184 WORLD-POWER AND EVOLUTION 



world-migrations are giving rise to revolutionary racial changes. 

 Immigrants who come from the Old World to New York may 

 experience one kind of change, those who go to southern California 

 another, and those to Alabama a third. Moreover, people from 

 one part of Europe are presumably influenced differently from 

 those from another. Which changes are good and which are bad 

 no one can tell. If our conclusions are correct, the whole human 

 race is in a state of flux, and the future may see profound re- 

 adjustments in harmony with the new environments. Remember 

 that two forces may be producing these changes. One is the 

 sudden mutations which apparently arise when people migrate to 

 new countries, or perhaps when children at the critical age are 

 exposed to climatic extremes. The other is the selective eff'ect of 

 the entire environment which in the course of generations will 

 weed out some types and give others a free opportunity. The 

 mutations and still more the selection may prove to be largely 

 within our control. Whether this is so or not, the world has before 

 it no more pressing task than to discover how and why. the 

 environment influences heredity. 



Before we leave this chapter a word of warning is necessary. 

 .1 am afraid that the people who magnify environment at the 

 expense of heredity will quote me in a sense that I have never 

 meant. I believe that in the long run environment — and by that 

 I mean physical environment — is the greatest of all factors in 

 evolution. From this point of view heredity is merely the sum 

 of all past environments, and training depends entirely upon the 

 powers and faculties developed as the result of past heredity and 

 past environment. But notice that I have said **all past environ- 

 ment." Part of that past environment is very far back. It in- 

 cludes the early geological times when animals first emerged from 

 the water to the dry land, the times when certain feeble animals 

 acquired the power to warm their own bodies, the hundreds of 

 thousands of years of the last Glacial Period when man's mind 

 was evolving most rapidly, and the thousands of years since the 



