Gibbons exploit information about what a competitor can see
How much nonhuman animals understand about seeing has been the focus of comparative cognition research for decades. Many social primates (and other species) are sensitive to cues about what others can and cannot see. Whether this sensitivity evolved in primates through shared descent or convergent evolution remains unclear. The current study tested gibbons—the apes that are least studied yet most distantly related to humans and one of the less social primates—in two food-competition tasks. Specifically, we presented eastern hoolock gibbons, Hoolock leuconedys, and silvery gibbons, Hylobates moloch, with a choice between a contested piece of food visible to both themselves and a human competitor and an uncontested piece visible only to themselves. Subjects successfully stole the uncontested food when the competitor turned away his body (N = 10, experiment 1) and his head (N = 9, experiment 2). However, when the head of the experimenter was oriented towards the contested piece of food, whether the competitor opened or closed his eyes made no difference. Subjects’ sensitivity to body- and head-orientation cues was comparable to that of chimpanzees, rhesus macaques, and ring-tailed lemurs—species living in much larger groups than gibbons. These findings support the continuity hypothesis that sensitivity to body- and head-orientation cues is a product of shared descent among primates.
KeywordsGibbon Hylobatidae Social cognition Perspective taking Social intelligence hypothesis Attention
We are grateful to Gabriella Skollar, Alma Rodriguez, Jodi Kleier, and other staff at GCC for hosting the current research and for their tremendous support. We want to thank Barbara Perez, Ergin Ozyazgan, Robert Ball, Emma Parker, Yuwei Zhang, and Catherine Hallsten for assistance with data collection. We thank Amelia Harrison for reliability coding.
The project was supported by a UCSD Academic Senate grant RG073623.
Compliance with ethical standards
Conflict of interest
The authors declare no conflict of interests.
The current research has been approved by the IACUC committee of the Gibbon Conservation Center (GCC) and complied with the rules of the IACUC office at University of California, San Diego.
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