refore, growing progressively more unlike with remoteness of
ancestral relationship. For thus only can we obtain any explanation of
the sundry puzzles and apparent paradoxes, which a working out of their
natural classifications revealed to botanists and zoologists during the
first half of the present century. It will now be my endeavour to show
how these puzzles and paradoxes are all explained by the theory that
natural affinities are merely the expression of genetic affinities.

First of all, and from the most general point of view, it is obvious
that the tree-like system of classification, which Darwin found already
and empirically worked out by the labours of his predecessors, is as
suggestive as anything could well be of the fact of genetic
relationship. For this is the form that every tabulation of family
pedigree must assume; and therefore the mere fact that a scientific
tabulation of natural affinities was eventually found to take the form
of a tree, is in itself highly suggestive of the inference that such a
tabulation represents a _family_ tree. If all species were separately
created, there can be no assignable reason why the ideas of earlier
naturalists touching the form which a natural classification would
eventually assume should not have represented the truth--why, for
example, it should not have assumed the form of a ladder (as was
anticipated in the seventeenth century), or of a map (as was anticipated
in the eighteenth), or, again, of a number of wholly unrelated lines,
circles, &c. (as certain speculative writers of the present century have
imagined). But, on the other hand, if all species were separately and
independently created, it becomes virtually incredible that we should
everywhere observe this progressive arborescence of characters common to
larger groups into more and more numerous, and more and more delicate,
ramifications of characters distinctive only of smaller and smaller
groups. A man would be deemed insane if he were to attribute the origin
of every branch and every twig of a real tree to a separate act of
special creation; and although we have not been able to witness the
growth of what we may term in a new sense the Tree of Life, the
structural relations which are now apparent between its innumerable
ramifications bear quite as strong a testimony to the fact of their
having been due to an organic growth, as is the testimony furnished by
the branches of an actual tree.

Or, to take ano