I would say reasoning is a satisfying process towards secure knowledge from beliefs that might have any bases. Reasoning itself, by creative induction and strict deduction to confirm it, is a process that provides our ability to progress, and it is always open to debate as to the security of its knowledge. Consequently, if one seeeks absolutes, one may be entering spirituality, because even though nature might be an absolute and structured machanism (or might not), individual humans cannot state that is is an absolute reality because we are limited to our reasoning process, which is always provisional as to truth - its just a process towards greater satisfaction. You are welcome to read a new book I have written on this as a free download at http://home.iprimus.com.au/marcus60/1.pdf or at my site www.thehumandesign.net (it's a non-spiritual Design, just science).
So your issue might be in why people seek spiritual absolutes when we might be restricted to a process of reasoning 'towards' satisfaction. Perhaps it is over confidence, or an easy half step to say that so much is regular (as we see it) that is 'just is' that way by the hand of a creator. Perhaps it is laziness, of lack of understanding, as we do develop the ideas in my post and this site generally over time. We learn our limitations by reasoning more and more about them. So, I would not look so much to the need to believe at the most basic level, as I would not say I have ever had any particular beliefs (except beliefs as those things I subject to reasoning to raise their status to more satisfying knowledge). The evolutionary psychology rationale, like all natural selection rationales, is open to interpretation as to what benefits survival, and there might some argument that its helps us to survive to believe without confirmation, but I would probably see it as a side issue with pluses and minuses for survival, and merely a slip into error.
Consequently, if one seeeks absolutes, one may be entering spirituality, because even though nature might be an absolute and structured machanism (or might not), individual humans cannot state that is is an absolute reality because we are limited to our reasoning process, which is always provisional as to truth - its just a process towards greater satisfaction.
Why would the "spiritual" nature of a hypothesis render it more certain? Or have I misunderstood you?
So, a little background- I've just come out as an atheist to my dad, a Christian pastor, who's convinced he can "fix" my thinking and is bombarding me with a number of flimsy arguments that I'm having trouble articulating a response to, and need help shutting down. The particular issue at the moment deals with non-theistic explanations for human psychology and things like love, morality, and beauty. After attempting to communicate explanations from evolutionary psychology, I was met with amused dismissal of the subject as "speculation".
There's one book in particular he's having me read- The Reason for God by Timothy Keller. In the book, he brings up evolutionary psychology as an alternative to theistic explanations, and immediately dismisses it as apparently self-defeating.
"Evolutionists say that if God makes sense to us, it is not because he is really there, it's only because that belief helped us survive and so we are hardwired for it. However, if we can't trust our belief-forming faculties to tell us the truth about God, why should we trust them to tell us the truth about anything, including evolutionary science? If our cognitive faculties only tell us what we need to survive, not what is true, why trust them about anything at all?" -Timothy Keller
The obvious answer is that knowing the truth about things is generally advantageous to survival- but it hardly addresses the underlying assertion- that without [incredibly specific collection of god-beliefs and assorted dogmas], human brains can't arrive at truth because they weren't designed for it. And of course, I'm talking to a guy with an especially exacting definition of "truth" (100% certainty about the territory)- I could use an LW post that succinctly discusses the role and definition of truth, there.
Another thing Dad likes to do is back me into a corner WRT morality and moral relativism- "Oh, but can you really believe that the act of rape doesn't have an inherent [wrongness]? Are you saying it was justified for [insert historical monster] to do [atrocity] because it would make him reproductively successful?" Armed only with evolutionary explanations for their behavior, I couldn't really respond- possibly my fault, since I haven't read the Morality sequence on account of I got stuck in the Quantum Physics ultrasequence, and knowing that reality is composed of complex amplitudes flowing between explicit configurations or aaasasdjgasjdga whatever the frig even (I CAN'T) has proven to be staggeringly unhelpful in this situation.
In addition to particular arguments WRT the question posed, I could also use recommendations for good, well-argued and accessible books on the subject of evolutionary psychology, with a focus on practical experimental results and application- the guy can't be given a book and not read it, so I'm hoping to at least get him to not dismiss the science as "speculation" or a joke. It's likely he's aware that the field evolutionary psychology is really prone to hindsight bias and thus ignores it completely, so along with the book, a good article or study demonstrating the accuracy and predictive power of the evolutionary psychological model would be appreciated.
Thanks!