This is really interesting research but I do have some misgivings. Whole languages does not just randomly jump from one population to another - but stories can,

This is really interesting research but I do have some misgivings. Whole languages does not just randomly jump from one population to another - but stories can, it just require a single travelling storyteller. And what they track is not full stories but “tropes” like woman marries magic animal who is really a man under a spell. It it really impossible that this trope could have appeared indepently in mutiple places?