The Mysterious East

on November 3, 2010

The expansion of modern humans into Europe and central Asia began only about 50,000 years ago, when the last ice age hit a warm patch and people from the Middle East started spreading out in all directions. That makes it relatively simple to reconstruct. But the arrival of modern humans in East Asia goes back considerably further and is a lot harder to figure out.

Some aspects of that story are reasonably clear. It seems well-established, for example, that by 80,000 years ago there were people living in India who were making tools similar to those made by early modern humans in Africa, and both genetics and linguistics suggest that around 70,000 years ago they began moving further east.

The most recent ice age was under way by then, and sea levels had dropped far enough that southeast Asia and the islands of Indonesia were united in a single land mass known to archaeologists as Sunda. Australia and New Guinea were also connected, and it is believed that the present-day Aborigines and Papuans arrived in their present locations, perhaps 60,000 years ago, by traveling down the west coast of Sunda and then doing some fairly modest island-hopping

Both of those peoples have marked physical similarities to early human remains from east Africa and Israel, and a recent study of the DNA of traditional tribes in India found that “several of the Indians studied had two regions of their mitochondrial DNA that were identical to those found in modern day Australian Aboriginal people.”

This scenario raises problems for the conventional timeline of the migration out of Africa, however. For one thing, it’s very hard to square the notion that there was a considerable human population in India 80,000 years ago with the belief that “genetic Adam” — the last common male ancestor — lived in Africa a mere 90,000 years ago. And when the DNA evidence is examined in detail, the dilemma becomes even more acute.

The three oldest variants of the male Y chromosome are known as A, B, and CT. A and B are confined to the most ancient peoples of Ethiopia, the Sudan, and southern and central Africa, however, while the offshoots of the now-extinct CT account for the vast majority of present-day men.

The generally accepted estimate is that CT first appeared in Africa about 70,000 years ago and its CF offshoot in the Middle East about 2000 years later. CF, in turn, gave rise to two further offshoots, with the C haplotype probably arising in India and spreading to Australia and New Guinea with those early migrants.

There’s no reason to doubt this sequence of events, but the dating seems wildly off. If the C haplotype was present in India 70,000 years ago, CF can’t possibly has appeared in the Middle East just 68,000 years ago. My guess, though I’m no expert, would be that CF is more likely to have appeared soon after modern humans entered the Middle East around 125,000 years ago — which would mean that CT must be older yet.

This is not a dilemma that I’m qualified to resolve — but there’s clearly a fair amount of tension between archaeologists and geneticists on the matter, and something is going to have to give sooner or later.

There are even thornier problem raised by the DNA evidence, however, which have to do with a second offshoot of CT, known as DE.

DE is generally said to have appeared in Africa slightly after CF appeared in the Middle East. One of its offshoots, E, is now the dominant type throughout the continent, having largely squeezed out the earlier A and B types. But it’s the other offshoot, D, which gives geneticists headaches.

The weird thing about the D haplotype is that although it’s closely related to E, it’s not found in Africa, in the Middle East, or even in India. It occurs only in certain widely separated areas of eastern Asia — primarily in Tibet, in Japan (where it is dominant among the Ainu and on Okinawa), and among the ancient peoples of the Andaman Islands, which lie off the coast of Burma.

This odd distribution is typically treated as a puzzle to be resolved scientifically. Wikipedia states, “The presence of DE across widely separated regions has confounded investigators trying to reconstruct the migration of humans from Africa to Asia. … Underhill et al. 2007, suggest the possibility that deleterious mutations in some DE carriers may explain the extinction of DE lineages in India.”

There is, however, a far simpler explanation than “deleterious mutations.” Just as the A and B types survive only in scattered pockets in Africa, because of the relatively recent expansion of E across their original territory, so the present-day distribution of D may represent a very ancient migration that was later overridden by the expansion of offshoots of CF.

That would mean, of course, there must have been not one but two genetically distinct movements out of Africa — which would place even greater strain on the currently accepted paradigm of a single, relatively recent migration event.

This notion of two separate migrations is not actually as radical as it might seem. It has been a subject of intermittent speculation on anthropological grounds since long before DNA evidence entered the picture.

