Oh dear - I'm thumping one of my familiar tubs again in this post. Bear with me.
I'm not sure about the quality of the studies, but there seems to be suggestion of a corrolation between religious belief and observance and longer life, as well as faster recovery from illness. I tried to find a few links on google, but a lot of them are to dodgy looking religious sites. This is quite ironic, considering that this effect is observed across all denominations and not reserved to one affiliation(as far as I can see), it would suggest that the power of the placebo effect, and not a supernatural power, is what is at work here. But regardless of that, what a power it is!
Of course, even if these studies are accurate, we can't be confident that these studies can be extrapolated up to prove the evolutionary benefit of the development of religious beliefs in humans. But it would be great if religious beliefs could be demonstrated to be advantageous in this way. But assuming that religious beliefs do offer health benefits and extended life, why is it so?
This is purely speculation, but I'm tempted to believe that it is because our mental state, as with many others creatures, heavily influences our physical wellbeing. Unlike other creatures however, ideas framed in linguistic terms can influence our state of mind for good or ill. Big questions, like 'what's happened to granny after she dies?' need pleasing answers or else we could face depression, ennui and accompanying damage to our health and wellbeing.
Being self-aware, language using creatures, we find it impossible to imagine an end to consciousness becuase such a thing is self defeating. It is also terribly scary. We need fictions - any fictions - to reasure us.
It seems to me that the common ground shared by most religions isn't in the similarities between their various deities but in their refusal to countenance a cessation of consciousness (Buddhism might be an exception to that - but as far as I'm aware, reaching Nirvana is the exception to reincarnation).
So I think that the problem is that self-aware, complex language using animals are inevitably going to be scared of an end of consciousness, and the most effective solution so far has been to deny the possibility - through religions. Mental trauma will have physical repercussions, and so it would make sense if there were some evolutionary advantage to solving this worry. It makes me wonder if there are any other solutions to the problem. The most obvious in our modern technological age is to put off the end of consciousness indefinitely by maintaining the body - or by freezing our heads in liquid nitrogen. I don't think that any religious memeplex could withstand such a challenge.
Just an idle thought.
™ Version 4.2