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 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 whole they are most like the species of the corresponding classes inhabiting South America.  Why should this be so?  On the hypothesis of special creation there is no reason why they should not be more like the species of Africa