CHAPTER XV.
PROGRESSIVE LOCALISATION OF ORGANISED BEINGS.—CENTRES OF APPEARANCE.—ORIGINAL LOCALISATION OF MAN.
I. An eminent man may draw incorrect conclusions from the existence of centres of appearance without their existence being any the less real. Unconnected with animal or vegetable centres, the human races might have their own; man might have come into existence wherever we meet with him. But, before we accept this original cosmopolitanism, we must assure ourselves that it subjects man to general laws. Now we shall see that this hypothesis is, on the contrary, at variance with all general facts presented by plants as well as animals.
II. Let us first prove that no animal or vegetable species inhabits, as man does, almost the entire globe.
The assertion of Ad. de Candolle could not be more precise as far as plants are concerned. “No phanerogamous plant,” he says, “is distributed over the entire surface of the earth. There are only eighteen whose area extends to half the globe. No tree or shrub figures among these plants, which are so widely distributed.” This latter remark belongs to an order of considerations which we shall meet with again.
Being unable to enter into an examination of all the facts which are offered by the various classes of the Animal Kingdom from this point of view, I shall confine myself to a few details upon birds and mammals.
We should expect to find the former presenting very extensive areas of habitation by reason of their mode of locomotion. It is, in fact, among them that we find some of the species which most deserve the epithet of cosmopolitan. They do not, however, equal man in this respect.
The stock-dove, the parent stock of our domestic pigeon, extends from the south of Norway to Madeira and Abyssinia, from the Shetland Islands to Borneo and Japan; but it does not reach as far as either the equator or the polar circle; and it is wanting both in America and Polynesia.
The fulvous vulture is found in all the temperate regions of the old world, crosses the equator in Africa and descends as far as the Cape. But we do not meet with it either in our polar regions, in America or in Polynesia.
The peregrine falcon has perhaps of all animals the widest area. It is found in America, as also in all the warm or temperate regions of the old world. It is supposed to exist in Australia, but we do not meet with it either in Polynesia or in the polar regions.
Among mammals, whales, on account of their immense powers of locomotion and the continuity of seas, would seem to be adapted to true cosmopolitanism. This, however, is not the case. They are almost all confined within relatively very limited areas, and rarely pass beyond their customary boundaries. Commodore Maury regarded the equatorial sea as forming an invincible obstacle to their passage from one hemisphere to the other. Two exceptions have, however, been observed to this rule. A rorqual (Megaptera longimana) and a Sibaldius laticeps are said to have crossed this barrier, and to have passed from our seas to those of the Cape and of Java. These exceptions might easily be explained by various accidental circumstances. Supposing however we were to accept them as testifying an exceptional relative cosmopolitanism, we still have the fact that they have never been met with in the Pacific Ocean.