Diet breadth in the Middle Stone Age: Evolutionarily important?

The Middle Stone Age (MSA, ca. 300,000 to 30,000 years ago), is a crucial period in terms of the emergence of our species. During this period anatomically Modern Humans evolved and spread out of Africa. A recent study published in Current Anthropology (free access) provides a new perspective on this phenomenon through an investigation of subsistence practices during the period of MIS 6-3. So far, this aspect has mainly been investigated by looking at the rising importance of shellfish and other smaller game animals. In this new work the authors seek a broader and more coherent analysis. They selected 60 sites from across South Africa from varying environmental and climatic regimes in order to investigate the presence of changes in dietary breadth.

Overall, the results indicate a change between MIS 6-4, with an increase in smaller game, which subsequently reduces again in MIS 3. Concurrent with this general trend the study investigates the increase or change in resources exploited. They highlight an increase in more dangerous game including suids (see photo), again between MIS 6-4, that again subsequently tails off into MIS 3. The study confirms the palaeoenvironmental data from this region with larger numbers of browsers procured during the glacial/stadial periods and greater numbers of grazers during the interglacial/interstadial periods.

A warthog or suid (Source: Wordlwildlife.org)

The authors also approach the oft cited increase in exploitation of shellfish resources during the MSA. Whilst at a broad scale the pattern of exploitation matches that for other game indicating an increase in diet breadth and again matches the palaeoenvironmental record. During higher sea-level events there is an increase in the exploitation of this resource. However, calculations of actual calorific yields provide interesting results indicating a limited input/calorific value. This indicates that whilst shellfish resources were exploited it does not appear to have been a systematic strategy.

The study then attempts to tie some of these patterns into broader evolutionary perspectives. This is limited due to problems of faunal taphonomy or linking specific subsistence behaviour to specific lithic technocomplexes. This is especially true considering the ongoing debate surrounding the position of specific MSA entities. Whilst some of these changes could relate to changes in population density this is difficult to approach based on the current data. Also whilst an increase in more dangerous game could indicate an increase in cognitive capacity the authors make the valid point that this could just represent an improvement in hunting technology. This is one of the first studies that document in detail the patterns in subsistence behaviour througout the MSA. Whilst the agencies and reasons for this change are not fully understood it is an important first step in approaching these problems.

Full reference: Clark, J and Kandel, W. 2013. The Evolutionary Implications of variation in human hunting strategies and diet breadth during the Middle Stone Age of southern Africa. Current Anthropology. DOI: http://www.jstor.org/stable/10.1086/673386

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