Such is what is ordinarily known as Lamarck's theory of evolution. We

may as well remember, however, that it really constitutes only one part

of his theory; for besides this hypothesis of the cumulative inheritance

of functionally-produced modifications--to which we may add the

inherited effects of any direct action exercised by surrounding

conditions of life,--Lamarck believed in some transcendental principle

tending to produce gradual improvement in pre-determined lines of

advance. Therefore it would really be more correct to designate the

former hypothesis by the name either of Erasmus Darwin, or, still

better, of Herbert Spencer. Nevertheless, in order to avoid confusion, I

will follow established custom, and subsequently speak of this

hypothesis as the Lamarckian hypothesis--understanding, however, that in

employing this designation I am not referring to any part or factor of

Lamarck's general theory of evolution other than the one which has just

been described--namely, the hypothesis of the cumulative transmission of

functionally-produced, or otherwise "acquired," modifications.

This, then, was the earliest hypothesis touching the causes of organic

evolution. But we may at once perceive that it is insufficient to

explain all that stands to be explained. In the first place, it refers

in chief part only to the higher animals, which are actuated to effort

by intelligence. Its explanatory power in the case of most

invertebrata--as well as in that of all plants--is extremely limited,

inasmuch as these organisms can never be moved to a greater or less use

of their several parts by any discriminating volition, such as that

which leads to the continued straining of a giraffe's neck for the

purpose of reaching foliage. In the second place, even among the higher

animals there are numberless tissues and organs which unquestionably

present a high degree of adaptive evolution, but which nevertheless

cannot be supposed to have fallen within the influence of Lamarckian

principles. Of such are the shells of crustacea, tortoises, &c., which

although undoubtedly of great use to the animals presenting them, cannot

ever have been _used_ in the sense required by Lamarck's hypothesis, i.

e. actively exercised, so as to increase a flow of nutrition to the

part. Lastly, in the third place, the validity of Lamarck's hypothesis

in any case whatsoever has of late years become a matter of serious

question, as will be fully shown and discussed in the next volume.

Meanwhile it is enough to observe that, on account of all these reasons,

the theory of Lamarck, even if it be supposed to present any truth at

all, is clearly insufficient as a full or complete theory of organic

evolution.

* * * * *

In historical order the next theory that was arrived at was the theory

of natural selection, simultaneously published by Darwin and Wallace on

July 1st, 1858.

If we may estimate the importance of an idea by the change of thought

which it effects, this idea of natural selection is unquestionably the

most important idea that has ever been conceived by the mind of man.

Yet the wonder is that it should not have been hit upon long before. Or

rather, I should say, the wonder is that its immense and immeasurable

importance should not have been previously recognised. For, since the

publication of this idea by Darwin and Wallace, it has been found that

its main features had already occurred to at least two other

minds--namely, Dr. Wells in 1813, and Mr. Patrick Matthew in 1831. But

neither of these writers perceived that in the few scattered sentences

which they had written upon the subject they had struck the key-note of

organic nature, and resolved one of the principal chords of the

universe. Still more remarkable is the fact that Mr. Herbert

Spencer--notwithstanding his great powers of abstract thought and his

great devotion of those powers to the theory of evolution, when as yet

this theory was scorned by science--still more remarkable, I say, is the

fact that Mr. Herbert Spencer should have missed what now appears so

obvious an idea. But most remarkable of all is the fact that Dr.

Whewell, with all his stores of information on the history of the

inductive sciences, and with all his acumen on the matter of scientific

method, should not only have conceived the idea of natural selection,

but expressly stated it as a logically possible explanation of the

origin of species, and yet have so stated it merely for the purpose of

dismissing it with contempt[26]. This, I think, is most remarkable,

because it serves to prove how very far men's minds at that time must

have been from entertaining, as in any way antecedently probable, the

doctrine of transmutation. In order to show this I will here quote one

passage from the writings of Whewell, and another from a distinguished

French naturalist referred to by him.

[26] For quotations, see Note A.

In 1846 Whewell wrote:--

Not only is the doctrine of the transmutation of species in itself

disproved by the best physiological reasonings, but the additional

assumptions which are requisite to enable its advocates to apply it

to the explanation of the geological and other phenomena of the

earth, are altogether gratuitous and fantastical[27].

[27] whewell, _indications of the creator_, 2nd ed., 1846.

Then he quotes with approval the following opinion:--

Against this hypothesis, which, up to the present time, I regard as

purely gratuitous, and likely to turn geologists out of the sound

and excellent road in which they now are, I willingly raise my

voice, with the most absolute conviction of being in the right[28].

[28] de blainville, _compte rendu_, 1837.

And, after displaying the proof rendered by Lyell of uniformitarianism

in geology, and cordially subscribing thereto, Whewell adds:--

We are led by our reasonings to this view, that the present order

of things was commenced by an act of creative power entirely

different to any agency which has been exerted since. None of the

influences which have modified the present races of animals and

plants since they were placed in their habitations on the earth's

surface can have had any efficacy in producing them at first. We

are necessarily driven to assume, as the beginning of the present

cycle of organic nature, an event not included in the course of

nature[29].

[29] Whewell, _ibid._, p. 162.

So much, then, for the state of the most enlightened and representative

opinions on the question of evolution before the publication of

Darwin's work; and so much, likewise, for the only reasonable

suggestions as to the causes of evolution which up to that time had been

put forward, even by those few individuals who entertained any belief in

evolution as a fact. It was the theory of natural selection that changed

all this, and created a revolution in the thought of our time, the

magnitude of which in many of its far-reaching consequences we are not

even yet in a position to appreciate; but the action of which has

already wrought a transformation in general philosophy, as well as in

the more special science of biology, that is without a parallel in the

history of mankind.

* * * * *

Although every one is now more or less well acquainted with the theory

of natural selection, it is necessary, for the sake of completeness,

that I should state the theory; and I will do so in full detail.

It is a matter of observable fact that all plants and animals are

perpetually engaged in what Darwin calls a "struggle for existence."

That is to say, in every generation of every species a great many more

individuals are born than can possibly survive; so that there is in

consequence a perpetual battle for life going on among all the

constituent individuals of any given generation. Now, in this struggle

for existence, which individuals will be victorious and live? Assuredly

those which are best fitted to live, in whatever respect, or respects,

their superiority of fitness may consist. Hence it follows that Nature,

so to speak, _selects_ the best individuals out of each generation to

live. And not only so; but as these favoured individuals transmit their

favourable qualities to their offspring, according to the fixed laws of

heredity, it further follows that the individuals composing each

successive generation have a general tendency to be better suited to

their surroundings than were their forefathers. And this follows, not

merely because in every generation it is only the "flower of the flock"

that is allowed to breed, but also because, if in any generation some

new and beneficial qualities happen to arise as slight variations from

the ancestral type, they will (other things permitting) be seized upon

by natural selection, and, being transmitted by heredity to subsequent

generations, will be added to the previously existing type. Thus the

best idea of the whole process will be gained by comparing it with the

closely analogous process whereby gardeners, fanciers, and

cattle-breeders create their wonderful productions; for just as these

men, by always "_selecting_" their best individuals to breed from,

slowly but continuously improve their stock, so Nature, by a similar

process of "_selection_" slowly but continuously makes the various

species of plants and animals better and better suited to the conditions

of their life.

Now, if this process of continuously adapting organisms to their

environment takes place in nature at all, there is no reason why we

should set any limits on the extent to which it is able to go, up to the

point at which a complete and perfect adaptation is achieved. Therefore

we might suppose that all species would eventually reach this condition

of perfect harmony with their environment, and then remain fixed. And

so, according to the theory, they would, if the environment were itself

unchanging. But forasmuch as the environment (i. e. the sum total of the

external conditions of life) of almost every organic type alters more

or less from century to century--whether from astronomical, geological,

and geographical changes, or from the immigrations and emigrations of

other species living on contiguous areas, and so on--it follows that the

process of natural selection need never reach a terminal phase. And

forasmuch as natural selection may thus continue, _ad infinitum_, slowly

to alter a specific type in adaptation to a gradually changing

environment, if in any case the alteration thus effected is sufficient

in amount to lead naturalists to name the result as a distinct species,

it follows that natural selection has transmuted one specific type into

another. Similarly, by a continuation of the process, specific types

would become transmuted into generic, generic into family types, and so

on. Thus the process is supposed to go on throughout all the countless

forms of life continuously and simultaneously--the world of organic

types being thus regarded as in a state of perpetual, though gradual,

flux.

* * * * *

Now, the first thing we have to notice about this theory is, that in all

its main elements it is merely a statement of observable facts. It is an

observable fact that in all species of plants and animals a very much

larger number of individuals are born than can possibly survive. Thus,

for example, it has been calculated that if the progeny of a single pair

of elephants--which are the slowest breeding of animals--were all

allowed to reach maturity and propagate, in 750 years there would be

living 19,000,000 descendants. Again, in the case of vegetables, if a

species of annual plant produces only two seeds a year, if these in

successive years were all allowed to reproduce their kind, in twenty

years there would be 11,000,000 plants from a single ancestor. Yet we

know that nearly all animals and plants produce many more young at a

time than in either of these two supposed cases. Indeed, as individuals

of many kinds of plants, and not a few kinds of animals, produce every

year several thousand young, we may make a rough estimate and say, that

over organic nature as a whole probably not one in a thousand young are

allowed to survive to the age of reproduction. How tremendous,

therefore, must be the struggle for existence! It is thought a terrible

thing in battle when one half the whole number of combatants perish. But

what are we to think of a battle for life where only one in a thousand

survives?

This, then, is the first fact. The second is the fact so long ago

recognised, that the battle is to the strong, the race to the swift. The

thousandth individual which does survive in the battle for

existence--which does win the race for life--is, without question, one

of the individuals best fitted to do so; that is to say, best fitted to

the conditions of its existence considered as a whole. Nature is,

therefore, always picking out, or selecting, such individuals to live

and to breed.

The third fact is, that the individuals so selected transmit their

favourable qualities to their offspring by heredity. There is no doubt

about this fact, so far as we are concerned with it. For although, as I

have already hinted, considerable doubt has of late years been cast upon

Lamarck's doctrine of the hereditary transmission of _acquired_

characters, it remains as impossible as ever it was to question the

hereditary transmission of what are called _congenital_ characters. And

this is all that Darwin's theory necessarily requires.

The fourth fact is, that although heredity as a whole produces a

wonderfully exact copy of the parent in the child, there is never a

precise reduplication. Of all the millions of human beings upon the face

of the earth, no one is so like another that we cannot see some

difference; the resemblance is everywhere specific, nowhere individual.

Now this same remark applies to all specific types. The only reason why

we notice individual differences in the case of the human type more than

we do in the case of any other types, is because our attention is here

more incessantly focussed upon these differences. We are compelled to

notice them in the case of our own species, however small they may

appear to a naturalist, because, unless we do so, we should not

recognise the members of our own family, or be able to distinguish

between a man whom we know is ready to do us an important service, and

another man whom we know is ready to cut our throats. But our common

mother Nature is able thus to distinguish between all her children. Her

eyes are much more ready to detect small individual peculiarities than

are the eyes of any naturalist. No slight variations in the cast of

feature or disposition of parts, no minute difference in the arrangement

of microscopical cells, can escape her ever vigilant attention. And,

consequently, when among all the innumerable multitudes of individual

variations any one arises which--no matter in how slight a degree--gives

to that individual a better chance of success in the struggle for life,

Nature chooses that individual to survive, and so to perpetuate the

improvement in his or her progeny.

Now I say that all these several component parts of Darwinian doctrine

are not matters of theory, but matters of fact. The only element of

theory in his doctrine of evolution by natural selection has reference

to the degree in which these observable facts, when thus brought

together, are adequate to account for the process of evolution.

