Razib Khan One-stop-shopping for all of my content

August 12, 2018

Live not by the haplogroup alone

Filed under: Historical Population Genetics,Y chromosomes — Razib Khan @ 11:21 pm

In The population genomics of archaeological transition in west Iberia the authors note that “the population of Euskera speakers shows one of the maximal frequencies (87.1%) for the Y-chromosome variant, R1b-M269…” In the early 2000s the high frequency of R1b-M269 among the Basques, a non-Indo-European linguistic isolate, was taken to be suggestive of the possibility that R1b-M269 reflected ancestry from European hunter-gatherers present when farmers and pastoralists pushed into the continent.

The paper above shows that the reality is that the Basque people have higher fractions of Neolithic farmer ancestry than any other Iberian people. Additionally, they have lower fractions of the steppe pastoralist ancestry than other Iberian groups. This, despite the fact that we also know from ancient DNA that R1b-M269 does seem to have spread with steppe pastoralists, likely Indo-Europeans.

Obviously the relationship between Y chromosomes and genome-wide ancestry is complex. The pattern here for the indicates that Indo-European male lineages were assimilated into the Basques. Perhaps the Basque were matrilineal? One can’t know. But, these men did not impose their culture. Instead, they were assimilated into the Basque. This is entirely not shocking. There history of contact between different peoples in the recent past shows plenty of cases where individuals have “gone native.” In some cases, many individuals.

I was thinking this when looking at South Asian Y chromosome frequencies. Though R1a1a is correlated with higher castes and Indo-European speakers, its frequency is quite high in some ASI-enriched groups. I suspect that the period after 2000 BC down to the Common Era witness a dynamic where particular patrilineal societies were quite successful in maintain their status over generations. Additionally, the ethnogenesis of “Indo-Aryan” and “Dravidian” India was occurring over this period, in some cases through a process of expansion, integration, and conflict. It seems some pre-Aryan paternal lineages were assimilated into Brahmin communities. For example, Y haplogroup R2, whose origin is almost certainly in the Indus Valley Civilization society.

Some population genetic models are stylized and elegant. They have to be to be tractable. But we always need to remember that real history and prehistory were complex, and exhibited a richer and more chaotic texture.

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