Three million years after leaving the forest, Lucy was walking upright, but she still looked far more like a chimp than a human. You probably wouldn’t bat an eye if you saw her in the zoo, as there is little about her outward appearance that reveals her emerging humanness (see Figure 2.1). But Lucy understood that stones made useful tools, and some evidence suggests that she sharpened their edges to make them more effective. If true, this was a big step beyond chimps, who use stones as tools but have never been known to modify them.
Figure 2.1. Australopithecus afarensis, aka Lucy. (Copyright © John Gurche)
A million years later, Homo erectus assuredly made tools of bones, sticks, and hides, but these have long since decomposed. The only tools we know they used when they first migrated to Europe and Asia were barely more sophisticated than the sharpened stones attributed to Lucy. These early stone tools Homo erectus adopted from their ancestor Homo habilis clearly made life easier—they were widely used and had remained unchanged for over a million years—but they were very simple indeed. I suspect that if you chanced upon one today, you could pick it up and skip it along the surface of a lake without ever knowing you’d held an object of great significance (see left side of Figure 2.3).
Figure 2.2. Homo erectus. (Copyright © John Gurche)
So how did Homo erectus successfully colonize Africa, Europe, and the southern half of Asia more than a million years ago with such a meager tool kit? No doubt their success stems from the fact that Homo erectus had a brain about two-thirds the size of our own. In contrast to Lucy, Homo erectus (Figure 2.2) would seem wildly out of place in a zoo as anything but a (rather rough-hewn) visitor.
The larger brain of Homo erectus enabled their most important tool: their enhanced capacity to work together. The fossilized remains of horses and elephants (often twice the size of modern elephants) butchered by groups of Homo erectus at multiple sites across Europe and Asia suggest that Homo erectus were not just living on the margins of their new world. Conceivably, Homo erectus were scavengers, nibbling on remains left behind by other predators, but the evidence suggests otherwise. Many of the marks that Homo erectus’ stone tools left on the bones of these fossilized remains were made prior to the tooth marks of local predators. Additionally, the marks of Homo erectus’ stone tools are often found high on the animals’ leg bones, up near the torso, which is a part of the animal that predators consume first. If Homo erectus were scavenging, there would be little to no meat left on this part, and thus little reason for cut marks to appear there. These findings suggest that Homo erectus discovered how to kill some large and speedy animals with incredibly simple tools, an accomplishment that would have required extensive planning and coordination among groups of hunters.
Figure 2.3. An Oldowan tool on the left (Rosalia Gallotti) and an Acheulian tool on the right (Fernando Diez-Martin), both from 1.7 million years ago.
There are several reasons to believe Homo erectus had the intellectual capacity to plan and coordinate hunts. First, Homo erectus went on to invent a much better set of stone tools than the Oldowan* tools they inherited from their comparatively dimwitted ancestor Homo habilis (left side of Figure 2.3). The Acheulian* tools created by Homo erectus were symmetrical and bifacial, which would have increased their utility and comfort of use (right side of Figure 2.3). In contrast to the stone tools of Homo habilis, if you chanced upon an Acheulian tool, I suspect you’d bring it home to show your friends.
One way to study the demands involved in making these ancient tools is to make them ourselves, and numerous anthropologists have learned the art of stone knapping—that is, shaping tools from rocks by carefully whacking them together as our ancestors did. In one such study, modern stone knappers were placed in an fMRI magnet, which is similar to MRI machines used in hospitals, but with the added capacity of measuring brain activity along with brain structure. The knappers were shown partially completed Oldowan and Acheulian tools and asked to make decisions about what they would do next to finish them. By measuring brain activity while they made these decisions, the study allows us to see what sort of mental work is involved in making these tools. The brain scans showed that production of Acheulian tools demanded more processing from the front of the brain (the region involved in planning and coordinating activities) than did the production of Oldowan tools. This seems fairly intuitive when you look at the tools in Figure 2.3: it’s clear that the Acheulian tools would require greater forethought than the simpler sharpening evident in Oldowan tools.
Not only did Homo erectus invent better tools, but the evidence suggests that they were the first species to plan for a world beyond their current needs. It seems odd, but monkeys and apes are incapable of planning for future needs they do not currently feel. For example, in one research lab, capuchin monkeys were put through a daily regimen in which they were fed only once per day. Capuchins can easily survive on such a diet, as long as the single meal is large enough, but they evolved to forage regularly, so they don’t really like just one meal per day. Still, the monkeys never learned to save any of their extra food in anticipation of future hunger. Instead, once they had eaten their fill, they tended to fling their food at each other or outside their enclosure, rather than set it aside for a midnight snack.
Chimps are far smarter than monkeys, but they, too, appear incapable of planning for unfelt needs. By way of example, consider what happens when chimps fish from a termite mound. They first find a suitable bush, pull a branch off and strip away its leaves, and then carry this stick to a termite mound. They then plunge the stick into the holes burrowed in the termite mound and lick the swarming termites off it. This sequence of events shows that they can work through a series of stages to achieve their goal, but how thoughtful is that? Not terribly. As soon as they finish eating, they discard their termite fishing rod as if they’ll never be hungry for termites again.
Similar results emerge in laboratory experiments, suggesting that chimps’ inability to plan for unfelt needs manifests itself across numerous domains, even when advance planning would be incredibly useful. Australopithecines and Homo habilis were probably no more capable than chimps in this regard, as there is no evidence that they ever made their tools for use beyond the needs of the moment. In particular, there is no sign that Oldowan tools were ever carried far from the point at which they were quarried and made.*
In sharp contrast, Homo erectus’ Acheulian tools have been found at great distances from where they were quarried and made. Thus, it’s clear that Homo erectus perceived the future utility of their Acheulian tools even after they had finished using them to dismember a carcass. This is a major cognitive leap, but it makes sense if you consider the effort and intelligence necessary to craft Acheulian tools in the first place. The mental advances that enabled Homo erectus to make more complex tools also allowed them to predict that their needs would recur. For the first time in any species that has ever lived on planet Earth, we see evidence that our Homo erectus ancestors engaged in complex planning about the future, envisioning a world beyond their immediate needs.*
Finally, the most impressive evidence for Homo erectus’ intelligence is that they invented division of labor. We saw clear hints of division of labor in the possibility that Homo erectus was successfully hunting large animals such as elephants and fast animals such as horses. When we look at their tool production sites, we see solid evidence that Homo erectus divided tasks among individuals to complete those tasks more effectively. For example, at a 1.2-million-year-old site in India, the manufacture of Acheulian tools was partitioned into different clusters, much as in a factory, with different aspects of production separated into different locations. The first step in the process of making these stone tools is to bash “flakes” loose from larger stones. Those flakes are subsequently shaped into different tools. At this Indian site, flakes were knocked loose in one location and retouched into their finished form elsewhere. If one person were making each tool from start to finish, there would be no reason to situate the production of different stages at different locations. Why carry a large stone ten meters away just to continue working on it? Rather, our ancestor would have sat down, knocked the flake loose, and then shaped it into a useful tool, all without moving around the site in any systematic fashion.
But different tasks require different abilities, so it makes sense to apportion the jobs among different people. Bashing the flakes loose required brute strength, as you have to give the larger stone a heck of a whack, in just the right spot, to dislodge a suitably shaped piece. This would have been a perfect job for the big, tough guys in the group, who could wield a large hammer stone and didn’t mind if shards of rock went flying everywhere. In contrast, the finer knapping at the retouching stage required delicacy and coordination (much like embroidery), so women and smaller men would have been well suited for this job.
Numerous other examples suggest that our Homo erectus ancestors relied on teamwork to achieve their goals, but my favorite comes from an elephant butchery site on the Jordan River, just north of the Sea of Galilee. At this site, nine hand axes were found around the carcass of an elephant, and the elephant’s skull appears to have been turned upside down with the use of a wooden branch as a lever, to allow the hunters access to the elephant’s brains (a superb source of fat). Dislodging the skull from the spine and turning it over would have required several Homo erectus working together to control the substantial weight and awkward shape of the head. If the branch was in fact used as a lever, it’s a virtual guarantee that some Homo erectus were pushing on the lever while others were balancing and rotating the head.
The chance of this endeavor working successfully in the absence of communication and coordination is near zero. Elsewhere in the site, there is evidence of nut cracking at one station, stone knapping at another, and processing of shellfish at still another. If these were modern remains, we might think they had set up food stalls, given how the tasks were so neatly divided into different locations.
Division of labor relies on the capacity to plan for the future, so it comes as no surprise that these two abilities would have emerged together. In combination, they greatly expanded what our ancestors were capable of achieving. These capacities moved us a good distance further down the social-cognitive pathway that Australopithecines put us on when they began to cooperate in their mutual defense.
Walking Upright
In chapter 1, I briefly mentioned that Australopithecines developed the body of a thrower as a by-product of bipedalism, or walking upright. But I failed to discuss why Lucy chose to walk upright in the first place. Now that we’ve discussed the different cognitive capacities of Australopithecines and Homo erectus, we can address this question, as it’s one of the most important events in our evolutionary history. If we had not become bipedal, we almost assuredly would never have learned to throw so well, in which case the social-cognitive revolution that made us human might not have happened, either. But why walk upright? What did our ancestors gain when they stopped using their knuckles as a front pair of feet?
There are two answers to this question. First, we don’t know.* Second, we have lots of ideas.* Some of our ideas have little or nothing to do with psychology. For example, long-distance walking appears to be more efficient for us on two legs than it is for apes on all four, and the disappearance of the forest would have put a premium on our ability to cover great distances. Part of the reason our ancestors started walking upright might have been simply to get from point A to point B without burning so many calories.
But some of our ideas are more psychological, in that they involve decisions about what to do with the hands. Perhaps our ancestors became bipedal to free up their hands to carry food, tools, or weapons. This proposal has been around for a long time, and it would certainly have given our ancestors an advantage to have extra food, tools, and weapons at their disposal.
As just discussed, the problem with this hypothesis is that there is no evidence prior to Homo erectus that our ancestors carried their stone tools any great distance, although they had been bipedal for a few million years. Our pre-Homo ancestors are unlikely to have carried food any great distance, either, for the same reason that they didn’t carry their tools: they were unable to anticipate unfelt needs. If they were hungry at the moment, they would have eaten their food rather than carry it. If they were not hungry at the moment, they would have left their food behind or given it away rather than carry it (not realizing that they would get hungry again later). So, what would have motivated our Australopithecine ancestors to carry anything at all? Why would an animal that couldn’t plan for unfelt needs ever choose to schlep anything across the savannah on a hot day?
To answer this question, we need only consider what emotion would have been experienced by Lucy and her ancestors every time they headed out across the grasslands. What emotion would you feel if you had to cross the savannah on foot? I think the answer is fear. Every time Lucy and her ancestors set out across open fields, they would have been acutely aware of their vulnerability and scared of a possible attack by large cats or dogs. That fear would have motivated them to carry anything they could use to defend themselves—most likely a stick that could serve as a club or spear.
Carrying a club or spear is a lot easier when you can free your hands from walking, which would have motivated Lucy and her ancestors to walk upright. Even though Lucy couldn’t plan for future needs, she could plan for current needs, and she would have felt the need for a weapon every time she set out across the savannah. Of course, we don’t know if the perpetual desire for a weapon played any role in our transition to upright walking. Still, it is consistent with our cognitive abilities at the time, and it would have given our ancestors an advantage in a manner similar to the increased efficiency provided by bipedalism.
From Homo Erectus to Homo Sapiens
Division of labor created a new golden age for our ancestors, enabling the outcome of our joint activities to be much more than the sum of our individual efforts. With division of labor, groups had emergent properties that made them much more effective and deadlier than any groups had ever been before. More than four million years after our ancestors left the rainforest, Homo erectus put us back on a path to the top of the food chain by giving us something far more important than the safety of the trees. With division of labor, animals that were once our predators were now our prey.
As if division of labor were not enough, Homo erectus then sealed the deal with the single most important innovation in human history: the control of fire. Fire provided protection from the elements and predators, and also released nutrients and calories from food that are hard to extract when it’s raw.* Compare the smell and taste of raw meat to a cooked steak or the palatability of a raw versus a cooked potato. In both cases, there is no comparison. One is nearly inedible; the other is delicious. With the control of fire, our ancestors changed their lives forever: no more returning to a cold, damp cave at the end of the day, no more night blindness, no more worrying about nocturnal predators while they slept, and no more living off the culinary equivalent of roadkill.
In his wonderful book Catching Fire, Richard Wrangham proposes that cooking played a critical role in enabling Homo erectus and later Homo sapiens to evolve such large brains. Despite having guts larger than ours, our fellow great apes cannot extract enough calories and nutrients from their diet of raw food to sustain a brain nearly as big as ours. Not only is our brain-to-gut ratio much greater than that of the other apes, but we also burn calories faster than they do. Cooking our food allowed us to evolve a faster metabolism to support such a large brain.
