The Cognitive Tradeoff Hypothesis

This is Inuyama, Japan, a historic city home to Japan's oldest original wooden castle. It is also home to Kyoto University's Primate Research Institute. Here, a group of chimpanzees have been trained to play a game that exposes something shocking about their memories. This is going to blow your mind. Here is how it works. Take a look at these numbers. 1, 2, 3. Remember where they are, because they're about to disappear. Can you point to where each number used to be in numerical order? Probably. It's pretty easy. 1, 2, 3. But what if we make it harder? Get ready to point to where each number was in order... now. If you feel like you didn't have enough time to memorize the screen, that's fine. It's nothing to be ashamed of. Or is it? Here is a chimpanzee taking exactly that long to memorize the same arrangement. Nailed it. Each of these puzzles is completely new to the chimpanzee, but just a glance is all it needs to completely capture all the numbers. How can a chimpanzee's memory be so much better than ours? Well, one theory is that we humans are worse at this task because we can talk.

What makes humans different from other animals? Well, one thing is language. We have the cognitive ability to communicate not just about what's happening now, but also about what did happen, and what could happen. We can tell stories, and it's awesome. But if language is so good, why didn't any other animal develop it like we did? A good approach to this question is one that looks at how we are different from those who were almost us. Around 7 million years ago, there were no chimpanzees and there were no humans. But there were CHLCAs, an acronym which stands for "Chimpanzee-Human Last Common Ancestor." Like us, CHLCAs didn't have great natural offenses or defenses, protective shells or claws, fangs or venom. So living in the safety of the trees was great. Those who stayed became the chimps we know today. But for reasons we're still not quite sure of, some of the CHLCAs decided to venture down to the savanna. Without appropriate physical abilities, things like cooperation, imagining new strategies, and the assigning of roles were necessary for survival, all of which are easier if you have a rich collection of symbols that can refer to things across time: language.

Many different types of creatures emerged with varying adaptations. But today, only one member of the family remains. Us. Language as we know it may have been one of the strategies that kept us alive in the savanna. But where did it move in? The brains of those who developed language and those who didn't aren't totally different. A brand-new brain structure didn't just pop into existence. Instead, anatomy used for other tasks must have been sacrificed. And as it turns out, for beautiful reasons, detailed short-term memory may have been a fair thing to lose in return for language. This trade-off between memory and language is the Cognitive Tradeoff Hypothesis.

The Cognitive Tradeoff Hypothesis is the culmination of decades of work by one of the world's leading primatologists, Professor Tetsuro Matsuzawa of Kyoto University's Primate Research Institute. Founded in 1967, the institute was created for scientific research in association with the nearby Japan Monkey Center. The collaborative centers house over 60 species and nearly 1,000 primates who live and play in open spaces. Look at monkeys. [monkeys chitter] Is there a baby on that one? -[Michael] Six months? -[Tetsuro] Yes. [gibbers] That's where they live. [Michael] Can you do it? [grunts] Dr. Matsuzawa has spent over 40 years researching non-human primates. He splits his time between fieldwork in the West African country of Guinea, and here in Japan, where he and his colleagues have developed a chimpanzee habitat designed to mimic life in the wild. This habitat is home to Skylab, a working laboratory set high atop the chimpanzee's climbing structure. In this open-air lab, chimpanzees are free to come and go as they please. And this is how you move? If they decide to stay, they participate in cognitively enriching tasks designed to mimic foraging behavior.

When the chimpanzees are interested in participating, they enter one of Skylab's specially designed computer booths, where a camera uses facial recognition software to recognize them and select a test based on that particular chimp's current familiarity with the task. Each trial takes about as long as it would for a chimp to forage a single bite. And each morsel of food they get is accounted for in their diet. Do the doors open when they approach? No human even needs to be...? So, what is for us a great way to collect data, is for them an experience similar in many ways to what they would be doing in the wild. Impressive. Dr. Matsuzawa has been running memory tests like these on chimpanzees since 1978. His research has shown the phenomenal and nearly photographic short-term memory of these primates. Two of the most famous chimps at the PRI are Ai, named after the Japanese word for "love," and her son Ayumu, whose name means "walk."

