Prometheus 6   

… When data and belief come into conflict, the brain does not automatically give preference to data. This is why beliefs-even bad beliefs, irrational beliefs, silly beliefs, or crazy beliefs-often don't die in the face of contradictory evidence. The brain doesn't care whether or not the belief matches the data. It cares whether the belief is helpful for survival. Period. So while the scientific, rational part of our brains may think that data should supercede contradictory beliefs, on a more fundamental level of importance our brain has no such bias.

… Even beliefs that do not seem clearly or directly connected to survival (such as our caveman's ability to believe in potential dangers) are still closely connected to survival. This is because beliefs do not occur individually or in a vacuum. They are related to one another in a tightly interlocking system that creates the brain's fundamental view of the nature of the world. It is this system that the brain relies on in order to experience consistency, control, cohesion, and safety in the world. It must maintain this system intact in order to feel that survival is being successfully accomplished.

This means that even seemingly small, inconsequential beliefs can be as integral to the brain's experience of survival as are beliefs that are "obviously" connected to survival. Thus, trying to change any belief, no matter how small or silly it may seem, can produce ripple effects through the entire system and ultimately threaten the brain's experience of survival. This is why people are so often driven to defend even seemingly small or tangential beliefs. A creationist cannot tolerate believing in the accuracy of data indicating the reality of evolution not because of the accuracy or inaccuracy of the data itself, but because changing even one belief related to matters of the Bible and the nature of creation will crack an entire system of belief, a fundamental worldview and, ultimately, their brain's experience of survival.