The mammalian diving reflex is a unique set of evolutionary adaptations leftover from a time when all life developed in the oceans. The diving reflex, as well as the swimming reflex, are an inherent part of human nature and can be observed in newborns and infants when placed in an aquatic environment.
Despite the majority of mammalian species losing many of the biological ties that connect us to the oceans (ie. our lungs don’t function particularly well underwater), we are still inherently connected to our ocean dwelling ancestors. The diving reflex is a remnant of some of the features that allowed those relatives of the past to survive in the water. It’s triggered when a mammal’s face comes in contact with or is submerged in cool water. When this occurs, receptors are activated within the nasal and sinus cavities as well as areas in the face connected to the trigeminal nerve. Information that the face has encountered water is transmitted to the brain and the autonomic nervous system through the vagal nerve, resulting in the immediate closure of the airway as well as a number of physiological changes to optimize the body’s conservation of oxygen. The changes that begin upon initiation of the diving reflex include: