Someone in the comments posted the results from The Genomic Formation of South and Central Asia. I put the percentages with a few ratios in a Google doc. I don’t know what a lot of these groups are. Can readers illuminate? We need to be careful about the sample size, but I think there are a lot of interesting patterns in there.
Remember that “Steppe”, “Indus Periphery” and “Onge” are populations artifacts within a model. The way I explain it to people is that rather than focusing on the percentage, look at how the populations vary across the parameters. That is a pretty robust result. No matter what outgroups you’re going to use, Brahmins in most of South Asia seem to have more “West Eurasian” type ancestry than other populations (except in the NW). Because “Indus Periphery” has a minority of “Ancient Ancestral South Indians” (AASI) as part of its ancestry, the “Onge” fraction should be seen as a floor on AASI ancestry (the Onge ancestors diverged from the AASI ~40,000 years ago, so it’s a very large difference).
To me this part of the preprint really jumped out:
Later samples from the Swat time transect from the 1 456 st millennium BCE had higher proportions of Steppe and AASI derived ancestry more similar to that found on the Indian Cline, showing that there was an increasing percolation of Steppe derived ancestry into the region and additional admixture with the ASI through time…
Here is a subset of the populations in the attached sheet. I’ve clearly differentiated four different groups:
What you see is enriched Onge in high caste groups with a lot of Steppe in North India compared to Sindh and Gujarat. What I think this suggests is that the matrix of the Indus Valley Civilization broke, and Aryan agro-pastoralists expanded across a landscape where there wasn’t necessarily preexistent complex society. On the eastern frontier in the Gangetic valley, relatively unmixed Aryans may have interacted with local AASI tribes, and assimilated them.
In contrast, in Sindh and Gujarat, the IVC matrix was denser, and the AASI had long been marginalized. Though Aryans moved into these regions, a huge proportion of the population remained classic “Indus Periphery”, and the AASI tribal populations were much more marginal than they were in the Gangetic valley.
Meanwhile, in South India, you have the phenomenon of large differences between lower caste and higher caste populations.
With all these data, I think the most plausible scenario is that we can imagine that the period between 1900 BC, when the IVC went into sharp decline, and the reemergence of South Asia into “history” around 500 BC, is one of massive churn, interaction, migration, and eventually social-cultural integration. Also, I assume that the Aryans must have come via a “northern route.” Steppe ancestry always seems higher in northern groups in Pakistan than southern ones (though not necessarily AASI ancestry), so a simple explanation is that this is where Aryans first entered the subcontinent. But how does this work with pastoralists?
Anyway, please give me your opinion on the Google doc.
(also, I’d kindly ask you to minimize long rants…otherwise I will just delete the comment anyhow)