Contributions to the theory of natural selection. A series of essays ... By Alfred Russel Wallace ...

I.
ON THE LAW WHICH HAS REGULATED
THE INTRODUCTION OF NEW SPECIES.*
Geogra]ph1ical Distribution dependent on Geologic
Calanges.
EVERY naturalist who has directed his attention to
the subject of the geographical distribution of animals
and plants, must have been interested in the singular
facts which it presents. Many of these facts are quite
different from what would have been anticipated,
and have hitherto been considered as highly curious,
but quite inexplicable. None of the explanations
attempted from the time of Linnaeus are now
considered at all satisfactory; none of them have
given a cause sufficient to account for the facts
known at the time, or comprehensive enough to
include all the new facts which have since been, and
are daily being added. Of late years, however, a
great light has been thrown upon the subject by
geological investigations, which have shown that the
present state of the earth and of the organisms now
* Written at Sarawak in February, 1855, and published im
the " Annals and Magazine of Natural History," September,
1855.
B