Istwa Nou

Traffic ran into Africa as well. Sheep and goats came south out of the Levant to northeastern Africa as early as the seventh millennium BCE, along with more cattle, and those two animals did eventually spread across most of the continent. The crops did much less. By the seventh and sixth millennia, barley and early wheats were growing along the Mediterranean fringe, where winter rain suited them, and in irrigated pockets of Egypt such as the Fayum. Sometime before the Sahara finished drying, probably in the fourth millennium, wheat, barley and chickpeas passed southeast into the highlands of Eritrea and northern Ethiopia, where cool-season rains gave them conditions close to Mediterranean ones. That is the whole list, and it stops at the coast, the Nile corridor and the highlands. Eurasian crops never reworked the farming of the African interior the way African crops reworked farming in South Asia. The exchange was real and the balance sat on Africa's side.

Wheat, barley and chickpeas came to the Horn of Africa from the Levant, and the obvious route looks like the short crossing of the Red Sea from Arabia. The lexical evidence points elsewhere. These crops travelled from Egypt, south along the Red Sea Hills, which stayed marginally farmable in places until around 3300 BCE and closed afterwards. The people who received them were Cushitic speakers in the Ethiopian highlands who had been farming for a long time already, on two indigenous grains of their own, finger millet and teff. They added the newcomers to a system that worked. The plough arrived with the same package and became the main implement across the northern and central highlands. Further south and west, in the Sudan belt and East Africa, warm-season rainfall and different soils stopped the spread. Ecology drew that boundary. Accounts that read the limit as a failure of African farmers have the mechanism backwards.