We all need sleep, but are you the type who likes to sleep in on Saturdays while your friends are already out for a run? You might not be lazy; it could be a result of your genetics. Scientists found that people with a certain gene—called ABCC9—sleep about half an hour more per night than those without the gene. The study involved more than 10,000 Europeans, who provided a blood sample for testing and reported how long they slept. Researchers were careful to only ask about the participants’ sleep patterns for their “free” days, when they did not have to get up early for work, weren’t taking sleeping pills and were not working shifts. In all, one-in-five Europeans carry the gene, which increases their need for sleep. They are in good company, too. Fruit flies with the gene—which is also involved in determining the energy level of the cell—also slept longer. Around half a dozen genes have been linked to sleep patterns. In another study, scientists found that a mutation in a separate gene causes insomnia in fruit flies, drastically shortening how long they slept. Flies with the gene also lived about two-thirds as long as the flies without the gene. Fortunately, the gene discovered in Europeans isn’t that extreme. Still, since genes are inherited, if you are a late sleeper, your children may be as well. So lay off them when they want to stay in bed instead of getting up to mow the lawn.