Susan Jacoby's analysis of why Americans reject rational thought and distrust intellectuals is so trenchant that examples proving her point can be found daily: 10,000 B.C. jumbles up prehistory in a way that reinforces the appalling statistic Jacoby quotes from a 1998 survey, "One out of four public school biology teachers believes that humans and dinosaurs inhabited the earth simultaneously." Jacoby criticizes the media's bad habit of lending credibility to what she calls junk science like "boy brain/girl brain," and just this month The New York Times Magazine runs an article called "Teaching Boys and Girls Separately," featuring one of Jacoby's targets, Michael Gurian, author of Boys and Girls Learn Differently. Jacoby explores the strains of anti-rationality that have run counter to the Enlightenment principles of the founding fathers, with an emphasis on both religious fundamentalism and pseudoscience. When intellectuals like Herbert Spencer hijacked Darwin's theory of natural selection and applied it to social selection, a large segment of the population began to distrust secular learning and logic. The sad fallout continues today, as people all the way up to the president are unclear on the real meaning of the word "theory" and want schools to "teach the controversy" about evolution. As Jacoby notes, this puts "observable scientific facts, subject to proof, on the same level as unprovable supernatural fantasy." The result is government policy that ignores good science on global warming, stem-cell research and environmental protections. Jacoby can sound painfully snobbish when complaining about the youth movement of the 1960s, which she blames for the general dumbing down of culture, but her chapter on "Middlebrow Culture" will appeal to readers of a certain age who still remember Will Durant and the Book-of-the-Month Club. Although Jacoby doesn't mention another middlebrow favorite—The Atlantic—one wonders if she survived the sight of the April issue, with Britney Spears on the cover and a 12-page article about paparazzi inside. (By Susan Jacoby; Pantheon; 356 pages; $26 hardback)

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