We must
think over all the causes of destruction to each organism,--to the seed,
the young shoot, the growing plant, the full-grown tree, or shrub, or
herb, and again the fruit and seed; and among animals, to the egg or
new-born young, to the youthful, and to the adults. Then, we must always
bear in mind that what goes on in the case of the individual or family
group we may observe or think of, goes on also among the millions and
scores of millions of individuals which are comprised in almost every
species; and must get rid of the idea that _chance_ determines which
shall live and which die. For, although in many individual cases death
may be due to chance rather than to any inferiority in those which die
first, yet we cannot possibly believe that this can be the case on the
large scale on which nature works. A plant, for instance, cannot be
increased unless there are suitable vacant places its seeds can grow in,
or stations where it can overcome other less vigorous and healthy
plants. The seeds of all plants, by their varied modes of dispersal, may
be said to be seeking out such places in which to grow; and we cannot
doubt that, in the long run, those individuals whose seeds are the most
numerous, have the greatest powers of dispersal, and the greatest vigour
of growth, will leave more descendants than the individuals of the same
species which are inferior in all these respects, although now and then
some seed of an inferior individual may _chance_ to be carried to a spot
where it can grow and survive.
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