Slightly modifying an oft-quoted line by the famous biologist Dobzhansky, Nesse and Williams conclude, "After all, nothing in medicine makes sense except in the light of evolution." In this lucidly written book, the authors make this assertion throughout. They lay out principles for interpreting aspects of human health from an evolutionary perspective. For example, some of the body's responses can be viewed as adaptive defenses (e.g. fever), others the products of novel environments (e.g. Sudden Infant Death Syndrome, or SIDS). The authors raise intriguing examples, from adaptive withholding of the body's iron stores to pregnancy sickness, that put flesh on the bones of these principles. This book does a fine job of overviewing the ways in which an evolutionary perspective can contribute to a richer understanding of medicine than the more proximate (e.g. what are the chemical and genetic bases to schizophrenia?) focus alone can provide. For this reason, it may long be seen as a seminal contribution.