Scientists have sequenced the genomes of human remains that date back to the Late Upper Palaeolithic period over 13,000 years ago for the first time, revealing a "fourth strand" of European ancestry that was previously unknown to science.
The lineage originated in a group of hunter-gatherers that spilt from western hunter-gatherers after the "out of Africa" migration 45,000 years ago and moved to the Caucasus region on the border of Russia and Georgia, the University of Cambridge reported.
These ancient hunter-gatherers are believed to have remained isolated during the ice age "Glacial Maximum" that occurred 25,000 years ago. The Caucasus mountains likely provided some shelter, until ice thawing allowed them to come into contact with other populations. Once the ice age was over, the Caucasus people mixed with populations from further east, resulting in the Yamnaya culture. These people were horse-borne Steppe herders that are believed to have moved into western Europe 5,000 years ago and may have even started the Bronze Age. The Yamnaya culture spread their DNA across Europe over the course of centuries.
"The question of where the Yamnaya come from has been something of a mystery up to now," said one of the lead senior authors Andrea Manica, from Cambridge's Department of Zoology. "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 who weathered much of the last Ice Age in apparent isolation. This Caucasus pocket is the fourth major strand of ancient European ancestry, one that we were unaware of until now."
Past studies of Eurasian genomes had only revealed three major DNA strands still present in modern-day Europeans. The sequencing of genomes from two separate burial grounds in Western Georgia revealed half of the Yamnaya's ancestry came from a "previously unknown and genetically distinct" hunter-gatherer group, or the "fourth strand." Further analyses demonstrated that the mysterious group diverged from the western hunter-gatherers shortly after the massive move from Africa into Europe.
The Caucasus hunter-gatherer genome appeared to be mixed with the ancestors of early farmers from the Levant area, but broke of right before the most recent Glacial Maximum. During this time the Caucasus hunter-gatherer genome showed signs of increasing homogenization, meaning those with closer and closer DNA were procreating. This persisted for thousands of years until the Glacial Maximum subsided.
"We knew that the Yamnaya had this big genetic component that we couldn't place, and we can now see it was this ancient lineage hiding in the Caucasus during the last Ice Age," Manica said.
Scientists are now wondering if the Caucasus hunter-gatherer ancestry had influences further east. They believe a similar population may have migrated to South Asia at once point in history.
"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 Eppie Jones, a PhD student from Trinity College who is the first author of the paper.
The findings were published in a recent edition of the journal Nature Communications.
