Editors ' Summary: Michael Little, in this chapter, discusses some basis principles of adaptation in the context of several other contributions to this volume. He focuses his discussion on environmental stress, the pitfalls of dealing with human sex ratios, and strategies of resource exploitation. Little emphasises the complexity of adaptive processes and the problems of reconciling human adaptation at the individual level, which involves the aggregate behaviors of individuals each striving to maximize access to or control over limiting resources. Human adaptation at the population level, which involves a need to maintain ecosystem equilibrium, and the persistence in time of ecosystem resources are also discussed.