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The oldest known humans in Europe have mated with Neanderthals surprisingly often

When some of the first human migrants to Europe encountered Neanderthals already living there about 45,000 years ago, connections flourished.

DNA analyzes found in human fossils at the time – the oldest known human remains in Europe – suggest that the cross between Homo sapiens and Neanderthals, which were on the verge of extinction, occurred more often than previously thought. two new studies suggest. Both reports appear on April 7 in Nature Ecology & Evolution.

Genetic evidence in the new reports indicates for the first time that different human populations arrived in Europe shortly after 50,000 years ago. Neanderthals have mixed with all the groups detected so far, ensuring that some of their genes live in our DNA today.

A team led by evolutionary geneticist Mateja Hajdinjak of the Francis Crick Institute in London, claims that the remains of three H. sapiens individuals unearthed in Bacho Kiro cave in Bulgaria have produced nuclear DNA containing Neanderthal contributions of 3 to 4 percent. The ancient DNA came from a tooth and two fragments of radiocarbon bone dated between about 43,000 and 46,000 years ago. Stone tools typical of humans of the last epoch have been found in the same sediment as fossils.

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“All of Bacho Kiro’s individuals had recent Neanderthal ancestors, from just five to seven generations in their family trees,” Hajdinjak says.

Other evidence of ancient mestizaje comes from an almost complete human skull discovered in 1950 in a cave in present-day Czech Republic. About 2 percent of the genes in the DNA of that fossil, identified as females, also come from Neanderthals, say evolutionary geneticist Kay Prüfer of the Max Planck Institute for Human History Science in Jena, Germany, and colleagues. Analysis of those DNA segments suggests that it also lived about 45,000 years ago.

H. sapiens fossils in Bulgaria and the Czech Republic are not the first to be found with pieces of Neanderthal DNA in their genome, but they are very likely to be the oldest. The long segments of Neanderthal DNA in Eastern European women, which would split into shorter segments in later human generations, suggest that she lived a few hundred to a few thousand years before a 45,000-year-old Siberian man who shared a 2.3 per cent. of their genes with Neanderthals (SN: 22/10/14). That discovery indicated that the crossing outside Europe dates back 60,000 years. And a Romanian man who lived about 40,000 years ago also possessed long stretches of Neanderthal DNA, indicating that he was separated from four to six generations of a Neanderthal relative (SN: 5/11/15).

Neanderthals became extinct about 40,000 years ago, although their genetic remains remain; today, non-African people carry, on average, almost 2 percent Neanderthal DNA. Today’s Africans have a small Neanderthal genetic legacy (SN: 30/01/20).

Taken together, new studies suggest that some of the first humans to enter Europe had a lasting impact on our DNA, while others reached the genetic dead. Bacho Kiro’s humans represent a newly identified population of ancient Europeans with genetic links to present-day East Asians and Native Americans, but not Western Eurasians, Hajdinjak’s group says. Like the ancient Romanian and Siberian men, the woman from the Czech Republic did not contribute genes to H. sapiens that she lived after about 40,000 years ago.

"It is remarkable that Bacho Kiro's discoveries may represent a population that stretched at least 45,000 years ago from Bulgaria to China," says evolutionary geneticist Carles Lalueza-Fox of the Barcelona Institute of Evolutionary Biology, who did not participate in neither of the two new research.

If H. sapiens and Neandertals mixed regularly as the latter population approached their extinction, then a relatively large number of incoming humans accumulated a surprising amount of DNA from smaller Neanderthal populations, Lalueza-Fox suspects. After 40,000 years ago, additional migrations to Europe of people with little or no Neanderthal ancestry would further dilute the Neanderthal DNA of the human gene set, he said.

Hajdinjak suggests that these humans made distinctive stone and bone tools and served as ancestors of modern Europeans. In the Bacho Kiro cave, for example, recently recovered DNA from a bone fragment of H. sapiens about 35,000 years old has a different composition from that of the first human inhabitants of the cave. This individual contributed genes primarily to later populations in Europe and western Asia, Hajdinjak says.

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