R&B laid the foundation for rock 'n' roll. Emerging after World War II, R&B was a stripped-down, upbeat form that mixed jazz and the blues over a back-shuffle snare beat. The raunchy lyrical content continued a time-honored African-American tradition of setting sexual innuendos and double entendres to a danceable beat. This was not a male-dominated music form -- artists such as Ray Charles and Little Willie John shared the limelight with R&B pioneers Ruth Brown, Big Maybelle and Big Mama Thornton. In the 1950s, R&B artists incorporated more pop-oriented time signatures and lyrical topics, moving the infectious sound into the popular mainstream.