The Descent of Man

there has always been sufficient variability in
their intellectual and moral faculties, for a steady
advance through natural selection. No
doubt such advance demands many favourable
concurrent circumstances; but it may well be
doubted whether the most favourable would
have sufficed, had not the rate of increase been
rapid, and the consequent struggle for existence
extremely severe. It even appears from what
we see, for instance, in parts of S. America, that
a people which may be called civilised, such as
the Spanish settlers, is liable to become indolent
and to retrograde, when the conditions of life
are very easy. With highly civilised nations
continued progress depends in a subordinate
degree on natural selection; for such nations do
not supplant and exterminate one another as do
savage tribes. Nevertheless the more intelligent
members within the same community will succeed
better in the long run than the inferior,
and leave a more numerous progeny, and this
is a form of natural selection. The more efficient