RESEARCH ARTICLE SUMMARY◥

ANTHROPOLOGY

Human sound systems areshaped by post-Neolithic changesin bite configurationD. E. Blasi*†, S. Moran†, S. R. Moisik, P. Widmer, D. Dediu, B. Bickel

INTRODUCTION:Human speech manifestsitself in spectacular diversity, ranging fromubiquitous sounds such as “m” and “a” to therare click consonants in some languages ofsouthern Africa. This range is generally thoughtto have been fixed bybiological constraints sinceat least the emergence of Homo sapiens. At thesame time, the abundance of each sound in thelanguages of the world is commonly taken todepend on how easy the sound is to produce,perceive, and learn. This dependency is alsoregarded as fixed at the species level.

RATIONALE: Given this dependency, we ex-pect that any change in the human apparatusfor production, perception, or learning affectsthe probability—or even the range—of thesounds that languages have. Paleoanthropo-logical evidence suggests that the productionapparatushasundergonea fundamental changeof just this kind since the Neolithic. Althoughhumans generally start out with vertical andhorizontal overlap in their bite configuration(overbite and overjet, respectively), mastica-tory exertion in the Paleolithic gave rise to an

edge-to-edge bite after adolescence. Preserva-tion of overbite and overjet began to persistlong into adulthood only with the softer dietsthat started to become prevalent in the wakeof agriculture and intensified food processing.We hypothesize that this post-Neolithic declineof edge-to-edge bite enabled the innovationand spread of a new class of speech soundsthat is now present in nearly half of theworld’slanguages: labiodentals, produced by position-ing the lower lip against the upper teeth, suchas in “f” or “v.”

RESULTS: Biomechanicalmodels of the speechapparatus show that labiodentals incur about30% less muscular effort in the overbite andoverjet configuration than in the edge-to-edgebite configuration. This difference is not pres-

ent in similar articula-tions that place the upperlip, instead of the teeth,against the lower lip (asin bilabial “m,” “w,” or“p”). Our models alsoshow that the overbite

and overjet configuration reduces the inci-dental tooth/lip distance in bilabial articu-lations to 24 to 70% of their original values,inviting accidental production of labiodentals.The joint effect of a decrease in musculareffort and an increase in accidental produc-tion predicts a higher probability of labio-dentals in the language of populations whereoverbite and overjet persist into adulthood.When the persistence of overbite and overjetin a population is approximated by the prev-alence of agriculturally produced food, wefind that societies described as hunter-gatherers indeed have, on average, only aboutone-fourth the number of labiodentals exhib-ited by food-producing societies, after con-trolling for spatial and phylogenetic correlation.When the persistence is approximated by theincrease in food-processing technology overthe history of one well-researched languagefamily, Indo-European, we likewise observe asteady increase of the reconstructed proba-bility of labiodental sounds, from a medianestimate of about 3% in the proto-language(6000 to 8000 years ago) to a presence of 76%in extant languages.

CONCLUSION: Our findings reveal that thetransition from prehistoric foragers to contem-porary societies has had an impact on thehuman speech apparatus, and therefore on ourspecies’main mode of communication and so-cial differentiation: spoken language.▪

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Blasi et al., Science 363, 1192 (2019) 15 March 2019 1 of 1

The list of author affiliations is available in the full article online.*Corresponding author. Email: damian.blasi@uzh.ch†These authors contributed equally to this work.Cite this article as D. E. Blasi et al., Science 363, eaav3218(2019). DOI: 10.1126/science.aav3218

A Overjet/overbite model B Edge-to-edge model C Pre-Neolithic edge-to-edge bite (Jomon Period, Japan)

D Hunter-gatherers

E Food producers

F Evolution of sounds in Indo-European

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Labiodentals depend on bite configuration. Biomechanical modeling shows that labiodentalsounds 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 andoverjet persisted only when exposed to the softer diets that became characteristic with foodproduction (D versus E) and more recently with intensified food processing (F). Bothdevelopments led to a spread of labiodental sounds.

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RESEARCH ARTICLE◥

ANTHROPOLOGY

Human sound systems areshaped by post-Neolithic changesin bite configurationD. E. Blasi1,2,3,4,5*†, S. Moran1,2†, S. R. Moisik6, P. Widmer1,2, D. Dediu7,8, B. Bickel1,2

Linguistic diversity, now and in the past, is widely regarded to be independent of biologicalchanges that took place after the emergence of Homo sapiens. We show convergingevidence from paleoanthropology, speech biomechanics, ethnography, and historicallinguistics that labiodental sounds (such as “f” and “v”) were innovated after the Neolithic.Changes in diet attributable to food-processing technologies modified the human bitefrom an edge-to-edge configuration to one that preserves adolescent overbite and overjetinto adulthood. This change favored the emergence and maintenance of labiodentals.Our findings suggest that language is shaped not only by the contingencies of its history,but also by culturally induced changes in human biology.

Speech is the chief mode of human com-munication. Its origin reaches deep intothe hominin lineage: Critical componentssuch as a continuously descended larynx,a modern hyoid bone, and breathing con-

trol were already in place around half a millionyears ago (1), building on even older capabilitiesof the primate vocal tract (2). Yet human speechmanifests itself in a bewildering diversity ofthousands of different sounds attested acrossthe ~7000 extant languages today (3), rangingfrom the almost ubiquitous point vowels (i, u,and a in English) to the rare click consonantsin some of the languages of southern Africa. Themechanisms that generate and maintain thisdiversity are mainly ascribed to errors in speechproduction or perception, coupled with socio-linguistic diffusion (4–6). The uniformitarianassumption in linguistics (7) takes these mech-anisms to have become fixed with the emergenceof anatomically modern humans. Current theo-ries take this assumption one step further andexpect that not only the mechanisms, but alsothe ecological conditions under which they ap-ply and the linguistic patterns they produce, havestable probabilities (8, 9). When their distribu-tions reach stationarity, sounds and grammar

structures are expected to have the same prob-abilities in all languages (10).Notwithstanding these ideas, linguist Charles

Hockett conjectured that labiodentals—speechsounds including “f” and “v” (see Fig. 1)—areoverwhelmingly absent in languages whose speak-ers live from hunting and gathering, because theassociated heavy-wear diet induces an edge-to-edge bite that makes the articulation of labioden-tals effortful, which would suggest a post-Neolithicchange in speech (11). Hockett’s hypothesis wasrejected at the time on the grounds that wearexplains bite configuration only partially, and thatedge-to-edge bite became less common consider-ably later than agriculture (12). However, as weshow below, recent anthropological evidence hasdemonstrated that tooth wear (and masticatoryexertion more generally) is indeed the principal

mechanism of post-adolescent bite change, andthat despite considerable variation, there hasbeen an overall decrease of edge-to-edge bitesince the Neolithic.Humans generally start out with horizontal

and vertical overlap in their bite configuration(overjet and overbite, respectively), not only indeciduous but also in adolescent dentition. How-ever, substantial tooth wear during the lifespaninduces loss of hard tissue and flattening of theocclusal plane and interproximal surfaces. Thisloss of hard tissue and modification of dentalocclusion triggers three major compensatoryprocesses: continuous dental eruption (movementof teeth to compensate for their lost height),mesialdrift (migration of teeth in the alveolar bone inthemesial direction to compensate for their lossof interproximal surfaces), and lingual tipping(tilt of anterior teeth in the lingual directionto compensate for incisal and occlusal wear)(13, 14). These processes eventually develop intoedge-to-edge bite, such that anterior teeth loseoverbite and overjet, forming a tight (and flat) in-cisal surface contact with few or no irregularities(see Fig. 2). Although the process is modulatedby population-specific factors, wear increasesmonotonically with age (15). This post-adolescentmodification is not only characteristic of anatom-ically modern humans; it likely has its roots farback in the Homo genus (14, 16), where substan-tial wear effects are found across the documentedspecies (17).In contrast, individuals living in most con-

temporary populations typically preserve over-bite and overjet long into adulthood (13, 18).Although the sources of occlusal wear are diverse(19), the most common cause of tooth abrasion isfood, which produces wear over the entire occlu-sal surface. Soft diets common in most contem-porary populations reduce the number of bitesfor chewing and the exposure of tooth surfacesto friction due to exogenous material contact,thus reducing wear throughout the lifetime ofthe individual (14). Moreover, soft diets exert

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1Department of Comparative Linguistics, University of Zurich,8032 Zurich, Switzerland. 2Center for the InterdisciplinaryStudy of Language Evolution, University of Zurich, 8032Zurich, Switzerland. 3Department of Linguistic and CulturalEvolution, Max Planck Institute for the Science of HumanHistory, 07745 Jena, Germany. 4Human Relations Area Files,Yale University, New Haven, CT 06511, USA. 5Laboratory ofQuantitative Linguistics, Kazan Federal University, 420000Kazan, Russia. 6Division of Linguistics and MultilingualStudies, Nanyang Technological University, 637332Singapore. 7Laboratoire Dynamique Du Langage UMR 5596,Université Lumière Lyon 2, 69363 Lyon Cedex 07, France.8Language and Genetics Department, Max Planck Institutefor Psycholinguistics, 6525 XD Nijmegen, Netherlands.*Corresponding author. Email: damian.blasi@uzh.ch†These authors contributed equally to this work.

