Horseshoe crabs and hibernating squirrels. Jet-lagged pilots and space station astronauts. Night owls and early birds. All of life is profoundly shaped by the daily, monthly and yearly cycles of planet Earth. This book takes the reader on a journey across a broad vista of science to make sense of the mysteries of biological time. How do the rotations of our planet shape our biology? What did human sleep cycles look like before artificial light? What happens to a person's waking and sleeping if they spend weeks in a dark cave? How adaptable are we to today's 24/7 living? Humans are relative latecomers in the story of life on Earth but we often think that technology has freed us from its constraints. Written by a world-leading chronobiologist, Night Owls and Early Birds illuminates the fascinating science of biological time and offers a stark warning to anyone giving up on a night's sleep to get more out of their busy waking hours.