arities as could possibly point to
genetic relationship.

Lastly, to adduce the only remaining argument from classification which
I regard as of any considerable weight, naturalists have found it
necessary, while constructing their natural classifications, to set
great store on what Mr. Darwin calls "chains of affinities." Thus, for
instance, "nothing can be easier than to define a number of characters
common to all birds; but with crustaceans any such definition has
hitherto been found impossible. There are crustaceans at the opposite
ends of the series, which have hardly a character in common; yet the
species at both ends, from being plainly allied to others, and these to
others, and so onwards, can be recognised as unequivocally belonging to
this, and to no other class of the articulata[3]." Now it is evident
that this progressive modification of specific types--where it cannot be
said that the continuity of resemblance is anywhere broken, and yet
terminates in modification so great that but for the connecting links no
one could divine a natural relationship between the extreme members of
the series,--it is evident that such chains of affinity speak most
strongly in favour of a transmutation of the species concerned, while it
is impossible to suggest any explanation of the fact in terms of the
rival theory. For if all the links of such a chain were separately
forged by as many acts of special creation, we can see no reason why B
should resemble A, C resemble B, and so on, but with ever slight though
accumulating differences, until there is no resemblance at all between A
and Z.

[3] _Origin of Species_, pp. 368-9.

* * * * *

I hope enough has now been said to show that all the general principles
and particular facts appertaining to the natural classification of
plants and animals, are precisely what they ought to be according to the
theory of genetic descent; while no one of them is such as might
be--and, indeed, used to be--expected upon the theory of special
creation. Therefore, the only possible way in which all this uniform
body of direct evidence can be met by a supporter of the latter theory,
is by falling back upon the argument from ignorance. We do not know, it
may be said, what hidden reasons there may have been for following all
these general principles in the separate creation of specific types.
Now, it is evident that this is a form of argument which admits of being