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Genomic Analysis of China's Bronze Age Tarim Basin Mummies Suggests Local Origins

Mummy

NEW YORK — The Tarim Basin mummies of modern-day northwestern China represent an ancient indigenous population, a new genomic analysis has found.

Three competing theories had been proposed to explain the origins of the Tarim Basin mummy population, which date back to the Bronze Age in what is now Xinjiang. One suggested that herders with west Eurasian ancestry moved into the region from southern Siberia, while another said that oasis farmers from southern Central Asia moved eastward. The third theory proposed the Tarim Basin population arose from agropastoral groups from the Tianshan and Altai mountains.

By generating genome-wide sequencing data on a dozen-and-half mummies from the region, an international team of researchers found that the Tarim Basin mummies instead appeared to be direct descendants of the Ancient North Eurasians, or ANE, a once-prevalent Pleistocene-era population. Additionally, the Tarim Basin population exhibited little genetic admixture with other groups but did adopt other cultural practices such as consuming dairy that suggested they were genetically but not culturally isolated.

"Archaeogeneticists have long searched for Holocene ANE populations in order to better understand the genetic history of Inner Eurasia. We have found one in the most unexpected place," Choongwon Jeong, a senior author of the study, appearing in Nature on Wednesday, and a professor at Seoul National University, said in a statement.

Hundreds of naturally mummified remains have been uncovered in the Tarim Basin since the 1990s, and Jeong and colleagues generated genome-wide sequence data for 13 mummies from the Tarim Basin dating back to the Early-Middle Bronze Age and from five Early Bronze Age mummies from the nearby Dzungarian Basin.

By comparing these individuals to other ancient and modern groups, the researchers found the Tarim Basin mummies were closely related to the nearby Dzungarian Basin mummies, but with certain differences. The older Dzungarian Basin individuals could be described by a three-way admixture marked by a majority of Afanasievo, or west Eurasian from southern Siberia, ancestry and a mix of local ancestries.

The Tarim Basin individuals, on the other hand, reflected the two ancient local ancestries: the ANE and the ancient Northeast Eurasians. The researchers noted that any modeling that included Afanasievo or other west Eurasian ancestry sources failed, rejecting the three previously posited theories for the origins of the Tarim Basin individuals.

The ANE population used to be more widespread, and the researchers suggested that a population bottleneck accounts for the predominance of ANE-related ancestry among the Tarim Basin individuals.

At the same time, the researchers examined the proteomes of dental plaque from seven Tarim Basin individuals. This analysis uncovered milk-specific proteins, including β-lactoglobulin, α-S1-casein, and α-lactalbumin, that could be traced to cattle, sheep, and goats. This finding indicated that they consumed dairy products and underscored the region as a site of cultural exchange.

"Despite being genetically isolated, the Bronze Age peoples of the Tarim Basin were remarkably culturally cosmopolitan — they built their cuisine around wheat and dairy from West Asia, millet from East Asia, and medicinal plants like Ephedra from Central Asia," co-senior author Christina Warinner from Harvard University and the Max Planck Institute for Evolutionary Anthropology added in a statement.

The researchers' findings raise additional questions, according to Paula Doumani Dupuy from Nazarbayev University in Kazakhstan. In a related commentary appearing in Nature, Dupuy wrote that outstanding questions include whether the Tarim Basin mummies' population arrived during the Bronze Age or earlier, as well as what knowledge or traditions they brought with them to the region.

"Zhang and co-workers have answered the question of the genetic origins of the Xiaohe culture," Dupuy wrote. "Now it is up to the collaborative input of scholars to further explain the dynamic and varied patterns of cultural exchange that define the Bronze Age of Inner Asia."

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