The Project Gutenberg ebook of Darwinism (1889), by Alfred Russel Wallace

protected, or the most intelligent, will inevitably, in the long run,

gain an advantage over those which are inferior in these qualities; that

is, _the fittest will survive_, the fittest being, in each particular

case, those which are superior in the special qualities on which safety

depends. At one period of life, or to escape one kind of danger,

concealment may be necessary; at another time, to escape another danger,

swiftness; at another, intelligence or cunning; at another, the power to

endure rain or cold or hunger; and those which possess all these

faculties in the fullest perfection will generally survive.
Having fully grasped these facts in all their fulness and in their

endless and complex results, we have next to consider the phenomena of

variation, discussed in the third and fourth chapters; and it is here

that perhaps the greatest difficulty will be felt in appreciating the

full importance of the evidence as set forth. It has been so generally

the practice to speak of variation as something exceptional and

comparatively rare--as an abnormal deviation from the uniformity and

stability of the characters of a species--and so few even among

naturalists have ever compared, accurately, considerable numbers of

individuals, that the conception of variability as a general

characteristic of all dominant and widespread species, large in its

amount and affecting, not a few, but considerable masses of the

individuals which make up the species, will be to many entirely new.

Equally important is the fact that the variability extends to every

organ and every structure, external and internal; while perhaps most

important of all is the independent variability of these several parts,

each one varying without any constant or even usual dependence on, or

correlation with, other parts. No doubt there is some such correlation

in the differences that exist between species and species--more

developed wings usually accompanying smaller feet and _vice versâ_--but

this is, generally, a useful adaptation which has been brought about by

natural selection, and does not apply to the individual variability

which occurs within the species.
It is because these facts of variation are so important and so little

understood, that they have been discussed in what will seem to some

readers wearisome and unnecessary detail. Many naturalists, however,

will hold that even more evidence is required; and more, to almost any

amount, could easily have been given. The character and variety of that

already adduced will, however, I trust, convince most readers that the

facts are as stated; while they have been drawn from a sufficiently wide

area to indicate a general principle throughout nature.

rapid multiplication and the struggle for existence, most of the

difficulties in the way of comprehending how species have originated

through natural selection will disappear. For whenever, through changes

of climate, or of altitude, or of the nature of the soil, or of the area

of the country, any species are exposed to new dangers, and have to

maintain themselves and provide for the safety of their offspring under

new and more arduous conditions, then, in the variability of all parts,

organs, and structures, no less than of habits and intelligence, we have

the means of producing modifications which will certainly bring the

species into harmony with its new conditions. And if we remember that

all such physical changes are slow and gradual in their operation, we

shall see that the amount of variation which we know occurs in every new

generation will be quite sufficient to enable modification and

adaptation to go on at the same rate. Mr. Darwin was rather inclined to

exaggerate the necessary slowness of the action of natural selection;

but with the knowledge we now possess of the great amount and range of

individual variation, there seems no difficulty in an amount of change,

quite equivalent to that which usually distinguishes allied species,

sometimes taking place in less than a century, should any rapid change

of conditions necessitate an equally rapid adaptation. This may often

have occurred, either to immigrants into a new land, or to residents

whose country has been cut off by subsidence from a larger and more

varied area over which they had formerly roamed. When no change of

conditions occurs, species may remain unchanged for very long periods,

and thus produce that appearance of stability of species which is even

now often adduced as an argument against evolution by natural selection,

but which is really quite in harmony with it.

summarised, we have been able, in the present chapter, to indicate how

natural selection acts, how divergence of character is set up, how

adaptation to conditions at various periods of life has been effected,

how it is that low forms of life continue to exist, what kind of

circumstances are most favourable to the formation of new species, and,

lastly, to what extent the advance of organisation to higher types is

produced by natural selection. We will now pass on to consider some of

the more important objections and difficulties which have been advanced

by eminent naturalists.

77.]
[Footnote 39: _Origin of Species_, p. 89.]

