University of Kentucky professor and self-proclaimed wine connoisseur Will M. Gervais recently published a research study in Cognition where he tried to get to the bottom of why so many people don't believe in evolution even after the pope said he was cool with it. As it turns out the folks who don't believe in evolution are just not really thinking hard enough about it.
Gervais's study claims that the difference stems from two kinds of thinking: people who are prone to think intuitively and rely on immediate gut reactions are more likely to reject evolution. But those of us who "engage in analytical thinking"—a more deliberate, calculated form of cognition—are better able to override our initial intuitive response and understand the facts behind evolution.
To test his hypothesis, Gervais rounded up a bunch of University of Kentucky kids to talk about their beliefs in God, political conservatism, and creationism. After questioning them, Gervais found that "intuitions regarding teleology, order, and agency may serve as initial stepping stones for creationist beliefs, but stumbling blocks for endorsement of evolution," because they easily influence intuitive cognitive thought.
The general point of the whole thing basically says that when we let institutions and beliefs override our ability to parse stuff out analytically, we are less likely to be able to let go of our first instinct and be convinced by the great wealth of evidence pointing to evolution as truth. The genuinely-not-boring study is available here. If you can't access it, find a lazy college student with a university login who can.