Fig. 1. Mid-sagittal and forward-facing schematics of labio-dental and bilabial strictures.Mid-sagittal views illustrate thepassive and active articulatorsincluding the supralaryngeal vocaltract, hard and soft palates,nasal cavity, tongue, and lips.(A) In the labiodental stricture, thebottom lip raises to make contactwith the upper teeth. (B) In thebilabial stricture, both lipsmake contact to form closure.(C) Labiodental is visuallydistinctive by the presence of theupper teeth. (D) True bilabial inwhich the upper and lower lipsare aligned and make contact;the teeth are not visible.

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less biomechanical pressure on the jaw. Thisleads to a shorter mandible (20, 21), representinganother potential cause of overbite and overjetpreservation. Softening food through cookingand the use of preservation techniques was con-siderably facilitated by the invention of pottery(22, 23), for which the earliest evidence is foundin the Epipaleolithic of eastern Asia (24, 25).Pottery use markedly increased with agricultureand the associated need for storage; therefore,these developments made softer diets more wide-ly accessible. As a result, edge-to-edge bite hasbecome exceedingly rare in populations withaccess to softer food, and the persistence ofoverbite and overjet is now largely consideredthe norm.

Biomechanical modeling oflabiodental production

Hockett’s hypothesis suggests that the morerecent bite configuration (with overbite andoverjet) eases and makes more likely the ar-ticulation of labiodentals. To assess the cost ofarticulation, we adapted a biomechanical simu-lation of the orofacial structures and muscula-ture to compare overbite and overjet with theedge-to-edge bite configuration using ArtiSynth(26) (see methods). Labiodental stricture is de-fined using the inverse model (27), which com-putes the muscle activity required to achievepreestablished time-varying targets. One inversetarget is defined for a midline node of the facialmesh found on the superior-posterior surface ofthe lower lip. This target starts at rest, then ismoved to a midsagittal reference vertex on thetip of the central incisors of the maxilla mesh,and then, after a brief sustain, finally returns toits resting position (see Movies 1 and 2 and figs.S1 and S2). Two additional targets are used oneither side of the upper lip to assist in raising itslightly. Following earlier work (28, 29), we mea-sure articulatory effort as the integral of the

force output of all muscles active in the simu-lation over time, expressed as a percentage ofthe total maximum force generation propertyof all musculature in the model (which is thesame in both models).The simulation results indicate that labio-

dental production in the overbite and overjetcondition is approximately 29% less costly thanin the edge-to-edge condition (see Fig. 3A). Themodel also indicates differential force exertionby specific muscles (Fig. 3B). The overbite andoverjet condition shows less force for most mus-cles than the edge-to-edge condition. Among themuscles that show more force in the edge-to-edge bite, the mentalis is important in drawingthe lower lip toward the upper incisors. Thezygomatic muscles are highly active as well andmay complement lower lip retraction and rais-ing, although they primarily act on the cor-ners of the mouth. The lip raisers (levator labiisuperioris and levator anguli oris) help to clear theupper oral vestibule (preventing collision betweenthe upper and lower lips) to admit the elevationof the lower lip to themaxillary incisors, but thelevator anguli oris musclesmay also help in draw-ing the lower lip upward (even though they alsoact primarily on the corners of the mouth).To determine whether these differences are

specific or particularly salient in the articulationof labiodentals, rather than general consequencesof bite configuration,we performed a second set ofsimulations where we examined the produc-tion of a pair of bilabial segments (a stop and anapproximant such as “p” and “w”), which are closeto labiodentals in place of articulation (see Fig. 1)and which should also be influenced by the po-sitioning of the teeth and the jaw. The two bi-labial segments differ in their degree of stricture,with the stop having complete closure of the lips,and the approximant having just a slightly nar-rowed lip aperture (see Movies 3 to 6). Interest-ingly, for both of these articulations, the overbite

and overjet condition actually requiresmoremus-cle effort than the edge-to-edge condition (seeTable 1), resulting from the fact that the lips arecloser together in the edge-to-edge case. How-ever, the relative increase in effort of labiodentalas opposed to bilabial articulation is weaker inthe overbite and overjet condition. Together,these results suggest that the transition to anoverbite and overjet configuration has a distincteffect on the ease of labiodentals, while bilabialsbecome more difficult.

Blasi et al., Science 363, eaav3218 (2019) 15 March 2019 2 of 10

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 andoverjet. 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, NaturhistorischesMuseum Wien, Austria]

Movie 3. Simulation of the production of abilabial stop (“p” or “b”) under overbite andoverjet.

Movie 2. Simulation of the production of alabiodental fricative (“f” or “v”) underedge-to-edge bite.

Movie 1. Simulation of the production of alabiodental fricative (“f” or “v”) underoverbite and overjet. Here and in the othermovies, the cyan dots in the lips serve asreference for the measurement of the proximitybetween lips and anterior upper teeth duringthe articulation.

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Our models furthermore suggest that bilabialstrictures in the overbite and overjet conditiondisplay greater incidental labiodental stricture(i.e., less distance between the lower lip and thecentral maxillary incisors) than in the edge-to-edge case. At the point of maximal bilabial stric-ture, for bilabial stops, the teeth and lips are0.8 mm away from a baseline labiodental tra-jectory in the overbite and overjet condition, incontrast to 3.4 mm in the edge-to-edge condi-tion; for bilabial approximants, the teeth andlips are 5.2 mm away from a baseline labiodentaltrajectory in the overbite and overjet condition,versus 7.0 mm in the edge-to-edge condition(Fig. 4). This suggests that bilabial targets maybe more prone to accidental realization as la-

biodentals under the overbite and overjet con-dition. Consistent with this, in the extreme caseof class IImalocclusion (i.e., excessive overjet) incontemporary populations, labiodentals are some-times used as substitutes for bilabials because ofdifficulty achieving contact between the upperand lower lip (30).

