Mythology has changed signifigantly throughout the years. These ancient stories have evolved from oral tradition to stories written in books; as well as evolving from being perceived as fact, to simply a collection of interesting stories. Infact, mythos, the root word that mythology derives from, originally meant fact or history; transforming to now mean a fictional tale in current times.
Thousands of years ago, people recited stories of past event to eachother. These stories often explained occurances that puzzled them, such as the stars in the sky, or the changing seasons. Because they did not understand the concept of science, people would create elaborate tales filled with mystical beings to explain these natural phenomena. For example, the Ancient Greeks used Demeter, the goddess of agriculture, to explain the drastic changing of the seasons. It was said that during the half of the year when Demeter's daughter, Persephone, was stuck in the underworld being the wife of Hades, Demeter became extremely distraught and all of the plant life would wither and die. Then, during the half of the year when Persephone was up on earth with Demeter, she would become ecstatic and the earth would be filled with beautiful calypsos and other greenery. As different people would pass these myths down through oral tradition, they would be altered and embelished, much like a game of telephone.
However, myths have emerged into something very different than what they were in ancient times. The stories that were once used to explain nature and its mysteries, have now been replaced with science and logic. In this day and age, we know that the seasons have nothing to do with the goddess of agriculture, and everything to do with the earth revolving around the sun. Although we have deemed these stories fictional, we still tell them today. However, instead of orally passing them down, we now write the myths down in books. An example of this is the Percy Jackson series which basically elaborates on the Greek Gods and Goddesses, telling the storie of their demi-god children. Telling these stories in books allows many people to read the same story and be able to discuss it with one another.
Although myths still do exist today, both the myths themselves, and our opinion of them has changed immensely. These collections of ancient stories, which were once the history books of ancient times, are now just entertaining stories for those of us in the present. The means of communicating these myths has changed as well: from oral tradition to words written in books.