Article pp.196-204 du Vol.26 n°3-4 (2014)

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NOTE /NOTE

Health and sexual dimorphism at Ban Non Wat: The effects

of the intensification of agriculture in prehistoric Southeast Asia*

État de santé et dimorphisme sexuel à Ban Non Wat: effets de l

’

intensification de l

’

agriculture dans l

’

Asie du Sud-Est préhistorique

A.-L. Clark

Received: 6 May 2014; Accepted: 10 September 2014

AbstractThe intensification of agriculture is regarded as a major transition in human prehistory that affected key aspects of the physical and cultural environments over time. One of the ways to measure human adaptation to this transition is through sexual dimorphism in body size. Previ- ous bioarchaeological studies have shown that when the difference in body size between males and females decreases over time, general population health also declines. Using a biocultural approach, this PhD research project examines health and sexual dimorphism in body size during the intensification of rice agriculture at the prehistoric site of Ban Non Wat, Northeast Thailand (1750-420 b.c.).

Based on a broad context of bioarchaeological research, three hypotheses were developed and tested using a sample of adults (n=190). Sexual dimorphism was quantified using bone lengths and breadths, and health was analysed using two indicators of non-specific systemic stress (linear enamel hypoplasia and subperiosteal new bone formation).

Contrary to expectations, the results indicated that when sexual dimorphism decreased over time, health improved.

Temporal changes in sexual dimorphism were attributed to greater variation in female body size, whereas male body size remained stable. No sex-specific differences were found in either indicator of non-specific systemic stress.

This research suggests that sexual dimorphism in body size is a complex, but useful, measure of human biocultural adaptation, but not necessarily of general population health.

KeywordsBioarchaeology · Non-specific indicators of stress · Northeast Thailand · Body size · Enamel defects · Periosteal new bone formation

Résumé L’intensification de l’agriculture est considérée comme une transition majeure de la Préhistoire, qui a eu un impact diachronique sur des aspects majeurs des envi- ronnements culturels et physiques. L’analyse du dimorphisme sexuel de stature est une des façons d’estimer l’adaptation humaine à cette transition. De précédentes anal- yses bioarchéologiques ont démontré que quand la diffé- rence de stature entre les hommes et les femmes décroit au cours du temps, l’état de santé général des populations décline. A travers une approche bioculturelle, cette thèse examine la santé et le dimorphisme sexuel de stature pen- dant l’intensification de l’agriculture du riz sur le site pré- historique de Ban Non Wat, dans le Nord-Est de la Thaï- lande (1750-420 bc).

Sur la base d’un large contexte bioarchéologique, trois hypothèses ont été développées et testées en utilisant un échantillon de 190 individus adultes. Le dimorphisme sexuel a été quantifié en utilisant les longueurs et les largeurs des os, et l’état de santé a été analysé en utilisant deux indicateurs de stress systémiques non-spécifiques (les hypoplasies linéaires de l’émail et les formations osseuses subpériostées).

Contrairement à ce que l’on pouvait attendre, les résul- tats indiquent que quand le dimorphisme sexuel diminue au cours du temps, l’état de santé des populations s’amé- liore. Les changements diachroniques du dimorphisme sexuel sont attribués à une plus grande variabilité de la stature des femmes, alors que celle des hommes était stable. Aucun des deux indicateurs de stress systémiques non- spécifiques n’a montré de différence liée au sexe. Cette recherche suggère que le dimorphisme sexuel de stature est une mesure certes complexe, mais utile, de l’adaptation bioculturelle humaine, mais pas nécessairement de l’état de santé général.

Mots clésBioarchéologie · Indicateurs de stress non spécifiques · Thaïlande du Nord-Est · Stature · Défauts de l’émail · Formation osseuse périostée

A.-L. Clark (*)

Department of Anatomy, University of Otago, P.O. Box 913, Dunedin 9054, New Zealand

e-mail : angela.clark@anatomy.otago.ac.nz

*Cette thèse a reçu le prix de la Société d’Anthropologie de Paris 2013 DOI 10.1007/s13219-014-0113-2

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Introduction

The intensification of agriculture is one of the most significant transitional events experienced by Homo sapiens [1]. This prehistoric period is ideal for assessing biocultural adaptations of past populations to major changes in their physical and cultural environments. In the literature, the effects of the intensification of agriculture are well established in Europe and the Americas [2-5]. These studies commonly report a decline in general health, which is usually attributed to declining nutritional quality during the intensification of agricultural subsistence practices involving wheat and maize.