* * * * *

So much, then, as a statement of the theory of natural selection. But

from this statement--i. e. from the theory of natural selection

itself--there follow certain matters of general principle which it is

important to bear in mind. These, therefore, I shall here proceed to

mention.

First of all, it is evident that the theory is applicable as an

explanation of organic changes in specific types only in so far as these

changes are of _use_, or so far as such changes endow the species with

better chances of success in the general struggle for existence. This is

the only sense in which I shall always employ the terms use, utility,

service, benefit, and so forth--that is to say, in the sense of

life-preserving.

* * * * *

Next, it must be clearly understood that the life which it is the

object, so to speak, of natural selection to preserve, is primarily the

life of the _species_; not that of the _individual_. Natural selection

preserves the life of the individual only in so far as this is conducive

to that of the species. Wherever the life-interests of the individual

clash with those of the species, that individual is sacrificed in favour

of others who happen better to subserve the interests of the species.

For example, in all organisms a greater or less amount of vigour is

wasted, so far as individual interests are concerned, in the formation

and the nourishment of progeny. In the great majority of plants and

animals an enormous amount of physiological energy is thus expended.

Look at the roe or the milt of a herring, for instance, and see what a

huge drain has been made upon the individual for the sake of its

species. Again, all unselfish instincts have been developed for the sake

of the species, and usually against the interests of the individual. An

ant which will allow her head to be slowly drawn from her body rather

than relinquish her hold upon a pupa, is clearly acting in response to

an instinct which has been developed for the benefit of the hive, though

fatal to the individual. And, in a lesser degree, the parental

instincts, wherever they occur, are more or less detrimental to the

interests of the individual, though correspondingly essential to those

of the race.

These illustrations will serve to show that natural selection always

works primarily for the life-interests of the species--and, indeed, only

works for those of the individual at all in so far as the latter happen

to coincide with the former. Or, otherwise stated, the object of natural

selection is always that of producing and maintaining specific types in

the highest degree of efficiency, no matter what may become of the

constituent individuals. Which is a striking republication by Science of

a general truth previously stated by Poetry:--

So careful of the type she seems,

So careless of the single life.

Tennyson thus noted the fact, and a few years later Darwin supplied the

explanation.

But of course in many, if not in the majority of cases, anything that

adds to the life-sustaining power of the single life thereby ministers

also to the life-sustaining power of the type; and thus we can

understand why all mechanisms and instincts which minister to the single

life have been developed--namely, because the life of the species is

made up of the lives of all its constituent individuals. It is only

where the interests of the one clash with those of the other that

natural selection works against the individual. So long as the interests

are coincident, it works in favour of both.

Natural selection, then, is a theory which seeks to explain by natural

causes the occurrence of every kind of adaptation which is to be met

with in organic nature, on the assumption that adaptations of every kind

have primary reference to the preservation of species, and therefore

also, as a general rule, to the preservation of their constituent

individuals. And from this it follows that where it is for the benefit

of a species to change its type, natural selection will effect that

change, thus leading to a specific transmutation, or the evolution of a

new species. In such cases the old species may or may not become

extinct. If the transmutation affects the species as a whole, or

throughout its entire range, of course _that_ particular type becomes

extinct, although it does so by becoming changed into a still more

suitable type in the course of successive generations. If, on the other

hand, the transmutation affects only a part of the original species, or

not throughout its entire range, then the other parts of that species

may survive for any number of ages as they originally were. In the one

case there is a ladder-like transmutation of species in time; in the

other case a possibly tree-like multiplication of species in space. But

whether the evolution of species be thus serial in time or divergent in

space, the object of natural selection, so to speak, is in either case

the same--namely, that of preserving all types which prove best suited

to the conditions of their existence.

* * * * *

Once more, the term "struggle for existence" must be understood to

comprehend, not only a competition for life among contemporary

individuals of the same species, but likewise a struggle by all such

individuals taken collectively for the continuance of their own specific

type. Thus, on the one hand, while there is a perpetual civil war being

waged between members of the same species, on the other hand there is a

foreign war being waged by the species as a whole against its world as a

whole. Hence it follows that natural selection does not secure survival

of the fittest as regards individuals only, but also survival of the

fittest as regards types. This is a most important point to remember,

because, as a general rule, these two different causes produce exactly

opposite effects. Success in the civil war, where each is fighting

against all, is determined by _individual_ fitness and _self-reliance_.

But success in the foreign war is determined by what may be termed

_tribal_ fitness and _mutual dependence_. For example, among social

insects the struggle for existence is quite as great between different

tribes or communities, as it is between different individuals of the

same community; and thus we can understand the extraordinary degree in

which not only co-operative instincts, but also largely intelligent

social habits, have here been developed[30]. Similarly, in the case of

mankind, we can understand the still more extraordinary development of

these things--culminating in the moral sense. I have heard a sermon,

preached at one of the meetings of the British Association, entirely

devoted to arguing that the moral sense could not have been evolved by

natural selection, seeing that the altruism which this sense involves is

the very opposite of selfishness, which alone ought to have been the

product of survival of the fittest in a struggle for life. And, of

course, this argument would have been perfectly sound had Darwin limited

the struggle for existence to individuals, without extending it to

communities. But if the preacher had ever read Darwin's works he would

have found that, when thus extended, the principle of natural selection

is bound to work in favour of the co-operative instincts in the case of

so highly social an animal as man; and that of these instincts

conscience is the highest imaginable exhibition.

[30] For cases, see _Animal Intelligence_, in the chapters on Ants

and Bees; and, for discussion of principles, _Mental Evolution in

Animals_, in the chapters on Instinct.

What I have called tribal fitness--in contradistinction to individual

fitness--begins with the family, developes in the community (herd, hive,

clan, &c.), and usually ends with the limits of the species. On the one

hand, however, it is but seldom that it extends so far as to embrace the

entire species; while, on the other hand, it may in some cases, and as

it were sporadically, extend beyond the species. In these latter cases

members of different species mutually assist one another, whether in the

way of what is called symbiosis, or in a variety of other ways which I

need not wait to mention. For the only point which I now desire to make

clear is, that all cases of mutual aid or co-operation, whether within

or beyond the limits of species, are cases which fall under the

explanatory sweep of the Darwinian theory[31].

[31] Prince Kropotkin in the _Nineteenth Century_ (Feb. 1888, Apr.

1891) has adduced a large and interesting body of facts, showing the

great prevalence of the principle of co-operation in organic

nature.

* * * * *

Another important point to notice is, that it constitutes no part of the

theory of natural selection to suppose that survival of the fittest must

invariably lead to _improvement_ of type, in the sense of superior

organization. On the contrary, if from change of habits or conditions of

life an organic type ceases to have any use for previously useful

organs, natural selection will not only allow these organs in successive

generations to deteriorate--by no longer placing any selective premium

upon their maintenance--but may even proceed to assist the agencies

engaged in their destruction. For, being now useless, they may become

even deleterious, by absorbing nutriment, causing weight, occupying

space, &c., without conferring any compensating benefit. Thus we can

understand why it is that parasites, for example, present the phenomena

of what is called _degeneration_, i. e. showing by their whole structure

that they have descended from a possibly very much higher type of

organization than that which they now exhibit. Having for innumerable

generations ceased to require their legs, their eyes, and so forth, all

such organs of high elaboration have either disappeared or become

vestigial, leaving the parasite as a more or less effete representative

of its ancestry.

These facts of degeneration, as we have previously seen, are of very

general occurrence, and it is evident that their importance in the field

of organic evolution as a whole has been very great. Moreover, it ought

to be particularly observed that, as just indicated, the facts may be

due either to a passive _cessation_ of selection, or to an active

_reversal_ of it. Or, more correctly, these facts are probably _always_

due to the cessation of selection, although in most cases where species

in a state of nature are concerned, the process of degeneration has been

both hastened and intensified by the super-added influence of the

reversal of selection. In the next volume I shall have occasion to recur

to this distinction, when it will be seen that it is one of no small

importance to the general theory of descent.

* * * * *

We may now proceed to consider certain misconceptions of the Darwinian

theory which are largely, not to say generally, prevalent among

supporters of the theory. These misconceptions, therefore, differ from

those which fall to be considered in the next chapter, i. e.

misconceptions which constitute grounds of objection to the theory.

* * * * *

Of all the errors connected with the theory of natural selection,

perhaps the one most frequently met with--especially among supporters of

the theory--is that of employing the theory to explain all cases of

phyletic modification (or inherited change of type) indiscriminately,

without waiting to consider whether in particular cases its application

is so much as logically possible. The term "natural selection" thus

becomes a magic word, or Sesame, at the utterance of which every closed

door is supposed to be immediately opened. Be it observed, I am not here

alluding to that merely blind faith in natural selection, which of late

years has begun dogmatically to force this principle as the sole cause

of organic evolution in every case where it is _logically possible_ that

the principle can have come into play. Such a blind faith, indeed, I

hold to be highly inimical, not only to the progress of biological

science, but even to the true interests of the natural selection theory

itself. As to this I shall have a good deal to say in the next volume.

Here, however, the point is, that the theory in question is often

invoked in cases where it is not even logically possible that it can

apply, and therefore in cases where its application betokens, not merely

an error of judgment or extravagance of dogmatism, but a fallacy of

reasoning in the nature of a logical contradiction. Almost any number of

examples might be given; but one will suffice to illustrate what is

meant. And I choose it from the writings of one of the authors of the

selection theory itself, in order to show how easy it is to be cheated

by this mere juggling with a phrase--for of course I do not doubt that a

moment's thought would have shown the writer the untenability of his

statement.

In his most recent work Mr. Wallace advances an interesting hypothesis

to the effect that differences of colour between allied species, which

are apparently too slight to serve any other purpose, may act as

"recognition marks," whereby the opposite sexes are enabled at once to

distinguish between members of their own and of closely resembling

species. Of course this hypothesis can only apply to the higher animals;

but the point here is that, supposing it to hold for them, Mr. Wallace

proceeds to argue thus:--Recognition marks "have in all probability been

acquired in the process of differentiation for the purpose of checking

the intercrossing of allied forms," because "one of the first needs of a

new species would be to keep separate from its nearest allies, and this

could be more readily done by some easily seen external mark[32]."

Now, it is clearly not so much as logically possible that these

recognition-marks (supposing them to be such) can have been acquired

by natural selection, "for the purpose of checking intercrossing of

allied forms." For the theory of natural selection, from its own

essential nature as a theory, is logically exclusive of the supposition

that survival of the fittest ever provides changes in anticipation of

future uses. Or, otherwise stated, it involves a contradiction of the

theory itself to say that the colour-changes in question were originated

by natural selection, in order to meet "one of the _first_ needs of a

_new_ species," or for the purpose of _subsequently_ preventing

intercrossing with allied forms. If it had been said that these

colour-differentiations were originated by some cause other than natural

selection (or, if by natural selection, still with regard to some

_previous_, instead of _prophetic_, "purpose"), and, when so "acquired,"

_then_ began to serve the "purpose" assigned, the argument would not

have involved the fallacy which we are now considering. But, as it

stands, the argument reverts to the teleology of pre-Darwinian days--or

the hypothesis of a "purpose" in the literal sense which sees the end

from the beginning, instead of a "purpose" in the metaphorical sense of

an adaptation that is evolved by the very modifications which subserve

it[33].

[32] _Darwinism_, pp. 218 and 227.

[33] Since the above was written Prof. Lloyd Morgan has published a

closely similar notice of the passage in question. "This language,"

he says, "seems to savour of teleology (that pitfall of the

evolutionist). The cart is put before the horse. The

recognition-marks were, I believe, not produced to prevent

intercrossing, but intercrossing has been prevented because of

preferential mating between individuals possessing special

recognition-marks. To miss this point is to miss an important

segregation-factor."--(_Animal Life and Intelligence_, p. 103.)

