24 A NEW THEORY OF EVOLUTION. 



proportion more of the blood of the parent 

 it resembles than of the other, from which 

 it differs in expression of type. 



This feature of heredity discloses one of 

 Nature's methods perhaps the most im- 

 portant after race hatred for maintain- 

 ing purity of race, and it is the guide to 

 success in selective breeding. 



As we have seen, the stock of hybrids, 

 without intermixture of pure or nearly pure 

 blood, disappears ; but if the hybrid and 

 its progeny are bred into the pure stock 

 of either parent, the descendants have in 

 two or three generations all the appearance 

 of that race. 



This result will evidently be accelerated 

 if such of the progeny as take after the 

 race of one parent are bred into that race. 

 And that is the practice in selective 

 breeding. 



If a calf shows any strain of alien blood 

 or inferiority in expression of type, it is 

 destined to the butcher ; and only if a bull- 

 calf promises to become a higher expres- 

 sion of the type of its race than either 

 parent, is it selected for improvement of 

 the herd. 



Selective breeding thus co-operates with 

 Nature, and thereby attains more promptly 



