Such
cases as the presence of peculiar species of bats on oceanic islands and
the absence of all other terrestrial mammals, are facts utterly
inexplicable on the theory of independent acts of creation.
The existence of closely allied representative species in any two areas,
implies, on the theory of descent with modification, that the same parent-
forms formerly inhabited both areas; and we almost invariably find that
wherever many closely allied species inhabit two areas, some identical
species are still common to both. Wherever many closely allied yet
distinct species occur, doubtful forms and varieties belonging to the same
groups likewise occur. It is a rule of high generality that the
inhabitants of each area are related to the inhabitants of the nearest
source whence immigrants might have been derived. We see this in the
striking relation of nearly all the plants and animals of the Galapagos
Archipelago, of Juan Fernandez, and of the other American islands, to the
plants and animals of the neighbouring American mainland; and of those of
the Cape de Verde Archipelago, and of the other African islands to the
African mainland. It must be admitted that these facts receive no
explanation on the theory of creation.
The fact, as we have seen, that all past and present organic beings can be
arranged within a few great classes, in groups subordinate to groups, and
with the extinct groups often falling in between the recent groups, is
intelligible on the theory of natural selection with its contingencies of
extinction and divergence of character.
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