他者の痛みに対するチンパンジー・ボノボの生理反応

抄録

Previous studies have shown that humans experience negative emotions (i.e., empathic pain) when observing pain in others. We investigated psycho-physiological reactions to others’ injury and pain in two species of great apes: six chimpanzees (Pan troglodytes) and six bonobos (Pan paniscus). Specifically, we used infrared thermal imaging to measure their nasal skin temperature when they were viewing a real-life theatrical demonstration by a human experimenter. Previous studies suggest that reduced nasal skin temperature is a characteristic of arousal, particularly arousal associated with negative valence. First, we presented apes with a realistic injury: a familiar human experimenter with a prosthetic wound and artificial running blood. Chimpanzees, especially adult females, exhibited a greater nasal temperature reduction in response to injury compared with the control stimulus, whereas such a clear difference was not observed in bonobos. Second, apes were presented with a familiar experimenter who stabbed their (fake) thumb with a needle, with no running blood, a situation that may be more challenging in terms of understanding the cause of pain. Apes did not physiologically distinguish this condition from the control condition. Lastly, apes were presented with a human experimenter who hurt themselves accidentally and expressed pain explicitly by behavioral cues. Again, apes did not physiologically distinguish this condition from the control condition. These results suggest that apes can infer the cause of pain from contextual cues, but have difficulty in understanding unfamiliar situations.