Book Summary: “The Gap: Science of What Separates Us from Animals” by Thomas Suddendorf

Title: The Gap: Science of What Separates Us from Animals
Author: Thomas Suddendorf
Scope: 4 stars
Readability: 3 stars
My personal rating: 4 stars
See more on my book rating system.

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Topic of Book

Suddendorf attempts to understand what separates humans from other animal species and how the gap arose.

If you would like to learn more about human history, read my book From Poverty to Progress: How Humans Invented Progress, and How We Can Keep It Going.

Key Take-aways

  • The key difference between humans other animals is how we think.
  • Humans, unlike even our closest ape relatives, can think about things that they do not perceive.
  • Humans also have a unique ability to link our minds together to form a higher collective intelligence.
  • Humans have memories that enables them to time travel into the future or back in the past.

Important Quotes from Book

Our extraordinary powers do not derive from our muscles and bones but from our minds.

It is our mental capacities that have allowed us to tame fire and invent the wheel. They enable us to construct tools that make us stronger, fiercer, faster, and more precise, resilient, and versatile than any beast.

Robin Dunbar established that the greater the typical group size of a primate species, the bigger their brain—or, more precisely, the ratio between the neocortex and the rest of the brain.

Unlike great apes, but like many humans, gibbons live in small, monogamous families composed of a mated pair and several dependent offspring. Pairs stay together for years, and males invest time and effort in the rearing of the young.

Like human two-year-olds, but unlike other primates, great apes have demonstrated that they can think about things they did not perceive.

The potential for mirror self-recognition evolved between eighteen million and fourteen million years ago in the shared ancestor of hominids.


To find out what might be unique about the human communication system, we need to have a closer look at what characterizes human language. The first thing to note is that we speak not one but over 6,000 different languages.

The most fundamental feature of language is that it allows us to exchange thought.

Because speakers have to establish agreement on meaning, languages are regional. Languages were not established by expert committees or by decree, but gradually evolved out of people’s interactions with each other and their desire to communicate. Separation, physical or social, breeds new dialects.

Language is open-ended, even though the building blocks of language are limited.

Language is about cooperation.

Indeed most animal vocalizations seem to be under emotional rather than cognitive control. When researchers stimulate a subcortical part of the brain known as the periaqueductal gray, it causes meowing and growling in cats, shrieking and barking in rhesus monkeys, echolocating in bats, and laughing in chimpanzees and humans.

Human speech, on the other hand, is primarily driven by cortical areas of the left hemisphere that allow for voluntary control and extreme flexibility. Animal vocalization may hence not be closely related to human speech.

What appears to be lacking, even in great apes, is a motivation to find means to exchange what is on each other’s minds.

Mental Time Travel:

The main benefit of memory for past events may be that it allows us to imagine future events.

However, you can do much more than predict reoccurrences of events. You can imagine situations you have never experienced before. For example, you might mentally simulate how you could distract the dog before going for his bone. You can imagine a virtually infinite number of future scenarios. You may consider a few options before pursuing the most promising path—no one likes being bitten. You do not need to suffer all the real-life consequences of trying out each possibility. We can test most things in our mind and assess how likely or pleasant they might be.

Mental time travel is complex, resource-intensive, and error-prone. But it is a key to how our minds conquered the world.

Mental time travel unlocked a new realm of possibilities for our species. We can hatch plans and make decisions that drastically increase our chances of future survival and reproduction. By foreseeing events we can seize opportunities that lie ahead and take steps to avoid approaching disaster. We can imagine the consequences of what we are going to do before we do it—and berate others for not doing the same. We can also benefit from the past in novel ways. We can mentally revisit past events, reflect on them, and draw new conclusions.

Mental time travel radically increases our opportunities to be prepared. Even foreseeing that the future is difficult to foresee can prompt us to prepare for common eventualities.

Much of the diversity of human expertise comes from our having the potential to decide what to spend time on, what we want to get better at, and what goals we aim to achieve.

We have radically improved our chances of getting it right through a wonderfully effective trick: we share our plans and predictions with others. We can transmit our mental plays and reflections to audiences around us and, in turn, consider their thoughts.

Animals clearly share with humans some procedural and semantic memory capacities. However, there is little evidence that they have episodic memory.

