Seventy-nine years ago last summer, a legal carnival convened in the little town of Dayton, Tennessee, as the trial of John Scopes got under way. Banners and lemonade stands lined the streets. People joked that chimpanzees, brought to town to perform in sideshows, actually were in Dayton as witnesses for the trial. On one side was the American Civil Liberties Union, which had offered to pay the legal expenses of anyone who would challenge a Tennessee law that banned the teaching of Darwin's theory of evolution in public schools and universities. Twenty-four-year-old local science teacher John Scopes was recruited to...