before Darwin and Wallace and Wagner had noticed that animals
and plants were by no means evenly distributed over the surface of the
globe, but until the doctrine of evolution cleared their vision they did
not see the meaning of these facts. As in the case of all the other
departments of zooelogy the immediate data themselves are familiar, but
because they are so obvious the mind does not look for their
interpretation but accepts the facts at their face value. While the
phenomena of distribution are no less fascinating to the naturalist, and
no less effective in their demonstration of evolution, their comprehensive
treatment would demand more space than the whole purpose of the present
description of organic evolution would justify. Thus a brief outline only
can be given of the salient principles of this subject in order that their
bearing upon the problem of species may be indicated.

Even as children we learn many facts of animal distribution; every one
knows that lions occur in Africa and not in America, that tigers live in
Asia and Malaysia, that the jaguar is an inhabitant of the Brazilian
forests, and that the American puma or mountain lion spreads from north to
south and from east to west throughout the American continents. The
occurrence of differing human races in widely separated localities is no
less familiar and striking, for the red man in America, the Zulu in
Africa, the Mongol and Malay in their own territories, display the same
discontinuity in distribution that is characteristic of all other groups
of animals and of plants as well. As our sphere of knowledge increases, we
are impressed more and more forcibly by the diversity and unequal extent
of the ranges occupied by the members of every one of the varied divisions
of the organic world. Another fact which becomes significant only when
science calls our attention to it is the absence from a land like
Australia of higher mammals such as the rabbit of Europe. The hypothesis
of special creation cannot explain this absence on the assumption that the
rabbit is unsuited to the conditions obtaining in the country named, for
when the species was introduced into Australia by man, it developed and
spread with marvelous rapidity and destructive effect. It may seem
impossible that facts like these could possess an evolutionary
significance, but they are actual examples of the great mass of data
brought together by the naturalists who have seen in them something to