Abstract # 34:

Scheduled for Thursday, June 21, 2007 02:15 PM-02:30 PM: Session 6 (North Main Hall F/G) Oral Presentation

Evolutionary Salience Predicts “Irrational” Pricing of Property in Chimpanzees

S. F. Brosnan1,2, O. D. Jones3,4, S. P. Lambeth2, M. C. Mareno2, A. S. Richardson2 and S. J. Schapiro2
1Emory University, Department of Anthropology, 1557 Dickey Drive, Atlanta, GA 30322, USA, 2Michale E. Keeling Center for Comparative Medicine and Research, The University of Texas M. D. Anderson Cancer Center, 3Vanderbilt University School of Law, 4Vanderbilt University Department of Biological Sciences
     Little is known about whether other species exhibit irrationalities observable in humans. This study investigated whether chimpanzees (Pan troglodytes) exhibit an “endowment effect,” a behavior in which humans value a good they have just come to possess more than they would have only a moment before. Thirty-three socially housed adult chimpanzees participated. Each was given a food or nonfood item and given the option to keep that item or exchange it back to the experimenter for a second, different, item of the same type (food or nonfood). Each subject was also given a preference test, to see which of the two items (of the same type) they preferred. Chi-squared tests [a=0.05] revealed that chimpanzees kept possession of food items (peanut butter; juice) they had just received (rather than exchanging for the other item) significantly more than expected given the results of the preference test. Moreover, the effect is far stronger for food than for less evolutionarily salient objects, toys (chew toy; rope toy), which the chimpanzees actually preferred to exchange rather than keep. These findings suggest that a variety of deviations from rational choice predictions may be common to humans and chimpanzees, and that the evaluation of this and other irrational behaviors in the context of evolutionary relevance may yield further insights in both nonhuman primates and humans.