Phylogenetic insight into the origin of tones

The origin of tone, also known as tonogenesis, has long been a topic of great interest in language evolution and human cognition studies. Several linguistic studies of tonal languages have proposed various hypotheses that tonal origin may be related to different changes of phonological structures. However, such hypotheses have not been quantitatively tested in an evolutionary framework. Here, we conducted phylogenetic comparative analyses to assess the likelihood of different hypotheses of tonogenetic mechanisms across 106 Sino-Tibetan languages, of which approximately 70% are tonal. Our results showed that the presence of tones has a strong phylogenetic pattern and that Proto-Sino-Tibetan languages were most likely non-tonal. Our findings identified that tonal origin was strongly associated with the evolution of specific phonological structures, such as the loss of syllable-final consonants and voice quality on vowels. Furthermore, we found that tonal origin probably did not influence the diversification rates of Sino-Tibetan languages. These findings enabled us to better understand that tone arose as a compensatory mechanism for the structural organization and evolution of languages.