  We address the problem of how cooperative (altruistic-like) behavior arises
in natural and social systems by analyzing an ultimatum game in complex
networks. Specifically, three types of players are considered: (a) empathetic,
whose aspiration level and offer are equal, (b) pragmatic, who do not
distinguish between the different roles and aim to obtain the same benefit, and
(c) agents whose aspiration level and offer are independent. We analyze the
asymptotic behavior of pure populations on different topologies using two kinds
of strategic update rules. Natural selection, which relies on replicator
dynamics, and Social Penalty, inspired in the Bak-Sneppen dynamics, in which
players are subjected to a social selection rule penalizing not only the less
fitted individuals, but also their first neighbors. We discuss the emergence of
fairness in the different settings and network topologies.
