October 26, 2010

100,000 year old anatomically modern humans from Zhirendong

I'm sure I'll have a lot to say about this paper once I read it, but right now I'm focusing on the pilot phase of the Dodecad Project.

I'll post my comments later in this post; For now, I'll just say: those pesky ancestors have a way of upsetting scientific theories. But, in a sense, that's the beauty of science.


Related: the previous "oldest modern human" was Liujiang.

The paper's section on populational implications:
Populational Implications. Assuming that modern human biology
emerged initially in the late Middle Pleistocene of equatorial
Africa (8, 31, 36), the presence of derived, modern human
mandibular features in East Asia by early MIS 5 implies early
modern human population dispersal or gene flow across at least
southern Asia sometime before the age of the Zhiren Cave human
remains or independent emergence of these features in East
Asia. The early modern human MIS 5 dispersal into Southwest
Asia may therefore have included further population dispersal or
gene flow eastward across southern Asia.

However, the Zhiren 3 complex mosaic of distinctly derived,
modern human features of the anterior mandibular symphysis,
combined with archaic features of the lingual symphysis and
overall mandibular robustness, indicates that any “dispersal”
involved substantial admixture between dispersing early modern
human populations (cf. 5) or gene flow into regional populations
(cf. 37, 38). The paleontological data are insufficient to assess the
levels of such gene flow or admixture, but the morphological
mosaic of Zhiren 3 is most parsimoniously explained as the result
of such populational processes. It is not easily accommodated
into any Out-of-Africa with populational replacement scenario.
The short story: anatomically modern humans (AMHs) first emerge in East Africa in examples like Omo and Herto about 200-150ky. The first undeniably modern finds in Eurasia were from Qafzeh in the Levant, roughly contemporaneous with the new Zhiren sample.

These Qafzeh AMHs were usually interpreted as the Out-of-Africa-that-failed, an early excursion of anatomically modern humans into Eurasia that seems to have fizzled as AMHs appear, first as isolated teeth, and then as skulls like the Oase mandible and Mladec in Europe, and Liujiang in East Asia only 50-60 thousand years later.

Until now, it was supposed that these later AMHs were descendants of the Out-of-Africa-that succeeded, which postdated Qafzeh, was contemporaneous with the Aurignacian and the emergence of full-blown behavioral modernity.

The new Zhirendong find upsets this standard model: anatomically modern humans existed 100 thousand years ago in Africa, the Levant, and East Asia. It's extremely difficult to make the argument now that two of these AMH populations died out and the African one repopulated the world.

The two pillars of Out of Africa are (i) the genetics, i.e., the evidence for greater African genetic diversity, diminution of heterozygosity from east Africa, and increase of linkage disequilibrium, (ii) the palaeoanthropology, i.e., the temporal gap between AMHs in Africa and Eurasia.

Factor (ii) has just taken a huge blow. Moreover, Out-of-Africa supporters must now either (a) come up with scenarios for dispersal of AMHs 50,000 years at least before their current models, or (b) accept the emergence of modernity in Eurasia without dispersals from Africa.

UPDATE: John Hawks questions the chin=African equation.

PNAS doi: 10.1073/pnas.1014386107

Human remains from Zhirendong, South China, and modern human emergence in East Asia

Wu Liu et al.

The 2007 discovery of fragmentary human remains (two molars and an anterior mandible) at Zhirendong (Zhiren Cave) in South China provides insight in the processes involved in the establishment of modern humans in eastern Eurasia. The human remains are securely dated by U-series on overlying flowstones and a rich associated faunal sample to the initial Late Pleistocene, >100 kya. As such, they are the oldest modern human fossils in East Asia and predate by >60,000 y the oldest previously known modern human remains in the region. The Zhiren 3 mandible in particular presents derived modern human anterior symphyseal morphology, with a projecting tuber symphyseos, distinct mental fossae, modest lateral tubercles, and a vertical symphysis; it is separate from any known late archaic human mandible. However, it also exhibits a lingual symphyseal morphology and corpus robustness that place it close to later Pleistocene archaic humans. The age and morphology of the Zhiren Cave human remains support a modern human emergence scenario for East Asia involving dispersal with assimilation or populational continuity with gene flow. It also places the Late Pleistocene Asian emergence of modern humans in a pre-Upper Paleolithic context and raises issues concerning the long-term Late Pleistocene coexistence of late archaic and early modern humans across Eurasia.

