Societies of strangers do not speak grammatically simpler languages

Many recent proposals claim that languages adapt to their environments. The Linguistic Niche hypothesis claims that languages with numerous native speakers and substantial proportions of non-native speakers (societies of strangers) will tend to lose grammatical distinctions. In contrast, languages in small, isolated communities should maintain or expand their range of grammatical markers. Here, we test such claims using a new global dataset of grammatical structures - Grambank. We model the impact of the number of native speakers, the proportion of non-native speakers, the number of linguistic neighbors, and the status of a language on grammatical complexity while controlling for spatial and phylogenetic autocorrelation. We deconstruct "grammatical complexity" into two separate dimensions: (i) how much morphology a language has ("fusion"), and (ii) the amount of information obligatorily encoded in the grammar ("informativity"). We find several instances of weak positive associations but no inverse correlations between grammatical complexity and sociodemographic factors. Our findings cast doubt on the widespread assumption that grammatical complexity is shaped by the sociolinguistic environment.