There is no need to go into a PhD level of detail to teach the students something that might be new and interesting to them. If their background is in popular music, jazz and art music, it may be news to them that:

- texts can have multiple tunes, which may be similar or very different

- the reasons for that are sometimes deliberate acts of creation and sometimes not

- it doesn't make sense to think of this process of variation as either corruption or evolution

- the process is not significantly a result of market forces

- it may be the result of variations in extra-musical human culture and human need rather than simple musical preference

- it largely disregards the ethic of intellectual property.

These large issues can all be illustrated by specific musical and historical facts, but don't bury the big picture in technicalities.