Rhythmic swaying induced by sound in chimpanzees (Pan troglodytes)

Yuko Hattori, Masaki Tomonaga

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Rhythmic movement in chimpanzees

A study explores how sound induces rhythmic movement in chimpanzees. Music influences rhythmic movement in humans, suggesting a link between the brain's auditory and motor areas. Understanding chimpanzees' predisposition to music could shed light on the evolutionary origins of humans' response to music. Yuko Hattori and Masaki Tomonaga examined how music affects rhythmic movement, or repetitive movement of the entire body or body parts, in 7 chimpanzees that listened to 6 2-minute piano sounds with different tempos for 6 days. In response to an auditory stimulus, the chimpanzees often swayed and sometimes executed rhythmic hand-clapping and foot-tapping movements. Compared with female chimpanzees, male chimpanzees were more likely to respond to sound with vocalization and sway rhythmically for longer durations. A separate experiment focused on the chimpanzee most responsive to the auditory stimuli. The chimpanzee was exposed to 4 2-minute sound sessions for 24 days. Both random and regular beats induced rhythmic swaying in the chimpanzee, and beat tempo affected the chimpanzee in a bipedal posture but not a quadrupedal posture. The chimpanzee also stayed longer in a sound source area when there was an auditory stimulus compared with when the area had no sound, suggesting that the chimpanzee sought auditory stimulation. The findings suggest a foundation for dancing in a common ancestor of chimpanzees and humans, according to the authors.

Abstract

Music and dance are universal across human culture and have an ancient history. One characteristic of music is its strong influence on movement. For example, an auditory beat induces rhythmic movement with positive emotions in humans from early developmental stages. In this study, we investigated if sound induced spontaneous rhythmic movement in chimpanzees. Three experiments showed that: 1) an auditory beat induced rhythmic swaying and other rhythmic movements, with larger responses from male chimpanzees than female chimpanzees; 2) random beat as well as regular beat induced rhythmic swaying and beat tempo affected movement periodicity in a chimpanzee in a bipedal posture; and 3) a chimpanzee showed close proximity to the sound source while hearing auditory stimuli. The finding that male chimpanzees showed a larger response to sound than female chimpanzees was consistent with previous literature about “rain dances" in the wild, where male chimpanzees engage in rhythmic displays when hearing the sound of rain starting. The fact that rhythmic swaying was induced regardless of beat regularity may be a critical difference from humans, and a further study should reveal the physiological properties of sound that induce rhythmic movements in chimpanzees. These results suggest some biological foundation for dancing existed in the common ancestor of humans and chimpanzees ∼6 million years ago. As such, this study supports the evolutionary origins of musicality.

Hattori Y, Tomonaga M (2019) Rhythmic swaying induced by sound in chimpanzees (Pan troglodytes) Proceedings of the National Academy of Sciences 201910318 , doi: 10.1073/pnas.1910318116