Nesse and Williams have written a lively discourse on the application of the principles of evolutionary biology to the dilemmas of modern medicine. Nesse, a physician and an associate professor of psychiatry, and Williams, a professor of ecology and evolution, provide a primer on Darwin's theory of natural selection. They explain that the functional design of organisms-e.g., our bodies-may suggest new ways of addressing illness. The book begins with a look at the causes of disease and their evolutionary influences. But the book mainly assesses the concept of adaptation by natural selection, and illustrates the ways Darwinian thinking can be applied to medical problems. As one example, the authors examine the use of penicillin over the past 60 years against bacterial infections. The book's quirky information may speak to a broad audience: researchers, for instance, have found that relatives of schizophrenics have an unusually high frequency of inclusion in Who's Who-which may counterbalance drawbacks of the disorder in evolutionary terms. The tendency toward child abuse, too, may be influenced, the authors say, by evolution and the passing on of genes. And there may well be an evolutionary reason to welcome morning sickness, they argue: nausea and food aversions during pregnancy apparently evolved to impose dietary restrictions on the mother so as to correspond with fetal vulnerability and, thereby, minimize fetal exposure to food toxins.