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

laws of variation are independent causes of modification of species,

shows us that their authors have, in every case, failed to establish

their contention. Any direct action of the environment, or any

characters acquired by use or disuse, can have no effect whatever upon

the race unless they are inherited; and that they are inherited in any

case, except when they directly affect the reproductive cells, has not

been proved. On the other hand, as we shall presently show, there is

much reason for believing that such acquired characters are in their

nature non-heritable.

_Variation and Selection Overpower the Effects of Use and Disuse._

nature of the effects produced. In each generation the effects of use or

disuse, or of effort, will certainly be very small, while of this small

effect it is not maintained that the whole will be always inherited by

the next generation. How small the effect is we have no means of

determining, except in the case of disuse, which Mr. Darwin investigated

carefully. He found that in twelve fancy breeds of pigeons, which are

often kept in aviaries, or if free fly but little, the sternum had been

reduced by about one-seventh or one-eighth of its entire length, and

that of the scapula about one-ninth. In domestic ducks the weight of the

wing-bones in proportion to that of the whole skeleton had decreased

about one-tenth. In domestic rabbits the bones of the legs were found to

have increased in weight in due proportion to the increased weight of

the body, but those of the hind legs were rather less in proportion to

those of the fore legs than in the wild animal, a difference which may

be imputed to their being less used in rapid motion. The pigeons,

therefore, afford the greatest amount of reduction by

disuse--one-seventh of the length of the sternum. But the pigeon has

certainly been domesticated four or five thousand years; and if the

reduction of the wings by disuse has only been going on for the last

thousand years, the amount of reduction in each generation would be

absolutely imperceptible, and quite within the limits of the reduction

due to the absence of selection, as already explained. But, as we have

seen in Chapter III, the fortuitous variation of every part or organ

usually amounts to one-tenth, and often to one-sixth of the average

dimensions--that is, the fortuitous variation in one generation among a

limited number of the individuals of a species is as great as the

cumulative effects of disuse in a thousand generations! If we assume

that the effects of use or of effort in the individual are equal to the

effects of disuse, or even ten or a hundred times greater, they will

even then not equal, in each generation, the amount of the fortuitous

variations of the same part. If it be urged that the effects of use

would modify all the individuals of a species, while the fortuitous

variations to the amount named only apply to a portion of them, it may

be replied, that that portion is sufficiently large to afford ample

materials for selection, since it often equals the numbers that can

annually survive; while the recurrence in each successive generation of

a like amount of variation would render possible such a rapid adjustment

to new conditions that the effects of use or disuse would be as nothing

in comparison. It follows, that even admitting the modifying effects of

the environment, and that such modifications are inherited, they would

yet be entirely swamped by the greater effects of fortuitous variation,

and the far more rapid cumulative results of the selection of such

variations.

_Supposed Action of the Environment in Initiating Variations._
It is, however, urged that the reaction of the environment initiates

variations, which without it would never arise; such, for instance, as

the origin of horns through the pressures and irritations caused by

butting, or otherwise using the head as a weapon or for defence.

Admitting, for the sake of argument, that this is so, all the evidence

we possess shows that, from the very first appearance of the rudiment of

such an organ, it would vary to a greater extent than the amount of

growth directly produced by use; and these variations would be subject

to selection, and would thus modify the organ in ways which use alone

would never bring about. We have seen that this has been the case with

the branching antlers of the stag, which have been modified by

selection, so as to become useful in other ways than as a mere weapon;

and the same has almost certainly been the case with the variously

curved and twisted horns of antelopes. In like manner, every conceivable

rudiment would, from its first appearance, be subject to the law of

variation and selection, to which, thenceforth, the direct effect of the

environment would be altogether subordinate.
A very similar mode of reasoning will apply to the other branch of the

subject--the initiation of structures and organs by the action of the

fundamental laws of growth. Admitting that such laws have determined

some of the main divisions of the animal and vegetable kingdom, have

originated certain important organs, and have been the fundamental cause

of certain lines of development, yet at every step of the process these

laws must have acted in entire subordination to the law of natural

selection. No modification thus initiated could have advanced a single

step, unless it were, on the whole, a useful modification; while its

entire future course would be necessarily subject to the laws of

variation and selection, by which it would be sometimes checked,

sometimes hastened on, sometimes diverted to one purpose, sometimes to

another, according as the needs of the organism, under the special

conditions of its existence, required such modification. We need not

deny that such laws and influences may have acted in the manner

suggested, but what we do deny is that they could possibly escape from

the ever-present and all-powerful modifying effects of variation and

natural selection.[212]

