Wizzy, we have discussed the evolution of Blues from earlier sources, and I think the Minstrel tradition is an essential link. It formalized many slave songs, often mixing them with current popular music forms and appalachian-style traditional music. In formalizing these older musics, it also popularized them and became a form in itself to be imitated. Frankie and Johnny is an example of a song that likely pre-existed the minstrel tradition, was used in it, and contains many of the elements of the subsequent Blues genre.