view to the preservation of the best traits of both. In establishing the stock farm at Palo Alto, Leland Stanford had the FIG. 69.--Improvement in geranium: at left, the original wild form, and at conception of strengthening the trotting horse by a cross with the larger running horse or thoroughbred. The result was the formation of a peculiar type of horse, large, strong, supple, FIG. 70. Sports found among crossed amaryllids, the size and form markedly changed; the flowers are three inches in diameter. (From photograph by Burbank.) and intelligent, very clean of limb and sleek of coat. This group of horses held for some years the world's records for speed in their various classes and ages, and the experiment was in the highest degree successful. In one sense such attempts are not experiments. The skillful breeder knows that out of the many combinations possible in crossing, some few will fall in line with his plans. He has only to preserve these, and to clinch them by in-and-in or segregated breeding to bring about a result he may have deemed possible or desirable. It is possible, by intentional selection, to turn a nonessential or race character into a selective or adaptive one. The Hampshire sheep have black ears, but by persistent selection the ears could probably be made white. Probably also the horns of the Dorsets could be bred on Hampshires by making use of possible occasional reversions to the horned stock. This result could be attained very rapidly by a crossing with Dorset stock, but this triumph of the breeder's art has rarely any homologue in the wild state or in the condition of unconscious selection. When selection ceases, the adaptive characters are likely to decline or disappear. Under cessation of selection, called by Weismann panmixia, no premium is placed on traits of excellence, from the human standpoint, such as long wool, plumpness or symmetry of form; and only the purely vegetative advantages of the individual count. But while the traits of excellence disappear, the race traits or nonadaptive characters persist unchanged. A herd of neglected Hampshire sheep is still a herd of Hampshires. The black face, cars, and legs remain black, with no tendency to fade. When the worst individuals are selected for breeding, we have the reversal of selection. A flock of Hampshire culls, feeble, loose-jointed, scant-wooled, unsymmetrical, could be used in breeding, and the adaptive characters usually sought for could be bred out of them. But they would still be Hampshires, for the hereditary characters which had persisted without the aid of selection would persist after selection ceases or even if it is reversed. When these same characters are made the object of selection, they are subject to the same laws as ordinary adaptive characters. What is true of a breed of sheep-a product of geographical isolation with segregative breeding is true in a general way of any wild species of animals or plants. Its adaptive characters are due to natural selection. These change more rapidly than the nonadaptive characters, and respond more readily to the conditions of panmixia or of reversal of selection. In matters of breeding we must distinguish between animals actually best and those potentially best. An animal is at its actual best when in prime condition, at the prime of its life. Another of far finer heredity, of far stronger ancestry, may be at any given time actually the inferior of the first. It may be too old, too young, in too poor condition to represent its own best status. It is generally recognized that, for all breeding purposes, the animal potentially best is superior to one which, otherwise inferior, may be actually best at the time. The tendency of heredity is to repeat the traits of the ideal individuals, which the parents ought to have been. More exactly, the tendency of heredity is to produce individuals which, under like conditions of food and environment, would develop as the parents have developed. But it is also recognized that the actual physical condition of the parent affects the offspring. A sick mother is likely to bear an enfeebled child. Immature or declining sires do not beget offspring as strong as those begotten by them when they are in perfect strength and health. In this matter, apparently, we have to deal with two different elements, as Weismann and others have pointed out. The first is true heredity, the quality of the germ cell, which is not affected by the condition of the parent. Weak or strong, the offspring is of the same kind or type as the parentage. The second element has been called Transmission. Its relations are with vegetative development. The embryo is ill nourished by the sick mother, and it enters on life with lowered vigor. The momentum, if we may use such a figure of speech, is reduced from the first, and the lost vitality may never be regained. The defects of the male parent are perhaps of less moment, but whatever their nature their results would be of the same kind. They would not enter into the heredity of the offspring, but they might play a large part in retarding its development. In the category of transmission, not of heredity, would