The Ape That Teaches
Chimps, bonobos, and other great apes may show signs of having rudimentary cultures. Yet their achievements—honing weapons from sticks, or crafting primitive tools to dig for termites, for instance—pale in comparison to what we humans accomplish. In this interview, Rebecca Saxe, a cognitive scientist at MIT, delves into a key reason why: While apes can "ape," humans are able and motivated to teach, passing along cultural knowledge to future generations.
Mimics and master teachers
NOVA: How does studying apes sharpen our understanding of the human mind?
Rebecca Saxe: What can we learn about human cognition from studying apes? Well, we can learn about what we have in common, we can learn about what's different, and those two inform each other. The more we have in common in our mental capacities, the more striking it is what we humans accomplish in the real world. And studying the differences gets at this question all of us want to know: What is it, intrinsically, to be human?
Why are many researchers looking at how apes and humans imitate actions?
Well, when you compare humans to other animals, the thing that's most striking is what we humans can build and create as communities—the skills we can pass down from one person to another and from one group to another. If one individual figures out a new skill, and the next individual starts where that first person left off, then you can really speed up the process of building a culture. A lot of things are involved in humans being able to do that, but one little part of it, and one part that we can study in both humans and apes, is the process of imitation.
How complicated is it to watch somebody do something clever and pick it up yourself?
It's an incredibly complicated skill, with loads of steps, so it's no wonder that very few animals can do it. First, you have to be able to see that what they're doing is goal-directed, that it leads to some goal, such as getting food. And you have to be able to recognize that you share that goal. Then you have to figure out what it is about their movements, maybe their use of a tool, that leads to getting food. How is it physically working? You also have to know enough about your body and other bodies to be able to line them up; when you see the physical motion that another animal is making, a particular way of moving its hands or moving its mouth, you have to know how to do that with your own body. This is called body-to-body mirroring.
Finally, you might need to discriminate relevant from irrelevant actions. In some ways, that's the hardest part. If you see somebody doing a really complicated action, you might have to work out which of the many things they're doing are actually relevant to achieving the goal. When you grasp this, you can go straight for the goal.
It's possible that [apes] just lack the initial impetus to deliberately pass on a new skill.
Apes can watch another ape do something—like use a stick to dig for termites—and somehow pick up that skill. Yet it doesn't seem like each generation stands on the shoulders of the previous. Is that right?
Yes. There are many steps to being able to build a skill across generations. The ability to imitate what somebody else is doing is only one part. A whole other problem is the ability to innovate new, exciting solutions to old problems. It might be that what's different between humans and other animals is the quality and complexity and richness of the innovation. Although there's reason to believe that the imitation is different, too.
Is that, in part, because of the explicit teaching we see in humans?
Right. And teaching somebody a new trick that you've just discovered is really complicated. It's not exactly clear why it's so much harder than imitation, but it seems to be. One reason may be that you need to work out which parts of what you're doing need to be taught. So what's the difficult bit? How do you show it? How do you slow it down? You need to have enough awareness of what you're doing yourself to slow down the right parts in the right way.
Another possibility is that it's hard to work out the coordination of your attention and the other person's attention on this third thing—the task you're trying to teach. You have to pay attention to all three elements continuously. That might be it. Although 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 may be even more critical. You need to understand that somebody else can't do what you're doing, and also have some reason, motivation, desire to help that person learn it. That desire to teach seems to be really pervasive in humans and may be mysteriously missing in apes.
Why do you think apes aren't good teachers?
Well, it's really hard even for human teachers to keep in mind that some task may be difficult when they already know how to do it. For humans, this is called the curse of knowledge. Human teachers struggle with it all the time, figuring out what makes something hard so they know how to help a student. That seems to be a part of what apes don't do very well.
But again, I don't think that's a full explanation of why apes don't teach, because if the problem was tracking what somebody else wasn't getting, you would expect to see failed attempts to teach, right? You would expect to see apes trying to teach other apes, but maybe they'd go too fast, maybe it wouldn't work very well. But that's quite different from what we see; apes don't seem to ever really start trying. It's possible that they just lack the initial impetus to deliberately pass on a new skill.
A magic triangle
You mentioned earlier that a part of teaching is being able to coordinate your attention with another person's attention, and then focusing both on the task you are teaching. I believe psychologists call this "triadic attention," which is a bit of a mouthful. Can you explain more about this?
Yes. This is a new idea. We don't know why exactly, but it seems that humans have a special cognitive ability. It's something that's hard to learn and that, perhaps, very few animals do. We can pay attention to a special triplet of things, the triplet that's me and another person and a third thing—a task or an object that we're both thinking about, or talking about, or working on together. It's the basic element of all cooperation and maybe most communication.
For some reason, kids, human kids, do this naturally almost immediately. One-year-olds are already really interested in tasks—or games, really—whose only pleasure is coordinating joint activity on similar objects. For instance, you can get a one-year-old really excited about a game where you hold your end of a stick, and I hold my end, and we both pull to make something happen. And curiously, apes can't get into that. So an ape baby or an ape adult isn't excited by a task whose only pleasure is the coordination of two different individuals' joint activity on a third object. We don't know why.
Can you give another example of this kind of coordination?
Sure. Picture a parent and a child sitting together playing with blocks. In order to build something, both of them are adding pieces to the same structure. And they're negotiating about it. Which piece goes where? Does the tower go here? Does the door go here? And they're doing this project together. They have to negotiate it, and they have to play with each other at the same time that they're both playing with the blocks. That's the kind of coordination that humans do naturally. Two minds work together, watching each other and watching the object that they're playing with. That's the kind of thing apes don't seem to do.
Is human cooperation really different from what we see in, say, social insects?
