Lifespan Development of Gaze Following in Wild Chimpanzees

The ability to follow another's gaze direction is a foundational skill in human cognition that underpins more complex social abilities. Other primate species also exhibit a variety of gaze-following behaviors, but previous experimental work has focused only on captive populations. Studies of cognition in wild animals are crucial to understanding the biological context of different psychological processes, as well as to characterize developmental change in cognition in animals interacting in natural social groups. We therefore conducted field experiments with wild chimpanzees (Pan troglodytes schweinfurthii) ranging from infancy to old age in Kibale National Park, Uganda. Chimpanzees observed a human demonstrator who either looked up on test trials or down on control trials across up to four trials presented on different days. We found that wild chimpanzees reliably followed the actor's gaze, looking up more often during test trials where she looked up compared to control trials where she looked down. We further characterized the development of this skill and found that whereas juveniles and younger adults consistently followed the demonstrator's gaze, infants and older adults did not. Our findings show that even chimpanzees without a history of social interactions with humans will reliably follow gaze, providing the first evidence that wild primates show such co-orienting responses. This work further provides support for the hypothesis that chimpanzees show distinct developmental trajectories for gaze-following compared to humans, even in wild social contexts. SUMMARY: Gaze-following is a foundational social cognitive skill shared with several other primate species, but all studies to date have been conducted with captive populations. We conducted the first test of gaze-following through field experiments on wild chimpanzees. We found that wild chimpanzees, who do not have a history of social interactions with humans, follow a human demonstrator's gaze even in the absence of prior experience. Robust gaze-following did not emerge until the juvenile period, providing support for the hypothesis that chimpanzees show developmental patterns of co-orienting that are distinct from human trajectories.