Human Sexual Dimorphism and Health in Prehistoric Thailand

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A review of Human Sexual Dimorphism and Health During the Intensification of Agriculture in Prehistoric Thailand, by Angela L. Clark.

This dissertation by Angela Clark is a biocultural exploration of sexual dimorphism and general health from the Neolithic through the Late Bronze Age at Ban Non Wat (1750-420 B.C.), Northeast Thailand. The primary focus is on the relationship of non-specific indicators of systematic stress, including both early childhood and adult indicators of health, and sexual dimorphism to archeologically defined periods of agricultural intensification. Clark tests three hypotheses: (1) that health will be maintained through time despite agricultural intensification, (2) sexual dimorphism in body size will positively correlate with health, and (3) males will be more sensitive to environmental changes when compared with females. The Ban Non Wat site (190 adult individuals) represents the one of the largest skeletal assemblages in Southeast Asia and the best current sample for assessing long-term diachronic relationships and change from the Neolithic and Bronze Age in Southeast Asia.

Chapter 2 is a discussion of the Ban Non Wat site, including an overview of archeological context, mortuary practices, landscape and environment, and resource availability. This chapter places Ban Non Wat in a larger Southeast Asian perspective, clearly articulating the chronological position of the site with other reported skeletal series in Southeast Asia as well as the relationship of Ban Nan Wat with larger trends in environmental change, subsistence patterns, and trade in Northeast Thailand.

The next several chapters (Chapters 3 to 5) present the sexual dimorphism, indicators of childhood non-specific stress, and indicators of non-specific stress later in life of the Ban Non Wat skeletal sample. These chapters include an in-depth examination the historical, theoretical, and methodological backgrounds of skeletal indicators of sexual dimorphism and non-specific indicators of stress.

The author explores sexual dimorphism in long bone lengths and epiphyseal diameter, developmental defects of the enamel including linear enamel hypoplasia, and non-specific inflammation of the periosteum leading to periostitis (subperiosteal new bone formation). Tables summarizing the data are comprehensive and accessible. These will prove to be valuable resources for data mining as other researchers attempt to expand our knowledge of the relationship of health and agricultural expansion in mainland and island Southeast Asia. These investigations will be made easier by the clear theoretical and methodological descriptions in the results chapters. These descriptions, including photographs and decision trees, will allow other researchers to follow the same methodology, or to easily compare slightly differing methodologies, therefore greatly expanding the utility of the results presented. More generally the theoretical discussions of the concepts of gender and identity, the evolution and sexual selection factors impacting sexual dimorphism, and the formation and development of defects of enamel in a Southeast Asian context help to tie research from Thailand to other areas of Southeast Asia and the world. The discussion is thorough, clearly examining the findings at the population-level in light of issues of preservation, taphonomy, statistical appropriateness, and the osteological paradox.

Contrary to initial expectations that health through the introduction and intensification of agriculture will be maintained, a combination of factors including sexual dimorphism, linear enamel hypoplasia, and subperiosteal new bone formation suggest an improvement in general health from the Neolithic through the Middle Bronze Age, then deteriorating health from the Middle to the Late Bronze Age.  The level of sexual dimorphism during this transition decreased or remained constant over the various time periods except when health declined from the Middle to the Late Bronze Age. Here sexual dimorphism increased with deteriorating health. Finally, females express more fluctuation between time periods in both long bone length and epiphyseal diameter. Therefore females and not males are the drivers of variation in sexual dimorphism. Unlike other areas of the world, females do not appear to be buffered from those environmental, genetic, or hormonal causes of sexual dimorphism. As Clark states in her discussion, these conclusions are consistent with other studies in Southeast Asia where the introduction and intensification of agriculture and the concomitant social and environmental changes did not negatively impact the health of adults during this subsistence shift. Clark’s findings on diachronic trends of health and sexual dimorphism suggest that, unlike other areas of the world, females of the Ban Nan Wat sample are more impacted by the effects of environmental change and agricultural adoption than males. Modern ethnographic evidence suggests that modern Thai women are more likely to be exposed to parasites and other infectious disease than men, while archeological evidence does not show clear differences in the treatment of the sexes it is likely similar differences existed in the past. It appears differences in health and sexual dimorphism are influenced by factors that are sex-specific.

Generally, population health from the initial use of agriculture in Northeast Thailand through the Middle Bronze Age improves. This finding is similar to other studies in Southeast Asia. However, the use of multiple lines of evidence encompassing both childhood and adult health and stress shows a more complicated picture suggesting most of the improvement in general health through the Middle Bronze Age is found in females with males maintaining overall levels of heath. The Late Bronze Age finds a general slight decline in health for the entire population. It appears that cultural buffers to biological and environmental stresses influenced the sexes differently while still helping to improve or maintain community health.

Perhaps the most important finding in Clark’s dissertation is the observation that the relationship between sexual dimorphism and health in Southeast Asia is more complicated than previous models may have allowed for. These finding reinforce the idea that bioarchaeologial models of health in Southeast Asia may not be applicable to other regions of the world and even within Southeast Asia we may need to reevaluate the complex relationship of biocultural adaptation and general health.

This dissertation provides an excellent package of theory, method, and data and will prove to be an important addition to our understanding of the bioarchaeology of Northeast Thailand and Southeast Asia.

Adam Lauer
Department of Anthropology
University of Hawai‘i at Mānoa
adam.lauer@hawaii.edu

Primary sources
Domett, K. and Tayles, N. (2006). Human biology from the bronze age to the iron age in the Mun River valley of northeast Thailand. In Oxenham, M. and Tayles, N. (eds.) Bioarchaeology of Southeast Asia. Cambridge: Cambridge University Press.

Newton, J. S., Domett, K. M., O’Reilly, D. J., Shewan, L. (2013). Dental health in Iron Age Cambodia: Temporal variations with rice agriculture. International Journal of Paleopathology 3:1-10.

Pietrusewsky, M. and Douglas, M. T. (2002). Ban Chiang, A Prehistoric Village Site in Northeast Thailand I: The Human Skeletal Remains.  Philadelphia: The University of Pennsylvania Museum of Archaeology and Anthropology.

Pietrusewsky, M and Ikehara-Quebral, R. (2006). The Bioarchaeology of the Vat Komnou Cemetery, Angkor Borei, Cambodia. Indo-Pacific Prehistory Association Bulletin 26:86-97.

Tayles, N. (1999). The Excavation of Khok Phanom Di, a prehistoric site in Northeast Thailand. Vol. V, The people. London.

Dissertation information
University of Otago 2013, 332 pages including appendices. Primary Advisors: Nancy Tayles and Siân Halcrow.

Image: Photograph from Ban Non Wat.  Wikimedia Commons.

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