Sexual dimorphism in body size is a population-specific phenomenon, not only reflecting genetivs, but is influenced by environmental factors, most commonly the nutritional quality of the diet [6,7]. The degree of sexual dimorphism in a population is therefore often used as an indicator of health.

Based on evidence from Occident populations, the prevailing theory posits that as health declines during the intensification of agriculture, the degree of sexual dimorphism in the population also decreases over time [8]. This positive correlation between health and sexual dimorphism is attributed to males being more sensitive to adverse environmental conditions during their growth and development. However, while the hypothesis of greater male sensitivity is widely accepted, there has been little direct research into the topic [9-11].

In prehistoric Southeast Asia, previous investigations of health do not fit the commonly suggested bioarchaeological model of negative health consequences with the intensification of agriculture [12-18]. These studies indicate stasis or improvement in health over time, and suggest that these Southeast Asian populations had access to a broad- spectrum diet in a rich tropical environment during and after the adoption of rice growing [17,18]. The extent to which the intensification of rice-based agriculture influenced the degree of sexual dimorphism in prehistoric Southeast Asian populations has received little attention until now.

In this PhD research project, a biocultural approach was adopted to conduct the first temporal investigation assessing whether there is a relationship between sexual dimorphism in skeletal size and health in prehistoric Thailand. The research was undertaken with a sample of 190 adult human skeletal remains from a single site, Ban Non Wat (Fig. 1), which is a major archaeological site in Southeast Asia representing a temporal sequence spanning over 1,000 years during the intensification of rice-based agriculture [19,20]. The prehistoric human remains examined for this research date from four archaeologically distinct periods, the Neolithic (1750 b.c.–1050 b.c.), Early Bronze Age (1050 b.c.–800 b.c.), Middle Bronze Age (800 b.c.–700 b.c.) and Late Bronze Age (700 b.c.–420 b.c.) [19] (Table 1). Based on a broad bioarchaeological research context, three hypotheses were

developed: 1) health would be maintained over time; 2) population sexual dimorphism would positively correlate with general health; 3) males would be more sensitive to environmental changes than females. By taking a comparative approach, the general health of populations in the different archaeological periods was determined through a combination of measurements of non-specific systemic stress. These included terminal adult skeletal size, the prevalence of linear enamel hypoplasia and the presence of subperiosteal new bone formation on the long bones. Health was quantified for each archaeological period and compared to the degree of sexual dimorphism in bone dimensions to assess how the populations survived and adapted to new challenges in the cultural and physical environments in which they lived.

Osteometric dimensions and sexual dimorphism

Sexual dimorphism, the distinct morphological differences between males and females, is a widely recognised but Fig. 1 Map of the terrain and river network in mainland Southeast Asia, highlighting the location of the Ban Non Wat site. Modified from original images courtesy of Kate Domett /Carte de la région et du système de rivière en Asie du Sud-Est continentale, avec la position du site de Ban Non Wat. Modifiée des images ori- ginales avec l’aimable autorisation de Kate Domett

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complex phenomenon. Understanding the differences in sexual dimorphism between human populations is important for building on current knowledge of the biological evolution of our species. Furthermore, as sex differences are not only structural, but also functional, behavioural, physiological, social, psychological and cultural [21,22], the degree of sexual dimorphism in body size can reflect specific conditions within the extrinsic environments of that population. Differences in skeletal size between populations, namely stature and cross- sectional bone geometry, are the focus of most bioarchaeological research on human sexual dimorphism [6-8,23-32].

