THEORIES IN PRACTICE 369 



sive. It could not be otherwise in a world in. 

 which the natural environing conditions are con- 

 stantly changing. 



The basal law of evolution, as we have seen, 

 is that the unchanging, the conservative organ- 

 ism, is doomed. It is only the progressive, 

 the changeable, the plastic organism that can 

 hope to maintain itself and perpetuate its kind 

 indefinitely. 



The price of specific life is that the species 

 shall not maintain its identity. 



And this interpretation of the situation gives 

 a clew, so it would seem, to that important and 

 interesting aspect of heredity to which we re- 

 ferred at the beginning of this chapter — the 

 phase conmionly spoken of as Mendelism. The 

 essential characteristics of this aspect of hered- 

 ity, as we have pointed out over and over, is 

 that heritable characteristics are transmitted in 

 a sense independently one of another, in such a 

 way that they may be segregated and put to- 

 gether again in new combinations in successive 

 generations. 



The detail within this scheme of transmission 

 with which ^lendel himself was chiefly con- 

 cerned, and which absorbed the attention of his 

 followers until it was found that there was need 

 of taking a wider view, was involved in the phe- 



