The southern part of East Africa was occupied until recent times by Khoisan hunter-gatherers, whereas in the Ethiopian Highlands the donkey and such crop plants as teff allowed the beginning of agriculture around 7,000 B.C. Lowland barriers and diseases carried by the tsetse fly, however, prevented the donkey and agriculture from spreading southwards. Only in quite recent times has agriculture spread to the more humid regions south of the equator, through the spread of cattle, sheep and crops such as millet. Language distributions suggest that this most likely occurred from Sudan into the African Great Lakes region, since the Nilotic languages spoken by these pre-Bantu farmers have their closest relatives in the middle Nile basin.