Nesse and Stearns' piece is particularly worth reading, it's both convincing and important. (Nesse, as many of you will know, published an influential book with George C. Williams in 1995 entitled Why We Get Sick: The New Science of Darwinian Medicine). Essentially, Nesse and Stearns' argument is that:
an evolutionary perspective fundamentally challenges the prevalent but fundamentally incorrect metaphor of the body as a machine designed by an engineer. Bodies are vulnerable to disease – and remarkably resilient – precisely because they are not machines built from a plan. They are, instead, bundles of compromises shaped by natural selection in small increments to maximize reproduction, not health. Understanding the body as a product of natural selection, not design, offers new research questions and a framework for making medical education more coherent.(See also: New Scientist's editorial on the new journal).