Animals can learn that one thing predicts another if the events are separated by only a few seconds. Many species have also evolved instincts that equip them to act in preparation for the future. However, evidence for flexibility in such future-directed behavior is scant. The cases that exist all deal with the immediate future only. There is no compelling evidence

that animals flexibly generate mental scenarios of remote future events the way humans do, or communicate mental scenarios to one another to obtain feedback or to coordinate actions.

Mental time travel is essential for explaining a vast array of characteristics of the human mind, ranging from emotions (such as hope and regret) to motivations (such as plans and revenge). It allows us to understand how things got to where they are and to wonder where everything is headed. It has given us unheralded powers to control plant and animal life to our advantage.

Mind Readers:

We are avid mind readers. We think, and often worry, about what others feel, desire, and believe. In conversation we customize what we say based on what we think the other person wants and does or does not know. We care about making others happy and empathize when they are sad. We may try to put them at ease, to tickle their fancy or blow their minds. We regularly interpret even the simplest acts in terms of mental states.

Knowing what others desire and think is immensely useful for predicting what they are going to do. We live in a world of minds aware of other minds, and mind reading is absolutely fundamental to our social lives.

With the development of language, the opportunities for making such links grow. Language turns mind reading into mind telling.

Without mind reading there can be no pedagogy, for deliberate transfer of knowledge requires some understanding of what is or is not known by the pupil to devise a way in which future knowledge can be acquired. In short, theory of mind is essential for normal human cultural and social interaction.

For primates, staring into another’s eyes is typically a threatening gesture. Therefore, primates largely avoid eye contact, and face-to-face interactions are surprisingly unusual. Even chimpanzees look into each others’ eyes only on rare occasions.

Human skill development is replete with examples in which behaviors that had once been governed by slow conscious processes become automatic with training. Just think of the complexities of driving a car. Initially you need to carefully think about what your arms and legs are supposed to be doing to control the vehicle.

Smarter Apes:

As much as half of the variability in IQ can be explained by variability in working memory.

Temporary storage and processing space are important for our ability to imagine multiple mental scenarios, to integrate them into a larger narrative, and to compare and evaluate them. It is essential for creating any kind of nested, recursive thought. Therefore, sufficient working-memory capacity is critical for language, mental time travel, and theory of mind.

It is now widely discussed as a potentially crucial factor in human cognitive evolution. Yet there is more to our smarts than a simple capacity increase.

A recurring theme has been that recursion is a key mechanism that unites “former images and ideas,” allowing us to produce novelty in language, music, technology, and art through recombination. Generating novel content is not enough, however, unless we want to grant creativity to a random number generator. Creativity also requires a capacity to assess what is generated.

Human generativity coupled with our ability to mentally project ourselves into future scenarios enables us to prudently design aspects of our environment. Designing is the capacity to imagine a new object or situation with a specific function or aesthetic in mind… When we design objects, we combine and recombine basic elements recursively and appraise their imagined constellation in terms of the desired function. Rather than adapting to the environment, we have increasingly used this design capacity to flexibly shape our world to meet our fancy.

I noted that the IQ testing community regards three components as essential to intelligence: to learn from experience, to adapt to the environment, and to reflect on one’s own performance. Many nonhuman animals meet the first two parts of this consensus definition of intelligence: they learn and adapt. Predation, for instance, would have exerted

strong selection pressures on these capacities; consider orcas or lions hunting in packs and their prey trying to avoid being caught. On the other hand, the third component, reflection, may point to something uniquely human. Embedded thinking, or to think about thinking, may well set humans apart.

Animals show “laser-beam intelligence.”.. Human teaching, by contrast, is domain general and can serve many goals… Premack argues that what sets human intelligence apart is our flexibility. The abilities we have discussed thus far—language, foresight, mind reading, reasoning—are not fixed to a particular domain but can be employed to virtually endless varieties of goals.

Humans can react to situations in flexible, diverse ways. We innovate new ways of responding to situations. We are also correspondingly curious. We seek out novel information and prefer situations that are likely to yield new insights…

We generally crave new information, and endorphins are released as we comprehend—they give us pleasure by activating the same opioid receptors that are activated by certain drugs.

Human response diversity is exponentially larger. Our inventiveness appears to know no bounds. We can generate virtually infinite combinations of elements, creating novelty in behavior, tools, and sentences. With language we can learn from the responses of others, even if we did not witness them ourselves. With mental time travel we can test consequences of potential actions, even if we do not physically try them out. We can therefore overcome obstacles and discover opportunities in our mind. We can treat scenarios as chunks of information and use placeholders to construct higher-order relations. We can decontextualize these relations and reason about entirely abstract concepts. We can construct elaborate theories about the forces that govern this world and systematically test whether they are correct. Only humans do science.


