I'll report something I have found to be strange.

First, my terms of reference. A guitarist learning very slowly from age 12. A poor, "by ear" piano player, learnt as a teenager. A piano accordion player of ten years, only four with any great effort. ...... and a fiddle player for the last six weeks! Piss poor, but I absolutely love it, as much as the Bloke in the Corner doesn't.

The strange thing is this. I struggled with melody (i.e. not straight chord strumming or later, picking) on the geetar, but with the fiddle, the tunes I learnt by ear on the squeezebox have just fallen beneath the fingers. As the guitar is tuned in fourths, and the fiddle fifths, does that suggest, for me, at least, that fifths are the more natural tuning?

BTW I am 'old', according to my children, at 42!