I'm going to imitate Rudyard Kipling and tell you a just-so story. Kipling was one of the most popular writers in the world 100 years ago. He wrote The Jungle Book. And also Just So Stories, which began as bedtime stories he told his daughter Josephine. They were about how animals got their famous features, like the camel's hump and the leopard's spots. Kipling was a wonderful writer but he made up his animal stories. My story is based on science, which means many people, through many recent experiments, have concluded things might "just so" be the way of this story. It's also a story about evolution, which is nature's research and development department. Like Kipling, I've given a human voice to certain things: Bacteria form committees and petition the research and development department for answers to their problems, as do plants and dinosaurs. And the R&D department (which is to say, evolution) tries to come up with solutions. I'm going to call evolution "Mr.