Question

Nearly all mammalian species display REM sleep, but not dolphins. Which of the following is most likely a reason for the absence of REM sleep in dolphins?

a) Lack of REM sleep significance
b) Unique brain structure
c) Environmental factors
d) Genetic differences

Answer 1

Dolphins likely lack REM sleep due to environmental factors that require them to remain partially conscious to breathe and protect themselves while asleep. Their adaptation of unihemispheric slow-wave sleep allows one brain hemisphere to rest while the other stays alert.

Step-by-step explanation:

The absence of REM sleep in dolphins is most likely due to environmental factors or unique adaptations to their aquatic lifestyle, not because of lack of REM sleep significance, unique brain structure, or genetic differences. Dolphins need to surface to breathe, even when sleeping, and they have evolved a method of sleep known as unihemispheric slow-wave sleep, where one hemisphere of the brain sleeps while the other remains awake. This adaptation allows them to maintain enough consciousness to breathe and to watch for predators and other threats.

REM sleep, characterized by rapid eye movement, dreaming, and paralysis of voluntary muscles, may not be compatible with the constant need for motor control that dolphins require to swim to the surface for air. Moreover, the paradoxical aspect of REM sleep, signified by active brain waves similar to when awake, is an intriguing state but not observed in dolphins due to their need to stay partially conscious for survival.