Population growth,climatic cooling,and the development of collector strategies on the Southern Plateau,western North America

A change in human adaptations on the Southern Plateau during the fourth millennium B.P offers the opportunity to investigate the process by which immediate-consumption strategies are replaced by delayed consumption strategies among hunter-gatherers. Assemblage structure and settlement pattern are used to infer the nature of resource acquisition strategies between 2000 and 6000 radiocarbon years B.P., and the results are compared with a proxy record of population and a detailed reconstruction of terrestrial and riverine paleoenvironments. Results show that a strategy of mobile and later occasionally sedentary foraging with little use of storage technology persisted until as late as 3500 B.P and was abruptly and without detectable gradation replaced by a strictly scheduled, semisedentary, logistically organized, storage-dependent collector strategy. The change took place at a time of depressed population and 400 years after a period of climatic cooling had begun, thus eliminating both demographic pressure and environmental determinism as explanations. The evidence could be explained by prolonged selective pressure of an increasingly seasonal environment acting on successively attempted behavioral variants, but the widespread rise of collector-like strategies throughout the west at about the same time leaves open the question of exogenous development and highlights the importance of climatic change.