The simple meaning I understand to 'evolution' is 'gradual change over a period of time'. Whether any change is for the better or worse is simply a matter of opinion surely and subject to fashion. Gibb is referring specifically to Darwin's theory and the spin-offs from it. Whilst some aspects in the methodology of studying biological evolution can be applied to folk music there have to be obvious differences. Scientists have tried to use the disciplines of evolution theory to study ballad evolution and some have been shot down and shown not to work. However, some very clever scholars have had a significant degree of success when applying the theory to a range of literature including ballads.

The way I see it, the evolution of any given folk song could include all of the processes, oral, print, scribal, editing, forgery etc.