It is reasonable, according to fact and historic usage, to include under the word "Negro" the darker peoples of Africa characterized by a brown skin, curled or "frizzled" hair, full and sometimes everted lips, a tendency to a development of the maxillary parts of the face, and a dolichocephalic head. This type is not fixed or definite. The color varies widely; it is never black or bluish, as some say, and it becomes often light brown or yellow. The hair varies from curly to a wool-like mass, and the facial angle and cranial form show wide variation. It is as impossible in Africa as elsewhere to fix with any certainty the limits of racial variation due to climate and the variation due to intermingling. In the past, when scientists assumed one unvarying Negro type, every variation from that type was interpreted as meaning mixture of blood. To-day we recognize a broader normal African type which, as Palgrave says, may best be studied "among the statues of the Egyptian rooms of the British Museum; the larger gentle eye, the full but not over-protruding lips, the rounded contour, and the good-natured, easy, sensuous expression. This is the genuine African model." To this race Africa in the main and parts of Asia have belonged since prehistoric times. The color of this variety of man, as the color of other varieties, is due to climate. Conditions of heat, cold, and moisture, working for thousands of years through the skin and other organs, have given men their differences of color. This color pigment is a protection against sunlight and consequently varies with the intensity of the sunlight. Thus in Africa we find the blackest men in the fierce sunlight of the desert, red pygmies in the forest, and yellow Bushmen on the cooler southern plateau. Next to the color, the hair is the most distinguishing characteristic of the Negro, but the two characteristics do not vary with each other. Some of the blackest of the Negroes have curly rather than woolly hair, while the crispest, most closely curled hair is found among the yellow Hottentots and Bushmen. The difference between the hair of the lighter and darker races is a difference of degree, not of kind, and can be easily measured. If the hair follicles of a China-man, a European, and a Negro are cut across transversely, it will be found that the diameter of the first is 100 by 77 to 85, the second 100 by 62 to 72, while that of the Negro is 100 by 40 to 60. This elliptical form of the Negro's hair causes it to curl more or less tightly.