Ape Genius

Ape Genius

PBS Airdate: February 19, 2008

NARRATOR: Something strange is happening in the forests of Africa. Chimpanzees are doing things no one has seen them do before: they are having pool parties. But that's not all. At a site called Fongoli, in Senegal, they have also invented a remarkable way to catch a meal. They are making spears and hunting, just like our ancestors.

Fresh steaks and a swimming pool? How long until they fire up the barbecue? After all, the great apes—chimpanzees, orangutans, gorillas, and bonobos—seem so much like us, it's hard not to feel a deep connection.

MICHAEL TOMASELLO (Max Planck Institute for Evolutionary Anthropology): We have come to see that we're much more similar to them than we ever imagined.

NARRATOR: But for every revelation about the power of their minds, another shows up a stunning difference.

REBECCA SAXE (Massachusetts Institute of Technology): If you think that human genetics and ape genetics are 99 percent the same, what we've managed to achieve in our current position on Earth is so strikingly different from that of apes.

BRIAN HARE (Duke University): We're trying to figure out, "What is it that makes us human? What's the little difference that makes the big difference?"

NARRATOR: How big is the gap between them and us? What's holding them back? Inside ape minds, right now on this NOVA/National Geographic special.

Major funding for NOVA is provided by David H. Koch. And...

Discover new knowledge: HHMI.

And by the Corporation for Public Broadcasting, and by contributions to your PBS station from viewers like you. Thank you.

NARRATOR: In a remote part of Africa, there's something new under the sun. Our closest living relatives are getting bold. Chimps are supposed to be afraid of water, but this young male is climbing down for a dip. He keeps a hand on a natural safety line as he overcomes his fear. Has a boy or girl ever had more fun in a swimming hole? Wild chimps have never before been seen playing like this.

At Fongoli, Senegal, anthropologist Jill Pruetz and psychologist Andrew Whiten are getting an extraordinary glimpse of chimp emotions.

ANDREW WHITEN (University of St. Andrews): The personality of a chimpanzee is extremely excitable. I've hardly ever seen a facial expression like that. I mean, that was extreme excitement to the stage of kind of losing control.

JILL PRUETZ (Iowa State University): It's not merely just to cool off. The juveniles have fun. I mean, they play in the water. They play a lot in the water.

NARRATOR: This is only one of a rush of discoveries that is painting a surprising new portrait of ape minds. They are more like us than most researchers ever imagined.

One by one, the skills and emotions we once thought were uniquely human are being found in apes. Still, certain specific mental gaps—the little differences that make the big difference—will ultimately explain why we study them and not the other way around.

While the swimming hole is revealing chimps' emotions in the field, a new laboratory study is showing off their amazing rational powers.

At the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, psychologist Josep Call places a peanut in a clear tube.

How can the chimpanzee get the snack? She has never seen this puzzle before.

JOSEP CALL (Max Planck Institute for Evolutionary Anthropology): For 10 minutes, there is no solution in sight. And all of a sudden, boom, they solve it. They have to understand that they can use the water as a tool. This is interesting, because the water itself, it doesn't have any shape.

NARRATOR: Using water as a tool seems like something we would do—on a good day.

Another tool is being put to remarkable use by wild chimps in their quest for a meal. Back in Senegal, Jill Pruetz has been keeping a close eye on chimps' eating habits. Throughout Africa, chimps eat almost anything, and they have a particular taste for meat. Here, their favorite prey is the bush baby, a small nocturnal primate.

But these chimps aren't catching bush babies barehanded. Pruetz has seen chimps making spears and using them to hunt.

Andrew Whiten hopes to join the ranks of the few who have witnessed this extraordinary behavior.

Pruetz has just collected a spear jammed in the top of a dead tree.

JILL PRUETZ: So I'd say, I guess, this one is longer than average.

ANDREW WHITEN: Yeah, this is a big, long and fairly stout one.

JILL PRUETZ: Yeah, yeah.

ANDREW WHITEN: But the length of it's interesting, because that's a big hole. And this thing's pretty well judged to more or less reach to the end of it in a firm way.

JILL PRUETZ: It's pretty precise.

