Great apes may have been laughing with a similar rhythm to modern humans for at least 15 million years, a University of Warwick study reveals. The finding offers unexpected clues to how human speech evolved.
All living great apes - chimpanzees, bonobos, gorillas, and orangutans - laugh. But until now, it has been unclear how our laughter may have changed over millions of years of evolution, and how it might relate to the evolution of speech in humans.
In a new Communications Biology study, Warwick researchers analysed laughter recordings from four orangutans, two gorillas, three bonobos, four chimpanzees, and four humans. Across 140 laughter sequences, they found the same pattern: all species produce laughter with evenly spaced rhythmic intervals between successive sounds.
The researchers propose this basic rhythmic structure was already present in a shared common ancestor 15 million years ago and has remained remarkably conserved with all living great apes still show the same underlying pattern.
Dr Chiara De Gregorio, Honorary Research Associate, Department of Psychology, University of Warwick said: "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. 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."
The researchers found that while the basic rhythm stayed constant, human laughter has become faster, more variable, and gained sophisticated context-dependent control. Of the great apes, humans alone have the ability to control when and how they laugh depending on context: an uncontrollable laugh when tickled differs sharply from a polite laugh in a meeting, a nervous laugh after a mistake, or the infectious laughter that spreads through a group of friends. The same underlying rhythm, shaped by conscious control to communicate different emotions and intentions.
The findings of this study suggest that throughout great ape evolution, our ancestors gradually developed greater control over the timing of their vocalisations, including laughter. Sophisticated vocal control is a fundamental building block of speech.
Dr Adriano Lameria, Associate Professor, ApeTank, Department of Psychology, University of Warwick said: "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. 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."
