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Prehistoric Dental Disease and the Dietary Shift from Cactus to Cultigens in Northwest Mexico

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Differences in dental health of prehistoric human groups are commonly attributed to specific subsistence practices, whereby food foragers generally have lower incidence of dental disease than agriculturalists. Dental health was assessed on a sample
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  Prehistoric Dental Diseaseand the Dietary Shift from Cactusto Cultigens in Northwest Mexico J. T. WATSON* Department of Anthropology, Indiana University-Purdue University Indianapolis, 425 University Boulevard, 413 Cavanaugh Hall, Indianapolis, IN 46202, USA ABSTRACT Differences in dental health of prehistoric human groups are commonly attributed to specificsubsistence practices, whereby food foragers generally have a lower incidence of dentaldiseasethanagriculturalists.Dentalhealthwasassessedonasampleof135humanskeletonsfrom northwest Mexico that date to the Early Agricultural period (1600 BC–AD 200), whichcoincides with the initial introduction of domesticated cultigens into the region c. 2000 BC.High rates of dental caries (13.5%) and antemortem tooth loss (17.6%) encountered in theseprehistoric forager-farmers from the Sonoran Desert were determined to be the result of theconsumption of highly cariogenic local wild resources such as cactus. These patterns maskthe degree of reliance on agriculture in the area and highlight the importance of constructinglocal nutritional histories to better understand the diversity of human diets and their relation-ships to health and disease. Copyright    2007 John Wiley & Sons, Ltd. Key words:  agriculture; antemortem tooth loss; cactus; caries; Sonoran Desert Introduction Dental caries epidemiology has proven to be oneof the most effective mechanisms for reconstruct-ing the diet of past populations (Hillson, 2001).Caries is a disease process characterised by thefocal demineralisation of dental hard tissuesresulting from acid production by bacterialfermentation of dietary carbohydrates (Larsen et al ., 2001). The corrosive action of these organicacidscontributestotheprogressivedestructionofthe tooth surface and can lead to perforation intothe pulp chamber, which can also causeinfection,abscessing, and eventual tooth loss. Antemortemtooth loss is an important factor to considerwhen addressing caries epidemiology in skeletalpopulations. The rate of antemortem tooth loss(AMTL) has also been documented to increasewith caries rates among archaeological samples(Hillson, 2001; Larsen, 2002). Rates of dentaldisease reflecting overall differences in diet aregenerally lower among food foragers than inagriculturalists (Turner, 1979; Larsen, 1981,2002; Martin  et al ., 1985; Hillson, 2001; Larsen et al ., 2001).The aim of this study is to assess the impact ofthe transition to agriculture on oral health in theSonoran Desert, and the degree of reliance ondomesticated cultigens, using a comprehensiveskeletal sample from the site of La Playa, locatedin northwest Me´ xico. The sample is composed ofprehistoric forager-farmers dating to the EarlyAgricultural period (1600 BC–AD 200). Thefrequencies of caries and AMTL were comparedover the course of the Early Agricultural period,with later temporal periods, and between regionsof the Desert West to assess diversity in dietcomposition over time and by local ecologies.Differences and effects of age and sex were alsoInternational Journal of Osteoarchaeology Int. J. Osteoarchaeol.  18 : 202–212 (2008)Published online 22 May 2007 in Wiley InterScience(www.interscience.wiley.com) DOI: 10.1002/oa.917 * Correspondence to: Department of Anthropology, IndianaUniversity-Purdue University Indianapolis, 425 University Boule-vard, 413 Cavanaugh Hall, Indianapolis, IN 46202, USA.e-mail: watsonjt@iupui.edu Copyright # 2007 John Wiley & Sons, Ltd.  Received 26 September 2005 Revised 1 September 2006 Accepted 8 October 2006  considered in order to elucidate intra-populational differences during this time period.According to traditional understandings of pre-historic oral health epidemiology: (1) frequenciesof caries and AMTL should increase over time atLa Playa as agricultural importance increases; and(2) these frequencies should be intermediatebetween those of foragers and fully agriculturalcommunities, reflecting the mixed subsistenceeconomy practiced at La Playa.Excavations at La Playa, Sonora, Me´ xico(Figure 1) over the past ten years have produceda suitably large (  n ¼ 246) and temporally repre-sentative (2000 BC–AD 500) skeletal sample toaddress some of the archaeological questionsabout the transition to agriculture