In the literature, three predominant extrinsic factors are said to account for the degree of sexual dimorphism in a population: 1) nutritional stress, 2) sex-biased parental investment, and 3) the sexual division of labour. The‘nutritional- stress hypothesis’is based on the idea that compared to males, females are genetically more buffered against fluctuations in the environment [6]. Consequently, in times of nutritional stress, the degree of sexual dimorphism declines as male body size decreases. However, sex-specific effects of nutritional stress may be compounded by other cultural factors, such as sex-biased parental investment [33]. The so-called

‘women’s work hypothesis’suggests that the degree of sexual dimorphism in stature decreased as women engaged more in subsistence-related activities [34]. From a review of the literature, it is evident that there are many opinions on the influencing or underlying factors that culminate in the degree of sexual dimorphism found in human populations. However, it is generally assumed in the majority of studies that it is males rather than females who change and influence the degree of dimorphism between the sexes in a population [6-8].

In the adult skeletal collection of Ban Non Wat (n= 293), 190 individuals (65%) were sufficiently well preserved to enable a confident assessment of their sex (Table 1), based on morphological features of the bony pelvis, as previously detailed in Clark et al. [35]. The lengths and articular surface breadths of the major long bones, including the humerus, radius, ulna, femur, tibia and fibula, were measured and

sexual dimorphism was quantified according to the methods outlined in Clark et al. [36]. All mean dimensions in males were significantly greater than in females, atα= 0.05. The results indicate a general increase, in both males and females, in long bone lengths and articular breadths from the Neo- lithic to the Early Bronze Age, after which the dimensions decreased in both sexes from the Middle to Late Bronze Age (Tables 2, 3). The most striking sex-specific difference was that, in comparison to females, males remain fairly constant in size over time whereas females show statistically significant changes (p≤ 0.05) in both lengths and breadths over time. These significant changes in female measurements resulted in the diachronic variation observed in the degree of sexual dimorphism (Table 2 and Table 3), which can be summarised by two trends: 1) a reduction in the degree of sexual dimorphism in lengths and stasis in sexual dimorphism in breadths from the Neolithic to the Middle Bronze Age; and 2) an increase in the degree of sexual dimorphism for both lengths and breadths from the Middle to Late Bronze Age.

Linear enamel hypoplasia as an indicator of non-specific systemic stress in early childhood

Stressful events can affect the normal formation of tooth enamel and are commonly observed as hypoplastic defects in the archaeological record. Enamel defects can arise through genetic abnormalities or traumatic insults, but mainly occur as a response to non-specific systemic stress during early childhood, from around one to eight years of age [37]. A non-specific stress response indicates that in addition to individual and nutritional factors, many unknown and unknowable factors contribute to the expression and formation of enamel defects [38,39]. A review of the dental anthropological literature concerning the documentation and methodological approaches for recording enamel defects provided insights to develop recording methods for the Table 1 Prehistoric chronological sequence for the sexed Ban Non Wat adult individuals used in this PhD research from the Neolithic, Early Bronze Age, Middle Bronze Age and Late Bronze Age, with Radiocarbon Dates as published in Higham and Higham [19] / Séquence chronologique pour les individus adultes et sexés de Ban Non Wat utilisés dans cette thèse datant du Néolithique, de l’âge du bronze ancien, de l’âge du bronze moyen et de de l’âge du bronze tardif, et dates radiocarbones d’après Higham et Higham [19].

Archaeological Periods

Radiocarbon Dates (cal. B.C) Adult Individuals (n)

Males Females Total

Neolithic 1750-1050 13 17 30

Early Bronze Age 1050-800 24 25 49

Middle Bronze Age 800-700 39 50 89

Late Bronze Age 700-420 8 14 22

Total sample 1750-420 84 106 190

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prehistoric Ban Non Wat population [35]. Important factors influencing the presence and identification of linear enamel hypoplasia (LEH) include: susceptibility within and among teeth [38-42], age-at-stress [38,42-45] and the duration and severity of stress [46,47]. Non-specific systemic stress can be identified by examining the full set of permanent teeth and noting differences in tooth susceptibility within and among the different tooth types. A key factor for the identification of systemic stress is that LEH must occur in multiple teeth at similar chronological positions. With consideration of the factors outlined above, a method was developed to analyse the presence of antimeric LEH, defined by the presence of discrete horizontal hypoplastic grooves or lines, either single, multiple or pitted on the enamel surface [35].

