Stress increases evolutionary fitness. Evidence!

Carrera, S. C., Godoy, I., Gault, C. M., Mensing, A., Damm, J., Perry, S. E., & Beehner, J. C. (2025). Stress responsiveness in a wild primate predicts survival across an extreme El Niño drought. Science Advances, 11(4), eadq5020. https://doi.org/10.1126/sciadv.adq5020

My early research was on neuroendocrine responses to fear, and I took great pleasure in writing chapters in the Handbook of Stress about the evolutionary origins and especially the functions of the stress response. It is such a universal, costly, reliable and carefully controlled response that it has to provide selective advantages. But strong evidence for my thesis was never there. Now it is.

In this wonderful report, my colleague Jacinta Beehner and her group at the University of Michigan, including first author Sofia Carrera, have demonstrated that individuals with a more intense stress response in one drought are more likely to survive the next one. The finding took decades of field work collecting fecal samples, and careful laboratory analysis and statistical analysis. But it was worth it. This is the first study to demonstrated the adaptive nature of the stress response in wild primates.

Abstract: We know more about the costs of chronic stress than the benefits of the acute stress response—an adaptive response that buffers organisms from life-threatening challenges. As yet, no primate study has empirically identified how the stress response adaptively affects evolutionary fitness. Here, we take advantage of a natural experimentan El Niño drought—that produced unprecedented mortality for wild white-faced capuchins. Using a reaction norm approach, we provide evidence from primates that a more robust stress response to a challenge, measured using fecal glucocorticoids, predicts a greater likelihood of survival. We show that individuals with greater stress responsiveness to previous droughts later had higher survival across a severe El Niño drought. Evolutionary models need empirical data on how stress responsivity varies in adaptive ways. While we cannot buffer subjects from catastrophic events, we can use them to understand which aspects of the stress response help animals to “weather the storm.”