NARRATOR: To make a spear, a chimp starts by breaking off a branch, then sharpening the tip, all in the quest to catch a bush baby in its daytime sleeping hollow.

JILL PRUETZ: So the next step would be that the chimp would approach the cavity and sometimes look in, take the tool, jab forcefully into the cavity, multiple times.

NARRATOR: It may not be ice-pick-sharp, but when driven by an arm up to five times as strong as a human's, it's a potentially lethal weapon.

JILL PRUETZ: They always either sniff it or lick it when they withdraw the tool. What they may do is actually break open the entire cavity and, if they're lucky, find a bush baby inside.

NARRATOR: Break, strip, sharpen, stab: these chimps take a series of distinct steps in a carefully premeditated hunt.

For Andrew Whiten, this discovery may offer a window on our own past.

ANDREW WHITEN: Hunting's fascinating to us humans, particularly if we're interested in the evolutionary story of how we got here. Our ancestor, five or six million years ago was somewhat like a chimpanzee, we know that. Then, later in the evolutionary story, we became big-game hunters, using a lot of weaponry, butchery tools. And we're bringing down large prey. So how did an animal like a puny ape reach that stage?

NARRATOR: Pruetz and Whiten are closing in on the answers. Most of the 20 spear hunts Pruetz has observed have taken place during the rainy season. Over time she has seen every stage of the kill.

A chimp is inspecting a hollow, looking for a bush baby. She breaks off a branch and makes a spear.

JILL PRUETZ: The first time I saw a chimp make a tool, I think I said something like, "Where is she going, and what is she going to do with that tool?"

NARRATOR: She nibbles the tip to sharpen it. Then, with the aid of her foot, she aims the point into a hollow.

Pruetz has made a landmark discovery. Never before has any non-human species been known to routinely make and use deadly weapons.

So what does spear-hunting reveal about how chimpanzees think? Pruetz and her team have seen about half the chimps here brandishing weapons, which means spear hunting has spread through much of the group. That seems natural to us. But generating ideas and sharing technologies? That's one scientific definition of culture.

For Whiten, culture includes the human arts from opera to Oprah, but it also covers the rudimentary traditions of ape societies.

ANDREW WHITEN: If you know enough about the behavior of an individual, you actually know where they come from. So if you know someone who wears a tartan kilt, and to play the bagpipes, if they enjoy porridge for breakfast, they probably, you can tell, come from Scotland. So if you know that a chimpanzee is one of several in its group that enjoy coming and dunking themselves in a pond, like this, and also that they sharpen sticks and actually use those as primitive kinds of weapons then, "Aha! That chimpanzee comes from Fongoli."

NARRATOR: Whiten is trying to discover what kind of mind can lead an ape to culture.

ANDREW WHITEN: Young watch their parents, sometimes very intently. And over the following months and years, they acquire that behavior. So you have to be able to copy.

NARRATOR: When apes live alongside people, they sometimes copy our behaviors naturally, without any training. Copying someone else's successful actions beats reinventing them from scratch, but it's a lot harder than it looks.

When these bonobos in the Congo started imitating each other, it seemed like play. But they were actually relying on a sophisticated skill-set for copying.

REBECCA SAXE: You see some other animal doing something that you want to do. And being able to figure out, just by watching how they're doing that, so you can do it yourself, is actually an incredibly complicated skill, with lots of steps to it.

You have to know what it is about what they're doing that leads to some goal that animal has. You have to be able to know enough about that goal to recognize that you share that goal. You have to know, "How is it physically working?" You have to know enough about your body and other bodies to be able to line them up.

NARRATOR: To prove that one ape can copy another, a student of Andrew Whiten's devised an experiment. At the Keeling Center of the University of Texas, Antoine Spiteri has built a kind of slot machine for apes. He loads it with a grape.

To get the fruit, a chimp must first turn a disk to allow the grape to drop through a hole. Next, a chimp has to move a handle that opens a door to release the fruit pay-out.

Spiteri now trains a chimp named Judy how to work the device. On her own, she'd never figure it out, but thanks to a sweet liquid reward, she learns the sequence of two steps: rotate, then push. Ka-ching!

