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

目前的理论认为，人类童年是一个评估阶段，在这个阶段，儿童利用他们对风险或不可预测性(例如，压力源)的经验来塑造未来的生活史策略。这表明，发育转变的时间可能取决于前一阶段的经验。博士生Courtney Helfrecht(华盛顿州立大学)在Courtney Meehan博士的指导下，测试了这一假说，即早期应激经历对中非共和国AKA采食者和Ngandu园艺家(CAR)的童年中期发病年龄及其生物学相关性(肾上腺原基)有显著影响。最初的数据表明，童年中期是一个文化定义的阶段，与认知和社会能力的变化有关。这项研究在此基础上增加了三个目标：1)评估文化和环境应激源；2)确定儿童期中期和肾上腺发育期的发病年龄；3)评估哪些应激源会影响儿童期中期和肾上腺发育期的发病时间。这项综合性研究是第一批使用观察、激素、访谈、人口统计学和跨文化数据对这种关系进行实证检验的研究之一。通过华盛顿州立大学和乔治华盛顿大学的合作，最初收集的头发样本提供了通过头发激素分析确定肾上腺发育时间的人群概况。第二个收集可以跟踪生物发育和重复测量经历过的压力(皮质醇)。通过研究压力、生物和文化之间的相互作用，我们有助于理解与发育可塑性相关的因素和生活史事件的时间安排，以及它们对人类童年进化的贡献。这项研究的结果将对包括生物文化人类学、儿童发展和认知心理学在内的多个领域具有价值。它将进一步增加两个小规模社会中关于童年的人种学数据，并促进与班吉大学的持续合作。这笔助学金将有助于推进对有前途的研究生的科学培训。

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.