MUTATION 323 



so, it will be isolated from the beginning, which will be 

 an advantage in avoiding the bad effects of inter- 

 crossing." 



"5. It is well known that the differences between 

 related species consists largely in differences of unim- 

 portant organs, and this is in harmony with the muta- 

 tion theory, but one of the real difficulties of the selec- 

 tion theory." 



"6. Useless or even slightly injurious characters 

 may appear as mutations, and if they do not seri- 

 ously affect the perpetuation of the race, they may 

 persist." 4 



L. Plate, who has written the most complete crit- 

 icism of the mutation theory, refuted the foregoing, 

 paragraph by paragraph, in the following terms : 



"1. De Vries' theory does not account any more 

 than the Darwinian theory does for the appearance of 

 useful characters, as infinitesimal differential charac- 

 ters do not attain, on Morgan's own admission, the 

 necessary degree of usefulness from the very begin- 

 ning. Only a large number of mutations following 

 one another in determined sequence can impart to a 

 character the necessary degree of usefulness. 



"2. The simultaneous appearance of the same mu- 

 tation in a large number of individuals is a very in- 

 frequent phenomenon and self-fecundation being ex- 

 ceptional in nature, intercrossing is unavoidable. 



*T. H. Mohgax. Evolution and Adaptation, pp. 298-299. 



