Almonds or pizza? Capuchins are even smarter than we thought

White-faced capuchin eating fruit at
Manuel Antonio Parque Nacional, Costa Rica
Photo by Sally Kneidel

I'm thinking about monkeys again tonight. (See my last post about capuchins.) Since that last post, I've read another Science News article about capuchins; this one says they've been shown to use "symbolic thought." At one time, symbolic thought was believed to be a unique and defining attribute of humans. But now capuchins have joined the growing ranks of animals that can think symbolically. Specifically, capuchins have been shown to recognize tokens as symbols for different kids of foods. I was thrilled to see that bit of information, but not too surprised. Capuchins are smart, and I know a little about the power of tokens.

My freshman year at Roanoke College, I had an internship with a clever psychiatrist who worked at a nearby VA hospital. He too experimented with tokens as symbols. He had devised a "token economy" program to motivate severely ill psychiatric patients who couldn't behave acceptably in the hospital. If the patients managed an entire day without eating cigarette butts or smearing feces on the wall or attacking somebody, etc, then they were rewarded with tokens. They could trade the tokens for valued prizes, such as candy bars, or TV time, or even a visit with family off the hospital grounds. The tokens worked well. Even the most troubled of the patients got the idea, and took advantage of it. Violent and noxious misbehavior plummeted on the token-economy ward. My mentor published paper after paper about the success of his model.

So what's the deal with monkeys and tokens? In behavioral experiments, capuchins have learned to regard arbitrary tokens as symbols for different foods, according to primatologist Elsa Addessi of the Institute of Cognitive Sciences and Technologies in Rome. These capuchins then spontaneously choose certain tokens over others in ways that correspond to how they choose particular foods over others. The exception occurs when a less preferred token or food is offered in big quantities, which increases its attraction. Yes, we can all relate to that. One toasted almond versus a whole pesto pizza? Easy.

Adessi's team began by establishing a preference ranking for 3 foods among the experimental capuchins. The foods were Cheerios, Parmesan cheese, and sunflower seeds. The monkeys then learned to exchange distinctive tokens for each of the three foods. For example, the capuchin "Carlotta" knew to give the experimenter a green poker chip to receive a Cheerio, a black plastic tube to get a piece of Parmesan cheese, and a brass hook to obtain a sunflower seed.

In the final experiment, the capuchins were allowed to choose from among the tokens that they had learned to associate with particular foods. They almost always chose the tokens that represented the foods they preferred, demonstrating that they understood that the tokens symbolized the food items.

The experiment, published online June 11 in PLoS ONE, shows that capuchins have at least a rudimentary capacity for symbolic thinking, agree the researchers. Symbolic thinking involves the use of an object to represent something other than itself. The finding is significant to evolutionary biology because these South American monkeys diverged from primate ancestors of modern humans about 35 million years ago - which suggests that symbolic thinking has been around for a lot longer than we thought. After all, Homo sapiens has existed as a distinct species for only about 200,000 years. Symbolic thinking is pretty significant in our own development. Humans have used symbolic thinking to develop spoken and written languages, among other things.

Experimenters have been trying to demonstrate symbolic learning in nonhumans for 30 years. Chimps long ago learned to press artibrary symbols on a key pad to ask for various foods and tools. When I was in graduate school at the University of Oklahoma, I worked under the guidance of Dr. Roger Fouts, teaching American Sign Language to chimps and orangutans, which of course involves complex use of symbols.

me at 22, teaching ASL to Pancho the chimp, at University of Oklahoma's Institute for Primate Studies


me with Foots the orangutan, another ASL pupil at OU

The chimps taught ASL to their own youngsters, used it among themselves, and used signs to ask us for things they wanted, like a snack, a drink, a ball, or a "tickle." There's no question that apes can understand and teach others the use of symbols. African grey parrots have also been shown to use symbols. If capuchins can reason symbolically too, then many other animals - primates, birds, and others - may also be able to. As I've said before, we're not as unique as some of us like to think. The more we learn about our furred and feathered relatives, the more blurred the distinctions become. Which, for me, makes our monopoly over the world's resources even more untenable and distressing! When I read about research like this, I pine for solutions to the habitat loss and climate change that threaten wildlife everywhere.

By Sally Kneidel, PhD

Sources:
Bruce Bower. Monkeys learn to deal with arbitrary tokens as if they are different foods. Science News Vol. 174 #1.

