Probably few people have ever wondered what it’s like to tickle a monkey. It turns out they absolutely love it and, just like us, go wild with laughter. However, tickling isn’t just about fun—it’s also serious science. For instance, researchers recently discovered something interesting about the evolution of human language, and they did it by tickling some of our closest relatives. The findings were published in the journal Communications Biology.
After analyzing the laughter of four orangutans, three bonobos, two gorillas, and four chimpanzees, the study authors found that great apes laugh with an isochronous rhythm—meaning their vocal bursts are evenly spaced out.
This same trait appears in human laughter, suggesting that this characteristic must have originated in the last common ancestor of humans and great apes, which lived around 15 million years ago.
“Before this study, I likely expected more irregularity in the laughter of our more distant relatives,” explains study author Chiara De Gregorio. “On the contrary, the rhythmic regularity of laughter seems to have been surprisingly well-preserved among great apes. This indicates we’ve been laughing this way for about 15 million years!”
However, unlike apes, humans show an ability to adjust the speed of their laughter depending on the social context.
For example, we tend to laugh faster when tickled than during play, while chimpanzees, bonobos, orangutans, and gorillas maintain roughly the same level of laughter across all situations.
“In great apes, laughter likely originated as a relatively stereotyped rhythmic signal used mainly in a limited set of social contexts, such as play or tickling,” says De Gregorio. “But in humans, laughter has become remarkably diverse. We can produce everything from a quiet, polite chuckle to a loud, unrestrained laugh, or even ironic or ‘fake’ laughter when we want to express something other than genuine amusement.”
Thus, the study authors suggest that the rhythmic flexibility of our giggling might serve as an indicator of overall vocal control, revealing how we developed the ability to modulate our sound signals in complex ways. This skill was probably fundamental to the emergence of speech and language.
“Of course, laughter isn’t language, but both rely on the ability to control and modulate vocal output,” says De Gregorio. “In this sense, the evolution of laughter may have gone hand in hand with the evolution of vocal abilities that ultimately laid the foundation for speech and language.”
Overall, the researchers found that the capacity to regulate laughter exists as a continuum and is most pronounced in apes that are closest to humans. This suggests that vocal control may have gradually developed over the last 15 million years, giving us a way to speculate about how Neanderthals and other extinct hominins might have laughed.
“While we can never know exactly what the laughter of extinct hominins sounded like, our data suggest they likely produced rhythmically regular sounds,” says De Gregorio. “I imagine their laughter was intermediate between that of modern humans and that of chimpanzees and bonobos: probably more variable and flexible than chimpanzees’ laughter, but less variable than that of modern humans.”
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