Again, on pp. 184-9, he furnishes an excellent discussion on the

whole subject of the fallacy alluded to in the text, and gives

illustrative quotations from other prominent Darwinians. I should

like to add that Darwin himself has nowhere fallen into this, or any

of the other fallacies, which are mentioned in the text.

* * * * *

Another very prevalent, and more deliberate, fallacy connected with the

theory of natural selection is, _that it follows deductively from the

theory itself_ that the principle of natural selection must be the sole

means of modification in all cases where modification is of an

_adaptive_ kind,--with the consequence that no other principle can ever

have been concerned in the production of structures or instincts which

are of any use to their possessors. Whether or not natural selection

actually has been the sole means of adaptive modification in the race,

as distinguished from the individual, is a question of biological

fact[34]; but it involves a grave error of reasoning to suppose that

this question can be answered deductively from the theory of natural

selection itself, as I shall show at some length in the next volume.

[34] Of course adaptive modifications produced in the individual

lifetime, and not _inherited_, do not concern the question at all.

In this and the following paragraphs, therefore, "adaptations,"

"adaptive modifications," &c., refer exclusively to such as are

hereditary, i. e. phyletic.

* * * * *

A still more extravagant, and a still more unaccountable fallacy is the

one which represents it as following deductively from the theory of

natural selection itself, that all _hereditary_ characters are

"necessarily" due to natural selection. In other words, not only all

adaptive, but likewise all non-adaptive hereditary characters, it is

said, _must_ be due to natural selection. For non-adaptive characters

are taken to be due to "correlation of growth," in connexion with some

of the adaptive ones--natural selection being thus the _indirect_ means

of producing the former _wherever_ they may occur, on account of its

being the _direct_ and the _only_ means of producing the latter. Thus it

is deduced from the theory of natural selection itself,--1st, that the

principle of natural selection is the only possible cause of adaptive

modification: 2nd, that non-adaptive modifications can only occur in the

race as correlated appendages to the adaptive: 3rd, that, consequently,

natural selection is the only possible cause of modification, whether

adaptive or non-adaptive. Here again, therefore, we must observe that

none of these sweeping generalizations can possibly be justified by

deductive reasoning from the theory of natural selection itself. Any

attempt at such deductive reasoning must necessarily end in circular

reasoning, as I shall likewise show in the second volume, where this

whole "question of utility" will be thoroughly dealt with.

* * * * *

Once more, there is an important oversight very generally committed by

the followers of Darwin. For even those who avoid the fallacies above

mentioned often fail to perceive, that natural selection can only begin

to operate if the _degree_ of adaptation is already given as

sufficiently high to count for something in the struggle for

_existence_. Any adaptations which fall below this level of importance

cannot possibly have been produced by survival of the fittest. Yet the

followers of Darwin habitually speak of adaptative characters, which _in

their own opinion_ are subservient merely to comfort or convenience, as

having been produced by such means. Clearly this is illogical; for it

belongs to the essence of Darwin's theory to suppose, that natural

selection can have no jurisdiction beyond the line where structures or

instincts already present a sufficient degree of adaptational value to

increase, in some measure, the expectation of life on the part of their

possessors. We cannot speak of adaptations as due to natural selection,

without thereby affirming that they present what I have elsewhere termed

a "selection value."

* * * * *

Lastly, as a mere matter of logical definition, it is well-nigh

self-evident that the theory of natural selection is a theory of the

origin, and cumulative development, of _adaptations_, whether these be

distinctive of species, or of genera, orders, families, classes, and

sub-kingdoms. It is only when the adaptations happen to be distinctive

of the first (or lowest) of these taxonomic divisions, that the theory

which accounts for _these_ adaptations accounts also for the forms which

present them,--i. e. becomes _also_ a theory of the origin of species.

This, however, is clearly but an accident of particular cases; and,

therefore, even in them the theory is _primarily_ a theory of

adaptations, while it is but secondarily a theory of the species which

present them. Or, otherwise stated, the theory is no more a theory of

the origin of species than it is of the origin of genera, families, and

the rest; while, on the other hand, it is _everywhere_ a theory of the

adaptive modifications whereby each of these taxonomic divisions has

been differentiated as such. Yet, sufficiently obvious as the accuracy

of this definition must appear to any one who dispassionately considers

it, several naturalists of high standing have denounced it in violent

terms. I shall therefore have to recur to the subject at somewhat

greater length hereafter. At present it is enough merely to mention the

matter, as furnishing another and a curious illustration of the not

infrequent weakness of logical perception on the part of minds well

gifted with the faculty of observation. It may be added, however, that

the definition in question is in no way hostile to the one which is

virtually given by Darwin in the title of his great work. _The Origin of

Species by means of Natural Selection_ is beyond doubt the best title

that could have been given, because at the time when the work was

published the _fact_, no less than the _method_, of organic evolution

had to be established; and hence the most important thing to be done at

that time was to prove the transmutation of species. But now that this

has been done to the satisfaction of naturalists in general, it is as I

have said, curious to find some of them denouncing a wider definition of

the principle of natural selection, merely because the narrower (or

included) definition is invested with the charm of verbal

associations[35].

[35] The question as to whether natural selection has been the only

principle concerned in the origination of species, is quite distinct

from that as to the accuracy of the above definition.

* * * * *

So much for fallacies and misconceptions touching Darwin's theory, which

are but too frequently met with in the writings of its supporters. We

must now pass on to mention some of the still greater fallacies and

misconceptions which are prevalent in the writings of its opponents.

And, in order to do this thoroughly, I shall begin by devoting the

remainder of the present chapter to a consideration of the antecedent

standing of the two theories of natural selection and supernatural

design. This having been done, in the succeeding chapters I shall deal

with the evidences for, and the objections against, the former theory.

* * * * *

Beginning, then, with the antecedent standing of these alternative

theories, the first thing to be noticed is, that they are both concerned

with the same subject-matter, which it is their common object to

explain. Moreover, this subject-matter is clearly and sharply divisible

into two great classes of facts in organic nature--namely, those of

Adaptation and those of Beauty. Darwin's theory of descent explains the

former by his doctrine of natural selection, and the latter by his

doctrine of sexual selection. In the first instance, therefore, I shall

have to deal only with the facts of adaptation, leaving for subsequent

consideration the facts of beauty.

Innumerable cases of the adaptation of organisms to their surroundings

being the facts which now stand before us to be explained either by

natural selection or by supernatural intention, we may first consider a

statement which is frequently met with--namely, that even if all such

cases of adaptation were proved to be fully explicable by the theory of

descent, this would constitute no disproof of the theory of design: all

the cases of adaptation, it is argued, might still be due to design,

even though they admit of being hypothetically accounted for by the

theory of descent. I have heard an eminent Professor tell his class that

the many instances of mechanical adaptation discovered and described by

Darwin as occurring in orchids, seemed to him to furnish better proof of

supernatural contrivance than of natural causes; and another eminent

Professor has informed me that, although he had read the _Origin of

Species_ with care, he could see in it no evidence of natural selection

which might not equally well have been adduced in favour of intelligent

design. But here we meet with a radical misconception of the whole

logical attitude of science. For, be it observed, this exception _in

limine_ to the evidence which we are about to consider does not question

that natural selection _may_ be able to do all that Darwin ascribes to

it. The objection is urged against his interpretation of the facts

merely on the ground that these facts might _equally well_ be ascribed

to intelligent design. And so undoubtedly they might, if we were all

simple enough to adopt a supernatural explanation whenever a natural one

is found sufficient to account for the facts. Once admit the irrational

principle that we may assume the operation of higher causes where the

operation of lower ones is sufficient to explain the observed phenomena,

and all our science and all our philosophy are scattered to the winds.

For the law of logic which Sir William Hamilton called the law of

parsimony--or the law which forbids us to assume the operation of higher

causes when lower ones are found sufficient to explain the observed

effects--this law constitutes the only barrier between science and

superstition. It is always possible to give a hypothetical explanation

of any phenomenon whatsoever, by referring it immediately to the

intelligence of some supernatural agent; so that the only difference

between the logic of science and the logic of superstition consists in

science recognising a validity in the law of parsimony which

superstition disregards. Therefore one can have no hesitation in saying

that this way of looking at the evidence in favour of natural selection

is not a scientific or a reasonable way of looking at it, but a purely

superstitious way. Let us take, as an illustration, a perfectly parallel

case. When Kepler was unable to explain by any known causes the paths

described by the planets, he resorted to a supernatural explanation, and

supposed that every planet was guided in its movements by some presiding

angel. But when Newton supplied a beautifully simple physical

explanation, all persons with a scientific habit of mind at once

abandoned the metaphysical one. Now, to be consistent, the

above-mentioned Professors, and all who think with them, ought still to

adhere to Kepler's hypothesis in preference to Newton's explanation;

for, excepting the law of parsimony, there is certainly no other

logical objection to the statement, that the movements of the planets

afford as good evidence of the influence of guiding angels as they do of

the influence of gravitation.

So much, then, for the illogical position that, granting the evidence in

favour of natural descent and supernatural design to be equal and

parallel, we should hesitate in our choice between the two theories.

But, of course, if the evidence is supposed _not_ to be equal and

parallel--i. e. if it is supposed that the theory of natural selection

is not so good a theory whereby to explain the facts of adaptation as is

that of supernatural design,--then the objection is no longer the one

which we are considering. It is quite another objection, and one which

is not _prima facie_ absurd. Therefore let us state clearly the distinct

question which thus arises.

Innumerable cases of adaptation of organisms to their environments are

the observed facts for which an explanation is required. To supply this

explanation, two, and only two, hypotheses are in the field. Of these

two hypotheses one is intelligent design manifested directly in special

creation; the other is natural causation operating through countless

ages of the past. Now, the adaptations in question involve an

innumerable multitude of special mechanisms, in most cases even within

the limits of any one given species; but when we consider the sum of all

these mechanisms presented by organic nature as a whole, the mind must

indeed be dull which does not feel astounded. For, be it further

observed, these mechanical contrivances[36] are, for the most part, no

merely simple arrangements, which might reasonably be supposed due,

like the phenomena of crystallization, to comparatively simple physical

causes. On the contrary, they everywhere and habitually exhibit so

deep-laid, so intricate, and often so remote an adaptation of means to

ends, that no machinery of human contrivance can properly be said to

equal their perfection from a mechanical point of view. Therefore,

without question, the hypothesis which first of all they suggest--or

suggest most readily--is the hypothesis of design. And this hypothesis

becomes virtually the only hypothesis possible, if it be assumed--as it

generally was assumed by natural theologians of the past,--that all

species of plants and animals were introduced into the world _suddenly_.

For it is quite inconceivable that any known cause, other than

intelligent design, could be competent to turn out instantaneously any

one of these intricate pieces of machinery, already adapted to the

performance of its special function. But, on the other hand, if there is

any evidence to show that one species becomes slowly transformed into

another--or that one set of adaptations becomes slowly changed into

another set as changing circumstances require,--then it becomes quite

possible to imagine that a strictly natural causation may have had

something to do with the matter. And this suggestion becomes greatly

more probable when we discover, from geological evidence and

embryological research, that in the history both of races and of

individuals the various mechanisms in question have themselves had a

history--beginning in the forms of most uniformity and simplicity,

gradually advancing to forms more varied and complex, nowhere exhibiting

any interruptions in their upward progress, until the world of organic

machinery as we now have it is seen to have been but the last phase of a

long and gradual growth, the ultimate roots of which are to be found in

the soil of undifferentiated protoplasm.

