NEW YORK (GenomeWeb) –Researchers from Sweden, Australia, and Spain have found genetic evidence for ties between ancient farmers in northern Spain and the present-day Basque population.
The team, which presented its findings in the early edition of the Proceedings of the National Academy of Sciences this week, focused on remains from eight individuals believed to have lived in farming populations on the Iberian peninsula between 3,500 and 5,500 years ago. These so-called Chalcolithic El Portalón individuals, named after a cave in Sierra de Atapuerca, Spain, where their remains were found, were tested using low-coverage genome sequencing, mitochondrial genome sequencing, and Y chromosome sequencing.
From genome-wide variant patterns deciphered from the sequences, the researchers concluded that these individuals shared ancestry with farming groups in northern and central Europe, but mixed with local hunter-gatherers in southwestern Europe en route to Iberia. Their results suggest the group was genetically similar to the present-day Basques, refuting earlier notions about that group's ancestry.
"Our results show that the Basques trace their ancestry to early farming groups from Iberia, which contradicts previous views of them being a remnant population that trace their ancestry to Mesolithic hunter-gatherer groups," senior author Mattias Jakobsson, an evolutionary biology researcher from Uppsala University, said in a statement.
Remains of the early farmers tested for the study were found in the El Portalón cave, a site containing human artifacts and bones that stretch back to the Stone Age.
Those involved in the study reasoned that an analysis of the individuals might offer clues to the transition from populations with subsistence or hunter-gatherer lifestyles to those that practiced agriculture in larger, settled groups.
"Genomic studies of Stone Age human remains from northern and central Europe have shown that the Neolithic transition [to agriculture] was driven by migration, followed by subsequent admixture with [hunter-gather] groups," Jakobsson and his colleagues explained, noting that this New Stone Age transition has been more difficult to discern in the Iberian Peninsula so far.
He and his team generated between 0.01-fold and more than 4-fold genome coverage on four male and four female individuals from the site.
Based on their mitochondrial genome and Y chromosome sequences, the team concluded that the individuals were likely descended from early European farmers who arrived in the region, mixing with local hunter-gatherer groups they encountered during this migration.
By comparing genome-wide SNP patterns in the samples with those in other ancient and modern European samples, the researchers were able to place the Iberian farmers in a genetic cluster with early farming groups in other parts of the continent.
That analysis also pointed to Chalcolithic El Portalón admixture with a hunter-gatherer group that was distinct from hunter-gatherers from Scandinavia that interacted with Central European farmers such as the Tyrolean Iceman. Instead, the Iberian farmers seem to have mixed with the same hunter-gatherers related to previously studied Mesolithic individuals from Luxembourg and La Braña.
Amongst present-day populations, the Iberian farmers are genetically closest to Spain's Basque population, which argues against the notion that the Basques are isolated descendants of an ancient Mesolithic group from that area.
"The Basque language … is a relict of the ancient, preagricultural linguistic diversity of Europe, with roots as far back as the Paleolithic," the study's authors explained. "Our data, suggesting that Basques trace their genetic ancestry to early Iberian farmers, challenges this assumption."