Beginning 4,500 years ago, three very different Tibetan populations occupied the northeastern, south-central, and southern and southwestern regions of the plateau, but they carry a common gene that allows them to function in high, low-oxygen areas. This gene may have come from Denisovan man
The Tibetan Plateau, the highest and largest plateau above sea level, is one of the harshest environments inhabited by humans. It has a cold and arid environment, and its altitude often exceeds 4000 meters above sea level (masl). The plateau covers a large area in Asia - about 2.5 million square kilometers - and is home to more than 7 million people, who mainly belong to the Tibetan and Sherpa ethnic groups.
However, our understanding of their origins and history is lacking. Despite a rich archaeological record spanning the plateau, DNA sampling from ancient human remains has been limited to a small portion of the southwestern Himalayan plateau.
Now, a study published in the journal Science Advances On March 17th led by Prof. FU Qiaomei from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences filled this gap by sequencing the genomes of 89 ancient human remains dating back to 5100 BC from 29 archaeological sites spanning the Tibetan Plateau.
The researchers found that ancient humans who lived across the plain shared a single ancestry, originating from a Northeast Asian population that intermingled with a highly conflicted, but unstudied, human population.
According to Prof. Fu: "This pattern has been found in populations since 5,100 years ago, before the arrival of domesticated plants on the plateau," because the introduction of Northeast Asian origin into plains populations occurred before barley and wheat were introduced and was not related to nomadic farmers of wheat or barley.
A closer comparison across the plateau reveals different genetic patterns prior to 2500 BCE, indicating that three very different Tibetan populations occupied the northeastern, south-central, and southern and southwestern regions of the plateau, with the previously sampled plateau populations , belong only to the last group.
Different population dynamics can be seen in these three regions. Northeast populations dated to before 4700 BCE show an influx of additional Northeast Asian ancestry in lower elevation areas (~3000 meters above sea level) such as the Ganga Basin. However, this influx is not observed in higher populations (~4000 meters above sea level) sea level) dating back to 2800 BC only 500 km away.
An extended network of humans also lived along the Yarlong Tsangpu River, with common ancestry found in southern and southwestern populations dating to 3400 BC, western populations from Nagari County dating to 2300 BC, and southeastern populations from Nyingchi County from 2000 B.C. The extended influence of these populations shows the important role this river valley played in Tibetan history.
"Between these two groups, core populations prior to 2500 BC share a different origin than those to the north and south. However, samples of core populations after 1600 BC show that they share a closer genetic relationship with southern and southwestern populations. These patterns capture dynamism in human populations on the plateau," said Melinda Young, assistant professor at the University of Richmond and former postdoctoral fellow at - IVPP.
"While ancient plains populations show mainly East Asian ancestry, Central Asian influences can be found in some ancient plains populations," said Wang Hongru, a professor at the Shenzhen Institute of Agricultural Genomics and a former IVPP postdoctoral fellow. "Western populations show partial ancestry from Central Asia as early as 2300 BC, and a specimen dated to 1500 BC from the southwestern plateau also shows ancestry related to Central Asian populations."
Present-day Tibetans and Sherpas show much influence from lowland East Asian populations, with varying levels of gene flow correlated with longitude. This pattern is not observed in populations from earlier transects, including those dated to 1200–800 BC, suggesting that lowland East Asian gene flow was largely a product of very recent human migration.
Previous studies have shown that today's highland populations have a high frequency of a variant of the endothelial domain protein that enables adaptation to life at high altitudes and probably originates from a past mixing event with the archaic humans known as Denisovans. "Humans from this study show an archaic ancestry typical of lowland East Asia, but the oldest human dated to 5100 BC is homozygous for the adaptive variant," according to Prof. Fu. "Therefore, the arrival of this variant occurred before 5100 BC in the early population and became widespread in all the plateau populations".
Through their extensive spatial survey of ancient human DNA from the Tibetan Plateau, Prof. Fu and the lab team uncovered a Tibetan lineage that began at least 5100 years ago on the Tibetan Plateau. The ancient population spread rapidly, so that three regional groups show unique historical patterns that began to merge after 2500 BC.
"This is the largest study conducted in the field of ancient genetics at the Tibetan level so far," said LU Hongliang, a professor at Sichuan University. The new evidence in this study about the formation of unique components in the ancient populations from the Qinghai-Tibet Plateau relies heavily on the collaboration of many teams of archaeologists and geneticists. Prof. LU points out that "ancient DNA analysis allows us to go beyond the study of cultural interaction using only archaeological evidence, and to raise new ideas for archaeological research on the plateau."
Future sampling is still necessary, as the origin of the unsampled, deeply diverging ancestry found in all plateau populations is still unknown. In addition, it is still unknown when and where Elle EPAS1 The adaptation first penetrated the ancient Tibetan population.
But this study is a step in the right direction. "These genomes reveal a deep and varied history of humans at the Tibetan level." According to Prof. Fu "these findings provide us with a much better understanding of an important part of human history in Asia".
More of the topic in Hayadan:
- When did the first Tibetans live?
- The power of evolution: an old-new race of humans in the mountains of Tibet?
- Nobel Prize for Medicine to the Swede Svante Pavo, the discoverer of the Denisovan man and the decipherer of the genome of extinct human species
- The tip of a pinky, that's all the researchers from the Hebrew University needed to reconstruct what the Denisovan man looked like
