A quantitative analysis of wear distributions on Middle Stone Age marine shell beads from Blombos Cave, South Africa

Early archaeological evidence for symbolically-mediated behaviour, which is our ability to create and share coded information between and within groups, comes from the African Middle Stone Age. Nassarius kraussianus shell beads, discovered in the Late Pleistocene, Still Bay archaeological deposits at Blombos Cave, Western Cape, South Africa, are some of the worlds earliest personal ornaments and their discovery significantly pushed back the origins of complex human symbolling. Further analyses of these beads led to the hypothesis that stringing arrangements at Blombos Cave changed through time, with important implications for the development and maintenance of social norms and style in early human populations. This hypothesis was supported by qualitative comparisons of archaeological and experimental wear distributions. Here, we present the results of a quantitative approach, applying a modified edge damage distribution method and statistical modelling to published diagrams (Vanhaeren et al. 2013 Journal of Human Evolution 64, 500-517) of wear on N. kraussianus shell beads. Our results support the original findings that different beading arrangements result in different wear distributions, and that the wear distributions on Blombos Cave beads exhibit temporal variability. However, our results vary with respect to which stringing arrangements best match the archaeological samples. Furthermore, we conclude that a combination of multiple processes may best explain the archaeological wear distributions, a finding more congruent with a long and complicated life history of curated objects like beads. These findings add to a growing record of early human social behaviours, and contribute methodologically to use-wear analyses of personal ornaments recovered from the archaeological record.