Yodelling has a very wide distribution when used as the top of a trio or quartet - you get that in the singing of north-west Greece and southern Albania, in Georgia, and sporadically across to Flores in the Malay archipelago. (I have once seen a diffusionist attempt to explain that but it doesn't seem to be online any more). For all of those cultures, solo singing is not a recognized form - maybe you get lullabies but that's it. The idea of yodelling on your own seems to be an isolated spinoff from the much more ancient polyphonic tradition. Maybe the Denisovans invented it?