If you've ever stayed up late and then gotten up early the next day， you know what it's like not to get enough sleep． It's very uncomfortable feeling． In fact， for many years scientists （1）　　（believe） that sleep is like food ﹣ if we don't get enough of it， we might get sick or even die． But now they （2）　　 （start）to wonder just how much sleep we need．

    Researchers at Imperial College London did a study on fruit flies（果蝇）． They found that flies that slept for very short periods of time ﹣ about72 minutes a day ﹣still（3）　　 （live） about as long as flies that slept for normal amounts of time． One of the female slept for just 4 minutes each day on average． This has led the researchers to wonder if sleep is less necessary than we previously thought．

    Humans are very different from fruit flies． Sleep（4）　　（help） repair tissue （组织） when our bodies perform a lot of maintenance （维护）． Sleeping allows our bodies（5）　　 （get） well again from the stress we experience each day．

    But can we really die from not seeping？ No humans have died so far from （6）　　（stay） awake for too long． The current（现在的）world record for sleeplessness （7）　　 （hold） by Randy Gardner from the US， who stayed awake for 11 days and 25 minutes in 1964．

    Scientist have not yet found any animals that don't sleep at all． Even animals that only seep for short periods are not completely sleepless．