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Protest in response to unequal reward distribution is thought to have played a central role in the evolution of human cooperation. Some animals refuse food and become demotivated when rewarded more poorly than a conspecific, and this has been taken as evidence that non-human animals, like humans, protest in the face of inequity. An alternative explanation—social disappointment—shifts the cause of this discontent away from the unequal reward, to the human experimenter who could—but elects not to—treat the subject well. This study investigates whether social disappointment could explain frustration behaviour in long-tailed macaques, Macaca fascicularis. We tested 12 monkeys in a novel ‘inequity aversion’ paradigm. Subjects had to pull a lever and were rewarded with low-value food; in half of the trials, a partner worked alongside the subjects receiving high-value food. Rewards were distributed either by a human or a machine. In line with the social disappointment hypothesis, monkeys rewarded by the human refused food more often than monkeys rewarded by the machine. Our study extends previous findings in chimpanzees and suggests that social disappointment plus social facilitation or food competition effects drive food refusal patterns.

* Correspondence should be addressed to Manuel Bohn (manyprimates@gmai l.com). Short-term memory is implicated in a range of cognitive abilities and is critical for understanding primate cognitive evolution. To investigate the effects of phylogeny, ecology and sociality on short-term memory, we tested the largest and most diverse primate sample to date (421 non-human primates across 41 species) in an experimental delayed-response task. Our results confirm previous findings that longer delays decrease memory performance across species and taxa. Our analyses demonstrate a considerable contribution of phylogeny over ecological and social factors on the distribution of short-term memory performance in primates; closely related species had more similar short-term memory abilities. Overall, individuals in the branch of Hominoidea performed better compared to Cercopithecoidea, who in turn performed above Platyrrhini and Strepsirrhini. Interdependencies between phylogeny and socioecology of a given species presented an obstacle to disentangling the effects of each of these factors on the evolution of short-term memory capacity. However, this study offers an important step forward in understanding the interspecies and individual variation in short-term memory ability by providing the first phylogenetic reconstruction of this trait’s evolutionary history. The dataset constitutes a unique resource for studying the evolution of primate cognition and the role of short-term memory in other cognitive abilities. Publisher PDF

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Delay of gratification involves the ability to resist the temptation of an immediate reward in order to receive a larger or better reward at a later point in time. It is a type of self-regulation and is closely related to concepts such as patience, impulse control, self-control, and willpower. Delay of gratification is involved in a variety of adaptive decision-making processes (e.g. planning, foraging, risk taking) and has been linked to health as well as economic, social, and academic achievement in humans. Several tasks have been used to assess delay of gratification in the past; we decided to use the accumulation task (Beran, 2002) as our main task. In this task, a limited number of food rewards slowly accumulate until the subject takes them and stops the accumulation process. We chose this task because we can include a wide range of difficulty levels (by varying the speed of accumulation) to capture the variation we expect to be present across species and individuals, and because it is a relatively easy task to implement. We would also like to include a second task: the exchange task (Auersperg et al., 2013). In this task, subjects are given a food item that they can later trade for a larger quantity. The level of difficulty is determined by how long subjects need to keep the food reward without eating it before they can exchange it.

Given a choice between social agents who demonstrate skills in different domains, preschoolers tend to recruit partners in an informed (rational) manner. From approximately four years of age, children attend to, copy and ask for help from the “expert”, at least in cooperative experimental settings (e.g. Hermes et al., 2015; Kushnir et al., 2013). In contrast to the cooperative setting, little is known about the partner recruitment choices children make in the competitive setting. Although children grow up surrounded by cooperative and well-meaning adults and peers, competition is by no means foreign to preschool and school age children (Sheridan & Williams, 2006). Children often compete with siblings and peers for resources and attention and take part in simple competitive games, for instance team sports. That children are able to correctly evaluate people’s abilities and demonstrate this ability when choosing between agents, should therefore be relevant not only in the cooperative but also in the competitive setting. In this online study, we will make domain-of-competence information available and contrast children’s partner recruitment decisions in these two settings. Our primary motivation is to establish whether the cognitive process thought to underlie decision-making in the cooperative context – sophisticated trait-based reasoning – is also evident in the competitive context. This study builds upon a previous preregistration from the same authors (Registration DOI 10.17605/OSF.IO/8R2HS). We anticipate that the current preregistration will be combined with the previous preregistration to form one publication.

Pre-schoolers who can choose between social agents who differ along a particular dimension (e.g., in degree of competence), make informed (rational) choices about who to attend to, copy or ask for help in cooperative experimental settings from the age of approximately four years. In the cooperative setting, pre-schoolers often take social evaluation one step further, generalising beyond the bounds of the observed domain and ascribing a competent person expertise or competency in an unrelated domain. In contrast to the cooperation setting, comparatively little is known about whether pre-schoolers make rational partner recruitment choices in other contexts, such as competitive settings. Although children grow up in relatively sheltered environments, where adults and peers are typically cooperative and well-meaning, the competition setting is not unfamiliar. For example, children often compete for toys or attention among siblings and playmates and take part in simple competitive games. Being able to evaluate others’ abilities or preferences is therefore important beyond the cooperative context. With our online study, we intend to fill this gap in the literature. The first question is whether the developmental trajectory for rational social decision-making differs with context - are children capable of applying competency information gleaned via social evaluation in a strategic (rational) manner in competitive and cooperative contexts from the same age? The second question is whether children generalise when asked to select a competitor from among a set of familiar agents in order to complete a task in a novel domain.

Judgements of wrongdoing in humans often hinge upon an assessment of whether a perpetrator acted out of free choice: whether they had more than one option. The classic inhibitors of free choice are constraint (e.g. having your hands tied together) and ignorance (e.g. being unaware that an alternative exists). Here, across two studies, we investigate whether chimpanzees consider these factors in their evaluation of social action. Chimpanzees interacted with a human experimenter who handed them a non-preferred item of food, either because they were physically constrained from accessing the preferred item (Experiment 1) or because they were ignorant of the availability of the preferred item (Experiment 2). We found that chimpanzees were more likely to accept the non-preferred food and showed fewer negative emotional responses when the experimenter was physically constrained compared with when they had free choice. We did not, however, find an effect of ignorance on chimpanzee's evaluation. Freedom of choice factors into chimpanzees' evaluation of how they are treated, but it is unclear whether mental state reasoning is involved in this assessment.

Individuals, Choice patterns in previous trials, Stability of risk preferences and analyses description

Individuals, Choice patterns in previous trials, Stability of risk preferences and analyses description