Isotope assessment of Holocene human diets in the southwestern Cape, South Africa

Models of seasonal mobility to exploit seasonally abundant food sources have been proposed for prehistoric hunter-gatherers in many parts of the world. Some such hypotheses involve fundamental and insufficiently tested assumptions about the nature of both hunter-gatherer societies and the archaeological evidence that they leave. The present study is an independent test of such a hypothesis proposed for the southwestern Cape of South Africa. In this strongly ecologically differentiated area there are four distinct ecological zones that would have offered four different sets of resources to prehistoric people. Obvious modern seasonal fluctuations in these resources, plus a considerable amount of archaeological evidence, led to the suggestion that prehistoric hunter-gatherers moved in a regular seasonal cycle across the zones; this would have allowed them to make maximum use of temporarily plentiful plant and animal foods in some areas, while avoiding lean periods in others. However, as reported here, direct measurements of food intake, as reflected in the stable carbon isotope ratios of archaeological human skeletons, reveal that this was not the case. The implications of this study extend beyond the relevance to local archaeology to more general questioning of the ways in which archaeological data should be used to generate hypotheses.