Why are folktales passed down?

Like all forms of folk literature, folktales circulate orally and are passed from generation to generation. They are anonymous, as no-one knows who their initial author was, and they have a collective character, as each times it passes from storyteller to storyteller each individual feels compelled to add a certain detail or to change the plot a little bit. Stories are immortal, as their main plot-lines can be found in every country of the world and in almost any period in recorded history. They answer a basic educational need: to teach people (as originally Fairy Tales were not intended for children only) right from wrong, but they also have a recreational purpose.