Whether we contemplate the human family from the point of view of the naturalist or of the philosopher, we are struck with the marked dissimilarity of the various groups. The obvious physical characteristics by which we distinguish what are termed different races, are not more clearly defined than the psychical diversities observable among them. "If a person," says the learned vindicator of the unity of the human species,[1] "after surveying some brilliant ceremony or court pageant in one of the splendid cities of Europe, were suddenly carried into a hamlet in Negro-land, at the hour when the sable tribes recreate themselves with dancing and music; or if he were transported to the saline plains over which bald and tawny Mongolians roam, differing but little in hue from the yellow soil of their steppes, brightened by the saffron flowers of the iris and tulip; if he were placed near the solitary dens of the Bushman, where the lean and hungry savage crouches in silence, like a beast of prey, watching with fixed eyes the birds which enter his pitfall, or greedily devouring the insects and reptiles which chance may bring within his grasp; if he were carried into the midst of an Australian forest, where the squalid companions of kangaroos may be seen crawling in procession, in imitation of quadrupeds, would the spectator of such phenomena imagine the different groups which he had surveyed to be the offspring of one family? And if he were led to adopt that opinion, how would he attempt to account for the striking diversities in their aspect and manner of existence?"