Qafzeh teeth like Neandertals

Debbie Guatelli-Steinberg and Donald Reid report on the perikymata spacing of a sample of fourteen anterior teeth from Qafzeh. These are "early modern humans", among the earliest to be located outside of Africa, but their anatomical position relative to Neandertals and other groups has been subject to frequent dispute.

As I've emphasized several times ("Neandertal teeth: the other shoe", "How modern is "modern tooth development"?"), this growth characteristic of teeth is variable among living human populations. What remains totally unclear is why it varies.

Neandertals are at the low end of the human range of variation for perikymata counts on their anterior teeth, and the patterning of packing across the tooth is somewhat different. In particular, Neandertals have fewer perikymata nearer the roots of these teeth (for details, I suggest Guatelli-Steinberg's 2009 review article).

The current paper follows up on earlier work by Janet Monge and colleagues (2006). They emphasized that the Qafzeh anterior teeth fit within the overall human range of variation, but observed that two individuals were very close to Neandertals in their packing patterns. Here, Guatelli-Steinberg and Reid include more specimens in the sample, confirming this similarity.

From their conclusion:

The purpose of this study was to investigate whether Qafzeh teeth are different from those of modern humans in the percentage of perikymata present in their cervical [sic] appear to fall in the lower 50% of the modern human distribution, and a few fall within the lowest 5% of the distribution. Thus, this sample of Qafzeh teeth appears to differ from those of modern humans in the same direction that Neandertals do: with generally lower percentages of perikymata in their cervical regions. As can be seen in the SEM montages in Figure 2, perikymata become much more closely spaced in the cervical relative to incisal halves of the Inupiaq LI2 than they do in either the Neandertal or Qafzeh LI2s. Although sample sizes precluded a similar test between the Qafzeh and Neandertal teeth, plots of the averages for these teeth (Fig. 1a,b) reveal the similarity of the Qafzeh and Neandertal teeth, particularly for the UI2, LC, LI2, and LC. Values for two of the Qafzeh UI1s and a single UC are closer to the modern human than Neandertal means for these tooth types, revealing overlap in the ranges of values, as is also true for Neandertals and modern humans (Guatelli-Steinberg et al., 2007).

It may be worth pointing out that the perikymata packing pattern was a key part of Ramirez-Rossi and colleagues' conclusion that the Les Rois B mandible as well as several other Les Rois dental specimens show affinities to Neandertals.

I think Monge and colleagues are correct in asserting that this packing pattern is not a taxonomic diagnosis. Notwithstanding that the precise Neandertal-like pattern, present at Qafzeh, does not occur in the known human samples, we still don't know why human patterns differ from each other. In their discussion, Guatelli-Steinberg and Reid suggest alternatives for the mechanism forming the straiae, but I'd like to have some kind of genetic answer -- what developmental processes changed, carrying this feature along with them?

Anyway, another contrary observation to the idea of "modern human dental development", I guess.

References:

Guatelli-Steinberg D, Reid DJ. 2010. Distribution of Perikymata on Qafzeh Anterior Teeth. Am J Phys Anthropol (in press). doi:10.1002/ajpa.21158

Guatelli-Steinberg D, Reid DJ, Bishop TA, Larsen CS. 2005. Anterior tooth growth periods in Neandertals were comparable to those of modern humans. Proc Nat Acad Sci USA 102:14197-14202. doi:10.1073/pnas.0503108102

Guatelli-Steinberg D. 2009. Recent studies of dental development in Neandertals: Implications for Neandertal life histories. Evol Anthropol 18:9-20. doi:10.1002/evan.20190

Monge JM, Tillier A-M, Mann AE. 2006. Perikymata number and spacing on early modern human teeth : Evidence from Qafzeh cave, Israel. Bull Mem Soc Anthropol Paris 18:25-33.

Ramirez Rozzi FV, d'Errico F, Vanhaeren M, Grootes PM, Kerautret B, Dujardin V. 2009. Cutmarked human remains bearing Neandertal features and modern human remains associated with the Aurignacian at Les Rois. J Anthropol Sci 87:153-185.