Humans share a fundamental rhythmic pattern in their laughter with great apes, a finding that suggests this vocalization has remained largely unchanged for at least 15 million years. The study, published in the journal Communications Biology, analyzed laughter recordings from orangutans, gorillas, bonobos, chimpanzees, and humans.
Researchers found that across all species, laughter consists of evenly spaced rhythmic intervals between successive sounds. This underlying rhythm appears to be conserved since the last common ancestor of these apes. "Speech leaves no fossils and complex language exists only in our own species," said Dr. Chiara De Gregorio, a study author from the University of Warwick. "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."
While the basic rhythm is consistent, human laughter has evolved to be faster, more variable, and subject to sophisticated context-dependent control. Humans are unique among great apes in their ability to modulate laughter based on social situations, such as laughing politely in a meeting or nervously after making a mistake. These variations are achieved through conscious control, shaping the sound to communicate different emotions and intentions, while maintaining the core rhythmic structure.
The findings suggest that vocal control over laughter gradually developed throughout great ape evolution. The researchers propose that this basic rhythmic pattern was present in a common ancestor 15 million years ago and has persisted, with all living great apes exhibiting the same underlying pattern. "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," stated Dr. Adriano Lameria, another study author. "Humans lay on a continuum, a prolongation of vocal control capacities that were already being cumulatively honed in for 15 million years."
This research offers a potential insight into the evolution of human speech, a complex trait that leaves no fossil record. By studying the conserved nature of laughter, scientists can explore the evolutionary steps that may have led to the development of complex vocal communication in humans.