Discrimination of Faces, Sex, and Relationships by Capuchin Monkeys

Whether attending a business function or moving to a new neighborhood, the ability to recognize, remember, and garner information about the social relationships of other individuals is critical for human survival. But to what degree is this unique to humans? Nonhuman primates provide us with the opportunity to study the evolutionary history and function of human socio-cognitive skills within a comparative framework. I tested capuchin monkeys on three computerized tasks that evaluated their ability to discriminate the faces, sexual identities and dominance relationships of conspecifics living in their own social group, a neighboring social group or completely unfamiliar individuals. This paradigm allowed for testing the effect of familiarity and parsed underlying mechanisms of these socio-cognitive skills, both of which help to elucidate how social knowledge emerges from the foundations of perception

Performance on a Face Discrimination Task by Orangutans Reflects a Possible Interaction between Familiarity and Novelty

Faces provide humans with information on the age, sex, individual identity, and emotional state of others. Although comparatively less is known about nonhuman primates’ face processing abilities, several gregarious group living species are able to discriminate conspecific faces. Here, we tested a less gregarious species, orangutans, to determine if they exhibit similar skills. Using a matching-to-sample paradigm, orangutans matched two identical portraits of unfamiliar orangutans. Next, subjects matched two different photographs of the same individual across viewpoints. During testing, subjects successfully transferred to novel photographs of familiar, but not unfamiliar, individuals with their first exposure to these stimuli. However, performance was not maintained throughout continued exposure to these stimuli, suggesting a possible novelty effect. Interestingly, orangutans performed significantly above chance when individuating familiar males, but not females. Further examination is needed to understand social organization and other social factors which were important in the evolution of face-processing

Squirrel Monkeys’ Response to Inequitable Outcomes Indicates a Behavioural Convergence Within the Primates

Although several primates respond negatively to inequity, it is unknown whether this results from homology or convergent processes. Behaviours shared within a taxonomic group are often assumed to be homologous, yet this distinction is important for a better understanding of the function of the behaviour. Previous hypotheses have linked cooperation and inequity responses. Supporting this, all species in which inequity responses have been documented are cooperative. In this study, we tested this hypothesis by investigating the response to inequity in squirrel monkeys, which share a phylogenetic Family with capuchin monkeys, but do not cooperate extensively. Subjects exchanged tokens to receive food rewards in conditions in which the level of effort required and reward received varied. Squirrel monkeys did not respond negatively to inequity. However, the monkeys were sensitive to the variation present in the task; male subjects showed a contrast effect and, as in previous studies, subjects were more sensitive to differences in reward in the context of a task than when rewards were given for free. Taken with other results, these results support the hypothesis that a negative response to inequity evolved convergently in primates, probably as a mechanism for evaluating outcomes relative to one’s partners in cooperative species

Orangutans (Pongo pygmaeus) do not Form Expectations Based on Their Partner’s Outcomes

Several primate species form expectations based on other’s outcomes. These individuals respond negatively when their outcomes differ from their partners’. The function and evolutionary pathway of this behavior are unknown, in part because all of the species which have thus far shown the response have similar life history patterns. In particular, all share traits related to a gregarious lifestyle, intelligence, and cooperativeness. The goal of the current paper was to test whether inequity is a homology among primates or a convergence based on some other characteristic by comparing one species known to show social comparisons, the chimpanzee, to another great ape which differs on several of these life history characteristics. Using a protocol identical to one used previously with chimpanzees, we tested whether orangutans, an intelligent but predominantly solitary species with few opportunities to cooperate, responded similarly. To allow for a strong comparison with chimpanzees (and other species), we used socially housed adults of both sexes, tested with members of their social group. We find that orangutans do not respond negatively to inequity, supporting previous findings and indicating that inequity responses in apes are likely a convergence based on either sociality or cooperative tendency. These results in such closely related species highlight the need for additional comparative studies to better understand the function and evolution of social behaviors

Mechanisms Underlying the Response to Inequitable Outcomes in Chimpanzees, Pan Troglodytes

Several species of non-human primates respond negatively to inequitable outcomes, a trait shared with humans. Despite previous research, questions regarding the response to inequity remain. In this study, we replicated the methodology from previous studies to address four questions related to inequity. First, we explored the impact of basic social factors. Second, we addressed whether negative responses to inequity require a task, or exist when rewards are given for ‘free’. Third, we addressed whether differences in the experimental procedure or the level of effort required to obtain a reward affected responses. Finally, we explored the interaction between ‘individual’ expectations (based on one’s own previous experience) and ‘social’ expectations (based on the partner’s experience). These questions were investigated in 16 socially-housed adult chimpanzees using eight conditions that varied across the dimensions of reward, effort, and procedure. Subjects did respond to inequity, but only in the context of a task. Differences in procedure and level of effort required did not cause individuals to change their behavior. Males were more sensitive to social than to individual expectation, while females were more sensitive to individual expectation. Finally, subjects also increased refusals when receiving a better reward than their partner, which has not been seen previously. These results indicate that chimpanzees are more sensitive to reward inequity than procedures, and that there is interaction between social and individual expectations that depends upon social factors

