WARWICK — A new study published in Communications Biology indicates that the isochronous nature of laughter was present in the last common ancestor of great apes and humans at least 15 million years ago. The analysis found that the isochronous nature of laughter, characterized by clear sound intervals, was likely present in the last common ancestor of the Hominid family.

The study analyzed recordings of laughter from four orangutans, two gorillas, three bonobos, four chimpanzees, and four human children. These recordings were made during playtime, roughhousing, and tickling. The Hominid family includes all great apes and extinct relatives such as Neanderthals.

Chiara De Gregorio, a primatologist at the University of Warwick, stated that one vocalization has been conserved across species and age-sex classes, despite ancestral branches of the Hominid family evolving distinct call repertoires. De Gregorio said, "While all ancestral branches of the Hominid family have evolved distinct call repertoires shaped by their species-specific socio-ecologies, one vocalization has been conserved across species and age-sex classes: laughter."

The study concluded that great apes have been laughing in a way recognizable to modern humans for at least 15 million years. De Gregorio stated, "In a way, we are very similar to other great apes because we’ve been laughing in a similar way for 15 million years."

Apes more closely related to humans exhibit more complex and variable laughs than those less closely related to humans. Compared with apes, human laughter has become faster and more complex. Human laughter also varies based on context, ranging from polite chuckles to full-bodied guffaws.