Planet Earth

Genetics' random truths

Gene ExpressionBy Razib KhanMay 27, 2012 5:05 AM

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Update:Please do not take the labels below (e.g., "Baloch") as literal ancestral elements. The most informative way to read them is that they indicate populations where this element is common, and, the relationship of proportions can tell us something. The literal proportion does not usually tell us much. End Update I was browsing the Harappa results, and two new things jumped out at me. Zack now has enough St. Thomas Christian samples from Kerala that I think we need to accept as the likely model that this community does not derive from the Brahmins of Kerala, as some of them claim. Their genetic profile is rather like many non-Brahmin South Indians, except the Nair, who have a peculiar attested history with the Brahmins of their region. But that's not the really interesting finding. Below is a table I constructed from Zack's data.

I was curious about the distribution of the "Northeast European" component in South Asia. This element is almost entirely lacking in non-Brahmin South Indians (except for the Nair), but, it is present in non-Brahmin Indo-European speaking Indians, including Biharis and Bengalis. And interestingly, it is present in the same rough fraction in North Indian and South Indian Brahmins regardless of locale, ~5 percent in the former case, and ~10-15 percent in the latter. I initially divided them into two language classes, but noticed that the Maharashtra samples were more like the South Indians. Then I remembered something random: there is a tradition dividing Indian's Brahmin communities in two, on a north-south split. The above partition does not perfectly reflect the oral history and custom, but it is very close. The Brahmins of South India are a particularly homogeneous lot. I'd bet that their diversity is a function of cultural evolution and adaptation to local circumstances, not disparate origins. Rather, they derive from some initial migration from a specific North Indian Brahmin community, and then admixed somewhat with another South Indian population (explaining their profiles being closer to the Southern average than that of Northern Brahmins). Finally, most readers will be aware that I broadly accept the outline in Reconstructing Indian History. But, I do think there were multiple waves of northwest population intrusions into South Asia. In particular, I think the demographically preponderant wave was probably West Asian, while a later group brought some Eastern European ancestry into the mix as well.

EthnicityLanguageS.IndianBalochCaucasianNE.Euro

Karnataka BrahminDravidian47%38%4%6%

Karnataka Hebbar Iyengar BrahminDravidian49%36%5%5%

Karnataka IyengarDravidian48%39%3%5%

Karnataka Iyengar BrahminDravidian48%37%3%7%

Karnataka Kannada BrahminDravidian51%35%3%5%

Karnataka Konkani BrahminDravidian47%37%2%6%

Kerala BrahminDravidian43%39%4%6%

Tamil BrahminDravidian46%40%3%6%

Tamil BrahminDravidian47%40%3%5%

Tamil BrahminDravidian48%39%9%4%

Tamil BrahminDravidian47%38%6%4%

Tamil BrahminDravidian48%37%6%5%

Tamil BrahminDravidian48%37%3%5%

Tamil BrahminDravidian48%35%5%6%

Tamil Brahmin IyengarDravidian47%38%6%4%

Tamil Brahmin IyengarDravidian47%35%6%6%

Tamil Brahmin IyengarDravidian50%35%2%8%

Tamil Brahmin iyer/iyengarDravidian48%38%2%5%

Tamil Brahmin iyer/iyengarDravidian48%38%4%5%

Tamil Brahmin iyer/iyengarDravidian47%37%2%5%

Tamil Brahmin iyer/iyengarDravidian47%37%6%8%

Bengali BrahminIE43%35%4%10%

Bengali BrahminIE45%35%2%11%

Bengali BrahminIE44%35%5%11%

Bihari BrahminIE39%38%5%11%

Maharashtra/Madhya Pradesh Saraswat BrahminIE47%39%1%6%

Mahrashtrian Desastha BrahminIE46%38%8%5%

Oriya BrahminIE47%36%0%9%

Punjabi BrahminIE33%41%13%10%

Punjabi BrahminIE35%40%8%11%

Rajasthani BrahminIE32%38%9%15%

Sindhi Pushtikar/Pushkarna BrahminIE31%36%12%10%

UP BrahminIE37%38%2%14%

UP BrahminIE41%37%7%11%

I think this explains nicely the fact that North Indian Brahmins have a "South Indian" cline but not a Northeast European cline 

(compare Bengali Brahmins to Punjabi Brahmins, and you'll see what I mean). One possible model is that a very rapid sweep of an Indo-European speaking population may have occurred across the North Indian plain, overlain upon a local set of populations which had an ANI-ASI cline. The Genographic Project reportedly is going to present results which suggest that the Indian caste system pre-dates the arrival of the Aryans. That would comport well with this model, where earlier groups of northwesterners established a caste-like system, which the Aryans, who later formed the core of the twice-born castes, simply suited to their own needs upon arrival. If you look at Zack's results using public data sets a very low proportion of "Northeastern European," equivalent to what you see in South India, is found in a few groups: - The Dravidian Brahui and Baloch - Tribes and Dalits - Austro-Asiatic populations

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