February 4, 2017

The patrilineage R1b-DF27 in North Iberia

Just weeks ago a new study on Northern Iberian Y-DNA, focused specifically on R1b-DF27, was published. It covers Asturias, Cantabria, Basque Country and Aragon, finding greater diversity in the Basque Country and Cantabria and lower in Aragon and Asturias.

Patricia Villaescusa et al., Characterization of the Iberian Y chromosome haplogroup R-DF27 in Northern Spain. FSI-Genetics 2017. Pay per viewLINK [doi:10.1016/j.fsigen.2016.12.013]


The European paternal lineage R-DF27 has been proposed as a haplogroup of Iberian origin due to its maximum frequencies in the Iberian Peninsula. In this study, the distribution and structure of DF27 were characterized in 591 unrelated male individuals from four key populations of the north area of the Iberian Peninsula through the analysis of 12 Y-SNPs that define DF27 main sublineages. Additionally, Y-SNP allele frequencies were also gathered from the reference populations in the 1000 Genomes Project to compare and obtain a better landscape of the distribution of DF27. Our results reveal frequencies over 35% of DF27 haplogroup in the four North Iberian populations analyzed and high frequencies for its subhaplogroups. Considering the low frequency of DF27 and its sublineages in most populations outside of the Iberian Peninsula, this haplogroup seems to have geographical significance; thus, indicating a possible Iberian patrilineal origin of vestiges bearing this haplogroup. The dataset presented here contributes with new data to better understand the complex genetic variability of the Y chromosome in the Iberian Peninsula, that can be applied in Forensic Genetics.

The study, quite conveniently, differentiates between "native Basques" (those whose patrilineal ancestors lived in the Basque Country for at least the last three generations) and "resident Basques" (those whose recent patrilineal ancestors immigrated, mostly from NW Iberia).

R1b-DF27 is one of four major R1b sublineages in Western Europe and one of the three "brothers" that can be tracked to an origin somewhere in what is now Southern France, most likely, i.e. together they form part of R1b-S116. The fourth lineage would be, naturally, R1b-U106, "brother" of S116 and found typically around the North Sea. It is the one with the southernmost distribution, being very dominant in Iberia and among Basques. Probably it is also important in all the south of modern France but clear data is missing as of now.

Reconstructed spread of R1b to Western Europe and within it (dates objectively unknown so far, own work)

This is the key data table of the study, showing the frequency of the various sublineages of R1b-DF27 ("*" means "others", so "DF27", without asterisk, means "all DF27" and "DF27*" means instead "remaining DF27 after exclusion of the other mentioned subclades"):

Click to expand (frequencies are absolute, relative to whole sample)
It is also worth sticking this other graph, which shows (top right) the (SNP-based) true phylogeny of the haplogroup R1b-DF27 and, complementarily, the (somewhat messy) haplotype structure based on a limited number of short tandem repeats (STR), in which only Z220 appears clearly defined:

Click to expand

The study is very limited in its scope but it does show that there is a very high diversity for this lineage among Basques. This however does not necessarily indicate that Basques are the direct origin: much more data from the rest of Iberia and very especially from France is required before we can jump to any conclusion. Based on the limited data we have, I am of the opinion that the lineage did not originate in Iberia most likely but rather in what is now Southern France, migrating southwards via the two natural corridors: the Basque Country and Catalonia. 

Sadly enough we just do not have enough modern data, much less ancient one, in order to issue a definitive judgment on the matter. However the overall pattern of distribution of R1b-S116 strongly suggest a "Southern French" origin, not just for "Iberian" DF27 but also for the other two "brother" lineages: "Alpine" U152 and "North Atlantic" M529. 

The big question is how and when did this expansion took place. A "South French" origin was much easier to explain when the Paleolithic continuity model seemed reasonable, however recent ancient DNA findings strongly suggest that the Neolithic and Chalcolithic saw major population changes in much of Europe until stabilization was achieved -- exact patterns vary on specific regions: in some cases this does not happen until the Bronze Age, in others, like the Basque Country and quite possibly the Atlantic parts of France, it may have happened much earlier, even as soon as the early Neolithic. 

So my best recipe for an explanation is that we have to look very carefully at what happened in Western Europe, particularly towards the Atlantic Ocean in that "transitional" period, when not just large cultural phenomena like Dolmenic Megalithism or later also Bell Beaker manifested in quite expansive and dynamic manner but also a dearth of smaller cultures were the actual social or ethnic pieces making them possible. For example it is plausible that Michelsberg culture (originating in Lower Rhineland apparently and swiftly replacing the early Neolithic LBK culture in Germany, North France and nearby areas) could be involved in the expansion southwards of R1b-U106 and other traits of the modern genetic pools we observe. Another culture well worth taking a look at is the Artenac culture, which expanded from Dordogne towards the North up to Belgium soon after the Michelsberg/SOM era. Rather than one single and sudden expansion of a well defined population, it seems to me that we are before a jigsaw puzzle of several cultures and several chronologies, related maybe but not exactly the same.

See also:

Thanks once again to Jean Lohizun.