Food sharing in bonobos: Tolerant sharing in a despotic society
The study of food sharing in apes can provide an interesting perspective on the evolution of altruism in early hominids. Sharing food can be an altruistic behaviour, entailing costs to food-owners and benefits to others,, but several alternative hypotheses have been proposed. For example, when food is shared between kin, kinship selection is at play. Chimpanzees often share food under pressure of their group members (harassment hypothesis). The reciprocal altruism hypothesis assumes that apes use mental bookkeeping: they may remember who groomed them and reward grooming effort by access to food, possibly following predictions of biological market models. Alternatively, apes could share food based on simple rules of thumb by sharing mostly with group members that are most similar to them (similarity hypothesis). Previous studies have focussed mainly on chimpanzees, and studies on bonobos are rare and often more descriptive. Moreover, different studies differ in kinds of food offered to the apes, in definitions used to describe patterns of food sharing, and in type of analysis. Here we used a test paradigm previously used for bonobos and chimpanzees in a new group of bonobos at Planckendael Wild Animal Park, Belgium. The first author studied the group of 6 adult and 2 immature bonobos for 295 hours in August and September 2010. First, bonobos were observed under standard feeding regime, with four feedings per day and no attempts to induce food sharing. Second, food was provided in large paper bags twice a day. Third, large bundles of willow were provided daily in addition to normal feeding regimes. Our results show that the dominance hierarchy in this group was very linear and strict. In contrast to expectations based on previous research, food sharing was very tolerant, with mostly relaxed food transfers, and no negative responses of food owners to approachers. This finding argues against the “harassment hypothesis”. Food sharing was however influenced by kinship: kin shared more frequently and more successfully than non-kin. In line with expectations of the biological market models for despotic groups, food was not exchanged reciprocally, but bonobos gave more food to group members that groomed them longer. In conclusion, we found that bonobos share more with group members that groom them longer as expected by biological market theory. However, sharing was more tolerant than previously reported, and it was influenced by kinship. This may be due to differences in group composition and/or personalities of the individuals involved in the study, effects that are possibly enlarged by small sample sizes.
RESPONDING TO BOLD TEXT It is really encouraging to learn that bonobos don’t fight and share food openly. That also share more with others that groom them.