Patterns of genetic differentiation and the footprints of historical migrations in the Iberian Peninsula

TLDR

The Iberian Peninsula is linguistically diverse and has a complex demographic history, including a centuries‑long period of Muslim rule. The study investigates the fine‑scale genetic structure of the Iberian population and the genetic impacts of historical events. Haplotype‑based statistical methods were applied to 1,413 individuals sampled across Spain. Fine‑scale population structure below 10 km was detected, an east‑west differentiation axis and north‑south migration were identified, 0–11 % northwest African ancestry varied regionally and dated to 860–1120 CE, and the results reveal clear genetic effects of the Muslim conquest and subsequent Reconquista.

Abstract

Abstract The Iberian Peninsula is linguistically diverse and has a complex demographic history, including a centuries-long period of Muslim rule. Here, we study the fine-scale genetic structure of its population, and the genetic impacts of historical events, leveraging powerful, haplotype-based statistical methods to analyse 1413 individuals from across Spain. We detect extensive fine-scale population structure at extremely fine scales (below 10 Km) in some regions, including Galicia. We identify a major east-west axis of genetic differentiation, and evidence of historical north to south population movement. We find regionally varying fractions of north-west African ancestry (0–11%) in modern-day Iberians, related to an admixture event involving European-like and north-west African-like source populations. We date this event to 860–1120 CE, implying greater genetic impacts in the early half of Muslim rule in Iberia. Together, our results indicate clear genetic impacts of population movements associated with both the Muslim conquest and the subsequent Reconquista .