment nearly balance each other, the sea will remain
shallow and favorable for many and varied fonns, and thus a

276 THE POORNESS OF OUR Chap. IX.

rich fossiliferous formation, thick cnougli, \\hvn 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 rlcJi in fos-
sils, have thus been formed during subsidence. Since publish-
ing my views on this subject in 1845, 1 have watched the prog-
ress 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. sub-
sidence. I may add that the only ancient tertiary formation
on the west coast of South America, which has been bulky
enough to resist such degradation as it has as yet suffered, but
which will hardly last to a distant geological age, was deposit-
ed during a downward oscillation of level, and thus gained
considerable thickness.

All geological facts toll us plainly that each area has under-
gone numerous slow oscillations of level, atid apparently these
oscillations have affected Avide spaces. Consequently forma-
tions rich in fossils and sufficiently thick and extensive to re-
sist subsequent degradation, may have been formed over wide
spaces during periods of subsidence, but only where the sup-
ply of sechment was sufficient to keep the sea shallow and to
embed and preserve the remains before they had time to deca3%
On the other hand, as long as the bed of the sea remained sta-
tionary, thich deposits could not hare been accumulated in the
shallow parts, which are the most favorable to life. Still less
could this have happened during the alternate periods of ele-
vation ; or, to speak more accurately, the beds which were
then accumulated Avill generally have been destroyed by being
upraised and brought within the limits of the coast-action.

These remarks appl}'" chiefly to littoral and sub-littoral de-
jiosits. In the case of an extensive and shallow sea, such as
that within a large part of the Malay Archipelago, Avhere the
depth varies from 30 or 40 to 60 fathoms, widely-extended for-
mation might be formed during a jicriod of elevation, and yet
not suffer excessively fr©m denudation during its slow up-
heaval ; but the thickness of the formation could not be great,
for owing to the elevatory movement it would be less than the
depth in whidi it was formed ; nor would the deposits be much
consolidated, nor be cajiped by ovcrlj-ing formations, so that
it would run a good chance of being worn away by atmos-
])heric dc^gradation and by the action of the sea during subse-
quent oscillations of level. It has, however, been suggested

CiiAr. IX. TALEONTOLOGICAL COLLECTIONS. 277

by Mr. Hopkins, lliat if one part of the area, after rising and
before being denuded, subsided, the deposit formed during the
rising movement, though not thick, might afterward become
protected by fresh accumuhitions, and thus be jireserved for a
long period.

Mr. Hopkins also expresses his belief that sedimentary beds
of considerable horizontal extent have rarely been completely
destroyed. But all geologists, excepting the; few who believe
that our present metamorphic schists and plutonic rocks once
formed the primordial nucleus of the globe, Avill admit that
tlicse latter rocks have been denuded on an enormous scale.
For it is scarcely possible that such rocks could have been
solidilied and crystallized while imcovered ; but if the meta-
morphic 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.,
w-ere once necessarily covered up, how can we account for the
naked and extensive areas of such rocks in many jiarts of the
world, except on the belief that they have subsequently been
completely denuded of all overl^ang strata ? lliat such ex-
tensive areas do exist cannot be doubted : the granitic region
of Parime is described by Humboldt as being at least nineteen
times as large as Switzerland. South of the Amazon, Boue
colors an area comjiosed of rocks of this nature as equal to tliat
of Spain, France, Italy, part of German}-, and the British Isl-
ands, all conjoined. This region has not been carefully ex-
plored, but, from tlie concurrent testimony of travellers, the
granitic area is very large : thus. Von Eschwege gives a de-
tailed section of these rocks, stretching from Rio dc Janeiro
for 260 geograjihical miles inland in a straight line ; and I trav-
elled for 150 miles in another direction, and saw nothing but
granitic rocks. Numerous specimens, collected along the whole
c(jast from near Rio Janeiro to tlie mouth of the Plata, a dis-
tance of 1,100 geographical miles, were examined l)y me, and
they all belonged to this class. Inland, along the whole north-
ern bank of the Plata, I saw, besides modern tertiary beds, only
one small patch of slightly-metamorphosed rock, ^\■hich alone
could have formed a part of the original capping of the granitic
scries. Tuining to a well-known region, namely, to the United
States and Canada, as shown in Prof. II. I). Rogers's beauti-
ful map, I have estimated the areas l)y (Hitting out and weigh-
ing the paper, and I find that liie metamorphic (including "the
Henii-metamorphic") and granitic rocks exceed, in the i)n)p()rtion

273 ABSENCE OF INTERMEDIATE VARIETIES Chap. IX.

of 19 to 1:2.5, the Avholc of the newer Paleozoic formations.
In many rcg'ions the metamorphic and granitic rocks would be
seen to be much more widely extended, if all the sedimentary
beds Averc removed which rest unconformably on them, and
whicli could not have formed part of the original mantle under
which they were crystallized. Hence it is probable that in some
parts of the world whole formations have been completely de-
nuded, with not a wreck left behind.

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

On the Absence of JVumcrous Intermediate Varieties in any
one Single Formatio7i,

From these several considerations, it cannot be doubted
that the geological record, viewed as a whole, is extremely im-
perfect ; but if we conline our attention to any one formation,
it becomes much more diilicult to understand why we do not
therein find closely-graduated varieties between the allied
species which lived at its commencement and at its close.
Several cases arc on record of the same species presenting va-
rieties in the upper and lower parts of the same formation :
thus, Trautschold gives a number of instances with Ammon-
ites ; and Hilgendorf has described a most curious case of ten
graduated forms of Planorbis multiformis in the successive
beds of a fresh-water formation in Switzerland. Although
each formation has indisputably required a vast number of
years for its deposition, several reasons can be given why each
should not connnonly include a graduated series of links be-
tween the species which lived at its commencement and close;
but I cannot assign due proportional weight to the following
considerations.

CiiAr. IX. IN ANY SINGLE lORMATION. 219

Although each formation may mark a very long lapse of
years, each probably is short compared with the period requi-
site to change one sjieoies into another. I am aware that two
paleontologists, whose opinions are worthy of much deference,
namely, Broim and AVoodward, have concluded that the aver-
age duration of each fcjrmation is twice or thrice as long as the
average duration of specific forms. But insuperable difficul-
ties, as it seems to me, prevent us from coming to an}"^ just
conclusion on this head. W^hen we see a species first appear-
ing in the middle of any formation, it would be rash in the ex-
treme to infer that it had not elsewhere previously existed.
So, again, when we find a species disappearing before the last
layers have been deposited, it would be equally rash to sup-
pose that it then became extinct. We forget how small the
area of Europe is compared with the rest of the world ; nor
have the several stages of the same formation throughout Eu-
rope been correlated Avith perfect accuracy.

With marine animals of all kinds, we may safelv infer a
large amount of migration during climatal and other changes ;
and when we see a species first appearing in any formation, the
probability is, that it only then first iimnigrated into that area.
It is well known, for instance, that several species ajipeared
somewhat earlier in the paleozoic beds of North America than
in those of Europe; time having apparently been required for
their Tnigration from the American to the European seas. In
examining the latest deposits in various quai'ters of the world,
it has everywhere been noted that some few still existing spe-
cies are common in the deposit, but have become extinct in the
immediately surrounding sea ; or, conversely, that some arc
now abundant in the neighboring sea, but are rare or absent in
tliis particular deposit. It is an excellent lesson to reflect on
the ascertained amount of migration of the inhabitants of Eu-
rope during the glacial epoch, which forms only a part of one
whole geolf)gical period ; and likewise to reflect on the changes
of level, on the extreme change of climate, and on the great
lapse of time — all included within this same glacial period. Yet
it may be doubted whether, in any quarter of the world, sedi-
mentary deposits, indiidlitf/ fossil rcmahis, have gone on ac-
cumulating within the same area during the whole of this
period. It is not, for instance, probable that S(Mliment was de-
posited during the whole of the glacial jieriod near the mouth
of the Mississippi, within that limit of (ie])th at which marine
animals can best flourish ; for we know that great geographical

280 ABSENCE OF INTERMEDIATE VARIETIES Chap. IX.

changes oocurrcd in other parts of America duriiifr this space
of time. "\\'h(ui such beds as were deposited in shallow water
near the mouth of the Mississippi during some part of the gla-
cial period shall have been upraised, organic remains will prob-
ably lirst appear and disappear at different levels, owing to
the migrations of species and to geographical changes. And
in the distant future, a geologist, examining these beds, would
be tempted to conclude that the average duration of life of the
embedded fossils had been less than that of the glacial period,
instead of having been really far greater, that is, extending
from before the glacial ejioch 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
will have to go on continuously accumulating during a very
long period, so that there may be time sufficient for the slow
procT^ss of modification ; hence the deposit will have to be a
very thick one ; and the species undergoing change will have
to live in the same district throughout this whole time. But
we have seen that a thick formation, fossiliferous throughout
its entire thickness, can accumulate only during a period of
subsidence ; and to keep the depth approximately the same,
which is necessary that the same marine species may hve on
the same space, the supply of sediment must nearly counter-
balance the amount of subsidence. But this same movement
of subsidence will tend to submerge the area whence the sedi-
ment is derived, and thus diminish the supply while the down-
ward movement continues. In fact, this nearly exact balancing
between the supply of sediment and the amount of subsidence
is probably a rare contingency ; for it has been observed, by
more than one paleontologist, that very thick deposits are
usually barren of organic remains, except near their upper or
lower limits.

It would seem that each separate formation, like the whole
pile of formations in any country, has generally been intermit-
tent in its accumulation. When we see, as is so often the case,
a formation composed of beds of dilVercnt mineralogical com-
position, we may reasonably suspect that the jirocess of deposi-
tion has been much intcrnij)t(Ml, as a change in the currents of
the sea, and a supply of sediment of a different nature will
generally have been due to geographical changes requiring
much time. Nor will the closest ins]iection of a formation give
any idea of the time which its deposition has consumed. Many
instances could be given of beds only a few feet in thickness,

riiAr. IX. IN ANY SINGLE FORMATION. ogj

roiM(\scntIiig formations, elsewhere thousands of feet in thick-
ness, and which must have required an enormous period for
(heir accumuhition ; yet no one ignorant of this fact woukl have
snspecled the vast lapse of time represented by the thinner for-
mation. Many cases could be f]fiven of the lower beds of a
formation havin*^ been upraised, denuded, submcrj^ed, and then
i('-covercd by the upper beds of the same formation — facts,
shcnving what wide, yet easily-overlooked, intervals have oc-
curred in its accumulation. In other cases we have the plainest
evidence in great fossilized trees, still standing upright as they
grew, of many long intervals of time and changes of level
(luring the process of deposition, which would never even have
been suspected, had not the trees chanced to have been pre-
served : tluis Sir C Lyell and Dr. Dawson found carboniferous
beds 1,400 feet tliick in Nova Scotia, with ancient root-bearing
strata, one above the other, at no less than sixty-eight diiferent
levels. Hence, when the same species occur at the bottom,
middle, and top of a formation, the probability is that they have
not lived on the same spot during the whole period of depo-
sition, but have disappeared and reapj)eared, perhaps many
times, during the same geological period. So that, if such spe-
cies were to undergo a consid(n-al)le amount of modification
during any one geological period, a section would not include
all the fin(^ intermediate gradations which must on our theory
have existed between them, but aljrupt, though perhaps slight,
changes of form.

It is all-important to remember that natin-alists have no
golden rule by which to distinguish species and varieties ; they
grant some little variability to each species, but when they
meet with a somewhat greater amount of dilference between
any two forms, they rank both as species, uidess tliey are en-
abled to coimect them together by the closest intermediate
gradations. And this from the reasons just assigned we can
seldom hope to effect in any one geological section. Supposing
B and C to b(; two sjiecies, and a third. A, to l)e found in an
older and underlying bed; even if A were strietly intermediate
l)(!tween B and C, it would simply be ranked as a tliird and
distinct sjiecies, unl(\ss at the sam«; time it could be most
closely coimected with either one or l)oth forms 1)>' intermediate
varieties. Nor should it be forgotten, as before explaitied, that
A might ])(; the actual ]irogenitor of B and C, and yet might
not necessarily be strictly intermediate between them in all re-
opccts. So that we might obtain the parcnt>specics and its

282 ABSENCE OF INTERMEDIATE VAEIETIP:S Chap. IX.

several modified descendants from tlu^ lower and upper beds of
the same formation, and unless "\ve obtained numerous transi-
tional gradations, we should not reco^ize their blood-relation-
ship, and should consequently be compelled to rank them as
distinct species.

It is notorious on what excessively slight differences many
paleontologists liave founded their species; and they do this
the more readily if the specimens come from different sub-
stages of the same formation. Some experienced conchologists
are now sinking many of the very fine species of D'Orbigny
and others into the rank of varieties ; and on this view we do
find the kind of evidence of change which on tlie theory we
ought to find. Look, again, at the later tertiary deposits,
which include many shells believed by the majority of natural-
ists to be identical with existing species ; but some excellent
naturalists, as Agassiz and Pictet, maintain that all these ter-
tiary species are specifically distinct, though the distinction is
admitted to be very slight ; so that here, unless we believe that
these 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 believe
that the great majority of naturalists are wrong, and that the
tertiar}' sjiecies are all truly distinct from the recent, we have
evidence of the frequent occurrence of sliglit modifications of
the kind required. If we look to rather wider intervals of time,
namely, to distinct but consecutive stages of the same great
formation, we find that the embedded fossils, though almost
universally ranked as specifically different, yet are far more
closely related to each other than are the species found in more
widely-separated formations ; so that here again we have un-
doubted evidence of change in the direction required by the
theory ; but to this latter subject I shall have to return in the
following chapter.

With animals and plants that propagate rapidly and do
not wander much, there is reason to suspect, as we have for-
merly seen, that their varieties are generally at first local ; and
that such local varieties do not spread widely and supplant
their parent-forms imtil they have been modified and perfected
in some considerable degree. According to this A'icw, the
chance of discovering in a fonnation in any one country all the
early stages of transition between any two such forms is small,
for the successive changes are supposed to liave been local, or
confined to some one spot. Most marine animals have a wide

Chap. IX. IN ANY SINGLE FORMATION. 033

range ; and wo have soon tliat with plants it is those wliicli
have the widest rani>-o, that oftonest present varieties; so that,
witli shells and other marine animals, it is pro])able that those
which liavc had the widest range, far exceeding the limits of
the known geological formations of Europe, have oftcnest given
rise, ilrst 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 for-
mation.

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 modification,
though long as measured by years, was, from the reasons
lately assigned, probably short in comparison with that during
which it remained without undergoing any ch.ange.

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, initil many specimens are collected from many
]ilaces ; and, in tlie case of fossil species, this can rarely be
effected by paleontologists. "We shall, perhaps, best perceive
the improbability of our being enabled to connect species by
numerous fine, intermediate fossil links, by asking ourselves
^^•hether, for instance, geologists at some future period will be
able to prove that our different breeds of cattle, sheep, horses,
and dogs, are descended from a single stock or from several
alwriginal stocks; or, again, Avhether certain sea-shells inliabit-
ing the shores of North America, which are ranked by some
conchologists as distinct species from their European represent-
atives, and by other conchologists as only varieties, are really
varieties, or are, as it is called, specifically distinct. This could
be effected only by the future geologist discovering in a fossil
state numerous intermediate gradations ; and such success is
imj>r(>bable in tlu; iiighest degree.

It has been assorted over and over again, l)y Avritors who
believe in the immutability of species, that geology yields no
linking forms. This assertion is entirely erroneous. As Sir
J. Lubbock has nMuarkod, "Every species is a link between
other allied forms." We clearly see this if we take a genus
having a score of recent and extinct species and destroy four-
lifths of thorn ; for in tliis case no one doubts that the ri'inain-
dor will stand much more distinct from each other. If the ex-
treme forn)s in the genus happen to have boon thus destroyed,

284 ABSENCE OF INTERMEDIATE VARIETIES Chap. IX.

the genus itself in most cases will stand more distinct from
ntlicr allied genera. The camel and the pig, or the horse and
the tapir, are now obviously very distinct forms ; but if we add
the several fossil quadrupeds which have already been discov-
ered to the families including the camel and pig, these forma
become joined by links not extremely wide apart. The chain
of linking forms does not, hovrever, in these cases, or in any
case, run straight from the one living form to the other, but
takes a circuitous sweep through the forms which lived during
long-past ages. What geological research has not revealed,
is the former existence of infinitely numerous gradations, as
fine as existing varieties, connecting nearly all our existing
species w'itli extinct species. But this ought not to be ex-
pected ; 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 liluvopc from the North Cape to the Mediterranean,
and fi'om Britain to Russia ; and therefore equals all the geo-
logical formations which have been examined with any accu-
racy, excepting those of the United States of America. I fully
agree with Mr. Godwin-x^usten, that the present condition of
the Malay Archipelago, with its numerous large islands sep-
arated by wide and shallow seas, probably represents the for-
mer state of Europe, while most of our formations were accu-
mulating. The Malay Archipelago is one of the richest re-
gions of the "whole world in organic beings ; yet, if all the
species were to be collected which have ever lived there, how
imperfectly would they represent the natural history of the
world !

But Ave have every reason to believe that the terrestrial
productions of the archipelago would be preserved in an ex-
tremely imperfect manner in the formations which we suppose
to be there accumulating. Not many of the strictly littoral
animals, or of those Avhich 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 accu-
mulate 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

Chap. IX. IN ANY SINGLE FORMATION. 285

the secondary formations lie in the past, -wonkl f^cncrally
be formed in the archipehigo only during poriods 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 sleeper 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 seas witiiin 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 ex-
tinction of life ; during the periods of elevation, there would
be much variation, but the geological record would then be
least perfect.

It may be doubted whether the duration of any one
great period of subsidence over the whole or part of the
archipelago, together with a contemporaneous accumulation
of sediment, would exceed the average duration of the same
specific forms; and these contingencies are indispensable for
the preservation of all the transitional gradations between
any two or more species. If such gradations were not all
fully preserved, transitional varieties would merely appear
as so many new and distinct species. It is also probable
that each great period of subsidence would be interrupted
by oscillations of level, and that slight climatal changes
would intervene during such lengthy periods ; and in these
cases the inhabitants of the archipehigo would migrate, and
no closely-consecutive record of their modifications could be
preserved in any one formation.

Very many of the marine inhabitants of the archipelago
now range: thousands of miles beyond its confines ; and
analogy plainly leads to the belief that it would be chiefly
these far-ranging species, though only some of them, which
would oftenest produce new varieties ; and the varieties
would at first generally be local or confined to one place ;
but if jiossessed of any decided advantage, or when further
modified and improve<l, they would slowly spread and supplant
their parent-forms. ^V^hen such varieties returned to their
ancient homes, as they would difTcr from their former state,
in a nearlv-unifonn, though ]>orhaj)s extremely-slight degree.

280 SUDDEN A^PEAPwA^X'E OF Chap. IX,

and as they would Ijc found embedded in sliglilly-different
sub-stages of the same formation, they would, according to
the principles followed l)y many paleontologists, be 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 forma
which, on our theor}', have connected all the past and present
species of the same gi-oup into one long and branching
chain of life. We ought only to look for a few links, and
such assuredly Ave do find — some more distantly, some more
closely, related to each other ; and these links, let them be
ever so close, if found in different stages of the same forma-
tion, would, by many paleontologists, be ranked as distinct
species. But I do not pretend that I should ever have suspect-
ed how poor was the record in the best preserved geologi-
cal sections, had not the absence of innumerable transitional
links between the species which lived at the commencement
and close of each formation, pressed so hardly on my theory.

On the sudden Apjjearance of ichole Groups of allied
/Species.

The abrupt manner in which Avhole groups of species
suddenly appear in certain formations, has been urged by
several paleontologists — for instance, by Agassiz, Pictet, and
Sedgwick — as a fatal objection to the belief in the trans-
mutation of species. If numerous species, belonging to the
same genera or families, have really started into life at
once, the fact would be fatal to the theory of descent with
slow modification through natural selection. For the devel-
opment of a group of forms, all of which have descended
from some one progenitor, nuist have been an extremely slow
process; and the progenitors must have lived long ages
before their mothfied descendants. But we continually over-
rate the perfection of the geological record and falsely infer,
because certain genera or families have not been foimd
beneath a certain stage, that they did not exist before that
stage. In all cases positive paleontological evidence may
be implicitly trusted ; negative evidence is worthless, as
experience has so often sho"wn. We continually forget how
large the world is, compared with the area over which our
geological formations have been carefully examined ; we

CiiAP. IX. GROUPS OF ALLIED SPECIES. 287

forf^ot that g-ioups of species may elsewhere have long:
existed, and liavc slowly multiplied, before they invaded
the ancient archipela^^oes of Europe and the United States.
We do not make due allowance for the enormous intervals
of time which have elapsed between our consecutive forma-
tions— loiiocr perhaps in many cases than the time required
for the accumulation of each formation. These intervals
will have g-iven time for the multiplication of species from
some one or some few parent-forms ; and in the succeeding^
formation such groups of species will appear as if suddenly
created.

I may here recall a remark formerly made, namely, that
it might require a long succession of ages to adapt an or-
ganism to some new and peculiar line of life, for instance,
lo liy through the air; and consequently that the transition-
al forms would often remain confined to some one region ;
but that, when this adaptation had once been effected, and
a few species had thus acquired a great advantage over
other organisms, a comparatively short time would 1)0 neces-
sary to produce many divergent forms, ■which would spread
rapidly and widely throughout the world. Prof. Pictet,
in his excellent review of this work, in commenting on
early transitional forms, and taking birds as an illustration,
cannot see how the successive modifications of the ante-
rior limbs of a supposed protot\'pe could possibly have been
of any advantage. But look at the penguins of the Southern
Ocean; have not these birds their front limbs in this precise
intermediate state of "neither true arms nor true wings?"
Yet these birds hold their place victoriously in the battle
for life; for they exist in infinite numbers and of many kinds.
I do not suppose that we here see the real transitional
grades through which the wings of birds have passed ; but
what special dilliculty is there in believing that it might
profit the modified descendants of the ]ienguin, first to become
enabled to flap along the surface of the sea like the logger-
headed duck, and ultimately to rise from its surface and glide
through the air?

I will now give a fmv examples to illustrate the fore-
going remarks, and to show how liable we are to error in
supposing that whole groups of sj^ecies have suddenly been
produced. Even in so short an interval as that between the
iirst and second editions of Pictet's great work on Paleon-
tologv, pu])lished in 18-i4-'4G and in ISSS-^o?, the conclusions

288 SUDDEN AITEAEANCE OF Cuap. IX.

on the first appearance and disappearance of several groups
of animals have l)ocn considerably modified ; and a third
edition •would rociuire still further changes. I may recall
the ■well-known fact that in geological treatises, published
not many years ago, mammals were always spoken of as
liaving abruptly come in at the commencement of the tertiary
series. And now one of the richest known accumulations of
fossil mammals, for its thickness, belongs to the middle of
the secondary series ; and true mammals have been discov-
ered in the new red sandstone at nearly the commencement of
tliis great series. Cuvier used to urge that no monkey oc-
curred 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 acci-
dent of the preservation of footsteps in the new red sandstone
of the United States, who would have A^entured to suppose
that, besides reptiles, no less than at least thirty kinds of birds,
some of gigantic size, existed during that period ? Not a frag-
ment of bone has been discovered in these beds. Notwith-
standing that the number of joints shown in the fossil impres-
sions corresponds with the number in the several toes of living
birds' feet, some authors doubt whether the animals which left
these impressions were really birds. Until quite recently these
authors might have maintained, and some have maintained, that
the whole class of birds came suddenly into existence during
the eocene period; but now we know, on the authority of
Prof. Owen, that a bird certainly lived during the deposition
of the upper greensand ; and still more recently, that strange
bird, the ArchcopterA'x, with a long, lizard-like tail, bearing a
pair of feathers on each joint, and with its wings furnished with
two free claAvs, has been discovered in the oolitic slates of So-
Icnhofcn. Hardly any recent discovery shows more forcibly
than this, how little we as yet know of the former inhabitants
of the Avorld.

I may give another instance, which, from having passed im-
der my own eyes, has much struck me. In a memoir on Fossil
Sessile Cirripedes, I have stated that, from the large number
of existing and extinct tertiary species ; from the extraordinary
abundance of the individuals of many sj:)ecies all over the world,
from the Arctic regions to the equator, inhabiting A-arious
zones of depths from the upper tidal limits to 50 fathoms ; from
the perfect manner in which specimens are preserved in the
oldest tertiary beds ; from the case with which even a frag-

Chap. IX. GROUPS OF ALLIED SPECIES. 289

nicnt of a valve can be recorrnizetl ; from all these circum-
stances, I infer that, had sessile cirripcdes existed durinn^ the
secondary periods, they would certainly have Ijcen preserved and
discovered ; and as not one species had then been discovered in
oeds of this age, I concluded that this grcjit jrroup had been
suddenly develo])ed at the commencement of the tertiary series.
This was a sore trouble to me, adding as I thought one more
instance of the abrupt appearance of a great group of species.
But my work had hardly been published, when a skilful pale-
ontologist, M. Bosquet, sent me a drawing of a perfect speci-
men of an unmistakable sessile cirripede, Avhich he had him-
self extracted from the chalk of Belgium. And, as if to make
tlio case as striking as possil)le, this sessile ciiripede was a
C'hthamalus, a very common, large, and ubiquitous genus, of
which not one specimen has as yet been foimd even in any ter-
tiary stratum. Hence we now positively know that sessile
cirripedes existed during the secondary period ; and these cir-
ripcdes might have been the progenitors of our many tertiary
and existhig species. Still more recently Tyrgoma has been
discovered by Mr, AA'oodward in the upper chalk.

The case most frecjucntly insisted on by paleontologists of
the apparently sudden appearance of a whole group of species,
is that of the teieostean iishes, low down in the Chalk period.
This group includes the large majority of existing species.
Lately, Prof. Pictet has carried their existence one sub-stage
further back ; and some paleontologists believe that certain
nmch older fishes, of which the affinities are as yet imperfectly
known, are really teieostean. Assuming, however, that the
whole of them did appear, as Agassiz maintains, at the com-
mencement of the chalk formation, the fact would certainly be
highly remarkal)lc ; but I cannot see that it would be an in-
superalile objection to these views, unless it could likewise be
shown that tlie species of this group appeared suddenly and
simultaneously throughout the world at tliis same period. It
is almost superfluous to remark that hardly an}' fossil-lish are
known from south of the equator; and by running tlu-ougli
Pictet's Paleontology it will be seen that very few species are
Ivtiown from several formations in Europe. Some few families
of (ish now have a confined range ; the teieostean fish miglit
formerly have had a simihirly confined range, and after having
been largely developed in some one sea, might have spread
widely. Nor have we any right to suppose that the seas of
the world have always been so freely open from eouth to north
13

£90 GROUPS OF ALLIED SPECIES Cuap. IX.

as they are at present. Even at tliis day, if the Malay Archi
pehigo "svcre converted into land, the tropical parts of the In-
dian Ocean would form a large and perfectly-enclosed basin,
in Avliich 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 geol-
ogy of other countries beyond the confines of Europe and the
United States, and fi'om the revolution in our paleontological
knowledge eflected by the discoveries of the last dozen years,
it seems to me to be about as rash to dogmatize on the succes-
sion of organic forms throughout the world, as it would be for
a naturalist to land for five minutes on a barren point in Aus-
tralia, and then to discuss the number and range of its jjroduc-
tions.

On the sudden A2)2)earance of Groups of allied Species in
the loicest Jcnoicn Fossil if eroiis Strata.

There is another and allied difficulty, which is much more
serious. I allude to the manner in Avhich many species in sev-
eral of the main divisions of the animal kingdom suddenly
appear in the lowest known fossiliferous rocks. Most of the
arguments which have convinced me that all the existing
species of the same group are descended from a single pro-
genitor, apply with nearly equal force to the earliest known
species. For instance, it cannot be doubted that all the Silu-
rian trilobites are descended from some one crustacean, which
must have lived long before the Silurian age, and which prob-
ably difl'ered greatly from an>' known animal. Some of the
most ancient Silurian animals, as the Nautilus, Lingula, etc.,
do not difter much from living sjiccies; and it cannot on our
theory be sujiposed that these old species were the progenitors
of all the species belonging to the same groups whicli have
subseciucntly appeared, for they are not in any degree inter-
mediate in character.

Consequently, if the tlicory be true, it is indis]nitable
that, before the lowest Silurian or Cambrian stratum was do-
posited long periods elapsed, as long as, or probably far longer
than, tlie whole interval from the Cambrian age to the present
day; I'.nd that during these vast periods the world swarmed

CuAP. IX. IN LOWEST FOSSILIFEROUS STRATA. ogj

■\vitli livinp; creatures. Here we encounter a formidable objec-
tion ; for it sceins dou])tful whether the eartli in a lit state for
the habitation of livin"^ creatures has lasted lono; cnouo-h. Sir
W. Tiionipson concludes that the consolidation of the crust can
hardly have occurred less than 20 or more than 400 million
years ago, Ijut probably not less than 98 or more than 200 mill-
ion years. Tliese very wide limits show how doubtful the
data are ; and other elements may have to be introduced into
tlie problem. Mr. C'roll estimates that about 00 million years
have elapsed since the Cambrian period, but this, judging from
the small amoiuit of organic change since the commencement
of the Glacial epoch, seems a very short time for the many and
great mutations of life, which have certainlv occurred since the
Cambrian formation; and the previous 140 million years can
hardly be considered as sufficient for the development of the
varied forms of life which certainly existed toward the close of
the Cambrian period. It is, however, probable, as Sir ^\^
Thompson insists, that the world at a verj- early period was
subjected to more rapid and violent changes in its physical con-
ditions than those now occurring; and such changes would
have led to corresponding rapid changes in the organic being-s
which inhabited the world at this remote period.

To the question why we do not hnd rich fossiliferous de-
posits belonging to these assumed earliest periods, I can give
no satisfactory answer. Several eminent geologists, with Sir
li. Murehison at their head, were until recently convinced that
we beheld in the organic remains of the lowest Silurian stratum
the first dawn of life. Other highly-competent judges, as Ja-qM
and E. Forbes, have disputed this conclusion. We should not
forget that only a small jiortion of the world is known with ac-
curacy. Not long ago, M. Barrande added another and lower
stage, abounding with new and peculiar species beneath the
old Silurian system. Henmants of several forms have also
been detected beneath BaiTande's so-called primordial zone in
the Longmynd group, now divided into two stages, and con-
stituting the Lower Cambrian system. The presence also of
])hosphatie nodules and bitunnnous matter in some of the low-
est azoic rocks, jirobably indicates life at these periods. Now
the great discovery of the Eozoon in the Laurent ian f(jrmation
of Canada has been made, for, after reading Dr. Carpenter's
description of tliis fossil, it is scarcely possible to doubt regard-
ing its organic nature. There are tiiree great series of strata
beneath tiie Siluriiin svslein in Canad:i, in the lowest of which

292 GROUPS OF ALLIED SPECIES Chap. IX.

the Eozoon was found ; and Sir W. Logan states that their
" united thickness may jiossibly far surpass that of all the suc-
ceeding rocks, fiom llie base of the paleozoic series to the pres-
ent time. We arc thus carried back to a period so remote,
that the appearance of the so-called Primordial fauna (of
Barraudc) may by some be considered as a comparatiyely
modern eyent." The Eozoon belongs to the most lowly or-
ganized of all classes of animals, but for its class is highly organ-
ized ; it existed in countless numbers, and, as Dr, Dawson has re-
marked, certainly preyed on other minute organic beings, which
must have lived in great numbers. Thus the words, which I
wrote in 1859, about the vast periods which had probably
elapsed before the Cambrian system, are almost the same with
those since used by Sir W. Logan. Nevertheless, the difliculty
of assigning any good reason for the absence beneath the up-
per Cambrian formations of vast piles of strata rich in fossils,
is very great. It does not seem probable that the most an-
cient beds have been quite worn away by denudation, or that
their fossils have been wholly obliterated liy raetamorphic ac-
tion, for if this had been the case we should have found only
small remnants of the formations next succeeding them in age,
and these -would always have existed in a partially-metamor-
])hoscd condition. But the descriptions which we possess of
the Silurian deposits over immense territories in Russia and in
North America, do not support the view, that the older a for-
mation is, the more it has invariably suffered extreme denuda-
tion and metamorphism.

The case at present must remain inexplicable ; and may be
truly urged as a valid argument against the views here enter-
tained. To show that it may hereafter receive some explana-
tion, I will give the following hypothesis : From the nature ot
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 Avhich the formations arc composed, we may
infer that from first to last large islands or tracts of land,
whence the sediment was derived, occurred in the neighbor-
hood of the now existing continents of Europe and North
America. But we do not know what Avas the state of tilings
in the intervals between the several successive fonnations ;
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
a lid unfathomable sea.

Chap. IX. IN LOWEST FOSSILIFEROUS STRATA. 293

Lookinp^ lo the existing oceans, whicli are thrice as exten-
sive as the hind, we see them studded with many ishmds ; but
not one truly oceanic ishind (with the exception of New Zea-
hind, if this can be called a truly oceanic island) is as ^-^et known
to afford even a renmant of any jialeozoic or secondary forma-
tion. Hence we may perhaps infer that, duriufr the paleozoic
and secondary periods, neither continents nor continental islands
existed where our oceans now extend ; for had they existed,
])aleozoicand secondary formations would in all j)roi)ability have
been accumulated from sediment derived from their wear and
tear ; and these would have been at least partiall}' upheaved
by the oscillations of level, which must have intervened during
these enormousl3'-long' periods. If, then, we may infer any
thing from these facts, we may infer that, where our oceans
now extend, oceans have extended from the remotest period of
which we have any record ; and, on the other hand, that where
cofitinents now exist, large tracts of hind have existc.'d, subjected
no doubt to great oscillations of level, since the earliest Silurian
j)criod. The colored map appended to my volume on Coral
lleefs led me to conclude that the great oceans are still mainly
areas of subsidence, the great archipelagoes still areas of oscil-
lations of level, and the continents areas of elevation. IJut we
have no reason to assume that things have thus remained from
the beginning of the world. Our continents seem to have been
formed by a jireponderance, during many oscillations of level,
of the force of elevation ; but may not the areas of preponder-
ant movement have changed in the lapse of ages ? At a period
long antecedent to the Silurian epoch, continents may have ex-
isted where oceans are now spread out ; and clear and open
oceans may have existed where our continents now stand. Nor
should we be justilied in assuming that if, for instance, the bed
of the Pacific Ocean were now converted into a continent, we
shouUl there find sedimentary formations in a recognizable con-
dition older than the Silurian strata, suj^posing such to have
been formerly deposited; for it might well happen that strata
which had subsided some miles nearer to the centre of the
earth, and which had been pressed on by an enormous weight
of superincumbent water, might have undergcme far more met-
amorphic action than strata Avhich have always remained
nearer to the surface. The immense areas in some parts of the
world, for instance in South America, of naked metamorphic
rocks, which must have been heated under great pressure, have
always seemed to me to require some special explanation; and

294 liirEEFECTION OF GEOLOGICAL RECOED. Chap. L\.

we ma}' pcrliaps believe that avc sec, in these large areas, the
many formations long anterior to the Silurian epoch in a com-
pletely metamorphosed and denuded condition.

The several difficulties here discussed — namely, that, though
•\vc find in our geological formations many links between the
species which now exist and which formerly existed, we do not
find infiiutely numerous fine transitional forms closely jouiing
them all together; the sudden manner in which several whole
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, undoubted-
ly, of the most serious nature. A\'e see this in the fact that
tlie most eminent paleontologists — namely, CuA-ier, Agassiz,
Barrande, Pictet, Falconer, E, Forbes, etc., and all our great-
est geologists, as Lyell, IMurchison, Sedgwick, etc., have unan-
imously, 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 other geologists
and paleontologists are much shaken in their former belief.
Those who believe that the geological record is in any d(>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 possess the last vol-
ume alone, relating only to two or three countries. Of this
volume, only here and there a short chapter has been pre-
served; and of each page, only here and there a few lines.
Each word of the slowly-changing language, more or less dif-
ferent in the successive chapters, may represent the forms of
life, which arc entombed in our consecutive formations, and
which falsely appear to us to have been abruptl}' introduced.
On this vicAV, the difficulties above discussed are greatly dimin-
ished, or even disappear.

CHAr. X. GEOLOGICAL SUCCESSION. 295

CHAPTER X.

ON TUE GEOLOGICAL SUCCESSION OF ORGA^^C BEINGS.

On the Slow nnd Snccci>9ivc Appearance of New Species— On their Diflfcrcnt Rates
of t'haii;,'C— Species once lost do not reappear — Groui)8 of Species follow the
game (Jc-ncnil Rules in their Appearance and Uisappearunce as do Sinfrlc Species
— On Extinction— On Sininltaneoiis C'hnn;,'es in the Forms of Life throu^rhout
the World— On the Affinities of Extinct Species to cacli other and to Li\ in;; Spe-
cies—On the State of Develo[)nKiit of Ancient Forms— On the Succession of tho
same Typea within the same Areas- Summary of preccdinjj and present Chapter.

Let us now see whether the several facts and laws relatint^
to the geological succession of organic beings better accord
with the common view of the immutability of species, or with
that of their slow and gradual modification, through descent
and natural selection.

New species have appeared very slowly, one after another,
both on the land and in the waters. Lyell has shown that it
is hardly possible to resist the evidence on this head in the
case of the several tertiary stages ; and every year tends to fill
up the blanks between the stages, and to make the percentage
system of lost and new forms more gradual. In some of the
most recent beds, though undoubtedly of high antitjuity if
measured by years, only one or two species arc extinct, and
only one or two arc new, having appeared there for the first
time, either locally, or, as far as we know, on the face of
the cartli. The secondary formations are more broken ; but,
as Bronn has remarked, neither the appearance nor. disappear-
ance of the many extinct species embedded in each formation
has been simultaneous.

Species of different genera iind 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 foimd in the midst of a
multitude of extinct fonns. Falconer has given a striking in-
stance of a similar fact, for an existing crocodile is associated
with many lost mammals and reptiles in the sub-IIimalayan
deposits. The Silurian Liiigula dilTcrs but little from the

296 TJIE GEOLOGICAL SUCCESSION Chap. X.

livinfj: spocics of this p^'onus ; whereas most of the other Silu-
rian Molhiscs and all the; Crustaceans have changed greatly.
The productions of the land seem to change at a quicker rate
than those of the sea, of whicli a striking instance has lately
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 JM. Barrande, which
intrude for a period in the midst of an older formation, and
then allow the preexisting fauna to reappear ; but Lyell's ex-
jjlanation, namely, that it is a case of temporary migration
from a distinct geographical province, seems to me satisfac-
tory.

These several facts accord well Avith our theory, which in-
cludes no fixed law of development, causing all the inhabitants
of an area to change abruptl}^, or simultaneously, or to an equal
degree. Tlic 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 quite independent of that of all
others. Whether such variations or individual differences as
may arise will be accumulated through natural selection in a
greater or less degree, thus causing a greater or less amount
of permanent modification, will depend on many complex con-
tingencies— on the variations being of a beneficial nature, on
the freedom of intercrossing, on the slowly-changing physical
conditions of the country, on the immigration of new colonists,
and on the nature of the other inhabitants with which the
varying species come into competition. Hence it is by no
means surprising that one species should retain the' same iden-
tical form much longer than others ; or, if changing, that it
should chang(! in a less degree. We find similar relations be-
tween the inhaljitants of distinct countries ; for instance, the
land-sliclls and coleopterous insects of jNIadeira have come to
diller considerably from their nearest allies oh the continent
of l^^urope, whereas the marine shells and birtls have remained
unaltered. We can perhaps understand the apparently quicker

Chap. X. OF ORGANIC BEINGS. 297

rate of change in terrestrial and in more higlily-org'anized pro-
ductions compared with marine and lower productions, by the
more complex relations of tlie hi<^her beings to tlieir organic
and inor^^nic conditions of life, as explained in a former chap-
ter. When many of the inhabitants of any area have become
modified and imjiroved, we can imderstand, on the principle of
competition, and from tlie all-important relations of organism
to organism in the struggle for life, that any form which does
not become in some deg'ree modified and improved, will be
liable to extermination. Ilencc we see why all the species in
the same region do at last, if we look to long-enougli intervals
of time, become niodilicd, for otherwise they would become
extinct.

In members of the same class the average amount of
change, during long and equal periods of time, may, perhaps, be
nearly the same ; but as the accumulation of long'-enduring' for-
mations, 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 inter-
mittent intervals of time ; consequently the amount of organic
change exhibited by the fossils embedded in consecutive for-
mations is not equal. Each formation, on this view, does not
mark a new and complete act of creation, but only an occa-
sional scene, taken almost at hazard, in an ever slowly-chan-
ging drama.

We can clearly understand why a species when once lost
should never reappear, even if the very same conditions of life,
organic and inorganic, should recur. For thougli the offspring
of one species might be ada])t{Hl (and no doubt this has occurred
in innunieral)le instances) to 1111 the place of another species' in
tlie economy of Nature, and thus supplant it; yet the two
forms — the- old and the new — would not be identically th.e
same ; for both would almost certainly inherit different char-
acters from their distinct progenitors, and organisms already
differing would vary in a different manner. For instance, it is
pist possible, if all our fantail jiigeons were destroyed, that
fanciers might make a new breed hardly distinguishable from
tlie present breed ; but if the parent rock-pigeon were likewise
destroyed, and imdcr Nature we have every reason to believe
that j»arent-fonns are generallv supplanted and exterminated
bv tlieir improved offspring, it is incredible that a fantail, iden-
tical with th(! existing breed, could he raised from any other
species of pigeon, or even from any other well-established race

298 GEOLOGICAL SUCCESSION, Chap. X.

of the domestic pigeon, for the successive variations would al-
most certainly be in some degree different, and the newly-
formed variety would probably inherit from its progenitor some
characteristic differences.

Groups of species, that is, genera and families, follow the
same general rules in their appearance and disappearance as
do single s))ecies, changing more or less qviickly, and in a
greater or lesser degree. A group, when it has once disap-
peared, never reappears ; that is, its existence, as long as it
lasts, is contiruious. I am aware that there are some apparent
excei:)tions to this rule, but the exceptions are surprisingly few,
so few that E. Forbes, Pictet, and Woodward (though all
strongly opposed to such views as I maintain), admit its truth ;
and the rule strictly accords with the theor}'. For all the
species of the same group, however long it may have lasted,
are the modified descendants of each other, and of some com-
mon progenitor. In the genus Lingula, for instance, the
species which have successively appeared at all ages nmst have
been connected by an unbroken series of generations, from the
loAvest Silurian stratum to the present day.

We have seen in the last chapter that many species of a
group sometimes falsely appear to have come in abruptly in a
body ; and I liavc attempted to give an explanation of tliis
fact, which if true would be fatal to my views. But such cases
are certainly exceptional ; the general rule being a gradual in-
crease 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 gen-
era Avithin a family, be represented by a vertical line of vary-
ing thickness, ascending through the successive geological for-
mations in which the species are found, the line will sometimes
falsely appear to begin at its lower end, not in a sharp point,
but al^ruptly ; it then gradually thickens upward, often keep-
ing for a space of equal thickness, and xdtimately thins out in
the upper beds, marking the decrease and final extinction of the
species. This gradual increase in number of the species of a
group is strictly conformable Avith the theory, for the species
of the same genus, and the genera of the same family, can in-
crease only slowly and progressively ; the process of modifica-
tion and the production 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 in-
to specie?, Avhich in their turn produce by equally slow steps

Chap. X. EXTINCTION. 099

other varieties and species, and so on, like tlie branching of a
great tree from a single stem, till the group becomes large.

On Extinction.

