When we compare the mental faculties and social instincts of animals, even of monkeys, with those of the superior races of civilized men, the distance seems immeasurable, and to fill the gap impossible. But, if we take the lower races of mankind, the differences appear less marked, and even analogies arise. Many of the moral and mental faculties, in fact, which we observe among the quadrumana appear common to them with savage peoples on the one side, and with some of the higher mammalia on the other side, which have well-developed social instincts—with, for instance, dogs, horses, and elephants. The animals which man has domesticated are, as a rule, those which belong to social species, and live in the natural state in more or less numerous groups. And, among the monkeys, it is not the large ones, those which most resemble men in stature, that are most social and most susceptible of domestication, but the smaller ones, the tree-climbers...