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

Laughter is an important, universal form of human non-linguistic vocal expression and, being shared by all extant great apes, offers a valuable proxy for tracing the evolution of vocal control that ultimately enabled language. Yet surprisingly little is known about the evolution of its defining feature, rhythm. Here we show, through comparative analyses of laughter across all extant great apes (orangutans, gorillas, bonobos, chimpanzees, humans), that the laughter of the last common ancestor was already isochronous, becoming faster, more variable, and increasingly context-sensitive over hominid evolution. The evolution of laughter's rhythm reveals a progressive increase in vocal rhythmic plasticity, with humans following the overall trajectory toward enhanced vocal control.