The analysis of systemic stress was based on a subsample of 167 adults (76 males and 91 females) from the Ban Non

Wat skeletal collection with preserved antimeric pairs of permanent teeth, or at least two permanent teeth known to be developing at the same time. Overall, males and females were not significantly different in the prevalence of non- specific systemic stress during early childhood (p≥ 0.05).

The general temporal trend was a statistically significant decrease in non-specific systemic stress during early childhood from the Neolithic to the Middle Bronze Age (p = 0.016), and then a slight but not statistically significant increase from the Middle to Late Bronze Age (p ≥ 0.05).

This temporal pattern with an initial decrease in early childhood systemic stress supports other studies of prehistoric Southeast Asian human remains during the intensification of agriculture [12,14,48]. These studies suggest that improvements in early childhood health over time can be attributed to the continuation of a diversified subsistence Table 2 Summary data and degree of sexual dimorphism for the measured lengths of the upper and lower limb bones for the sexed adult individuals (N = 190), by archaeological period /Données résumées et degré de dimorphisme sexuel pour les longueurs des os des membres supérieurs et inférieurs pour les individus adultes sexés (N = 190), par période archéologique.

Measurements Period Males Females Sexual Dimorphism

n Mean (mm)

Standard Deviation (mm)

Min (mm)

Max (mm)

n Mean (mm)

Min (mm)

Max (mm)

