... is the title of an excellent and well-informed article by David Sloan Wilson. Some highlights:
It is absurd, in retrospect, that evolutionists have spent much more time evaluating the major evolutionary hypotheses for guppy spots than for the elements of religion. This situation is beginning to remedy itself as scholars and scientists from all backgrounds begin to adopt the evolutionary perspective in their study of religion.
[Large-scale empirical studies reveal that o]n 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.
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.
He then goes on to give an extended example based on the Indian ascetic tradition of Jainism:
Jainism is one of the oldest and most ascetic of all the eastern religions and is practiced by approximately three percent of the Indian population. Jain ascetics filter the air they breathe, the water they drink, and sweep the path in front of them to avoid killing any creature no matter how small. They are homeless, without possessions, and sometimes even fast themselves to death by taking a vow of “santhara” that is celebrated by the entire community. How could such a religion benefit either individuals or groups in a practical sense? It is easy to conclude from the sight of an emaciated Jain ascetic that the religion is indeed a cultural disease — until one reads the scholarly literature.
Hopefully that will induce you to read the whole piece. it is long, but well worth the effort.
UPDATE: Dawkins' reply is also worthwhile, if only for balance.