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Study raises questions about roots of lactose tolerance in Africa

About 5500 years ago—around the same time herding of animals like cattle, sheep, and goats began in Europe—the practice was also catching on in East Africa. Now, a new study reveals how such pastoralism spread throughout the region.

Researchers examined ancient DNA from 41 individuals who lived in what are now Kenya and Tanzania. According to past archaeological research, the first herders moved into East Africa about 5000 years ago; the genetics show they had ancestry from both the Near East and what is now Sudan. At first, these early herders mixed with local hunting and gathering people in East Africa, much as the early Yamnaya herders who brought pastoralism to Europe from Central Asia almost immediately began to have babies with local farmers and hunter-gatherers. After about 1000 years, however, the East African herders seem to have genetically kept to themselves, becoming isolated from other local people.

Unlike contemporary herders, most of the ancient individuals were lactose intolerant. One individual, who lived just over 2000 years ago near Gishimangeda Cave in Tanzania, however, had a key lactose-digestion gene, hinting at when this trait may have started to evolve in the region. If his herding ancestors and compatriots ate dairy, they might have fermented it to allow digestion, as lactose-intolerant Mongolian herders have likely done for millennia.

*Correction, 31 May, 5 p.m.: This story has been corrected to note the pattern of mixing followed by isolation in early East African herders.