Late Holocene Dietary Change in the San Francisco Bay Area Stable Isotope Evidence for an Expansion in Diet Breadth

Scholars of California prehistory continue to debate the importance of different food resources to the native diet during the late Holocene. Resource intensification models for central California predict temporal declines in the abundance of large game relative to smaller fauna, as well as a shift towards greater use of vegetal foods. These changes are commonly linked to human-driven resource depression and overpopulation, although climatic factors may also have played a role. This study uses data from stable carbon and nitrogen isotopes of human bone to evaluate evidence of paleodietary change among late Holocene human populations (ca. 4950-200 cal B.P.) from the eastern shore of San Francisco Bay, California. Carbon and nitrogen isotope values of bone collagen demonstrate significant temporal variation and indicate a shift in emphasis from high trophic-level marine protein toward a greater emphasis on terrestrial resources and lower trophic-level marine foods. Carbon isotope values of bone apatite provide additional information not recorded in bone collagen, and suggest an increased emphasis on vegetal resources during the latter part of the prehistoric sequence (after ca. 2150 cal B.P.). Alternatively, the isotopic data presented here could provide evidence for regionally specific diets or variation due to human population movement throughout the San Francisco Bay area.