Next, Judy's group mates enter the corral. Spiteri wants to know if, just by watching, the chimps in the peanut gallery will learn the technique. Can these apes ape to win this food-finding game? One chimp seems to think she's got it and shoves Judy aside.

A minute ago, Judy was the only one with the knowledge. Now another has it, and, quickly, the trick spreads throughout the group.

But for Spiteri, the most important question remains. Have the kibitzers next door also learned the solution? They have no social ties to the original group. In fact, they are hostile to them. Would they set that aside to keep with the Joneses next door?

In no time flat, they're working the slot machine like old pros. Rotate. Then push the handle. Call it the Texas two-step.

Learning by imitation is an essential skill for culture. And culture, along with the complex thoughts and emotions behind it, were long believed to be uniquely human.

MICHAEL TOMASELLO: The history of Western thought has always been premised on the idea that there are beasts and there are humans; and humans are touched by the spark of God, and beasts are just beasts.

NARRATOR: Something of a revolution came in 1960, when a young researcher, with support from the National Geographic Society, set up camp in Tanzania. Jane Goodall observed that chimps' emotions seemed much like ours, especially the tenacious bond between mother and baby.

At a site called Bossou, in Western Africa, Japanese researchers recorded the story of an ill two-year-old chimp. Her mother touches her forehead as if to check for fever. As the baby's strength ebbs her mother remains devoted.

TETSURO MATSUZAWA (Kyoto University): When I see the scene of the mother looking at the baby, I really recognize the emotional life of chimpanzees are so similar to us.

NARRATOR: For weeks after the baby's death, her mother carries the body. Is the mother grieving? Defiant? Can an ape be in denial? It's impossible to say exactly what the mother is thinking, but hard to dismiss her feelings.

Putting ape emotions on the map was only one of Goodall's accomplishments. She also found powerful evidence of their intelligence. Goodall was the first to report chimps making and using tools—in this case to "fish" for termites.

TETSURO MATSUZAWA: When she found termite-fishing, people were so surprised, and thought we should change the definition of humans, or we should include chimpanzee as humans.

NARRATOR: What Goodall couldn't have known was that at a place called Goualougo, other chimps had an even more sophisticated way to catch termites. First they use a big stick like a shovel to open the ground, then they switch to a slender probe to pull up the insects.

Perhaps Goodall's most astonishing discovery was that chimps are hunters. She watched a troop catching colobus monkeys by hand.

Although no one has established that they actually coordinate their efforts, the chimps seem to be cooperating. And cooperation is, after all, one of the key drivers of human culture. Could apes rev up their culture by working together? Imagine a group of chimps, armed and dangerous, hunting as a band.

So why isn't Earth Planet of the Apes?

Do apes even have the capacity to cooperate? A series of new studies reveals the rudiments of teamwork in the great apes. But they still come up short.

In an experiment at the Great Ape Research Institute in Japan, a chimp knows that food is hidden under a stone. Then researchers swap in a heavier stone. If two chimps each know about the food, can they work together?

In repeated trials, no pair of chimps ever communicated to synchronize their pulling. Swap in a person—researcher Satoshi Hirata—and chimps still don't collaborate, at first. But, eventually, they figured out the sweet rewards of cooperation. Ultimately, the chimps learned to ask for a helping hand.

A needy chimp may recruit help from a person, but will it ever offer assistance?

MICHAEL TOMASELLO: One of the most surprising findings of all of my years of studying apes has been that they will actually help humans. If you're reaching for an out-of-reach object, if they understand what your goal is, then they will help you.

NARRATOR: Of course if you've dropped your banana, forget it, you won't get it back.

Chimps can understand what someone else wants. And one study shows that they can even interpret another's actions as good or bad.

In Leipzig, Germany, a chimpanzee is about to receive a tray of monkey chow. At the same time he's given a rope under the platform he can pull anytime to collapse the platform and end the experiment. Another chimp now enters the cage. This chimp is free to pull a second rope on top of the tray. The first chimp is ticked off. He pulls the hidden rope, and the game's over.

Was he just generally outraged? Or was he taking specific revenge on the thief? To find out, the researcher now moves the food. Once again the first chimp has lost his food to the second. All that's changed is who's responsible.

