130 THE PROBLEMS OF EVOLUTION 



we must still explain the origin of variations from 

 less varied ancestral stocks. The value of the 

 theory seems distinctly limited. 



Returning to mutations as one explanation of 

 variation, we find in the writings of Cuenot a sug- 

 gestion of three degrees of importance of muta- 

 tions.^^ If inferior to the parental form in their 

 capacity to survive, they must gradually disappear; 

 if superior, they tend to replace the parent form ; if 

 on an equal footing, they introduce variability. 

 The supplanting of a parent species by mutations 

 of sufficient degree would satisfy all of the require- 

 ments for the origin of species. 



The problem of the relation of mutations to 

 selection demands the consideration of still another 

 point. Granting that a mutation of slight degree 

 appears in a certain character, and that it aids the 

 individuals possessing it to meet existing condi- 

 tions of environment more effectively than the 

 ancestral form, we have the necessary conditions 

 for the action of natural selection in the preserva- 

 tion of the mutation and the possible elimination 

 of the individuals which are without it. The fact 

 that the mutation is a permanent departure from 

 the previous range of variation of the character 

 in question is not, however, a guaranty of further 

 change in the same direction. Nothing assures us 

 that the character will undergo cumulative muta- 



" Op. ciL, p. 87. 



