Evolutionary biologists have begun studying the rise of antibiotic resistance, one of the most urgent problems in public health. Their work suggests that old dogmas about the best way to prevent resistance may be wrong. Contrary to what most doctors think, for instance, using high doses of antibiotics may sometimes help spread resistance rather than prevent it. Combining antibiotics could backfire as well, and long treatments may sometimes do more harm than good. However, many researchers and clinicians are skeptical about these new ideas, which are difficult to test in humans because it might involve giving some patients a suboptimal dose of a life-saving drug.