WHAT EVOLUTION IS 141 



Whether a mutation persists or not 

 depends upon its nature. If it is in 

 a favorable direction, the individual 

 possessing it is likely to be preserved 

 and find a mate. As such changes are 

 handed down undiminished by Men- 

 delian inheritance, the mutation would 

 be expected to reappear in many of 

 the descendants in full vigor. In this 

 way, it could establish itself in the 

 stock and help to modify that stock so 

 as to form a new species. As de Vries 

 rightly states, this process of preser- 

 vation involves natural selection, for 

 the retention of such a character de- 

 pends upon this principle. All muta- 

 tions must run the gantlet of natural 

 selection. In this sense, the mutation 

 theory and natural selection are 

 mutually dependent. The mutation 

 theory yields the grain for the natural 

 selection hopper. 



It must be evident that the muta- 



