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Ancient DNA Sequences Spell Out Population History in Eastern Eurasian Steppe Region

NEW YORK – An international team led by investigators at the Max Planck Institute for the Science of Human History has retraced population dynamics going back more than 6,000 years in the Eastern Steppe region of Eurasia using ancient genetic profiles.

"This study represents the first large-scale paleogenomic investigation of the Eastern Eurasian Steppe, and it sheds light on the remarkably complex and dynamic genetic diversity of the region," senior and co-corresponding author Christina Warinner, a researcher affiliated with the Max Planck Institute, Friedrich Schiller University Jena, and Harvard University, and her colleagues wrote.

As they reported in Cell on Thursday, the researchers used low-coverage shotgun sequencing on hundreds of tooth and petrous bone sample from 214 ancient individuals found at burial sites in the Eastern Steppe region. Samples ranged in age from around 600 years to more than 6,600 years and came from sites that are now located in Mongolia and Russia's Lake Baikal region.

The team analyzed the genome-wide sequence data in combination with already available sequences from present-day human populations, as well as previously published sequences for ancient individuals in northern Mongolia, Russia, and Kazakhstan. Along with insights on the age of the samples, the genetic sequences revealed a series of complicated interactions between individuals from different ancestral and cultural backgrounds in the Eastern Steppe — a region that has been less extensively profiled than its Western Steppe neighbor.

"While also covering parts of modern-day China and Russia, most of the Eastern Steppe falls within the national boundaries of present-day Mongolia," the authors explained. "Recent paleogenomic studies suggest that the eastern Eurasian forest steppe zone was genetically structured during the Pre-Bronze and Early Bronze Age periods, with a strong west-east admixture cline of ancestry stretching from Botai in central Kazakhstan to Lake Baikal in southern Siberia to Devil's Gate Cave in the Russian Far East."

By digging into samples from 85 sites in Mongolia and three sites near Lake Baikal, the researchers got a glimpse at Eastern Steppe population features that popped up during the Pre-Bronze Age, Bronze Age, Iron Age, and Early and Late Medieval periods.

"The population history of the Eastern Steppe is one marked by the repeated mixing of diverse eastern and western Eurasian gene pools," they wrote. "However, rather than simple waves of migration, demographic events on the Eastern Steppe have been complex and variable."

Their results suggested that hunter-gatherer individuals from the area were genetically related to hunter-gatherers from sites in the Russian Far East and western Baikal area around the same time, for example, together forming an "Ancient Northeast Asian" group.

The genetic data also pointed to an Early Bronze Age expansion of pastoralist herding populations from the Western Steppe into Mongolia, the team reported. By the Late Bronze Age, meanwhile, Mongolian populations were marked by ancestry from three different groups known for dairy pastoralism that mixed with one another in the lead up to the emergence of the Xiongnu Empire.

Fast-forwarding in time, the investigators uncovered a pronounced uptick in ancestry from eastern Eurasia in individuals from the so-called Mongol Empire that came to prominence in the Late Medieval Period. They noted that the ancestry of the Mongol group overlapped with ancestry found in current populations speaking Mongolic languages today.

Together, the study's findings illustrate "the complex interplay between genetic, sociopolitical, and cultural changes on the Eastern Steppe," the authors concluded, though they cautioned that "there is still a great need for further genetic research in central and eastern Eurasia, and particularly in northeastern China, the Tarim Basin, and the eastern Kazakh steppe in order to fully reveal the population history of the Eurasian Steppe and its pivotal role in world prehistory."