The Tribe as the Human Evolutionary Unit.

What is the Purpose of Religion? - Beliefnet

As the human evolutionary selection unit is the tribe, as long as tribes were small enough and cohesive, a god was a useful entity to take the responsibility of leadership from the tribal leaders. 'Hey, it isn't me making bad things happen, it is God. I only take credit for the good things that happen.' Religion codifies the social necessities of tribal cohesion, providing the moral and social rules that allow the tribe to function. Another important function of religion is to codify and preserve the stories that transmit those moral and social rules. Humans are story telling animals and the stories told in the gatherings are the way the mores are transmitted and preserved.