Cooking also allowed us to evolve greater fat storage, as a big brain is a risky drain on metabolic resources without a bit of blubber to serve as backup when times are lean. Finally, cooking freed our ancestors from the incessant chewing required by raw food. A typical chimp day involves about eight hours of chewing to soften food before it can be effectively digested. It’s hard to imagine just how disruptive eight hours of chewing per day would be, particularly for a species like ours that is so dependent on spoken language. Indeed, language might have evolved more slowly in a world of incessant chewing, due to the challenges of talking with one’s mouth full.*
The control of fire illustrates one of the many ways our ancestors created the cognitive niche we occupy, and how culture and innovation can shape subsequent evolution. Once we learned to barbecue, we no longer needed such large teeth and jaw muscles to chew our food. This change allowed us to benefit from random mutations in genes that decreased the size of our jaw and teeth. These mutations would have been costly had they occurred earlier, as anyone with small or weakened jaws would have had greater difficulty subsisting on a diet of raw food. But once we learned to control fire, we moved further down the line from our large-jawed, small-brained ancestors to our small-jawed, large-brained selves. In this manner, our innovation played an important role in the subsequent shape of our head and facilitated our increasing emphasis of brain over brawn.
Our brains continued expanding as we evolved from Homo erectus to Homo sapiens, as did our capacities to plan and to understand each other. You and I are the outcome of this evolutionary process, as Homo sapiens emerged in Africa over two hundred thousand years ago. The complex cultures we developed with our large brains made us a success in every environment, and before long we had colonized all of Africa and begun looking beyond its borders. We see tentative signs of Homo sapiens in Arabia 125,000 years ago; and by 80,000 years ago we were heading out in earnest. By 65,000 years ago we’d made it to Australia; 45,000 years ago, we were pushing north into the Arctic; and 20,000 years ago, we reached the Americas. The Pacific Islands were the last places to be colonized, with New Zealand coming in last place, only 700 years ago.
Around the same time that we started colonizing the globe, there was an explosion of culture, art, and other evidence of symbolic thought. Although our species is more than 200,000 years old, the cultural richness commonly associated with Homo sapiens doesn’t appear until less than 100,000 years ago. This does not mean there was a lack of symbolic thinking for more than 100,000 years, but more than likely it speaks to the minuscule chance that the products of our culture will remain intact for such long periods of time. Today we hang paintings in climate-controlled museums, but our ancestors just painted on cliff walls. Given their lack of concern with posterity, it’s astonishing that we’ve found any art or artifacts from so long ago at all.
Whether complex culture emerged with the gradual onset of our species (or possibly even before us), or whether it took more than a hundred thousand years to accumulate, the eventual impact of our sociality was an extraordinary growth of knowledge and innovation. New tools, weapons, and art proliferated with the spread of Homo sapiens, and the key underlying changes that enabled this explosion were psychological. Long before the invention of writing (which is only about five thousand years old), human culture had become cumulative by virtue of our oral storytelling traditions.
Storytelling may have been another by-product of the control of fire, as the conversations of hunter-gatherers during the day differ notably from the stories they tell around the fire at night. During the day, people spend most of their time talking about ongoing social concerns and matters of economic necessity. But once night falls, communal fires are lit, and people gather in small groups, conversations blend into stories, and stories often reveal important lessons about how to live one’s life and follow cultural rules.
Fire enabled us to extend our community time past daylight without the added risk of predation, and in so doing gave us a unique opportunity for socializing and reflecting, as the work of the day was no longer possible. The fact that hunter-gatherers use this time to pass on important cultural information raises the possibility that fire played a critical role in the creation of our knowledge base. Storytelling allows each generation to build on the information gathered by their ancestors, as cultures accumulate knowledge about how to deal with their local environment.
The importance of cumulative culture can be seen in almost every aspect of our lives, but one of the clearest examples can be found in the harrowing tales of early European explorers to the Arctic, Americas, Africa, Australia, and Asia. On countless occasions, intrepid and well-prepared adventurers perished or nearly died, while just around the corner, indigenous people who lacked their modern technology were well fed and sheltered. It was our capacity to learn from the experiences of others that gave Homo sapiens an enormous local advantage, with new strategies and innovations built on a platform of prior discoveries. As a consequence, each generation had no need to reinvent the wheel, and a child could acquire an understanding of the world that a few generations back would have been available only to geniuses. We see this effect today, with schoolchildren learning of the discoveries of Copernicus, Darwin, and Galileo, and there is no doubt that a somewhat slower version of this cumulative process has existed for over a hundred thousand years. No other animal can do this.
