Monday, December 02, 2019

The Basques May Not Be Who We Think They Are

discover |  In terms of historical genetics these assumptions result in the Basque population be used as a “reference” for the indigenous component of the European ancestry which reaches back to the Last Glacial Maximum, and expanded from the Iberian refugium after the ice retreated. One of reasons for the assumption of Basque antiquity & purity are genetic peculiarities of the Basques. Foremost among them is that the Basque seem to have the highest frequency of Rh- in the world, primarily because of the high frequency of the null allele within the population (it is a recessively expressed trait). Rh- is very rare outside of Europe, but its frequency exhibits a west-east gradient even within the continent. It has been suggested that the mixing of Rh- and Rh+ blood groups reflects the mixing of hunter-gatherers and farmers in after the Ice Age. The map above the illustrates the frequencies of this trait, and you can see how the Basque region is cordoned off. It’s an old map because blood group were widely collected in the early 20th century. Because of the early knowledge of this heritable trait you have a lot of weird anthropological theories which hinge around blood group genetics having emerged in the early 20th century. But even as late as the mid-90s L. L. Cavalli-Sforza reported in The History and Geography of Human Genes using classical markers that the Basques exhibited some distinctiveness. Over the years with the rise of Y and mtDNA phylogenetics this distinctiveness has taken a hit. I think the data have a tendency of confirming expectations, or it is often interpreted as such. But the recent story of the R1b haplogroup strongly implied that the Basques are no different from other west Europeans, and are likely the descendants of Neolithic farmers themselves! A new paper in Human Genetics supports the contention that the Basque are just like other Europeans, A genome-wide survey does not show the genetic distinctiveness of Basques:

Basques are a cultural isolate, and, according to mainly allele frequencies of classical polymorphisms, also a genetic isolate. We investigated the differentiation of Spanish Basques from the rest of Iberian populations by means of a dense, genome-wide SNP array. We found that F ST distances between Spanish Basques and other populations were similar to those between pairs of non-Basque populations. The same result is found in a PCA of individuals, showing a general distinction between Iberians and other South Europeans independently of being Basques. Pathogen-mediated natural selection may be responsible for the high differentiation previously reported for Basques at very specific genes such as ABO, RH, and HLA. Thus, Basques cannot be considered a genetic outlier under a general genome scope and interpretations on their origin may have to be revised.