Check out this article from Popular Science's Brilliant 10 for '07. Basically it's about some of the cognitive similarities between monkeys and humans, and whether we seem to "miscalcuate" expectation in the same way. First, let me say that my only experience with the brains of monkeys is in the first person-- i.e. my own relatively unevolved mind. But, the article is interesting because the monkeys are put in 2 scenarios: In scenario 1 they "pay" 1 token for 1 slices of apple, but are given 2 with probability 0.5; In scenario 2 they "pay" 1 token for 2 slices of apple, but are only given 1 with probability 0.5. In both scenarios they can expect 1.5 slices. It is unclear to what extent the monkeys understand the "rules" before hand, or what group is used as a control, but scenario 1 seemed to be much preferred by the monkeys, and it seems it is more preferred by the more evolved primates that have opposable thumbs. I would guess that playing the game many many times with the monkeys would converge to a more uniform reaction in terms of "monkey mood."
But, people are the same way, at times, especially when uncertainty is involved. I'm not sure what the appropriate economic explanation, but there seems to be some argument here for a more integrated role of psychology in explaining economic behavior, and may explain some of the puzzles in economics. Small deviations from "full rationality" at the micro level can easily perpetuate persistent deviations from the rational equilibria that are used in neoclassecal macro/finance mondels. Mostly, I'm looking for comments and/or discussion.