i HEREDITY n 



claims to add some subsidiary help from 

 another physical cause which is wholly 

 separate. But if natural selection is a 

 mere phrase, vague enough and wide 

 enough to cover any number of the 

 physical causes concerned in ordinary 

 generation, then the whole of Mr. 

 Spencer's laborious argument in favour 

 of his " other factor " becomes an argu- 

 ment worse than superfluous. It is 

 wholly fallacious in assuming that this 

 " factor " and " natural selection " are at 

 all exclusive of, or even separate from, 

 each other. The factor thus assumed 

 to be new is simply one of the sub- 

 ordinate cases of heredity. But heredity 

 is the central idea of natural selection. 

 Therefore natural selection includes and 

 covers all the causes which can possibly 

 operate through inheritance. There is 

 thus no difficulty whatever in referring 

 it to the same one factor whose solitary 



