The evolutionary dynamics of language change
Languages evolve – they are comprised of a set of traits, which vary between sister languages, and some of these variants survive better as the language diversifies. Understanding why and how the subsystems of languages differ in their evolutionary dynamics is a key question for linguistics. One of the most fundamental dynamics is the rate of change. It is commonly thought that the rapid rate of change hampers the reconstruction of deep language relationships and there are suggestions that grammatical structures might be more stable over time than other subsystems such as basic vocabulary. However, stability is not the only thing we care about. Rather, the relative rates and patterns can tell us about the different forces driving language change.
Here we apply a novel evolutionary method to infer the rates of change in lexical and grammatical data from 81 Austronesian languages. Our results show that most grammatical features actually change faster than items of basic vocabulary, but that there is a core that are highly stable. Strikingly, the slowly evolving grammatical features tend to be those that are more covert and less available to sociolinguistic reflection by speakers. Further, the lexicon shows more changes linked to language diversification events than the grammar, while the grammar shows higher rates of conflicting signal ('homoplasy'). Our results suggest that different subsystems of language have differing dynamics driven by different causal factors.