Apparently humans aren't the only ones filled with self-doubt and uncertainty. A recent study found that certain monkeys question their own thinking as well.
Professor John David Smith and Michael Beran trained macaques, which are of the Old World group (native to Africa, Asia, and Europe), to play a computer game where if they got an answer right, they received a treat. A wrong answer meant no treat, but a brief pause before the next question. But there was a third option -- the question mark. By selecting the question mark, the screen skipped the present question, considered too hard, and moved on to the next.
The macaques responded in the exact same way as humans -- the monkeys chose to skip the tricky questions. (Unlike Georgia Rep. Jack Kingston who recently hit the evolution question head on when he stated, "I came from God, not from a monkey.") Meanwhile, Dr. Smith told the BBC, "Monkeys apparently appreciate when they are likely to make an error... They seem to know when they don't know..."