The settlement practices of the prehistoric Anasazi of the North American Southwest exhibited shifts from the occupation of dispersed settlements to aggregated villages in many locales both concurrently and at different times. Explaining the nature and timing of these shifts has long been a focus of interest to researchers working in the Southwest. We present a model that outlines the relations among population growth, population dispersion and aggregation, regional abandonments, the nature of specialized systems of production, labor organization, climatic change, and the role of natural selection in producing evolutionary explanations. We offer the hypothesis that aggregation is the product of changes in the organization of corporate labor related to the stabilization of specialized strategies of resource production in response to changes in environmental conditions.