The question of how modern human behaviour emerged from pre-human hominid behaviour is central to discussions of human evolution. This important book argues that the capacity to use signs in a symbolic way, identified by the authors as language, is the basis for the behaviour that can be described as human. The book is the product of a unique collaboration between the key disciplines in the debate about human evolution and mentality - psychology and archaeology. It examines the significance and nature of the evolutionary emergence of linguistic behaviour. Central to the book is the interface between the psychology of human behaviour and its evolutionary emergence. The authors trace the characteristics of the ancestors common to modern African apes, including humans, to determine which aspects of human nature must be accounted for in evolution. The text critically examines the archaeological record of hominid evolution and argues that evidence of behaviour is the key to detecting signs of awareness and self-conscious perception. The authors conclude that linguistic behaviour emerged no earlier than 100,000 years ago. The book's interdisciplinary approach allows critical attention to be given to an impressively broad range of relevant literature. Thus for the first time, all the known pieces in the puzzle are analysed, so that numerous contexts and behavioural practices are part of the authors' explanation for the prehistoric discovery that signs could function as symbols.