1. The Biology of Moral Systems;Alexander,1987
2. The evolution of cooperation;Axelrod;Science,1981
3. Brown, W. M. (1998). Signaling Benevolence: An Evolutionary Perspective on the Encoding and Decoding of Altruism. Master of Science Thesis, Department of Psychology, Dalhousie University: The National Library of Canada.
4. Distinguishing mechanisms for the evolution of cooperation;Bull;Journal of Theoretical Biology,1991
5. Evolution, partnerships and cooperation;Cooper;Journal of Theoretical Biology,1998