Rhythm and timing in laughter reveal that human vocal plasticity falls on a hominid continuum

Key Points:

• Laughter is a conserved vocalization across all great ape species, occurring primarily during social play and affiliative interactions, and serves as a key model to study the evolution of vocal control and rhythmic capacities leading to human speech and language.
• Comparative analysis of laughter from all five extant great ape taxa revealed that laughter is isochronous (regularly timed) across species, with tickling laughter showing more rhythmic regularity than play laughter, likely due to the physical dynamics of social play.
• Phylogenetic analyses demonstrated that laughter tempo has accelerated along hominid evolution, with humans showing faster and more context-sensitive laughter rhythms, particularly producing quicker laughter during tickling than play, a feature absent in other great apes.
• Humans exhibit greater temporal variability in laughter tempo compared to other great apes, reflecting enhanced vocal flexibility and rhythmic control that likely contributed to the emergence of speech and language.
• The study provides empirical evidence that laughter's rhythmic features evolved over 15 million years, highlighting it as an accessible model for understanding the deep evolutionary roots of human vocal communication and social signaling.