While making decisions, we generally try to maximize outcomes, even if it means cooperating and sharing a reward with another person. But does this ability set humans apart from the rest of the animal kingdom?
A recent study in the journal Proceedings of the National Academy of Sciences shows that humans' closest living relatives — non-human primates — are also capable of this kind of organization. Though more research is needed, the findings contribute to scientists' understanding of the evolutionary origins of cooperation and weighing decisions in humans.
The researchers, led by scientists at Georgia State University, tested the "Assurance Game" in pairs of college students, chimpanzees and capuchin monkeys. Each subject tested next to a member of the same species and was given two tokens — one labeled "Stag," and the other "Hare" (more on that here).
In every trial, each subject had to return one of the tokens to the experimenter without knowing what the other subject planned to do. If the subjects turned in the same token, they received a reward — money for humans and fruit for non-human primates.
When both subjects gave back the "Stag" token, they received a larger reward than any other combination. A "Hare-Hare" match-up yielded a reward, but not as much as the "Stag-Stag" combo. Subjects were not rewarded when their tokens didn't match up.
To maximize the reward, participants had to cooperate and learn quickly which combinations yielded the largest reward.
None of the human subjects received instructions for the game. The researchers focused on ways to make experimental conditions as similar as possible so one species didn't have an advantage.
After analyzing the results from each species, the scientists found that five of the 26 pairs of humans maximized their rewards by playing "Stag-Stag" 75 percent or more of the time. Humans cooperated and optimized their rewards more than chimpanzees and capuchins, but still did not perform as well as the researchers expected.
Eight of the chimp pairs cooperated to receive rewards but none of these groups chose "Stag-Stag" or "Hare-Hare" more than the other. Only one of the six capuchin pairs, however, chose the most fruitful combination ("Stag-Stag") as a non-random behavior, as opposed to just by chance.
In all species, subjects cooperated for a reward. Surprisingly, some non-human primate pairs cooperated more than some human pairs, although humans were generally better at maximizing rewards.
Based on these findings, it appears that chimpanzees, capuchins and other primates are able to understand the benefits of working together.