Kyoto, Japan -- In February 2023, a resident at Kyoto University's Center for the Evolutionary Origins of Human Behavior -- EHUB -- treated researchers to a spontaneous musical performance. Ayumu, a 26 year-old male chimpanzee, removed floorboards from a walkway and used them to drum while he let out complex and structured sounds similar to vocal expressions. It was something the researchers had never seen him do before.
Ayumu's drumming is nothing new. Chimpanzees are well know for their instrumental behaviors, and are particularly adept at drumming. But on this occasion, Ayumu's combination of drumming and vocalization -- exhibiting multiple rhythmic components -- was a completely novel case.
After recording 89 of Ayumu's spontaneous performances between February 2023 and March 2025, a team of EHUB researchers started analyzing the videos. The recordings also provided proof of the process by which Ayumu removed floorboards from the walkway and used them as tools to make music.
"It was fascinating for me to see how the chimpanzee used tools to produce various sounds while also expressing a vocal display," says first author Yuko Hattori.
Past research has suggested that music, particularly instrumental performance, may have evolved as a result of the externalization of emotional expression through vocalization combined with the use of tools. However, ancient percussion instruments were usually made from perishable materials such as wood and animal skins, making it difficult to trace them directly through archaeological evidence. Observing musical behavior in our primate cousins provides a key to understanding the evolution of musicality.
Using Ayumu's performances, the research team examined the possibility that vocal expression could transition into instrumental sound. They began by assessing his behavior and breaking it down into elements such as striking, dragging, and throwing. Then they evaluated the connections between these elements using transition analysis, determining which transitions occurred by chance, and which were deliberate. Finally the team analyzed the intervals between strikes, and compared the rhythmic stability of tool use with the rhythm of drumming performed using the hands or feet.
Their analysis revealed that the sequence of sounds produced by the instruments was not random, and that the intervals between strikes were isochronous, or maintaining a constant tempo, like a metronome. In fact, using tools for striking produced a more stable rhythm than just the hands or feet alone. The team also observed facial expressions such as play face, expressed during play, indicating positive emotions. These expressions are not typically reported in vocal displays, suggesting that emotional expressions previously conveyed vocally may have been externalized and developed into tool sounds.
Ayumu's performances prove that non-human primates also possess the ability to externalize vocal-like expressions with instruments. Next, the team is interested in analyzing the reactions of the other chimpanzees at EHUB, and the impact Ayumu's display has within his social group.