Complex Social Relationships Demand Large Brains
When you consider the vast body of knowledge required to survive in every climate on earth, it might seem that the social challenges our ancestors faced were trivial by comparison. The Inuit had to learn to hunt enormous creatures in treacherous seas and build temporary homes from ice to survive long trips on a featureless landscape. Sub-Saharan Africans had to learn to hunt monkeys using arrows tipped in poisons, such as those extracted from the Strophanthus kombe seed. And Aboriginal Australians had to learn to avoid deadly snakes and spiders while somehow finding food and water in one of the hottest and driest places on earth.
These challenges were extraordinarily difficult when humans first moved into these environments, but in the age before modern transport, humans moved slowly. Even our most nomadic ancestors spent most of their lives in familiar environments. The unchanging rules for dealing with the piece of the world they inhabited could easily be passed down to each subsequent generation around the campfire. As a result, cumulative culture and social learning ensured that the physical problems associated with predator, prey, and shelter weren’t very cognitively challenging.
Unlike the physical world, however, the social world is dynamically interactive; my social strategies impact other people, who often change their behavior in response. Other people also hatch their own plans, and I need to figure out what’s going on when I come home from a long hunt and everyone is whispering and giggling around the fire. Do I have mammoth fur stuck in my teeth? Was I cuckolded while I was out on the ice? Does that giggling even relate to me? Such complexities ensure that you cannot learn to deal with other people simply by following an unchanging set of rules that work well in the natural world, such as “avoid the spider with the red line on its back” or “find water in deep ravines.” The shifting sands of the social world provide an ongoing challenge, as fellow humans change their behavior at their own whim, particularly if they think others are taking advantage of them.
All this might seem like little more than an intellectual game for our ancestors, but it’s important to remember what life was like before the creation of government, law, police forces, and the various institutions of modern living that make our world safe and secure. As Steven Pinker notes in his superb book The Better Angels of Our Nature, life among hunter-gatherers was a dicey proposition, with murder rates that were typically much higher than those in the most dangerous cities of today. Being a hunter-gatherer might seem like an idyllic and carefree existence, but it was riskier than living in the scariest neighborhoods of the most dangerous cities today.
In the world of Australopithecines, Homo erectus, and eventually Homo sapiens, friends and neighbors did whatever they could get away with. Our closest analogue to their way of life is criminal gangs such as the Mafia and drug cartels, whose primary constraints are one another. Every morning when our ancestors got up from the cave floor, they joined a prehistoric episode of The Sopranos. If they wanted to survive until nightfall, they had to find a way to navigate the minefield of competing goals, complex and changing coalitions, jealous rivalries, and potentially dangerous outbursts from their peers.
Even being the strongest wasn’t much of an insurance policy. Everyone sleeps eventually, and if others in your group decide you’re more trouble than you’re worth, any given night could be your last. Without law enforcement, everyone had to get by on his wits. The less savvy individuals were less likely to navigate this complex social world safely and less likely to convince someone to mate with them. As a consequence of these intense social pressures, we evolved a variety of new cognitive capabilities that were explicitly social in nature. The most important of these is Theory of Mind.
Theory of Mind
In their efforts to form and maintain alliances, create cooperative ventures, and just get through the day without getting whacked, our ancestors learned to anticipate one another’s behavior. The best way to predict other people’s behavior is to know their reasoning and goals, so we evolved Theory of Mind: the understanding that the minds of others differ from our own. Small children don’t have this capacity, which is one reason why their sudden announcements and stories can be so difficult to follow—they don’t realize that their listeners are often not thinking the same thing they are. But you can see the penny drop when it occurs to children that preferences and knowledge vary. Life suddenly becomes richer and easier when they realize that the world offers many mutually beneficial deals: I prefer red jelly beans, but you like the black ones; I’ll play hide-and-seek if you’ll play tag.*
Once our ancestors understood that others have different thoughts and feelings from their own, they began guessing what those thoughts and feelings might be. Other people’s behavior provides the clearest clues to their thoughts and feelings, but behavior is most useful if you can discern the underlying intentions. Did she do that by accident, on purpose, or because she had no choice? This elementary form of mind reading is mission critical for understanding competing coalitions, particularly if the coalitions change in membership or goals across time.
