DieRuhe: Did this really need a study? :-) If you're not subjected to or experience anything outside of your own little world, of course you're going to have ideas and generalizations that may seem "primitive" to others.
But does it explain why those who receive more education can still be prejudiced?
And what about tribes who still live in the Stone Age, apart from society? Are they "ignorant"? Surely they would be "prejudiced" against anyone who isn't a part of their tribal society.
The only problem with studies like these are that they seem to come from the perspective that they know what is "correct" and everyone who doesn't fit is somehow fundamentally wrong. Human nature, and the human experience, is way too broad to paint with so few colors.
People with more education are more likely to have been exposed to opposing view points during the process. I know my views changed significantly during my time in college.
What's more college, when done properly, gives one more tools for seeing through the lies that the GOP is presently using to justify some pretty ridiculous positions. For instance a recent bit of legislation that would require doctors to forcibly penetrate women planning to get an abortion whether or not it's medically necessary and whether or not there's any consent by the parties involved. I forget which state it is, and AFAIK it hasn't yet been signed into law, but those sorts of positions are completely unconscionable to anybody with the slightest amount of ethical integrity. Agreeing to sleep with the QB shouldn't require one to then sleep with all the other football players, likewise agreeing to have sex should not represent permission to be penetrated by a doctor for no good reason.
And that assumes the sex was consensual in the first place, AFAIK, that bit of legislation doesn't make any distinctions between consensual sex and rape or molestation.
As for remaining prejudice, nothing's perfect, we all do live in our own subjective bubble. Zen and Ch'an are the only paths that offer any meaningful hope of seeing the world as it is, and even those take decades and most people don't have the time or discipline. The question probably shouldn't be why do some people remain biased, it probably should be how significant is the bias and how closely does it reflect reality.