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Western Eurasia witnessed several large-scale human migrations duringthe Holocene15. Here, to investigate the cross-continental effects of these migrations, we shotgun-sequenced 317 genomes-mainly from the Mesolithic and Neolithic periodsfrom across northern and western Eurasia. These were imputed alongside published data to obtain diploid genotypes from more than 1,600 ancient humans. Our analyses revealed a'great divide'genomic boundary extending from the Black Sea to the Baltic. Mesolithic hunter-gatherers were highly genetically differentiated east and west of this zone, and the effect ofthe neolithization was equally disparate. Large-scale ancestry shifts occurred in the west as farming was introduced, including near-total replacement of hunter-gatherers in many areas, whereas no substantial ancestry shifts happened east ofthe zone duringthe same period. Similarly, relatedness decreased in the west from the Neolithic transition onwards, whereas, east ofthe Urals, relatedness remained high until around 4,000 bp, consistent with the persistence of localized groups of hunter-gatherers. The boundary dissolved when Yamnaya-related ancestry spread across western Eurasia around 5,000 bp, resulting in a second majorturnoverthat reached most parts of Europe within a 1,000-year span. The genetic origin and fate ofthe Yamnaya have remained elusive, but we showthat hunter-gatherers from the Middle Don region contributed ancestry tothem. Yamnaya groups later admixed with individuals associated with the Globular Amphora culture before expanding into Europe. Similar turnovers occurred in western Siberia, where we report newgenomic data from a 'Neolithic steppe' cline spanning the Siberian forest steppe to Lake Baikal. These prehistoric migrations had profound and lasting effects on the genetic diversity of Eurasian populations.
Genetic diversity in west Eurasian human populations was largely shaped by three major prehistoric migrations: anatomically modern hunter-gatherers (HGs) occupying the area from around 45,000 bp (refs. 4,6); Neolithic farmers expanding from the Middle East from around 11,000 bp (ref. 4); and steppe pastoralists coming out of the Pontic Steppe around 5,000 bp (refs. 1,2). Palaeogenomic analyses have uncovered the early post-glacial colonization routes7 that led to a basal ancestral dichotomy between HGs in central and western Europe and HG groups represented further east8. Western HG (WHG) ancestry appears to be derived directly from ancestry sources related to Epigravettian, Azilian and Epipalaeolithic cultures (the Villabruna cluster)9, whereas eastern HG (EHG) ancestry shows further admixture with an Upper Palaeolithic Siberian source (Ancient North Eurasian; ANE)10. The...