Influences on music go further back than most people know. Most things that we, initially, believe are original, are usually an evolution of something tried long before. The real difference between rap and other songs is that it is spoken, with music. Many songs begin as poems, and are changed to fit a style and be more like what is marketable at that current time. As a style, speaking with music is not new. I have heard such things in ceremonies of primitive tribes, though how well they rhymed is debatable.

"Big John" does rhyme, by the way.