The progressive localisation of organised beings, increasing in degree as they become more perfect, is, then, a general law. Physiology will readily account for this fact.
The perfection of organisms is the result of division of labour, which demands the multiplication of functional apparatus. As the anatomical instruments become more numerous and special, the functions do the same. From this cause alone the conditions of harmony between the living being and the conditions of life which surround it become more and more definite. Consequently, the animal or the plant only finds its really favourable conditions in a constantly diminishing area. Beyond these limits the conditions of life change, the struggle for existence becomes more hazardous, and the spread of the species, genus, family, or even order is arrested. Man alone, armed against the conditions of life by his intelligence and industry, is capable of overcoming conditions of existence which would be an impassable barrier to his material organisation.
The law of progressive localisation is in direct opposition to the doctrine of the original cosmopolitanism of the human species. In putting it aside, polygenists, properly so called, might draw attention to the diffusion of the genera of dolphins and rorquals; polygenistic monogenists of the school of Agassiz might argue from the facts mentioned above in connection with the genera of megaptera and sibaldius; they might both say: The general law of localisation offers two exceptions; why should not man form a third?
The analogy, it is clear, is fundamentally wrong. Dolphins, rorquals and sibaldius belong to the lowest order of mammals; man, even if his body alone is considered, belongs incontestably to the highest order. Unless we make him a solitary exception, it is to the laws of the superior groups that he should be subject, and not to those of the inferior.
Thus, we are so far justified in affirming that man could not have been originally cosmopolitan. But we can go further.
VI. Without having come into existence in every place where we now meet with him, man may have had several centres of appearance. Let us examine this latter question. The laws of progressive localisation and the characterisation of centres enable us both to put the question and to solve it.
Let us re-examine from this point of view the animal groups, setting aside all inferior groups and confining our attention to anthropoid apes. In this family, which most closely resembles man in its organisation, there are degrees also. The law of progressive localisation applies to this limited group equally with the entire kingdom.
We meet with the entire family in Asia, in the peninsula of Malacca, in Assam to 26° N. Lat., in Sumatra, Java, Borneo and in the Philippine Islands; in Eastern Africa from 10° S. to 15° N. Lat. The gibbon genus, however, which is the lowest, is the only one which occupies the whole of Asia. The orang is confined to Borneo and Sumatra. In Africa the chimpanzee extends almost from the Zaïre to Senegal; the gorilla has only been found on the Gaboon, and perhaps in Ashantee. Were he to occupy all the space which is still left blank upon that part of our maps by travellers, his area of habitation would even then be very limited. Thus, the higher the anthropoid type, the more limited the area of habitation.
If we consider the material organism alone, the human type is incontestably superior to that of the orang or gorilla. He must then have been originally localised just as much as these animal types. It will perhaps be objected that the great apes are gradually disappearing, and that the few survivors do no more than show that they once existed in greater numbers. This would be an entirely gratuitous hypothesis having no foundation in facts, and we shall at least be permitted to reply, that the gorilla and the orang might very well have continued to exist in those places where the chimpanzee and gibbon are still living. Now, what are the areas occupied by the latter compared with the human area?