in the SonoranDesert. The La Playa skeletal sample is evenlydistributed between sexes, across age groups, andhas no identifiable patterns of distribution withinthe site or by burial treatment (Table 1). Inaddition, 26 radiocarbon dates from inhumationburials, ranging from 3720  320 to 1530  40 b.p. (3100 BC–AD 620), document that thesample spans the entire course of the EarlyAgricultural period. A subsample of 98 skeletonscould further be assigned to either the San Pedroor Cienega phases according to their verticalplacement in the floodplain of the site (Watson,2005).The early agriculturalists at La Playa exhibitgood overall skeletal health, suggestingthat there Figure 1. Location of La Playa.Table 1. DistributionofLaPlayaskeletalsample( n  ¼ 135)Individuals( n  )Teeth( n  )Alveolarsegments ( n  )SexMale 66 923 967Female 61 973 951NA 8 49 34Age groupYoung adult 8 134 75Adult 39 548 509Mature 30 440 426Old adult 58 823 942PhaseSan Pedro 41 487 535Cienega 57 959 936 Copyright # 2007 John Wiley & Sons, Ltd.  Int. J. Osteoarchaeol.  18 : 202–212 (2008)DOI: 10.1002/oa  From Cactus to Cultigens  203  was very little infectious disease present andnutrition was adequate during both developmentand adulthood (Watson  et al ., 2006). Trauma wasthe most common pathology observed in theskeletal sample – most of which were related toviolence – and thus suggesting that some level ofconflict was present in these early settledcommunities (Watson  et al ., 2006). The La Playaburials represent the largest, earliest and mostcomprehensive skeletal sample in the DesertWest and provide the ideal instrument to test thehealth consequences of the adoption of agricul-ture in the Sonoran Desert. The Early Agricultural period  Recent radiocarbon dates from maize cobsrecovered from deeply buried floodplain sitesin southern Arizona have pushed back the arrivalof domesticated cultigens in the North AmericanDesert West to approximately 2000 BC (Mabry,2005). However, changes in subsistence patternsassociated with the adoption of agriculture arenot identified in the area until approximately1600 BC, marking the beginning of the EarlyAgricultural period (1600 BC–AD 200). Thetiming of these events indicates that localforaging groups had been exposed to, and wereprobably experimenting with, maize for at leastseveral hundred years prior to establishingpermanent settlements (Huckell, 1995; Diehl,2005). Archaeological evidence associated withthe Early Agricultural period suggests that, oncesettled, although these groups became reliant onmaize to some extent, they probably practiced amixed subsistence economy equally based onforagingwildresourcesandfarmingdomesticatedcultigens (Roth & Wellman, 2001; Watson,2005). This period is divided into two phasesbased upon changes in the archaeological recordthat reflect a general trend in increasing localinvestment: the San Pedro phase (c. 1600–800BC) and the Cienega phase (800 BC–AD 200).San Pedro phase sites and their characteristicsvary according to their location on the landscape.San Pedro sites located high on valley bajadasrepresent resource exploitation localities (Roth,1996), whereas sites located on the valleyfloodplain represent farming settlements andare generally characterised by small, shallowdomestic depressions (‘pit’ structures), largeextramural storage pits, ubiquitous groundstone, and expedient lithic technology (Huckell,1995; Roth & Wellman, 2001). Maize remains areubiquitous from lowland San Pedro phase sites insouthern Arizona (Mabry, 1999; Gregory, 2001;Diehl, 2005), and evidence for the earliestirrigation canals in the Desert West have beendocumented in the Tucson Basin by about 1200BC (Ezzo & Deaver, 1998; Mabry, 1999). Theseearly canals demonstrate that San Pedro groupswere using technologies designed for intensifyingagricultural production, butthe diversityinherentin San Pedro phase sites suggests that bothagriculture and wild plant collection were equallycritical parts of the whole system (Huckell, 1995;Roth, 1996).Cienega phase sites appear to represent anincreased complexity in cultural characteristicsfrom those defined for the San Pedro phase. Thisphase is characterised by a greater local invest-mentandincreasedsedentism,largervillages,andgenerally including deeper and larger subterra-nean houses, increased size and ubiquity ofstorage features, increased technological com-plexity in artefacts (especially in ground- andchipped-stone assemblages), and the establish-ment of both local and long-distance commercenetworks(Mabry et al .,1997).Inaddition,thefirstformal ceramic tradition ( Incipient Plainware )appears during the Cienega phase (Heidke,1999).The sum of the archaeological evidencesuggests that the Early Agricultural periodrepresents roughly 2000 years of relative dietarystability in the Sonoran Desert, during whichtime populations grew larger and more sedentary,resulting in an intensified exploitation of theexisting mixed subsistence strategy. Schurr &Gregory (2002) identified a discrete example ofthis increase in local investment as a dramaticincrease in maize ubiquity from storage featuresover a 200-year period during the middle part ofthe Cienega phase at Los Pozos. They alsodocumented concomitant increases in the ubi-quity of every other plant resource in thesestorage features, including seeds, grasses, cactiand mesquite: a trend mirrored by the increased Copyright # 2007 John Wiley & Sons, Ltd.  