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

the jaws in the races of civilised men, and the diminution of the

muscles used in closing the jaws in the case of pet-dogs fed for

generations on soft food. He argues that the minute reduction in any one

generation could not possibly have been useful, and, therefore, not the

subject of natural selection; and against the theory of correlation of

the diminished jaw with increased brain in man, he urges that there are

cases of large brain development, accompanied by jaws above the average

size. Against the theory of economy of nutrition in the case of the

pet-dogs, he places the abundant food of these animals which would

render such economy needless.

withdrawal of the action of natural selection in keeping up the parts in

question to their full dimensions, which, of itself, seems to me quite

adequate to produce the results observed. Recurring to the evidence,

adduced in Chapter III, of the constant variation occurring in all parts

of the organism, while selection is constantly acting on these

variations in eliminating all that fall below the best working standard,

and preserving only those that are fully up to it; and, remembering

further, that, of the whole number of the increase produced annually,

only a small percentage of the best adapted can be preserved, we shall

see that every useful organ will be kept up nearly to its higher limit

of size and efficiency. Now Mr. Galton has proved experimentally that,

when any part has thus been increased (or diminished) by selection,

there is in the offspring a strong tendency to revert to a mean or

average size, which tends to check further increase. And this mean

appears to be, not the mean of the actual existing individuals but a

lower mean, or that from which they had been recently raised by

selection.[199] He calls this the law of "Regression towards

Mediocrity," and it has been proved by experiments with vegetables and

by observations on mankind. This regression, in every generation, takes

place even when both parents have been selected for their high

development of the organ in question; but when there is no such

selection, and crosses are allowed among individuals of every grade of

development, the deterioration will be very rapid; and after a time not

only will the average size of the part be greatly reduced, but the

instances of full development will become very rare. Thus what Weismann

terms "panmixia," or free intercrossing, will co-operate with Galton's

law of "regression towards mediocrity," and the result will be that,

whenever selection ceases to act on any part or organ which has

heretofore been kept up to a maximum of size and efficiency, the organ

in question will rapidly decrease till it reaches a mean value

considerably below the mean of the progeny that has usually been

produced each year, and very greatly below the mean of that portion

which has survived annually; and this will take place by the general law

of heredity, and quite irrespective of any _use_ or _disuse_ of the part

in question. Now, no observations have been adduced by Mr. Spencer or

others, showing that the average amount of change supposed to be due to

_disuse_ is greater than that due to the law of regression towards

mediocrity; while even if it were somewhat greater, we can see many

possible contributory causes to its production. In the case of civilised

man's diminished jaw, there may well be some correlation between the jaw

and the brain, seeing that increased mental activity would lead to the

withdrawal of blood and of nervous energy from adjacent parts, and might

thus lead to diminished growth of those parts in the individual. And in

the case of pet-dogs, the selection of small or short-headed individuals

would imply the unconscious selection of those with less massive

temporal muscles, and thus lead to the concomitant reduction of those

muscles. The amount of reduction observed by Darwin in the wing-bones of

domestic ducks and poultry, and in the hind legs of tame rabbits, is

very small, and is certainly no greater than the above causes will well

account for; while so many of the external characters of all our

domestic animals have been subject to long-continued artificial

selection, and we are so ignorant of the possible correlations of

different parts, that the phenomena presented by them seem sufficiently

explained without recurrence to the assumption that any changes in the

individual, due to disuse, are inherited by the offspring.

_Supposed Effects of Disuse among Wild Animals._
It may be urged, however, that among wild animals we have many undoubted

results of disuse much more pronounced than those among domestic kinds,

results which cannot be explained by the causes already adduced. Such

are the reduced size of the wings of many birds on oceanic islands; the

abortion of the eyes in many cave animals, and in some which live

underground; and the loss of the hind limbs in whales and in some

lizards. These cases differ greatly in the amount of the reduction of

parts which has taken place, and may be due to different causes. It is

remarkable that in some of the birds of oceanic islands the reduction is

little if at all greater than in domestic birds, as in the water-hen of

Tristan d'Acunha. Now if the reduction of wing were due to the

hereditary effects of disuse, we should expect a very much greater

effect in a bird inhabiting an oceanic island than in a domestic bird,

where the disuse has been in action for an indefinitely shorter period.

