Speech adapts to differences in dentition within and across populations

Abstract

We test the hypothesis that a specific anatomical feature, the dental malocclusion associated with reduced dental wear, causes languages to adapt by relying more heavily on labiodental consonants. In contrast to previous work on this topic, we adopt a usage-based approach that directly examines the relative frequency of such labiodental sounds within phonetically transcribed word lists and texts from thousands of languages. Labiodentals are shown to be very infrequent in the languages of hunter gatherers, who tend to have edge-to-edge bites as opposed to the overbite and overjet observed in populations that consume softer diets and rely heavily on eating utensils. This strong tendency is evident after controlling for Galton’s problem via multiple methods including frequentist and Bayesian linear mixed modeling. Additionally, we discuss data from Amazonian hunter gatherers with edge-to-edge bites. The languages of these populations are shown not to use labiodentals frequently, or to have only recently begun doing so. Finally, we analyze the speech of English speakers with varying bite types, demonstrating how the sounds used by individuals reflect the same phenomenon. The diverse findings converge on the same conclusion: speech adapts to anatomical differences within and across populations.

The sounds of prehistoric speech

“…Most critically, perhaps, it was demonstrated that labiodentals are notably lacking in the phoneme inventories of contemporary hunter–gatherer populations. In follow-up work, the hypothesis was tested with frequency-based data [34]. It was found that labiodental consonants represent about 2% of all consonants in the word lists of agricultural populations but are nearly absent in the word lists of hunter–gatherers.…”

The Sound Systems of Languages Adapt, But to What Extent?

“…The production of such prefixes actually varies across individuals with distinct bite types, at least in some cases. Some of the individuals we observed in Everett & Chen (2021) do not actually produce [im-] with a bilabial nasal but with a labiodental nasal. Now let us imagine that in a given population the amount of people that produce bilabial nasals as labiodentals is 2%, but in another it is 20% given clear disparities in overbite/overjet prevalence across populations.…”

“…In response to Blasi et al (2019), some suggested that well-established lenition processes, principally the lenition of /p/ to /f/, are sufficient to account for the global distribution of labiodentals observed in that study. While we know that lenition is common crosslinguistically, however, a lenition-based account alone could not in principle explain the typological distributions noted by Blasi et al (2019) or Everett & Chen (2021). A key question is whether certain bite types cause such lenition to be more prevalent in populations with overbite/overjet.…”

“…In recent work (Everett & Chen 2021), Sihan Chen and I present new sorts of evidence that cross-population variations in bite type impact not just the likelihood that a given population's language has labiodental phonemes but actually impact the frequency with which labiodental sounds are used. Across 2,729 phonetically transcribed word lists (again using the ASJP data), we found that the languages of hunter gatherers use labiodentals at extremely low rates, when contrasted to the languages of agriculturalists with softer diets.…”

“…The only study that has actually looked at the effect of bite type on the production of labiodentals across speakers shows that bite type is a clear synchronic predictor of whether some bilabials are produced as labiodentals. (Everett & Chen 2021) We need data from many individuals within populations to test such hypotheses, data that are coded for factors like bite type in addition to the factors typically considered in research on sociolinguistically mediated sound change (e.g. gender, age, socioeconomic class).…”