Animals That Sleep the Least and the Most

Strange as it may sound, we still haven’t pinpointed why exactly humans and other animals sleep. Ongoing research poses many theories, often related to memory generation or learning. Maybe it helps restore DNA damage in neurons, as suggested by a Nature study last year. But back in 2017, scientists had learned that the upside-down jellyfish also appears to sleep, despite the lack of a brain or central nervous system. So, the jury is still out on the why behind sleep.