Abstract
The introduction and intensification of agriculture is regarded as a major transition experienced by humans. This period in prehistory provides a suitable framework to evaluate adaptation of the past populations to changes in the physical and cultural environments over time. This thesis aims to address an aspect of this issue by a temporal investigation of whether there is a relationship between sexual dimorphism in skeletal size and general health from a sample of 190 adult human skeletal remains from a single site, Ban Non Wat, in Northeast Thailand. This site was chosen as the skeletal sample spans from approximately 1750 B.C to 420 B.C, during the intensification of agriculture.
Central to this thesis is the investigation of sexual dimorphism, the size and shape differences between males and females, which has been commonly employed as a measure of human biocultural adaptation. A decline in population sexual dimorphism and a decline in general health is generally associated with a shift to intensified subsistence practices in Western populations, where the nutritional quality of the diet decreased over time. This positive correlation is assumed to be the result of males being more sensitive to adverse environmental conditions. Although the extent to which the intensification of rice-based agriculture influenced the level of sexual dimorphism in Southeast Asia has received little attention, previous investigations of health of late prehistoric populations in mainland Southeast Asia do not fit this model of a decline in health.
This research tests three hypotheses, that: 1) health would be maintained over time; 2) sexual dimorphism in body size will positively correlate with general health; 3) males will be more sensitive to environmental changes compared with females. General health was investigated through the analysis of three indicators: long bone lengths and epiphyseal dimensions; non-specific systemic stress during childhood reflected in linear enamel hypoplasia; and non-specific systemic inflammation characterising stress later in life reflected in subperiosteal new bone formation.
The results of this research do not support the first hypothesis as general health improved from the Neolithic to the Middle Bronze Age although it deteriorated from the Middle to Late Bronze Age. Sexual dimorphism in body size decreased and then increased over time, indicating a negative correlation with general health; therefore, the second hypothesis is not supported. The results demonstrated that females show greater variation in skeletal dimensions over time, whereas there is stability in male body size. Furthermore, there is a lack of sex-specific differences in either indicator of non-specific systemic stress. Therefore, the third hypothesis is also not supported.
Overall, these findings support previous research that indicates that the general health and quality of life of the prehistoric people in mainland Southeast Asia did not deteriorate from the Neolithic to Middle Bronze Age and therefore, do not fit the model of a decline in health. This may be a result of a nutritious rice-based diet, supplemented by a diverse range of foods from hunting, fishing and foraging wild plants and animals. The slight deterioration in health from the Middle to Late Bronze Age may be related to climate changes, which necessitated the extensive modification of the physical environment and management of the waterways in the subsequent Iron Age, leading to an increase in infectious diseases, and/or a decline in availability of a nutritious diet. Although these results have shown a relationship between sexual dimorphism and general health, there is no evidence that they are positively correlated, as it is the females that are changing, not the males. This thesis demonstrated that the assumptions regarding the relationship between changes in health and sexual dimorphism with agricultural intensification are complex, and regionally variable.