Ancient Incest Uncovered in Neanderthal Genome

Data obtained from a Neanderthal woman's toe bone points to incest and inbreeding among early humans, an international genetics team reported on Wednesday.

The fossil's genetic map, or genome, reported from Denisova cave in Siberia's Altai Mountains dates to more than 50,000 years ago. The cave was home at separate times to both Neanderthals and the so-called Denisovans, two sister families of now-extinct early humans. (See also "New Type of Ancient Human Found.")

Adding to increasing evidence of a tangled human family tree, the new Neanderthal genome study released by the journal Nature also suggests that another previously unknown archaic human species shared its genes with some of our ancestors. The study authors suggest that it was Homo erectus, one of the earliest human species, which first arose around 1.8 million years ago. (See also "Why Am I a Neanderthal?")

The report, led by Germany's Kay Prfer of the Max Planck Institute for Evolutionary Anthropology in Leipzig, builds on recent prehistoric genetics results that argue against theories that modern humans arose completely from one "out of Africa" migration more than 60,000 years ago that spread worldwide without mating with other early humans.

Instead, it looks like early modern humans sometimes mated with archaic human cousins they met along the way. People of non-African origin broadly have genes that are 1.5 percent to 2.1 percent Neanderthal, according to the study, with proportions higher among Asians and Native Americans. Similarly, 5 percent of the genome of people of Australian and Papua New Guinea descent looks Denisovan, as does 0.2 percent of the genes of people from Asia.

"We don't have one ancestral group, but proportions of ancestral groups," says computational biologist Rasmus Nielsen of the University of California, Berkeley, who was not part of the study team. "I think they make a convincing argument."

"In my view, this paper heralds the completion of the Neanderthal genome project in terms of mapping an entire genome," says paleontologist and human origins expert Richard Potts of the Smithsonian's National Museum of Natural History in Washington, D.C. "That's pretty cool science."

Kissing Cousins

In 2010, the study's toe bone first turned up at Denisova Cave, where excellent fossil preservation conditions had allowed for the genetic mapping of the then-surprising Denisovan finger bone found in 2008. Gene tests showed the toe belonged to a Neanderthal, and Prfer and colleagues began calculating its full genetic map.

Photograph by B. Viola, MPI f. Evolutionary Anthropology

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Ancient Incest Uncovered in Neanderthal Genome