Well, Jerry,

You have managed to make me feel rather silly for getting technical, but I agree that the evolution of street corner harmony came from what worked, what was simple and what was repeatable.

My own personal theory on how the 1st inversion harmony developed is that it is so simple for a non- piano player to learn on the piano. It is also a very easy harmony for the other three middle parts to sing, and being stacked so tight, it makes the special Do-wop sound. But what do I know? I am just an ole Georgia cracker, and should always defer to an ole Janesville Badger like you!grin