It's possible that we humans possess a sense of altruism, a desire to put others' best interests before our own. Those who subscribe to evolutionary theory say such a mechanism shouldn't exist; some psychologists believe it's evidence of a higher mind that humans possess. This second theory is supported by findings from a 2007 study by the Max Planck Institute.
In the study, chimpanzees were offered a choice of trays containing raisins in sets. Just as in the human version of the ultimatum game, the chooser could keep one, but had to give the second one away. The sets of raisins were divided differently. Some were more fair than others, and in a few cases, one chimpanzee in the pair would receive no raisins at all. Researchers found that the chimpanzees weren't concerned with the concept of fairness, and they accepted any offer that included raisins, no matter how equally they were divided. The only time a chimpanzee rejected an offer was in a case when the receiver was offered no raisins [source: Max Planck Institute].
But this study doesn't discount the possibility that we do possess a sense of fairness, especially when we're being treated unfairly. What's more, a sense of fairness may not be exclusive to humans.
This is evidenced by a study that took place in 2003. Researchers from Emory University in Atlanta conducted a study featuring capuchin monkeys. The subjects in the study, all females, were taught to trade pebbles in return for a slice of cucumber. Once they learned that pebbles equaled cucumber, the monkeys were paired together. At first, the trades were equitable. But as the research progressed, the monkeys witnessed their partners receiving a grape from researchers in return for pebbles, while others continued to get cucumbers. To make matters worse, some monkeys received grapes or cucumbers for doing nothing, while their partners still had to retrieve a pebble and bring it to the researcher. As the inequitable trades continued, the shortchanged partners became upset [source: Emory University].
Neither of these studies touches upon another aspect found in studies of the ultimatum game -- not the absence of fairness, as in the capuchin monkey study, but the presence of fairness. Why would anyone give more than they had to, as was discovered in the dictator game? One study, conducted in 2001, concluded that people who engaged in bargaining games like the ultimatum game actively search for and exhibit nonverbal cues during the bargaining stage. We humans, the researchers theorize, are simply good at sizing others up and making a judgment about how they will respond to a low offer in the case of the ultimatum game [Eckel and Wilson].
An ability to infer how another person will react to being shortchanged, coupled with the existence of a sense of fairness, would certainly explain the results found in studies of the ultimatum game. Of course, one could make the case that it's a pretty depressing explanation, though.
For more information on evolution and the human brain, as well as other related topics, visit the next page.