Usually long heads are associated with long faces and vice versa, the face being then termed harmonic. A certain use of this fact has been made for classificatory purposes. There are other features of facial form which appear to be characteristic of different races, but are difficult to measure exactly.
and Nose Form.—The average stature is a useful criterion. The form of the nose is estimated by an index formed by taking the length from the root to the junction with the upper lip as ioo and expressing the breadth across the nostrils as a percentage. Professor Thomson, to whom the idea was due, and Buxton have shown that the nasal index tends to be high in those countries where the air is moist and hot and low where it is cold and dry, the various combinations of these two factors being associated with corresponding nasal indices. The correlation is high with certain very marked exceptions, of which the most important is the Australian aborigines. It seems probable that they migrated from a hot, moist climate, and that they have retained the form of nose most appropriate to such a climate. The evolu tion of any character needs the time factor, especially when, as in this case, evolution by elimination has played an important part.
On the basis of the form of the hair, mankind may be divided into straight-haired (leiotrichous), woolly-haired (ulotrichous) and an intermediate group of wavy or curly-haired (cymotrichous). Certain types are difficult to define, but usually the distinction is clear-cut. All types of hair may occur in the same population, where racial admixture has taken place, but normally the variation is slight in the same group.
In section the woolly hair is flat and ribbon-like, straight hair is round, wavy and curly hair showing an elliptical form. Here also there may be a certain correlation with environment. The woolly hair occurs for the most part in the Tropics and may form a protection against the sun, being associated with special sweat glands. The period at which the evolution of the hair form took place is uncertain, but it remains the most convenient basis for the ultimate classification of the great groups of man, the other criteria being subordinated to it. In this classification physical
criteria alone have been used ; all cultural or linguistic terms have been avoided. Owing to historical reasons certain peoples have been named after the languages they speak, and subsequently these terms have been applied to physical types. Terms like Malay, Dravidian, Mongol and Bantu are used as if they could be applied to races and not merely to peoples speaking certain groups of languages.
The classification given below is based on the anatomical characters already discussed; attention has, however, been recently directed towards certain physiological characters as a basis of racial differentiation. Several criteria have been put forward, amongst them the different reactions of the blood sera in divergent races and the effect of the ductless glands on the macroscopical anatomical characters. Although great stress has been laid on the latter, especially by Sir Arthur Keith, neither this nor other physiological criteria have to the present time been sufficiently investigated to form a basis for a novel classificatory method.
The straight-haired peoples cor respond to a large extent to the races called by some writers Mongol or Mongoloid, or "the Yellow-Brown Race." All these peoples possess cheek-bones of a greater or lesser degree of prominence. In most cases the face is flattened, often markedly so. The skin is usually yellow, shading into a coppery yellow or brown on one side, and on the other, especially in women, a pale almost white yellow tinge. In Asia the cephalic index tends to vary between mesocephaly and brachycephaly, with some marked cases of the latter form. In America the Eskimo are dolicho cephalic and a wide range of mesocephaly and brachycephaly occurs among the other tribes.
While Haddon divides this race into three groups on the basis of a cephalic index, it is probably more convenient to adopt a primary geographical division and to separate the Leiotrichi into an Asiatic and American group, since the latter have been separated from their kinsmen in Asia for a long time and have to a certain extent specialised.