That behavior varies by species is both a basic proposition and a basic finding of comparative psychology. Implicit in the idea of behavioral variation across species is the complementary idea of behavioral similarity within species. The two ideas form a complex, neither element of which fully makes sense without the other. The second element of the complex, the idea of be havioral similarity within species, is the central focus of the concept of species-typical behavior. The concept refers to behaviors that typify or characterize entire species and that, in the realm of behavior, provide each species with its dis tinctive character among all others.