'Fourth strand' of ancient European ancestry spread to India

London: The first-ever sequencing of ancient genomes extracted from human remains has revealed a previously unknown “fourth strand” of ancient European ancestry that eventually spread into south Asia, including India, a new study reported.

This new lineage stems from populations of Caucasus hunter-gatherers that split from western hunter-gatherers shortly after the “out of Africa” expansion some 45,000 years ago.

While the Caucasus hunter-gatherer ancestry would eventually be carried west by the Yamnaya culture, the researchers found it also had a significant influence further east.

“A similar population must have migrated into south Asia at some point,” says Eppie Jones, Ph.D. student from Trinity College who is the first author of the paper.

"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," Jones elaborated.

Researchers say this strand of ancestry may have flowed into the region with the bringers of Indo-Aryan languages.

The hunter-gatherers went on to settle in the Caucasus region, where southern Russia meets Georgia today.

This led to a genetic mixture that resulted in the Yamnaya culture -- horse-borne Steppe herders that swept into Western Europe around 5,000 years ago, arguably heralding the start of the Bronze Age and bringing with them metallurgy and animal herding skills.

"The question of where the Yamnaya come from has been something of a mystery up to now," said Dr Andrea Manica from the University of Cambridge and one of the lead senior authors.

“We have 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,” he explained.

This Caucasus pocket is the fourth major strand of ancient European ancestry, one that we were unaware of until now, Manica added.

According to professor Daniel Bradley, leader of the Trinity team, “this is a major new piece in the human ancestry jigsaw, the influence of which is now present within almost all populations from the European continent and many beyond.”

Previously, ancient Eurasian genomes had revealed three ancestral populations that contributed to contemporary Europeans in varying degrees.

The widespread nature of the Caucasus hunter-gatherer ancestry following its long isolation makes sense geographically.

“The Caucasus region sits almost at a crossroads of the Eurasian landmass, with arguably the most sensible migration routes both west and east in the vicinity,” said professor Ron Pinhasi, lead senior author from the University College Dublin.

The sequencing of genomes from this key region will have a major impact on the fields of palaeogeneomics and human evolution in Eurasia, as it bridges a major geographic gap in our knowledge, the authors concluded.

The findings were published in the journal Nature Communications.