We may, also, believe that a part formerly of high importance
has often been retained (as the tail of an aquatic animal by its
terrestrial descendants), though it has become of such small
importance that it could not, in its present state, have been acquired
by natural selection,--a power which acts solely by the preservation
of profitable variations in the struggle for life.
Natural selection will produce nothing in one species for the
exclusive good or injury of another; though it may well produce parts,
organs, and excretions highly useful or even indispensable, or highly
injurious to another species, but in all cases at the same time useful
to the owner. Natural selection in each well-stocked country, must act
chiefly through the competition of the inhabitants one with another,
and consequently will produce perfection, or strength in the battle
for life, only according to the standard of that country. Hence the
inhabitants of one country, generally the smaller one, will often
yield, as we see they do yield, to the inhabitants of another and
generally larger country. For in the larger country there will have
existed more individuals, and more diversified forms, and the
competition will have been severer, and thus the standard of
perfection will have been rendered higher. Natural selection will not
necessarily produce absolute perfection; nor, as far as we can judge
by our limited faculties, can absolute perfection be everywhere found.
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