Process of Evolution 



number of possible diverse combinations that could appear 

 would be definitely limited. All change would be a regroup- 

 ing of what already exists. 



Therefore it becomes most important to examine what 

 happens when there is no such regrouping, in heredity from 

 a single parent. Here we discover, as we have already set 

 forth, that actual changes in the hereditary materials are 

 occurring, independently of recombinations. New charac- 

 teristics appear that are heritable. 



Are such new characters bound up with the other primary 

 hereditary characters, and subject to the same processes of 

 recombination at mating? In Drosophila this question is 

 answered clearly in the affirmative; the new characters that 

 appear recombine at mating as do the old ones. There is lit- 

 tle reason to doubt that they do so in all organisms. 



Thus a new character arising in a particular individual 

 having a given combination of characters, is transferred by 

 mating to other individuals with other combinations. With 

 some it may work harmoniously ; with others, not. Further, 

 several new characters arising in diverse individuals may by 

 mating become transferred to a single one, where they may 

 form a combination working more harmoniously together 

 and with the environment than any that has before existed. 

 Thus all sorts of combinations arise, of new and old charac- 

 ters, such as could not possibly occur without mating. 

 Some are more vigorous and harmonious; some less; some 

 fit one set of outward conditions; some another. Mating 

 thus contributes enormously to the differentiation of organ- 

 isms into hereditarily diverse stocks. Its general result is to 

 give all sorts of combinations of characters, new or old; 

 some persisting, others not. Added to the slow production 

 of new characters, it greatly hastens the changes in organic 

 nature that we call evolution. 



