Relationships of Ancient African Languages

Almost all of the more than 1,000 African languages spoken today belong to just four families, Afroasiatic, Niger-Kordofanian, Nilo-Saharan, and Khoesan. Each family is relatively ancient, with its mother language, or protolanguage, spoken during the late Pleistocene. As these language families spread out across the continent in the early Holocene, they gradually drove out of use hundreds of other languages that used to be spoken in African. But in the late Pleistocene these mother languages were just four among many languages spoken in the continent. Only about three of those other languages survived in use down to the present. What were the relationships of these languages to the existing African families and to the language families of the rest of the world, and what can this information tell us about human origins and early human history?