THE CHIEF PROBLEMS OF HEREDITY 323 



such as a sense of duty ? (2) Do men differ in their ' by nature ' 

 susceptibility to the charm of alcohol ? (3) Is alcohol a lethal agent ; 

 and, if so, is it selective ? (4) Bearing in mind the universal truth 

 that races are temperate when exposed to alcohol in proportion to 

 their past experience of it, but show no other change that can be 

 traced to it, is alcohol a cause of protective evolution or of degenera- 

 tion? The very obvious truths that men of the same race drink, 

 as a general rule, more when their opportunities for drinking are 

 greater, and that the amounts they drink depend to some extent 

 ou their previous moral training, are not in dispute. 



546. Two problems of heredity are of outstanding importance. 

 The first is the problem of the causation of variations. The second 

 is the problem of the proportion which the ' innate ' characters of 

 any species bears to its ' acquirements.' In the section of this 

 work just concluded we have considered, by the light of the evidence 

 furnished by microbic diseases and narcotics, the problem of the 

 causation of variations, and have concluded that, when we take all 

 the evidence into account, it is inconceivable that the great mass 

 of variations can be other than spontaneous. In the next section 

 we shall consider the second problem. For this the study of mind 

 affords peculiar facilities. 



