One ancient evening, lost in the mists of time, someone looked into the sky and wondered for the first time: What are those lights? Where did plants and animals come from? How did I come to be? Since then, humans have tried to answer those questions. At first, the answers our ancestors came up with involved tales of magic or legends like the one that accounted for the eye-like markings on the peacock's tail in Figure 1-1. Then, slowly, humans began to explore the natural world using a scientific approach.