[36] It is often objected to Darwin's terminology, that it embraces

such words as "contrivance," "purpose," &c., which are strictly

applicable only to the processes or the products of thought. But

when it is understood that they are used in a neutral or

metaphorical sense, I cannot see that any harm arises from their

use.

Lastly, when there is supplied to us the suggestion of natural selection

as a cause presumably adequate to account for this continuous growth in

the number, the intricacy, and the perfection of such mechanisms, it is

only the most unphilosophical mind that can refuse to pause as between

the older hypothesis of design and the newer hypothesis of descent.

Thus it is clear that the _a priori_ standing of the rival hypotheses of

naturalism and supernaturalism in the case of all these pieces of

organic machinery, is profoundly affected by the question whether they

came into existence suddenly, or whether they did so gradually. For, if

they all came into existence suddenly, the fact would constitute

well-nigh positive proof in favour of supernaturalism, or creation by

design; whereas, if they all came into existence gradually, this fact

would in itself constitute presumptive evidence in favour of naturalism,

or of development by natural causes. And, as shown in the previous

chapters, the proof that all species of plants and animals came into

existence gradually--or the proof of evolution as a fact--is simply

overwhelming.

From a still more general point of view I may state the case in another

way, by borrowing and somewhat expanding an illustration which, I

believe, was first used by Professor Huxley. If, when the tide is out,

we see lying upon the shore a long line of detached sea-weed, marking

the level which is reached by full tide, we should be free to conclude

that the separation of the sea-weed from the sand and the stones was due

to the intelligent work of some one who intended to collect the sea-weed

for manure, or for any other purpose. But, on the other hand, we might

explain the fact by a purely physical cause--namely, the separation by

the sea-waves of the sea-weed from the sand and stones, in virtue of its

lower specific gravity. Now, thus far the fact would be explained

equally well by either hypothesis; and this fact would be the fact of

_selection_. But whether we yielded our assent to the one explanation or

to the other would depend upon a due consideration of all collateral

circumstances. The sea-weed might not be of a kind that is of any use to

man; there might be too great a quantity of it to admit of our supposing

that it had been collected by man; the fact that it was all deposited on

the high-water-mark would in itself be highly suggestive of the agency

of the sea; and so forth. Thus, in such a case any reasonable observer

would decide in favour of the physical explanation, or against the

teleological one.

Now the question whether organic evolution has been caused by physical

agencies or by intelligent design is in precisely the same predicament.

There can be no logical doubt that, theoretically at all events, the

physical agencies which the present chapter is concerned with, and which

are conveniently summed up in the term natural selection, are as

competent to produce these so-called mechanical contrivances, and the

other cases of adaptation which are to be met with in organic nature,

as intelligent design could be. Hence, our choice as between these two

hypotheses must be governed by a study of all collateral circumstances;

that is to say, by a study of the evidences in favour of the physical

explanation. To this study, therefore, we shall now address ourselves,

in the course of the following chapters.

CHAPTER VIII.

EVIDENCES OF THE THEORY OF NATURAL SELECTION.

I will now proceed to state the main arguments in favour of the theory

of natural selection, and then, in the following chapter, the main

objections which have been urged against it.

In my opinion, the main arguments in favour of the theory are three in

number.

First, it is a matter of observation that the struggle for existence in

nature does lead to the extermination of forms less fitted for the

struggle, and thus makes room for forms more fitted. This general fact

may be best observed in cases where an exotic species proves itself

better fitted to inhabit a new country than is some endemic species

which it exterminates. In Great Britain, for example, the so-called

common rat is a comparatively recent importation from Norway, and it has

so completely supplanted the original British rat, that it is now

extremely difficult to procure a single specimen of the latter: the

native black rat has been all but exterminated by the foreign brown rat.

The same thing is constantly found in the case of imported species of

plants. I have seen the river at Cambridge so choked with the inordinate

propagation of a species of water-weed which had been introduced from

America, that considerable expense had to be incurred in order to clear

the river for traffic. In New Zealand the same thing has happened with

the European water-cress, and in Australia with the common rabbit. So it

is doubtless true, as one of the natives is said to have philosophically

remarked, "the white man's rat has driven away our rat, the European fly

drives away our fly, his clover kills our grass, and so will the Maoris

disappear before the white man himself." Innumerable other cases to the

same effect might be quoted; and they all go to establish the fact that

forms less fitted to survive succumb in their competition with forms

better fitted.

* * * * *

Secondly, there is a general consideration of the largest possible

significance in the present connexion--namely, that among all the

millions of structures and instincts which are so invariably, and for

the most part so wonderfully, adapted to the needs of the species

presenting them, we cannot find a single instance, either in the

vegetable or animal kingdom, of a structure or an instinct which is

developed for the exclusive benefit of another species. Now this great

and general fact is to my mind a fact of the most enormous, not to say

overwhelming, significance. The theory of natural selection has now been

before the world for more than thirty years, and during that time it had

stood a fire of criticism such as was never encountered by any

scientific theory before. From the first Darwin invited this criticism

to adduce any single instance, either in the vegetable or animal

kingdom, of a structure or an instinct which should unquestionably be

proved to be of exclusive use to any species other than the one

presenting it. He even went so far as to say that if any one such

instance could be shown he would surrender his whole theory on the

strength of it--so assured had he become, by his own prolonged

researches, that natural selection was the true agent in the production

of adaptive structures, and, as such, could never have permitted such a

structure to occur in one species for the benefit of another. Now, as

this invitation has been before the world for so many years, and has not

yet been answered by any naturalist, we may by this time be pretty

confident that it never will be answered. How tremendous, then, is the

significance of this fact in its testimony to Darwin's theory! The

number of animal and vegetable species, both living and extinct, is to

be reckoned by millions, and every one of these species presents on an

average hundreds of adaptive structures,--at least one of which in many,

possibly in most, if not actually in all cases, is peculiar to the

species that presents it. In other words, there are millions of adaptive

structures (not to speak of instincts) which are peculiar to the species

presenting them, and also many more which are the common property of

allied species: yet, notwithstanding this inconceivable profusion of

adaptive structures in organic nature, there is no single instance that

has been pointed out of the occurrence of such a structure save for the

benefit of the species that presents it. Therefore, I say that this

immensely large and general fact speaks with literally immeasurable

force in favour of natural selection, as at all events one of the main

causes of organic evolution. For the fact is precisely what we should

expect if this theory is true, while upon no other theory can its

universality and invariability be rendered intelligible. On the

beneficent design theory, for instance, it is inexplicable that no

species should ever be found to present a structure or an instinct

having primary reference to the welfare of another species, when, _ex

hypothesi_, such an endless amount of thought has been displayed in the

creation of structures and instincts having primary reference to the

species which present them. For how magnificent a display of divine

beneficence would organic nature have afforded, if all--or even

some--species had been so inter-related as to have ministered to each

others wants. Organic species might then have been likened to a

countless multitude of voices, all singing in one great harmonious

psalm. But, as it is, we see absolutely no vestige of such

co-ordination: every species is for itself, and for itself alone--an

outcome of the always and everywhere fiercely raging struggle for life.

In order that the force of this argument may not be misapprehended, it

is necessary to bear in mind that it is in no way affected by cases

where a structure or an instinct is of primary benefit to its possessor,

and then becomes of secondary benefit to some other species on account

of the latter being able in some way or another to utilise its action.

Of course organic nature is full of cases of this kind; but they only go

to show the readiness which all species display to utilise for

themselves everything that can be turned to good account in their own

environments, and so, among other things, the structures and instincts

of other animals. For instance, it would be no answer to Darwin's

challenge if any one were to point to a hermit-crab inhabiting the

cast-off shell of a mollusk; because the shell was primarily of use to

the mollusk itself, and, so far as the mollusk is concerned, the fact of

its shell being afterwards of a secondary use to the crab is quite

immaterial. What Darwin's challenge requires is, that some structure or

instinct should be shown which is not merely of such secondary or

accidental benefit to another species, but clearly adapted to the needs

of that other species in the first instance--such, for example, as would

be the case if the tail of a rattle-snake were of no use to its

possessor, while serving to warn other animals of the proximity of a

dangerous creature; or, in the case of instincts, if it were true that a

pilot-fish accompanies a shark for the purpose of helping the shark to

discover food. Both these instances have been alleged; but both have

been shown untenable. And so it has proved of all the other cases which

thus far have been put forward.

Perhaps the most remarkable of all the allegations which ever have been

put forward in this connexion are those that were current with regard to

instincts before the publication of Darwin's work. These allegations are

the most remarkable, because they serve to show, in a degree which I do

not believe could be shown anywhere else, the warping power of

preconceived ideas. A short time ago I happened to come across the 8th

edition of the _Encyclopaedia Britannica_, and turned up the article on

"Instinct" there, in order to see what amount of change had been wrought

with regard to our views on this subject by the work of Darwin--the 8th

edition of the _Encyclopaedia Britannica_ having been published shortly

before _The Origin of Species by means of Natural Selection_. I cannot

wait to give any lengthy quotations from this representative exponent of

scientific opinion upon the subject at that time; but its general drift

may be appreciated if I transcribe merely the short concluding

paragraph, wherein he sums up his general results. Here he says:--

It thus only remains for us to regard instinct as a mental faculty,

_sui generis_, the gift of God to the lower animals, that man in

his own person, and by them, might be relieved from the meanest

drudgery of nature.

Now, here we have the most extraordinary illustration that is imaginable

of the obscuring influence of a preconceived idea. Because he started

with the belief that instincts _must_ have been implanted in animals for

the benefit of man, this writer, even when writing a purely scientific

essay, was completely blinded to the largest, the most obvious, and the

most important of the facts which the phenomena of instinct display.

For, as a matter of fact, among all the many thousands of instincts

which are known to occur in animals, there is no single one that can be

pointed to as having any special reference to man; while, on the other

hand, it is equally impossible to point to one which does not refer to

the welfare of the animal presenting it. Indeed, when the point is

suggested, it seems to me surprising how few in number are the instincts

of animals which have proved to be so much as of secondary or accidental

benefit to man, in the same way as skins, furs, and a whole host of

other animal products are thus of secondary use to him. Therefore, this

writer not only failed to perceive the most obvious truth that every

instinct, without any single exception, has reference to the animal

which presents it; but he also conceived a purely fictitious inversion

of this truth, and wrote an essay to prove a statement which all the

instincts in the animal kingdom unite in contradicting.

This example will serve to show, in a striking manner, not only the

distance that we have travelled in our interpretation of organic nature

between two successive editions of the _Encyclopaedia Britannica_, but

also the amount of verification which this fact furnishes to the theory

of natural selection. For, inasmuch as it belongs to the very essence of

this theory that all adaptive characters (whether instinctive or

structural) must have reference to their own possessors, we find

overpowering verification furnished to the theory by the fact now before

us--namely, that immediately prior to the enunciation of this theory,

the truth that all adaptive characters have reference only to the

species which present them was not perceived. In other words, it was the

testing of this theory by the facts of nature that _revealed_ to

naturalists the general law which the theory, as it were, predicted--the

general law that all adaptive characters have primary reference to the

species which present them. And when we remember that this is a kind of

verification which is furnished by millions of separate cases, the whole

mass of it taken together is, as I have before said, overwhelming.

It is somewhat remarkable that the enormous importance of this argument

in favour of natural selection as a prime factor of organic evolution

has not received the attention which it deserves. Even Darwin himself,

with his characteristic reserve, has not presented its incalculable

significance; nor do I know any of his followers who have made any

approach to an adequate use of it in their advocacy of his views. In

preparing the present chapter, therefore, I have been particularly

careful not to pitch too high my own estimate of its evidential value.