% Differ- ence

Mean Difference (mm) Maximum

Clavicle Length

Neo 6 141.8 4.6 133.0 145.5 10 125.2 6.9 115.0 142.0 11.7% 16.6

EarlyBA 19 149.8 9.3 135.0 166.0 15 132.7 6.7 123.0 145.0 11.4% 17.1

MidBA 23 150.1 8.6 134.0 167.0 17 133.6 6.8 122.5 146.0 11.0% 16.5

LateBA 2 146.3 13.8 136.5 156.0 4 124.6 7.6 120.0 136.0 14.8% 21.6

Maximum Humerus Length

Neo 7 313.6 10.5 306.0 335.5 8 275.5 9.4 261.0 287.0 12.2% 38.1

EarlyBA 16 317.9 11.0 296.5 336.5 19 289.8 10.7 258.5 303.5 8.8% 28.1

MidBA 25 322.0 14.6 301.0 365.0 17 297.7 11.8 275.0 321.0 7.6% 24.3

LateBA 4 320.4 24.6 302.5 355.0 5 286.5 11.7 271.5 303.0 10.6% 33.9

Maximum Ulna Length

Neo 4 277.4 10.4 266.0 286.5 8 240.0 8.3 227.0 249.3 13.5% 37.4

EarlyBA 19 278.2 10.1 259.5 298.0 18 251.6 8.3 237.5 268.0 9.6% 26.7

MidBA 22 281.4 10.5 264.0 311.0 17 258.6 9.0 245.5 271.0 8.1% 22.7

LateBA 3 273.7 8.5 265.0 282.0 3 259.3 17.2 241.0 275.0 5.2% 14.3

Maximum Radius Length

Neo 4 257.5 6.6 251.0 265.0 6 213.8 7.1 205.8 223.0 17.0% 43.7

EarlyBA 20 257.0 10.7 240.5 279.0 17 230.0 7.1 216.5 240.0 10.5% 27.1

MidBA 22 257.7 9.1 244.5 279.0 14 236.6 6.6 227.0 247.5 8.2% 21.0

LateBA 3 255.3 11.4 246.0 268.0 7 230.4 13.6 216.0 255.0 9.8% 24.9

Maximum Femur Length

Neo 4 435.6 30.2 410.0 477.5 6 396.7 6.4 388.0 404.0 8.9% 38.9

EarlyBA 14 458.0 12.7 441.8 484.5 14 414.3 25.4 364.0 449.0 9.5% 43.7

MidBA 20 455.4 23.0 420.0 517.0 13 420.4 16.9 388.0 450.0 7.7% 35.0

LateBA 2 439.8 8.1 434.0 445.5 2 401.5 6.4 397.0 406.0 8.7% 38.3

Maximum Tibia Length

Neo 8 369.1 20.4 344.0 405.0 4 324.1 10.4 314.5 335.3 12.2% 45.0

EarlyBA 11 377.9 18.3 350.0 422.8 14 347.5 13.8 312.0 366.8 8.0% 30.4

MidBA 20 380.5 21.1 355.0 438.5 15 357.8 14.6 329.5 382.0 6.0% 22.7

LateBA 2 369.3 21.6 354.0 384.5 2 338.5 4.9 335.0 342.0 8.3% 30.8

Maximum Fibula Length

Neo 5 370.6 20.4 350.5 401.0 4 319.2 11.8 308.8 333.0 13.9% 51.4

EarlyBA 8 379.4 17.3 358.0 416.5 13 344.3 15.5 310.0 368.5 9.3% 35.1

MidBA 17 378.0 19.2 352.0 424.0 8 355.1 13.4 338.5 384.0 6.1% 22.9

LateBA 2 363.5 17.7 351.0 376.0 1 362.0 . 362.0 362.0 0.4% 1.5

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Table 3 Summary data and degree of sexual dimorphism for the articular breadths of the upper and lower limb bones for the sexed adult individuals (N = 190), by archaeological period /Données résumées et degré de dimorphisme sexuel pour les largeurs articu- laires des os des membres supérieurs et inférieurs pour les individus adultes sexés (N = 190), par période archéologique.

n Mean (mm)

Min (mm)

Max (mm)

n Mean (mm)

Min (mm)

Max (mm)