In trials where the researcher moves the chow, the first chimp is much less likely to crash the platform. That would punish an innocent chimp who had no intent to do him wrong.

JOSEP CALL: They can gauge who is responsible for something that has been done. Humans make a big distinction on...intentions are very important for humans. For instance, take the case...in our judicial system, manslaughter and murder; the difference between those two is simply the intent.

NARRATOR: So chimps have a sense of justice, and they can cooperate with people. Can they collaborate spontaneously with each other?

Researchers, also from the Max Planck Institute, placed fruit on a board just out of a chimpanzee's reach. The chimps are behind bars, both to keep them from the food, and because they can be impulsive, strong and dangerous.

When a solo chimp can reach both ends of a rope, it hauls them in and gets all the food. But on some trials the ends are too far apart. If the chimp pulls just one end, the rope unthreads.

The chimp has another option. He can unlock a door to bring in a helper who's been watching. The two chimps now work together.

But a series of trials shows that this teamwork doesn't come easily. The helper must be a friend, and the food divided into separate dishes.

Can a more loving ape cooperate better? At Lola Ya Bonobo Sanctuary in the Congo, victims of the pet trade are raised by human mothers. When these bonobos grow up, they will spend their days outdoors, becoming savvy about life in the forest. Bonobos are the most social of the great apes. And in their groups, all friends are "friends with benefits," a simple way to diffuse tension.

Calmer than chimps, how do bonobos do on the cooperation test? Brian Hare places food in a central shared well.

BRIAN HARE: All the food is in the same dish, so it's very easy for one individual to bump the other individual out of the way and steal it all.

NARRATOR: It takes the bonobos a while to get on task. But soon they get the hang of it.

BRIAN & ESTHER : Yay, bonobos! Yay!

NARRATOR: With their more congenial temperaments, bonobos are more cooperative than chimps are. In fact, bonobos may take cooperation even further.

When a young male died at Lola Ya Bonobo, workers were trying to remove his body.

BRIAN HARE: The staff decided to use sticks and try to move the bonobo towards a door. They mounted an incredible defense of this body that surprised everybody and was extremely moving. That's a fascinating reaction on the part of the bonobos. They were not related to that individual, and yet, they took extreme risks to protect his body.

NARRATOR: As they fend off the humans, it seems as if they're cooperating. But what does it take to work together? Are they comparing the number of staff to their own troops? Can they calculate at all?

At Kyoto University, Tetsuro Matsuzawa's experiments are revealing that chimps can in fact develop an astonishing facility for numbers. He first trained a chimpanzee named Ai to touch the numeral that matched the number of dots. Once Ai knew zero through nine, Matsuzawa displayed the numerals helter-skelter on a screen. Ai quickly learned to touch them in ascending order.

In the final test, Matsuzawa piled on. As soon as Ai touches the numeral one, white squares cover up the remaining numerals. Can the chimp possibly remember all the locations and touch them in order?

TETSURO MATSUZAWA: The performance was really amazing. Much, much better than we had expected.

NARRATOR: But for Ai, learning numbers was a struggle.

TETSURO MATSUZAWA: Almost the same amount of training was necessary to teach three, teach four or teach five. Or, even worse, it takes more time to teach five and then six.

NARRATOR: Ai never got the "aha" feeling that children have when they realize that you just add one to get to the next number.

In the United States, another ape shows a surprising gift for language.

SUE SAVAGE-RUMBAUGH: Going to go help get some sticks? Good.

NARRATOR: A bonobo named Kanzi, now at the Great Ape Trust in Iowa, picked up English without being directly taught.

SUE SAVAGE-RUMBAUGH: Put the keys in the refrigerator.

NARRATOR: Wearing a mask to avoid cueing Kanzi, researcher Sue Savage-Rumbaugh tests his comprehension.

SUE SAVAGE-RUMBAUGH: Good job!

Go get the ball that's outdoors.

Very nice. Thank you, Kanzi.

NARRATOR: Savage-Rumbaugh measures Kanzi's vocabulary at 3,000 spoken English words.