_Weismann's Theory of Heredity._
Professor August Weismann has put forth a new theory of heredity founded

upon the "continuity of the germ-plasm," one of the logical consequences

of which is, that acquired characters of whatever kind are not

transmitted from parent to offspring. As this is a matter of vital

importance to the theory of natural selection, and as, if well founded,

it strikes away the foundations of most of the theories discussed in the

present chapter, a brief outline of Weismann's views must be attempted,

although it is very difficult to make them intelligible to persons

unfamiliar with the main facts of modern embryology.[213]
The problem is thus stated by Weismann: "How is it that in the case of

all higher animals and plants a single cell is able to separate itself

from amongst the millions of most various kinds of which an organism is

composed, and by division and complicated differentiation to reconstruct

a new individual with marvellous likeness, unchanged in many cases even

throughout whole geological periods?" Darwin attempted to solve the

problem by his theory of "Pangenesis," which supposed that every

individual cell in the body gave off gemmules or germs capable of

reproducing themselves, and that portions of these germs of each of the

almost infinite number of cells permeate the whole body and become

collected in the generative cells, and are thus able to reproduce the

whole organism. This theory is felt to be so ponderously complex and

difficult that it has met with no general acceptance among

physiologists.

only the general characters of the species, but many of the individual

characteristics of the parents or more remote ancestors, and that this

process is continued from generation to generation, can be accounted

for, Weismann thinks, only on two suppositions which are physiologically

possible. Either the substance of the parent germ-cell, after passing

through a cycle of changes required for the construction of a new

individual, possesses the capability of producing anew germ-cells

identical with those from which that individual was developed, or _the

new germ-cells arise, as far as their essential and characteristic

substance is concerned, not at all out of the body of the individual,

but direct from the parent germ-cell_. This latter view Weismann holds

to be the correct one, and, on this theory, heredity depends on the fact

that a substance of special molecular composition passes over from one

generation to another. This is the "germ-plasm," the power of which to

develop itself into a perfect organism depends on the extraordinary

complication of its minutest structure. At every new birth a portion of

the specific germ-plasm, which the parent egg-cell contains, is not used

up in producing the offspring, but is reserved unchanged to produce the

germ-cells of the following generation. Thus the germ-cells--so far as

regards their essential part the germ-plasm--are not a product of the

body itself, but are related to one another in the same way as are a

series of generations of unicellular organisms derived from one another

by a continuous course of simple division. Thus the question of heredity

is reduced to one of growth. A minute portion of the very same

germ-plasm from which, first the germ-cell, and then the whole organism

of the parent, were developed, becomes the starting-point of the growth

of the child.

_The Cause of Variation._
But if this were all, the offspring would reproduce the parent exactly,

in every detail of form and structure; and here we see the importance of

sex, for each new germ grows out of the united germ-plasms of two

parents, whence arises a mingling of their characters in the offspring.

This occurs in each generation; hence every individual is a complex

result reproducing in ever-varying degrees the diverse characteristics

of his two parents, four grandparents, eight great-grandparents, and

other more remote ancestors; and that ever-present individual variation

arises which furnishes the material for natural selection to act upon.

Diversity of sex becomes, therefore, of primary importance as _the cause

of variation_. Where asexual generation prevails, the characteristics of

the individual alone are reproduced, and there are thus no means of

effecting the change of form or structure required by changed conditions

of existence. Under such changed conditions a complex organism, if only

asexually propagated, would become extinct. But when a complex organism

is sexually propagated, there is an ever-present cause of change which,

though slight in any one generation, is cumulative, and under the

influence of selection is sufficient to keep up the harmony between the

organism and its slowly changing environment.[214]

