222 Changing Human Nature 



As to the actual process which has resulted in distinct 

 races, we know nothing. It is true that Cunningham was 

 able to reverse the pigmentation of flatfish by arranging mir- 

 rors so that the animals were illuminated from the under 

 surface with the result that the adults were white on top and 

 speckled underneath (see page 170). So far as concerns 

 the human race, however, the probabilities are that the 

 various pigment-races represented distinct mutational di- 

 vergences from more primitive stocks. Hereditary traits 

 such as characterize both the recognized races and numerous 

 strains or families within each population are not the im- 

 mediate result of the action of the environment. New types 

 have undoubtedly arisen as a result of crossing and segre- 

 gating groups carrying special combinations of heritable 

 traits. Climatic and social forces probably play an important 

 role in this process. The human race as a whole shows its 

 radical deviation from ancestral types in the relatively sudden 

 appearance of a large brain and in the liberation of the hand 

 from the task of locomotion. Such a radical departure was 

 probably a mutation, and in the ensuing lines of descent 

 numerous other mutations have added traits that in their 

 totality give us the human race of today — a very heteroge- 

 neous population and yet all human. 



The Race in Transition 



The question whether human nature has changed or 

 is changing cannot be answered categorically. If change is 

 going on today it is so slow that we cannot observe it directly. 

 If it has gone on in the past our knowledge of it must suf- 

 fer from the limitations of all historical knowledge. It is 

 worth while to note, however, that not only do the interests 

 and the behavior of peoples vary from place to place, but 

 they have varied through the ages. Fashions have changed 

 in our major values, in estimates of success, in leisure pursuits. 

 Head-hunting is important for some people, while privateer- 

 ing and gambling engage others. The peaceful arts fluctuate 