While apes can master words and numbers, other research shows that something else is limiting their cooperation: apes have emotional issues—rivalry, violence—and most of all, they're impulsive.

In a celebrated study that investigated impulse control, Sally Boysen of Ohio State University asked chimps to choose between two dishes of M&Ms^®.

SALLY BOYSEN: Now, you watch real carefully. We're going to put one, two, three, four down here. Are you watching, Miss Priss? Sheeby? And we're going to put two in here.

Give those to Sarah. Okay.

Well, I have to give these to Sarah, and Sheeba gets two. So Sarah gets four and Sheeba only gets two. Aw, too bad.

NARRATOR: The twist was that the chimp got the candy she didn't point to. Could the chimp learn to resist her impulse to reach for the bigger pile?

SALLY BOYSEN: You want Sarah to have these? It's okay, it's okay. You get to have that one. Yeah, Sarah gets five, and Sheba gets one. Oh, that is such a shame.

NARRATOR: Amazingly, chimps never overcame their greedy urges. They always reached for more and, so, ended up with less.

SALLY BOYSEN: And Sheba gets two, so Sarah gets four. See?

NARRATOR: Impulse studies have also been run on humans. In a classic experiment from the 1970s, a researcher gave a four-year-old a simple choice.

RESEARCHER : So, if you wait for me to get back, I'll give you this bowl with all of these gummy bears, okay? But if you can't wait, you can push that button, like this, and then I'll come back and you can have this bowl with just this one gummy bear, okay? Okay, I'll be right back.

NARRATOR: According to an inconclusive but intriguing study, the longer children resisted temptation, the higher their S.A.T. scores were years later. In any case, the differences between people are small compared to the gap separating humans and apes.

BRIAN HARE: Maybe one of the first things that happened during our species evolution is we became much less emotionally reactive. And maybe that's one of the big differences that may explain why we solve problems so differently. We sort of got control of our emotions.

NARRATOR: Can apes be given skills to help them master their emotions? Sally Boysen trained a chimp to understand numerals. Then she repeated her M&Ms experiment, but now offered different pairs of numerals rather than treats.

SALLY BOYSEN: You want to give two to Sarah? Okay. Two goes to Sarah, and you get six.

NARRATOR: Remarkably, chimps were now able to learn what they couldn't before: point to the smaller number to get the bigger prize.

Symbols can make you free. They can help distance an ape from its impulses. But outside of the lab, apes don't seem to use symbols. Still, ape minds seem to share many of the amazing features of the human mind. They have sophisticated social emotions. They can cooperate. They have culture.

Their mental rocket is on the launch pad. Why isn't it taking off?

The human brain rocket certainly had lift-off. On an average day, human beings file thousands of patents, post tens of thousands of internet videos, and think millions of thoughts that have never been thought before.

Our closest relatives are different. On a good day, an ape is lucky to use a tool to crack a nut. What prevents ape culture from igniting like the human version?

Recent studies that compare the human and ape minds are revealing something surprising. Bonobos like Kanzi show their own kind of genius.

SALLY BOYSEN: Kanzi, could you take off Sue's shoe? Could you take my shoe off, please? You might need to untie it.

NARRATOR: Even skeptics agree that Kanzi understands more words than any other non-human animal. He also uses an array of visual symbols to communicate. But on closer inspection, Kanzi, like all great apes, lacks the full mental package.

Take Kanzi's use of language.

JOSEP CALL: Most of the time, he will use these symbols to request things, to say "Take me there," or "Give me that." Now, Kanzi will not use those symbols to talk about the weather or to just make small talk, which is a very human thing.

MICHAEL TOMASELLO: When human infants communicate with others, they engage in a real conversation where each conversational turn is responsive to the turn that came before. And they even ask for clarification if they need. So you say "Huh?" or you say "Yeah," and you let the other one know how the communication is going.

NARRATOR: To engage in a real conversation, each speaker needs a sense of what the other is thinking. Call this skill mind-reading.

Young children haven't fully developed it.

RESEARCHER: Hey, so Zoe, guess what we're going to do today? We're going to play a game with my Princess Sally here. See, this is Princess Sally. And she's got a ball that she really likes. This is her ball. But she needs to go away for a little bit, so Princess Sally is going to hide her ball right over here in the bag. See Princess Sally hiding her ball right over there in the purple bag? Yeah?