_The Non-Heredity of Acquired Characters._

afford direct proof of this theory of heredity, but they are too

technical to be made clear to ordinary readers. A logical result of the

theory is the impossibility of the transmission of acquired characters,

since the molecular structure of the germ-plasm is already determined

within the embryo; and Weismann holds that there are no facts which

really prove that acquired characters can be inherited, although their

inheritance has, by most writers, been considered so probable as hardly

to stand in need of direct proof.
We have already shown, in the earlier part of this chapter, that many

instances of change, imputed to the inheritance of acquired variations,

are really cases of selection; while the very fact that _use_ implies

_usefulness_ renders it almost impossible to eliminate the action of

selection in a state of nature. As regards mutilations, it is generally

admitted that they are not hereditary, and there is ample evidence on

this point. When it was the fashion to dock horses' tails, it was not

found that horses were born with short tails; nor are Chinese women born

with distorted feet; nor are any of the numerous forms of racial

mutilation in man, which have in some cases been carried on for hundreds

of generations, inherited. Nevertheless, a few cases of apparent

inheritance of mutilations have been recorded,[215] and these, if

trustworthy, are difficulties in the way of the theory. The undoubted

inheritance of disease is hardly a difficulty, because the

predisposition to disease is a congenital, not an acquired character,

and as such would be the subject of inheritance. The often-quoted case

of a disease induced by mutilation being inherited (Brown-Sequard's

epileptic guinea-pigs) has been discussed by Professor Weismann, and

shown to be not conclusive. The mutilation itself--a section of certain

nerves--was never inherited, but the resulting epilepsy, or a general

state of weakness, deformity, or sores, was sometimes inherited. It is,

however, possible that the mere injury introduced and encouraged the

growth of certain microbes, which, spreading through the organism,

sometimes reached the germ-cells, and thus transmitted a diseased

condition to the offspring. Such a transference of microbes is believed

to occur in syphilis and tuberculosis, and has been ascertained to occur

in the case of the muscardine silkworm disease.[216]

_The Theory of Instinct._

commends itself to many physiologists as being inherently probable, and

as furnishing a good working hypothesis till displaced by a better. We

cannot, therefore, accept any arguments against the agency of natural

selection which are based upon the opposite and equally unproved theory

that acquired characters are inherited; and as this applies to the whole

school of what may be termed Neo-Lamarckians, their speculations cease

to have any weight.

inherited habits; though Darwin gave very little weight to this, but

derived almost all instincts from spontaneous useful variations which,

like other spontaneous variations, are of course inherited. At first

sight it appears as if the acquired habits of our trained

dogs--pointers, retrievers, etc.--are certainly inherited; but this need

not be the case, because there must be some structural or psychical

peculiarities, such as modifications in the attachments of muscles,

increased delicacy of smell or sight, or peculiar likes and dislikes,

which are inherited; and from these, peculiar habits follow as a natural

consequence, or are easily acquired. Now, as selection has been

constantly at work in improving all our domestic animals, we have

unconsciously modified the structure, while preserving only those

animals which best served our purpose in their peculiar faculties,

instincts, or habits.
Much of the mystery of instinct arises from the persistent refusal to

recognise the agency of imitation, memory, observation, and reason as

often forming part of it. Yet there is ample evidence that such agency

must be taken into account. Both Wilson and Leroy state that young birds

build inferior nests to old ones, and the latter author observes that

the best nests are made by birds whose young remain longest in the nest.

So, migration is now well ascertained to be effected by means of vision,

long flights being made on bright moonlight nights when the birds fly

very high, while on cloudy nights they fly low, and then often lose

their way. Thousands annually fly out to sea and perish, showing that

the instinct to migrate is imperfect, and is not a good substitute for

reason and observation.

of the selection during its development, any failure involving

destruction. The chick which cannot break the eggshell, the caterpillar

that fails to suspend itself properly or to spin a safe cocoon, the bees

that lose their way or that fail to store honey, inevitably perish. So

the birds that fail to feed and protect their young, or the butterflies

that lay their eggs on the wrong food-plant, leave no offspring, and the

race with imperfect instincts perishes. Now, during the long and very

slow course of development of each organism, this rigid selection at

every step of progress has led to the preservation of every detail of

structure, faculty, or habit that has been necessary for the

preservation of the race, and has thus gradually built up the various

instincts which seem so marvellous to us, but which can yet be shown to

be in many cases still imperfect. Here, as everywhere else in nature, we

find comparative, not absolute perfection, with every gradation from

what is clearly due to imitation or reason up to what seems to us

perfect instinct--that in which a complex action is performed without

any previous experience or instruction.[217]

