Before civilization, life alone was hard, probably impossible. You were safer being part of a group, not only was it easier to “go along to get along,” it was necessary for survival.
A group looks for signals that you’re a reliable member of their group and can be trusted. Think of a politician wearing a hard hat and a cheap, shiny nylon AFL-CIO windbreaker while touring a factory, or Lance Armstrong with a crucifix swinging like a metronome from his neck while he pedaled up alpine passes in the Tour de France. The politician has probably never done physical labor and Lance isn’t religious, but both are sending signals to the groups they want to be part of – that they’re reliable members.
Religion does a good job of using our need, to belong to a tribe, to their advantage by using rituals and symbols. If you see someone who’s at church every Sunday, or who wears a yarmulke most days, or who dances for rain when there’s no rain you begin to feel like that other person shares some fundamental beliefs with you. You’ll be willing to help them out and they’ll likely help you out too.
We believe in lots of things for which there’s no evidence. For example, a yoga instructor says that a certain pose “wrings out” the kidneys, does it really? The instructor probably just heard it from her instructor, who heard it from his instructor…
Religion becomes attractive because faith is easier than critical thinking. Being skeptical just takes more brain cycles, more effort. So there’re more religious folk than nonreligious folk. The rituals and symbols in religion take the place of evidence. And people want to belong. So it became a big daisy chain. But I think it’s starting to unravel a bit.