Cultural ecology is the study of human adaptations to social and physical environments. Human adaptation refers to both biological and cultural processes that enable a population to survive and reproduce within a given or changing environment. This may be carried out diachronically (examining entities that existed in different epochs), or synchronically (examining a present system and its components). The central argument is that the natural environment, in small scale or subsistence societies dependent in part upon it, is a major contributor to social organization and other human institutions.