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Sequencing Study Shines Light on Population Dynamics Spanning Copper Age in Western Eurasia

NEW YORK – New research on ancient DNA samples spanning the Neolithic, Copper, and Early Bronze Age has spelled out population events that accompanied the spread of farming and subsequent shifts to pastoralist lifestyles in western Eurasia.

"Our study highlights the importance of integrating archaeological evidence on the socio-economic background of individuals and cultures under study in order to better understand the drivers and push/pull factors of the genetic transformations we observe," Wolfgang Haak, an archaeogenetics researcher at Max Planck Institute for Evolutionary Anthropology, said in an email.

For a paper published in Nature on Wednesday, Haak and his colleagues used targeted enrichment sequencing to profile 1.24 million SNPs across the genome in 135 Neolithic, Copper Age, and Early Bronze Age individuals found at eight sites in western Eurasia, including 113 individuals with new radiocarbon dating.

The researchers explained that sites in western Eurasia underwent technological transitions ranging from horse domestication to the use of wagons and metallurgy during the time period between the spread of farming some 8,000 to 9,000 years ago and a post-Copper Age pastoralist expansion going back more than 5,300 years. However, the series of events and interactions that prompted Copper Age settlements to dwindle are less clear.

"We document the contact between late farming and early pastoralist societies through clear signals of admixture in Eneolithic [Neolithic to Bronze Age transition] individuals from the contact zones between the eco-geographic regions," Haak said.

Along with published genetic data for more than 1,200 ancient and modern individuals from 77 populations from present-day sites such as Ukraine, Lithuania, Latvia, Turkey, Russia, and the Caucasus, the new SNP data pointed to genetic stability in populations from the Neolithic and Copper Age.

"The genomic data from the Copper Age individuals across many tell [Copper Age] settlement sites is largely homogeneous, which mirrors the homogeneity in archaeological material culture across a relatively large region of southeastern Europe," Haak explained. "It also tells us that this network of contact, trade, and exchange must have been relatively stable over many centuries (at least 500 years)."

Even so, the team's analyses suggested populations found in the northwestern Black Sea region after about 6,500 years ago had ancestry from both Copper Age and forest/steppe zone populations, consistent with a rise in settlements in the northwestern forest/steppe zone and related lifestyle changes after the Copper Age.

"We propose that the transfer of critical innovations between farmers and transitional foragers/herders from different ecogeographic zones during this early contact was integral to the formation, rise, and expansion of pastoralist groups around 3300 BC," the authors wrote, adding that "[f]urther integrated archaeogenomic studies are needed to disentangle the dynamics at play around the Black Sea during the formative periods of the admixture clines demonstrated in this study."