Dynamic Inconsistency in Great Apes

Abstract

This paper studies the nature of temporal preferences in humans by studying their basic structure in our closest living primate relatives. We investigate whether intertemporal choices in three great ape species are dynamically consistent. We present orangutans (Pongo abelii ), bonobos (Pan paniscus) and gorillas (Gorilla gorilla) with several series of choices among different quantities of food available after different delays. When apes can select either a reward that is available immediately or one reward three times bigger available three minutes later, they tend to act impatiently choosing the sooner, smaller reward. They also show high within-group variability. However, when a six-minute delay is added to both alternatives, apes tend to act patiently and show a more homogeneous behavior. Additional tests with constant size or delay suggest that participants trade-off the size and delay of the rewards in a temporal horizon extended up to several minutes. These results represent the first time that dynamic inconsistency is documented in our closest living primate relatives. As such, they are consistent with the hypothesis that time-inconsistent preferences are part of our evolutionary heritage.