NEW COMBINATIONS OF GENES 25 



brings about diversification. There being given a great variety 

 of different types of genes, it brings about adaptation and 

 progress — through the method of selective survival and elim- 

 ination. But it requires the previous existence of many diverse 

 types of genes, and it does not produce these diverse types. 

 What it can do is limited by the potentialities of the different 

 genes already existing. These as yet unrealized potentialities 

 of the genes now existing are doubtless very great, and these 

 may in the future be brought to realization by the making of 

 new combinations among them. But the actual production 

 of diverse types of genie materials is required; it is the essen- 

 tial feature of evolution. To understand evolutionary progress, 

 the method of producing new types of genie materials must 

 be sought. 



To this search for the fundamental factor in evolution 

 much effort has been devoted. The sought-for changes in the 

 nature of genes have been called mutation; and many discov- 

 eries of mutation have been announced. But often the 

 announcements have been later discovered to be errors; the 

 changes observed were something much less fundamental. 

 This is a history which at the present moment appears to be 

 repeating itself on a grand scale. 



But in this search, other types of genetic variation, of only 

 less importance, have been discovered. Great numbers of 

 genetic variations have been found to be the result of irreg- 

 ularities in the structure and operation of the genetic system. 

 These things we examine in the next chapter. 



