For example, researchers have disagreed over whether the cultural changes of the Bronze Age were the result of migration or simply the spread of ideas. Allentoft and his colleagues found evidence for migration, in the form of a massive shift in the genetic make-up of northern and central Europeans at the start of the Bronze Age. Before 3000 bc, their genomes resembled those of early farmers from the Middle East and even earlier European hunter-gatherers. By 2000 bc, their genomes looked more like those of people from the Yamnaya culture, which arose on the steppe around 2900 bc.

The findings echo those of a team that sequenced 69 ancient Europeans3. Both groups speculate that the Yamnaya migration was at least partly responsible for the spread of the Indo-European languages into Western Europe.