Some participants in this thread may not realize that "evolution" has more than one accepted (and acceptable) meaning.

In addition to several other senses, including the Darwinian, Oxford gives:

"A process of gradual change occurring in a system, institution, subject, artefact, product, etc., esp. from a simpler to a more complex or advanced state. Also: a gradual and natural development as opposed to a sudden or instigated change (often in contrast with 'revolution')."

Printed examples go back to the early 18th century, long before Darwin.

According to this definition, folk tunes and songs commonly "evolve." It's one reason they're considered "folk."

Academics may want to avoid the words "evolution" and "evolve" because they could be misunderstood as meant to suggest "survival of the fittest" or "continual improvement or increased complexity," but those connotations are not essential to the meaning of these familiar words.