Problem of Human Heiiedity 151 



The facts seem to indicate that abnormal 

 conditions of the nervous system, resulting in 

 alcoholic 'mania, epilepsy, feeble-mindedness, 

 and insanity, are also heritable, and probably in 

 Mendelian fashion; at least the evidence is suffi- 

 cient to induce the cautious individual to base 

 action on such a hypothesis. Similarly, the evi- 

 dence seems to show that mental ability also is 

 heritable, though so many facts are involved in 

 such a complicated thing as "ability" that we 

 may make this assertion in a tentative way only. 



With these facts in mind, what policies may 

 be adopted to guide action that aims at an 

 improvement of a family, a race, or a people ? 

 We must bear in mind that improving the 

 environment may enlarge opportunity. Train- 

 ing may develop individual capacity to the limit, 

 but that limit is set by the hereditary equip- 

 ment. The hope of racial improvement is in 

 selective breeding, and this hope must be 

 realized by (i) stimulating reproduction in the 

 best stock, (2) checking it in the poorest. The 

 same method has been effective in man's 

 improvement of domestic plants and animals. 



