Abstract # 35:

Scheduled for Thursday, August 18, 2005 04:00 PM-04:15 PM: Session 5 (Mayfair Room) Oral Presentation

Endowment effects and consistency of preferences in chimpanzees

S. F. Brosnan1,2, M. Grady3, S. P. Lambeth2, E. Thiele2 and S. J. Schapiro2
1Emory University, Department of Anthropology, 1557 Pierce Drive, Atlanta, GA 30322, USA, 2The University of Texas M. D. Anderson Cancer Center, Department of Veterinary Sciences, Bastrop, TX 78602 USA , 3UCLA School of Law, Center for Law and Economics, Los Angeles, CA 90095 USA
     Economic models posit that individuals endowed exclusively with one good will trade that good for another to obtain some combination of both, with some consistency in preference for one over the other. Moreover, among humans, different individuals possess different preferences for a good (in terms of another good) and this variation among individuals yields spot exchanges (barter) between them. Our experiments challenge the applicability of this model to chimpanzees. Here grapes could be exchanged item-for-item for a 30-piece endowment of carrots (low value; 2 sessions, potential of 30 exchanges), apples (high value; 2 sessions), or cucumbers (middle value; 8 sessions). First, chimpanzees seemed to have difficulty with the concept of spot exchanges involving food and required extensive training. After training, all chimpanzees (n = 10) exchanged all carrot for grapes and virtually never exchanged apple for grapes (1.7% of apples exchanged). When endowed with cucumber, the responses were less extreme and the average number of cucumbers exchanged was consistent across trials (range: 12.8% - 20.1%). These preferences were more uniform across individuals than is commonly assumed for humans, a characteristic that may limit the development of barter and markets. This difficulty with food-related spot exchange, in conjunction with such characteristics as difficulty with prepotent responses, may have led to chimpanzees possessing a radically different economic culture from that found among humans.