March 13, 2012

Pre-Roman genetic structure has persisted in modern Basque populations

This is a fairly interesting study that paints a picture of continuity of genetic structure among Basques since pre-Roman times. I am not sufficiently familiar with either Basque history or geography to comment on this in detail, but the central conclusion that Basques differ from their neighbors in being more isolated and less cosmopolitan is something that I have also noticed in my own experiments (see for example the K12b population portraits, contrasting French_Basque and Pais_Vasco_1KG with other Iberian/French populations).

For those who know more, does the following scheme make sense?

Y-haplogroup frequencies, showing a preponderance of R-M269 related lineages and a strong showing of the the I-M26 lineage are shown below. The latter links Basques with Sardinians, as well as probably with Neolithic France.

Codes (from the paper): BIG, Bigorre; BEA, Béarn; CHA, Chalosse; ZMI, Lapurdi/Baztan; NLA,Lapurdi Nafarroa; SOU, Zuberoa; RON, Roncal and Salazar valleys; NCO, CentralWestern Nafarroa; NNO, North Western Nafarroa; GUI, Gipuzkoa; GSO, SouthWestern Gipuzkoa; ALA, Araba; BBA, Bizkaia; BOC, Western Bizkaia; CAN,Cantabria; BUR, Burgos; RIO, La Rioja; NAR, North Aragon.

The picture of continuity is further strengthened by ancient Basque Y-chromosomes, showing the same picture of R1b-majority/I minority as today. What we really need now is to bridge the gap between late antiquity and the Neolithic, and beyond to better understand the temporal sequence of settlement.

Mol Biol Evol (2012)doi: 10.1093/molbev/mss091

Evidence of pre-Roman tribal genetic structure in Basques from uniparentally inherited markers

Begoña Martínez-Cruz et al.

Basque people have received considerable attention from anthropologists, geneticists and linguists during the last century due to the singularity of their language and to other cultural and biological characteristics. Despite the multidisciplinary efforts performed to address the questions of the origin, uniqueness and heterogeneity of Basques, the genetic studies performed up to now have suffered from a weak study-design where populations are not analyzed in an adequate geographic and population context. To address the former questions and to overcome these design limitations, we have analyzed the uniparentally inherited markers (Y chromosome and mitochondrial DNA) of ∼900 individuals from 18 populations, including those where Basque is currently spoken and populations from adjacent regions where Basque might have been spoken in historical times. Our results indicate that Basque-speaking populations fall within the genetic Western European gene pool and they are similar to geographically surrounding non-Basque populations, and also that their genetic uniqueness is based on a lower amount of external influences compared to other Iberians and French populations. Our data suggest that the genetic heterogeneity and structure observed in the Basque region results from pre-Roman tribal structure related to geography and might be linked to the increased complexity of emerging societies during the Bronze Age. The rough overlap of the pre-Roman tribe location and the current dialect limits supports the notion that the environmental diversity in the region has played a recurrent role in cultural differentiation and ethnogenesis at different time periods.



Maju said...

"does the following scheme make sense?"

Nobody knows the exact prehistorical phylogeny of Basques/Gascons, although it does make sense to me that Gascons ("Aquitanians") are more diverse because all flows except Neolithic ones (i.e. all Paleolithic flows) arrived from there. So, unless you want to beat the dead horse of Neolithic origin, Gascony and the Northern Basque Country should be more diverse and old, all the rest being equal.

The rest of the structure may actually be an effect of Neolithic/Celtic admixture advancing by the banks of the Ebro river. The dates naturally make no sense to me: there are archaeological sites which are continuous, layer on layer, from Gravettian to the Iron Age. But the structure may make sense if you accept that "foreign" Mediterranean-Neolithic and, to lesser extent, later Celtic inflows have expanded the genetic diversity of Ebro Valley peoples.

This admixture may also have affected Gascons but the areas surveyed are close enough to the Basque core zone to have probably remained quite unmixed.


Besides, it is interesting that:

1. R1b: confirmed that 2/3 relevant basal lineages of the South Clade (P312), plus large numbers of P312* (still unresolved) are very dominant. The third (the "Celtic" or rather Sub-Alpine clade, U152) is also present and rather widespread (subclade L2 specially), although not too numerous. The "Irish" clade L21 is instead quite numerous (>5% everywhere except CAN, BUR and NAR, >20% in Lapurdi, Roncal,Gipuzkoa, Araba...) and also widespread.

2. The possibly Neolithic lineages >5% are specially I2a1a (almost everywhere) and J2a (Navarre, Rioja and Burgos). Also T only in Cantabria and E-V65 in Araba. That's it. Previous reports of high E in Cantabria and Valle del Pas (near Biscay) are not confirmed here.

3. NW I is also found: I2b in Bigorre and Dax, I1 in Araba (always so special!)

(I'm still unable to subscribe to email feedback for comments).

anthrospain said...

Interesting to see that R-L21 surpasses 20% in many places on the Spanish side, for a total of 16% overall for all the spanish samples.

SimonW said...

I'm a little late with commenting on this, but it's really striking how the three main Basque haplogroups, i.e.: R1b-P312, R1b-L21 and R1b-M153 get more frequent as we move from the general research area to the most Basque regions.

Together they make up,

- in the whole area, which may or may not have been Basque in previous times: 67,3%

- in the mixed areas: 74%

- in the Basque core areas: 85%

This is completely the opposite of what we would expect if R1b-S116 introgressed from surrounding IEs into Basques! It's strong evidence for the idea that it has originally been a Basque haplogroup, not Celtic, leave alone Italo-Celtic, as some have suggested. Actually Italic seems rather associated with J2a, in fact, despite its undeniable similarity with Celtic.

Furthermore, there's also the curious fact that the "British" R1b-L21 gets more frequent towards the Basque core area, where it reaches an astounding incidence of 19,1%.
Conversely, there's a subvariant of the Basque/Gascon/Catalan (i.e. Basque + Iberian) R1b-Z196, namely L165/S28 found at appreciable frequencies in Scotland. This taken together is strong evidence for intimate contacts and exchange between Britain and the Basque country at some time in the past. And YET there are only very few Celtic loanwords in Basque. This indicates to me that the Britons were not yet Celtic speaking back then.