It was only 20 years ago that we barely understood the importance of a biological function as basic as sleep. We still don’t know why such an extended and vulnerable state of being is necessary to our evolution. Dolphins can go a month without sleep after giving birth, or sleep with only one half of their brain at a time (unihemispheric sleep). Meanwhile plants follow circadian rhythm.

We do know that sleep evolved before brains did, a primordial remnant of when all living things synchronized rest with the day-night cycle? Maybe that cycle could also be part of the reason why brains evolved. So that animals could be able ignore sleep and decide for themselves when they are clear of predators and can rest.