With the exception of whales, we shall find nothing at all resembling cosmopolitanism. Setting aside the whole of Oceania, we only find, as common to both the Old and the New World, two or three ruminants, perhaps a bear, a fox and a wolf. All these species are, moreover, more or less polar, and are wanting in the central regions of the two worlds. Finally, there is not one species of cheiroptera or quadrumana which is indigenous both in America and the Old World.
Beyond those species which man has disseminated by making them follow his migrations, animals and plants evidently occupy their natural area, wherein lies the centre from which they have spread. We see that even after this dispersion none of them have acquired an area of habitation which can be compared to that of man.
The admission that the human species appeared in every place in which it is found, attributing to it an original cosmopolitanism, would make it a solitary exception in contradiction to the facts presented by all other species. An hypothesis which leads to such a conclusion should be rejected as irreconcilable with the results of observation. If man is now to be found everywhere, it is owing to his intelligence and industry.
III. This conclusion is forced even upon polygenists themselves; unless, indeed, they would reject, as inapplicable to man, the laws of zoological and botanical geography.
In fact, to whatever extent they may have multiplied their human species, they have been obliged, upon even the slightest study of natural history, to unite them into a single genus. Now, all that has just been said of species applies equally to genera. The area of habitation is doubtless increased, and, for example, some genera of cetaceans, as dolphins and rorquals, are found in all seas; and amongst terrestrial mammals, some genera of ruminants and carnivora inhabit, in a greater or less degree, both the Old and the New World. But they are all absent in the greater part of Oceania.
Moreover, the higher the types, the fewer is the number of these genera of widely extended areas. Cheiroptera, which are not provided with a nasal membrane, have some genera common to both the Old and the New World. This is no longer the case in cheiroptera, in which the nose is provided with a membrane. There is not a single genus among them, any more than among quadrumana, which inhabits both America and the Old World.
Consequently, polygenists must admit that the species of which their human genus is composed could not have come into existence in every place where man is now found, unless they wish to make a striking exception of this human genus.
IV. Should we wish to regard the human races as forming a family composed of several genera, or even as an order comprising several families, the same difficulties would present themselves.
Setting aside the marsupials and edentata, to which we shall return, it is true that the great normal orders of terrestrial mammals, the ruminants, rodents, insectivora, and carnivora are almost as cosmopolitan as man. But this is no longer the case with the cheiroptera, not one of which passes the polar circle. As to the quadrumana, it is well-known that they are wanting in Europe, with the exception of the Rock of Gibraltar, in North America and in the greater part of Asia and Oceania. Thus it appears that, even in the extreme hypothesis which I have here indicated, it would not be in the animal types which present the greatest resemblance to man, but among the carnivora or ruminants that we should be forced to seek for geographical analogies in favour of the pretended cosmopolitanism of the human order.
V. This limitation of the areas of habitation of animals, which is evidently related to their degree of elevation in the scale of beings, is a general fact which we also meet with in plants. On this point Ad. de Candolle speaks as follows:—“The mean area of species is smaller according as the class to which they belong has a more complete, a more highly developed, or, in other words, a more perfect organisation.”