What was indicated by the emphasized backbeat in the rhythm and blues hits of the late 1940s?

A rhythm was emphasised in the transformation of blues and R&B into rock and roll in late 1940s hits. It was a style in music that combined elements of jazz and blues to syncopated rhythms with a strong backbeat.
 African American developed it in the late 1940s incorporating horns incorporated to R&B., while the rhythm in blues is a swung eighth note.