The art of the deal has been on display in recent days. On 4 August former US president Bill Clinton sealed the release of two journalists held in North Korea, and last week Senator Jim Webb persuaded Burma's rulers to free a US citizen held in prison. However, a knack for negotiation may not be unique to power brokers like these.
Lower-ranking chimpanzees, new research suggests, know how to bargain with their superiors to achieve a fairer split of food. These findings suggest that an aptitude for deal-making may have existed millions of years before phrases like "you've got a deal."
"It looks like you can have a quite successful way of dealing with conflicting interests without any language or any very sophisticated communication," says Alicia Melis, a psychologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who led the study.
Chimpanzees in the wild show flickers of this ability. Some populations appear to cooperate on hunts, while others seem to exchange back scratches. Deciding where to travel and forage for food could require arbitration, Melis says.
But such behaviour could simply arise because the interests of individuals overlap. Melis argues that's not the case in a true negotiation, which she defines as "a way of dealing with conflicting interests and coming to a solution which is somehow OK with all parties".
Top bananasTo test for this ability, she and her colleagues Michael Tomasello at the Max Planck Institute and Brian Hare at Duke University in Durham, North Carolina, presented six pairs of semi-captive chimpanzees with a task that demanded cooperation and compromise. All the animals lived in Ngamba Island Chimpanzee Sanctuary in Uganda, a 39-hectare reserve for chimpanzees orphaned by the bushmeat trade.
Each pair - four male, two female - contained a dominant and a subordinate member; Melis's team had established their status from previous observations.
In the negotiation task, the researchers first released the dominant chimp into a set of two adjacent rooms, each containing two plates of bananas resting on a single - but out-of-reach - tray.
In one room, there was half a banana on each plate; in the other, one plate had a whole banana, the other just a slice of a banana.
To bring a snack tray within reach, both chimpanzees had to pull simultaneously on two ropes connected to the tray. If just one animal yanked a rope, it would come loose.
Enter the chimpEnter the subordinate chimp, 10 seconds later. This gave the dominant ape enough time to scope out all four plates and sit down in front of the reward he or she wanted most, which tended to be the plate with a whole banana.
What ensued could be described as a delicate negotiation. The subordinate chimp occasionally accepted the initial unfair offer of a meagre banana slice so that the superior could take the whole banana. But more often than not he or she sat down in front of a plate containing half a banana - implying that the superior chimp might consider lowering her or his sights in the interests of fairness.
This strategy worked more than half of the time, with the dominant animal eventually joining the subordinate. Other times, the subordinate relented and agreed that one banana piece was better than none.
"The subordinate knew their bargaining power, and they knew what their limits were in this situation," Melis says. Only a small proportion of trials ended without a deal.
That changed when Melis's team raised the stakes, raising the maximum reward to two whole bananas. Now nearly a quarter of the trials ended in a standoff. Still, subordinates accepted the unfair offer only half the time, and in a quarter of these trials, they managed to convince their superiors to settle for less.
Terse exchangesAll of these deals occurred with little communication between pairs, Melis says. Only one subordinate made much noise when she was wronged, and the researchers noticed no hand signals pass between any of the chimps.
Instead, one chimp - usually the dominant one - occasionally stood up to peer at the other before switching rooms or sitting back down. "You could interpret these monitoring events as some kind of 'recruiting' behaviour - 'Are you coming?'" Melis says.
We may want to hold off on sending chimps to Copenhagen to broker the next UN climate treaty, however, as the apes aren't perfect negotiators. The best strategy would be to take turns winning the plate with the most bananas, and chimpanzees did not appear to intentionally adopt this strategy, Melis says.
Rather, the results show that our closest living relatives can make deals without complex language. "It seems that the basic capacities for negotiating over conflicting interests probably arose before we split from our last common ancestor with chimpanzees and bonobos," Melis and her colleagues write.
"We are getting closer and closer to a full understanding of the complexities of primate cooperation," comments Frans de Waal, a primatologist at Emory University and Yerkes National Primate Research Center in Atlanta, Georgia. "Chimpanzees are masters at figuring out optimal cooperative strategies, including how to manipulate others to do their bidding," he says.
Journal reference:
Evolution and Human Behavior, DOI:
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