Editors' Summary: In the first chapter, Rada Dyson-Hudson emphasizes an evolutionary perspective, based on Darwinian theory, on human biological and behavioral adaptation. Her approach differs from more deterministic scientists in its attempt to deal with the environmental lability of most human genetic systems and the tight interaction among behavioral, biological, and environmental features of human populations. Dyson-Hudson believes that if there is to be a unified theory of biological and cultural adaptation, it must be based on an explicit recognition that natural selection is the only force which can generate and maintain adaptation.