Sleep is confusing because it is universal but diverse, dangerous but necessary, and routine but mysterious. Each species slumbers in a different way, but they all enter the same vulnerable state that prevents them from doing important tasks like mating, eating, and hunting. Many scientists believe that sleep is important because it provides the brain with the chance to reset itself after working all day. Other scientists believe sleep has evolved to give brains time to solidify memories that are created while awake and to clear the brain of toxins that have accumulated throughout the day.

Of all the species in the animal kingdom, the African Savanna Elephant is the lightest sleeper. These elephants sleep just two hours, spread out over several bursts, while some nights they won’t even sleep because they’re protecting their family from predators. The elephants are able to function normally the next day without the need the make up for their sleepless nights, unlike most other species. This is because their brains have unknown adaptations that could actually be the answer to why animals vary in sleep and why sleep has evolved.