Dealing with uncertainty: risk preference in tufted capuchin monkeys and human children

Introduction: Individuals must constantly make decisions among multiple options, judging and balancing their costs and benefits, and often they do not know what consequences will follow from their choices. This “lack of knowledge” is called uncertainty, but some researchers, especially economist, have distinguished between ambiguity and risk. Ambiguity occurs when individuals do not know the well-defined probabilities associated with each choice, whereas risk applies only when individuals know the precise probabilities involved, as for example when betting on a coin toss. According to normative economic models, rational decision makers should be indifferent when choosing between a safe option and a risky option leading on average to the same payoff. However, in laboratory experiments, humans are generally risk averse for gains, although outside of the laboratory they often show a very different behaviour and pathological gambling affects 0.2–5.3 % of adults in western societies. Moreover, risk propensity in human changes with age and adolescents are more risk seeking than adults. Thus, it is important to elucidate what are the psychobiological bases of this behavior - by investigating risk preferences in non-human primates, our closest relatives - and how decision-making under risk changes in the course of human development. Methods: We tested 10 capuchin monkeys, and 40 children with the same methodology. Both capuchins and children were presented with a series of choices between a “safe” option (yielding always 4 food items) and a “risky” option (yielding either 1 or 7 food items with 50% of probability). Only for capuchins, in order to evaluate the flexibility of their risk preferences, we tested the same subjects in two additional conditions in which the average payoff of the risky option was either higher or lower than that of the safe option. Results: When the safe and the risky option yielded on average the same payoff, capuchins were risk prone whereas children did not show a preference for either option. Moreover, when the average payoff of the risky option was higher than that of the safe option, all capuchins were again risk prone, but when the average payoff of the risky option was lower than that of the safe option, they became indifferent between the options. Conclusions: Capuchins’ decision-making under risk mirrors their risk-prone behaviour in the wild, where they often rely on unpredictable and/or hazardous food sources, they hunt vertebrates that can strike back, process and eat cashew nut despite its caustic protection, and use tools on the ground where the potential risk of being predated is high. Human children, instead, behave like rational decision makers, although our results are too preliminary to draw definitive conclusions. Future research should investigate (i) how older children behave in the same task and (ii) how younger and older children behave in conditions in which the average payoff of the risky option is either higher or lower than that of the safe option.