Ying-Hui Fu: When these people have this mutation, their sleep amount is less. Normal people need eight to eight-and-a-half hours of sleep. These people sleep five and a half to six.

　　Even though the pair weren’t sleeping as much, they seemed fine.

　　 Fu: It’s not like they have sleep problem. They just don’t sleep as much.

　　Do they feel tired?

　　Fu: Not more than most regular people.

　　 Fu’s group wanted to study the effect of the mutation in a more controlled way, so they created a strain of mice with the same genetic change. Sure enough, they found that these mice slept less than the average mouse. What’s more, they seemed to recover more quickly from periods of sleep deprivation. The work is an important step forward, says Charles Czeisler, a sleep expert at Harvard Medical School.

　　Charles Czeisler: This study really shows that uh, the amount of sleep that we need each night is genetically hard-wired; this tiny genetic change is making a huge change in the behavior of both the people and the animals.

　　In some ways, this study raises as many questions as it answers about sleep. Czeisler says that it doesn’t prove that people with the mutation function as well as the rest of us; it’s possible that they’re just unable to get the sleep they need. He says it’s hard to tell because we really don’t understand the process of sleep at all.

　　Czeisler: No one really knows what the function of sleep is, although the leading hypothesis is that sleep’s core function relates to the repair and reorganization of brain cells.

　　 Still, studying this gene could help give clues about how and why we sleep. As for those of us who don’t have the mutation, Ying-Hui Fu says that we shouldn’t try and beat our genetic code.