One day in 2014, primatologist Yuko Hattori was trying to teach a mother chimpanzee in her lab to keep a beat. Hattori would play a repetitive piano note, and the chimp would attempt to tap out the rhythm on a small electronic keyboard in hopes of receiving a tasty piece of apple.
Everything went as expected in the experiment room, but in the next room over, something strange was happening. Another chimpanzee, the mother’s son, heard the beat and began to sway his body back and forth, almost as if he were dancing. “I was shocked,” Hattori says. “I was not aware that without any training or reward, a chimpanzee would spontaneously engage with the sound.”
Hattori has now published her research showing that chimps respond to sounds, both rhythmic and random, by “dancing.”
“This study is very thought-provoking,” says Andrea Ravignani, a cognitive biologist at the Seal Rehabilitation and Research Centre who researches the evolution of rhythm, speech, and music. The work, she says, could shed light on the evolution of dancing in humans.
For their the study, Hattori and her colleague Masaki Tomonaga at Kyoto University played 2-minute clips of evenly spaced, repetitive piano tones (heard in the video above) to seven chimpanzees (three males and four females). On hearing the sound, the chimps started to groove, swaying back and forth and sometimes tapping their fingers or their feet to the beat or making howling “singing” sounds, the researchers report today in the Proceedings of the National Academy of Sciences. All of the chimps showed at least a little bit of rhythmic movement, though the males spent much more time moving to the music than females.
To find out whether the animals were dancing to a specific beat—or whether any series of sounds would move them—Hattori singled out one chimp, Akira, who was an enthusiastic dancer on past trials. She and her colleagues tested Akira over a period of 24 days to see whether he would sway in response to random sounds as well as rhythmic beats. Unlike humans, Akira danced just as much on average when he heard a random sequence of sounds than when the sounds were lined up in a measured tempo, the team found. (Experiments testing for rhythmic responses in human babies show that people are much more likely to move in response to a sound when it’s rhythmic, like music, instead of random, like speech.)
The lab chimps’ lack of discrimination lines up with chimpanzees’ behavior in the wild, Hattori says. The animals are known to perform “rain dances,” swaying and strutting when they hear the random sound of raindrops falling in the forest. Movements in response to random natural sounds may be “the beginning of the evolution of dance,” Hattori says, with humans later narrowing the behavior to rhythmic sounds.
The matching of sound and movement, Ravignani says, was likely the most important event in the development of dance. “One of the key differences between us and our closest living relatives might be that somewhere our evolutionary history, these two things got connected,” he says.
Chimps and other animals likely began to make rhythmic sounds as a coping mechanism for loud and overwhelming stimuli in nature, Hattori speculates. Somewhere along the line, human ancestors probably developed an awareness of rhythms, and then began to match their body movements to the beat.
Other animals such as Snowball the cockatoo and some California sea lions have been observed bobbing their heads in time to music or beats. What makes the chimps different, Hattori says, is the fact that they do it spontaneously, with no reward offered—and that they’ve been seen “dancing” in nature.
“The study raises the idea that great apes are perhaps better living models for human ancestors than they have been acknowledged for,” says Adriano Lameira, a primatologist and evolutionary psychologist at the University of Warwick. (Lameira himself has shown that chimpanzees have dance moves: He recently analyzed zoo chimps caught on camera in the midst of a “conga line,” although no music was playing in that case.)
But Lameira says the new study might not add much to the current understanding of the evolution of dance for a number of reasons. For instance, previous studies had already shown primates showing rhythmic displays, so although the new works reveals that the creatures dance in response to a few different kinds of sounds, the behavior itself is not entirely novel.
Lameira also notes the researchers use a loose definition of “rhythmic.” For the chimps in the study to exhibit a “rhythmic” behavior, they simply had to do the same action three times. Instead, he says, rhythm should be defined as “a behavior that obeys a precise, strict tempo.”