Link

11 comments:

Andrew Oh-Willeke said...

Interesting, but I'm skeptical.

A 60,000 year gap between this find and the next most recent one anywhere in East Asia, the 40,000 year gap between this find and any sign of modern humans in Australia or New Guinea, the 25,000 years+ gap between this find and any in South Asia, the very fragmentary evidence that this is a modern human rather than some other archaic hominin (with John Hawks opining that it is not inconsistent with a Neanderthal), the known existence of archaic hominins for hundreds of thousands of years before then, and the discovery of new archaic human types in Flores and Desova, all cast doubt on this being a modern human.

It isn't that there weren't modern humans around 100,000 years ago. We have evidence of their appearance in the Levant and subsequent retreat from there around then. And, given the rate of modern human expansion in the Americas, it wouldn't be too remarkable to think that a hunter-gatherer species could have gotten from the Levant to East Asia in just a few thousand years.

But, the hard question is, if a modern human made it beyond the Levant 100,000 years ago as far as East Asia, where is the corroborating evidence? Why isn't there evidence of human presence in the intervening 60,000 years? One would think that a population that made it that far would have left traces along the way. Where are the extinctions? Where are the tool kits?

Is the amount of digging done from South Asia to China so thin that we just haven't found it yet? There is some evidence for pre-Toba in India, but that is still a big gap with nothing in between. Convergent evolution towards modern human-like teeth and jaws from an archaic human (e.g. Flores or Neanderthal) seems like it deserves to consideration given that the claim is extraordinary.

Suppose that this find is of a modern human close relative of the Levantine and African modern humans of 100,000 years ago. Given the absence of extinctions then, and the massive wave of extinctions 40,000-50,000 years ago, does it follow that the current find's wave was a sucky hunter compared to the megafauna extinction causing wave, and hence was probably wiped out as well in the expansion?

terryt said...

"right now I'm focusing on the pilot phase of the Dodecad Project".

This paper seems to suggest a continuation of the same thing back through time. Quote:

"any 'dispersal'
involved substantial admixture between dispersing early modern
human populations (cf. 5) or gene flow into regional populations
(cf. 37, 38)".

I've long considered that to be the case.

"But, the hard question is, if a modern human made it beyond the Levant 100,000 years ago as far as East Asia, where is the corroborating evidence? Why isn't there evidence of human presence in the intervening 60,000 years? One would think that a population that made it that far would have left traces along the way. Where are the extinctions? Where are the tool kits?"

There is a paper out (I'll try to find it, if you insist) that claims human habitation is virtually continuous across Central Asia from the Altai to the Upper Amur River over the last 160,000 years. So that could be the evisdence you're looking for.

eurologist said...

We certainly need a bit more evidence, here. Having one find is almost as bad as the previous situation (having zero AMH finds until about 20,000 to 30,000 later than expected).

One should also note that besides the old H. erectus, a heidelbergensis-like population made it all the way to China, including bringing a more modern tool set. If they could do it, even the earliest AMHs certainly would have been able to do it, as well. And heidelbergensis is also a more likely source of interbreeding, since (a) they were much less different physically, (b) they showed through their tool set, weapons, and tent-like living structures an advanced culture, and (c) they would have known how to exploit the local flora and fauna under local climatic conditions.

I don't believe this jaw is some parallel development - it seems to clearly show AMH features that don't appear elsewhere in Asia for another 60,000 years. But it also doesn't prove Asian continuity. Firstly, we don't know if these people survived. Secondly, only genetic studies can prove continuity, and the level of it. And so far, what has been measured is pretty slim, and is not significantly higher or different in Asia than in Europe.

Annie Mouse said...

Absence of evidence is not evidence of absence.

I am not going to place too much weight on 3 teeth, but this discovery is not inconceivable.

A couple of years ago anyone suggesting a Flores hobbit-type humanoid would have been thought to have been a complete nut or intoxicated.

Modern humans were around. We know they had left Africa at least once. They did not stop in Arabia the second time so why would they have stopped the first time.

