Fades In Slowly offers a brief history of sheet music:
The Comprehension of, for example, piano sheet music requires an extraordinary form of literacy: the ability to read musical notation. I'm in awe of anyone who can do this. On the other hand, the capability to read or write music is not a prerequisite to compose music. In fact, many composers, take Captain Beefheart and Mark Edward Smith as two prime examples, have been capable of producing music without the capacity themselves to interpret or inscribe in musical notation, so long as an amanuensis of some sort is available.