I've wondered if it wasn't an adaptation that came about in our ancestral evolutionary environment when those with the "gene" for religion proved more daring and more likely to take risks, therefore they gained more status (due to being better hunters,warriors, etc), mated more prolifically and soon became dominant.
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Or perhaps religion is a secondary result of some other factor that does provide a more obvious advantage. For example, religion could be related to a tendency to obey group hierarchies. The idea that everyone in the tribe/pack has someone that they defer to leads to a more coherent group, and could easily be "extrapolated". Or alternatively, it could be a result of our ability to pattern-spot. The abilty to see patterns is a great advantage. For example, spotting the pattern that whenever antelope start to run away, a lion is probably close, would enable humans to avoid lions. However, our pattern spotting is often a little too active. For example, people see the Virgin Mary in a teacup, or in a oil spill. Perhaps somehow, the false-pattern of sacrifice/reward would be born from the accidental leaving of some food in a particular spot, just before a huge mammoth was found that provided even more food.
But isn't true that evolution only cares about the individual? I'm certainly no expert, but from what I understand evolution, the coherentcy of the group plays no part in natural selection except in some cases of kin.
Your idea of sacrifice/reward is something I've never heard before and certainly would make sense
But I wonder what the "evolutionary explanation" (or rather, the "Just-so story") is for atheism? Dawkins often seems stuck in a view from nowhere, sometimes pretending to a god's eye view of the universe and thus outside of his own theory, sometimes not. If meme-theory explains away religion, it also explains away irreligion.
Meme theory also easily segues into postmodernist irrationalism: "truth" is an outmoded concept, all ideas simply suceeded because of the power, reproductive and otherwise, of those who propagated them.
I can't think of Dawkins without remembering Stephen Barr's amusing description of his three roles:
One encounters in A Devil’s Chaplain at least three Dawkinses: there is Dawkins the Humanist, Dawkins the Reasoner, and Dawkins the Darwinist. Each sits on a different branch, sawing away at the branches on which the others sit. (source)