Diminishing returns of ancestry analysis (for me)

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Zack has finally started posting results from HAP. To the left you see the results generated at K = 5 from his merged data set with the first 10 HAP members. I am HRP002. Zack is HRP001. Paul G., who is an ethnic Assyrian, is HRP010. Some others have already “outed” themselves, so I could proceed via process of elimination for the other bars. There isn’t anything very surprising here. Zack is 1/4 Egyptian, so he has a rather diverse ancestry. Jatts, who are from Northwest India, are known to have more affinity with populations to the west than those of us from the east or south of the subcontinent. With just that knowledge you can make some educated guesses as to what the “ancestral components” inferred from ADMIXTURE might correspond with in a concrete sense. After submitting to Dodecad and the BGA Project I pretty much know what to expect in relation to me. I’m a rather generic South Asian, except, I have an obvious input of “eastern” ancestry.

This is what Dienekes also found. Aggregating various ancestral components together to be analogous to what Zack produced at K = 5, you get the bar plot below from his runs:

I assume that all ancestry analyses will find that I have a substantial minority of East Eurasian ancestry. I have a similar amount of ancestry which is obviously connected to West Eurasia. And the rest of my ancestry is going to fall into the catchall which is “South Asian,” which Reich et al. in Reconstructing Indian History argued was in fact a compound between a West Eurasian-like population (“Ancestral North Indian,” ANI) and a South Eurasian population (“Ancestral South Indian,” ASI) which was more closely related to East Eurasians than West Eurasians, though distantly so at that (modern West Eurasians are interchangeable with ANI, but ASI do not exist in unadmixed form).

Finally, here’s an analysis of chromosome 1 and its affinities to various reference populations. I’ve labelled myself. No surprises:

I am HRP002 in HAP. DOD075 in Dodecad. IN8 in BGA. I am willing to submit to any of these new grassroots ancestry projects if they want me. But I doubt I’ll find anything too surprising now. They converge upon the same rough proportions (as they should).

I’m at the stage where I want to look more deeply into the details of how long ago the “eastern” admixture occurred. It seems to come down from both parents. If it was very recent there should be some linkage disequilibrium detectable because recombination should not have broken down the allelic associations distinctive to each ethnic group yet (this is noticeable in African Americans). But I am not so sure it is recent anymore, as I’d thought. I suspect a Tibeto-Burman and Munda element were absorbed by Bengali peasants in the course of demographic expansion in what became Bangladesh between 1000 and 1500 A.D., and that ancestry is well distributed across the population now.

But even though I won’t find anything out for myself, the reason HAP and projects like it are useful is that we need better coverage of the world’s variation. There are big coarse questions which we’ve tapped out, but there are still lots of gaps to fill. I’m willing to do my part in that (or, more precisely, at this point I’ve drafted my parents into the role, since they aren’t related and so represent two independent data points for Bengal).

Addendum: I know for many people of European ancestry this sort of thing doesn’t tell them anything new. Not so for me. I always suspected East Asian admixture due to the phenotype of my extended family (and to some extent, me. I did not need to shave regularly until my 20s), but I was always curious as to its extent. Additionally, for the reasons of phenotype I had assumed my mother had very little of such ancestry while my father had a great deal. It turns out that in fact my mother may marginally be more “eastern” than my father.

2 Comments

  1. I am IN9 on Davidski’s chromosome 1 chart there. As HRP0016, I should be in Zack’s next batch.

  2. [...] week I suggested that in some ways I had hit a wall of sharply reduced diminishing returns when it came to [...]

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