Ill 



Results of Intense and Long Continued Study of Changes 

 in a Stock. Inherited Variations in the Pure Race. Visible 

 Evolution. 



T N our last chapter I tried to picture the first results of 

 * the attempts to study evolution experimentally to ac- 

 tually see evolution occurring to see variations take place 

 and to see their inheritance. 



These first results were: 



That any kind of organism is really composed of a great 

 number of diverse stocks or races, whose differences are 

 hereditary, lasting from generation to generation; 



That the supposed effect of selection in modifying organ- 

 isms consists in isolating certain pre-existing races, having 

 the characteristics that one is selecting; or in making, 

 through biparental inheritance, new combinations of charac- 

 ters that already exist ; 



That in general, the apparent variations in organisms 

 are not real changes in their hereditary constitution, but 

 are merely these static diversities persisting from genera- 

 tion to generation ; 



That when one takes a single one of these races and tries 

 to discover in it hereditary variations, or to modify it by 

 selection, he finds it extraordinarily constant, and his efforts 

 are without result. That seemingly the only variations 

 which appear are sudden large mutations; that gradual 

 alterations do not show themselves. 

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