and to suffer great destruction.
When we reflect on this struggle, we may console ourselves with the full
belief that the war of Nature is not incessant, that no fear is felt,
that death is generally prompt, and that the vigorous, the healthy, and
the happy survive and multiply.

_IV.--The Survival of the Fittest_

How will the struggle for existence act in regard to variation? Can the
principle of selection, which we have seen is so potent in the hands of
man, apply under Nature? I think we shall see that it can act most
efficiently. Let the endless number of slight variations and individual
differences occurring in our domestic productions, and, in a lesser
degree, in those under Nature, be borne in mind, as well as the strength
of the hereditary tendency. Under domestication, it may be truly said
that the whole organisation becomes in some degree plastic.

But the variability, which we almost universally meet with in our
domestic productions, is not directly produced by man; he can neither
originate variations nor prevent their occurrence; he can only preserve
and accumulate such as do occur. Unintentionally he exposes organic
beings to new and changing conditions of life, and variability ensues;
but similar changes of condition might and do occur under Nature.

Let it also be borne in mind how infinitely complex and close-fitting
are the mutual relations of all organic beings to each other and to
their physical conditions of life, and consequently what infinitely
varied diversities of structure might be of use to each being under
changing conditions of life. Can it, then, be thought improbable, seeing
what variations useful to man have undoubtedly occurred, that other
variations, useful in some way to each being in the great complex battle
of life, should occur in the course of many successive generations? If
such do occur, can we doubt, remembering that many more individuals are
born than can possibly survive, that individuals having any advantage
over others, would have the best chance of surviving and of procreating
their kind? On the other hand, we may feel sure that any variation in
the least degree injurious would be rigidly destroyed. This preservation
of favourable individual differences and variations, and the destruction
of those which are injurious, I have called Natural Selection, or the
Survival of the Fittest.

The term is too frequently misapprehended. Variations neither useful nor
injurious w