Contributions to the theory of natural selection. A series of essays ... By Alfred Russel Wallace ...

THE ILNTRODUCTIOXN OF NEW SPECIES. 25
of them, had we a view of all the forms which have
ceased to live. The great gaps that exist between
fishes, reptiles, birds, and mammals would then, no
doubt, be softened down by intermediate groups, and
the whole organic world would be seen to be an
unbroken and harmonious system
Conclusion.
It has now oeen shown, though most briefly and
imperfectly, how the law that "Every species has come
into existence coincident both in time and space with a
pre-existing closely allied species," connects together
and renders intelligible a vast number of independent
and hitherto unexplained facts. The natural system
of arrangement of organic beings, their geographical
distribution, their geological sequence, the phanomena
of representative and substituted groups in all their
modifications, and the most singular peculiarities of
anatomical structure, are all explained and illustrated by it, in perfect accordance with the vast
mass of facts which the researches of modern naturalists have brought together, and, it is believed,
not materially opposed to any of them. It also
claims a superiority over previous hypotheses, on
the ground that it not merely explains, but necessitates what exists. Granted the law, and many of
the most important facts in Nature could not have
been otherwise, but are almost as necessary deductions from it, as are the elliptic orbits of the planets
from the law of gravitation.