CROSS-BREEDING AND INBREEDING 307 



is surer than that inbreeding will bring these to the surface. Cross- 

 breeding might succeed in masking such recessive characters, but they 

 remain in the germ plasm, nevertheless. All inbreeding does is to 

 reveal that which was masked behind dominant characters. Therefore 

 it is not inbreeding itself that is to blame, but a poor heredity. In- 

 breeding is a valuable instrument for detecting the unfavorable heredi- 

 tary characters in a race and giving the breeder a chance to cull out the 

 defective factors from his stock. 



Inbreeding should be followed by cross-breeding inbred stocks. — 

 Whatever loss of vigor or productiveness may be incidental to the in- 

 breeding method of standardizing stock may be entirely done away 

 with by suitable cross-breeding or outbreeding. No matter how good 

 an inbred stock may be, great improvement can be brought about by 

 introducing new blood even from an apparently very similar strain 

 which is unrelated. It is well known that when two pure breeds are 

 crossed there is an effect quite equivalent to that which we have called 

 hybrid vigor. The animal-breeder commonly practices close inbreed- 

 ing in building up families of superior excellence, which he maintains as 

 pure-line stock, used for crossing with other stocks in order to produce 

 exceptional F t offspring. Man, of course, cannot practice this scheme 

 in the present state of society, but it seems obvious that there lie in 

 this method almost untold possibilities for racial improvement 



