Scientists report a genetic mutation, appropriately called "after-hours" (Afh), which affects our internal body clock and might help explain why some of us are “evening people”, only falling asleep in the early hours of the morning. The research has important implications for human health in an increasingly 24/7 culture, where shift work and continental travel (and the associated jet lag problems) are already linked to several diseases. It can also be important for the many brain disorders, such as dementia, bipolar disease and mental retardation, which are associated to disruptions in the sleep/awake cycle.