Structurally speaking, square dance calling is as close to rap as it gets. And that goes way back.
Sorry, Geenius, (and to everyone else for this hijack) but I must disagree:
“In 1962, a time when Jamaica was copying the musical style of America, Cecil Bustamente Campbell, later known as Prince Buster, knew that something new was needed. He had his guitarist Jah Jerry emphasize the afterbeat instead of the downbeat. To present day, the afterbeat is esencial to Jamaican syncopation. Ska was born.”
From http://www.slip.net/~skajam/history.html
Prior to 1964, when rock steady emerged, even the Wailers (Bunny Wailer, Peter Tosh, Bob Marley) were considered a “ska” band.
Also note that the above quote shows that ska was deliberately created, not misinterpreted due to radio interference as I had speculated earlier.
(Hijacked out of deference to my friends, The Pietasters, talented artists and music historians committed to dispelling the myth that ska originated in England.)