A week ago or so Lee asked the following question:
So just for fun, do you care to speculate about what the evolutionary basis for strongly held beliefs in humans may be? Social coherence? It doesn't seem to me that strongly held beliefs need to reflect some sort of underlying reality in order to accomplish whatever their evolutionary role is.
This question has been percolating in my head, and I have communed with Boehm's Moral Origins, and I'm now ready to speculate. Hunter-gatherer communities, the essential proto-human societies spend a lot of time and energy in social talk, talk devoted to discussing and propagating how people are behaving and should behave. This talk performs the central function of defining and enforcing moral communities - the shared systems of belief and behavior that make possible the extraordinary human capabilities for cooperating in large groups. A good case can be made that the existence of these moral communities is the fundamental difference between humans and our animal relatives, and the reason we have gone from being an obscure African ape to dominating the planet.
The most serious crimes in such communities are crimes that undermine social cohesion and the altruistic cooperative behavior that makes it possible. Social cohesion requires a very substantial shared belief system, so anti-social behavior of any sort is highly suspect. A friend of mine, an archaeologist who had lived for some time among so Peruvian Indians, mentioned that he had once asked his best friend among them why after a long time association and working together, many of the Indians still didn't seem to trust him.
"Most people think you are a [certain kind of witch who steals children and turns them into butter]", the friend replied.
How could they think that?
It seems that his habit of taking long walks by himself was the key cause for suspicion. This kind of preference for solitude was so unnatural that it made him highly suspect.
Back to Lee's question. Maybe the evolutionary pressure is not so much for beliefs strongly held, even in the face of evidence, but for consistency of belief. Birds of a feather may flock together, or not, but people have a strong impulse to attach themselves to real and imagined moral communities, and enforce consistent beliefs within them.
It's an essential survival tool for HG bands, but it can be a damn nuisance in an avowed pluralistic society. From another point of view, one might argue that true multiculturalism is impossible magical thinking, and against human nature.