Ancient DNA research reveals the population history of the Western Tibetan Plateau

According to a study published in Current biology on 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 for the past 3,500 years. Furthermore, these ancient populations on the western Tibetan Plateau had complex and frequent interactions with ancient populations within and outside the plateau.

The study was conducted 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 Conservation and Research of Cultural Relics and other institutions.

Ngari Prefecture, located in the western part of the Tibetan Plateau, is the junction connecting the Tibetan Plateau, South Asia and Central Asia, and a potential migration channel for early human populations. Previous research has confirmed that genetic components associated with Central Asian populations hit this region about 2,300 years ago, but the genetic history of earlier populations in this region was unclear.

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

By combining the recently sequenced data with previously published ancient genomic data, the evolutionary history of the populations on the western Tibetan Plateau over the past 3,500 years has now been reconstructed.

This study is a systematic, long-term genomic investigation of ancient populations on the western Tibetan Plateau. It is of great importance for the in-depth understanding of the history of interactions between ancient populations on the Western Plateau and ancient populations on the Plateau and in adjacent South Asia and Central Asia, the researchers said.

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

Previously, understanding of the genetic history of the ancient populations of the Western Plateau was extremely limited. Based on just one site dating back 2,300 years, researchers have speculated that genetic influence occurred between Western Plateau populations and Central Asians. However, the specific time, place and extent of this influence were unknown.

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

They showed that the ancient Ngari populations of 3,500 years ago had genetic components similar to the Southern Plateau populations 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 during this period mainly carried the genetic components of ancient populations on the Southern Plateau, while genetic components from Central Asia and South Asia were introduced much later.

Then, from 2300 years ago, Central Asian components appeared in some locations in northwestern Ngari Prefecture, but until 150 years ago the proportion of Central Asian components was still less than 15%. Overall, Ngari local genetic components remained dominant from 3,500 to 150 years ago.

The researchers also found complex population interactions and migrations within the plateau. The genetic components of ancient populations in the southern and western parts of the plateau were very similar 3,500 years ago, indicating that population migration and expansion from south to west may have occurred earlier.

Furthermore, compared to the population in northwestern Ngari, populations from 1,800 to 1,600 years ago from the Kongque River to the headwaters of the Xiangquan River in southeastern Ngari were further influenced by ancient populations from the Southern Plateau. This indicates that the people of the Southern Plateau may have begun to expand westward again before the Tubo Empire expanded westward in the early 7th century.

In summary, the interactions between the ancient populations of the Southern and Western Plateau were much more complex than recorded in historical documents. As early as 1,800 years ago, multiple east-west human migrations had occurred between the two places, and in these east-west populations a gradient of genetic components introduced by the expansions can be observed.

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 for the 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 admixtures.

From 2000 years ago, genetic components associated with South Asia also influenced the region of Ngari Prefecture. Interestingly, the South Asian genetic components that influenced ancient Ngari populations came from mixed 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 genetic components in ancient populations on the Tibetan Plateau, and provides clues to the 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 founded the Guge Kingdom in what is now Ngari Prefecture. It was not until the 17th century AD that the Guge kingdom collapsed. 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 the researchers from Guge Cave showed the influence of Central Asian populations, and the share of Central Asian components was as much as 31%. This mixing event is estimated to have occurred around 1,353 AD, coinciding with the prosperity of the Guge Kingdom.

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

Kinship practices in early western plateau communities

The researchers also examined the relationships between individuals from early western plateaus. At the Gebusailu tomb dating back 2,300 years, a second-generation family structure was discovered, consisting of a father and two sons.

At the same time, individuals at this site and the 1800-year-old Pulanduowa site were mainly male, and the diversity of Y chromosome haplotypes is clearly lower than that of mitochondrial haplotypes, indicating that both may have been communities dominated by paternal inheritance. .

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

Nevertheless, this study is a preliminary exploration of kinship practices on early plateaus, 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 rugged natural environment of the western Tibetan Plateau, anthropological and archaeological research in this region 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 adjacent areas.

Using a combination of genetics and archaeology, the researchers thoroughly investigated the evolutionary history of ancient populations on the Western Plateau over the past 3,500 years. Although the major genetic components of the ancient populations on the Western Plateau show continuity, those populations had complex and frequent interactions with the ancient populations in the adjacent Southern Plateau region, Central Asia, and South Asia outside the Plateau.

Because the Tibetan Plateau forms 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 those populations with ancient Central and Southern Asians.