Who, for instance, has duly reflected upon all the consequences of the
marvellous struggle for existence which is daily and hourly going on
among living beings? Not only does every animal live at the expense of
some other animal or plant, but the very plants are at war. The ground
is full of seeds that cannot rise into seedlings; the seedlings rob one
another of air, light and water, the strongest robber winning the day,
and extinguishing his competitors. Year after year, the wild animals
with which man never interferes are, on the average, neither more nor
less numerous than they were; and yet we know that the annual produce of
every pair is from one to perhaps a million young,--so that it is
mathematically certain that, on the average, as many are killed by
natural causes as are born every year, and those only escape which
happen to be a little better fitted to resist destruction than those
which die. The individuals of a species are like the crew of a
foundered ship, and none but good swimmers have a chance of reaching
the land.

Such being unquestionably the necessary conditions under which living
creatures exist, Mr. Darwin discovers in them the instrument of
natural selection. Suppose that in the midst of this incessant
competition some individuals of a species (A) present accidental
variations which happen to fit them a little better than their fellows
for the struggle in which they are engaged, then the chances are in
favour, not only of these individuals being better nourished than the
others, but of their predominating over their fellows in other ways, and
of having a better chance of leaving offspring, which will of course
tend to reproduce the peculiarities of their parents. Their offspring
will, by a parity of reasoning, tend to predominate over their
contemporaries, and there being (suppose) no room for more than one
species such as A, the weaker variety will eventually be destroyed by