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Social risk is a domain of risk in which the costs, benefits, and uncertainty of an action depend on the behavior of another individual. Humans overvalue the costs of a socially risky decision when compared with that of purely economic risk. Here, we played a trust game with 8 female captive chimpanzees ( Pan troglodytes) to determine whether this bias exists in one of our closest living relatives. A correlation between an individual's social- and nonsocial-risk attitudes indicated stable individual variation, yet the chimpanzees were more averse to social than nonsocial risk. This indicates differences between social and economic decision making and emotional factors in social risk taking. In another experiment using the same paradigm, subjects played with several partners with whom they had varying relationships. Preexisting relationships did not impact the subjects' choices. Instead, the apes used a tit-for-tat strategy and were influenced by the outcome of early interactions with a partner.

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Tufted or brown capuchin monkeys (Sapajus apella) have been shown to recognize conspecific faces as well as categorize them according to group membership. Little is known, though, about their capacity to differentiate between emotionally charged facial expressions or whether facial expressions are processed as a collection of features or configurally (i.e., as a whole). In 3 experiments, we examined whether tufted capuchins (a) differentiate photographs of neutral faces from either affiliative or agonistic expressions, (b) use relevant facial features to make such choices or view the expression as a whole, and (c) demonstrate an inversion effect for facial expressions suggestive of configural processing. Using an oddity paradigm presented on a computer touchscreen, we collected data from 9 adult and subadult monkeys. Subjects discriminated between emotional and neutral expressions with an exceptionally high success rate, including differentiating open-mouth threats from neutral expressions even when the latter contained varying degrees of visible teeth and mouth opening. They also showed an inversion effect for facial expressions, results that may indicate that quickly recognizing expressions does not originate solely from feature-based processing but likely a combination of relational processes. (PsycINFO Database Record

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Oxytocin has been suggested as a treatment to promote positive social interactions in people with Autism Spectrum Disorders (ASD). However, it is difficult to test this effect outside of the laboratory in realistic social situations. One way to resolve this issue is to study behavioral changes in closely related species with complex social relationships, such as chimpanzees. Here, we use captive, socially housed chimpanzees to evaluate the effects of oxytocin in a socially complex environment. After administering intranasal oxytocin or a placebo to an individual chimpanzee (total n = 8), she was returned to her social group. An experimenter blind to the condition measured the subject's social behavior. We failed to find a behavioral difference between conditions. As one of the goals for oxytocin administration as a treatment for ASD is increasing prosocial behaviors during 'real world' encounters, it is problematic that we failed to detect behavioral changes in our closest living relatives. However, our null findings may be related to methodological challenges such as determining an effective dose of oxytocin for chimpanzees and how long oxytocin takes to cross the blood-brain barrier. Thus, more research on intranasal oxytocin dosing and uptake are needed to continue exploring whether oxytocin changes social behavior in naturalistic settings and as a treatment for ASD.

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As a result of environmental variability, animals may be confronted with uncertainty surrounding the presence of, or accessibility to, food resources at a given location or time. While individuals can rely on personal experience to manage this variability, the behavior of members of an individual's social group can also provide information regarding the availability or location of a food resource. The purpose of the present study was to measure how captive chimpanzees individually and collectively adjust their foraging strategies at an artificial termite mound, as the availability of resources provided by the mound varied over a number of weeks. As predicted, fishing activity at the mound was related to resource availability. However, chimpanzees continued to fish at unbaited locations on the days and weeks after a location had last contained food. Consistent with previous studies, our findings show that chimpanzees do not completely abandon previously learned habits despite learning individually and/or socially that the habit is no longer effective.

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Whether or not nonhuman primates exhibit population-level handedness remains a topic of considerable scientific debate. Here, we examined handedness for coordinated bimanual actions in a sample of 777 great apes including chimpanzees, bonobos, gorillas, and orangutans. We found population-level right-handedness in chimpanzees, bonobos and gorillas, but left-handedness in orangutans. Directional biases in handedness were consistent across independent samples of apes within each genus. We suggest that, contrary to previous claims, population-level handedness is evident in great apes but differs among species as a result of ecological adaptations associated with posture and locomotion. We further suggest that historical views of nonhuman primate handedness have been too anthropocentric, and we advocate for a larger evolutionary framework for the consideration of handedness and other aspects of hemispheric specialization among primates.

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Predominance of right-handedness has historically been considered as a hallmark of human evolution. Whether nonhuman primates exhibit population-level manual bias remains a controversial topic. Here, we investigated the hypothesis that bimanual coordinated activities may be a key-behavior in our ancestors for the emergence and evolution of human population-level right-handedness. To this end, we collected data on hand preferences in 35 captive gorillas (Gorilla gorilla) during simple unimanual reaching and for bimanual coordinated feeding. Unimanual reaching consisted of grasping food on the ground, while bimanual feeding consisted of using one hand for holding a food and processing the food item by the opposite hand. No population-level manual bias was found for unimanual actions but, in contrast, gorillas exhibited a significant population-level right-handedness for the bimanual actions. Moreover, the degree of right-handedness for bimanual feeding exceeds any other known reports of hand use in primates, suggesting that lateralization for bimanual feeding is robust in captive gorillas. The collective evidence is discussed in the context of potential continuity of handedness between human and nonhuman primates.

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