Artificial selection

“ I further believe, that this very slow, intermittent action of natural selection accords perfectly well with what geology tells us of the rate and manner at which the inhabitants of this world have changed.
Slow though the process of selection may be, if feeble man can do much by his powers of artificial selection, I can see no limit to the amount of change, to the beauty and infinite complexity of the coadaptations between all organic beings, one with another and with their physical conditions of life, which may be effected in the long course of time by nature’s power of selection. ”

“ The difference between the two forms of selection consists in this: in artificial selection the will of man makes the selection according to a plan, whereas in natural selection, the struggle for life (that universal inter-relation of organisms) acts without a plan, but otherwise produces quite the same result, namely, a selection of a particular kind of individuals for propagation. The alterations produced by artificial selection are turned to the advantage of those who make the selection; in natural selection, on the other hand, to the advantage of the selected organism. ”

“ Artificial selection.—When a selection among the individuals of a species, that is, the choosing and preserving of individuals which show a certain trait or traits and the destroying of those individuals not possessing this trait, is done by man, it is called artificial selection. To artificial selection we chiefly owe all the many races or varieties of our domesticated animals and plants. ”

“ 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. ”

“ Instead of treating first the comparatively difficult and unfamiliar details of variation, I commence with the Struggle for Existence, which is really the fundamental phenomenon on which natural selection depends, while the particular facts which illustrate it are comparatively familiar and very interesting. It has the further advantage that, after discussing variation and the effects of artificial selection, we proceed at once to explain how natural selection acts. ”

“ It may be objected however, and it often is objected, that natural selection is not the same thing as artificial selection; but the objection cannot be sustained, for in effect it is the same thing, artificial selection being merely natural selection with man as the governing agent. Man, for instance, has caused the evolution of speed in the greyhound and in the race-horse by breeding, on the whole, from the swiftest animals of each species ”

“ Artificial selection, such as this, is after all only imitation of that natural selection which has derived the horse from a progenitor little larger than a fox, in response, age after age, to changing food, climate, enemies, and the needs of his human master. ”

“ It was the spectacle of human contrivance that suggested to Darwin his conception of natural selection. It was in studying the methods of pigeon breeders that he divined the processes by which nature, in the absence of design, obtains analogous results in the differentiation of types. As soon as the importance of artificial selection in the transformation of species of animals was understood, reflection naturally turned to the human species, and the question arose, How far do men observe, in connection with themselves, those laws of which they make practical application in the case of animals? ”

“ 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? ”

“ 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. ”

“ In Artificial Selection man does but take advantage of the natural laws of Inheritance and Variation, and while he is seeking by means of these to produce one alteration, Nature herself is producing perhaps a hundred others. For, by the law of Correlation, when one part changes, some other or others almost inevitably change with it. Whether it be shortening the beak of a pigeon or lengthening the neck of a giraffe that is in question, Nature takes care, along with the change, to make other adaptations of the structure in the creature’s interest under its altered circumstances. ”

“ It is true that some biologists have urged certain technical objections to the employment of domesticated animals and their history as analogies to the processes and results in wild nature. To my mind, however, artificial selection is truly a part of the whole process of natural selection. Man is but one element of the environment of tame forms, and his fancy or need is therefore one of the varied series of external criteria that must be met if survival is to be the result; failing this, elimination follows as surely as under the conditions of an area uninhabited or uninfluenced by mankind. ”

“ And as the pigeon-fancier or other person who devotes himself to the breeding of animals can produce any form he wishes by selecting its progenitors and pairing them together, exercising thus artificial selection, so if any of the chance-forms that have arisen should be better adapted than others for perpetuation, they will be perpetuated, or Nature may be said to have made a selection. Hence the term "natural selection," which has been made to designate this hypothesis. ”

“ Exactly in the same way artificial selection isolates and preserves some elementary species, while it destroys others. Of course the time is not sufficient to secure new mutations, or at least these are only rare at present, and their occurrence is doubtful in historic periods. Apart from this unavoidable difference the analogy between natural and artificial selection appears to me to be very striking. ”

“ They are analogous only within certain narrow limits; and, in the great majority of cases, natural selection is utterly incapable of doing that which artificial selection does.
To see this it needs only to de-personalize Nature, and to remember that, as Mr. Darwin says, Nature is "only the aggregate action and product of many natural laws [forces] ." Observe its relative shortcomings. Artificial selection can pick out a particular trait, and, regardless of other traits of the individuals displaying it, can increase it by selective breeding in successive generations. ”

