Mating and Selection 197 



that worked well together and under the conditions of the 

 environment ; the families produced were vigorous, some of 

 them flourishing even better than the original stocks through 

 whose mating they were produced. In the same manner a 

 poor family of human beings may produce a Lincoln among 

 its children ; a combination of characteristics is formed by 

 mating that never before existed and that meets the condi- 

 tions of existence in a more vigorous and successful manner 

 than the individuals from which it was derived. 



Experimentally, or under natural conditions, of course 

 these newly formed stocks in which life and reproduction are 

 vigorous, gradually replace the weakened stocks, in which 

 mating has resulted, not in reinvigoration but in degenera- 

 tion ; in the formation of combinations of primary hereditary 

 characters that cannot develop vigorously under the condi- 

 tions. The formation of such "degenerated" stocks is as 

 much a characteristic of mating as the formation of more 

 vigorous ones. 



By this formation of new combinations with gradual re- 

 placement of the unenduring ones by those that are vigor- 

 ous, the stocks in existence come to be very diverse from 

 those that existed at an earlier time. Mating is a continued 

 process of forming new combinations of the primary heredi- 

 tary characters; of the chemicals on which the vigor and 

 the nature of development depend; with suppression of the 

 combinations that are weak or imperfect, leaving the more 

 harmonious and vigorous combinations in existence, to carry 

 the process further. 



