In ten weeks, one female fruit fly can produce more descendants than there are people on Earth. Some fruit flies are born without genitals - scientists call these mutants Ken and Barbie - whereas others are born with their legs on their heads. They can be trained by punishment and reward, and have a work-and-rest schedule based on the 24-hour clock. They can become addicted to crack cocaine. Males have toxic semen, which is bad news for females: too much sex can kill them. And there are more than 1,000 species living in Hawaii. The amazing fruit fly is, in fact, an unsung hero in the history of science. This is the story of modern biology - from genetics to evolution, physiology to ecology, medicine to psychology - told through the life of the fly.