Increasing Behavioral Flexibility? An Integrative Macro-Scale Approach to Understanding the Middle Stone Age of Southern Africa

The Middle Stone Age (MSA) of southern Africa represents a period during which anatomically modern humans adopted a series of diverse cultural innovations. Researchers generally attribute these behavioral changes to environmental, neurological, or demographic causes, but none of these alone offers a satisfactory explanation. Even as patterns at site level come into focus, large-scale trends in cultural expansions remain poorly understood. This paper presents different ways to view diachronic datasets from localities in southern Africa and specifically tests hypotheses of environmental and cultural causality. We employ an array of analyses in an attempt to understand large-scale variability observed during the MSA. We evaluated the diversity of stone tool assemblages to model site use, examined transport distances of lithic raw materials to understand patterns of movement, assessed the cultural capacities required to manufacture and use different sets of tools, applied stochastic models to examine the geographic distribution of sites, and reconstructed biome classes and climatic constraints. Our large-scale analysis allowed the research team to integrate different types of information and examine diachronic trends during the MSA. Based on our results, the range of cultural capacity expanded during the MSA. We define cultural capacity as the behavioral potential of a group expressed through the problem-solution distance required to manufacture and use tools. Our dataset also indicates that the actual behavior exhibited by MSA people, their cultural performance as expressed in the archaeological record, is not equivalent to their cultural capacity. Instead we observe that the main signature of the southern African MSA is its overall variability, as demonstrated by changing sets of cultural performances. Finally, at the scale of resolution considered here, our results suggest that climate is not the most significant factor driving human activities during the MSA. Instead, we postulate that behavioral flexibility itself became the key adaptation.