This volume aims to illuminate long-standing questions about cause-and-effect relations between an animal's behaviour and its environment. By focusing on biological mechanisms - the sum of an animal's cognitive, neural, developmental and hormonal processes - researchers demonstrate how the integrated study of animal physiology, cognitive processes and social interaction can yield a better understanding of behaviour. With studies of species ranging from insects to primates, the contributors examine how various animals identify and use environmental resources and deal with ecological constraints, as well as the roles of learning, communication and cognitive aspects of social interaction in behavioural evolution. Taken together, the chapters demonstrate how the study of internal mechanistic foundations of behaviour in relation to their ecological and evolutionary contexts and outcomes provides valuable insight into such behaviours as predation, mating and dispersal. This volume shows how a mechanistic approach unites various levels of biological organization to provide a broader understanding of the biological bases of behavioural evolution.