20 December 2009
Modern humans colonized Tibetan plateau 21,000 years ago
Chinese scientists have found through genetic studies that modern humans had successfully colonized the Qinghai-Tibet Plateau in the Late Paleolithic Age, at least 21,000 years ago. The plateau, with an average altitude above 4,000 meters, is one of the most challenging areas in the world for human settlement due to its environmental extremes, such as extreme cold and low oxygen levels.
"Through Paleolithic era stone tools excavated from the plateau years ago, archaeologists believed human beings possibly inhabited the plateau 30,000 years ago," said Zhao Mian, a researcher from the Kunming Institute of Zoology with the Chinese Academy of Sciences. But, with the drastic drop of temperature on the Earth in the Last Glacial Maximum of the Late Paleolithic Age, about 23,000 years ago, many species could not adapt to the changes and died out, she said. "Scientists have been debating heatedly whether modern humans on the plateau had survived the adverse conditions," she said.
Led by her tutor Zhang Yaping, director of the the Kunming Institute of Zoology, Zhao and 14 other geneticists, including a German scientist, set up a research group three years ago. They collected 680 genome samples of genetic structure from Tibetans in several major Tibetan-populated areas. "Based on studies of their mitochondrial DNA genome variation, our results confirm the vast majority of Tibetan matrilineal components can trace their ancestry to Epipaleolithic and Neolithic immigrants from what is now northern China, or about 10,000 years ago, which accords with previous studies," Zhao said.
In genetic studies, mitochondrial DNA is a tool for tracking ancestry through females and has been used in this role to track the ancestry of many species back hundreds of generations. "Another significant finding was that researchers identified an infrequent novel haplo group, M16," she said. In human genetics, haplo groups can be used to define human beings' ancestral groups and genetic populations. "M16 branched off directly from the genetic components of the ancestors of modern Eurasians," Zhao said. "M16 has an ancient age of at least 21,000 years, based on calculations through various dating methods in genetics," she said. "Its nearly exclusive distribution in Tibetan populations and ancient age suggest that M16 may represent the genetic relics of the Late Paleolithic inhabitants on the plateau," she said. "We believe the research results give a relatively clear answer to the debate on when modern humans settled down on the Qinghai-Tibet Plateau successfully," she said.
Archaeologists have discovered Paleolithic human hand and footprints near Lhasa, the heart of the plateau, and reckoned they dated back about 20,600 years to 21,700 years, she said. "The age of the relics is close to that of M16, so we believe that supports our research results to some extent," she added.
Source: China View (14 December 2009)