Int. J. Osteoarchaeol.  18 : 202–212 (2008)DOI: 10.1002/oa 204  J. T. Watson  presence of faunal remains, flaked stone andfire-cracked rock from middens (Schurr &Gregory, 2002). Adams (1998) found similarparallels in groundstone assemblages from EarlyAgricultural sites in the Tucson Basin. Sheobserved increases in the ubiquity and complex-ity of ground-stone artefacts from San Pedro toCienega phase sites, which she interpreted as asign of intensified mechanical processing ofexisting resources (Adams, 1998). Steadyincreases in the exploitation of all resourcesduring the Early Agricultural period reflect astable mixed economy, in which exploitationintensified as villages grew larger.A small number of studies have examined theoral health of these early agriculturalists in theSonoran Desert (Minturn & Lincoln-Babb, 1995,2001; Minturn  et al ., 1998; McClelland, 2005).However, reconstructing diet and subsistencestrategies of these Early Agricultural communitieshas been restricted to some extent by aconspicuous lack of human remains from thesesites. To date, 13 Early Agricultural sites fromsouthern Arizona have produced a total of 102human burials; the largest sample attributable toone site is 24 individuals (Minturn & Lincoln-Babb, 1995, 2001; Minturn  et al ., 1998; Wellman,2000; McClelland, 2005). Studies of these smallburial samples are limited and severely reduce theability of researchers to produce accurateinterpretations of the diet and health of theseearly agriculturalists. Additionally, very little canbe said about dietary change over the 1800-yearspan of the Early Agricultural period because of afurther lack of San Pedro phase burials (total  n ¼ 17). In spite of their restricted nature, each ofthese studies identifies patterns of skeletal andoral health that appear to support the generalassertion that these groups practiced a mixedsubsistence economy (Minturn & Lincoln-Babb,1995, 2001; McClelland, 2005). Materials The sample analysed in this study is part of theosteological collection held in the repository atthe Centro Instituto Nacional de Antropologı´ a eHistoria in Hermosillo, Sonora, Me´ xico (INAH).Dental segments of maxilla, mandibles andcomplete crania of a total of 135 adult individualsfrom the La Playa site were included in this study.Table 1 demonstrates that the La Playa sample isevenly distributed by sex, age, and between thetwo archaeological phases of the Early Agricul-tural period. The condition of the dentitions inthe sample varies widely, from individualsrepresented by one loose tooth to an individualwith a complete maxilla and mandible, butentirely edentulous.Sex was estimated for individuals in the LaPlaya sample by examining the classic macro-scopic aspects of the pelvis and/or cranium(Buikstra & Ubelaker, 1994). This resulted in aneven number of males (  n ¼ 66) and females(  n ¼ 61) in the sample, with eight individuals ofindeterminatesex.Agewasestimatedfor adultsinthe sample using relative rates of dental attritionfollowing generalised standards established byBrothwell (1989). There were no statisticallysignificant differences in the distribution of eachsex across age groups ( x 2 ¼ 2.269, df ¼ 3,  n ¼ 127,  P ¼ 0.518,  V  ¼ 0.134), indicating thatobservations can be made between sexes withoutconfounding effects of age. A subsample of 98 ofthe La Playa skeletons (San Pedro  n ¼ 41;Cienega  n ¼ 57) have been assigned to anarchaeological phase based on radiocarbon datesand geomorphological analysis (Watson, 2005).There were no statistically significant differencesin the distribution of each sex between phases( x 2 ¼ 0.217, df ¼ 1,  n ¼ 95,  P ¼ 0.641), orbetween individuals of either phase across agegroups ( x 2 ¼ 1.782, df ¼ 3,  n ¼ 98,  P ¼ 0.619, V  ¼ 0.135), indicating that observations can bemade between archaeological phases withoutconfounding effects of sex or age. Methods Dental data were recorded for each individual inthe La Playa skeletal sample with at least onedental segment present. These data included thenumber and type of observed dental segments perindividual (tooth and/or alveolar portion); con-dition of each dental segment (tooth present, orante- or post-mortem loss); number of caries pertooth; and nature and location of the caries Copyright # 2007 John Wiley & Sons, Ltd.  