226 HEREDITY AND EUGENICS 



Saunders (1922) holds, man's mental evolution has 

 consisted largely in the handing down of accumulated 

 tradition, but there must also have been a reaction 

 of man's mind' — that is, a mental evolution — in order 

 to make the continued accumulation and advance of 

 tradition possible. That such a mental evolution has 

 accompanied the accumulation of tradition is evident 

 from the recent history of the Japanese. They were 

 able in one generation to absorb a great part of 

 Western science and begin making independent 

 contributions to that science. This remarkable 

 phenomenon, resulting from contact with Western 

 civilisation, has not been approached by any truly 

 primitive people, which shows that primitive peoples 

 w^ould require a long period of mental evolution before 

 they were capable of grasping or profiting by the 

 views of nature held in the civilised world. 



As we have already pointed out, crossing between 

 more or less related races or tribes of mankind has 

 been going on at intervals throughout the whole of 

 historical and prehistoric time. Nevertheless, at any 

 given period it has usually been confined to definite 

 areas of contact between tribes, and has been very 

 limited in its scope, except at times of migrating or 

 shifting populations. Primitive man, in particular, 

 was far less of a roving animal than is commonly 

 supposed. This is shown by the great number of 

 local native tribes which existed among the Indians 

 of North and South America at the time of their first 

 contact with European civilisation. Such differentia- 

 tion, like that of any other species, could only have 

 occurred under conditions of relative isolation and 

 segregation — i.e., absence or infrequency of inter- 

 marriage. Carr-Saunders (1922) has pointed out that 

 as soon as early man began to have am^ social organ- 

 isation at all, probabty even as earty as the Upper 

 Palaeolithic, families and groups began to develop 



