That's a really interesting question. My experience is in playing Clarinet since I was about 10 years old, professionally for a year or two and more sporadical

That's a really interesting question. My experience is in playing Clarinet since I was about 10 years old, professionally for a year or two and more sporadically over the last 10 years. (I'm 50ish) I can play clarinet (even now) without any difficulty, can (re)play music I've heard a couple of times (memory is getting worse as I get older) and sight read music fairly easily as long as it's not too fast or complex. For the last 20 or so years, I've had access to a piano, and have attempted to teach myself how to play two handed. I can play melodies by ear, and add some simple chord accompaniment but have not a hope of reading two handed music to play. Most other instruments, as long as I can master the technique for producing a decent sound and get my hands around the fingering, I can also play fairly successfully by ear. So I can pick up a guitar and pluck out a melody, pick up my daughters violin (groan) and squeak out someting that you can recognise. My technique sucks and I'm prob not doing it correctly. I can also do a pretty decent job of singing anything I hear. My experience leads me to suspect that playing by ear is, like singing something you have heard, the natural way of making music. The only difference is that you need to have physical mastery of the sound making process, hence my difficulty with two handed playing piano as I've no experience with making music with each had playing something different.