That is to say, I have considered, both in the domain of structures and

of instincts, what instances admit of being possibly adduced _per

contra_, or as standing outside the general law that adaptive structures

and instincts are of primary use only to their possessors. In the result

I can only think of two such instances. These, therefore, I will now

dispose of.

The first was pointed out, and has been fully discussed, by Darwin

himself. Certain species of ants are fond of a sweet fluid that is

secreted by aphides, and they even keep the aphides as we keep cows for

the purpose of profiting by their "milk." Now the point is, that the use

of this sweet secretion to the aphis itself has not yet been made out.

Of course, if it is of no use to the aphis, it would furnish a case

which completely meets Darwin's own challenge. But, even if this

supposition did not stand out of analogy with all the other facts of

organic nature, most of us would probably deem it prudent to hold that

the secretion must primarily be of some use to the aphis itself,

although the matter has not been sufficiently investigated to inform us

of what this use is. For, in any case, the secretion is not of any vital

importance to the ants which feed upon it: and I think but few impartial

minds would go so far to save an hypothesis as to maintain, that the

Divinity had imposed this drain upon the internal resources of one

species of insect for the sole purpose of supplying a luxury to

another. On the whole, it seems most probable that the fluid is of the

nature of an excretion, serving to carry off waste products. Such, at

all events, was the opinion at which Darwin himself arrived, as a result

of observing the facts anew, and in relation to his theory.

* * * * *

The other instance to which I have alluded as seeming at first sight

likely to answer Darwin's challenge is the formation of vegetable galls.

The great number and variety of galls agree in presenting a more or less

elaborate structure, which is not only foreign to any of the uses of

plant-life, but singularly and specially adapted to those of the

insect-life which they shelter. Yet they are produced by a growth of the

plant itself, when suitably stimulated by the insects' inoculation--or,

according to recent observations, by emanations from the bodies of the

larvae which develop from the eggs deposited in the plant by the insect.

Now, without question, this is a most remarkable fact; and if there were

many more of the like kind to be met with in organic nature, we might

seriously consider whether the formation of galls should not be held to

make against the ubiquitous agency of natural selection. But inasmuch as

the formation of galls stands out as an exception to the otherwise

universal rule of every species for itself, and for itself alone, we are

justified in regarding this one apparent exception with extreme

suspicion. Indeed, I think we are justified in regarding the peculiar

pathological effect produced in the plant by the secretions of the

insect as having been in the first instance accidentally beneficial to

the insects. Thus, if any other effect than that of a growing tumour had

been produced in the first instance, or if the needs of the insect

progeny had not been such as to have derived profit from being enclosed

in such a tumour, then, of course, the inoculating instinct of these

animals could not have been developed by natural selection. But, given

these two conditions, and it appears to me there is nothing very much

more remarkable about an accidental correlation between the effects of a

parasitic larva on a plant and the needs of that parasite, than there is

between the similarly accidental correlation between a hydated parasite

and the nutrition furnished to it by the tissues of a warm-blooded

animal. Doubtless the case of galls is somewhat more remarkable,

inasmuch as the morbid growth of the plant has more concern in the

correlation--being, in many instances, a more specialized structure on

the part of a host than occurs anywhere else, either in the animal or

vegetable world. But here I may suggest that although natural selection

cannot have acted upon the plant directly, so as to have produced galls

ever better and better adapted to the needs of the insect, it may have

so acted upon the plants indirectly _though the insects_. For it may

very well have been that natural selection would ever tend to preserve

those individual insects, the quality of whose emanations tended to

produce the form of galls best suited to nourish the insect progeny; and

thus the character of these pathological growths may have become ever

better and better adapted to the needs of the insects. Lastly, looking

to the enormous number of relations and inter-relations between all

organic species, it is scarcely to be wondered at that even so

extraordinary an instance of correlation as this should have arisen thus

by accident, and then have been perfected by such an _indirect_ agency

of natural selection as is here suggested[37].

[37] Note B.

* * * * *

The third general class of facts which tell so immensely in favour of

natural selection as an important cause of organic evolution, are those

of domestication. The art of the horticulturist, the fancier, the

cattle-breeder, &c., consists in producing greater and greater

deviations from a given wild type of plant or animal, in any particular

direction that may be desired for purposes either of use or of beauty.

Cultivated cereals, fruits, and flowers are known to have been all

derived from wild species; and, of course, the same applies to all our

domesticated varieties of animals. Yet if we compare a cabbage rose with

a wild rose, a golden pippin apple with a crab, a toy terrier with any

species of wild dog, not to mention any number of other instances, there

can be no question that, if such differences had appeared in nature, the

organisms presenting them would have been entitled to rank as distinct

species--or even, in many cases, as distinct genera. Yet we know, as a

matter of fact, that all these differences have been produced by a

process of artificial selection, or pairing, which has been continuously

practised by horticulturists and breeders through a number of

generations. It is the business of these men to note the individual

organisms which show most variation in the directions required, and then

to propagate from these individuals, in order that the progeny shall

inherit the qualities desired. The results thus become cumulative from

generation to generation, until we now have an astonishing manifestation

of useful qualities on the one hand, and of beautiful qualities on the

other, according as the organisms have been thus bred for purposes of

use or for those of beauty.

Now it is immediately obvious that in these cases the process of

artificial selection is precisely analogous to that of natural selection

(and of sexual selection which will be considered later on), in all

respects save one: the utility or the beauty which it is the aim of

artificial selection continually to enhance, is utility or beauty in

relation to the requirements or to the tastes of man; whereas the

utility or the beauty which is produced by natural selection and sexual

selection has reference only to the requirements or the tastes of the

organisms themselves. But, with the exception of this one point of

difference, the processes and the products are identical in kind.

Persevering selection by man is thus proved to be capable of creating

what are virtually new specific types, and this in any required

direction. Hence, when we remember how severe is the struggle for

existence in nature, it becomes impossible to doubt that selection by

nature is able to do at least as much as artificial selection in the way

of thus creating new types out of old ones. Artificial selection,

indeed, notwithstanding the many and marvellous results which it has

accomplished, can only be regarded as but a feeble imitation of natural

selection, which must act with so much greater vigilance and through

such immensely greater periods of time. In a word, the proved

capabilities of artificial selection furnish, in its best conceivable

form, what is called an argument _a fortiori_ in favour of natural

selection.

Or, to put it in another way, it may be said that for thousands of years

mankind has been engaged in making a gigantic experiment to test, as it

were by anticipation, the theory of natural selection. For, although

this prolonged experiment has been carried on without any such intention

on the part of the experimenters, it is none the less an experiment in

the sense that its results now furnish an overwhelming verification of

Mr. Darwin's theory. That is to say, they furnish overwhelming proof of

the efficacy of the selective principle in the modification of organic

types, when once this principle is brought steadily and continuously to

bear upon a sufficiently long series of generations.

In order to furnish ocular evidence of the value of this line of

verification, I have had the following series of drawings prepared.

Another and equally striking series might be made of the products of

artificial selection in the case of plants; but it seems to me that the

case of animals is more than sufficient for the purpose just stated.

Perhaps it is desirable to add that considerable care has been bestowed

upon the execution of these portraits; and that in every case the latter

have been taken from the most typical specimens of the artificial

variety depicted. Those of them which have not been drawn directly from

life are taken from the most authoritative sources; and, before being

submitted to the engraver, they were all examined by the best judges in

each department. In none of the groups, however, have I aimed at an

exhaustive representation of all the varieties: I have merely introduced

representatives of as many as the page would in each case accommodate.

[Illustration: FIG. 91.--Pigeons. Drawn from life (prize

specimens).]

[Illustration: FIG. 92.--Pigeons, continued. Drawn from life (prize

specimens).]

[Illustration: FIG. 93.--Fowls. Drawn from life (prize specimens).]

[Illustration: FIG. 94.--Fowls, continued. Drawn from life (prize

specimens).]

[Illustration: FIG. 95.--Pair of Japanese Fowls, long-tailed breed.

Drawn from stuffed specimens in the British Museum.]

[Illustration: FIG. 96.--Canaries. Drawn from life (prize

specimens).]

[Illustration: FIG. 97.--Sebastopol, or Frizzled Goose. Drawn from a

photograph.]

[Illustration: FIG. 98.--The Dingo, or wild dog of Australia, 1/10

nat. size. Drawn from life (_Zoological Gardens_).]

[Illustration: FIG. 99.--Dogs. Drawn from life (prize specimens).]

[Illustration: FIG. 100.--Dogs, continued. Drawn from life (prize

specimens).]

[Illustration: FIG. 101.--The Hairless Dog of Japan, 1/10 nat. size.

Drawn from a photograph kindly lent for the purpose by the

proprietor.]

[Illustration: FIG. 102.--The skull of a Bull-dog compared with that

of a Deerhound. Drawn from nature.]

[Illustration: FIG. 103. Rabbits. Drawn from life (prize

specimens).]

[Illustration: FIG. 104.--Horses. Drawn from life (prize

specimens).]

[Illustration: FIG. 105.--Sheep. The illustrations are confined to

British breeds. Drawn from life (prize specimens).]

[Illustration: FIG. 106.--Cattle. The illustrations are confined to

British breeds. Drawn from life (prize specimens).]

[Illustration: FIG. 107.--Wild Boar contrasted with a modern

Domesticated Pig. Drawn from life (_Zoological Gardens_, and prize

specimen).]

The exigencies of space have prevented, in some of the groups, strict

adherence to a uniform scale--with the result that contrasts between

different breeds in respect of size are not adequately rendered. This

remark applies especially to the dogs; for although the artist has

endeavoured to draw them in perspective, unless the distance between

those in the foreground and those in the background is understood to be

more considerable than it appears, an inadequate idea is given of the

relative differences of size. The most instructive of the groups, I

think, is that of the Canaries; because the many and great changes in

different directions must in this case have been produced by artificial

selection in so comparatively short a time--the first mention of this

bird that I can find being by Gesner, in the sixteenth century.

* * * * *

Now, it is surely unquestionable that in these typical proofs of the

efficacy of artificial selection in the modification of specific types,

we have the strongest conceivable testimony to the power of natural

selection in the same direction. For it thus appears that wherever

mankind has had occasion to operate by selection for a sufficiently long

time--that is to say, on whatever species of plant or animal he chooses

thus to operate for the purpose of modifying the type in any required

direction,--the results are always more or less the same: he finds that

all specific types lend themselves to continuous deflection in any

particulars of structure, colour, &c., that he may desire to modify.

Nevertheless, to this parallel between the known effects of artificial

selection, and the inferred effects of natural selection, two objections

have been urged. The first is, that in the case of artificial selection

the selecting agent is a voluntary intelligence, while in the case of

natural selection the selecting agent is Nature herself; and whether or

not there is any counterpart of man's voluntary intelligence in nature

is a question with which Darwinism has nothing to do. Therefore, it is

alleged, the analogy between natural selection and artificial selection

fails _ab initio_, or at the fountain-head of the causes which are taken

by the analogy to be respectively involved.

The second objection to the analogy is, that the products of artificial

selection, closely as they may resemble natural species in all other

respects, nevertheless present one conspicuous and highly important

point of difference: they rarely, if ever, present the physiological

character of mutual infertility, which is a character of extremely

general occurrence in the case of natural species, even when these are

most nearly allied.

I will deal with these two objections in the next chapter, where I shall

be concerned with the meeting of all the objections which have ever been

urged against the theory of natural selection. Meanwhile I am engaged

only in presenting the general arguments which support the theory, and

therefore mention these objections to one of them merely _en passant_.

And I do so in order to pledge myself effectually to dispose of them

later on, so that for the purposes of my present argument both these

objections may be provisionally regarded as non-existent; which means,

in other words, that we may provisionally regard the analogy between

artificial selection and natural selection as everywhere logically

intact.

