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Thursday, December 29, 2011

100k Anatomically Modern Human in Asia

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.

Press release, National Geographic, Anthropology.net, and Razib have more info.

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.
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