146 THE PROBLEMS OF EVOLUTION 



but only modified beyond its former limits of ac- 

 tivity. The demonstrated eflfects of alcoholism in a 

 parental generation upon the heredity of the de- 

 scendants has been flouted on the ground that 

 alcohol may actually reach and injure the germinal 

 tissues. Is the difference between these two cases 

 as great as the present attitude of geneticists would 

 have us believe? If the action of X-rays on genes 

 is similar to their demonstrated action on inorganic 

 substances, then certainly it is on a par with other 

 modifications forced upon the organism by the 

 environment, even though it occurs on such a small 

 scale that the result may be only a slight modifica- 

 tion of the previous expression of the gene. 



Returning to the paper cited above, we are told 

 that a comprehensive series of breeding experi- 

 ments to determine the effects of other external 

 factors on the fruit fly has failed to demonstrate a 

 significant response in the production of mutations. 

 Two alternatives present themselves : We may con- 

 clude either that mutations do occur in response 

 to fluctuations occurring in some phase of the 

 normal environment and that we have merely 

 failed to accomplish this result experimentally, or 

 that mutations are always the result of penetrating 

 rays which reach the chromosomes and act upon 

 them directly. The latter view puts a terrible 

 burden on rays and a greater one on our credulity. 

 Considering the fact that the existence of the 



