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Consider genetic evolution by itself. When a new mutation arises, the total population consists of one group with a single mutant and many groups with no mutants. There is not much variation among groups in this scenario for group selection to act upon. Now imagine a species that has the ability to socially transmit information. A new cultural mutation can rapidly spread to everyone in the same group, resulting in one group that is very different from the other groups in the total population. This is one way that culture can radically shift the balance between levels of selection in favor of group selection. Add to this the ability to monitor the behavior of others, communicate social transgressions through gossip, and easily punish or exclude transgressors at low cost to the punishers, and it becomes clear that human evolution represents a whole new ball game as far as group selection is concerned.
In this context, the human major transition probably began early in the evolution of our lineage, resulting in a genetically evolved psychological architecture that enables us to spontaneously cooperate in small face-to-face groups.
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(...) The ability to acquire and socially transmit new behaviors enabled our ancestors to spread over the globe, occupying hundreds of ecological niches. Then the invention of agriculture enabled group sizes to increase by many orders of magnitude, but only through the cultural evolution of mechanisms that enable groups to hang together at such a large scale. Defining, motivating, coordinating, and policing groups is not easy at any scale. It requires an elaborate system of proximate mechanisms, something akin to the physiological mechanisms of an individual organism. Might the elements of religion be part of the “social physiology” of the human group organism?
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On average, religious believers are more prosocial than non-believers, feel better about themselves, use their time more constructively, and engage in long-term planning rather than gratifying their impulsive desires. On a moment-by-moment basis, they report being more happy, active, sociable, involved and excited. Some of these differences remain even when religious and non-religious believers are matched for their degree of prosociality. More fine-grained comparisons reveal fascinating differences between liberal vs. conservative protestant denominations, with more anxiety among the liberals and conservatives feeling better in the company of others than when alone.
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By my assessment, the majority of religions in the sample are centered on practical concerns, especially the definition of social groups and the regulation of social interactions within and between groups. New religious movements usually form when a constituency is not being well served by current social organizations (religious or secular) in practical terms and is better served by the new movement. The seemingly irrational and otherworldly elements of religions in the sample usually make excellent practical sense when judged by the only gold standard that matters from an evolutionary perspective — what they cause the religious believers to do.
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Explaining religions as primarily group-level adaptations does not make them benign in every respect. The most that group selection can do is to turn groups into super-organisms. Like organisms, super-organisms compete, prey upon each other, coexist without interacting, or engage in mutualistic interactions. Sometimes they form cooperative federations that work so well that super-super-organisms emerge at an even larger spatial scale. After all, even multi-cellular organisms are already groups of groups of groups.
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American democracy can be regarded as a cultural super-super-organism. The founding fathers realized that religions work well for their own members but become part of the problem at a larger social scale. That is why they worked so hard to accomplish the separation of church and state, along with other checks and balances to prevent some members of the super-super-organism from benefiting at the expense of others.
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