Sleeping
Research over the past 20 years has finally begun to provide at least a partial explanation for why we must sleep. The clearest finding is that sleep does not serve just a single purpose. Instead, it appears to be needed for the optimal functioning of a multitude of biological processes – from the inner workings of the immune system to proper hormonal balance, to emotional and psychiatric health, to learning and memory, to the clearance of toxins from the brain. At the same time, none of these functions fails completely in the absence of sleep. In general, sleep seems to enhance the performance of these systems instead of being absolutely necessary. And yet, anyone who lives for months without sleep will die.