Quoting Jessica Marshall from ZooGoer blog at the Smithsonian
Anyone who has ever stayed up too late and regretted it the next day knows just how much humans need sleep. Animals need it, too. Every animal studied so far—from whales to octopuses to fruit flies—sleeps, although animal sleep takes various forms, and even among mammals the human eight hours is not the norm. Horses, elephants, and giraffes, for instance, sleep only about two to four hours a day, while bats and opossums sleep up to 20.
Oh sleep! it is a gentle thing,
Beloved from pole to pole.
—Samuel Taylor Coleridge