Journal of Evolution and Health: A joint publication of the Ancestral Health Society and the Society for Evolutionary Medicine and Health

Posttraumatic stress disorder (PTSD) is a burdensome condition that has been made worse by the Covid-19 pandemic and that can lead to suicide, especially among childhood trauma victims, rape victims, military service members, and law enforcement. PTSD is thought to be an evolutionary mechanism that functions to promote survival by heightening the stress response in an anticipatory fashion, allowing the organism to react quickly to recurring stressors or threats, even when stressors or threats are not present in the immediate environment. Frequent and sudden activation of the stress response can be uncomfortable and deleterious to health. The mammalian dive response (MDR) is another evolutionary adaptation that functions to promote survival by conserving oxygen when submerged underwater, and like the stress response, it disrupts the homeostatic environment. However, the physiological reactions induced by the MDR include slowing of the heart rate, conservation of oxygen, and conservation of energy, while the fight or flight response has opposite physiological effects. I hypothesize that frequent activation of the MDR and its parasympathetic components might inhibit brain regions involved with stress, and condition neural circuitry to anticipate aquatic submersion stimuli, thereby reversing the sympathetic mechanisms involved in the fight or flight response and PTSD.