Christopher Ehret, Professor of African History at UCLA, is a major figure in African history and African historical linguistics, particularly known for his efforts to correlate linguistic taxonomy and reconstruction with the archeological record. His historical books include An African Classical Age, in which he argues for a conception of the period from 1000 BC to 400 AD in East Africa as a "classical age" during which a variety of major technologies and social structures took shape. His linguistic works include reconstructions of Afro_Asiatic, Nilo_Saharan, and on a smaller scale Southern Cushitic.
The language and civilizational groups are the Nilo-Saharan speakers of north central and northeastern Africa, the Niger-Congo speakers of western and central Africa, the Afrasan (also known as Afroasiatic) speakers of northern and northeastern Africa, and the Khoisan speakers of eastern and southern Africa.
Ehret focuses as much on material culture as Childe did, centering especially on food production, but he emphasizes gradual change rather than sudden developments.
In the early times that are the focus of Ehret's book, the African proportion of the human population was surely much greater than the 10% of human population that now lives there.
Other researchers (such as ChristopherEhret, for example) have put forward the western Red Sea coast and the Sahara.
Tonal languages appear in the Omotic, Chadic, and South and East Cushitic branches of Afro-Asiatic, according to Ehret (1996).
Little agreement exists on the sub-classification of the five or six branches mentioned; however, ChristopherEhret (1979), Harold Fleming (1981), and Joseph Greenberg (1981) all agree that the Omotic branch to split from the rest first.