Hi all.
In the Spring I'll be teaching an Ethnomusicology class about how folk songs evolve through oral tradition. The students are asked to listen to and analyze a number of versions of the same song, as collected from far flung locations from sources believed to represent orally transmitted tradition. We'll look at the similarities and differences between the different versions to find evidence of common origin, evidence that songs gradually change when passed on by oral tradition, and observe how the interaction of culture and folk songs impacts this process. (Being a Biologist by training, I apply concepts from evolutionary theory: mutation, migration, isolation, drift, fixation, extinction, selective pressure, divergent vs. convergent evolution, etc.).

I have lots of great examples, but they are all text-based - songs that share a common origin of the text/story, while diverging greatly in tune and more or less in textual details.

Given that the course is being offered in the Music department, however, I feel I should have at least some examples in which we examine the evolution of *tunes* - where the same melody is used, but gradually morphed and mutated, resulting in local variants; or where other cultural factors such as dance traditions, religion, contact with other cultures, etc., systematically altered the tunes; and/or where the same tune is used to set entirely different texts. My knowledge is much weaker on this point, so I'd like to study up.

Can anyone suggest good examples, or a good reference work on this topic? Is there a melody equivalent of textual concepts like commonplaces and floating verses?

Since I am teaching in English, I'm restricting myself to English language folk traditions for the textual examples. But tunes that crossed language barriers would be of particular interest.

Many thanks,
Pamela