* * * * *

To sum up, then, the results of the foregoing exposition thus far, what

I hold to be the three principal, or most general, arguments in favour

of the theory of natural selection, are as follows.

First, there is the _a priori_ consideration that, if on independent

grounds we believe in the theory of evolution at all, it becomes obvious

that natural selection _must_ have had _some_ part in the process. For

no one can deny the potent facts of heredity, variability, the struggle

for existence, and survival of the fittest. But to admit these facts is

to admit natural selection as a principle which must be, at any rate,

one of the factors of organic evolution, supposing such evolution to

have taken place. Next, when we turn from these _a priori_

considerations, which thus show that natural selection _must_ have been

concerned to some extent in the process of evolution, we find in organic

nature evidence _a posteriori_ of the extent to which this principle

_has_ been thus concerned. For we find that among all the countless

millions of adaptive structures which are to be met with in organic

nature, it is an invariable rule that they exist in relation to the

needs of the particular species which present them: they never have any

primary reference to the needs of other species. And as this

extraordinarily large and general fact is exactly what the theory of

natural selection would expect, the theory is verified by the fact in an

extraordinarily cogent manner. In other words, the fact goes to prove

that in _all_ cases where adaptive structures or instincts are

concerned, natural selection must have been either the sole cause at

work, or, at the least, an influence controlling the operation of all

other causes.

Lastly, an actually experimental verification of the theory has been

furnished on a gigantic scale by the operations of breeders, fanciers,

and horticulturists. For these men, by their process of selective

accumulation, have empirically proved what immense changes of type may

thus be brought about; and so have verified by anticipation, and in a

most striking manner, the theory of natural selection--which, as now so

fully explained, is nothing more than a theory of cumulative

modifications by means of selective breeding.

So much, then, by way of generalities. But perhaps the proof of natural

selection as an agency of the first importance in the transmutation of

species may be best brought home to us by considering a few of its

applications in detail. I will therefore devote the rest of the present

chapter to considering a few cases of this kind.

There are so many large fields from which such special illustrations may

be supplied, that it is difficult to decide which of them to draw upon.

For instance, the innumerable, always interesting, and often astonishing

adaptations on the part of flowers to the fertilising agency of insects,

has alone given rise to an extensive literature since the time when

Darwin himself was led to investigate the subject by the guidance of his

own theory. The same may be said of the structures and movements of

climbing plants, and in short, of all the other departments of natural

history where the theory of natural selection has led to the study of

the phenomena of adaptation. For in all these cases the theory of

natural selection, which first led to their discovery, still remains the

only scientific theory by which they can be explained. But among all the

possible fields from which evidences of this kind may be drawn, I think

the best is that which may be generically termed defensive colouring. To

this field, therefore, I will restrict myself. But, even so, the cases

to be mentioned are but mere samples taken from different divisions of

this field; and therefore it must be understood at the outset that they

could easily be multiplied a hundred-fold.

_Protective Colouring._

A vast number of animals are rendered more or less inconspicuous by

resembling the colours of the surfaces on which they habitually rest.

Such, for example, are grouse, partridges, rabbits, &c. Moreover, there

are many cases in which, if the needs of the creature be such that it

must habitually frequent surfaces of different colours, it has acquired

the power of changing its colour accordingly--e. g. cuttle-fish,

flat-fish, frogs, chameleons, &c. The physiological mechanism whereby

these adaptive changes of colour are produced differs in different

animals; but it is needless for our purposes to go into this part of the

subject. Again, there are yet other cases where protective colouring

which is admirably suited to conceal an animal through one part of the

year, would become highly conspicuous during another part of it--namely,

when the ground is covered with snow. Accordingly, in these cases the

animals change their colour in the winter months to a snowy white:

witness stoats, mountain hares, ptarmigan, &c. (Fig. 108.)

[Illustration: FIG. 108.--Seasonal changes of colour in Ptarmigan

(_Lagopus mutus_). Drawn from stuffed specimens in the British

Museum, 1/6 nat. size, with appropriate surroundings supplied.]

Now, it is sufficiently obvious that in all these classes of cases the

concealment from enemies or prey which is thus secured is of advantage

to the animals concerned; and, therefore, that in the theory of natural

selection we have a satisfactory theory whereby to explain it. And this

cannot be said of any other theory of adaptive mechanisms in nature that

has ever been propounded. The so-called Lamarckian theory, for instance,

cannot be brought to bear upon the facts at all; and on the theory of

special creation it is unintelligible why the phenomena of protective

colouring should be of such general occurrence. For, in as far as

protective colouring is of advantage to the species which present it, it

is of corresponding disadvantage to those other species against the

predatory nature of which it acts as a defence. And, of course, the

same applies to yet other species, if they serve as prey. Moreover,

the more minutely this subject is investigated in all its details,

the more exactly is it found to harmonise with the naturalistic

interpretation[38].

[38] Were it not that some of Darwin's critics have overlooked the

very point wherein the great value of protective colouring as

evidence of natural selection consists, it would be needless to

observe that it does so in the _minuteness_ of the protective

resemblance which in so many cases is presented. Of course where the

resemblance is only very general, the phenomena might be ascribed to

mere coincidence, of which the instincts of the animal have taken

advantage. But in the measure that the resemblance becomes minutely

detailed, the supposition of mere coincidence is excluded, and the

agency of some specially adaptive cause demonstrated. Again, it is

almost needless to say, no real difficulty is presented (as has been

alleged) by the cases above quoted of seasonal imitations, on the

ground that natural selection could not act alternately on the same

individual. Natural selection is not supposed to act alternately on

the same individual. It is supposed to act always in the same

manner, and if, as in the case of a regularly recurring change in

the colours of the environment, correspondingly recurrent changes

are required to appear in the colours of the animals, natural

selection sets its premium upon those individuals the constitutions

of which best lend themselves to seasonal changes of the needful

kind--probably under the influence of stimuli supplied by the

changes of external conditions (temperature, moisture, &c.).

In the first place, we always find a complete correspondence between

imitative colouring and instinctive endowment. If a caterpillar exactly

resembles the colour of a twig, it also presents the instinct of

habitually reposing in the attitude which makes it most resemble a

twig--standing out from the branch on which it rests at the same angle

as is presented by the real twigs of the tree on which it lives.

Here, again, is a bird protectively coloured so as to resemble stones

upon the rough ground where it habitually lives; and the drawing shows

the attitude in which the bird instinctively reposes, so as still

further to increase its resemblance to a stone. (Fig. 109.)

[Illustration: FIG. 109.--_Oedicnemus crepitans_, showing the

instinctive attitude of concealment. Drawn from a stuffed specimen

in the British Museum, 1/6 nat. size, with appropriate surroundings

supplied.

To take only one other instance, hares and rabbits, like grouse and

partridges--or like the plover just alluded to,--instinctively crouch

upon those surfaces the colours of which they resemble; and I have often

remarked that if, on account of any individual peculiarity of

coloration, the animal is not able thus to secure concealment, it

nevertheless exhibits the instinct of crouching which is of benefit to

all its kind, although, from the accident of its own abnormal colouring,

this instinct is then actually detrimental to the animal itself. For

example, every sportsman must have noticed that the somewhat rare

melanic variety of the common rabbit will crouch as steadily as the

normal brownish-gray type, notwithstanding that, owing to its abnormal

colour, a "nigger-rabbit" thus renders itself the most conspicuous

object in the landscape. In all such cases, of course, there has been a

deviation from the normal type in respect of colour, with the result

that the inherited instinct is no longer in tune with the other

endowments of the animal. Such a variation of colour, therefore, will

tend to be suppressed by natural selection; while any variations which

may bring the animal still more closely to resemble its habitual

surroundings will be preserved. Thus we can understand the truly

wonderful extent to which this principle of protective colouring has

been carried in many cases where the need of it has been most urgent.

Not only colour, but structure, may be profoundly modified for the

purposes of protective concealment. Thus, caterpillars which resemble

twigs do so not only in respect of colour, but also of shape; and this

even down to the most minute details in cases where the adaptation is

most complete: certain butterflies and leaf-insects so precisely

resemble the leaves upon which, or among which, they live, that it is

almost impossible to detect them in the foliage--not only the colour,

the shape, and the venation being all exactly imitated, but in some

cases even the defects to which the leaves are liable, in the way of

fungoid growths, &c. There are other insects which with similar

exactness resemble moss, lichens, and so forth. A species of fish

secures a complete resemblance to bunches of sea-weed by a frond-like

modification of all its appendages, and so on through many other

instances. Now, in all such cases where there is so precise an

imitation, both in colour and structure, it seems impossible to suggest

any other explanation of the facts than the one which is supplied by

Mr. Darwin's theory--namely, that the more perfect the resemblance is

caused to become through the continuous influence of natural selection

always picking out the best imitations, the more highly discriminative

becomes the perception of those enemies against the depredations of

which this peculiar kind of protection is developed; so that, in virtue

of this action and re-action, eventually we have a degree of imitation

which renders it almost impossible for a naturalist to detect the animal

when living in its natural environment.

[Illustration: FIG. 110.--Imitative forms and colours in insects.

Drawn from nature (_R. Coll. Surg. Mus._).]

_Warning Colours._

In strange and glaring contrast to all these cases of protective

colouring, stand other cases of conspicuous colouring. Thus, for

example, although there are numberless species of caterpillars which

present in an astonishing degree the phenomena of protective colouring,

there are numberless other species which not only fail to present these

phenomena in any degree, but actually go to the opposite extreme of

presenting colours which appear to have been developed for the sake of

their conspicuousness. At all events, these caterpillars are usually the

most conspicuous objects in their surroundings, and therefore in the

early days of Darwinism they were regarded by Darwin himself as

presenting a formidable difficulty in the way of his theory. To Mr.

Wallace belongs the merit of having cleared up this difficulty in an

extraordinarily successful manner. He virtually reasoned thus. If the

_raison d'etre_ of protective colouring be that of concealing agreeably

flavoured caterpillars from the eye-sight of birds, may not the _raison

d'etre_ of conspicuous colouring be that of protecting disagreeably

flavoured caterpillars from any possibility of being mistaken by birds?

Should this be the case, of course the more conspicuous the colouring

the better would it be for the caterpillars presenting it. Now as soon

as this suggestion was acted upon experimentally, it was found to be

borne out by facts. Birds could not be induced to eat caterpillars of

the kinds in question; and there is now no longer any doubt that their

conspicuous colouring is correlated with their distastefulness to birds,

in the same way as the inconspicuous or imitative colouring of other

caterpillars is correlated with their tastefulness to birds. Here then

is yet another instance, added to those already given, of the

verification yielded to the theory of natural selection by its proved

competency as a guide to facts in nature; for assuredly this particular

class of facts would never have been suspected but for its suggestive

agency.

As in the case of protective imitation, so in this case of warning

conspicuousness, not only colour, but structure may be greatly modified

for the purpose of securing immunity from attack. Here, of course, the

object is to assume, as far as possible, a touch-me-not appearance; so

that, although destitute of any real means of offence, the creatures in

question present a fictitiously dangerous aspect. As the

Devil's-coach-horse turns up his stingless tail when threatened by an

enemy, so in numberless ways do many harmless animals of all classes

pretend to be formidable. But the point now is that these instincts of

self-defence are often helped out by structural modifications,

expressly and exclusively adapted to this end. For example, what a

remarkable series of protective adjustments occurs in the life-history

of the Puss Moth--culminating with so comical an instance of the

particular device now under consideration as the following. I quote the

facts from Mr. E. B. Poulton's admirable book on _The Colours of

Animals_ (pp. 269-271).

[Illustration: FIG. 111.--The larva of Puss Moth (_C. vinula_)

when undisturbed; full-fed; natural size.]

