ial manner. If we wished to increase its average
numbers in its new home, we should have to modify it in a different way to
what we should have done in its native country; for we should have to give
it some advantage over a different set of competitors or enemies.

It is good thus to try in our imagination to give any form some advantage
over another. Probably in no single instance should we know what to do, so
as to succeed. It will convince us of our ignorance on the mutual relations
of all organic beings; a conviction as necessary, as it seems to be
difficult to acquire. All that we can do, is to keep steadily in mind that
each {79} organic being is striving to increase at a geometrical ratio;
that each at some period of its life, during some season of the year,
during each generation or at intervals, has to struggle for life, and to
suffer great destruction. When we reflect on this struggle, we may console
ourselves with the full belief, that the war of nature is not incessant,
that no fear is felt, that death is generally prompt, and that the
vigorous, the healthy, and the happy survive and multiply.

* * * * *

{80}

CHAPTER IV.

NATURAL SELECTION.

Natural Selection--its power compared with man's selection--its power
on characters of trifling importance--its power at all ages and on both
sexes--Sexual Selection--On the generality of intercrosses between
individuals of the same species--Circumstances favourable and
unfavourable to Natural Selection, namely, intercrossing, isolation,
number of individuals--Slow action--Extinction caused by Natural
Selection--Divergence of Character, related to the diversity of
inhabitants of any small area, and to naturalisation--Action of Natural
Selection, through Divergence of Character and Extinction, on the
descendants from a common parent--Explains the Grouping of all organic
beings.

How will the struggle for existence, discussed too briefly in the last
chapter, act in regard to variation? Can the principle of selection, which
we have seen is so potent in the hands of man, apply in nature? I think we
shall see that it can act most effectually. Let it be borne in mind in what
an endless number of strange peculiarities our domestic productions, and,
in a lesser degree, those under nature, vary; and how strong the hereditary
tendency is. Under domestication, it may be truly said that the whole