Well, right. Humans naturally fear ‘outsides.’ It was a very useful trait back in the day. Religion was initially used to help get over that. “Why should I not steal from the guy 3 blocks down, I don’t even know him?” “Because the storm god might burn your hut down if you do.”

Larger tribes that worked well together did better than the smaller tribes that did not. And the larger tribes had superstition/religion holding them together.