Like many a scholar before and since, Bertrand Russell confidently asserts that certain traits—”speech, fire, agriculture, writing, tools, and large-scale cooperation”—set humans apart from animals. Although we appear to excel in many domains, such claims are not typically founded in any thorough comparison. In fact, if you set the bar low, you can conclude that parrots can speak, ants have agriculture, crows make tools, and bees cooperate on a large scale. We need to dig deeper to understand to what we owe our unique success—what separates us from other animals in the domains of language, mental time travel, theory of mind, intelligence, culture, and morality. In each domain, various nonhuman species have competences, but human ability is special in some respects—and they have much in common.
In all six domains I’ve repeatedly found two major features that set us apart: our open-ended ability to imagine and reflect on different situations, and our deep-seated drive to link our scenario-building minds together. It seems to be primarily these two attributes that carried our ancestors across the gap, turning animal communication into open-ended human language, memory into mental time travel, social cognition into theory of mind, problem solving into abstract reasoning, social traditions into cumulative culture, and empathy into morality.
Humans are avid scenario builders. We can tell stories, picture future situations, imagine others’ experiences, contemplate potential explanations, plan how to teach, and reflect on moral dilemmas. Nested scenario building refers not to a single ability but to a complex faculty, itself built on a variety of sophisticated components that allow us to simulate and to reflect.
A basic capacity to simulate seems to exist in other animals. When rats are in a well-known maze, the sequential firing of so-called place cells in the hippocampus suggests that the rats can cognitively sweep ahead, considering one path and then the other, before making a decision about where to go. Appropriate place-cell sequences have also been recorded during sleep and rest, suggesting a neural basis for the learning of the maze layout and its options. The challenges of navigation may well have selected for the fundamentals of mental scene construction. Moreover, great apes have demonstrated several other relevant capacities. They can think about hidden movements, learn and interpret human symbols,
solve some problems through mental rather than physical computation, have complex sociality and some traditions, console each other, recognize themselves in mirrors, and show signs of pretense in play and deception. Great apes have a basic capacity to imagine alternative mental scenarios of the world. In certain contexts their abilities are comparable to those of 18- to 24-month-old human children.
Human development of mental scenario building explodes after age 2, however, while great apes’ capacities do not. Children spend a considerable amount of their waking life in fantasy play. They conjure up and untiringly repeat scenarios with props such as dolls and toys. Thinking, in a fundamental way, is imagining actions and perceptions, and it has been argued that in play children test hypotheses, consider probabilities, and make causal inferences not entirely unlike (adult) scientists. Play certainly provides opportunity to practice, to build up expectations, and to test them. Children take on roles and act out narratives of what happens in certain situations. Gradually, they learn to deliberately imagine scenarios and their consequences without having to act them out. They learn to simulate mentally. They learn to think.
Eventually, children can imagine an almost limitless array of events. They begin to deploy counterfactual reasoning in which they contrast what did happen with scenarios of what did not happen. They increasingly consider what might happen in the future. A key to our open-ended, generative capacity is our ability to recursively embed one thing in another, as
It is generally good advice to consider advice—preferably from a variety of sources before making up your own mind.
it enables us to combine and recombine basic elements such as people, objects, and actions into novel scenarios. Such nesting is also essential for reflection: our capacity to think about our own thinking. Nested thinking allows us to reason about the mental scenarios we entertain (just as we can draw pictures of ourselves drawing a picture).
We can connect diverse scenarios into larger plots. Narratives provide us with explanations for why things are the way they are and with opportunities for predicting how they will be. We can compare alternative routes to the future and deliberately select one plan over another—giving us a sense of free will and an edge over creatures with less foresight. We can prepare for what lies ahead and actively shape the future to our design. However, this capacity also burdens us with the responsibility of getting it right.
Individual simulation is flexible and powerful but also a risky way of making decisions that can lead us fatally astray. In the heat of Australia’s north a river may appear inviting for a swim—until you note the sign about the crocodiles. Individually, we often miscalculate, harbor false expectations, and become confused as to which option to pursue. Nested mental scenario building is not a crystal ball, nor is it a logical supercomputer. For flexible scenario building to really take off as the ultimate survival strategy, it required a second leg to stand on.
Our ancestors discovered that they could dramatically improve the accuracy of their mental scenarios by increasingly connecting their minds to others. We give each other advice—for instance, by posting signs about the possible presence of crocodiles. We can broadcast our imaginary play not only throughout our own system but to others around us. We exchange our ideas and give feedback. We ask others, and we inform them—for instance, by recounting what it was like when we were in a similar situation. We take an interest even without knowing whether anything important or useful comes of it. There are individual differences in how much an interest people display in what certain others have to say, but we are generally driven to wire our minds to those around us. Our expectations and plans are subsequently a lot better than they could have been if we didn’t listen. It is generally good advice to consider advice—preferably from a variety of sources before making up your own mind.
Nested scenario builders can benefit from cooperating with other scenario builders in many other ways. For instance, our audience can be recruited for common goals. We can hatch complex plans, divide labor, and pledge cooperation. We can accumulate our achievements and pass them on to the next generation. To ensure all this happens, we appear to be hardwired with an insatiable urge to connect our minds.
Primates are social creatures, and evidence that social pressures have driven the evolution of primate intelligence is mounting. Humans have taken this sociality to another level. Unlike other primates, children sob to attract attention and sympathy. We ask what’s wrong and try to make things better. We look each other in the eye, share what’s on our minds, and absorb what is on the other’s. This urge to connect must have been crucial to the establishment of signs and words that allow us to effectively read others’ minds and express our own.
As Michael Tomasello and colleagues have demonstrated, we make and pursue shared goals where our closest animal relatives do not. Even 2-year-old children outperform great apes on tasks of social learning, communication, and intention reading. Other animals may give alarm calls and food calls but otherwise do not show many signs of a drive to share their experience and knowledge with others. Again, in all six domains this cooperative drive is evident and plays a significant role. Language is the primary means by which we exchange our minds. We talk to each other about the past and make plans about the future. We read and tell each other what is on our minds. We reason and solve problems collectively. We build social narratives that explain the world around us. We teach, and we learn from each other. And we argue about what is right and what is wrong. These examples serve to remind us how pervasive the urge to connect is. Those who lack this drive have severe social difficulties (and may be diagnosed as autistic). Our urge to connect was essential for the creation of cumulative cultures that shape our minds and endow us with our awesome powers.
Our capacity for nested scenario building even allows us, drawing on past experiences, to imagine others’ advice internally. (Hearing voices is quite normal. Relax. The trouble starts when you attribute these internal voices to external sources.) So you might ask yourself what your mother would have said about the situation you find yourself in. We care about whether our parents, friends, heroes, or gods would be proud of what we do, even if they no longer exist (or never did). We can consider what others might remember us for. These thoughts can be important drivers motivating us to go beyond satisfying immediate personal self-interests in pursuit of “higher” notions of honor, valor, and glory.
We might aspire to nobility in character and virtue in action. We can invest heavily in unselfish actions, such as fighting oppression or pollution or helping a club, a person, or an animal. When we take on a cause, we seem to become part of something bigger and from such endeavors may derive some of the deepest feeling of meaning. One of the most remarkable things about humans is that we can strive to make some kind of difference. We may deliberately practice random acts of kindness, spread the word, fight injustice, teach the next generation, or start a revolution. Without the urge to connect our minds, such traits could not exist.
In sum, nested scenario building and the drive to link our scenario-building minds turned ape qualities into human qualities. They created powerful feedback loops that dynamically changed much of the human condition. They carried us where other animals could not go.