Social bonds do not mediate the relationship between early adversity and adult glucocorticoids in wild baboons

In humans and other animals, harsh conditions in early life can have profound effects on adult physiology, including the stress response. This relationship may be mediated by a lack of supportive relationships in adulthood. That is, early life adversity may inhibit the formation of supportive social ties, and weak social support is itself often linked to dysregulated stress responses. Here we use prospective, longitudinal data from wild baboons in Kenya to test the links between early adversity, adult social bonds, and adult fecal glucocorticoid hormone concentrations (a measure of hypothalamic-pituitary-adrenal (HPA) axis activation and the stress response). Using a novel causal inference framework, we found that experiencing one or more sources of early adversity led to a 9-14% increase in females’ glucocorticoid concentrations across adulthood. However, these effects were not mediated by weak social bonds: the direct effects of early adversity on adult glucocorticoid concentrations w...