In the case of many other birds, however--as some of the New Zealand

rails and the extinct dodo of Mauritius--the wings have been reduced to

a much more rudimentary condition, though it is still obvious that they

were once organs of flight; and in these cases we certainly require some

other causes than those which have reduced the wings of our domestic

fowls. One such cause may have been of the same nature as that which has

been so efficient in reducing the wings of the insects of oceanic

islands--the destruction of those which, during the occasional use of

their wings, were carried out to sea. This form of natural selection may

well have acted in the case of birds whose powers of flight were

already somewhat reduced, and to whom, there being no enemies to escape

from, their use was only a source of danger. We may thus, perhaps,

account for the fact that many of these birds retain small but useless

wings with which they never fly; for, the wings having been reduced to

this functionless condition, no power could reduce them further except

correlation of growth or economy of nutrition, causes which only rarely

come into play.
The complete loss of eyes in some cave animals may, perhaps, be

explained in a somewhat similar way. Whenever, owing to the total

darkness, they became useless, they might also become injurious, on

account of their delicacy of organisation and liability to accidents and

disease; in which case natural selection would begin to act to reduce,

and finally abort them; and this explains why, in some cases, the

rudimentary eye remains, although completely covered by a protective

outer skin. Whales, like moas and cassowaries, carry us back to a remote

past, of whose conditions we know too little for safe speculation. We

are quite ignorant of the ancestral forms of either of these groups, and

are therefore without the materials needful for determining the steps by

which the change took place, or the causes which brought it about.[200]

and others of organs that have been reduced or aborted, there seems too

much diversity in the results for all to be due to so direct and uniform

a cause as the individual effects of disuse accumulated by heredity. For

if that were the only or chief efficient cause, and a cause capable of

producing a decided effect during the comparatively short period of the

existence of animals in a state of domestication, we should expect to

find that, in wild species, all unused parts or organs had been reduced

to the smallest rudiments, or had wholly disappeared. Instead of this we

find various grades of reduction, indicating the probable result of

several distinct causes, sometimes acting separately, sometimes in

combination, such as those we have already pointed out.

effect on the individual, being transmitted to the offspring, still less

can we find such evidence in the case of the _use_ of organs. For here

the very fact of _use_, in a wild state, implies _utility_, and utility

is the constant subject for the action of natural selection; while among

domestic animals those parts which are exceptionally used are so used in

the service of man, and have thus become the subjects of artificial

selection. Thus "the great and inherited development of the udders in

cows and goats," quoted by Spencer from Darwin, really affords no proof

of inheritance of the increase due to use, because, from the earliest

period of the domestication of these animals, abundant milk-production

has been highly esteemed, and has thus been the subject of selection;

while there are no cases among wild animals that may not be better

explained by variation and natural selection.

_Difficulty as to Co-adaptation of Parts by Variation and Selection._
Mr. Spencer again brings forward this difficulty, as he did in his

_Principles of Biology_ twenty-five years ago, and urges that all the

adjustments of bones, muscles, blood-vessels, and nerves which would be

required during, for example, the development of the neck and fore-limbs

of the giraffe, could not have been effected by "simultaneous fortunate

spontaneous variations." But this difficulty is fully disposed of by the

facts of simultaneous variation adduced in our third chapter, and has

also been specially considered in Chapter VI, p. 127. The best answer to

this objection may, perhaps, be found in the fact that the very thing

said to be impossible by variation and natural selection has been again

and again effected by variation and artificial selection. During the

process of formation of such breeds as the greyhound or the bulldog, of

the race-horse and carthorse, of the fantail pigeon or the otter-sheep,

many co-ordinate adjustments have been produced; and no difficulty has

occurred, whether the change has been effected by a single variation--as

in the last case named--or by slow steps, as in all the others. It seems

to be forgotten that most animals have such a surplus of vitality and

strength for all the ordinary occasions of life that any slight

superiority in one part can be at once utilised; while the moment any

want of balance occurs, variations in the insufficiently developed parts

will be selected to bring back the harmony of the whole organisation.

