Rather interesting story Alan Lomax told about the origins of the spectacular Genoese 'Tralaliri' choral songs he recorded.
During the Garabaldi Revolution, the authorities banned the public singing of the songs that had sprung up during the events.
The men would gather in the cafes and hum and la-la the tunes of the banned songs - because there were no seditious words being sung, the police were powerless to stop them.
Eventually, the practice evolved into a genre of its own, appled to any subject
If you haven't heard it - Google it - there are some beautiful examples
One of the best was used to end A L. Lloyd's Folk Song Virtuoso programme
Jim Carroll