25 March 2011

Homo Erectus Era In India Dated UPDATED

Current research in India therefore indicates that the Acheulean industry ranges from 1.5 million years ago to 120,000 years[.]

From here.

Generally speaking, Archeulean industry (which basically amounts to a certain kind of ancient stone tools), is associated with archaic hominins and most prominently, with Homo Erectus. It follows "the more primitive Oldowan technology some 1.8 million years ago" associated with Homo habilis, and is found in a period often called the Lower Paleolithic.

Acheulean tools were not made by fully modern humans that is, Homo sapiens although the early or non-modern (transitional) Homo sapiens idaltu did use Late Acheulean tools as did proto-Neanderthal species. Most notably however it is Homo ergaster (sometimes called early Homo erectus), whose assemblages are almost exclusively Acheulean, who used the technique. Later, the related species Homo heidelbergensis also used it extensively.

The 1.5 million years ago date suggests that Homo Erectus, or a similarly sophisticated hominin arrived in India within 300,000 years after this species of hominin evolved in Africa.

If the dating is upheld, the implication is that ancestors, such as Homo erectus, reached India at an early stage. . . . we opine that these Late Acheulean industries were probably made by an archaic, but somewhat bigger brained ancestor, such as Homo heidelbergensis.

While there is evidence of overlap between archaic hominin populations and modern humans, and even genetic evidence of admixture between Neanderthals and modern humans and between Denisovians and modern humans, the evidence also seems to suggest in the Neanderthal case that the period over overlap was not very long, probably not more than a few thousand years, or perhaps ten thousands years at the outside with a moving boundary in which the hominin species overlapped. There is also no good reason to think that overlaps of different human species, the Denisovians perhaps in Southeast Asia, or Homo floresiensis found in Flores about 20,000 years ago, was much longer. Likewise, there is no evidence of a long period of overlap between Neanderthals and the archaic hominins that preceded them in Europe.

The implication is that Neanderthals and/or modern humans first took hold in South Asia and replaced the hominins associated with Archeulean industry at that point in time sometime in the vicinity of 120,000 to 140,000 years ago, give or take ten or twenty thousand years. This provides an independent line of evidence to support an oldest possible date for an Out of Africa event for modern humans. The presence of Archeulean industry in South Asia 140,000 years ago makes the presence of modern humans in India or anywhere to the East of this point on the coastal route more than 150,000 years ago.

In fact, we don't see that. While we see Java man which might be Homo Eretus or something similar about 1.9 million years ago in Indonesia, the oldest skeletons claimed to be modern human anywhere outside of Africa are about 100,000 years old (including skeletons in China and the Levant), and there are direct signs of modern humans in India around 75,000 years ago. This coincides reasonably closely with the timing of the demise of Archeulean industry in South Asia. Indeed, at this point, it isn't even entirely clear that there was an overlap from the archaeology, although it is hard to see what could have wiped out archaic hominins in Asia other than a new species of hominin that replaced them in their ecological niche.

In Europe, the Archeulean industry was followed by the Mousterian industry of the Middle Stone Age associated mostly, but not entirely, with Neanderthals:

Mousterian tools that have been found in Europe were made by Neanderthals and date from between 300,000 BP and 30,000 BP (from Layer 2A dated 330 ± 5 ka, (OIS) 9 at Pradayrol, France). In Northern Africa and the Near East they were also produced by anatomically modern humans. In the Levant for example, assemblages produced by Neanderthals are indistinguishable from those produced by Qafzeh type modern humans. It may be an example of acculturation of modern humans by Neanderthals because the culture after 130,000 years reached the Levant from Europe (the first Mousterian industry appears there 200,000 BP) and the modern Qafzeh type humans appear in the Levant another 100,000 years later. It was superseded by the Châtelperronian industry around 35,000-29,000 BP.

One of the oldest stone industries associated with modern humans is the Aterian from about 82,000 years ago "in the region around the Atlas Mountains and the northern Sahara. The industry was probably created by modern humans (Homo sapiens), albeit of an early type, as shown by the few skeletal remains known so far from sites on the Moroccan Atlantic coast extending to Egypt."

There is no evidence, however, that the Neanderthal range range reached as far as South Asia:

It appears incorrect, based on present research and known fossil finds, to refer to any fossil outside Europe or Western and Central Asia as a true Neanderthal. True Neanderthals had a known range that possibly extended as far east as the Altai Mountains, but not farther to the east or south, and apparently not into Africa. At any rate, in Africa the land immediately south of the Neanderthal range was possessed by "modern" H. sap., since at least 160,000 years before the present.

The Shanidar site in Iran (also here) is one of the most easternmost Neanderthal sites yet discovered, although this could be simply a product of preservation conditions. A 2010 academic paper argues that there is "evidence of human occupation in Lower Sindh (Pakistan) during the Middle Pleistocene, which is demonstrated by the recovery of chipped stone assemblages with evident Levallois characteristics." This could have been either early modern humans or Neanderthals, and is the part of India most closely adjacent to the known Neanderthal range.

According to the few absolute dates so far available, Middle Palaeolithic complexes are represented in the region since roughly 150 ky, while the Late (Upper) Palaeolithic ones make their appearance at least just after 40 ky from the present, although the dispersal of modern individuals, following a coastal route, is suggested to have taken place some 10 ky before. The problem related to the makers of the Middle Palaeolithic tools is still debated, mainly because of the absence of fossil human remains of this period in the entire Subcontinent.