CHAPTER VI

Difficulty as to smallness of variations--As to the right

variations occurring when required--The beginnings of important

organs--The mammary glands--The eyes of flatfish--Origin of the

eye--Useless or non-adaptive characters--Recent extension of the

region of utility in plants--The same in animals--Uses of

tails--Of the horns of deer--Of the scale-ornamentation of

reptiles--Instability of non-adaptive characters--Delboeuf's

law--No "specific" character proved to be useless--The swamping

effects of intercrossing--Isolation as preventing

intercrossing--Gulick on the effects of isolation--Cases in

which isolation is ineffective.

In the present chapter I propose to discuss the more obvious and often

repeated objections to Darwin's theory, and to show how far they affect

its character as a true and sufficient explanation of the origin of

species. The more recondite difficulties, affecting such fundamental

questions as the causes and laws of variability, will be left for a

future chapter, after we have become better acquainted with the

applications of the theory to the more important adaptations and

correlations of animal and plant life.
One of the earliest and most often repeated objections was, that it was

difficult "to imagine a reason why variations tending in an

infinitesimal degree in any special direction should be preserved," or

to believe that the complex adaptation of living organisms could have

been produced "by infinitesimal beginnings." Now this term

"infinitesimal," used by a well-known early critic of the _Origin of

Species_, was never made use of by Darwin himself, who spoke only of

variations being "slight," and of the "small amount" of the variations

that might be selected. Even in using these terms he undoubtedly

afforded grounds for the objection above made, that such small and

slight variations could be of no real use, and would not determine the

survival of the individuals possessing them. We have seen, however, in

our third chapter, that even Darwin's terms were hardly justified; and

that the variability of many important species is of considerable

amount, and may very often be properly described as large. As this is

found to be the case both in animals and plants, and in all their chief

groups and subdivisions, and also to apply to all the separate parts and

organs that have been compared, we must take it as proved that the

average _amount_ of variability presents no difficulty whatever in the

way of the action of natural selection. It may be here mentioned that,

up to the time of the preparation of the last edition of _The Origin of

Species_, Darwin had not seen the work of Mr. J.A. Allen of Harvard

University (then only just published), which gave us the first body of

accurate comparisons and measurements demonstrating this large amount of

variability. Since then evidence of this nature has been accumulating,

and we are, therefore, now in a far better position to appreciate the

facilities for natural selection, in this respect, than was Mr. Darwin

himself.
Another objection of a similar nature is, that the chances are immensely

against the right variation or combination of variations occurring just

when required; and further, that no variation can be perpetuated that is

not accompanied by several concomitant variations of dependent

parts--greater length of a wing in a bird, for example, would be of

little use if unaccompanied by increased volume or contractility of the

muscles which move it. This objection seemed a very strong one so long

as it was supposed that variations occurred singly and at considerable

intervals; but it ceases to have any weight now we know that they occur

simultaneously in various parts of the organism, and also in a large

proportion of the individuals which make up the species. A considerable

number of individuals will, therefore, every year possess the required

combination of characters; and it may also be considered probable that

when the two characters are such that they always _act_ together, there

will be such a correlation between them that they will frequently _vary_

together. But there is another consideration that seems to show that

this coincident variation is not essential. All animals in a state of

nature are kept, by the constant struggle for existence and the survival

of the fittest, in such a state of perfect health and usually

superabundant vigour, that in all ordinary circumstances they possess a

surplus power in every important organ--a surplus only drawn upon in

cases of the direst necessity when their very existence is at stake. It

follows, therefore, that _any_ additional power given to one of the

component parts of an organ must be useful--an increase, for example,

either in the wing muscles or in the form or length of the wing might

give _some_ increased powers of flight; and thus alternate

variations--in one generation in the muscles, in another generation in

the wing itself--might be as effective in permanently improving the

powers of flight as coincident variations at longer intervals. On either

supposition, however, this objection appears to have little weight if we

take into consideration the large amount of coincident variability that

has been shown to exist.

