EFFECTS OF STRESS ON ONSET OF MIDDLE CHILDHOOD AMONG SIDAMA AGROPASTORALISTS

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

Age and sex differences in aggression among the Aka foragers of the Central African Republic

Aggression is often considered a maladaptive behavior, and is an important social problem cross-culturally. There are two primary theoretical arenas examining the origins of age and sex differences in aggression. Evolutionary theories assert that sexual selection has shaped the age and sex differences in physical (e.g., hitting) and indirect (e.g., gossiping) aggression, suggesting that males make use of physical aggression in resource competition and social dominance while females rely on less risky strategies of indirect aggression for the same purposes. Biosocial theory ties sex differences in aggression to the inculcation of sex roles, with social norms serving to reinforce these divergences via expected behaviors with punitive consequences for violations. The majority of previous work on aggression in small-scale societies has emphasized its absence, particularly among hunter-gatherers. This paper examines age and sex differences in physical and indirect aggression, and in cultural norms surrounding aggression, among the Aka forest foragers of the Central African Republic. Both peerrankings and self-report data were collected from 98 Aka (children, adolescents, and adults) on physical and indirect aggression; additional data on anger, reputation, and alliances were obtained from adults. A Likert scale was used to obtain measures of social norms, perpetration, and victimization. The results provide only mixed support for evolutionary theories on aggression. Although the expected sex-bias in hitting emerged among children and adolescents, this effect disappeared among adults. An adult female bias in gossiping emerged only when anger was added to the model, and no bias was found in children or adolescents. Our negative findings might be due to unmeasured social and cultural factors, such as high levels of relatedness, the role of women as disciplinarians, and reduced male testosterone due to high levels of paternal investment. As there is little research on hunter-gatherer aggression, it is currently unclear where the Aka fit on aggression measures among small-scale societies. However, these results indicate the importance of quantifying aggressive behaviors in order to clarify the effects of biology, environment, and culture in the development and evolution of aggression, and perhaps reveal current biases derived from the emphasis on Western populations in the literature