Early modern humans mated with Neanderthals and possibly other archaic hominid species from Asia at least 100,000 years ago, according to a new study that describes human remains from that period in South China.
The remains are the oldest modern human fossils in East Asia and predate, by over 60,000 years, the oldest previously known modern human remains in the region.
The fossils — a chin and related teeth — belonged to a modern human that also featured more robust Neanderthal-type characteristics, indicates the study, published in the latest Proceedings of the National Academy of Sciences.
Co-author Erik Trinkaus, who is one of the world's leading experts on Neanderthals, told Discovery News that the new findings mean "there was mating between these 'archaic' and 'modern' groups across Asia, and not just in Europe and the remainder of Africa."
"Of more interest than who had sex with whom is the fact that modern humans had spread across southern Eurasia by 100,000 years ago, and yet archaic humans remained across the more northern areas, and even displaced the modern humans in Southwest Asia for an additional 50,000-70,000 years," added Trinkaus, a professor of physical anthropology at Washington University in St. Louis. "It argues for very little adaptive advantage on the part of these modern humans."
He and his colleagues studied the newly discovered remains, which were unearthed at Zhirendong, a cave in Chongzuo City, Guangxi Zhuang Autonomous Region in South China. The fossils are well dated, based on isotopic analysis of the site and associated remains of now-extinct mammals and other animals.
Trinkaus and his team now believe that after anatomically modern humans first emerged in equatorial Africa, they either began to disperse into Asia 102,000 to 130,000 years ago, or gene flow through populations caused their biology to wind up in South China during the Late Pleistocene.
Either way, the researchers argue that modern human interbreeding with regional archaic populations, such as Neanderthals, must have happened.
In terms of what happened to the Asian Neanderthals, Trinkaus believes "that eventually they were partially absorbed into expanding modern human populations" around 40,000 years ago. He said, "We don't know why those modern humans expanded then, after remaining in Africa and southern Asia for 50,000 plus years."
It's also presently unclear why, despite the likely interbreeding, the various hominid populations in Eurasia, including our own, remained distinct for so long.
"This is the first paper to document that they did," Trinkaus said.
Fred Smith, chair of the Department of Sociology and Anthropology at Illinois State University sees the paper as "a major contribution to paleoanthropology."
"It is very important to have solid evidence concerning the appearance of the earliest modern people everywhere in the Old World," Smith said. "The Zhirendong mandible tells us that modern people appear far earlier in East Asia than many, including me, would have thought."
He concluded, "Hopefully this discovery will usher in more finds that will more completely tell the story of early modern humans in this part of the world."