title: Chimpanzees do not take advantage of very low cost opportunities to deliver food to unrelated group members.
abstract: We conducted experiments on two populations of chimpanzees,Pan troglodytes, to determine whether they would take advantage of opportunities to provide food rewards to familiar group members at little cost to themselves. In both of the experiments described here, chimpanzees were able to deliver identical rewards to themselves and to other members of their social groups. We compared the chimpanzees' behaviour when they were paired with another chimpanzee and when they were alone. If chimpanzees are motivated to provide benefits to others, they are expected to consistently deliver rewards to others and to distinguish between the partner-present and partner-absent conditions. Results from both experiments indicate that our subjects were largely indifferent to the benefits they could provide to others. They were less likely to provide rewards to potential recipients as the experiment progressed, and all but one of the 18 subjects were as likely to deliver rewards to an empty enclosure as to an enclosure housing another chimpanzee. These results, in conjunction with similar results obtained in previous experiments, suggest that chimpanzees are not motivated by prosocial sentiments to provide food rewards to other group members.
authors.affiliation: Cognitive Evolution Group, University of Louisiana, Lafayette, LA, U.S.A; University of Southern Mississippi Gulf Coast, Long Beach, MS, U.S.A.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Vonk
authors.affiliation: Department of Anthropology, Emory University, Atlanta, GA, U.S.A; Michale Keeling Center for Comparative Medicine and Research, University of Texas M.D. Anderson Cancer Center, Bastrop, TX, U.S.A; Department of Psychology, Georgia State University, Atlanta, GA, U.S.A.
authors.forename: Sarah F
authors.initials: SF
authors.lastname: Brosnan
authors.affiliation: Department of Anthropology, University of California, Los Angeles, CA, U.S.A.
authors.forename: Joan B
authors.initials: JB
authors.lastname: Silk
authors.affiliation: Department of Anthropology, Emory University, Atlanta, GA, U.S.A; Department of Psychology, Economics, University of British Columbia, Vancouver BC, Canada.
authors.forename: Joseph
authors.initials: J
authors.lastname: Henrich
authors.affiliation: Department of Anthropology, University of California, Los Angeles, CA, U.S.A.
authors.forename: Amanda S
authors.initials: AS
authors.lastname: Richardson
authors.affiliation: Michale Keeling Center for Comparative Medicine and Research, University of Texas M.D. Anderson Cancer Center, Bastrop, TX, U.S.A.
authors.forename: Susan P
authors.initials: SP
authors.lastname: Lambeth
authors.affiliation: Michale Keeling Center for Comparative Medicine and Research, University of Texas M.D. Anderson Cancer Center, Bastrop, TX, U.S.A.
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Schapiro
authors.affiliation: Cognitive Evolution Group, University of Louisiana, Lafayette, LA, U.S.A.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Povinelli
keywords: Pan troglodytes; altruism; chimpanzee; other-regarding preference; prosocial behaviour