Waiting for grapes: Expectancy and delayed gratification in bonobos

Responses to delayed rewards vary widely across individuals and have important implications for personality and temperament. Animals may avoid delayed rewards because the future is uncertain. Therefore, expectations about receiving a future reward should influence the response to delayed payoffs. Here, we offered bonobos (Pan paniscus) a delayed gratification task in which food accumulated over time. Once subjects chose to consume the reward, food stopped accumulating. We tested their willingness to wait with a reliable and an unreliable experimenter to vary the subjects’ expectations that they would receive the food. Subjects waited less often with the unreliable experimenter but showed individual differences in the degree to which reliability generalized across experimental tasks. These data suggest that the expectations generated about the likelihood of receiving future rewards influence how individuals balance current and future needs.