THEORIES OF EVOLUTION 115 



ess may well be active in limiting a species to a 

 certain portion of its possible range of develop- 

 ment. 



Some other writers have out-Darwined Darwin 

 in their insistence upon the unlimited potency of 

 natural selection, not contenting themselves as he 

 did with the recognition of its validity as one pos- 

 sible process. Fortunately these over-zealous 

 selectionists have not dominated the field, for there 

 have been equally ardent supporters of Darwin who 

 recognized with him that his work was not perfect. 

 Among them Weismann occupies a commanding 

 place. Certainly his work has done as much to 

 turn thought into the channels of Darwinism as 

 that of any other man, although his own selection 

 theories have gained little acceptance. He recog- 

 nized the failure of natural selection to explain the 

 degeneration of organs or their development be- 

 yond the point of usefulness, and just as clearly 

 saw the uselessness of his own early theory of 

 panmixia. His germinal selection was an ingenious 

 but unwarranted extension of the principle of 

 struggle for existence to the minute and then 

 hypothetical determinants within the germ cells. 

 The most potent objection to it is that the idea of 

 formative influence of nourishment gives a de- 

 cidedly Lamarckian character to his argument. 

 Elsewhere I have also advanced the criticism that 

 there is no basis for the belief that parts of the 



