Friday, March 3, 2017

Two 105 to 120 ky BP Skulls From China

A new paper in the journal Science examines two skulls from 105,000 to 120,000 years ago from China. It note similarities to both Neanderthals and early modern humans in East Asia.  The authors call it "archaic Homo" without clearly venturing a hypothesis on a species.

Notably, the skulls are associated lithic technology (i.e. stone age tools) that is Middle Paleolithic, a phrase that would usually be used to describe Mousterian industry which is associated with Neanderthals. But, I have never heard of Mousterian industry this far east and it isn't clear what the authors mean by that description. On the other hand, there are bone tools present, which is usually a litmus test for the presence of modern humans rather than archaic hominins.

The use of the word "human" in the paper is slippery (as best I can tell, referring generally to members of the genus Homo rather than to Homo sapiens sapiens, i.e. anatomically modern humans) as in the following passage from a blog that appears to be quoting or paraphrasing the paper:
The layer contains a Middle Paleolithic lithic industry, along with bone tools on diaphyseal splinters, and it has produced a consistent series of optically stimulated luminescence (OSL) ages, placing the human remains at about 105,000 to 125,000 years, and the overlying layers have provided ages of about 100,000 and 90,000 years. The human crania are therefore securely dated to marine isotope stage (MIS) 5, within MIS 5e or 5d. 
The Xuchang early Late Pleistocene archaic human crania exhibit a mosaic morphological pattern. They exhibit features that are ancestral and reminiscent particularly of early Middle Pleistocene eastern Eurasian humans, and derived and shared by earlier Late Pleistocene humans elsewhere, whether morphologically archaic or modern. 
In common with other early Late Pleistocene humans (whether morphologically archaic or modern), they share neurocranial expansion and gracilization. The endocranial volume (ECV) of Xuchang 1, about 1800 cm3, is at the high end of Neandertal and early modern human variation, and its neurocranium closely approximates the shape of those of Middle Pleistocene humans, especially eastern Eurasians. 
In combination with these derived and ancestral features, the Xuchang crania also display two complexes that primarily align them with the Neandertals. They share occipital (suprainiac and nuchal torus) and temporal labyrinthine (semicircular canal) morphology with the Neandertals.
The paradigm in this area is that modern humans arrive in East Asia in the Upper Paleolithic, and that prior to that Homo Erectus is the only well described hominin species in Asia. So, it appears that the reference to similarities to "early Middle Pleistocene eastern Eurasian humans" is to similarities to East Asian Homo Erectus. Similarly, the phrase "Middle Pleistocene humans, especially eastern Eurasians" is clear as mud, as there are not other well documented anatomically modern humans in the Middle Pleistocene in eastern Eurasia, but it isn't clear what archaic hominin species is being referenced either.

But, the size of the brain case at 1800 cubic centimeters is too big to be a conventional Homo Erectus which is the only species well documented to exist that far East at that time, although it would be consistent with either Neanderthals or anatomically modern humans.

There are clear examples of Neanderthals in northern Asia as far as the Altai mountains, and there are examples of Neanderthals in southern Asia are far as Pakistan. But there has never been any clear archaeological evidence for Neanderthals at any time in India, Southeast Asia or East Asia.

There is Denisovan DNA in Melanesians and aboriginal Australians and Negritos from the Philippines, as well as very low level in mainland Asians and in island Southeast Asia west of the Wallace line of uncertain provenance. And, of course, we have ancient Denisovan DNA from a Siberian cave near the far eastern extent of Neanderthal expansion (Altai Neanderthals also show traces of modern human admixture dating to 100,000 years ago). But, we have only a tooth, a pinky bone and some DNA from the Denisovans which tells us that they were a sister clade to Neanderthals with Neanderthal admixture of their own that existed at about the right time to have affinity with these old skulls from China, but little more. This could be a Denisovan skull, but we wouldn't know without extracting ancient DNA from it (according to prefatory material in Science "the investigators have not extracted DNA" from the Chinese skulls.)

Questions

Are these skulls from early anatomically modern humans who were part of a first, almost failed wave of modern humans and has significant archaic hominin admixture?

Or, are these skulls misdated? 

