Is sleep an evolutionary mechanism developed to keep us out of harm's way in the dark hours, or is it a way to repair and recuperate after the day before? Scientists are still unsure exactly why we sleep, but they can agree that sleep is an essential part of our day. Lack of sleep can be incredibly dangerous - ten rats subjected to long-term total sleep deprivation in 1989 died within 11 -32 days, with no obvious anatomical cause of death'-. The rats had a debilitated appearance, lesions on their tails and paws, and lost a considerable amount of weight. While it is impossible for humans to be completely deprived of sleep over long periods - the brain shuts down and takes microsleeps, falling into a sleep state for a period of up to 30 seconds - sleep deprivation can affect the brain and cognitive function, leading to other problems.
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