Testing models on the emergence and nature of modern human behavior: Middle Stone Age fauna from Sibudu Cave (South Africa)

It has often been argued that the success and spread of modern humans after ∼50,000 years ago was due to a series of key behavioral shifts that conferred particular adaptive advantages---in other words, it was the evolution of modern behavior that allowed them to out-compete archaic populations such as the Neanderthals. And yet, particularly during the African Middle Stone Age (MSA), some of these behaviors see only patchy expression across time and space. What were the factors that rendered modern behaviors advantageous in some contexts but not in others? Recent models have proposed a link between the emergence of modern behaviors and environmental degradation and/or demographic stress. Under these models, modern behaviors represent a form of social and economic intensification in response to stress; if this were the case, then signs of subsistence intensification, including expanded dietary breadth and more intensive processing strategies, should be more common during periods in which these behaviors are manifested than when they are not. In order to test these models, I analyzed MSA faunal remains from Sibudu Cave (South Africa). Sibudu was particularly well suited for this analysis because it is one of the only known sites to have been occupied during the transition from the Howieson's Poort (HP), a phase in which modern behaviors are evidenced, to the post-HP MSA, when classic signatures of such behaviors have disappeared. The data show significant variability in hunting behavior between the HP and post-HP MSA. While much of this variability appears to correspond with changes in the local environment, evidence for resource stress is more common during the HP. The implications of these results to our broader understanding of the emergence and nature of modern human behavior are discussed.