onship, such was
not the inference which was drawn from it. Dominated by the theory of
special creation, naturalists either regarded the resemblance of type
subordinate to type as expressive of divine ideals manifested in such
creation, or else contented themselves with investigating the facts
without venturing to speculate upon their philosophical import. But even
those naturalists who abstained from committing themselves to any theory
of archetypal plans, did not doubt that facts so innumerable and so
universal must have been due to some one co-ordinating principle--that,
even though they were not able to suggest what it was, there must have
been some hidden bond of connexion running through the whole of organic
nature. Now, as we have seen, it is manifest to evolutionists that this
hidden bond can be nothing else than heredity; and, therefore, that
these earlier naturalists, although they did not know what they were
doing, were really tracing the lines of genetic descent as revealed by
degrees of structural resemblance,--that the arborescent grouping of
organic forms which their labours led them to begin, and in large
measure to execute, was in fact a family tree of life.

Here, then, is the substance of the argument from classification. The
mere fact that all organic nature thus incontestably lends itself to a
natural arrangement of group subordinate to group, when due regard is
paid to degrees of anatomical resemblance--this mere fact of itself
tells so weightily in favour of descent with progressive modification in
different lines, that even if it stood alone it would be entitled to
rank as one of our strongest pieces of evidence. But, as we have seen,
it does not stand alone. When we look beyond this large and general fact
of all the innumerable forms of life being thus united in a tree-like
system by an unquestionable relationship of some kind, to those smaller
details in the science of classification which have been found most
useful as guides for this kind of research, then we find that all these
details, or empirically discovered rules, are exactly what we should
have expected them to be, supposing the real meaning of classification
to have been that of tracing lines of pedigree.

In particular, we have seen that the most archaic types are both simpler
in their organization and more generalized in their characters than are
the more recent types--a fact of which no explanation can be given on
the theory of sp