Reduced risk-seeking in chimpanzees in a zero-outcome game

Abstract

A key component of economic decisions is the integration of information about reward outcomes and probabilities in selecting between competing options. In many species, risky choice is influenced by the magnitude of available outcomes, probability of success and the possibility of extreme outcomes. Chimpanzees are generally regarded to be risk-seeking. In this study, we examined two aspects of chimpanzees' risk preferences: first, whether setting the value of the non-preferred outcome of a risky option to zero changes chimpanzees' risk preferences, and second, whether individual risk preferences are stable across two different measures. Across two experiments, we found chimpanzees (Pan troglodytes, n = 23) as a group to be risk-neutral to risk-avoidant with highly stable individual risk preferences. We discuss how the possibility of going empty-handed might reduce chimpanzees' risk-seeking relative to previous studies. This malleability in risk preferences as a function of experimental parameters and individual differences raises interesting questions about whether it is appropriate or helpful to categorize a species as a whole as risk-seeking or risk-avoidant. This article is part of the theme issue 'Existence and prevalence of economic behaviours among non-human primates'.

Keywords: chimpanzees; individual differences; risk; zero outcome.

Figure 1.

General setup with covered safe option (blue/tall cup) and risky option (pink/shallow cup). The centres of the two plastic lids on which the options were presented were 42 cm apart.

Figure 2.

Proportion of risky choices per individual per session in Exp. 1. Left: for the full sample. Right: for the subset with no side bias. Black lines/points represent mean per test session and 95% confidence intervals.

Figure 3.

Relationship between the proportion of risky choices in Exp. 1 and the average size of the safe option in Exp. 2. Left: for the full sample. Right: for the subset with no side bias. (Online version in colour.)