288 THE PEINCIPLES OF HEREDITY 



reserve its treatment for a separate chapter. We shall then 

 be in a better position to judge how far the mental peculi- 

 arities of individuals and classes deserve to be regarded as 

 innate. Since individuals have only one life each, we cannot 

 test our theories by rearing the same people first in one 

 environment and then in another. But races have sometimes 

 changed their mental environments very rapidly. Under 

 these conditions whatever psychical alterations occur must be 

 considered, not as innate, but as acquired. 



