The main interesting thing about Bangladeshi genetics is how East Asian Bangladeshis are

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I got a question about endogamy and Bangladeshis on of my other weblogs, as well as their relatedness to western (e.g., Iranian) and eastern (e.g., Southeast Asian) populations. Instead of talking, what do the data say? Most of you have probably seen me write about this before, but I think it might be useful to post again for Google (or Quora, as Quora seems to like my blog posts as references).

The 1000 Genomes project collected samples a whole lot of Bangladeshis in Dhaka. The figure at the top shows that the Bangladeshis overwhelmingly form a relatively tight cluster that is strongly shifted toward East Asians. There is one exception: about five individuals, several of which were collected right after each other (their sample IDs are sequential) who show almost no East Asian shift.

This to me is very strange.

Looking at other Bengali samples, whether it be a Kayastha and/or Brahmins from West Bengal, there tends to be a noticeable East Asian shift. The Brahmins though are mostly genetically similar to Brahmins from further north and west, with a minority of their ancestry probably indigenous Bengali, judging by the fact that they usually have less than 5% East Asian ancestry (depending on your metric). I have one Bengali Brahmin in the sample. You can see it as the outlier shifted to the Northwest Indian/Pakistani populations. This individual has very little East Asian shift. In contrast, the West Bengal Kayasthas, a typical “middle caste”, look similar to the Bangladeshi samples, except they have a lot less East Asian ancestry. In other words, they would plot between the Bangladeshi cluster and the other South Asian populations.

I suspect that the individuals with no East Asian ancestry may be from one of the Telugu migrant Dalit communities which settled in Dhaka during the British period.

There are some other East Bengalis on the plot that I added from the SAGP. Four of them are from Comilla. Though now a city, traditionally this region encompassed the area to the south and east of Dhaka, to the border with Tripura. Two of these individuals are my parents. I also added several from Sylhet, which borders Assam to the north (Syhlet people speak an unintelligible language to standard Bengali, similar to the people of Chittagong and the Rohingya). Two things to note.

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First the Comilla individuals are found in the most East Asian shifted portion of the distribution. This suggests, along with the position of West Bengalis, that the eastern ancestry in Bengalis exhibits a west to east cline. My father is somewhat atypical, in that he is shifted out of the main Bangladesh cluster ever so slightly. A genealogical fact though is that his maternal grandfather was reputedly from a Bengali Brahmin family (more likely looking at the attenuated extent of the skew, his mother’s paternal grandfather was a Brahmin).

Second, the Syhlet individuals seem to have something of a shift to Northwest Indians and Pakistanis. But the individual who sent me these data noted that several of the individuals have family records and memory of partial descent from Muslims from Afghanistan and such. That seems likely looking at their position.

Using Treemix, it is notable to me that both the Syhlet and Comilla groups show gene flow more directly from the Dai than the Bangladeshis more generally. I think this is likely an artifact…but there is some slight structure in the Bangladesh population which is probably being missed. The eastern ancestry in Bengalis probably comes from both Austro-Asiatic and Tibeto-Burman people, and this fraction must vary across the region (or normal variation as part of Mendelian segregation).

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Earlier I said the Bangladeshi population is relatively unstructured. Click the Treemix plot above. Or check this Admixture run at K = 5. The Bangladeshi sample has only modest quantitative differences in comparison to most of the other South Asians. To the left are plots of Telugus sampled in the UK, along with South Indian Brahmins. Notice the relatively large range of variance. This is not atypical in sampling from South Asian populations. You see the same pattern in the Gujuratis sampled from Houston, and the Punjabis sampled from Lahore. The partial exception here at the Tamils from Sri Lanka sampled in the UK. There are a small number of individuals who cluster with Dalit groups, but far less than the Telugus. Why? I suspect that panmixia is somewhat along the way in Sri Lankan Tamil populations.

So what’s going on in eastern Bengal? One thing to note is that Muslim Punjabi populations seem to have a huge amount of genetic variation. On par with what you see in Indian populations. The relatively well-mixed character of eastern Bengalis isn’t just a function of caste-less Islam. Bengali Muslims are no more strictly Muslim than Muslims from Punjab. In fact, the stereotype arguably goes in the other direction. Additionally, the variation in East Asian ancestry in Bangladeshis is significant, but aside from what are likely scheduled caste (Dalit) groups which may descend from Indian colonial migrants, I suspect that range in quantum is probably mostly due to geography. The only group of Bangladeshi genotypes where I’ve seen a higher East Asian fraction than my own is of individuals from Chittagong, which is entirely expected from on history and geography.

