Abstract
This study explores contagious yawning in adult chimpanzees (Pan troglodytes) in the presence of a non-biological humanoid agent, an android. Chimpanzees observed an android portraying specific facial expressions, including yawns and gapes. The results showed that adult chimpanzees exhibited across-agent yawn contagion, with a graded response: the highest contagion occurred when the android displayed a fully wide-open mouth (Yawn condition), a reduced response when the mouth was partially opened (Gape condition), and no contagion when the android's mouth was closed (Close condition). Additionally, chimpanzees engaged in behaviours associated with drowsiness, such as gathering bedding materials, constructing nests, and lying down, while observing the android yawning. This suggests that yawning by an unfamiliar model may act as a contextual cue for rest, rather than merely triggering a motor resonance response. These findings contribute to the understanding of non-human primates' susceptibility to contagiously induced behaviours, specifically yawns, even when triggered by an artificial agent. This study highlights the role of social factors in shaping yawn contagion and calls for further research on cross-species and cross-agent interactions.