HUMAN GENETICS 347 



half-caste is probably the greatest influence on half-caste mentality, 

 and from such cases no genetical conclusions can be drawn. Castle^ goes 

 so far as to say "Human race problems are not biological problems any 

 more than rabbit crosses are social problems." One cannot deny, how- 

 ever, that the human problem has a biological element, and perhaps in 

 the future it will be possible to analyse this more adequately in coimtries 

 like the U.S.S.R. where an attempt is being made to preserve strict 

 race-equality in social matters. 



We should expect the later generations from wide crosses to produce 

 segregates more extreme than either of their parents. This does not 

 often seem to happen. Muller^ has discussed the question thoroughly, 

 and suggests that the extremes of variation in a single "race" are 

 probably due to rather rare genes, so that unless some of these happen 

 to be included in the parents of the cross there will not be an adequate 

 genetic basis for the cross-breds to produce extreme segregates. 



5. Genetic Differences Between Classes^ 



Men are not only divided into racial and national groups, but, in all 

 civilizations except some of the most primitive and the most advanced, 

 they are also stratified into classes. In societies founded on the labour 

 of slaves captured in war, we should expect to find considerable genetic 

 differences between the ruler and the ruled. But few such societies now 

 exist. In this section we shall discuss the genetic differences between 

 classes in present-day capitalist civilizations. 



If mental tests (I.Q. tests, performance tests, etc.) are made on 

 individuals belonging to different classes, it is commonly found that the 

 average score for professional men is higher than for shopkeepers, for 

 those again higher than for skilled workers, and for unskilled workers 

 lowest of all. There is of course an enormous overlap; and since the 

 lower categories are much more numerous than the higher, the greatest 

 number of individuals above normal may come from one of the inter- 

 mediate groups such as the skilled workers. Even the average differ- 

 ences, though statistically significant, are not large, the Hmits of the 

 range being about 15 to 30 per cent in different investigations. 



Before any genetical significance can be attached to these results, we 

 must discuss how large a part enviroimiental agencies play in producing 

 them. Unfortunately this question is nearly always confused by poli- 



^ Casde 1926. 2 Midler 1936. 



^ General references: Cf. Freeman 1934, Gray 1935, Haldane 1938, Holmes 

 1934, Lorimer and Osbom 1934. 



