 Linguist Christopher Ehret proposes that between 1000 and 700 BC, the Southern Nilotic speaking communities, who kept domestic stock and possibly cultivated sorghum and finger millet, 
lived next to an Eastern Cushitic speaking community with whom they had significant cultural interaction.The general location of this point of cultural exchange being somewhere near the common border between Sudan, Uganda, Kenya, and Ethiopia.He suggests that the cultural exchange perceived in borrowed loan words, adoption of the practice of circumcision and the cyclical system of age-set organisation dates to this period.