rain and storm, by flood and fire. There is thus a
perpetual struggle among them which shall live and which shall die; and
this struggle is tremendously severe, because so few can possibly remain
alive--one in five, one in ten, often only one in a hundred or even one
in a thousand.

Then comes the question, Why do some live rather than others? If all the
individuals of each species were exactly alike in every respect, we
could only say it is a matter of chance. 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. This is the way in which all our fine garden fruits and
vegetables and flowers have been produced, as well as all our splendid
breeds of domestic animals; and they have thus become in many cases so
different from the wild races from which they originally sprang as to be
hardly recognisable as the same. It is therefore proved that if any
particular kind of variation is preserved and bred from, the variation
itself goes on increasing in amount to an enormous extent; and the
bearing of this on the question of the o