INHERITANCE 



317 



together albino three-quarter lops may be obtained in the 

 next generation. By continuing this process of back-cross- 

 ing with the lop-eared stock, and selecting the albino off- 

 spring obtained, the lop-eared character may be steadily 

 improved in the albinos until it is practically as good as in 

 the original lop-eared stock. The rate of improvement pos- 

 sible can be readily calculated. The albino young will be: 



After 2 generations, one half lops, 



After 4 generations, three fourths lops, 



After 6 generations, seven eighths lops, 



After 8 generations, fifteen sixteenths lops, 



After 10 generations, thirty-one thirty-seconds lops, etc. 



This will be the result on the hypothesis that no secondary 

 variation occurs in the lop-eared character. If, however, 

 variation is induced by the cross-breeding, then it is possible 

 that the desired end may be reached sooner, or that an even 

 better lop may be obtained in the albino cross-breds, than 

 that of the original pigmented stock. 



' 'Latent characters are an important element in practical 

 breeding. Sometimes they greatly aid the breeder's work; 

 sometimes they impede it. If a stock contains undesirable 

 latent characters which are brought into activity by cross- 

 breeding, these latent characters will have to be eliminated, 

 or a new stock tried." 



Obviously, without variation no new characters are 

 obtained by such intercrossing, but merely new combina- 

 tions of characters that previously existed apart. But 

 when new characters appear among the variants of a species, 

 and especially when a number of new characters appear 

 simultaneously as in typical cases of mutation, then inter- 

 crossing may be the means of bringing these characters 

 together in all sorts of combinations, some of which may be 

 of value to man, and some of which may be -fit, and may, 

 therefore, furnish a basis for further natural evolution. 



