Imputed genomes and haplotype-based analyses of the Picts of early medieval Scotland reveal fine-scale relatedness between Iron Age, early medieval and the modern people of the UK

Abstract

22 The origins and ancestry of the Picts of early medieval Scotland (ca. AD 300-900) has been traditionally 23 seen as a problem, prompted in part by exotic medieval origin myths, their enigmatic symbols and 24 inscriptions, and the meagre textual evidence. The Picts, first mentioned in the late 3rd century AD 25 resisted the Romans and went on to form a powerful kingdom that ruled over a large territory in 26 northern Britain. In the 9th and 10th centuries Gaelic language, culture and identity became dominant, 27 transforming the Pictish realm into Alba, the precursor to the medieval kingdom of Scotland. To date, 28 no comprehensive analysis of Pictish genomes has been published, and questions about their 29 biological relationships to other cultural groups living in Britain remain unanswered. Here we present 30 two high-quality Pictish genomes (2.4 and 16.5X coverage) from central and northern Scotland dated 31 from the 5th-7th century which we impute and co-analyse with >8,300 previously published ancient 32 and modern genomes. Using allele frequency and haplotype-based approaches, we can firmly place 33 the Pictish genomes within the Iron Age gene pool in Britain and demonstrate local biological affinity. 34 We also demonstrate the presence of population structure within Pictish groups, with Orcadian Picts 35 being genetically distinct from their mainland contemporaries. When investigating Identity-By- 36 Descent (IBD) with present-day genomes, we observe broad affinities between the mainland Pictish 37 genomes and the present-day people living in western Scotland, Wales, Northern Ireland and 38 Northumbria, but less with the rest of England, the Orkney islands and eastern Scotland - where the 39 political centres of Pictland were located. The pre-Viking Age Orcadian Picts evidence a high degree of 40 IBD sharing across modern Scotland, Wales, Northern Ireland, and the Orkney islands, demonstrating 41 substantial genetic continuity in the Orkney for the last ~2,000 years. Analysis of mitochondrial DNA 42 diversity at the Pictish cemetery of Lundin Links (n = 7) reveals absence of female endogamy, with 43 implications for broader social organisation. Overall, our study provides novel insights into the genetic 44 affinities and population structure of the Picts and direct relationships between ancient and present- 45 day groups of the UK. 2 bioRxiv preprint doi: https://doi.org/10.1101/2022.08.01.502257; this version posted August 3, 2022. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under a CC-BY 4.0 International license. 46