In the investigation of the moral and intellectual diversities of races, there is no difficulty so great as an accurate classification. I am disposed to think a separation into three great groups sufficient for all practical purposes. These groups I shall call primary varieties, not in the sense of distinct creations, but as offering obvious and well-defined distinguishing characteristics. I would designate them respectively by the terms white, yellow, and black. I am aware of the inaccuracy of these appellations, because the complexion is not always the distinctive feature of these groups: other and more important physiological traits must be taken into consideration. But as I have not the right to invent new names, and am, therefore, compelled to select among those already in use, I have chosen these because, though by no means correct, they seemed preferable to others borrowed from geography or history, and not so apt as the latter to add to the confusion which already sufficiently perplexes the investigator of this subject. To obviate any misconception here and hereafter, I wish it to be distinctly understood that by "white" races I mean those usually comprised under the name of Caucasian, Shemitic, Japhetic; by "black," the Hamitic, African, etc.; by "yellow," the Altaic, Mongolian, Finnic, and Tartar. These I consider to be the three categories under which all races of the human family can be placed. I shall hereafter explain my reasons for not recognizing the American Indians as a separate variety, and for classing them among the yellow races.[167] It is obvious that each of these groups comprises races very dissimilar among themselves, each of which, besides the general characteristics belonging to the whole group, possesses others peculiar to itself. Thus, in the group of black races we find marked distinctions: the tribes with prognathous skull and woolly hair, the low-caste Hindoos of Kamaoun and of Dekhan, the Pelagian negroes of Polynesia, etc. In the yellow group, the Tungusians, Mongols, Chinese, etc. There is every reason to believe that these sub-varieties are coeval; that is, the same causes which produced one, produced at the same time all the others. It is, moreover, extremely difficult to determine the typical character of each variety. In the white, and also in the yellow group, the mixture of the sub-varieties is so great, that it is impossible to fix upon the type. In the black group, the type is perhaps discernible; at least, it is preserved in its greatest purity.