Phylogeny in Phonology: How Tai Sound Systems Encode Their Past

The study of sound change is foundational to traditional historical linguistics, particularly the linguistic comparative method. It is well established that the phonology of modern languages encodes useful data for studying the history of those languages, and their genetic relationships to one another. However, phonology has typically been the means to the end, enabling the comparative method, and coding of a comparative lexicon for cognacy. Once coded, the particular sounds involved no longer factor into the analysis. This study examines whether the phoneme inventories and phonotactic profiles of a set of languages themselves contain phylogenetic signal detectable using established statistical tests D statistic (Fritz & Purvis 2010), K (Blomberg et al 2003), and NeighborNet delta score (Holland et al 2002) and Q-residual (Gray et al 2010). This study adds to the growing body of work on the use of phonological traits in computational phylogenetics for linguistics. Using data from 20 Tai lects from the Kra-Dai language family, this study confirms and extends previous findings. This includes detection of strong phylogenetic signal in phoneme frequency and biphone transition probabilities, but also relatively strong phylogenetic signal detected in even coarse-grained phoneme and biphone presence/absence, which previous work was unable to do