Characters as Adaptive and Specific. 281 



side in the debate, because even any small degree 

 of uncertainty with regard to it would render the 

 generalization in question proportionally unsound. 

 Yet it is notorious that no word in existence is more 

 vague, or more impossible to define, than the word 

 "species." The very same men who at one time 

 pronounce their great generalization with regard to 

 species, at another time asseverate that "a species 

 is not a definite entity/' but a merely abstract term, 

 serving to denote this that and the other organic type, 

 which this that and the other systematist regards 

 as deserving such a title. Moreover it is acknow- 

 ledged that systematists differ among themselves 

 to a wide extent as to the kinds and degrees of 

 peculiarity which entitle a given form to a specific 

 rank. Even in the same department of systematic 

 work much depends on merely individual taste, while 

 in different departments widely different standards 

 of delimination are in vogue. Hence, our reductio 

 ad absurdum consists in this — that whether a given 

 form is to be regarded as necessarily due to natural 

 selection, and whether all its distinctive characters 

 are to be regarded as necessarily utilitarian characters, 

 will often depend on whether it has been described by 

 naturalist A or by naturalist B. There is no one 

 criterion — there is not even any one set of criteria- 

 agreed upon by naturalists for the construction of 

 specific types. In particular, as regards the principle 

 of heredity, it is not known of one named species 

 in twenty — probably not in a hundred — whether its 

 diagnostic characters are hereditary characters ; while, 

 on the other hand, even in cases where experiment 

 has proved " constant varieties " to be hereditary — 