Yes. When humans cooperate, it's not just two people working on the same project side-by-side like ants that build an ant house or bees that build a beehive. There's definitely cooperation among these insects, since it takes lots of different individual bees to build a beehive. But there's no coordination in the cooperation; they don't have to check with each other in order to do it. And that might be the distinctive feature of human cooperation—we don't just do our piece of the task, each in parallel, but rather we actively coordinate between individuals when we're working together.
Do you see early signs of this ability in human babies?
Yes. Pointing might be the simplest and earliest example of coordination of attention. It emerges really early—individual children start to point informatively when they're 10 months old, before they talk. Now, it's important to distinguish between two kinds of pointing. One kind of pointing is a demand; you point to ask for something. That kind of pointing isn't uniquely human, and it emerges even earlier in child development. What seems distinct and special to humans is the desire to point informatively, just to show that there is something interesting there, to attract attention.
Pointing seems like such an everyday gesture that no one would even notice it.
Oh, parents totally notice it! 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.
Is it true that there might be a brain region dedicated to this coordinating of two minds?
Well, what we do know is that there are definitely regions in the human brain that seem to play special roles in social cognition—in seeing and thinking about other people. And different parts of your brain get involved in coordinating and reasoning about different kinds of social tasks. It appears that this kind of cooperation recruits a very specific part of your brain, right behind the middle of your forehead.
In the last five years, there's been a huge explosion of research with new tools, new imaging tools, that make it possible to study the living, thinking human brain. And that's allowed us to study the brain basis of all kinds of things that are uniquely human.
Mind reading
There's another aspect of human psychology that seems to be very different from what you see in apes. Psychologists use the term "theory of mind." Can you explain what this means?
Well, human behavior is really complicated. And one of the best ways we have of describing and predicting and explaining what people do is in terms of what they are thinking.
Here's an example: Imagine you see a hand reaching through space towards a bottle of liquid. You could describe that just in terms of its visual properties—say, the physical shape of the hand and how it moves closer to the bottle. But what human infants can do, what we all do without even thinking about it, is interpret that movement as goal-directed, as reaching towards the bottle. A little later in development, a child can think about the intention and desire to drink the liquid in the bottle. And later still, an older child or adult is able to interpret the action in terms of a complex background of desires and beliefs.
For instance, if you know that it's Romeo who is reaching, and that he believes Juliet is dead, then you know why he is reaching for the bottle: He is reaching for the bottle because he believes it's a bottle of poison. He believes it will kill him. He wants to die. And he wants to die because he believes Juliet is dead. That's an example of theory of mind. Romeo and Juliet is one of those cases where you can't understand anything about what they're physically doing in the world unless you know what they're thinking. Romeo and Juliet is also a good example because it's about a false belief. We use false beliefs as a standard experimental paradigm.
If a human community gets together, a new human community with no common language, they immediately invent a new language so they can speak to each other.
Can you describe the experiment you do to look at theory of mind in young children?
The standard paradigm is you have a puppet, Sally, who has a ball, and she puts the ball one place. And then she leaves, and you tell the child that Sally can't see or hear what's happening. And while Sally's out of the room, the ball's hidden someplace else. The question is, when Sally comes back in, where is she going to look for her ball? To figure that out, you need to know where she thinks the ball is. She's going to look for it where she first put it, because that's where she thinks it is, even though it's really in the other place.
So what happens when you test this with, say, three-year-olds?
Three-year-olds are amazing! The thing that's amazing is not that they fail, because there're lots of things three-year-olds can't do. The thing that's amazing 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.
They'll show their confidence by betting tokens. If you give them 10 tokens, they'll bet all 10 tokens that she's going to look for it where it really is. The other thing that's amazing is that it's not a local cultural phenomenon; it's been found all over the world. It's been found in hunter-gatherer societies. It's been found in the Peruvian mountains. Three-year-olds are committed to the mistaken notion that human action is best predicted by what's really true. And so the achievement in psychological development is to realize that we should predict human action by what people think rather than by what's really true.
When does the ability to grasp that emerge?
It's not a sudden insight. It takes a long time to work it out. People are just starting to study the process, and it can take months. In some cases, it can take almost a year for kids to really switch to being 100 percent successful in predicting where Sally will look for the ball.
The talking ape
There was a lot of research, and certainly media attention, in the past on whether apes are able to learn language when humans try to teach it to them. Has the focus shifted?
Well,people have now gotten interested in why apes don't create language for themselves, so it's a different kind of question. What are the basic competencies that are necessary for the original invention and then sustaining of language without any external support? If a human community gets together, a new human community with no common language, they immediately invent a new language so they can speak to each other, in one generation. What are the things that make a community of people so desperate to share and communicate information that, in one generation, they will inevitably invent a new language? That's a new hot topic.
When you kind of size up human cognition versus ape cognition, are you more impressed with the similarities or the differences?
If you start out thinking that human minds and ape minds are going to be completely unrelated, completely different, as people might have thought 200 years ago, then it wouldn't be surprising that we have institutions and governments and postal services that work. But if you understand, as modern science suggests, that human genetics and ape genetics are 99 percent the same, then it seems really astonishing. What we've managed to achieve in our current position on Earth is so strikingly different from that of the apes.
What do you think is the key to this huge difference in what humans have accomplished?
I really don't have the answer to that. One possible key is the ability to transmit information and ideas and innovations from one generation to another, both nonverbally through imitation, through teaching, but maybe also specifically through language. We create records and describe new ideas in ways that can be transmitted across long distances and into new environments. In order to learn a new skill, you don't have to go sit beside somebody else who already knows it. You can read a book about it and learn it wherever you are. Maybe that's one key to this big difference.