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- 