Based on LD decay the admixture between the East and South Asian components in modern Bangladeshis dates to about 52 generations ago. That’s 1,300 years ago assuming 25 year generation times. A single pulse admixture is a better fit than two distinct events. Because of the range of physical appearance in my family, from mildly East Asian looking (I have family members who can easily pass for Malay or Filipino, at least judging by the languages people speak to them in cosmopolitan areas) to not very East Asian looking, I had assumed that a great deal of the admixture was recent due to proximity (several branches of my family lived in the princely state of Tripura; my grandmother almost killed by a rampaging elephant owned by the Maharani of Tripura). So, I was surprised that my parents both had about the same amount of East Asian ancestry (~15%). This is not entirely shocking, but consider that my mental model of the admixture process was similar to that of African Americans. So if you are a black American, and our parents both turn out to be ~15% European, rather than say 12% vs. 18%, you have to start wondering. So when the LD decay estimate suggested an older, but singular, admixture I was not entirely surprised.

In The Rise Of Islam And The Bengal Frontier 1204-1760 the author presents a model whereby the collapse of Hindu rule in Bengal in the 13th century was coincident with the emergence of a frontier society which expanded the zone of intensive agriculture through reclamation projects. Though the expansion and settlement was directed by Muslims of originally West Asian provenance (Turanian Turks and Afghans), the settlers themselves were peasants who spoke the proto-Bengali language. Curiously, both West Bengalis and Burmese individuals have told me that there is a belief that the indigenous people of Bengal were of East Asian character. The LD decay statistics indicate that most of the admixture occurred well before the arrival of Islam to South Asia, but if settlers were drawn already from the eastern fringe of Indo-Aryan speech, then they would be more enriched to East Asian ancestry. That still leaves one to explain the west-to-east cline of East Asian ancestry even within Bangladesh (East Bengal). That is probably due to secondary  admixture, combined with further gene flow from the west diluting the original admixture signal.

Going back the original question in terms of affinities to western and eastern population and Bengalis. There is a northwest to southeast gradient of “Ancestral North Indian” (Iranian farmer + Indo-Aryan) ancestry in South Asia, and that is evident in Bengal. But, Bengalis clearly have a substantial minority ancestral component from Eastern Eurasia, probably via Austro-Asiatic and Tibeto-Burmans tribes. Though some Bengalis have a small proportion of distinct West Asian ancestry that is distinct from what is found typically in South Asians, that’s about one order of less magnitude significant than the East Asian ancestry.

All of this was pretty clear about five years ago. The more genotypes I get, the more clear and obvious the above assertions are.

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9 thoughts on “The main interesting thing about Bangladeshi genetics is how East Asian Bangladeshis are

  1. I wish I could get involved. I come from the eastern fringe of sylhet and score high East Asian ancestry in most calculators (13-17%). My mtdna is M49 which traces back to NE Indian tribal groups (both Austro asiatic and Tibetan burmese).

    I just feel uncomfortable sending my raw data. I trust you as a person but it’s just the idea of handing over your genetic data to someone you’ve never met.

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  2. Razib, I have a quick question. Is it safe to assume that bengalis are mostly East Eurasian in ancestry?

    My ASI (~20% Iran_N (West Eurasians) + ~80% AASI (East Eurasians))is around ~40-50% .

    My ANI (Iran_BA + Steppe) is ~27%

    So bearing in mind that most of our makeup is AASI + Austro Asiatic Munda + Tibeto Burmese, is it safe to assume we are an ‘East Eurasian’ people as opposed to NW Indians (highly ANI shifted)?

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  3. in the supp of this paper you get a fraction around 55% east eurasian for their bengali (bangladesh) samples.

    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5003663/

    Table S9.4: Mixture proportions for South Asian populations. onge fraction in bengalis is 42%. pathans it is 15%. UP brahmins it is 31%. sindhis 23%. guj. patels it is 42%. bengali fraction would be higher if you correct for the east asian (which drops both ANI and ASI).

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  4. I’ve been waiting a long time for a post like this! ie integrating other regional Bengali / Bangladeshi samples in addition to the BEB academic samples, trying to ease out the finer granularity. Thanks!

