NEW YORK — While Basques are genetically similar to other European populations, a new genomic analysis has found that they also exhibit distinct differences that are likely due to their isolation.
Basques, who traditionally live in the western Pyrenees in both Spain and France, have drawn interest from researchers as a unique European population, as the Basque language, Euskara, is a non-Indo-European language and as initial studies have demonstrated an unusually high frequency of Rh-negative blood groups among Basques.
By analyzing the genomes of nearly 2,000 modern and ancient individuals from the Basque Country and surrounding area, researchers led by David Comas at Pompeu Fabra University in Spain investigated the genetic origins of Basques. They found a clear distinction between Basques and other Europeans, but also noted genetic heterogeneity within the Basque population. As they reported in Current Biology on Thursday, they traced both this internal heterogeneity and the origins of the Basques to genetic continuity since the Iron Age that has been marked by limited gene flow.
"Our analysis shows that the Basques are within the European genetic landscape, but with slight differences and a smooth distinction to surrounding populations," Comas said in an email. "They show some different genetic characteristics due to their population history, but they are not extremely different from other southwestern European populations as it has been claimed in some previous studies."
He and his colleagues examined genome-wide data from 1,970 modern and ancient individuals, including 190 new individuals hailing from 18 sites in the Basque region. Through a principal components analysis that included further samples from West Eurasia and North Africa, they found that the Basque samples fall to one edge of the European samples and away from the North African samples. Neighboring groups that traditionally speak Gascon or Spanish — Peri-Basques — fall between Basques and other European groups.
Through an admixture analysis, the researchers found that Basques have two main genetic ancestry components: a major component that is found in other European samples as well as at low levels in samples from the Middle East or the Caucasus and North Africa, and a minor component that is found at high frequency among samples from Central or Eastern Europe.
A haplotype-based analysis similarly places Basques among other European populations, though as a distinct cluster, and with Peri-Basques again appearing as a buffer between Basques and other populations.
By folding ancient samples into their analysis, the researchers found that Basques are most closely related to Pre-Neolithic hunter-gatherers and European Neolithic farmers, but also have ancestry similar to that of post-Neolithic steppe herders. At the same time, they and Peri-Basques have a lower proportion of Levant- and Iran-related Neolithic ancestry than other European groups and a higher proportion of Anatolian/European farmer ancestry.
The findings, the researchers said, support the notion of genetic continuity among Basques since the Iron Age with limited subsequent influence from Roman Empire or North African populations. This, they noted, is in line with archaeological and historical records, and they suggested that the language barrier between Basques and other European groups could have contributed to this isolation.
Additionally, within the Basque population, the researchers noted, there is a heterogenous genetic landscape that largely correlates with geography, with Central, Eastern, and Western Basque clusters. They further found that these clusters are not due to external contributors and instead could be due to periods of isolation and low gene flow, as well as possibly reflect the influence of Euskara dialects.
Comas added that their study shows that deeply sampling a small geographical area in combination with haplotype-based and other analyses can provide insight into recent human population history. "It would be interesting to explore in depth not only the population history of Basques, but other populations, joining data from extant populations together with ancient data," he said.