Europe was no balmy paradise during the Ice Age, with the vast glaciers that blanketed large parts of the continent rendering wide swathes inhospitable for humans. But our species - a new immigrant to Europe - endured, though with great hardship.
Researchers on Wednesday unveiled an analysis of genome data from 356 hunter-gatherers who lived in the region between 35,000 and 5,000 years ago, a span that included the Ice Age's coldest interval between 25,000 and 19,000 years ago. This enabled them to decipher prehistoric Europe's population dynamics, including the movement of groups of people and some key physical traits.
While some populations hunkered down and survived in relatively warmer parts of Europe, including France, Spain and Portugal, others died out on the Italian peninsula, the study showed. It also provided insight into the advent of characteristics such as light skin and blue eyes in Europeans.
"It is the largest ancient genomic dataset of European hunter-gatherers ever produced," said palaeogeneticist Cosimo Posth of the University of Tübingen in Germany, lead author of the study published in the journal Nature.
"It refreshes our knowledge of how human beings survived the Ice Age," added palaeogeneticist and study co-author He Yu of Peking University in China.
Europe had been the domain of the Neanderthals, our robust and large-browed cousins, but they went extinct roughly 40,000 years ago once our species, Homo sapiens, established a firm foothold on the continent. Homo sapiens arose roughly 300,000 years ago in Africa, then spread worldwide, reaching Europe at least 45,000 years ago.
Various groups of hunter-gatherers roamed the European landscape, hunted large mammals including woolly mammoths, woolly rhinos and reindeer, and collected edible plants. During the Ice Age's coldest period, known as the Last Glacial Maximum, ice sheets called continental glaciers covered half of Europe, with much of the rest in tundra conditions with frozen subsoil.
The only people who survived this harshest period in Europe were hunter-gatherers who had found refuge in portions of France and the Iberian peninsula, the study found. The Italian peninsula, previously thought to have been a refuge for people during this period, was just the opposite - all its inhabitants perished.
"It is a big surprise that humans went extinct on the Italian peninsula," said study senior author Johannes Krause, director of the Max Planck Institute for Evolutionary Anthropology in Germany.
That region was repopulated around 19,000 years ago by hunter-gatherers from the Balkans, who subsequently expanded throughout Europe and by around 14,500 years ago had replaced everyone who had lived there, the researchers found.
"From around 14,000 to 13,000 years ago, the climate became warmer and most parts of Europe gradually turned into forest, similar to today," Yu said.
The Homo sapiens individuals who entered Europe after a migration out of Africa were dark-skinned. The genome data showed a change toward light skin among people in Europe between 14,000 and 8,000 years ago that accelerated with the subsequent spread of farming on the continent.
Certain traits of Western European hunter-gatherers, known for blue eyes and dark skin, differed from their counterparts in Eastern Europe, who had light skin and dark eyes. Those two populations started to interbreed around 8,000 years ago only after the first farmers arrived in Europe from Anatolia - modern Turkey - and pushed all the hunter-gatherers northward.
The genome data showed that populations associated with what is called the Gravettian culture dating to around 34,000 to 26,000 years ago - known for certain types of stone tools, cave paintings and small sculptures called "Venus" figurines - were not in fact homogeneous. Instead, there were two largely unrelated populations sharing cultural attributes.
"A big surprise for me," Yu said, "is the fact that Gravettian populations carried two genetically distinct ancestries and that one of those disappeared from Europe."