We have as yet spoken only incidentally of the disappear-
ance of species and of groups of species. On the theory of
natural selection the extinction of old forms and the produc-
tion of ne\v and improved forms are intimately connected to-
gether. The old notion of all tlie inhabitants of the earth hav-
ing been swept away by catastrophes at successive periods is
very generally given up, even by tliose geologists, as Elie de
Beaumont, ]\Iurcliison, Barrande, 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 disap-
pear, one after another, first from one sj^t, then from another,
and finally from tlie world. In some few cases, however, as by
the breaking of an isthmus and the conseciuent irrujition of a
multitude of new inhabitants into an adjoining sea, or by the
final subsidence of an island, the process of extinction may have
been rapid. Both single species and whole groups of species
last for very unequal periods ; some groups, as we have seen,
have endured from the earliest known dawn of life to the pres-
ent day ; some have disappeared before the close of the paleo-
zoic period. No fixed law seems to determine the length of
time during which any single species or any single genus en-
dures. There is reason to believe that tlic extinction of a
whole group of species is generally a slower process than their
production : if their appearance and disappearance be repre-
sented, as before, by a vertical line of varying tliickness, tlie
line is found to taper more gradually at its ujiper end, wliich
marks tlie 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 extermina-
tion of whole groups, as of ammonites toward the close of the
secondary periofl, 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 liav<; species
a definite duration. No 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 witli the remains of Mas-

300 EXTINCTION, Chap. X.

iodon, Mcgaihcrium, Toxodon, and other extinct monsters,
^vllich all coexisted with still liviiii? sliells at a very late geolo-
gical period, I Avas filled Avilh astonishment; for, seeing that
the horse, since its introduction by the Spaniards into South
America, has run wild over the Avholc country, and has in-
creased in numbers at an unparalleled rate, I asked myself
what could so recently have exterminated the former horse un-
der conditions of life apparently so favorable. But my aston-
ishment was groundless. Prof. Owea 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 Avould have felt the least sur-
prise 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 what that something
is, we can hardly ever tell. On the supposition of the fossil-
horse still existing as a rare species, we might have felt certain,
from the analogy of all other mammals, even of the slow-breed-
ing ele])hant, and from the history of the naturalization of the
domestic horse in South Amei'ica, that, xuider more favorable
conditions, it would, in a very few years, have stocked the
whole continent. 13ut wc could not have told what the un-
favorable conditions Avere which checked its increase, Avhether
some one or several contingencies, and at what period of the
horse'^s life, and in what degree, they severally acted. If the
conditions had gone on, however slowly, becoming less and
less favorable, we assuredly should not have perceived the fact,
yet the fossil-horse w^ould certainly have become rarer and
rarer, and finally extinct — its place being seized on by some
more successful competitor.

It is most diilicult alwa3's to renaembcr that the increase
of every creature is constantly being checked by imperceived
hostile agencies ; and that these same unperceived agencies
are amply sufficient to cause rarity, and finally extinction. So
little is this subject understood, that I have heard surprise re-
peatedly expressed at such great monsters as the Mastodon
and the more ancient Dinosaurians having become extinct; as
if mere bodily strength ga\e victory in the battle of life. Mere
size, on the contrary, would in some cases determine, as has
been remarked by Owen, quicker extermination from the greater
amount of requisite food. Before man inhabited India or Africa,
some cause must have checked the continued increase of the

CiiAP. X. EXTINCTION. 301

existing; elephant. A lii;;lily-capablc judge, Dr. Falconer, be-
lieves that it is chielly insects which, from incessantly harass-
ing and weakening the elephant in India, check its increase ;
and this was Bruce's conclusion with respect to the African
elephant in Abj'ssinia. It is certain that insects and blood-
sucking bats determine the existence of the larger naturalizec
quadrupeds in several parts of South America.

We sec 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 animals which have
been exterminated, eillier locally or wholly, through man's
agency. I may repeat what I published in 1815, uamel}', that
to admit that sjiecies generally become rare before they be-
come extinct — to feel no surprise at the rarity of a species,
and yet to marvel greatly when the species ceases to exist, is
much the same as to admit that sickness in the individual is
t)ie forerunner of death — to feel no surprise at sickness, but,
when the sick man dies, to wonder and to suspect that he died
by some deed of violence.

The theory of natural selection is grounded on the belief
that each new variety, and ultimately each new species, is pro-
duced and maintained by having some advantage over those
with which it comes into competition ; and the consequent
oxtinctioii of the less-favored forms almost inevitably follows.
It is the same with our domestic productions ; when a new
and slightly-improved variety has been raised, it at first sup-
plants the less improved varieties in the same neighborhood;
Avhen 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 a})pcarance of new forms, and the disap-
pearance of old forms, both those naturally and those artifi-
cially produced, are bound together. In nourishing groups,
the number of new specific f(jrms which have been produced
within a given time, has at some periods probably been greater
than the number of the old specific forms which have been ex-
terminated; but we know tliat species have not gone on indefi-
nitely increasing, 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.

llie competition will generally be most severe, as formerly
explained and illustrated by examples, between the forms
which are most like each other in all respects. Hence the

302 EXTINCTION. Chap. X.

improved and modified dcsrcudants of a species will generally
cause the externiiiiatiou 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
he the most liable to extermination. Thus, as I believe, a
number of new speci(3s descended from one species, that is, a
new genus, comes to sujiplant an old geiuis, belonging to the
same family. But it must often have happened that a new
species belonging to some one group has seized on the placfa
occupied by a species belonging to a distinct group, and thus
have caused its extermination. If many allied forms be de-
veloped from the successful intruder, many will have to yield
tlunr places ; and it Avill generally be the allied forms which
will suffer from some inherited inferiority in common. But
whetlicr it be species belonging to the same or to a distinct
class, which have yielded their places to other modified and
improved species, a few of the sufferers may often be preserved
for a long time, from being fitted to some peculiar line of life,
or from inhabiting some distant and isolated station, where
they will have escaped severe competition. For instance,
some species of Trigonia, a great genus of shells in the second-
ary formations, survive in the Australian seas; and a few mem-
bers of the great and almost extinct group of Ganoid fishes
still inhabit our fresh waters. Therefore the utter extinction
of a group is generalh', as Ave have seen, a slower process than
its production.

With res^DCct to the apparently svidden extermination of
whole families or orders, as of Trilobites at the close of the
paleozoic period and of Ammonites at 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 exter-
mination. I\Ioreover, when, by sudden immigration or by un-
usually 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
fonns Avhich thus yi(^^ld their places vrill commonly be allied,
for they Avill partake of the same inferiority in common.

Thus, as it seems to me, the manner in which single species
and Avliole groups of species become extinct accords well with
the theory of natural selection. We need not marvel at ex-
tinction ; if we must marvel, let it be at our own presumption
in imagining for a moment tliat wc understand the many com-

CiiAr. X. FOKMS OF LIFE CHANGING. 3O3

plex cuntinoencies, on which ilic existence of e;ich species de-
pends. If "SVC for<ret, for an instant, that each species tends to
-Ticreasc inordinately, and that some check is always in action,
yet seldom perceived l)y us, the whole economy of Nature will
be utterly obscured. Whenever we can precisely say why this
species is more alnmdant in individuals than that ; why this
species and not another can be naturalized in a given country;
then, and not until then, we may justly feel surprised why we
cannot account for the extinction of any j)articular species or
any grouj) of species.

On the Forms of Life changlnff almost simultaneously
throughout the World.

Scarcely any jialeontological discovery is more striking
than the fact that the forms of life change almost simultane-
ously throughout the world. Thus our European Chalk for-
jnation can be recognized in many distant parts of the world,
imder the most different climates, where not a fragment 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 the Chalk. It is not that
the same species are met with ; for in some cases not one
species is identically the same, but they belong to the same
families, genera, and sections of genera, and sometimes arc
Kimilarly characterized in such trilling points as mere superficial
sculpture. Moreover, other forms, which are not found in the
Chalk of Europe, but which occur in the formations either above
or below, occur in the same order at these distant points of the
world. In the several successive paleozoic formations of Rus-
sia, Western Europe, and North America, a similar parallelism
in the forms of life has been observed by several authors : so it
is, according to Lycll, with the several European and North
American tertiary deposits. Even if the few fossil species
which are common to the Old and New Worlds were kept
wholly out of view, the general ])arallelism in the successive
forms of life, in the paleozoic and tertiary stages, would still
be manifest, and the several formations could be easily corre-
lated.

These observations, however, relate to the marine inhabit-
ants of the Avorld: we have not sufTirient data to judge whelhcr

304 FORMS OF LIFE CHANGING Ciiai-. X.

the productions of llie land and of fresh water at distant points
clianfj^e in the same jiarallcl manner. We may doubt wliethcr
thoy have tluis changed: if the Meg-atherium, Milodon, Macra-
iiclicnia, 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 coexisted
with sea-shells all still living; but as these anomalous monsters
coexisted with the Mastodon and Horse, it might at least have
been inferred that they had lived during one of the later ter-
tiary stages.

When the marine forms of life are spoken of as haWng
changed simultaneously throughout the world, it must not be
supposed that tliis expression relates to the same thousandth
or ten-thousandth year, or even that it has a very strict geologi-
cal sense ; for if all the marine animals now living in Europe,
and all those that lived in Europe during the pleistocene period
(a very remote period as measured by years, including the
Avhole glacial epoch) Avcre compared Avith those now existing
in South America or in Australia, the most skilful naturalist
would hardly be able to say whetlicr the present or the pleis-
tocene inhabitants of Europe resembled most closely those of
the southern hemisphere. So, again, several highly-competent
obs(>rvers 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 inhabit-
ants of Europe ; and if this be so, it is e\ddent that fossilifer-
ous beds now being deposited on the shores of North America
would hereafter be liable to be classed with somewhat older
European beds. Nevertheless, looking to a remotely future
epoch, there can be little doubt that all the more modern ma-
rine formations, namely, the upper pliocene, the pleistocene
and strictly modern beds, of Europe, North and South Amer-
ica, and Australia, from containing fossil remains in some de-
gree allied, and from not including those forms which are found
only in the older underlying deposits, would be correctly
ranked as simultaneous in a geological sense.

The fact of the forms of life changing simultaneously, in the
above large sense, at distant parts of the Avorld, has greatly
struck those admirable observers, MM. do Verneuil and d'Arcli-
iac. After referring to the parallelism of the paleozoic forms
of life in various pails of Europe, they 'add : " If. struck by tliis
strange sequence, Ave turn our attention to North AmcricM,
and there discover a series of analogous iihenomena, it wi!.'

CiiAP. X. THROUGHOUT THE WORLD 305

appear certain that all these modifications of species, tlieir ex-
tinction, and the introduction of new ones, cannot be owin^r to
move chani^es in marine currents or other causes more or less
local and temporarv, but de])cnd on general laws which govern
the whole animal kingdom." M. Barrande has made forcible
remarks to j)recisely tin; same eflect. It is, indeed, quite futile
to look to changes of currents, climate, or other physical con-
ditions, as the cause of these great mutations in the forms of
lift; throughout the world, under the most different climates.
Wc must, as Barrande has remarked, look to some special law.
AVe shall see this more clearly when Ave treat of the present
distribution of organic l)cings, and find how slight is the rela-
tion between the ])hysical conditions of various countries, and
the nature of their inhabitants.

This great fact of the parallel succession of the forms of life
througlu^ut the world, is explicable on the theory of natural
selection. New species arc formed by having some advantage
over older forms ; and the forms, whicli are already dominant,
or have some advantage over the other forms in their own
country, would be the most likely to give birth to the greatest
number of new varieties or incipient sjiccies. 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 numljcr of new varieties. It is also natural that
the dominant, varying, and far-spreading species, which already
'lave invaded to a certain extent the territories of other species,
should be those which would have the best chance of spreading
still further, and of giving rise in new countries to other new
varieties and species. The process of diffusion would often be
very slow, depending on climatal and geographical changes,
on strange accidents, and on the gradual acclimatization of new
species to the various climates through which they might have
to jxiss, but in the course of time the dominant forms would
generally succeed in spreading, and would ultimately prevail.
Th(' diffusion would, it is probable, be slower with the terres-
trial inhabitants of distinct continents than with the marine
inhabitants of llie 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 through-
out the world, accords well witli tlic j>rinciple of new species

306 FORMS OF LIFE CHANGING Chap. X.

havinfi^ been formed by dominant species spreading widely and
varying; the new species thus produced being themselves dom-
inant, owing to their having had some advantage over their
already dominant parents, as well as over other species, ana
again spreading, varying, and producing new forms. The old
forms which are beaten and Avhicli yield their places to the new
and victorious forms, will generally be allied in groups, from
inheriting some inferiority in common ; and therefore, as new
and imjjroved groups spread throughout the world, old groups
disappear from the world ; and the succession of forms every-
where tends to corres])ond both in their first appearance and
final disappearance.

There is one other remark connected with this subject worth
making. I have given my reasons for believing that most of
our great formations, rich in fossils, were deposited during
periods of subsidence ; and that blank intervals of vast dura-
tion, as far as fossils are concerned, occurred during the periods
when the bed of the sea was cither stationary or rising, and
likewise when sediment was not thrown down quiclcly enough
to embed and preserve organic remains. During these long
and blank intervals I suppose that the inhabitants of each re-
gion underwent a considerable amount of modification and ex-
tinction, and that there was much migration from other parts
of the world. As we have reason to believe that 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 invari-
ably been the ease, and that large areas have invariably been
affected by the same movements. Wlien two formations have
been deposited in two regions during nearly, but not exactly,
the same period, we should find in both, from the causes ex-
plained in the foregoing paragraphs, the same general succes-
sion in the forms of life ; but the species would not exactly
correspond ; for there will have been a little jnore time in the
one region than in the other for modification, extinction, and
immigration.

I suspect that cases of this nature occur in Europe. Mr.
Prestwich, in his admirable memoirs on the eocene dejiosits of
England and France, is able to draw a close 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

Chap. X. TIIIIOUGIIOUT THE WOULD. ,^07

of tlie species bclongiiijr to the same genera, yet the species
thetiisehes diircr in a manner very difTicult to account for, con-
sidcrin<x the proximit}- of tlic tuo areas, unless indeed it be
assumed that an isthmus separated two seas inhabited by dis-
tinct but contemporaneous faunas. Lyell has made similar
observations on some of the later tertiary formations. Barrande,
also, shows that there is a striking general parallelism in the
successive Silurian deposits of Bohemia and Scandinavia ; never-
theless he finds a surprising amount of dillcrence in the species.
If the several formations in these regions have not been de-
jiosited during the same exact periods — a formation in one re-
gion often corresponding with a blank interval in the other —
and if in both regions the species have gone on slowly chan-
ging during tlie accumulation of tlie several formations, and
(hning the long intervals of time between tliem ; 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 aiiparcntly corresponding stages in the two regions.

On the Affinities of J^xtinct Species to each other, and to
Livinf/ J/ornis.

Let us now look to the mutual affinities of extinct and liv-
ing species. They all fall into a few grand classes ; and this
fact is at once explain(Ml on the princij)le 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, all extinct
species can be classed eitlier in still existing grou})s, or between
tliem. That the extinct forms of life help to fill up the inter-
vals between existing genera, families, and orders, cannot be
disputed. For if we confine our attention cither to the living
or to the extinct alone, the series is far less perfect than if we
combine both into one general system. With respect to the
vertebrata, whole pages could be filled with illustrations from
Owen, showing how extinct animals fall in between existing
groups. Cuvier ranked the Ruminants and Pachyderms, as the
two most distinct orders of mammals ; but Owen has discovered
so many fossil links, that he has had to alter th(; whole classifi-
cation, and has placed certain j)achyderms in the same sub-order
with nnuinants : for example, he dissolves by fine gradations
the apparently wide difference between the pig and the camel.

SOS AFFINITIES OF EXTINCT SPECIES. Cii.vp. X.

Another distinguished paleontologist, M. Gaudry, shows, in
the most striking manner, that very many of the fossil mam-
mals discDvered by him in Attica, connect in the plainest man-
ner existing genera. AMiat a -wonderful intermediate form is
the Tyiiotherium from South America, as the name given to it
by Prof. Gervais expresses, and Avliich cannot be placed in any
existing order of mammals ! Even the wide interval between
lairds and reptiles has been shown by Prof. Huxley to be par-
tially bridged over in the most unexpected manner, by, on the
one hand, the ostrich and extinct Archeopteryx ; and, on the
other hand, the Compsognathus, one of the Dinosaurians — that
group which includes the most gigantic of all terrestrial rep-
tiles. Turning to the Invertebrata, Barrande asserts, and a
higher authority could not be named, that he is every day
taught that, although paleozoic animals can certainly be classed
under existing groups, yet that at this ancient period the
groups were not so distinctly separated from each other as they
now are.

Some writers have objected to an}' extinct species or group
of species being considered as intermediate between living
species or groups. If by this term it is meant that an extinct
form is directly intermediate in all its characters between two
living forms, the objection is valid. But in a natural classifi-
cation many fossil species certainly stand between living spe-
cies, and some extinct genera between living genera, even
between genera belonging to distinct families. The most
common case, especially with respect to very distinct groups,
such as fish and reptiles, seems to be, that, supposing them to
be distinguished at the present day by a dozen characters, the
ancient members are separated by a somewhat lesser number
of characters, so that the two groups, though formerly quite
distinct, made at that period a somewhat nearer approach to
each other.

It is a common belief that the more ancient a form is, by
so much the more it tends to connect by some of its characters
groups now widely separated from each other. This remark
no doubt must be restricted to those groups Avhich have mider-
gone 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 Batra-
chians, the older Fish, the older Cephalopods, and the eocene

Chap. X. AFFINITIES OF EXTINCT SPECIES. 309

Mammals, witli llio more recent members of the same classes,
we must admit that there is truth in tlie i-emark.

Let us see how far these several facts and inferences accord
with tlic theory of descent with modification. As the subject
is somewhat complex, I must request the reader to turn to the
diafi^ram in the fourth chapter. We may suppose that the
numbered letters represent genera, and the dotted lines di-
verging from them the species in each genus. The diagram
is much too simple, too few genera and too few species being
given, but this is unimportant for us. The horizontal lines
may represent successive geological formations, and all the
forms beneath the uppermost line may be considered as ex-
tinct. The three existing genera, «'*, Q^*,])'*, will form a small
family ; i'* and _/"'*, a closely-allied family or sub-family ; and
o'*, e'*, Wi", a third lamily. These three families, together vvitli
the many extinct genera on the several lines of descent di-
verging irom the parent-form (A), will form an order; for all
Avill have inherited something in common from their ancient
and common ])rogenitor. On the principle of the continued
tendency to divergence of character, which was formerly illus-
trated 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 ditfer most
from existing forms. We must not, hoAvever, assume that di-
vergence of character is a necessary contingency; it depends
solely on the descendants from a species being thus enabled
to seize on many and different places in the economy of Natme.
Therefore it is quite possible, as we have seen in the case of
some Silurian forms, that a species might go on being slightly
modified in relation to its slightly-altered conditions of life,
and yet retain throughout a vast period the same general
characteristics. This is represented in the diagram by the let-
ter f'\

All the many forms, extinct and recent, descended from
(A), mak(% as Ix-fore remarked, one order;' and this order, from
the continued eflects of extinction and divergence of character,
has l)ecoine divided into several sul>families and families, some
of which are supposed to have perished at dilVercnt periods,
and some to have endured to the present da}'.

By looking at the diagram we can sec that if many of the
extinct forms, supposed to be embedded in the successive for-
mations, were discovered at several jioints low down in the
series, the three existing families on the uppermost line would

310 AFFINITIES OF EXTINX'T SrFX'IKS. Chap. X.

be rendered less distinct from each otlior. If, for instance, the
g'enera «', «V ^'"5 /*» ''^*» ^''^S ''^'^ Averc disinterred, these three
families would be so closely linked together that they proba-
bly M'ould have to be xniited into one great family, in nearly
the same manner as has occurred -with ruminants and certain
pach^'dtM-ms. Yet he who objected to call the extinct genera
which thus linked the living genera of three families together,
intermediate in character, would be justified, as they are inter-
mediate, not directly, but only by a long and circuitous course
through many "vndely-different forms. If many extinct forms
were to be discovered above one of the middle horizontal lines
or geological formations — for instance, above No. VI. — but
none from beneatli this line, then only two of the families
(those on the left hand, «'*, etc., and b^*, etc.) would have to be
imited into one ; and there wovild 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 («" to ni^*), on the uppermost line,
be supposed to differ from each other by half a dozen impor-
tant characters, then the families which existed at the peiiod
marked VI. would certainly have differed from each other by
a less numljer 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 some slight degree intermediate in character be-
tween their modilled descendants, or between their collateral
relations.

In Nature the case will be far more complicates! 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 Avill have been modified in various degrees.
As we possess only the last volume of the geological record,
and that in a very broken condition, Ave have no right to expect,
except in rare cases, to fill up the wide intervals in the natural
system, and thus imife distinct fiimilies or orders. All that we
have a right to expect is, that those groups which have within
knoA\ni 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 the existing members
of the same groups; and this, by the concurrent evidence of
our best paleontologists, is frequently the case.

Thus, on the thcorv of dcsrcnt witli modification, the main

CujLT.X. AFFINITIES OF EXTINCT SPECIES. 31 1

facts with respect to the mutual affinities of the extinct forms
of life to each other and to livinf^ 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 of any
one great ])eriod in the earth's history will be intermediate
in g'eneral character between that which preceded and that
which succeeded it. Thus the species which lived at the sixth
p^reat stage of descent in the diagram are the modified ofTsjjring
of those which lived at the fifth stage, and are the parents of
1 hose which became still more modified at the seventh stage;
hence they could hardly fail to be nearly intermediate in char-
acter between the forms <jf life above and below. We must, hoAV-
ever, allow ior the entire extinction of some preceding forms,
and in any one region for the immigration of new fijrms from
other regions, and for a large amount of modification during
the long and blank intervals between the successive forma-
tions. Subject to these allowances, the fauna of each geolo-
gical 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 Devo-
nian system, when this system was first discovered, were at
once recognized by paleontologists as intermediate in charac-
ter between those of the overlying carboniferous, and under-
lying Silurian system. But each fauna is not necessarily ex-
actly intermediate, as unequal intervals 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 intermediate in
character between the preceding and succeeding faunas, that
certain genera offer exceptions to the rule. For instance,
mastodons and elephants, when arranged by Dr. Falconer in
two scries, first according to their mutual affinities and then
according to their periods of existence, do not accord in ar-
rangement. The species extreme in character are not the old-
est or the most recent ; nor are those which are intermediate
in character, intermediate in age. But supposing for an
instant, in this and other sucli cases, "that the recoril of the
lir^t appearance and disappearance of the species was perfect,
we have no reason to believe that forms successively produced
necessarily endure for corresponding lengths of time : a very
ancient form might occasionally last much longer than a form
elsewhere subsequently produced, csjiecially in the case of

312 AFFINITIES OF EXTINCT SrECIES. Chap. X.

ten-estrial productions inliabiting separated districts. To com-
pare small tliiii;^s with p^reat : if the principal living and ex-
tinct races of the domestic pigeon were arranged as well as
they could be in serial affinity, this arrangement would not
accord closely with the order in time of their production, and
even less with the order of their disappearance ; for the par-
cnt-rock-pigeon still lives ; and many varieties between the
rock-pigeon and the carrier have become extinct ; and carriers
Avhich are extreme in the important character of length of
beak originated earlier than short-beaked tumblcrs,which are
at the opposite end of the series in this respect.

Closely connected with tlie statement that the organic re-
mains from an intermediate formation are in some degree in-
termediate in character, is the fact, insisted on by all paleon-
tologists, that fossils from two consecutive formations are far
more closclj' related to each other than are the fossils from
two remote formations. Pictet gives us a well-known in-
stance, 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 Prof. Pictet in his firm belief in the im-
mutability of species. He who is acquainted with the distribu-
tion of existing species over the globe, will not attempt to
account for the close resemblance of distinct species in close-
ly consecutive formations, by the ph^-sical conditions of the
ancient areas having remained nearly the same. Let it be re-
membered that the forms of life, at least those inhabiting the
sea, have changed almost simultaneously throughout the Avorld,
and therefore under the most different climates and conditions.
Consider the prodigious vicissitudes of climate during the pleis-
tocene period, which includes the whole glacial epoch, and note
how little the specific forms of the inhabitants of the sea have
been affected.

On the theory of descent, the full meaning of the fossil re-
mains from closely-consecutive formations being closely related,
though ranked as distinct species, is obvious. As the accumu-
lation of each formation has often been interrupted, and as
long blank intervals have intervened between successive forma-
tions, we ought not to expect to find, as I attempted to show
in the last chapter, in any one or in any two formations all the
intermediate vaiietics between the species which appeared at
the commencement and close of these periods : but we ought
to find after intervals, very long as measureil by years, but

CnAP. X. STATE OF DEVELOPMENT. 31 3

only moderately lonp;' as measured f^coloo-ically, closely-allied
Forms, or, as they have been called by some authors, represent-
ative species ; and these assuredly we do find. We find, in
short, such evidence of the slow and scarcely-sensible muta-
tion of specific forms as we have the right to expect.

On the State of DevelojJmoit of AncieJit comjtared with Liv-
ing Forms.

We have seen in the fourth chapter that the degree of
differentiation and specialization of the parts in all organic
beings, when arrived at maturity, is the best standard, as yet
suggested, of their degree of perfection or highness. We
have also seen that, as the specialization of parts and organs
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 that it may and
will leave many creatures with siin])li' and unimproved struct-
ures 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 will become
superior to their predecessors; for they will have to beat in the
struggle for life all the older forms with which they come into
close competition. We may therefore conclude that, if under
n nearly similar climate the eocene inhabitants of the world
could be put into competition with the existing inhobitants,
(he former would be beaten and exterminated by the latter, as
would the secondary by the eocene, and the paleozoic by the
secondary forms. So that by this fundamental test of victory
in the battle for life, as well as by the standard of the spociali-
zaticjn of organs, modern forms ought on the theory of natu-
ral selection to stand higher than ancient fonns. Is this the
case ? A large majority of paleontologists wcnikl answer in
the affirmative ; and I suppose that the answer must he ad-
mitted as true, though dillicult of full proof.

It is no valid objection to this conclusion, that certain
BrachiopcKls have been but slightly modilied from an extremely
remote geological epoch. It is not an insuperable diniculty
that Foramiiiifera have not, as insisted on b}* Dr. ('arp<'nter,
])rogress*ed in organization since even the Laurentian epoch :
for some organisms would have to remain iitted for simple con-
ditions of life, and what could be better fitted for this end than
14

314 STATE OF DEVELOPMENT OF Chap. X.

these lowly-organized Protozoa ? It is no great difficulty that
fresh-water shells, as Prof, Piiillips has urged, have remained
almost unaltered from the time when they first ajipeared to
the present day ; for these shells will have been subjected to
less severe competition than the moUusks inhabiting the more
extensive area of the sea with its innumerable inhabitants.
Such objections as the above v/ould be fatal to any view which
included advance in organization as a necessary contingent.
They would likewise be fatal to my view if Foraminifera, for
instance, could be proved to have first come into existence,
during the Laurentian epoch, or Brachiopods during the Cam-
brian formation ; for, in this case, there Avould not have been
time sufficient for the development of these organisms up to
the standard which they then reached. When once advanced
up to any given point, there is no necessity on the theory of
natvu'al selection for their further continued progress ; though
they will, during each successive age, have to be slightly
modified, so as to hold their places in relation to the changing
conditions of life. All such objections hinge on the question
whether w^e I'eally know how old the world is, and at what
periods the various forms of life first appeared ; and this may
be disputed.

The problem whether organization on the whole has ad-
vanced is in many ways excessively intricate. The geological
record, at all times imperfect, does not extend far enough back,
as I believe, to show Avith unmistakable clearness that within
the known history of the world organization has largely ad-
vanced. Even at the present day, looking to members of the
same class, naturalists are not unanimous which forms are to be
ranked as highest: thus, some look at the selaceans or sharks,
from their approach in some important points of structure to rep-
tiles, as the highest 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 retro-
graded in organization. To attempt to compare in the scale
of highness members of distinct types seemed hopeless : who
will decide whether a cuttle-fish be higher tlian a bee — that in-
sect which the great Von Baer believed to be " in fact more
highly organized than a fish, although upon another type?"
In the comjilex struggle for life it is quite credible that cms-

Chap. X. ANCIENT AND LIVING FORMS. 315

taceaus, not very high in tlrcir own class, might beat cephalo-
pods, tlic highest nioUusks ; and such crustaceans, though not
highlv devek)pccl, wouhl stand very high in the scale of inverte-
brate animals if judged by the most decisive of all trials — the
law of battle. Besides these inherent difficulties in deciding
which forms are the most advanced in organization, we ouglit
not solely to compare the highest members of a class at any
two periods — though undoul)tcdly this is one and perhaps the
most important element in striking a balance — but we ought
to compare all the members, high and low, at the two periods:
At an ancient epoch the highest and lowest mollusks, namely,
cephalopods an(l brachiopods, swarmed in numbers ; at the pres-
sent tim(^ both ordei*s are greatly reduced, while other orders,
intermediate in organization, have largely increased; conse-
quently some naturalists maintain that mollusks were formerly
more highly developed than at present ; but a stronger case
Clin be made out on the opposite side, by considering the vast
reduction of the lowest mollusks, and the fact that our existing
cephalopods, though few in nimibcr, arc more highh'' organized
than their ancient representatives. We ought also to compare
the relative proportional numbers of the high and low classes
throughout the world at any two periods : if, for instance, at
the present day fifty thousand kinds of A-ertebrate animals ex-
ist, and if we knew that at some former period only ten thou-
sand kinds existed, we ought to look at this increase in num-
ber in the highest class, which implies a great displacement of
lower forms, as a decided advance in the org-anization of the
world. AVe thus see how hopelessly dillicnlt it is to compare
with perfect fairness, under such extremely complex relations,
tlw; standard of organization of the imperfectly-known faunas
of successive j^eriods.

We shall apjireciatc this difficnlly the more cleaily, by
looking to certain existing faimas and iioras. From the extraor-
dinary manner in which European productions have recently
spread over New Zealand, and have seized on places whicli
must have lieen previously occupied, we must believe that, if
nil the animals and plants of Great Britain were set free in
New Zeahuul, in the course of time a multitude of ]3ritish forms
would become thoroughly naturaliz("d there, and would exter-
minate many of the natives. On the other hand, from hardly a
single inhabitant of the southern hemisphere having become
Anld in any jiart of Emope, we may well doubt whether, if all
the productions of New Zealand vicrc set free in Great Britain,

310 SUCCESSION OF THE Cuap. X.

any considcriiblc number -would be enabled to seize on jilaces
now occupied by our native plants and animals. Under this
point of view, the productions of Great Britain stand much
hioher in the scale than those of New Zealand. Yet the most
skilful naturalist, from an examination of the species of the two
countries could not have foreseen this result.

Agassiz and several other hif^hly-competent judges insist
that ancient animals resemble to a certain extent the embryos
of recent animals belonging to the same classes ; and that the
geological succession of extinct forms is nearly parallel Avith
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,
OM'ing to variations supervening at a not early age, and being
inherited at a corresponding age. This process, while it leaves
the embryo almost unaltered, continually adds, in the course
of successive generations, more and more difference to the adult.
Thus the embryo comes to be left as a sort of picture, preserved
by Nature, of the ancient and less modified condition of the
animal. This view may be true, and yet may never be capable
of full proof. Seeing, for instance, that the oldest known mam-
mals, reptiles, and fishes, strictly belong to their proper classes,
though some of these old forms are in a slight degree less dis-
tinct 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 Yertebrata,
until beds rich in fossils are discovered far beneath the lowest
Silurian stratum — a discovery of which the chance is small.

On the Succession of the same Types xcitJtin the same Areas,
during the later Tertiary Periods.

Mr. Clift many years ago showed that the fossil mammals
from the Australian caves were closely allied to the living mar-
supials of that continent. In South America, a similar relation-
ship is manifest, even to an uneducated eye, in the gigantic
pieces of armor, like those of tlie armadillo, found in several
parts of I^a Plata ; and Prof. Owen has shown in the most
striking manner that most of the fossil manmials, buried there
in such lunnbers, are related to South American t^-pes. This
relationship is even more clearl}' seen in the wonderful collection
of fossil bones made by MM. Lund and Clausen in the caves of
Urazil. I was so much injprcssed with these facts that I

Chap. X. SAME TYPES IN THE SAME AREAS. 317

stroni^ly insisted, in 1839 and 1845, on tliis " law of the suc-
cession of types," on " tliis -wonderful relationship in the same
continent between the dead and the livinrr." Prof. Owen has
subsecjuentlv extended the same ^"eneralization to tlie mammals
of the Old World. We see the same law in this author's res-
torations of the extinct and ^ijj^antic birds of New Zealand.
We see it also in the birds of the caves of Brazil. Mr. ^V^)^)d-
ward has shown that the same law holds good with sea-shells,
but, from the wide distribution of most genera of mollusks, it
is not well dis})layed by them. Other cases could be added, as
the relation between the extinct and living land-shells of Ma-
deira ; and between the extinct and living brackish-water shells
of the Aralo-Casjiian Sea.

Now what does this remarkable law of the succession of
the same types within the same areas mean ? He would be a
bold man, who, after comparing the present climate of Aus-
tralia and of parts of South America under the same lati-
tude, would attempt to account, on the one hand,bv dissimilar
physical conditions, for the dissimilarity of the inhabitants of
these two continents, and, on the other hand, by similarity of
conditions, for the uniformity of the same types in each 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 otln^r
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
])ublications above alluded to, that in America the law of dis-
tribution of terrestrial matnmals was foniierly dillV-rent from
what it now is. North America formerly 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 Falconer and Cautley's discoveries, that Northern
India was formerly more closely related in its mammals to
Africa than it is at the present time. Analogous facts could
be given in relation to the distribution of marine animals.

On the theory of descent with modillcation, the great law
of the long-enduring, but not inmiutable, succession of the
same t^'pes within the same areas, is at onct; explained; for the
inhabitants of each <|uarter of tin; world will obviously tend to
leave in that quarter, during the next succeeding period of
time closely-allied though in some degree modified descend

318 SUMMAKY OF THE Cuap. X.

ants. If llio inhabitants of one continent formerly differed
greatly from those of another continent, so will their modified
descendants still dillcr in nearly the same manner and degree,
lint after very long intervals of time, and after great geo-
graphical changes, permitting much inter-migration, the fee-
bler will yield to the more dominant forms, and there will be
nothing innnutable in the laws of past and present distribu-
tion.

It may be asked in ridicule, whctlier I suppose tliat the
megatherium and other allied huge monsters, which formerly
lived in South America, have left behind them the sloth, arma-
dillo, and anteater, as their degenerate descendants. This can-
not for an instant be admitted. These huge animals have
become wlioll^'^ extinct, and have left no progeny. But in the
caves of Brazil, there are many extinct species Avhich are close-
ly allied in size and in all other characters to the species still
liv-ing in South America ; and some of these fossils may be the
actual progenitors of living species. It must not be forgotten
that, on our theory, all the species of the same genus are the
descendants of some one species; so that, if six genera, each
having eight species, be found in one geological formation, and
in a succeeding formation there be six other allied or repre-
sentative genera each Avith the same number of species, then we
may conclude that generally only one species of each of the
older genera has left modified descendants, which constitute
the several species of the new genera ; the other seven species
of each old genus ha^ang died out and left no progeny. Or,
and this probably 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 whole genera having become utterly extinct. In failing
ordcre, 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 andprese7it Chapter.

I have attempted to show that the geological record is ex-
tremely imperfect ; that only a small portion of the globe has
been geologically explored with care ; that only certain class-
es of organic beings have been largely preserved in a fossil
state; that the number both of specimens and of species, pre-
served in our museums, is absolutely as notliing, compared

CiiAi". X. PRKCKDING AND PKESENT CHAPTER. 319

with the number of p^encralions which must have iiasscd away
even during a siii<:;le formation; lliat, owinfj;' to subsidence
being ahuost necessary for the accumulation of deposits rich in
fossil species of very many kinds and thick enough to resist fu-
ture degradation, great intervals of time must have elapsed
between most of our successive formations; that there has
probably been more extinction during the periods of subsi-
dence, and more variation during tlie periods of elevation,
and during the latter the record will have been least perfectly
kept ; that each single formation has not been continuously
deposited; that tlH> duration of each formation is, probably,
short compared with the average duration of specidc forms ;
that migration has played an important part in the first ap-
pearance of now forms in any one area and fonnation ; that
widely-ranging species are those which have varied most fre-
quently, and have oftenest given rise to new species ; that va-
rieties have at first been local ; and lastly, although each spe-
cies must have j^asscd through numerous transitional stages, it
is probable that the periods, during which each underwent
modification, though many and long as measured l)y years,
have been short in comparison with the periods during which
each remained in an unchanged condition. These causes, taken
conjointly, will, to a large extent, explain why — though we do
find many links — we do not find interminable varieties, con-
necting together all extinct and existing forms liy the finest
graduated steps. It should also be constantly borne in mind
that any linking varieties between two or more forms, which
might be found, would be ranked, unless the whole chain could
be perfectly restored, as so many new and disthict species ; for
it is not pretended that we have any sure criterion by which
species and varieties can be discriminated.

H(! who rejt;cts these views on the imperfection of tlie 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 rep-
resentative species found in the successive stages of the same
great formation ? lie may disbelieve in the immense intervals
of time which have elapsed between our consecutivt; forma-
tions ; he may overlook how important a part migration has
tjlaycd, when the fonnations of any one gieat region alone, as
that of Europe, are considen-d ; he may urge the apparent, but
often falsely appanMit, sudden coming in of whole groups of
species. He may ask where are the remains of those infinitely-

3J0 SUMMARY OF THE Chap. X.

numerous or<Tanisnis wliicli must have existed long before the
Cambrian system ^vas deposited ? We now know that at least
one animal did then exist ; but I can answer the above ques-
tion only l)y supjiosin<^ that where our oceans now extend tliey
have extended for an enormous .period, and wliere our oscillat-
ing continents now stand, they have stood since the coinmence-
mcnt of the Cambrian system ; but that, long before that
epoch, the world presented a Avidcly-diirerent aspect ; and that
the older continents, formed of formations older than any
known to us, exist now only as remnants in a metamorphosed
condition, or he still buried under the ocean.

Passing from these difficulties, the other great leading
facts in paleontology seem to me simply to follow on the the-
ory of descent with modification through natural selection.
We can thus understand how it is that new species come in
slowly and successively ; how species of different classes do
not necessarily change together, or at the same rate, or in the
same degree ; yet in the long-run that all undergo modification
to some extent. The extinction of old forms is the almost
inevitable consequence of the production of new fonns. We
can imderstand Avhy Avhcn a species has once disappeared it nev-
er reappears. Groups of species increase in numbers slowly,
and endure for unequal periods of time ; for the process of
modification is necessarily slow, and depends on many com-
plex 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 infe-
riority inherited from a common progenitor, tend to become
extinct together, and to leave no modified oQ'spring on the face
of the earth. But the utter extinction of a whole group of
species has sometimes been a slow process, from the surnval
of a few descendants, lingering in protected and isolated situ-
ations. When a group has once wholly disappeared, it does
not reappear; for the link of generation has been broken. -

AVe can understand how the dominant fonns which spread
widel}' and yield the ;;Teatest number of varieties Avill tend to
people the world with allied, but modified, descendants ; and
these will generally succeed in displacing the groups which are
their inferiors in the struggle for existence. Hence, after long
intervals of time, the jiroductions of the world apjicar to have
changed sinmltaneously.

We can understand how it is that all the forms of life

CiiAP. X. PRECEDING AND PRESENT CHAPTER. 321

ancient and recent, make tog-ctlier a (c\v f^rand classes ; for all
arc at least thus far connected by generation. We can undci'-
stand, from the continued tendency to divergence of character,
why the more ancient a form is, the more it gcnc^rally differs
from those now living; why ancient and extinct forms often
tend to fill up gaps between existing forms, sometimes blend-
ing two groups, previously classed as • distinct, into one ; but
more connnonly 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 direct-
ly intermediate between existing forms ; but are intermcfhate
onl}' by a long and circuitous course through other extinct and
difl'erent forms. We can clearly sec why the organic remains of
closely-consecutive formations are closely allied ; for they are
closely linked togetlier by generation. ^Ve can clearly see why
the remains of an intermediate formation are intermediate in
cliaracter.

The inhabitants of each successive period in the world's
history must have beaten their predecessors in the race for life,
and are, in so far, higher in the scale of Nature, and tlieir
structure has generally become more specialized ; and this may
account for the common belief held by so many paleontolo-
gists, 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 explanation according to
our views. The succession of the same types of structure with-
in the same areas during the later geological periods ceases to
be mysterious, and is intelligible on the principle of inlierit-
ancc.

If, then, the geological record be as imperfect as many be-
lieve, and it may at least be asserted that the record cannot be
jiroved to be much more perfect, the main ol)jections to the
theory of natural selection are greatly diminished or disappear.
On the other hand, all the chief laws of paleontology plainly
jiroflaim, as it seems to me, that species have been produced
by ordinary generation: old forms having been supjilanted by
new and imjjroved forms of life, the products of Variation and
the Survival of the Fittest.

322 GEOGKAPIIICAL DISTRIBUTION. Cuai-. XI.

CHAPTER XI.

GKOGRAPIIICAL DISTKiCUTION.

f resent Distribution cnnnot be accounted for by Differences in Phj-sical Conditions
— Importance of Barriers — Afllniiy of the Prodnctiotis of the same Continent —
Centres of Creation — Means of Dispersal by Changes of Climate and of the Level
of the Land, and by Occasional Means — Dispersal during the Glacial Period —
Alternate Glacial Periods in the North and South.

In' considering the distribution of organic beings over the
face of the globe, the first great fact which strikes us is, that
neither the similarity nor the dissimilarity of the inhabitants
of various regions can be accoimted for by their climatal and
other jihysical conditions. Of late, almost every author who
has studied the subject has come to this conclusion. The case
of America alone would almost sulllce to prove its truth : for, if
we exclude th.e northern parts where the circumpolar land is
almost continuous, all authors agree that one of the most fun-
damental divisions in geographical distribution is that between
the New and Old Worlds ; yet, if Ave travel over the vast
American Continent, from the central parts of the United
States to its extreme southern point, we meet with tin;
most diversified conditions ; liinnid districts, arid deserts, lofty
moimtains, grassy plains, forests, marshes, lakes, and great
rivers, under almost every temperature. Tlierc is hardly a
climate or condition iii the Old World which cannot be paral-
leled in the New — at least as closely as the same species gen-
erally require. No doubt small areas can be jiointed out in
the Old A\''orld hotter than any in the New A^'orld, but these
are not inhabited by a fauna different from that of the sur-
rounding districts ; for it is very rare to find a group of organ-
isms conilned to a small area, having conditions peculiar in
only a slight degree. Notwithstanding this general parallel-
ism in the conditions of the Old and New Worlds, how widely
different are their living productions!

In tho southern hemisphere, if wc compare large tracts of

CuAP. XI. GEOGRAPHICAL DISTRIBUTION. 323

land in Australia, South Africa, and Western South America,
between latitudes 20"^ and 35°, we shall find parts extremely
similar in all their conditions, yet it would not he possible to
point out three faunas and floras more utterly dissimilar. Or
again, we may compare the productions of South America
south of hit, 35° with those north of 25°, which consequently
are separated by a space of ten deg'rces of latitude and are ex-
posed to considerably different conditions, yet they are incom-
I)arably more closely related to each other than they arc to the
productions of Australia or Africa under nearly the same cli-
mate. Analog'ous facts could be given with respect to the
inhabitants of the sea.

A second great fact which strikes us in our general review
is, that barriers of any kind, or obstacles to free migration, are
related in a close and important manner to the differences be-
tween the productions of various regions. We sec this in the
great difference of nearly all the terrestrial productions of the
New and Old Worlds, excepting in the northern parts, Avhere
the land almost joins, and where, under a slightly-different cli-
mate, there might have been free mij^Tation for the northern
temperate forms, as there now is for the strictly arctic produc-
tions. We see the same fact in the great difference betwefMi
the inhabitants of Australia, Africa, and South America, under
the same latitude : for these countries are almost as much iso-
lated from each other as is possible. On each continent, also,
we see the same fact ; for, on the opposite sides of lofty and
continuous mountain-ranges, of great deserts, and even of large
rivers, we find different productions ; though as mountain-
chains, deserts, etc., are not as impassable, or likely to have
endured so long, as the oceans separating continents, the differ-
ences are very inferior in degree to those characteristic of dis-
tinct continents.

