118 THE PROBLEMS OF EVOLUTION 



preserved while others are lost. Even though 

 useful characters may determine survival, an evo- 

 lution of indifferent characters will follow as a 

 corollary. 



The results of selection may therefore be summed 

 up as threefold. First, useful characters are pre- 

 served; second, harmful characters are destroyed; 

 third, indifferent characters are modified through 

 their association with the other two. 



We are justified in questioning whether this is 

 the only possible end of natural selection. Grant- 

 ing that overproduction and consequent crowding, 

 or interspecific competition, make necessary some 

 adjustment of the organisms involved, are survival 

 or death the only alternatives.^ Obviously, as has 

 been contended, if some individuals are better 

 fitted to secure the necessities of life they will 

 survive at the expense of the others, but need the 

 others die.^^ In a few cases of dearth of food which 

 have come to my attention the result was an ex- 

 tensive migration in search of food, and it seems 

 likely that lack of any necessity from any cause 

 might first of all impel the organism to seek ac- 

 tively for that necessity. Moreover if a species has 

 a variety of food habits of which certain ones are 

 preferred, the effect of overcrowding might well be 

 the adoption of the less favored habits by the in- 

 dividuals which are less fitted to secure the pre- 

 ferred foods. 



