Chimpanzees are vengeful but not spiteful

Abstract

People are willing to punish others at a personal cost, and this apparently antisocial tendency can stabilize cooperation. What motivates humans to punish noncooperators is likely a combination of aversion to both unfair outcomes and unfair intentions. Here we report a pair of studies in which captive chimpanzees (Pan troglodytes) did not inflict costs on conspecifics by knocking food away if the outcome alone was personally disadvantageous but did retaliate against conspecifics who actually stole the food from them. Like humans, chimpanzees retaliate against personally harmful actions, but unlike humans, they are indifferent to simply personally disadvantageous outcomes and are therefore not spiteful.

Fig. 1.

Mean percentage of trials (±SEM) in which chimpanzees collapsed an inaccessible food table (Study 1). In the baseline, plastic pieces were on the table; in the self-feeding condition, food was accessible to the actor; in the nobody-feeding condition, food was inaccessible, and no partner was present; and in the partner-feeding condition, food was accessible to the partner but not to the actor.

Fig. 2.

Experimental setup for Study 2. A sliding platform sits on a collapsible table in an inaccessible booth. The actor is in the actor's cage; in test conditions, the door to the partner's cage (on the right) would be closed. The actor can pull a rope causing the platform to collapse and the food to fall to the floor and out of reach.

Fig. 3.

Mean percentage of trials (±SEM) in which chimpanzees collapsed a food table in response to losing the food (loss), losing the food to a conspecific (outcome disparity), and having the food taken by a conspecific (theft) (Study 2). In the baseline condition, plastic pieces were on the table, which was out of reach of the actor.

Fig. 4.

Mean percentage of trials (±SEM) in which arousal (displays and tantrums) was exhibited by actors in Study 2 in response to nonfood items (baseline), losing food (loss), losing food to a conspecific (outcome disparity), and having the food stolen (theft).