natural.

The gist of Mr. Darwin's work is to show that such varieties are gradually
diverged into species and genera through natural selection; that natural
selection is the inevitable result of the struggle for existence which all
living things are engaged in; and that this struggle is an unavoidable
consequence of several natural causes, but mainly of the high rate at which
all organic beings tend to increase.

Curiously enough, Mr. Darwin's theory is grounded upon the doctrine of
Malthus and the doctrine of Hobbes. The elder DeCandolle had conceived the
idea of the struggle for existence, and, in a passage which would have
delighted the cynical philosopher of Malmesbury, had declared that all
Nature is at war, one organism with another or with external Nature; and
Lyell and Herbert had made considerable use of it. But Hobbes in his theory
of society, and Darwin in his theory of natural history, alone have built
their systems upon it. However moralists and political economists may
regard these doctrines in their original application to human society and
the relation of population to subsistence, their thorough applicability to
the great society of the organic world in general is now undeniable. And to
Mr. Darwin belongs the credit of making this extended application, and of
working out the immensely diversified results with rare sagacity and
untiring patience. He has brought to view real causes which have been
largely operative in the establishment of the actual association and
geographical distribution of plants and animals. In this he must be allowed
to have made a very important contribution to an interesting department of
science, even if his theory fails in the endeavor to explain the origin or
diversity of species. "Nothing is easier," says our author, "than to admit
in words the truth of the universal struggle for life, or more difficult--at
least I have found it so--than constantly to bear this conclusion in mind.