So here she goes. She's going to go away for just a little bit. Now while Princess Sally is away, we're going to play a little trick on her, okay? We're going to move her ball from the purple bag over here to the green bag. See how we moved the ball over there? Okay, so guess what? Princess Sally is coming back. Here she is. She came back. Can you tell me, where is Princess Sally going to first look for her ball? Over here in the green bag? Can you tell me, why is Princess Sally...

NARRATOR: Classic studies showed that three-year-olds make consistent mistakes about what others know.

REBECCA SAXE: The thing that's amazing about three-year-olds is how convinced they are about their wrong answer. They're so sure that she's going to look for her ball where it really is because she wants it and that's where it is.

NARRATOR: But by the age of four, most children are accomplished mind-readers.

RESEARCHER: Where is Sally first going to look for her ball?

BOY: She's going to look in the purple bag, so she can find her ball.

SALLY BOYSEN: She's going to look in the purple bag?

NARRATOR: That's the right answer.

As recently as 2001, studies seemed to show that apes don't know what others are thinking. But then new experiments began to reveal unexpected skills.

In one study, as a chimp approached a treat, Brian Hare moved it out of reach, establishing himself as a competitor. Next Hare blocked his own view of one treat but left another in his sight.

BRIAN HARE: It looks like they're generating a plan and saying to themselves, "Okay, I want that food, and the one I'm most likely to get is the one he's not looking at, or the one that, if I sneak around, he won't see me, and therefore I can have my yummy banana treat."

NARRATOR: This chimp seems to know what's on Hare's mind, what he can see and what he can't. So chimps seem to share a bit of our talent for mind-reading.

Do we have any mental skills that are uniquely our own?

A key clue comes from a new experiment. Back at the University of Texas, Victoria Horner shows a chimp how to operate a puzzle box to get a piece of candy.

First, she taps. Then she slides. Next she pokes.

The chimp copies pretty well and gets the sweet.

DEREK: This game we're going to play is about this special box I brought, alright? There's a gummy bear. It's your turn.

NARRATOR: Children copy the actions, much as the chimps did.

DEREK: Look, you got him. Alright! There's the gummy bear. Good job.

VICTORIA HORNER (Emory University/ University of St. Andrews): The second box that I show the chimpanzees is this one, and it's identical to the opaque box except that it's made out of material which is see-through.

NARRATOR: Only now is it obvious that Horner's tapping and poking don't achieve a thing: the box has a false ceiling.

The chimps cut to the chase. They skip the needless steps. For the apes it's all about the treat.

ANDREW WHITEN: What this study shows is that apes don't just mindlessly ape. They also understand something more about cause and effect.

VICTORIA HORNER: We found something quite surprising. The children were pre-disposed to copy, even when it meant that they were doing something that was really rather silly. So this seems a little like the chimps are outsmarting the kids in this particular study.

DEREK: There he is. You got him out.

NARRATOR: Why do kids imitate slavishly?

VICTORIA HORNER: At the root of the children's behavior is the fact that they viewed me as a grownup, possibly as a teacher.

NARRATOR: That children expect to be taught is a vital difference. While apes can copy, most researchers believe they don't teach each other. Learning from someone else is the fastest way to get a new idea: faster than learning by imitation, faster than inventing a new technology in the first place.

In children, a penchant for teaching appears—even before language kicks in—in the form of a deceptively simply gesture: pointing. A toddler knows that the cup being pointed to is the one that hides a treat.

REBECCA SAXE: Parents love it when their kids start pointing because it's evidence that the kid's trying to communicate with them. Parents definitely notice the difference between babies who just point to ask for things and babies who point to show them things.

NARRATOR: Apes don't seem to get that kind of pointing. It doesn't matter whether Brian Hare points or stares or orients his body, this young bonobo can't fathom that he is trying to communicate.

BRIAN HARE: They were clueless at using the information. Even after lots and lots of trials, they didn't use the information I provided them. And it was a big surprise to everybody.

