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Genetic studies show modern humans on Qinghai-Tibet Plateau 21,000 years ago

December 15, 2009

2009-12-14

KUNMING, Dec. 14 (Xinhua) -- 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 and known as
"the Roof of the World" in southwestern China, 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.

 From the perspective of genetic continuity studies, geneticists had
also attempted to find out when modern humans settled on the plateau by
determining the age of the ancient components found in the genes of
modern-day Tibetans.

"But due to few DNA samples of Tibetans, especially from Tibet, and lack
of distinguish ability in previous studies, geneticists found it hard to
judge whether Tibetans have ancient components in their genes," 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, including Tibet,Qinghai, Gansu,
Sichuan and Yunnan. Of those, 388 were sampled from Tibet.

"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.

"Unlike Tibetan matrilineal components inherited from north China
immigrants, 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.

Zhao and her group's article about the research will be published on a
leading science periodical, the Proceedings of the National Academy of
Sciences (PNAS) of the United States of America.

PNAS articles are usually published on-line before print, and Zhao's
article, "Mitochondrial genome evidence reveals successful Late
Paleolithic settlement on the Tibetan Plateau", can be found in the
on-line edition of PNAS.
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