Chimpanzee and Human Risk Preferences Show Key Similarities—In the world of chimpanzees, too, young males take the greatest risks, to get a better position in the hierarchy

Chimpanzee and Human Risk Preferences Show Key Similarities. Lou M. Haux et al. Psychological Science, January 3, 2023. https://doi.org/10.1177/09567976221140326

Abstract: Risk preference impacts how people make key life decisions related to health, wealth, and well-being. Systematic variations in risk-taking behavior can be the result of differences in fitness expectations, as predicted by life-history theory. Yet the evolutionary roots of human risk-taking behavior remain poorly understood. Here, we studied risk preferences of chimpanzees (86 Pan troglodytes; 47 females; age = 2–40 years) using a multimethod approach that combined observer ratings with behavioral choice experiments. We found that chimpanzees’ willingness to take risks shared structural similarities with that of humans. First, chimpanzees’ risk preference manifested as a traitlike preference that was consistent across domains and measurements. Second, chimpanzees were ambiguity averse. Third, males were more risk prone than females. Fourth, the appetite for risk showed an inverted-U-shaped relation to age and peaked in young adulthood. Our findings suggest that key dimensions of risk preference appear to emerge independently of the influence of human cultural evolution.

Discussion

Risk preference is central to human and nonhuman behavior. The current results demonstrate that chimpanzee and human risk preference share key structural similarities and converge in crucial ways. Consistent with recent findings in humans (Frey et al., 2017), our results showed that chimpanzees’ willingness to take risks appears to manifest as a traitlike preference, with high rank-order stability across a set of important domains (based on observers’ assessments) and economic choice behavior. The social-risk domain proves to be the exception (Josef et al., 2016). Furthermore, chimpanzees are, like humans, ambiguity averse and less willing to choose options with unknown risks (Ellsberg, 1961; Trautmann & van de Kuilen, 2015). Our results indicate that males are more risk seeking than females, mirroring the same difference in human risk preference (Frey et al., 2021). Finally, chimpanzee risk taking shows an inverted-U-shaped relation to age, peaks in young adulthood, and is lower in older age—again mirroring similar trends in humans (Frey et al., 2021; Josef et al., 2016; Mata et al., 2016).

According to life-history theory, risk preference should be elevated in periods in which the goal of reproduction and associated proximal goals (e.g., gaining social status) is paramount (Stearns, 1992). Young adulthood is an indispensable transitional stage for male chimpanzees to learn the techniques of socially mature males in order to establish their own social position (Kawanaka, 1993; Watts, 2018). Consistent with the young male syndrome in humans (Wilson & Daly, 1985), our results show that male chimpanzees are especially risk prone around their 20s and particularly willing to take risks in order to get a better position in the hierarchy. Higher rank is associated with both relatively high mating (Kaburu & Newton-Fisher, 2015; Muller et al., 2011) and paternity (Boesch et al., 2006; Langergraber et al., 2013; Newton-Fisher et al., 2010; Wroblewski et al., 2009) success. Furthermore, our finding of heightened general risk tolerance during young adulthood converges with a recent overview of risk behavior in humans concluding that risk taking is heightened during emerging adulthood (Willoughby et al., 2021).

The current findings, in combination with the multimethod design, enrich the comparative approach in important ways. First, the general and traitlike preference for risk is congruent with evidence suggesting that animal personalities exist across a range of species and that risk-related traits are common characteristics (Wolf et al., 2007). Second, we found that the strangers risk domain was only weakly correlated with the other risk domains. This finding is in line with those of earlier studies indicating that trusting other individuals is not just a special case of risk taking but is based on important forms of social preferences, such as betrayal aversion (Fehr, 2009; Haux et al., 2021). Moreover, in humans, willingness to trust does not follow an inverted-U-shaped pattern but instead remains relatively stable across the adult life span (Josef et al., 2016). These results fit ideas that in humans and chimpanzees, the social domain remains prioritized across adulthood (Carstensen et al., 1999; Rosati et al., 2020). Third, chimpanzees’ observed ambiguity aversion is in line with results by Rosati and Hare (2011). They found that chimpanzees and bonobos are sensitive to ambiguity in the first trials of their experiment, suggesting that subjects dislike choosing options with unknown risks. Yet it remains unclear to what extent chimpanzees knew that only probability but not the information about outcomes was missing. This raises the question of whether ambiguity attitudes in Ellsberg’s (1961) implementation of the construct can be measured in nonverbal populations.

