I’ve been rather busy with other things and the South Asian Genotype Project has fallen a bit by the wayside. But, I plan on allocating a day on a weekend soon to getting through the backlog. But, before that, I thought I would submit something that might clarify or illuminate an aspect of South Asian history and culture that the data have shown.
The public data have a large number of Bangladeshis. Sampled in Dhaka. Unlike most South Asians they don’t exhibit much structure. But unfortunately, we don’t have too many samples from West Bengal. That being said, I do get some through this project. As you can see on the plot (round dark point) the Brahmins of Bengal are genetically very distinct from the Bangladesh samples (I have more samples, but this position is always the same for all of them). In fact, they are closer to Brahmin samples from Uttar Pradesh. Using modeled based clustering though I have become strongly convinced that the Bengali Brahmins do have a minor contribution from the non-Brahmin Bengali population because they have East Asian ancestry.
The triangles on the plot are from Kayastha individuals from West Bengal. I have seen a few Kayasthas from this region, and two trends about them:
- closer to Bangladeshis than Bengali Brahmins
- a lower fraction of East Asian ancestry than Bangladeshis
The lower fraction of East Asian ancestry is explained by an admixture cline which is a function of geography. My own East Asian admixture is high, and that is easily explained by the fact that my family is from the very east of eastern Bengal. As far as number one, one hypothesis some have presented is in Bengal the influence of Buddhism relatively late in history (down to ~1000 AD) resulted in a relatively panmictic population with low amounts of structure (a problem with this model is that Buddhism was strong in Punjab relatively late, but that region has lots of structure).
In any case, socially this is relevant because the Brahmins and Kayasthas of Bengal have traditionally been the two groups which are the pillars of the gentry class of the region (“bhadralok”). But there have been subtle differences between them. The Kayasthas have traditionally been more willing to work with Muslim rulers as a literate service class, as their ritual status is lower than Brahmins, and so presumably they had less to lose from “pollution” through contact with these foreign groups.
Looking at the genetic differences between the two major castes of the gentry in Bengal is interesting because it is a test of a model of the origin of caste in South Asia. Overall I think Nicholas Dirks’ Castes of Mind has not had a good effect on how we understand caste and jati, but it isn’t totally uninformative for what we see in Bengal. Like South Indian Brahmins, Bengali Brahmins can be modeled as a mixture of Brahmins from the upper Gangetic plain, with a minority local substrate contribution (~25% or less). They are genetically a distinct population whose endogamy is ancient and thorough. In contrast, the Kayasthas are “generic Bengalis,” who likely did increase their social status by becoming a literate bureaucratic class (“clerks”).