e been required to change in many ways according
to the varied experiences of different branches of the same family.
Here, then, we have an empirically discovered rule in the science of
classification, the _raison d'etre_ of which we are at once able to
appreciate upon the theory of evolution, whereas no possible explanation
of why it should ever have become a rule could be furnished upon the
theory of special creation.

Here, again, is another empirically determined rule. The larger the
_number_, as distinguished from the _importance_, of structures which
are found common to different groups, the greater becomes their value as
guides to the determination of natural affinity. Or, as Darwin puts it,
"the value of an aggregate of characters, even when none are important,
alone explains the aphorism enunciated by Linnaeus, namely, that the
characters do not give the genus, but the genus gives the characters;
for this seems founded on the appreciation of many trifling points of
resemblance, too slight to be defined[1]."

[1] _Origin of Species_, p. 367.

Now it is evident, without comment, of how much value aggregates of
characters ought to be in classification, if the ultimate meaning of
classification be that of tracing lines of pedigree; whereas, if this
ultimate meaning were that of tracing divine ideals manifested in
special creation, we can see no reason why single characters are not
such sure tokens of a natural arrangement as are aggregates of
characters, even though the latter be in every other respect
unimportant. For, on the special creation theory, we cannot explain why
an assemblage, say of four or five trifling characters, should have been
chosen to mark some unity of plan, rather than some one character of
functional importance, which would have served at least equally well any
such hypothetical purpose. On the other hand, as Darwin remarks, "we
care not how trifling a character may be--let it be the mere inflection
of the angle of the jaw, the manner in which an insect's wing is folded,
whether the skin be covered with hair or feathers--if it prevail
throughout many and different species, especially those having very
different habits of life, it assumes high value; for we can account for
its presence in so many forms, with such different habits, only by
inheritance from a common parent. We may err in this respect in regard
to single points of structure, but when several characters, let them be
ever so