Human enthusiasm for progress--particularly when shortsighted, misguided, or tainted by self-interest--can ricochet, marring the global environment and the lives of millions. As a gasoline additive, lead suppresses engine knock. Lead is also a well-known poison, and yet during the 1920s it was championed over safer alternatives--and even backed by the U.S. surgeon general. Why? Money, of course, and the tremendous power of oil and automobile companies....