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Indian Y chromosomes in Thailand

The region of modern Thailand has gone through a major cultural shift over the last 1,000 years. Today the zone of Austro-Asiatic speech in mainland Southeast Asia is fragmented. To the east, there are the Khmer people of Cambodia, as well as various “hill-tribes” in Thailand and Laos who also speak Austro-Asiatic dialects. To the west, there are the Mon people of Burma.

But around 1000 A.D. the whole zone from the India ocean out toward the Mekong was dominated by Austro-Asiatic peoples. Modern-day Thailand was dominated by the Dvaravati polity, of which little is known, but possible Mon associations are assumed.

I have posted several times about the reality that it seems the whole zone between Burma and Cambodia seems to be impacted by a non-trivial proportion of South Asian (Indian) ancestry. A new preprint has a lot of Y chromosomes from various groups in Thailand. Below are frequencies I pulled out of two ethnic groups with large sample sizes (from table 3 in the supplements):

R1a+RLJ2HSample Size
Mon15%2%5%2%105
Central Thai13%0%3%5%129

These lineages are clearly more evidence of Indian males settling in this region.

18 thoughts on “Indian Y chromosomes in Thailand

  1. What a strange and epic tale R1a has – from the icy, frozen steppe of eastern Europe – and some rather robust and hirsute fur clad mammoth hunters, to the small brown lithe hairless semi-nude Thais in their steamy jungle habitat.

    No fiction writer could ever spin such a weird and improbable tale!

  2. That’s more than expected and proves two things:

    1. There was a major colonisation event of dominant Indian males forming new social units, obviously without changing the language all too much. I would presume the total genetic input was rather low, primarily dominant male founder lineages.

    2. The Thai, even though it was a brutal ethnic conquest at first, assimilated huge portions of the local population after the conquest. There are even historically documented cases of local “hill people” gathering around a Thai market place and central village, becoming dependent and switching to Thai speech and customs in a couple of generations.

  3. Any R2 Y-DNA. For a haplogroup so common in South Asia, we barely see it make headlines.

    go clean the latrines! 😉

    though seriously, in the supplements they have R* haplogroup. i think some of those must have been R2.

  4. Well then, dominant R1a without indo-European language.

    Does this mean R1a can be uncoupled from “Aryans”?

  5. I think both in South India and SEA R1a was transmitted by Indo-Aryan male lineages primarily, but they changed their ethnicity and integrated into local communities where they couldnt turn them.
    Even most Indian “tribals” seem to have got it from “renegades”, refugees and infringements.
    The high percentage of R1a and J2, the most important Caucasoid markers in South Asia, speaks for itself.
    There were elite males from India taking opportunities in a wild country. The Khmer civilisation was the product of this fusion.

  6. “The high percentage of R1a and J2, the most important Caucasoid markers in South Asia, speaks for itself.”

    What do you mean by Caucasoid? Original H and L males probably had caucasoid traits too.

  7. Yes, but R1a and J2 are the most clearly associated with Northern Indian elites of recent, fully Caucasoid origin. I pointed that out because this is true for the vast majority of these lineages regardless of where they appear later.
    They don’t descend from local SA and SEA “tribals”, they just spread to those too.

    The same can be said for the Northern East Asian lineages which spread from the other side of the temperate-cold zone.

  8. Y-HGs: J2a1-L26, R1b1a2 (in supplement)

    The U.S. Air Force maintained 7 air bases in Thailand between 1961-1975 (check the map in Wikipedia)… just saying.

    I thought the material in this paper could have been better organized.

  9. Yes, but R1a and J2 are the most clearly associated with Northern Indian elites of recent, fully Caucasoid origin. I pointed that out because this is true for the vast majority of these lineages regardless of where they appear later.

    two points

    1) all indian groups are like 25 to 75 AASI. even high caste groups are like what 40% aasi? i would need to check the numbers

    2) J in particular is found in high % among south indian non-brahmins

    but yeah, r1a is enriched weirdly. so that leans to north, but isn’t dispositive of south (south indian brahmins have high r1a %)

  10. It seems a shame there’s no autosomal panel to compare.

    A study a couple years back “Characterising private and shared signatures of positive selection in 37 Asian populations ” – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5386408/ had about 400 Central Thais who were very scattered in position.

    Their crude ADMIXTURE K=4 looks about 15-20% Tamil-like, so that seems reasonably consistent with around 20-25% South Asian like y (11% R1a1+ 3%J2+ 5%H1+miscelleanous others) give or take statistical variance.

    (Fig S1 and S2 above: https://imgur.com/a/qECLpoi)

  11. @Razib: Both R1a and J2 are enriched in higher castes relatively. It depends on exact caste and ethnicity.

    Southern Brahmins have Northern relations and J represent the Iranian-related Dravidian element, of which some clans made it to the top.

    If you look at the Indian derived frequencies in SEA, wouldnt this paternal pool fit best into high caste/Northern Indians? I’d say so.

    Clearly the clans, priests, warriors, adventurers and tradesfolk which transformed SEA with Indian genes and culture in the Khmer civilisation are more likely to have come from the top and middle of India.

    Its intriguing however that one can see both Northern (IA) and Southern (Drav) influences in the Khmer culture. Probably different layers of Northern founders and later priests and traders keeping contacts?

    @Matt: Pre-Thai Khmer might have had much more Indian influence, especially paternally.

  12. I tend to favour the conventional and consensual narrative where it’s mostly South Indian traders and priests providing religious material and luxury goods to late Bronze and Iron Age kingdoms centered around local elites, which then define some religious identity and this continues over time, with foreign origin stories for dynasties and kings and military elites mostly as made up as claims that Aeneas the Trojan founded Rome (as probably anyone could tell from previous convo with Obs).

    But of course, that isn’t to say that a group with both the high autosomal AASI input that seems to define South Asian input to SE Asia and high relatively high R1a frequency did not exist in the past and migrate to SE Asia (whatever their economic and political roles), even if it is not the typical combination in S Asia today. Just because that is not the typical association today, does not mean a group (or groups) in the past could have existed which went deep into S Asia and accrued heavy AASI ancestry while remaining in contact with the cultural core, and then moved to SE Asia.

    If you assume the association of R1a with priestly elites (and probably within early Theravada Buddhism too!), and then the association of AASI ancestry with geographical position that makes migration to SE Asia more likely, migration by high AASI+high R1a group even seems like a plausible outcome (even if the association is somewhat inverse to the general one)?

  13. Rather I think that some of the AASI related autosomal profile might be actually independent from the elite males lineages. Which means: The AASI-like component was probably there already, the R1a+J came in later and had a fairly low overal genetic impact, because they mixed and married local women in a row. Similar to R1b in West Africa.

  14. That seems genetically possible, though I don’t think it seems as parsimonious to me to postulate parallel shadow movements that look one signal where the autosomal and y signal look reasonably similar, as a single group forming in South Asia and then moving into SE Asia.

    Likely reality is between the two (and a single group or two shadow movements are a stylized version of ground truth), but it seems unless you had some strong bias for having as West Eurasian as possible males spreading culture and reproducing with local SE Asian women, there seems like there would be no reason to prefer such a scenario.

    But that’s just what seems simplest to me. I don’t know if we will ever get plentiful enough data to actually test scenarios like this in detail. To some degree you can probably test association of South Asian y-dna with AASI though – only if it’s completely unassociated would you find such a scenario I think, although that could still be false due to association breaking up over time. If you instead have a cline of increasing AASI with R1a over thousands of samples, that probably inclines more to that group and R1a entering together (you probably can’t really get a false positive there). You’d probably need a Biobank scaled sample set to do that properly though.

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