52 6 BIOLOGY AND HUMAN LIFE 



Today breeders apply these principles and produce varieties 

 of animals that are new in the sense that they have combina- 

 tions of qualities that have never appeared before. The Orping- 

 ton fowl is an artificial breed of this kind, and new breeds are 

 being brought out every year, both among the strictly utilitarian 

 varieties and among the fancy breeds, or pet animals, such as 

 dogs, pigeons, cats, rabbits, and so on. 



The breeder looks in the third generation (the segregating 

 generation) for individuals that have the desired combination 

 of characters, all in a pure state. He then proceeds to multiply 

 his stock by inbreeding, that is, by mating similar types, or 

 members of the same litter, for several generations. It has 

 been found that this inbreeding, instead of causing degenera- 

 tion, as was formerly believed, only tends to bring out and fix 

 the characters that are present from both lines of ancestry. Of 

 course, if there are any undesirable characters, these will also 

 become fixed. Outbreeding, or the mating of individuals having 

 diverse ancestry, is now practiced by breeders only for the pur- 

 pose of making new combinations of characters in the hope of 

 discovering more valuable or more interesting varieties. 



One form of inbreeding which is of great value is that of 

 ^^ grading up" stock. Pure-blooded animals are very rare and 

 very expensive. It is not possible for most farmers or raisers to 

 replace their poor stock with pure-bred animals. Accordingly 

 they get the services of a pure-bred male for their flock or herd. 

 The following generation of hybrids will be 50 per cent pure 

 bred. The following generation is again served by the same 

 male, and the grade is further advanced. In the course of a few 

 years or generations the scrub, or mixed, varieties are replaced 

 with high-grade animals at a comparatively low cost to the 

 owner. 



382. The value of animal breeding. Within recent times a 

 great change has been brought about in the character of the 

 animals under cultivation. In some parts of the country the 

 farmers have not yet discovered that the old breeds ought to be 

 replaced. In a survey of dairy cattle made a few years ago in 



