Existence amongst all organic beings throughout the world, which
inevitably follows from their high geometrical powers of
increase, will be treated of. This is the doctrine of Malthus, applied
to the whole animal and vegetable kingdoms. As many more individuals of
each species are born than can possibly survive; and as, consequently,
there is a frequently recurring struggle for existence, it follows that
any being, if it vary however slightly in any manner profitable to
itself, under the complex and sometimes varying conditions of life,
will have a better chance of surviving, and thus be _naturally
selected_. From the strong principle of inheritance, any selected
variety will tend to propagate its new and modified form.
This fundamental subject of Natural Selection will be treated at some
length in the fourth chapter; and we shall then see how Natural
Selection almost inevitably causes much Extinction of the less improved
forms of life and induces what I have called Divergence of Character.
In the next chapter I shall discuss the complex and little known laws
of variation and of correlation of growth. In the four succeeding
chapters, the most apparent and gravest difficulties on the theory will
be given: namely, first, the difficulties of transitions, or in
understanding how a simple being or a simple organ can be changed and
perfected into a highly developed being or elaborately constructed
organ; secondly the subject of Instinct, or the mental powers of
animals, thirdly, Hybridism, or the infertility of species and the
fertility of varieties when intercrossed; and fourthly, the
imperfection of the Geological Record. In the next chapter I shall
consider the geological succession of organic beings throughout time;
in the eleventh and twelfth, their geographical distribution throughout
space; in the thirteenth, their classification or mutual affinities,
both when mature and in an embryonic condition. In the last chapter I
shall give a
brief recapitulation of the whole work, and a few concluding remarks.
No one ought to feel surprise at much remaining as yet unexplained in
regard to the origin of species and varieties, if he makes due
allowance for our profound ignorance in regard to the mutual relations
of all the beings which live around us. Who can explain why one species
ranges widely and is very numerous, and why another allied species has
a narrow range and is rare? Yet these relations are of the highest
importance, for they determine the present welfare, and, as I believe,
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