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, 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