Excerpted from The Civilations of Africa: A History to 1800, "Chapter 3: Culture and Technology in Africa, 8500-3500 BCE" by Christopher Ehret, 2002.
The Saharo-Sahelian Peoples and the Beginnings of Crop Cultivation
"Sometime between 8000 and 7000 BCE, the Saharo-Sahelian descendants of the Northern Sudanian people set in motion an economic shift of even greater social and cultural impact: they began the first deliberate cultivation of at least some of the grains - sorghum may have been one - that they previously had gathered as wild. The timing of this development may have something to do with the still further increase in rainfall at this particular period. More rainfall meant more areas of the Sahara in which sorghum could be successfully grown and so would have made grain cultivation seem a less chancy venture than it would have been before. (Our knowledge of the next several thousand years of pre-Kunama history is virtually nil, so the remaining discussion focuses on the Saharo-Sahelians, who in any case seem to have been the major innovating group of peoples.)
"The keeping of cattle had previously added considerably to the meat resources of the Northern Sudanic lands, otherwise poorly endowed with large mammals. But with cultivation the Saharo-Sahelians created a set of subsistence practices that gave them the potential, over the long run of history, to expand their food supply many times over and to support a growing population. We can call the set of crops and the cultivating practices pioneered by the Saharo-Sahelians "Sudanic seed agriculture" or just "Sudanic agriculture." The term "seed" is included to bring attention to the fact that the key crops of this agriculture were all propagated from seed. We sometimes also call the combined livestock-raising and cultivating practices of these peoples the Sudanic "agripastoral" tradition. Progressively over the period between 7000 and 5000 BCE, the Saharo-Sahelians and their descendants brought under cultivation new crops in addition to sorghum, domesticating more of the indigenous wild food plants of the region - first, before 6000 BCE, a variety of gourds and calabashes including the edible gourd, and then, by perhaps 5000 BCE, cotton, pearl millet, and watermelons."
The onset of food production among Proto-Northern Sudanic speakers (Link)
Origins of Nilo-Saharan and Cushitic Speakers (Link)