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Student Prize Award Abstract
2001 Oral Paper Award


S. Brosnan1,2 and F. de Waal1,2,3
1Emory University, Population Biology, Ecology, and Evolution Program, Atlanta, Georgia, 30329, USA, 2Living Links Center, Yerkes Regional Primate Research Center, 3Department of Psychology, Emory University

A general concept of value seems a prerequisite for any intentional system of reciprocity or cooperation. Since capuchins engage in some form of these behaviors, it is important to establish whether they are capable of associating value with different goods or services. The response of capuchins to two differentially-valued tokens was evaluated. Ten subjects were taught to give the experimenter an inedible token in return for a food reward. Once a hierarchy of food preferences was established, the monkeys were trained to associate one token with low-value food and another token with high-value food (i.e. "valuable" token). After training, the experimenter held up a reward and subjects had to return the token that matched its value. In one case, the supply of valuable tokens was unlimited (100 trials/subject), while in the second case it was limited (50 trials/subject). Subjects did not return tokens that matched the reward. Males returned tokens randomly. In the unlimited case, females returned valuable tokens, regardless of the reward offered (t = 4.115, p = 0.015) whereas in the limited case, females returned valuable tokens until they ran out (t = 3.81, p = 0.019). Only females appeared to follow a short-term strategy for acquiring the high-value food items, which may be a consequence of the capuchin's social system.

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