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' eye gaze and gaze following has been studied extensively, whereas less is known about bonobos' eye gaze.

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.

Investigating individual differences in chimpanzee mirror self-recognition and cortical thickness: A vertex-based and region-of-interest analysis.

Mirror self-recognition (MSR), a recently evolved cognitive trait, is one of the most significant abilities that separate humans and great apes from more distantly related nonhuman primates. MSR may serve as the foundation for a number of related but more complex social cognitive abilities unique to humans and great apes including imitation, empathy, theory-of-mind, perspective taking and deception. However, our understanding of the neural basis of MSR in nonhuman primates remains largely unknown.

Chimpanzees gesture to humans in mirrors: using reflection to dissociate seeing from line of gaze.

There is much experimental evidence suggesting that chimpanzees understand that others see. However, previous research has never experimentally ruled out the alternative explanation that chimpanzees are just responding to the geometric cue of 'direct line of gaze', the observable correlate of seeing in others. Here, we sought to resolve this ambiguity by dissociating seeing from direct line of gaze using a mirror.

Genetic Factors and Orofacial Motor Learning Selectively Influence Variability in Central Sulcus Morphology in Chimpanzees ().

Captive chimpanzees () have been shown to learn the use of novel attention-getting (AG) sounds to capture the attention of humans as a means of requesting or drawing their attention to a desired object or food. There are significant individual differences in the use of AG sounds by chimpanzees and, here, we examined whether changes in cortical organization of the central sulcus (CS) were associated with AG sound production. MRI scans were collected from 240 chimpanzees, including 122 that reliably produced AG sounds and 118 that did not.

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.

Age-related motor dysfunction: Manual slowing in Gorilla gorilla gorilla.

Aging in humans and rhesus monkeys is commonly associated with motor function decrements including dexterity, speed, and strength. Despite their longevity and phylogenetic relatedness to humans, the effects of aging on motor function in non-human apes have been minimally studied. We conducted two experiments with western lowland gorillas (11-54 years of age) to determine whether aged gorillas exhibit motor deficits similar to those seen in other species.