We usually accept without argument the notion that man is at the top of the animal hierarchy. After all, only mammals have a neocortex – the most recently evolved part of the brain and the center of higher mental functions – and ours is the most advanced variation, so it makes sense that we’d be at a higher stage of development.

But is this true? Does the neocortex always make us more rational than other animals?

Most of the time, the answer is yes. For instance, it’s thanks to our neocortex that we are able to plan for the future, something that animals have a hard time doing. (They are even worse at saving than we are!)

Still, this isn’t always the case, as the following chimpanzee experiment suggests. In “Chimpanzees are rational maximizers in an ultimatum game,” researchers Keith Jensen, Josep Call, and Michael Tomasello looked into how chimps fare at one of the classic tests of human rationality, the ultimatum game.

In the human version of this game, a “proposer” is handed some money, say $10, and must suggest a division of the sum for himself and another participant. This other person, the “responder,” can then either accept or reject the offer. If he chooses to accept the division, both participants receive their share; if he opts to reject it, neither gets compensated.

Now, if we were to go by the traditional economic model of man as a self-interested rational maximizer, we would suppose that the proposers would always suggest a division that maximized his self-interest (an $9/$1 division) and that the responders would always accept a nonzero offer ($1 may not be $9, but it’s still better than nothing).

Except, this is not what happens. Research has shown that we human beings not only consider how best to maximize our compensation, but we also factor in such notions as cooperation and fairness when we make our decisions. For example, responders in the ultimatum game will often reject a monetary division that is particularly unfair for them (such as a $8/$2 division) – even when this comes at their own cost (they lose the $2, after all). This behavior is of course wonderfully human — but it is not part of the standard rational model.

Chimpanzees, however, go about the ultimatum game (which involves divisions of raisins in their case) without giving fairness any thought. In this experiment, the researchers found that the chimp responders tended to accept any nonzero offer, however unfair. And conversely, the chimp proposers rarely suggested a fair division, choosing instead to maximize their own share.

In this case, then, animals are more rational than we are. Whereas we’re willing to lose a couple bucks so that the other guy gets punished for his inequitable offer, chimps only act according to what will guarantee them the most raisons.

This curious turning-of-tables suggests that we might want to think differently about the neocortex. Overall, we’re better off having it, as without our sense of right and wrong, we would lack empathy and the ability to reinforce societal rules. Yet, in certain contexts, the neocortex can cause us not to maximize our self-interest. Evolution, then, is a mixed blessing: it makes us better some things, and worse at others.