ROBIN DUNBAR is Professor of Evolutionary Psychology at the University of Liverpool (previously Professor of Biological Anthropology at University College, London). He is the author of 9 books and 103 articles for, among others, Nature and New Scientist. LOUISE BARRETT is Lecturer in Evolutionary Psychology and Behavioural Ecology at the University of Liverpool. Her research interests lie in the evolution of cognition and the socioecology of human and non-human primates and she is co-director of the De Hoop Baboon Project in South Africa. JOHN LYCETT is Lecturer in Evolutionary Psychology at the University of Liverpool. His current research interests are in human reproductive decision making and parental investment decisions. AE(00): Robin Dunbar is Professor of Evolutionary Psychology at the University of Liverpool (previously Professor of Biological Anthropology at University College London). He is the author of 9 books and 103 articles for, among others, Nature and New Scientist. His most recent book, Gossip, Grooming and the Language of Evolution , published by Faber in '96, was reviewed in New Statesman as "one of those rare books that changes the way you see things and teaches you more about how human societies really work than a dozen sociological treatises". New York Review of Books wrote of the US (Harvard UP) edition, "a wonderful book...fresh and witty". Louise Barrett is Lecturer in Psychology at the University of Liverpool hwere she teaches and carries out reserach on evolutionary psychology and behavioural ecology. She has published numerous papers and articles in New Scientist.