62 BIOLOGICAL ASPECTS OF HUMAN PROBLEMS 



features of these theories will lead to their being 

 subjected to tests more carefully planned than any 

 heretofore used, and that these tests will definitely 

 settle one moot point after another. I feel that the 

 evolution of the human brain and mind is much easier 

 to explain on the mnemic than on any other, and 

 that this hypothesis in some form is destined to be 

 ultimately accepted. The triumph of this theory 

 over that of Weismann would give an additional 

 incentive to human individuals to acquire improved 

 mental and physical characters and to avoid the 

 acquisition of objectionable ones, since it would be 

 felt that the offspring is certain to be in at least a 

 slight degree influenced by these acquisitions. 



The part played by natural selection in bringing 

 about and maintaining new species or new qualities 

 has been the subject of even more discussion than the 

 rival theories of heredity which have just been dis- 

 cussed, for Charles Darwin's claims for the impor- 

 tance of this factor in evolution have now been before 

 men for half a century, while the theories of Weis- 

 mann and Hering-Semon are relatively youthful. 

 There has in recent years been a tendency to mini- 

 mize the importance of natural selection. That 

 the mnemic conception of heredity operates to re- 

 habilitate this factor in evolution is, it seems to me, 

 evident enough. And never has the bearing of the 

 mnemic theory on natural selection been stated 

 more fairly or more eloquently than by Francis 

 Darwin in closing his admirable address before the 