The fact that, in all domestic animals, variations do occur, rendering

them swifter or stronger, larger or smaller, stouter or slenderer, and

that such variations can be separately selected and accumulated for

man's purposes, is sufficient to render it certain that similar or even

greater changes may be effected by natural selection, which, as Darwin

well remarks, "acts on every internal organ, on every shade of

constitututional difference, on the whole machinery of life." The

difficulty as to co-adaptation of parts by variation and natural

selection appears to me, therefore, to be a wholly imaginary difficulty

which has no place whatever in the operations of nature.

_Direct Action of the Environment._

the agency of natural selection is, that organisms are acted upon by the

environment, which produces in them definite changes, and that these

changes in the individual are transmitted by inheritance, and thus

become increased in successive generations. That such changes are

produced in the individual there is ample evidence, but that they are

inherited independently of any form of selection or of reversion is

exceedingly doubtful, and Darwin nowhere expresses himself as satisfied

with the evidence. The two very strongest cases he mentions are the

twenty-nine species of American trees which all differed in a

corresponding way from their nearest European allies; and the American

maize which became changed after three generations in Europe. But in the

case of the trees the differences alleged may be partly due to

correlation with constitutional peculiarities dependent on climate,

especially as regards the deeper tint of the fading leaves and the

smaller size of the buds and seeds in America than in Europe; while the

less deeply toothed or serrated leaves in the American species are, in

our present complete ignorance of the causes and uses of serration,

quite as likely to be due to some form of adaptation as to any direct

action of the climate. Again, we are not told how many of the allied

species do not vary in this particular manner, and this is certainly an

important factor in any conclusion we may form on the question.

highly selected American varieties was cultivated in Germany, and in

three years nearly all resemblance to the original parent was lost; and

in the sixth year it closely resembled a common European variety, but

was of somewhat more vigorous growth. In this case no selection appears

to have been practised, and the effects may have been due to that

"reversion to mediocrity" which invariably occurs, and is more

especially marked in the case of varieties which have been rapidly

produced by artificial selection. It may be considered as a partial

reversion to the wild or unimproved stock; and the same thing would

probably have occurred, though perhaps less rapidly, in America itself.

As this is stated by Darwin to be the most remarkable case known to him

"of the direct and prompt action of climate on a plant," we must

conclude that such direct effects have not been proved to be accumulated

by inheritance, independently of reversion or selection.
The remaining part of Mr. Spencer's essay is devoted to a consideration

of the hypothetical action of the environment on the lower organisms

which consist of simple cells or formless masses of protoplasm; and he

shows with great elaboration that the outer and inner parts of these

are necessarily subject to different conditions; and that the outer

actions of air or water lead to the formation of integuments, and

sometimes to other definite modifications of the surface, whence arise

permanent differences of structure. Although in these cases also it is

very difficult to determine how much is due to direct modification by

external agencies transmitted and accumulated by inheritance, and how

much to spontaneous variations accumulated by natural selection, the

probabilities in favour of the former mode of action are here greater,

because there is no differentiation of nutritive and reproductive cells

in these simple organisms; and it can be readily seen that any change

produced in the latter will almost certainly affect the next

generation.[201] We are thus carried back almost to the origin of life,

and can only vaguely speculate on what took place under conditions of

which we know so little.

_The American School of Evolutionists._
The tentative views of Mr. Spencer which we have just discussed, are

carried much further, and attempts have been made to work them out in

great detail, by many American naturalists, whose best representative is

Dr. E.D. Cope of Philadelphia.[202] This school endeavours to explain

all the chief modifications of form in the animal kingdom by fundamental

laws of growth and the inherited effects of use and effort, returning,

in fact, to the teachings of Lamarck as being at least equally important

with those of Darwin.

