EFFECTS OF STRESS ON ONSET OF MIDDLE CHILDHOOD AMONG SIDAMA AGROPASTORALISTS
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Current research suggests that human childhood evolved as a phase of assessment, where children use experience with their social and physical environments to determine future development and reproductive strategies. Yet, few studies have empirically tested this hypothesis and much of the research examining the evolution of childhood focuses on infancy or adolescence, leaving a significant gap in our understanding of middle childhood, a period comprising one-third of our development. To address this gap, this dissertation examines the relationship between stress and middle childhood among Sidama agropastoralists of southwestern Ethiopia. Data on age categories, social and cognitive development, and cultural/physical stressors were collected from both adults and children. In addition, hair samples from 160 children (aged 3-18 years old) were collected to assess two biomarkers (cortisol and dehydroepiandrosterone sulfate [DHEAS]), along with anthropometrics and demographic data. As in most cultures, onset of Sidama middle childhood (shiima beto) coincides with onset of reason. The primary stressor believed to affect children is a shortage of economic resources, and the impact of this is reflected in hair cortisol concentrations (HCC). Average age of onset for adrenarche is slightly delayed in comparison to Western populations, but examination of the associated biomarker (DHEAS) revealed an unexpected pattern—involution of the adrenal fetal zone is significantly delayed, indicating important variation from known life history patterns. Additionally, analyses examining differences in DHEAS concentrations based on HCC and nutritional status found that girls with lower HCC, but not boys, deviated from the sample-level pattern, expressing a relatively flattened line for DHEAS following the early childhood decline. This study contributes novel data both on two biomarkers, extending our understanding of the range for “normal” child development, and on adrenarche in an environment where nutritional stress and extrinsic mortality are high. It additionally provides ethnographic data on age categories, stressors, and socio-cognitive development during middle childhood among Sidama agropastoralists. The results demonstrate not only that stress impacts patterns of ontogeny during middle childhood, but also the importance of integrating biology, culture, and ecology if we are to fully understand the role of stress in shaping the evolution of human life history.