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’.

Negative Reinforcement in the Description-Experience Gap

“…here: the presence of both choice patterns across conditions within the same experiment) was also observed by human participants) andKeupp et al (2021; non-human participants). The inconsistent effect of recent outcome type on choice behaviour in the current data is in line with mixed findings in the recency effect literature that used a sampling procedure (see General Introduction Possible Explanations for Why We Observe a Description-Experience Gap with Partial Feedback section above).Despite this inconsistent effect of recent outcome type on choice behaviour in the current data, participants' choice patterns showed a slight difference in decisions about negative punishment than in decisions about positive and negative reinforcement: Decisions about negative punishment showed a win-shift/lose-stay choice pattern more often than decisions about positive reinforcement and decisions about negative reinforcement.…”

Economic behaviours among non-human primates

“…Stefanie Keupp et al [39] studied risk-attitudes in a population of chimpanzees (Pan troglodytes). The experimental design and procedure they opted for are perfectly standard.…”

Rationality and cognitive bias in captive gorillas’ and orang-utans’ economic decision-making

“…Further indications for biases and suboptimal decision-making in primates derive from the fact that there can be considerable variability in performance between studies. Indeed, while risk-aversion is frequently described in humans [ 22 ] and non-primates [ 23 ], risk-preference is harder to generalise in primates, due to inter-species variability (for instance, bonobos appear more risk-averse than chimpanzees [ 24 – 26 ]) and between-study variance within a given primate species: Rhesus macaques appear risk-prone in [ 27 – 29 ] and risk-averse in [ 30 ], chimpanzees appear risk-prone in [ 31 – 33 ] and risk-averse in [ 34 – 36 ], and bonobos appear risk-prone in [ 19 , 32 ] and risk-averse in [ 24 , 25 , 31 ]. One major issue in this line of research is the diversity of the experimental designs that are used to test primates (see [ 37 ] for a review).…”

“…Across species, this experimental design generally (but not always [ 38 ]) leads to risk-aversion: bonobos showed 28% of risky choices when both options were equivalent [ 24 ], and around 30% of risky choices when the safe option is an intermediately-preferred food reward and the risky option either preferred of non-preferred food reward, with equal probabilities [ 25 ]. Chimpanzees showed around 40% of risky choices when the safe option is an intermediately-preferred food reward and the risky option either preferred of non-preferred food reward, with equal probabilities [ 25 ], and 34% of risky choices when both options were equivalent [ 36 ]. Alternatively, this experimental design can lead to weak risk-proneness: Chimpanzees showed 64% of risky choices when both options were equivalent [ 24 ], and chimpanzees and bonobos showed 57% of risky choices when the safe option is an intermediately-preferred food reward and the risky option either preferred of non-preferred food reward, with equal probabilities [ 39 ].…”

“…However, consistent experimental findings show that human economic behaviours often appear irrational, i.e., not aimed at maximising utility [3]. Investigating the factors that lead to seemingly or real irrational choices shows that the way utility is assessed can highly modulate to generalise in primates, due to inter-species variability (for instance, bonobos appear more risk-averse than chimpanzees [24][25][26]) and between-study variance within a given primate species: Rhesus macaques appear risk-prone in [27][28][29] and risk-averse in [30], chimpanzees appear risk-prone in [31][32][33] and risk-averse in [34][35][36], and bonobos appear risk-prone in [19,32] and risk-averse in [24,25,31]. One major issue in this line of research is the diversity of the experimental designs that are used to test primates (see [37] for a review).…”