Phylogenetic ancestral state reconstruction of bilabial trills in the languages of Malekula Island (Vanuatu), and the historical evolution of rare sound changes

It is unknown how rare sound changes appear and spread through the lexicon. The bilabial trills of Malekula are one such example of a rare sound, and the recent assembly of a lexical database for Vanuatu (the Vanuatu Voices database) affords a unique opportunity for a quantitative historical analysis. We built a linguistic phylogeny of Malekula languages, and performed phylogenetic ancestral state reconstruction of fourteen semantic values which exhibit bilabial trills to track their historical evolution. We found a surprising degree of dynamism, with trills spreading gradually through the lexicon and showing frequent losses and reappearances. Our results are consistent with frequent borrowing of trills between neighbouring languages. We suggest that the rapid dynamism and evidence for borrowing are explained by the low functional load and identity attachment of trills respectively.