Dear old Mudcat... what an interesting and esoteric discussion. I'm really enjoying reading it. And thanks for correcting me on Claude Jeter. At least I didn't call him Derrick. As always, we get into definitions of music, and I might as well give mine. Or, at least what I consider falls under the umbrella of "folk" music. Bluegrass does, but straight country doesn't. Allison Krause I could comfortably include in "folk," although she has often strayed pretty far away from her roots. I wouldn't put Shania Twain under folk, because I don't hear many vestiges of folk in her music. When I make a statement that, not including bluegrass(although I consider it folk music) I don't remember hearing falsetto used in white southern gospel or white southern folk music. I ain't talking Southern France, or monks, or Mexicans... God love 'em all. My generalization is very specific. If that's possibile. It may not be 100% correct, and if someone can produce a recording with Mother Maybelle, or Charlie Poole, or more traditional American folk singers singing falsetto, I'll add an asterisk to my generalization.
The other area I've mentioned is some country music... Jimmie Rodgers immediately comes to mind for slipping up into falsetto. Yodelling is as falsetto as you can get.
As for rhythm and blues (Doo wop), listen to the Five Blind Boys of Mississippi, or many other black gospel quartets and you won't have any problem figuring out where it came from. Same with the "Why is everrrbody always pickin' on me" bass line.... Straight out of black gospel.