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. The same rule will apply to every period
of life and to every danger to which plants or animals are exposed. The
best organised, or the most healthy, or the most active, or the best
protected, or the most intelligent, will inevitably, in the long run,
gain an advantage over those which are inferior in these qualities; that
is, _the fittest will survive_, the fittest being, in each particular
case, those which are superior in the special qualities on which safety
depends. At one period of life, or to escape one kind of danger,
concealment may be necessary; at another time, to escape another danger,
swiftness; at another, intelligence or cunning; at another, the power to
endure rain or cold or hunger; and those which possess all these
faculties in the fullest perfection will generally survive.

Having fully grasped these facts in all their fulness and in their
endless and complex results, we have next to consider the phenomena of
variation, discussed in the third and fourth chapters; and it is here
that perhaps the greatest difficulty will be felt in appreciating the
full importance of the evidence as set forth. It has been so generally
the practice to speak of variation as something exceptional and
comparatively rare--as an abnormal deviation from the uniformity and
stability of the characters of a species--and so few even among
naturalists have ever compared, accurately, considerable numbers of
individuals, that the conception of variability as a general
characteristic of all dominant and widespread species,