With the largest dataset of prehistoric European hunter-gatherer genomes ever generated, an international research team has rewritten the genetic history of Europe’s human ancestors. This study was led by researchers from the University of Tübingen and the Senckenberg Center for Human Evolution and Palaeoenvironment, Peking University, and the Max Planck Institute for Evolutionary Anthropology in Leipzig, in collaboration with 125 international scientists including The University of New Mexico Leslie Spier Distinguished Professor Emeritus of Anthropology Lawrence Straus.

Lawrence Straus

The results Palaeogenomics of Upper Palaeolithic to Neolithic European hunter-gatherers were published recently in the journal Nature. The team analyzed the genomes of 356 prehistoric hunter-gatherers from different archaeological cultures, including new data sets of 116 individuals from 14 different European and Central Asian countries.

Among the key Stone Age human remains whose DNA were analyzed in the study are those of the 18,800-year-old “Red Lady” of El Mirón Cave discovered by Straus and Spanish colleague Manuel González Morales, a professor at the University of Cantabria. Straus also provided Solutrean-age human remains and information from the site of La Riera Cave, also in northern Spain, which he excavated with Arizona State University professor Geoffrey Clark in 1976-79.

Human remains from the Solutrean culture, which dates to the time of the climatic crisis of the Last Glacial Maximum (LGM) c. 25-21,000 years ago are exceedingly rare, said Straus, in relative contrast to the preceding Gravettian and succeeding Magdalenian periods, making the 21,000-year-old La Riera teeth and cranial bone fragments also very important to the study by helping to show western European genetic continuity from before, during, and after the LGM.

Modern humans began to spread across Eurasia around 45,000 years ago, but previous research showed that the first modern humans who arrived in Europe did not contribute to later populations. This study focuses on the people who lived between 35,000 and 5,000 years ago and who are, at least partially, the ancestors of the present-day population of Western Eurasia, including – for the first time – the genomes of people who lived during the LGM, the coldest phase of the last Ice Age.

Climatic refugium or dead end?
Surprisingly, the research team found that populations from different regions associated with the pre-LGM Gravettian culture, which was widespread across the European continent between 32,000 and 24,000 years ago, were not closely related, Straus noted. However, they were linked by a common archaeological culture: They used similar weapons, produced similar portable art, and had a common set of human burial practices.

Genetically, however, the populations from western and southwestern Europe (today's France and Iberia) differed from contemporaneous populations from central and southern Europe (today's Czech Republic and Italy). Furthermore, the gene pool of the western Gravettian populations is found continuously for at least 20,000 years: Their descendants, who are associated with the Solutrean and Magdalenian cultures, stayed in southwestern Europe during the coldest period of the last Ice Age (between 25,000 and 19,000 years ago) and later spread north-eastward to the rest of Europe.

“With these findings, we can for the first time directly support the hypothesis that during the Last Glacial Maximum people found refuge in the climatically more favorable region of southwestern Europe," said first author Cosimo Posth. This was a hypothesis (i.e., human range “retreat” to the south during the Solutrean followed by recolonization of the north during the Magdalenian) put forth by Straus in the 1980s on the basis of archeological evidence, long before the development of ancient human DNA analysis by recent Nobel Prize winner Svante Pääbo, who personally sampled the Lower Magdalenian-age El Mirón remains and led the team at the Max Planck Institute in Leipzig that successfully extracted DNA and published the Red Lady’s genome in Nature in 2016.

The Italian peninsula was previously considered to be another climatic refugium for humans during the LGM. However, the research team found no evidence for this. On the contrary, hunter-gatherer populations associated with the Gravettian culture and living in central and southern Europe are no longer genetically detectable after the LGM. People with a new gene pool settled in these areas, instead.

"We find that individuals associated with a later culture, the Epigravettian, are genetically distinct from the area‘s previous inhabitants," said co-author He Yu. "Presumably, these people came from the Balkans, arrived first in northern Italy around the time of the glacial maximum and spread all the way south to Sicily."

Large-scale genetic replacement
The analyzed genomes also show that the descendants of these Epigravettian inhabitants of the Italian peninsula spread across the rest of Europe about 14,000 years ago, replacing populations associated with the Magdalenian culture. The research team describes a large-scale genetic replacement that may have been caused, in part, by climatic changes that forced people to migrate:

"At that time, the climate warmed up quickly and considerably and forests spread across the European continent. This may have prompted people from the south to expand their habitat. The previous inhabitants may have migrated to the north as their habitat, the ‘mammoth’ steppe, dwindled," said Johannes Krause, the study's senior author.

Furthermore, the findings show that there had been no genetic exchange between contemporaneous hunter-gatherer populations in western and eastern Europe for more than 6,000 years. Interactions between people from central and eastern Europe can only be detected again from 8,000 years ago.

"At that time, hunter-gatherers with distinct ancestries and appearances started to mix with each other. They were different in many aspects, including their skin and eye color," said He Yu. Recall that the Mirón Red Lady had dark skin and eyes, Straus noted.

During this time agriculture and a sedentary lifestyle spread from Anatolia to Europe.

"It is possible that the migration of early farmers into Europe triggered the retreat of hunter-gatherer populations to the northern edge of Europe. At the same time, these two groups started mixing with each other, and continued to do so for around 3,000 years," Krause said.

"The data we gained from this study provides us with astonishingly detailed insights into the developments and encounters of West Eurasian hunter-gatherer groups," Posth summarized. "Further interdisciplinary research will clarify which exact processes were responsible for the genetic replacements of entire Ice Age populations.”

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