% Differ- ence

Mean Difference (mm) Humeral

Epicondylar Breadth

Neo 11 63.1 3.2 59.1 67.7 12 55.3 1.4 52.6 57.8 12.4% 7.8

EarlyBA 20 65.7 2.1 61.0 70.2 24 56.9 3.2 50.5 62.5 13.3% 8.7

MidBA 33 64.7 3.2 58.0 72.0 34 56.0 3.1 51.6 63.5 13.6% 8.8

LateBA 5 65.4 3.2 60.1 67.8 9 54.6 2.9 51.5 59.2 16.6% 10.9

Vertical Humeral Head Diameter

Neo 9 46.3 2.0 43.8 48.7 10 39.0 1.5 35.8 41.1 15.6% 7.2

EarlyBA 19 46.7 1.9 41.4 49.4 22 39.9 1.6 37.0 43.8 14.4% 6.7

MidBA 29 46.1 2.4 41.0 51.5 25 40.3 2.3 36.2 44.7 12.5% 5.8

LateBA 6 47.7 4.2 41.7 54.5 7 39.7 1.9 37.1 42.0 16.7% 8.0

Antero-Posterior Proximal Ulna Diameter

Neo 11 26.1 2.5 22.3 31.4 15 22.3 1.5 19.0 24.9 14.5% 3.8

EarlyBA 21 25.4 1.6 20.8 28.9 24 23.1 1.5 20.7 26.4 8.9% 2.3

MidBA 37 25.2 1.8 21.9 29.6 41 22.5 1.5 19.5 25.6 10.8% 2.7

LateBA 7 25.9 2.7 22.6 30.9 13 23.1 2.0 20.1 27.1 10.8% 2.8

Transverse Proximal Ulna Diameter

Neo 11 20.9 1.6 19.0 24.3 16 17.6 2.0 13.3 21.2 15.7% 3.3

EarlyBA 22 22.2 3.4 19.2 33.8 24 19.1 1.8 15.9 22.4 13.9% 3.1

MidBA 37 21.7 1.5 17.6 25.3 42 18.5 1.9 14.5 21.7 14.4% 3.1

LateBA 7 21.5 0.7 20.6 22.3 13 18.8 2.5 16.3 25.6 12.3% 2.7

Coronoid Process Breadth

Neo 9 35.6 1.3 33.7 38.3 12 31.3 1.4 29.7 34.6 11.9% 4.2

EarlyBA 21 36.8 1.9 32.0 40.2 22 33.0 2.1 29.2 37.4 10.5% 3.9

MidBA 36 36.7 2.0 30.2 42.1 40 32.0 1.6 29.0 35.7 12.7% 4.7

LateBA 7 36.9 1.9 34.3 39.9 9 32.2 1.9 30.0 34.4 12.7% 4.7

Antero-Posterior Radial Head Diameter

Neo 8 22.7 1.4 20.9 24.6 9 19.8 1.4 17.2 21.5 12.8% 2.9

EarlyBA 20 22.8 1.0 20.9 24.8 23 19.6 0.8 18.4 21.2 13.9% 3.2

MidBA 31 23.0 1.4 20.7 26.3 28 20.3 1.2 17.7 22.1 11.9% 2.8

LateBA 5 23.0 1.4 20.8 24.7 7 19.6 1.0 18.5 21.4 15.1% 3.5

Medio-Lateral Radial Head Diameter

Neo 7 22.5 0.9 21.5 23.7 9 19.8 1.6 17.2 21.4 12.1% 2.7

EarlyBA 22 23.1 1.1 21.3 25.9 23 20.1 0.9 18.3 21.8 13.2% 3.1

MidBA 35 23.4 1.4 21.2 26.0 34 20.0 1.3 17.4 22.2 14.4% 3.4

LateBA 6 23.0 1.0 21.1 23.7 7 19.1 1.0 17.9 20.5 16.8% 3.9

Distal Radial Epicondylar Breadth

Neo 7 33.3 1.8 31.5 36.1 8 29.6 1.7 26.4 31.5 11.3% 3.8

EarlyBA 20 34.7 1.9 31.5 39.5 19 29.9 1.3 27.1 31.8 14.0% 4.8

MidBA 29 34.1 2.2 30.5 38.8 27 29.5 1.5 26.3 32.4 13.5% 4.6

LateBA 4 34.6 2.1 32.9 37.4 6 28.6 0.9 27.6 30.0 17.3% 6.0

Maximum Femoral Head Diameter

Neo 11 45.9 2.7 41.5 49.8 12 40.8 1.4 38.0 43.0 11.1% 5.1

EarlyBA 21 47.2 2.3 41.7 50.2 24 42.0 1.8 37.2 45.3 11.1% 5.2

MidBA 34 47.4 2.2 43.1 52.6 45 41.8 2.1 37.9 46.5 11.6% 5.5

LateBA 6 46.7 1.8 43.9 48.8 10 40.7 2.3 36.5 43.9 12.8% 6.0

Supero-Inferior Femoral Neck Diameter

Neo 12 31.8 2.0 27.8 34.5 12 28.3 1.9 25.3 31.6 10.9% 3.5

EarlyBA 20 32.6 2.4 29.3 37.9 23 28.4 2.1 25.0 31.8 12.7% 4.1

MidBA 31 31.9 2.2 27.5 37.3 37 28.1 1.9 24.8 31.9 11.8% 3.8

LateBA 5 32.9 2.8 28.7 36.3 8 26.9 1.8 24.4 30.5 18.1% 6.0

Femoral Epicondylar Breadth

Neo 6 76.7 6.4 64.8 81.3 5 70.8 1.6 68.7 72.6 7.6% 5.9

EarlyBA 18 81.5 2.8 78.0 88.0 12 71.1 3.3 65.7 78.1 12.8% 10.4

MidBA 24 80.4 3.6 73.5 86.6 18 70.7 3.3 62.2 75.9 12.1% 9.7

LateBA 4 76.1 2.8 72.9 79.6 4 68.3 3.1 63.6 70.1 10.3% 7.8

Proximal Tibial Breadth

Neo 6 73.5 4.0 66.4 77.6 7 67.0 3.2 61.2 71.3 8.9% 6.5

EarlyBA 11 72.8 7.7 50.8 78.0 15 67.1 2.5 62.4 72.2 7.8% 5.6

MidBA 21 75.4 3.4 70.6 82.4 16 68.1 3.6 62.0 73.4 9.7% 7.3

LateBA 3 71.7 3.3 68.3 74.9 7 61.1 10.4 38.1 66.9 14.8% 10.6

(Suite page suivante)

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diet, which included game and gathering wild plants, in con- junction with more intensified rice cultivation [12,17,18].

