steadily in mind that each 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.
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 organisation becomes in some degree plastic. Let it
be borne in mind how infinitely complex and close-fitting are the
mutual relations of all organic beings to each other and to their
physical conditions of life. Can it, then, be thought improbable,
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