Genomic history and selection in Roman and early medieval Britain

Leading biomedical resources rely on genome variation in Britain ^1–3 , but the historical processes that shaped present-day fine-scale diversity remain debated ^4–13 . Here we sequenced 1039 ancient shotgun genomes from Britain (median 1.4-fold coverage), primarily dating to the first millennium CE. We imputed ∼660 million variants in the UK Biobank ^14–16 and employed genealogy-based ancestry reconstruction. We found an association between Iron Age consanguinity and matrilineal burial practices ¹⁷ , later disrupted following the Roman Conquest. Despite this societal impact, only 20% of Roman-period individuals carried detectable ancestry from outside Britain. In contrast, from the 6th century CE we detect widespread influx of ancestry in over 70% of individuals in southern’Anglo-Saxon’ Britain, with limited local admixture. We find previously underappreciated heterogeneity, with ancestries associated with Central and Southern Europe rising in prevalence from the 7th century CE. We demonstrate distinct Scandinavian-related ancestry in many Viking-associated contexts, but show that the population-level impact of the Viking Age in Britain was limited. Finally, we detect pre-medieval selection on variants linked with key immunity genes TLR10-TLR1 and IRF8 . These results identify population-level and selective processes that shape variation and disease risk in Britain today.