_Concluding Remarks._
Having now passed in review the more important of the recent objections

to, or criticisms of, the theory of natural selection, we have arrived

at the conclusion that in no one case have the writers in question been

able materially to diminish its importance, or to show that any of the

laws or forces to which they appeal can act otherwise than in strict

subordination to it. The direct action of the environment as set forth

by Mr. Herbert Spencer, Dr. Cope, and Dr. Karl Semper, even if we admit

that its effects on the individual are transmitted by inheritance, are

so small in comparison with the amount of spontaneous variation of every

part of the organism that they must be quite overshadowed by the latter.

And if such direct action may, in some cases, have initiated certain

organs or outgrowths, these must from their very first beginnings have

been subject to variation and natural selection, and their further

development have been almost wholly due to these ever-present and

powerful causes. The same remark applies to the views of Professor

Geddes on the laws of growth which have determined certain essential

features in the morphology of plants and animals. The attempt to

substitute these laws for those of variation and natural selection has

failed in cases where we can apply a definite test, as in that of the

origin of spines on trees and shrubs; while the extreme diversity of

vegetable structure and form among the plants of the same country and of

the same natural order, of itself affords a proof of the preponderating

influence of variation and natural selection in keeping the many diverse

forms in harmony with the highly complex and ever-changing environment.

of the germ-plasm and the consequent non-heredity of acquired

characters, while in perfect harmony with all the well-ascertained facts

of heredity and development, adds greatly to the importance of natural

selection as the one invariable and ever-present factor in all organic

change, and that which can alone have produced the temporary fixity

combined with the secular modification of species. While admitting, as

Darwin always admitted, the co-operation of the fundamental laws of

growth and variation, of correlation and heredity, in determining the

direction of lines of variation or in the initiation of peculiar organs,

we find that variation and natural selection are ever-present agencies,

which take possession, as it were, of every minute change originated by

these fundamental causes, check or favour their further development, or

modify them in countless varied ways according to the varying needs of

the organism. Whatever other causes have been at work, Natural Selection

is supreme, to an extent which even Darwin himself hesitated to claim

for it. The more we study it the more we are convinced of its

overpowering importance, and the more confidently we claim, in Darwin's

own words, that it "has been the most important, but not the exclusive,

means of modification."

p. 336.]
[Footnote 199: _Journal of the Anthropological Institute,_ vol. xv. pp.

246-260.]
[Footnote 200: The idea of the non-heredity of acquired variations was

suggested by the summary of Professor Weismann's views, in _Nature_,

referred to later on. But since this chapter was written I have, through

the kindness of Mr. E.B. Poulton, seen some of the proofs of the

forthcoming translation of Weismann's Essays on Heredity, in which he

sets forth an explanation very similar to that here given. On the

difficult question of the almost entire disappearance of organs, as in

the limbs of snakes and of some lizards, he adduces "a certain form of

correlation, which Roux calls 'the struggle of the parts in the

organism,'" as playing an important part. Atrophy following disuse is

nearly always attended by the corresponding increase of other organs:

blind animals possess more developed organs of touch, hearing, and

smell; the loss of power in the wings is accompanied by increased

strength of the legs, etc. Now as these latter characters, being useful,

will be selected, it is easy to understand that a congenital increase of

these will be accompanied by a corresponding congenital diminution of

the unused organ; and in cases where the means of nutrition are

deficient, every diminution of these useless parts will be a gain to the

whole organism, and thus their complete disappearance will, in some

cases, be brought about directly by natural selection. This corresponds

with what we know of these rudimentary organs.
It must, however, be pointed out that the non-heredity of acquired

characters was maintained by Mr. Francis Galton more than twelve years

ago, on theoretical considerations almost identical with those urged by

Professor Weismann; while the insufficiency of the evidence for their

hereditary transmission was shown, by similar arguments to those used

above and in the work of Professor Weismann already referred to (see "A