Int. J. Osteoarchaeol.  18 : 202–212 (2008)DOI: 10.1002/oa  From Cactus to Cultigens  205  lesions following Moore & Corbett (1971).Carious lesions were identified macroscopicallywith a dental probe, and a magnifying glass whennecessary, a methodology that shows littleinterobserver error and has been shown to yieldreliable results (Rudney  et al ., 1983). Althoughpreservation of the skeletal remains in the LasPlaya sample is highly variable, the teethobserved for this study are in excellent condition,providing accurate identification of cariouslesions. Antemortem tooth loss (AMTL) wassimply recorded as present or absent as indicatedby partial or complete resorption of the alveolus(Buikstra & Ubelaker, 1994).Although many researchers identify theimportance of recording and comparing cariesepidemiology, debates continue over propermethods for recording, quantifying and inter-preting caries in samples of skeletons fromarchaeological contexts (Lukacs, 1995; Erdal &Duyart, 1999; Hillson, 2001). Archaeologicalskeletal samples are plagued by problems ofdifferential preservation of teeth and antemortemtooth loss, some of which may have been lost as adirect result of caries. In addition, the differencein significance and comparability of cariesprevalence (number of individuals with at leastone carious lesion) versus frequency (number ofcaries per individual) has led to problems ofinterpretation.The conventional method used for calculatingcaries frequencies in archaeological samples hasbeen the ‘observed caries rate’ (Lukacs, 1995),calculated by dividing the total number of cariousteeth by the total number of observed teeth(multiplied by 100). The observed caries rate hasbeen criticised by a number of researchers for itsinabilitytoaccuratelyreflecttherealfrequencyofdental caries in a sample because of ante- andpost-mortem tooth loss, and differential suscepti-bility to caries and loss between anterior andposterior teeth (Lukacs, 1995; Erdal & Duyart,1999). Several alternatives and correction pro-cedures have been proposed to account for theseinaccuracies. The caries correction proceduresproposed by Lukacs (1995) and Erdal & Duyart(1999) are of particular interest for the presentstudy, and will be used in conjunction to addressthe influence of differential preservation, AMTL,and differential tooth susceptibility.The ‘Corrected Caries Factor’ was developedby Lukacs (1992) for his study of Harrapan dentalhealth, to control for the effects of AMTL on thecalculation of caries frequencies in skeletalsamples. It specifically attempts to correct fortheproportionofteeththatwerelostasthedirectresult of caries, creating pulp exposure, infection,and subsequent tooth loss (Lukacs, 1995). Theresulting corrected caries rate represents thefrequency of caries per individual in a skeletalsample, accounting for caries within lost teeth.Erdal & Duyart (1999) took this even further andproposed a ‘Proportional Correction Factor’,designed to consider the expected ratio betweenanterior and posterior teeth to account for theeffects of post-mortem tooth loss in skeletalsamples. Caries frequencies are calculated separ-ately for anterior and posterior teeth, accordingto Lukacs (1995). The anterior caries rate is thenmultiplied by 3/8 (0.375) or the ratio of anteriorto total tooth number for a quadrant of jaws, andthe posterior caries rate is multiplied by 5/8(0.625) or the ratio of posterior to total toothnumber for a quadrant of jaws (Erdal & Duyart,1999). The results are added together to gain thefinal corrected caries rate that best accounts forantemortem and post-mortem tooth loss inrelation to caries aetiology.Proportions of individuals with at least onecarious lesion or exhibiting evidence of AMTLwere compared between sexes and archaeologicalphases by means of the chi-square test. Thefrequencies of AMTL and caries were comparedbetween sexes and archaeological phases bymeans of Student’s  t -test. All statistical tests wereperformed using the SPSS 11.5 for Windowsprogram (Statistical Package for Social Sciences,Chicago, IL). Results  Prevalence of individuals withoral pathology The proportion of individuals within the La Playaskeletal sample that exhibit at least one cariouslesion reached 61.9%. This pattern was similarbetweenbothmales(63.3%)andfemales(63.8%)( x 2 ¼ 0.003, df ¼ 1,  n ¼ 118,  P ¼ 0.959). The Copyright # 2007 John Wiley & Sons, Ltd.  Int. J. Osteoarchaeol.  18 : 202–212 (2008)DOI: 10.1002/oa 206  J. T. Watson

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