What is most powerful here is the accumulation of knowledge, skills, and artifacts over time. We benefit from what others have done long ago.

Although our individual understanding is often flawed and our foresight misguided, by linking our minds to those of others we have enormously increased our predictive capacities and powers of control. With theory of mind and language we are able to wire our scenario-building minds into much larger networks. We teach each other and copy each other, allowing us to pass on what we have experienced, abstracted, innovated, or learned from another. Thus are populations able to socially maintain and accumulate knowledge, customs, and survival strategies.

Our minds are shaped by the cultural heritage of our group. Alone we may be weak, but together we are strong. Human culture has led to civilizations that, for better or worse, have changed much of the planet.

Whatever you might think about humanity, we are a remarkably cooperative lot.

We also cooperate economically. For the right price most people will trade goods and services with almost anyone. Most of your possessions were likely made by others: your clothes, furniture, music, spices, art— certainly, the book you are reading right now.

It is this cooperation with nonrelatives that appears to be unusual in the animal

kingdom and is essential for explaining human societies and cultures.

Through cooperative rules humans have been able to establish flourishing, cooperative societies. The big prize this persistent cooperation brought is that our ancestors could complement genetic evolution with a powerful new way of rapidly meeting adaptive challenges: cultural inheritance.

The most important characteristic of human culture, then, is that it acts as a second inheritance system, in addition to genetic inheritance.

One obvious advantage of cultural evolution is that it enables us to adapt much faster than we ever could biologically.

Cultural knowledge evolves in response to local demands.

Cultural forms fit local functions.

To achieve high-fidelity social learning in the absence of written language, humans had to rely on two processes. Information is passed on either with the intent of the possessor or with the intent of the receiver. Teaching and imitation are the two recognized pillars of human cultural inheritance. Each new generation acquires the material, social, and symbolic traditions of its group in these ways.

Teaching is the flip side of imitation: while imitation is based on the ignorant trying to learn from the knowledgeable, in teaching the knowledgeable party is trying to impart information to the ignorant.

Language is crucial for our teaching of facts. In teaching skills, however, such as how to play an instrument, a teacher may model and instruct the pupil to imitate. In such cases the two pillars of cultural learning are frequently combined. Learning may be encouraged by drawing attention to the crucial steps, perhaps by slowing down, by breaking down the process into more manageable chunks and teaching them one by one, or by repeating the sequences with the teacher highlighting the value of the reward it can bring.

Though there is great variation in nature and extent, teaching appears to be a cross-cultural universal.

They also crucially benefit from mental time travel. Choosing to practice to get better at something in the future is essential for many types of complex learning. As we saw, differential practice must be partly responsible for the great diversity of human expertise.

Of course, language immensely improves teaching and learning, as it enables us to directly exchange ideas. Thus all four domains of the mental gap discussed in the previous chapters contribute to our capacity to teach effectively.

Much of the rapid transfer of ideas was likely due to trading, migration, and war.

Rather than wholesale exchange, cultures traditionally import subsets of the cultural heritage of other groups and then modify them to their own liking or circumstances. We pass on not only solutions but potential solutions.

Finally, cultural innovation can be deliberate and goal directed. People set out to find a solution to a problem. With mental time travel, we can even start working on problems that do not yet exist.

Your mind would no doubt be unimaginably different. Other animals raised in human cultural environments, even the language-trained apes, do not quite import our culture the way our children do. We appear to be predisposed to acquiring culture.

There is, in fact, mounting experimental evidence that behavioral patterns can socially spread in groups of various species.

Given that we know that behaviors can spread socially in captive populations, it is now generally accepted that this diversity in behaviors between wild groups is due, at least in part, to socially maintained traditions. In other words, chimpanzees have a kind of culture.

Subsequent studies on the learning of the manufacturing skill, however, suggest that individual trial-and-error learning plays a pivotal role. Social transmission may be

limited to providing the young with exposure to tools and tool use.

Other animals do not appear to fully exploit the powerful potential of a flexible, cumulative cultural inheritance system. They do not show anything like the ratchet effect by which numerous solutions are continually refined and improved. Given the limits in language, mental time travel, theory of mind, and innovation discussed so far, this may not be a surprise. A key reason may be that animals’ cultural transmission mechanisms are not appropriate for the spread and accumulation of vast amounts of information.

