One of the real strengths of their analysis lies in the sample size they have at their disposal: to date, they've recovered fully 270 pieces of decorated ostrich eggshell, a number that dwarfs that of any contemporaneous sample of decorated objects, for instance those from the site of Blombos where only about 20 pieces of engraved ochre have been found distributed in deposits spanning about 25,000 years (Henshilwood 2009). To put this in perspective, this is less than one engraved piece per thousand years at Blombos, while the frequency of decorated objects at Diepkloof in more than an order of magnitude greater (i.e., ca. 27 pieces per thousand years), and likely much more than that in some cases, since most pieces appear to come from two stratigraphic units. What is more, as Texier et al. (2010: 1) argue, the engraved pieces from other MSA sites (including Blombos) "are characterized by a noticeable diversity of patterns, of raw materials selected for marking, and of chronocultural contexts." In contrast, at Diepkloof, "the large smaple size of EOES [engraved ostrich eggshell], its well-documented context, and the unequivocal ature of the markings offers a unique opportunity to study what constitutes the most reliable collection of an early graphic tradition" (ibid). The image below shows some of the decorated fragments in questions, as well as some of the range in engraved motifs:
Note that this is not the same figure as that illustrating the fragments in the actual paper, and they establish that the colors of the different fragments were caused by post-depositional exposure to heat and fire.
The analysis of the fragments themselves is quite interesting, and very well done. The authors document a shift over time in the predominant engraved pattern, from a 'hatched band motif' (as seen in the figure above) in the lower HP levels at Diepkloof to 'series of deeply engraved, straight, subparallel lines' in the upper levels (as seen in vignettes A and C in the figure below):
From: Texier et al. (2010): 2, Fig. 1.
The fact that Texier et al. (2010) manage to convincingly demonstrate the presence of diachronic trends in the patterns used to decorate pieces of ostrich eggshell is cool enough in and of itself (there are also two other, much more infrequent patterns that they identify). However, identifying this begs the question of why this material was being decorated in the first, and how it was used, since it clearly wasn't used as part of, say, ornaments. This is all the more intriguing given the abundance of fragments at Diepkloof, and given that the vast majority of them are very small (less than 20x20mm). An answer to this question is provided, at least partially, by the following figure comes in:
Texier et al. (2010: 5) indicate that the circular denting seen in both fragments above appears very similar in shape and position to the holes punctured through the top of ostrich eggs today to empty them out and subsequently use them as "a flask to store and transport various fluids, usually water" (which makes you wonder what other fluids people may have needed or wanted to carry around). In the ethnographic record, such canteens are often decorated in various ways to indicate either ownership or what was contained in it. If the analogy is appropriate, then, we have at least two potential interpretations for the meaning of the Diepkloof engravings. If one had to chose between those two, the diachronic trend described above, and the fact that there is some internal variability in both the hatched band and linear line motifs may suggest that it reflects individual 'signatures' of sorts within an accepted iconographic tradition. This is, of course, highly speculative and only one of potentially many interpretations, but no matter how you slice it, it gives us some very interesting insights in the social norms of the Howiesons Poort. Additionally, as alluded to in some of the press coverage of this report, it also provides some strong insights into how people might have dealt with climatic variability at the time to explore and exploit arid landscapes largely devoid of water. This is one of those far-ranging aspects I was referring to in my introductory sentence.
As with most reports of 'extraordinary' finds in HP levels, however, this paper also indicates that this remarkable behavioral innovation appears to have been a short-lived one (by Paleolithic standards, anyway!), and that after about 55kya, traces of such behaviors largely disappear from the record. Sooner or later, people are going to have to propose a coherent explanation for this apparently generalized pattern of discontinuous behavioral innovation. Either that, or new finds are needed to 'fill in' the long stretches of the Middle Stone Age that apparently lack the conspicuous evidence that has recently been coming to light in HP assemblages. In that light, I was pretty surprised to see Richard Klein as a coauthor on this paper, given his long-held position that convincing evidence for 'modern' behavior doesn't exist before ca. 50kya... could we be witnessing a change in perspective? I'll be curious to see how he discusses the Diepkloof material in upcoming papers...
Lastly, I have to give a Colbert-like' wag of the finger' to PNAS for its timing in publishing this paper... seriously, 60,000 year old decorated eggs! Had you waited a few more weeks, this paper could have been published in the weeks running up to Easter! I jest, of course; there's no sense in delaying the publication of a good paper, but still... I just can't help thinking about how an angle like that would have worked in the popular press!
Henshilwood, C., d'Errico, F., & Watts, I. (2009). Engraved ochres from the Middle Stone Age levels at Blombos Cave, South Africa Journal of Human Evolution, 57 (1), 27-47 DOI: 10.1016/j.jhevol.2009.01.005
Texier, P., Porraz, G., Parkington, J., Rigaud, J., Poggenpoel, C., Miller, C., Tribolo, C., Cartwright, C., Coudenneau, A., Klein, R., Steele, T., & Verna, C. (2010). A Howiesons Poort tradition of engraving ostrich eggshell containers dated to 60,000 years ago at Diepkloof Rock Shelter, South Africa Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.0913047107