Overview
Haplogroup R-L371 is a regionally distinctive branch of R-DF13 under R-L21 and has often been described as a Welsh focused lineage. It originated during the late Bronze Age or early Iron Age, at a time when Atlantic European societies were undergoing transitions toward more complex hierarchical structures and when early Celtic language communities were taking shape in western Britain. L371 represents one of the paternal founder groups that later contributed to the genetic makeup of medieval Welsh polities. The distribution of L371 shows a strong concentration in Wales, particularly in western and central regions, with additional representation in western England and among emigrant communities with Welsh ancestry. Some genetic genealogy projects have associated L371 with lineages that appear in medieval Welsh royal and noble genealogies, leading to its popular nickname as a Welsh modal haplogroup. While it is methodologically difficult to connect a haplogroup directly to specific named dynasties, the geographic and historical context supports the idea that L371 expanded among influential Iron Age and early medieval groups in Wales. Internally, L371 contains several downstream branches that diversified during the first millennium CE. These lines align chronologically with the documented era of early Welsh kingdoms, when elite lineages and regional dynasties became fixed in the written record. For this reason, L371 is widely used in surname based projects and in research focused on the genetic history of Wales. At the same time, its presence outside Wales and within mixed British populations illustrates the continuous movement and intermarriage that have shaped the British Isles over the last two millennia.