Interindividual vocal tract diversity influences the phonetic diversification of spoken languages

Abstract

Vocal tracts, like other physical traits, exhibit extensive interindividual variation. However, little is known about how this variation translates into phonetic diversity between speakers, and ultimately, across languages. We demonstrate that different vocal tract shapes and associated articulatory strategies leave consistent acoustic signatures, which show congruent patterns of phonetic variation both within and across speech communities. Recalling a central tenet of evolutionary biology - that within-group variation feeds processes of between-group diversification - our findings suggest that the sounds of language evolve according to a neutral-like evolutionary process. Our "neutral-like evolution model" serves as a null hypothesis for disentangling the biological versus cultural mechanisms at play in phonetic diversification, where deviations from the neutral expectation indicate culturally mediated processes of language change at work.