But they are not alike. We find
that they vary in many different ways. Some are stronger, some swifter,
some hardier in constitution, some more cunning. An obscure colour may
render concealment more easy for some, keener sight may enable others to
discover prey or escape from an enemy better than their fellows. Among
plants the smallest differences may be useful or the reverse. The
earliest and strongest shoots may escape the slug; their greater vigour
may enable them to flower and seed earlier in a wet autumn; plants best
armed with spines or hairs may escape being devoured; those whose
flowers are most conspicuous may be soonest fertilised by insects. We
cannot doubt that, on the whole, any beneficial variations will give the
possessors of it a greater probability of living through the tremendous
ordeal they have to undergo. There may be something left to chance, but
on the whole _the fittest will survive_.
Then we have another important fact to consider, the principle of
heredity or transmission of variations. If we grow plants from seed or
breed any kind of animals year after year, consuming or giving away all
the increase we do not wish to keep just as they come to hand, our
plants or animals will continue much the same; but if every year we
carefully save the best seed to sow and the finest or brightest
coloured animals to breed from, we shall soon find that an improvement
will take place, and that the average quality of our stock will be
raised.
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