A recent cognitive study involving monkeys and dolphins seems to indicate that higher mammals can actually think about thinking.  Long believed to be the purview of humans, the ability to be unsure is a higher brain function that is not wired in genetics.  The study is important in that, for the first time, scientific results exist that show some animals are capable of functioning outside of training and the inherent knowledge they have from genetics (such as survival instincts, fight-or-flight, and so on).  Although I've long believed that dolphins are far more intelligent that we realize and are presently able to understand, the study indicates that the cognitive ability to be unsure may not be solely a human trait.  Although there are skeptics of the study, I would recommend you make your own decision on what the results actually mean.  You can read a news article on the study here at MSNBC.com.