To what extent is human morality the outcome of a continuous development from motives, emotions and social behaviour found in nonhuman animals? Psychologist Jerome Kagan, primatologist Hans Kummer, philosopher Peter Railton and others discuss the principal paper by primatologists Jessica Flack and Frans de Waal. Cultural anthropologist Christopher Boehm synthesizes social science and biological evidence to support his theory of how our hominid ancestors became moral by establishing purposeful social control over individual behaviour. Can an evolutionary understanding of human nature allow or predict sacrifice for others and ultimate desires for another's good? Philosopher Elliott Sober and evolutionary biologist David Sloan Wilson argue 'Yes' in their book Unto Others: The Evolution and Psychology of Unselfish Behavior (Harvard, 1998), summarized here. How can fairness to others at one's own expense evolve or survive in competition with selfish strategies? Brian Skyrms (Evolution of the Social Contract, Cambridge, 1996) argues that game theory based on adaptive dynamics must join the social scientist's use of rational choice and classical game theory to explain cooperation.