The larva of the Puss Moth (Cerura vinula) is very common upon

poplar and willow. The circular dome-like eggs are laid, either

singly or in little groups of two or three, upon the upper side of

the leaf, and being of a reddish colour strongly suggest the

appearance of little galls, or the results of some other injury to

the leaf. The youngest larvae are black, and also rest upon the

upper surface of the leaf, resembling the dark patches which are

commonly seen in this position. As the larva grows, the apparent

black patch would cover too large a space, and would lead to

detection if it still occupied the whole surface of the body. The

latter gains a green ground-colour which harmonises with the leaf,

while the dark marking is chiefly confined to the back. As growth

proceeds the relative amount of green increases, and the dark mark

is thus prevented from attaining a size which would render it too

conspicuous. In the last stage of growth the green larva becomes

very large, and usually rests on the twigs of its food-plant (Fig.

111). The dark colour is still present on the back but is softened

to a purplish tint, which tends to be replaced by a combination of

white and green in many of the largest larvae. Such a larva is well

concealed by General Protective Resemblance, and one may search a

long time before finding it, although assured of its presence from

the stripped branches of the food-plant and the faeces on the ground

beneath.

[Illustration: FIG. 112.--The larva of Puss Moth in its terrifying

attitude after being disturbed; full-fed; natural size.]

As soon as a large larva is discovered and disturbed it withdraws

its head into the first body-ring, inflating the margin, which is

of a bright red colour. There are two intensely black spots on this

margin in the appropriate position for eyes, and the whole

appearance is that of a large flat face extending to the outer edge

of the red margin (see Fig. 112). The effect is an intensely

exaggerated caricature of a vertebrate face, which is probably

alarming to the vertebrate enemies of the caterpillar. The

terrifying effect is therefore mimetic. The movements entirely

depend on tactile impressions: when touched ever so lightly a

healthy larva immediately assumes the terrifying attitude, and

turns so as to present its full face towards the enemy; if touched

on the other side or on the back it instantly turns its face in the

appropriate direction. The effect is also greatly strengthened by

two pink whips which are swiftly protruded from the prongs of the

fork in which the body terminates. The prongs represent the last

pair of larval legs which have been greatly modified from their

ordinary shape and use. The end of the body is at the same time

curved forward over the back (generally much further than in Fig.

112), so that the pink filaments are brandished above the head.

_Mimicry._

Lastly, these facts as to imitative and conspicuous colouring lead on to

the yet more remarkable facts of what is called mimicry. By mimicry is

meant the imitation in form and colour of one species by another, in

order that the imitating species may be mistaken for the imitated, and

thus participate in some advantage which the latter enjoys. For

instance, if, as in the case of the conspicuously-coloured caterpillars,

it is of advantage to an ill-savoured species that it should hold out a

warning to enemies, clearly it may be of no less advantage to a

well-savoured species that it should borrow this flag, and thus be

mistaken for its ill-savoured neighbour. Now, the extent to which this

device of mimicry is carried is highly remarkable, not only in respect

of the number of its cases, but also in respect of the astonishing

accuracy which in most of these cases is exhibited by the imitation.

There need be little or virtually no zoological affinity between the

imitating and the imitated forms; that is to say, in some cases the

zoological affinity is not closer than ordinal, and therefore cannot

possibly be ascribed to kinship. Like all the other branches of the

general subject of protective resemblance in form or colouring, this

branch has already been so largely illustrated by previous writers,

that, as in the previous cases, I need only give one or two examples.

Those which I choose are chosen on account of the colours concerned not

being highly varied or brilliant, and therefore lending themselves to

less ineffectual treatment by wood-engraving than is the case where

attempts are made to render by this means even more remarkable

instances. (Figs. 113, 114, 115.)

[Illustration: FIG. 113.--Three cases of mimicry. Drawn from nature:

first two pairs nat. size, last pair 2/3 (_R. Coll. Surg. Mus._).]

[Illustration: FIG. 114.--Two further cases of mimicry; flies

resembling a wasp in the one and a bee in the other. Drawn from

nature: nat. size (_R. Coll. Surg. Mus._).]

[Illustration: FIG. 115.--A case of mimicry where a non-venomous

species of snake resembles a venomous one. Drawn from nature: 1/3

nat. size (_R. Coll. Surg. Mus._).]

It is surely apparent, without further comment, that it is impossible to

imagine stronger evidence in favour of natural selection as a true cause

in nature, than is furnished by this culminating fact in the matter of

protective resemblance, whereby it is shown that a species of one

genus, family, or even order, will accurately mimic the appearance of a

species belonging to another genus, family, or order, so as to deceive

its natural enemies into mistaking it for a creature of so totally

different a kind. And it must be added that while this fact of mimicry

is of extraordinarily frequent occurrence, there can be no possibility

of our mistaking its purpose. For the fact is never observable except in

the case of species which occupy the same area or district.

Such being what appears to me the only reasonable view of the matter, I

will now conclude this chapter on the evidences of natural selection as

at all events the main factor of organic evolution, by simply adding

illustrations of two further cases of mimicry, which are perhaps even

more remarkable than any of the foregoing examples. The first of the two

(Fig. 115) speaks for itself. The second will be rendered intelligible

by the following few words of explanation.

There are certain ants of the Amazons which present the curious instinct

of cutting off leaves from trees, and carrying them like banners over

their heads to the hive, as represented in Fig. 116, B, where one ant is

shown without a leaf, and the others each with a leaf. Their object in

thus collecting leaves is probably that of growing a fungus upon the

"soil" which is furnished by the leaves when decomposing. But, be this

as it may[39], the only point we are now concerned with is the

appearance which these ants present when engaged in their habitual

operation of carrying leaves. For it has been recently observed by Mr.

W. L. Sclater, that in the localities where these hymenopterous insects

occur, there occurs also a _homopterous_ insect which mimics the ant,

leaf and all, in a wonderfully deceptive manner. The leaf is imitated by

the thin flattened body of the insect, "which in its dorsal aspect is so

compressed laterally that it is no thicker than a leaf, and terminates

in a sharp jagged edge." The colour is exactly the same as that of a

leaf, and the brown legs show themselves beneath the green body in just

the same way as those of the ant show themselves beneath the leaf. So

that both the form and the colouring of the homopterous insect has been

brought to resemble, with singular exactness, those belonging to a

different order of insect, when the latter is engaged in its peculiar

avocation. A glance at the figure is enough to show the means employed

and the result attained. In A, an ant and its mimic are represented as

about 2-1/2 times their natural size, and both proceeding in the same

direction. It ought to be mentioned, however, that in reality the margin

of the leaf is seldom allowed to retain its natural serrations as here

depicted: the ants usually gnaw the edge of the real leaf, so that the

margin of the false one bears an even closer resemblance to it than the

illustration represents. B is a drawing from life of a group of five

ants carrying leaves, and their mimic walking beside them[40].

[39] For a full account of this instinct and its probable purpose,

see _Animal Intelligence_, pp. 93-6.

[40] Both drawings are reproduced from Mr. Poulton's paper upon the

subject (_Proc. Zool. Soc._, June 16, 1891).

[Illustration: FIG. 116 PROTECTIVE MIMICRY]

CHAPTER IX.

CRITICISMS OF THE THEORY OF NATURAL SELECTION.

I will now proceed to consider the various objections and difficulties

which have hitherto been advanced against the theory of natural

selection.

Very early in the day Owen hurled the weight of his authority against

the new theory, and this with a strength of onslaught which was only

equalled by its want of judgment. Indeed, it is painfully apparent that

he failed to apprehend the fundamental principles of the Darwinian

theory. For he says:--

Natural Selection is an explanation of the process [of

transmutation] of the same kind and value as that which has been

proffered of the mystery of "secretion." For example, a particular

mass of matter in a living animal takes certain elements out of the

blood, and rejects them as "bile." Attributes were given to the

liver which can only be predicated of the whole animal; the

"appetency" of the liver, it was said, was for the elements of

bile, and "biliosity," or the "hepatic sensation," guided the gland

to their secretion. Such figurative language, I need not say,

explains absolutely nothing of the nature of bilification[41].

[41] _Anatomy of Vertebrates_, vol. iii. p. 794.

Assuredly, it was needless for Owen to say that figurative language of

this kind explains nothing; but it was little less than puerile in him

to see no more in the theory of natural selection than such a mere

figure of speech. To say that the liver selects the elements of bile, or

that nature selects specific types, may both be equally unmeaning

re-statements of facts; but when it is explained that the term natural

selection, unlike that of "hepatic sensation," is used as a shorthand

expression for a whole group of well-known natural causes--struggle,

variation, survival, heredity,--then it becomes evidence of an almost

childish want of thought to affirm that the expression is figurative and

nothing more. The doctrine of natural selection may be a huge mistake;

but, if so, this is not because it consists of any unmeaning metaphor:

it can only be because the combination of natural causes which it

suggests is not of the same adequacy in fact as it is taken to be in

theory.

Owen further objected that the struggle for existence could only act as

a cause of the extinction of species, not of their origination--a view

of the case which again shows on his part a complete failure to grasp

the conception of Darwinism. Acting alone, the struggle for existence

could only cause extermination; but acting together with variation,

survival, and heredity, it may very well--for anything that Owen, or

others who followed in this line of criticism, show to the

contrary--have produced every species of plant and animal that has ever

appeared upon the face of the earth.

Another and closely allied objection is, that the theory of natural

selection "personifies an abstraction." Or, as the Duke of Argyll states

it, the theory is "essentially the image of mechanical necessity

concealed under the clothes, and parading in the mask, of mental

purpose. The word 'natural' suggests Matter, and the physical forces.

The word 'selection' suggests Mind, and the powers of choice." This,

however, is a mere quarrelling about words. Darwin called the principle

which he had discovered by the name natural selection in order to mark

the analogy between it and artificial selection. No doubt in this

analogy there is not necessarily supposed to be in nature any

counterpart to the mind of the breeder, nor, therefore, to his powers of

intelligent choice. But there is no need to limit the term _selection_

(_se_ and _lego_, Gr. [Greek: lego]) to powers of intelligent choice. As

previously remarked, a bank of sea-weed on the sea-shore may be said to

have been selected by the waves from all the surrounding sand and

stones. Similarly, we may say that grain is selected from chaff by the

wind in the process of winnowing corn. Or, if it be thought that there

is any ambiguity involved in such a use of the term in the case of

"Natural Selection," there is no objection to employing the phrase which

has been coined by Mr. Spencer as its equivalent--namely, "Survival of

the Fittest." The point of the theory is, that those organisms which are

best suited to their surroundings are allowed to live and to propagate,

while those which are less suited are eliminated; and whether we call

this process a process of selection, or call it by any other name, is

clearly immaterial.

A material question is raised only when it is asked whether the process

is one that can be ascribed to causation strictly natural. It is often

denied that such is the case, on the ground that natural selection does

not originate the variations which it favours, but depends upon the

variations being supplied by some other means. For, it is said, all that

natural selection does is to preserve the suitable variations _after

they have arisen_. Natural selection does not _cause_ these suitable

variations; and therefore, it is argued, Darwin and his followers are

profoundly mistaken in representing the principle as one which

_produces_ adaptations. Now, although this objection has been put

forward by some of the most intelligent minds in our generation, it

appears to me to betoken some extraordinary failure to appreciate the

very essence of Darwinian doctrine. No doubt it is perfectly true that

natural selection does not produce variations of any kind, whether

beneficial or otherwise. But if it be granted that variations of many

kinds are occurring in every generation, and that natural selection is

competent to preserve the more favourable among them, then it appears to

me unquestionable that this principle of selection deserves to be

regarded as, in the full sense of the word, a natural cause. The

variations being expressly regarded by the theory as more or less

promiscuous[42], survival of the fittest becomes the winnowing fan,

whose function it is to eliminate all the less fit in each generation,

in order to preserve the good grain, out of which to constitute the next

generation. And as this process is supposed to be continuous through

successive generations, its action is supposed to be cumulative, till

from the eye of a worm there is gradually developed the eye of an eagle.

