title: Chimpanzee (Pan troglodytes) anticipation of food return: coping with waiting time in an exchange task.
abstract: Despite controversial expectations that animals achieve reciprocal altruism, it is unclear if nonhuman species possess the necessary cognitive abilities. For reciprocal altruism, individuals must anticipate the loss of a commodity and accept a delay before some return. The authors investigated the abilities of 5 chimpanzees (Pan troglodytes) to cope with increasing waiting duration in exchange tasks. Subjects had to keep a small cookie before returning it to a human partner to obtain a larger piece. For a piece 2, 4, or 8 times the size of the small piece, 3 of the 5 subjects waited for up to 4 min. For a piece 40 times larger, 4 of the 5 subjects waited up to 8 min. At long time lag, renouncement to wait occurred earlier than predicted by subjects' general waiting capacity, suggesting that the decision to wait was based on a trade-off between reward quantity and expected costs of the waiting duration. Chimpanzees could anticipate a delayed reward at a time scale of several minutes. If this reflects a cognitive limit in chimpanzees' anticipation capacity, reciprocal altruism by keeping track of costs and benefits over extended periods may be unlikely in chimpanzees.
authors.affiliation: Ethology Research, Animal Science Department, Biomedical Primate Research Centre, Rijswijk, Netherlands. valerie.dufour@c-strasbourg.fr
authors.forename: V
authors.initials: V
authors.lastname: Dufour
authors.forename: M
authors.initials: M
authors.lastname: Pelé
authors.forename: E H M
authors.initials: EH
authors.lastname: Sterck
authors.forename: B
authors.initials: B
authors.lastname: Thierry
mesh_terms: D000533:Altruism; D000818:Animals; D001070:Appetitive Behavior; D005260:Female; D006801:Humans; D008297:Male; D009042:Motivation; D002679:Pan troglodytes / Q000523:psychology*; D012055:Reinforcement Schedule; D012201:Reward; D013998:Time Perception