Generative vocal plasticity in chimpanzees.

Modern theory posits that human-ape differences in voice command account for speech evolution. However, comparison has been indirect and conjectural based on vocal learning taxa far related from Hominids, instead of direct and quantitative based on great ape calls that, like all speech sounds, are local-specific and non-universal to the species. Moreover, the null hypothesis that the great ape voice command is purely reflexive has never been directly tested. Here, we show that in controlled, constant experimental settings, captive chimpanzees exhibit high-dimensional dexterity over voice activation and modulation in two atypical vowel-like calls. Subjects made unrestricted, multidimensional, and distinct voice changes within and between individuals, inducing parameter changes up to 10,000%, rejecting null hypothesis' predictions. Forecasting models indicated unmitigated voice novelty, altogether demonstrating emancipated and vast real-time voice control. Findings show that, contrary to traditional assumptions, speech and song evolution likely hinged on prolific voice command already available in ancestral ape-like ancestors.