200 Evolution and Genetics hair of a child would be largely guessing. Data collected 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 standard than popular designations of shades of color. The Inheritance of Mental Traits Man's success as a social animal depends as much on his mental qualities as on his physical characteristics. No one will deny, I suppose, that men behave in different ways, but who can say how far differences 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 defects, there are a few extremely abnormal conditions where the evidence indicates that something is inherited, 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 recessive, 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 [end]