CHAPTER XI. ON THE GEOLOGICAL SUCCESSION OF ORGANIC BEINGS.
2. ON EXTINCTION. (continued)
Thus, as it seems to me, the manner in which single species and whole
groups of species become extinct accords well with the theory of natural
selection. We need not marvel at extinction; if we must marvel, let it be
at our presumption in imagining for a moment that we understand the many
complex contingencies on which the existence of each species depends. If
we forget for an instant that each species tends to increase inordinately,
and that some check is always in action, yet seldom perceived by us, the
whole economy of nature will be utterly obscured. Whenever we can
precisely say why this species is more abundant in individuals than that;
why this species and not another can be naturalised in a given country;
then, and not until then, we may justly feel surprise why we cannot account
for the extinction of any particular species or group of species.