Do all creatures sleep?
Sleep might seem pretty simple, but scientists are still scratching their heads over questions surrounding this slumbering state. It’s unclear exactly why organisms need to sleep, let alone whether every last species actually settles down for siestas. Sleep itself isn’t all that straightforward, so let’s start by describing what’s typically defined as sleep. During times of sleep, there’s usually a reduction in physical activity and a decreased response to outside stimuli. Sleeping creatures often assume a customary posture — whether that’s lying down for people, hanging upside down for bats, or standing up as is sometimes the case for horses, giraffes and elephants. Sleep is also easily reversible, meaning it’s a relatively simple matter to wake up, especially when compared to other states along the continuum of reduced consciousness, such as hibernation
