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Ice Age European History Refined With Ancient DNA Sequences

NEW YORK – A pair of new studies has spelled out ancient European population patterns going back some 30,000 years to the Upper Paleolithic period, providing a more refined view of human migrations and interactions, along with the southern locations used to survive the peak of the Ice Age, known as the Last Glacial Maximum (LGM).

For the first of these studies, published in Nature on Wednesday, researchers did enrichment capture sequencing on 116 ancient hunter-gatherer individuals going back 5,000 to 35,000 years from sites spanning more than a dozen present-day countries in western or central Eurasia. These sequences, along with those from another 240 ancient hunter-gatherer individuals analyzed for past studies, made it possible to tease out ancestry profiles found in different parts of the continent over time.

"The data we gained from this study provides us with astonishingly detailed insights into the developments and encounters of West Eurasian hunter-gatherer groups," co-first and co-corresponding author Cosimo Posth, a researcher affiliated with the University of Tübingen and the Max Planck Institute for Evolutionary Anthropology, said in a statement. "Further interdisciplinary research will clarify which exact processes were responsible for the genetic replacements of entire Ice Age populations."

When the team considered Upper Paleolithic representatives sampled from 24,000 to 32,000 years ago from sites with weapons, art, and other archaeological features consistent with the Gravettian culture, it saw distinct ancestry in Gravettian individuals from western and southwestern Europe compared to individuals from groups with similar Gravettian artifacts at sites in central and southern Europe.

The researchers found that that western-southwestern Gravettian ancestry turned up in individuals from the Solutrean and subsequent Magdalenian cultures in southwestern Europe. Together with their other data, such results suggested western hunter-gatherer individuals waited out the LGM of the Ice Age from 19,000 to 25,000 years ago in a region that is now southern France, Spain, and Portugal.

In contrast, the researchers did not see such ancestry persistence for pre-LGM groups in Italy after the Ice Age, arguing against the notion the Italian peninsula served as an Ice Age refuge for Gravettian culture hunter-gatherers. Instead, post-LGM individuals from an Epigravettian cultural group showed ancestry ties to the Balkans, potentially arriving in Sicily by way of northern Italy.

"In conclusion, our study reveals that western and southwestern Europe served as climatic refugia for the persistence of human groups during the coldest phase of the Ice Age," the authors wrote, "whereas populations in the Italian peninsula and the eastern European plain were genetically overturned, challenging the role of these regions as glacial refugia for humans."

The team's analyses suggested that the Epigravettian group, in turn, was ancestral to individuals who migrated from Italy to other parts of Europe roughly 14,000 years ago as the climate became more favorable, ultimately replacing individuals from the Magdalenian culture in other parts of Europe.

The researchers' results suggested western- and eastern-European hunter-gatherer groups remained isolated until roughly 8,000 years ago, when genetically distinct European hunter-gatherer groups met and mixed, potentially due to migrations spurred by the arrival of agricultural groups from Anatolia.

"It is possible that the migration of early farmers into Europe triggered the retreat of hunter-gatherer populations to the northern edge of Europe," senior and co-corresponding author Johannes Krause, a researcher at the Max Planck Institute for Evolutionary Anthropology's archaeogenetics department, said in a statement. "At the same time, these two groups started mixing with each other, and continued to do so for around 3,000 years."

In a related study appearing in Nature Ecology & Evolution on Wednesday, members of the same team turned to targeted capture sequencing to assess more than 1.2 million SNPs in 16 ancient individuals found at sites in southern Spain's Andalusia region — a group that included an individual dated to 23,000 years ago during the LGM.

The individual, dubbed Malalmuerzo (MLZ) based on the Cueva del Malalmuerzo site in Granada, Spain, where the remains were found, appeared to have ancestry linking western European groups from before and after the peak of the Ice Age, consistent with the notion that Iberia served as a climate refuge during this time.

In particular, the MLZ representative shared genetic features with a previously sequenced 35,000-year-old individual from a Belgian cave site known as Goyet, who appeared to be part of a so-called Aurignacian culture.

"The MLZ lineage contributed substantially to post-LGM Magdalenian-associated individuals, which attests to genetic continuity in western Europe that spans the LGM," the authors reported, noting that southern Iberia "retained a higher proportion of [hunter-gatherer] ancestry related to Solutrean- and Magdalenian-associated individuals than other regions of the peninsula."

Ludovic Orlando, a researcher with Paul Sabatier University's Centre for Anthropobiology and Genomics of Toulouse, discussed findings from the new studies in a corresponding News and Views article appearing in Nature, touching on the importance of bringing in as many lines of evidence as possible to understand past population origins, interactions, and migrations.

"The European continent has a long tradition of archaeology, where excavation methods were developed in the early 19th century. It is therefore not surprising that this continent is also the best characterized archaeologically, with extensive genomic time series now extending from the present day to the Upper Paleolithic (50-12ka)," Orlando wrote.

"The resulting resources and increased understanding of the human past should be commended," he explained, "but are also an invitation to redouble efforts outside Europe, to avoid developing a Eurocentric vision of human prehistory."