A small group of people separated from the rest of humanity for more than 10,000 years went on to make a major contribution to European and Indian genetics. The previously unrecognized inhabitants of the Caucasus region have been identified from a study of an ancient bone and tooth with intact DNA found in Georgian caves.
Humans traveled north between the Black and Caspian Seas 45,000 years ago, and then spread into Europe and northern Asia. New evidence, presented in Nature Communications, suggests that one group of people who remained in the Caucasus Mountains became largely disconnected, initially from their counterparts who continued the journey, and subsequently from populations further south.
Thousands of years of solitude passed from the Glacial Maximum when the last Ice Age was at its most intense, ending as the world warmed up around 10,000 years ago. Such a long period of estrangement inevitably left this population with distinct genetics. When they reconnected with humanity these Caucasus hunter-gatherers, as they have been dubbed, became part of the ancestry of the Yamnaya people, senior author Dr. Andrea Manica of Cambridge University reports.
"The question of where the Yamnaya come from has been something of a mystery up to now," Manica said in a statement, "We can now answer that as we've found that their genetic make-up is a mix of Eastern European hunter-gatherers and a population from this pocket of Caucasus hunter-gatherers."
The Yamnaya inhabited what is now the Ukraine and western Russia before riding their horses into Europe around 5,000 years ago. Like so many Steppe herders after them the Yamnaya settled in Europe and made a major contribution to the genetics, and probably culture, of central Europe.
The importance of the presumably tiny number of Caucasus hunter-gatherers to the genetics of the Yamnaya, and through them modern Europeans, is large enough that Manica and his co-authors have dubbed their contribution a “fourth strand” in European heritage. The other three strands are the early Western European hunter-gatherers, farmers from the Middle East and the North Eurasians who make up the other component of Yamnaya ancestry.
The authors established the genetics of Caucasus hunter-gatherers from a 13,300-year-old bone and 9,700-year-old tooth from Satsurblia and Kotias caves, respectively. Interbreeding appears to have ceased with Western European hunter-gatherers soon after their migration. On the other hand, the authors found signs of continued interchange with populations to the south for almost 20,000 years, until the glacial maximum ended contact in that direction as well.
The view from Satsurblia Cave, where the older DNA was found. For thousands of years this cave, and a few others like it, was home to a people entirely cut off from the rest of humanity. Credit: Eppie Jones.
Reconnection with the wider world only occurred with the end of the Ice Age. Once able to travel freely, the genes that had become fixed through a long period of interbreeding spread rapidly. "India is a complete mix of Asian and European genetic components. The Caucasus hunter-gatherer ancestry is the best match we've found for the European genetic component found right across modern Indian populations," said first author Eppie Jones, a PhD student at Trinity College, Dublin.