_The Beginnings of Important Organs._

than any other, and which Darwin himself felt to have much weight--the

first beginnings of important organs, such, for example, as wings, eyes,

mammary glands, and numerous other structures. It is urged, that it is

almost impossible to conceive how the first rudiments of these could

have been of any use, and, if not of use they could not have been

preserved and further developed by natural selection.
Now, the first remark to be made on objections of this nature is, that

they are really outside the question of the origin of all existing

species from allied species not very far removed from them, which is all

that Darwin undertook to _prove_ by means of his theory. Organs and

structures such as those above mentioned all date back to a very remote

past, when the world and its inhabitants were both very different from

what they are now. To ask of a new theory that it shall reveal to us

exactly what took place in remote geological epochs, and how it took

place, is unreasonable. The most that should be asked is, that some

probable or possible mode of origination should be pointed out in some

at least of these difficult cases, and this Mr. Darwin has done. One or

two of these may be briefly given here, but the whole series should be

carefully read by any one who wishes to see how many curious facts and

observations have been required in order to elucidate them; whence we

may conclude that further knowledge will probably throw light on any

difficulties that still remain.[41]

that the ancestral mammals were allied to the marsupials. Now in the

very earliest mammals, almost before they really deserved that name, the

young may have been nourished by a fluid secreted by the interior

surface of the marsupial sack, as is believed to be the case with the

fish (Hippocampus) whose eggs are hatched within a somewhat similar

sack. This being the case, those individuals which secreted a more

nutritious fluid, and those whose young were able to obtain and swallow

a more constant supply by suction, would be more likely to live and come

to a healthy maturity, and would therefore be preserved by natural

selection.
In another case which has been adduced as one of special difficulty, a

more complete explanation is given. Soles, turbots, and other flatfish

are, as is well known, unsymmetrical. They live and move on their sides,

the under side being usually differently coloured from that which is

kept uppermost. Now the eyes of these fish are curiously distorted in

order that both eyes may be on the upper side, where alone they would be

of any use. It was objected by Mr. Mivart that a sudden transformation

of the eye from one side to the other was inconceivable, while, if the

transit were gradual the first step could be of no use, since this would

not remove the eye from the lower side. But, as Mr. Darwin shows by

reference to the researches of Malm and others, the young of these fish

are quite symmetrical, and during their growth exhibit to us the whole

process of change. This begins by the fish (owing to the increasing

depth of the body) being unable to maintain the vertical position, so

that it falls on one side. It then twists the lower eye as much as

possible towards the upper side; and, the whole bony structure of the

head being at this time soft and flexible, the constant repetition of

this effort causes the eye gradually to move round the head till it

comes to the upper side. Now if we suppose this process, which in the

young is completed in a few days or weeks, to have been spread over

thousands of generations during the development of these fish, those

usually surviving whose eyes retained more and more of the position into

which the young fish tried to twist them, the change becomes

intelligible; though it still remains one of the most extraordinary

cases of degeneration, by which symmetry--which is so universal a

characteristic of the higher animals--is lost, in order that the

creature may be adapted to a new mode of life, whereby it is enabled the

better to escape danger and continue its existence.

even to the last, Mr. Darwin says, "gave him a cold shiver"--is

nevertheless shown to be not unintelligible; granting of course the

sensitiveness to light of some forms of nervous tissue. For he shows

that there are, in several of the lower animals, rudiments of eyes,

consisting merely of pigment cells covered with a translucent skin,

which may possibly serve to distinguish light from darkness, but nothing

more. Then we have an optic nerve and pigment cells; then we find a

hollow filled with gelatinous substance of a convex form--the first

rudiment of a lens. Many of the succeeding steps are lost, as would

necessarily be the case, owing to the great advantage of each

modification which gave increased distinctness of vision, the creatures

possessing it inevitably surviving, while those below them became

extinct. But we can well understand how, after the first step was taken,

every variation tending to more complete vision would be preserved till

we reached the perfect eye of birds and mammals. Even this, as we know,

is not absolutely, but only relatively, perfect. Neither the chromatic

nor the spherical aberration is absolutely corrected; while long-and

short-sightedness, and the various diseases and imperfections to which

the eye is liable, may be looked upon as relics of the imperfect

condition from which the eye has been raised by variation and natural

selection.

complex organs must suffice here; but the reader who wishes further

information on the matter may study carefully the whole of the sixth

and seventh chapters of the last edition of _The Origin of Species_, in

which these and many other cases are discussed in considerable detail.

