206 COOK 



" identity of form and structure." Characters changed when 

 conditions change are to be reckoned as alternative characters, 

 no less than sexual differences. Indeed, the sex determination 

 itself sometimes appears as an incident of environmental adjust- 

 ment. 1 



Alternation of generations and dimorphism afford further 

 analogies. There is no warrant for the supposition that the evo- 

 lutionary status of any of these kinds of characters is different 

 from that of characters which appear in all individuals of the 

 species. Professor Metcalf says : 



"A high degree of plasticity hinders evolution b} r selection, 

 of characters similar to those acquired by plastic response to the 

 environmental influences." 



This seems to imply that alternative characters which appear 

 responsively have to be acquired over again by selection in order 

 to become genuine results of evolution. If this were true selec- 

 tion might indeed be impeded. Such a distinction is not illogical, 

 but it applies only in the metaphysical systems of evolution 

 which assume that selection causes evolution and that environ- 

 ment causes characters. 



A character which can be varied readily and which thus 

 increases the power of the species to accommodate itself to varied 

 environments is much more valuable than one which is not 

 capable of such adjustment, and there is no reason to suppose 

 that selection would favor the development of a non-adjustable 

 form of the same character. Moreover, both the character itself 

 and its adjustability or " plasticity" are already genuine evolu- 

 tionary results reached by the same processes as any other 

 characters. 



It is only when we have allowed our meanings to slip from 

 harmless abstractions to fictitious concretions that we explain 

 evolution by selection and characters by plastic response to 

 environmental influences. However unobjectionable such ex- 

 pressions may be if used in sufficiently general, literary senses, 

 they are dangerously misleading as the basis of physiological 

 inferences, because they take for granted unproved and improb- 

 able assumptions, such as the causing of characters by environ- 



1 See Fink, B., 1906. Plant World, 9 : 183. 