    I actually expected the Sylheti samples to show greater East Asian given the geography, but the region is buffered by highlands on all three sides, and I suspect after encountering and mixing with the local tribal people (Khasi etc), the remainder moved up into the hills and the plains remained predominantly Bengali. With Chittagong and Comilla, I suspect there was less of a geographical barrier and into less historic times. And similarly with Rangpur (in the North) opening up to Assam plains where the balance of power was different – three samples I’ve seen, and all score the higher/st East Asian.

    I suspect the geographical cline in East Asian is not as straight forward as one might assume ie W to E. The austroasiatic tribes in the environs of W Bengal must have a larger impact on the Bengalis there compared to tibeto-burman groups on the fringes of the Northern and Eastern Bangladesh. Perhaps that might explain the extra Dai input on the background of a relatively earlier austroasiatic and TB mix.

    The extra W Asian in some Sylhetis may or may not be a real thing. On my mother’s side there is this record dating back a few hundred years, and my maternal cousin and her always seem to plot further out, but so many Bangladeshis seem to have a similar ‘creation myth’, and they date back so many generations, that I question if it would be genuine / so prevalent and that the signal would be preserved.

    Might it represent either a. cosmopolitan higher status muslim society with genuine NW input (not necessarily all foreign to the subcontinent) tending to marry in with each other or b. some actual preserved structure in Bangladeshis – ie from brahmin converts which historically did happen – and subsequently occupying higher status – not just with adopted muslim titles, but also landowning titles which is a big thing in Bangladesh. My father is taluqdar, but have an alleged kayastha ancestor.

    Is there anyway to tease that difference out?

    Maybe it’s a more real life variation of Bangladeshi society which is not picked up solely by the BEB samples (collected at a diarrhoeal centre in Dhaka) but there is more structure out there, which can only be teased out by sampling other social groups ie expats, middle class, rural vs urban. Ie societal structure as well as geography.

    Certainly you seem to have a greater number of Bangladeshi samples on your SAGP – 7 sylhetis and various other groups. How do they all plot?

    The relative clustering of Bangladeshis I wonder might be related to the nature of pre Muslim society in Bengal – Buddhism was highly prevalent before the resurgence of Hinduism pre Muslim conquest. I *assume* caste structure was alot weaker in Buddhist society, and then relatively weak in Muslim society when they eventually converted. And perhaps Buddhists were more likely to mix with local tribal people.

    That might explain the lack of strong structure in both Muslim and non-Brahmin groups.

    Interesting results!

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  5. @Reza Hey Reza, Nice to see you again. I agree with you, Bengalis from different parts likely got the east Asian from local tribes,Khasi in Sylhet, Tripuri in Comilla, Austroasiatic in West Bengal and Western Bangladesh ect.

    It’s also pretty obvious the bulk of East Bengalis are converted Buddhist or converted mid-caste hindus.My ghusti title is “Mullah”, and after talking with some relatives I discovered my ancestors were Imam by profession during Mughal era. None of my relatives claimed any possible foreign origin anyway,so I guess they were local convert possibly of Buddhist origin, As for family status im modern Bengali muslim, that plays a very important role during marriage.For example,the elite ghustis in my ancestral area are Sarkar(Kayastha converts maybe?), Bhuiyan, Mullah, ect. And these ghustis try to maintain good relation.
    The expat Bengalis could be from any social class, and the middle class in both urban and rural area have same root most likely.
    Among Brahmins,Maybe there are differences between Kulin Brahmins and other brahmins, even Vaidyas claimed to be Brahmins but they clustered with Bangladeshis IIRC.

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  6. what is ghusti?

    i think the buddhist thing needs to be careful. in pre-modern world popular religion was very different from elite religion. it is clear that buddhism was strong in bengal in comparison to areas further (at least until u get to punjab and afghanistan, where again it was strong on the eve of islam). but i think what’s more relevant is not buddhism, but that hindu social structures were weak and not robust, because the elites did not support them formally except for the *sena* interregnum.

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  7. “what is ghusti?”

    Ghusti(গোষ্ঠী) means “family(clan,house,dynasty ect.)”, another bengali word is Bongsho(বংশ).

    “i think the buddhist thing needs to be careful. in pre-modern world popular religion was very different from elite religion.”

