BREEDS AND BREEDING. 455 BREEDS AND BREEDING. The following are important contributions to the subject of Plant Breeding: United States Department of Agriculture Year-books for 1S97, X89S and lS9f) ; Experiment i^tation Record. Vol. VII. (Wasliington, ISOti) and Vol. XI. (Wash- ington, 1S90) ; Carri&ro, Production et fixation des varietcs dans les veg^taiix (Paris, 1865). AxiMAi Breeding. The art of breeding ani- mals, as practiced at the present day, is found- ed on the practice of the most successful breed- ers, and its rules are almost e.vclusively empirical in their origin. They have not been worked out on the basis of scientific investigation and ex- periment, but may bo regarded rather as con- tributions to science than deductions from it. Hence, while many interesting and instructive experiences and observations have been recorded, and these have been brought together and dis- cussed in the light of tlie best knowledge avail- able, comparatively few general principles have been deduced as yet, and many important points upon which it would be exceedingly valuable to have definite information remain in obscurity. The breeding of animals has not yet been placed upon the scientific basis that, thanks to syste- matic investigation, many other lines of agri- cultural practice now occupy. Breeding has been practiced from the earliest times, the horse having apparently received more attention from the ancients than the other kinds of farm animals. The ancients evidently had some knowledge of the laws of heredity, al- though much stress appears to have been laid upon the exercise of e.xtet-nal influences as well. I'p to the middle of the Eighteenth Century the theory that "like produces like," and the rule to breed from the best," comprised what was known of the principles of breeding, but it is evident that the extended applications of these empirical expressions were not fully appreciated. The early breeders had no consistent system of selection — their standards of excellence were, in fact, constantly changing, so that the conception of the 'best' differed widely from time to time, and this prevented any very high development of the most valuable qualities. Soon after the middle of the Eighteenth Century, Robert Bake- well, of England, originated a new system of breeding, based upon careful selection from a single variety or breed, and close breeding to develop certain desirable qualities. The cross- ing of different breeds had previously been held to be the road to improvement. He believed that the maxim, "like begets like," was not limited to the external or more obvious characteristics, but extended to the minutest detail of the animal organism. He regarded the animals he worked with as plastic, and he sought so to mold these plastic forms as "to give expression to his ideal conception of the qualities that constitute per- fection." His work and teachings produced a very marked effect on the practice of breeding, and the following out of his theories by a long line of able breeders has given us many improved breeds of live stock, each adapted to special con- ditions and purposes. Our knowledge of the principles of breeding rests to-day upon the development and the more intelligent application of the old maxim that like produces like — i.e. upon the law of heredity. According to this law, every animal embodies the sum of the characters inherited from its parents and ancestors, and those acquired as a result of its environment. The animal "inherits an assemblage of peculiarities representing the aggregate of parental charac- ters," thus presenting a composite of its ances- tors, which has been likened to a composite photograph of a number of persons, containing traces of each individual, some hardly discern- ible, but strongest along certain lines common to all. Jliles has advanced the theory that while all the characters are directly transmitted, some may become dominant in the offspring, and thus determine its external form and general char- acteristics, while others remain latent until the conditions finally become favorable to their de- velopment in an offspring, when thej- in turn may become dominant, and thus obscure other characters. This theory has some degree of plausibility, and would account for many ap- parent exceptions to the law of heredity. Those who do not accept it entirely hold that only such characters as have become fixed are trans- mitted with certainty, and that the theoretical effect of the law of heredity is only realized or approximated in proportion as the 'ancestry has acquired a fi.xed and unvarying type. At all events, heredity may be depended upon to govern the general cliaracteristics 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 ditficult to retain than are the less divergent characters of the original type. The.v can only be secured in their greatest per- fection by persistent effort in the sj-stematic accumulation of slight variations in the desired direction, and they can only be made the domi- liant characters of a family or breed by breed- ing exclusively from animals in which they are the most conspicuois. As soon as the breeder relaxes his efforts — i.Ci 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 been 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 bre<l 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 inheritance 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.