There also appears to be differences in teaching. Mammals may provide opportunities for their young to learn in a safe environment. Adults encourage or discourage certain behaviors. But do they structure learning events in light of their assessment of the pupils’ knowledge? There is no obvious evidence of animals having anything like a curriculum.

A simple definition of teaching is that a teacher modifies his or her behavior in the presence of a naïve pupil without immediate benefit, and that this behavior fosters learning in the pupil. Even using this definition there is only limited evidence of teaching in the animal kingdom.

Human teaching relies heavily on language, theory of mind, and mental time travel, so animal teaching may be limited for all the reasons already discussed. Just as great apes are not particularly motivated to share intentionality and experiences with others, their capacity and motivation to teach appears to be profoundly limited.

Humans have a strong urge to link their minds, to overimitate, and to teach. In this way our inventions, skills, and knowledge spread and are adjusted to local conditions, fine-tuned, or optimized by others. Human social groups cooperate to accumulate cultural capital over many generations to an extent that has seriously altered the fitness of its members.


The foundation of morality can be subdivided into three broad levels: (1) the basic building blocks of empathy and reciprocity; (2) the group pressures that keep individuals in line; and (3) the capacity for self-reflective moral reasoning and judgment.

Between ages three and seven children begin to increasingly direct their helping to those who (a) are closely related, (b) have reciprocated in the past, and (c) have been observed

sharing with others. In other words, with experience they increasingly cooperate with those with whom cooperation ultimately makes the most sense: family, friends, and people with a good reputation for reciprocity.

Most evil in this world is perpetrated by people who think, at some level, that they are doing the right thing. The fight of good versus evil, when examined from both sides, is

often the fight between two definitions of what is good.

In sum, the evidence for morality in animals declines as we move from de Waal’s level 1 to level 3. At level 1 there is reasonably good evidence that other animals may have something like compassion, and there are examples of reciprocal cooperation between unrelated individuals. At level 2, there are a few signs that our closest relatives exert pressures that support cooperative group living, but there is no compelling case for animals moralizing explicit norms and third parties punishing/rewarding moral violations/virtuous acts. At level 3, there is as yet no evidence that nonhuman animals engage in self-reflective moral reasoning.

The Gap

In all six domains we repeatedly find 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.

Great apes have a basic capacity to imagine alternative mental scenarios of the world. In certain contexts their abilities are comparable to those of eighteen- to twenty-four-month-old human children.

Human development of mental scenario building explodes after age two, however, while great apes’ capacities do not.

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.

We make and pursue shared goals where our closest relatives do not. Even two-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.

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.

The Gap may, then, may in one sense be much smaller than we might have anticipated. Only a couple of basic differences appear to have evolved between ape and human over the last six million years. In another sense, the gap clearly is vast. The two qualities represent profound differences that have had countless cognitive, emotional, and motivational consequences.

Play gives children opportunities to practice thinking. They begin to select skills they want to get better at, typically with encouragement from their parents, and playfully rehearse…

Our scenario-building minds even allow us to practice just mentally rather than physically, and we can improve as a result. We provide our own feedback, or imagine the feedback we think others might give, without actual reward or punishment. Our capacity to create future scenarios and to consult others with expertise allows us to gradually become experts in our own right. Much of the human diversity of expertise is a function of the fact that different people expend effort in learning and perfecting particular skills… Our extensive cooperation and division of labor means that groups, and the individuals within it, benefit less from everyone being good at the same thing than from being good at a host of complementary skills… Perhaps we have evolved to be so individually different because our species is extraordinarily social and cooperative.

Whereas chimpanzees groom each other to bond and keep the peace, human cultural groups bond through sharing mental experiences. People gather at festivals to reaffirm their cultural identity through rituals and celebrations. They wear specific clothes, engage in traditional ceremonies, perform and act, tell stories of legends and ancestors. We sing and dance together, and we enjoy watching others perform. We hold concerts, parades, and shows. We celebrate birthdays and weddings, commemorations, and seasons. Animals do not appear to care about any of this.

I have reviewed here current evidence on the nature and origin of what makes us human. The data led me to propose that the peculiarity of the human mind primarily stands on two legs: our open-ended capacity to create nested mental scenarios and our deep-seated drive to connect to other scenario-building minds.

If you would like to learn more about human history, read my book From Poverty to Progress: How Humans Invented Progress, and How We Can Keep It Going.

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