AI interpretationAI-generated
Brittany's genomes reveal deep steppe ancestry and medieval links to Western Europe.
This study analysed 856 whole genomes from northern France and 3,234 present-day individuals, plus six medieval genomes from western France. It found fine-scale genetic structure across Brittany and the Loire basin, with a clear north-south divide in steppe versus Neolithic ancestry. Western Brittany shows the highest steppe ancestry in France, similar to Bell Beaker-associated individuals, suggesting a lasting genetic legacy from around 2500 BCE.
- Present-day Western Brittany carries the highest levels of steppe ancestry in France, comparable only to northwestern European populations.
- The Loire River marks a genetic boundary, with northern and southern sides showing different proportions of steppe versus Neolithic-related ancestry.
- Medieval individuals from Western France (300-1100 CE) provide first whole-genome insights into the Migration Period's genetic impact.
Sample interpretation
The site includes six medieval individuals from Western France, dated 340-1024 CE. Five have resolved Y-chromosome haplogroups: R-L2, R-Y146438, R-ZP75, E-PF2348, and J-Z1853. Mitochondrial haplogroups include U4b1b1b, K1a4a1, H3n, U5b2b3, H1aj, and H7h. These diverse lineages reflect a mix of local and potentially migrant ancestries during the Migration Period.
For genealogy enthusiasts
For ancestry enthusiasts, this study shows that local French populations, especially in Brittany, preserve distinct genetic signatures from ancient migrations. It highlights the importance of regional data to trace rare variants and disease-related alleles shared with Britain and Ireland.
Abstract
European genetic ancestry originates from three main ancestral populations - Western hunter-gatherers, early European farmers and Yamnaya Eurasian herders - whose edges geographically met in present-day France. Despite its central role to our understanding of how the ancestral populations interacted and gave rise to modern population structure, the population history of France has remained largely understudied. Here, we analysed 856 high-coverage whole-genome sequences along with genome-wide genotyping data of 3,234 present-day individuals from the northern half of France and merged them with publicly available present-day and ancient Europe-wide genotype datasets. We also analysed, for the first time, the whole-genome sequences of six medieval individuals (300-1100 CE) from Western France to gain insights into the genetic impact of what is commonly known as the Migration Period in Europe. We found extensive fine-scale population structure across Brittany and the downstream Loire basin, emphasizing the need for investigating local populations to better understand the distribution of rare and putatively deleterious variants across space. Overall, we observed an increased population differentiation between the northern and southern sides of the river Loire, which are characterised by different proportions of steppe vs. Neolithic-related ancestry. Samples from Western Brittany carry the largest levels of steppe ancestry and show high levels of allele sharing with individuals associated with the Bell Beaker complex, levels that are only comparable with those found in populations lying on the northwestern edges of Europe. Together, our results imply that present-day individuals from Western Brittany retain substantial legacy of the genetic changes that occurred in Northwestern Europe following the arrival of the Bell Beaker people c. 2500 BCE. Such genetic legacy may explain the sharing of disease-related alleles with other present-day populations from Western Britain and Ireland.