It seems obvious that when someone stumbles and steps on our toes it was an accident, and when they walk over and stamp on our toes it was purposeful, but you know this only because your social information processor works so well. If you have pets, pay attention to the next time you accidentally hurt or scare them. My dogs become just as submissive and penitent when I accidentally step on their paws as when I scold them. With no capacity to differentiate intended from unintended actions, their ability to understand me and predict my future behavior is severely limited.
Along with these fundamental capacities of social perception, our highly interdependent lives ensured that we also evolved new social emotions such as pride, guilt, and shame. These are often referred to as self-conscious emotions, as their development requires awareness of how others are appraising us, and they differ from other social emotions, such as anger and love, in that the focus is inward. These self-conscious emotions evolved to help us feel about ourselves as others feel toward us. They tell us immediately and forcefully which behaviors make us more valuable to our group and which behaviors devalue us.
We feel pride when we’ve done something that increases our value to our group, and the positive feelings associated with pride ensure that we seek out further such opportunities. We feel guilt when we’ve harmed someone in our group, and the negative self-directed feelings associated with guilt help us learn from the experience and avoid doing it again (before our friends give us the heave-ho). Shame is felt when we’ve done something to devalue ourselves in front of our group, and again the negative self-directed feelings ensure that we don’t repeat the shameful behavior and experience further loss in status. Pride, guilt, and shame are critical parts of being human, and they help us function in the highly interdependent and cooperative groups that emerged with Homo erectus and that have made us so successful ever since.
The importance of these emotions can be seen in sharp relief when you consider the lives of people with a limited ability to experience them, such as sociopaths. Sociopaths are often charming and fun when you first meet them, but they struggle to get along with other people over any length of time because of their tendency to ruthlessly exploit others. If I experience no guilt or shame, there are no internal forces putting on the brakes when I see an opportunity to take what I want from you.
Taking rather than sharing or asking might seem like a successful strategy in the short term, but memories are long, and people who have been exploited or abused often recount this experience to others. Gossip plays a critical role in the spread of this type of social information, and soon even the most charming sociopaths find they are unwelcome in their community. In the hunter-gatherer groups of our ancestors, sociopaths struggled to find a community that would allow them to stay. As we will see in chapter 3, the creation of cities changed all that (and then social media changed it back again).
Theory of Mind for Teaching and Learning
Theory of Mind evolved to help us navigate our social world, but it has other advantages. Perhaps most notably, it dramatically increases our ability to teach (and learn from) others. If I have no idea what you’re thinking, or that your knowledge differs from mine, it’s hard for me to teach you. Where do I start? What do you already know, what do you need to know, and how can I best show you? But if I can discern the answers to these questions, I can intentionally use your knowledge base as a starting point for sharing new information. As a result, humans are incredibly effective teachers.
My favorite example of just how effective we are as teachers can be seen in the case of chimps learning to use stones to crack nuts. Chimps use simple tools, and in many parts of Africa, they have developed strategies for opening nuts by wielding stones as a hammer and anvil. When nuts are in season, mother chimps will often place some on a large stone and then use a smaller stone to crack them open. Their offspring typically sit nearby during this operation, and the mothers tolerate their children grabbing some of the fruits (or in this case, nuts) of their labor. The critical question for our purposes is how long it takes the offspring to learn this nut-cracking skill.
When I first heard about research on nut cracking, I guessed that young chimps would probably need about a year to learn the skill. After all, it’s not easy manipulating irregularly shaped rocks and hard little nuts, and a few unintended finger smashings would dampen any student’s enthusiasm. Additionally, chimps don’t get the chance to practice very often, as nut cracking is a relatively rare event for them. So, it’s not something they’re going to learn overnight. You can imagine how stunned I was, then, to find that it takes chimps in the wild about ten years to learn to crack the various nuts they eat!
An animal trainer could teach a young chimp to crack a wide variety of nuts in less than a tenth of the time, but animal trainers have Theory of Mind, and chimp mothers do not. Chimp mothers do not know what their offspring do not know, and thus are limited in their capacity to teach them (and in their awareness that they ought to teach them). When they see their offspring make an error, they do seem to be able to correct it (such as when the young chimps hold the hammer stone wrong or place the nut poorly), but chimp mothers’ lack of understanding of the error’s source limits them to only infrequent and highly specific corrections. Small children are also poor teachers for the very same reason. Even when they have mastered a skill themselves, they don’t know that others don’t know it, and thus they struggle to teach their knowledge and skills to others.
