The beauty of a perfectly calibrated argument: That's what Adam Gopnik celebrates in Angels and Ages: A Short Book About Darwin, Lincoln, and Modern Life. The English scientist and the American politician, both born on February 12, 1809, dismantled the dogmas of their age by seeing clearly (as visionaries do) and writing persuasively, with eloquence born of conviction. Gopnik revels in the revolutionary ideas that helped create our "moral modernity" as he reveals the complex characters who unearthed startling truths about nature, human and otherwise.