WHY WE GET SICK

Some surprising answers to questions about why our bodies are designed the way they are and why we get the diseases we do. Nesse, a physician (Psychiatry/Univ. of Michigan) and Williams (Ecology and Evolution/SUNY, Stony Brook) first teamed up to write an article on Darwinian medicine, which applies the concept of adaptation by natural selection to medical questions. That article, published in 1991 in The Quarterly Review of Biology, has been expanded into the present book, in which the authors look at the design characteristics of the human body that make it susceptible to disease. Their conclusions? First, sometimes it's our genes that make us vulnerable to disease. Some genetic defects arise through mutations, but more often, genes with deleterious effects are maintained through natural selection because their benefits outweigh their costs. Second, there's a mismatch between our present environment and the one that over thousands of years shaped our hunter-gatherer ancestors. There simply hasn't been time for our bodies to adapt, and we suffer the consequences. Third, disease results from design compromises. For example, the structural changes that allowed us to develop from horizontal four-footed creatures to upright two-footed ones left us vulnerable to back problems. Fourth, our evolutionary history has left us some troublesome legacies, such as the unfortunate intersection in our throats of the passages for food and air. Some of the areas Nesse and Williams apply their Darwinian approach to are infectious diseases, allergies, cancer, aging, reproduction, and mental disorders. Happily, they write with impeccable clarity, and when they are speculating (which they do freely), they are careful to say so. They also offer numerous suggestions for research studies, thoughtful proposals for reshaping medical textbooks and medical education, and a scenario dramatizing Darwinian medicine's possible clinical application. Fascinating reading for doctors and patients alike.