Adapted from The Gap: The Science of What Separates Us From Other Animals by Thomas Suddendorf, out now from Basic Books.
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 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.