Europeans Returned to Africa 3,000 Years Ago
Posted by addisethiopia on February 5, 2014
“DNA sequences in the Khoisan people most closely resemble some found in people who today live in southern Europe.”
Call it humanity’s unexpected U-turn. One of the biggest events in the history of our species is the exodus out of Africa some 65,000 years ago, the start of Homo sapiens’ long march across the world. Now a study of southern African genes shows that, unexpectedly, another migration took western Eurasian DNA back to the very southern tip of the continent 3000 years ago.
According to conventional thinking, the Khoisan tribes of southern Africa, have lived in near-isolation from the rest of humanity for thousands of years. In fact, the study shows that some of their DNA matches most closely people from modern-day southern Europe, including Spain and Italy.
Because Eurasian people also carry traces of Neanderthal DNA, the finding also shows – for the first time – that genetic material from our extinct cousin may be widespread in African populations.
The Khoisan tribes of southern Africa are hunter-gatherers and pastoralists who speak unique click languages. Their extraordinarily diverse gene pool split from everyone else’s before the African exodus.
“These are very special, isolated populations, carrying what are probably the most ancient lineages in human populations today,” says David Reich of Harvard University. “For a lot of our genetic studies we had treated them as groups that had split from all other present-day humans before they had split from each other.”
So he 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 (see “Back to Africa – but from where?”). Dating methods suggested they made their way into the Khoisan DNA sometime between 900 and 1800 years ago – well before known European contact with southern Africa (see map).
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 2200 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.
Reich and his team found that the proportion of Eurasian DNA was highest in Khoe-Kwadi tribes, who have up to 14 per cent of western Eurasian ancestry. What is more, when they looked at the east African tribes from which the Khoe-Kwadi descended, they found a much stronger proportion of Eurasian DNA – up to 50 per cent.
That result confirms a 2012 study by Luca Pagani of the Wellcome Trust Sanger Institute in Hinxton, UK, which found non-African genes in people living in Ethiopia. Both the 2012 study and this week’s new results show that the Eurasian genes made their way into east African genomes around 3000 years ago. About a millennium later, the ancestors of the Khoe-Kwadi headed south, carrying a weaker signal of the Eurasian DNA into southern Africa.
- Ethiopians and Khoisan Share the Deepest Clades of the Human Y-Chromosome Phylogeny
- Paleoanthropologist John Hawks’ recent travels in Ethiopia