Evolution and trade-off dynamics of functional load

TL;DR

This study investigates the evolution of functional load (FL) in 90 Pama-Nyungan languages, revealing a phylogenetic signal and a historical trade-off dynamic between vowel length and following consonant contrasts, supporting language drift hypotheses.

Contribution

It is the first to demonstrate phylogenetic signal in phonological function measures and uncovers a deep-time trade-off dynamic in FL across a large language family.

Findings

High phylogenetic signal in FL across languages

Negative correlation between vowel length and following consonant FL

Evidence of historical contrast flow and language drift

Abstract

Function Load (FL) quantifies the contributions by phonological contrasts to distinctions made across the lexicon. Previous research has linked particularly low values of FL to sound change. Here we broaden the scope of enquiry into FL, to its evolution at all values. We apply phylogenetic methods to examine the diachronic evolution of FL across 90 languages of the Pama-Nyungan (PN) family of Australia. We find a high degree of phylogenetic signal in FL. Though phylogenetic signal has been reported for phonological structures, such as phonotactics, its detection in measures of phonological function is novel. We also find a significant, negative correlation between the FL of vowel length and of the following consonant, that is, a deep-time historical trade-off dynamic, which we relate to known allophony in modern PN languages and compensatory sound changes in their past. The finding reveals a historical dynamic, similar to transphonologization, which we characterize as a flow of contrastiveness between subsystems of the phonology. Recurring across a language family which spans a whole continent and many millennia of time depth, our finding provides one of the most compelling examples yet of Sapir's 'drift' hypothesis, of non-accidentally parallel development in historically related languages.