Humans and great apes show similar rhythmic pattern in laughter

Humans and Great Apes Show Similar Rhythmic Pattern in Laughter

Laughter, often viewed as a uniquely human expression, is shared by all living great apes. New research indicates that humans, chimpanzees, bonobos, gorillas, and orangutans all utilize the same underlying rhythmic structure when laughing, suggesting the behavior originated in a common ancestor roughly 15 million years ago in East or Central Africa.

The study, published in the journal Communications Biology, used acoustic analysis to examine 140 sequences of laughter. Researchers recorded sounds from four chimpanzees, three bonobos, two gorillas, four orangutans, and four humans. The recordings of apes were captured in their home environments in zoos located in Malaysia and Germany while the animals were engaged in play or were being gently tickled by familiar human caretakers.

Across all species, laughter adhered to a regular rhythmic pattern characterized by evenly spaced intervals between successive sounds. According to the researchers, this suggests the basic rhythmic machinery for vocalization was established millions of years ago and has remained remarkably conserved.

Despite these shared roots, human laughter has diverged in key ways. Researchers found that human laughter is faster, more variable, and more sensitive to social context than that of other great apes. While chimpanzees and bonobos show laughter more similar to humans than gorillas or orangutans do, human laughter is distinguished by its degree of flexibility and rhythmic complexity.

A primary difference is the ability to modify the temporal structure of laughter based on the situation. While great apes typically laugh as an involuntary response to physical stimulation, humans can consciously control their laughter to communicate nuanced intentions—such as a nervous giggle after a mistake or a polite laugh during a meeting. Researchers found little evidence that great apes alter their rhythmic structure across different situations in the same way.

"Human laughter shares the same basic evolutionary roots as great ape laughter, but it differs in important ways,"

Chiara De Gregorio, primatologist and research fellow at the University of Warwick, via Reuters

These findings provide a "vocal fossil" to help scientists understand the origins of human speech, which leaves no physical record. The study challenges the theory that early humans experienced a sudden genetic mutation that granted them advanced vocal control. Instead, the data suggests a gradual prolongation of skills that primate ancestors had been honing for 15 million years.

According to De Gregorio, the evolutionary increase in rhythmic flexibility indicates that human ancestors may have possessed more sophisticated vocal control than modern apes, serving as a stepping stone toward language. Laughter is thought to have evolved as a social signal to maintain positive interactions and strengthen bonds, specifically communicating that rough-and-tumble play is friendly rather than aggressive.

"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,"

Adriano Lameria, Associate Professor at the University of Warwick, via PopSci

The research also noted that other mammals exhibit similar behaviors. Dogs, for instance, use a "play face" and a specific play panting vocalization to indicate non-aggressive intentions during social play.

While the fundamental rhythm of laughter is now clearer, De Gregorio noted that researchers still do not know exactly how early ancestors communicated. Future research may explore whether great apes possess subtler forms of rhythmic variation across different contexts.