One of the most important issues consists of the south-easternmost spread of the Neanderthal Levalloisian assemblages that is so far badly defined. Although typical Levalloisian Mousterian industries are known from south-eastern Arabia, Iran, Afghanistan, and former Soviet Central Asia, characteristic Levalloisian assemblages are almost unknown in the Indian Subcontinent, except for a few surface sites in Lower Sindh and the Indus Valley, which have been discussed in a recent paper. Furthermore the more recent studies seem to support the impression that “the early Middle Palaeolithic (or Middle Stone Age) of India and Nepal probably developed indigenously”, which suggests the existence of a distinctive boundary between the west and the east marked by the axis of Indus river valley.

Thus, the archaeology simultaneous puts what might very well have been a Neanderthal presence in the Indus River Valley and seems to argue against their presence elsewhere in South Asia. Very crudely speaking, there were probably Neanderthals at some point in Pakistan, but not in India, Bangladesh, or Nepal.

The implication seems to be that in most of India the first modern humans would have encountered Homo heidelbergensis, or some similar species of hominin, when they first arrived, and that this South Asian hominin was sufficiently successful to prevent Neanderthals from encroaching upon their range.

This matters a lot as we try to decipher the meaning of the fact that modern humans have an average of about 1-4% Neanderthal ancestry, as determined by comparing ancient Neanderthal DNA with modern Eurasian DNA and identifying genes found in Eurasians and Neanderthals but not in Africans as Neanderthal source genes. The plot thickens as we learn that Melanesians apparently have about 4% Denisovian genes (based on a similar comparison with ancient DNA found in a Central Asian cave) on top of their Neanderthal inheritance, and that the Neanderthal genes found in Chinese people are mostly different ones than the Neanderthal genes found in Europeans.

Of course, a wild card is that some of what appear to be Neanderthal genes in some or all modern humans may be genes from some other kind of archaic hominin that shared those genes with Neanderthals. Indeed, it isn't even clear if the distinct pattern of Neanderthal genes in China and Europe respectively are due to founder effects after admiture while part of a common population, or separate admixture events.

Still, these facts, taken together, greatly narrow the scenarios in which Neanderthal admixture which seems clear to have taken place, happened. Let's review them, all of which seem to be a pretty solid footing:

* Neanderthals never had a range further east than Pakistan.
* Neanderthals never made it into Africa.
* Neanderthals were present in the Levant and Europe and Persia and Central Asia when modern human proto-Eurasians left Africa starting around 100,000 years ago.
* Neanderthals went extinct 22,000 to 30,000 years ago (the younger date is the most recent Mousterian find, the older date is the youngest skeletal remains).
* Modern human started to migrate along the Southern Route around 100,000 years ago or so.
* The Chinese have their roots overwhelmingly peoples who took a Southern route out of Africa, as the genetic evidence overwhelmingly indicates, although this may have involved multiple waves of migration.
* Modern humans did not reach Europe any earlier than about 50,000 years ago, and redating of the oldest modern human remains in Europe suggest that it could have been less than 30,000 years ago.
* Modern humans appear to have been absent from the Levant from 75,000 years ago to 50,000 years ago.
* Papuans and Australian aboriginal ancestors reached their respective lands around 45,000 to 50,000 years ago and had about 4% Neanderthal admixture at that point.
* A significant portion of modern European genetics has its sources in waves of migration to Europe from outside Europe after the Last Glacial Maximum ca. 20,000 years ago, after the Neanderthals were extinct.

The overlap between Neanderthal range and the Southern route of migration out of Africa is pretty narrow, fixing a time and place where Neanderthal admixture with proto-East Asians could have happened to a region limited to the Arabian Pennisula, Anatolia, Persia, or the Indus River Valley sometime between 50,000 and 100,000 years ago. While this is somewhat vague and subject to caveats, it does narrow the scope of what could have happened a great deal.

Moreover, given that we know modern humans were present in India at the time of the Toba explosion around 75,000 years ago, and if we can assume continuity between those modern humans and subsequent ones in terms of levels of Neanderthal admixture (this is "the big if"), then the time frame for Neanderthal admixture may be 75,000 years ago to 100,000 years ago, in the same region, before rather than during or after the time period in which modern humans appear to have retreated from or gone extinct in the Levant.

In contrast, the admixture events that gave rise to Neanderthal admixture in Europeans are not nearly so constrained. This could have happened as late as about 30,000 years ago or as early as about 100,000 years ago in either Europe or any of the places it could have happened for the East Asian populations.

It would be interesting to see which Neanderthal genes are most common in South Asians, and if there is a cline similar to the ANI/ASI cline in those genes.

UPDATE (3-28-2011):

John Hawks has more to add to this story:

The "Homo heidelbergensis" model is in such utter disarray right now, I'm not sure many paleoanthropologists have realized the full extent of the problems. You should know that I don't believe in Homo heidelbergensis, never have. A couple of months ago, I was discussing some of the issues about mutation rate estimation with a very prominent geneticist, and the conversation turned to Homo heidelbergensis. What a shock the Denisova sequence should have been to those itching to see a H. heidelbergensis incursion into Asia!

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