et with allied species in different
biological regions, notwithstanding that their climates may be similar,
and, consequently, just as well suited to maintain some of the allied
species. Hence we must further conclude, if all species were separately
created, that in the work of creation some unaccountable regard was paid
to making areas of distribution correspond to degrees of structural
affinity. A great many species of the rat genus were created in the Old
World, and a great many species of another, though allied, genus were
created in the New World: yet no reason can be assigned why no one
species of the Old World series should not just as well have been
deposited in the New World, and _vice versa_. On the other hand, the
theory of evolution may claim as direct evidence in its support all the
innumerable cases such as these--cases, indeed, so innumerable that, as
Mr. Wallace remarks, it may be taken as a law of nature that "every
species has come into existence coincident both in space and time with a
pre-existing and closely allied species." A general law which, while in
itself most strongly suggestive of evolution, is surely impossible to
reconcile with any reasonable theory of special creation. Furthermore,
this law extends backwards through all geological time, with the result
that the extinct species which now occur only as fossils on any given
geological area, resemble the species still living upon that area, as we
should expect that they must, if the former were the natural progenitors
of the latter. On the other hand, if they were not the natural
progenitors, but all the species, both living and extinct, were the
supernatural and therefore independent creations which the rival theory
would suppose, then no reason can be given why the extinct species
should thus resemble the living--any more than why the living species
should resemble one another. For, as we have seen, there are almost
always many other habitats on other parts of the globe, where any
members of any given group of species might equally well have been
deposited; and this, of course, applies to geological no less than to
historical time. Yet throughout all time we meet with this most
suggestive correlation between continuity of a geographical area and
structural affinity between the forms of life which have lived, or are
still living, upon that area.

Similarly, we find the further, and no less suggestive, correlation
between the birth of new spe