When did the first Tibetans live?

By Jane Q, the article is published with the permission of Scientific American Israel and the Ort Israel network 07.05.2017

The first humans who ventured up to the Tibetan Plateau, often referred to as the "Roof of the World", encountered one of the harshest and most brutal living environments the human race has ever encountered. In this cold and arid region, which lies at an average altitude of 4,500 meters above sea level, the oxygen concentration reaches About half from its concentration at the sea. Although scientists have long believed that no one walked on this level until 15,000 years ago, genetic data and new archaeological findings suggest that this event occurred much earlier—perhaps even 62,000 years ago, in the middle of the last ice age. A better understanding of the history of migration to the region and the growth of the population there may help in uncovering the mystery surrounding the origin of the Tibetans. The findings may provide clues to explain how humans adapted to the low-oxygen conditions prevailing at these altitudes.

בA recently published article In the American Journal of Human Genetics, researchers reported how they were able to better and decipher the history of human settlement at the Tibetan level. They did this by determining the complete genetic sequence of 38 native Tibetans and comparing the results to the genomic sequences of people from other ethnic groups. "[The data analysis] revealed a complex patchwork of prehistoric migrations," he says Shuhua Shu, a population geneticist at the Shanghai Biological Sciences Centers affiliated with the Chinese Academy of Sciences. "The most surprising thing was to discover how ancient the DNA sequences unique to Tibetans are," says Shaw. "You can associate them with ancient fathers and mothers who lived 62,000 years ago and up to 38,000 years ago. These sequences probably represent the earliest settlement on the Tibetan Plateau.”

When the Ice Age intensified after the first migration, genetic mixing between Tibetans and non-Tibetan populations stopped for tens of thousands of years, indicating that the movement of humans into Tibet was reduced to a minimum. "The migration routes were probably blocked by blocks of ice," says Shaw. "It was just too hard for even the toughest hunter-gatherers." After the peak of cold has passed, the peak of the machine LGM, thousands of people began flocking to Tibet en masse in a wave of migration that began about 15,000 years ago and continued until about 9,000 years ago. "This is the most significant migration wave that shaped the modern Tibetan gene pool," says Shaw. This analysis fits well with several independent lines of evidence showing that 12,800 years ago to 8,000 years ago genetic mutations began to appear in Tibetan DNA that protected them from hypoxia, or lack of oxygen in the body.

Shaw's team was the first to fully sequence the Tibetan genome, and "the resolution of the sequence is very impressive," says the archaeologist. Mark Aldenderfer from the University of California, Merced, who was not involved in the research. According to him, the study "tells in detail how the genes of different populations, coming from different directions, were combined to eventually create the people we call Tibetans today." The results show that 94% of today's Tibetan genetic composition originates from modern humans, who may have migrated to Tibet in the second migration wave, and the rest of the genes came fromHominins that are extinct The modern part of the Tibetan genome reflects a mixed genetic heritage of people from different regions of Asia: 82% from East Asia, 11% from Central Asia and 6% from South Asia.

In addition, Shaw's team identified a DNA segment unique to Tibetans, very similar to the genome of the machine skeleton Adam Aust-Ishim (representing a population of modern humans who lived in Siberia 45,000 years ago) and to the genomes of several extinct human species, including Neanderthals, Denisovans and other unknown groups. The segment contains eight genes, one of which is known to be essential for adaptation to life at high altitude. Shaw suspects that a hybrid of all these human species may be the common ancestor of the population living on the Tibetan Plateau before the LGM.

The study also reveals a remarkable genetic continuity since humans first settled in the Tibetan Plateau. "This indicates that Tibet was always inhabited, even during times of the most severe climatic conditions," says Shaw. This idea contradicts the popular opinion that the early inhabitants of the plateau became extinct during the harsh climate periods, including the LGM period, says David Zhang, a geographer from the University of Hong Kong, who was not involved in Shaw's work. Aldenderfer and others argue that people may have found refuge in certain areas of the plateau and survived the Ice Age there. "There were many places that allowed [these early populations] to live in conditions that were not so harsh, such as in the valleys of the great rivers that cross the plateau," he says.

Another study, supporting the evidence that the population of Tibet is very ancient, was presented at the 33rd International Geographical Congress held in the summer of 2016 in Beijing, where a research team revealed the earliest archaeological evidence found so far for human presence on the Tibetan Plateau, from 39,000 years ago to 31,000 years ago. sleep. The site, located on the bank of the Selwyn River in the southeast of the Tibetan Plateau, is rich in stone tools and animal remains.

Different lines of evidence are therefore now converging and pointing to continuous human settlement on the Tibetan Plateau, which began much earlier than we thought until now, but parts of the annexation are still missing, Aldenderfer says. According to him, "more archaeological excavations are needed to fill these gaps."