The human stress response has been shaped by natural selection to manage acute environmental challenges. While short-term activation of this response is imperative for survival, its chronic stimulation can lead to negative health consequences due to dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis and its end product, the glucocorticoid cortisol. In fact, chronic psychosocial stress has been identified as an important pathway through which lifestyle alterations associated with market integration (MI; the degree of production for and consumption from a market-based economy) impact traditionally-living societies experiencing rapid cultural changes. Few studies, however, have systematically examined the relationships between MI and HPA axis activity. Moreover, limited research has examined how factors associated with MI influence children's perceptions of the shifting cultural milieu. The primary goal of this dissertation was to illuminate the dynamic features of the human stress response among the indigenous Shuar of Amazonian Ecuador with four objectives: 1) To examine HPA axis activity among the Shuar to address fundamental questions about the basic biological mechanisms of the human stress response; 2) To examine individual differences in HPA axis activity as shaped by age, sex, and body mass index (BMI); 3) To evaluate how factors associated with MI influence the HPA axis activity of Shuar children and adolescents; and 4) To utilize a conceptual model (cultural consonance) to better understand how Shuar youth perceive changes in the sociocultural environment. Results suggested that age was positively associated with cortisol levels, while age and sex moderated the relationship between BMI and the decline in cortisol across the day. Factors associated with MI did not directly affect the cortisol patterns of Shuar children and adolescents; however, age, sex, and BMI moderated these relationships. For example, Shuar youth experiencing greater exposure to MI displayed age-related increases in waking cortisol levels. Finally, Shuar children and adolescents with less exposure to MI demonstrated more incongruity with their locally-defined model of lifestyle success due to limited access to items identified as important for “a good life”. These studies illustrate the complexity of the human stress response in the context of culture change. This dissertation includes unpublished, co-authored materials. / 10000-01-01