The year of the great unraveling: a tale of seven caves

2010 is almost over, and how appropriate that the new Denisova paper would come right at its coda. Here we have what appears to be a sister clade of Neandertals, which apparently contributed their DNA to modern Melanesians. A link has been found between a tooth and a finger from a cave in the Altai (image source on the left) to people living a lot further to the south and east, in Papua and Bougainville?

That's 2 for 2 for Denisova surprising us: its mtDNA, reported earlier this year is discordant with the autosomal evidence: the Denisovans trace their mtDNA ancestry to a much earlier time than the division of humans and Neandertals. And, yet, the Denisova remains are about 50,000 years old, i.e., at a time close to the appearance of modern humans in Asia.

Who would have expected a fairly young specimen in South Siberia to have really archaic morphology and mtDNA, to tie itself to West Eurasian Neandertals on the one hand and to modern Melanesians on the other?

The other big paper of the year was the Neandertal one which tested Neandertal DNA from another cave, Vindija in Croatia (image on the right: Johannes Krause, Max Planck institute of evolutionary anthropology) threw another curveball at theories of human origins. Prior to the appearance of this paper there were two theories about possible Neandertal admixture in humans: one that there was none, and another that it might have affected West Eurasians (where Neandertals lived) and could be detected in either their genes (stories about the "red hair gene" that circulated a few years ago), or the morphology of late Upper Paleolithic anatomically modern humans from Europe.

And, yet, the Neandertal paper gave a startling conclusion: Neandertals were more related to non-Africans in general than they were to Africans. This evidence must be explored further: how is affinity to Neandertals distributed within Africa itself? Within Eurasia? In America?

No one would have expected this outcome: that people in the far east would be at least as related to Neandertals as Europeans are.

Speaking of the far east, it was another cave, Zhirendong that threw the third curveball on mainstream theories of human origins. Here we have palaeoanthropological remains that look especially modern, but with some archaic traits as well.

The story so far had been of a recent African Exodus of anatomically modern humans 40-60 thousand years ago. The presence of anatomically modern humans in other caves in the Levant such as Qafzeh around 100 thousand years ago was acknowledged, but it was usually brushed off, as the Out-of-Africa-that-failed, an early settlement of modern humans outside Africa that contributed little to the later pulse of humans that went on to populate the world.

The fossil evidence of Homo sapiens and pre-existing humans is notoriously difficult to make sense of. But, it certainly becomes more difficult to view Qafzeh as an experiment-that-failed when a similar mix of modern-and-archaic features can be found from roughly the same time all the way to the east in China.

Interpretation of these new findings will take some time, and the fact that we're getting regular DNA reads from samples that are a few myriad years old suggests to me that we should expect more surprises to come. I've voiced my opinions on many of these papers, but I'm ready to be surprised.

It was only a few decades ago that the notion of a common recent African descent of mankind was surprising and revolutionary (thanks to mitochondrial Eve & co.). The pendulum has begun to swing the other way, with all sorts of dead folks that were once considered to be irrelevant side-branches re-asserting themselves as our ancestors or kin.

Vindija, Denisova, Qafzeh, Zhiren, Vindija, Mezmaiskaya: expect these names to be passed around in scholarly discussions for years to come (and add Liang Bua cave, home of the "hobbits" to the company, to make them seven).

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.

Link