360 EVOLUTION AND GENETICS 



What Is Inherited? The application of conscious thought to 

 the prol^lems of existence is a comphcating factor which it is 

 exceedingly difficult to avoid in a scientific consideration of human 

 behaviour. Every-day interpretations of factors in human life 

 must be translated into the accuracy of scientific observation. 

 We hear of the inheritance of drunkenness, disease and special 

 ability, as well as of structural characters, whereas these things 

 are phases of Ijehaviour, and behaviour can only be the expression 

 in the individual of its hereditary properties. There is necessarily 

 some basis in the individual for anything which it does, and that 

 basis is at least indirectly associated with some inherited character. 

 It is not enough to say that a great musician inherits musical 

 talent; he inherits an exceptional sense of hearing, great manual 

 dexterity and the wonderful nervous coordination which any 

 skilful performance demands. The use to which he puts these 

 things is response. The skilled mechanic who builds an instru- 

 ment of precision has an equally fine inheritance, but his ability 

 attracts less attention. 



Man, like other organisms, has a heritage and an environment 

 to which the heritage responds. Ilesponscs are the things that 

 interest us chiefly. They are so conspicuous that they usually 

 obscure the heritage from which they arise but careful considera- 

 tion will show that a structural heritage is present for every 

 function. Mental activity, although it is exceedingly complex, is 

 no less definitely based on structure than other functions. It is 

 none too well understood in detail but of its anatomical source 

 we need have no doubts. Whatever the inherited structure, in 

 so far as it finds the proper environment for its expression, it will 

 manifest itself in the same way in successive generations. 



The distinction between heritage and response, since they are 

 so likely to correspond in successive generations, is not essential 

 from the popular point of view. In efi'ect, a talent may be inherited. 

 From the point of view of the scientist, however, no talent is the 

 simple thing into which ordinary language resolves it. In no 

 case can exceptional ability be looked upon as a unit character, 

 nor can conditions of mental deficiency always be so simply 

 handled. These things are the result of many conditions present 

 in the body. They may be based upon unit characters, but are 

 due to complex immediate causes. The things actually handed 

 down from generation to generation in man as in other organisms 