Kate Wong. An interview with Alex, the African grey parrot. 60-Second Science Blog.

The Alex Foundation. www.alexfoundation.org/

Keywords:: capuchins use of symbols primate intelligence symbolic thinking

Wild monkeys use tools - and choose the right one for the job

The first monkeys I ever saw in the wild were white-faced capuchins in Costa Rica. Or maybe black howlers were first. But the capuchins were much more charming than the howlers. I fell in love with them. We were on the beach at Manuel Antonio Parque Nacional the first time, and my son Alan had a banana in his pocket. The capuchins were interested in us because of the banana, and they had no fear. The howlers and spider monkeys and squirrel monkeys will stay up in the trees, far away from you, no matter what you have or do. But the capuchins come right down. They even ran out on the beach and snatched things from people's picnic baskets. The capuchins, with their human-like faces and hands, sat in the trees eating bags of crackers and throwing the cellophane wrappers down.

A white-faced capuchin at Manuel Antonio Parque Nacional in Costa Rica, smelling the banana in Alan's pocket
Photo by Sally Kneidel

As a biologist, I know that's not a good thing at all. But yet, I could see myself in the capuchins. I also do what I'm not supposed to do, eat things I know aren't good for me, make choices that endanger my well-being. We were tempted to give the capuchins the banana, but we didn't. We didn't give them anything to eat, we knew better than that. Monkeys that eat human food get sick eventually from malnutrition.

But the next day, we asked the ranger what time the troop of capuchins usually moved through the trees over the beach, on their daily foraging rounds. Our Spanish communication wasn't precise, but he told us and we got the idea. We waited for the monkeys. They came. And they were mad that Alan and I were standing under the trees while they were cavorting from branch to branch, just overhead. The head honcho, a male capuchin, came down and bared his teeth at us and shook the branches to frighten us. We trembled with delight instead.... the pleasure of recalling it even now makes my heart beat fast. We took his photo while he railed at us, infuriated. I was sorry to distress him, but I couldn't help it. Monkeys are territorial, they get angry just like anyone whose space is invaded. It wouldn't hurt him to bare his teeth and shake a few branches. His social stature with his troop may have benefitted from the display.

The capuchin was angry that we were standing under the trees in his foraging route. He bared his teeth aggressively.
Photo by Sally Kneidel

Anyway, I started this post to write about a news story that just came out about capuchins. Capuchins used to be "organ grinder" monkeys. These days they're sometimes trained as "helping hand" monkeys for people with paraplegia or quadriplegia. They're very smart monkeys. This recent piece of research shows that capuchins in Brazil are adept at tool use - an ability that used to be attributed only to humans but has now been demonstrated by numerous species from birds to apes. The capuchins use stones to crack open hard-shelled nuts. But the research goes far beyond just demonstrating tool use. The capuchins don't just grab the nearest rock at hand. They select the best tool for the job. Primatologist Elisabetta Visalberghi of the Institute of Cognitive Sciences and Technologies in Rome has shown that these monkeys draw on knowledge of a variety of nuts and stones to select the most effective implement. She studied the monkeys in the wild and observed that they generally approached two or three stones that differed in hardness, size, or weight. In nearly every case, the monkeys chose the most appropriate stone.

"The present findings make capuchins a compelling model to track the evolutionary roots of stone-tool use," says Visalberghi. Because capuchins shared a common ancestor with humans 35 million years ago, Visalberghi feels that their behavior may demonstrate that the capacity for tool use evoloved earlier than thought.

But primatologist Frans de Waal of Emory University has a different interpretation. He says the work highlights the monkeys' capacity for trial-and-error learning, that planning may not have been a part of their tool preferences. The monkeys may be simply applying life lessons about the success of various stones at cracking nuts.

Capuchins in Brazil selecting stones for cracking nuts, from Wired Science

Whether their discriminatory skills are the result of planning or of learning, they're still a step beyond simple tool use. They demonstrate in a non-human animal the ability to select and apply an appropriate tool for a particular job. We humans are not so unique after all. Do we really deserve to claim the whole planet all for ourselves and crowd out every other species of animal, leaving only the pest species, the livestock, and the companion species? I hope not. I hope the capuchins will always be alive and well in Costa Rica and Brazil, not displaced by cattle pastures.

Source:
Bruce Bower. Monkeys pick the right rock. Science News. February 14, 2009.

Keywords:: capuchins tool use animal behavior monkeys Costa Rica