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 leads to what I have called divergence of character.
In the next chapter I shall discuss the complex and little known laws
of variation. In the five succeeding chapters, the most apparent and
gravest difficulties in accepting the theory will be given: namely,
first, the difficulties of transitions, or how a simple being or a
simple organ can be changed and perfected into a highly developed
being or into an 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 twelfth and thirteenth, their geographical
distribution throughout space; in the fourteenth, 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 make due allowance
for our profound ignorance in regard to the mutual relations of the
many 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, the future
success and modification of every inhabitant of this world. Still less
do we know of the mutual relations of the innumerable inhabitants of the
world during the many past geological epochs in its history. Although
much remains obscure, and will long remain obscure, I can entertain no
doubt, after the most deliberate study and dispassionate judgment of