At all events, heredity may be depended upon to govern the general characteristics which de termine the species, and the less general ones which distinguish the breed. Beyond this it is the object of the breeder to maintain the standard of excellence which has been attained, and to intensify certain desirable qualities as they appear and make them fixed characteristics of the breed or family. The highly artificial characters which render the animals of a breed valuable for a specific purpose are, from their very nature, more difficult to retain than are the less divergent characters of the original type. They can only be secured in their greatest per fection by persistent effort in the systematic accumulation of slight variations in the desired direction, and they can only be made the domi nant characters of a family or breed by breed ing exclusively from animals in which they are the most conspicuous. As soon as the breeder relaxes his efforts—i.e. neglects the selection of the breeding stock—degeneration will inevitably set in, and it will not long bo prevented by any supposed constancy of the breed.
One annoying factor which the breeder often meets with, and which sometimes sets his cal culations at naught, is atavism. or reversion. as Darwin has called it. This is the appearance in an offspring of peculiarities of a more or less remote ancestor, as form, color, or traits, which have not bee'n observed in the parents. It is a form of heredity, and has long been known to breeders under a variety of names, as 'throwing back,' 'crying back.' etc. If the qualities which crop out in this way are sufficiently pronounced or undesirable, the value of the animal may be materially decreased; but practically atavism is not often a matter of great importance in breeding animals which have been bred for a long time, as it usually manifests itself In small and unessential details. It is referred to by .Miles as an evidence that no limit can be set to the of characters, and that the oretically a defect or peculiarity cannot be en tirely 'bred out,' although it may be removed so far as to scarcely merit attention.
In practice the offspring nearly always shows a closer resemblance to one parent than to the other. This is attributed by stock-breeders to prepoteney, which may be defined as the superior influence of one parent over the other in deter mining the characteristics of the offspring. Like atavism, prepoteney is a well-established phe nomenon, recognized by all breeders, but about which little is known or can be prophesied in a particular ease. It is an important factor, espe cially in the ease of the male, as he is selected for special desirable qualities which be is ex pected to impress upon his numerous progeny.
Reference was made above to the part played by variation in the evolution of breeds. It is also the factor which is responsible for the de generation of improved breeds when left to them selves. It may be defined as the tendency which domestic animals exhibit under certain condi tions to differ or depart from the parental type, contrary to the law of heredity. The principal causes of animal variation are climate, food, habits, and environment in general. It may be in the direction of improvement, in which ease it can be taken advantage of by the breeder. or it may be in the opposite direction. Such varia tions are usually prepotent over the normal characteristics, and are usually complex rather than simple, affecting more than one organ. This is in agreement with the law of eorrelation, according to which any peculiarity in the de velopment of one organ or set of organs is usu ally accompanied by a corresponding modifica tion or suppression of organs belonging to an other part of the system. On account of this tendency to variation, it is only by the closest watchfulness that the excellence of many of the higher developed breeds of animals can be main tained.
Success in breeding depends primarily on skill in selecting and managing the breeding stock. The animals selected should be as nearly perfect as possible in conformation and build, have the valuable qualities which it is desired to per petuate developed in the highest possible degree, and be capable of transmitting these qualities to the offspring. Special attention should be given to selecting the male, not because of any special known influence of sex, aside from prepoteney, but because lie impresses his characters upon It numb larger number of progeny than does the female. A further reason for this is the sup posed influence which previous impregnations, and especially the first, may. exert upon the fe male. The hypothesis is that the influence of the male is not Ihnited to his immediate offspring, but may extend through the female that lie has impregnated to the offspring which she pro duces subsequently by coupling with another male. This influence is designated technically as telegony, A large number of instances of such an apparent influence are on record. and it is quite widely believed in by English breeders. The leading authorities in Oermany have not accepted it, and those who have admitted the possibility of it emtsider that it has not been proved. Seine interesting experiments with horses and yx-bras, recently reported by Prof. ,.I. C. Ewart, of Edinburgh, seem to support the belief In telegony, but for the present. it must be regarded as open to some doubt.