THE ORIGIN OF THE HUMAN BODY 307 



Whether this is true or not, I will not pretend to say, but at 

 any rate wingless insects may also arise, not through a slow 

 process of elimination, but at a single step." ("A Critique of 

 the Theory of Evolution," 1916, pp. 66, 67.) 



In directing attention to the fact that a permanent and 

 inheritable reduction of organs to the vestigial state can re- 

 sult from mutation, we do not, of course, intend to exclude the 

 possible occurrence of somatic atrophy due to lack of exercise 

 rather than to germinal change. Thus the blind species of 

 animals in caves may, in some instances, be persistently blind, 

 because of the persistent darkness of the environment in 

 which they live, and not by reason of any inherited factor for 

 blindness. Darwin gives one such instance, namely, that of 

 the cave rat Neotoma. To test such cases, the blind animals 

 would have to be bred in an illuminated environment. If, 

 under this condition, they failed to develop normal eyes, the 

 blindness would be due to a germinal factor, and would be 

 inherited in an illumined, no less than a dark, environment. 



In any case, a mutation which suppresses a character is not, 

 as we have seen, a specific change, but merely one of the 

 varietal order, which does not result in the production of a 

 genuine new species. The factorial mutant with a vestigial 

 wing or eye belongs to the same species as its wild or normal 

 parent stock. Moreover, neither disuse nor natural selection 

 has the slightest power to induce mutations of this kind. If 

 mutation be the cause of the blindness of cave animals, then 

 their presence in such caves must be accounted for by sup- 

 posing that they migrated thither because they found in the 

 cave a most suitable environment for safety, foraging, etc. 

 Darkness alone, however, could never induce germinal, but, at 

 most, merely somatic blindness. The Lamarckian factor of 

 disuse and the Darwinian factor of selection have been defi- 

 nitely discredited as agents which could bring about heredi- 

 tarily-transmissible modifications. 