_Useless or non-adaptive Characters._

characters which distinguish species are of no service whatever to their

possessors, and therefore cannot have been produced or increased by

natural selection. Professors Bronn and Broca have urged this objection

on the continent. In America, Dr. Cope, the well-known palaeontologist,

has long since put forth the same objection, declaring that non-adaptive

characters are as numerous as those which are adaptive; but he differs

completely from most who hold the same general opinion in considering

that they occur chiefly "in the characters of the classes, orders,

families, and other higher groups;" and the objection, therefore, is

quite distinct from that in which it is urged that "specific characters"

are mostly useless. More recently, Professor G.J. Romanes has urged this

difficulty in his paper on "Physiological Selection" (_Journ. Linn.

Soc._, vol. xix. pp. 338, 344). He says that the characters "which serve

to distinguish allied species are frequently, if not usually, of a kind

with which natural selection can have had nothing to do," being without

any utilitarian significance. Again he speaks of "the enormous number,"

and further on of "the innumerable multitude" of specific peculiarities

which are useless; and he finally declares that the question needs no

further arguing, "because in the later editions of his works Mr. Darwin

freely acknowledges that a large proportion of specific distinctions

must be conceded to be useless to the species presenting them."

acknowledgment, and I think Mr. Romanes has not sufficiently

distinguished between "useless characters" and "useless specific

distinctions." On referring to all the passages indicated by him I find

that, in regard to specific characters, Mr. Darwin is very cautious in

admitting inutility. His most pronounced "admissions" on this question

are the following: "But when, from the nature of the organism and of the

conditions, modifications have been induced which are unimportant for

the welfare of the species, they may be, and apparently often have been,

transmitted in nearly the same state _to numerous, otherwise modified,

descendants_" (_Origin_, p. 175). The words I have here italicised

clearly show that such characters are usually not "specific," in the

sense that they are such as distinguish species from each other, but are

found in numerous allied species. Again: "Thus a large yet undefined

extension may safely be given to the direct and indirect results of

natural selection; but I now admit, after reading the essay of Nägeli on

plants, and the remarks by various authors with respect to animals, more

especially those recently made by Professor Broca, that in the earlier

editions of my _Origin of Species_ I perhaps attributed too much to the

action of natural selection or the survival of the fittest. I have

altered the fifth edition of the _Origin_ so as to confine my remarks to

adaptive changes of structure, _but I am convinced, from the light

gained during even the last few years, that very many structures which

now appear to us useless, will hereafter be proved to be useful, and

will therefore come within the range of natural selection_. Nevertheless

I did not formerly consider sufficiently the existence of structures

which, _as far as we can at present judge_, are neither beneficial nor

injurious; and this I believe to be one of the greatest oversights as

yet detected in my work." Now it is to be remarked that neither in these

passages nor in any of the other less distinct expressions of opinion on

this question, does Darwin ever admit that "specific characters"--that

is, the particular characters which serve to distinguish one species

from another--are ever useless, much less that "a large proportion of

them" are so, as Mr. Romanes makes him "freely acknowledge." On the

other hand, in the passage which I have italicised he strongly expresses

his view that much of what we suppose to be useless is due to our

ignorance; and as I hold myself that, as regards many of the supposed

useless characters, this is the true explanation, it may be well to give

a brief sketch of the progress of knowledge in transferring characters

from the one category to the other.

botanist could have suggested a reasonable use, for each species of

plant, of the infinitely varied forms, sizes, and colours of the

flowers, the shapes and arrangement of the leaves, and the numerous

other external characters of the whole plant. But since Mr. Darwin

showed that plants gained both in vigour and in fertility by being

crossed with other individuals of the same species, and that this

crossing was usually effected by insects which, in search of nectar or

pollen, carried the pollen from one plant to the flowers of another

plant, almost every detail is found to have a purpose and a use. The

shape, the size, and the colour of the petals, even the streaks and

spots with which they are adorned, the position in which they stand, the