What can we learn about ourselves by studying chimpanzees like them? Well, I want to find out. If we and chimpanzees come from a common ancestor, what can explain the split where the chimpanzees don't seem to need or to develop language like we did? Why would that happen? Was it an accident? Ah-ha. Our habitat... provided a pressure to develop language. Yes. -That's incredible. -Mm. So, in a way, we should be really grateful that our ancestors were so weak, they got pushed out of the trees. [thumping] -Bang, bang. -[laughs] [Michael] I'd invite you to be a part of this interview, but you don't have language. Right now. Mm-hmm. Quick decisions. Our ancestors didn't have that same pressure? Hmm. [Michael] The Cognitive Tradeoff Hypothesis suggests that in the dangerous world beyond the trees, early humans needed to teach each other and use abstract symbols that could refer not just to the immediate here and now, but to hypotheticals and generalities. Making room for that kind of abstract thinking meant sacrificing the immediate and detailed memory of their ancestors. Yeah. I'm able to imagine past and future. I'm able to describe things in an abstract way. And I don't need the details, because I have the label. So it seems like a pretty good trade-off. Yeah. Yeah. What a great message, right? Sharing is what makes us "us." I would love to see your working memory tests on chimpanzees in action. I would also really love to participate myself and see how well I can do compared to a chimpanzee. Yes. Have you ever had a human and a chimpanzee compete like that together? -[hooting] -[Michael] They're excited about the idea too. -[laughs] [gibbering] [Michael] An opportunity to do the memory task just like a chimpanzee is really special. Who knows how it will go? Let's see who shows up. -[clapping] -[Michael] Yeah! You're really good at this, Ai. Looks like today, it will be celebrity chimp, Ai. Ai is older now, and just like in humans, her cognitive abilities have decreased with time. So I may actually stand a chance. To face off against Ai, I will be sitting in the booth next to her. Normally, her son Ayumu plays against her. But today, well, she's in for some Michael time. I'm not your child, though, am I? The tests are going to get harder as we go along. How will my memory compare to that of a chimp who never made the same cognitive trade-off? [exhales] In the first round, the task is to remember where each of the three numbers are in numerical order. But here's the trick: as soon as I touch one of them on the screen, the other two will be covered by solid squares, so I can no longer see where they are. Now, well, it's up to my memory. [Tetsuro] Okay, let's go. [Michael] If I make a mistake, I get an error noise like this... [buzzer] ...while a correct answer sounds like this. [computer chirps] When the chimpanzee gets it right, they are rewarded with apples. The human, me, well, just gets the bragging rights. I'm not getting apples. [laughs] [computer chirps] You really actually have to focus more than I expected. Almost messed that one up. [buzzer] [computer chirps] [Tetsuro] How did Michael do? 95. [Michael] On my first run, I've managed to beat Ai. What is the next task? How many symbols? Whoa. [computer chirps] This is a lot harder. This game is similar to the last, but starts a little bit differently. This time, three numbers appear on a blank screen, but as soon as I touch the first one, the entire screen is covered in boxes. [computer chirps] Whew. [buzzer] [computer chirps] [buzzer] [Michael] Ai... you having fun? -Whoa! -[grunts] Ai is used to Ayumu, her son, playing the game beside her, so my presence may be throwing her off. I'm here for moral support, Ai. It was fun squaring off against Ai, but I want to see how I would do against her son, Ayumu. I'm ready. Okay... [Michael] Ayumu is currently Matsuzawa's best pupil, able to ace the memory tests at blazingly fast speeds. [computer chirps] But today, Ayumu is not interested in mental combat. He's busy flirting with some young ladies who live with him here at the PRI. And since free choice is the guiding principle of Matsuzawa's research, we can't make him join us. The good news is that Ayumu doesn't need to be here for me to compete against him. The game can be presented to me just as Ayumu does it: with nine numerals. Let's see if my luck is the same against Ayumu as it was against Ai. Oh, man. Okay. -[buzzer] -Wow. [laughs] Even when I take time I can't do it right. Okay, more time. [buzzer] I thought I had that one. It takes a long time to memorize nine numerals' positions. [buzzer] It's embarrassing how long this takes me. I can do this one. [computer chirps] All right. Yeah. You don't need to laugh about it. Thirteen. I got better, yeah, because you were pressuring me. Jesus. Six times worse, six times slower. Yeah. I would love to. [Michael] This is the most difficult test. I have to remember all nine numbers in numerical order at Ayumu's speed, which is to say, I have to do what I could barely do before, but now I have to memorize them all within the amount of time it takes to blink. So I get half a second to prepare? I'm going to prove you wrong. As a reminder, this is how Ayumu performs, which is standard for a young chimp. You got to be kidding me. -That's way too fast. -[buzzer] I got the first three. [buzzer] It's like a joke. [buzzer] [laughs] I don't know where the 2 is. [buzzer] It's too fast. Trying to think of this very holistically. [buzzer] [clears throat] [buzzer] After the first three, if I see them, I'm just having to guess. [laughs] [buzzer] Yeah. It's impossible. Well, I hope this was helpful for you. It was the first time you had had a chimpanzee and a human together in the booth. What do you think--? [both laugh] If you ever need me to study as a primate, I give myself to you. -Okay. Wow. And we need to make sure to preserve them. -They're already endangered. -Yes. And yet they are our closest link to understanding what we came from and where we might go. [Tetsuro] Mm. [Michael] It's like taking care of your family. -[Tetsuro] Mm, right. -[Michael] Quite literally. [Tetsuro] Yes. [snarling] The fact that humans alone use complex symbolic language doesn't make us any better than any other species. It just means that the path we took required it. In fact, in some ways we aren't better, because we can talk. Today, we study those who took different paths as a way to learn more about ourselves. If we lose them, we lose part of our story, where we came from, who we are, and who we can be in the future. [gibbering] [shrieks] And, as always, thanks for watching. This season, on Mind Field. I will die. But should I? I want to perform a reverse exorcism. There was like a glowing figure, man. [man] I would love to do the Stanford prison experiment again. There, let's blast them again. Number three. [electricity hums] Have you ever had a human and a chimpanzee compete like that together? You having fun? -Whoa! -No, not really. [shrieks] I am going to make my hometown function like a brain. [cheering] Doing a good moral deed can actually make you more likely to do something immoral. We're going to see if we can get people to allow a child to take the blame for a crime they committed. -How old are you, son? -Twelve. [guard] We're going to need to talk to the police. This facility is where you both cryo-preserve people and store them. We have 159 patients in these tanks. We're offering an unknown extension of human lifespan. -[Michael] You spied on their dream. -Yeah. That's pretty spooky. [Michael] We received a message from outer space. Please figure out what this message is saying. -[man] You ready? -I'm ready. Hey, I have to leave and go over to the next episode, but you can come with me. Click below to check out the next episode of Mind Field. I'll see you there.