Daily Mail (London), February 4, 2014
When humans first left Africa some 60,000 years ago, they went on to leave their genetic footprints around the world.
These same footprints have revealed that some humans decided to return to Africa, carrying genes from the rest of the world back to the continent.
Now a new study of southern African genes reveals that a previously unknown migration took western Eurasian DNA back to continent 3,000 years ago.
Writing in the New Scientist, Catherine Brahic reports on a study that looked at the DNA of Khoisan tribes of southern Africa.
The Khoisan tribes are thought to have lived in near-isolation from the rest of humanity for thousands of years.
The study by Harvard University revealed that some of their genes closely match people from modern-day southern Europe, including Spain and Italy.
Researchers have now identified two migrations: One about 3,000 years ago, of non-Africans entering east Africa, and a second one 900–1,800 years ago.
‘These are very special, isolated populations, carrying what are probably the most ancient lineages in human populations today,’ David Reich of Harvard University told New Scientist.
Dating methods suggest the European DNA made their way into the Khoisan DNA sometime between 900 and 1,800 years ago, before known European contact with the region.
Meanwhile, archaeological studies of the region suggest that a subset of the Khoisan, known as the Khoe-Kwadi speakers, arrived in southern Africa from east Africa much earlier.
Professor Reich found that the proportion of Eurasian DNA was highest in Khoe-Kwadi tribes, who have up to 14 per cent of western Eurasian ancestry.
‘These populations were always thought to be pristine hunter-gatherers who had not interacted with anyone for millennia,’ added Professor Reich’s collaborator, linguist Brigitte Pakendorf.
‘Well, no. Just like the rest of the world, Africa had population movements too. There was simply no writing, no Romans or Greeks to document it.’
It is uncertain why humans first left Africa, but researchers believe it has something to do with major climatic shifts that were happening around that time.
The recent research confirms a 2012 study by Luca Pagani of the Wellcome Trust Sanger Institute which found non-African genes in people living in Ethiopia.
They found that the genomes of some Ethiopian populations bear striking similarities to those of populations in Israel and Syria, a potential genetic legacy of the Queen of Sheba and her companions.
The team detected mixing between some Ethiopians and non-African populations dating to approximately 3,000 years ago.