Saturday, January 23, 2010

295. Aftermath 10: The Later Migrations

Starting from where I left off in Post 293, I'll continue with item 4 of my Later Migrations scenario:

4. ca 73,000 - 70,000 ya: Assuming a bottleneck or bottlenecks after Toba, or some other disaster in the same region, we can't be sure how many such bottlenecks would have occurred. It's even conceivable that only one group might have survived in the general area, either in India itself or to the east. Or possibly there were many groups with at least a few survivors, and thus many different founder effects. It's also very difficult if not impossible to correlate such founder effects with the genetic evidence. A major disaster at that time may well have produced one or many population bottlenecks by destroying human life en masse, but we have no reason to assume it would have produced even a single mutation. So it would be a mistake to read a separate founder effect into each different branch of M, N, or R.

Following Oppenheimer, I will at this point explore the possibility he raises, that the eruption would have completely destroyed all humans caught within range of the thickest fallout, which means that the tribal (and many of the lower caste) populations we now see in India originated either west or east of the subcontinent, from where various scenarios of repopulation would have occurred. If the pocket we identified in the northwest Punjab-Kashmir region survived, then west India might have been repopulated from there. As for repopulation from the east, any groups living just east of India during the Toba blast would almost certainly have suffered serious bottlenecks and may well have lost at least some of their original African traditions.

This could explain the absence of significant P/B characteristics in their music, especially since P/B is a highly group-oriented practice and the major loss of life coupled with scarcity of food and other resources might well have seriously eroded the social fabric -- as documented by Turnbull for the Ik. It could also have affected their woodworking and mask making traditions since many if not all the old rituals might have been suspended during a period when survival may have depended, literally, on the survival of the strongest and most ruthless, rather than the most cooperative and selfless, which would have been the traditional HMC ethic.

So the gap we now see centered in India, might well represent a displacement of a gap that really began farther east -- and was transmitted to India over time by neighboring groups east of the border that eventually migrated there. It's important to remember that a great many groups now living in East and Southeast Asia have also lost many of the same African traditions, probably as a result of the same disastrous event, so it would be a mistake to locate the gap only in South Asia.

Survivals of the old HMC traditions, at least the musical ones, can be found today largely among marginalized groups living in isolated refuge areas, in a vast region stretching from the Malay Peninsula to Indonesia, the Philippines and Melanesia, and also northward among certain tribal groups of South China and Taiwan. Since we see so many of the old African traditions (and often African morphology as well) among such groups, it's not difficult to conclude that they must originally have been located far enough to the east to suffer least from the effects of Toba (or other disaster based in the same area) and thus manage to hold on to most (though clearly not all) of their original traditions.

5. ca 70,000 - 40,000 ya. As the genetic evidence suggests, the population of India seems to have undergone a major expansion at some point after the Out of Africa migration. But the same evidence, in which very few haplotypes characteristic of the oldest populations of the subcontinent can be found elsewhere, suggests that there was very little migration elsewhere. As the maps suggest, India seems to have been relatively self-contained during most of the paleolithic and neolithic as well. Many groups migrated into the region but few seem to have migrated out. It could be that the lack of migration elsewhere contributed to the accumulation of population within one large but constricted area. It's also possible that the same disaster that produced the bottleneck(s) may have wiped out what could have been a large population of pre-modern humans, Neanderthals or Homo Erectus, thus elimating competition for resources in this region, as Homo Sapiens from the west and east resettled there.

6. ca. 60,000 - 20,000. According to the maps I posted, revealing population clines emanating from East Asia in all directions, but mainly from the southeast to the northwest, it looks as though there were major migrations into Central Asia and probably also directly north to Siberia at various points during this very long period.

Most of this entire region, from Southeast Asia to Northeast Asia, north to Siberia and northwest to Central Asia is now dominated by solo singing, or else group singing in unison or heterophony, in a manner radically different from anything we find in Africa today (aside from groups heavily influenced by Islam). This is the dominant style in India as well, even among the lower castes. The tribal groups of India have somewhat different styles, less oriented toward solo singing and with some traces of polyphony, but nevertheless very different from P/B.

It's possible that this style, often dominated by elaborate and virtuosic solo singing with heterophonic instrumental accompaniment, originated as part of the radically altered culture of a single surviving founder group, spreading with them as they expanded throughout the East in all directions, a process that probably began during the Paleolithic and extended well into the Neolithic as their most aggressive and warlike descendants ultimately subjugated those weaker or less aggressive, with those least willing or able to submit heading for sanctuaries in the hills and/or dense forests. Those groups that we now find only in the most remote, isolated regions may well have at one time dominated much of Asia to the east and south of India, but would have been forced to the margins by the same conquerers who eventually subjugated everyone else.

3 comments:

Maju said...

So it would be a mistake to read a separate founder effect into each different branch of M, N, or R.

I don't think it'd be any mistake. Actually I think it's the only correct way to approach the issue.

Maybe if you detect two or more lineages with a similar distribution (and timeline, if you're willing to trust molecular clock), then you can suggest a multiple founder effect from different lineages migrating together but otherwise it's only logical to treat each haplogroup on its own merits.

Doing otherwise will only mislead you.

DocG said...

Maju: "I don't think it'd be any mistake. Actually I think it's the only correct way to approach the issue."

Maybe, but if so we have to be more precise. A disaster can produce a bottleneck, which can lead to a founder effect (or founder effects). But it cannot in itself produce a mutation. So a founder effect is not necessarily signaled by a fresh mutation and is thus not necessarily reflected in the cladistic structure of any phylogenetic tree.

What a founder effect CAN do is increase the likelihood that an already existing mutation, which may originally have been insignificant, could become the "founder" of an important new lineage, after all or most of the other lineages have died out. But this is a matter of chance and probabilities, and is by no means an absolute law.

Maju said...

A disaster can produce a bottleneck, which can lead to a founder effect (or founder effects). But it cannot in itself produce a mutation.

This is very much correct.

But a small population tends to fixation in one or very few lineages (normally one), so the founder effect should be obvious in the existence of one (or few) founder lineages.

We don't see anything like that.

What a founder effect CAN do is increase the likelihood that an already existing mutation, which may originally have been insignificant, could become the "founder" of an important new lineage, after all or most of the other lineages have died out. But this is a matter of chance and probabilities, and is by no means an absolute law.

Try calculating the probabilities yourself. You'll see that they are so extremely high that it's a practical "law".

You can't understand Paleolithic genetics until you understand drift very well. It is of course a matter of probability but not getting a signal of the bottleneck it's harder than tossing a coin a hundred times and getting all them tails. If you believe such things actually happen, you should start playing lottery.