The ancestral human population of 50,000 years ago, to judge from living hunter-gatherers, would have lived in small, egalitarian groups without chiefs or headmen. Religion served them as an invisible government. It bound people together, committing them to put their community?s needs ahead of their own self-interest. For fear of divine punishment, people followed rules of self-restraint toward members of the community. Religion also emboldened them to give their lives in battle against outsiders. Groups fortified by religious belief would have prevailed over those that lacked it, and genes that prompted the mind toward ritual would eventually have become universal.

In natural selection, it is genes that enable their owners to leave more surviving progeny that become more common. The idea that natural selection can favor groups, instead of acting directly on individuals, is highly controversial. Though Darwin proposed the idea, the traditional view among biologists is that selection on individuals would stamp out altruistic behavior (the altruists who spent time helping others would leave fewer children of their own) far faster than group-level selection could favor it.