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May 2, 2016

Analysis unlocks genetic secrets of Ice Age Europe

A new genetic analysis of prehistoric humans has led to the discovery of two significant shifts in population across Europe, both of which were linked to the end of the last Ice Age, researchers at Harvard Medical School reported in Monday’s edition of the journal Nature.

As part of their new study, Howard Hughes Medical Institute Investigator David Reich and his colleagues found that, as the ice sheet began to retreat and the Ice Age grew less intense roughly 19,000 years ago, prehistoric humans from southwest Europe repopulated the continent.

Then, in a separate event some 5,000 years later, humans from the southeast (including Turkey and Greece) spread into Europe and displaced the previous group. The study sheds new light on how human populations migrated and evolved during the era spanning from 45,000 years ago to 7,000 years ago by providing never-before-seen genomic data from the period.

Previously, there were only four samples of prehistoric European modern humans available for analysis, which Reich compared to “trying to summarize a movie with four still images.” Thanks to his team’s work, however, they now have access to 51 samples, which allows them to “follow the narrative arc” and “get a vivid sense of the dynamic changes” that occurred over time.

“What we see,” he said in a statement, “is a population history that is no less complicated than that in the last 7,000 years, with multiple episodes of population replacement and immigration on a vast and dramatic scale, at a time when the climate was changing dramatically.”

DNA analysis reveals two expansion events, mixing with Neanderthals

Based on the DNA analysis, the authors concluded that, starting 37,000 years ago, Europeans all came from a single founding population that was able to survive through the Ice Age. However, this group included different branches from different regions of the continent, including one that is represented from a Belgium population apparently displaced some 33,000 years ago.

About 19,000 years ago, a population related to this Belgium branch was able to once again re-expand throughout Europe, Reich explained. Based on the DNA evidence, he believes that this group may have expanded from the southwest, near modern-day Spain, after the Ice Age reached its peak. Then, 14,000 years ago, there is a second expansion event that takes place, he said.

“We see a new population turnover in Europe, and this time it seems to be from the east, not the west,” the Harvard researcher said. “We see very different genetics spreading across Europe that displaces the people from the southwest who were there before. These people persisted for many thousands of years until the arrival of farming.”

Reich and his colleagues Svante Pääbo and Johannes Krause also detected some intermingling with Neanderthals as modern humans spread throughout Europe some 45,000 years ago. These discoveries were made possible by a technique in-solution hybrid capture enrichment, which enabled them to extract and study DNA from ancient human remains without fear of the samples being contaminated by anyone who had previously handled the specimens.

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Image credit: Martin Frouz and Jií Svoboda