I believe in a mix of intelligent design and evolution. I believe that God made the first humans and a large selection of the first animals/plants etc, then evolution kinda took over and created the life forms we know today.
I choose to believe that becuase of my spiritual beliefs and because I don't see how it's possible for 2 humans to magically rise out of the ocean within 30/40 years of each other. I don't see how that's possible. But I do believe that it's likely for horses, for instance, to have all started out with a common ancestor then changed over the years into the horses we know as horses today. Same thing with dogs and wolves, if God created a wolf I don't see why a dog could have come from that eventually.
That's just my belief.
With your 39% poll number thingy, I think that mostly stems from that fact that the US is still, fundamentally, based on christian values. Most of my friends in school (public school) would have called themselves "christians" and would have reverted back to the creation story from the Bible when anyone questioned them about evolution/creatonism. Those kids were not living any semblance of a "christian" life and if you asked them what they believed in, they most likely wouldn't know, but for some reason they held on the creation story like their lives depended on it. Haha
Also, at least at my high school, biology was not a required course for most kids. None of the more advanced sciences were actually, so most kids at my school never learned about genetics/how plants work/chemistry, that sorta thing. I took Biology and even though the teacher was an evolution fanatic, her way of explaining how evolution worked mainly revolved around her overhead projector, a few overheads of neonatal animals that looked like each other and the question "why do these fetuses look the same if they aren't related through evolution?". Needless to say, that didn't really convince anyone.
Goodness, I wrote a lot. Haha