GENERAL SUMMARY. 167 



The (assumed) indefinite accumulation of 

 beneficial differences. 



The modifications that arise from changed 

 conditions of life and from use, disuse, 

 or adaptation of organs. 



But in the preceding chapters we have 

 submitted facts and arguments to prove 



That the inference from the similarity of 

 successive types, that a new race was 

 evolved from its predecessor by second- 

 ary causes, is negatived by the geological 

 record and by the facts of retrogression. 



That the differences between animals of 

 the same species do not indicate any 

 tendency to specific variation, but are 

 merely variations in expression of type 

 arising from differences in conditions of 

 life or selective breeding. 



That development of type under selective 

 breeding is limited by sterility or 

 precocity. 



That the accumulation of beneficial differ- 

 ences (development) does not go on 

 indefinitely, but may attain its maxi- 

 mum in three generations. 



That no new type has been evolved by 

 selective or by cross breeding, and that, 

 so far as known, no new persistent type 

 has ever appeared. 



