I'd love to know who invented these expressions - and why.

I mean, someone, somewhere must have been the first to say:

shilly shally
harem scarum
hocus pocus
airy fairy
wishy washy
namby pamby
jiggery pokery
etc

and the fact that so many are 'rhyming pairs' can't just be a coincidence, can it?

I love 'em by the way.