turned on its head by recognition of a broader, more profound view of what constitutes self-interest. It does not matter why the individuals cooperate. The individuals may be prompted to the exchange of "altruistic" acts by entirely different genes, or no genes in particular, but both individuals (and their genomes) can benefit simply on the basis of a shared exchange. In particular, "the benefits of human altruism are to be seen as coming directly from reciprocity – not indirectly through non-altruistic group benefits". Trivers' theory is very powerful. Not only can it replace group selection, but it also predicts various observed behavior, including moralistic aggression, gratitude and sympathy, guilt and reparative altruism, and the development of abilities to detect and discriminate against subtle cheaters. The benefits of such reciprocal altruism were dramatically demonstrated by a pair of tournaments held by Robert Axelrod around 1980. Axelrod's tournaments Axelrod initially solicited strategies from other game theorists to compete in the first tournament. Each strategy was paired with each other strategy for 200 iterations of a Prisoner's Dilemma game and scored on the total points accumulated through the tournament. The winner was a very simple strategy submitted by Anatol Rapoport called "TIT FOR TAT" (TFT) that cooperates on the first move, and subsequently echoes (reciprocates) what the other player did on the previous move. The results of the first tournament were analyzed and published, and a second tournament was held to see if anyone could find a better strategy. TIT FOR TAT won again. Axelrod analyzed the results and made some interesting discoveries about the nature of cooperation, which he describes in his book In both actual tournaments and various replays, the best-performing strategies were nice: that is, they were never the first to defect. Many of the competitors went to great lengths to gain an advantage over the "nice" (and usually simpler) strategies, but to no avail: tricky strategies fighting for a few points generally could not do as well as nice strategies working together. TFT (and other "nice" strategies generally) "won, not by doing better than the other player, but by eliciting cooperation [and] by promoting the mutual interest rather than by exploiting the other's weakness." Being "nice" can be beneficial, but it can also lead to being suckered. To obtain the benefit – or avoid exploitation – it is necessary to be provocable and forgiving. When the other player defects,