h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Religion probably started as a story. One fine day, some little kid asked his dad
"How was everything created?"
His dad not actually knowing the answer, but wanting to seem like he did, made up some story to answer this question. The little kid went around and told all his friends, who told his friends, and this story rapidly spread and was believed by many people. Finally people added, filled in the blanks and then wrote ita all down. This became a solid beliefe that was taught to many generations of people to come, and was the start of a religion.

There are so many different religions, because so many different people told different stories to answer the same question. As for the similarities between several religions, some people heard a story and then changed and added to it, and the new edited and altered version was considered to be the truth and people believed in it.

But thats just one story about how religion started.