摘要
Sleep is a universal process with vital functions.Animals deprived of sleep for a long period of time will die.Despite its crucial functions,fundamental questions about sleep remain unexplored.For instance,why do animals sleep since it disconnects animals from the external world and exposes them to danger（we really do not know!）？
Sleep is a universal process with vital functions.Animals deprived of sleep for a long period of time will die.Despite its crucial functions,fundamental questions about sleep remain unexplored.For instance,why do animals sleep since it disconnects animals from the external world and exposes them to danger（we really do not know!）？
