June 11, 2013

Mellars challenges the 'early out of Africa' model

I do not have yet access to this potentially key paper, so first of all I want to make an appeal here to share a copy with me (→ email address). Thanks in advance. Update: got it (thanks to all who shared, you people are just great!) I will review it again as soon as possible.

Update (Jun 18): complementary review of the full paper now available here.

Paul Mellars et al., Genetic and archaeological perspectives on the initial modern human colonization of southern Asia. PNAS 2013. Pay per view (6-month embargo) → LINK [doi:10.1073/pnas.1306043110]

Abstract

It has been argued recently that the initial dispersal of anatomically modern humans from Africa to southern Asia occurred before the volcanic “supereruption” of the Mount Toba volcano (Sumatra) at ∼74,000 y before present (B.P.)—possibly as early as 120,000 y B.P. We show here that this “pre-Toba” dispersal model is in serious conflict with both the most recent genetic evidence from both Africa and Asia and the archaeological evidence from South Asian sites. We present an alternative model based on a combination of genetic analyses and recent archaeological evidence from South Asia and Africa. These data support a coastally oriented dispersal of modern humans from eastern Africa to southern Asia ∼60–50 thousand years ago (ka). This was associated with distinctively African microlithic and “backed-segment” technologies analogous to the African “Howiesons Poort” and related technologies, together with a range of distinctively “modern” cultural and symbolic features (highly shaped bone tools, personal ornaments, abstract artistic motifs, microblade technology, etc.), similar to those that accompanied the replacement of “archaic” Neanderthal by anatomically modern human populations in other regions of western Eurasia at a broadly similar date.

A review has been published at Live Science.

South Asian artifacts from ~30-50 Ka BP.

By "genetic evidence" they obviously mean "molecular clock" nonsense, so it is not evidence at all but mere speculation. However I am indeed very interested in knowing in detail what they mean by "archaeological evidence", because they seem to get into direct confrontation with much accumulated evidence, first and foremost all of Petraglia's research in both India and Arabia but also with the quite strong evidence for pre-60 Ka human presence in Australia and growing evidence for pre-60 Ka modern humans in SE Asia (in some cases even as old as 100 Ka). 

It must be said that Paul Mellars has been criticized before a lot for several reasons but very especially for his adherence to the quite speculative "modern human behavior" conjecture and, relatedly, bigotric attitudes against Neanderthal intellectual capabilities, based on nothing too solid. Therefore I'm generally skeptic about what Mellars has to say on this matter because this kind of conclusion is what one would expect from him. 

However Mellars is certainly a distinguished academic and, even if prejudiced and stuck to his own old-school and somewhat Eurocentric interpretations, he knows his trade as archaeologist and prehistorian. So he may be onto something, even if it is not exactly what he wants us to believe. 

For example, it is not impossible that this research may have, unbeknown to the authors, found evidence of a secondary OoA wave (maybe related to the spread of Y-DNA D and mtDNA N?) or even a distinctive evolution in Southern Asian technology prior to the expansion of Western Eurasia. 

It is interesting that they suggest that the 80-60/50 Ka toolkits of India would have been made by Neanderthals, when they are not describing them at all as Mousterian, the almost exclusively Neanderthal techno-culture, or Mousterian-related.

I have some difficulties judging before reading the whole study. However the supplemental material (quite extensive) is freely accessible and for what I can see there:
  1. They dedicate much text to attempt to justify a particular version of mainstream "molecular clock" hypothesis, which are clearly broke in my understanding. The kind of arguments "rebated" are more or less what I have been putting forward since many years ago. Ironically their "molecular clock" estimates make N and R much older than M, what I absolutely oppose (just count mutations downstream of the L3 node).
  2. No real attention is given instead to the geographical structure/distribution of major mtDNA haplogroups, only mentioned in relation to "molecular clock" speculations.
  3. The criticism of the African affinity of the Jwalapuram (Jurreru Valley) cores (Petraglia 2007) focuses on dismissal of any possibility of comparison, rather than on alternative comparisons. 
  4. Another "criticism" is that there is no apparent connection between Jwalapuram and the Nubian Complex (why there should be any?, it is not the only East African techno-culture, nor the only group that shows indications of traveling to Arabia in the Abbassia Pluvial).
  5. Also it is "criticized" that the most comparable African culture, Howiesons Poort) is not recorded before c. 71 Ka BP (what IMO may indicate late cultural dispersals to Southern Africa from East Africa, for example, but, hey!, Mellars is fencing off balls like crazy at his conservative goal). 
  6. They find clear similitudes between Indian and African microlithic industries (apparently related to the development of "mode 4" in both areas, as well as in West Eurasia). Indian industries are dated to c. 38-40 Ka BP, while African ones are dated to c. 49 Ka BP (Kenya) or later. However West Eurasian ones have dates as old as 55 Ka BP (not for Mellars, who remains stuck in older date references which he describes as ∼40–45 ka [calibrated (cal.) before present (B.P.)]), what really suggest that we are talking here not of the "out of Africa" but of the West Eurasian colonization process (necessarily from further into Asia, genetic phylo-geographic structure demands) with offshoots to the nearby regions. 
  7. Another element of late Africa-India "similitude" they find is "the remarkable, double bounded criss-cross design incised on ostrich eggshell", dated in India (Patne) to at least ∼30 ka (cal. B.P.), much earlier in South Africa. For Mellars this is beyond the range of either pure coincidence or entirely independent and remarkably convergent cultural evolutionary processes. Hmmm, really? Or are we before a clear case of wishful thinking as happens with the Solutrean-Clovis relationship hypothesis? Isn't it 30 Ka BP anyhow well beyond any reasonable expectations for the OoA time frame, including Mellar's own conjectures?
  8. Mellars accepts the paradox that the geographical limits of these highly distinctive microblade and geometric microlithic technologies are confined to the Indian subcontinent, with no currently documented traces of these technologies in regions farther to the east. And then makes up excuses for it, such as biological and cultural bottlenecks caused by "founder effects", mysteriously leading to a loss or simplification of cultural and technological know-how, as well as fininding new and contrasting environments (in the same latitudes?!)
  9. Even in the case of Arabian colonization, Mellars shows to be in a very defensive attitude, admitting only to the reality of the Palestinian sites with clearly modern skulls, as well as to the area of Nubian Complex colonization (on whose peculiarities he insists a lot, as if it would be the only expression of the wider MSA techno-complex), disdaining all the other MSA colonization areas and, often ill-defined, variants.

