Now, this tree-like arrangement of species in nature is an arrangement for which Darwin is not responsible. For, as we have seen, the detecting of it has been due to the progressive work of naturalists for centuries past; and even when it was detected, at about the commencement of the present century, naturalists were confessedly unable to explain the reason of it, or what was the underlying principle that they were engaged in tracing when they proceeded ever more and more accurately to define these ramifications of natural affinity. But now, as just remarked, we can clearly perceive that this underlying principle was none other than Heredity as expressed in family likeness,--likeness, therefore, 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