Biomechanical effects onlanguage change

As in other aspects of language production (31),relative differences in effort and error lead tosystematic biases in production frequencies thatin turn shape the probability of perceptual re-categorization and change over time, especiallywhen errors are perceptually salient (6, 28, 32, 33).Our biomechanical models suggest that suchprocesses were likely to have affected labio-dentals. The post-Neolithic emergence of overbiteand overjet persistence led to reduced effortwhen producing labiodentals, and at the sametime it increased the risk of accidental labiodentalarticulation. The resulting labiodentals are in-deed perceptually highly distinctive, both aurally(34–36) and visually (37) (see Fig. 1). Given this,we hypothesize that labiodentals became likelyto establish themselves and spread in popula-tions with overbite and overjet persistence.Furthermore, consistent with findings in his-

torical linguistics (38), our biomechanical modelsuggests that bilabials are a common source oflabiodentals. Given the fact that bilabials arepresent in the vast majority of languages [inthe PHOIBLE database (3), 95% have “m,” 87%have “p,” 71% have “b”], a transition to labio-dentals is therefore expected to be frequent inpopulations with overbite and overjet persist-ence. However, our models also show that bi-labials incur less effort overall, under either biteconfiguration (see Table 1). Moreover, bilabialsbenefit from positive biases arising from bio-mechanical saturation of lip contact (39, 40)and other physical domains of speech, such asquantal effects in articulatory-acoustic relationsand acoustic-auditory properties (41). Therefore,we expect bilabial articulations to remain abun-dant in the overbite and overjet condition, despitethe emergence of labiodentals. More specifi-cally, when bilabials develop into labiodentals,we expect this to happen only in certain posi-tions (e.g., only word-internally), leaving otherbilabials (e.g., word-initially) in place; wholesalereplacement is expected to be compensated bynew bilabials derived from other sources.Change-relevant biases of the production and

perception system are generally small (29, 42, 43),and the findings from our biomechanical mod-els are no exception to this. Furthermore, biasesare typically attenuated by additional factors,such as word structure and other aspects of thelinguistic system (44), as well as by the complexsocial diffusion mechanisms that characterizelanguage change (5, 8). However, virtually everyword and every articulation of a sound con-stitutes a trial for potential language change.We therefore expect that over generations ofspeakers, change-relevant biases leave clear sig-

nals when tested in sufficiently large cross-linguistic datasets.We tested our hypotheses as described below.

In the absence of detailed global registers of biteconfiguration through time, we used two inde-pendent proxies to assess the predicted differ-ence in the probability of labiodentals.

Worldwide association betweensubsistence type and labiodentals

Although the relation between subsistence andbite is mediated by both dietary and nondietaryfactors (45), food-producing societies are asso-ciated with less extensive tooth wear in compar-ison to hunter-gatherers (19), particularly in theanterior teeth (46). This in turn predicts thatfood-producing populations are more prone todevelop and maintain labiodentals than hunter-gatherer populations. To test this prediction, weused a global dataset of phonological invento-ries (3) along with associated information onsubsistence of the corresponding populations(47, 48) (see methods and the map on the sum-mary page). Labiodentals in our sample includefricatives (“f,” “v”), affricates (“pf,” “bv”), a nasal(“ɱ”), a tap (“ⱱ”), and an approximant (“ʋ”). Thedistribution of these sounds is heavily skewedglobally: 49% of languages sampled have “f,”37% “v,” and 2% “pf,” while the rest (“bv,” “ɱ,”“ⱱ,” “ʋ”) occur in no more than 1% of languages(n = 1672) (3).For modeling the effect of subsistence on the

number of labiodentals, we adopted a Bayesianmixed-effects Poisson regression model. Themodel includes random intercepts and slopesfor language family and area in order to controlfor phylogenetic and spatial correlation. As afurther control covariate, we included the totalnumber of nonlabiodental segments, becauseit is important to guarantee that any patternsfound in relation to labiodentals cannot be di-rectly explained by an overall increase or de-crease of the total number of segments.We found that, on average, hunter-gatherer

societies have only about 27% the number oflabiodentals exhibited by food-producing soci-eties [GMR dataset: l = –1.31, 95% credibleinterval: (–2.8, –0.27); AUTOTYP dataset: l =–1.41, 95% credible interval: (–3.37, –0.08); seeFig. 5 and methods]. As a way of evaluating thesupport for our model, we performed pseudo-Bayesian model averaging (49). We comparedthree nested models: the full model, a modelwithout a subsistence population effect butwith all subsistence group effects, and a modelwith no fixed or random effects for subsistence(the baseline condition). The results indicate thatthe first two models leverage more than 90% ofthe total weight (see fig. S3), thus lending sup-port to the notion that subsistence plays a role inaccurately predicting labiodental counts.Full models for both datasets yield empiri-

cally adequate posterior predictive distributionsof labiodentals when compared with the observa-tions (see fig. S4). Although some underdisper-sion can be detected in the data in comparison tothe Poisson model, a Conway-Maxwell-Poisson

Blasi et al., Science 363, eaav3218 (2019) 15 March 2019 3 of 10

Movie 6. Simulation of the productionof a bilabial approximant (“w”) underedge-to-edge bite.

Movie 5. Simulation of the production ofa bilabial approximant (“w”) under overbiteand overjet.

Movie 4. Simulation of the productionof a bilabial stop (“p” or “b”) underedge-to-edge bite.

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model tailored for underdispersed distributionsyields similar results (see methods). In additionto testing the association in the whole datasets,we performed the same analyses under morestringent conditions against our hypothesis byremoving all observations in Australia, becausefricatives and labiodentals are very scarce in theregion (50, 51), and by using the total number ofnonlabiodental fricatives (rather than the totalnumber of nonlabiodental segments) as a maincontrol. All of these alternative models yieldsmaller estimates for the mean posterior values,but nonetheless they coincide in showing thatsubsistence carries predictive power (see figs. S5and S6).Random intercepts for language family and

area are consistently estimated to play a rolein the model (see Fig. 5). Random slopes aremore spread, yet their means and medians areof a magnitude roughly comparable to that ofrandom intercepts. The mean posterior coefficientof subsistence on the presence of labiodentals,while displaying a wide posterior, is compara-ble in magnitude to the characteristic differencesbetween linguistic families and areas—in otherwords, the models suggest that differences insubsistence have as substantial an impact onlabiodentals as do the differences among fam-ilies or geographical areas. This association standsout against the fact that subsistence type hasno other known impact on linguistic structure(52, 53).Although these statistical trends are robust

on a worldwide scale, we also examined in moredetail the languages spoken by native populationsof Greenland, southern Africa, and Australia be-cause for these groups, heavy anterior tooth wearand concomitant edge-to-edge bite are particu-larly well documented (54–57), while at the sametime they represent vastly different areas andcultural traditions. We expect that the languagesspoken in these three areas will either lack labio-dentals, or in the cases where labiodentals doexist, they will be attributable to recent contact—for example, by borrowing words from popula-tions that are less exposed tomasticatory exertion.This expectation is borne out even though the

languages in the target areas have very different

sound inventories. In some cases, labiodentalsare reported, but closer inspection shows thatthese are artifacts of orthographic practices andnot confirmed by closer scrutiny (58) (see sup-plementary text). In the few cases where labio-dentals do exist, they tend to be the result of recentborrowings through contact with European lan-guages that have them (Fig. 6).In Greenland, three dialects bordering on

mutual unintelligibility (59) are spoken on the

northern, eastern, and southwestern coasts. BothNorthwestern and East Greenlandic (which aresmaller and endangered) lack labiodental con-trasts (60). These dialects lack official standardstatus, spoken or literary, and their speakers re-portedly resist assimilation (61). West Greenlandic,however, is spoken in the hospitable area on thesouthwest coast, where its people (roughly 45,000today)havebeen insustainedcontactwithEuropeanssince the 18th century, includingDanes, Germans,

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

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

Labiodental fricative 0.7 1. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .

Bilabial stop 0.5 0.25. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .

Bilabial approximant 0.7 0.5. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... .. ... ... .. ... ... .. ... ... .. ... .. ... ... .