Theory of Mind is a boon to learners as well. If I understand that another person has knowledge that I don’t have, then I also understand that this person might impart that knowledge to me. This understanding prompts me to pay close attention to potential teachers, and to imitate their actions even if I don’t discern their purpose. For example, if you are teaching me how to pitch a baseball, and you raise your front knee all the way to your chest before hurling the ball, then perhaps I should try to do the same. The motion looks ungainly and pointless, but you know better than I do.
This sort of imitation in the absence of understanding has clear links to Theory of Mind, and hence it’s no surprise that it is uniquely human. In their classic experiment demonstrating this effect, Victoria Horner and Andrew Whiten of the University of St. Andrews presented kids and chimps with a complex treasure box that had a treat inside. Horner and Whiten showed the kids or chimps how to open the box, but they made sure they included some irrelevant actions that played no actual role in opening it. For example, they first poked a stick into a hole in the top of the box, even though the only latch was on the side. When the external surface of the treasure box was opaque and observers couldn’t see that the hole on the top had no function, the kids and the chimps both copied all the actions to open the box. When the treasure box was transparent, however, it was obvious which actions were relevant and which were not. In this case, the chimps modeled only the necessary actions and ignored the irrelevant ones, but the children continued to model the actions that were now obviously unnecessary.
This tendency has been labeled over-imitation, and it appears to be a universal human trait. It emerges among children in highly educated and industrialized societies, and also among children in small-scale societies in the Kalahari and remote regions of Australia who have little or no formal education. Over-imitation is an important human propensity, as it allows us to learn to do things even when we can’t fully understand them. By assuming that our teacher knows best, we engage in the highest-fidelity copying we can, which enhances our effectiveness.
Over-imitation has great survival value, as it can facilitate the transmission of complex techniques that are often necessary in the preparation or detoxification of foods. Consider, for example, how people in the lowlands of Papua New Guinea have figured out how to eat the sago palm, which appears anything but edible. It turns out that the trunk of the tree contains a high concentration of starch, which can be harvested via a complex multistep procedure. After the tree is chopped down and the outer layer of the trunk peeled off, the inner part is pounded into sawdust. At this point the sawdust is entirely inedible, but it is then repeatedly rinsed with water. The warm tropical waters of New Guinea break down the starch molecules, causing them to separate from the wood of the tree and enabling them to pass through cloth filters.
The starchy water is then collected in large containers and left overnight so the starch can settle to the bottom. The water is then poured off the top, leaving a thick, starchy paste. This paste must be spread out and dried in the sun to prevent fermentation, which would otherwise make it toxic.* The subsequent flour is then stored in tubes made of sago palm fronds, where it can be kept for months and prepared in a variety of ways. No doubt a lot of trial and error went into the development of this process, but the beauty of over-imitation is that people don’t need to know why they prepare the sago flour in this manner. They do it that way because they have observed others doing it that way.
Theory of Mind and Social Manipulation
It couldn’t have been long from the origins of Theory of Mind to the day the first lie was told. I should clarify this statement by noting that deception existed long before lying. Deception is often practiced by plants and animals that pretend to be something they’re not, such as insects that look like twigs and chameleons that change colors to match their background. These beings don’t need to understand the mental states of others to achieve their deception.
Even complex acts of animal deception don’t demand representation of the minds of others. For example, capuchin monkeys will occasionally make an alarm call in the absence of predators and then quickly eat the available food when the other monkeys scamper for the trees. Their use of this strategy is more likely when the food is concentrated in a nearby position, and hence more quickly consumed when the others run away. But even this rather complex strategy could be learned over time without any ability to know what the other monkeys are thinking.
In contrast to these types of deception, lying is a uniquely human form of social manipulation that requires substantially greater cognitive sophistication. To tell a lie is to intentionally plant a false belief in someone else’s mind, which requires an awareness that the contents of other minds differ from one’s own. Once I understand what you understand, I’m in a position to manipulate your understanding intentionally to include falsehoods that benefit me. That is the birth of lying.
Researchers have found that they can teach small children to lie simply by teaching them Theory of Mind. In the first test of this possibility, Xiao Pan Ding of Zhejiang Normal University and her colleagues brought three-year-old children into the lab who did not yet understand Theory of Mind, and either taught them Theory of Mind or an irrelevant task. In the Theory of Mind training, Ding and her colleagues showed the children containers, such as a pencil box, and then opened them to reveal that they held unexpected objects. They then asked the children what other people would think the box contained. Over time it began to dawn on the children that other people would tend to think as they had prior to seeing the unexpected contents. Children were trained across six different days on such tasks, with the goal of teaching them that other people don’t necessarily know the information they have just learned.
