Food sharing: a model of manipulation by harassment

Red colobus monkeys (Colobus badius) are an important and desirable source of protein for chimpanzees (Pan troglo-dytes; Goodall, 1986). A monkey kill attracts beggars that si-dle up to the carcass owner, extend their hands, vocalize, and sometimes grab a scrap of meat. In some situations, the carcass owner may share with the beggar, breaking off a piece of meat and handing it to a beggar. Why would the owner give away food that it could consume? Food sharing, defined here as joint use of a monopolizable food source, can be as active as this chimpanzee example or as passive as a lioness allowing another lioness to feed on her ga-zelle carcass. Either way, sharing appears to exemplify animal altruism because one individual accepts a fitness cost while another receives a fitness benefit. Although sharing may be al-truistic at the time of the sharing event, mechanisms such as kin selection (Hamilton, 1964) and reciprocal altruism (Trivers