Turning to the sea, we find the same law. The marine in-
habitants of the eastern and western shores of South America
arc very distinct, with extremely few fishes, shell, or crabs, in
common ; but Dr. GUnther has recently shown that on opjio-
site sides of the Isthmus of Panama, about thirty jier cent, of
the fishes are the same ; and this fact has led naturalists to be-
lieve that the istlnnus was formerly open. Westward of the
shores of America, a wide space of open ocean extends, with
not an island as a hahing-place for emigrants ; here we have a
barrier of another kind, and as soon as this is passed we meet
in the eastern islands of the Pacilic with another and totally

324 GKOGKAPIIICAL DISTRIBUTION. Chap. XI.

distinct fauna. So that three marine faunas range far north-
ward and southward in parallel lines not far from each other,
imder corrcspondini^ climates ; but from beinf^ separated from
each other by impassable barriers, either of land or open sea,
they are almost wholly distinct. On the other hand, proceed-
ing still farther westward from the eastern islands of the tropi-
cal parts of the Pacific, we encounter no impassable barriers,
and we have innumerable islands as halting--places, or continu-
ous coasts, imtil after travelling over a hemisphere we come to
the shores of Africa ; and over this vast space we meet witli
no well-defined and distinct marine faunas. Although so few
shells, crabs, or fishes, arc common to the above-named three
approximate faunas of Eastern and Western America and the
eastern Pacific islands, yet many fish 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 state-
ment, is the ailinity of the productions of the 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 innumerable instances.
Nevertheless the naturalist, in travelling, for instance, from
north to south, never fails to be struck by the manner in which
successive groups of beings, specifically distinct, nearly related,
replace each other. He hears from closely-allied, yet distinct
kinds of birds, notes nearly similar, and sees their nests simi-
larly constructed, but not quite alike, with eggs colored in
nearly the same manner. The plains near the Straits of Magel-
lan 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 in-
habiting Africa and Australia imdcr 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 of biz-
cacha ; we look to the waters, and we do not find the beaver
or nuisk-rat, but the coypu and capybara, rodents of the South
Americaii ty\)C. Inmunerable 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

Chap. XI. GEOGRAPHICAL DISTRIBUTION. 305

(>sscnlially Aniorlcan, though they may be all peculiar species.
We may look back to past ages, as shown in tli(j last chapter,
and we lind American types then prevailing on the American
Continent and in the American seas. AVe see in these fact.s
some deep organic bond, throughout space and time, over the
same areas of land and water, and indej)endent of physical con-
ditions. 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 positive!}' know, produces organisms quite Hke each
other, or, as we see in the case of varieties, nearly alike. The
dissimilarity of the inhabitants of different regions may be at-
trilnited to modification througli natural selection, and in a
subordinate degree to the definite inlluence of different phys-
ical conditions. The degree of dissimilarity will depend on
the migration of the more dominant forms of life from one re-
gion into another having been prevented more or less effectually,
at periods more or less remote — oii the nature and number of
the former inmiigrants — and on the action of the inhabitants
on each other in leading to the preservation of different modifi-
cations; the relation of organism to organisin in the struggle
for life being, as I have already often remarked, the most im-
portant of all relations. Thus the high importance of barriers
comes into play by checking migration ; as does time for the
slow process of modification througli natural selection. Widely-
ranging species, abounding in individuals, which have already
triumphed over many competitors in their own widelj'-extendcd
homes, will have the best chance of seizing on new places, when
they spread into new countries. In their new homes they will
be exposed to new conditions, and will fre(iuently undergo
further modification and improvement ; and thus they will be-
come still further victorious, and will produce grou[is of modi-
fied descendants. On this principle of inheritance with modili-
eation, we can uiidci-stand how it is that sections of genera,
whole genera, and even families, are confined to the same areas,
as is so commonly and notoriously the case.

I believe, as was remarked in the last chapter, in no law of
necessary d(?velopment. As the variability of each species is
an independent property, and will Ix; taken advantage of by
natural selection, only so far as it jirolits each individual in its
complex struggle for life, so the amount of modification in
difierent species Avill be no uniform (juantity. If a number of
species, after having long conipeteil witli each otlier in their

32G SINGLE CENTRES OF CREATION. Chap. XI.

old home, were to mi^^atc in a body into a new and afterward
isolated country, they Avould be little liable to modification ;
for n('itli(>r niig-ration nor isolation in themselves can effect any
tiling. These principles come into play only by bringin*:^ or-
ganisms into new relations with each other, and in a lesser de-
gree Avith the surrounding physical conditions. As we have
seen in the last chai)tcr that some forms have retained nearly
the same character from an enormously remote geological
period, so certain s})ecies have migrated over vast spaces, and
have not become greatly or at all modified.

According to these views, it is obvious that the several
species of the same genus, though inhabiting the most distant
quarters of the world, must originally have proceeded from the
same source, as they are descended from the same progenitor.
In the case of those species, which have undergone during
whole geological periods but little modification, there is not
much difficulty in believing that they may have migrated from
the same region ; for, during the vast geographical and climatid
changes which have supervened since ancient times, almost
any amount of migration is possible. But in many other cases,
in Avhich we have reason to believe that the species of a genus
have been produced within comparatively recent times, there is
great difficulty on this head. It is also obvious that the individ-
uals of the same species, though now inhabiting distant and
isolated regions, must have proceeded from one spot, where
their parents were lirst produced: for, as explained in the last
chajiler, it is incredible that individuals identically the same
should have been produced from parents specifically distinct.

Single Centres of supposed Creation. — We are thus brought
to the question which has been largely discussed by naturalists,
namely, whether species have beeia created at one or more
points of the earth's surface. Undoubtedly there are many
cases of extreme difficulty in understanding how the same species
could possibly have migrated from some one point to the several
distant and isolated points where noAV found. Nevertheless the
simplicity of the view that each species was first produced
within a single region captivates the mind. lie Avho rejects it,
rejects the vera causa of ordinary generation with subsequent
migration, and calls in the agency of a miracle. It is univer-
sally admitted that in most cases the area inhabited by a spe-
cies 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 be easily passed over

CuAP. XI. SINGLE CENTRES OF CREATION. . 327

by mip^raliun, the fact is g'iv^cn as something njiiarkablc and
exceptional. The incapacity of migrating across a wide sea is
more clear in the case of terrestrial mannnals than perhaps with
any other organic beings; and, accordingly, Ave iind no inex-
plicable instances of the same mammals inhabiting distant
points of the world. No geologist feels any dilliculty in Great
Britain possessing tlu^ same (juadrupeds 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 Soutlx
America ? The conditions of life are nearly the same, so that
a multitude of European animals and plants have become nat-
uralized 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
]>lants, from their varied means of disp(>rsal, have migrated
across the wide and broken interspaces. The great and striking
influence of barriers of all kinds is intelligible only on the view
that the great majority of species have been produced on one
side, and have not been able to migrate to the opposite side.
Some few families, many sub-families, very many genera, and a
still greater number of sections of genera, are conlined to a sin-
gle region ; and it has been oljserved by several naturalists that
the most natural genera or those genera in whicii the species are
most closely related to each other, are generally confined to the
same countr}', or if they have a wide range that their range
is continuous. What a strange anomaly it woidd be, if a di-
rectly opposite rule were to prevail, when we go down one step
lower in the series, namely, to the individuals of the same spe-
cies, 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 naturalists,
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 pres-
ent conditions permitted, is the most jirobable. Undoubtedly
many cases occur, in which we cannot explain how the same
species could have jiassed from one point to the other. But
tlic geographical and dimatal dianges, which have certainly
occurred within recent geological times, nuist have rendered
discontinuous the formerly conliinious range of many species.
So that we are reduced to consider whether the exceptions to

328 • SINGLE CENTKES OF CKEATION. Cii.vr. XI.

contiiuiity of rani^c arc 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
^vould be hopelessly tedious to discuss all the exceptional cases
of the same species, now living- at distant and separated points;
nor do I for a moment i)retend that any explanation could l)c
olVercd of many instances. But after some jireliminary remarks,
I will discuss a few of the most striking classes of facts ; namely,
the existence of the same species on the summits of distant;
mountain-ranges, and at distant points in the arctic and ant-
arctic regions; and secondly (in the following chapter), tlic
wide distribution of fresh-water productions ; and thirdly, the
occurrence of the same terrestrial species on islands and on the
main-land, 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 ex-
plained on the view of each species having migrated from a
single birthplace; then, considering our ignorance Avith respect
to former climatal and geographical changes, and to the various
occasional means of transport, the belief that a single birthplace
is the law, seems to me 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 the
iheorj- all be descended from a common progenitor, can have
migrated, undergoing modification during their migration, from
some one area. When most of the species inhabiting one re-
gion are diflcrcnt from those of another region, but are closely
allied or belong to the same genera, if in all such cases it can
be shown that there probably has been at some former period
migration from the one region to the other, our general view
will be much strengthened ; for the explanation is obvious on
the principle of descent with modification. A volcanic island,
for instance, upheaved and fomied at the distance of a few
hundreds of miles from a continent, would prol^ably 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 tlicory of
indi'pendent 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 spc-

Chap. XI. MEANS OF DISPERSAL. 329

cics has come into existence coincident both in sjKice and time
with a preexist ino- closely-allied species." And I now know that
he attributes this coincidence to descent with modification.

The discussion on " single and multiple centres of crea-
tion " does not directly l)ear on another allied question —
namely, whether all the individuals of the same species are
descended from a single pair, or single hermaphrodite, or
whether, as some authors suppose, from many individuals si-
uuiltan<'()usly created. With organic beings which never inter-
cross, if such exist, each species must be descended from a suc-
cession of modified varieties, which have sujiplanted each
other, but which have never blended with other individuals
or varieties of the same species ; so that, at each successive
stage of modification and improvement, all the individuals
of the same variety will be descended from a single parent.
IJut in the great majority of cases, namely, with all organisms
which habitually unite for each birth, or which occasionally inter-
cross, 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 chfler 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 difliculty on the
theory of " single centres of creation," I must say a few words
on the means of dispersal.

Means of Dlq:)crsaL

Sir C Lyell and other authors have ably treated this sub-
ject. I can give here only the l^riefest abstract of the more
important facts. Change of climate must have had a p(jwcr-
ful influence on migration ; an impassable region when its
climate was different from what it now is, may have been a
high-road for migration; I shall, however, presently 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 isthnuis now separates two marine faunas ; submerge
it, or let it fonncrly have been submerged, and the two faunas

330 MEANS OF DISPERS^IL. Chap. XI.

\vill now Ijlend or may fonnerly have blended : where the sea
now extends, land may at former pciiods have connected
islands or possibly even continents together, and thus have
allowed terrestrial productions to pass from one to the other.
No geologist will dispute 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 Europe or Africa, and Europe
likewise with America. Other authors have thus hj'potheti-
cally bridged over every ocean, and united almost every island
to some main-land. 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 conti-
nent. This view cuts the Gordian knot of the dispersal of the
same species to the most distant points, and removes many a
dilhculty : but, to the best of my judgment, we are not author-
ized in admitting such enormous geograplucal 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 exten-
sion of our continents, as to have imited them within the
recent period to each other and to the several intervening
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-pi'oducing oceans such sunken islands
are now marked by rings of coral or atolls standing over them.
AVhcneverit is fully admitted, as no doubt it Avill some day be,
that each species has proceeded from a single birthplace, and
Avlien 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 be-
lieve that it Avill 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 oth-
er, and Avith the many existing oceanic islands. Several facts in
distribution — such as the great difference in the marine faunas
on the opposite sides of almost every continent — the close re-
lation 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 of the nearest con-
tinent, being in ])art determined (as we shall hereafter see) by
the depth of the intervening ocean — these and other such facts

CiiAP. XI. MEANS OF DISPERSAL. 331

sceni to me oj^poscd to tlic julinissioii of such jirodigious geo-
graphical revolutions -within the recent period, as are necessary
on the view advanced b}^ Forbes and admitted by his many-
followers. The nature and relative proportions of the inhab-
itants of oceanic islands likewise seem to me opposed to the
belief of their former continuity with continents. Nor does
the almost universall}' volcanic composition of such islands
iavor the admission that they are the wrecks of sunken conti-
nents; if they had originally existed as continental mountain-
ranges, some at least of the islands would ha^-e been formed,
like other mountain-sinnmits, of granite, metamorphic schists,
old fossiliferous and other rocks, instead of consisting of mere
pih.'S of volcanic matter.

I nmst now say a few words on -what are called accidental
means, but which more properly should be called occasional
means of distribution. 1 shall here coniine myself to plants. In
botanical works, this or tliat plant is stated to be ill adapted for
-wide dissemination ; but for transport across the sea the greater
or less facilities may be said to be almost wholly unknown.
Until I tried, -with JMr. ]5erkeley's aid, a few experiments, it
-was not even known how far seeds could resist the injurious
action of sea-water. To my surprise, I found that, out of 87
kinds, 6-4 germinated after an immersion of 28 days, and a few
survived an inmiersion of 137 days. It deserves notice that
certain orders Avere far more injured than others : nine Legu-
minoste were tried, and, with one exception, they resisted the
salt-water badly ; seven species of the allied orders, Hydro-
phjdlaccw and Polemoniace:e were all killed by a month's im-
mersion. For convenience' sake I chiefly tried small seeds,
without the cajisule or fruit ; and, as all of these sank in a few
(laj-s, they could not have been floated across wide spaces of
th(^ sea, whether or not they were injured by the salt--water.
Afterward I tried some larger fruits, capsules, etc., and some
of these floated for a long time. It is well kncnvn what a dif-
ference there is in the buoyancy of green aiid seasoned tim-
ber; and it occurred to me that floods might wash down plants
or branches, and that these might be dried on the banks, and
then liy a fresh rise in the stream be washed into the sea.
Hence I was led to dry stems and branches of 9-i ])lants with
ripe fruit, and to plac(; them on sea-water. The majority sank
quickly, but some, which while green floated for a very short
time, when drietl floated nmch longer ; for instance, ripe hazel-
nuts sank immediately, but when dried they floated for 90

332 MEANS OF DISPERSAL. Chap. XI.

days, and afterward -wlioii planted tliey cremunatcd ; an aspar-
a2:u.s-j)lant with ripe berries floated for ^3 days, when dried it
floated for 85 (lays, and the seeds afterward germinated; the
ripe seeds of llelosciadimn sank in two days, when dried they
floated for above 90 days, and afterward germinated. Alto-
gether, out of the 94 clried plants, 18 floated for above '28
days, and some of the 18 floated for a very much longer period.
So that as -J;^- seeds germinated after an immersion of 28 days ;
and as 1} ])lants with ripe fruit (but not all the same species
as in the foregoing experiment) floated, after being dried, for
above 28 days, as far as we may infer any thing from these
scanty fticts, we may conclude that the seeds of ^^ plants of
any country might be floated by sea-currents during 28 days,
and would retain their power of germination. In Johnston's
Physical Atlas, the average rate of the several Atlantic cur-
rents is 33 miles per diem (some currents running at the rate
of GO miles per diem) ; on this average, the seeds of -jJ^g- plants
belonging to one country might be floated across 924 miles
of sea to another country ; and when stranded, if blown to a
favorable spot by an inland gale, they Avould germinate.

Subsequently to my experiments, M. Martens tried similar
ones, but in a much better manner, for he placed the seeds in
a box in the actual sea, so that they were alternately wet and
exposed to the air like really floating plants. He tried 98
seeds, mostly different from mine ; but he chose many large
fruits and likewise seeds from plants which live near the sea;
and this would have fiivored the average length of their flota-
tion and of their resistance to the injurious action of the salt-
water. On the other hand, he did not pre^^iously 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 ^ of his seeds floated for 42 days, and
were then capable of germination. But I do not doubt that
plants exposed to the waves would float for a less time than
tliose protected from violent movement as in our experiments.
Therefore it would perhaps be safer to assume that the seeds
of about -^/g- plants of a flora, after having been dried, could
be floated across a space of sea 900 miles in Avidth, and would
then germinate. The fact of the larger fruits often floating
longer than the small, is interesting ; as plants with large
seeds or fruit could hardly be transported by any other means ;
and Alph. do Candollo has shown that such plants generally
have restricted ranges.

CiiAP. XI. MEANS OF DISPERSAL. 833

But seeds 111:13' l)c occasionally transported in another man-
ner. 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 valualjle
royal tax. I find, on examination, that, when irregularly-
shaped stones are embedded in the roots of trees, small parcels
of earth are very frequently enclosed in their interstices and
behind them — so perfectly that not a particle could be washed
away in the longest transport : out of one small portion of.
earth thus completely enclosed by wood in an oak about 50
years old, three dicotyledonous plants germinated : I am cer-
tain of the accuracy of this observation. Again, I can show
that the carcasses of birds, when floating on the sea, sometimes
escape being immediately devoured ; and seeds of many kinds
in the crops of floating birds long retain their vitality : peas
andvetches, for instance, are killed by even a few days' immer-
sion in sea-water ; but some taken out of the crop of a pigeon,
which had floated on artificial salt-water for 30 days, to my
surprise nearly all germinated.

LiWng 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 bloAvn by gales to vast
distances across the ocean. We may safely assume that undei"
such circumstances their rate of flight would often be 35 miles
an hour ; and some authors have given a far higher estimat'C.
1 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 ctHirse of two months, I picked up in my garden 12 kinds
of seeds, out of the excrement of small birds, and these seemed
jierfect, and some of them, which were tried, germinated. But
the following fact is more important : the crops of birds do iif)t
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 tli<? distance of 500 miles, and hawks are known to
look out for tired birds, and the contents of their torn crops
might thus readily get scattered. Some hawks and owls bolt
their prey whole, and, after an interval of from twelve to
twenty hours, disgorge pellets, which, as I know from cxperi-

S34 MEANS OF DISPERSAL. Cuap. XI.

iiicnls iimdc in the Zoological Gardens, include seeds capable of
genniiiiit ion. Some seeds of the oat, -wheat, millet, canary, hemp,
clover, and beet, germinated after ha\nng 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 d;iys and fourteen hours. Fresh-water fisli, I find, eat
seeds of many land and water plants : fish are frequently de-
voured by birds, and thus the seeds might Ije transported fi-om
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 excre-
ment ; and several of these seeds retained the power of ger-
mination. Certain seeds, however, were always killed by this
process.

Locusts are sometimes blown to great distances from the
land; I myself caught one 370 miles from the coast of Africa,
and have heard of others caught at greater distances. The
Kev. R. T. Lowe infonns Sir C. Lyell that, in November, 1844,
swarms of locusts visited the island of Madeira. They were in
countless numbers, as thick as the fiakes of snow in the heavi-
est snow-storm, and extended upward as far as could be seen
with a telescope. During two or "three days they slowly ca-
reered round in the air in an immense ellipse, at least five or
six miles in diameter, and at night alighted on the taller trees,
which were completely coated with them. They then disap-
peared over the sea, as suddenly as they had appeared, and
have not since visited the island. Now, in parts of Natal it is
believed by some of the farmers, thougli on quite insufficient
evidence, that injurious seeds are introduced into their grass-
land in the dung left by the great fiights of locusts which often
visit that country. In consequence of this belief, Mr. Weale
sent me in a letter a small jiacket of the dried pellets, out of
which I extracted imder the microscope several seeds, and
raised from them seven gi-ass-i)lants, belonging to two spe-
cies, in two genera. Hence a swarm of locusts, such as that
which visited Madeira, might readily be the means of introdu-
cing several kinds of plants into an island lying far from the
main-land.

Although the beaks and fix-t of birds are generally clean,
earth sometimes adheres to them : in one easel removed sixty-
one grains, and in another case twenty-two grains of dry argil-
laceous earth from one foot of a partridge, and in the earth

Chap. XI. MEANS OF DISPERSAL. 335

there was a pebble as larf^e as the seed of a vetch. Here is a
better case : the h\2: <if a woodcock was sent to mo by a friend,
with a little cake of dry earth attached to the sliaiik, weighini^
only nine 2,rains ; and this contained a seed of the toad-
rush (Juncus bufonius) which germinated and flowered. Mr.
Swaysland, of Brighton, who has paid such close attention to
our migratory birds during the last forty years, informs me that
he has often shot wagtails (motacilla?)', wheatears, and whin-
chats (saxicoloe), on their first arrival, before they had alight-
ed on our shores, and has several times noticed little cakes of
earth on their feet. Many facts could be given showing how
the soil is almost everywhere charged with seeds. For in-
stance. Prof. Newton sent me the leg of a red-legged partridge
(Caccabis rufa) which had been wounded and could not fly,
with a ball of hard earth adhering to it, and weighing six and
a half ounces. The earth had been kept for three years, but
•when broken, watered, and jilaced under a bell glass, no less
than 82 plants sprung from it: these consisted of 13 monoco-
tyledons, including the common oat, and at least one kind of
grass, and of 70 dicotyledons, which consisted, judging from
tlie young leaves, of at least three distinct species. With such
facts before us, can we doubt that the many birds which are
annually blown l)y gales across great spaces of ocean, and which
annually migrate — for instance, tlie millions of quails across
the ^Mediterranean — nuist occasionally transport a few seeds
embedded in dirt adiiering 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 transported seeds
from one part to another of the arctic and antarctic regions ;
and, during the Glacial period, from one part of the now tem-
Ijcrate rcgiims to another. In the Azores, from the large
number of plants common to Europe, in comparis(m with the
species in the otlier islands of thi^ Atlantic, which stand nearer
to the main-land, and (as remarked by Mr. H. C Watson) from
their somewhat northern character in comj^arison with the lati-
tude, I suspected that th(>S(^ islands had been partly stocked
by ice-borne seeds, during the Glacial epoch. At my request
Sir C. Lyell wrote to M. llartung to incjuire whether he had
observed erratic bowlders on these islands, and he answered
that lie had found large fragments of granite and other rocks,

330 MEANS OF DISPERSAL. Chap. XI.

■wliicli do not occur in the archipelago. Hence we may safely
infer that icebergs formerly landed their rocky burdens on the
shores of these niid-occau islands, and it is at least possible
that they may have brought thither the seeds of northern
plants.

Considering that tliese several means of transport, and that
other means, which without doubt remain to be discovered,
have been in action year after year, for tens of thousands of
years, it would, I think, be a marvellous fact if many plants had
not thus become widely transported. These means of trans-
port 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
Avhen exposed for a great length of time to the action of sea-
water; nor could they be long carried in the crops or intes-«
tines of birds. These means, however, would suffice for occa-
sional transport across tracts of sea some hundred miles in
breadth, or from island to island, or from a continent to a
neighboring island, but not from one distant continent to
another. The floras of distant continents would not by such
means become mingled ; but would remain as distinct as tliey
now are. The currents, from their course, would never bring
seeds from North America to Britain, though they might and
do bring seeds from the West Indies to our western shores,
where, if not killed by their very long immersion in salt-water,
they could not endure our climate. Almost every year, one or
two land-birds are blown across the whole Atlantic Ocean,
from North America to the western shores of Ireland and
England ; but seeds could be transported by these rare wan-
derers only by one means, namely, by dirt adhering to their
feet or beaks, which is in itself a rare accident. Even in this
case, how small the chance would be of a seed falling on fa-
vorable soil, and coming to matuiity ! But it would be a great
error to argue that because a well-stocked island, like Great
Britain, has not, as far as is known (and it would be very diffi-
cult to prove this), received within the last few centuries,
through occasional means of transport, immigrants from Eu-
lope or any other continent, that a poorly-storked island,
though standing more remote from the main-land, would not
receive colonists by similar means. Out of a hundred seeds
or animals transported to an island, even if far less well

CnxF. XI. DISPERSAL DURING THE GLACTAL PERIOD. 337

stocked than Britain, perhaps not more than one would be so
well litted to its new home as to become naturalized. But
this, as it seems to me, is no valid arf^ument against "what
would be effected by occasional means of transport, during tlu;
long lapse of geological time, while the island was being up-
heaved, and before it had become fully stocked with inhabit-
ants. 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,

Disjyersal durbuj the Glacial Period.

The identity of many plants and animals, on mountain-
gunnnits, separated from each other by hundreds of miles of
lowlands, where Alpine species could not possibly exist, is one
of llie most striking cases known of the same species living at
distant points, without the apparent possibility of their having
migrated from one point to the other. It is indeed a remark-
able fact to see so many plants of the same species living on
the snowy regions of the Alps or Pyrenees, and in the extreme
jiorthern parts of Europe ; but it is far more remarkable that
the plants on the White Mountains, in the United States of
America, arc all the same with those of Labrador, and nearly
all the sanie, as we hear from Asa Gray, with those on the
loftiest mountains of Europe. Even as long ago as 1747, such
facts led Gmelin to conclude that the same species must have
Ijcen independently created at several 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 exfjlanation of these
facts. We have evidence of almost every conceivable kind,
organic and inorganic, that, within a very recent geological
jx'riod, central Em-ope and North America suffered under an
arctic climate. The ruins of a house burnt by lire do not tell
their tale moni plainly than do the mountains of Scotland and
Wales, with their scored flanks, polishi^d surfaces, and perched
bowlders, of the icy streams with which their valleys W(M-e late-
Iv filled. So grcatlv has the climate of Europe clianged, thai,
in Northern Jtalv, gigantic moraines, left bv old glaciers, are
now clothed by tlie vine and maize, 'J'hroughout a larg(^ part
of the United States, erratic bowlders and scored rocks ])jainly
reveal a former cold j)eriod,

Tlie former influence of the glacial climate on the distribu-
15

338 DISPERSAL Cuat, Xi.

lion of the inliabitiints of Europe, as cxj)lained hy Edward
Forbes, is substantially as follows. But we shall follow the
changes more readil}', by supposing a new glacial period slowly
to come on, and then pass away, as formerly occurred. As the
cold came on, and as each more southern zone became fitted
for the inhabitants of the north, they would take the places of
the former inhabitants of the temperate regions. The latter,
at the same time, would travel farther and farther southward,
unless thoy were stopped by bairiers, 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 maximum,
we should have an arctic fauna and flora, covering the central
parts of Europe, as far south as the Alps and Pyrenees, and
even stretching into Spain. The now temperate regions of the
United States would likewise be covered by arctic plants and
animals, and these would be nearly the same with those of
Europe ; for the present cireumpolar inhabitants, which we sup-
pose to have everywhere travelled southward, are remarkably
uniform round the world.

As the warmth returned, the arctic forms would retreat
northward, closely followed up in their retreat by the produc-
tions of the more temperate regions. And as the snow melted
from the bases of the mountains, the arctic forms Avould seize
on the cleared and thawed ground, always ascending, as the
warmth increased and the snow still further disappeared, higher
and higher, while their brethren were pursuing their northern
journey. Hence, when the warmth had fully returned, the
same species, which had lately lived together in a body on the
European and North American lowlands, Avould 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 understalid the identity of many plants at
points so immensely remote as on the mountains of the United
States and of Europe. We can thus also understand the fact
that the Alpine plants of each mountain-range are more espe-
cially 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 remigration on the returning warmth, would generally
have been due south and north. The Alpine plants, for exam-
ple, of Scotland, as remarked by Mr. II. C. Watson, and those
of the Pyrenees, as remarked by Ramond, are more especially
allied to the plants of northern Scandinavia ; those of the

CiiAi'. XI. DUKING THE GLACIAL PERIOD. 339

United States to Labrador ; those of the mountains of Siberia
to the arctic regions of that country. These views, f^rounded
as they are 011 the perfectly well-ascertained occurrence of a
former Glacial period, seem to me to explain in so satisfactory
a manner the present distribution of the Alpine and arctic pro-
ductions of Europe and .Vmcrica, that, when in other regions
we lind the same species on distant mountain-summits, Ave may
almost conclude, without other evidence, that a colder climate
lV)rnierly permitted their migration across the intervening low-
lands, now become too warm for their existence.

As the arctic forms moved first southward and afterward
backward to the north, in unison with the changing climate,
they w ill not have been exposed during their long migrations
to any great diversity of temperature ; and, as they all migrated
in a body tog-ether, their mutual relations will not have been
much disturlicd. Hence, in accordance with the principles in-
culcated in tliis volume, these forms will not have been liabli>
to much modification. But with the Alpine productions, left
isolated fi-om 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, antl have survived there ever since;
they will, also, in all probability, have become mingled Avitli
ancient Alpine species, which must have existed on the moun-
tains before tlie commencement of the Glacial epoch, and which
during its coldest ])eriod will have been temporarily driven
down to the plains ; they will, also, have been exposed to some-
what different climatal influences. Their mutual relations will
thus have been in some degree disturbed ; consequiMitlv they
will have been liable to modification ; and this we find has been
the case : for if we compare the present Alpine j)lants and ani-
mals of the several great European mountain-ranges one with
another, though many of the species remain idmitically the same,
some exist as varieties, some as doubtful forms or sub-species,
and some as certainly distinct yet closely-allied species repre-
senting each other on the several ranges.

In the foregoing illustration T have assumed that at the
commencement of our imagin.ary Glacial period, the arctic pro-
ductions were as uniform round the polar regions as they arc
at the present day. But it is necessary also to include many
sulvarctic and some few temperate forms, for some of these are
the same on the lower mountain-slopes and on the plains of

340 DISPERSAL Chaj-. XI.

North America and Europe ; and it may be asked how I ac-
count for tliis degree of uniformity in the sub-arctic and temper-
ate forms round tlie world, at the commencement of the real
Glacial period. At the present day, the sub-arctic and northern
temperate productions of the Old and New Worlds are sepa-
rated from each other by the whole Atlantic Ocean and by the
nortliern part of the Pacific. During the Glacial period, when
the inhabitants of the Old and New Worlds lived farther south-
ward than they do at present, they must have been still more
completely separated from each other by wider spaces of ocean ;
so that it may well be asked how the same species could have
entered the two continents then so widely separated. The ex-
planation, I believe, lies in the nature of the climate before the
commencement of the Glacial period. At this, the newer Plio-
cene period, the majority of the inhabitants 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 the organisms which now live un-
der latitude 60°, lived during the Pliocene jieriod farther north
under the Polar Circle, in latitude CG°-G(° ; and that the pres-
ent arctic productions then lived on the broken land still nearer
to the pole. Now, if we look at a terrestrial globe, we see un-
der the Polar Circle that there is almost continuous land from
western Europe, through Siberia, to eastern America. And
this ccHitinuity of the circumpolar land, with the consequent
freedom imder a more favorable climate for intermigration, will
account for the supposed uniformity of the sub-arctic and tem-
perate productions of the Old and New Worlds, at a period
anterior to the Glacial epoch.

Believing, from reasons before alluded to, that our conti-
nents have long remained in nearly the same relative position,
though sul)jected to large but partial oscillations of level, I
am strongly inclined to extend the above view, and to infer
that during some still earlier and still vrarmer period, such as
the older Pliocene period, a large number of the same plants
and animals inhabited the almost continuous circumpolar land ;
and that these plants and animals, both in the Old and New
Worlds, began slowly to migrate southward as the climate be-
came less warm, long before the commencement of the Glacial
period. We now see, as I believe, their descendants, mostly
in a modified condition, in the central parts of Europe and the
United States. ( )n this A-iew we can understand tlie relation-
shi]), ^^itll very little identity, l)etween the productions of

Chap. XI. DURING TIIP: GLACIAL PEKIOD. 34I

North America and Europe — a relationship whicli is highly
romarkai)lc, considering the distance of the two areas, and
tlieir separation hy tlie whole Atlantic Ocean. We can fur-
ther understand the 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 tliese
warmer periods the northern parts of the Old and New Worlds
will have been almost conthiuously united by land, serving as
a bridge, since rendered impassable by cold, for the intermi-
gration of their inhabitants.

During the slowly-decreasing warmth of the Pliocene pe-
riod, as soon as the species in common, which inliabitcd the
New and 0!d Worlds, migrated south of the Polar Circle, they
would be 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 would become mingled in the one
great region with the native American productions, and would
have had to compete with them ; and, in the other great region,
with those of the Old World. Consequently we have here
every tiling favorable for much modification — for far more
modification than with the Alpine productions, left isolated,
within a much more recent period, on tlie several mountain-
ranges and on the arctic lands of Europe and North America.
Hence it has come that, when we compare the now living pro-
ductions of the temperate regions of the New and Old Worlds,
we find very few identical species (though Asa Gray has late-
ly shown that more plants are identical than was formerly sup-
j)Osed), but we find in every great class many forms, which
some naturalists rank as geographical races, and others as dis-
tinct species ; and a host of closely-allied or representative
forms which are ranked by all naturalists as specifically dis-
tinct.

As on the land, so in the waters of the sea, a slow southern
migration of a marine fauna, which, during the Pliocene or
even a somewhat earlier pcried, was nearly imiform along the
continuous shores of tlie Pohir Circle, will account, on tlie the-
ory of modification, for many closely-allied forms now living
in marine areas completely sundered. Thus, I tliink, we can
imderstand the ])resence of some still existing and of some ter-
tiary closely-allied fijrms on the eastern anti western shores of
temperate North America ; and the still more striking fact of

342 alti:i:nate glacial tliuods chap. xl

many clost'ly-allicd crustaceans (as described in Dana's admir-
able work), of some fish and other marine animals, in the Med-
iterranean and in the seas of Japan — these two areas being
now completely separated by the breadth of a whole continent
and by a wide space 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 tem-
perate lands of North America and Europe, are inexplicable
on the theory of creation. AVc cannot maintain that such spe-
cies have been created alike, in correspondence with the neai'-
ly similar physical conditions of the areas ; for if we compare,
for instance, certain parts of South America with j^arts of
South Africa or Australia, Ave see countries closely similar in
all their j^hysical conditions, hut with inhabitants utterly dis-
similar.

Alternate Glacial Periods of the Korth and South.

But we must return to our more immediate subject. I am
convinced that Forbes's view may be largely extended. In
Europe we meet with the plainest evidence of the Glacial pe-
riod, from the Avcstcrn 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 aflected. In the Lebanon, according to Dr.
Hooker, perpetual snow formerly covered the central axis, and
fed glaciers which rolled 4,000 feet down its valleys. Along
the Himalaya, at points 900 miles apart, glaciers have left the
marks of their former low descent ; and, in Sikkim, Dr. Hooker
saw maize growing on gigantic ancient moraines. Southward
of the Asiatic Continent, on the opposite side of the equator,
we now know, from the excellent researches of Dr. J. Haast
and Dr. Hector, that immense glaciers formerly descended to
a low level in New Zealand ; and the same plants foimd by
Dr. Hooker on wideh'-separated mountains in this island tell
the same story of a former cold period. From facts commimi-
catcd to me by tlie Rev. W. B. Clarke, it appears also that
there are traces of former glacial action on the mountains of
the southeastern corner of Australia.

Looking to America: in the northern half, ice-born frag-
ments of rock have been observed on the eastern side of the
oontinent, as far south as kit. 3G°-37°, and on the shores of the

Cjur. XI. OF THE NORTH AND SOUTH. 343

Pncific, where tlic climate is now so difiercnt, as far south as
lat 4G''. Erratic bowlders have, also, been noticed on the
Rocky Mountains. In the Cordillera of South America, nearly
under the equator, glaciers once extended far Ix'low their pres-
ent level. In central Chili I examined a vast mound of detri-
tus with grciit bowlders, crossing the Portillo valle}', which
there can hardly be a doubt once formed a huge moraine ; and
Mr. D. Forbes informs me that he found in various parts of the
Cordillera, from lat, 13° to 30° S., at about the height of
12,000 feet, deeply-furrowed rocks, resembling those with
which he was familiar in Norway, and likewise great masses
of detritus, including grooved pebbles. Along this whole
space of the Cordillera true glaciers do not now exist even at
nmcli more considerable heights. Farther south on both sides
of the continent, from lat. 41° to the southernmost extremity,
we have the clearest evidence of former glacial action, in nu-
merous immense bowlders transported far from their parent
source.

From these several facts, namely, from the glacial action
having extended all round the northern and southern hemis-
pheres— from tlic period having been in a geological sense re-
cent in both hemispheres — from its having lasted in both dur-
ing a great length of time, as may be inferred from the amount
of work effected — and lastly from glaciers having recently de-
scended to a low level along the whole line of the Cordillera, it
formerly appeared to me that we could not avoid the conclusion
that the temperature of the whole world had been simultane-
ously lowered during the Glacial period. But now Mr. CroU,
in a series of admirable memoirs, lias attempted to show that
a glacial condition of climate is the result of various physical
causes, brought into operation by an increase in the eccentricity
of the earth's orlnt. All these causes tend toward the same
end ; but the most powerful appears to be the influence of the
oocentricity of the orbit upon oceanic ciuTcnts. It follows, from
Mr. Croll's researches, that cold periods regularly recur every
ten or fifteen thousand years; but that at much longer inter-
vals the cold, owing to certain contingencies, is extremely se-
vere, and lasts for a great length of time. Mr. Cn)ll believes
that the last great Glacial period occurred about 2-40,000 years
ago, and endured with slight alterations of climate for about
160,000 years. With respect to more ancient Glacial periods,
several geologists arc convinced from direct evidence that such
occurred during the Miocene and Eocene fonnations, not to

"344 ALTERNATE GLACIAL TEKIODS Chap. XI.

mention still more ancient formations. But in relation to our
present subject, the most important result arrived at by Mr,
Croll is, that whenever the northern hemisphere passes through
a cold period, the temperature of the southern hemisphere is
actually raisctl, with the winters rendered much milder, chiefly
through changes in the direction of the ocean-currents. So,
conversely, it is with the northern hemisphere, when the south-
ern passes through a glacial period. These conclusions have,
as we shall immediately see, a most important bearing on geo-
graphical distribution ; but I will first give the facts which de-
mand an explanation.

In South America, Dr. Hooker has shown that, besides many
closely-allied species, between forty and fifty of the flowering
plants of Terra del Fuego, forming no inconsiderable part of
its scanty flora, are common to North America and Europe,
enormously remote as these areas in opposite hemispheres are
from each other. On the lofty mountains of equatorial America
a host of peculiar species belonging to European genera occur.
On the Organ Mountains of Brazil, some few temperate Euro-
pean, some Antarctic, and some Andean genera were found
by Gardner, which do not exist in the low intervening 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 some
few representatives of the flora of the Cape of Good Hope oc-
cur on the Mountains of Abj'ssinia. At the Cape of Good
Hope a very few European species, believed not to have been
introduced by man, and on the mountains several representa-
tive European forms are found, which have not been discovered
in the intertrojDical 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 Cam-
eroon Mountains, in the Gulf of Guinea, are closely related to
those on the Mountains of Abyssinia, and likewise to those of
Icinperate P^urope. It now also appears, as I hear froni Dr.
Hooker, tliat some of these same temperate plants have been
discovered by the R;'v. R. T. Lowe on the mountains of the
Cape de V^erde Islands. This extension of the same temperate
forms, almost under the equator, across the whole continent of
Africa and to the mountains of the Cape de Verde archipelago,
is one of the most astonishing facts ever recorded in the dis'
tribution of plants.

CnAP. XI. OF THE NORTH AND SOUTH. 345

On the Himalaya, and on the isolated mountain-ranges of
the Peninsula of India, on the heights of Cejlon, and on the
volcanic cones of Java, many plants occur, cither identicall}' the
same or representing each other, and at the same time repre-
senting plants of Europe, not found in the intervening hot low-
lands. A list of the genera of plants collected on the loftier
peaks of Java raises a picture of a collection made on a hillock
in Europe ! Still more striking is the fact that pecidiar south-
ern Australian forms are represented by certain j)lants grow-
ing 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 nortli as
Japan.

On the southern mountains of Australia, Dr. F. Muller has
discovered several European species ; other species, not intro-
duced by man, occur on the lowlands; and a long list can be
given, as I am informed by Dr. Hooker, of European genera,
found in Australia, but not in the intermediate torrid regions.
In the admirable " Introduction to the Flora of New Zealand,"
by Dr. Hooker, analogous and strilving facts are given in re-
gard to the ])lants of that 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 identical species or
varieties of the same species. It should, however, be observed
that these plants are not strictly Arctic forms ; for, as Mr. H.
V. Watson has remarked, " in receding from polar toward
equatorial latitudes, the Alpine or mountain floras really be-
come less and less Arctic." Besides these identical and closely-
allied forms, many species inhabiting the same widely-sundered
areas behjng to genera not now found in the intermediate trop-
ical lowlands.

These brief remarks a]iply to plants alone ; but some few
analogous facts could be givi'U in regard to terrestrial animals.
In marine productions, similar cases likewise occur; as an ex-
ample, I may quote a statement by the highest authority, Prof.
Dana, that ''it is certainly a wonderful fact that New Zealand
should have a closer reseml)lanc«; in its Crustacea to Great
Ijiitain, its anlijiode, than to anv otiier part of the world."
Sir J. Kiclianlson, also, speaks of the reappearance on the
shores of New Zealand, Tasnianiii, etc., of northern forms of
fish. Dr. Hooker informs me that twenty-five species of Algaj

346 ALTERNATE GLACIAL I'EKIODS CirAr. XI.

arc common to Ncn' Zealand and to Europe, Inti Iiave not beer
found in the inlennediate tropical seas.

From the foregoing^ facts, namely, the presence of temperate
forms on the highlands across the whole of equatorial iVfrica,
and along the Peninsula of India to Ceylon and the Malay archi-
pelago, and in a less ■\vell-raarked mann(T across the wide ex-
panse of tropical South America, it appears almost certain that
at some former period, no doubt during the most severe part
of the Glacial period, the lowlands of these great continents
were everyAvhere tenanted under the equator by a considerable
number of temperate forms. At tliis ])criod the equatorial cli-
mate at the level of the sea was probably about the same with
that now^ experienced at the height of from five to six thousand
feet vmder the same latitudes, or perhaps even rather cooler.
During this, the coldest period, the lowlands under the equator
must have been clothed with a mingled tropical and temperate
vegetation, like that described by Hooker as growing luxuri-
antly at the height of from four to five thousand feet on the
lower slopes of the Himalaya, but with perhaps a still greater
preponderance of temperate forms. So, again, on the moun-
tainous island of Fernando Po, in the Gulf of Guinea, Mr. Mann
found temperate European forms beginning to appear at 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, " Avith forms of the
torrid zone harmoniously blended with those of the temperate."

Now let us see Avhether Mr. Croll's conclusion, that Avhen
the northern hemisphere sufTcred fi-om the extreme cold of the
great Glacial period, the southern hemisphere Avas actually
Avarmer, throAvs any clear light on the present apparently inex-
])licable distribution of A^arious organisms in the temperate
jiarts of both hemispheres, and on mountains of the tropics.
The Glacial period as measured by ^-ears, 7uust have been very
long; and, Avhcn avc remember OA'cr Avhat vast spaces some
naturalized plants and animals have spread Avithin a fcAV cen-
turies, this period Avill haAC been ample for any amoimt of mi-
gration. As the cold became more and more intense, Ave knoAV
that Arctic forms iuA'aded the temperate regions ; and, from the
facts just given, there can hardly be a doubt that some of the
more A'igorous, dominant, and widest-spreading temperate forms
actually then iuA'aded the equatorial loAvlands. The inhabitants
of these lowlands Avould at the same time migrate to the tropi-
Ciil and sub-tropical regions of the south, for the southern hemi-

CiiAr. XI. OF THE NOKTII AND SOUTH. 347

splicre was at this period warmer. On the decline of the Ghi-
cial ]>eriod, as both liemis])heres gradually recovered their
former temperatures, the northern temperate forms, livins; on
the lowlands under tlie equator, would be driven to their former
homes or be destroyed, being replaced by the equatorial forms
returning from the south. Some, howeveK, of the northern
temperate forms would almost certainly ascend any adjoining
highland, where, if sufficiently lofty, they would long survive,
like the Arctic forms on the mountains of Europe. They might
survive, even if the climate was not perfectly fitted for them,
for the change of temperature must have been very slow, and
plants undoubtedly possess a certain capacity for acclimatiza-
tion, as slio\\Ti by their transmitting to their offspring different
constitutional powers of resisting heat and cold.

In the regular course of events the southern hemisphere
would be subjected to a severe Glacial period, with the northern
hemisphere rendered warmer ; and then the southern temperate
forms would in their turn invade the equatorial lowlands. The
northern forms which had before been left on the mountains
would now descend and mingle Avith the southern forms.
These latter, Avhen the warmth returned, Avould return to their
former homes, leaving some few species on the mountains, and
carrying southward with them some of the northern temper-
ate 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 moun-
tains of the intermediate tropical regions. But the species left
during a long time on these mountains, or in opposite hemi-
spheres, would have to compete Avith many new forms, and
would be exposed to somewhat clifTerent physical conditions ;
hence tlicy would be eminently lialjle to modification, and
would generally now exist as varieties or as representative s]>c-
cies ; and this is the case. We must, also, bear in mind the
occurrence in both hemispheres of former Glacial jieriods ; for
these will account, in accordance with the same principles, for
the many quite distinct species inhabiting the same widely-
separated areas, and belonging to genera not now found in the
intermediate torrid zones.