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andNorwegians.West Greenlandic has long beendocumented as having bilabial fricatives (62–64),but only recently has it been documented ashaving a labiodental, which varies in pronun-ciation with some older speakers producing itbilabially (65). The voiceless labiodental fric-ative only occurs in Danish loanwords such as“filmi,” which suggests that a labiodental con-trast is being acquired through prolonged lan-guage contact.The non-Bantu languages spoken in south-

ern Africa, collectively referred to as Khoisan,provide another example of recent language con-tact situations that led to the adoption of labio-dentals. Although Khoisan-speaking people sharea common ancestry before the southward ex-pansion of Bantu groups into their range (66),linguistically they fall into several unrelatedfamilies (67). In Khoekhoe, the largest Khoisanlanguage, “f” and “v” are found in loanwordsfrom Germanic languages (68), barring a “v”that serves as an allophonic variant of “b” inroot medial position (69). Similarly, within theSan languages (i.e., Tuu and Kx’a), the onlywords containing “f” and “v” are loans (70, 71).Sandawe, a click language spoken in Tanzaniathat might be distantly related to some of theKhoisan languages, has the labiodental fricative“f,” but it occurs in only 5 of 1450 dictionaryentries (72, 73). In general, labiodentals are ab-sent across the board in the description of Khoisan

languages. This is particularly remarkable be-cause these languages possess the largest con-sonant inventories worldwide (3).In the Australian languages sampled (N =

343), there are only two languages, Kunjen andNgan’gikurrungkurr, that reportedly contain alabiodental “f.” Kunjen (Oykangand dialect) hasa fricative labiodental “f” with allophones (“f,”“v,” “f,” “b”) (74). In general, dialects of Kunjenhave phonological characteristics that areatypical of other Australian languages (74).Ngan’gikurrungkurr has a fricative/stop con-trast, which is usually pronounced as a bilabialfricative by older speakers but is usually labio-dental among younger speakers (75, 76). Thisvariation across age suggests the effects of in-creasing influence from English, in parallel towhat is observed for West Greenlandic.The absence of labiodentals in Australia has

also been argued to derive from a general con-straint against fricatives, potentially linked tochronic otitis media during language acquisitionand its detrimental effects on fricative percep-tion (51). However, a general fricative constraintis unlikely to account for the facts alone, forthree reasons. First, the incidence of fricativesin Australia is in fact unclear, as there is a sizablenumber of languages with nonlabiodental frica-tives (50). Second, the effect of subsistence typeon labiodentals remains even when we explicitlycontrol for the number of fricatives in our stat-

istical model. Third, labiodentals need not befricatives. Nonfricative labiodentals, such as la-biodental taps (as in the realization of German“w”) or labiodental approximants (as in the re-alization of “v” in some variants of Hindi), areoptions that could have easily arisen in Australiaif there were no bias against labiodentals andonly a bias against fricatives.

Increase of labiodentals during thehistory of Indo-European

We also investigated whether the spread ofoverbite and overjet persistence was influencedby the development of agricultural and foodprocessing technology over historical time. Ourprediction was that over the past few thousandyears, the increase in the production and avail-ability of softer diets caused a gradual rise inthe probability of developing and maintaininglabiodentals.To test this prediction, we reconstructed the

evolution of labiodentals in high-resolution phy-logenies of the Indo-European language family.This family is an ideal test case for two reasons.First, the sheer size of the familymakes it possibleto pick up subtle statistical signals of languagechangewhile its wide geographic extent—rangingfrom Iceland to eastern India—ensures that anysuch signal is not simply due to the contingenciesof local history and language contact. Second,both the linguistic evolution and the cultural

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Fig. 5. Posterior distributions of target parameters in a Bayesian Poisson regression model with log link function for two subsistencedatabases, GMR and AUTOTYP. Vertical lines indicate median (blue) and mean (orange) of each distribution. The number of nonlabiodental segmentswas used as control. The target parameters comprise the main fixed effect of hunter-gatherer subsistence (with inverted sign so as to maximizecomparability between parameters) and four random effects, intercepts, and slopes for both geographic area and linguistic family.

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evolution of the Indo-European family are wellunderstood, with sources of evidence in un-paralleled richness. On the side of language, acentury of detailed research on the relationshipamong the sound systems in the family (77)makesit possible to reconstruct individual articulationswith probabilisticmodels. Critically, we even havedetailed records on how sounds were producedfrom more than 2500 years ago (78), so modelscan be reliably calibrated in time.On the side of culture, the evolution of food

processing is also relatively well known. There areample records of processed dairy products andcereals in societies as old as 3500 BP throughoutthe Indo-European family, reflecting traditionsreaching back even earlier (79, 80). In line withthis, the archaeological record of skulls offersevidence of overbite and overjet persistence asearly as 4300 years ago in Pakistan (81), 3600years ago in Europe (82), and 2400 years ago inCentral India (83). For the western part of theIndo-European family, the Greco-Roman tradi-tion includes strong intensification of food pro-cessing in the form of water-driven milling.Industrial milling started at least 2300 yearsago and led to a massive spread of softer diets(84–86). Together with a growth in dairy process-ing, this spread even left a trace in several bio-logical pathways of European populations (87).Although an ascertainment bias cannot be ex-cluded, these findings on food processing led usto expect that overbite and overjet persistence,and hence the spread of labiodentals, was par-ticularly prominent in the western part of Indo-European since antiquity.We based our reconstruction of articulation

change on sets of sounds that correspond to eachother historically, as traceable through cognatewords. Historical linguistics has established 10such correspondence sets that include labio-dentals in at least one daughter language. Forexample, one set relates Italian “p” to English“f,” as attested in the cognacy of words such as“padre” in Italian and “father” in English; an-other set relates Italian “v” to English “k,” asattested by words such as Italian “venire” andEnglish “come” (77). These sets are convention-ally denoted by symbols that hypothesize theirvalue in the proto-language—for example, *pfor the {p, f,…} set and *gw for the {v, k,…} set—but the actual proto-articulation is not in factestablished (see methods). To reconstruct theproto-articulation, we applied Bayesian phylo-geneticmethods to each of the 10 sets, estimatingthe probability of labiodental versus nonlabio-dental articulation over time.Stochastic character mapping (88–90) suggests

that in all 10 sets, labiodental articulations areconsiderably less likely in earlier time periods ofthe family (Fig. 7). The median probability of alabiodental articulation at the root is about 3%[a result that converges with estimates fromBayesTraits (91) (supplementary text and fig. S12)].There is only one correspondence set that reaches50%. This is the set *w, as reflected in English“wind” or its Latin cognate “ventus,” which fre-quently changes back and forth so that recon-

struction becomes highly uncertain (see Fig. 7B,supplementary materials, and figs. S11, S17, andS18). Probabilities well above 50% emerge onlyconsiderably later, slowly starting between6000 and 4000 years ago. Under an alternativephylogeny with a younger root estimate (92),the probability estimates at the root are similar,but the increase of labiodentals is estimated tohave started only between 3500 and 4500 yearsago (see supplementary materials and fig. S33).Allowing for the uncertainty in the phylogenies,both estimates are consistent with the time rangein which dairy products and cereal are docu-mented to have become prominent in early Indo-European societies.Under either phylogeny, our models further-

more suggest a steep rise of labiodental prob-abilities after about 2500 years. This rise affectsseveral correspondence sets and is particularlypronounced in the Italo-Celtic (from Irish toFrench in the lower part of Fig. 7A), Germanic(from Gothic to German), and Greek branches.This fits with the strong impact of industrialmilling in the western part of the family thatbegan at around the same time. Beyond this,there are other geographical and branch-specificpatterns that emerge from our model, but fur-ther research is needed to disentangle the inter-play of linguistic and social factors that mayhave accelerated or slowed down individualdevelopments.Note that the low probability of ancestral la-

biodentals and the slow rise of this probabilitydo not simply follow from the modern frequencyof these sounds. Consider, for example, the firsttwo sets in Fig. 7A: *bh as reflected, for example,in English “brother” and “navel” (with labio-dentals depending on position) and *p as reflectedin “father” and “have.” Both have labiodentalreflexes in 52% and 46% of the extant languagesin our sample, but their labiodental probability

at the root is only 14% and 18%, respectively (or9% and 24% in the alternative phylogeny). Thismeans that they are much more likely to havebeen articulated as nonlabiodental sounds, pos-sibly indeed as “bh” and “p,” in line with tra-ditional hypotheses (77).

Discussion

Our findings suggest that the wane of edge-to-edge bite configuration since the Neolithic grad-ually facilitated the emergence and spread oflabiodental sounds in languages. Specifically,we find a substantial difference in labiodentalproduction effort and production stability be-tween bite configurations, a well-establishedmechanism of bite change resulting from wear,a worldwide association between subsistence-induced diet differences and the presence oflabiodentals, and a recent increase of labioden-tals driven by diet changes in a large and well-studied language family spanning at least six orseven millennia.Although more work is now needed in re-

constructing the precise time course of labio-dentals in other language families of the world,our findings open prospects for embedding suchwork in amore comprehensive, cross-disciplinaryview of language dynamics. Specifically, our re-sults suggest that the global socioeconomic his-tory of food affected not only bite configuration,but also humanity’s most distinctive marker ofsocial differentiation, language. If labiodentalsserved as an index of social class as a result ofdiet, prestige-driven processes of language change(93, 94) predict their potential to become selectedas a general trait of a language. Thus, by com-bining sociolinguistic and anthropological work,it becomes possible to tackle not only how achange in language has taken place through time,but also why it has taken place, thus addressingan old yet unresolved problem (95).

