Some 7,500 years ago, brown-eyed, pale-skinned farmers began migrating into Europe from the Near East. These migrants not only spread a new way of life to the resident blue-eyed, dark-skinned hunter-gatherers through the introduction of agriculture, but they also contributed their DNA by interbreeding along the way. Genetic analysis suggested that modern Europeans descended from the mixing of these two distinct populations, but this was largely based on samples from living people. Now, thanks to DNA samples from ancient humans, scientists have revealed that there was in fact a third party on the scene: ancient north Eurasians.
For the new study, scientists from Harvard Medical School and the University of Tübingen sequenced the DNA of 2,345 present-day humans from all over the world alongside that of several ancient humans from Sweden, Luxembourg and Germany.
The ancient remains belonged to eight hunter-gatherers that lived some 8,000 years ago, prior to the introduction of agriculture to Europe, and one farmer that lived about 1,000 years later. They also added in previously obtained sequence data from other ancient humans, such as Ötzi the Iceman.
They found that ancient north Eurasian DNA was not present in the hunter-gatherers, nor the early farmers, suggesting this population arrived on the scene later. However, almost all modern Europeans have DNA from all three ancient groups. According to first author of the Nature study Iosif Lazaridis, differences in present-day Europeans can be attributed to the relative proportions of ancestry. “Northern Europeans have more hunter-gatherer ancestry—up to about 50 percent in Lithuanians—and Southern Europeans have more farmer ancestry,” he added.
While ancient north Eurasian ancestry never made up more than 20% of the ancestry of present-day Europeans, it was found in virtually every group studied. Interestingly, this new population on the block was previously only known from traces of DNA in present-day humans and thus was considered a “ghost population.” However, the discovery of two ancient north Eurasians by a separate group in January allowed the researchers to investigate relationships with other populations for the first time.
Unfortunately, this study was limited by the small number of ancient specimens available for analysis, meaning some questions are left unanswered. For example, these three populations are insufficient to explain some present-day European groups such as the Maltese who were found to have far more Near East ancestry than predicted. Similarly, some far northeastern Europeans had more East Asian ancestry than anticipated.
“We are only starting to understand the complex genetic relationship of our ancestors,” study co-author Johannes Krause said in a news release. “Only more genetic data from ancient human remains will allow us to disentangle our prehistoric past.”