It is a remarkaljlc fact, strongly insisted on by Hooker in
regard to America, and by Alph. de Candolle in regard to Aus-
tralia, that inany more identical or now slightly-modified spe-
cies have migrated from the north to the south, than in a re-
versed direction. We see, however, a few southern forms on

348 ALTERNATE GLACIAL PERIODS Chap. XI.

tlie mountains of Borneo and Abyssinia. I suspect that this
preponderant niij^ration from the north to t!ie south is due to
the f^rcatcr extent of hmd in the north, and to tlie noi'tbeni
forms liaviuii;' existed in their own homes in g-reater numbers,
and havini^ eonsccfucntly been advanced throu<>;h natural selec-
tion and comjM'tition to a liigher stage of perfection, or domi-
nating jKnver, tliiui the soutliern forms. And thus, when the
two sets became commingled in the equatorial regions, during
the alternations of the Glacial periods, the northern forms were
the more powerful and were able to hold their places on the
mountains, and afterward to migrate southward with the south-
ern forms ; but not so the southern in regard to the northern
forms. In the same manner we see, at the present day, that
very many European productions cover the groimd in La Plata,
New Zealand, and to a lesser degree in Australia, and have
beaten the natives ; whereas extremely few southern 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
ccnturietj from La Plata, and during the last thirty or forty
years from Australia. The Ncilgherric Mountains in India,
however, offer a part ial exception ; for here, as I hear from Dr.
Hooker, Australian forms are rapidly sowing themselves and
becoming naturalized. Before the last great Glacial period,
no doubt the intertropical mountains Avere stocked with en-
demic 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 pi'oductions are nearly equalled, or even outnumbered,
by those which have become naturalized ; and this is the llrst
stage toward their extinction. Mountains are islands on the
land, and their inhabitants have yielded to those produced with-
in 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 naturalizetl through man's
agency.

The same principles apply to the distribution of terrestrial
animals and of marine productions, in the northern and south-
ern temperate zones, and on the intertropical mountains.
When during the height of the Glacial period the ocean-cur-
rents Avere Avidely diiferent to Avhat thev noAV are, some of the
inhabitants of the temperate seas might have reached the equa-
tor ; of these a fcAV would perhaps at once be able to migrate

CiFAP. XI. OF THE NORTH AND SOUTH. 349

southward, by kpcpiiiG^ to the cooler currents, Avhile others
might remain and survive in the cooler depths, until the south-
ern hemisphere was in its turn subjected to a glacial climate
and permitted of their lurtlier progress ; in nearly the same
manner as, accortling to Forbes, isolated spaces inhabited by
Arctic productions exist to the present day in the deeper parts
of the temperate seas.

I am far from supposing that all dilhculties in regard to
the distribution and ailinities of the identical and allied spe-
cies, which now live so widely separated in the north and
south, and sometimes on the intermediate mountain-ranges,
are removed on the views above given. The exact lines of mi-
gration cannot be indicated. We cannot say why certain spe-
cies and not others have migrated ; why certain species have
been modified and have given rise to new forms, while others
liave remained unaltered. We cannot hope to explain such
facts, until we can say why one species and not another be-
comes naturalized l^y man's agency in a foreign land ; Avhy 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 in-
stance, the occurrence, as shown by Dr. Hooker, of tiie same
plants at points so enormously remote as Kerguelen Land,
New Zealand, and Fuegia; but icebergs, as suggested by Ly-
cll, may have l)een concerned in tlieir dispersal. The existence,
at these and other distant points of the southern hemisphere,
of species, which, though distinct, belong to genera exclusively
confined to the south, is a more remarkable case. Some of
these species are so distinct, that we cannot suppose that there
has been time since the commencement of the last Glacial
period for their migration and subsequent modification to the
necessary degree. The facts seem to me to indicate that dis-
tinct species belonging to the same genera have migrated in
radiating lines from a common centre ; and I am inclined to
look in tiie southern, as in the northern heniisphere, to a former
and warmer ])erio(l, before the commencement of the Ghicial
period, when the Antarctic lands, now covere^l with ice, sup-
ported a liighly pecuhar 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 dispersed to vari-
ous points of the southern hemisphere l)y occasional means of
transport, and by the aid, as halting-places, of now sunken
islands. Thus tlie southern shores of America, Australia, and

350 ALTERNATE GLACIAL PERIODS. Cuap. XI.

New Zealand, niio^'ht have become slightly tinted by the same
peculiar forms of life.

Sir C. Lycll in a striking' passage has speculated, in lan-
guage almost identical Avith mine, on the effects of great alter-
nations of climate throughout the world on geographical dis-
tribution. And we have uow seen that Mr. Oroll's conclusion,
that successive Glacial periods in the one hemisphere coin-
cided with warmer periods in the opposite hemisphere, to-
gether with the admission of the slow modification of species,
explains a multitude of facts in the distribution of the same
and of the allied forms of life in all parts of the globe. The
living waters have flowed during certain periods from the
north and afterward 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 Hving 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 com-
pared with savage races of man, driven up and surviving in
the mountain-fastnesses of almost every land, Avhich serve as a
record, full of interest to us, of the former inhabitants of the
surroundinjr lowlands.

Chat. XII. FRESH-WATER PRODUCTIONS. 851

CHAPTER XII.

GEOGnAPiiicAL DisTKiBUTiox — Continued.

Distribution of Prcsh-wnfcr Productions— On the Inhabitants of Ocranic IrJlands—
Absence of 15atrucl)ian8 and of Terrestrial Mammals— On the Relation of tlie In-
tuibitants of I^landx to those of the nearest Main-land— On Colouizaticm from tho
nearest Source with subsequent Modification— Summary of the last and present
Chapter.

Fresh-water Productions.

As lakes and river-sj'stenis arc 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 for-
midable barrier, that they never would have extended to dis-
tant countries. But the case is exactly the reverse. Not only
have many fresh-water species, belonging to quite different
classes, an enormous range, but allied species prevail in a re-
markable manner throughout the world. I well remember,
when first collecting in the fresh waters of Brazil, 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 this power in fresh- water productions of ranging wide-
ly, though so imcxpected, can, I think, in most cases be ex-
plaiiiod 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 ; and liability to wide disper-
sal would follow from this capacity as an almost necessary con-
seipience. We can here consider only a few cases. In regard
to fish, I believe that the same species never occur in the
fresh waters of distant continents. But on the same continent
the species often range widely and almost capriciously ; for
two river-systems will have some fish in common and some
different. A few facts seem to favor the possibility of their
occasi(mal transport by accidental means ; like that of the live

352 FEESII-WATER PRODUCTIONS. Ciixr. XII.

fish not rarely dropped hy Avhirlwinds in India, and the vitality
t)f their ova when removed from the Avater. ]3ut I am inclined
to attribute the dispersal of frcsh-Avater iish mainly to changes
in the level of the land within the recent period having caused
rivers to flow into each other. Instances, also, coidd be given
of this having occniTcd during floods, without any change of
level. The wide dilTerence of the fish on the opposite sides
of continuous mountain-ranges, -which from an early period
must have completely prevented the inosculation of the river-
systems, seems to lead to the same conclusion. "With respect
to allied fresh-water fish occurring at very distant points of the
world, no doubt there arc many cases which cannot at present
be explained : but some fresh- Avater fish belong to very ancient
fonns, and in such cases there will have been ample time for
great geograpliical changes, and consequently time and means
for such migration. In the second place, salt-water fish can
Avith care be sloAvly accustomed to Ha'c in fresh Avater; and,
according to Valenciennes, there is hardly a single group of
Avhich all the members are confined exclusively to fresh Avatcr,
so that a marine species of a frcsh-Avater group might travel
far along the shores of the sea, and subsequently liecome modi-
fied and adapted to the fresh Avaters of a distant land.

Some species of fresh-Avater shells haA'e A'crA' Avide ranges,
and allied species Avhich, on our theory, are descended from a
common parent, and must haA'C proceeded from a single source,
prevail throughout the Avorld. Their distribution at first per-
plexed me much, as their OA'a are not likely to be transported
by birds, and are immediately killed by sea-Avater, as are the
adults. I could not even understand hoAV some naturalized
species have spread rapidly throughout the same country. But
tAvo facts, Avhich I have observed — and no doubt many others
remain to be observed — throAV some light on this subject.
^^'hen a duck suddenly emerges from a pond coA'cred Avith
duck-Avced, I have tAvicc seen these little plants adhering to
its back ; and it has happened to me, in remoAing a little
duck-AVoed from one aquarium to another, that I have quite un-
intentionally stocked the one Avith fresh-water shells from the
other. 13ut another agency is perhaps more eftectual : I sus-
pended a duck's feet in an aquarium, Avhere many ova of fresh-
Avater shells Avere hatching ; and I found that numbers of the
extremely minute and just-hatched shells craAvled on the feet,
and clung to them so firmly that, Avhen taken out of the Avater,
they could not be jarred off, though at a someA\hat more ad-

CuAr. XII. FRESn-WATER PRODUCTIONS. 353

vanced a;^c ihoy would voluntarily drop olT. These just-
hatched moUusks, thoui^h aquatic in their nature, survived on
the duck's feet, in damp air, from twelve to twenty hours ; and
in this lenp^tli of time a duck or heron mij^ht (ly 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 Dj'tiscus
has been cau2;ht with an Ancylus (a fresh-water shell like a
limpet) firmly adhering- to it ; and a Avater-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 with 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
isFands, This is strikingly shown, as remarked by Alph. de
Candolle, in large groups of terrestrial plants, ^vluc]l have only
a very few aquatic members ; for these latter seem immediate-
ly to acquire, as if in consequence, a very wide range. I
think favorable means of dispersal explain this fact. I have be-
fore mentioned that earth occasionally, though rarely, adheres
in some quantity to the feet and beaks of birds. Wading-
birds, which frequent the muddy edges of ponds, if suddenly
flushed, would be the most likely to have muddy feet. Birds
of this order, I can show, arc the greatest wanderers, and are
occasionally found on the most remote and barren islands in
the open ocean ; they would not be likely to alight on the sur-
face of the sea, so that the dirt would not be washed off their
feet ; and, when making land, they would be sure to fly to their
natural fresh-water haunts. I do not believe that botanists
an; aware how charged the mud of ponds is with seeds : I
have tried several little experiments, l)ut will here give only
the most striking case : I took in February three table-spoon-
fuls of mud from three different points, beneath water, on the
edge of a little pond: this mud when dry weighed only GJ
ounces ; I kcjit it covered up in my study for six months, pull-
ing up and CHjunting each plant as it grew ; the plants were
f)f many kinds, and were altogether 537 in number; and yet
the viscid mud was all contiiined in a breakfast cup ! Consid-
ering these facts, I think it would be an inexplic;d)l(> circum-
stance if water-birds did not transport the seeds of the same
fivsh-water plants to unstocked ponds and streams, situated at

364 FRESU-WATEK PRODUCTIONS. Chap, XII.

very distant points. The same ag'ency may lia\'C come into
play with tlic e<xgs 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 man}' other lands after having swal-
lowed them ; even small fish swallow seeds of moderate size,
as of tlie yellow water-lily and Potamogeton. Herons and
other birds, century after century, have gone on daily devour-
ing fish ; they then take flight and go to other waters, or are
blown across the sea ; and Ave have seen that seeds retain their
power of germination, when rejected in pellets or in excre-
ment, many hours afterward. AVhen I saw the great size of
the seeds of that fine water-lily, the Nelumbium, and remem-
bered Alph. de Candolle's remarks on this plant, I thought
that its distribution must remain quite inexplicable ; but
Audubon states that he found the seeds of the great southern
water-lily (probably, according to Dr. Hooker, the Nelumbium
luteum) in a heron's stomach ; although I do not know the
fact, yet analogy makes me believe that a heron, fl^'ing to an-
other pond and getting a heai-ty meal of fish, Avould probably
reject from its stomach a pellet containing the seeds of the
Nelumbium undigested ; or the seeds might be dropped by the
bird Avhile feeding its young, in the same way as fish are known
sometimes to be dropped.

In considering these several means of distribution, it shoukl
be remembered that Avhen a pond or stream is first formed, for
instance, on a rising islet, it Avill be unoccupied ; and a single
seed or e^^g will have a good chance of succeeding. Although
there Anil always be a struggle for life between the inhabitants
of the same pond, hoAvever few in Idnd, yet, as the number even
in a Avell-stocked pond is small in comparison Avitli the number
of species inhabiting an equal area of land, the competition
Avill probably be less severe between aquatic than betAveen ter-
restrial species ; consequently an intruder from the waters of
a foreign country Avillhave a better chance of seizing on a ncAV
place, than in the case of terrestrial colonists. We should also
remember that many frcsh-AAMter productions are low in the
scale of nature, and Ave have reason to believe that Ioav beings
change or become modified less quickl}^ than the high ; and this
Avill giA'e a longer time than the aA'erage for the rj;igration of
the same aquatic species. We should not forget the probability
of many species having formerly ranged as continuously as
fresh-Avater productions ever can range, over immense areas

Chap. XI [. INHABITANTS OF OCEANIC ISLANDS. 355

and having subseqiienlly become extinct in intermediate re-
gions. But the wide distribution of fresli-wuter pkxnts and of
the lower animals, whether retaining the same identical form
or in some degree modifieJ, I believe mainly depends on the
wide disjiersal of their seeds and eggs by animals, more es-
pecially by fresh-water birds, which have great poAvers of
flight, and naturally travel from one piece of water to another.

On the InJuihltayds of Oceanic Islcmds.

We now come to the last of the three classes of facts,
which I have selected as presenting the greatest amount of
dilliculty, if we accept the view that not only all the individ-
uals of the same species, wherever found, have migrated from
some one area, but that allied species, although now inhabiting
the most distant points, have proceeded from a single area —
tlie birthplace of their early prog(Miitor. I have already stated
that I cannot honestly admit For])es's view en continental ex-
tensions, which, if legitimately followed out, would lead to the
belief that all existing islands have been continuously or
almost continuously joined to some continent within the recent
period. This view Avould remove many dilliculties, but it
would not explain all the facts in regard to insular produc-
tions. In the following remarks I shall not confine myself to
the mere question of dispersal ; but shall consider some other
facts, which bear on the truth of the two theories of indepen-
dent creation and of descent with modification.

The species of all kinds which inhabit oceanic islands are
few in number compared Avith those on equal continental
areas : Alph. de Candolle admits this for plants, and AVollas-
ton for insects. New Zealand, for instance, with its lofty
moimlains and diversified stations, extending over 780 miles
of latitufle, together with the outlying islands of Auckland,
Campbell, and Chatham, contain altogether only DCO lands
of flowering plants; if we compare this moderate number with
the species which swann over equal areas in Southwestern
Australia or at the Cape of Good Ilojie, we nnist admit that
somclliing, quite indcpenilently of a difVerence in tlie ])hvsical
conditions, has caused so great a difVerence in number. Even
the uniform county of Cambridge has 847 plants, and the little
island of Anglesea 704, but a few ferns and a few introduced
plants are included in these nundiers, and the comparison in
some other respects is not quite fair, "\\'e have evidence that

350 INHABITANTS OF OCEANIC ISLANDS. Cuai-. XII.

the barren isluiul of Ascension aboriginally possessed less than
half a dozen lowering plants ; yet many have now become
naturalized on it, as they have on New Zealand and on every
other oceanic island Avhich 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.

Although in oceanic islands the species are few in number,
the proportion of endemic kinds (i. e., those found nowhere
else in the Avorld) is often extremely large. If Ave compare,
for instance, the number of endemic land-shells in Madeira, or
of endemic birds in the Galapagos Archipelago, Avith the num-
ber found on any continent, and then compare the area of the
island Avith that of the continent, Ave shall see that this is true.
This fact might have been theoretically expected, for, as al-
ready explained, species occasionally arriving after long inter-
A'als of time in a ncAV and isolated district, and having to com-
pete AA'ith ncAV associates, Avould be eminently liable to modifi-
cation, and Avould often produce groups of modified descend-
ants. But it by no means folloAvs that, because in an island
nearly all the species of one class are peculiar, those of an-
other class, or of another section of the same class, are pecu-
liar ; and this difference seems to depend partly on the species
Avhich are not modified having immigrated in a body, so that
their mutual relations haA^e not been much disturbed; and
partly on the frequent arrival of immodified immigrants from
the mother-country, Avith Avhich the insular forms have inter-
crossed. It should be borne in mind that the offspring of such
crosses AA'ould almost certainly gain in vigor ; so that even an
occasional cross AA'ould produce more effect than might have
been anticipated. I Avill give a fcAV illustrations of the forego-
ing remarks : in the Galapagos Islands there are 20 land-birds;
of these, 21 (or perhaps 23) are peculiar, AA'hereas of the 11
marine birds only 2 are peculiar ; and it is obvious that marine
lairds could arrive at these islands much more easily and fre-
quently than land-birds. Bermuda, on the other hand, Avhich
lies at about the same distance from North America as the
Galapagos Islands do from South America, and Avhich has a
A'cry peculiar soil, does not possess a single endemic land-bird ;

CiiAr. XII. INHABITANTS OF OCEANIC ISLANDS. 357

and we know, from Mr. J. M. Jones's admirable account of Ber-
muda, that very many North American birds occasional!}' or
even frequently visit this island. Almost every year, as I am
informed l)y !Mr. E. V. Harcourt, many EuropeaTi and African
birds arc blown to Madeira ; this island is inhaljited by 99
kinds, of which one alone is peculiar, though very closely
related to a European form ; and three or four other species
are confined to this island and to the Canaries. So that the
islands of 13ermuda and Madeira have been stocked from the
neighboring continents with birds, whicli for long ages have
struggled together, and become mutually adapted ; hence,
when settled in their new homes, each kind wduld be kept by
the others to its proper place and habits, and would conse-
quently be but little liable to modification. Any tendency to
modification would also be checked by intercrossing with the
unmodified immigrants from the mother-country. Madeira,
again, is inhabited by a wonderful lumiber of peculiar land-
sliells, whereas not one species of sea-shell is peculiar to its
shores : now, though we do not know how sea-shells are dis-
persed, yet we can sec that their eggs or larva?, perhaps at-
tached to seaweed or floating timber, or to the feet of wading-
birds, might be transported across three or four hundi'cd miles
of open sea far more easily than land-shells. Tlie dilTerent
orders of insects inhabiting Madeira present nearly similar
cases.

Oceanic islands are sometimes deficient in animals of cer-
tain Avhole 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
j)lace of mammals. Altliough New Zealand is here spoken of
as an oceanic island, it is in some degree doubtful whether it
should 1)0 so ranked ; it is of large size, and is not separated
from Australia by a profoundly deep sea; from its geological
character and tlie direction of its mountain-ranges, the Rev.
W. 15. Clarke has lately maintained that this island, as well
as New Caledonia, should be considered as appurtenances of
Australia. Turning to plants. Dr. Hooker has shown that in
the Galapagos Islands tlie ])roportional numbers of the difl'er-
ent orders are very different from what they are elsewhere.
All such diflerences in luimber, and the absence of certain
whole grou]\s of animals and jilants on islands, are gtMierally
account(>d for by su]iposed ditVerences in their ])hysical condi-
tions; but this explanation is not a little doubtful. Facility

358 ABSENCL OF TERKESTEIAL MAMMALS Chap. XII.

of inimioTalion seoins to liavc been fully as impoptant as the
nature of the conditions.

JIany remarkable little facts could bo given with respect to
the inhabit:iuts of oceanic islands. For instance, in certain
islands not tenanted Iiy a sing-le mammal, some of the endemic
plants have beautifully hooked seeds; and few relations arc
more manifest than that hooked seeds are adapted for trans-
portal in the wool or fin- of quadi-upeds. But a hooked seed
might be carried to an island by other means ; and the plant
then becoming modified Avould form an endemic species, Avhich
might still retain the hooks, Avhich would not form a more use-
less appendage than the shrivelled wings imder the soldered
elytra of many insular beetles. Again, islands often possess
trees or bushes belonging to orders elsewhere including only
herbaceous species ; now trees, as Alph. de Candolle has shown,
generally have, whatever the cause may be, confined ranges.
Hence trees Avould be little likely to reach distant oceanic
islands ; and an herbaceous plant, which had no chance of suc-
cessfully competing Avitli the many fully-developed trees grow-
ing on a continent, might, when established on an island, gain
an advantage by growing taller and taller and overtopping the
other herbaceous plants. In this case, natural selection would
tend to add to the stature of the plant, to whatever order it
belonged, and thus convert it first into a bush and then into a
tree.

Absence of Batrachians and Terrestrial j[Tammals on Oce-
anic Islands.

"With resjiect to the absence of whole orders of animals on
oceanic islands, I5ory St. Vincent long ago remarked that Ba-
trachians (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 strictly
true, with the exception of New Zealand, of the Andaman
Islands, and perhaps of the Salomon Islands. But I have al-
ready remarked that it is doubtful whether New Zealand ought
to be classed as an oceanic island ; and this is still more doubt-
ful with respect to the Andaman and Salomon groups. This
general absence of frogs, toads, and newts, on so many oceanic
islands cannot be accounted for by their physical conditions;
indeed, it seems that islands are peculiarly well fitted for these
animals: for frogs have been introduced into Madeira, the

Chap. XII. ON OCEANIC ISLANDS. 359

Azores, and Mauritius, and liavo multiplied so as to become a
nuisance. But, as these animals ami their spawn are known to
be immediately killed hy sea-wat<^r, there wovdd be great dilfi-
culty in their transportal across the sea, and therefore we can
sec why they do not exist on any oceanic island. But why, on
tlie theory of creation, they should not have been created there,
it would be very dillicult to explain.

Mammals ofler another and similar case. I have carefully
searched the oldest voyao-es, and as yet I have not found a
single instance, free frt)m doubt, of a terrestrial mammal (ex-
cluding domesticated animals kept by the natives) inhabiting'
an island situated above 300 miles from a continent or great
continental island ; and many islands situated at a much less
distance are equally l)arren. The Falkland Islands, which are
inhabited by a wolf-like fox, come nearest to an exception ; but
tlws group cannot be considered as oceanic, as it lies on a bank
in connection with the main-land at the distance of about 280
miles ; moreover, icebergs formerly brought bowlders to its
western shores, and they may have formerly transported foxes,
as now frequently 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 oin- smaller quadrupeds have not be-
come naturalized and greatly nuiltiplicd. It capnot be said,
on the ordinary view of creation, tliat there has not been time
for the creation of mammals; many volcanic islands are sufTi-
ciently ancient, as shown l)y the stupendous degradation which
they have suffered, and by their tertiary strata : there has also
bcHMi time for the production of endemic species belonging to
other classes ; and on continents it is known that mammals ap-
pear and disappear at a quicker rate than any other and lower
animals. Although terrestrial mammals do not occur on oce-
anic 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 Mariannt" Archipelagoes, and Mauritius,
all possess their jieculiar bats. N\ hy, it may be asked, has
the supposed creative force ])roduced bats and no other mam-
mals on remote islands ? On my view this (juestion 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 wandering by d:iy far over the Atlantic Ocean; and

3 GO ABSENCE OF TERKESTKIAL MAMMALS Chap. XII.

two North American species either ref^ularly or occasionally
visit Bermuda, at the distance of GOO miles from the main-land.
I hear from Mr. Tomes, who has specially studied this family,
that many species have enormous ranj^es, and are found on con-
tinents and on far-distant islands. Hence we have only to sup-
pose that such wandering species have been modified in their
new homes in relation to their new position, and we can under-
stand the presence of endemic bats on oceanic islands, with the
absence of all other terrestrial mammals.

Another interesting relation exists, namely, between the
depth of the sea separating islands from each other or from the
nearest continents, and the degree of affinity of their mamma-
lian inhabitants. Mr. Windsor Earl has made some striking
observations on this head, since greatly extended by Mr. Wal-
lace's admirable researches, in regard to the great Malay Ar-
chipelago, which is traversed near Celebes by a space of deep
ocean, and tliis separates two widely-distinct mammalian fau-
nas. On either side the islands stand on a moderately shallow
submarine bank, and these are inhabited by the same or by
very closely-allied quadrupeds. I have not as yet had time to
follow uj") this subject in all quarters of the world ; but, as far
as I have gone, the relation generally holds good. For in-
stance, 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 1,000 fathoms in depth, and here we find American
forms, but the species and even the genera arc quite distinct.
As the amount of modification which animals of all kinds un-
dergo partly depends on the lapse of time, and as islands sep-
arated from each other or from the main-land by shallow chan-
nels are more likely to have been continuously united within a
recent period than islands separated by deeper channels, we
can imdcrstand how it is that a relation exists l)etween the
depth of the sea separating two mammalian fiiimas, and the de-
gree of their affinity — a relation which is quite inexplicable on
the theory of independent acts of creation.

The foregoing statements in regard to the inhabitants of
oceanic islands — namelv, the fewness of the species, with a
large proportion consisting of endemic forms — the members
of certain groups, and not of other groups in the same class,
having hoen modified — the absence of certain whole orders, as
of batrachians and of terrestrial mammals, notwithstanding the

CuAP. XII. ON OCEANIC ISLANDS. 301

presence of aerial bats — the singular proportions of certain
orders of plants — herbaceous forms having been develoi)cd into
trees, etc., seem to me to accord better with the belief in the
cfiiciency of occasional means of transport, carried on during a
long course of time, than Avith the belief in the former connec-
tion of all oceanic islands with the nearest continent ; for, on
this latter view, it is probable that the various classes would
have immigrated more uniformly, and, from the species having
entered in a body, their mutual relations would not have been
much distiu-bed, and consequently tliey would have been modi-
fied citlier not at all or in a more equal manner.

I do not deny that there arc many and serious difficulties
in understanding how many of the inhabitants of the more
remote ishxnds, whether still retaining the same specific form
or subsequently modified, have reached their present homes.
Hut the probability of islands having existed as halting-places,
of which not a wreck now remains, must not he overlooked.
T will specify one such dillicult case. Almost all oceanic
islands, even the most isolated and smallest, are inhabited l)y
land-shells, generally by endemic species, but sometimes l)y
species found elsewhere — striking instances of which have
been given by Dr. A. A. Gould in relation to the Pacific.
Kow, 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 l)e, according to our view, some
luiknown, but occasionally eflicient, means for their trauspor-
tal. ^Vould the just-hatched young sometimes adhere to the
fe(>t of l)irds roosting on the ground, and thus get transported?
It occurred to me that land-shells, when hj'bcrnating, and hav-
ing a nuMnljranous dia]ihragm over the mouth of the shell,
might be floated in chinks of drifted tunl)er across moderately
wide arms of the sea. And I found that several species in this
state withstood uninjured an immersion in sea-water during
seven days : one shell, the Helix pomatia, after having been
thus treated and again hybernating, was put into sea-water for
twenty da\s, and ])erfectly recovered. During tliis length of
time tlie shell might have been carried, by a marine current of
average sv.iftness, to a distance of GGO geogra])liical miles.
As this Helix has a thick calcareous operculum, I removed it,
and, when it had formed a new membranous one, I again im-
mersed it for fourteen days in se:irwater, and again it recov-
ered and crawled away. Baron Aucapitaine has recently tried
similar experiments: he placed 100 land-shells, belonging to
IG

3C2 RELATIONS OF THE INHABITANTS OF Chap. XII.

ten species, in :i ])ox pierced with holes, and immersed it for a
fortnight in the sea. Out of the hundred shells, twenty-seven
recovered. The presence of an ojierculum seems to have been
of importance, as out of twelve sj^ecimcns of Cydostoma cle-
gans, which is thus furnished, eleven revived. It is remarkable,
seeing how well with me the Helix pomatia resisted the salt-
water, that not one of fifty-four specimens, l^elonging to four
species of Helix tried by Aueapitaine, recovered. It is, how-
ever, not at all probable that land-shells have often been thus
transported ; the feet of birds is a more probable method.

On the Relations of the Inhabitants of Islaiids to those oftJie
nearest Main-land.

The most striking and important fact for us is the affinity
of the species which inhabit islands to those of the nearest
main-land, without being actually the same. Numerous in-
stances could be given. The Galapagos Archipelago, situated
under the equator, lies at the distance of between 500 and GOO
miles from the shores of Soutli America. Here almost every
jiroduct of the land and the water l)ears the unmistakable
stamp of the American Continent. There are twenty-six land-
birds, and twenty-one, or, perhaps, twenty-three, of these arc
)"anked as distinct species, and are supposed to have been
created here ; yet the close affinity of most of these birds to
American species in every character, in their habits, gestures,
and tones of A^oice, was manifest. So it is with the other ani-
mals, 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 hundred miles from the continent,
yet feels that he is standing on American land. Why should
this be so ? why should the species which are supposed to
have been created in the Galapagos Archipelago, and nowhere
else, bear so plain a stamp of affinity to those created in Amer-
ica ? There is nothing in the conditions of life, in the geologi-
cal nature of the islands, in their height or climate, or in the
proportions in which the several classes are associated to-
gether, which closely resembles the conditions of the South
American coast : in fact, there is a considerable dissimilarity
in all the foregoing respects. On the other hand, there is a
considerable degree of resemblance in the volcanic nature of
the soil, in the climate, height, and size of the islands, be-

Chap. XII. ISLANDS TO THOSE OF THE MAIN-LANJ). 303

twccn the Galap.'ifjos aiul Capo dc Verde Arcliipclaii-oes : but
Avhat an entire and absolute difTorence in their inlialjitants !
The inliabitants of the Cape de Verde Islands are related to
those of Africa, like those of the Galapagos to America.
Facts such as these admit of no sort of explanation on the
ordinary view of independent creation ; whereas, on the view,
here maintained, it is obvious that the Galapagos Islands
would be likely to receive colonists, whether by occasional
means of transport or by formerly continuous land, fi'om Amer-
ica ; the Cape de Verde Islands from Africa : and that such
colonists would be liable to modification — the principle of in-
heritance still betraving their original birthplace.

Many analogous facts could be given : indeed, it is an al-
most universal rule that the endemic productions of islands
are related to those of the nearest continent, or of the nearest'
island. The exceptions are few, and most of them can be
explained. Thus, although Kerguelen Land stands nearer to
Africa than to America, the plants are related, and that very
closely, as we know from Dr. Hooker's accoimt, to those of
America : but, on the view that this island has been mainly
stocked by seeds brought with earth and stones on icel)ergs,
drifted by the prevailing currents, this anomaly disappears.
New Zealand in its endemic plants is much more closely re-
lated to Australia, tlie nearest main-land, than to any other
region: and this is what might have been ex])ccted ; but it is
also plainly related to South America, which, although the
next nearest continent, is so enormously remote, that the fact
becomes an ancjinaly. But this difFiculty almost disajipears on
the view that New Zealand, South America, and tlie other
southern lands, have been partially stocked from a nearly in-
termediate though distant point, namely, from the antaictic
islands, when they were clothed with vegetation, during a
warmer tertiary period, before the commencement of the last
Glacial period. The allinity, which, though feeble, I am
assured by Dr. Hooker is real, between the flora of the S(juth-
western corner of Australia and of the Ca]ie of Good Ilojie, is
a far more remarkable case ; but this ailinity is ccmlined to the
])lan(s, and will, no doubt, be some day explained.

The same law which has determined the relati(mshi|) be-
tween the inhabitants of islands and the nearest main-land i.s
sometimes displayed on a small scale, but in a most interesting
manner, within tlie limits of the same archipelago. Thus each
separate island of the Galapagos Archipelago is ti-nanted, and

564 EELATIONS OF TlIK INHABITANTS OF Chap. XII.

the fact is a iiiarvcllous ono, by distinct species; but these
species arc related in a very much closer manner to each other
than to the inhabitants of any other quarter of the world. Tliis
is what mii^ht have been expected, for islands situated so near
each other would almost necessarily receive immi<Ti"ants from
the same orig'inal source, and from each other. But how is it
that many of the immif^rants have been differently modified,
though only in a small degree, in islands situated within sight
of each other, having the same geological nature, the same
height, climate, etc. ? This long appeared to me a great diffi-
culty: but it ai-ises in chief part from the deeply-seated error
of considering the physical conditions of a country as the most
important ; whereas it cannot be disputed that the nature of
the other inhabitants with Avhich each has to compete is at
least as important, and generally a far more important element
of success. Now, if we look to the species Avliich inhabit the
Galapagos Archipelago and are likewise found in other parts
of the world, Ave find that they differ considerably in the sev-
eral islands. This difference might indeed have been expected
if the islands have been stocked by occasional means of trans-
port— a seed, for instance, of one plant having been brought to
one island, and that of another plant to another island, though
all proceeding from the same general source. Hence, when in
former times an 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 different
islands, for it would have to compete with a different set of or-
ganisms : a plant, for instance, would find the ground best
fitted for it occujiied by somewhat different species in the dif-
ferent islands, and would be exposed to the attacks of some-
what dillerent enemies. If, then, it varied, natural selection
would probably ffivor 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 degrcx; in some analogous cases,
is, that each new species, after being formed in any one island,
did not quickly spread to the other islands. But the islands,
though in siglit of each other, are se])arated by deep arms of
the sea, in most cases wider than the Britisli Channel, and
there is no reason to suppose that they have at any former

CiiAi'. XII. ISLANDS TO THOSE OF THE MAIN-LAND. 2G5

period boon continuously uuitccL The currcuts of the sea arc
rapid and sweep across the archipela;^o, and gales of wind arc
extraordinarily rare ; so that the islands are far more ciTcct-
iially separated from each other than they appear on a map.
Nevertlieless, some of tlie species, both those foimd in other
parts of tlic world and tliose confined to the archii)elag-o, are
common to the several islands; and we may infer from their
present manner of distribution that they have spread frona one
island to the othei-s. But we often take, I think, au erroneous
view of the probability of closely-allied species invading each
other's territory, when put into free intercommunication. Un-
doubtedly, if one species has any 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 proba-
bly will hold their jilaces and keep separate for almost any
length of time. Being familiar with the fact that many spe-
cies, naturalized through man's agency, have spread with as-
tonishing raj)idity over wide areas, we are apt to infer that
most species would thus spread ; but we should remember that
the speci(;s which become naturalized in new countries are not
generally closely allied to the aboriginal inhabitants, but are
very distinct forms, belonging in a large proportion of cases,
as shown by Alph. de CandoUe, to distinct genera. In the
(jrulapagos Archipelago, many even of the birds, though so
well adapted for Hying from island to island, are distinct on
each ; thus there are three closely-allied species of mocking-
thrush, each confined to its own island. Now let us suppose
the mocking-thrush of Cliatham Island to be blown to Charles
Island, which has its own mocking-thrush ; why should it suc-
ceed in establishing itself there ? We may safely infer that
Charles Island is well stocked with its own species, for aiuiu-
ally more eggs are laid and yv>ung birds hatched, than can
possibly be reared ; and we may infer that the mocking-tlirush
l)eculiar to Charles Island is at least as well fitted for its home
as is the species pecuhar to Chatham Island. Sir C. Lyell and
Mr. Wollaston have communicated to me a remarkable fact
bearing on this subject ; namely, that Madeira and the adjoining
islet of Porto Santo possess many distinct but representative
species of land-shells, some of which live in crevices of stone;
and, although large quantities of stone are annuallv transported
from Porto Santo to Madeira, yet this latter island has not be-
come coloniz(vl by the Porto Santo species : nevertheless, both
islands have been colunized by European land-shells, which no

3G6 KELATIONS OF THE INIIABITAXTS OF Ciia.-. XII.

doubt liad some advanta<Te over tlie indig-cnous species. From
these considerations I think wc need not g^reatl}- marvel at the
endemic and representative species, Avliicli inhabit the several
islands of tlic Galapag-os Archipelago, not Laving universally
spread from island to island, Preoccu])ation has also probably
played an important part in checking the connningling of the
species Avhich inhabit different districts with nearly the same
physical conditions on the same continent. Thus, the south-
cast and southwest 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.

The same principle which governs the general character of
the inhal)itants of oceanic islands, namely, their relation to tho
source whence colonists could have been most easily derived,
together with their subsequent modification, is of the widest
apjilication throughout Nature. We see this on every moun-
tain-summit, in every lake and marsh. For Alpine species,
cxcci)ting in as far as the same species have become widely
spread during the recent Glacial epoch, are related to those of
the surrounding lowlands : thus we have, in South America,
Aljiine humming-birds, Alpine rodents, Alpine plants, etc., all
strictly belonging to American forms ; and it is obvious that
a mountain, as it liccamo slowly upheaved, Avould he colonized
from the surrounding lowlands. So it is with the inhabitants
of lakes and marshes, excepting in so far that great facility of
transport has allowed many of the same species to prevail
through large portions of the world. AVe see this same prin-
ciple 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 universally found 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 sjiecies ; and wherever many
closely-allied species occur, there Avill be found many fonns
wliich 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 l)etweeu the power and extent of migration in
certain species, either at the present or at some fomier jieriod,
and the existence at remote jioints of the world of allied spe-
cies, is shown in another and more general way. Mr. Gould
remarked to me long ago, that, in those genera of birds which

CiiAr. XII. ISLANDS TO THOSE OF THE MAIN-LAND. 3^7

range over tlic world, many of the species have very wide
rana^es. I can hardly doubt that this rule is generally true,
though it would be difficult to prove it. Among mammals, we
see it strikingly displayed in bats, and in a lesser degree in
the Felid;e and CanidiV. We see the same rule in the distribu-
tion of butterflies and beetles. So it is with most of the in-
habitants of fresh water, for many of the genera in the most
distinct classes range over the world, and many of the species
have enonnous ranges. It is not meant that all^ but that some
of the species in the genera which range very widely, have
themselves very wide ranges. 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 modilicatiou has
gone; for instance, two varieties of the same species inhabit
America and Europe, and thus the species has an immense
rjtnge ; but, if variation were to be carried a little further, the
two varieties would be ranked as distinct species, and the
range Avould 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 powerfullj'-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 ^'ictorious in distant
lands in the struggle for life with foreign associates. But, ac-
cording to the vi(.'w that all the species of the same genus,
though now distributed at the most remote points of the worhl,
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, in relation to all organic beings,
that many genera arc of very ancient origin, and the species in
this case will have had ample time for dispersal and subsequent
modificati(.)n. There is also reason to believe, fiom geological
evidence, that Avithin each great class the lower organisms
change at a slower rate than the higher; consequently they
will liave had a better chance of ranging widely and of still re-
taining the same sjjeeific character. This fact, together with
the seeds and eggs of almost all lowly-organized forms l)eing
very minute and better fitted for distant transportal, probably
accounts for a law which has long been observed, and which
has lately been discussed by Alpli. de CandoUe in regard to
plants, namely, that the lower any group of organisms stands,
the more widely it ranges.

368 SUM.MAliY OF THE LAST Chap. XII.

The relations just discussed — namely, lower oriranisms ran-
ging' more "widely than the higher — some of the species of widely-
ranging genera themselves ranging widely — such facts, as al-
l)ine, lacustrine, and marsh productions being generally related
to those which live on the surrounding low-lands and drylands
— the striking relationship between the inhabitants of islands
and tliose of the nearest main-land — the still closer relationship
of the distinct inhabitants of the islands in the same archipelago
— are inexplicable on the ordinary view of the independent
creation of each species, l)ut arc explicable if we admit coloni-
zation from the nearest or readiest source, together with the
subsequent adaptation of the colonists to their new homes.

Summary of the last and 2)^'c^C}it Chapter.

In these chapters I have endeavored to show that, if we
make due allowance for our ignorance of the full effects of the
changes of climate and of the level of the land, which have cer-
tainly occurred within the recent period, and of other changes
which have probably occurred — if Ave remember how ignorant
M'e are with respect to the many curious means of occasional
transport — if we bear in mind 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 insuper-
able 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 centres of
creation, by various general considerations, more especially
from the importance of barriers of all kinds, and from the ana-
logical distribution of sub-genera, genera, and families.

With respect to distinct species belonging to the same
genus, Avhich on our theory must have spread from one parent-
source ; if Ave make the same allowance as before for our igno-
rance, and remember that some forms of life have changed A'cry
slowly, enormous periods of time having been thus granted for
tlieir migration, the difficulties are far from insuperable; though
in this case, and in that of the individuals of the same species,
they are often great.

As exemplifying the effects of climatal changes on distribu-
tion, I liaA'c attempted to shoAV how important a part the Gla-
cial period has played, Avhich affected even the equatorial
regions, and Avhich, during the alternations of the cold in the

Chap. XII. AND TKESENT CHAPTER. 3(J9

north and soutli, allowed the productions of ojipositc hemi-
spheres to mingle, and left some of them stranded in all parts
of the world on the mountain-summits. As showing how diver-
sified are the means of occasional transport, I have discussed
at some little length the means of dispersal of fresh-water pro-
ductions.

If the difliculties be not insuperable in admitting that in
the long course of time all the individuals of the same species,
and likewise of the several species belonging to the same ge-
nus, have proceeded from some one source ; then all the grand
leading facts of geographical distribution are explicable on the
theory of mioTation, together with subsetiuent modification and
the multiplication of new forms. We can thus understand the
high imixtrtancc of barriers, whether of land or water, in not
only s{'j)arating, but in apparently forming the several zoologi-
cal and botanical provinces. We can thus understand the
concentration of related species within the same areas; and
how it is that under different latitudes, for instance in South
America, the inliabitants of the i>lains and mountains, of the
forests, marshes, and deserts, are linked together in so mysteri-
ous a manner, and are likewise linked to the extinct beings
which fonnerly inhabited the same continent. Bearing in mind
that the mutual relation of organism to organism is of the high-
est importance, we can see why two areas liaving nearly the
same phj'sical conditions sliould 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 coinpetiti(m with
each other and with the aborigines ; and according as the im-
migrants were capable of varying more or less rapidly, there
would ensue in the two or more regions, indejiendently of their
phj-sical conditions, infinitcly-diver.sified conditions of life —
there would be an almost endless amount of organic action and
reaction — and we should lind, as we. do find, some groups of
beings greatly, and some only slightly, modified — some devel-
oped in great force, some existing in scanty numbers — in the
several great geographical provinces of the world.

On these same principles we can undc^rstand, as I have en-
deavored to show, why oceanic islands should have few in-
habitants, but of these a great number should be endemic or

370 SUMMAKY OF THE LAST Ciiai-. XII.

peculiar; aii<l 'wliy, in rclalion to tlie means of iiii<>ration, one
group of beings, even Avithin the same class, should have all its
species peculiar, and another group should have all its species
the same Avith those in other quarters of the world. We can
see why "whole groups of organisms, as batrachians and terres-
trial mammals, should be absent from oceanic islands, Avhilc the
most isolated islands should possess their own peculiar species
of aerial mammals or bats. We can see why there should be
some relation between the presence, in islands, of mammals, in
a more or less modified condition, and the depth of the sea be-
tween such islands and the main-land. We can clearly see why
all the inhabitants of an archipelag-o, though specifically distinct
on the several islets, should be closely related to each other,
and likewise be related, but less closely, to those of the nearest
ccnitinent or other source whence immigrants might have been
derived. AVe can sec why, in two areas, however distant from
each other, where very closely-allied or representative species
exist, there should almost always exist some identical species.
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 successioni of fonns in past times being
nearly the same with those governing at the present time the
differences in difTerent areas. We see this in many facts, llie
endurance of each species and group of species is continuous in
time ; for the exceptions to the rule are so few, that they may
be fairly attributed to our not having as yet discovered in an
intermediate dei")Osit certain forms which are absent in it, but
which occur both above and below : so in space, it certainly is
the general rule that the area inhabited by a single species, or
by a grouji of species, is continuous, and the exceptions, which
are not rare, may, as I have attempted to show, be accounted
for by former migrations mider difTerent 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 maxi-
mum development. Groups of species, living during the same
j)eri(jd of time, or living jvitliin the same area, are often char-
acterized by trifling features in common, as of sculpture or
color. In looking to the long succession of past ages, as in
now looking to distant provinces throughout the world, we
find that species in certain classes differ little from each other,
while others in a different class, or only in a different family of
the same order, differ greatly from each other. In both time

CiiAP. XII. AND PRESENT CHAPTER. 37I

and space the lowly-orn^auized members of each class generally
change less than the highly-organized ; but there are in botli
cases marked exceptions to the rule. According to our theory
these several relations throughout time and space arc intelli-
gible ; for, whether we look to the forms of life which have
changed during successive ages, or to those which have changed
after having migrated into distant quarters, in both cases the
forms witliin each class arc connected by the same bond of or-
dinary generation ; and in both cases the laws of variation have
been the same, and modifications have been accumulated by
the same means of natural selection.

37S CLASSIFICATION. Cuap. XIII.

CHAPTER XIII.

