212 INBEEEDING AND OUTBREEDING 



serve no purpose. We have seen from our consideration 

 of the facts of heredity that both inbreeding and out- 

 breeding must be used if one would succeed in improving 

 the products of domestication. There must be cross-breed- 

 ing to furnish a variety of character combinations from 

 which to select; there must be inbreeding to provide the 

 opportunity to isolate the combinations desired. "What 

 we want to know now is the manner of their use, the degree 

 of inbreeding permissible under given conditions, the efS- 

 cacy of crossing for particular purposes. 



While there has always been a certain amount of in- 

 breeding as a necessary adjunct in building up breeds of 

 livestock because of the necessity of mating near relatives 

 in order to establish uniformity, the opinions of breeders 

 have differed and still differ as to how long or how close 

 intermating can be practiced with safety. Yet some of 

 the most noted modern livestock strains owe their excel- 

 lence to a close and continuous inbreeding that would be 

 looked upon with misgivings by the majority of animal 

 raisers. In fact, some of the inbreeding actually prac- 

 ticed was due more to enforced isolation, or the expense 

 or difficulty of securing unrelated animals with desirable 

 characteristics, than to a firm belief in the desirability of 

 the method. This might be said of the Shetland pony, the 

 Angora goat, the Merino sheep in America, and of many 

 breeds of dogs. 



Notwithstanding these facts, it would be a mistake not 

 to recognize how great an amount of continuous and ex- 

 tended inbreeding has been practiced intentionally with 

 the best of results after the general characteristics of a 

 breed have been established. This is true as a generalized 

 statement for the modem trotting horse and saddle horse 



