ORGANIC EVOLUTION 37 



part the more frequent discovery of new types in 

 these forms. 



Many, probably most, of the extreme mutant 

 types could not compete with the native types from 

 which they have sprung, and this has been urged as 

 an argument against the view that mutants could 

 furnish the materials for evolution; because, it is 

 said, only better adapted types coidd survive that 

 have an advantage of some sort over the parent 

 types so that they can replace the original types, or 

 else find a new environment to which they are 

 better suited than were the original forms. This ar- 

 gument, if it could be substantiated, would be a fatal 

 blow to the mutation theorv of evolution. It calls, 

 therefore, for careful and impartial consideration. 

 That it is not justified is shown, I think, by the fol- 

 lowing evidence. 



While it is true that manv of the mutant charac- 

 ters that are preserved by geneticists for a study of 

 heredity are extreme departures from the original 

 type, these are utilized rather than smaller differ- 

 ences because thev are easilv observed and their 

 classification readilv determined. Those characters 

 that depart little from the jjarent type, or are diffi- 

 cult to distinguish from the fluctuating variations of 

 that type, are more difficult to study and are neg- 

 lected. Hence has arisen in some quarters the er- 

 roneous idea that all mutant types are defectives 