MUTUAL AFFINITIES OF ORGANIC BEINGS: MOEPHOLOGY : EM-
BRYOLOGY: RUDIMENTARY ORGANS.

Classifiriition. Groups subordinate fn Group? — Natural System— Rnlcs ;ind Difficiiltica
in Chissilio.'UiDii. explained on tlio Theory of Descent with Moditicalion — Classi-
fication of Vnrieliew— Descent alwavH used in Classification — Analofrical or Adap-
tive Characters — Affinities, General. Complex, and liadiatincj— Extinction sepa-
rates and defines Groups — Morpliolou'V- between members of the same Class, be-
tween parts of the same Individual — Embryoloiry. Laws of. explained by Vari.i-
tions not supervening at an early Age, and being inherited at a corresponding
Age — Kudimeutary Organs ; their Origin explainuU — Suinniar3'.

Classijtcation.

From a very remote period in the history of the world or-
ganic beings have resembled each other iu descending degrees,
so that they can be classed in groups under groups, litis
classiftcation is not arbitrary, like the grouping of the stars in
constellations. The existence of groups would have been of
simple signification, if one group had been exclusively fitted to
inhtibit the land, and another tlie water; one to feed on flesh,
another on vegetable matter, and so on ; but the case is widely
different in Nature ; for it is notorious how commonly members
of even the same sub-group have dilfercnt habits. In the second
:ind fourth chapters, on Variation and on Natural Selection, I
have attempted to show that within each country it is the
Avidel^'-ranging, the much-dilfused and common, that is, the
dominant sj^ccies belonging to the larger genera in each class,
which vary most. The varieties, or incipient species, thus pro-
duced, ultimately become converted into new and distinct spe-
cies ; and these, on the principle of inheritance, tend to pro
duce other new and dominant species. Consequently, the
groups which are now large, and which generally include many
dominant sjiecies, tend to go on increasing in size. I further
attempted to show that, from the varying descendants of each
species t tying to occupy as many and as different places as pos-

Chap. XIII. CLASSIFICATION. 373

siblc in the economy of Nature, there is a constant tendency in
their characters to diverge. This latter conclusion is supported
by observing tlio 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 constant tendency
in the forms -which arc 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 ex-
])lained, of these several jmnciples ; and he will see that the
inevitable result is, that tlie modilied descendants proceeding
from one progenitor become broken up into groups subordi-
nate to groups. In the diagram each letter on the uppermost
line may represent a genus including sevei'al species ; and the
whole of tlie genera along this upper line form together one
class, for all arc descended from one ancient parent, and, con-
sequentl}', have inherited something in common. But the
three genera on the left hand have, on this same principle,
nnich in common, and form a sul>family, distinct from that in-
cluding the next two genera on the right hand, w^hich diverged
from a common parent at the fifth stage of descent. These
five genera have also much, though less, in common ; and they
form a faniilv distinct from that including the three genera still
fartlier to tlie right liand, which diverged at a still earlier
period. And all these genera, descended from (A), form an
order distinct from the genera descended from (1). So tliat
we here have many species descended from a single progenitor
groujied into genera ; and the genera in sub-families, families,
and orders, all in one great class. Thus, the grand fact of the
natural suliordination of all organic beings in groups under
groups, which, from its familiarity^, does not always sulliciently
strike us, is in my judgment explained. No doubt organic
lieings, like all other objects, can be classed in many ways,
either artificially by single characters or more naturally by a
number of characters. We know, for instance, that minerals
and the elemental substances can be thus aiTanged ; in this
case there is of course no relation to genealogical succession,
and no cause can at present be assigned for tlicir falling into
group.s. But with organic beings the case is different, and the
view above given explains their natural an-angement in group
under gr(jup ; and no other explanation has ever hccn at-
tcm])lc(l.

r,74 CLASSIFICATION. Chap. XIII

Naturalists, as we have seen, try to arraiioc the species,
genera, and families in each class, on what is called the Natu-
ral System. But -what is meant by this system ? Some
authors look at it merely as a scheme for arranginj^ tog'ethcr
those llvina^ objects which are most alike, and for separating
those which are most inilike ; or as an artificial means for
enunciating, as briefly as possible, general propositions — that
is, by one sentence to give the characters common, for instance,
to all mammals, by another those common to all carnivora, by
another those conunon to the dog-genus, and then, by adding
a single sentence, a full description is given of each kind of
dog. The ingenuity and utility of this system are indispu-
table. But many naturalists think that something more is
meant ])y the Natural System ; they believe that it reveals the
plan of the Creator ; but, unless it be specified Avhether 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. Such expressions as that fiimous one by Lin-
nieus, and which wc often meet with in a more or less con-
cealed form, that the characters do not make the genus, but
that the genus gives the characters, seem to imply that some-
thing more is included in our classification than mere resem-
blance. I believe that something more is included, and that
propin(juity of descent — the only known cause of the similarity
of organic beings — is the bond, hidden as it is by various de-
grees of modification, which 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 imknown plan of creation, or is
simply a scheme for enunciating general propositions and of
jilacing together the forms most like each other. It might
have been thought (and Avas in ancient times thought) that
those parts of the structure which determined the habits of life,
and the general place of each being in the economy of Nature,
would be of very high importance 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 reseml)lances, though so intimate-
ly connected with the whole life of the being, are ranked as
merely " adaptive or analogical characters ; " but to the con-
sideration of these resemblances we shall recur. It may even
be given as a general rul(>, that the less nny part of the organi-

CriAr. XIII. CLASSIFICATION. 375

zation is concerned with special habits, the more important it
becomes for chissilication. As an instance — Owen, in speak-
inf];' of the dufjonp:, says : " The generative or<^ans, Ijein^r those
wiiich are most remotely related to the habits and food of an
animal, I have always regarded as alTordinti; very clear indica-
tions of its true airmities. We are least likely in the modifi-
cations of these organs to mistake a merely adaptive for an
essential character." With plants, how remarkable it is that
the organs of vegetation, on which tlieir nutrition and life de-
]icnd, are of little signification ; whereas the organs of repro-
duction, with their product tlie seed and embr^'o, are of ])ara-
mount importance ! So, again, in formerly discussing morpho-
logical dilleronces M'hich are not jihysiologically important, we
have seen that they are often of the highest service in classifi-
cation. Tliis depends on their constancy througliout many
allied groups ; and the constancy depends chiefly on any shght
deviations of structure in such parts not having been pre-
served and accumulated by natural selection, wliich acts only
on useful characters.

That tlie mere jihysiological 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 w^e have
every reason to suppose, has nearly the same physiologi-
cal value, its classificatory value is widely difltM-ent. No
naturalist can have worked at aily group without being struck
with this fact ; and it has been fully acknowledged in the
writings of almost every author. It will suffice to quote the
highest aulhorily, Kobert ]}ro'\\Ti, who, in speaking of certain
organs in the Proteacere, says, their generic importance, " like
that of all their parts, not only in this, Init, as I apprehend, in
every natural familv, is verv unequal, and in some cases seems
to be entirely lost." Again, in another work, he says, the
genera of the Connaracea? " differ in having one or more
ovaria, in the existence or absence of albumen, in the imbri-
cate or valvular rcstivation. Any one of these characters
singly is fref|uently of more than generic importance, though
here even when all taken together they a])pear insufficient
to separate Cnestis from Connarus." To give an example
among insects: in one great division of the Ilymenoptera,
the antenna?, as Westwood has remarked, arc most constant
in structure ; in another division they differ nuich, and the
differences are of (juitc subordinate vahie in classification ; yet
no one will say that the antennif in these two divisions of the

37G CLASSIFICATION. CriAr. XIII.

same order are of unequal jilijsiological importance. Any
number of instances could be given of the varying importance
for classification of the same important organ williin the same
group of beings.

Agahi, no one Avill say that rudimentary or atrophied or-
gans are of high physiological or ^ital importance ; ^-et, un-
doubtedly, organs in this condition are often of high value in
classification. No one will dispute that the rudimentary 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 rudi-
mentary florets is of the highest importance in the classification
of the Grasses.

Numerous instances could be given of characters derived
Ij-om parts which must be considered of Acry trifling physiolo-
gical importance, but which are universally admitted as highly
serviceable in the definition of Avhole groups. For instance,
whether or not there is an open passage from the nostrils to
the mouth, the only character, according to Owen, which abso-
lutely disting-uishcs fishes and reptiles — the inflection of the
angle of the jaws in ^larsupials — the manner in which the
wings of insects are folded — mere color in certain Alga; — mere
pubescence on parts of the tlower in grasses — the nature of
the dermal covering, as hair or feathers, in the Vertebrata.
If the Ornithorhyncluis 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 degree of affinity of this strange creature to birds.

The importance, for classilication, of trifling characters,
mainly depends on their being correlated Avith several other
characters of more or less importance. The value indeed of an
aggregate of characters is very evident in natural history.
Hence, as has often been remarked, a species may depart from
its allies in several characters, both of high physiological im-
portance and of almost universal prevalence, and A'ct leave us
in no doubt where it sliould be ranked. Hence, also, it has
been found that a classification founded on any single charac-
ter, however important that may be, has always failed ; for no
part of the organization is invariably constant. The impor-
tance of an aggregate of characters, even when none are im-
portant, alone explains the aphorism by Linuiens, naTuely, that
the characters do not give the genus, but the genus gives the

CiiAP. .\III. CLASSIFICATION. 377

characters ; for this seems foun Jed on an .appreciation of many
trillinp;' points of resemblance, too slif^ht to be delinetl. Cer-
tain plants, belongiiii^ to the Mali)igliiacene, bear perfect and
degraded fio\vcrs; in the hitter, as A. do Jussicuhas remarked,
" the grc'iter nuinl)er of the characters proper to the species,
to the genus, to tlie family, to the class, disappear, and thus
laugh at our classification." But when Aspicarpa produced in
France, during several years, only degraded flowers, departing
so wonderfully in a number of the most important points of
structure from the proper type of the order, yet M. Richard
sagaciously saw, as Jussieu observes, that this genus should
still be retained among the MalpighiacefO. This case seems to
me well to illustrate the spirit of our classification.

Practically, Avhen naturalists are at work, they do not
trouble themselves about the physiological value of the charac-
ters which they use in defining a group or in allocating any
particular species. If they find a character nearly uniform, and
common to a great number of forms, and not common to
others, they use it as one of high value ; if common to some
lesser number, they use it as of subordinate value. This prin-
ciple has been broadly confessed by some naturalists to be the
true one; and by none more clearly than by that excellent
botanist, Aug. St. Hilaire. If certain characters are always
found correlated with others, though no apparent bond of con-
nection can be discovered between them, especial value is set
on them. As in most groups of animals, important organs,
such as those fc^r propelling the blood, or for aerating it, or
those for propagating the race, arc foimd nearly uniform, they
are considered as highly sernceable in classification; but in
some groups of anim:ds all these, the most important vital
organs, are found to ofler characters of quite subordinate value.
Thus, as Fritz MllUer has lately remarked, in the same group
of crustaceans, ('ypridina is furnished Avith a heart, while in
two closely-allied genera, namely, C^-pris and Cytherea, there
is no such organ : one species of Cypridina has well-developed
branchi.'C, while another species is destitute of them.

Wo can see why characters derived from the embrj^o 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 ol)vious, on the ordinary view, why the structure
of the embryo should be more important for this purpose than
that of the adult, which alone plays its full part in the econo-
my of Nature. Yet it has been strongly urged by those great

378 CLASSIFICATION. Chap. XIII.

naturalists, iMiliic Edwards and Ag'assiz, tliat embryoloijifal
characters ai o the most important of all ; and this doctrhie has
very g'encrally been admitted as true. Nevertheless, their im-
portaTicc has sometimes been exaggerated; in order to show
tlii.s, Fritz Miillcr arranged by the aid of such characters the
great class of crustaceans, and the arrangement did not prove
a natural one. But there can be no douljt that characters de-
rived from tlie embryo are generally of the highest value, not
only Avith animals but Avith plants. Thus the two main divis-
ions of flowering plants are founded on differences in the em-
bryo— on the number and position of the cotyledons, and on
the mode of development of the plumule and radicle. Wc
shall immediately see why these characters possess so high a
value in classification, namely, from the natural system being
genealogical in its arrangement.

Our classifications are often plainly influenced by chains of
aflinities. Nothing can be easier than to define a number of
chanicters common to all birds ; but in the case of crustaceans,
such definition has hitherto been found impossible. There are
crustaceans at the opposite ends of the series, which 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 Articulata.

Geographical distribution has often been used, though per-
haps not quite logically, in classification, more especially in
very largo groups of closely-allied forms. Temminck insists
on the utility or even necessity of this practice in certain
groups of birds ; and it has been followed by several entomol-
ogists and botanists.

Finally, wutli respect to the comparative value of the vari-
ous groups of species, such as orders, sub-orders, families, sub-
families, and genera, they seem to be, at least at present,
almost arbitrary. Several of the best botanists, such as Mr.
IJontham and others, have strongly insisted on their arbitrary
value. Instances could be given among plants and insects, of
:i group of forms, first ranked by ])ractised naturalists as only
a genus, and then raised to the rank of a sub-family or family ;
and this has been done, not because further research has de-
tected important structural differences, at first overlooked, but
because nmnerous allied species, with slightly-different grades
of difference, have been subsequently discovered.

All the foregoing rules and aids and difBcultics in classifi-

Chap. XIII. CLASSIFICATION. 3-79

cation arc explained, if I do not greatly deceive myself, on the
view that the Natural System is founded on descent Avitli
modification; that the characters which naturalists consider as
showing true allinity between any two or more species, are
those which have been inherited from a connnon parent, all true
classification being genealogical ; that community of descent
is the hidden bond Avhich naturalists have been unconsciously
seeking, and not some unknown plan of creation, or the enun-
ciation 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 arret)} rjcment of the groujis within each class, in due sub-
ordination and relation to each other, must be strictly genea-
logical in order to be natural ; but that the amount of diflerence
in the several branches or groups, though allied in the same
(h'grce in blood to their common progenitor, may diller greatly,
In'ing duo to the different degrees of modification Avhich they
have luidergone ; 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 sup]iose the letters A to L to rcpi'csent during the Silurian
epoch allied genera, descended from some still earlier forms.
In three of these genera (A, F, and I) the species have trans-
mitted modified descendants to the present day, represented l)y
the fifteen genera («'* to s'*) on the uppermost horizontal line.
Now all these modified descendants from a single species, are
related in blood or descent to the same degree ; they may
metaphorically be called cousins to the same millionth degTce ;
y(}t tiiey differ widely and in diU'ercnt degrees from each other.
The forms descended from A, now broken up into two or three
families, constitute a distinct order from those descended from
I, also broken up into two families. Nor can the existing sjie-
cies, desecnded from A, be ranked in the same genus with the
parent A; or those from I, with the parent I. But the exist-
ing geiuis f" may be supposed to have been but slightly modi-
tied ; and it will then rank with tlie parent-genus F ; just as
some few still living organisms belong to Silurian genera. So
Ihat the amount or value of the differences between these or-
ganic beings which arc all related to each other in the same
degree in blood, has come to be widely different. Nevertheless,
their genealogi(Ml arranffcment remains strictly true, not only
at tlie present time, but at each successive period of descent.

380 CLASSIFICATION. Cnxr. XIII.

All the modified descendants from A will have inherited some-
thing' in common from their common parent, as will all the de-
scendants from I ; so will it be with each subordinate branch of
descendants, at each successive stage. If, however, we suppose
any descendant of A or of I to have been so much modified as
to have lost all traces of its parentage, in this case, its place in
the natural system will likev>dse be lost — as seems to have oc-
curred 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 modified, and they form a single genus
But this genus, tliough much isolated, will stiil occupy its projv
er intermediate position. This natural arrangement is shown
in the diagram as far as is possible on paper, but in much too
simple a manner. If a branching diagram had not been used,
and only the names of the groups had been written in a linear
series, it would have been still less possible to have given a
natural arrangement ; and it is notoriously not possible to rep-
resent in a series, on a flat surface, tlic aflinities which we dis-
cover in Nature among the beings of the same group. Thus,
on the view which I hold, the natural system is genealogical
in its arrangement, like a i^edigrcc ; but the amount of modifi-
cation which the different groups have undergone has to be
expressed by ranking them und(?r different so-called genera,
sub-families, families, sections, orders, and classes.

It may be worth while to illustrate this view of classification,
by taking the case of languages. If we possessed a perfect
jiedigree of mankind, a genealogical arrangement of the races
of man would afford the best classification of the various lan-
guages now spoken throughout the world ; and if all extinct lan-
guages, and all intermediate and slowly-changing dialects, had
to be included, such an arrangement would be the only pos-
sible 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, o\\'ing to the spreading, isola-
tion, and state of civilization of the several co-descended races,
and liad thus given rise to many new dialects and languages.
The various degrees of difference between the languages of
tlie same stock would have to be expressed by groups subordi-
nate to groups ; but the proper or even only possible arrange-
ment would still be genealogical ; and this would be strictly
natimal, as it would connect together all languages, extinct and
recent, by the closest affmitics, and would give the filiation and
origin of each tongue.

Chap. XIII. CLASSIFICATION. 381

In confirmation of this view, let us glance at the classifica-
tion of varieties, which are believed or known to be descended
i'roin a sinu:le sjiecies. These are grouped under the species,
witli the sub-variclies under the varieties ; and in some cases,
as with domestic pigeons, several otlier grades of dilVerence are
requisite. Nearly the same rules are followed as in classifj-ing
species. Authors have insisted on the necessity of arranging
varieties on a natural instead of an artificial system ; we are
cautioned, for instance, not to class two varieties of the pine-
apple together, merely because their fruit, though the most
important part, happens to be nearly identical; no one puts
llie Swedish and conunon turnijjs together, though the escu-
h'nt and thickened stems are so similar. Whatever part is
found to be most constant, is used in classing varieties : thus
the great agriculturist Marsiiall says the liorns are very useful
loE this purpose with cattle, because they are less variable than
tlie shape or color of the body, etc. ; whereas with sheep the
horns are nuicli less serviceable, because less constant. In
classing varieties, I apprehend that if we had a real pedigree,
a genealogical classification would be universally preferred ;
and it has been attempted in some cases. For we might feel
sure, wlicther there had been more or less modification, the
])rinciple of inheritance would keep the forms together which
were alHed in the greatest number of points. In tundjler
])igeons, tliougli some of the sul>varieties difler in the impor-
tant character of having a longer beak, yet all are kept togeth-
er, from having the common habit of tumbling; but the shoit-
faccd breed has nearly or quite lost this haljit; nevertheless,
without any thought on the sul)ject, these tumblers arc 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 lie includes in
his lowest grade, that of the species, the two sexes ; and how
enormously these sometimes dilh^r in the most important char-
acters, is known to every naturalist : scarcely a single fact can
be predicated in common of the adult males and hermajihro-
• lites of certain cirripedes, and yet no one dreams of sejiarating
ihem. As soon as the three Orchidean forms, Monachanthus,
-Myanthus, and Catasetum, which had jireviously been ranked
as three distinct genera, were known to bo sometimes pro-
duced on the same plant, they were inunediately considered as
varieties; and now 1 have been able to show that they are the

382 CLASSIFICATION. Chap. XIII.

male, female, and hermaphrodite forms of the same species.
The naturalist ineludes as one species the various larval stages
of the same individual, however much they may differ from
each other and from the adult, as Avell as the so-called alter-
nate generations of Stcenslrup, which can only in a technical
sense be considered as the same individual. He includes
monsters and varieties, not from their partial resemblance to
the parent-form, but because they are descended from it.

As descent has universally been used in classing together
the individuals of the same species, though the males and fe-
males and larvfc are sometimes extremely different ; and as it
has been nscd in classing varieties which have undergone a
certain, and sometimes a considerable amount of moditication,
may not this same element of descent have been unconsciously
used in grouping species under genera, and genera imder
higher groujis, all under the so-called natural system? I be-
lieve it has been unconsciously used; and thus only can I im-
derstand the several rules and guides which have been fol-
lowed by our best systematists. We have no written pedi-
grees ; Ave have to make out community of descent by resem-
blances of any kind. Therefore Ave choose those characters
Avhich, as far as Ave can jucige, are the least likely to Ikia'C been
modified in relation to the conditions of life to Avhich each spe-
cies has been recently exposed. Rudimentary structures on
this vicAV are as good as, or CA'en sometimes better than, other
]")arts of the organization. We care not hoAV trilling a charac-
tcn- may be — let it be the mere inflection of the angle of the
jaAv, the manner in Avhich an insect's Aving is folded, Avhet'licr
the skin be covered b}' hair or feathers— if it prevail thn^ugh-
out many and different species, especially those haA'ing very
different habits of life, it assumes high A'alue ; for Ave can ac-
coimt for its presence in so many forms Avith such different
habits, only by inheritance from a common ]iareut. A\^e may
err in this resjiect in regard to single points of structure, but
Avhen scA'eral characters, let them be eA'cr so trifling, concur
throughout a large group of beings haA'ing different habits, aa'C
may feel almost sure, on tlieory of descent, that these charac-
ters have been inlierited from a common ancestor. And aa-g
knoAV that such correlated or aggregated charactei's haA'e es
jiecial value in classification.

We can understand Avhy a sjiecies or a group of sjiecies
may depart, in several of its most important characteristics,
from its allies, and yet be safely classed Avith them. This may

Chap. XIII. ANALOGICAL RESEMBLANCES, 3S3

be safely doiip, aiul is often done, as long as a sufficient num-
ber of characters, let them be ever so unimportant, betrays the
hidden bond of community of descent. Let two forms have
not a single character in conunon, yet if these extreme forms
are connected together by a chain of intermediate groups, we
may at once infer their community of descent, and we put
them all into the same class. As we find organs of high
physiologiortl importance — those which serv'C 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 our classi-
fication. We sliall presently see why embryological charac-
ters are of such high classiticatpry importance. Geographical
distribution may sometimes be brought usefully into play in
classing large genera, because all the species of the same
genus, inlial)iting any distinct and isolated region, are in all
probability descended from the same ]>arents.

jinalof/lcal Resemhlanccs. — We can understand, on the
above views, the very important distinction between real af-
finities and analogical or adaptive resemblances. Lamarck
first called attention to this distinction, and he has been ably
followed by Macleay and others. The resemblance in the
shape of the body and in the fin-like anterior limbs, between
the dugong, which is a pachydermatous animal, and the
whale, and between both these mammals and fishes, is analo-
gical. Among insects there are innumerable instances: tlujs
Linnicus, misled by external appearances, actually classed an
ho;noi)terous insect as a moth. We see something of the same
kind even in our domestic varieties, as in the thickened stems
of the common and Swedish turnips. The resemblance of the
greyhound and race-horse is hardly more fanciful than the
analogies whicli have been drawn by some authors between
widely-distinct animals. On my view of characters being of
real importance for classification, only in so far as they reveal
descent, we can clearlv understand why analogical or adaj^tive
characters, although of the utmost importance to the welfare
of tlie being, are almost valueless to the systematists. For
aniiMiils belonging to two most distinc-t lines of descent may
readily have become adapted to similar conditions, and thus
have assumed a close external resemblance ; but such resem-
blances will not reveal — will rather tend to conceal their
blood-rclalionsliip. We can thus also understand the appar-

384 ANALOGICAL KESEMBLANCES. Chap. XIIL

cut paradox, that the very same characters are analogical
when one class or one order is compared -with another, but
give true aflniities Avhen the members of the same class or or-
der are compared together: thus, the shape of the body and
iin-likc Hmbs are only analogical "when whales are compared
AviLli fishes, being adaptations in both classes for swimming
through the water; but the shape of the body and fin-like
limbs serve as characters exhibiting true aflinity between the
several members of the whale family ; for these cetaceans
agree in so many characters, great and small, that we cannot
doubt that they have Hiherited their general shape of body and
structure of limbs from a common ancestor. So it is with
fishes.

The most remarkable case of analogical resemblance ever
recorded, though not dependent on adaptation to similar con-
ditions of life, is that given by Mr. Bates with respect to cer-
tain butterflies in the Amazonian region closely mimicking
other kinds. This excellent observer shows that in a district
where, for instance, an Ithomia abounds in gaudy swarms,
another butterfly, namely, a Leptalis, is often found mingled
in the same flock, and so closely resembles the Ithomia in
every shade and stripe of color, and even in the shape of its
wings, that jNIr. Bates, with his eyes sharpened by collecting
during eleven years, was, though always on his guard, con-
tinually deceived. When the mockers and the mocked are caught
and comjiared, they are found to be totally different in essen-
tial 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 imitates an Ithomia, another mocking and mocked
species belonging to the same genera, equally close in their re-
semblance, will be found. Altogether no less than ten genera
are enumerated, which include species that iinitate other but-
terflies. The mockers and mocked alwaj's inhabit 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 aboimd in
swanns. In the same district in which a species of Lcjitalis
closely imitates an Ithomia, there are sometimes other Lejn-
doptera mimicking the same Ithomia ; so that in the same
place, species of three genera of butterflies and even a moth
are found nil closely resembling a butterfly belonging to a fourth

Chap. XIII. ANALOGICAL EESEMBLANCES. 385

p^emis. It deserves especial notice that many of the mimick-
inn^ forms of the Lcptalis, as ■well as of the mimicked forms,
can be shown hy a g^raduated series to be merely varieties of
the same species ; while others are undoubtedly distinct spe-
cies. But why, it may be asked, are certain Jbrms treated as
tlie mimicked and othei's as tlic mimickers ? Mr. Bates satis-
factorily answers this question, by showing);' that the form
Avliicli is imitated keeps the usual dress of the f^roup to which
it lielongs, while the counterfeiters have changed their dress
and do not resemble their nearest allies.

^\'e are next led to inquire what reason can possibly be as-
signed for certain butterflies and moths so often assuming the
dress of another and quite distinct form ; why, to the perplexity
of naturalists, has Nature condescended to the tricks of the
stage? ]Mr. Bates has, no doubt, hit on the true explanation.
The mocked forms, wliich always aboimd in numbers, nuist
habitually escape destruction to a large extent, otherwise they
could not exist in such swarms ; and Mr. Bates never saw
them preyed on l)y birds and certain large insects which at-
tack other butterllies. He has good reason to believe that
this innnunity is owing to a peculiar and offensive odor which
they emit. The mocking forms, on the other hand, that in-
habit the same district, are comparatively rare, and belong to
lare groups ; hence they must suffer habitually from some
danger, A^r otherwise, from the number of eggs laid bv all but-
terflies, they would in three or four generations swarm over the
wliole country. Now if a member of one of these persecuted
and rare groups were to assume a dress so like that of a well-
])rotected species that it continually deceived the practised
eyes of an entom(ilogist, it would often deceive predacious birds
and insects, and thus escape much destruction. Mr. Bates
may almost be said to have actually witnessed the process
by which the mimickers have come so closely to resemble the
mimicked ; for he found that some of the forms of Lcptalis
which mimic so many other butterflies, varied in an extreme
degree. In one district several varieties occurred, and of these
one alone resembled, to a certain extent, the conunon 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 I^op-
talis first varies ; and when a variety hajipens to resemble in
some degree any common butterfly inhabiting the same district,
17

386 AFFINITIES CONNECTING Cuap. XIII.

tliis variety, from its rcseinl)lancc to a flourishing aiul little-per-
secuted kind, has a better chance of escaping' destruction from
predacious birds and insects, and is consequently oftener pre-
served ; " the less ];)erfect degrees of resemblance being gener-
ation after generation eliminated, and only the others left to
]')ropagate their kind." So that here we have an excellent il-
lustration of natural selection.

Mr, Wallace has recently described several equally striking
cases of mimicry in the Lepidoptera of the Malay Archipelago,
and other instances could be given with other orders of insects.
Mr. Wallace has also described one case of mimicry among
birds, but we have no such cases Avith the larger quadrupeds.
Tlie much greater fi-equency of mimicry with insects than with
other animals, is probably the consequence of their small size ;
insects cannot defend themselves, excepting indeed the kinds
that sting, and I have never heard of an instance of these
mocking other insects, though they are mocked ; insects can-
not escape by flight from the larger animals ; hence they are
reduced, like most weak creatures, to trickery and dissimula-
tion.

But to return to more ordinary cases of analogical resem-
l:)lance : as members of 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 sometimes been observed between
the sub-groups in distinct classes. A naturalist, struck by a
])arallelism of this nature in any one class, by arbitrarily rais-
ing or sinking the value of the groups in other classes (and all
our experience shows that their valuation is as j'et arbitrary)
could easily extend the parallelism over a wide range ; and
thus the septenary, quinary, quaternary, and ternary classifica-
tions have probably arisen.

0)1 tlic N'ature of the Affinities connecting Organic be-
ings.— As the modified descendants of dominant species, be-
longing to the larger genera, tend to inherit the advantages
which made the groups to which they belong large aud 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
ttMid to go on increasing in size ; and they consecjjiently sup-
j>lant many smaller and feebler groups. Thus wc can account
for the fact that a]l organisms, recent and extinct, are included

Chai-. XIII. ORGANIC BEINGS. 337

under a few p^rcat orders, and under still fewer classes. As
sho\vin<j:; how few the hi<>her frroups are in number, and how
widely they are spread throuf^hout the world, the fact is strik-
in;i-, that the discovery of Australia has not added an insect
l)(>l()n<2,"iiij^ to a new class ; and that in the vegetable kingdom,
as I learn fi-om 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
nuich in character during the long-C(jntinued process of modifi-
cation, how it is that the more ancient forms of life often pre-
sent characters in some degree intermediate between existing
groups. Some few of these old and intermediate forms hav-
ing transmitted to the present day descendants but little modi-
lied, constitute our so-called osculant or aberrant species. The
more aberrant any form is, the greater must be the number
of connecting forms Avhicli have been exterminated and utterly
lost. And we hav(! some evidence of aberrant groups having
suffered severely from extinction, for they are almost always
represented by extremely f(jw species ; and such species as do
occur are generally very distinct from each other, which again
implies extinction. The genera Ornithorhynchus and Lepi-
(losiren, for example, woulil not have been less aberrant had
each been represented by a dozen species instead of by a single
one, or by one; or two. We can, I think, account for this fact
only by looking at aberrant groups as forms which have been
con([uered by more successful competitors, with a few mem-
bers still preserved under unusually favorable conditions.

Mr. Waterhouse has remarked that, when a member be-
longing to one group of animals exhibits an alTinity to a cpiite
distinct group, this alVmity 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 ajiproaches this order, its relations are gen-
eral, and not to any one marsupial species more than to an-
other. As \]ui jjoints of allinity are believed to be real and
not merely adaptive, they nnist be due, in accordance with our
view, to inheritance from a conunon ])rogenitor. Therefore we
must su])j)ose either that all Rodents, including the bizcacha,
branched olV from some ancient Marsupial, which will naturallv
have been more or less intermediate in character with respect
to id! existing Marsupials; or that both Rodents and Marsu-
jjials branched olV iVom a cominou progenitor, and that both

388 AFFINITIES CONNECTING Chap. XIII.

g^roups have since undergone miicli modification in divergent
directions. On citlicr view we must suppose that the bizcacha
has retained, by inheritance, more of the character of its an-
cient progenitor than have other Kodents ; and therefore it
will not be specially rchited to any one existing Marsupial, but
indirectly to all or nearly all Marsupials, from having partially
retained the character of their conimon progenitor, or of some
earl}"^ member of the group. On the other hand, of all Mar-
suj>ials, as Mr. Waterhousc has remarked, the Phascolomys
resembles most nearly, not any one species, but the general
order of Rodents. In this case, however, it may be strongly
suspected that the resemblance is only analogical, owing 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 common
progenitor, together with their retention by inheritance 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 up by
extinction into distinct groups and sub-groups, will have trans-
mitted 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 up through many predecessors. As it is difficult to
show the blood-relationship between the numerous kindred of
any ancient and noble family even by the aid of a genealogical
irco, and almost impossible to do so without this aid, we can
understand the extraordinary difficulty which naturalists have
experienced in describing, without the aid of a diagram, the
various affinities which tliey perceive between the many hving
and extinct members of the same great natural class.

Extinction, as we have seen in the fourth chapter, has
played an imjiortant part in defining and M-idening the inter-
vals between the several groups in each class. AVe may thus
account for the distinctness of whole classes from each other —
for instance, of birds from all other vertebrate animals — by the
belief that many ancient forms of life have been utterly lost,
through which the earlv progenitors of l)irds were formerly

CiiAi-. Xlll. ORGANIC BEINGS. 339

connected with the early progenitors of the other and at that
time less diirercntiated vertebrate classes. Tlicre has been
less complete extinction of the forms of life which once con-
nected fishes with batrachians. There has been still less in
some other classes, as with the Crustacea, for here the most
wonderfully diverse forms are still linked together hy a long
and only partially-broken chain of allinities. Extinction has
only se})arated the groups : it has by no means made them ;
for, if every form which has ever lived on this earth were sud-
denly to reappear, tliough it would l)e cjuite impossi])le to give
(Iclinitions by which each group could be distinguished, still a
natural classification, or at least a natural arrangement, Avould
l)c j)ossible, AVe shall see this by turning to the diagram:
tlie letters, A to L, may represent eleven Silurian genera, some
of which have produced large groups of modified descendants,
Avjtli every link in each branch and sub-branch still alive ; and
the links not greater than those between the finest varieties.
In this case it would be quite im{)ossible to give definitions by
which the several members of the several groups could be dis-
tinguished from their more immediate parents and descendants.
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, front A, Avould have something
in common. In a tree we can distinguisli this or that branch,
though at the actual fork the two unite and blend together.
AV'e could not, as I have said, define the several groups ; but
we could pick out t\'pes, or forms, representing most of the
characters of each group, whether large or small, and thus give
a general idea of the value of the differences between them.
This is what Ave should be driven to, if we were over to suc-
c(^ed in collecting all the foi-ms in any one class which have
lived througliout all time and sjiace. Assuredly we shall never
succeed in making so perfect a colh^ction : nevertheless, in cer-
tain classes, we arc tending toward this end; and Milne Ed-
wards has lately insisted, in an able paper, on the high impor-
tance of looking to types, whetlier or not we can separate and
define the groups to which such types belong.

Finally, we have seen that natural selection, which results
from the struggle for existence, and which almost inevitably
leads to extinct ion and divergence of character in the descend-
ants from one dominant ]ia rent-species, explains that great and
universal feature in tlie atlinities of all organic beings, namely,
their suboiilination in group under group. We use the clc-

3'JO MORPHOLOGY. Chap. XIII.

ment of ilrst'cnt in chissint!^ the in(livi<luals of both sexes and
of all ag"C3 imjcr one species, altliougli they niay hare but few
cliaracters in common ; avc use descent in chissing acknowl-
ed<:;ed varieties, liowever different they may be from tlicir par-
ent; and I believe this element of descent is the hidden bond
of connection -wliich naturalists have sought under the term of
the Natural System. On this idea of the natural SA'stem being,
in so far as it has been perfected, genealogical in its arrange-
ment, with tlie grades of difference exjoressed by the terms
genera, families, orders, etc., we can understand the rules
Avhich we are compelled to follow in our classification. We can
imderstand why we value certain resemblances far more than
others ; why we use rudimentary and useless organs, or others
of trifling physiological importance ; why, in finding the rela-
tions between one grouji and another, we summarily reject
analogical or adaptive characters, and yet use the same char-
acters, within the limits of the same group. Wc can clearly
see how it is tliat all living and extinct forms can be grouped
together within a few great classes; and how the several mem-
bers of each class are connected together l)y the most complex
and radiating lines of affinities. We shall never, probably,
disentangle tlie 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 luiknown plan of creation,
we mav hojie to make sure but slow jirogress.

Prof. Iliickel, in his " Generelle Morphologic " and in sever-
al 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 se-
ries he trusts chiefly to embryological characters, but draws aid
from homologous and rudimentary organs, as well as from the
successive periods at which the various forms of life first ap-
peared in our geological formations. He has thus boldly made
a great beginning, and shows us how classification will in the
future l)e treated.

Morphology,

AVe have seen that the members of the same class, indepen-
dently of their habits of life, resemble each other in the general
j)lan of their organization. This resemblance is often expressed
by the term " unity of t>*])e ; " or by saying that the several
parts and organs in the different species of the class are homol-

CuAP. XIII. MORPHOLOGY. 39I

ogous. The wliole subject is included under the general term
of Morphology. This is the most interesting department of
natural history, and )nay be said to be its very soul. What
ean bo 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 porpoise, and the wing of the Ijat, should all be
constructed on the same pattern, and should include similar
bones, ia the same relative positions ? Geoflroy St.-Hilaire
has insisted strongly on the high importance of relative posi-
tion or connection in homologous parts ; they naay diifer to
almost any extent in form and size, and yet will remain con-
nected together in the same invariable order. We never find,
lor instance, the bones of the arm and forearm, or of the thigh
and leg, trans^wsed. Hence the same names can be given to
tJie homologous lx)ncs in widely-dillercnt animals. Wc see
the sanje great law in the construction of the mouths of in-
sects ; what can be more diflerent than the immensely long
spiral pn>])oscis of a sphinx-moth, the curious folded one of a
hcc or bug, and the great jaws of a beetle ? — yet all these or-
gans, serving for such Avidely-diflerent purjwses, are formed by
infinitely-numerous modifications of an upper lij"), mandibles,
and two pal is of maxilkc. The same law governs the con-
struction of the mouths and limbs of crustaceans. So it is
with the flowers of plants.

Nothing can be more hopeless than to attempt to explain
this similarity of pattern in members of the same class, by util-
ity or by the doctrine of final causes. The hoi^elessness of the
attempt has been expressly admitted by Owen in his most
interesting work on the " Nature of Limbs." On the ordinary
\iew f)f 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 p^eat class on a uniform
j)lan : but this is not a scientific explanation.

The exjilanatitjn is manifest according to the theory of the
si'lection of successive slight modifications — each modification
Ijeing profitable in some way to the modified form, but often
alVecting by correlation other parts of the organization. In
clianges of this nature, there Avill be little or no tendency to
alter tlie origiiud pattern, or to trans[)ose the parts. The
l)ones of a limb might be shortened and ilattencil to any ex-
tent, becoming at the same time enveloj)ed in tliick membrane,
so as to serve as a fin ; or a webbed liand might have all its
bones, or certain bones, lengthened to any extent, with the

392 MORPHOLOGY. Ciiai-. XIII,

ineinl)rane connectin*^ them increased, so as to serve as a wing;
yet all this modification would not tend to alter the framework
of the lx)nes or tlie relative connection of the parts. If wo
suppose that an early progenitor — the archetype as it may be
called — of all mammals, had its limbs constructed on the ex-
isting general pattern, for wliatever puq->ose they served, we
can at once perci'ive the plain signification of the homologous
construction of the limbs throughout the class. So ^vith the
mouths of insects, we have only to suppose that their common
}>rogeiiitor had an upper lip, mandibles, and two pair of max-
illiT?, these i>arts being jjerhaps very simple in form; and then
natural selection will account for the infinite diversity in the
structure and functions of the mouths of insects. Neverthe-
less, it is conceivable that the general pattern of an organ
might become so much obscured as to be finally lost, by the
redaction and ultimately by the complete abortion of certain
jKirts, by the fusion of other parts, and by the doubling or mul-
tii)li('ation of others — variations which we know to be within
the limits of possibility. In the paddles of the gig-antic ex-
tinct sea-lizards, and in the mouths of certain suctorial crusta-
ceans, the general pattern seems thus to have been partially
obscured.

There is another and equally curious branch of our present
subject ; namely, the comparison, not of the same parts or or-
gans in different members of the same class, Init of the differ-
ent parts or organs in the same individual. Most physiologists
believe that the bones of the skvill are homologous with — that
is, correspond in number and in relative connection with — the
elemental parts of a certain number of vertebnv. llie anterior
and pt)sterior limbs in all the higher vertebrate classes are
])lainly homologous. So it is with the wonderfully complex
jaws and legs of crustaceans. It is familiar to almost every
one, that in a flower the relative ]x>sition of the sepals, petals,
stamens, and pistils, as well as their intimate structure, are in-
telligible on the view that they consist of metamorphosed
l(\ives, 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 em-
bryonic stages of development in flowers, as well as in crusta-
ceans and many other animals, that organs, which when mature
become extremely different, are at first exactly alike.

How inexplicable are these facts on the ordinary view of
creation ! Why should the brain be enclosed in a box com-

CiiAr. XIII. MOKPIIOLOGY. 393

posed of such nimicrous and such cxtraordinarily-shajicd pieces
of bone ? As Owen has remarked, the benefit derived from
tlie yiokling of the separate pieces in the act of j^arturition of
nianiiiials, will by no means explain the same construction in
the sl-:ulls of birds and reptiles. Why should similar bones
have been created to form the wiufi;' and the leg- of a bat, used
as they are for such totally diflcrcnt purposes? Why should
one crustacean, which has an extremely complex mouth formed
of many parts, conseciuently always have fewer leg's ; or, con-
versely, those with many legs have sim])ler mouths? ^Vhy
should the sepals, petals, stamens, and pistils, in each flower,
tlunigh litted for such widely-different purposes, be all con-
structed on the same pattern ?

On the theory of natural selection, we can answer these
({uestions. In the vertebrata, Ave see a series of internal verte-
bra? bearing certain processes; in the arliculata, the body di-
vided into a series of segments, bearing' external appendag^es ;
and, in flowering' plants, spiral whorls of leaves. An indefinite
repetition of the same part or organ is the common character-
istic, as Owen has observed, of all low or little-modified forms;
therefore the unknown progenitor of the vertebrata no doubt
possessed man}' vertebrae ; the unknown progenitor of the ar-
liculata, many segments; and the unknown progenitor of
(lowering ])lants, many leaves arranged in one or more spires.
AV(5 have formerly seen that parts many times repeated are
eminently liable to vary in number and structure. Conse-
(juenlly, such ])arts being already present, and being highly
variable, would atford the materials for adaptation to the most
different purposes; and they would generally retain through
the force of inheritance plain traces of their original or funda-
mental resemblance.

In the great class of moUusks, though it can easily be
shown that the parts in distinct species are homologous, but
few serial homologies can be indicated ; that is, we are seldom
enabled to say that one part is homologous with another jiart
in the same individual. And we can imdersfand this fact ; for
ill mollusks, 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
]>:ingdoms.

Naturalists frequently speak of the skull as fonnc.d of meta-
morphosed verlebni' ; the jaws of crabs as metamorphosed legs;
the stamens and pistils in flowers as metamorphosed leaves ; but

394 DEVELOPMENT Chap. XIII.

itwouldinmosl cases probably be more corrcrf, as Prof. Huxley
has remarked, to speak of both skull and vertebnc, both jaws
and lef^s, etc., as having been metamoqihosed, not one from
the other, as they now exist, but from some common and
simpler clement. Most naturalists, however, use such lan-
guage only in a metaphorical sense ; they are far from mean-
ing that, ckiring a long course of descent, primordial organs
of any kind — vertebra? in the one case and legs in the other
— have actually been converted into skulls or jaws. Yet so
strong is the appearance of this having occurred, that nat-
uralists can hardly avoid employing language having this
plain signification. According to the views here maintained,
such language may be used literally ; and the wonderful fact
of the jaws, for instance, of a crab retaining numerous charac-
ters, Avhich they probably would have retained through inheri-
tance, if they had really been metamorjihosed from ti-uc though
extremely simple legs, is explained.

Develojinient and Emhryology.

This is one of the most important subjects in the whole
round of natural liistor}^ The metamorphoses of insects, Avitli
which every one is familiar, are generally eflectcd abruptly by
a few stages ; but the transformations are in reality numerous
and gradual, though concealed. A certain ephemerous insect
(Chloeon) during its development, moults, as shown by Sir J.
Lubljock, about twenty times, and each time undergoes a cer-
tain amount of change ; and in this case avc see the act of
metamorphosis performed in a primary and gradual manner.
Many insects, and especially certain crustaceans, show us what
woiulerful changes of structure can be etTected during develop-
ment. Such changes, however, reach tlieir climax in the so-
called alternate generations of some of the lower aTiimals. It
is, for instance, an astonishing fact that a delicate branching
coralline, studded with polypi and attached to a submarine
I'ock, should jiroduce, first by budding and then by transverse
division, a host of huge floating jelly-lishes ; and that these
should ])roduce eggs, from which are hatched swimming ani-
malcules, 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

CiiAr. XIII. AND EMBRYOLOGY. 395

of a lly, namely, the Cecidomyia, producing ascxually other
and similar larvie.

