Competitive and cooperative responses to climatic instability in coastal southern California

Archaeological data indicates that socially and politically complex hunter- gatherer societies had become well established on the southern California c oast by A.D. 1300. Major developmental changes in sociopolitical complexity are generally considered to have taken place rapidly between AD 1150 and 1 300. Recently, two hypotheses have been proposed to account for this rapid cultural evolution, both invoking stressful climatic conditions as an impor tant trigger for cultural change. One suggests that the sociopolitical deve lopment was stimulated in part, by multiple marine and terrestrial subsiste nce stresses, particularly low marine productivity resulting from regional warming. The other suggests that these developments were largely driven by decreases in terrestrial productivity and water availability linked to drou ght. Resolution of this debate has been hampered by insufficient paleoclima tic and archaeological data. We present a well-dated, relatively high resol ution (25-year intervals) oxygen isotopic marine climate record and new arc haeological data from the Northern Channel Islands Sor the last 3,000 years . These data strongly suggest that changes in human behavior associated wit h increasing cultural complexity: 1) accelerated after A.D. 500 and became dominant by A.D. 1300, 2) occurred during one of the coldest and most unsta ble marine climatic intervals of the Holocene (A.D. 450-1300), and 3) coinc ided with cool, dry terrestrial conditions. Incipient cultural complexity e merged during an interval marked by inferred high marine productivity, redu ced terrestrial food and water availability and large, unpredictable variat ions in terrestrial resource availability. Our records suggest a strong rel ationship during this rime between climatically induced changes in environm ental conditions and social, political, and economic responses, including t he emergence of more intensified fishing, and increased sedentism, violence , and trade.