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Fig. 6. Languages spoken in Greenland, southern Africa (Khoisan), and Australiathat have gained labiodentals through language contact. (A) West Greenlandic hasacquired a labiodental through contact with Danish. (B) Some Khoisan languages havelabiodentals through contact with Germanic languages such as Afrikaans. (C) Twolanguages in Australia have labiodentals (3), Kunjen and Ngan'gikurrungkurr, the latterthrough contact with English.

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Our studies reveal that the range and probabil-ities of speech sounds found across languages arenot independent of large-scale changes in humanecology and biology, and thus we can no longer takefor granted that the diversity of speech has remained

stable since theemergenceofHomosapiens. As such,claims of language universals, deep linguistic history,and language evolution cannot rely on a uniformi-tarian assumption (96) without considering thewider anthropological context of language.

MethodsBiomechanical modeling of labiodentalproductionWe examined orofacial biomechanics usingthe ArtiSynth biomechanical modeling toolkit

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Fig. 7. Estimated probabilities of labiodental articulation across setsof historically related sounds in Indo-European. Sets are labeled bytraditional conventions in Indo-European studies (e.g., *p is the set thatgroups “p” in Italian with “f” in English; *gʷ is the set that groups Italian “v”with English “k”). (A) Extant distribution of labiodental (red) versusnonlabiodental (blue) articulation of cognate sounds (an open squaremeans that the actual articulation is unknown), mapped to one of two

phylogenies (104) used in our models (for the other phylogeny, seefig. S8). (B) Estimated labiodental probability as inferred by stochasticcharacter mapping (88–90). Languages and clades are ordered as in (A).(C) Traitgram of the simultaneous increase in labiodental probabilityacross correspondence sets. For zoomed-in displays on each individualcorrespondeme, see figs. S13 to S32; for estimates based on an alternativephylogeny (92), see fig. S33.

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(www.artisynth.org/) (26). ArtiSynth has previ-ously been used to examine how (biomechanical)articulatory effort influences speech variation(27, 29). Here, our model consists of a three-dimensional finite-element face (40) integratedwith rigid body skeletal structure for the max-illa, mandible, and hyoid bone (40, 97, 98) andconnected via point-to-point axial muscles. Thegeometries, material properties, and couplingare based on these source models. Details onthe setup and geometry of the bite models andthe articulations can be found in the supple-mentary text.All simulations feature an onset (narrowing/

constricting) phase from 0.0 to 0.2 s, followedby a sustain phase from 0.2 to 0.3 s, and then arelease phase from 0.3 to 0.5 s. The bilabialapproximant design has temporal targets forfour nodes, three on the edge of the lower lip(one medial and two closer to the corners ofthe mouth) and a medial one on the upper lip.These cause the lips to protrude slightly andcompress in a lip-rounding movement (similarto common productions of “w”). The medialnode targets were specified to be lower by1 mm and to be separated by 4 mm at maximalstricture (from 0.2 to 0.3 s). The bilabial stopdesign specifies that a single medial node onthe edge of the lower lip will move 1.5 mm pasta projected location on the upper lip (and hencelying in the upper lip), causing compressionof the upper and lower lips. Finally, the labio-dental fricative design has temporal targets forthree nodes. One of these specifies that a me-dial node on the edge of the lower lip moves tothe location of a reference vertex on the max-illa mesh situated at the point where the uppercentral incisors meet. To prevent contact be-tween the lower and upper lips during thismovement (which is especially important inthe edge-to-edge case), the upper lip is raised(and slightly advanced) by targets for two lat-erally situated nodes. Note that both conditionswere subject to the same set of relative inversetarget specifications to ensure full comparability.Also, note that the simulations were only of thearticulatory-biomechanical properties (i.e., aero-dynamics and acoustics were not simulated).

Worldwide association betweensubsistence type and labiodentals

Weused the phonological inventory data and thephonetic feature system from PHOIBLE Online(3). For the subsistence data, we used two sources:(i) the data from AUTOTYP (47) where speakerpopulations are classified as “hunting/fishing/gathering/foraging” versus “food production”based on the majority of the population’s dietuntil recently, and (ii) the list of languages spokenby hunter-gatherers (48) with the extra conditionthat all Australian societies are coded as hunter-gatherers. This list is meant by the compilers toexhaust the known hunter-gatherer languages ofthe world, and we therefore assumed that alllanguages that are in PHOIBLE but not in the listare spoken by food-producing societies. We referto this list asGMR. TheAUTOTYP list has positive

specifications for both subsistence types and isthereforemore reliable, whereas the GMR samplepossibly underestimates hunter-gatherer socie-ties. However, because GMR is about five timesthe size of AUTOTYP (N = 2030 versusN = 406),we performed all analyses on each list separately,assessing convergence of the evidence.We included the language family fromGlottolog

(99) and different regions (North America, SouthAmerica, Mesoamerica, Africa, Papua NewGuinea,western and southwesternEurasia, southand southeast Asia, Pacific, Australia, and northcentral Asia) from AUTOTYP (47) as random in-tercepts and random slopes. Language familywas preprocessed in two ways to improve con-vergence and interpretability: For the intercept,all language families represented by a singlelanguage were aggregated into a common dummycategory, and for the slope we performed the sameprocedure for all families that have uniform sub-sistence. Because of this coding decision, the levelsof the random intercept and slope of languagefamily did not always match. As a result, we didnot also model the correlation between the ran-dom intercept and the random slope.We carried out the statistical evaluation in a

Bayesian regression framework (100), usingweakly informative normal priors for the fixed(population-level) effects (mean = 0, SD = 5), ahalf–Student t distribution with three degreesof freedomand ad hoc large variance for the prioron the variance of the random (group-level) ef-fects, and a flat distribution on the correlationmatrix of the random effects for region. We ranfour chains with 4500 iterations each (out ofwhich 1000 were for warm-up). In all cases, allof the parameters showed that convergence hadbeen achieved asmeasured by the Gelman-Rubinstatistic (101). The posterior distributions for thetarget parameters for all three conditions (alldata, all data minus Australia, all data minusAustralia and nonlabiodental fricatives as con-trol instead of nonlabiodental segments) in thetwo datasets can be seen in figs. S4 and S5.The posterior predictive distributions of the

models adequately approximated the empiricaldistributions of labiodentals (see fig. S6), al-though they seemed to be underdispersed incontrast to the Poissonmodel. To evaluate wheth-er this potential difference in the distributionof the response variable could affect the overallconclusions, we compared the Poisson modelwith a Conway-Maxwell-Poisson (CMP) model[which allows for an extra parameter k con-trolling for the excess (k > 1) or deficit (k < 1) ofvariance in relation to the basic Poissonmodel,which is effectively k = 1]. We compared thesemodels in a frequentist framework because anefficient package is available for this purpose(102). Keeping in mind the limitations of modelselection in a M-open context (49), the Akaikeinformation criterion showed that the best fit ofGMRdata is CMP (followed by the Poissonmodelwith DAIC = 95.5), whereas in the AUTOTYP datathe basic Poisson model comes on top (followedclosely by CMPwith DAIC = 1.9). As expected, theCMPmodel revealed underdispersion (AUTOTYP:

k = 0.92, GMR: k = 0.53). However, in bothdatasets, the role of subsistence remained neg-ative, significant at a = 0.05. Furthermore,comparing the fitted values of the CMP and theBayesian Poisson model yielded a consistent pic-ture (see fig. S7).The analyses were performed with the R stat-

istical software version 3.4.3 (103). Code and dataare available at https://osf.io/gc6sd/.

