God has always been a puzzle for Scott Atran. When he was 10 years old, he scrawled a plaintive message on the wall of his bedroom in Baltimore. “God exists,” he wrote in black and orange paint, “or if he doesn’t, we’re in trouble.” Atran has been struggling with questions about religion ever since — why he himself no longer believes in God and why so many other people, everywhere in the world, apparently do.

If they don’t believe in God, what exactly are they afraid of?

The magic-box demonstration helped set Atran on a career studying why humans might have evolved to be religious, something few people were doing back in the ’80s. Today, the effort has gained momentum, as scientists search for an evolutionary explanation for why belief in God exists — not whether God exists, which is a matter for philosophers and theologians, but why the belief does.

In short, are we hard-wired to believe in God? And if we are, how and why did that happen?