Connected Across the Ice Age
AAround 30,000 years ago, Europe was a cold and difficult place to live. Small groups of hunter-gatherers moved across a landscape shaped by the Ice Age, and the people of this period are associated by archaeologists with a way of life known as the Gravettian culture. This culture flourished across much of the continent from roughly 34,000 to 25,000 years ago. Evidence from archaeological sites had long suggested that Gravettian groups maintained contacts over great distances. Studying their genes is far from easy, because human remains from this period are rare and the DNA they contain is often poorly preserved. Yet when geneticists began to study ancient DNA from this period, the picture they produced seemed rather different.
BEarlier genetic research pointed to two fairly distinct ancestral groups, one in the east of Europe and one in the west. On this view, people in the two halves of the continent had remained largely separate from one another. A new study, published in the journal Science Advances, now challenges that interpretation. The work was led by researchers in the Department of Evolutionary Anthropology at the University of Vienna, with Pere Gelabert as first author and Ron Pinhasi as senior author. By analysing new genetic material and combining it with DNA that had already been published, the team was able to look again at how these early Europeans were related.
CThe most important new evidence comes from Isturitz Cave in southwestern France. There, the remains of a woman who lived about 30,000 years ago produced the oldest genome-wide dataset yet obtained from a modern human in southwestern Europe. Most of her ancestry was western European, as might be expected from her location. However, part of it was linked to populations in central and eastern Europe. Using the patterns in her DNA, the researchers estimated that this mixing of eastern and western ancestry had taken place between about 32,500 and 31,500 years ago. A second individual, from Ormesson, also in France, showed a similar genetic signature, suggesting that the Isturitz woman was not an isolated case.
DThe study also sheds light on what happened during the harshest part of the Ice Age. This period, known as the Last Glacial Maximum, was the time when the great ice sheets reached their largest extent. Evidence from Chufín Cave in northern Spain indicates that western European ancestry continued in the southwest of the continent for a long time. Combined with other evidence from the region, the results suggest that this ancestry survived through the Last Glacial Maximum itself. This supports the idea that the Iberian Peninsula acted as a refuge, a place where people could survive some of the coldest conditions of the Ice Age.
EOne of the most remarkable results did not come from a skeleton at all. At El Mirón Cave in Cantabria, northern Spain, the team examined a layer of sediment about 22,000 years old that contained no human bones or teeth. Even so, they were able to recover human nuclear DNA directly from the sediment. This genetic material was sufficient to identify the ancestry of the people who had once occupied the site. The technique, known as sedimentary DNA analysis, makes use of the fact that genetic traces left in cave floors can survive for thousands of years. Its great advantage is that it allows researchers to connect an archaeological layer with a particular genetic ancestry even when no human remains have been found.
FThe researchers also studied a male fetus from southern Italy, known as Ostuni1b. His mother had been examined in a previous study, and the new analysis showed that his father probably came from the same ancestral population. Importantly, however, the two parents were not closely related to each other. For small communities, choosing partners who are close relatives can lead to inbreeding, which may harm the health of later generations. The researchers suggest that the mating patterns of these Ice Age groups may have helped them to limit this risk.
GTaken together, the findings suggest that the populations of eastern and western Europe were less genetically isolated than scientists had assumed. As first author Pere Gelabert put it, the two populations "were not as genetically isolated as previously assumed." People, and the genes they carried, appear to have moved across the continent more often than earlier studies implied. The team now plans to combine sedimentary DNA with proteomics, the study of ancient proteins, which can provide further clues about past life. They hope to use these methods to investigate the earliest spread of modern humans across Europe. They also want to learn how these people interacted with carnivores in places where organic remains are scarce.