Page:The naturalist on the River Amazons 1863 v2.djvu/349

 tute of monkeys, and why should Madagascar have stopped short at Lemurs, whilst America has gone on to prehensile-tailed Cebidæ, and the Old-World continent continued to Gibbons, Orangs, Chimpanzee, and Gorilla? Is it that the greater land masses have seen a larger amount of geological and climatal changes with corresponding changes in the geographical relations of species? Moreover, why should the smaller groups of the order be confined to smaller areas within the greater areas peopled by the families to which they belong? For, it must be added, the true Lemurs are confined to Madagascar, the Gibbons and others to South Eastern Asia, the dog-faced baboons to Africa, and, as we have seen, the scarlet-faced monkeys to a limited area on the Upper Amazons. May we be allowed to explain the absence of these animals from New Guinea with Australia, by the supposition that those lands were separated from South Eastern Asia before the first forms of the order came into existence? If so, it may be concluded that Madagascar became separated from Africa, and America from the continental mass of the old world before the Pithecidæ originated. But, if these explanations, founded on natural causes, be entertained, we commit ourselves, by the fact of entertaining them, to the admission that natural causes are competent to explain the existence or non-existence of forms in a given area, and why may not the exercise of our reason, founded on carefully observed and collated facts, be carried a step farther, namely to the origin of the species of monkeys themselves? I have already shown how singularly species of monkeys vary in different localities, and have