On the eve of Daylight Saving Time, I flew home to Vermont from California. Crossing several time zones, I arrived near midnight. At 2 a.m., the clock jumped ahead an hour, leaving me discombobulated. “How messed up am I?” I asked sleep researcher and evolutionary anthropologist David Samson days later. Jet lag can make people feel moody and hungry at weird times, but my extreme state probably masked chronic sleep dysregulation, he told me. For most of human history, people woke with the sun and slept with the stars. Environmental cues like light and temperature synchronized the body’s clock, or circadian rhythm, to the day-night cycle. Nowadays, many of us spend more time indoors than out, where we bathe in artificial light and temperatures set for optimal comfort. Sign up for our newsletter We summarize the week's scientific breakthroughs every Thursday.