DNA study reveals third group of ancient ancestors of modern Europeans

Europeans are a mixture of hunter-gatherers, agriculturalists, and also a third wave of migrants from north Eurasia

Strands of DNA taken from ancient corpses have revealed an unexpected addition to the ancestral roots of modern Europeans.

The first Homo sapiens arrived in Europe around 45,000 years ago, and these hunter-gatherers were replaced by early farmers who brought agriculture to the continent more than 7,000 years ago from Anatolia and the Levant in the near east.

The arrival of the first farmers set the stage for Europeans to be the descendents of the agriculturalists and indigenous hunter-gatherers, but genetic studies found that a piece of the puzzle was missing: some European DNA came from elsewhere.

To clear up the mystery, researchers in Germany and the US sequenced the full genetic code of nine ancient humans. Among them were a 7,000-year-old farmer from Germany and 7,000- to 8,000-year-old hunter-gatherers from Luxembourg and Sweden. The scientists then compared these genomes with DNA taken from more than 2,000 modern-day people from all over the world and with other ancient genomes.

They found that nearly all modern Europeans had a mixture of western European hunter-gatherer and early European farmer DNA, but with a good measure of ancient north Eurasian ancestry thrown in.

The north Eurasian DNA was identified from the 24,000-year-old remains of a young boy buried at Mal'ta near Lake Baikal in eastern Siberia.

"It became very clear that all Europeans have hunter-gatherer as well as early farmer DNA to varying degrees, but it was also very clear that something was missing here in the makeup of modern Europeans," said Johannes Krause, at the University of Tubingen's Institute for Archaeological Sciences.

The findings suggest that the arrival of modern humans into Europe more than 40,000 years ago was followed by an influx of farmers some 8,000 years ago, with a third wave of migrants coming from north Eurasia perhaps 5,000 years ago. Others from the same population of north Eurasians took off towards the Americas and gave rise to Native Americans.

Modern Europeans are various mixes of the three populations. Sardinians are more than 80% early European farmer, with less than 1% of their genetic makeup coming from the ancient north Eurasians. In the Baltic states such as Estonia, some modern people are 50% hunter-gatherer and around a third early European farmer.

The modern English inherited around 50% of their genes from early European farmers, 36% from western European hunter-gatherers, and 14% from the ancient north Eurasians. According to the study, published in Nature, modern Scots can trace 40% of their DNA to the early European farmers and 43% to hunter-gatherers, though David Reich, a senior author on the study at Harvard University, said the differences were not significant.

In the absence of writings from ancient times, researchers are left with only archaeology, palaeontology and genetics to understand our distant pasts. "The genetics can tell us a bit about who these people were, how they interacted, where they came from, what their subsistence strategy was, and whether they had adaptations to their environment and diet," said Krause.

"The neolithic revolution spread agriculture across the continent in a couple of thousand years. Suddenly you have settlements that cover square kilometres, large cemeteries, large population increases. Suddenly the whole of central Europe becomes deforested because people are clearing it to make fields and produce crops. Everything changes and we don't have any historical information about that. We can look at the archaeology, but we can also look at the genes. They tell us how all those people are related, and you can't tell that from staring at a skeleton."

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