Different Responses to Reward Comparisons by Three Primate Species

Background: Recently, much attention has been paid to the role of cooperative breeding in the evolution of behavior. In many measures, cooperative breeders are more prosocial than non-cooperatively breeding species, including being more likely to actively share food. This is hypothesized to be due to selective pressures specific to the interdependency characteristic of cooperatively breeding species. Given the high costs of finding a new mate, it has been proposed that cooperative breeders, unlike primates that cooperate in other contexts, should not respond negatively to unequal outcomes between themselves and their partner. However, in this context such pressures may extend beyond cooperative breeders to other species with pair-bonding and bi-parental care. Methods: Here we test the response of two New World primate species with different parental strategies to unequal outcomes in both individual and social contrast conditions. One species tested was a cooperative breeder (Callithrix spp.) and the second practiced bi-parental care (Aotus spp.). Additionally, to verify our procedure, we tested a third confamilial species that shows no such interdependence but does respond to individual (but not social) contrast (Saimiri spp.). We tested all three genera using an established inequity paradigm in which individuals in a pair took turns to gain rewards that sometimes differed from those of their partners. Conclusions: None of the three species tested responded negatively to inequitable outcomes in this experimental context. Importantly, the Saimiri spp responded to individual contrast, as in earlier studies, validating our procedure. When these data are considered in relation to previous studies investigating responses to inequity in primates, they indicate that one aspect of cooperative breeding, pair-bonding or bi-parental care, may influence the evolution of these behaviors. These results emphasize the need to study a variety of species to gain insight in to how decision-making may vary across social structures

Responses to the Assurance Game in Monkeys, Apes, and Humans Using Equivalent Procedures

There is great interest in the evolution of economic behavior. In typical studies, species are asked to play one of a series of economic games, derived from game theory, and their responses are compared. The advantage of this approach is the relative level of consistency and control that emerges from the games themselves; however, in the typical experiment, procedures and conditions differ widely, particularly between humans and other species. Thus, in the current study, we investigated how three primate species, capuchin monkeys, chimpanzees, and humans, played the Assurance (or Stag Hunt) game using procedures that were, to the best of our ability, the same across species, particularly with respect to training and pretesting. Our goal was to determine what, if any, differences existed in the ways in which these species made decisions in this game. We hypothesized differences along phylogenetic lines, which we found. However, the species were more similar than might be expected. In particular, humans who played using “nonhuman primate-friendly” rules did not behave as is typical. Thus, we find evidence for similarity in decision-making processes across the order Primates. These results indicate that such comparative studies are possible and, moreover, that in any comparison rating species’ relative abilities, extreme care must be taken in ensuring that one species does not have an advantage over the others due to methodological procedures

Comparative Economics: Responses to the Assurance Game in Monkeys, Apes, and Humans Using Equivalent Procedures

There is great interest in the evolution of economic behavior. In typical studies, species are asked to play one of a series of economic games, derived from game theory, and their responses are compared. The advantage of this approach is the relative level of consistency and control that emerges from the games themselves; however in the typical experiment, procedures and conditions differ widely, particularly between humans and other species. Thus, in the current study we investigated how three primate species, capuchin monkeys, chimpanzees, and humans, played the Assurance (or Stag Hunt) Game using procedures which were, to the best of our ability, the same across species, particularly with respect to training and pre-testing. Our goal was to determine what, if any, differences existed in the ways in which these species made decisions in this game. We hypothesized differences along phylogenetic lines, which we found. However, the species were more similar than might be expected. In particular, humans who played using ‘non-human primate-friendly’ rules did not behave as is typical. Thus, we find evidence for similarity in decision-making processes across the Order Primates. These results indicate that such comparative studies are possible and moreover that in any comparison rating species’ relative abilities, extreme care must be taken in ensuring that one species does not have an advantage over the others due to methodological procedures

Embedding open and reproducible science into teaching: A bank of lesson plans and resources

Recently, there has been a growing emphasis on embedding open and reproducible approaches into research. One essential step in accomplishing this larger goal is to embed such practices into undergraduate and postgraduate research training. However, this often requires substantial time and resources to implement. Also, while many pedagogical resources are regularly developed for this purpose, they are not often openly and actively shared with the wider community. The creation and public sharing of open educational resources is useful for educators who wish to embed open scholarship and reproducibility into their teaching and learning. In this article, we describe and openly share a bank of teaching resources and lesson plans on the broad topics of open scholarship, open science, replication, and reproducibility that can be integrated into taught courses, to support educators and instructors. These resources were created as part of the Society for the Improvement of Psychological Science (SIPS) hackathon at the 2021 Annual Conference, and we detail this collaborative process in the article. By sharing these open pedagogical resources, we aim to reduce the labour required to develop and implement open scholarship content to further the open scholarship and open educational materials movement