Tianyuan04 Apr 2007
OK, NEWS FLASH: "Out of Africa dispersal was not as simple as once thought."
That's the lede in the press release about the Tianyuan skeleton.
That's very nice and all, but as someone who never thought things were very simple, I have a bit more latitude to talk about why this specimen is interesting.
I have an early edition of the paper by Hong Shang and colleagues. Here is the abstract:
Thirty-four elements of an early modern human (EMH) were found in Tianyuan Cave, Zhoukoudian, China in 2003. Dated to 35,500 -33,500 radiocarbon years before present by using direct accelerator mass spectrometry radiocarbon, the Tianyuan 1 skeleton is the among the oldest directly dated EMHs in eastern Eurasia. Morphological comparison shows Tianyuan 1 to have a series of derived modern human characteristics, including a projecting tuber symphyseos, a high anterior symphyseal angle, a broad scapular glenoid fossa, a reduced hamulus, a gluteal buttress, and a pilaster on the femora. Other features of Tianyuan 1 that are more common among EMHs are its modest humeral pectoralis major tuberosities, anteriorly rotated radial tuberosity, reduced radial curvature, and small talar trochlea. It also lacks several mandibular features common among western Eurasian late archaic humans, including mandibular foramen bridging, mandibular notch asymmetry, and a large superior medial pterygoid tubercle. However, Tianyuan 1 exhibits several late archaic human features, such as its anterior to posterior dental proportions, a large hamulus length, and a broad and rounded distal phalangeal tuberosity. This morphological pattern implies that a simple spread of modern humans from Africa is unlikely.
The paper is largely descriptive (which is certainly appropriate for an initial publication), but there aren't many pictures. I imagine they are holding pictures for a more extensive publication on the skeleton. There are also few comparisons presented. These are all fine; it's not a monograph, it's a short descriptive paper. But the brevity means that there might be interesting comparisons beyond those presented, so this is possibly an abbreviated list.
How does the skeleton affect the "Out of Africa" story? It dates to 34,430 +/- 510 radiocarbon years, which is approximately the same age as the earliest "modern" European remains, from Pestera cu Oase, Romania. That makes it important, regardless -- but it is also by far the most complete skeleton in China from this early time period. The other remains that may represent the early modern Chinese population generally have some uncertainty about their dates (such as Liujiang) or more fragmentary (and also insecurely dated, like the Salawusu remains). The Upper Cave specimens from Zhoukoudian are substantially later, less than 25,000 and possibly as young as 12,000 years old. So the skeleton's date makes it very important
What about its features? In terms of morphology, it shares much with early modern humans in Europe. I got a chance to discuss the paper very briefly with Dave Frayer and Milford Wolpoff, who know this morphology better than me -- although any errors here are my own. The skeleton is relatively robust, but fits within the range of robusticity of post-Neandertal Upper Paleolithic Europeans. The paper discusses a number of pathological details of the skeleton, mostly age-related.
The abstract says that the anterior-to-posterior dental proportions of the mandible are similar to late archaic humans. Here is what the text says about this feature on page 4:
The buccolingual diameters of the I2 to M3 are similar to those of most Late Pleistocene humans, samples of which differ principally in their anterior dental dimensions (35; Table 4). However, an index of summed anterior (I2, C1) to posterior (M1, M2) crown breadths (Table 5) differentiates the Neandertals from most modern humans. The Tianyuan 1 index of 73.4 is matched among the EMHs only by the Upper Paleolithic Arene Candide 1, Dolni Vestonice 13, and Mladec 54 (11.5% of the EMHs), whereas it is exceeded by 81.3% of the Neandertals, the lowest of which is still 72.9. It is above all of the Middle Paleolithic modern human (MPMH) plus Nazlet Khater 2 values. Tianyuan 1 is even closer to the Neandertal pattern if the premolar breadths are added to the molar breadths; its value of 41.6 is exceeded only by the same three European EMHs and 60.0% of the Neandertals. The Tianyuan 1 dental proportions therefore fall in the overlap zone of late archaic and Upper Paleolithic EMHs and separate from the MPMH.
In other words, this specimen has a big lateral incisor and canine relative to its molars. This particular feature is interesting, but maybe not not all that informative relative to the comparative samples. The data make clear that both the lateral incisor and molars of the specimen are smaller than the average size of the Skhul-Qafzeh hominids; it's just that the molars have reduced more (and the canine is a bit larger, but easily in the range of variation).
About those hand bone features, here is what the paper says on page 5:
The hamulus has the reduced palmar projection of the EMHs (Table 8), but its relative proximodistal length aligns it with the Neandertals (Fig. 3). The one distal manual phalanx, probably from the second ray based on articular and osteoarthritic matching with the left second more proximal phalanges, has a moderately large distal tuberosity that is circular and lacks proximal ungual spines (Fig. 3). The relative breadth of the tuberosity falls between the Neandertals and modern humans (including the MPMH) (Table 8). The form of the tuberosity is the archaic Homo (and Neandertal) pattern, although it is occasionally seen in EMHs.
This is probably more interesting from a biobehavioral perspective than a phylogenetic one. In other words, these help us to infer the behavior of early Upper Paleolithic people, which for the hands appears to match that of the Neandertals in many respects. The strong robusticity of the femur, tibia, and humerus of the skeleton confirm that behavioral interpretation. These may still be informative in a phylogenetic sense -- that is, they may show the retention of genes from earlier Eurasian hominids. But more importantly, they show that the adaptive context of modern humans changed across the time span from 35,000 to 15,000 years ago or so, and modern human anatomy evolved as a consequence.
Probably the most interesting observation along biobehavioral lines is that shoe wear may have influenced the individual's foot development. This is from the BBC article:
The single toe bone which was unearthed seems to suggest the individual wore shoes, pushing back the earliest known evidence for footwear by about 10,000 years.
An earlier study by Professor Trinkaus shows that human small toes became weaker during the stage of prehistory known as the Upper Palaeolithic, and that this can probably be attributed to the adoption of sturdy shoes.
The invention of rugged shoes reduced humans' reliance on strong, flexile toes to grip and balance.
Or, as the paper puts it:
The second proximal pedal phalanx, however, is gracile, similar to MUP humans and distinct from the MPMH and Neandertals (Table 6). Given the apparent tibial robusticity, this suggests, as with MUP humans (43), the reduction of anterior pedal bending stress through the habitual use of footwear.
OK, so what have we learned? The skeleton is certainly important, but some more comparative work will help to place it in a broader context. As it stands, it may be the most important single specimen for interpreting the Late Pleistocene population history of China, but it lacks many of the anatomical areas that would inform us more clearly of its relationships -- in particular, no face, upper teeth, or vault. Some of the most informative observations are relevant to interpreting its behavior. But it would help if we knew for sure whether it was male or female!
For more information on other Chinese Late Pleistocene sites, I can recommend Dennis Etler's excellent table of Chinese fossil hominids.
Shang H, Tong H, Zhang S, Chen F, Trinkaus E. 2007. An early modern human from Tianyuan Cave, Zhoukoudian, China. Proc Nat Acad Sci USA (online early) doi:10.1073/pnas.0702169104