belong the theme of Ibsen's "Ghosts" (Gjengängere), the development of softening of the brain in the son of a debauchee, the alleged cause being that the father's nervous system was vermoulu (worm-eaten), if we are to accept the ghastly drama as an exposition of possible facts.. The rôle played by the phenomena of transmission as distinguished from that of heredity has never been clearly ascertained. Many eminent writers ascribe to it a large importance. It is a central element in Mr. Casper Redfield's theory of heredity, and he brings together a considerable array of facts and statistics to justify his conclusions. But the value of statistics in such matters is easily exaggerated, because of the difficulty in ascertaining the real causes behind the phenomena we try to record. It is fair to say as a broad proposition that, as a sound mind requires a sound body, soundness both of mind and body are factors in giving to offspring the best possible start in life. The heredity unchanged, there is still a great value in vigor of early development. The relation of these matters to the theory of organic evolution is mainly here: artificial selection as a process is of the same general character as natural selection; both represent a form of isolation or segregation, which prevents indiscriminate mating, and which holds certain groups of individuals as the agents of reproduction of the species within a given time or in a special area. Artificial selection intensifies useful or adaptive characters, using these words in a broad sense. At the same time, it perpetuates a series of characters, in no wise useful, and in no fashion adaptive. These characters remain unchanged for long periods, and hence have more value in race distinction or in classification than the strictly adaptive characters have. A Southdown sheep is plump and fat, on the whole perhaps more so than any other type of sheep. Nevertheless, it is not by its plumpness that we know a Southdown. It is rather by the character of its wool, the color of its face and feet, the form of its head. So it is with breeds and races generally. They are formed primarily by isolation in breeding, the separation of a few from the many by geographical or similar causes, by the perpetuation of the traits of these few (the "survival of the existing"), all this being modified by the new range of natural and artificial selection and the new reactions under the varying conditions of a new environment. It interests us to know that a similar process takes place in nature. Geographical and topographical barriers are crossed in migration. These isolate a portion of a species under new conditions, with new reactions to the environment, and a new range of natural selection. Adaptive characters change rapidly, and in ways more or less parallel, with similar alterations in related species. Characters nonadaptive, often slight in appearance and bearing no relation to the life of the animal, become slowly but surely fixed as characters of the species. As two closely allied breeds of animals are never found in the same region unless purposely restrained from free interbreeding, so two closely related species never develop in the same breeding area. As the nearest relative of some given breed of domestic animals is found in a given region nearly related geographically, so is the nearest relative to any given wild species found, in most cases, not far away. It is to be looked for on the other side of some geographic, topographic, or climatic barrier. In other words, the interrelation of variation, heredity, geographic isolation and environmental features generally seems to be the same in the formation of domestic races as in that of the formation of natural species. The principal new element introduced in the art of selective breeding is that of purposeful crossing, the removal of the barriers which separate welldifferentiated forms, for the purpose of beginning a new series to be selected toward a predetermined end. It has been recently repeatedly stated that most races of domesticated animals or plants find their origin in a mutation or saltation of some sort. In our judgment, there is not sufficient evidence to prove this view. There are few cases of either races or species known to have originated in this way. That such is in fact the general law of race or species origin, we see little reason to believe. One of the few well-known illustrations of race-forming through saltation is that of the Ancon sheep. In 1791, in Massachusetts, a ram was born with unusually short legs. As this character was useful, preventing the sheep from leaping over stone walls, the owner of this sheep used the ram for breeding purposes, and succeeded in isolating a short-legged strain of sheep known as the Ancon sheep. So far as known to us, this type of sheep differed in this character alone from the common sheep of Connecticut. With the later advent of the more heavy-wooled, and therefore more profitable, Merino, the Ancon sheep disappeared. A recent similar case of race origin from a prepotent sport is that of the polled Herefords arising in Kansas from a hornless Hereford bull. |