Every scientist wants to be an iconoclast, but most end up doing rather conventional work. Understandably, because it takes a special sort of nerve to risk your career and reputation on an idea or approach that could be very, very wrong - so wrong that it would be tough to recover from. And yet risk-taking is often at the root of the best science. The historians of science Oren Harman and Michel Dietrich take a look at what makes scientific risk-takers tick (subscription required). These two are the editors of the recently published Rebels, Mavericks, and Heretics in Biology. Harman and Dietrich argue for several generalizations about iconoclasts (although the warn that "While all conventional practitioners in the life sciences may be said to be conventional in the same way, all rebels seem to rebel in their own particular fashion"): - They often cross disciplinary boundaries. Thinking that is conventional in one field can be very radical when applied to problems in another one. - "Rebels, it seems, often look back as much as they look forward." Like Alfred Russel Wallace, who ultimately came to believe that humans were excepted from natural selection, iconoclasts will win big on one thing, but may not be able to repeat the performance. Or in other cases, by taking inspiration from past approaches to science and applying them to the present, some rebels can reshape the thinking in their field. So what are the key ingredients for being a good rebel? "First, the rebel must choose an important and relevant problem; those who tackle irrelevancies are never remembered." It may also be that the people who tend to be rebels get bored taking on anything less than a big question. With an important problem in hand, "the scientific rebel exhibits, invariably and across the board, what the Anglican clergyman and writer Charles Kingsley once called 'divine discontent.'" Dissatisfaction drives these rebels to stubbornly pursue ideas that otherwise would look unfruitful, or too risky. There is also a lesson here on how real scientific iconoclasts operate - in contrast to the typical behavior of pseudoscientists posing as rebels. These rebels take as their departure point a serious and sincere understanding of the current scientific consensus. Like great iconoclastic artists or writers, who are always very well versed in the work of their predecessors, scientific iconoclasts know very well what they are rebelling against. They maybe stubborn, sometimes unreasonable, and often wrong, but the successful ones do know how to challenge mainstream science on its own terms.