142 WHAT EVOLUTION IS 



tion theory presents a means of avoid- 

 ing the chief difficulty with which 

 Darwinian natural selection has to 

 contend. That difficulty, it will be 

 remembered, had to do with the first 

 steps in the origin of favorable traits. 

 These steps are not necessary in the 

 origin of mutations, for mutations 

 appear fully formed and are not built 

 up by slow degrees. This is the great 

 advantage that the mutation idea has 

 over Darwin's view of the way in 

 which new traits are supposed to be 

 ushered in. As mutations they enter 

 fully formed. 



Difficulties with the mutation the- 

 ory can be easily found. First of 

 all this theory depends upon Men- 

 delian inheritance and what that kind 

 of inheritance implies as to the sep- 

 arateness of characters. But char- 

 acters often blend, in fact there may 

 be such a condition as blended in- 



