Comment on 'The Still Bay and Howiesons Poort, 77-59 ka: Symbolic Material Culture and the Evolution of the Mind during the African Middle Stone Age' by Christopher Stuart Henshilwood and Benoit Dubreuil

Inference about the evolution of cognition can take several forms (for some discussion of this, see Barnard 2010; Davidson 2010a). The most secure starts with a model of the cognition of the last common ancestor of humans and other apes and then looks at the differences between modern humans and modern nonhuman apes. The third step is to produce a model of how cognitive processes must work if natural selection took our ancestors from that ancestor to ourselves (e.g., Barnard et al. 2007). This model should then be tested against the evidence of the archaeological and paleoanthropological record. Bridging arguments are often needed to show how archaeological materials demonstrate the cognition needed to bring them about (e.g., see how the recognition criteria for working memory may be assessed individually for one archaeological problem in Davidson 2010b). Similarly, the paleoanthropological record is most generally thought to contribute to discussions of cognition through arguments about aspects of brain function and mind (e.g., Bruner 2010). The evidence of changes in the size and shape of the external form of the brain needs arguments linking it to cognition, and these must recognize that the brains of our ancestors were different from ours. If we are to avoid circular reasoning, however, the only evidence of the way in which those different brains functioned is through inference from the behavioral evidence in the archaeological record. Finally, there is a whole body of theory about how the brain comes to be how it is in both developmental and evolutionary terms. One important element of this is the question of the impact of learning and changes in the learning environment through time on brain and cognitive function (for the impact of changes in life history, see, e.g., Nowell and White 2010).