It has already been stated that various parts and organs in the
same individual are exactly like each other during an early em-
bryonic period, but in the adult state become widely different
and serve for widely-different puqioses. So again it has been
slated that the embryos of the most distinct species within the
same class are generally closely similar, but become when fully
developed widely dissimilar. A better proof of this latter fact
cannot be given than that by Von 15aer, namely, that " the em-
bryos of mammalia, of birds, lizards, and snakes, probably also
of eheloniii, are in their earliest states exceedingly like one
another, both as a whole and in the mode of development of
their parts ; so niuch so, in fact, that we can often distinguish
the emlnyos only by their size. In my possession are two
little embryos in sj)irit, whose names I have omitted to attach,
and at ]iresent I am quite unable to say to what class they be-
long. They may be lizards or small birds, or very young-
mammalia, so complete is the similarity in the mode of forma-
tion of the head and trunk in these animals. The extremities,
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 arise from the same fundamental form." The vermi-
form larva? of moths, flies, beetles, etc., generally resemble each
other much more closely than do the mature insects ; but in
these cases the embryos arc active, and from having been
adapted for special lines of life sometimes differ much from
each other. A trace of the law of embryonic resemblance oc-
casionally lasts till a rather late age : thus birds of the same
genus, and of closely-allied genera, often resemble each other
in their inunature plumage ; as Ave see in the spgtted feathers
in the young of the thrush group. In the cat tribe, most of
the species arc striped or spotted in lines; and stripes or spots
can be plainly distinguished in the whelp of the lion and the
puma. We occasionally though rarely sec something of this
kind in ])lants; thus the first leaves of the ulex or furze, and
tlu! lirst leaves of the j)hyllodincous acacias, are pinnate or di-
vided lik<^ the ordinary leaves of the leguminosa\

The points of structure, in which the embryos of widely-
different animals within the same class rcsend^le each other,
often have no tlirect relation to their conditions of existence.

396 DEVELOPMENT Chap. XIII.

We cannot, for instance, suppose tliat in the embryos of the
vcrtebrata the pccuhar loop-like courses of the arteries.near the
branchial slits are related to similar conditions — in the young
mammal wliich is nourished in the womb of its mother, in the
c<rg 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, wing of a bat, and fm of a por-
j)oise, are related to similar conditions of life. No one sup-
poses tliat the stripes on the whelp of a lion, or the spots on
the young blackbird, are of use to these animals.

Tlie case, however, is different when an animal during any
part of its embryonic career is active, and has to provide for
itself. The period of activity may come on earlier or later in
life ; but whenever it comes on, the adaptation of the larva to
its conditions of life is just as perfect and as beautiful as in the
adult animal. In how important a manner this has acted, has
recently been well shown by Sir J. Lubbock in his remarks
on the close similarity of the larvne of some insects belonging
to very different orders, and on the dissimilarit}^ of the larva;
of other insects within the same order, according to their
habits of life. From such adnptations, especially when they
im]>ly a division of labor during the different stages of develop-
ment, as Avheu the same larva has during one stage to search
for fooil, and has during another stage to search for a place of
attachment, the similarity of the lan'te of allied animals is
sometimes greatly obscured ; and cases could be given of the
larv;V3 of two species, or of two groups of species, differing
more from each other than do the adults. In most cases, how-
ever, the larv:c, though active, still obey, more or less closel}',
the law of common embrj^onic resemblance. Cirripedes afford
a good instance of this : even the illustrious Cuvier did not
perceive thai a barnacle was a crustacean ; but a glance at
the larva shows this to be true in an unmistakable manner.
So, again, the two main divisions of cirripedes, the peduncu-
lated and sessile, though differing M-idely in external appear-
ance, have larvoi in all their stages barely distinguishable.

The cml>ryo in the course of development gencrall}- rises
in organization : I use this expressiDU, though I am aware that
it is hardly possible to deiinc clearly what is meant by the
organization being higher or lower. But no one probably will
dispute that the butterfly is higher than the caterpillar. In
some cases, however, the mature animal nmst be considered as

Chap. XIII. AND EilBEYOLOGY. 397

lower in the scale than the larva, as witli certain parasitic
crustaceans. To refer once a<?ain to cirripcdes : the larvas in
the lirst stage have three pairs of legs, a very simple single
eye, and a proboscifonned mouth, with which they feed largely,
for they increase much in size. In the second stage, answer-
ing to the chrysalis stage of butterflies, they have six pairs of
beautifully-constructed natatory legs, a pair of magnificent
comi)Ound eyes, and extremely complex antenmxj ; but they
have a close and imperfect mouth, and cannot feed : their func-
tion at this stage is, to search by their well-developed organs
of sense, and to reach, by their active powers of swimming, a
projier j)lacc on which to become attached and to undergo their
final metamorphosis. When this is completed, they are fixed
for life : tlicir l(\gs arc now converted into prehensile organs ;
they again obtain a well-constructed mouth ; but they have no
antenna', and their two eyes are now reconverted into a mi-
nute, single, and very simple e^e-spot. In this last and com-
plete state, cirripedes may be considered as either more highly
or more lowly organized than they were in the larval condi-
tion. But in some genera the larva? become developed either
into hermaphrochtes having the ordinary structure, or into
what I have called comj)lemcntal males, and, in the latter, the
development has assuredly been retiograde ; for the male is a
mere sack, which lives for a short time, and is destitute of
mouth, stomach, or other organs of importance, excepting
those for reproduction.

AVe are so much accustomed to see a difference in structure
between the embryo and the adult, that we are tempted to
look at this diflerence as in some manner necessarily contin-
gent on growth. But there is no reason why, for instance, the
wings of a bat, or the fins c^f a porpoise, should not have been
sketched t)ut with all their parts in projier proportion, as soon
as an}' structure became visible. In some whole groups of
animals and in certain inemliers of other groups tin's is the
case, and the cmljryo does not at any period difler widely from
the adult : thus Owen has remarked in regard to cuttle-fish,
" there is no metamorphosis ; the ceplialopodic character is
manifested long before the parts of the embryo are com-
pleted." Land-shells and fresh-Avater crustaceans are born
having their proper form, while the mafine members of the
same two great classes pass through considerable and often
great changes during their develoj^ment. Spiders, again,
barely undergo any metamoqihosis. The larvae of most insects

398 DEVELOPMENT Chap. XIII.

pass throuu'li a worm-like sta_o;o, Avhcthcr they arc active and
adapted to diversified habits, or are inactive from lieing placed
in the midst of proper nutriment or from bcinpf fed by their
parents ; but in some few cases, as in that of Aphis, if we look
to the admiraljle drawings of the development of this insect, by
Prof. Huxley, wc sec hardly any trace of the vermiform stage.

Sometimes it is only the earlier developmental stages
which fail. Thus Fritz Miiller has made the remarkable dis-
covery tliat certain shrimp-like crustaceans (allied to Penoeus)
first appear imder 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 Avhole
great malacostracan class, to which these crustaceans belong,
no other member is as yet known to be first developed under
the nau})lius-form, though many appear as zoeas; nevertheless,
Miiller assigns reasons for his belief that all these crustaceans
would luiA-c appeared as nauplii, if tliere had been no suppres-
sion of development.

How, then, can we explain these several facts in embryology
— namely, the very general, though not universal, diflerence
in structure between the embryo and the adult — the various
parts in the same individual embryo, which ultimately become
very unlike and serve for diverse purposes, being at an early
period of growth alike — the general, but not invariable, resem-
blance between the embryos or larvre of the most distinct
species in the same class — the embryo retaining, Avhile within
the egg or womb, structures which are of no service to it,
either at that period or later in life ; Avhile embryos at a later
]icriod, or larvie, which have to provide for their own wants,
are perfectly adapted to the surrounding conditions — and lastly
the fact of certain larvas standing higher in the scale of organi-
zation than the mature animals into which they are developed ?
I believe tliat all these facts can be explained, as follows :

It is commonly assumed, perhaps from monstrosities affect-
ing the embryo at a very early period, that slight variations or
individual dilferences necessarily appear at an equally early
l)eriotl. ^Vc have little evidence on this head, but what we
liave certainly points the other way ; for it is notorious that
l)recders of cattle, horses, and various fancy animals, cannot
positively tell, until "some time after birth, what the merits or
form of their young animals will turn out. We see this plainly
in our own children ; wc cannot tell whether a child Avill be
tall or short, or what its jirecise features will be. The ques-

CuAP. XIII. AND EMBRYOLOGY. 399

tion is not, at what period of life each vaiiation may have been
caused, but at wliat period the effects arc disphiyed. The
cause may have acted, and I beheve generally has acted, on
one or both parents before reproduction. It deserves notice
that it is of no importance to a very yoimi^ 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, wlicther most of its
characters are acquired a little earlier or later in life. It
"would not signify, for instance, to a bird Avhich obtained its
food by having a much-curved beak, Avhether or not "while
young it possessed a beak of this shape, as long as it was fed
by its parents.

I have stated, in tlu^ first chapter, that at whatever age a
variation first appears in the parent, it tends to reappear at a
corresponding age ni tlie offsjiring. Certain variations can
only appear at corresponding ages: for instance, peculiarities
in the caterpillar, cocoon, or imago states of the silk-moth ; or,
again, in the full-grown horns of cattle. But variations,
which, for all that we can see might have appeared either ear-
lier or later in life, likewise tend to appear 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 excep-
tional cases of variations (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 gener-
ally appear at a not very early period of life, and are inher-
ited at a corresponding not early period, explain, as I believe,
all the aljove specilieil leading facts in embryology. But first
let us look to a few analogous cases in our domestic varieties.
Some authors who have written on Dogs, maintain that the
greyhound and bull-dog, though a})pearing so different, are
really closely-allied varieties, descended from the same wild
stock; hence I was curious to see how far their puppies dif-
fered from each other: I was told by breeders that they dif-
fered just as much as their parents, and this, judging by the
eye, seemed almost to l)e the case ; but on actually measuring
the old dogs and their six-days-old jnijipies, I found that the
]>iipI)i('S had not acquired nearly their full amount of propor-
tional difference. So, again, I was t(jld that the foals of cart
and race lujrses — breeds which have been almost wholly formed
by selection imder domestication — differed as mmh as the full-
grown animals ; but having had careful measurements made

400 DEVELOPMENT Chap. XIII.

of llic dciiiis and of threc-days-old colts of racc-horscs and
heavy cart-horses, I find tliat tliis is by no means tlic case.

As we have conckisivc ev-idcnce that the breeds of the Pig-
con are descended from a single -wild species, I compared the
young within twelve hours after being hatched ; I carefully
measured in the wild jnu-ent-species, in pouters, fantails, runts,
barl)s, dragons, carriers, and tumblers, the i)roportlons (but
will not here give the details) of the beak, width of mouth,
length of nostril and of eyelid, size of feet and length of leg.
Now some of these birds, Avhen mature, differ in so extraor-
dinary a degree in the length and form of beak, and in other
characters, that they would certainly be 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, yet the projiortional
differences in the above-specified points were incomparably
less than in the full-grown birds. Some characteristic points
of difference — for instance, that of the width of mouth — could
hardly be detected in the young. But there was one remark-
able excejition to this rule, for the young of the short-faced
tumbler difiered in all its proportions from the young of the
wald rock-pigeon and of the other breeds, almost exactly as
much as in the adult state.

The above two principles explain these facts. Fanciers
select for breeding their dogs, horses, pigeons, etc., when
nearly grown \ip : they are indifferent whether the desired
qualities arc acquired earlier or later in life, if the full-grown
animal possesses them. And the cases just given, more espe-
cially that of pigeons, show that the characteristic differences
which give value to the breeds, and which have been accumu-
lated by man's selection, have not generally appeared at a very
early period of life, and have been inherited at a corresponding
not early period. But the case of the short-faced tumbler,
which when twelve hours old possessed its ]iroper characters,
proves that this is not the imiversal rule ; for here the charac-
teristic dillerences must either have appeared at an earlier
period than usual, or, if not so, the differences must have been
inlieritcd, not at a corresponding, but at an earlier age.

Now let us ajiply these two principles to species in a state
of nature. Let us take a group of birds, desccmded from some
ancient form and modified through natinwl selection for differ-
ent habits. Then, from the many slight successive variations
having supervened in the several species at a not early age,

Cii.vr. XIII. AND EMBRYOLOGY. 401

and having been inherited at a corresponding age, the young
will be left l)iit little modifuMl and will resemble each other
much more closely than do the adults — just as we have seen
with the breetls of the pigeon. We may extend this view to
widely-distinct structures and to whole classes. The fore-
liiiihs, for instance, which once served as legs to a remote ])ro-
genitor, may have become, through a long course of modiJica-
tioii, 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 the embryonic forc-
liinb will differ greatly from that in the adult. Whatever in-
fluence, moreover, long-continued use or disuse may have had
in modifying the limbs or other parts of animals, this will
chiefly or solely have affected them when mature, and when
they hatl to use their full powers to gain their own living;
and the elTect thus jiroduced will be transmitted to the oil-
spring at a ccjrrcsponding mtitvn'e age. Thus the young will
not be modified or will be modiiied in a less degree.

In other cases successive variations may have supervened
at a very early period of life, or the steps may have been in-
herited at an earlier age than that at which they first occurred.
In either case, as we have seen Avith the short-faced tumbh^r,
the young or embryo would closely resemble tlie mature par-
ent-form. And this is the rule of development in certain whole
groups or sub-grouj^s, as Avith cuttle-fish, land-shells, fresh-wa-
ter crustaceans, spiders, and some members of the great class
of insects. AVith respect to the fmal cause of the 3'^oung in
these groups not passing through any metamorphosis, we can
see that this would follow from the following contingencies ;
namely, from the young having to provide at a very early age
for Iheir own Avants, and from their following the same habits
of life with their parents ; for, in this case, it would be indis-
]iensable for their existence that they should be modiiied in
the same manner as their parents. Again, with respect to the
singular fact of so many terrestrial and fresh-water animals not
undergoing any metamorphosis, while marine members of the
same groups pass through various 1 ransformal ions, Fritz MuUer
has suggested that the process of slowlv modifying and adapt-
mg an animal to live on the land or in fresh water, insttnvd
of in the sea, would be greatly simjjliHed 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

402 DEVELOPMENT CiiAr. XIII. '

and greatly-changed habits of life, could be found unoccupied
or ili-occupit'd by other organisms. In this case the gradual
acquirement at an earlier and earlier age of the adult structure
would be favored by natural selection, and all traces of formei
metamorphoses would finally be lost.

If, on the oilier liand, it })rofitetl the young of an animal to
follow hal)its of life slightly dillerent from those of the parent-
form, and consequently to be constructed in a slightl^'-dif-
ferent manner, or if it profited alarva already widely different
from its parent to change still further, then, on the principle
of inheritance at corresponding ages, the young or the larvas
might be rendered by natural selection more and more differ-
ent from their parents to any conceivable extent. Differences
in the larvie might, also, become correlated with successive
stages of development ; so that the larvee, in the first stage,
might come to differ gTcatly from the larva? in the second
stage, as is the case Avith many animals. The adult might
also become fitted for sites or habits, in which organs of loco-
motion 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 Avith changed habits
of lif(% together with inheritance at corresponding ages, animals
in certain cases might come to pass through stages of develop-
ment, perfectly distinct from their primordial, adult condition.
Fritz Muller, Avho has recently discussed this subject with much
ability, believes that the progenitor of all insects resembled an
adult insect, and that the caterpillar or maggot stages, as
Avell as the cocoon or pupal stages, have subsequently been ac-
(|uired; but from this view many naturalists, for instance, Sir
J. Lubbock, who has likewise recently discussed this subject,
would, it is probable, dissent. That certain unusual stages in
the metamorphoses of insects have been acquired through adap-
tation to peculiar habits of life, there can hardly be a doubt ;
thus the hrst larval form of a certain beetle, the Sitaris, as de-
scribed by M. Fabre, is an active, minute insect, furnished with
six legs, two long antenna^, and four eyes. These larvro are
hatched in the nests of bees ; and Avhen the male-bees emerge
fiom their burrows in the spring, which they do before the
females, the larvte spring on them, and afterward crawl on the
female while paired with the males. As soon as the females
lay their eggs on tlie surface of the honey stored in their cells,
the larvas of the Sitaris leap on the eggs and devour them.

CiiAr. XIH. AND EMBIIYOLOGY. -40:}

Afterward these lan'flQ undergo a complete change ; their eyes
disapjiear ; tlicir legs and autenna3 become rudimentary-, and
tl ley feed on honey ; so that they now more closely reseniljlc
the ordinary larva? of insects ; ultimately they undergo a fur-
ther transformation, and hnally 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, their course of development would probably be
M-idely dillerent from what it now is ; and the hrst larval stage
certainly would not represent the former condition of any
adult and ancient insect.

On the other hand, it is highly probable that with many
animals the embryonic or larval stages show us, more or less
coni])letely, the state of the progenitor of the whole group in
its adult condition. In the great class of the Crustacea, forms
wondeifully distinct from each other, namely, suctorial para-
sites, cirripedes, entomostraca, and even the malacostraca, ap-
pear at iirst as larva; imder the nauplius-form ; and as these
larva; feed and live in the open sea, and are not adapted for
any peruliar habits of life, and from other reasons assigned by
Fritz Midler, it is probable that an independent adult animal,
i-estMubling the nauplius, existed at some very remote period,
and subsef(ncntly produced, along several diverg(;nt lines of
descent, the several above-named great Crustacean groups.
So again it is pr(»l:)able, fi-om what we know of the emljryos of
mannnals, birds, fishes, and reptiles, that these animals are the
niodilied descendants of some one ancient progenitor, which
Avas furnished in its adult state with branchia', a swim-1)ladder,
four simple 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, formerly
licen connected together by fine gradations, the best, and, if
our collections were nearly perfect, the only possible arrange-
ment, would be genealogical; descent being the hidden bond
(if connection which naturalists have been seeking vmder the
term of the Natural System. On tliis view we can under-
stand how it is that, in the eyes of most naturalists, the
structure of the eml)ryo is even more important for classifica-
lion than that of the adult. In two or more groups of ani-
mals, however much they may dilTer from each other in struct-
ure and habits, if they pass tlirough closely similar embryonic
stagt'S, we may feel assured that they all arc descended from one

iO\ RUDIMENTARY, ATEOPIIIED, Chap. XHI.

parent-form, and are therefore closely related. Thus, coumumi-
iy in emlHyonic structure reveals community of descent ; but
dissimilarity in embryonic development does not prove discom-
munity of ilescent, 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 bo
no longer recognizaljle. Even in groups, in which the adults
have been moditied to an extreme degree, community of
origin is often revealed by the structure of the larva? ; we have
seen, for instance, that cirripedes, though externally so like
shell-fish, are at once known by their larvae to belong to the
gTeat class of crustaceans. As the structure of the cmbrj-o
generally shows us more or less plainly the structure of its less
modified and ancient progenitor, Ave can see why ancient and
extinct forms so often resemble the embryos of existing spe-
cies in the same class. Agassiz believes this to be a univer-
sal law of Nature ; and I hope to see it hereafter shown in
most cases true. It can, however, be proved true only in
those cases in which the ancient state has not been wholly ob-
literated either by successive variations being supervened at a
very early period of growth, or by such variations having been
inherited at an earlier period than that at which they first ap-
peared. It should also be borne in mind, that the law may be
true, but yet, o\ving to the geological record not extending far
enough back in time, may remain for a long period, or for ever,
incapable of demonstration. The laAV will not hold good in those
cases in which an ancient form became adapted in its larval
state to some special line of life, and transmitted the same larval
state to a whole group of descendants ; for these in their lar^'al
condition will not resemble any ancient form in its adult state.
Thus, as it seems to me, the leading facts in embryology,
M'hich are second to none in importance, are explained on the
principle of modifications in the many descendants from some
one ancient progenitor, not having appeared at an early period
of life, and having been inherited at a corresponding period.
Embryology rises greatly in interest, when we look at the em-
bryo 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.

liudimentart/, Atrophied, and Aborted Organs.

Organs or jiarts in this strange condition, bearing the plain
stamp of inutihtv, arc extremely common, or even general

Chap. XIII. AND ABOIITED ORGANS. 405

lliroiighout Nature. It 'would be difficult to name one of the
his/her animals in which some part is not in a rudimentary
condition. In the mammalia, for instance, the males always
possess rudimentary mamma?; in snakes one lobe of the lunj^s
is rndimentary ; in birds the "bastard-wing" may safely be
considered as a rudimentary digit, and in not a few species the
wings cannot be used for ilight or are reduced to a rudiment.
AVhat can be more curious than the presence of teeth in
fetal 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 unliorn calves ?

Hudimentary organs declare their origin and plain meaning
in various wa3's. There are beetles belonging to closely-allied
species, or even to the same identical species, which have
either full-sized and perfect wings, or mere minute rudiments
of membrane, not rarely lying under wing-covers firmly
soldered together ; and in this case it is impossible to doubt
that the rudiments represent wings. Rudimentary organs
sometimes retain tlieir potentiality ; this occasionally occurs
with the mamma? of n)ale mammals, for they 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 become well developed and yield milk. In
regard to plants the petals are sometimes rudimental, and
sometimes well-develojied in individuals of the same species.
In certain dicccious ])lants Kolreuter found that by crossing a
species, in which the male flowers included a rudiment of a
jiistil, with an hermaphrodite species, having of course a Avell-
devel()j)ed ])istil, the rudiment in the hybrid ofl'spriiig Avas
nuich increased in size ; and this clearly shows that the rudi-
mentary and perfect pistils are essentially alike in nature. An
animal may ])ossess various parts in a perfect state, and yet
they may in one sense be rudimentary, for they are useless:
thus tlie tadpole of the connnon Salamander or newt, as Mr.
G. II. Lewes remarks, "lias 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
.•'.nimal never lives in the water. Yet if we open a gravid le-
male, we find tadpoles inside her with exquisitt^ly-feathered
gills ; and when jilaced in water they swim about like the t^id-
])oles of the water-newt. Obviously, this aquatic organization
has no reference to the future life of the animal, nor has it any

40G KUDIMENTAHV, ATROPHIED, Chat. XIII.

adaptation to its cniljrvonic condition ; it has solely reference
to ancestral adaptations, it repeats a phase in the development
of its profi^enitors."

An ornj-an, serving; for two purposes, may become rudimen-
tary or utterly aborted for one, even the more important pur-
pose, and remain perfectly eflicient for the other. Thus in
plants, the oflice 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 Composita?, the
male florets, which of course cannot bo fecundated, have a ru-
dimentary pistil, for it is not crowned with a stigma ; but the
stylo remains Avell developed, and is clothed with hairs, in the
usual manner, for brushing the pollen out of the suiTOunding
and conjoined anthers. Again, an organ may become rudi-
mentary for its proper purpose, and be used for a distinct ob-
ject : in certain fish the swim-bladder seems to be nearly rudi-
mentary for its proper function of giving buoj-ancy, but has
become converted into a nascent breathing-organ, or lung.
Other similar instances could be given.

Organs, however little developed, if of use, should not
be considered as rudiincntarv : they may be called nascent,
and may hereafter be developed by natural selection to any
further extent. Kudimentary oigans, on the other hand, are
essentially useless, as teeth which never cut through the gums.
As they would be of even less use, Avhen in a still less devel-
oped condition, they cannot have been formed through varia-
tion and natm-al selection, which latter acts solely by the pres-
ervation of useful modilications. They relate to a former
state of things, and have been partially retained by the power
of inheritance. It is difficult to know what organs are nas-
cent ; looking to the future, we cannot of course tell how
any part will be developed, and whether it is now in a nascent
condition ; looking to the past, creatures with an organ in this
condition will generally have been supplanted by their suc-
cessors with the same organ in a more perfect state, and con-
sequently will have become long ago extinct. The wing of
the penguin is of high service, acting as a fin ; it may, there-
fore, represent the nascent state of the Aving ; not that I be-
li(>ve this to be the case ; it is more probably a reduced organ,
modilied for a new function: the wing of the Apteryx, on the
otiier hand, is c[uite useless, and is ti-uly rudimentary. Tlic
simple lilamentary limbs of the Lepidosiren ajiparently are in
a nascent state; for, as Owen lias remarked, th(>v are the

Chap. XIII. AND ABORTED ORGANS. 407

" Ijpo^liuiinjif.s of oro^ans which attain full functional develop-
ni(Mit in hiij^hcr verteliratcs." The mammary j^lands of the
Oniithorhyncluis may be considered, in comparison Avith the
udders of a cow, as in a nascent condition. The oviji^erous
frena of certain cirripodes, which are only slightly developed,
and which have ceased to give attachment to the ova, are nas-
cent branchiir.

Rudimentary organs are very liable to vary in development
and in other respects in the individuals of the same species.
Moreover, in closely-allied species, the degree to which the
same organ has been reduced occasionally differs much. Tiiis
latter fact is well exemplilied in the state of the wings in fe-
male moths in certain group.s. Rudimentary organs may be
utterly aborted ; and this implies that, in certain animals or
plants, parts are entindy absent which analogy would lead us
to expect to find, and which are occasionally found in mon-
strous individuals. Thus in most of the ijcrophulariaceoe the
tifth stamen is utterly aborted ; yet we may conclude that a
fifth stamen once existed, for a rudiment of it is found in many
species of the family, and this rudiment occasionally becomes
])('rfectly developed, as may be seen in the common snap-
dragon. In tracing tlie homologies of any part in diflerent
members of the same class, nothing is more common, or more
necessary, in order fully to understand the relations of the
])arts, than the discovery of rudiments. This is well shown in
llic drawings given hy Owen of the bones of the leg of the
horse, ox, and rhinocero.s.

It is an important fact that rudimentary organs, such as
teeth in the upper jaws of whales and ruminants, can often
1)e detected in the embryo, but afterward wholly disappear. It
is also, I believe, a universal rule, tliat a rudimentary part is
of greater size relatively to the adjoining parts in the embryo,
than in the adult ; so that the organ at this early age is less
rudimentary, or even cannot l)e said to be in any degree rudi-
mentary. Hence rudimentary organs in the adult are often
said to have retained their embryt)nic condition.

I have now given the leading facts witli 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 e.\(iuisitely adai)ted for
C{>rtain purposes, tells us with e([ual plainness that these rudi-
mentary or atrophied organs are imperfect and useless. In
works o;i n:iiu!Ml liislnrv, rudimentary organs arc generally

408 RUDIMENTAIJY, ATKOPUIED, Cii.vr. XIII.

said to have been created " for the sake of synnnetry,'" or in
order " to complete the scheme of Nature." But this is not an
explanation, merely a restatement of the fact. Nor is it con-
sistent Avith itself : thus the boa-constrictor has rudiments of
hind-limbs and of a pelvis, and if it be said that these bones
have been n^taincd " to complete the scheme of Nature," why,
as Prof. Wcismann 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
niuintained that the satellites revolve in elliptic courses round
their planets "for the sake of symmetry," because the planets
thus revolve round the sun ? An eminent physiologist ac-
counts for the j)rescneo of rudimentary organs, by supposing
that they serve to excrete matter in excess, or matter injurious
to the system ; but can we sujipose that the minute papilla,
Avhich often represents the pistil in male flowers, and wliich is
formed of mere cellular tissue, can thus act ? Can we suppose
that rudimentary teeth, which ai'e subsequently absorbed, are
beneficial to the rapidly-growing embryonic calf by removing
matter so precious as phosphate of lime ? When a man's fin-
gers have been amputated, imperfect nails have been known to
appear on the stumps, and I could as soon believe that these
vestiges of nails have been developed in order to excrete homy
matter, as that the rudimentary nails on the fin of the mana-
tee have been developed for this same purpose.

On the view of descent Avith modification, the origin of
rudimentary organs is simple. We have plenty of cases of
rudimentary organs in our domestic productions — as the stump
of a tail in tailless breeds — the vestige of an ear in earless
breeds of sheep — the reappearance of minute dangling horns
in hornless breeds of cattle, more especially, according to
Youatt, in young animals — and the state of the whole flower
in the cauliflower. We often see rudiments of various parts
in monsters. But I doubt whether any of these cases throw
light on tlie origin of rudimentary organs in a state of nature,
further than by showing that rudiments can be produced ; for
I doubt whether species under Nature ever undergo- abrupt
changes. I believe that disuse has been the main agency ;
that it has led in successive generations to the gradual redut»-
tion of various organs, imtil tliey have become rudimentary —
as in the case of tlie eyes of animals inhabiting dark caverns,
and of the wings of birds iidiabiting oceanic islands, which
h:ive seldom be(Mi forced ])y l)e;ists of prey to take flight, and

Chap. XIII. AND ABORTED ORGANS. 409

have ultimately lost tlie power of flying. Again, an organ
useful under certain conditions, might become injurious under
others, as with tlic wings of beetles living on small and ex-
posed islands; and in tliis case natural selection would con-
tinue slowly to reduce the organ, until it was rendered harm-
less and ruihmentary.

Any change in structure, and function, which can be ef-
fected by insensibly small steps, is within the power of natural
selection ; so that an organ rendered, through changed haliits
of life, useless or injurious for one purpose, might he modified
and used for another purpose. An organ might, also, be
retained for one alone of its f(jrmer functions. An organ, ori-
ginally formed by the aid of natural selection, when rendered
useless, may well be vai-iable, for its variations can no longer be
checked by natural selection. At whatever period of life either
disuse or selection reduces an organ, and this will generally 1)C
when the being has come to maturity and has to exert its full
powers of action, the principle of inheritance at corresponding
ages will reproduce the organ in its reduced state at the same
mature age, but will seldom affect it in the cmbrj-o. Thus we
can understand the greater size of rudimentary organs in the
embryo relatively to its other parts, and their lesser relative
size in the adult. But if each step of the process of reduction
wore to be inlierited, not at a corresponding age, but at a Aery
early perioil of life, the rudimentary part would tend to be
whoUv lost, and we should have a case of complete abortion.
Tlie principle, also, of the economy of organization, explained
in a former chapter, by which the materials forming any part,
if not useful to tlie possessor, will be saved as for as is pos-
sible, may often have come into play, and aided in the entire
obliteration of a rudimentary organ.

As the presence of rudimentary organs is thus due to the
tendency in every part of the organization, which has long
existed, to be inherited — we can understand, on the genealo-
gical view of classification, how it is that systematists have
found rudimentary parts as useful as, or even sometimes more
useful than, parts of high ])hysiological importance. Kudimen-
tary organs may be comjiared with the letters in a word, still
retained in the spelling, but become useless in the pronuncia-
tion, but which serve as a clew for its derivation. On the view
of descent with modilication, we may conclude that the exist-
I'uce of organs in a rudimentary, imperfect, and useless condi-
tion, or quite al)orled, far from presenting a strange diilicultv,
18

410 SUMMARY. Cuap. XIII.

as they assuredly do on the ordinary doctrine of creation^
might even have been anticipated in accordance with the ^'iews
here explained.

Summary.

In this chapter I have attempted to show that the arrange-
ment of all organic beings throughout all time in group under
group — that the nature of the relationship, by which all living
and extinct organisms are united by complex, radiating, and
circuitous lines of affinities in 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 the most trifling importance, or,
as with rudimentary organs, of no importance — the wide oppo-
sition in value between analogical or adaptive characters, and
characters of true aflinity, and other such rules — all naturally
follow if we admit the common parentage of allied forms, to-
gether with their modification through natural selection, with
its contingencies of extinction and divergence of character.
In considering tliis view of classification, it should be borne in
mind that the element of descent has been universally used in
ranlcing together the sexes, ages, dimoi-jihic forms, and acknowl-
edged varieties of the same species, however different they
may be in structure. If we extend the use of this element of
descent — the one certainly known cause of similarity in or-
ganic beings — we shall understand what is meant by the Nat-
ural System : it is genealogical in its attempted arrangement,
with the grades of acquired difference marked by the terms,
varieties, species, genera, families, orders, arid classes.

On this same view of descent with modification, all 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 pur-
pose applied ; or to the homologous parts in each individual
animal and plant.

On this principle of successive slight variations, not neces-
sarily or generally supervening at a very early period of life,
and being inherited at a corresponding period, we can under-
stand the great leading facts in Embryology ; namely, the
close resemblance in the individual embryo of the parts which
are homologous, and which when matured become widely dif-
ferent in structure and function ; and the resemblance in allied
though very distinct species of their homologous parts or

CuAP. XIII. SUMMARY. 411

organs, though fitted in the adult state for purposes as differ-
ent as is possible. Liirv:i3 are active embryos, ^vhich have
been specially modified in a greater or less degree in relation
to their habits of life, with their modifications inherited at a
corresponding age. On these same principles — and bearing in
mind that, when organs are reduced in size, either from disuse
or through natural selection, it will generally be at that period
of life when the being has to provide for its own wants, and
bearing in mind how strong is the force of inheritance — the
occurrence of rudiment;iry organs might even have been anti-
cipated. The importance of embryological characters and of
rudimentary organs in classification is intelligible, on the view
that a natural arrangement must be genealogical.

Final]}-, 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 connnon parents, and have all been modified in
the course of descent, that I should without hesitation adopt
this view, even if it were unsupported by any other facts or
arguments.

412 RECAPITULATION. Cillt. XIV.

CHAPTER XIV.

RECAPITULATIOX AND CONCLUSION.

Recapitulation of the Ohjoctiors to the Tlieoiy of Natural Selection— Reeapitulafion
of the General and Special Circumstances in its favor— Causes of the General Be-
lief in the Immutability of Species— How far the Theory of Natural Selection may
l>o extended— ElTccts of its Adoption on the Study of Natural History— Concluci-
ing Kemarks.

As this whole volume is one long argument, it may be con-
venient to the reader to have the leading facts and inferences
briefly recapitulated.

That many and serious objections ma}- be advanced against
the theory of descent with modification through natural selec-
tion, I do not den}'. I have endeavored to give to them their
full force. Nothing at first can appear more difficult to be-
lieve than that the more complex organs and instincts have
])ocn perfected, not by means superior to, though analogous
witli, human reason, but by the accumulation of innumerable
slight variations, each good for the individual possessor. Nev-
ertheless, this difficulty, though appearing to our imagination
insuperably great, cannot be considered real if we admit the
following propositions, namely, that all ]>arts of the organiza-
tion and instincts offer, at least, individual differences — that
there is a struggle for existence leading to the preservation 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 Idnd. The truth of these propositions
cannot, 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 Ave ought to be extremely
cautious in saying that any organ or instinct, or the whole
structure, could not have arrived at its present state by many

CMiAP. XIV. RECAPITULATION. 413

graclutited .steps. There are, it must be admitted, cases of
special diiriculty oppo.se(l to tlie theory of natural selection ;
and one of the most curious of tlicse is the existence of two or
three defined castes of workers or sterile female ants in the
same community ; but I have attempted to show how these
dilKculties 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 tlie facts given at the
end of the eighth chapter, which seem to me conclusively to
show that this sterility is no more a special endowment than
is the incapacity of two distinct trees to be grafted together;
but that it is incidental on differences confined to the repro-
ductive systems of the intercrossed species. We see the truth
of this conclusion in the vast difference in the results of cross-
ing the same two species reciprocall}- — that is, when one
species is first used as the father and then as the mother :
analogy from the consideration of dimorphic and triraorphic
plants clearly leads to tlic same conclusion, for when the forms
are illegitimately united, they yield few or no seed, and their
offspring arc more or less sterile ; and these forms of the same
undoulited species dlfler in no respect from each other 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
U) 1)0 universal, this cannot be considered correct after the fiicts
given on the authority of Gartner and Kijlreuter. Nor is the
very general fertility of varieties, when crossed, surprising,
when we remember that it is not likely that their reproductive
sj-stems should have been profoundly modified. Moreover,
most of the varieties which have been experimente(l on have
been produced under domestication ; and as domestication (I
do not mean mere confinement) almost certainly tends to elim-
inate sterility, we ought not to expect it also to produce
sterility.

The sterility of hyl)rids is a different case from that of a
first cross, for tli(» reproductive organs of hybrids arc more or
less functionally impotent ; whereas in first crosses, the organs
of both species arc of course in a perfect condition. As we
continually see that organisms of all kinds are rendered in
some degree sterile from being exposed to slightly-changed
conditions, wc need not feel surprise at hybrids being in some

414 RECAPITULATION. Cuap. XIV.

(lep^ree sterile, for their constitutions can hardly fail to bo dis-
turbed from beinf^ compounded of two distinct organizations ;
but -whether this is the true cause of their sterility I will not
pretend to decide. The above parallelism is supported by
another parallel, but directly opposite, class of facts, namely,
that the vig'or and fertility of all organic beings are increased
by slight changes in their conditions of life, and that the
oifspring of slightly-modified forms or varieties when crossed
acquire increased vigor and fertility. So that, on the one
hand, a considerable change in tlie conditions of life and crosses
between greatly-modified forms, lessen fertility; and, on the
other hand, lesser changes in the conditions of life and crosses
between less-modified forms, increase fertility.

Turning to geographical distribution, the difficulties en-
countered on the theory of descent with modification are seri-
ous enough. All the individuals of the same species, and all
the species of the same genus, or even higher group, must have
descended from common parents; and therefore, in however
distant and isolated parts of the world they may now be found,
they must in the course of successive generations have travelled
from some one point to all the others. We are often wholly
unable even to conjecture how this could have been effected.
Yet, as we have reason to believe that some species have
retained the same specific form for very long periods of time,
immensely long as measured by years, too much stress ought
not to be laid on the occasional wide diffusion of the same spe-
cies ; for during very long periods there will always be a good
chance for wide migration by many means. A broken or in-
terrupted range may often be accounted for by the extinction
of the species in the intermediate regions. It cannot be de-
nied that Ave arc as yet very ignorant of the full extent of the
various climatal and geographical changes which have affected
the earth during modern periods; and such changes may obvi-
ously have facilitated migration. As an exam])le, I have at-
tempted 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 process of modification has neces-
sarily been slow, all the means of migration will have been
possible during a very long period ; and consequently the ■

Chap. XIV. RECAPITULATIOiN. 4I5

difBculty of the wide diffusion of tlic species of the same genus
is in some def^ree lessened.

As uccording' to the theory of natural selection an intermi-
nable number of intermediate forms must have existed, linking*
together all the species in each group by gradations as fine as
are our [jrescnt varieties, it may be asked, Why do v,'o not
see these linking forms all around us ? Wliy are not all organ-
ic beinfTS blended tos:ether in an inextricable chaos ? AVith
respect to existing forms, we should remember that we have
no right to expect (excepting in rare cases) to discover directhj
connecting links between them, but only between each and
some extinct and supplanted form. Even on a Avide area,
which has during a long period remained continuous, and of
which the climate and other conchtions of life change insensibly
in proceeiling fi'om a district occupied by one species into
another district occupied by a closely-allied species, we have
HO just right to expect often to find intermediate varieties in
the intermediate zone. For we have reason to believe that
only a few species of a genus ever imdergo change ; the other
species becoming utterly extinct and leaving no modified pro-
geny. Of the species which do change, only a few Avithin the
same country change at the same time ; and all modifications
are slowly effected. I have also shoAvn that the intermediate
varieties which prcjbably 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 numbers,
would generally be modified and improved at a quicker rate
than the intermediate varieties, which existed in lesser num-
bers ; so that the intermediate varieties Avould, 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 inhabitants
of the Avorld, and at each succcssIa'C period betAA'cen the ex-
tinct and still older species, Avhy is not every geological forma-
tion charged Avith such links ? Why does not every collection
of fcjssil remains afford plain evidence of the gradation and
mutation of the forms of life? Although geological research
has undoubtedly rcA'caled the former existence of many links,
bringing numerous forms of life much closer together, it does
not yield the infinitely many fine gradations between i)ast and
present species required on the theory ; and this is the most
obvious of the many objections Avhich may be urged against it.
Why, again, do Avhole groups of allied sjiecies apj)car, though

41G EECAl'ITULATION. Chap. XIV.

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 incalculably
remote, long befc^re the lo^vest bed of the Cambrian system was
deix)sited, why do we not lind beneath this system great piles of
strata stored with the remains of the progenitors of the Cam-
brian fossils ? For on tlic theory such strata must somewhere
have been deposited at these ancient and utterly unknown
epochs in the world's history.

I can answer these ciuestions and olijcctions only on the
supposition that the geological record is far more imperfect
than most geologists believe. The number of s]x;cimens in all
our museums is absolutely as nothing compared with the
countless generations of countless species wliich have certainly
existed. The parent-form of any two or more sjx^cies would
not be in all its characters directly intermediate between its
modified odspring, any more than the rock-pigeon is directly
intermediate in crop and tail between its descendants the
pouter and fantail pigeons. We should not l>e able to recog-
nize a species as the parent of another and modified species, if
we were to examine both ever so closely, unless we possessed
most of the intermediate links ; and owing to the imjxjrfection
of the geological record, we have no just right to expect to
find so many hnks. If two or three, or even more linking
forms were discovered, they would simply be ranked as so
many new species, more especially if found in different geolo-
gical sub-stages, let their differences be ever so slight. Nu-
merous existing doubtful forms could be named which are prob-
ably varieties ; but who will pretend that in future ages so
man}- fossil links Avill be discovered, that naturalists will be
able to decide whether or not these doubtful forms ought to be
called varieties ? Only a small portion of the world has been
geologically explored. Only organic beings of certain classes
can be preserved in a fossil condition, at least in any great
i\uinl)er. Many species when once formed never undergo any
further change, but become extinct without leaving modified
descendants ; and the periods, during which species have un-
dergone modification, though long as measured by years, have
])r()l)ably been short in comparison with the periods during
which tliey have retained the same fonn. It is the dominant
and widely-ranging species which vary most frequently anil vary
most, and varieties are often at first local — both clauses render-
ing the discovery of intermediate links in any one formation

Chap. XIV. RECAPITULATION. 417

less likely. LckmI varieties will not spread into other and dis-
tant reg^ions until they are considerably modilied and improved ;
and when they have spread, and are discovered in a ji^eological
formation, they will appear as if silddenly created there, and
will be simply classed as new species. Most formations have
been intermittent in their accumulation; and their duration
has probably been shorter than the average duration of spe-
cific forms. Successive formations are in most cases separated
from each other by. blank intervals of time of great length ; for
fossiliferous formations thick enough to resist future degrada-
tion 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
recortl will generally be blank. During these latter periods
tliere will i^robably be more variability in the forms of life ;
during periods of subsidence, more extinction.

Witii respect to the absence of strata rich in fossils beneath
the Caml)rian formation, I can recur only to the hypotliesis
given in the ninth chajiter. That the geological record is im-
perfect all will admit ; but that it is imperfect to the degree re-
quired l)y 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, for they have changed slowly and in a grad-
uated manner. We clearly see this in the fossil remains from
consecutive formations invariably being much more closely re-
lated to each other than are the fossils from widely-separated
formations.

Such is the sum of the several chief objections and dilhcul-
ties which may justly be urged against the theory ; and 1 have
now briefly recapitulated the answers and explanations which
can be given. I have felt these diiliculties far too heavily dur-
ing many years to doubt their weight. But it deserves espe-
cial notice that the more important objections relate to ques-
tions on which we are confessedly ignorant ; nor do we know
how ignorant we are. AVe do not know all the possible tran-
sitional gradations between the simplest and the most perfect
organs; it cannot be pretendecl that we know all the varied
means of Distril)uti()n during the long lapse of years, or that
we know how imperfect the Geological Kecord is. ^ferious as
these several objections are, in \uy judgment they are not
suflicient to overthrow the theory of descent with subsequent
modification.

418 RECAPITULATION. Chap. XIV.

Now let us lum to the other side of the argument. Under
domestication Ave see much variability, caused, or at least ex-
cited, liy changed conditions of life. This variability is gov-
erned by many complex laws — by correlation, by use and dis-
use, and by the definite action of the surrounding conditions.
There is much difficulty in ascertaining hoAV largely our do-
mestic productions have been modified ; but we may safely in-
fer 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 modifi-
cation, Avhich has already been inherited for many generations,
may continue to be inherited for an almost infinite number of
generations. On the other hand, Ave haAO evidence that vari-
ability, AA-hen it has once come into play, does not cease under
domestication for a very long period; for noAV A'arieties are
still occasionally produced by our oldest domesticated produc-
tions.

