For years, scientists have debated the purpose of sleep. According to some evolutionary scientists, sleep evolved primarily as a survival mechanism. Before the discovery of fire, our early human ancestors were unable to see and avoid approaching dangers at night, such as stalking animals or precarious cliffs. Thus, humans—as well as all other animals—slept to keep themselves safe.
While this evolutionary approach partly explains the reasons for when we sleep, it doesn’t answer why we sleep. The obvious clue is to ameliorate their feelings of exhaustion. But researchers have struggled with the missing link between the desire for and the purpose of sleep: Why can’t the body replenish its vitality without delving into a netherworld of dreams and diminished consciousness? What is it about sleep that enables the body to fix itself? At present, it appears that sleep—particularly the sleep-inducing hormone melatonin—plays a crucial role in keeping the brain free of free radicals and in stimulating the immune system. Studies prove that without sleep, the body would break down and die.