    So do you think majority of folks under Palas weren’t Buddhist? Palas were the founder of Bengali nationalism and the society was liberal, I guess hindu-buddhist mixed marriages were accepted by the society, same with the upper caste-lower caste marriages among hindus.
    If the common folks were hindu majority, then why many of them embraced Islam and many didnt?
    I heared from a Bangladeshi history teacher that, one of the main reason why Buddhist folks converted to Islam was the strict Brahminic rule under the Senas. Dont know how reliable though.

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  8. So do you think majority of folks under Palas weren’t Buddhist? Palas were the founder of Bengali nationalism and the society was liberal,

    1) most illiterate peasants don’t have a very coherent religious confession no matter what they say. mass religious confessionalization is a feature of the early modern period. i’m not saying that most people were not, or where, buddhist. i’m saying most people practiced a peasant folk religion.

    2) what changed is the elite religion practiced and patronized. this is not irrelevant, but neither is particularly important for the mass of a pre-modern population.

    3) no, i don’t believe that the palas were responsible for bengali nationalism and liberal. liberal/conservative doesn’t make sense in the pre-modern period. the palas were pro-buddhist and presumably not pro-brahman. as for bengali nationalism…i think that’s confused and a ‘not even wrong’ statement. the language spoken in bengal during that time wouldn’t be recognized as bengali, just as we can not understand ‘old english’, which is one of many north germanic dialects of the period. alfred the great is a ‘english national hero’, but that’s really retconning the idea of english nationalism, which didn’t exist in a coherent way in the late first millennium. rather, modern english nationalism has more plausible roots in the synthesis of the anglo-norman culture and the conflict with the french during the 100 years war (and the later identification of the english with protestantism i think had a major impact, just like iran’s relatively recent identification with shia islam).

    eaton seems to suggest the a proto-bengali identity emerged during the period under the afghan rulers, because for them patronizing the vulgar indo-aryan dialect of region undermined the prestige of sanskritic hindu elite culture. though during the mughal period he suggests that bengali identity went into elite hibernation, only to reemerge with the british conquest (sort of like lithuanian nationalism?).

    i don’t know if that’s true. but it’s a definite possibility.

    I heared from a Bangladeshi history teacher that, one of the main reason why Buddhist folks converted to Islam was the strict Brahminic rule under the Senas. Dont know how reliable though.

    we know from genetics that caste endogamy become strict 0 to 1000 AD. that being said, pre-modern states were not totalitarian and could not be totalitarian. strictness was not enforced from above as much as from below (the religous cleansing of the middle east has occurred in the 20th and 21st century for a reason; religious diversity was common under 1,400 years of islam prior).

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  9. “i’m not saying that most people were not, or where, buddhist. i’m saying most people practiced a peasant folk religion.”

    That’s right to the point, the peasant folks and the folks of other professions practised various sects of Buddhism-Hinduism.Even the Pala rulers preferred the tantric practices of Vajrayana sect.
    The Pala Era was also the golden period of Bengal,during that time apart from illiterate peasant society, there was formed an educated middle class as well, for their educational facilities many Viharas were built, our local Shalban Vihara in Maynamoti is one of them(though it was built by an early Deva dynasty).

    “eaton seems to suggest the a proto-bengali identity emerged during the period under the afghan rulers, because for them patronizing the vulgar indo-aryan dialect of region undermined the prestige of sanskritic hindu elite culture.”

    The Pala era was backbone of Bengali identy anyway if we exclude the language part, but the culture,lifestyle,dressing,festivity ect. are still observable in modern society, for example The festivity like Nabanna utshab.
    The Hindu elites like kayastha or Vaidya are the educated version of peasant folk as genetic suggests.

    “though during the mughal period he suggests that bengali identity went into elite hibernation, only to reemerge with the british conquest (sort of like lithuanian nationalism?).”

    In mughal era the Bengali muslims contribution to Bengali literature was notable,Syed Alaol was one of the greatest poets of medieval Bengali literature. He translated many famous works in Bangla as well as wrote his own songs and poetry. Then there was Daulat Qazi,another medieval Bengali poet,Qazi is believed to the first Bengali poet to write under the patronage of the Arakan court.
    In the 18th century, There were muslim bengali women like Rahimunnessa,probably the first female poet of Muslim Bengali origin and nawab Faizunnessa of Comilla,the first female Nawab in south Asia.

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