But, besides such differences, all
naturalists admit that natural varieties exist, which are considered
sufficiently distinct to be worthy of record in systematic works. No one
has drawn any clear distinction between individual differences and slight
varieties; or between more plainly marked varieties and subspecies and
species. On separate continents, and on different parts of the same
continent, when divided by barriers of any kind, and on outlying islands,
what a multitude of forms exist, which some experienced naturalists rank as
varieties, others as geographical races or sub species, and others as
distinct, though closely allied species!
If, then, animals and plants do vary, let it be ever so slightly or slowly,
why should not variations or individual differences, which are in any way
beneficial, be preserved and accumulated through natural selection, or the
survival of the fittest? If man can by patience select variations useful
to him, why, under changing and complex conditions of life, should not
variations useful to nature's living products often arise, and be preserved
or selected? What limit can be put to this power, acting during long ages
and rigidly scrutinising the whole constitution, structure, and habits of
each creature, favouring the good and rejecting the bad? I can see no
limit to this power, in slowly and beautifully adapting each form to the
most complex relations of life.
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