Foragers among farmers in the Early Iron Age of Botswana? Dietary evidence from stable isotopes

摘要

The thesis attempts to identify human skeletal remains of Later Stone Age (LSA) hunter-gatherersudon sites associated with Early Iron Age (EIA) farmers in east central and north western parts ofudBotswana and to identify individuals who may have shifted between foraging and farming. Becauseudof the sources of dietary carbon, EIA farmers were expected to have δ13C values of approximately -ud8‰, which are distinguishable from those of the LSA hunter-gatherers (δ13C values of around -ud17‰). Individuals who shifted from foraging to farming would have significant differences in δ13Cudvalues of bones and teeth that form or remodel at different ages and rates.udIn the east central, 76 humans from Toutswe sites were analysed. From the Tsodilo Hills andudOkavango River there were five individuals. Animal samples from EIA contexts at of the sitesudmentioned above were analysed to provide reference standards necessary for the interpretation ofudhuman isotope values. Moreover, animal isotope values were used to reconstruct pastudenvironmental and climatic conditions.udTwo adults from N!oma appear to have shifted from a childhood subsistence based on foragingudand most probably fishing to full-time farming in adulthood. The two adults from Xaro have boneudcollagen δ13C values associated with both foraging and freshwater fishing. Though samples areudsmall, there is some support for the argument that some LSA foragers had adopted the farmers’udmode of subsistence during the Iron Age.udNitrogen isotope values of domestic herbivores from the east central suggest annual rainfall ofudabout 500mm while carbon isotope results indicate heavy reliance on C4 photosynthetic grasses.udResult from the north west suggest rainfall on 450mm with some degree of browsing. Mordenudherbivore samples from Toutswe area show that rainfall patterns have not changed but in contrast,udthe feeding habits of both cattle and small have changed to include significant amount of C3udphotosynthetic plants. This change is attributed to the general degradation of the environment.