Fourth, our results suggest that chimpanzees are risk neutral to (minimally) risk prone. Past research offers inconsistent findings in this regard. The variation in risk sensitivity in studies may be explainable in terms of the presentation and experience of probabilities (see Hau et al., 2010; Heilbronner & Hayden, 2016; Hertwig, 2015; Wulff et al., 2018), that is, whether decisions were based on experienced frequencies (see Calcutt et al., 2019; Haux et al., 2021; Heilbronner et al., 2008; Keupp et al., 2021), or whether subjects had to infer probabilities from the task design (see Haun et al., 2011; Rosati & Hare, 2011, 2012, 2013, 2016). Furthermore, the possibility of coming away empty-handed—whether the risky option included the possibility of receiving nothing or always provided at least some amount of food—could also alter the decision (see Haux et al., 2021; Keupp et al., 2021).

Finally, the relatively small sample sizes and the concomitant sex and age distributions of past studies limit the generalizability of previous findings. Future research should expand the multimethod approach, for instance, by including several behavioral measures. This would allow researchers to examine the causes behind the variation in previous work and delineate which task characteristics influence chimpanzee risk sensitivity. Studies involving chimpanzees from different groups and environments will further enrich the discussion about the generalizability of behavioral variations. Because of their early-life experiences, sanctuary chimpanzees might display different risk preferences and behavior from those living in zoos and those in the wild (for a discussion on the generalizability across groups, see King et al., 2005; Laméris et al., 2021; Lutz et al., 2022; Weiss et al., 2007; Wobber & Hare, 2011). Last but not least, because it has been proposed that bonobos (Pan paniscus) and chimpanzees (humans’ two closest living relatives) show divergent risk preferences (see Rosati, 2017), for a complete reconstruction of our last common ape ancestors preferences, it is essential to also study bonobos’ willingness to take risks in more depth in the future.

In the behavioral sciences, risk preference is a mainstay of and a key building block in theories of choice (Barseghyan et al., 2013; Brailovskaia et al., 2018; Clark & Lisowski, 2017; Dohmen et al., 2011; Mata et al., 2018; Schonberg et al., 2011; Slovic, 1987). In recent years, the measurement and stability has been central to the debate about the nature of risk preferences (Frey et al., 2017, 2021; Josef et al., 2016; Schildberg-Hörisch, 2018; Weber et al., 2002). Our multimethod approach can enrich this discussion, indicating that across various aspects of risk preference, both observer ratings (for a discussion on the validity of human ratings, see the Supplemental Material) and behavioral choices are directionally consistent. These findings offer an important first step toward a general mapping of the construct of risk preference in chimpanzees. Understanding the degree of temporal stability and systematic individual change in chimpanzee risk preference will be an important endeavor for future research (Schildberg-Hörisch, 2018). In addition, “actuarial” data such as the frequency of injuries from hierarchy fights will offer another important addition to a multimethod approach to study risk preference in chimpanzees.

In humans, scholars have proposed that the willingness to take risks and to trust others is transmitted across generations through socialization experiences (Dohmen et al., 2012; Roberts et al., 2005; Slovic, 1966) but is also subject to genetic influences (Karlsson Linnér et al., 2019). Our findings suggest that human risk preference may in addition also have deeper phylogenetic roots than previously suspected. Structural similarities in risk preferences of humans and one of our closest living relatives are likely to reflect adaptations to similar dynamics in primate life histories.