Breeding (animal)

“ If the Japanese breeders were able to lengthen the tail-feathers of the cock to six feet, it can only have been because the determinants of the tail-feathers in the germ-plasm had already struck out a path of ascending variation, and this movement [50] was taken advantage of by the breeder, who continually selected for reproduction the individuals in which the ascending variation was most marked. For all breeding depends upon the unconscious selection of germinal variations. ”

“ If he wish to perpetuate the difference, to form a breed with the peculiarity in question strongly marked, he selects such male and female individuals as exhibit the desired character, and breeds from them. Their offspring are then carefully examined, and those which exhibit the peculiarity the most distinctly are selected for breeding; and this operation is repeated until the desired amount of divergence from the primitive stock is reached. ”

“ As cross-bred animals are generally of large size and vigorous, they have been raised in great numbers for immediate consumption. But for breeding they are found to be utterly useless; for though they may be themselves uniform in character, when paired together they yield during many generations offspring astonishingly diversified. The breeder is driven to despair, and concludes that he will never form an intermediate race. ”

“ From a species in this condition modern poultry breeders have made hundreds of distinct varieties. The easiest method of making a variety in domestication is to select specimens for breeding as near the desired type as possible, and to breed only from a few individuals in each generation which come nearest to the ideal type. ”

“ STERILITY OF DOMESTICATED ANIMALS FROM CHANGED CONDITIONS. With respect to domesticated animals, as their domestication mainly depends on the accident of their breeding freely under captivity, we ought not to expect that their reproductive system would be affected by any moderate degree of change. Those orders of quadrupeds and birds, of which the wild species breed most readily in our menageries, have afforded us the greatest number of domesticated productions. ”

“ The same methods of selection that establish a breed are used to maintain it, or to establish strains. In ordinary breeding there are two other principles that are sometimes called into play. One is prepotency, the other is inbreeding. By prepotent we mean having unusual power to transmit characters to offspring. Suppose a breeder has five yards headed by five cock birds. The male in yard two he does not consider quite as fine as the bird in yard one, but in the fall he finds the offspring of bird from two much better than the offspring from yard one. ”

“ If even in such minute particulars as these, hereditary transmission may be distinctly seen, it becomes the breeder to look closely to the "like" which he wishes to see reproduced. Judicious selection is indispensable to success in breeding, and this should have regard to every particular—general appearance, length of limb, shape of carcass, development of chest; if in cattle, the size, shape and position of udder, thickness of skin, "touch," length and texture of hair, docility, &c., &c. ”

“ The origin of the domesticated breeds is ascribed by Darwin, Blyth and other naturalists to the Bankiva fowl, much stress being laid on the comparative want of fertility in the hybrids produced between this species or the domesticated breeds and the other three forms of wild Galli, but it is probable that this want of fertility was due in great part to the unnatural conditions under which the parent and offspring were placed, as, if bred under more natural conditions, there is no difficulty in rearing these hybrids or in breeding from them with the domesticated varieties. ”

“ But the breeders cause every visible part of the body to vary as seems good to them, and within the last fifty years they have really brought about very considerable changes in many breeds. Their method of procedure is carefully to select for breeding those birds which already possess a faint beginning of the desired character. Domesticated animals have on the whole a higher degree of variability than wild species, and the breeder takes advantage of this. ”

“ Some of our earlier kings passed laws against the slaughtering rams of any good breed before they were seven years old, so that they might have time to breed. In Spain Cardinal Ximenes issued, in 1509, regulations on the selection of good rams for breeding. ”

“ All breeding is founded on the principle, that like begets like. This is, however, liable to some exceptions, and is much more generally true when breeding down than when breeding up. If two animals (which can never be exactly similar in all respects) are requisite to the perpetuation of the species, it necessarily results, that the progeny must differ in a more or less degree from each parent. ”

“ The sheep-breeder can, however, avoid the effects of in-and-in breeding, and at the same time preserve the character of his flock, by seeking rams of the same breed, possessing, as nearly as possible, the characteristics which he wishes to preserve in his own flock. ”

“ Hence this difference may well account for the difference in the power of reproduction between domestic races when crossed and species when crossed. It is probably in chief part owing to the same cause that domestic races can be suddenly transported from one climate to another, or placed under widely different conditions, and yet retain in most cases their fertility unimpaired; whilst a multitude of species subjected to lesser changes are rendered incapable of breeding. ”

“ Although animals of pure blood will obviously be deteriorated by crossing, as far as their characteristic qualities are concerned, there seems to be no exception to the rule that advantages of the kind just mentioned are thus gained, even when there has not been any previous close interbreeding. The rule applies to all animals, even to cattle and sheep, which can long resist breeding in-and-in between the nearest blood-relations. It applies to individuals of the same sub-variety but of distinct families, to varieties or races, to sub-species, as well as to quite distinct species. ”

“ It is not surprising, seeing the great difference between many domestic breeds, that some few naturalists have concluded that each is descended from a distinct aboriginal stock, more especially as the principle of selection has been ignored, and the high antiquity of man, as a breeder of animals, has only recently become known. Most naturalists, however, freely admit that our various breeds, however dissimilar, are descended from a single stock, although they do not know much about the art of breeding, cannot show the connecting links, nor say where and when the breeds arose. ”

