Gratuitous cooperation (in favour of non-relatives and without repeated interaction) eludes traditional evolutionary …, conformism and gratuitous cooperation co-evolve, and group selection is a necessary ingredient for the co-evolution to take place …-mutations (e.g., the rare emergence of a charismatic leader that brings order to the group) are necessary to sustain cooperation in …

cooperation may be less than additive. Using a utility function embodying both reciprocity and altruism we show that unconditional … contribution costs and punishment costs. The range over which altruism inhibits cooperation and reduces material payo¢´s is greater … support near e¡Ë cient levels of contributions to a public good. Cooperation may also be supported if altruistic individuals …

cooperation may be less than additive. Using a utility function embodying both reciprocity and altruism we show that unconditional … contribution costs and punishment costs. The range over which altruism inhibits cooperation and reduces material payoffs is greater … support near efficient levels of contributions to a public good. Cooperation may also be supported if altruistic individuals …

in unequal groups does not accord with models of inequality aversion or egocentric altruism which require an equal …

cooperation and are consistent with motivations for voluntary contributions of reciprocity and conformity. We also find that there …