Researchers have genetically linked the origins of present-day Europeans to three ancestral groups that mixed with one another more than 7,000 years ago.

It has previously been believed that Europeans can trace their ancestry back to two ancient groups: the hunter-gathers indigenous to western Europe and farmers who migrated into Europe from the Near East, known as modern day Syria, Iraq and Israel. The new study reveals that the genetic origins of modern Europeans also have ties to a third line that originated in northern Eurasia.

Published in the journal Nature, a team of researchers from the University of Tubingen and Harvard Medical School partnered with scientists from the Centre for Cellular and Molecular Biology to study DNA from three different kinds of ancient human bone samples.

Researchers studied the genomic DNA in the bones of seven hunter-gathers from Scandinavia, along with the bones of a hunter found in a cave in Luxembourg and bones from an early farmer in Germany. They then compared the genomes to those of 2,345 people living today.

They found that the indigenous hunters that arrived in Europe before the age of agriculture have a genetic profile that lives on to modern-day Europeans, especially those in the northern Baltic states. Southern Europeans had 90 percent of DNA tied to Sardinian farmers.

The team of researchers found that while blue-eyed hunters socialized with brown-eyed, pale skinned farmers that came to Europe from the Near East, a third group of northern Eurasians with Siberian similarities also contributed to the genetic mix.

"It really does look like the indigenous West European hunter gatherers had this striking combination of dark skin and blue eyes that doesn't exist any more," says David Reich one of the researchers from the Harvard Medical School.

The study found that the ancestry of almost all modern day Europeans could be linked to all three of the ancient groups.

"Our study does indeed show that European origins were more complex than previously imagined," says Iosif Lazaridis, a postdoctoral research fellow at Harvard Medical School. "These Ancient North Eurasians must have spread into Europe at a later time, and so encountered early farmer- or hunter-gatherer-type populations and mixed with them," he adds. 

The research explains the recent discovery regarding the genetic connection between Europeans and Native Americans because this third group was related to Native Americans. The genetic findings show that the north Eurasians were related to the ancient people that traveled across the frozen lands that connected Siberia to Alaska over 15,000 years ago.