An analysis of 101 ancient genomes has revealed how Eurasian populations moved around during the Bronze Age 3,000 to 5,000 years ago. The work, published in Nature this week, is one of the largest studies of ancient DNA ever. And it may help explain the prevalence of traits like skin color and lactose intolerance, as well as the spread of ancient languages.
Lots of major cultural changes took place during the Bronze Age of Eurasia, but researchers disagree over whether these were the results of the broad circulation of ideas or large-scale migrations. Proto-Indo-European, for instance, is the ancestral tongue of 400 languages and dialects, including English, Greek, and Hindi. We know it’s at least 3,700 years old, but where and when the language originated and how it spread is still hotly debated. Some say it happened around 9,000 years ago in Anatolia, or modern-day Turkey, and then dispersed along with agriculture (Anatolian hypothesis). Others think that it arose around 6,000 years ago in the grassy steppe lands of Ukraine, Kazakhstan, and Russia, north of the Black and Caspian seas, and it spread westward along with innovations related to pastoral farming, like wheeled vehicles (steppe hypothesis).
Ancient genomes can provide much-needed information on the histories of past populations, but it’s been difficult to get enough non-degraded DNA for detailed genetic analyses. Now, a large international team led by Eske Willerslev from the University of Copenhagen has managed to obtain “low-coverage” genome sequences from 101 ancient humans from the Late Neolithic through the Iron Age. These data are poor by modern DNA standards, but they’re sufficient to discern broad brushstrokes of migration, University of Chicago’s John Novembre writes in an accompanying News & Views article.
The Bronze Age, the team found, was a highly dynamic period involving large-scale population migrations and replacements. And it was responsible for shaping major parts of the demographic structure in Europe and Asia today.
Their findings support the theory that migrations during the early Bronze Age played a role in the spread of Indo-European languages. This fits with a genetic analysis published earlier this year that favored the steppe hypothesis. The Corded Ware people, who lived in northern Europe 4,500 years ago, can trace three-fourths of their ancestry to the Yamnaya steppe herders living in Russia from 6,000 to 5,000 years ago. That means a massive migration of the Yamnaya Culture into northern Europe from its eastern edge had to have taken place (see map below). A Yamnaya skull from the Samara region colored with red ochre is pictured above to the right.
Furthermore, the team found that light skin pigmentation was already frequent among Europeans in the Bronze Age. But lactose tolerance, which is prevalent among modern northern Europeans, was relatively low in Bronze Age Europeans: The mutation that allowed humans to drink milk was only just beginning to spread at the time, and that’s later than previously thought.
Images: Alexey Nechvaloda (top), Natalia Shishlina (middle), modified map after an original by Richard Potter (bottom)