of each area are related to the inhabitants of the
nearest source whence immigrants might have been derived. We see this in
nearly all the plants and animals of the Galapagos archipelago, of Juan
Fernandez, and of the other American islands being related in the most
striking manner to the plants and animals of the neighbouring American
mainland; and those of the Cape de Verde archipelago and 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
constitute one grand natural system, with group subordinate to group,
and with extinct groups often falling in between recent groups, is
intelligible on the theory of natural selection with its contingencies
of extinction and divergence of character. On these same principles
we see how it is, that the mutual affinities of the species and genera
within each class are so complex and circuitous. We see why certain
characters are far more serviceable than others for classification;--why
adaptive characters, though of paramount importance to the being, are
of hardly any importance in classification; why characters derived from
rudimentary parts, though of no service to the being, are often of high
classificatory value; and why embryological characters are the most
valuable of all. The real affinities of all organic beings are due
to inheritance or community of descent. The natural system is a
genealogical arrangement, in which we have to discover the lines of
descent by the most permanent characters, however slight their vital
importance may be.

The framework of bones being the same in the hand of a man, wing of
a bat, fin of the porpoise, and leg of the horse,--the same number of
vertebrae forming the neck of the giraffe and of the elephant,--and
innumerable other such facts, at once explain themselves on the theory
of descent with slow and slight successive modifications. The similarity
of pattern in the wing and leg of a bat, though used for such different
purpose,--in the jaws and legs of a crab,--in the petals, stamens, and
pistils of a flower, is likewise intelligible on the view of the
gradual modification of parts or organs, which were alike in the early
progenitor of each class. On the principle of successive variations
not always supervening at an early age, and being inherited at a
corresponding not early period of life, we