Nesse (Why We Get Sick), director of the Center for Evolutionary Medicine at Arizona State University, thought-provokingly comments on modern medicine's continuing difficulties in treating mental illness. Nesse notes that identifying the brain abnormalities and genes responsible for specific disorders has not, contrary to expectations, led to much progress; for example, there have been "no major breakthroughs in the treatment of depression in the last 20 years." He hypothesizes that since natural selection did not eliminate "anxiety, depression, addiction, anorexia, and the genes that cause autism, schizophrenia, and manic-depressive illness," they must have some benefits. He does not claim to know what all of those benefits are, making clear at the outset that since this is a new field, his conjectures may well prove wrong. Nesse shows a particular knack for clearly explaining his concepts, such as anxiety's value as a survival mechanism against predators and how the cost of fleeing in panic unnecessarily is outweighed by the benefit of doing so from a genuine threat, which he terms the smoke detector principle. Nesse fully meets his modest but laudable goal of providing a conversation-starter on why mental illness should be viewed from an evolutionary perspective. Agent: Katinka Matson, Brockman, Inc. (Feb.)