Man does not actually produce variability ; he only unin-
tentionally exposes organic beings to ncAV conditions of life,
and then Nature acts on the organization, and causes .A'ari abil-
ity. But man can and docs select the A-ariations given to him
by Nature, and thus accumulate them in any desired manner.
lie thus adapts animals and plants for his OAvn benefit or
pleasure. He may do this methodically, or he may do it un-
consciously, by preserving the indiA'iduals most useful or pleas-
ing to hini Avithout any intention of altering the breed. It is
certain that he can largely influence the character of a breed
Ijy selecting, in each successive generation, individual differ-
ences so slight as to be inap{)reciable except by an educated
eye. This process of selection has been the great agency in
f lie formation of the most distinct and useful domestic breeds.
That many breeds produced by man have to a large extent the
character of natural species, is shown by the inextricable
doubts AA'hether many of them are Aarietics or aboriginally dis-
tinct species.

There is no obvious reason why the principles Avhich have
acted so cfficientl}^ under domestication should not act under
Nature. In the survival of favored individuals and races, dur-
ing the constantly-recurrent Struggle for Existence, Ave see a
jKnverful and ever-acting form of Selection. The struggle for
existence inevitably follows from the high geometrical ratio of
increase Avhich is common to all organic beings. This high
rate of increase is proved by calculation — l)y the rapid increase

CiiAr. XIV. RECAPITULATION. 419

of many animals and plants during a succession of peculiar
seasons, and when naturalized in a new country. More indi-
viduals 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 linally become extinct. As the
individuals of the same species come in all respects into the
closest competition with each other, the struggle will gener-
ally 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 very severe between beings re-
mote in the scale of nature. The slightest advantage in cer-
tain 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 condi-
tions, will turn tlic balance.

With animals having separated sexes there will be in most
cases a struggle between the males for the possession of the
females. The most vigorous males, or those which have most
successfully struggled with then' conditions of life, will gener-
ally leave most progeny. But success will often depend on
the males having special weapons, or means of defence, or
charms ; and a slight advantage Avill lead to victory.

A3 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 be any
variability under Nature, it would be an unaccountable fiict if
natural selection did 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 fjuantity.
i\Ian, though acting on external characters alone and often
capriciously, can produce w'ithin a short peritxl a great result
by adding up mere individual differences in his domestic pro-
ductions; and every one admits that species present individual
difFerences. 15ut, besides such dill'erences, all naturalists admit
that varieties exist, which are considered sulliciently distinct
to be worthy of record in systematic works. No one has
drawn any clear distinction between individual dilVerences and
slight varieties ; or between more plainly-marked varieties
and sub-species, and species. f)n separate contincMits, and on
dilFercnt parts of the same continent when divided hy l)arriers

420 RECAPITULATION. Chap. XIV.

of any kind, and on outlying islands, Mliat a multitude of
forms exist, ■which some experienced naturalists rank as vari-
eties, others as geographical races or sub-species, and others
as distinct though closely-allied species !

If, then, animals and plants do vary, let it be ever so little
or so slowlv, why should we doubt that the variations or in-
dividual dill'erences, which are in any way beneficial, would be
preserved and accumulated through natural selection, or the
survival of tlie fittest ? If man can by patience select varia-
tions useful to him, Avhy, under changing and complex condi-
tions 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 — fiworing the good and rejecting the
bad ? I can see no limit to this power, in slowly and beauti-
fully adapting each form to the most complex relations of life.
The theory of natural selection, even if we looked no further
than this, seems to me to be in itself 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 fii-st 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 A\hicli arc
acknowledged to have been produced by secondary laws. On
this same view we can imderstand how it is that in each region
where many sjiecies of a genus have been produced, and where
they now ilourish, these same species should present many
\ aricties ; for whei'e the manufactory of species has been
active, Ave might expect, as a general rule, to find it still iu
action ; and this is the case if varieties be incipient species.
^Moreover, the; species of the larger genera, which ailord the
greater number of varieties or incipient species, retain to a
certain degree the character of varieties ; for they dilfer froiu
cacli other by a less amount of dilference than do the species
of smaller genera. The closely-allied species also of the larger
genera ap])arently have restricted ranges, and in their affinities
tliey are clustered in little groups round other species — in both
of Avhich respects they resemble varieties. These are strange

Chap. XIV. RECAPITULATION. 421

relations on the view that each species was independently
created, but are intelligible if each existed fust as a variety.

As each species tends by its jji:eoinelrical ratio of rei)roduc-
tion to increase inordinately in number ; and as the modified
descendants of each species will be enabled to increase by so
much the more as they become diversified in habits and struct-
ure, so as to be enabled to seize on many and widely diflerent
jilaces in the economy of Nature, there will be a constant ten-
dency in natural selection to preserve the most divergent oft-
spriiior 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 characteristic of the species of the same
genus. New and improved varieties will inevitably supplant
and exterminate the older, less improved, and inteimediate
varieties ; and thus species are rendered to a large extent de-
fined and distinct objects. Dominant species belonging to the
larger groups within each class t(>nd 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 tlius succeed in increasing in size, for
the world would not hold them, the more dominant groups
beat tlie less dominant. This tendency in the large groups to
go on increasing in size and diverging in character, together
with the almost inevitable contingency of much extinction, ex-
plains the arrangement of all the forms of life, in groups sub-
ordinate to groujis, all within a few great classes, which has
prevailed throughout all time. This grand fact of the group-
ing of all organic beings under what is called the Natural
System, is utterly inexplicable on the tlieory of creation.

As natural selection acts solely by accumulating slight,
successive, favorable variations, it can produce no great or sud-
den modification ; it can act only by short and slow steps.
Hence the canon of " Natura iion facit saltum," which every
fresh addition to our knowledge! lends to make truer, is on
this theory intelligible. We can sec; why throughout Nature
the .same general end is gained by an almost inliiiite diversity
of Tneans ; for every peculiarity when once acquired is long
inherited, and structures already diversified in many ways
have to be adapted for the same general purpose. AVe can,
in short, see why Nature is prodigal in variety, though nig-
gard in innovation. But why this .should be a law of Nature
if each species had been independently created, no man can
ex])lain.

422 RECAPITULATION. Cuap. XIV.

Many other facts arc, as it seems to me, explicable on this
theory. How strange it is that a bird, under the form of
woodj)ecker, should have been created to prey on insects on
the ground ; that upland geese, which never or rarely swim,
should have been created with webbed feet ; that a thrush-
like bird should have been created to dive and feed on sub-
aquatic insects ; and that a petrel should have been created
with the habits and structure fitting it for the life of an auk !
— and so in endless other cases. But, on the view of each
species constantly trying to increase in number, with natural
selection always ready to adapt the slowly-varying descend-
ants of each to any unoccupied or ill-occupied place in Nature,
these facts cease to be strange, or might even have been an-
ticipated.

We can understand how it is that such harmonious beauty
generally prevails throughout Nature. That there are excep-
tions according to our ideas of beauty, no one will doubt who
Avill look at some of the venomous snakes, at some fish, and at
certain hideous bats with a distorted resemblance to the hu-
man face. Sexual selection has given the most brilliant colors
and other ornaments to the males, but sometimes to both sexes
of many birds, butterflies, and a few 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 gaudy colors in contrast with the
green foliage, in order that the flowers might be easily seen,
visited, and fertilized by insects, and the seeds disseminated
by birds. Lastly, some living objects have become beautiful
through mere symmetry of growth.

As natural selection acts by competition, it renders the in-
habitants of each country perfect only in relation to the other
inhabitants ; so that we need feel no surprise at the species of
an}'^ one country, although on the ordinary view supposed to
have been created and specially adapted for that country,
1)cing beaten and suj^planted by the naturalized productions
from another land. Nor ought we to marvel if all the contriv-
ances in Nature he not, as far as we can judge, absolutely per-
fect ; and if some of them be abhorrent to our ideas of fitness.
We need not marvel at the sting of the bee when used against
an enemy often causing the bee's own death ; at drones being
))roduced 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

Chap. XIV. EECAPITULATION. 423

the queen bee for lier own fertile daughters ; at it lincumoiiid:c
fcediiifr within the livin"^ bodies of ciiterpilhirs ; und ut 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 observed.

The complex and little-known laws governing acknowl-
edged variations are the same, as far as we can see, with the
laws which have governed the production of so-called specific
dillcrences. In both cases physical conditions seem to have
produced some direct and definite eflect, but how much we
cannot say. Thus when varieties enter any new station, they
occasionally assume some of the characters proper to the spe-
cies of that station. In I'otli varieties and species, use and dis-
use seem to have produced a considerable eflfect ; for it is im-
possible to resist this conclusion when we look, for instance,
at the logger-headed duck, which has wings incajiable of flight,
in nearly the same condition as in the domestic duck; or when
we look at the burrowing tncutucu, v.hich is occasionally
l)lind, and then at certain moles, which are habitually blind
and have tlieir eyes cov^ercd witli skin ; or wlicn we look at
the blind animals inhabiting the dark caves of America and
Europe. In varieties and species correlated variation seems to
have played an im})ortant part, so that when one part has
been modified other parts have been necessarily modified. In
both varieties and species reversions to long-lost characters oc-
cur. How inexplicable on the theory of creation is the occa-
sional ajipearance 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
arc all descended from a stri{)ed progenitor, in the same man-
ner as the several domestic breeds of the pigeon are descended
from the blue and barred rock-pigeon !

On the ordinary view of eacli species having been iudc-
ju'!id('iitly created, why should the specific characters, or those
l)y which the species of the same genus diflcr from each other,
be more variable than the generic characters in which they all
agree? Why, for instance, should the color of a flower be
more likel}' to vary in any one species of a genus, if the other
species, supposed to have been created independently, have
diffenMitly-colored flowers, than if all the species of the genus
have the same colort'd flowers? If species are only well-
marked varieties, of which the characters have become in a
high degree pcnnanent, Ave can understand this fact; for they

424 KECAriTULATION. Chap. XIV.

have already varied since they branched off from a common
progenitor in certain characters, by which they have come to
be specifically distinct from each other ; therefore these same
characters -would be more likely again to vary than the generic
chaiacters Avhich have been inherited Avithout change for an
cjiormous period. It is inexplicable on the theory of creation
ivhy a part developed in a very unusual manner in any one
species 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 progenitor, an
luuisual amount of variability and modification, and therefore
we might expect the part generally ^o 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 othci
structure, if the part be common to many subordinate forms,
that is, if it has been inherited for a very long period ; for in
this case it will have been rendered constant by long-continued
natural selection.

Glancing at instincts, marvellous as some are, they offer no
greater difliculty than does corporeal structure on the theory of
the natural selection of successive, slight, but profitable modi-
iications. We can thus imderstand why Nature moves by
graduated steps in endowing different animals of the same
class Avith their several instincts, I have attempted to show
how nmch light the principle of gradation throws on the ad-
mirable architectural powers of the hive-bee. Habit no doubt
sometimes comes into play in modifying instincts ; but it cer-
tainly is not indispensable, as we see in the case of neuter in-
sects, which leave no progeny to inherit the effects of long-
continued habit. On the view of all the species of the same
genus having descended from a common parent, and having in-
herited nuich 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 instance, line
their nests with mud like our British species. On the -view of
instincts having been slowly acquired through natural selec-
tion, we need not marvel at some instincts being apparently
not ])erfect and liable to mistakes, and at many instincts caus-
ing 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

CiiAi'. XIV. •recapitulation. 425

same coinph^x laws in tlieir deforces and kinds of resemblance
to their parents — in Ix'in;];' al)sorbcd into each other by suc-
cessive crosses, and in other such points — as do the crossed
oll'spring^ of aeknowledij^ed varieties. Tiiis sinuhiritj would be
a strange fact, if species liave been independently created and
varieties have been produced thronj^h secondary' laws.

If we admit that the geolog-ical record is imperfect ia 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 successive
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 princii)le 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. Tlie gradual diffusion
of dominant 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 throughout the
world. The fact of the fossil remains of each formation being
in some degree intermediate in character between the fossils
in the formations above and below, is simpl}' ex])lained by
their intermediate position in the chain of descent. The grand
fact that all extinct beings can be classed with all recent
beings, naturally follows from the liWng and the extinct being
the ofispring of common parents. As species have generally
diverged in character during their long course of descent and
modiiication, we can understand why it is that the more an-
cient forms of early progenitors of each group so often occu-
py a position in some degree intermediate between existing
groups. Recent forms are generally looked at as being, on
the whole, higher in the scale of organization than ancient
forms ; and they must bo higher, in so far as the later and
more improved forms have conqu(>red the older and less im-
proved forms in the struggle of life; they have also generally
had their organs more spccializtnl for different functions. This
fact is ])('rfectly cfjmpatible with numerous beings still retain-
ing simpl(! and but little improved structures, iitled for simple
condilicjns of life ; it is likewise compatible with some forms
haWng retrograded in organization, by having become at each
stage of descent better fitted for changed and degraded habits

420 BECAPITULATION. • Chap. XIV.

of life. Lastly, the wonderful law of the long endurance of
allied forms on the same continent — of marsupials in Australia,
of edenlatii in America, anct other such cases — is intelligible,
for generally within the same country the existing and the ex-
tinct will be; closely allied l)y descent.

Looking to geographical distribution, if wc admit that
there has been during the long course of ages much migration
from one part of the world to another, owing to former clima-
tal and geographical changes and to the many occasional and
unknown means of dispersal, then wc can understand, on the
theory of descent with modification, 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 through-
out time ; for in both cases the beings have been connected by
the bond of ordinary generation, and the means of modifica-
tion have been the same. We see the full meaning of the
wonderful fact, which has struck every traveller, namely, that
on the same continent, under the most diverse conditions,
luider 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 descendants of the same pro-
genitors and early colonists. On this same principle of former
migration, combined in most cases with modification, we can
unclerstand, by the aid of the Glacial period, the identity of
some few plants, and the close alliance of many others, on the
most distant mountains, and in the northern and southern tem-
perate zones ; and likewise the close alliance of some of the
inhabitants of the sea in the northern and southern temperate
latitudes, though separated by the whole intertropical ocean.
Although two countries may present physical conditions as
closely similar as the same species ever reqviire, we need feel
no surprise at their inhabitants being widely different, if they
have been for a long period completely sundered from each
other ; for, as the relation of organisn\ to organism is the most
important of all relations, and as the two countries will have
received colonists at various periods and in difi'erent propor-
tions, from some other country or from each other, the course
of modification in the two areas will ineWtably have been dif-
ferent.

On this view of migration, with subsequent modification,
we see why oceanic islands arc inhabited by only few species,
but of these, why many arc peculiar or endemic forms. We

CiiAi-. XIV EECAPITULATION. 497

clearly sec why species belonging to those groups of animals
which cannot cross wide spaces of the ocean, as frogs and ter-
restrial niumnials, do not inhabit oceanic islands ; and wliy, on
the' other hand, new and peculiar species of bats,, animals
wliich can traverse the ocean, are so often found on islands far
distant from any contni(?nt. Such cases as the presence of pe-
culiar species of bats on oceanic islands, and the absence of
all other terrestrial mammals, are facts utterly inexplicable on
the theory of independent acts of creation.

The existence of closely-allied or representative species in
any two areas, implies, on the theory of descent with modifica-
tion, that the same parent-forms formerly ' inhabited both
areas ; and we almost invariably find that, wherever many
closely-allied species inhabit two areas, some identical species
are still conunon 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 gener-
ality that the inhabitants of each area are related to the inhabi-
tants of the nearest source whence innnigrants might have
been derived. We see this in the striking relation uf 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 main-land ; and
of those of the Cape de Verde archipelago and of the other
African islands to the African main-land. It must be admitted
that these facts receive no explanation on the theory of crea-
tion.

The fact, as we have seen, that all past and present organ-
ic beings can be arranged within a few great classes, in groups
subordinate to groups, and with the extinct groups often fall-
ing in between the recent groups, is intelligible on the tlieory
of natural selection with its contingencies of extinction and
divergence of character. On these same princijilcs we see how
it is that the mutual affinities of the forms Avithin each class
are so complex and circuitous. We see why cert^iin charac-
ters are far more seniceable than others fur classification —
why adaptive characters, though of paramount imjiortance to
the beings, are of hardly any importance in classification ;
why characters derived from rudimentary parts, though of no
service to the beings, are often of high classiiicatory value;
and why embryological charactei-s are often the most valuable
of all. The real affinities of all organic beings, in contradis-
tinction to tiieir adaptive resemblances, are due to inheritance

428 EECAPITDLATION, Chap. X[V.

or coinimniity of descent. The Natural System is a genealo-
gical arrangement, with the acquired grades of difference,
marked by tlic terms, varieties, species, genera, families, etc. ;
and we kavc to discover the lines of descent by the most per-
manent characters, whatever they may be and of however slight
vital importance.

The singular framework of bones in the hand of a man,
wing of a bat, fin of the porpoise, and leg of the horse — the same
ninuber of vertebras 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 suc-
cessive modifications. Tlic similarity of pattern in the w'ing
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 likewise intelligible on the view of the
gradual modification of parts or organs, which were aborigi-
nally alike in an early progenitor in each of these classes. On
the principle of successive variations not always supervening at
an early age, and being inherited at a corresponding not early
period of life, we clearly see why the embryos of mammals,
birds, reptiles, and fishes, are so closely similar, and so unlike
the adult forms. We may cease marvelling 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 air dissolved in water by the aid of well-developed
branchiiv.

Disuse, aided sometimes by natural selection, has often
reduced organs when they have become useless under changed
halnts or conditions of life ; and we can clearly understand on
this vfew 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 struggle for ex-
istence, and Avill 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 in-
herited teeth, which never cut through the gums of tlie upper
jaw, from an early progenitor having well-developed teeth ;
and we may believe, that the teeth in the mature animal were
reduced, during successive generations, by disuse, or by the
tongue and palate, or lips, ha^^ng become better fitted by
natural selection to browse without their aid ; whereas in the
calf, tlie teeth have been left imtouched by selection or disuse,
and on the principle of inheritance at corresponding ages have

CuAP. XIV. CONCLUSION. 429

been inherited from a remote period to llie present day. On
the view of each organic being with all its separate parts hav-
ing been specially created, how utterly inexplicable it is that
(Mgans bearing the plain stamp of inutility, such as the teeth in
the embryonic calf or the shrivelled wings under the soldered
\ving-covers of many beetles, should so frequently occur ! Na-
ture may be said to have taken pains to reveal her schejne of
modification, by means of rudimentary organs, embryological
and homologous structures, but we wilfully will not understand
the scheme.

I have now recapitulated the facts and considerations
which have thoroughly convinced me that species have been
modiiied, (hiring a long course of descent, chiefly through the
natural selection of numerous successive, slight, favorable va-
riations. I cannot believe that a false theory would explain,
as it seems to me that the theory of natural selection does ex-
plain, the several large classes of facts above specified. It is
no valid objection that science as yet throws no light on the
far higher problem of the essence or origin of life. A\'ho can
explain what is the essence of the attraction of gravity ? No
()n<; now objects to following out the results consequent on
this xmknown element of attraction; notwithstanding that
Leibnitz formerly accused Newton of introducing "occult
qualities and miracles into philosophy."

I see no good reason Avhy the views given in this volume
should shock the religious feelings of any one. It is satisfac-
tory, as showing how transient such impressions are, to remem-
Ixn- thiit 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 inferentially of revealed reli-
gion." A celebrated author and divine has written to me that
" he has gradually learned to see that it is just as noble a con-
eej^tion of the Deity to believe that lie created a few original
forms capable of self-development into other and needful
forms, as to believe that He recpiired a fresh act of creation to
suj)])ly the voids caused by the action of His laws."

Why, it may be asked, imtil recently did nearly all the
most eminent living naturalists and geologists reject this view
of tin; mutability of species. It cannot be asserted that
organic b(Mngs in a state of nature are subject to no variation;
it caimot be jiroved that the amount of variation in the course
of long ages is a limited quantity ; no clear distinction has

430 CONCLUSION. Chap. XIV.

been, or cjin bo, (hawn between species and well-marked varie-
ties. 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 be-
lief tliat species were immutable productions was almost una-
voidable ;is lon;!^ as the history of the world was thought to be
of shoct duration ; and now that we have acquired some idea
of the lapse of time, Ave are too apt to assume, without proof,
that the geological record is so perfect that it would have
alforded us plain evidence of the mutation of species, if they
had undergone nmtation.

But the chief cause of oin- natural unwillingness to admit
that one species has given birth to other and distinct species,
is, that we are always slow in admitting any great change of
which we do not see the steps. The difficulty is the same as
that felt by so many geologists, Avhen Lyell first insisted that
long lines of inland cliffs had been formed, and great valleys
excavated, by the agencies Avhich we see still at Avork. The
mind cannot possibly grasp the full meaning of the term of
even ten million years ; it cannot add up and perceive the full
effects of many slight A'ariations, accumulated during an almost
hillnite number of generations.

Although I am fully convinced of the truth of the A'ieAVS
giA'en in this Aolume under the fonn of an abstract, I by no
means expect to convince experienced naturalists Avhose minds
are stocked Avitli a multitude of facts all A'iewed, during a long
course of years, from a point of vicAV directly opposite to mine.
It is so easy to hide our ignorance under such expressions as
the " plan of creation," " unity of design," etc., and to think
that Ave giA'e an ex2:)lanation Avhen Ave only restate a fact !
Any one Avhose disposition leads him to attach more Aveight
to unexjilained difficulties than to the explanation of a certain
numl)er of facts, Avill certainly reject the theory. A fcAV natu-
ralists, endoAA'ed Avith much flexibility of mind, and Avho liaA'e
already begun to doubt the immutability of species, may be
induouced by this volume ; but I look Avith confidence to the
future, to young and rising naturalists, Avho Avill be able to
view both sides of the question Avith impartiality, ^^'hoeve^
is led to bclicA'e that species are mutable Avill do good service
by conscientiously expressing his conA'iction ; for thus only
can tlie load of prejudice by Avhich this subject is overwhelmed
be removed.

Several eminent naturalists have of late published tluir

Chap. XIV. CONCLUSION. 431

belief that a multitude of reputed species in each genus arc
not real species ; but tliat othor species are real, that is, have
been independently created. This seems to me a strange con--
elusion to arrive at. They admit tliat a multitude of forms,
which till lately they themselves thought were special crea-
tions, and which arc still thus looked at by the majority of
naturalists, and which consequently have all the external char-
acteristic 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 defuie, or even conjecture,
which are the created forms of life, and which arc those pro-
duced by secondary laws. They admit variation as a vera
causa in one case, they arbitrarily reject it in another, without
assigning any distinction in the two cases. The day will come
when this will be given as a curious illustration of the blind-
ness of preconceived opinion. These authors seem no more
startled at a miraculous act of creation than at an ordinary
birth. But do they really believe that at innumerable periods
in the earth's history certain elemental atoms have been com-
manded suddenl}' to flash into living tissues ? Do they believe
that at each supposed act of creation one individual or many
were jiroduced ? 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 fron^ the mother's womb ? Un-
doubtedly these same questions cannot be answered by those
who believe in the appearance or creation of only a few forms
of life, or of some one form alone. It has been maintained by
several authors that it is as easy to believe in the creation of
a hundred million beings as of one ; but Maupertuis's philo-
sophical axiom " of least action" leads the mind more willing-
ly to admit the smaller number ; and certainly we ought not
to believe that innumerable l)eings within each great class
have been created with plain, but deceptive, marks of descent
from a single parent.

It may be asked how far I extend the doctrine of the mod-
ification of species. The question is diiricult to answer, be-
cause the more distinct the forms are which we consider, by so
much the arguments fall away in force. But some arguments
of the greatest weight extend very far. All the memliers of
whole classes are connected together by a chain of affinities,
and all can be classified on the same principle, in groups subor-

432 CONCLUSION. Chap. XIV.

dinatc to groups. Fossil remains sometimes tend to fill up
very wide intervals between existing orders. Organs in a rudi-
mentary condition plainly show that an early progenitor had
the organ in a fully-developed state ; and this in some instances
implies an enormous amount of modification in the descend-
ants. Tlnoughoiit whole classes various structures are formed
on the same ])attcrn, and at a very early age the embryos
closely resemble each other. Therefore I cannot doubt that
tlie theory of descent with modification embraces all the mem-
bers of the same class. I believe that animals are descended
from at most only four or five progenitors, and plants from an
equal or lesser number.

Analogy 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. Neverthe-
less all living things have much in common — in their chemical
composition, their cellular structure, their laws of growth, and
their liability to injurious influences. We see this even in so
trifling a fact as that the same poison often similarly affects
plants and animals ; or that the poison secreted by the gall-fly
produces monstrous growths on the wild rose or oak-tree.
^Vith all organic beings sexual reproduction seems to be essen-
tially 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 tlie animal and vegetable kingdoms — certain low
forms arc so fiir intermediate in character that naturalists have
disputed to which kingdom they should be referred, and, as
Prof. Asa Gray has remarked, " tlie spores and other reproduc-
tive bodies of many of the lower alga3 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 admit that all the organic beings Avhich have
ever lived on this earth may be descended from some one pri-
mordial form. But this infei'ence is chiefly grounded on anal-
ogy, 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 commencement of life many difl'erent forms were evolved;
but if so, we may conclude that only a very few have left modi-
fied descendants. For, as I have recently remarked in regard to

CflAP. XIV. CONCLUSION. 433

the members of each great class, such as the Vertebrata, Artio-
ulataj etc., Ave have distinct evidence in their embryological,
homologous, and rudimentary structures, that within each class
all are descended from a single progenitor.

When the views advanced by me in this volume, and by
Mr. Wallace in the Linncan Journal, or when analogous views
on the origin of species are generally admitted, Ave can dimly
foresee that there will be a considerable revolution in natural
liistory. Systematists will be able to pursue their labors as at
present ; but they Avill not be incessantly haunted by the shad-
owy doubt whether this or that form be a true species. This
I feel sure, and I speak after experience, will be no slight re-
lief. The endless disputes whether or not some fifty species
of British brambles are good species will cease. Systematists
will have only to decide (not that this will be easy) whether
any form be sufficiently constant and distinct from other forms,
to be capable of definition ; and if definable, whether the dif-
ferences be sufficiently important to deserve a specific name.
Tliis latter point Avill 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 Ave shall be compelled to
acknoAvledgc that the only distinction Ijctween species and
Avell-maiked varieties is, that the latter arc knoAvn, or believed,
to be connected at the ]iresent day by intermediates gradations,
whereas species Avere formerly thus connected. Hence, Avith-
out rejecting the consideration of the present existence of in-
Icnnediate gradations between any two forms, Ave shall be led
to Avelgh more carefully and to A'alue higher the actual amount
of dillcrence between them. It is quite jiossible that forais noAV
generally acknowledged to be merely varieties may hereafter
l)o thought Avorthy of specific names ; and in this case scien-
tific and common language Avill come into accordance. In
short, Ave shall liaA'C to treat species in the same manner as
those naturalists treat genera, Avho admit that genera are
merely artificial combinations made for conA'cnience. Tliis
may not be a cheering prospect; but avc shall at least be freed
from the A'ain search for the undiscovered and undiscoverable
essence of the term sj)ecies.

The other and more general departments of natural history
Avill rise greatly in interest. The terms used l>y naturalists of
allinitv, relationship, community of type, paternitv, morpholo-
10

434 CONCLUSION. Cbap. XIV

gy,* adaptive cliaraclcrs, rudimeiitaiy and abortive organs, etc.,
Avill cease to be nietaphorica], and will have a plain significa-
tion. AVhen we no longer look at an organic being as a sav-
age looks at a ship, as something wholly beyond his compre-
hension ; when we regard every production of Nature as one
which has had a long history ; when we contemplate every com-
plex structure and instinct as the summing up of many con-
trivances, 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
workmen ; 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 tlie 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 sjiecies added to the infinitude of already-re-
corded species. Our classifications will come to be, as far as
they can be so made, genealogies ; and Avill then truly give
what may be called the plan of creation. The rules for classi-
fying will no doubt become simpler when we have a definite
object in view. We possess no pedigrees or armorial bear-
ings ; and we have to discov' cr and trace the many diverging
lines of descent in our natural genealogies, by characters of
any kind wliich have long been inherited. Rudimentary or-
gans will speak infallibly with respect to the nature of long-
lost structures. Species and groups of species, which are
called aberrant, and wliich may fancifully be called living fos-
sils, 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.

A\'lien we can feel assured that all the individuals of the
same species, and all the closely-allied species of most genera,
have within a not very remote period descended from one
parent, and have migrated from some one birthplace; and
Avhen 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 admirable man-
ner the former migrations of the inhabitants of the whole

Chat. XIV. CONCLUSION. • 435

world. Even at present, by comparing the differences of the
inluibitaiits of tlie sea on the opposite sides of a continent,
and the nature of the various inhabitants of that continent in
relation to tlicir apparent means of immig-ration, some light
can be thrown on ancient geography.

The noble science of Geology loses glory from the ex-
treme imperfection of the record. The crust of the earth Avith
its embetlded remains must not be looked at as a well-filled
museum, but as a poor collection made at hazard and at rare
intervals. The accumulation of each great fossiliferous forma-
tion will be recognized as having depended on an nnusual con-
currence of favorable circumstances, and the l)lank 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 comparison of the preceding and suc-
ceeding organic forms. We must be cautious in attempting to
correlate as strictly contemporaneous two formations, wliicli do
not include many identical species, by the general succession
of the forms of life. As species are produced and extermi-
nated by slowly acting and still existing causes, and not hy mi-
raculous acts of creation and by catastrophes ; and as the most
important of all causes of organic change is one which is al-
most independent of altered and perliaps suddenly-altered
])hysical conditions, namely, the mutual relation of organism to
organism — the improvement of one organism entailing the im-
provement or the extermination of others — it follows that the
amount of organic change in the fossils of consecutive forma-
tions probably serves as a fair measure of the lapse of actual
time. A number of species, however, keeping in a body
might remain for a long period unchanged, while within this
same period, sevend of these species, by migrating into new
countries and coming into competition with foreign associates,
might become modilied ; so that we nmst not overrate the ac-
curacy of organic change as a measure of time. During earlv
periods of the earth's liistory, when the forms of life were proba-
i)ly fewer and simpler, the rate of change was ])rol)ably slower;
and at the fust dawn of life, when very few forms of the sim-
plest structure existed, the rate of change niav have been slow
in an extreme degree. The history of tlie wt)rld, as at present
known, although of innnense length, will liereaiter be reco""-
nized as short, compared with the ages which must have
eUipsed since the first organic beings, the progenitors of in-
numerable extinct and living descendants, appeared on the
stay-e.

436 • CONCLUSIOxV. Cuap. XIV.

In the distant future I see open fields for far more impor-
tant researclics. Psychology Avill be based on a new founda-
tion, that of the necessary acquirement of each mental power
and capacity by gradation. Light Avill 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 cre-
ated. To my mind it accords better with what avc know of
the laws impressed on matter by the Creator, that the pro-
duction and extinction of the past and present inhabitants of
the world should have been due to secondary causes, like
those determining the birth and death of the individual.
"When I Adew all beings not as special creations, but as the
lineal descendants of some few beings which lived long be-
f<.)rc the first bed of the Silurian system was deposited, tliey
seem to me to become ennobled. Judging from the past, we
may safely infer that not one living species will transmit its
imaltcred likeness to a distant futurit}'. 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 be-
ings 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 connnon and widely-spread species, belonging to the larger
and.<l<)minant groups within each class, nvhich 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 Silurian epoch, we may feel certain that
the ordinary succession by generation has never once been
broken, and that no cataclysm has desolated the whole world.
Hence we may look with some confidence to a secure future
of equally inappreciable 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 perfec-
tion.

It is interesting to contemplate a tangled bank, clothed
with many plants of many kinds, with birds singing on the
bushes, witli various insects Hitting about, and Avith Avorms
crawling through the damp earth, and to reflect that these elab-
orately constructed forms, so dift'erent from each other, and
dependent on each other in so complex a manner, have all been
produced by laAvs acting around us. Tliesc laws, taken in the

Cir.u-. XIV. CONCLUSION. 437

largest sense, being Growth with Reproduction ; Inheritance
which is ahnost inipUed by reproduction ; Variahility from the
inchrcct and direct action of the conditions of Ufe, and from
use and disuse ; a Katio of Increase 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 Avhich we are capable of
conceiving, namely, the production of the higher animals, di-
rectly follows. There is grandeur in this view of life, with its
several powers, having been originally breathed by the Crea-
tor into a few forms or into one ; and that, while this planet
has gone cycling on according to the fixed law of gravity, from
so simple a beginning endless forms most beautiful and most
wonderful have been, and are being, evolved.

INDEX

Aberrant groups, 387.

AbvKsinin, plants of, 3-18.

Acclimatization, 111.

Atloxa, 12i).

Affinities of extinct species, 307.

of organic beings, 3S6.
Agassiz, on Amblj'opsis, 113.

on groups of species suddenly ap-
peiiriiiLT, 2'M.

on enibry<il()L'ical succession, 316.

on the (ilaci;il period, 837.

ou cnibrvological characters, 378.

on the lalep't tertiary forms, 2S2.

ou parallelism of embryological de-
velopment and geological bucccs-
sion, 534.
AIotj of Kew Zealand. 3-1.5.
Alligators, males. fii:li!iii'_', 91.
Alternate ji^eneralions, '.','.)[.
Amblyopsis. blind lish, 1 13.
America, North, productions allied to
tliose of Europe, 340.

North, bowlders and glaciers of, .343.

South, no modern formations ou west
coast, 275.
Ammcmites, sudden extinction of, .302.
Anagallis, sterility of, 235.
Analogy of variations, 100.
Ancylus, a")3.
Andaman Islands inhabited by a toad,

aj8.
Animals, not domesticated from being

variable, 30.
Animals, domestic, descended from sev-
eral stocks, .32.

domestic, acclimatization of, 11-4.

of Australia, 113.

with thicker fur in cold climates, 133.

blind, in caves. 111.

extinct, of Australia, 310.
Anoinma, 229.

Antarctic islands, ancient flora of, 303.
Ants atlondiiiL: aphides, 201.

sluve-TiKikiiii: instinct. 212.

neuter, strnctiire of, 22ti.
Aidiides, attended by ants, 203.
Aphis, development'of, 898.
Apteryx, 170.
Anil) horses, 41.
Arulo-C'aspian Sea, 317.

Archeopteryx, 288.

Archiac, M. de, ou the succession of spe-
cies, 3(M.
Artichoke, Jerusalem. 110.
Ascension, plants of, :i55.
Asclepias, pollen of, 185.
Asparagus, 3.32.
Aspicarpa. .377.
Asses, striped, 101.

improved by selection, 49.
Atenchus, 140.

Aucanitaine, ou land-shells, 301.
Audubon, on habits of friL'ate-bird. 178.

on variation in birds'-nests, 204.

on heron eating seeds, 351.
Australia, animals of, 113.

dogs of, 207.

extinct animals of, 310.

European plants in, 345.

glaciers of, 342.
Azara, on flies destroying cattle, 78.
Azores, flora of, 335.

Babington, Mr., on British plants, 57.
Baer, Von, standard of Iliirnness, 122.

comparison of bee and fish, 314.

embryonic similarity of the vertcbra-
ta, 395.
Balancement of growth, 149.
Barbeny, flowers of, 100.
BarrandV, !M., on Silurian colonies, 296.

on the succession of species, 205.

on parallelism of paleozoic forma-
tions, .307.

on afflnities of ancient species, 308.
Barriers, importance of, .323.
Bates, Mr., on mimetic butterflies, 884.
Batrachians on islands, 3.5S.
Bats, how structure acquired, 174.

distribution of, 3,")4.
Bear, catching water-insects. 176.
Beauty, how acquired, 194, 422.
Bee, sting of, 197.

queen, killing riv.nls, 197.

Australian, extermination of, 81.
Bees fertilizing flowers, 7'.).

hiye, not sucking the red-clover, 97.

Ligurian, 9S.

hive, cell-making instinct, 216.

variation in habits, 201.

INDEX.

439

Bees, humble, cells of, 217.

parasitic, 212.
Bcellpf", wiiifriffn, in MadciM, Ml.

with dcliciciit tnri<i, 110.
Dcutlinm, ^Ir., on Uritish plants, 57.

on claeslQcation, .'JTS.
Berkeley, Mr., ou seeds in salt-water,

a31.
Bermuda, birds of, 357.
Birds acquirin*; fear, 201.

beauty of, I'JO.

annually eross flic Atlantic, 3.3C.

color of^ ou continents, l.'iS.

footbteps, and remains of, in eecouda-
ry rocks, 2SS.

fossil, In caves of Brazil, 31C.

of Madeira, Bermuda, audCialapagos,
a")((.

8on<; of males, 01.

transportiu!,' seeds, 333.

waders, 353.

windless, 139, 17 k
Bizcaeli.i, .•}2l.

atllniti.'s of, 3S7.
Bladder for swimmin? in fish, 183.
Blinducss of cave animals, 142.
Blyth, Mr., ou distiuctuess of Indiau cat-
tle, 31.

on striped hcmionus, IGl.

on crossed geese. 2."i!(.
Borrow, Mr., on the Spai'isli pointer. 44.
Bory, St. Vincent, on lial i-icliijins, ;35S.
Bosquet, M., on fossil Clitlininaltis, 2,S!).
Bowlders, erratic, ou the ^Vzores, 333.
Brauchioc, 1&3, IRl.

of crustaceans, 187.
Brancliiostoma, 123.
Brent, Mr., ou liouso-tuinblera, 207.
Britain, mammals of, 300.
Bronu, Prof., ou duration of specific
forms, 2711.

Various objections by, 120.
Brown, Kobert, on classiiication, .375.

Seciuard, on iidieritod epilepsy, 140.
Buttcrllies, mimetic, ;iHl.
Buzareingucs, ou sterility of varieties,
25<J.

Cabbajje, varieties of, crossed, 101.
Calceolaria, 237.

Canary birds, sterility of hybrids, 2.38.
Cape do Verde islands, productions of,
.3(i3.

plants of, on mountains, 311.
Cape of (iood Hope, plants of. 133, 355.
Carpenter, Dr., on CKZonn, 291.

on foi-aminifcra, 313.
Cafasetum, 189, 381.
Cats, with blue eves, deaf, 26.

variation in habits of, 20,").

curlinj; tail wheu jjoin;^ to spring,
19.S.
Cattle destroyin? flr-trees, 78.

destroyed by flies in Panirruay, 78.

bn-eds of, locally extinct, KKI.

fertility of Indian and European
breeds, 2.39.

Indian, 31. 2.!9.
Cave, iuhabitauts of, blind, 112.

Cecidomyia, SO."*.

Celts, proviuj; antiquity of man, 31.

Centres of creation, 32(i.

Ccphalopodie, development of, 397.

Cervulus, 2:58.

Cetacea, teeth and hair, 117.

Cfvlon. plants of, ;>l(i.

Chalk formation, ;i03.

Characters, divergence of, 110.

sexual, variable, 152.

adaptive or analogical, 382.
Charlock, 81.
Checks to increase, 74.

mutual, 77.
Chickens, instinctive tamcncss of, 208.
(■Iithani;ilin;e, 273.

Clithaiiialus, cretaccan species of, 289.
Circumstunees favorable to selection of
domestic products, 48.

favorable to natural selection, 103.
Cirripcdes capable of crossing, 102.

carajjace aborted, 150.

their ovigerous freua, 183.

fossil, 28.><.

larvKi of, 396.
Clarke, Rev. W. B., on old glaciers in Aus-
tralia, 3t2.
Clnpsifiealion, 372,

('lilt. -Mr., on the succession of types, 316.
Climate, eftecta of, in checking increase
of beings, 75.

adaptation of, to organisms, 111.
Climbing plants, IS2.
Clover visited by b('es. 97.
Cobites, inti'stiiie of, 182.
Cockroacli, 81.

Colleclicms, jjaleontnloLrieal, poor, 273.
Color, inllucnced bv eliiiiate. 138.

in relation to ail icks by flies, 19.3.
Columba livia, parent of domestic pig-
cons, .35.
Colymbetes, 353.
Compensation of growth, 149.
Compositic, flowers and seeds of, 129.

outer and inner florets of, 148.

male flowers of, 40(j.
Conclusion, general, 429.
Conditions, slitrht changes of, favorable

to fertility, 253.
Converp:ence of genera, 132.
Coot, 177.
Coral-islands, seeds drifted to, .3.33.

reefs, indicating movements of earth,
293.
Corn-crake, 178.

Correlated variation in domestic produc-
tions, 25.
Coryanthcs, 1.h8.
Creation, single centres of, 32C
Criiium, 23fi.

Croll, Mr, on subaerial denudation, 269,
271.

on the age of our oldest formatious,
291.

on nlternnte Glacial periods in the
north and south, 31.3.
Crosses, reciprocal. 213.
Crossing of domestic animals, impor
taucc in altering breeds, 32, 33.

440

INDEX.

Croseincr, mlrantajrcs of, 00.

uiifiivorable to selection, 102.
CrnETcr, Dr.. on Coryanthes, 18tj.
Cnistacca of New Zealand, 345.
Crus'acenn, blind, \i'2.

nir- breathers, 18tj.
CryptocerujJ. a-2>!.
Ctenomvs, blind, 1 11.
t'lickoo," instinct of. 200.
("urrantp, praftsof. 2-15.
Currents of sea, rale of, 332.
Cuvier, on conditions of existence, 200.

on foBsil monkeys, 288.

Frcfl., on instinct, 201.
Cyclostouia, resisting salt-water, 3C2.

Dana, Prof, on blind cave-animals, lt.3.

on relations of crustaceans of Japan,
342.

on cnistaccans of New Zealand, 345.
Dawson, Dr., on cozoon, 202.
Do CandoUo, Aujr. Pyr., on etnissle for
existence, 70.

on nmbelliferic, 140.

<m frcneral affinities, .388.
Dc Candolle, Alpb., on the variability of
oaks, GO.

on low plants, widely dispersed,
307.

on widely-ranging plants being vari-
able, ()•).

on naturalization, 113.

on winged seeds, 149.

on Alpine species suddenly becoming
rare, KiO.

on distribution of plants with large
seeds, 3.32.

on vegetation of .\nstralia, 317.

on fresh-watvr plants, 353.

on insular i)lants, .3.55.
Degradation ol rocks. 269.
Deuudatioii, rate of, 271.

of oldest rocks, 202.

of granitic areas, 277.
Development of ancient forms, 313.
Devonian system, 311.
Dianthus. fertility of crosses, 241.
Dimorphism in plants, .55, 253.
Dirt ou feet of birds, :i34.
Dispersal, means of, 329.

during Glacial period, .3.37.
Distribution, geographical, .322.

means of, 330.
Disuse, effects of, under nature, 1.39.
Divergence of character, 110.
Diversification of means for same general

purpose, ISO.
Division. physioloL'ical. of labor, 113.
Dogs, hairless, with imi)orfect teeth, 26.

descended from several wild slocks,
32.

domestic instincts of, 207.

inherited civilization of. 207.

fertility of breeds together, 2.30.

■ of crosses, a5<i.

pmporticms of body in dlflferent
breeds, when young, 399.
Domestication, variation under, 22.
Double flowers, 227.

Downing, Mr., on fmlt-trees in America,

80.
Dragon-flies, intestines of, 182.
Drifi-timber. 32).
Driver-ant. 2-30.

Drones killed by other bees, 197.
Duck, domestic, wings of, reduced, 25.

logger-headed, 174.
Duckweed. 352.
Dugong, affinities of. 375.
Dung-beetles with deficient tarsi, 140.
Dytiscus, .353.

Earl, Mr. W., on the Malay Archipelago,

3(X).
Ears, drooping, in domestic animals, 26.

rudimentary. 408.
Earth, seeds in roots of trees, 333.

charged with seeds, 335.
Eciton, 228.

Economy of organization, 150.
Edentata, teeth and hair, 147.

fossil species of, 318.
Edwards, Milne, on physiological divis-
ion of labor, 122.

on gradations of structure, 190.

on cmbryological characters, 378.
Egsrs. young" birds escaping from, 90.
E'rypt.jiroductions of, not modified, 125.
Electric organs, 184.
Elephant, irate of increase, 72.

of Glacial period, 145.
Embrj'ology, 394.
Eozoon Caiiadense, 201.
Epilepsy inherited, 140.
Existence, sfrngu'le for, CO.

conditions of, 200.
Extinction, as bearing on natural selec-
tion, 114.

of domestic varieties, 118.

290.
Eye, stnictnre of, 170,

correction for aberration, 197.
Eyes, reduced iu moles, 1-12.

