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

12 ON THE LAW WHICH IHAS REGULATED
recent mountain elevations, separates faunas and floras
which scarcely differ more than may be due to climate
and latitude alone.
The series of facts alluded to in Proposition (3),
of closely allied species in rich groups being found
geographically near each other, is most striking and
important. MIr. Lovell Reeve has well exemplified it
in his able and interesting paper on the Distribution
of the Bulimi. It is also seen in the HIImmingbirds and Toucans, little groups of two or three
closely allied species being often found in the same
or closely adjoining districts, as we have had the
good fortune of personally verifying. Fishes give
evidence of a similar kind: each great river has
its peculiar genera, and in more extensive genera
its groups of closely allied species. But it is the
same throughout Nature; every class and order of
animals will contribute similar facts. HIitherto no
attempt has been made to explain these singular
phmnomena, or to show how they have arisen. Why
are the genera of Palms and of Orchids in almost
every case confined to one hemisphere? Why are
the closely allied species of brown-backed Trogons all
found in the East, and the green-backed in the
West? Why are the Macaws and the Cockatoos
similarly restricted? Insects furnish a countless
number of analogous examples;-the Goliathi of
Africa, the Ornithopterme of the Indian Islands, the
Heliconidam of South America, the Danaidoe of the
East, and in all, the most closely allied species found