This is not impossible.

We dont yet know, what we dont yet know.

German Dziebel said...

"Firstly, we don't know if these people survived."

We don't know if AMH in Africa survived. In West Asia, they didn't.

"don't believe this jaw is some parallel development - it seems to clearly show AMH features that don't appear elsewhere in Asia for another 60,000 years."

Archaeologists have seen technological continuities in Asia between Middle and Upper Paleolithic for ages. Now we have anatomical continuities. As far as the gap goes, archaeology and paleontology evolve by evidence accretion. It's only 2010 now.

"only genetic studies can prove continuity, and the level of it."

Then they haven't proven anything in Africa, as we don't have aDNA from African AMH showing mtDNA L1 lineages or Y-DNA A lineages.

terryt said...

Here's a paper about the Paleolithic and Pleistocene environment of Siberia. It's not the paper I was looking for, but I'm sure most will find it interesting:

http://ejournal.anu.edu.au/index.php/bippa/article/view/84/75

terryt said...

I'm pretty sure this is the one. Maju very kindly tracked down for me:

http://www.geology.cz/sbornik/antropozoikum/no23/23-17-the%20middle%20and%20upper...pdf

eurologist said...

I am not an expert, but to me it looks like the mandible features are quite similar to the contemporaneous Skhul and Qafzeh finds, and to other, old African AMH finds. That is all fine and dandy and fits the picture.

But to throw a curve ball into this, how did the anatomy become (more or less) fully modern (i.e., losing ancient features) between ~100,000 years ago and ~20,000 years ago, almost simultaneously, on 3-4 different continents?

Part of it certainly is related to general ontogenic skull development, and things like the chin may also be related to a higher forehead or less prognathism and a shorter skull. But why everywhere, at roughly the same time?

I can only think of the second migration OOA, 60,000 to 80,000 years ago as being crucial to this. Before then, AMHs really where not successful outside Africa, at all. After that, they where - with a vengeance.

Something was missing with the first OOA - either the gene set was too small, or too idiosyncratic, or early admixture with Neanderthals and/or heidelbergensis simply diluted it to the point of (almost complete) failure.

Even in Africa, documented early cultural success of AMHs is limited to the extreme south. Perhaps, we weren't truly ready until the second migration.

Andrew Oh-Willeke said...

@eurologist

One could also imagine OOA earlier, but with AMHs only thriving once Toba did more harm to the competition than it did to the AMHs. Toba wouldn't have to wipe the competition out, just tip the balance enough to give AMHs with more flexibility a modest selective advantage that reached a tipping point.

terryt said...

"But to throw a curve ball into this, how did the anatomy become (more or less) fully modern (i.e., losing ancient features) between ~100,000 years ago and ~20,000 years ago, almost simultaneously, on 3-4 different continents?"

Gene flow?

"I can only think of the second migration OOA, 60,000 to 80,000 years ago as being crucial to this".

Probably so.

"Before then, AMHs really where not successful outside Africa, at all".

Perhaps they were successful in places. The people through Central Asia 'may have been involved in the early expansion. The same movement may have taken people south through the Far East to Australia. We have mtDNA M inSouth Asia but mtDNA N is far more common in the Far East and in Australia.

"with AMHs only thriving once Toba did more harm to the competition than it did to the AMHs".

I'm certain that the effect of Toba has been greatly exaggerated. H. erectus survived long after Toba even in SE Asia, where one would expect Toba's effect to be greatest.

Gnarlodious said...

There is plenty of evidence that anatomically advanced and more intelligent humans evolved much earlier... and then proceeded to go extinct. No doubt the reason was that they were more frail (gracile) and easily wiped out when times got tough. Here in the Southwest we have seen constant evidence of this as a guiding force in natural selection. One of the more dramatic discoveries was The Massacre at Sacred Ridge.

Notice that in every case the weaker species was using more symbolism, advanced tools, was peaceful and had a lower birthrate than their competitors. As a result, they just weren't equipped to defend themselves against brutal primitive tribes around them. And when famine hits, it got ugly.

I believe this is a much more important factor in our evolution than we care to admit. And probably... deeply embedded in our DNA.