Tool Use in Pan: Two Modalities, Two Species

A notable difference between the two Pan species is their tool using ability. Though many studies on physical tool use exist, few investigate social tool use and, to my knowledge, none focus on their potential relationship or cognitive foundations.While captive and wild chimpanzees are recognized as proficient tool users, captive bonobos exhibit some tool using skills but evidence in wild bonobos is rare. An important similarity, however, is their flexible and intentional use of communicative signals. Captive bonobos and chimpanzees are known to use their communicative behaviors to manipulate humans to obtain an unreachable food, a form of social tool use. With growing interest in social tool use, an emerging central question is to what extent different species utilize these two tool strategies. Thus, 27 bonobos and 29 chimpanzees were given a physical tool task requiring retrieval of a reward at increasing distances such that the physical tool no longer solved the problem while a human who could be solicited was present. Although both species successfully retrieved rewards with the physical tool and solicited the human, chimpanzees showed greater proficiency and flexibility by making fewer attempts to retrieve rewards, retrieving rewards faster, and making more solicitations. For both species, solicitation behavior was prevalent at further distances where the reward was unable to be retrieved, supporting previous research showing these species intentionally produce attention-getting/directing behaviors to indicate toward desired out-of-reach items. In this study, bonobos and chimpanzees exhibited cognitive flexibility by switching tool strategies from using a physical tool at closer distances to using a social tool (a human) at further distances. Regardless of species, physical and social tool performance was related to performance on previous physical and social cognition tasks, including the Primate Cognition Test Battery. The results of this study support the idea that physical and social cognition may not be two separate cognitive domains, as they are so often treated. Rather, cognition may be a single entity in which certain behaviors and processes are elicited by physical and/or social contexts, allowing the transition between physical and social tool modalities

Handedness for Unimanual Grasping in 564 Great Apes: The Effect on Grip Morphology and a Comparison with Hand Use for a Bimanual Coordinated Task

A number of factors have been proposed to influence within and between species variation in handedness in non-human primates. In the initial study, we assessed the influence of grip morphology on hand use for simple reaching in a sample of 564 great apes including 49 orangutans Pongo pygmaeus, 66 gorillas Gorilla gorilla, 354 chimpanzees Pan troglodytes and 95 bonobos Pan paniscus. Overall, we found a significant right hand bias for reaching. We also found a significant effect of the grip morphology of hand use. Grasping with the thumb and index finger was more prevalent in the right compared to left hand in all four species. There was no significant sex effect on the patterns of handedness. In a subsample of apes, we also compared consistency in hand use for simple reaching with previously published data on a task that measures handedness for bimanual actions. We found that the ratio of subjects with consistent right compared to left hand use was more prevalent in bonobos, chimpanzees and gorillas but not orangutans. However, for all species, the proportion of subjects with inconsistent hand preferences between the tasks was relatively high suggesting some measures may be more sensitive in assessing handedness than others

Mirror self-recognition and its relationship to social cognition in chimpanzees

Chimpanzees and humans are capable of recognizing their own reflection in mirrors. Little is understood about the selective pressures that led to this evolved trait and about the mechanisms that underlie it. Here, we investigated the hypothesis that mirror self-recognition in chimpanzees is the byproduct of a developed form of self-awareness that was naturally selected for its adaptive use in social cognitive behaviors. We present here the first direct attempt to assess the social cognition hypothesis by analyzing the association between mirror self-recognition in chimpanzees, as measured by a mirror-mark test, and their performance on a variety of social cognition tests. Consistent with the social cognition hypothesis, chimpanzees who showed evidence of mirror self-recognition in the mark test tended to perform significantly better on the social cognition tasks than those who failed the mark test. Additionally, the data as a whole fit the social cognition hypothesis better than the main competing hypothesis of mirror self-recognition in great apes, the secondary representation hypothesis. Our findings strongly suggest that the evolutionary origins of great apes’ and humans’ capacity to understand ourselves, as revealed by our capacity to recognize ourselves in mirrors, are intimately linked to our ability to understand others

Differences in the mutual eye gaze of bonobos (Pan paniscus) and chimpanzees (Pan troglodytes)

Eye gaze is widespread in nonhuman primate taxa and important for social cognition and communicative signaling. Bonobos and chimpanzees, two closely related primate species, differ in social organization, behavior, and cognition. Chimpanzees\u27 eye gaze and gaze following has been studied extensively, whereas less is known about bonobos\u27 eye gaze. To examine species differences using a more ecologically relevant measure than videos or pictures, the current study compared bonobo and chimpanzee mutual eye gaze with a human observer. A multivariate analysis of variance revealed significant species differences in frequency and total duration, but not bout length, of mutual eye gaze (p \u3c.001). Specifically, bonobos engage in mutual eye gaze more frequently and for longer total duration than chimpanzees. These results are likely related to species differences in social behavior and temperament and are consistent with eye-tracking studies in which bonobos looked at the eye region of conspecifics (in pictures and videos) longer than chimpanzees. Future research should examine the relationship between mutual eye gaze and gaze following, as well as examine its genetic and neurological correlates