NEW YORK – A new ancient DNA analysis has highlighted the genetic diversity and range of ancestry groups present on the Mongolian steppe thousands of years ago. The findings shore up the notion that a nomadic, imperial group ruled a region spanning the Eastern Eurasian steppe during the Iron Age from more than 1,900 years ago to around 2,200 years ago.
"We wanted to know how such genetic diversity was structured at different social and political scales, as well as in relation to power, wealth, and gender," Juhyeon Lee, a biological sciences researcher at Seoul National University and co-first author of a paper published in Science Advances on Friday, said in a statement.
After using shallow shotgun sequencing to screen ancient samples, researchers from SNU, the Max Planck Institute for Evolutionary Anthropology, Harvard University, and elsewhere turned to targeted capture sequencing to profile more than 1.2 million ancestry informative SNPs in samples from 18 representatives from the Xiongnu Empire, which was previously shown to have diverse ancestry stemming from both eastern and western pastoralist populations.
The Xiongnu era samples came from two cemeteries in western Mongolia: the Takhiltyn Khotgor (TAK) cemetery, a burial site for aristocratic individuals, and the Shombuuzyn Belchir (SBB) cemetery, where local elite individuals appeared to be buried.
"Most identified graves of the late Xiongnu period are shaft pits set beneath thick stone rings on the surface. These conspicuous burials represent the vast network of regional and local elites of Xiongnu society, while commoners were likely buried under less conspicuous stone piles or in unmarked pits," the authors wrote in their paper, noting that "uppermost aristocratic ruling elites of the empire were buried in large square stone tombs often flanked by satellite burials of lower-status individuals, forming a mortuary complex."
When the team analyzed the sequences in combination with array-based SNP patterns for other ancient and modern-day individuals in Mongolia and beyond, for example, it identified a range of genetic diversity patterns that appeared to track with individuals' status within the ancient Xiongnu population despite high overall diversity.
"[I]ndividuals with the lowest status (based on grave form and mortuary remains) have the highest degree of genetic heterogeneity," the authors reported. "In contrast, higher-status individuals are less genetically diverse and have high levels of eastern Eurasian ancestry."
Together, this "suggests the existence of an aristocracy in the Xiongnu empire," they explained, adding that these and other results suggested "elite status and power was concentrated within specific subsets of the broader population."
By combining genetic, archaeological, and other clues, the team also got a look at status among women and children in Xiongnu society. In particular, the elaborate elite tomb monuments and grave items at sites where aristocratic women were buried were consistent with archaeological and other evidence of high female status, while analyses of burial sites for children suggested that boys likely began taking on hunter- or warrior-type roles at around the age of 11 or 12 years old.
"Children received differential mortuary treatment depending upon age and sex, giving clues to the ages at which gender and status were ascribed in Xiongnu society," Christina Warinner, with the Max Planck Institute for Evolutionary Anthropology and Harvard University, said in a statement.