Doctoral Dissertation Improvement: Effects of Stress on Onset of Middle Childhood among Aka Foragers and Ngandu Horticulturalists

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Current theory proposes that human childhood is an assessment phase where children use their experience with risk or unpredictability (e.g., stressors) to shape future life history strategies. This suggests that timing of developmental transitions may depend on experience in the preceding phase. Doctoral student Courtney Helfrecht (Washington State University), under the guidance of Dr. Courtney Meehan, tests the hypothesis that early experience of stress has significant effects on age of onset for middle childhood and its biological correlate (adrenarche) among Aka foragers and Ngandu horticulturalists of the Central African Republic (CAR). Initial data indicate that middle childhood is a culturally-defined phase associated with changes in cognitive and social abilities. This research builds from that with three additional goals: 1) assessment of cultural and environmental stressors; 2) determination of chronological age of onset for middle childhood and adrenarche; and 3) evaluation of which stressors affect timing of onset for both middle childhood and adrenarche. This integrative study is among the first to empirically examine this relationship using observational, hormonal, interview, demographic, and cross-cultural data. An initial collection of hair samples provides population profiles for timing of adrenarche using hair hormone analysis, conducted via collaboration between Washington State University and The George Washington University. A second collection allows tracking of biological development and a repeated measure of experienced stress (cortisol). By investigating the interaction between stress, biology, and culture, we move toward understanding the factors associated with developmental plasticity and the timing of life history events, as well as their contributions to the evolution of human childhood. The results of this study will be valuable to multiple fields, including biocultural anthropology, child development, and cognitive psychology. It will further add to ethnographic data on childhood among two small-scale societies and foster continued collaboration with the University of Bangui. This grant will help to advance the scientific training of a promising graduate student.