After training in either the Theory of Mind or the irrelevant task, the children played a hide-and-seek game with the experimenter. In this game, the experimenter covered her eyes while the children hid a candy in one of two cups. When the experimenter opened her eyes, she asked, “Where did you hide the candy?” and then looked in whichever cup the child indicated. When the child told the truth, the experimenter picked up the candy and declared it her own. When the child lied by pointing to the wrong cup, the experimenter looked in the empty cup and then announced that she had lost and said that the candy now belonged to the child.
The critical question in this experiment was how often the children lied to keep the candy across this hide-and-seek game. Prior to the Theory of Mind training, the children never lied. After Theory of Mind training, the children lied an average of six out of the ten rounds. Knowledge is power, and this experiment demonstrates that Theory of Mind gives us the power of knowledge manipulation.
If you know small children, you can watch the development of lying in real time, because their early lies are so transparent. Children often begin lying to get out of trouble, such as when my three-year-old brother blamed our kitten when my mother asked him why he had splashed so much water out of his bath. This simple version of lying need not involve Theory of Mind,* but it does show that Theory of Mind is beginning to develop. From there it doesn’t take long to start lying to gain all sorts of benefits that are difficult to come by honestly.*
I remember one afternoon in the park when a little boy joined my then-four-year-old son on the playground. After a few minutes on the monkey bars, the boy suddenly announced that he had a Spider-Man lunch box. My son hadn’t seen Spider-Man before and must have been mystified about the nature of this apparently desirable object. Not to be outdone, however, he responded that he owned a “Leafman” and a “Grassman” lunch box. When the boy looked at me for confirmation, to see if my son had really bested him in both the lunch box and superhero departments, I did my best not to spill the beans by laughing. Although one naturally tries to discourage lying in one’s children, I was pleased to see the developing signs of sociality in my son’s use of lying to maintain his status on the playground. Such uniquely human capabilities are products of our social nature and the critical importance of social success in the small groups in which we evolved.
Lying may be handy, but it is also a threat to relationships and to the social fabric of entire communities, as the advantages of our incredible communicative abilities emerge primarily when we tell the truth. People delight in the utility of their own lies but are furious when they catch others lying to them. Moral rules differ across cultures, but there are some universals, and one of the foremost rules in all cultures is not to lie. No one minds if you lie when you compliment their bad haircut, but self-serving and destructive lies are frowned on by every society on earth. When we see such universality in moral rules, we know that they combat a tendency in people to do otherwise, and serve an important human need. The pancultural condemnation of lying is clear evidence that all humans are tempted to lie, and that lying is a threat to group cohesiveness and coordination everywhere. Those facts, in turn, speak to the importance of cooperation and interdependence in human affairs.
If you track our cranial expansion across the six million years covered by the first two chapters of this book, you see that the story is quite extraordinary. A chimpanzee has a brain that weighs about 380 grams. Three million years of eking out a living on the savannah changed our bodies in important ways, but Australopithecus afarensis’ 450-gram brain was barely larger than that of a chimp. Fast-forward another one-and-a-half million years to Homo erectus, and now our ancestors have a 960-gram brain, twice the size of that of Australopithecus (although they were a fair bit bigger as well, so the relative change wasn’t as dramatic). Another million and a half years later, and Homo sapiens has an average brain weight of 1,350 grams. We added an entire chimp brain onto that of our Homo erectus ancestors. Why did the first three million years of evolution on the savannah give us a paltry 70 grams of brainpower, when the next three million years endowed us with almost a kilo?
The answer to this question lies in the fact that our expanding social capacities led us to evolve greater cognitive capacities to exploit new social opportunities. Without such a big brain, Homo erectus could never have controlled fire, and without controlling fire, Homo erectus could never have evolved an even larger brain. More important, without the social complexity of Homo erectus’ lifestyle, there would have been little reason to spend the metabolic energy necessary to support such a large brain in the first place.
The accelerating brainpower that emerged over the last six million years was both cause and consequence of the social changes experienced by our ancestors. We created the social-cognitive niche when we learned to cooperate on the savannah for mutual defense. Over the next several million years we continually invented new ways to leverage and exploit our expanding social-cognitive abilities.* We remained hunter-gatherers for the six million years that elapsed from when we left the trees until very recently, but our place in this world changed dramatically. Cooperation and division of labor expanded our capabilities, transitioning us from prey to top predator.