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 be
interpreted, and who have sought and found an explanation in the
formularies of science.

The general principles of distribution appear with greatest clearness when
an examination is made of the animals and plants of isolated regions like
islands. The Galapagos Islands constitute a group that has figured largely
in the literature of the subject, partly because Darwin himself was so
impressed by what he found there in the course of his famous voyage around
the world in the "Beagle." They form a cluster on the Equator about six
hundred miles west of the nearest point of the neighboring coast of South
America. Although the lizards and birds that live in the group differ
somewhat among themselves as one passes from island to island, on the