Research Article

Human sound systems are shaped by post-Neolithic changes in bite configuration

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Science  15 Mar 2019:
Vol. 363, Issue 6432, eaav3218
DOI: 10.1126/science.aav3218
  • Labiodentals depend on bite configuration.

    Biomechanical modeling shows that labiodental sounds like “f” are easier to produce (and to accidentally arise) under overbite and overjet (A) than under the edge-to-edge bite (B) that prevailed before the Neolithic (C). Overbite and overjet persisted only when exposed to the softer diets that became characteristic with food production (D versus E) and more recently with intensified food processing (F). Both developments led to a spread of labiodental sounds.

  • Fig. 1 Mid-sagittal and forward-facing schematics of labiodental and bilabial strictures.

    Mid-sagittal views illustrate the passive and active articulators including the supralaryngeal vocal tract, hard and soft palates, nasal cavity, tongue, and lips. (A) In the labiodental stricture, the bottom lip raises to make contact with the upper teeth. (B) In the bilabial stricture, both lips make contact to form closure. (C) Labiodental is visually distinctive by the presence of the upper teeth. (D) True bilabial in which the upper and lower lips are aligned and make contact; the teeth are not visible.

  • Fig. 2 Adult skulls displaying edge-to-edge bite versus overbite and overjet.

    (A) Female, ~30 years old, Arene Candide Cave (Italy), late Upper Paleolithic, displaying edge-to-edge bite. (B) Female, ~30 years old, Schela Cladovei (Romania), Mesolithic, displaying edge-to-edge bite. (C) Male, ~40 years old, Hainburg (Austria), Early Bronze Age (~3600 BP), displaying overbite and overjet. Images are not to scale. [Photo credits: (A) David Frayer, Department of Anthropology, University of Kansas, USA; (B) Mihai Constantinescu, Institutul de Antropologie “Fr. J. Rainer,” Bucharest, Romania; (C) Karin Wiltschke-Schrotta, Department of Anthropology, Naturhistorisches Museum Wien, Austria]

  • Fig. 3 Relative muscle effort in the production of labiodentals between the edge-to-edge and the overbite and overjet bite configurations.

    (A) Sum of the total muscle force expressed as a percentage of the total maximum force of all muscles in the model. (B) Specific effort by muscle. Overall, labiodental articulation incurs less muscular effort in the overbite and overjet configuration than in the edge-to-edge configuration.

  • Fig. 4 Tooth-lip distance during production across articulations and bite configurations, defined as the distance between the lower lip and upper incisors.

    Note that in bilabials, this distance results merely as a by-product of the main stricture of these sounds, which is between the lower and upper lips (not shown in the figure). In the overbite and overjet condition, the approximant and stop bilabials follow a trajectory similar to that of labiodental fricatives.

  • Fig. 5 Posterior distributions of target parameters in a Bayesian Poisson regression model with log link function for two subsistence databases, GMR and AUTOTYP.

    Vertical lines indicate median (blue) and mean (orange) of each distribution. The number of nonlabiodental segments was used as control. The target parameters comprise the main fixed effect of hunter-gatherer subsistence (with inverted sign so as to maximize comparability between parameters) and four random effects, intercepts, and slopes for both geographic area and linguistic family.

  • Fig. 6 Languages spoken in Greenland, southern Africa (Khoisan), and Australia that have gained labiodentals through language contact.

    (A) West Greenlandic has acquired a labiodental through contact with Danish. (B) Some Khoisan languages have labiodentals through contact with Germanic languages such as Afrikaans. (C) Two languages in Australia have labiodentals (3), Kunjen and Ngan'gikurrungkurr, the latter through contact with English.

  • Fig. 7 Estimated probabilities of labiodental articulation across sets of historically related sounds in Indo-European.

    Sets are labeled by traditional conventions in Indo-European studies (e.g., *p is the set that groups “p” in Italian with “f” in English; *gʷ is the set that groups Italian “v” with English “k”). (A) Extant distribution of labiodental (red) versus nonlabiodental (blue) articulation of cognate sounds (an open square means that the actual articulation is unknown), mapped to one of two phylogenies (104) used in our models (for the other phylogeny, see fig. S8). (B) Estimated labiodental probability as inferred by stochastic character mapping (8890). Languages and clades are ordered as in (A). (C) Traitgram of the simultaneous increase in labiodental probability across correspondence sets. For zoomed-in displays on each individual correspondeme, see figs. S13 to S32; for estimates based on an alternative phylogeny (92), see fig. S33.

  • Table 1 Relative total muscle effort of labiodental fricatives, bilabial stops, and bilabial approximants in the biomechanical model under the overbite and overjet configuration and the edge-to-edge configuration.

    The total cost of a labiodental fricative in the edge-to-edge bite is used as the unit of comparison, with estimates rounded to the nearest decimal. Labiodentals require more effort than bilabials in either bite configuration, but the effort increases more in the edge-to-edge configuration than in the overbite and overjet configuration.

    Speech soundConfiguration
    Overbite and overjetEdge-to-edge
    Labiodental fricative0.71
    Bilabial stop0.50.25
    Bilabial approximant0.70.5
  • Movie 1. Simulation of the production of a labiodental fricative (“f” or “v”) under overbite and overjet.

    Here and in the other movies, the cyan dots in the lips serve as reference for the measurement of the proximity between lips and anterior upper teeth during the articulation.

  • Movie 2. Simulation of the production of a labiodental fricative (“f” or “v”) under edge-to-edge bite.
  • Movie 3. Simulation of the production of a bilabial stop (“p” or “b”) under overbite and overjet.
  • Movie 4. Simulation of the production of a bilabial stop (“p” or “b”) under edge-to-edge bite.
  • Movie 5. Simulation of the production of a bilabial approximant (“w”) under overbite and overjet.
  • Movie 6. Simulation of the production of a bilabial approximant (“w”) under edge-to-edge bite.
  • Human sound systems are shaped by post-Neolithic changes in bite configuration

    D. E. Blasi, S. Moran, S. R. Moisik, P. Widmer, D. Dediu, B. Bickel

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

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    • Supplementary Text
    • Figs. S1 to S33 
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