Unlike Sober and Wilson, I suggest that in all cases of benefits conferred on others the direct fitness of the altruist increases. The benefit to others created by the altruistic act is only a consequence of the altruistic adaptation, and not the evolutionary mechanism that created it. In many cases the investment in the altruistic act, like handicaps required for signalling in general, attests to the social prestige of the altruist and thus increases its fitness. In other cases the ‘altruist’ (...) is a phenotype that has only minute chances to reproduce, and what seems to be an altruistic act actually increases somewhat these meagre chances. It is easy to overlook this marginal benefit to the ‘altruist'. Still, if that selfish benefit to the altruist -- i.e., an increase in its direct fitness -- did not exist, the altruistic acts that benefit the group could not have evolved. (shrink)

I agree with Gurven that costly signaling can explain food-sharing phenomena. However, costly signaling may also explain the role of food sharing in deterring rivals. Details of food-sharing interactions may reveal gains and losses in the social prestige of the interacting parties. The evolutionary models of kin selection and of reciprocal altruism are unstable and should be avoided.