Do chimpanzees have voluntary control of their facial expressions and vocalizations?

It has been argued that only humans have volitional control of their vocalizations and that this ability allowed for the evolution of speech. Here we argue that recent studies in chimpanzees suggest that they do, in fact have some degree of voluntary control of both their vocalizations as well as their facial expressions. We further argue, based on recent studies, that chimpanzees understand the functional significance of using vocalizations or sounds in communicative and social contexts, specifically as a means of obtaining the attention of an otherwise inattentive human. The ability of chimpanzees to voluntarily produce and functionally manipulate social agents with vocal signals may be an important precursor in the evolution of human spoken language.