How to Spend a Token? Value Representation and Food Choice inTufted Capuchin Monkeys (Cebus apella)

摘要

Money is a medium of exchange to obtain a virtually unlimited variety of goods and services, but how did humans start to exchange valueless objects for goods? We explored the evolutionary roots of trading behaviour in capuchin monkeys, South American primates, which separated from humans 35 million years ago. We aimed to evaluate (a) how eight capuchins represent the value of a token (Multi-token) that allowed them to choose one among 10 different foods (one favourite food and nine less preferred foods), in comparison with a token (Mono-token) that allowed them to choose one among 10 pieces of the same favourite food, and (b) whether quality of the less preferred foods affected their choices. In the first condition, the Multi-token was exchangeable for a variety of mid-preferred foods (B-foods), whereas in the second condition the Multi-token was exchangeable for a variety of low-preferred foods (C-foods). Each condition involved twenty 20-trial sessions, each consisting of (i) 20 binary choices between one Mono-token and one Multi-token, (ii) the exchange of the selected token, and (iii) the choice of one piece of food from a tray. Though the marginal utility of the Mono- and the Multi-token is the same, the Multi-token dominated both in terms of value and variety since in both conditions capuchins consistently preferred the Multi-token and opted for one of the less preferred foods. Thus, variety seeking, an individual’s tendency to look for diversity in the choice of services and goods, is a powerful force affecting token value representation in capuchins.