The mammalian diving reflex refers to an adaptive characteristic that permits the mammals to stay underwater for an elongated duration of time. It is more noticeable in aquatic mammals, however, is weaker in mammals like humans.
This reflex is initiated when the face encounters with cold water. The initial influence is bradycardia in which the rate of the heart slows down up to 25 percent. There is peripheral vasoconstriction that comprises a reduction in the supply of blood to the arms and legs, and the supply upsurges towards the brain.
It can be stated that in humans, it is not an evolutionary vestige, but yes it is not much amended as aquatic mammals due to their terrestrial habitat.