Modern Europeans' DNA has long been believed to come from three strains of ancestors, but new research may have uncovered a fourth.

According to BBC News, researchers detailed this fourth ancestral DNA strain thanks to scientific advances in recent years. Geneticists were able to better examine DNA extracted from ancient burials.

The study was published in the journal Nature Communications.

"The question of where the Yamnaya come from has been something of a mystery up to now," study lead senior authors Andrea Manica, a zoologist at the University of Cambridge, said in a press release. "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."

The three known ancestors to modern Europeans are hunters indigenous to the area, hunters from the Middle East, and eastern settlers that migrated during the Bronze Age. The fourth is a hunter-gatherer population that originated in the Caucasus near the Russia-Georgia border today.

Called the Yamnaya, the hunter-gatherers came into Western Europe from Central Eurasia, according to remains 10,000 to 13,000 years old.

"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," study lead senior author Ron Pinhasi, of University College Dublin, said in the release. "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."