Great Ape Economics
Scientists Learn as Chimpanzees Trade Tokens for Treats
The currency in question at Regenstein Center for African Apes is a piece of white PVC tubing, about 4 inches long and 1 inch in diameter. Like any unit of exchange, its worth depends on where you try to trade it.
Exchange it right at the point of distribution, and you get a piece of carrot—a tasty treat, sure, but hardly the hot fudge of the chimpanzee world. But walk a little further to hand in your little token, and you get a grape instead, vastly preferred in this area of great ape gastronomy.
The tokens are distributed in half-hour sessions planned by Research Scientist Lydia Hopper, Ph.D., and adjunct scientist Kristin Bonnie, Ph.D., an assistant professor of psychology at Beloit College. As experiments go, the set-up is easy to grasp, but the results will deepen our understanding of how great ape social groups function.
“With Lydia’s work, we can follow along as the zoo’s apes potentially learn that different degrees of effort produce different degrees of reward,” says Steve Ross, Ph.D., director of the Lester E. Fisher Center for the Study and Conservation of Apes. “Well, that’s basic economics.”
Testing the Tried—and Trend-Setting
Token-exchange studies are a tested method for primate studies. In her previous role with Georgia State University, Hopper used token exchanges to study how species including chimpanzees, squirrel monkeys, owl monkeys and rhesus macaques responded to inequity.
What does that mean? Basically, scientists gave different animals different rewards for the same task: handing back the token. Some species, such as owl monkeys, don’t react to unequal treatment. But chimpanzees certainly do, as a range of studies have shown. When the unequal treatment crosses a certain threshold, these social animals reject the lesser reward, even if a carrot, in this case, is obviously better than nothing.
“It might sound strange, but humans respond in the same way,” says Hopper. “We would rather accept no reward than an unfair outcome.”
Data suggests the inequity response may be tied to the species’ social networks. In chimpanzee groups, individuals cooperate with non-family members for day-to-day living. If a chimpanzee is looking for a partner toward some end, it has options to choose from.
Owl monkeys, on the other hand, live in simple pairs with their offspring. Mom and dad always need to cooperate to successfully rear young; no decisions about partners are necessary.
The difference could suggest the inequity response is an adaptation to stave off being exploited by non-kin members of your group. To evaluate that hypothesis, it helps for researchers to study it in as many species as possible. At Regenstein Center for African Apes, that means gorillas as well as chimpanzees.
“Scientists know very little about whether gorillas respond to inequity,” says Ross. “Our unique setting here gives us the perfect opportunity to explore some key unanswered questions.”
In research settings around the world, chimpanzees have proved adept at trading tokens for treats. At Regenstein Center for African Apes, though, this was a new behavior to learn. The members of Hank’s chimpanzee troop weren’t sure what to do at first with the tokens being distributed through the mesh of their exhibit.
The slow start was part of Hopper and Ross’ plan. Researchers elsewhere had given the apes a helping hand by training them how to exchange. But to truly study the social-learning element of the project—how the behavior is transmitted through the group—the Fisher Center scientists wanted the chimpanzees to pick up the exchange on their own.
It made for a nerve-wracking first few days, Ross admits. “We were wondering if we might have miscalculated,” he says. The chimpanzees played with the tokens, putting them in their mouths and filling them with water. They pushed other items through the mesh, such as wood chips and sticks. Hopper and Research Assistant Laura Kurtycz stood motionless through it all, avoiding any cues that might influence the group’s behaviors.
Then a breakthrough. Chimpanzee Optimus pushed one of the tokens back through the mesh, receiving a carrot piece in exchange. This caught the group’s attention. Female Chuckie figured out the next step not long after, taking the token around the corner for a tasty grape.
The trades have since accelerated, with most of the group members—Chuckie, Optimus, Nana, Cashew and Kathy—readily swapping tokens for treats. Now that the basic exchange is established, the researchers plan to start adding wrinkles.
“Soon we’re going to move the grape station, placing it farther up in the exhibit and eventually outside,” says Hopper. By scaling up the amount of effort required to get the preferred treat, scientists can gain a deeper understanding of how chimpanzees value it. It’s key information for teasing apart—and tweaking—this system of rewards.
Part of a Spectrum of Studies
The token-exchange project isn’t the only behavioral study taking place at Regenstein Center for African Apes. Scientists still conduct daily monitoring of chimpanzee and gorilla behavior, recording activity patterns on tiny tablets. Indeed, interns record behavioral data during the token-exchange sessions.
Their data may help Hopper and her peers better understand the chimpanzee social interactions that facilitate learning. The artificial termite mound in the central exhibit is periodically stocked with treats, offering researchers a controlled environment for studying the apes as they use tools similar to those they wield in the wild. (The treats are different, though; termites in Africa give way to ketchup and mustard at the zoo.)
Fisher Center researchers also employ technology that is decidedly not available in the wild. Scientists are studying the ability of chimpanzees and gorillas to sequence objects on a computer touch-screen. Beyond offering insight into ape perception, the puzzles are also a platform for high achievement.
Bachelor gorilla Azizi has recently showcased the ability to reproducibly sequence nine objects on the touch-screen. That’s something of a record for gorillas, and it opens him up to new tasks previously only undertaken by chimpanzees.
Advancing Understanding, Treat By Treat
All this research is voluntary. Each successful task is sweetened by little rewards, but every participant always has the option to walk away.
Beyond building knowledge for the zoo’s scientists, though, the research projects offer extra enrichment for these complex, curious and social animals. Much like their human counterparts, the apes can show a deep appetite for play…and solving puzzles.
“When we first tried the token exchange and the chimpanzees were pushing any object through the mesh, one conclusion could be, ‘Oh, they’re doing it wrong,’” says Hopper. “But another take could be, ‘Oh, they’re trying everything to figure out how this works.’”
It’s this rich cognitive framework that makes the chimpanzees and gorillas so rewarding to study. They resemble ourselves, in many ways. Learning how they see the world can also cast light on our own rich interactions.
By James Seidler • Originally published in Summer 2013 Lincoln Park Zoo Magazine
Making New Milestones
For some Lincoln Park Zoo apes, including gorilla Azizi, sequencing objects is old news. In the video below, Fisher Center Director Steve Ross explains how the next step will test their memory--and reveal more about how chimpanzees and gorillas think.
Can You Sequence Better Than a Gorilla?