The Defensive Activation Theory of Blindness

The fall-off in REM sleep is seen across species, including puppies and kittens. Blind people have dreams because their visual system was taken over by other senses like hearing and touch. Some animals are born with a lot of plasticity at night so they need this defensive activation to go to sleep. The human primate doesn't walk for a year until it's 13 years old; the vervet monkey stops walking within three weeks.