200 EVOLUTION AND GENETICS 



hair of a child would be largely guessing. Data col- 

 lected by the questionnaire method, that has been 

 used in the study of the inheritance of hair color, can 

 not be relied upon without some more definite stand- 

 ard than popular designations of shades of color. 



The Inlieiitance of Mental Traits 



Man's success as a social animal depends as much 

 on his mental qualities as on his physical character- 

 istics. No one will deny, I suppose, that men behave 

 in different ways, but who can say how far differ- 

 ences in human behavior depend on the physique of 

 the individual, how far on his early experiences and 

 training, and how far on differences in his sense 

 organs and central nervous system? Until some of 

 these questions are better understood it is impossible 

 to know how far observed differences are innate and 

 how far acquired. 



Here again, as in the case of man's physical de- 

 fects, there are a few extremely abnormal conditions 

 where the evidence indicates that something is in- 

 herited, but even here there is much that is obscure. 

 The case most often quoted is feeble-mindedness 

 that has been said to be inherited as a Mendelian re- 

 cessive, but until some more satisfactory definition 

 can be given as to where feeble-mindedness begins 

 and ends, and until it has been determined how many 

 and what internal physical defects may produce a 

 general condition of this sort, and until it has been 



