t if the rarity is
occasionally carried a step farther,--to extinction?"[989]

CHAPTER XLIII.

EXTINCTION AND CREATION OF SPECIES.

Theory of the successive extinction of species consistent with a
limited geographical distribution--Opinions of botanists respecting
the centres from which plants have been diffused--Whether there are
grounds for inferring that the loss, from time to time, of certain
animals and plants, is compensated by the introduction of new
species?--Whether any evidence of such new creations could be
expected within the historical era?--The question whether the
existing species have been created in succession must be decided by
geological monuments.

_Successive Extinction of Species consistent with their limited
Geographical Distribution._

In the preceding chapters I have pointed out the strict dependence of
each species of animal and plant on certain physical conditions in the
state of the earth's surface, and on the number and attributes of other
organic beings inhabiting the same region. I have also endeavored to
show that all these conditions are in a state of continual fluctuation,
the igneous and aqueous agents remodelling, from time to time, the
physical geography of the globe, and the migrations of species causing
new relations to spring up successively between different organic
beings. I have deduced as a corollary, that the species existing at any
particular period, must, in the course of ages, become extinct one after
the other. "They must die out," to borrow an emphatical expression from
Buffon, "because Time fights against them."

If the views which I have taken are just, there will be no difficulty in
explaining why the habitations of so many species are now restrained
within exceedingly narrow limits. Every local revolution, such as those
contemplated in the preceding chapter, tends to circumscribe the range
of some species, while it enlarges that of others; and if we are led to
infer that new species originate in one spot only, each must require
time to diffuse itself over a wide area. It will follow, therefore, from
the adoption of this hypothesis, that the recent origin of some species,
and the high antiquity of others, are equally consistent with the
general fact of their limited distribution; some being local, because
they have not existed long enough to admit of their wide dissemination;
others, because circumstances in the ani