Why do We Sleep?

Sleep is one of the few universal behaviors. Sleep is seen even in species that would seem better off without sleep, for example, the Indus dolphin. Living in muddy waters, over the ages, it has become blind, presumably because vision is not useful in their natural habitat. However, despite the dangers caused by sleeping, sleep has not disappeared. It never stops swimming; doing so would result in injury, because of the dangerous currents and the large amounts of debris carried by the river during the monsoon season. Studies showed that they slept a total of seven hours a day, in very brief naps of four to sixty seconds each. If sleep did not perform an important function, we might expect that, like its vision, sleep would have been eliminated in this species through the process of natural selection. But why is sleep that important?

Despite centuries of inquiry, scientists have yet to reach a consensus why we sleep.