220 THE BREEDING OF ANIMALS 



cesses which result in simplifying the germ-plasm and 

 intensifying the powers of transmission act impartially 

 on all characters alike, bad as well as good. Lurking 

 tendencies to evil may become strengthened along with 

 the good, and thus be more strongly transmitted than 

 before. 



Such a result cannot always be foreseen and hence 

 when breeding closely related animals, there is always 

 the risk that we will produce offspring which are not only 

 more prepotent in respect to the good qualities we are 

 seeking to develop and perpetuate, but we may at the 

 same time bring about the same result in connection with 

 the bad qualities. 



But aside from the bad results following in-breeding 

 which may be ascribed to the simplifying of the germ- 

 plasm and the intensifying of the tendencies to evil, it 

 has long been held by many eminent biologists and by 

 practical breeders that certain definite evil results always 

 follow long-continued in-breeding. The most important 

 of these necessary evils are loss of vigor, decreased fer- 

 tility and diminished size. 



206. Decreased fertility and vigor from in-breeding. 

 Many breeders believe that continuous in-breeding results 

 in a loss of fertility. It is admitted that most other 

 qualities may be advantageously improved by close- 

 breeding, but that the quality of fertility is an exception. 

 This belief is firmly implanted in the minds of the greater 

 number of breeders and of many biologists. The basis 

 for such a belief is found in the results of certain specific 

 investigations and the general experience of breeders. 

 Fertility is a character of prime importance in the domestic 

 animals. This character is undoubtedly subject to the 

 same general laws of transmission as are all other hered- 



