Tag: Y chromosomes

The persistence of Neolithic Y chromosomes at Orkeny

Posted on by Razib Khan

Ancient DNA at the edge of the world: Continental immigration and the persistence of Neolithic male lineages in Bronze Age Orkney:

Within the European context, the Orkney BA stands in stark contrast as a location, at the northwestern extreme of the continent, where the majority of the genome was overwritten between the Late Neolithic and the end of the EBA but the male lineages somehow persisted. Even so, we can understand this phenomenon in terms of the same patrilocal marriage practices that we see throughout west Eurasia. The ancestral distribution in Orkney demonstrates deliberate marriage patterns involving local men and incoming women. This process of preferential assimilation seems likely to have continued for many generations, given the extent of replacement of the remainder of the Orcadian Neolithic genome.

The existence of a powerful and likely strongly hierarchical strand in Neolithic society has been proposed on the basis of the discovery of an incestuous first-degree union at Newgrange in Ireland (41) and was prefigured by earlier analyses of Ireland and other megalithic cultures in both northwest and central Europe (32, 48). Cassidy et al. (41) argue that it encompassed the whole of Ireland, adding that it may have incorporated the similar megalithic communities of Wales and Orkney, most likely originating in Brittany (1, 49). I2a1b-M423 is seen in both Mesolithic and Neolithic Ireland, and the main cluster seen in Late Neolithic Ireland, I2a2a1a1-M284—found in the putative elite lineage at Newgrange—matches an Orcadian Neolithic lineage from the Isbister Chambered Cairn (“Tomb of the Eagles”) on South Ronaldsay (Fig. 3 and SI Appendix, Fig. S13) (13). Both our data from BA Orkney and the Neolithic circumcoastal distribution of the Y-chromosome I2a1b-M423 haplogroup lend further support to this suggestion. European Neolithic society, at one extreme (but hardly peripheral) edge of its distribution, may have been patrilineal, patrilocal, and hierarchical long before the arrival of the Beaker complex and (most likely) Indo-European speech (27, 28, 31, 50).

Basically, a Y chromosomal lineage assimilated from Iberian hunter-gatherers, and assimilated into Neolithic farmers, seems to have spread over the British Isles and persisted in a part of Orkney as the dominant paternal line for 1,000 years after it was overwhelmed elsewhere.

Live not by the haplogroup alone

Posted on by Razib Khan

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.