Ancient DNA study reveals population history of western Tibetan Plateau

According to a study published in Contemporary Biology May 22, the genetic components of the ancient populations on the western Tibetan Plateau are closest to the ancient populations on the southern Tibetan Plateau, and their major genetic components have been preserved over the past 3,500 years. Moreover, these ancient populations on the western Tibetan Plateau had complex and frequent interactions with ancient populations both inside and outside the plateau.

The study was carried out by the team of Prof. Fu Qiaomei from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences and archaeologists from the Tibet Institute for Cultural Relics Conservation and Research and other institutions.

Located in the western part of the Tibetan Plateau, Ngari Prefecture is a crossroads connecting the Tibetan Plateau, South Asia, and Central Asia and a potential migration channel for early human populations. Previous research confirmed that genetic components related to Central Asian populations influenced the area about 2,300 years ago, but the genetic history of earlier populations in the area was unclear.

In this study, researchers sequenced whole-genome nuclear data from a total of 65 individuals from six sites dating from 3,500 to 300 years ago in Ngari Prefecture. The newly sequenced data covers six archaeological sites, including Gebusail, Laga, Sangdalongguo, Pulanduowa, Qulongsazha and Guge Ganshi Cave.

By combining recently sequenced data with previously published ancient genomic data, the evolutionary history of populations on the western Tibetan Plateau over the past 3500 years has now been reconstructed.

This study is a systematic, long-term genomic study of ancient populations on the western Tibetan Plateau. According to the researchers, it is of great importance for a deeper understanding of the history of interactions between the ancient populations of the Western Plateau and the ancient populations on the Plateau and in neighboring South Asia and Central Asia.

Genetic characteristics of ancient populations of the Western Plateau and their interactions with ancient populations on the Plateau

Previously, understanding of the genetic history of the ancient populations of the Western Plateau was extremely limited. Based on a single site dated to 2,300 years ago, the researchers speculated that genetic influence occurred between Western Plateau populations and Central Asians. However, the specific time, place and extent of this influence were not known.

In this study, the researchers reconstructed the evolutionary history of the Western Plateau population over thousands of years using genetic information from various ancient Tibetan populations.

They showed that the ancient Ngari populations of 3500 years ago had genetic components similar to those of the southern plateau and did not carry additional genetic components from Central Asia or South Asia.

This genetic composition has been stably maintained in northwestern Ngari prefecture for more than a thousand years: The genetic composition of the late Gebusailu and Laga populations from 2,300 years ago is almost the same as that of the Gebusailu population from 3,500 years ago.

In other words, the Ngari population in this period mainly carried the genetic components of the ancient southern plateau populations, while genetic components from Central Asia and South Asia were introduced much later.

Then, starting 2,300 years ago, Central Asian components appeared in some places in northwestern Ngari Prefecture, but until 150 years ago, the proportion of Central Asian components was still less than 15%. Overall, local Ngari genetic components remained dominant between 3,500 and 150 years ago.

The researchers also found complex population interactions and migrations within the plateau. The genetic components of the ancient populations in the southern and western parts of the plateau 3500 years ago were very similar, suggesting that migration and population expansion from the south to the west may have occurred earlier.

Moreover, compared to the population in the northwestern Ngari, the populations from 1,800 to 1,600 years ago from the Kongque River to the upper reaches of the Xiangquan River in the southeastern Ngari were further influenced by ancient populations from the southern plateau. This suggests that the southern plateau people may have begun to expand westward again before the Tubo Empire expanded westward in the early 7th century.

In short, the interactions between the ancient populations of the southern and western plateaus were much more complex than is recorded in historical documents. As early as 1,800 years ago, there were multiple migrations of people from east to west between these two places, and a gradient of genetic components introduced by the expansions can be observed in these populations from east to west.

Interactions between ancient populations on the Western Plateau and off the Plateau

Although Central Asian components began to influence some Ngari populations about 2,300 years ago, the proportion of Central Asian components in the genomes of these populations is low (<5%).

On the one hand, these results provide genetic evidence of cultural interactions between ancient populations on the plateau and ancient populations in neighboring Xinjiang, Central Asia, and South Asia. On the other hand, they also reflect that such cross-plateau cultural interactions were accompanied by limited population migrations or mixings.

Beginning 2000 years ago, genetic components related to South Asia also influenced the area of ​​Ngari Prefecture. Interestingly, the South Asian-related genetic components that influenced the ancient Ngari populations originated from admixed populations that settled in Central Asia. These populations are genetically related to Central Asians, but are culturally typical South Asians. Previous research suggested that they were immigrants from the Indus Valley Civilization who settled in Central Asia.

This is the first identification of South Asian-related genetic components in ancient populations on the Tibetan Plateau, providing clues to interactions between ancient populations on the plateau and those related to the Indus Valley Civilization.

In the 9th century AD, with the decline of the Tubo regime, descendants of the Tubo royal family established the Kingdom of Guge in what is now Ngari Prefecture. The Guge kingdom collapsed only in the 17th century AD. As a continuation of the Tubo lineage, the Guge population is an important window into the genetic characteristics of the last Tubo people.

An ancient human sample collected by researchers from Guge Cave showed the influence of Central Asian populations, and the proportion of Central Asian components was as high as 31%. This admixture is estimated to have occurred around 1353 AD, coinciding with the prosperity of the Guge Kingdom.

This new result shows that in addition to historical connections with South Asian kingdoms, the Guge kingdom also had population interactions with people from Central Asian kingdoms.

Kinship Practices in Early Western Plateau Communities

Researchers have also examined kinship among individuals from early Western Plateau sites. A second-generation family structure consisting of a father and two sons was discovered in the tomb of Gebusail, which dates back to 2,300 years ago.

At the same time, individuals at this site and at the 1,800-year-old Pulanduowa site were predominantly male, and the diversity of Y chromosome haplotypes is evidently lower than that of mitochondrial haplotypes, suggesting that paternal inheritance may have dominated both. .

The 1,600-year-old tomb of Qulongsazha includes a family line in which second- and third-generation descendants are related by maternal kinship, suggesting the role of maternal kinship in the family line. Combined with the sex ratio and paternal and maternal genetic diversity, this pattern reflects a relatively balanced paternal and maternal inheritance pattern.

However, this study is a preliminary survey of early Plateau kinship practices, and future research with more samples will shed more light on the details and diversity of the community structure of ancient Tibetans.

Due to the high altitude and harsh natural environment of the western Tibetan Plateau, anthropological and archaeological research in this area is relatively limited. In particular, large gaps exist in previous research on the evolutionary history of the early ancient populations of the western Tibetan Plateau and their interactions with ancient populations in neighboring regions.

Using a combination of genetics and archaeology, scientists have thoroughly explored the evolutionary history of ancient populations on the Western Plateau over the past 3,500 years. While the major genetic components of ancient western plateau populations show continuity, these populations had complex and frequent interactions with ancient populations in the adjacent southern plateau region, Central Asia, and off-plateau South Asia.

As the Tibetan Plateau is a bridge between East, Central and South Asia, the results of this study are important for understanding the genetics of ancient populations on the Plateau and the interactions of these populations with the ancient inhabitants of Central and South Asia.