The so-called red-haired branch of the Nordic race has special characters in addition to red hair, such as a greenish cast of eye, a skin of delicate texture tending either to great clarity or to freckles and certain peculiar temperamental traits. This was probably a variety closely related to the blonds and it first appears in history in association with them. While the three main European races are the subject of this book and while it is not the intention of the author to deal with the other human types, it is desirable in connection with the discussion of this character, hair, to state that the three European subspecies are subdivisions of one of the primary groups or species of the genus _Homo_ which, taken together, we may call the Caucasian for lack of a better name. The existing classification of man must be radically revised, as the differences between the most divergent human types are far greater than are usually deemed sufficient to constitute separate species and even subgenera in the animal kingdom at large. Outside of the three European subspecies the greater portion of the genus _Homo_ can be roughly divided into the Negroes and Negroids, and the Mongols and Mongoloids. The former apparently originated in south Asia and entered Africa by way of the northeastern corner of that continent. Africa south of the Sahara is now the chief home of this race, though remnants of Negroid aborigines are found throughout south Asia from India to the Philippines, while the very distinct black Melanesians and the Australoids lie farther to the east and south. The Mongoloids include the round skulled Mongols and their derivatives, the Amerinds or American Indians. This group is essentially Asiatic and occupies the centre and the eastern half of that continent. A description of these Negroids and Mongoloids and their derivatives, as well as of certain aberrant species of man, lies outside the scope of this work. In the structure of the head hair of all races of mankind we find a regular progression from extreme kinkiness to lanky straightness and this straightness or curliness depends on the shape of the cross section of the hair itself. This cross section has three distinct forms, corresponding with the most extreme divergences among human species. The cross section of the hair of the Negroes is a flat ellipse with the result that they all have kinky hair. This kinkiness of the Negroes’ hair is also due somewhat to the acute angle at which the hair is set into the skin and the peppercorn form of hair probably represents an extreme specialization. The cross section of the hair of the Mongols and their derivatives, the Amerinds, is a complete circle and their hair is perfectly straight and lank.