Ancestral South Indians may be from Southeast Asia

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51OftfuYlSL._SX316_BO1,204,203,200_The Monkey’s Voyage is a book I’ve spotlighted before. Probably the main reason is that it highlights the importance of migration/dispersion on an evolutionary timescale. That is, change is the norm, and turnover is ubiquitous. The Tuatara is the exception, not the rule, when it comes to the biogeographic diversity of New Zealand.

As I’m not particularly focused on macroevolutionary dynamics, I’ve taken a microevolutionary lesson. That is, attempts to understanding variation within species. Updating one’s priors with the above the finding that Palearctic wolves descend from a core founder population which flourished after the Last Glacial Maximum is a lot less surprising. Wolves have been around a lot time, but meta-population dynamics and local extinctions may be the rule.

The same probably applies to another Ice Age megafauna, humans. For a long time it was something of a mystery why macro-haplogroup M, so common in South Asia, East Asia, the New World and Oceania, had no presence it Europe. Turns out it did, at least during the Pleistocene. Some of this is is just drift acting on smaller effective population size of uniparental markers. But, we know now some of this was population turnover.

This explains my casual comment below that I think “Ancestral South Indians” may have origins outside of India itself. My theoretical expectations have just shifted over time. Imagine that you have population X in a constrained geographic region. It is divided into two components, X0, at 50%, and X1 at 50%, while X1 is just the remainder after you remove X0. When you look at worldwide variation you see that X0 is modal in the region in question that you are focusing on. From this can you conclude that X0 is indigenous to/originates from this region?

I don’t think that that is necessarily true for a variety of reasons. More concrete, if you looked at ancient DNA 5,000 years before the present in the region I think X0 is probably likely to be dominant. 10,000 years before the present though I’m sure. At 20,000 years before the present I’d be skeptical. Finally, at 40,000 years before the present I’d think continuity is unlikely.

That’s the theoretical/abstract reason why I think ASI are likely to be intrusive to India. But there’s a concrete reason. The table above is from a preprint, Carriers of human mitochondrial DNA macrohaplogroup M colonized India from southeastern Asia. What you see is that the coalescence for M lineages, which are the modal haplogroups in South Asia, seem higher to the east than in South Asia itself. The authors take that to suggest M probably diversified in Sundaland and even Sahul before it became prominent in South Asia.

A few caveats. First, the paper is quite uneven, and there’s a lot of talk about “Out of Africa” routes which I think are neither here nor there (Y/mtDNA work isn’t going to resolve this issue, ancient DNA is). Second, these coalescence dates aren’t “proof” of anything, they simply make the case for shifting priors. Finally, the differences between South Asia and Southeast Asia are modest, suggesting that there was a very large effective population of females in both areas. In all likelihood there were multiple waves of migration west…and east, during the Pleistocene (some of the M in Northeast South Asia is almost certainly very recent Holocene gene flow from Burma).

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