One of the last places to be populated by people in their migration around the globe is the Tibetan Plateau. Our extinct cousins, the Denisovans, reached the "roof of the world" about 160,000 years ago, which is 120,000 years earlier than previous estimates for our species, according to a new paper by archaeologists at the University of California, Davis.
The article, which was published online this month in the journal Trends in Ecology & Evolution, suggests that a cross-look at archaeological and genetic evidence can provide clues to reconstruct the history of the peopling of the region.
archaic hominins once existed throughout Asia. After several instances of interbreeding with early modern humans in the region, one of their hybridizations benefited Tibetans' survival and settlement at high altitudes.
Peiqi Zhang, a UC Davis PhD student who has participated in excavations of an archaeological site above 15,000 feet in Tibet, and Xinjun Zhang, a UCLA PhD student who studies Denisovan and other human genes, asked the question after seeing those conclusions. She earned her genetic anthropology doctorate at UC Davis. Two researchers are not related.
Two scholars conducted a review of evidence of human dispersal and settlement in the Tibetan Plateau. "Before our article, there was a lack of comprehensive review bringing both fields together, especially with an equal emphasis."
There are 4 periods of occupation.
The first major periods of occupation are believed to have begun around 160,000 years ago with Denisovans, followed by three periods of humans who arrived around 40,000 years ago and 8,000 years ago.
There are gaps between the occupation periods, based on archaeological evidence. The work on the Tibetan Plateau is very limited. We haven't found enough data to confirm the existence of continuous human occupation since the late ice age.
The first Denisovans were identified in 2010 after a girl's finger bone was found in a cave in the Altai Mountains. The haplotype she carried was similar to the EPAS1 gene, which improves oxygen transport in the blood. The EPAS1 gene is carried by most modern Tibetans.
The Denisovan was not determined if the mandible carried the same genes as the other one. "We don't know if the Denisovans are adaptive to the hypoxia of the Tibetan Plateau at this point," Peiqi Zhang said.
The biology and behavior of the Denisovans is not well known.
The people of Australia, New Zealand, Melanesia, Micronesia and Polynesia have different amounts of Denisovan DNA.
She said that it could mean that the interbreeding happened somewhere in Asia before the further subdivisions of local populations.
It happened more than once. "From the genetic studies, we can detect that all East Asians, including the Tibetans, interbred with two distinct Denisovan groups, with one of such events unique to East Asians and the other shared with other South Asians," said Xinjun Zhang.
The interbreeding event that is unique to East Asians happened somewhere in the lowland instead of on the plateau, and we have reason to believe that since all East Asians show the same patterns.
Two models of human occupation of the Tibetan Plateau are proposed as a framework for scholars that can be tested in the future.
It took about 9000 years for the area to settle after the end of the ice age.
30,000 to 40,000 years ago, continuous occupation began.
The EPAS1 haplotype could have been passed to modern humans about 48,000 years ago.
The main question is whether they're staying there all year-round, which would mean that they were adapted biologically to hypoxia. Did they just end up there by accident or did they just disappear?
It's not clear when Denisovans went extinct, but some studies suggest it was as late as 20,000 years ago. "Although we don't know if they were adapted to the high altitude, the transmission of some of their genes to us will be the game-changer thousands of years later for our species to get adapted to hypoxic environments," Zwyns said. That is a great story.
The Chinese Academy of Sciences in Beijing and the Brown University in Providence, Rhode Island are both involved in the project.
The National Institutes of Health supports Peiqi Zhang's research, as well as the Baldwin Foundation and the Leakey Foundation.
The story was told
The materials were provided by the University of California - Davis. The original was written by Kathleen. Content can be edited for style and length.