Subperiosteal new bone formation as an indicator of non-specific systemic stress in later life

Subperiosteal new bone formation on the surface of the long bone shafts, commonly called periosteal reactions, are a systemic inflammatory response to stress [49]. When examined in a human skeleton, periosteal reactions can appear as dis- organised and porous woven bone, which remodels over time into lamellar bone [49,50]. From a review of the current literature, many investigations use periosteal reactions as evidence of non-specific infections [50-52] or specific infectious diseases [53,54]. However, as this research project examines only the shafts of the long bones and not the entire skeleton, it was appropriate to use periosteal reactions as evidence of non-specific systemic inflammation within the biocultural model [55]. Methods for the assessment of periosteal reactions were assessed and a methodological system developed from a combination of principles outlined in standard bioarchaeological guidelines [53]. Non-specific systemic inflammation for the Ban Non Wat population was identified by subperiosteal new bone formation on at least two long bone shafts, as either woven or lamellar bone.

Bones that showed periosteal reactions together with clear evidence of fractures were not considered as indicators of systemic inflammation.

The analysis of non-specific systemic inflammation was based on a subsample of 138 adults (60 males and 78 females), where at least two long bones were present with more than 50% of the cortical bone surface observed. 53 individuals (38% [53/138]) demonstrated subperiosteal new bone formation on at least two elements, and were identified as experiencing non-specific systemic inflammation during their lifetimes. Overall, no statistically significant differences were found between the sexes (p≥ 0.05). However, in all periods except the Late Bronze, the males had a slightly higher prevalence of non-specific systemic inflammation

than the females. Initially, a statistically significant increase in the prevalence of non-specific systemic inflammation was found from the Neolithic to Early Bronze Age (p= 0.013) and up to the Middle Bronze Age (p= 0.010). This was followed by a slight and statistically non-significant decline in prevalence from the Middle to Late Bronze Age (p≥0.05).

The initial increase in the prevalence of periosteal reactions during periods of agricultural intensification supports other study results in mainland Southeast Asia [15,56,57], suggest- ing that although a nutritious broad-spectrum diet was maintained, an increase in pathogen loads occurred with the expan- sion of trade networks and, possibly, increased migration.

Discussion: health and sexual dimorphism at Ban non Wat

A successful interpretation of the skeletal evidence of health in a prehistoric population requires discussion and consideration of multiple potentially influencing factors within a given biocultural framework [58-60]. The lengthy archaeological excavations at the site of Ban Non Wat have provided an adequate sample from one site to address some important aspects of human health during the intensification of rice-based agriculture. For a period of over one thousand years, the changes at Ban Non Wat included technological advancements, expanded trade networks and changes in social complexity, which are identified through isotopic evidence of migration, chemical analysis of diet [61] and examination of the archaeological record [20,62,63].

In this PhD research project, health was indicated by terminal adult skeletal size, the prevalence of linear enamel hypoplasia (LEH) and the presence of subperiosteal new bone formation on the long bones, and compared to the degree of sexual dimorphism across four archaeological periods in prehistoric Thailand. In general, the results suggest an inverse relationship between the prevalence of non- specific systemic stress during childhood, as indicated by LEH, and the prevalence of non-specific systemic inflammation in later life, as suggested by subperiosteal new bone formation. Furthermore, it is apparent that diachronic increases in both long bone lengths and articular breadths

Table 3(suite)

n Mean (mm)

Min (mm)

Max (mm)

n Mean (mm)

Min (mm)

Max (mm)

% Differ- ence

Mean Difference (mm) Distal Tibial

Epicondylar Breadth

Neo 9 46.4 2.7 41.5 50.3 11 40.3 3.1 35.8 46.5 13.1% 6.1

EarlyBA 16 48.7 2.4 44.7 53.8 17 42.9 2.1 39.2 47.2 11.9% 5.8

MidBA 26 48.5 2.3 43.9 52.8 28 44.5 1.9 40.7 48.7 8.3% 4.0

LateBA 3 46.4 1.9 44.2 47.7 5 41.6 1.4 40.7 44.1 10.3% 4.8

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correlate positively with a decrease in LEH prevalence. This is to be expected given the nature and timing of growth and development for these two indicators of health. There are two main diachronic trends in general health and sexual dimorphism during the intensification of rice agriculture.

