conflict they could have evolved jointly. They do not claim that humans have actually evolved in this way, but that computer simulations show how war could be promoted by the interaction of these behaviors. A crucial open research question, thus, is how realistic the assumptions are which these simulation models are based on. Summary and current understanding When Richard Dawkins set out to "examine the biology of selfishness and altruism" in The Selfish Gene, he reinterpreted the basis of evolution, and therefore of altruism. He was "not advocating a morality based on evolution", and even felt that "we must teach our children altruism, for we cannot expect it to be part of their biological nature." But John Maynard Smith was showing that behavior could be subject to evolution, Robert Trivers had shown that reciprocal altruism is strongly favored by natural selection to lead to complex systems of altruistic behavior (supporting Kropotkin's argument that cooperation is as much a factor of evolution as competition), and Axelrod's dramatic results showed that in a very simple game the conditions for survival (be "nice", be provocable, promote the mutual interest) seem to be the essence of morality. While this does not yet amount to a science of morality, the game theoretic approach has clarified the conditions required for the evolution and persistence of cooperation, and shown how Darwinian natural selection can lead to complex behavior, including notions of morality, fairness, and justice. It is shown that the nature of self-interest is more profound than previously considered, and that behavior that seems altruistic may, in a broader view, be individually beneficial. Extensions of this work to morality and the social contract may yet resolve the old issue of individual interests versus group interests. Software Several software packages have been created to run prisoner's dilemma simulations and tournaments, some of which have available source code. The source code for the second tournament run by Robert Axelrod (written by Axelrod and many contributors in Fortran) is available online PRISON, a library written in Java, last updated in 1999 Axelrod-Python, written in Python Recommended reading See also Co-operation (evolution) References Bibliography Most of these references are to the scientific literature, to establish the authority of various points in the article. A few references of lesser authority, but greater accessibility are also included. External links The Iterated Prisoner's Dilemma and The Evolution of Cooperation The Evolution of Trust 1984