However, I should probably offer my 2 cents on the issue of whether religion is good for those who are religious.
Being religious is certainly correlated with health, life satisfaction, having kids and many other fine traits. Corrleation is not causation - but this isn't an area where it is easy to perform randomised, controlled trials.
Susan Blackmore is one of those who has pointed this out recently - in her article: Why I no longer believe religion is a virus of the mind.
Most religion has probably been adaptive for most of its believers in the past. However, there's also another possibility to consider: that religion might be adaptive for a minority of those who promote it - but not so much for average believers. This is a picture of religion as manipulation. Not so much manipulation directly by memes, but rather manipulation by other humans using memes. We know of many cases in which religious influences have been used by those in power to help prevent violence and revolutions. In the past, rich English folk gave a lot of money to the church - and the church used this money to build cathedrals - where the poor could go to feel grand - and where they could be told how stealing from the rich people was wrong. Turning down requests for donations may not have been so wise - the church was a powerful and influential force. A similar situation led to the promotion of Buddhism within China - if happiness lies within, then you don't need to steal the rich people's stuff. This picture still has religious memes spreading because they are adaptive to DNA genes - but it would be more like smoking or obseity - where the benefits accrue to only a few. The beneficiaries may not necessarily have been priests - they could also have been "friends of the church" - politicians, royalty, the rich, etc.
It also seems obvious that - in societies dominated by a single religion - there would have been immense pressure to conform. Not being religious under such circumstances would typically have been very, very bad for both you and your DNA. If this is a parasite it is a pretty weird one - since it makes infected hosts punish the uninfected. The movie Shivers portrayed such a parasite - so it's not totally impossible, I suppose. However, even then, lacking "religious" cultural symbionts is still bad for you - if you are in an environment where there are may others who have "religious" cultural symbionts.
It looks as though most major religions have been beneficial to some religious humans historically in at least one of these ways. Maybe these religions will become maladaptive in modern times - but that's a bit of a different issue.
Ben Cullen pointed out that many religions can be expected to be beneficial - on grounds associated with parasite ecology - long ago, in a paper entitled: Parasite Ecology and the Evolution of Religion. Ben pointed out that a lot of religion is transmitted with a significant vertical component. Vertically-transmitted memes tend to coevolve with their hosts to become more benign. The hosts adapt to ameliorate their negative aspects, and both benefit from host reproduction - so their interests become more aligned. Of course, some religions spread horizontally better than others - this argument applies with reduced force to ones that are good at spreading horizontally.
All this is not really news. David Sloane Wilson has been pointing out that religions show every sign of being adaptive to their hosts for a long time.
Anyway, I think that the Dawkins speculation that major religions are like deleterious viruses - that spread because they spread - has been proven wrong - so wrong that Dawkins should probably recant. It was an interesting idea - but an incorrect one.
- Richerson, P. J., & Newson, l. (2007) Is Religion Adaptive? Yes, No, Neutral, but Mostly, We Don’t Know.
- Dawkins, R. (2008) Dawkins on the evolutionary advantage of religious belief.
- Dawkins, R. (2006) The God Delusion. London, UK: Bantam.
- Thomson, J. Anderson (2009) Why We Believe in Gods - "byproduct" theory of religion
- Cullen, Ben (1998) Parasite Ecology and the Evolution of Religion Blackmore, Susan (2013) Religion as meme and virus? Blackmore, Susan (2010) Why I no longer believe religion is a virus of the mind