Middle holocene climate change and human population dispersal in western north America

Linguistic diversity and the patchwork distribution of language groups in western North America reflect a complex history of early settlement, in situ development, and periodic population movement. Available climate records in western North America (7000-3800 cal yr BP) indicate a severe dry interval between 6300 and 4800 cal yr BP embedded within a generally warm and dry Middle Holocene. Dry conditions in western North America between 6300 and 4800 cal yr BP correlate with cold to moderate sea-surface temperatures (SST) and relatively high marine productivity along the Southern California Coast evident in Ocean Drilling Program (ODP) Core 893A/B (Santa Barbara Basin). Marine climate data from the Santa Barbara Basin indicates that SSTs oscillated during the Middle Holocene between warm and cold states. Based on archeological, linguistic, and genetic data, this chapter argues for a movement of Uto-Aztecan people from western desert environments to the Southern California Coast, including the southern Channel Islands, and into portions of the Central Valley by at least 5500-4500 cal yr BP. It hypothesizes that population dispersal from the desert interior was primarily in response to severe and prolonged drought and that people moved selectively to coastal and aquatic habitats because of the ameliorated effects of drought and their overall productivity. Furthermore, it suggests that some Uto-Aztecan groups were displaced as conditions in the southern California desert became dryer and less productive. Finally, it demonstrates the linkages between environmental change and human adaptive response during the arid Middle Holocene in western North America.