The research was done on the Tibetan Plateau. Credit: Peiqi Zhang.
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, 120,000 years earlier than previous estimates for our species, according to a new paper by archeologists 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 archeological and genetic evidence provides essential 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 archeological 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, integrating the archeological and genetic discoveries so far. "Before our article, there was a lack of comprehensive review bringing both fields together, especially with an equal emphasis."
There are four periods of occupation.
Archeological investigations show that there were four major periods of occupation, beginning with Denisovans about 160,000 years ago and followed by three periods of humans who arrived around 40,000 years ago, 16,000 years ago and 8,000 years ago.
There are gaps between the occupation periods, based on archeological evidence. There is limited archeological work on the Tibetan Plateau. 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 was there before the end of the Ice Age and there were intermittent visits before that.
The occupation began 30,000 to 40,000 years ago.
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.
Trends in Ecology and Evolution is about dispersals and adaptation. There is a tree in the journal.
Trends in ecology and evolution are in a journal.
The first person to settle permanently on the Tibetan Plateau was Denisovans.
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