this school as original discoverers, and as having made important

additions to the theory of evolution:
"Wallace and Darwin have propounded as the cause of modification in

descent their law of natural selection. This law has been epitomised by

Spencer as the 'survival of the fittest.' This neat expression no doubt

covers the case, but it leaves the origin of the fittest entirely

untouched. Darwin assumes a 'tendency to variation' in nature, and it is

plainly necessary to do this, in order that materials for the exercise

of a selection should exist. Darwin and Wallace's law is then only

restrictive, directive, conservative, or destructive of something

already created. I propose, then, to seek for the originative laws by

which these subjects are furnished; in other words, for the causes of

the origin of the fittest."[203]
Mr. Cope lays great stress on the existence of a special developmental

force termed "bathmism" or growth-force, which acts by means of

retardation and acceleration "without any reference to fitness at all;"

that "instead of being controlled by fitness it is the controller of

fitness." He argues that "all the characteristics of generalised groups

from genera up (excepting, perhaps, families) have been evolved under

the law of acceleration and retardation," combined with some

intervention of natural selection; and that specific characters, or

species, have been evolved by natural selection with some assistance

from the higher law. He, therefore, makes species and genera two

absolutely distinct things, the latter not developed out of the former;

generic characters and specific characters are, in his opinion,

fundamentally different, and have had different origins, and whole

groups of species have been simultaneously modified, so as to belong to

another genus; whence he thinks it "highly probable that the same

specific form has existed through a succession of genera, and perhaps in

different epochs of geologic time."
Useful characters, he concludes, have been produced by the special

location of growth-force by use; useless ones have been produced by

location of growth-force without the influence of use. Another element

which determines the direction of growth-force, and which precedes use,

is effort; and "it is thought that effort becomes incorporated into the

metaphysical acquisitions of the parent, and is inherited with other

metaphysical qualities by the young, which, during the period of growth,

is much more susceptible to modifying influences, and is likely to

exhibit structural change in consequence."[204]
From these few examples of their teachings, it is clear that these

American evolutionists have departed very widely from the views of Mr.

Darwin, and in place of the well-established causes and admitted laws to

which he appeals have introduced theoretical conceptions which have not

yet been tested by experiments or facts, as well as metaphysical

conceptions which are incapable of proof. And when they come to

illustrate these views by an appeal to palaeontology or morphology, we

find that a far simpler and more complete explanation of the facts is

afforded by the established principles of variation and natural

selection. The confidence with which these new ideas are enunciated, and

the repeated assertion that without them Darwinism is powerless to

explain the origin of organic forms, renders it necessary to bestow a

little more time on the explanations they give us of well-known

phenomena with which, they assert, other theories are incompetent to

grapple.
As examples of use producing structural change, Mr. Cope adduces the

hooked and toothed beaks of the falcons and the butcher-birds, and he

argues that the fact of these birds belonging to widely different groups

proves that similarity of use has produced a similar structural result.

But no attempt is made to show any direct causal connection between the

use of a bill to cut or tear flesh and the development of a tooth on the

mandible. Such use might conceivably strengthen the bill or increase its

size, but not cause a special tooth-like outgrowth which was not present

in the ancestral thrush-like forms of the butcher-bird. On the other

hand, it is clear that any variations of the bill tending towards a hook

or tooth would give the possessor some advantage in seizing and tearing

its prey, and would thus be preserved and increased by natural

selection. Again, Mr. Cope urges the effects of a supposed "law of polar

or centrifugal growth" to counteract a tendency to unsymmetrical growth,

where one side of the body is used more than the other. But the

undoubted hurtfulness of want of symmetry in many important actions or

functions would rapidly eliminate any such tendency. When, however, it

has become useful, as in the case of the single enlarged claw of many

Crustacea, it has been preserved by natural selection.

_Origin of the Feet of the Ungulates._

the theory of use and effort in modifying structure are, his chapters

"On the Origin of the Foot-Structure of the Ungulates;" and that "On the

Effect of Impacts and Strains on the Feet of Mammalia;" and they will

serve also to show the comparative merits of this theory and that of

natural selection in explaining a difficult case of modification,

especially as it is an explanation claimed as new and original when

first enunciated in 1881. Let us, then, see how he deals with the

problem.
The remarkable progressive change of a four or five-toed ancestor into

the one-toed horse, and the equally remarkable division of the whole

group of ungulate animals into the odd-toed and even-toed divisions, Mr.

Cope attempts to explain by the effects of impact and use among animals

which frequented hard or swampy ground respectively. On hard ground, it

is urged, the long middle toe would be most used and subjected to the

greatest strains, and would therefore acquire both strength and

development. It would then be still more exclusively used, and the extra

nourishment required by it would be drawn from the adjacent less-used