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Study Finds Genetic Continuity Among Ancient Xinjiang Populations Alongside Influx From Other Groups

NEW YORK — Using a range of ancient DNA samples, researchers have unraveled the genetic population history of Xinjiang, finding stretches of genetic continuity over time despite an influx of other ancestries.

Xinjiang in northwest China lies in a key region connecting east and west Eurasia where people and goods historically traveled along the Silk Road. By sequencing more than 200 ancient genomes from more than two dozen sites across Xinjiang that dated back to the Bronze Age, Iron Age, and the historical era, researchers from the Chinese Academy of Sciences pieced together how the genetic ancestry of the population there changed over time.

As they reported in Science on Thursday, the researchers found that Bronze Age residents of the region had ancestry linked to both western Steppe cultures and Central Asian populations, while later Iron Age residents of Xinjiang had increasing ancestry associated with East Asian groups. Still, there has been genetic continuity in the region, the researchers found.

"What is striking about these results is that the demographic history of a crossroads region as Xinjiang has been marked not by population replacements, but by the genetic incorporation of diverse incoming cultural groups into the existing population, making Xinjiang a true 'melting-pot,'" senior author Fu Qiaomei from the Chinese Academy of Sciences said in a statement.

The researchers generated genome-wide data for 201 ancient individuals who hailed from the Bronze Age, Late Bronze Age, Iron Age, and the historical era of less than 2,000 years ago. Of these samples, 40 came from northern Xinjiang, 105 from the western part of the region, three from central, three from eastern, and one from an unknown subregion of Xinjiang. About a dozen samples additionally underwent shotgun sequencing.

There have been two main theories describing the origins of Bronze Age Xinjiang residents, the researchers noted. One suggests that the region in that time was settled by people from the Afanasievo Steppe culture from the north, while the other posits people from the Bactria-Margiana Archaeological Complex (BMAC) culture to the west settled there.

In their analyses, the researchers uncovered evidence supporting both hypotheses. Bronze Age individuals from Xinjiang had four major ancestries derived from populations associated with the local Tarim Basin mummies as well as the Afanasievo, Northeast Asian, and BMAC populations. A recent Nature study found that the Tarim Basin mummies, in turn, appeared to be related to Ancient North Eurasians, who lived in southern Siberia about 25,000 years ago.

Late in the Bronze Age, Xinjiang residents had a higher level of Central Asian BMAC-related ancestry, which the researchers said likely reflects an influx of people through the Inner Asian Mountain Corridor.

The researchers also noted that some of the Bronze Age individuals they studied had unmixed ancestry linked to the Afanasievo, an Indo-European group. This coincides with the timing of when the Tocharian language — an Indo-European language — was introduced into Xinjiang.

In the Iron Age, residents of Xinjiang, though, had an increase in Steppe-related ancestry as well as East Asian ancestry. The portion of East Asian ancestry increased along a west-to-east cline, with increasing amounts of East Asian ancestry to the east. Genetic ancestry linked to the Sakas, a nomadic group with links to Indo-Iranians, also emerged among Iron Age residents of Xinjiang.

In more recent historical times, the inhabitants of Xinjiang have harbored similar genetic ancestry as the Iron Age population. This, the researchers noted, reflects two periods of genetic continuity in Xinjiang: from the Bronze Age to the Iron Age and from the historical era to the present day.

"With the widespread population movements documented in the study, it is intriguing to see the degree of genetic continuity that has been maintained in Xinjiang over the past 5,000 years," first author Vikas Kumar from the Chinese Academy of Sciences said in a statement.