Or, are these skulls from archaic hominins who were present in Asia after Homo Erectus and before anatomically modern humans, of a species not well characterized until now that might or might not be Denisovans?

Did this species, whatever it is, replace Homo Erectus in Asia?

Is this a new kind of lithic and bone industry, or does it correspond to an existing one?

Without Answers

John Hawks tweets that he doesn't think that they are Denisovan skulls. I'm not so confident. There is more commentary on this issue in prefatory material from Science which notes that:
The skulls lack faces and jaws. But they include enough undistorted pieces for the team to note a close resemblance to Ne­andertals. One cranium has a huge brain volume of 1800 cubic centimeters—on the upper end for both Neandertals and moderns—plus a Neandertal-like hollow in a bone on the back of its skull. Both cra­nia have prominent brow ridges and inner ear bones that resemble those of Neander­tals but are distinct from our own species, Homo sapiens. . . . 
However, the crania also differ from the western Neandertals of Europe and the Middle East. They have thinner brow ridges and less robust skull bones, similar to early modern humans and some other Asian fossils. “They are not Neandertals in the full sense,” says co-author Erik Trinkaus, a paleoanthropologist at Washington Univer­sity in St. Louis in Missouri. 
The skulls do share traits with some other fossils in east Asia dating from 600,000 to 100,000 years ago that also defy easy classification, says paleoanthropologist Rick Potts of the Smithsonian Na­tional Museum of Natural History in Washington, D.C. Those features include a broad cranial base where the skull sits atop the spinal column and a low, flat plateau along the top of the skull. The Lingjing crania also resemble another archaic early human skull that dates to 100,000 years ago from Xujiayao in China’s Nihewan Ba­sin 850 kilometers to the north, according to co-author Xiu-Jie Wu, a paleoanthropologist at IVPP. 
Nor are the new fossils late-occurring representatives of other archaic humans such as H. erectus or H. heidelbergensis, two species that were ancestral to Nean­dertals and modern humans. The skulls are too lightly built and their brains are too big, according to the paper. 
Wu thinks those fossils and the new skulls “are a kind of unknown or new ar­chaic human that survived on in East Asia to 100,000 years ago.” Based on similari­ties to some other Asian fossils, she and her colleagues think the new crania repre­sent regional members of a population in eastern Asia who passed local traits down through the generations in what the re­searchers call regional continuity. At the same time, resemblances to both Nean­dertals and modern humans suggest that these archaic Asians mixed at least at low levels with other archaic people.
To other experts, the Denisovans fit that description: They are roughly dated to ap­proximately 100,000 to 50,000 years ago, and their DNA shows that after hundreds of thousands of years of isolation, they mixed both with Neandertals and early modern humans. “This is exactly what the DNA tells us when one tries to make sense of the Denisova discoveries,” says paleoanthropologist Jean-Jacques Hublin of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. “These Chinese fossils are in the right place at the right time, with the right features.”
This paper does not provide a conclusive answer one way or the other to these question and, if anything, it seems to obscure that statements that is does make with ambiguous terminology.

4 comments:

capra internetensis said...

They *really* don't look like modern humans. To my inexpert eye they look like some evolved eastern Homo erectus (really needs a better term), with the very low forehead and pronounced postorbital constriction.

Denisovans are in the modern human-Neanderthal clade, so I wouldn't expect them to look so erectusy. But the Neanderthal-like features would maybe fit. The Altai Denisovans did have a minority of more divergent ancestry, plausibly from Homo erectus. So maybe these are on a continuum between Denisovans and late Homo erectus, but much more toward the latter than the Altai Denisovans were?

I really have no idea what I'm talking about though.

bellbeakerblogger said...

Well, it has a huge brain and it is living in Asia about the time and place where the ancestors of Asians mixed with Denisovans.
So not totally buying John Hawks complex argument.

Hain Gardner VI said...

It seems that there may have been more of a spectrum of Erectus/Densiovan/Early Modern Humans in this region, and during this particular period, as opposed to more clearly defined species or sub-species.. Why not ? That seems to be the logical conclusion from these finds anyway. Would be really interesting to see dna results from these skulls.

Ryan said...

Remember that Denisovans were admixed by some very deeply diverged human lineage that could explain odd features.