Stop the presses! Sharks do get cancer. This normally wouldn't qualify as big medical news, and I barely noticed the item when it appeared not long ago in the New York Daily News. But think of the huge amount of mythology-and business-that has mushroomed out of a single, easy-to-grasp and, as it happens, false anecdote. If sharks are immune to cancer, wishful thinking went, they must make a protein or molecule that prevents cancer from developing. From this appealing little fiction emerged a thriving branch of alternative medicine: the use of shark cartilage to treat cancer.

It's easy to dismiss the shark-cartilage hypothesis as fairy-tale science. But appealing stories are nonetheless an integral part of the research process, as Peter Medawar shrewdly observed in his book Pluto's Republic. Scientific theories, he wrote, "begin, if you like, as stories, and the purpose of the critical or rectifying episode in scientific reasoning is precisely to find out whether or not these stories are stories about real life."Nowadays, telling a good story-whether it holds up or not-has become a big part of contemporary biotech and pharma.