“ In natural selection, such a crossing can be avoided only when the new variety by migration separates from the original and isolates itself.
Natural selection therefore acts much more slowly; it requires much longer periods than the artificial process of selection. But it is an essential consequence of this difference, that the product of artificial selection disappears much more easily, and that the new form returns rapidly to the earlier one, which is not the case in natural selection. ”

“ In artificial selection, through which, with or without conscious intention, our domesticated animals and cultivated plants have arisen, there must obviously be three kinds of co-operative factors: first, the variability of the species; second, the capacity of the organism for transmitting its particular characters to its progeny; and third, the breeder who selects particular qualities for breeding. ”

“ As regards plants having been brought under cultivation, and yielding variations that prove heredity, I knew there were innumerable cases where artificial selection had been brought into play. But of course they are all out of court until the question on which you are engaged has been decided in your favour, i.e. until you have succeeded in disproving natural selection as analogous or parallel to artificial. ”

“ The process of selecting the fittest to breed from, as it is carried on by Nature in her blind way, is called natural selection; and when men, in breeding stock, select the specimens possessing the most desirable variations to breed from, the process is named artificial selection.
The great variety of our domestic animals and plants we owe to artificial selection. ”

“ It is impossible not to recognize the fact so clearly illustrated by these patterns in the thumbs that natural selection has no monopoly of influence in the construction of genera, but that it could be wholly dispensed with, the internal conditions acting by themselves being sufficient. Not only is it impossible to substantiate a claim for natural selection that it is the sole agent in forming genera, but it seems, from the experience of artificial selection, that it is scarcely competent to do so by favoring mere varieties in the sense in which I understand the term. ”

“ It appears of interest here to remark that not only natural selection, but also artificial selection exercises its influence in many ways in universal history. A remarkable instance of artificial selection in man, on a great scale, is furnished by the ancient Spartans, among whom, in obedience to a special law, all newly-born children were subject to a careful examination and selection. ”

“ I came to think from geographical distribution, etc., etc., that species probably change; but for years I was stopped dead by my utter incapability of seeing how every part of each creature (a woodpecker or swallow, for instance) had become adapted to its conditions of life. This seemed to me, and does still seem, the problem to solve; and I think Natural Selection solves it, as artificial selection solves the adaptation of domestic races for man's use. But I suspect that you mean something further,—that there is some unknown law of evolution by which species necessarily change ”

“ Darwin frequently complained that very few of his critics took the trouble to find out what he meant by the term natural selection. A few illustrations will make his meaning clear. Let us first think of artificial selection as it is applied by breeders of cattle, fanciers of pigeons and of other fowls, etc. It is well known that by selecting particular variations in animals and plants, even when the variations are slight, the breeder or the horticulturalist will be able in a short time to produce new races of organic forms. ”

“ If, then, the decision as to which is to perish and which is to reach maturity is not a matter of chance alone, but is in part due to the constitution of the growing individual; if the 'fittest' do on the average survive, and the 'least fit' are on the average eliminated, we have here a process of selection entirely comparable to that of artificial selection, and one whose result must be the 'improvement' of the species, whether that depends on one set of characters or on another. ”

“ Observation shows that many different kinds—as pigeons—may be traced back to a single ancestral form, and thus the doctrine of the fixity of species is overthrown.
Now, since it is demonstrated by observation that variations occur, if there be a selective principle at work in nature, effects similar to those caused by artificial selection will be produced. The selection by nature of the forms fittest to survive is what Darwin meant by natural selection. ”

“ Evidence of analogous changes in animals is difficult to disentangle. Only among domesticated kinds have we any opportunity of tracing the results of altered habits; and here, in nearly all cases, artificial selection has obscured them. Still, there are some facts which seem to the point. Mr. Darwin, while ascribing almost wholly to "natural selection" the production of those modifications which eventuate in differences of species, nevertheless admits the effects of use and disuse. ”

“ The new species arising from natural selection maintain themselves much more permanently, and return much less easily to the original form, than is the case with products of artificial selection, and accordingly maintain themselves during a much longer time than the artificial races produced by man. ”

“ And if we find no positive evidence of disuse, acting by its direct 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. ”