It is said to be the survival of a pagan fertility play, formerly found widely in Europe. It deals with the killing and miraculous resurrection of a central character. I have read that in the fullest (Euorpean) versions, there are parents, grandparents and children as well, but I don't have any references to check it out.

Incidentally, a version of the speech often made by the (quack) doctor is in the Bodleian Ballad Library as a song, 'The Infallible Doctor'