DNA extracted from a skull and a molar tooth of ancient human remains discovered in the southern Caucasus region of Georgia is helping sort out the multifaceted ancestry of modern Europeans.
Scientists said on Monday they sequenced the genomes of two individuals - one from 13,300 years ago and the other from 9700 years ago - and found they represented a previously unknown lineage that contributed significantly to the genetics of almost all modern Europeans.
These individuals were members of hunter-gatherer groups who settled in the Caucasus region, where southern Russia meets Georgia, about 45,000 years ago, after our species trekked out of Africa to populate other parts of the world. At the time, Europe was populated by Neanderthals.
The Caucasus hunter-gatherers later became isolated there for millennia during the last Ice Age, the scientists said.
The thaw at the end of the Ice Age brought them into contact with other peoples, leading to the advent of a culture of horse-riding herders who swept into Western Europe around 5000 years ago.
"Modern Europeans are a mix of ancient ancestral strands," Trinity College Dublin geneticist Daniel Bradley said. "The only way to untangle the modern weave is to sequence genomes from thousands of years ago, before the mixing took place."
Until now, only three such ancestral strands had been identified flowing from ancient populations.
The Caucasus inhabitants comprised a previously unidentified "fourth strand", said University of Cambridge geneticist Andrea Manica, noting that they contributed significantly not only to the ancestry of Europe but also to people in Central Asia and the Indian subcontinent.
Bradley called the finding "a major new piece in the human ancestry jigsaw."
The Caucasus hunter-gatherers lived in caves and in small groups of probably no more than 20 to 30 people, University College Dublin archaeologist Ron Pinhasi said.