Monkeys choose as if maximizing utility compatible with basic principles of revealed preference theory

Significance Revealed preference theory scrutinizes utility maximization based on tradeoffs between goods. This notion concerns the transition from biological rewards (necessary for survival) to tradable economic goods (beneficial for welfare and evolutionary fitness). However, these assumptions have never been tested empirically in species closely related to humans, as would be necessary to infer a general biological mechanism. In this experiment, rhesus monkeys repeatedly chose between bundles of two goods. Their choice frequencies conformed to curves of equal choice frequency (indifference curves) and satisfied crucial consistency and axiomatic tests involving out-of-sample prediction from modeled indifference curves, transitivity, and axiomatic change of option set size. In satisfying stringent theoretical criteria, the data suggest the existence of well-structured preferences consistent with utility maximization.