Phylogenetic study

The supplementary text lists all correspondencesets used here, with cognate words that supporteach correspondence. See Fig. 7 for how thesemap to a phylogeny of Indo-European (104) andfig. S8 for an alternative phylogeny (92). Recon-structing the actual sound at the origin of anysuch set is nontrivial. Traditional attempts aredenoted by an asterisk (e.g., *gw for the {v, k, ...}set), and they rely on considerations of maxi-mum parsimony, coupled with a tacit assump-tion that the proto-articulations closely reflectwhat is reported in the earliest descriptions oflanguages such as Latin or Ancient Greek. How-ever, maximum-parsimonymethods are ill-suitedbecause sound changes can be completely re-versed within relatively short time spans. Forexample, the Germanic nasal “m” became “f”before “n” in early Old Swedish nafn (“name”)but reverted to namn soon after (105). More-over, even the earliest attestations are approxi-mately only half as old as Proto-Indo-European(92, 104), leaving substantial uncertainty in theearly history.We therefore took a fresh approach and

modeled sound change as continuous-timeMarkov chains (CTMC), allowing for reversalsand different transition rates between states.We fit CTMC models using the Markov chainMonte Carlo sampling (MCMC) implementedin BayesTraits version 2 (91). We then took thebest-fitting models to estimate ancestral valuesand to reconstruct values for each time intervalof Indo-European. For this we applied stochasticcharacter mapping (88–90), a method that hasproven valid for linguistic reconstruction else-where (106). We report details of parameterchoices, rate estimates, and model fits in thesupplementary text. An R (103) script perform-ing all analysis, as well as the input data, areavailable at https://osf.io/9hjcx/.

REFERENCES AND NOTES

1. S. C. Antón, R. Potts, L. C. Aiello, Evolution of early Homo: Anintegrated biological perspective. Science 345, 1236828(2014). doi: 10.1126/science.1236828; pmid: 24994657

2. W. T. Fitch, Empirical approaches to the study of languageevolution. Psychon. Bull. Rev. 24, 3–33 (2017). doi: 10.3758/s13423-017-1236-5; pmid: 28150125

3. S. Moran, D. McCloy, R. Wright, PHOIBLE Online (Max PlanckInstitute for Evolutionary Anthropology, Leipzig, 2014);https://phoible.org/.

4. B. Lindblom, S. Guion, S. Hura, S.-J. Moon, R. Willerman, Issound change adaptive? Riv. Linguist. 7, 5–37 (1995).

5. J. L. Bybee, in The Oxford Handbook of Language Evolution,M. Tallerman, K. R. Gibson, Eds. (Oxford Univ. Press, 2012),pp. 528–536.

6. A. Garrett, K. Johnson, in Origins of Sound Change:Approaches to Phonologization, A. C. L. Yu, Ed. (Oxford Univ.Press, 2013), pp. 51–97.

Blasi et al., Science 363, eaav3218 (2019) 15 March 2019 8 of 10

RESEARCH | RESEARCH ARTICLEon D

ecember 7, 2020

http://science.sciencem

ag.org/D

ownloaded from

7. W. Labov, Some principles of linguistic methodology. Lang.Soc. 1, 97–120 (1972). doi: 10.1017/S0047404500006576

8. R. Lass, Historical Linguistics and Language Change(Cambridge Univ. Press, 1997).

9. H. Hammarström, Linguistic diversity and language evolution.J. Lang. Evol 1, 19–29 (2016). doi: 10.1093/jole/lzw002

10. W. Croft, Typology and Universals (Cambridge Univ. Press,ed. 2, 2003).

11. C. F. Hockett, Distinguished lecture: F. Am. Anthropol. 87,263–281 (1985). doi: 10.1525/aa.1985.87.2.02a00020

12. C. L. Brace, Egg on the face, F in the mouth, and the overbite.Am. Anthropol. 88, 695–697 (1986). doi: 10.1525/aa.1986.88.3.02a00150

13. Y. Kaifu, Tooth wear and compensatory modification of theanterior dentoalveolar complex in humans. Am. J. Phys.Anthropol. 111, 369–392 (2000). doi: 10.1002/(SICI)1096-8644(200003)111:3<369:AID-AJPA6>3.0.CO;2-#;pmid: 10685038

14. Y. Kaifu, K. Kasai, G. C. Townsend, L. C. Richards, Toothwear and the “design” of the human dentition:A perspective from evolutionary medicine. Am. J. Phys.Anthropol. 122 (suppl. 37), 47–61 (2003). doi: 10.1002/ajpa.10329; pmid: 14666533

15. J. A. Kaidonis, Tooth wear: The view of the anthropologist.Clin. Oral Investig. 12 (suppl. 1), S21–S26 (2008).doi: 10.1007/s00784-007-0154-8; pmid: 17938977

16. A. Margvelashvili, C. P. E. Zollikofer, D. Lordkipanidze,T. Peltomäki, M. S. Ponce de León, Tooth wear anddentoalveolar remodeling are key factors of morphologicalvariation in the Dmanisi mandibles. Proc. Natl. Acad.Sci. U.S.A. 110, 17278–17283 (2013). doi: 10.1073/pnas.1316052110; pmid: 24101504

17. Y. Kaifu, Was extensive tooth wear normal in our ancestors?Anthropol. Sci. 108, 371–385 (2000). doi: 10.1537/ase.108.371

18. C. L. Brace, in The Biology of Occlusal Development,J. A. McNamara Jr., Ed. (Center for Human Growth andDevelopment, Ann Arbor, MI, 1977), pp. 179–209.

19. C. A. Deter, Gradients of occlusal wear in hunter-gatherersand agriculturalists. Am. J. Phys. Anthropol. 138, 247–254(2009). doi: 10.1002/ajpa.20922; pmid: 18773466

20. N. von Cramon-Taubadel, Global human mandibular variationreflects differences in agricultural and hunter-gatherersubsistence strategies. Proc. Natl. Acad. Sci. U.S.A. 108,19546–19551 (2011). doi: 10.1073/pnas.1113050108;pmid: 22106280

21. D. C. Katz, M. N. Grote, T. D. Weaver, Changes in humanskull morphology across the agricultural transition areconsistent with softer diets in preindustrial farming groups.Proc. Natl. Acad. Sci. U.S.A. 114, 9050–9055 (2017).doi: 10.1073/pnas.1702586114; pmid: 28739900

22. Y. V. Kuzmin, Origin of Old World pottery as viewed from theearly 2010s: When, where and why? World Archaeol. 45,539–556 (2013). doi: 10.1080/00438243.2013.821669

23. J. Dunne, A. M. Mercuri, R. P. Evershed, S. Bruni, S. di Lernia,Earliest direct evidence of plant processing in prehistoricSaharan pottery. Nat. Plants 3, 16194 (2016).pmid: 27991880

24. X. Wu et al., Early pottery at 20,000 years ago inXianrendong Cave, China. Science 336, 1696–1700 (2012).doi: 10.1126/science.1218643; pmid: 22745428

25. O. E. Craig et al., Earliest evidence for the use of pottery.Nature 496, 351–354 (2013). doi: 10.1038/nature12109;pmid: 23575637

26. J. E. Lloyd, I. Stavness, S. Fels, in Soft Tissue BiomechanicalModeling for Computer Assisted Surgery, Y. Payan, Ed.(Springer, Berlin, 2012), pp. 355–394.

