INTRODUCTION TO SOCIOLOGY 237
Positive sociology is not directly interested in the adoption of this hypothesis of special centers of creation. Even supposing it incorrect, sociology can satisfy itself with the statement, con- formable alike to the champions and adversaries of this doctrine, according to which from the beginning there has been a natural tendency for each species to multiply, then to come out of its one or several centers of creation, which had become too narrow, and to adapt itself to the conditions, at first poorly, and afterwards with more and more facility. These eccentric dis- placements are active or passive, voluntary or involuntary. They are involuntary when they are occasioned by displace- ments of other natural bodies. 1
The more easily a species displaces itself, the more rapidly it scatters itself. So it is with winged articulate and vertebrate animals. Hence the great uniformity of their structure, in spite of the enormous diversity of their superficial exterior forms. This law finds its most complete application in the human spe- cies, the most mobile of all, and whose peculiar uniformity dominates all of the special varieties.
Adjoining centers never contain radically different faunas. The transition is by imperceptible degrees from one fauna to the other. These transitions, however, are less in man than in other species. The identical species of animals are found over vast continents, and present, from one region to the other, only some local differences or varieties, due to special influences. Thus each region from the north to the south of Africa has, so to speak, its special variety of antelope. These graduated differ- entiations are observed equally, or still more, in the distribution of the human species, whose extreme types are connected, even in their geographical distribution, by quite regular transitions.
Throughout, where there exists a certain congeniality of habi- tat, not necessarily perfect congeniality, races and varieties of the same species are found. Some conditions of habitat serve to limit them. For instance, in Borneo and Sumatra, according to the naturalist Schlegel, the orang-outang is always found in analogous localities. It never frequents different localities of
"DARWIN, The Origin of Species, chaps, xi, xii.
