Although the connection might seem unexpected, looking deeper into the intricacies of laughter offers a rare glimpse at the origins of speech itself.
Laughter in great apes and humans is inherently repetitive and cyclic – the well-known ha-ha-ha-ha. By studying the subtle variations in how that rhythm is timed and structured across different species, scientists can learn how breathing, sound-making and vocal control – all important building blocks of speech – have evolved over time.
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All major branches of the Hominidae family have evolved unique ways of communicating through sound, shaped by their specific needs and circumstances. The one remaining connection is laughter – we share it with all great apes (chimpanzees, bonobos, gorillas, orangutans). But until now, little was known about its defining feature: rhythm.
In a new study published in the journal Communications Biology, researchers analysed recordings of spontaneous laughter from four orangutans, two gorillas, three bonobos, four chimpanzees and four humans. Across 140 laughter sequences, they found all species’ laughter follows the same general pattern: evenly-spaced rhythmic intervals between successive sounds.
“How did humans evolve the remarkable ability to speak? Speech leaves no fossils, and complex language exists only in our own species. But we've found a 15-million-year-old clue in an unexpected place: our laughter,” says Chiara De Gregorio, an honorary research associate at the University of Warwick.
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“Unlike speech, laughter is shared by all living great apes. By comparing how different species laugh, we can see that a basic rhythmic structure has remained unchanged since our last common ancestor. That's extraordinary.”
This basic underlying rhythm is where human laughter diverges. At some point, our laughter evolved into something faster and more variable, and more crucially – we gained the ability to control when and how it occurs.
A nervous chuckle, a quiet giggle, a snicker, a full-belly cackle – we use these various ways of laughing in different social situations to communicate emotions and intentions. Out of all great apes, humans alone possess that amount of control over their laughter.
The last common ancestor of all living great apes, including humans, is estimated to have existed approximately 15 million years ago. According to the researchers’ theory, this newly discovered rhythmic structure within laughter was already present in that common ancestor – and has remained remarkably well conserved until today.
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“It is impossible to assess the precursor forms of language directly from our extinct ancestors. Laughter, being evolutionarily older and having remained shared between all living great apes, provides a rare evolutionary window into the vocal transformations that unfolded across hominid evolution until the first humans appeared on scene,” explains Adriano Lameira at the University of Warwick.
“Contrary to the classic notion that the first humans suddenly acquired vocal control capacities remarkably different from their predecessors, laughter evolution tells us that humans lay on a continuum, a prolongation of vocal control capacities that were already being cumulatively honed in for 15 million years.”
Top image credit: Lukas Klinge/Getty Images
