Four principal papers and a total of 43 peer commentaries on the evolutionary origins of morality. To what extent is human morality the outcome of a continuous development from motives, emotions, and social behaviour found in nonhuman animals? Jerome Kagan, Hans Kummer, Peter Railton, and others discuss the first principal paper by primatologists Jessica Flack and Frans de Waal. The second paper, by cultural anthropologist Christopher Boehm, synthesizes social science and biological evidence to support his theory of how our hominid ancestors became moral. In the third paper philosopher Elliott Sober and evolutionary biologist David Sloan Wilson argue that an evolutionary understanding of human nature allows sacrifice for others and ultimate desires for another's good. Finally, Brian Skyrms 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.