Digging deeper: Late Holocene Dietary Change in the San Francisco Bay Area

This month's Digging Deeper comes to you from California Archaeology and one of the most popular articles in its online archive, 'Late Holocene Dietary Change in the San Francisco Bay Area' by Eric Bartelink.

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.

The following is an extract from the article's introduction:

"With an estimated population of at least 310,000 individuals, native California was one of the most densely settled landscapes in North America at the time of European contact. Early researchers attributed this demographic anomaly to California’s natural resource abundance of large game, fish, shellfish, and plant foods. This abundance is often cited as the reason agriculture failed to develop in prehistoric California—it simply was not needed, although some scholars have argued that intensive use of stored food staples (such as acorns and small seeds) can be considered a type of proto-agriculture. The richness and diversity of the central California landscape described in early ethnohistoric accounts further advanced the notion that native peoples had little impact on their natural environment, producing an archaeological record lacking evidence of significant culture change.

Recently, this paradigm has been questioned by scholars arguing that rebounds in game populations during the historic period occurred only after human population numbers declined due to the spread of foreign-introduced infectious diseases. Resource abundance in prehistoric California has been seriously challenged by a number of recent zooarchaeological studies. Archaeofaunal research in the San Francisco Bay area, the Sacramento Valley, and the Pacific Coast shows evidence of resource depression, measured by temporal declines in high return, large game relative to low return, smaller fauna in late Holocene sites. The widespread distribution of mortar and pestle technology, beginning around 4500 cal B.P. in California, has been linked to the shift toward more intensified use of lower return vegetal resources such as acorns and small seeds. These different lines of evidence all suggest that an expansion in diet breadth occurred during the late Holocene in central California."

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