Fabre, M., on hymenopfera fighting, 91.

on parasitic sphex, 212.

on sitaris, 402.
Falconer, Dr., on naturalization of plants
in India, 73.

on elephants and mastodons, 311.

and Cautley, on mammals of snb-llim-
alavan beds, 317.
Falkland" Islands, wolf of, 359.
Fanlts, 270.
Faunas, marine, 323.
Fear, instinctive, in birds. 208.
Feet of birds, young mollusks adhering

to, :K2,
Fertilization varionslv effected, 188, 105.
Fertility ofhvbrids, 2.37.

from sliirlit changes in conditions, 252.
Fertility of crossed varieties, 257.
Fir-trees dcstroved by cattle, 78.

pollen of, 198.
Fish, flying. r.S.

teleostean, sudden appearance of, 290

catini,' seeds, 3.31, .3.51.

fresh-water, distribution of, 352.

INDEX.

441

Fl8hcB, canoid, now confined to frceh-
wator, 107.
electric orirans of, ItC).
ganoid, living in frcHli-wntcr, 302.
of Boutlicrn licminplu're, 'H'>.
Flight, powers of, liow acquired, 17.5.
P'liiit tools, provini; antiquity of man, 31.
Florida, pi^'s of, 89.

FlowerH, flrutiure of, in relation to
crosfin}:. 95.
of composita; and umbellifene, 146.
beauty of, 195.
double, 2*27.
Flyech formation, destitute of organic re-

niaiuB, 273.
Forbcp, Mr. D.. on glacial action in the
Andes. iU:i.
E., on colors of shells, l.'Jft.
on abrupt range of bliella in depth,

lot.

on jioomess of palcontological col-
lections, 273.
on coutiuuous succession of genera,

29S.
on ronfinental extension. 330.
on distribution during Glacial period,

:W7.
on parallelism in time and spnce, 370.
Forests, chanires In. in America, 80.
Formatiim, Devonian, 311.

Cambrian with monocotyledonous
plant, 201.
Formations, Ihirkness of, in Britain, 271.

intermittent, 280.
Formica ntfesceiis, 212.
sanguinea, 213.
flava, neuter of, 220.
Forms, lowly organized, long-enduring,

124.
Frena, ovi^crons. of cirripedea. 183.
Fresh-water productions, dispersal of,

351.
Fries, on species and large genera being

clbsely allied to other species, 60.
Frigate-bird, 178.
Frogs on islands. .S.W.
Fruit-trees, gradual improvement of, -15.
in United States, SO.
varieties of, acclimatized in United
States, 110.
Fuci, crossed, 219.
Fur, thicker in cold climates, 1.38.
Furze, 395.

Oalapasos Archipclaco. birds of, 30C.

productions of, 302, .304.
Galeopitliccus, 174. *

tiame, increase of. checked by vermin. 7.'.
tiiirtner, on sterility of hyhrills, 2.3.5, 210.

on reciprocal crosses. 212.

on crossed maize and verbasrnm. 2.50.

ou com|)arison of hybrids and mon-
trrels, 2(il.
Oaudrj-, Prof., on Intermediato genera of

rossil mammals. :i0s.
Geese, fertility when crossed, 2.39.

upland. 177.
fSeikle, Mr., on subaTrial deiindation,269.
3encalogy important in claselflcation, ii?0.

Generations, alternate, 304.

GeolTrov St.-llilaire, on balancement, 110.

on nonioloL'ODs organs, 391.

Isidore, on variability of repeated
parts, 151.

on correlation, in monstrosities, 20.

on correlation, 147.
GeoflVoy .st.-llilaire, Isidore, on variable

parts being oltcn monstrous, 155.
Geographical distribution, 322.
Geograpliy, ancii'iit, 4;i5.
Geology, future iirogrees of, 435.

imperfection of the record, 200.
GiraflTc, tail of, 191.
Glacial period. 3.37.

aflfecling the North and South, 450.
Gmelin, on dii^tribution, .337.
Godwin-Austen. Mr., ou the Malay Archi-
pelago, 284.
Goethe, on compensation of growth, 142
Gomphia. 131.
Gooseberry, grafts of. 245.
Gould, Dr. Aug. A., on land-shells, 301.

Mr., on colors of birds. l:}8.

on instincts of cuckoo, 211.

on distribution of genera of birds, .300.
Gourds, crossed, 250.
Graba, on the Uria lacrymans, 94.
Grafts, capacity of, 245.
Granite, areas of denuded, 277.
Grasses, varieties of, 112.
Gray, Dr. Asa, on the variability of oaks,
00.

on man not causing variability, 81.

on sexes of the holly, 97.

on trees of United States, 101.

ou naturalized plants in the United
States. 113.

on wstivation. 130.

on rarity of intermediale varieties,
170.

on Alpine plants. 337.

Dr. J. E., on stripeil mule, 10;5.
Grebe, 177.

CJroups, aberrant, .387.
Grouse, colors of, 88.

red, a doubtful species. 58.
Growth, compensation of, 149.
Giiuther, Dr., on the lishcs of Panama, 323.

Haast. Dr., on glaciers of New Zealand,

:i42.
nabit. effect of. nnder domestication, 25.
effect of. under nature. 13!).
diversitled, of same species, 17.5.
Iliickel, Prof., on classiflcation and the

lines of descent, :«)0.
Tlairand teeth, correlated. 147.
llarcourt, Mr. E. V.,on birds of Madeira,

:J57.
IlartunL'. M., on bowlders in the Azores,

3;i5.
Hazel-nuts. .3.31.

Hearne, on habits of bears, 170.
Ili-ath. clmntes in veL't'lation, 77.
lleer Oswald, on ancient cultivated plant.s

80.
on plants of Madeira, 100.
Ileliiuithemum, 131.

442

INDEX.

Helix pomalia. Hfil.

Ili'loscmdium, 3.T.J.

Ilciniomis. eiriix'd, KIO.

Herhort, W.. on stru£ri.'Io foroxistencc, 70.

on Picrilitv of hybrids. 2.3(5.
ITccior, Dr., on glaciers of New ZcaLind,

llormaphroditcs cropiiinsr. 98.
Ilclix, res>i*tin','t^nlt-\vater, 361.
Heron enlin^ seed, .354.
Heron, Sir K., on peacockp. 92.
Heusinsrer. on white animals poisoned by

certain plant?, 2(5.
Hewitt. Mr., on sterility of first crosses,

249.
Hildcbrand. Prof., on the self-sterility of

Corvdalis, 2;«.
Hilprcndorf, on intermediate varieties, 278.
Himalaya, jrlaciors of, 342.

plants of, .34.1.
Hippeastrnm, 2-37.
Hollv-trees, sexes of, 9<>.
Hooker, Dr.. on trees of New Zealand, 101.

on acclimatization of Himalayan
trees, 144.

on flowers of umbellifene, 148.

on placiers of Himalaya, 342.

on alpc of New Zealand. 34."i.

on ve^'ctation at the base of the Him-
alaya, 3-l(;.

on plants of Tierra del Fiiecro, 3+1.

on Australian plants, 31(), .3(1'!.

on relations of flora of .America, 347.

on flora of the Antarctic lands, 349,
.303.

on the plants of the Galapagos, 357,
302.

on glacicys of the Lebanon, 342.

on uinn not causin<r variability, 84.

on plants of mountains of Fernando
Po, 345.
Hooks on palms, 192.

on seeds on islands. 3.-)8.
Hopkins, Mr., on denndation, 277.
Hiirnbill, remarkable instinct of, 232.
Horns, rudimentary. 408.
Horse, fcissil, in L.a" Plata, 299.
Horses destroyed l)y flies in Paraguay, 78.

striped. 102.

projiortions of, ivhen young, .399.
Horticulturists, selection "applied by, 42.
Huber, on cells of bees, 221.

P.. on reason blended witli instinct,
201.

on habitual nature of instincts, 202.

on slnye-makiiig ants, 212.

on Melipona doniestica, 217.
Humble-bees, cells of, 217.
Hunter, J., on secondary sexual char-
acters, 152.
HuKon, Captain, on crossed geese, 239.
Huxley, Prof., on stnicture of hermaph-
rodites, 102.

on forms connecting birds and rep-
tiles, .308.

on homologous organs, 394.

on I lie development of aphis, 398.
Hybrids and mongrels compared, 260.
Hybridism, 2;«.

Hydra, slructnre of, 182.
Hymenoptera, fighting, 91.
Hymenopterous insect, diving, 177.

Hila, 150.

Icebergs transporting seeds, 3.35.
Increase, rate of, 71.

Individuals, numbers favorable to se.ec
tion, 103.

many, >vhether simultaneously cre-
ated, .329,
Inheritance, laws of, 27.

at corresponding ages. 27. 89.
Insects, color of, fitted for habitations, 88.

sea-side, colors of, 138.

blind in caves, 142.

luminous, 185,

neuter, 226.
Instinct, 201.

not varying simultaneously with
strncture, 223,
Instincts, domestic, 205.
Intercrossing, advantages of, 98.
Islands, oceanic, 35.5.
Isolation favorable to selection, 104.

Japan, productions of, 342.

Java, plants of, .345.

Jones, Mr. J. M., on the birds of Ber-
muda. .357.

Jourdain, M.. on the eve-spots of star-
fishes, 179.

Jukes, Prof., on subaerial denudation,
2<i9.

Jnssieu, on classification, ,377.

Kentnckv, caves of. 142.
Kercuelen-land, flora of, 349, 3^3.
Kidney-bean, acclimatization of, 146.
Kidneys of birds. 141.
Kirby, on tarsi deficient in beetles, 140.
Knight, Andrew, on cause of variation,

22,
KOlreuter, on the barberry, 100.

on sterility of hybrids. 2.34.

on reciprocal crosses, 242.

on crossed varieties of nicotiana, 2.')9.

on crossing male and hermaphrodite

flowers, 405.

Lamarck, on adaptive characters, 383.
Laucelet, 12.3.

eves of, ISO.
Land-shells, distribution of. 361.

of Madeira, naturalized. 305.

resisting salt-water. 362.
Languages, classification of, 380.
Lapse, great, of time, 268.
Larrip, 396.

Laurel, nectar secreted by the leaves, 95.
Lanrentiau foi-mation. 291.
Laws of variation. 137.
Leech, varieties of, 81.
Leguniinoste, nectar secreted by glands,

95.
Leibnitz's attack on Newton, 430.
Lepidosircn, 107. 308.

limbs in a nascent condition, 406.

INDEX.

443

Lcwcs, Mr. G. II., ou the Salamandra atra,
405.
on many forms oTlifc having been at
flrnt evolved, -i:}-.'.
Life, Ptriit,'L'lc lor, 70.
Linf,'ula, .Silurian, 290.
LinuiruH, aphorism-of, 371.
Lion, mane of, 91.

vonnjj of, striped, 095.
Lobelia ful;,'ens, 79. 1(K). . .

Lobelia, sterility of crosses, 2.17.
LoeuKtf". transport in;; seeds, 331.
Lo;;au, Sir W., ou Laurentian formation,

292.
Lowe, IJev. R. J., on locusts visiting Ma-
deira, XU.
Lowncss of Btrncture connected with vari-

abillly. 151.
Lowncss, related to wide distribution,

3(i7.
Lubboek, Sir J., on the nerves of coccus,
51.
on seeondary sexual characters, 157.
on a divini,' li vmenoptcrous insect, 177.
on aninitics,"2HS.
on nu'taniorpho-es. .391, .390.
Lucas, Dr. P.. on inherit.nncc, 27.

on resemblance of child to parent. 2(J-3.
Lund and Clausen, on fossils of Brazil,

MH.
Lyell, Sir C, on the stniggle for exist-
ence, 70.
on modem changes of the earth, 98.
ou a carboniferous land-shell, 274.
on strata beneath Silurian system,

291.
on the imperfection of the geological

record, 291.
on the appearance of species, 294.
on Barrande's colonies, 29f).
on tertiary formations of Knropc and

North .\merica, 303.
on i)arallelism of tertiary formations,

307.
on transport of seeds by icebergs. 335.
on great alternationH of climate, ;J50.
on the distribution of fresh-water

shells, a-)3.
on land-shells of Madeira, STto.
Lvcll and Dawson, on fossilized trees in

Nova Scotia, 2H1.
Lythrum salicaria trimoqihic, 255.

Macleay, on analogical characters, ;jfl3.
^IcDonni'll, Dr., on electric organs, 181.
JIadcira, jilaiits of, 1(»7.

beetles of, wingless, 110.

fos^.il land-shells of, 317.

birds of, ;i57.
Magi)ie, tame, in Norway, 205.
Males ngliting. 91.
Maize, crossed. 258.

Malay .\rchipelago compared with Eu-
rope, 2H1.

mammals of. .3*!0.
Malpighiacea>, small imperfect flowers of,
12'J.

377.
Mammn, rudimentary, 405.

Mammals, fossil, in secondary formation,
288.

insular, 3.59.
Man, origin of races of. 193.
Manatee, rudimentary nails of, 408.
Marsupials of .Vustralia, 113.

fossil species of, 316.
Martens. ^1.. experiment on seeds, 332.
Martin, Mr. W. C, on striped mules, 163
Masters, Dr., on Sanonaria, 131.
Matteucci, ou the electric organs of rays

187.
Matthiola, reciprocal crosses of, 212.
Means of dispersal, .331.
Melipoiia domestica, 217.
^IiTrell, Dr., on tlie American cuckoo, 209.
M(tiiinori)liism of oldest rocks, 292.
>lice destroying bees, 80.

accliinafizaticm of. 14.5.
Miller. Prof., on tlie cells of bees, 218,221.
Mirabilis, erot^ses of, 242.
Missel-tlimsh, 81.
Mistletoe, complex relations of, 19.
Mockiiig-tlirnsli of the Galapagos, ;)66.
Modification of species, how far applica-
ble. 431.
Moles, blind, 141.
Mongrels, fertility anil sterility of, 256.

and hybrids compared, 200.
Monkeys, fossil, 2.S.S.
ISIonachauthus. 381.

Mons Van, on the origin of fruit-trees, .39.
Monstrosities, 52.

Monquin-Tandon, on sea-side plants, 1.38.
MorplioloL'v. .31)0.
Mozart, musical powers of, 202.
Mud, seeds in, ,3.M.
Mules, striped, 163.

Muller, Dr. Ferdinand, on Alpine Aus-
tralian plants, 352.
Miiller, Fritz, on dimorphic crustaceans,
55, 230.

on the lancelet, 124.

on air-breathinir crustaceans, 1S6.

on the self-sterility of orchids, 2.37.

on embryology in relation to classifi-
cation ,378.

on the metamorplioscs of crustaceans,
398. 403.

on terrestrial and fresh-water organ-
isms not undergoing any metamor-
phoses, 401.

on the metamorphoses of insects, 402.
Multiplication, indetlnife, of species, 132.
Murchison, Sir K., on the formations of
liussia. 274.

on iizoic formations, 291.

on extinction, 2'.>9.
Murray, Mr. A., on cave-insects, 143.
-Mustela vision, 173.
Myan thus. 381.
Myrmecocystus. 22-''.
Myrmica, eyes of, 229.

Nilgeli, on morphological characters, 129.
Nails, rudimentary, 40.S.
Nathusius, Von, rm pigs, 19.3.
Natural history, future progress of, 4;J3.
selucliou, hi.

444

INDEX.

Kat.iirnl pvptom, 374.

Is'atunilizntion of forms distinct from tlie
iii(lif;ei)0U8 species, ll.'J.

in New Zealand, l'.»7.
Naudin, on analof,'ou3 variations in
gourds, 15'.t.

on hyhrid f^ourds, S259.

on reversion, 'M.
Nantilus, Sihirian, 290.
Nectar of plants, il.j.
Nertaries, how formed, 93.
Nelumbinm lutenm, :io4.
Nests, variation in, 204, 22o, 2.31.
Neuter insects, 22(i.
Newman, Colonel, on hnmble-hees, 79.
New Zealand, productions of, not per-
fect, 197.

naturalized products of, 315.

fossil birds of. .317.

placiers of, .342.

cnistaceans of, 345.

alpn of, 315.

number of plants of, 355.

nora of, 363.
Newton. Sir I., attacked for irrelip;ion, 429.

Prof, on earth attached to a par-
tridge's foot, .3.35.
Nicotiana, cros-ed varieties of, 2fi0.

certain species very sterile, 242.
Noble, Mr., on fertility of Rhododendron,

237.
Nodules, phosphatic, iu azoic rocks, 291.

Oaks, variability of fiO.

(Enonis, small imperfect flowers of, 129.

Onites ap|)elles, 1 10.

Orchestia, dimorphic, .5.5.

Orchids, fertilization of, 188.

forms of, 381.
Orchis, pollen of, 1S.5.
Oriranization, tendency to advance, 121.
Orjjans of extreme perfection, 178.

electric, ofllshes, 18.5.

of little importance, 190.

homoloijous. 391.

nidimcnts of, and nascent, 4W.
Ornithorhynchus, 107, 3T(i.
Ostrich not capable of lliirht, 140.

habit of laying eggs together, 212.

American, two species of, 321.
Otter, habits of. how acquired, 173.
Ouzel, water, 17fi.
Owen, Prof, on birds not flying, 139.

on vegetative repetition", 151.

on variability of unusually developed
parts, 152.

on the eyes ofllshes, ISO.

on the swim-bladder ofllshes, 1S3.

on the brancbiie ofcirripedes, 183.

on electric organs. 181.

on fossil horse of La Plata, 300.

on relations of ruminants and pachy-
derms, 307.

on fossil birds of New Zealand, 317.

on succession of types, 31R.

on alliiiities of the dugong, 374.

on homologous organs, 391.

on the mclamorphoaU of ccphalo-
pods, 397.

Pacific Ocean, fannas of, .32'1.

Pacini, on electric organs, ls,5.

Paley, on no organ formed to give pain,

190.
Pallas, on the fertility of the domesticated

descendants of wild stocks, 239.
Palm with books, l!^i
Paraguay, cattle destroyed by flics, 78.
Parasites, 212.
Partridge, with ball of earth attached to

foot, .331, .3.35.
Parts greatly developed, variable. 152
Parus major. 176.
Passiflora, 2:30.
Peaches in United States, 89.
Pear, grafts of 2-15.
Pelargonium, flowers of, 148.

sterility of, 237.
Pelvis of women, 147.
Peloria, 148.
Period, glacial, .3:57.
Petrels, habits of, 177.
Phasianus, fertility of hybrids, 239.
Pheasant, young, wild, 208.
Phillips, Prof, on fresh-water shells,

.314.
Pictct, Prof., on groups of species sud-
denly appearing, 286, 287.

on rate of organic change, 296.

on continuous succession of genera,
298.

on change in latest tcrtiory forms, 282.

on close alliance of fossils in consec-
utive formations, 312.

on early transitional links, 287.
Pierce, Mr., on varieties of wolves. 93.
Pigeons with feathered feet and skin be-
tween toes. 26.

breeds described, and origin of, 3.3.

breeds of, how produced, 46, 49.

tumbler, not being able to get out of
cgc:. 90,

reverting to blue color. 161.

instinct of tumbling, 207.

young of, 399.
Pigs, black, not aflected by the paint-
root, 26.

modified by want of exercise, 193.
Pistil, rudimentary, 105,
Plants, poisonous", not affecting certain
colored animals, 26.

selection applied to, 42.

gradual improvement of. 45.

not improved in barbarous countries,
46.

destroyed hy insects, 75.

dimorphic, 55, 2,5;J.

in midst of range, have to strugijla
with other plants, 82.

nectar of, 95.

fleshy, on sea-shores, 138.

climbing, 182.

fresh-water, distribution of, .35.3.

low in scale, widely-distributed, 307.
Plumage, laws of change in sexes of

birds, 92,
Plums in the United Slates, 89.
Pointer dog. origin of, 44.

habits of, 207.

INDEX.

445

Poison not nfTccting certain colored nni-

nialn. 'X.
eimilar effect of, on animals and

plants, -IIK.
Pollen of flr-treea, 198.

transported by various means, 188,

1!)5.
Pool, Colonel, on striped hcmionns, 162.
Potamoireton. :V>1.
PreBlwich. Mr., on Knijlisli and French

eocene formations, .'JUO.
Proctotrupes, 177.
Proleolepas, 150.
Protens, 1 13.
Tsycbology, future progress of, 4;3C.

Quap^a, striped, 16.3.
(Jnerens, variability of, CO.
Quince, grafts of, 245.

Rabbit, disposition of young, 207.
Kiices, domestic, characters of, 29.
Kace-horses, .\n»b, 4-1.

English, 329.
Hamond, on ])lants of Pyrenees, S3f<.
lliimsay. Prof., on suba'erial denudation,
209.

on thickness of the British forma-
tions. 271.

on faults, 270.
Kamsay. Mr., ou instincts of cuckoo, 282.
Ratio of increase, 71.
Itats supplant ini: each other, 81.

acclimatization of, 145.

blind in cave, 142.
Rattlesnake, 19«.
Reason and instinct, 201.
Recapitulation, general, 412.
Reciprocity of crosses, 242.
Record, gcoloirical, imperfect, 2fi6.
Reng^rer on (lies destroying cattle, 78.
Jti'produclion, rate of, 71.
Resemblance to parents in mongrels and

hybrids, 2(jl.
Reversion, law of inheritance, 28.

in i)igeons to blue color. 100.
Rhododendron, sterilitv of, 2.'J.S.
Itichard, Prof., on Asp{caii)a. 377.
Richardson, Sir. J., on structure of
squirrels. 173.

on llshes of the southern hemispliere,
3t5.
Robinia, grafts of, 245.
Rodents, blind. 141.

Roi.'ers.Pri»r.,Mnp of North America, 277.
Itudimentarv organs, 404.
Rudiments iuiportuut for classification,

37C.
RQtimeyer, on Indian cattle, 31, 239.

Balnmandm atra, 405.

Saliva used in nests. 225.

Sageret on grafts, 245.

Salmons, males, fighting, and hooked

jaws of, 91.
Salt-water, how far injurious to seeds,

3.32.
not destructive to landehells, SCI, 3C2.

Salter, Mr., on early death of hybrid cm

bryos, 249.
Sanrophagus suli)hnrntiis, 17(>.
Schiodte, on blind insects, 112.
Schlegel, on snakes, 147.
Scott, J., Mr., on the self-sterility of or-
chids, 2.37.

on the crossing of varieties of ver
bascnm, 2.59.
Sea-water, how far injurious to seeds. 332.

not destructive to land-shells, 361, .362.
Sebright, Sir J., on crossed animals, 32.
Sedgwick, Prof., on groups of species

suddenly appearing, 2,sC.
Seedlings destroyed by insects, 74.
Seeds, nutriment in, 82.

winged, 149.

means of dissemination, 187, 194, 2.34.

powers of resisting salt-water, 3.32.

in crops and intestines of birds, 333.

eaten by fish, 334, 355.

in mud, 353.

hooked, on islands, 358.
Selection of domestic products. 40.

principle not of recent origin, 4.3.

unconscious, 43.

natural, 84.

eexnal, 90.

objections to term. 85.

natural, has not induced sterility, 2-16.
Sexes, relations of, 90.
Sexual characters variable, 156.

selection, 90.
Sheep, Merino, their selection, 41.

two sub-breeds unintentionally pro-
duced, 44.

mountain, varieties of, 81.
Shells, color of. ViS.

hinges of, 188.

littoral, seldom embedded, 273.

fresh-water, long retjiin the same
forms, .314.

fresh-water, dispersal of, 353.

of Madeira. 3.'J7.

land, distribution of, ^58.

land, resistin'T salt-water, .361, .362.
Silene, infertility of crosses, 241.
Silliman, Prof., on blind rat. 142.
Sitaris, metamorphosis of, 402.
Skulls of young mammals, 192, 303.
Slave-makiiiir instinct, 212.
Smith, Col. Hamilton, on striped horses,
163.

Mr. Fred., on slave-making ants, 214.

on neuter ants. 229.
Snake with tooth for cutting through egg-
shell, 212. ^ ^^
Somerville, Lord, on selection of slicep,

41.
Sorbns, grafts of, 215.
Spaniel. "King Charles's breed, 44,
Specialization of organs. 121.
Species, polymorphic, M.

dominant, M.

common, variable, 62.

in large grneni variable. Gt.

groups of, suddenly ap|)earing, 28G
289.

beneath Silurian formations, 291.

440

INDEX,

Species Hnccci'sivi-ly appearinjr, 205.

clmn^'ini; riiinultaneously tliroii'^hout
the world, M-i.
Ppenccr, Lord, on increase in size of cat-
tle, 44.
Ucrbcrt. Mr., on the first steps indif-

feri'ntialion, liO.
Mr. II., on tin? tendency to an equi-
librium in all forces, 252.
Sphex, parasitic, 212.
Spiders, development of. .3^7.
Spilz-doi; crossed with fox, 2o7.
Sports in plants, 25.
Sprengel, C. C, on crossing, 100.

on ray-florets, 118.
Squirrels, sradafions in structure, 174.
Si;ifri)rdsliirc, heath, changes iu, 77.
Stag-beetles, fighting. 91.
Star-fishes, eyes of, 179.
Sterility from changed coaditions of life,
2i.
of hybrids, ?.3.3.

' , laws of, 240.

, causes of, 246.

from unfavorable conditions, 251.
not induced through natural selec-
tion, 2ir,.
S;. Helena, productions of, 350.
St.-Ililaire, Aug., variability of certain
plants, i:50.
on classification, 377.
St. John, Mr., on habits of cats, 205.
Sting of bee, 197.
Slocks, aboriginal, of domestic animala,

32.
Strata, thickness of. in Britain, 271.
Stripes on horses, 162.
Structure, degrees of utility of, 19 1.
Straggle for existence, 69.
Succession, geological, 295.
Succession of types in same areas, 316.
Swallow, one species supplanting an-
other, 81.
Swifts, nests of, 225.
Swim-bladder, 183.
Switzerland, lake habitations of, 31.
System, natural, 374.

Tail of giraffe, 191.

of atpuitic animals, 191.

rudinientarv, 408.
Tanais, dimorpliic, 55.
Tarsi deliciciit. 1 li).
T.Miscli, on umlu'lliferjc, 129.
Tectli and l.nir correlated, 147.

rudimentary, in embryonic calf, 406.
428.
Tciretmeier, Mr., on cells of bees, 219, 223.
Temminrk on distribution, aiding classi-

llcation. 378.
Thompson, Sir W., on the age of the hab-
itable world, 272, 2tW.
Thoiiin, on grafts, 215.
Thrush, aquatic species of, 177.

mocking, of the (}alai)agos, 366.

young of. spotted, 395.

nest of, 232.
Thuret, M., on crossed faci. 242.
Thwalles, Mr., on acclimatization, 144.

Tierra del Fuego, dogs of, 207.

plants of, .319.
Timber-drift, a33.
Time, lapse of, 268.

by itself not causing modification, 10.5.
Titmouse, 176.
Toads on islands, 358.
Tobacco, crossed varieties of, 259.
Tomes, Mr., on the distribution of bats,

360.
Torell. on a monocotyledonous Cambrian

plant, 291.
Transitions in varieties rare, 168.
Trautschold, on intermediate varieties,

279.
Trees on islands belonging to peculiar
orders, :J57.

with separated sexes, 101.
Trifolium pratense, 79, 97.

incamatum, 97.

Trigonia, 302.

Trilobites. 290.

sudden extinction of. 302.
Triraorphism in plants, 55, 253.
Troglodytes, 232.
Tuco-tuco, blind, 141.
Tumbler, pigeons, habits of, hereditary,
207.

young of, 400.
Turkey-cock, tuft of hair on breast, 92.

nakotl skin on head, 192.

young of, instinctively wild. 208.
Turnip and cabbage, analogous variationa

of, 159.
Type, unity of, 200.
Types, succession of, in same areas, 316.

Udders enlarged by use, 25.

rudimentary, 405.
nex, young leaves of, 395.
Umbeilifene, flowers and seeds of, 129.

outer and inner florets of, 148.
Unity of type, 200.
Uria lacrymans, 94.
Use, effects of. under domestication, 26.

eflVcts of, iu a state of nature, 139.
Utility, how far important in the con-
struction of each part, 193.

Valenciennes on fresh-water fish, 352.
Variability of mongrels and hybrids, 260.
Variation under domestication, 22.

caused by reproductive system being
afTected by conditions of life, 23.

under nature, 52.

laws of, 137.

correlated, 25. 1 16, 194.
Variations appear at corresponding ages,
27, 89.

analogous in distinct speciea, 15S.
Varieties, natural, 52.

struggle between, SO.

domestic, extinction of, 109.

transitional, rarity of, 168.

when crossed, fertile, 257.

when crossed, sterile, 256.

classification of, 381.
Verbascum. sterility of. 2.37.
Vcrbascum, varieties of, crossed, 259.

INDEX.

447

Verlot, M., on double stocks, 227.
Vcnieul, M. dc. on the succession of

species, ;J04.
Viola, email imperfect flowers of, 129.

tricolor, 7!t.
Vlrcliow, on the structure of the crj-stal-

line lens, l!>().
Volcanic islands, denudnllon of. 270.
Vulture, naked skin on head, l!t2.

Wadincr-birds, .3,'J.3.

Wagner, Moriiz, on the importance of iso-
lation, 105.
on Cecidoniyia, .3M.
Wallace, Mr., on ori^'in of species, 17.
on the limit of variaiiou under do-
mestication, 50.
on laws of gcojjraphical distribution,

32!t.
on the Malav .Vrchtpela^o, HOO.
on dimorj)hic Icpidopterji, 55, 2.30.
on races in the Malay Archipelago, 57.
on mimetic animals, 38(!.
Walsh. Mr. B. D., on phytophagic forms,
58.
on equable variability, 1.5ft.
Water, fresh, productions of, 351.
Water-hen, 177.

Waterhouse, Mr., on Australian marsu-
pials, 113.
on LTcatly-developcd parts being vari-
able, 152.
on the cells of bees, 217.
on general afflnities, 387.
Water-ouzel, 177.

Watson, Mr. II. C, on range of varieties
of British plants, 07.
on acclimatization, 111.
on tlora of Azores, .33.5.
on Alpine plants, 3.38.
on rarity of intermediate varieties,
170.
. on convergence, 132.
on the indefinite multiplication of
species, 132.
Weale, Mr., on locusts transportingseeds,

;m.

Web of feet in the water-birds, 177.
Weismann, Prof., on the causes of vari-
ability, 2.3.

on morphological characters, 127.

on nidiincntary organs, 408.

West-Indian Islands, mammals of, .360.
Wcstwood, on species in large genera be-
ing closely allied to others, (iO.
on the tar^i of Kn-ridie, ].")7.
on the antenna; of hymeuopterous in-
sects, 375.
Wheat, varieties of. 111.
White Mountains, flora of, 337.
Whitlaker, Mr., on lines of escarpment,

Wichura.Max. on hybrids, 250, 251, 261.
Wings, reduction of size, 140.

of insects homologous with branchise,

18;^.
nidimentarv, in insects, 405.
Wolf crossed w'ilh dog, 200.

of Falkland Isles, 35!).
WoUaslon, Mr., ou varieties of insects,
58.
on fossil varieties of shells in Ma-
deira, 62.

on colors of insects on sea-shore, 138,
on wingless beetles, 141.
on rarity of intermediate varieties

170.
on insular insects. .3."5.
on land-shells of Madeira, naturalized
300.
Wolves, varieties of, 0.3.
Woodcock, with earth attached to leg, 3.35,
Woodpecker, habits of, 170.

green color of, 102.
Woodward, Mr., on the duration of spe
citic forms, 279.
on the continuous succession of gen-

era, 208.
on the succession of tyjies, 317.
World, sijccios changing simultaneously

throughout. :j03.
Wrens, nest of, 232.

Wyniaii, Prof., on correlation of color and
eft'ect of pcison, 20.
on the cells of the bee, 218.

Yonatt, Mr., on selection, 41.
on sub-breeds of sheep, 44.
on rudimentary horns in young cat-
tle, 408.

Zanthoxylon, 1,30.
Zebra, strii)e8 on, 102.

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advanced, iho published volumes being: Firel I'rindples, T/ie Princ/jiles cf lii-
olo'jy, (wo volumes, and The Principles of PsyclLology, vol. i., which will bo
shortly printed.

This philosophical system differs from all its predecessors in being solidly
bised on the sciences of observation and induction ; in representing the order
and course of Nature ; in bringing Nature and man, life, mind, and society, under
one great law of action ; and in developing a method of thonglit which may serve
for praclical guidance in dealing with the affairs of life. That Mr. Spencer is tho
man for this great work will bo evident from the following statements :

"The only complete and systematic statement of the doctrine of Evolution
with which I am acquainted is tliat contained in Mr. Herbert Spencer's 'System
of Pliilosophy ; ' a work which should be carefully studied by all who desire to
know whither scientific thought is tending."— T. II. IIuxley.

" Of all onr thinkers, he is the one who has formed to himself the largest new
scheme of a systematic philosophy." — Prof. Masson.

"If any individual influence is visibly encroaching on Mills in this country, it
iB his." — Ibid.

" Mr. Spencer is one of the most vigorous as well as boldest Ihkikers that
English speculation has yet produced." — Joiix Stuaut Mo,!..

" One of the acutcst nietaphysiciaus of modern times." — Ibid.

"One of our deepest thinkers."— Dr. Joseph D. IIooker.

It is questionable if any thinker of liner calibre has appeared i.i onr coun-
try."—QEonoE IIentiy Lewes.

"He alone, of all British thinkers, has organized a philosophy."— /77rf.

"lie is as keen an analyst as is known in the histoiy of philotophy ; I do not
esccpt either Aristotle or Kant."— George Kiplet.

"If we were to givo our own judgment, we should say that, since Newton,
there has not in England been a philosopher of more remarkable speculative and
«ysteraatizing talent than (in spite of some errors and some narrowness) Mr. Iler-
bcrt Spencer."— £.on</on Saturday lieview.

" We cannot refrain from offering onr tribute of respect to one who, whether
for the extent of his positlvo knowledge, or for the profundity of his spcculutivo
ln.«lj?ht, has already achieved a name second to none In the whole ningt of Ensr-
lleh pliilosopliy, and whoi^e works will worthily sustain the credit of EnLjUsb
thought in <hc present gwierallon."— Westminster lieview.

D. AppUton rC Companifa Piiblications.

LAY SERMOI^^!S,
ADDllESSES, AND EEYIEWS,

By THOMAS EEXRY HUXLEY.

Cloth, 12mo. 390 pages. Price, $1.75
Tins is tlie latest and most popxilar of the ■works of this in-
trepid and accomplished English thinker. The American edition
of the work is the latest, and contains, in addition to the English
edition, Professor Huxley's recent masterly address on " Spon-
taneous Generation," delivered before the British Association for
the Advancement of Science, of which he was president.
The following is from an able article in the Independent :

The " Lay Sermons, Addresses, and Reviews " is a book to be read
by every one who would keep up with the advance of truth — as well by
those who are hostile as those who are friendly to his conclusions. In
it, scientific and philosophical topics are handled with consummate abil-
ity. It is remarkable for purity of style and power of expression. No-
where, in any modern work, is the advancement of the pursuit of that
natural knowledge, which is of vital importance to bodily and mental
well-being, so ably handled.

Professor Huxley is undoubtedly the representative scientific man of
the age. His reverence for the right and devotion to truth have estab-
lished his leadership of modern scientific thought. He leads the beliefs
and aspirations of the increasingly powerful body of the younger men of
science. His ability for research is marvellous. There is possible no more
equipoise of judgment than that to which he brings the phenomena of
Nature. Besides, he is not a mere scientist. His is a popularized phi-
losoi)liy ; social questions have been treated by his pen in a manner most
masterly. In his popular addresses, embracing the widest range of top-
ics, he treads on ground with which he seems thoroughly familiar.

There are those who hold the name of Professor Huxley as synony-
mous with irreverence and atheism. . Plato's was so held, and Galileo's,
and Descartes's, and Newton's, and Faraday's. There can be no greater
mistake. No man has greater reverence for the Bible than Huxley. No
one more acquaintance with the text of Scripture. He believes there is
definite government of the universe ; that pleasures and pains are distrib-
uted in accordaTice with law ; and that the certain proportion of evd
woven up in the life even of worms will help the man -.rho thinks to bear
his own share with courage.

In the estimate of Professor Huxley's future influence upon science,
Ills youth and health form a large element. He has just passed his forty-
fiflh year. If God spare his life, truth can hardly fail to be the gainer
from a mind that is stored with knowledge of the laws of the Creator's
operations, and that has learned to love all beauty and hale a.^ rileucss of
Nature and art.

Works of Herbert Spencer puldialied by D. Appktoii d: Co.

ILLUSTRi.TIONS OF UNIVERSAL PROGRESS.

A SERIES OF DISCUSSIONS.

1 Vol Larire 12mo. 470 FaRes. Pxioe (2.50.

American Notice of Spencer's New Sjstcm of Philosophy.

L Progress : its Law and Cause.

II Manners and Pashion.

III. The Genesis of Science.

IV. The Physiology of Laughter.

V. The Origin and Function of Music.

VL The Nebular Ilj-pothesis.

VIL Baia on the Emotions and the Will.

VIIL Illogical Geology.

IX. The Development Hypothesis.

X. The Social Organism.

XL Use and Beauty.

XIL The sources of Architectural Types.

XIII. The Dbc of Anthropomorphism.

These Esstys constitute a body of massive and original thought upon a
large variety of important topics, and will be read with pleasure by all who
appreciate a bold and powerful treatment of ftmdamental themes. The
gi.'neral thought which pervades this book is beyond doubt the most iuipor
tant that the human mind has yet reached. — N. Y. Independent.

Those who have read the work on Education, will remember the ana-
lytic tendency of the author's mind — his clear perception and admirable ex-
position of lirst principles — his wide gra.=p of facts — his lucid and vigorous
ityle, and the constant and controlling bearing of the discussion on practical
results. These traits characterize all Mr. Spencer's writings, and mark, m
an eminent degree, the present volume. — N. Y. IVibune.

We regard the distinguishing feature of this work to be the peculiarly
Interesting character of its matter to the general reader. This is a groat
literary aa well as pliiIo.«oi)hic triumph. In the evolution of a system of
Philosophy which demands serious attention, and a keen exercise of the in-
tellect to fathom and appreciate, he has mingled much that is really populof
uid entertaioing. — KocJuxlcr DemocraL

Wo)ks of Herbert Spencer publislied btj D. .dpptcton. d- Ob.
A NEW SYSTEM OF PHILOSOPHY.

FIRST PPvINOIPLES.

', VoL I^LTge 12mo. 515 Pages. Price $2 50.

Contents :
Part Fikst. — llie Unknowable.

C/kiaptei 1. Religion and Science; II. Ultimate Religious Ideas; III
DlUmatc Scientific Ideas; IV. The Relativity of all Knowledge; V Tht
Reconciliation.

Part Secoxd — Laws of tlie Knowable.

I. Laws in General; II. The Law of Evolution; III. Tiie same con-
tinued; IV. The Causes of Evolution; V. Space, Time, Matter, Motion, and
Force ; VI. The Indestructibility of Matter ; VII. The Continuity of Motion ;
VIII. The Persistence of Force ; IX. The Correlation and Equivalence of
Forces; X, The Direction of Motion ; XI. The Rhythm of Motion ; XII. The
Conditions Essential to Evolution ; XIII. The Instability of the ilomoge-
neous ; XIV. The Multiplication of Eflects ; XV. Diflerentiation -.nd Inte-
gration ; XYI. Equilibration ; XVII. Summary and Conclusion.

In the first part of this work Mr. Spencer defines the province, limits, and
relations of religion and science, and determines the legitimate scnpc of
philosophy.

In part second he unfolds those fundamental principles which have been
arrived at within the sphere of the knowable ; which are true of all orders
of phenoncma, and thus constitute the foundation of all philosophy. Tho
law of Evolution, Mr. Spencer maintains to be universal, and he has hero
worked it out as the basis of his system.

These First Principles are the foundation of a system of Philosophy
bolder, more elaborate, and comprehensive perhaps, than any other which
oat been hitherto designed in England. — British Quarterly Ikview.

A work lofty in aim and remarkable in executioa — CorrJiill Mayannt.

In the works of Herbert Spencer we have the rudiments of a positita
Theology, and an immense step toward the perfection of the science of Psy-
chology.— Christian Examiner.

If we mistake not, in spite of the very negative character of liis own r&
toltB, he has foreshadowed some strong arguments for the doctrine of a po»
lire Christian Theology. — New Englanda:

As far as the frontiers of knowledge, where the hitcllect may go, iJierc li
to living man whose guidance may more safely be trusted. — AtUmtit

Worki o/ Herbert Spencer published by D. AppUUm d: Co

A NEW SYSTEM OF PHILOSOPHY.

PKINCIPLES OF BIOLOGY.

Tbifl work is now in course of publication in quarterly numbcre (from 80
to 100 pages each), by subscription, at $2 per annum. It is to form two vol-
Bmes, of which the first is nearly completed, four numbers having been
jsued. \Vhile it comprises a statement of those general principles and laws
of life to which science has attained, it is stamped with a marked originality»
both in the views propounded and in the method of treating the subject. Il
will be a standard and invaluable work. Some idea of the discussion may
be formed by glancing over a few of the first chapter headin^rs.

Part Fikst. — Data of Biology.

I. Organic Matter; XL The actions of Forces on Organic Matter; III
The Reactions of Organic Matter on Forces ; IV. Proximate Definition of
Life ; V. The Correspondence between Life and its Circumstances ; VI. The
Degree of Life Varies with the Dcgi'ce of Correspondence ; VII Scope of
Biology.

Paut Second. — I.vdcctions of Bior.oai.

L Growth; IL Development; III. Function; IV. Waste and Repait ,
V. Adaptation; VL Individuality; VIL Genesis; VIIL Heredity; IX.
Variation; X. Genesis, Ileredity, and Variation; XI. Classification; XIL
Distribution.

Mr. Spencer is equally remarkable for his search after first principles;
tat his acute attempts to decompose mental phenomena into their primary
oemcnta ; and for his broad generalizations of mental activity, mind in coi>
nection with instinct, and all tlie analogies presented by life in its univerM]
npf'^ts — Medico- (Jhirttr^jical Hcviev.

Works of Uerbcri Spencer publuJud by D. App don it V«.

ESSAYS:

MORAL, POLITICAL, AND ESTIIEriC.

In one Voltime. liargre 12mo. 386 pafrea.

contests:
I. The Philosophy of Style.
II. Ovcr-Lcfrislation.

III. Morals of Trade.

IV. Personal Beauty.

V. Representative Government
VI. Prison-Ethics.

VII. Railway Morals and Railway Policy.
VIII. Gracefulness.
IX. State Tamperings with Money and Banks.
X. Reform ; the Dangers and the Safeguards.

" These Kssays form a new, and if we arc not misuiken, a most popular Lnstallmenl
sf the intellectual benefactions of that earnest writer anil profound philosopher, Her-
bert Spencer. There ia a remarkaMo union of the speculative and practicil in thee*
papers. They arc the fruit of studies alike economical and psychological; they touch
the problems of the passing hour, and they grasp truths of universal application ; they
will be founu as instructive to the general reader as interesting to political and 3<icial
et ude n t s." — JJoslon Tra m«c ript.

••These Essays exhibit on a;nQost every iia^re the powers of an independent human.
Itiirian thinker. ^Ir. Spencer's ethics are rigid, his political views libenilistic, and hi*
kim is the production ol the highest eai-thly good." — JletJiodUt Quarterly Jleview.

"It abounds iij the results of the sharp observation, the wide reach of ktnwledgei,
and the capacity to write clearly, forcibly, and pointedly, for which this wiitef Is pre-
eminent. The subjects are all such,as concern us most intimately, and they are treated
with admirable tact and knowledge. The first essay on the Philosophy of Style \t
Worth tlie cost of the volume; it would be a deed of charity to print It by itself^ and
•end it to the editor of every newsp.iper in the land." — Keio Eiigkinder.

"Spencer is continually gaining ground with Americans; he makes a book fbr oil:
more serious moods. His remarks upon legislation, upon the nature of political lu»ti-
tutlons and of their fundamental principles; his elucidation of those foundation trutli*
wliich control the policy of government, are of peculiar value to the American stii
dcnV—IloKlon Post.

"ITiis volume will receive the applause of every serious reader tor the profound
earnestness and thoroughness with which its views arc flaborated, the infinite scientlfle
knowledge brought to bear on every question, and the acute and subtle tblukjng 'U»-
Vrtfcycd In every chapter."— A'. W. Christian Advocate.

"A more In«tructivo, suggestive, and stimulating volume has net r«acDed on t» •
Mn tlmo." — PiociJence Journiu.

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