Birds May Hold Clues to Role of Time in Teamwork
for National Geographic News
|December 12, 2002|
"You scratch my back and I'll scratch yours." That sentiment has probably existed in some form or another since early humans first started walking upright and needed a hand getting down out of trees.
Cooperation enables humans and other animals to ensure their own long-term welfare and to build communities, societies, and civilizations.
Since such behavior is mutually beneficial, why is it so hard to achieve lasting cooperation? Biologists and other scientists have been intrigued by this question for years, but many studies have produced puzzling or conflicting results.
Now, one possible explanation comes from a team of scientists in Minnesota who use captive blue jays to study animal behavior. In this week's issue of the journal Science, they describe the results of a study showing that sustained cooperation depends not only on reciprocitya mutually advantageous give-and-takebut also on the timing of the benefits.
The lead author of the paper, David Stephens of the Department of Ecology, Evolution, and Behavior at the University of Minnesota in St. Paul, said the results demonstrate the importance of an effect known as temporal discounting, which refers to the tendency to devalue something over time.
"We look at delayed things as worth lesswe would rather have $100 today instead of tomorrow," he explained.
Many previous studies have shown that when animals are given a choice between a small reward now or a bigger one later, they usually prefer the immediate payoff. Even when the animals have been trained to cooperate with others for shared benefits, they are often tempted to "cheat" and act selfishly.
"We have known from work in animal psychology that non-human animals are impulsive and seem to be driven by immediate consequences," said Stephens. "They 'discount' at phenomenally high rates. The shorter the delay [of the reward], the stronger the preference for immediate gratification."
But Stephens and his colleagues found through their lab experiments that pairs of hungry blue jays were capable of sustained cooperation. It occurred most often under a combination of two specific conditions: when the birds were less concerned about an immediate reward (because the food couldn't be released for some time and gradually accumulated) and the jays' partners also showed a willingness to reciprocate.
The results suggest that "when we look at cooperation in nature, we ought to know something about the consequences and rewards organized in time related to the action," said Stephens.
As in many animal studies, the findings might hold clues to human behavior. "In human terms," said Stephens, "the kinds of conditions that promoted cooperation in jays would also be likely to promote cooperation in humans."
Over the past two decades, researchers have been building an elaborate theoretical framework to explain the evolution of cooperative behavior among animals. Much of it is based on the findings of animal studies involving a classic experiment known as the "Prisoner's Dilemma."
A scenario commonly employed in game theory, Prisoner's Dilemma forces two players to choose individually whether to cooperate with one another for a shared reward or to "defect" by making a selfish bid to secure the reward only for themselves.
Each player stands to benefit handsomely by defecting. If both choose to defect, however, they risk losing out on the payoff because they could be outfoxed by the partner.
This situation leads to an unstable level of cooperation. Different strategies must be employed, then, to move toward greater equilibrium.
As theories about cooperation have evolved, many scientists have come to believe that the possibility of mutual cooperation is likely to be higher when partners interact repeatedly and engage in a give-and-get strategy. Yet that hasn't been consistently borne out in lab experiments.
In previous work with blue jays, for example, Stephens and a colleague found that even when the birds were trained to cooperate with one another, they eventually switched strategies and regularly chose to put their own interests first by defecting.
In the new experiments, Stephens said he and his present colleagues "wanted to look at why it's so hard to get animals in this kind of situation to cooperate." They modified the Prisoner's Dilemma testing scenario to investigate the potential effect of temporal discounting.
Stephens said it's important to keep in mind that the new study was set up to examine behavior in a very particular type of situation, known as a social dilemma. "It's like the 'tragedy of the commons,'" he noted. The tragedy of the commons is a classic situation in which some individuals selfishly use shared resources for their own needs to the detriment of the larger community.
Toward Greater Cooperation
In their experiments with blue jays, the researchers studied 16 unrelated birds whose sex and past behavior was unknown; the birds were arranged in pairs and placed side by side in individual compartments.
The experiments were rigged so that the payoff was delayed. All the birds had to complete a sequence of four interactions with their partners before the desired food was accessible to them. The food was visible in transparent boxes, enabling the blue jays to see the seeds but not consume them until after the sequence of cooperative behaviors was finished.
"Accumulation forced the birds to care about the long term," Stephens explained.
In a parallel set of experiments, the birds underwent the same sequence of interactive moves but the food did not accumulate; instead, dispensed seeds were dispensed after every play.
One bird in each pair was randomly assigned to be a subject and the other a "stooge." The subject could choose to cooperate or defect in a Prisoner's Dilemma situation. The stooge was preprogrammed to respond to stimuli in one of two ways: the bird could either defect or it could cooperate initially but then switch to copying the opponent's previous move on all subsequent plays (a strategy known as tit-for-tat).
Thus, there were four possible outcomes for each pair of blue jays that underwent the random sequence of interactions.
When the researchers assembled the data into a matrix, it showed that whenever a subject's opponent defected, there was no cooperation between the jays. When the opponent reciprocated, there were varying levels of cooperation.
What really made a strong difference was whether the seeds accumulated during the sequence of plays: When the food accumulated, the levels of cooperation between the bird pairs were high.
The researchers concluded that "stable cooperation requires both reduced discounting and reciprocity."
In a companion article in Science, Michael Mesterton-Gibbons of Florida State University and Eldridge Adams of the University of Connecticut at Storrs wrote: "The study is timely because it forces behavioral ecologists not only to rethink the potential importance of temporal discounting, but also to address a number of other issues," such as why some individuals of a species appear to have a greater propensity than others to cooperate.
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