SPECIES BY INFINITESIMAL VARIATIONS. 3 



adaptations were found in almost every structure, very often 

 without any evidence whatever, and the extremely ingenious 

 and fanciful nature of the explanations of these adaptations, 

 we should expect that by this time some explanation at least 

 of some of the innumerable differences that characterize 

 species would have been brought forward, but as yet this 

 has only been done in very rare cases, and in the vast majority 

 of instances we are entirely in the dark as to any meaning that 

 there may be in them. 



Now, upon the theory of natural selection of infinitesimal 

 variations, it is evident that any structure whatsoever must be 

 capable of being shown to be or to have been — 



(1) Of some actual use now; or 



(2) Of some use in the past, in its present or in a different, 



and perhaps larger (less aborted) form ; or 



(3) Correlated with some useful structure, whether 



visible or not. 



But in the vast majority of specific differences none of these 

 things can be shown to hold, and considering the ingenuity 

 that has been already devoted to this question, it seems very 

 doubtful if it ever will or ever can be done. This alone, when 

 one thinks it over, would seem to be almost sufficient argument 

 against the origin of species by natural selection of infinitesimal 

 variations, and affords a very good argument also in favour of 

 their origin by mutation, for on this theory there is no need 

 for the new variations to be actually useful. Can it, for 

 instance, be supposed that the hereditary fasciation of the 

 cockscomb is of any use to that form ? Or, again, take the 

 case of the Podostemacese, which have flowers (standing 

 vertically and not horizontally) of the most pronounced 

 dorsiventrality, though insects do not visit them, and the 

 dorsi ventral structure is a decided disadvantage, so far as we 

 can tell. As I have pointed out elsewhere,* we cannot suppose 



* Willis, Morphology and Ecology of the Podostemacese. Ann. 

 Perad. I., 1902,p. 434. 



