34 Darwin, and after Darwin. 



or by the oldest, forms of any two natural groups that 

 the affinities between the two groups admit of being 

 best detected. And it is obvious that this is just 

 what ought to be the case on the' theory of descent 

 with divergent modification ; while, upon the alter- 

 native theory of special creation, no reason can be 

 assigned why the lowest or the oldest types should 

 thus combine the characters which afterwards become 

 severally distinctive of higher or newer types. 



Again, I have already alluded to the remarkable 

 fact that there is no correlation between the value of 

 structures to the organisms which present them, and 

 their value to the naturalist for the purpose of tracing 

 natural affinity ; and I have remarked that up to the 

 close of the last century it was regarded as an axiom 

 of taxonomic science, that structures which are of 

 most importance to the animals or plants possessing 

 them must likewise prove of most importance in any 

 natural system of classification. On this account, all 

 attempts to discover the natural classification went 

 upon the supposition that such a direct proportion 

 must obtain with the result that organs of most 

 physiological importance were chosen as the bases of 

 systematic work. And when, in the earlier part of 

 the present century, De Candolle found that instead 

 of a direct there was usually an inverse proportion 

 between the functional and the taxonomic value of a 

 structure, he was unable to suggest any reason for 

 this apparently paradoxical fact. For, upon the 

 theory of special creation, no reason can be assigned 

 why organs of least importance to organisms should 

 prove of most importance as marks of natural affinity. 

 But on the theory of descent with progressive modi- 



