Data Points About The Mostly Iberian Y-DNA Clade R1b-DF27

A new paper explores the predominantly Iberian branch of Y-DNA haplogroup R1b which is timely because the narrative that explains the population genetics of Iberia is much less clear than most other places in Europe.

The most common Y-DNA clade in Western Europe is R1b-M269. As Bernard's Blog explains (note that all translations are Google translated from the original French with my editorial improvements of those translations):

The most important branches of M269 are U106 common in the Netherlands and Northwestern Germany, and P312 common in Western Europe. The latter is divided into three main branches: U152 common in Switzerland and Northern Italy, L21 common in the British Isles and DF27 frequent in the Iberian Peninsula.

Y-DNA R1b-DF27 predominant in Iberia and especially in Basques and parts of Eastern Spain that were Vasconic linguistically in historically attested times. 

This Y-DNA R1b clade is a sister clade to the R1b haplogroups found in the British Isles and in Switzerland and Northern Italy. But, it is a more distant relative of the R1b clades around in the Netherlands and Northwest Germany (which is close to the area where the Germanic languages emerged, probably much later based upon linguistic evidence).

The new blog post focuses on a paper analyzing Y-DNA R1b-DF27 which is the most common in Iberia (especially Basque territory and Catalonia), and spills over into France as illustrated in the geographic distributions below:

DF27 is found at a frequency ranging from 30% to 50% in the Iberian Peninsula except in the Basque Country where Frequency reached 74%. In France, the frequency varies from 6% to 20% with an average of 11%. Elsewhere the frequency is 15% in Great Britain but almost nil in Ireland and 8% in Tuscany.

The subclade just downstream of DF27 is Z195. The frequency of the latter varies from 29% to 41% with two main peaks in the Basque Country and in Eastern Spain. Then Z195 divides into two main branches: L176 and Z220. L176 has a peak frequency in Eastern Spain while Z220 has a peak frequency in the Basque Country.

The inferred ages of these clades coincides well with an arrival fairly early in the Bell Beaker era, followed by local differentiation.

Within each population, DF27 is older in Aragon (4530 years) than in the Basque Country (3930 years). Z195 is older in Catalonia (4580 years) In the Basque Country (3260 years). Conversely, Z220 is older in Central North Spain (3720 years). Thus, the greater diversity in eastern Spain and the older age in this same region, point towards an origin of the haplogroup R1b-DF27 in eastern Spain.

Models of Bayesian analysis show that DF27 extended in the Iberian Peninsula mainly between 3500 and 3000 years, i.e. in the Middle Bronze Age. These results are to be compared with those of ancient DNA in Portugal which show the dominance of haplogroup R1b in the Middle Bronze Age. This points to an origin of the haplogroup R1b-DF27 in eastern Spain. 

Analysis

Our access to ancient DNA is limited, but the ancient Iberian Bell Beaker DNA that we do have shows quite modest levels of autosomal steppe ancestry, but basically total replacement of Y-DNA R1b, which would be consistent with a male dominated migration event that was diluted in autosomal impact by multiple generations of marriages to non-steppe women with early European farmer and Western hunter-gather ancestry.

If Y-DNA R1b-DF27 mere were the source of the Bell Beaker phenomena, one would expect an age for the clade of about 4900 years and a point of origin based on clade ages and maximum diversity in Southern Portugal. But, that isn't what we see. Indeed, many important sub-clades of Y-DNA R1b-DF27 are entirely absent from Portugal and the clades we do see are heavily concentrated within Iberia in historically attested Vasconic areas, casting doubt on the hypothesis of a broader Vasconic linguistic area, particularly within Iberia.

Origins for R1b-DF27 in Eastern Spain ca. 2600 BCE to 2500 BCE suggest a maritime or southern European coastal route of these R1b men into Spain. The location of the Northern Italian sister clade of DF27 also supports a maritime or coastal route. This is several hundred years after the Bell Beaker phenomena begins in Southern Portugal ca. 2900 BCE. Presumably, these men adopt the Bell Beaker culture when it expands to their territory, rather than playing a part in its formation.