Rock and roll was the product of a few main genres of the 1940's and 50's, these being gospel, blues, and jazz. The birth of rock and roll was strongly assisted by the latest inventions like the electric guitar, amplifier, microphone, and 45 rpm record, which served to promote smaller and more upbeat bands, rather than huge jazz bands of 20 or 30 pieces.
Now rock and roll is a very broad genre, and it's hard to tell what song is the first rock and roll song recorded, but the best definition I've found is from Supreme Court Justice Potter Stewart, who stated in 1964:
"Rock and Roll? I know it when I hear it."
Very simple, very precise. Some say it's the beat, some say it's the instruments, nah, I'd prefer to go with his definition.
Ah, doo wop... Now I'm a huge fan of this brand of rock and roll because it's vocally dominated, and I just love a good harmony. Doo wop originated as choir in churches, but later evolved into a prominent form of rock and roll.
Which sub-genres of rock are your favourite?