Though we often think of early humans emerging from Africa, geneticists have learned that a population of humans from western Eurasia made the trek back into Eastern Africa some 3,000 years ago. The discovery shows there was more intermingling between the continents than previously thought.
Humans started to leave Africa some 65,000 years ago, though the Neanderthals occupied Europe long before that. At the same time, the Khoisan tribes of southern Africa (hunter-gatherers and pastoralists who speak unique click languages) lived in near-isolation from the rest of humanity for thousands of years. At least that's what we thought; new evidence suggests otherwise.
From New Scientist:
[David Reich of Harvard University] and his colleagues were not expecting to find signs of western Eurasian genes in 32 individuals belonging to a variety of Khoisan tribes. "I think we were shocked," says Reich.
The unexpected snippets of DNA most resembled sequences from southern Europeans, including Sardinians, Italians and people from the Basque region. Dating methods suggested they made their way into the Khoisan DNA sometime between 900 and 1,800 years ago – well before known European contact with southern Africa.
Archaeological and linguistic studies of the region can make sense of the discovery. They suggest that a subset of the Khoisan, known as the Khoe-Kwadi speakers, arrived in southern Africa from east Africa around 2,200 years ago. Khoe-Kwadi speakers were – and remain – pastoralists who make their living from herding cows and sheep. The suggestion is that they introduced herding to a region that was otherwise dominated by hunter-gatherers.
Fascinatingly, the study shows — for the first time — that genetic material from Neanderthals may be more widespread in African populations than previously assumed.
Read the entire study at PNAS: "Ancient west Eurasian ancestry in southern and eastern Africa."