> In science and philosophy, a just-so story is an untestable narrative explanation for a cultural practice, a biological trait, or behavior of humans or other animals. The pejorative[1] nature of the expression is an implicit criticism that reminds the listener of the essentially fictional and unprovable nature of such an explanation. Such tales are common in folklore and mythology (where they are known as etiological myths—see etiology).

https://en.wikipedia.org/wiki/Just-so_story