27. I. Stavness, J. E. Lloyd, S. Fels, Automatic predictionof tongue muscle activations using a finite element model.J. Biomech. 45, 2841–2848 (2012). doi: 10.1016/j.jbiomech.2012.08.031; pmid: 23021611

28. R. M. Kirchner, An Effort Based Approach to ConsonantLenition (Routledge, 2001).

29. S. R. Moisik, D. Dediu, Anatomical biasing and clicks:Evidence from biomechanical modeling. J. Lang. Evol 2, 37–51(2017). doi: 10.1093/jole/lzx004

30. L. D. Vallino, B. Tompson, Perceptual characteristics ofconsonant errors associated with malocclusion. J. OralMaxillofac. Surg. 51, 850–856 (1993). doi: 10.1016/S0278-2391(10)80101-6; pmid: 8336222

31. M. C. MacDonald, How language production shapes languageform and comprehension. Front. Psychol. 4, 226 (2013).doi: 10.3389/fpsyg.2013.00226; pmid: 23637689

32. D. J. Napoli, N. Sanders, R. Wright, On the linguistic effects ofarticulatory ease, with a focus on sign languages. Language90, 424–456 (2014). doi: 10.1353/lan.2014.0026

33. J. Blevins, Evolutionary Phonology: The Emergence of SoundPatterns (Cambridge Univ. Press, 2004).

34. J. A. Utman, S. E. Blumstein, The influence of language onthe acoustic properties of phonetic features: A study of thefeature [strident] in Ewe and English. Phonetica 51, 221–238(1994). doi: 10.1159/000261978; pmid: 7938204

35. P. Ladefoged, I. Maddieson, The Sounds of the World’sLanguages (Blackwell, 1996).

36. K. N. Stevens, Acoustic Phonetics (MIT Press, 2000).37. I. Maddieson, Bilabial and labio-dental fricatives in Ewe. Stud.

Afr. Linguist. 35, 159–175 (2005).38. M. Kümmel, Konsonantenwandel: Bausteine zu einer Typologie

des Lautwandels und ihre Konsequenzen für die vergleichendeRekonstruktion (Reichert, Wiesbaden, 2007).

39. B. Gick, I. Stavness, C. Chiu, S. Fels, Categorical variation inlip posture is determined by quantal biomechanical-articulatory relations. Can. Acoust. 39, 178–179 (2011).

40. M. A. Nazari, P. Perrier, M. Chabanas, Y. Payan, Simulation ofdynamic orofacial movements using a constitutive lawvarying with muscle activation. Comput. Methods Biomech.Biomed. Engin. 13, 469–482 (2010). doi: 10.1080/10255840903505147; pmid: 20635263

41. K. N. Stevens, On the quantal nature of speech. J. Phonetics17, 3–45 (1989).

42. B. Bickel, in The Oxford Handbook of Linguistic Analysis,B. Heine, H. Narrog, Eds. (Oxford Univ. Press, ed. 2, 2015),pp. 901–923.

43. D. Dediu, R. Janssen, S. R. Moisik, Language is not isolatedfrom its wider environment: Vocal tract influences on theevolution of speech and language. Lang. Commun. 54, 9–20(2017). doi: 10.1016/j.langcom.2016.10.002

44. L. M. Lavoie, Consonant Strength: Phonological Patterns andPhonetic Manifestations (Routledge, 2001).

45. V. Eshed, A. Gopher, I. Hershkovitz, Tooth wear and dentalpathology at the advent of agriculture: New evidence fromthe Levant. Am. J. Phys. Anthropol. 130, 145–159 (2006).doi: 10.1002/ajpa.20362; pmid: 16353225

46. R. J. Hinton, Form and patterning of anterior tooth wearamong aboriginal human groups. Am. J. Phys. Anthropol. 54,555–564 (1981). doi: 10.1002/ajpa.1330540409;pmid: 7234993

47. B. Bickel et al., The AUTOTYP Typological Databases, Version0.1.0 (GitHub Repository, 2017); https://github.com/autotyp.

48. T. Güldemann, P. McConvell, R. A. Rhodes, Eds., TheLanguage of Hunter-Gatherers: Global and HistoricalPerspectives (Cambridge Univ. Press, 2019).

49. Y. Yao, A. Vehtari, D. Simpson, A. Gelman, Using stacking toaverage Bayesian predictive distributions. Bayesian Anal. 13,917–1007 (2018). doi: 10.1214/17-BA1091

50. E. Gasser, C. Bowern, in Proceedings of the 2013 AnnualMeeting on Phonology (2014); https://journals.linguisticsociety.org/proceedings/index.php/amphonology/article/view/17.

51. A. Butcher, in Speech Production: Models, PhoneticProcesses, and Techniques, J. Harrington, M. Tabain, Eds.(Psychology Press, 2006), pp. 187–210.

52. B. Bickel, J. Nichols, in The Language of Hunter-Gatherers:Global and Historical Perspectives, T. Güldemann,P. McConvell, R. A. Rhodes, Eds. (Cambridge Univ. Press,2019), chapter 3.

53. C. Bowern, Correlates of language change in hunter-gathererand other ‘small’ languages. Lang. Linguist. Compass 4,665–679 (2010). doi: 10.1111/j.1749-818X.2010.00220.x

54. P. O. Pedersen, Dental investigations of Greenland Eskimos.Proc. R. Soc. Med. 40, 726–732 (1947). pmid: 19993661

55. A. F. Clement, S. W. Hillson, I. de la Torre, G. Townsend, Toothuse in Aboriginal Australia. Archaeol. Int. 11, 37–40 (2009).

56. A. F. Clement, S. W. Hillson, Intrapopulation variation inmacro tooth wear patterns—A case study from Igloolik,Canada. Am. J. Phys. Anthropol. 149, 517–524 (2012).doi: 10.1002/ajpa.22153; pmid: 23125036

57. D. Botha, M. Steyn, Dental health of the late 19th and early20th century Khoesan. Homo 66, 187–202 (2015).doi: 10.1016/j.jchb.2015.02.004; pmid: 25882044

58. J. Rischel, Topics in West Greenlandic Phonology: RegularitiesUnderlying the Phonetic Appearance of Word Forms in aPolysynthetic Language (Akademisk, Copenhagen, 1974).

59. M. P. Lewis, G. F. Simons, C. D. Fennig, Ethnologue:Languages of the World (SIL International, Dallas, ed. 19,2016).

60. L.-J. Dorais, Inuit Uqausiqatigiit: Inuit Languages and Dialects(Arctic College, Nunatta Campus, 1990).

61. M. E. Krauss, in Native Languages of the Americas,T. A. Sebeok, Ed. (Springer, 1976), pp. 175–281.

62. S. Kleinschmidt, Grammatik der grönländischen Sprache(Reimer, Berlin, 1851).

63. C. W. Schultz-Lorentzen, A Grammar of the West GreenlandLanguage (Reitzels, Copenhagen, 1945).

64. M. Swadesh, in Linguistic Structures of North America,H. Hoijer et al., Eds. (Viking Fund Publications inAnthropology, New York, 1946), vol. 7, pp. 30–54.

65. M. D. Fortescue, West Greenlandic (Croom Helm, London, 1984).66. A. Salas et al., The making of the African mtDNA landscape.

Am. J. Hum. Genet. 71, 1082–1111 (2002). doi: 10.1086/344348; pmid: 12395296

67. T. Güldemann, E. D. Elderkin, in Khoisan Languages andLinguistics, M. Brenzinger, C. König, Eds. (Köppe, Cologne,2003), pp. 15–52.

68. D. M. Beach, The Phonetics of the Hottentot Language(Heffer, Cambridge, 1938).

69. W. H. G. Haacke, in The Khoesan Languages, R. Vossen, Ed.(Routledge, 2013), pp. 325–346.

70. A. Traill, A! Xóõ Dictionary (Köppe, Cologne, 1994).71. P. Dickens, English-Ju/’hoan Ju/’hoan-English Dictionary

(Köppe, Cologne, 1994), vol. 8.72. D. A. Hunziker, E. Hunziker, H. C. Eaton, A Description of

the Phonology of the Sandawe Language (SIL ElectronicWorking Papers, 2008), pp. 1–81.

73. H. Eaton, Sandawe. J. Int. Phon. Assoc. 36, 235–242 (2006).doi: 10.1017/S0025100306002647

74. B. A. Sommer, Kunjen Phonology: Synchronic and Diachronic(Australian National University, 1969).

75. N. Reid, thesis, Australian National University (1990).76. W. G. Hoddinott, F. M. Kofod, The Ngankikurungkurr Language

(Daly River Area, Northern Territory) (Australian NationalUniversity, 1988).