In brief, for what I could see in the supplemental material, along with some potentially interesting references to the relative cultural community spanning from East Africa to South Asia at the time of emergence of "mode 4" industries, it seems that Mellars and allies are essentially putting the cart (their models) before the horses (the facts), what is bad science. 

In 2008, Zilhao and d'Errico angrily accused Mellars of being an obsolete armchair prehistorian (different words maybe, same idea). Back in the day I was tempted to support Mellars but nowadays I must agree that he is clearly stuck in a one-sided interpretation of prehistory whose time is long gone. Whatever the case I welcome the debate and can only hope that will help to produce even more evidence to further clarify the actual facts of the Prehistory of Humankind.

4 comments:

  1. I agree that the molecular date arguments aren't too impressive.

    First, you ought to be using archaeological dates to calibrate molecular clocks and not the other way around. Given uncertainties associated with mutation rates, one just can't draw strong inferences based on mutation rates alone.

    Second, mutation rates, even if they were prefect time indicators only tell a story of when and not where. We have no definitively way of knowing where mtDNA M and N, and Y-DNA F and D mutations arose. It could have been in East Africa not long before an Out of Africa migration or could have been, for example, in SW Asia (and the story need not be the same for each of the four most basal predominantly Eurasian uniparental lineages). It could very well be that these mutations arose tens of thousands of years after an initial Out of Africa to Arabia (that archaeology suggests happened ca. 120kya) and/or Arabia to India migration (prior to 75 kya) with legacy mutations lost to genetic drift during bottlenecks when a very early Out of Africa modern human population was small and fragile. The population genetics aren't even unequivocal in tell us if M and N were in the same wave or different ones, and if F and D were in the same wave or different ones. It is possible, for example, that there was a 120kya Out of Africa wave and a second wave ca. 60kya, each bringing different basal lineages.

    The identification of the Toba spanning tool sets in India at Jwalapuram as Neanderthal v. modern human is admittedly tenuous link. The strongest argument for the latter is the apparent continuity between the early lithic technologies that span Toba ash with later clearly modern human technological cultures in the same place, and that there is no path of Mousterian tools in the vicinity leading up to this techno-culture.

    We have skeletal evidence of modern humans in the Levant at 100kya which is very powerful evidence of an earlier date, and the tool affinities between interior Arabian artifacts and the Nubian complex ones both at pre-100kya times is very powerfully suggestive and reinforced the Levant skeletal remains.

    The strong argument against this evidence for early Out of Africa is not that it isn't modern human, but that it may represent a first modern human Out of Africa wave that failed, followed by a later one from which modern non-Africans are derived. The evidence distinguishing a failed first wave hypothesis from a successful first wave hypothesis is thin indeed until you get to the Toba spanning lithic tools at Jwalapuram.

    The case for early Out of Africa that succeeded isn't absolutely rock solid. The evidence is thin. But, an abundance of Upper Paleolithic evidence by itself certainly doesn't contradict thinner evidence of an earlier presence.

    The case for Out of India at 50kya to 60kya with no obvious mechanism making that time frame different v. Out of India at 75kya with a clear mechanism to make the population movement possible (particularly in light of a recent pre-60kya set of remains in SE Asia) really seems like splitting fine hairs and giving undue credibility to molecular clocks.

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  2. "The evidence is thin." I agree. On both sides of the argument.

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  3. '"The evidence is thin." I agree. On both sides of the argument.'

    It's so much thinner on Mellars' side, it's thin ice I would never dare to cross.

    There are too many straw-man arguments and logical fallacies to take this garbage seriously. Sorry for the verbiage - it truly is garbage.

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  4. Update: full paper review: http://forwhattheywereweare.blogspot.com/2013/06/mellars-2013-second-round.html

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