From Volokh Conspiracy's Orin Kerr on Summer for the Gods, a history of the famous Scopes "monkey" trial by Prof. Edward Larson that won the Pulitzer Prize for history in 1997:

"The ACLU placed advertisements in local Tennessee papers looking for someone who would challenge the law. Local citizens of Dayton, Tennessee saw the advertisment, and realized that a prosecution under the law in Dayton would help the local economy by making people come to Dayton for the trial. A local prosecutor agreed to bring a prosecution if they would find a local teacher who would go along. John Scopes agreed to be the defendant for the test case. Scopes wasn't actually a biology teacher, but he had taught a biology class as a substitute teacher, and had used a state-assigned textbook that taught evolution. The "prosecution" was designed to be a friendly affair. The ACLU would get its test case to bring before the appellate courts, and Dayton's economy would benefit from all the attention brought by the trial. Scopes would face a fine in theory, but it was understood that he wouldn't actually have to pay it."