Looking back on his 1940 hit with Lorenz Hart, Pal Joey, the composer Richard Rodgers judged that this was the work that “forced the entire musical comedy theater to wear long pants for the first time.” Is that really true? The standard historical line has it that the American musical started with pure froth and frivolity in the 1920s (Guy Bolton, P. G. Wodehouse, the Gershwins, Vincent Youmans, etc.), interpolated more sophisticated material during the course of the 1940s (Pal Joey, South Pacific, etc.), and finally came of age with Stephen Sondheim’s dark, ambivalent, thoroughly adult mid-career works such as Company and Follies.

This potted history is an extreme simplification, and only partly correct. Early musicals were never quite as silly as they are made out to be, and contemporary ones are not all that sophisticated. Musicals after all have been dealing with...