Now that the technical wave has passed a bit, maybe an un-trained chap can follow up on the "de-evolve" or "devolve" concept. The lead singer for the Orioles, Sonny Til, stated that the Mills Brothers were his inspiration. The Mills Bros first recorded in 1931, as a very straight barber shop based group. Three brothers and their father, who played rhythm guitar and, I believe, sang bass as needed. They gradually added more swing and syncopation and jazz artifacts until the old sound was almost gone, leaving their impecable timing and intonation. At least a few Mills Bros songs were coveded in the 1950's by Do-Wop groups.