Rhythmic Roots: The Adaptive Functions of Vocal Isochrony and Its Role in Human Music and Language Evolution

Abstract

Isochrony, or the regular timing of sounds, is a prominent rhythmic feature of human music and can also be found in the vocalisations of non-human animals. In the evolution of music and language, the capacity for vocal learning is hypothesised to have played a key role, with vocal learning species thought to have more advanced rhythmic capabilities. However, studies show that vocal isochrony is also present in vocal non-learners, indicating that it is perhaps a highly conserved property providing adaptive benefits across taxa. As mechanisms that are shared across multiple species are likely to have been the bedrocks of our current abilities, comparative research into vocal isochrony can give clues on how rhythms in human music and language might have evolved, even though modern speech is not typically isochronous. This review summarises possible adaptive functions of vocal isochrony by describing its presence across different species and call types found in recent research. Thus, it represents a narrative synthesis of the adaptive functions of vocal isochrony. Here, we highlight three major possible functions of vocal isochrony: firstly, isochrony could improve communication by enhancing signal transmission from one individual and auditory detection by others and possibly function in conveying meaning. Secondly, vocal isochrony could inform others about mate quality, indicating a role in sexual selection. Lastly, isochrony could facilitate vocal coordination between two or more individuals, as the predictability of isochrony can help individuals to adjust the timing of their vocalisations to each other more readily. These functions seem to be highly intercorrelated, which might provide clues for the evolution of human music and speech.