Color representation of the mixture and genetic structure in the Basque Country; the green symbolizing the Basques, and the blue and red blends it with the surrounding populations.
Credit: André Flores-Bello.
Isolated populations can either stay completely isolated and so gradually diverge from other populations of the same species by a combination of natural selection and genetic drift, or they can continue to exchange DNA with other neighbouring groups and so eventually merge and disappear as genetically distinct populations.
This true for all species, whether birds, mammals, reptiles or insects or, as in the case of the Basque people of Northeast Spain and Southwest France, humans.
A study by a mixed team from Spain and France, led by David Comas of the Departament de Ciències de la Salut i de la Vida, Institut de Biologia Evolutiva (CSIC-UPF), Universitat Pompeu Fabra, Barcelona, Spain has shown how the Basque people have retained genetic continuity with their Iron Age ancestors and have resisted genetic mixing with their neighbours, by a combination of linguistic, cultural and geographical barriers to gene flow.
As the news item from Universitat Pompeu Fabra, Barcelona, auto-translated from Catalan, explains:
The origin and present day status of the Basques and their relationship with other European populations is a classic example of how gene flow, or in this case, a lack of introgression from neighbouring groups because of physical and cultural barriers, can shape the evolution of a population as a distinct genetic group or see it dissipate into and be absorbed by neighbouring groups.A new study shows that the genetic singularity of the Basque population is not due to its external origin with respect to other Iberian populations, but to the decrease in contacts since the Iron Age. Genomic analysis points to the language barrier as a possible bulwark that led to the isolation of the population.
Basques are a unique population in Western Europe, as their language is not related to any Indo-European language. In addition, they have been genetically considered to have different characteristics. However, so far there has been no conclusive study explaining the origin of its peculiarity.
Now, an international research team led by UPF has confirmed that the genetic uniqueness of Basques is the result of their genetic continuity since the Iron Age, characterized by periods of isolation and lack of gene flow, and not of its external origin with respect to other Iberian populations.
The research, which has been led by David Comas, principal investigator at UPF and the Institute of Evolutionary Biology (IBE : CSIC-UPF), has had the most exhaustive geographical sampling to date of the Basque population, with more than 600,000 genetic markers throughout the genome for each individual.
The result of the multidisciplinary study, which has had a team of linguists and geneticists, reveals in the journal Current Biology that the cultural barrier of language could promote the isolation of the Basque population from subsequent population contacts, such as the influence of the Roman Empire or the Islamic occupation of the peninsula, and even acted as an internal barrier in some cases over the use of dialects.
“The sampling included micro-regions within the Basque Country and also of the surrounding areas. In this way, we obtained samples from a geographical region where Basque has always been spoken, others where it has historically been spoken but lost and regions where it has never been spoken ”, points out André Flores-Bello , first author of the article. He also emphasizes that "our study is a clear example of the importance of the interaction between different disciplines such as linguistics, genetics and archaeological evidence in reconstructing our history."
In the work they have compared the Basque population with other current European populations and also with data from ancient DNA. The results show that the Basques have a similar genetic composition to other populations in Western Europe but have slight differences. These are due to a lack of genetic flow from the Iron Age, i.e. there has been less mixing with other populations.
David Comas, Professor of Biological Anthropology in the Department of Experimental and Health Sciences ( DCEXS ) at UPF, explains that “for example, we do not find influence from North Africa that is seen in most populations of the The Iberian Peninsula also does not find the imprint of other migrations such as Romanization ”.
On the other hand, they have also addressed the question: how different are the Basques from each other genetically? Within the Basque Country they have observed that those populations that are closer geographically, are more genetically similar. This correlation between genetics and geography is common, as the nearest populations have had a shared history.
What is unique in this case is that there is a lot of compartmentalization within an extremely small geographical region, which is not common in populations of this size. This genetic heterogeneity corresponds to the dialects of the Basque language. "Until now it was thought that these were formed from the Middle Ages but we postulate that they may have arisen much earlier and therefore relate to the genetic structure," says David Comas, head of the Human Genome Diversity group of the IBE.
With new existing methodologies we are increasingly able to reconstruct stories on a smaller scale. "The large number of markers and samples we use in conjunction with computational sophistication allow us to resolve issues that until now we could not address and open the door to knowledge of the most local and recent history of our species," concludes Comas.
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