Risk, Climatic Variability, and the Study of Southwestern Prehistory: An Evolutionary Perspective

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Abstract
Two recent developments in southwestern archaeology are brought together in this paper. First, theoreticians have begun to argue that the archaeological record should be viewed as the product of selection-driven evolution. Second, tree-ring research has produced a highly detailed history of climate for a large area of the northern Southwest. We view the record of climatic oscillations and extreme events as a record of the strength of selection favoring stabilization of specialized agricultural strategies in the arid northern Southwest. Published data from Black Mesa provide a cultural record of sufficient precision to permit comparison with the climatic record, while new data from Vermillion Cliffs, southern Utah, document one local end-product of an evolutionary sequence shaped to an important degree by the long-term variability of climate. Anasazi occupation of many regions failed to persist through the “Great Drought” of the 1270s. From a local perspective, this extreme climatic event caused adaptations shaped by selection prior to the 1270s to fail; from a broader temporal-spatial perspective, however, the drought must be seen as part of the selective regime that shaped subsequent human adaptation to the northern Southwest.