DARWINISM'S PRESENT STANDING. 381 



of an evolution explanation is a double one ; it must explain 

 not only diversity or variety in life, but adaptive diversity 

 or variety. And there is no gainsaying to the selection 

 explanation its claim to stand among all proposed explana- 

 tions of adaptation as that one least shaken by the critical 

 attack of its adversaries. However mightily the scientific 

 imagination must exert itself to deliver certain difficult 

 cases into the hands of selection, and however sophisticated 

 and lawyer-like the argument from the selection side may 

 be for any single refractory example, the fact remains that 

 the selectionist seems to be able to stretch his explanation 

 to fit all adaptations with less danger of finding it brought 

 up against positive adverse facts than is possible to the 

 champion of any other so far proposed explanation. The 

 explanation of adaptation by natural selection steers wide 

 of teleology on one hand and of unproved assumptions con- 

 cerning heredity on the other. The protoplasmic conscious- 

 ness of Cope and the automatic perfecting principle of 

 Nageli and those of his manner of explanation, are only 

 indirect ways of attributing to natural forces visions and 

 anticipations of what does not yet exist ; while the influence 

 of the ambient medium of St. Hilaire and of the extrinsic 

 factors of Eimer, and the impressing photographically on 

 the species and the carrying over into phylogeny, with 

 approximate identity, of characteristics and modifications 

 acquired ontogenetically by the individual as a result of 

 functional stimulation all these are assumptions not only 

 apparently unproved, but in the light of our present 

 knowledge of the mechanism of heredity seemingly un- 

 provable. 



Yet the explanation of species transformation and of 

 adaptation by the introduction into phylogeny of modifica- 

 tions (reaction effects) arising in the individual during its 

 ontogeny, has to its credit a certain logical proof, or 

 basis, which has great validity in my mind, and yet which 