“ With our true domestic animals, on the other hand, fertility is perfect, and is very little affected by changed conditions. Thus, we see the common fowl, a native of tropical India, living and multiplying in almost every part of the world; and the same is the case with our cattle, sheep, and goats, our dogs and horses, and especially with domestic pigeons. It therefore seems probable, that this facility for breeding under changed conditions was an original property of the species which man has domesticated—a property which, more than any other, enabled him to domesticate them. ”

“ The breeder who wishes to combine fancy and utility properties in any kind of live stock must breed only from specimens that are meritorious in both directions, selecting much more carefully than when breeding for one class of properties. ”

“ By reference to the habit of the fur-seal, which I have discussed at length, it is now plain and beyond doubt that two-thirds of all the males which are born, and they are equal in numbers to the females born, are never permitted by the remaining third, strongest by natural selection, to land upon the same breeding-ground with the females, which always herd thereupon en masse. ”

“ Now it has always been known that breeders could produce a race of markedly peculiar form or characteristics by selecting the individuals possessing this quality in the highest degree and breeding only from these. The breeder depends upon heredity, variation, and his selection of the individuals from which to breed. Similarly in nature new species have arisen through heredity, variation, and a selection according to the laws of nature of those varying in conformity with their environment. ”

“ Line-breeding is a systematic form of breeding which preserves the excellence and characteristics of the parent stock. In other words, it perpetuates the blood of both sire and dam so that it is not eventually lost as is the case in cross-breeding. ”

“ This strong tendency in crossed breeds to revert has given rise to endless discussions in how many generations after a single cross, either with a distinct breed or merely with an inferior animal, the breed may be considered as pure, and free from all danger of reversion. No one supposes that less than three generations suffices, and most breeders think that six, seven, or eight are necessary, and some go to still greater lengths. ”

“ In breeding, the smallest individuals which are suitable in other respects for breeders, should be selected in order to keep down the size and offset the tendency to breed larger in successive generations. ”

“ High breeding. When uniformity of plumage can be effected in mixed breeds or varieties without a resort to in-and-in, or close breeding, and without sacrificing the health and vigor of the race, it is desirable ”

“ The risk attending too close breeding as in the breeding of pure breds is also avoided provided that the herd from which the sires are bought is sufficiently large to furnish a change of blood, yet of similar breeding. ”

“ It is well known that too close breeding, or consanguineous breeding, or breeding in and in, as it is variously called, if continued long, has a bad effect on the offspring, weakening the stock, while judicious crossing of varieties within certain limits of difference has a good effect, strengthening the stock and increasing its fertility. ”

“ In the breeding of animals the closest inbreeding is frequently resorted to in order to improve the stock, and many examples can be given of the closest possible inbreeding for generations without apparent detriment, but it is universally admitted that the animals selected for such inbreeding must be sound constitutionally, and free from disease. After a certain number of generations however, degeneration apparently sets in. The number of generations through which inbreeding may be carried varies with the species, and the purpose for which the animals are bred. ”

“ The slight differences, however, which characterise each individual animal and plant would in most, probably in all, cases suffice for the production of distinct races through careful and prolonged selection. We see what selection, though acting on mere individual differences, can effect when families of cattle, sheep, pigeons, etc., of the same race, have been separately bred during a number of years by different men without any wish on their part to modify the breed. ”

“ It is free intercrossing which chiefly gives uniformity, both under nature and under domestication, to the individuals of the same species or variety, when they live mingled together and are not exposed to any cause inducing excessive variability. The prevention of free crossing, and the intentional matching of individual animals, are the corner-stones of the breeder’s art. No man in his senses would expect to improve or modify a breed in any particular manner, or keep an old breed true and distinct, unless he separated his animals. ”

“ These breeds are always produced in the same way. The breeder selects a pair, one or other, or both, of which present an indication of the peculiarity he wishes to perpetuate, and then selects from the offspring of them those which are most characteristic, rejecting the others. ”

“ He who will explain in a definite manner why, for instance, air elephant or a fox will not breed under confinement in its native country, whilst the domestic pig or dog will breed freely under the most diversified conditions, will at the same time be able to give a definite answer to the question why two distinct species, when crossed, as well as their hybrid offspring, are generally rendered more or less sterile, whilst two domesticated varieties when crossed and their mongrel offspring are perfectly fertile. ”

“ The degree of fecundity or lack of fecundity between different species varies in extraordinary and inexplicable fashion in different families of mammals. In the horse family, for instance, the species are not fertile inter se; whereas among the oxen, species seemingly at least as widely separated as the horse, ass, and zebra—species such as the domestic ox, bison, yak, and gaur—breed freely together and their offspring are fertile; the lion and tiger also breed together, and produce offspring which will breed with either parent stock ”

“ It is not yet positively determined that these cross-breeds will procreate their species in a natural way, nor even that they will be the improvement, which has been hoped, but that they can be bred artificially there is no further doubt. ”

“ But neither in the case of a breed which has been contaminated by a single cross, nor when, in the attempt to form an intermediate breed, half-bred animals have been matched together during many generations, can any rule be laid down how soon the tendency to reversion will be obliterated. It depends on the difference in the strength or prepotency of transmission in the two parent-forms, on their actual amount of difference, and on the nature of the conditions of life to which the crossed offspring are exposed. ”