When Stanley Kramer offered the role of E.K. Hornbeck to Gene Kelly, Kelly initially turned it down. Kramer told him that his co-stars would be Fredric March and Spencer Tracy, and Kelly changed his mind. This was a risky move on Kramer's part, as he had not yet asked March or Tracy to participate.
When Drummond's attempt to call scientific experts to the stand to testify in behalf of the defense is thwarted, Stanley Kramer adds a couple of elements from the actual Scopes Trial, combining the fiery closing of Clarence Darrow's speech on the motion to quash the indictment with the change in which Judge Raulston cited Darrow for contempt.
Writers Jerome Lawrence and Robert E. Lee named the overzealous prosecutor "Matthew Brady". When Roscoe 'Fatty' Arbuckle was tried for manslaughter three times in 1921/22, the real overzealous prosecuting San Francisco District Attorney was named Matthew Brady. Matthew Brady was also the name of the famous portrait and landscape photographer of the American Civil War.