Neanderthals And Europeans Had Sex, Scientists Confirm Using Human Genome Study

By Ben Wolford on April 8, 2014 11:12 AM EDT

This is the skull of a Neanderthal who lived about 30,000-50,000 years ago in Europe, on display at the American Museum of Natural History. (Photo: Wikimedia Commons)

This is the skull of a Neanderthal who lived about 30,000-50,000 years ago in Europe, on display at the American Museum of Natural History. (Photo: Wikimedia Commons)

Geneticists in Europe say they've confirmed beyond doubt what mounting evidence already suggests: that early European humans had children with Neanderthals. Their study, to be published this week in GENETICS, "allows us to conclusively reject" an alternate theory that humans and Neanderthals evolved from the same subpopulation, they said. Their genome analysis also indicates that modern Europeans and Asians inherited more Neanderthal DNA than previously thought.

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"Our approach can distinguish between two subtly different scenarios that could explain the genetic similarities shared by Neandertals and modern humans from Europe and Asia," Konrad Lohse, a population geneticist at the University of Edinburgh, said in a statement Tuesday. Lohse wrote the paper along with Laurent A. F. Frantz, of the Wageningen University in The Netherlands.

Scientists began reimagining human origins when, in December, geneticists sequenced the most complete Neanderthal genome yet. In a related paper published in Nature, the researchers argued that modern non-African humans share between 1.5 and 2.1 percent of their DNA. Neanderthals are genetically distinct enough from modern humans to earn them their own species designation, Homo neanderthalensis. They lived among Homo sapiens in Europe, the Middle East, and central Asia as recently as 28,000 years ago before either going extinct or being incorporated into the modern human species.

Already, scientists knew that Neanderthals probably behaved similarly to humans. According to the Smithsonian Institution, they used "tools, controlled fire, lived in shelters, made and wore clothing, were skilled hunters of large animals and also ate plant foods, and occasionally made symbolic or ornamental objects." They may have even buried their dead and placed flowers on their graves. Another study of a special bone needed for complex speech bolstered the idea that Neanderthals could talk like humans.

Recently, even more research has emerged linking the two species. Some humans may have inherited extra fat from Neanderthals. And scientists have pinpointed several genetic traits (and problems like Crohn's disease) that may have been passed down from the Neanderthal version of those DNA.

But even as this genetic evidence grew, there was an alternate explanation for it that wouldn't require inter-species sex. After the first humans migrated out of Africa, proponents of this theory said the same genetic traits could have been inherited in modern humans from a common ancestor to both humans and Neanderthals. In other words, Neanderthals and humans could simply be two branches of the same stem.

This new research attempted to close that gap by using a different kind of genetic testing they had previously developed with rare species of European insects and Southeast Asian pigs. They compared the genome of a Neanderthal, a European human, an African human, and a chimpanzee. "The method makes maximum use of the information contained in individual genomes," Lohse said. In their paper, the authors wrote: "Our analysis allows us to conclusively reject a model of ancestral structure in Africa and instead reveals strong support for Neandertal admixture in Eurasia at a higher rate (3.4 percent-7.3 percent) than suggested previously."

Mark Johnston, the editor of the journal GENETICS, said, "This work is important because it closes a hole in the argument about whether Neandertals interbred with humans. And the method can be applied to understanding the evolutionary history of other organisms, including endangered species."

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