Therefore it follows from these suppositions (which are not disputed by

the present objection), that if it had not been for the process of

selection, such development would never have been begun; and that in the

exact measure of its efficiency will the development proceed. But any

agency without the operation of which a result cannot take place may

properly be designated the cause of that result: it is the agency which,

in co-operation with all the other agencies in the cosmos, produces that

result.

[42] The degree in which variability is indefinite, or, on the

contrary, determinate, is a question which is not yet ripe for

decision--nor even, in my opinion, for discussion. But I may here

state the following general principles with regard to it.

(1) It is evident that up to some point or another variations _must_

be pre-determined in definite lines. Men do not gather grapes from

thorns, figs from thistles, nor even moss-roses from sweet-briars.

In other words, "the nature of the organism" in all cases

necessitates the limiting of variations within certain bounds.

(2) But when the question is as to what these bounds may be, we can

only answer in a general way that, according to the general theory

of evolution, they must be such as are imposed by heredity, coupled

with the degree to which external conditions of life (and possibly

also use-inheritance) are capable, in given cases, of modifying

congenital characters. These are the only causes which the theory of

descent can consistently recognise as producing variations in

determinate directions.

(3) Inasmuch as variation presupposes the existence of parts that

vary, and inasmuch as the variation of parts can only be in the

alternative directions of increase or decrease around an average, it

follows that, in the first instance at all events, every variation,

if determinate, must be so only in one or other of these two

opposite directions.

(4) In as far as variations are summated in successive generations,

so as eventually to give rise to new structures, organs, mechanisms,

&c., natural selection is theoretically competent to explain the

facts, without our having to postulate the operation of unknown

causes producing variations in determinate lines,--or not further

than is stated in paragraphs 1 and 2.

(5) Nevertheless, it does not follow that there are not such other

unknown causes; and, if there are, of course the importance of

natural selection as a cause of adaptive modification would be

limited in proportion to their number and the extent of their

operation. But it is for those who, like the late Professors Asa

Gray and Naegeli, maintain the existence of such causes, to

substantiate their belief by indicating them.

Take any analogous case. The selective agency of specific gravity which

is utilised in gold-washing does not create the original differences

between gold-dust and dust of all other kinds. But these differences

being presented by as many different bodies in nature, the gold-washer

takes advantage of the selective agency in question, and, by using it as

a cause of segregation, is enabled to separate the gold from all the

earths with which it may happen to be mixed. So far as the objects of

the gold-washer are concerned, it is immaterial with what other earths

the gold-dust may happen to be mixed. For although gold-dust may occur

in intimate association with earths of various kinds in various

proportions, and although in each case the particular admixture which

occurs must have been due to definite causes, these things, in relation

to the selective process of the washer, are what is called accidental:

that is to say, they have nothing to do with the causative action of the

selective process. Now, in precisely the same sense Darwin calls the

multitudinous variations of plants and animals accidental. By so calling

them he expressly says he does not suppose them to be accidental in the

sense of not all being due to definite causes. But they are accidental

in relation to the sifting process of natural selection: all that they

have to do is to furnish the promiscuous material on which this sifting

process acts.

Or let us take an even closer analogy. The power of selective breeding

by man is so wonderful, that in the course of successive generations all

kinds of peculiarities as to size, shape, colour, special appendages or

abortions, &c., can be produced at pleasure, as we saw in the last

chapter. Now all the promiscuous variations which are supplied to the

breeder, and out of which, by selecting only those that are suited to

his purpose, he is able to produce the required result--all those

promiscuous variations, in relation to that purpose, are accidental.

Therefore the selective agency of the breeder deserves to be regarded as

the cause of that which it produces, or of that which could not have

been produced but for the operation of such agency. But where is the

difference between artificial and natural selection in this respect?

And, if there is no difference, is not natural selection as much

entitled to be regarded as a true cause of the origin of natural

species, as artificial selection is to be regarded as a true cause of

our domesticated races? Here, as in the case of the previous

illustration, if there be any ambiguity in speaking of variations as

accidental, it arises from the incorrect or undefined manner in which

the term "accidental" is used by Darwin's critics. In its original and

philosophically-correct usage, the term "accident" signifies a property

or quality not essential to our conception of a substance: hence, it has

come to mean anything that happens as a result of unforeseen causes--or,

lastly, that which is causeless. But, as we know that nothing can happen

without causes of some kind, the term "accident" is divested of real

meaning when it is used in the last of these senses. Yet this is the

sense that is sought to be placed upon it by the objection which we are

considering. If the objectors will but understand the term in its

correct philosophical sense--or in the only sense in which it presents

any meaning at all,--they will see that Darwinians are both logically

and historically justified in employing the word "accidental" as the

word which serves most properly to convey the meaning that they

intend--namely, variations due to causes accidental to the struggle for

existence. Similarly, when it is said that variations are "spontaneous,"

or even "fortuitous," nothing further is meant than that we do not know

the causes which lead to them, and that, so far as the principle of

selection is concerned, it is immaterial what these causes may be. Or,

to revert to our former illustration, the various weights of different

kinds of earths are no doubt all due to definite causes; but, in

relation to the selective action of the gold-washer, all the different

weights of whatever kinds of earth he may happen to include in his

washing-apparatus are, _strictly speaking_, accidental. And as at

different washings he meets with different proportions of heavy earths

with light ones, and as these "variations" are immaterial to him, he may

colloquially speak of them as "fortuitous," or due to "chance," even

though he knows that at each washing they must have been determined by

definite causes.

More adequately to deal with this merely formal objection, however,

would involve more logic-chopping than is desirable on the present

occasion. But I have already dealt with it fully elsewhere,--viz. in

_The Contemporary Review_ for June, 1888, to which therefore I may refer

any one who is interested in dialectics of this kind[43].

[43] Within the last few months this objection has been presented

anew by Mr. D. Syme, whose book _On the Modification of Organisms_

exhibits a curious combination of shrewd criticisms with almost

ludicrous misunderstandings. One of the latter it is necessary to

state, because it pervades the quotation which I am about to supply.

He everywhere compares "natural selection" with "the struggle for

existence," uses them as convertible terms, and while absurdly

stating that "Darwin defines natural selection as the struggle for

existence," complains of "the liability of error, both on his own

part and on the part of his readers," which arises from his not

having everywhere adhered to this definition! (p. 8).

"Darwin has put forth two distinct and contradictory theories of the

functions of natural selection. According to the one theory natural

selection is selective or preservative, and nothing more. According

to the other theory natural selection creates the variations(!) ...

It certainly seems absurd to speak of natural selection, or the

struggle for existence, as selective or preservative, for the

struggle for existence does not preserve at all, not even the fit

variations, as both the fit and the unfit struggle for existence,

the unfit naturally more than the fit, and the fit are preserved,

not in consequence of the struggle, but in consequence of their

fitness. Suppose two varieties of the same species are driven, by an

increase of their numbers, to seek for subsistence in a colder

region than they have been accustomed to, and that one of these

varieties had a hardier constitution than the other; and let us

suppose that the former withstood the severe climate better than the

latter, and consequently survived, while the other perished. In this

case the hardier survived, not because of the struggle, but because

it had a constitution better adapted to the climate. I wish to

ascertain if a certain metal in my possession is gold or some baser

metal, and I apply the usual test; but the mere fact of my testing

this metal would not make it gold or any other kind of metal."

I have thought it worth while to quote this passage for the sake of

showing the extraordinary confusion of mind which still prevails on

the part of Darwin's critics, even with reference to the very

fundamental parts of his theory. For, as I have said, the writer of

this passage shows himself a shrewd critic in some other parts of

his essay, where he is not engaged especially on the theory of

natural selection.

I will now pass on to consider another misconception of the Darwinian

theory, which is very prevalent in the public mind. It is virtually

asked, If some species are supposed to have been improved by natural

selection, why have not all species been similarly improved? Why should

not all invertebrated animals have risen into vertebrated? Or why

should not all monkeys have become men?

The answers are manifold. In the first place, it by no means follows

that because an advance in organization has proved itself of benefit in

the case of one form of life, therefore any or every other form would

have been similarly benefited by a similar advance. The business of

natural selection is to bring this and that form of life into the

closest harmony with its environment that all the conditions of the case

permit. Sometimes it will happen that the harmony will admit of being

improved by an improvement of organization. But just as often it will

happen that it will be best secured by leaving matters as they are. If,

therefore, an organism has already been brought into a tolerably full

degree of harmony with its environment, natural selection will not try

to change it so long as the environment remains unchanged; and this, no

doubt, is the reason why some species have survived through enormous

periods of geological time without having undergone any change. Again,

as we saw in a previous chapter, there are yet other cases where, on

account of some change in the environment or even in the habits of the

organisms themselves, adaption will be best secured by an active

_reversal_ of natural selection, with the result of causing

_degeneration_.

But, it is sometimes further urged, there are cases where we cannot

doubt that improvement of organization would have been of benefit to

species; and yet such improvement has not taken place--as, for instance,

in the case all monkeys not turning into men. Here, however, we must

remember that the operation of natural selection in any case depends

upon a variety of highly complex conditions; and, therefore, that the

fact of all those conditions having been satisfied in one instance is no

reason for concluding that they must also have been satisfied in other

instances. Take, for example, the case of monkeys passing into men. The

wonder to me appears to be that this improvement should have taken place

in even one line of descent; not that, having taken place in one line,

it should not also have taken place in other lines. For how enormously

complex must have been the conditions--physical, anatomical,

physiological, psychological, sociological--which by their happy

conjunction first began to raise the inarticulate cries of an ape into

the rational speech of a man. Therefore, the more that we appreciate the

superiority of a man to an ape, the less ought we to countenance this

supposed objection to Darwin's theory--namely, that natural selection

has not effected the change in more than one line of descent.

Even in the case of two races of mankind where one has risen higher in

the scale of civilization than another, it is now generally impossible

to assign the particular causes of the difference; much more, then, must

this be impossible in the case of still more remote conditions which

have led to the divergence of species. The requisite variations may not

have arisen in the one line of descent which did arise in the other; or

if they did arise in both, some counterbalancing disadvantages may have

attended their initial development in the one case which did not obtain

in the other. In short, where so exceedingly complex a play of

conditions are concerned, the only wonder would be if two different

lines of descent _had_ happened to present two independent and yet

perfectly parallel lines of history.

These general considerations would apply equally to the great majority

of other cases where some types have made great advances upon others,

notwithstanding that we can see no reason why the latter should not in

this respect have imitated the former. But there is yet a further

consideration which must be taken into account. The struggle for

existence is always most keen between closely allied species, because,

from the similarity of their forms, habits, needs, &c., they are in

closest competition. Therefore it often happens that the mere fact of

one species having made an advance upon others of itself precludes the

others from making any similar advance: the field, so to speak, has

already been occupied as regards that particular improvement, and where

the struggle for existence is concerned possession is emphatically nine

points of the law. For example, to return to the case of apes becoming

men, the fact of one rational species having been already evolved (even

if the rational faculty were at first but dimly nascent) must make an

enormous change in the conditions as regards the possibility of any

other such species being subsequently evolved--unless, of course, it be

by way of descent from the rational one. Or, as Sir Charles Lyell has

well put it, two rational species can never _coexist_ on the globe,

although the descendants of one rational species may in time become

_transformed_ into another single rational species[44].

[44] _Principles of Geology_, vol. ii. p. 487 (11th ed.).