Caveman DNA helps track ancient migration

More than 3,000 years ago a cataclysm struck Egypt. ‘‘A blast of God smote us,’’ one chronicler wrote, ‘‘and unexpectedly from the regions of the East, invaders of obscure race marched in confidence of victory against our land.’’

These invaders, he recorded, razed temples, massacred men and enslaved their wives.

Many millennia after humans left Africa in search of food and land, some of their descendants, the Hyksos people, had returned, rather less peacefully.

Now scientists have shown that, at about the same time that the Hyksos were invading Egypt, ultimately founding a new kingdom, a major genetic invasion of Eurasian blood was occurring across Africa – possibly as a consequence of the turmoil they brought.

The result is that as much as 20 per cent of east African DNA comes from Europe and Asia, falling to 6-7 per cent in west and south Africa – and providing evidence of a major movement of peoples back into the continent that first gave us life.

‘‘There were already hints at this backflow,’’ Andrea Manica, from the University of Cambridge, said. ‘‘If you look at the archaeology, all of a sudden 3,000 years ago we find barley and wheat crops, that are typical of the Near East. But was it a smallish movement into east Africa? In fact it is huge – a fifth to a quarter of the modern east African is Eurasian.’’

He and his colleagues were able to quantify the extent of the Eurasian return to Africa after extracting DNA from an Ethiopian who lived 4,500 years ago. Initial analysis showed that this man, who they called Mota after the cave where he was found, was closely related to people still living near by, which was itself extraordinary. ‘‘We can say there is a continuity of populations in the Ethiopian highlands over the past 4,000 years,’’ Manica said.

What was found, they reported in the journal Science, was that the difference between a modern Ethiopian and a prehistoric one can largely be made up by injecting a bit of a Sardinian.

‘‘To make a modern eastern African you want Mota, and an early farmer gene,’’ Manica said. Taking this individual as a base, the scientists were then able to see the proportions of DNA that came from Eurasian populations in today’s modern Africans, and found that the DNA spread right to the fringes of the continent. What they could not say is quite how this happened – but Manica’s theory is it may be related to the Hyksos invasion.

‘‘Perhaps this pushed farmers out of an expanding area? Or maybe they were part of the general movement of people at the time.

‘‘It seems a fair bet that these changes in Egypt would have been a major upheaval.’’