We cooperate more than other primates, right? With our extensive systems of governance and such global cooperative networks as the United Nations and the World Health Organization, humans are expert cooperators when compared with other animals or even relative primates, such as chimpanzees and capuchin monkeys.
But how much of this cooperation depends on our ability to speak? Apparently more than you'd believe. That is the take-away message of a study published Monday in the Proceedings of the National Academy of Sciences.
At the core of the study was a cooperative-rewards game in which participants -- be they man, monkey or chimp -- had to work in pairs. The game required participants to cooperate to get the biggest payout -- quarters and dollars for the humans, tasty fruit for the primates. While there was a less-than-ideal cooperation scenario that gave each partner in a pair a quarter, "winning the game" meant figuring out which scenario offered a dollar reward at each round.
When humans were not told the rules of the game and had to figure things out nonverbally, the way their chimp and capuchin monkey primate counterparts had to, human cooperation did not far outperform that of the other primates.
"Normally, we expect to see 100 percent cooperation with humans when they know the rules of the game. When we had them go in blind, only five pairs out of 26 developed the best scenarios of cooperation. That's only 20 percent," says lead author Sarah Brosnan, a psychologist at the Language Research Center at Georgia State University.
Humans still outperformed the other primates, who were chosen because they were notoriously cooperative species, but the extent to which the lack of language handicapped the human pairs was surprising, Brosnan noted.
"We can explain that because it means that humans are very reliant on language," she said.
The study also found that a third of the human pairs happened upon the low reward scenario, just a quarter per round, and then stuck with it throughout the rest of the game. This means that the humans were risk-resistant, or they assumed they had "beat" the game already.
Brosnan and colleagues designed the study to make a point. So often in studies that compare human and primate behaviors, humans are given an inherent advantage because they get to know the rules of the game or task while the primates have to just "figure it out."
"In normal experimental economic games, people are brought into the lab and given a full explanation of what the payoffs are ahead of time. In more complicated games, they even do a pretest to be sure that everyone understands the task at hand. But you can't do that with primates. So in this case, we wanted to see what would happen if we did everything the same," Brosnan said.
So the humans were told they were part of an experiment involving decision making using red and blue chips, but they were not told anything else. Perhaps surprisingly, despite the simplicity of the game, several of the pairs never quite figured it out, and only 58 percent developed a specific game strategy. When all was said and done, 31 percent of human pairs failed to perform better than chance.
"This tells us that when doing human-primate comparisons, it's essential to make the situation as comparable as possible," Brosnan says.
But this experiment tells us more than that, says Daniel Houser, a professor of economics at George Mason University.