The map to the right indicates the locations where two different ancient peoples either live today or might have lived in the relatively recent past. The orange area marks the presence of the so-called Veddoids — among them those tribal peoples of India who are genetically close to Australian Aborigines — and it appears to trace out the route of the migration which followed the western coast of Sunda some 60,000 years ago

But the yellow marks another set of ancient peoples, the Negritos — who were called that by the first Europeans to encounter them because they resemble small Africans, with dark skin and peppercorn hair. And that area gives the impression of tracing out a rather different migration — one that might have moved across southeast Asia to the Pacific before the onset of the last ice age and then continued down the eastern coast of Sunda as the sea level dropped.

If the Negritos do represent a separate and earlier migration, it raises the question of when and how they departed from Africa. One possibility is that that they might have left Ethiopia more than 125,000 years ago, crossing the mouth of the Red Sea to southern Arabia while most of the Middle East was still a chilly desert and moving quickly along the coast until they reached the more welcoming climates of India and southeast Asia.

This scenario is frankly speculative on my part — but it appears to gain some reinforcement from the distribution of mitochondrial DNA, which is handed down from mother to daughter.

The three oldest mtDNA types all arose in Africa — L1 and L2, which are roughly comparable to the A and B y-chromosome types, and L3, which probably originated in Ethiopia and has two non-African offshoots, M and N.

The offshoots of N are now found everywhere outside of Africa, but M and its offshoots appear almost exclusively in India, where M is very ancient and diverse, as well as further east. Oddly enough, however, M also occurs in Ethiopia and East Africa — a fact which is conventionally explained as the result of a reverse migration from India, even though there is no archaeological evidence of such a migration and there are only slight traces of M in the Middle East.

In other words, the distribution of M seems very comparable to that of the male D haplotype and similarly suggests an early and rapid migration from Ethiopia to India and beyond. The chief difference is that M and its offshoots are far more common than D — presumably because male reproductive success is strongly skewed by social dominance.

If all of this speculation is correct, we arrive at an image of two non-African human communities thriving during the interglacial period from about 125,000 to 75,000 years ago. One was located in the Middle East and extended from Israel and Arabia to Iran or even Pakistan. But the other, and older, was centered in eastern India and southeast Asia and also extended north along both the Pacific coast and the great rivers of the region, like the Brahmaputra of Bangladesh and the Mekong of Vietnam, both of which lead towards Tibet.

A number of human fossils have been found in the region that display archaic characteristics and may represent that second community. Earlier this year, for example, a footbone was found in Luzon, the northernmost island of the Philippines, and dated to 67,000 years ago. According to its discoverer, its size matches that of the Negrito people of the area, but “it’s not a perfect match with any known group of humans.”

Other extremely ancient remains have been discovered in an area of southern China bordering on Vietnam. A skull found in 1958 was dated by its discoverers as being at least 68,000 — and possibly more than 111,000 — years old. And just last week, the announcement was made of a jawbone with “a mixture of modern and archaic features” that was found in the same general region and dated to more than 100,000 years ago.

Two events probably brought this early flowering to an end. One was the eruption roughly 74,000 years ago of supervolcano Toba on the Indonesian island of Sumatra, which spread a blanket of ash as far as India. It didn’t wipe out the human communities in the area, but it must have had a significant negative impact on them.

And the second was the onset of a new ice age — possibly triggered by the eruption — which once again brought desert cold to much of the Middle East and pushed its inhabitants to embark on a second wave of eastern migration that partly displaced and partly assimilated the earlier inhabitants.

Related:

A follow-up on these materials can be found here.

A listing of all my posts on deep prehistory can be found here.

A general overview of the areas of interest covered at this blog can be found here.

A chronological listing of all entries at this blog, with brief descriptions, can be found here.

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One Response to “The Mysterious East”

  1. allynh says:

    Here are two different copies of the NewScientist article.

    Mystery seafaring ancestor found in the Philippines: at least 67,000 years old, between Homo habilis and Homo floresiensis
    http://www.ufs.ph/2009-10/node/3575

    Mystery seafaring ancestor found in the Philippines
    http://www.tseatc.com/smf/index.php?action=printpage;topic=682.0

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