77. I. V. Fortson, Indo-European Language and Culture: AnIntroduction (Wiley-Blackwell, 2010).

78. G. Cardona, Pān.ini (Mouton, The Hague, 1976).79. J. Gonda, Vedic Ritual: The Non-Solemn Rites (Brill, Leiden,

1980).80. V. Haas, Geschichte der hethitischen Religion (Brill, Leiden,

1994).81. J. R. Lukacs, B. E. Hemphill, Traumatic injuries of prehistoric

teeth: New evidence from Baluchistan and Punjab Provinces,Pakistan. Anthropol. Anz. 48, 351–363 (1990).pmid: 2076032

82. O. Vyslozil, R. Slavicek, Vergleichsuntersuchung an künstlichdeformierten und undeformierten Schädeln. Ann.Naturhistorisch. Mus. Wien 201A, 245–274 (2001).

83. J. R. Lukacs, Dental pathology and nutritional patterns ofSouth Asian megalith-builders: The evidence from Iron AgeMahurjhari. Proc. Am. Philos. Soc. 125, 220–237 (1981).pmid: 11620764

84. A. Wilson, Machines, power and the ancient economy.J. Roman Stud. 92, 1–32 (2002). doi: 10.1017/S0075435800032135

85. M. J. T. Lewis, Millstone and Hammer (University of Hull, 1997).86. Ö. Wikander, Ed., Handbook of Ancient Water Technology

(Brill, Leiden, 2000).87. E. Chekalin et al., Changes in biological pathways during

6,000 years of civilization in Europe. Mol. Biol. Evol. 36,127–140 (2019). doi: 10.1093/molbev/msy201;pmid: 30376122

88. R. Nielsen, Mapping mutations on phylogenies. Syst. Biol. 51,729–739 (2002). doi: 10.1080/10635150290102393;pmid: 12396587

89. J. P. Huelsenbeck, R. Nielsen, J. P. Bollback, Stochasticmapping of morphological characters. Syst. Biol. 52, 131–158(2003). doi: 10.1080/10635150390192780; pmid: 12746144

90. L. J. Revell, phytools: An R package for phylogeneticcomparative biology (and other things). Methods Ecol. Evol.3, 217–223 (2012). doi: 10.1111/j.2041-210X.2011.00169.x

91. M. Pagel, A. Meade, BayesTraits V2.0 (2014); www.evolution.rdg.ac.uk/BayesTraits.html.

92. W. Chang, C. Cathcart, D. Hall, A. Garrett, Ancestry-constrained phylogenetic analysis supports Indo-Europeansteppe hypothesis. Language 91, 194–244 (2015).doi: 10.1353/lan.2015.0005

93. A. M. S. McMahon, Understanding Language Change(Cambridge Univ. Press, 1994).

94. W. Labov, Principles of Linguistic Change: Social Factors(Blackwell, 2001).

Blasi et al., Science 363, eaav3218 (2019) 15 March 2019 9 of 10

RESEARCH | RESEARCH ARTICLEon D

ecember 7, 2020

http://science.sciencem

ag.org/D

ownloaded from

95. U. Weinreich, M. Herzog, W. Labov, in Directions for HistoricalLinguistics: A Symposium, W. Lehmann, Y. Malkiel, Eds.(Univ. of Texas Press, 1968), pp. 95–195.

96. F. J. Newmeyer, in The Transition to Language, A. Wray, Ed.(Oxford Univ. Press, 2002), pp. 359–375.

97. I. Stavness, J. E. Lloyd, Y. Payan, S. Fels, Coupled hard-softtissue simulation with contact and constraints applied tojaw-tongue-hyoid dynamics. Int. J. Numer. Methods Biomed.Eng. 27, 367–390 (2011). doi: 10.1002/cnm.1423

98. I. Stavness, M. A. Nazari, P. Perrier, D. Demolin, Y. Payan,A biomechanical modeling study of the effects of the orbicularisoris muscle and jaw posture on lip shape. J. Speech Lang.Hear. Res. 56, 878–890 (2013). doi: 10.1044/1092-4388(2012/12-0200); pmid: 23811472

99. H. Hammarström, R. Forkel, M. Haspelmath, S. Nordhoff,Glottolog 2.3 (Max Planck Institute for EvolutionaryAnthropology, Leipzig, 2014); http://glottolog.org.

100. P.-C. Bürkner, brms: An R package for Bayesian multilevelmodels using Stan. J. Stat. Softw. 80, 1–28 (2017).doi: 10.18637/jss.v080.i01

101. A. Gelman, D. B. Rubin, Inference from iterative simulationusing multiple sequences. Stat. Sci. 7, 457–472 (1992).doi: 10.1214/ss/1177011136

102. A. Magnusson et al., glmmTMB: Generalized Linear MixedModels Using Template Model Builder, R package version0.0.2 (Github Repository, 2016); https://github.com/glmmTMB.

103. R Core Team, R: A Language and Environment for StatisticalComputing (R Foundation for Statistical Computing, Vienna,2018); www.R-project.org.

104. R. Bouckaert et al., Mapping the origins and expansion ofthe Indo-European language family. Science 337,957–960 (2012). doi: 10.1126/science.1219669;pmid: 22923579

105. A. Noreen, Altschwedische Grammatik mit Einschluss desAltgutnischen (Niemeyer, Halle, 1904).

106. M. Widmer, S. Auderset, J. Nichols, P. Widmer, B. Bickel,NP recursion over time: Evidence from Indo-European.Language 93, 799–826 (2017). doi: 10.1353/lan.2017.0058

ACKNOWLEDGMENTS

We thank A. Margvelashvili for helpful advice on thepaleoanthropological literature, Y. Kaifu for the Jomon skullimage, D. Frayer for the Upper Paleolithic skull image,A. D. Soficaru and M. Constantinescu for the Mesolithic skullimage, and K. Wiltschke-Schrotta for the Bronze Age skull image.S.R.M. thanks I. Stavness, S. Fels, J. Lloyd, P. Anderson,A. Sanchez, and B. Gick, among many others, for the use ofArtiSynth. We also thank C. Anderson, C. Bowern, C. Cathcart,R. Corruccini, N. von Cramon-Taubadel, T. Güldemann,P. Heggarty, J. Mansfield, D. McCloy, H. Nakagawa, E. Round,S. Wichmann, R. Wright, and C. Zollikofer for helpful commentsand suggestions. The views expressed in this article are those of

the authors and do not necessarily reflect the views of theacknowledged, funding agencies, or the authors’ institutions.Funding: Supported by NWO VIDI grant 276-70-022, an EURIASfellowship 2017–2018, and an IDEXLyon Fellowship 2018–2021(D.D.) and by a subsidy of the Russian Government to support theProgramme of Competitive Development of Kazan FederalUniversity (D.E.B.). Author contributions: D.E.B., S.M., and B.B.conceived the research; D.E.B., D.D., and P.W. surveyed thepaleoanthropological literature; S.R.M. conducted thebiomechanical simulations; S.M. collected the phonologicalinventory data, processed it for statistical analysis, andperformed the qualitative analysis with D.E.B.; D.E.B. performedthe statistical analyses of worldwide data; B.B. and P.W. undertookthe phylogenetic analysis; and all authors discussed the resultsand contributed to the final version of the paper. Competinginterests: The authors declare no competing interests. Data andmaterials availability: All data are available in the main text orthe supplementary materials.

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www.sciencemag.org/content/363/6432/eaav3218/suppl/DC1Supplementary TextFigs. S1 to S33References (107–143)

26 September 2018; accepted 6 February 201910.1126/science.aav3218

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Human sound systems are shaped by post-Neolithic changes in bite configurationD. E. Blasi, S. Moran, S. R. Moisik, P. Widmer, D. Dediu and B. Bickel

DOI: 10.1126/science.aav3218 (6432), eaav3218.363Science 

, this issue p. eaav3218Sciencehuman bite configuration owing to changes in dietary and behavioral practices since the Neolithic.change in the sound systems of the world's languages. Spoken languages have thus been shaped by changes in thespeech sciences, historical linguistics, and methods from evolutionary biology to provide evidence for a Neolithic global

combined paleoanthropology,et al.conjectured that these sounds were a recent innovation in human language. Blasi populations makes consonants produced with lower lip and upper teeth (''f'' and ''v'' sounds) hard to produce. He thus

In 1985, the linguist Charles Hockett proposed that the use of teeth and jaws as tools in hunter-gathererThe first fricatives

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