These are summarised and discussed below:

•

Neolithic to Middle Bronze Age: Overall improvement in general health despite increases in non-specific systemic inflammation during later life, a decline in sexual dimorphism in long bone lengths and relative stasis in sexual dimorphism in articular breadths

•

Middle to Late Bronze Age: Deterioration in general health from the Middle to Late Bronze Age despite decreases in non-specific systemic inflammation during later life, and increases in sexual dimorphism in long bone lengths and articular breadths

The first trend is an improvement in general health from the Neolithic to the Middle Bronze Age period, followed by deterioration from the Middle to Late Bronze Age [2-5].

These results differ from those expected based on the West- ern agricultural model, and furthermore, they do not support the first hypothesis that health was maintained over time.

Regarding the second hypothesis, health was negatively cor- related with sexual dimorphism over time, which does not support the second hypothesis that lower levels of sexual dimorphism result from a deterioration in environmental conditions and indicate poorer population health [8]. Tem- poral fluctuations in skeletal measurements for females, but relative stability for males and the absence of sex-specific differences in the skeletal indicators of health mean that the third hypothesis, that males are more sensitive to environmental changes than females [9-11], is not supported either.

Overall, these results support previous research findings that the general health and quality of life of prehistoric people in mainland Southeast Asia did not deteriorate from the Neo- lithic to Middle Bronze Age. This may be a result of a nutritious diet, as the subsistence base remained diverse attibuted to hunting, fishing and foraging for wild plants and animals, despite increasing rice consumption [e.g. 13,14,17,18,57].

The deterioration in health from the Middle to Late Bronze Age may be related to climate change, requiring extensive modifications of the physical environment and management of waterways in the subsequent Iron Age and leading to an increase in infectious diseases, and/or declining availability of a nutritious diet [20].

Conclusions

The examination of human skeletal remains is central to understanding how populations adapted to, and interacted with, their environment during major transitional periods in

prehistory. This PhD research satisfied the aim of investigating whether there is a relationship between sexual dimorphism in body size and general health during the intensification of rice agriculture, in a sample of adults from the Ban Non Wat skeletal assemblage. The biocultural approach was employed, which emphasised the importance of combining both archaeological and skeletal evidence for investigating the relationship between the intensification of agriculture and human population health. Overall, it was found that there is a negative correlation between sexual dimorphism in body size and general health. That is, when sexual dimorphism declines, general health improves. This is contrary to expectations based on previous bioarchaeological research in the Occident. As such, sexual dimorphism in body size is a complex, but useful, measure of human cultural and biological adaptation, but not necessarily of general health. This analysis demonstrated that it is imperative to examine the raw skeletal measurements for both males and females in order to determine which sex differs, and not make assumptions of sex-specific biological buffering.

Furthermore, these results have implications for the applica- tion of existing bioarchaeological models of health change based on Europe and the Americas to prehistoric mainland Southeast Asian populations, and suggest caution in applying these models elsewhere.

Acknowledgements I am extremely honoured to have received the prize for best dissertation in 2013 and wish to thank theSociété d’Anthropologie de Parisfor this presti- gious award. I am most grateful to Nancy Tayles and Siân Halcrow who supervised my PhD research. Thanks to the Thai Fine Arts Department, the National Research Council and the Kingdom of Thailand for the opportunity to learn about the past lives of the prehistoric people of Ban Non Wat. Thanks also to the directors of the Ban Non Wat archaeological excavations: Professor Charles Higham, Dr Racha- nie Thosarat and Dr Amphan Kijngam, Dr Nigel Chang, Dr Kate Domett, Dr Warrachai Wiriyaromp and Professor William Boyd. This research project was funded by a Uni- versity of Otago Doctoral Scholarship and the University of Otago Department of Anatomy.

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