Zhiren Cave in southern China is an important site for the study of the origin and the environmental background of early modern humans.
The combination of Elephas kiangnanensis, Elephas maximus, and Megatapirus augustus, indicates an early representative of the typical Asian elephant fauna.
Previous U-series dating of flowstone calcite has pinpointed an upper age limit for the fossils of about 100 ka. In order to achieve a better comprehension of the chronology of the modern human and contemporaneous faunal assemblage, paleomagnetic, stratigraphic, and optically stimulated luminescence (OSL) dating methods have been applied to the cave sediments. Paleomagnetic analyses reveal that there is a reversed polarity excursion below the fossiliferous layer. This excursion can be regarded as the Blake excursion event, given the U-series ages of the overlying flowstone calcite, the OSL measurements, the virtual geomagnetic pole (VGP) path of the excursion, the two reverse polarity zones within this excursion event, and the characteristic of the fauna assemblage.
The human remains and mammalian fauna assemblage can be bracketed to 116–106 ka. Application of OSL dating leads to erroneous ages, largely due to the uncertainty associated with the estimation on the dose rates.Yanjun Cai et al., "The age of human remains and associated fauna from Zhiren Cave in Guangxi, southern China" Quaternary International (March 24, 2016) (emphasis and paragraph breaks added).
This is an update of a find previous made in 2007:
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.Wu Liu et al., "Human remains from Zhirendong, South China, and modern human emergence in East Asia", PNAS (2007).
The basic issue here is that given everything else we know about modern human evolution and migration, from archaeology of hominin remains and tools, from genetics, from the fates of megafauna in places where humans appear, and so on, modern humans have no business leaving remains in East Asia between 116,000 and 106,000 years ago.
We have a comparatively uninterrupted period in which modern human remains are found in East Asia starting ca. 40,000 years ago. We have evidence of modern humans in Australia and Papua New Guinea ca. 50,000 years ago. We have human remains in Southeast Asia ca. 65,000 years ago. We have tool assemblies in India similar to those associated with modern humans in Arabia that both predate and post-date the Toba volcano explosion, ca. 75,000 years ago. We have modern humans just barely out of African in the Levant, ca. 100,000 years ago. We have tool assemblies and structures in the interior of Arabia similar to tool assemblies and structures found in Nubia contemporaneously in connection with modern human remains that are consistent with a first modern human emergence from Africa, ca. 125,000 years ago. We have modern human remains in Africa dating back to at least 150,000 years ago.
There are a few other claimed East Asian modern human remains of about the same time period where the dating and species identification are not as reliable as Zhiren Cave which is the most recent and methodologically sound of the finds, and the 2016 result tends to argue strongly against the date being inaccurate, which would be one way to solve the riddle, as its its routine for later investigation to result in the redating of remains found in a cave.
The other possibility is that the very fragmentary evidence two molars and part of a jaw bone, look modern because they contain archaic human remains that have independently evolved derived traits similar to those of modern humans in these teeth and jaws, over the roughly 1.7 million years since Homo Erectus was the first human ancestors to leave Africa, even though the species who left these remains is not actual an anatomically modern human. (Alternately, these could be remains of a non-Out of Africa Homo Erectus derived species and instead represented another archaic species, such as Denisovans, who briefly replaced Homo Erectus in East Asia, only to be replaced in turn by modern humans no so long afterwards.)
A third possibility is that a very small number of modern humans migrated very rapidly from Africa to East Asia, but that they lacked critical mass and went extinct soon after, with modern humans achieving a permanent presence in East Asia only 60,000 years later. Archaic features in the samples could reflect some degree of archaic introgression into modern humans acquire en route to East Asia.
There are several problems with this third possibility.
* Why is there no other evidence of modern humans pre-100kya, between Arabia and South China? Surely, such a long distance migration would have left some settlements in between?
* If these first wave modern humans could make the trip to South China, albeit to fail there, why is there a 60,000 year gap between the next group of modern humans to appear there?
* Modern humans have thrived and seen their populations grow exponentially in all other virgin territory they encountered, and the population density of archaic hominins during the Homo Erectus era must have been quite low (given their inferior technologies and already low hunter-gatherer population density), so why did modern humans who would have made a very early foray into East Asia not have thrived? The Zhiren Cave evidence seems to indicate that these hominins where quite successful elephant hunters, after all? Were these purported anatomically modern humans still behaviorally primitive? And, if so, what behavioral change so profoundly improved their selective fitness?
* Should early modern humans from ca. 116,000 to 106,000 years BP be almost identical to early modern humans from ca. 100,000 in the Levant, such that no other correspondence would be possible? There wouldn't be much time for evolutionary differentiation of the two populations, although founder effects and introgression could lead to some rather rapid morphological changes.
One can imagine satisfactory answers to each of these questions. But, we have really no solid evidence to support satisfactory answers to any of them.
Therefore, at this point, in the absence of ancient DNA from purportedly modern human remains in East Asia that are so old, the stark absence of corroborating evidence of a modern human presence in East Asia at this early date for the next 60,000 years or so, and the sharp deviation from a paradigm that explains all of the other data that this interpretation would require, is simply not strong enough to convince me that these remains are really modern human in origin.
A story that could fit this outlier to the rest of the data would have to be truly extraordinary, and I'm not convinced that this evidence is sufficiently extraordinary to support such an extraordinary claim.
I'm not dogmatically opposed to being convinced by future corroborating evidence that a modern human classification at the date determined is the correct interpretation.
One also has other weird data points in South China, like a purportedly archaic set of remains dated to just 14,000 years ago. (Also discussed at this blog here). It is less weird for a small relict archaic hominin population to survive long after all others of their kind go extinct, in a place that we know was inhabited by at least one, and most probably two species of archaic hominins before modern humans appeared on the scene, particularly prior to the Neolithic revolution, when modern human hunter-gatherers may have had less of a decisive advantage over other archaic hominin species.
But, it is still part of an overall picture in East Asia in which the few pieces we have are all outliers that don't make any sense in isolation and don't even form a really coherent story when viewed together. This is particularly odd because in the New World, in Europe and in Southeast Asia, new evidence seems to be strengthening the very paradigms that the East Asian finds seem to contradict.
But, the evidence so far just isn't enough, particularly given the lack of clarity over what happened to Homo Erectus in the time frame roughly after 200,000 years BP. Did Homo Erectus go extinct or suffer diminished numbers in the face of competition from another archaic hominin species such as the Denisovans? Did Homo Erectus thrive until modern humans arrived and then rapidly go extinct, but left few traces due to insufficient archaeological exploration, low population densities and tools that are too crude to distinguish from mere ordinary rocks?
(The latest evidence in Homo Erectus archaeology is the discovery of Homo Erectus remains in Vietnam dated to ca. 800,000 years ago, which is right when and where we would expect to find them under current paradigms.)
I don't think that we have good enough evidence, yet, to resolve these questions, although I'd like to hope that our knowledge base might improve enough to understand this period much more accurately and definitively in the years to come during my lifetime.