Increasing scales of social interaction and the role of Lake Cahuilla in the systemic fragility of the Hohokam system (A.D. 700-1100)
Exchange is fundamental to human society, and anthropologists have long documented the large size and complexity of exchange systems in a range of societies. Recent work on the banking system of today's world suggests that complex exchange systems may become systemically fragile and in some types of complex exchange systems that involve feedbacks there exists a fundamental trade-off between robustness (stability) and systemic fragility. These properties may be observable in the archaeological record as well. In southern Arizona, the Hohokam system involved market-based exchange of large quantities of goods (including corn, pottery, stone, and shell) across southern Arizona and beyond, but after a few generations of expansion it collapsed rapidly around A.D. 1070. In this case, increasing the scale of a pre-existing system (i.e., expanding beyond the Hohokam region) may have reduced the efficacy of established robustness-fragility trade-offs, which, in turn, amplified the fragility of the system, increasing its risk of collapse. My research examines (1) the structural and organizational properties of a transregional system of shell exchange between the Hohokam region and California, and (2) the effect of the presence and loss of a very large freshwater lake (Lake Cahuilla) in southeastern California on the stability of the Hohokam system. I address these issues with analysis of ethnographic, ethnohistoric, and archaeological data, and with mathematical modeling. My study (1) produced a simple network model of a transregional system of interaction that links the Hohokam region and California during the centuries from A.D. 700 to 1100; (2) uses network and statistical analysis of the network model and archaeological data to strongly suggest that the transregional exchange system existed and was directional and structured; (3) uses network and other analysis to identify robustness-fragility properties of the transregional system and to show that trade between Lake Cahuilla fishers and the Hohokam system should be included in a mathematical model of this system; and (4) develops and analyzes a mathematical model of renewable resource use and trade that provides important insights into the robustness and systemic fragility of the Hohokam system (A.D. 900-1100).