I think the field of evolutionary psychology can make some useful insights into human nature, but I find in some studies--like this one, for instance--the psychologists' interpretations seem far more speculative than empirically demonstrable.
But, so long as we're open to speculation, I'll add some of my own. I think among the religious and non-religious in Western culture, faith is widely viewed as a feeling of certainty about a set of beliefs. Being that it's impossible to prove any religious tenet empirically, it should come as no surprise that more people who approach the world from a scientific/rational perspective wouldn't arrive at a belief in God. Also, someone's IQ is a factor in his or her educational path and career choice, two things that help shape religious and political beliefs.
Not surprisingly, though the author adds, ". . . the data should not be used to stereotype or make assumptions about people, experts say," the comments below the article show plenty of people doing just that.