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."