The genomic history of the Iberian Peninsula over the past 8000 years

We assembled genome-wide data from 271 ancient Iberians of whom 176 are from the largely unsampled period after 2000 BCE, thereby providing a high resolution time transect of the Peninsula. We document high genetic substructure between northwestern and southeastern hunter-gatherers prior to the spread of farming. We reveal sporadic contacts between Iberia and North Africa by ~2500 BCE, and by ~2000 BCE the replacement of 40% of Iberia's ancestry and nearly 100% of its Y-chromosomes by people with Steppe ancestry. In the Iron Age, we show that Steppe ancestry had spread not only into Indo-European-speaking regions but also into non-Indo-European-speaking ones, and we reveal that present-day Basques are best described as a typical Iron Age population without the admixture events that later impacted the rest of Iberia. Beginning at least in the Roman period, we document how the ancestry of the Peninsula was transformed by gene flow from North Africa and the eastern Mediterranean.