This conversation was led by Sarah Mathew, Associate Professor in the School of Human Evolution and Social Change at Arizona State University, and Matthew Zefferman, Assistant Professor in the Department of Defense Analysis at the Naval Postgraduate School. Military personnel in industrialized societies often develop Post-traumatic Stress Disorder (PTSD) during combat. It is unclear whether combat-related PTSD is a universal evolutionary response to danger, or a culture-specific syndrome of industrialized societies. We interviewed 218 Turkana pastoralist warriors in Kenya, who engage in lethal cattle raids, about their combat experiences and PTSD symptoms. Compared to American combat veterans, Turkana suffer PTSD symptoms at high rates, but have lower prevalence of depression-like PTSD symptoms. Symptoms that facilitate responding to danger were better predicted by combat exposure, whereas depressive symptoms were better predicted by exposure to combat-related moral violations. The findings suggest that some PTSD symptoms stem from a universal response to danger, while depressive PTSD symptoms may be caused by culturally-specific moral norm violations.
- Zefferman and Mathew 2021, “Combat stress in a small-scale society suggests divergent evolutionary roots for posttraumatic stress disorder symptoms”
- Zefferman and Mathew 2020, “An evolutionary theory of moral injury with insight from Turkana warriors”