I found this New York Times article via The Edge. I've read some of the recent works speculating on the neuro-biological origins of religious belief, such as Daniel Dennett's Breaking the Spell. This often makes for great reading, but I often think that the question is not always properly framed. Briefly, here are my two main issues.
1. I'm not sure that the beliefs associated with religion are necessarily different enough from other more mundane beliefs (patriotism, for instance, which is also expansive, spiritual, and communitarian)- which may involve their own distortions and misapprehensions - such that religious belief requires some special explanation. It seems to me that someone should at least attempt to demonstrate that there is a difference before they go about explaining the source of this difference.
2. Wouldn't we need to find a neuro-biological basis for atheism?
My own sense of the matter is that religious beliefs, which most students of consciousness studies claim arose at the very early stages of human evolutionary development, coincide with the development of the human capacity to form imaginary narratives in general. This, too, would have originated early, along with the development of language and intelligence. The ability to form a narrative is, as I see it, the basis of reason (and un-reason), since it allows the mind to organize facts and ideas outside of the flow of external time. The willful organization of internal (i.e.mental) time is the basis for self-awareness and speculation. Even simple math and logic problems are forms of narrative (a statement that 2 + 2 = 4 takes a simultaneous reality and lays it out in a sequence, which is how it becomes comprehensible as an abstract concept). I suspect that the non-fictional narrative (how Throg killed the buffalo) was followed rather quickly by the fictional narrative (how Throg killed an even bigger buffalo when no one was looking) once the power of narrative to create socially influential ideas became clear to early storytellers.
Religion is not just a set of rules, institutions, and social prohibitions. These are merely the consequences of religious belief. Fundamentally, religion is based on stories, myths, fables - in short, on narratives. Religious mythology, in fact, is in a sense the ultimate narrative, because, whether implicitly or explicitly, all of humanity is a character. It is an inclusive, interactive narrative. To get to the heart of why religious belief endures, I think it is necessary to look more generally at the relationship between narrative and consciousness.
I often find that these debates are overly fixated on belief in the supernatural, and as a result misuse (in my opinion) the word "illusion." Internal narratives are, by definition, "supernatural," precisely because they allow for effortless visualization of impossible occurrences. They are above and beyond the strictures of the natural world, which is why they are useful. A correct interpretation of the external world only comes about after contemplating many incorrect interpretations. All of these must be weighed against actual observations. The mind would not be able to reason if it could not un-reason. The ability to imagine the supernatural is a prerequisite for understanding nature.
The corollary here, regarding the nature of "illusion", is that the word is stigmatized by its synonymous relationship to "false" or "mistaken." This is where I think some cognitive scientists are guilty of a misleading error. A perception exists, period. The perception may be an accurate analogue of external reality, or it may not be, but the inaccurate perception is no less a part of the real world than the accurate one. I think I see a unicorn, but it turns out to be a motorcycle. For convenience's sake, we would usually say that I was "mistaken", but that is because in everyday life, our goal is to apprehend external reality. Nonetheless, the electrical blips in my visual cortex that created the "unicorn" are every bit as real and physically measurable as those that register the motorcycle. What happens, then, when the perception is its own purpose, as it often is in spiritual experience? At what point can mythological or psychological symbolism be treated as mere illusion, as opposed to a separate reality?