NARRATOR: But Hare suspected a certain domesticated animal would succeed.

BRIAN HARE: I sort of was thinking to myself, "Well, wait a second. I have a dog at home. And, you know, he plays fetch. And when he loses his ball, he comes and looks at me. And if I point in a certain direction, he runs off in that direction and tries to find the ball."

NARRATOR: Sure enough, dogs get it.

Why dogs and people but not apes? The answer may spring from the way emotions collide with reason.

BRIAN HARE: It's possible that, like dogs, there may have been selection against aggression in humans, and selection for tolerant behavior, pro-social behavior, that actually then allowed us to use these cooperative communicative cues in a very different way than other species, even our closest relatives.

NARRATOR: Pointing has a rational component too. It relies on a particular mental skill, a little difference that makes a big difference.

BRIAN HARE: Whenever I point, I'm actually directing your attention towards a third object. And you have to understand that my attention is on that object, and that I'm asking you, now, to attend to the same object. So there's sort of a triangle between us and the object.

NARRATOR: This mental skill, call it "the triangle," turbocharges teamwork.

MICHAEL TOMASELLO: What you'll see with the human mother and baby is that the mother is constantly trying to show the baby what to do, and the baby is trying to tune into what the mother wants. And so you have a full triangle of mother and baby and the thing in the environment that they are trying to work on.

REBECCA SAXE: It's a special cognitive achievement. For some reason kids do this naturally, almost immediately. And curiously, apes can't get into that.

MICHAEL TOMASELLO: At the moment we have no evidence that apes have shared goals based on shared commitments. They do things together, they coordinate their actions together, but they don't have a shared commitment to a shared goal.

NARRATOR: The triangle is the core skill that makes teaching possible. Humans have it; apes seem to lack it. But apes are also missing one more thing. It's a key emotional driver: the passion to cheer each other on.

TETSURO MATSUZAWA: "Good," "good job," "well done." This kind of facilitation, giving a hand, encouragement, is the base of teaching.

REBECCA SAXE: It seems like it's not just a cognitive capacity that's necessary for teaching. There's this other thing, which is wanting to teach, that seems to be really pervasive in humans and maybe mysteriously missing in apes.

NARRATOR: The pieces are now coming together. Apes have culture, a rare achievement in the animal world. They can learn from each other by imitation. But this process is passive, often slow and can easily backslide.

BRIAN HARE: Probably there's a lot of slippage. There's a lot of loss of cultural innovations between generations when you're talking about a chimpanzee.

MICHAEL TOMASELLO: If an ape invents something new and important and interesting, maybe some others will learn it, maybe they won't.

NARRATOR: Unique among animals, humans have both the passion and mental skill to teach each other. When you're a student rather than a spectator, learning jumps to warp speed. That's because teaching locks in progress.

MICHAEL TOMASELLO: Human culture traditions have a cumulative quality that each generation builds on the things of the previous generation. So if you looked at the history of any interesting technology, it started out simple, and the children of that generation learned the simple version. But then some genius made an improvement to it, and everyone follows right away, and we get this ratcheting up in complexity.

NARRATOR: An ape may stand on another's shoulders, but only humans can stand on the intellectual shoulders of giants.

BRIAN HARE: It's such a great privilege to be able to work with these animals and try to understand what's going on in their head when they look at you so gingerly and softly. Is it they're thinking, "Oh, he's such a nice guy, and boy, I wish I knew what was going on in his head?" Or is she thinking, "Gosh, what's that spot? Is it dirt? Could I eat that?"

NARRATOR: In spite of their limitations, when we look into the eyes of a fellow ape, we don't feel a gap but a deep connection. We can't dismiss a chimp reaching out for help, or a group of unrelated bonobos rallying to the defense of another, or a mother refusing to let go of her dead baby. But as the most social of apes, we can't help reading thoughts and feelings into the mind behind any familiar face.

And perhaps that says more about us than them.

On NOVA's Ape Genius Web site, watch other tests of primate intelligence, hear about an amazing bonobo named Kanzi, and more. Find it on PBS.org.

Major funding for NOVA is provided by David H. Koch. And...

Discover new knowledge: HHMI.

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