Since humans left Africa less than a hundred thousand years ago there has been a staggering explosion of cultures. What caused this blooming of diversity? Why are there so many mutually incomprehensible languages, even within small territories? Why do we rejoice in rituals, wrap ourselves in flags, or define ourselves in opposition to others? In Wired for Culture Mark Pagel, one of the world's leading experts on human development, shows how our facility for culture is the key to our success as a species.

Humans are usually seen as differing from other animals because of our inherent traits of consciousness, language and intelligence. But Mark Pagel shows we've had it the wrong way round. Many of these things would not exist without our propensity for culture - our ability to co-operate in small tribal societies, enabling us to pass on knowledge, beliefs and practices so that we prospered while others declined. Mark Pagel's extraordinary history of the role of culture in natural selection shows how humans developed a mind that is hardwired for culture - so that it has outstripped our genes in determining who we are, how we think and speak, who we love and kill - and how it equips us for the challenges of life in the modern world.

Weaving together evolutionary biology, anthropology, natural history, philosophy and Pagel's years of observing human behaviour around the globe, this extraordinary book sheds light on everything from art, morality and affection to jealousy, self-interest and prejudice. It will change how we view ourselves, not just as individuals, but within the wider story of our species.

Introduction – THE GAMBLE
That human nature is defined by our response to culture

THE english 4th Baron Raglan, Major FitzRoy Richard Somerset of the Queen’s Grenadier Guards, once remarked that “culture is roughly everything we do and monkeys don’t.” This comment nicely summarizes one of the main messages of this book. Human beings have not always been as we know us now—sentient, big-brained, naked, prolix, artistic, wary, scheming, generous, warlike, forgiving, vengeful, religious, and moralistic. Instead, we were launched as recently as 80,000 years ago when our genes undertook a remarkable gamble. Around that time a species of upright apes, close evolutionary relatives to the chimpanzees, began to perfect a new way of life. Nothing in this species’ predecessors would have hinted at what was about to emerge, or that it would have such startling effects. Where previously they had roamed the African savannah for at least a million years, hunting and foraging in small family groups, the new species now came to live in larger tribal societies in which people worked together, customs and systems of beliefs arose, ideas, skills, and technologies were shared, languages evolved, and dance, music, and art appeared. Within a few tens of thousands of years, these tribal groups would spread out to occupy the world as some of them developed the means to live near the sea, others the ability to survive the desert or to inhabit jungles, forests, mountains, or plains. In what was little more than an instant in our long evolutionary history, we had become a single species with a global reach and ways of life as varied as collections of different biological species, and we were soon to become the sole survivor of an evolutionary lineage that had spawned at least six previous human branches.

The world was witnessing the final stages of a shift in the balance of power between our genes and our minds. Human beings had discovered culture. It was not high art and symphonies—those would come—but knowledge, beliefs, and practices acquired from watching, imitating, and learning from others. Today, we take our possession of culture for granted, but it was a development that had to await nearly the entire history of life on Earth. Our world is four and a half thousand million (4.5 billion) years old, and might have been a harsh, rocky place devoid of life for its first 700 million to 1 billion years. Th en, from fossil traces buried deep in ancient rocks, we know that life sparked into existence and for the next 3.5 billion years genes ruled, transmitting the instructions that organisms used to survive and reproduce. For most of that time, life consisted of simple one celled organisms, direct ancestors of today’s bacteria; but these gave way around 1 billion years ago to the first multicellular organisms, simple creatures like today’s sponges. Five hundred million years after that the first animals with arms and legs would rise up out of the sea and walk on land. These land animals would in turn evolve for yet another 500 million years before the evolutionary lineage that we call the hominins came on the scene, a mere 7 million years ago.

Even then, it was only when our species arose within this hominin lineage just 160,000–200,000 years ago that a competitor to the rule of genes finally appeared. Our invention of culture around that time created an entirely new sphere of evolving entities. Humans had acquired the ability to learn from others, and to copy, imitate and improve upon their actions. This meant that elements of culture themselves—ideas, languages, beliefs, songs, art, technologies—could act like genes, capable of being transmitted to others and reproduced. But unlike genes, these elements of culture could jump directly from one mind to another, shortcutting the normal genetic routes of transmission. And so our cultures came to define a second great system of inheritance, able to transmit knowledge down the generations. For humans, then, a shared culture granted its members access to a vast store of information, technologies, wisdom, and good luck. The only other example like this in nature is the lowly bacteria. These simple one-celled organisms cannot exchange ideas, but they have acquired a variety of means for exchanging genes among individuals and even among different species, granting them access to a vast store of genetic technology. And, like us, they have shown great inventiveness and versatility, occupying nearly every environment on Earth.

Our cultural inheritance is something we take for granted today, but its invention forever altered the course of evolution and our world. This is because knowledge could accumulate as good ideas were retained, combined, and improved upon, and others were discarded. And, being able to jump from mind to mind granted the elements of culture a pace of change that stood in relation to our genetical evolution something like an animal’s behavior does to the more leisurely movement of a plant. Where you are stuck from birth with a sample of the genes that made your parents, you can sample throughout your life from a sea of evolving ideas. Not surprisingly, then, our cultures quickly came to take over the running of our day-to-day affairs as they outstripped our genes in providing solutions to the problems of our existence. Having culture means we are the only species that acquires the rules of its daily living from the accumulated knowledge of our ancestors rather than from the genes they pass to us. Our cultures and not our genes supply the solutions we use to survive and prosper in the society of our birth; they provide the instructions for what we eat, how we live, the gods we believe in, the tools we make and use, the language we speak, the people we cooperate with and marry, and whom we might fight or even kill in a war.

Most of us assume without reflection that it has always been this way, that human beings have always occupied the world, and that somehow we are the natural and rightful rulers of its domains. But we are new on the scene, and even newer around the world, having only ventured permanently out of Africa probably sometime in the last 60,000 to 70,000 years. Even as recently as 80,000 years ago, our species’ continued existence still hung in the balance. An extraordinary degree of similarity in the genes of people from all over the world tells us that we all share a recent common ancestry. In fact, genetic studies now reveal that our ancestors might have dwindled to as few as 10,000 individuals—some say even fewer—making humans as endangered 80,000 years ago as a rhinoceros is today. Then our numbers began to grow and human culture began to flourish, and our species, having come perilously close to extinction, reached a point of no return. Our minds were now firmly in executive control of our fates, and we were showing the adaptability, and producing the artifacts and culture that would propel us out of Africa, and then around the world—specialized stone tools and spear points, carved fishhooks, clothes, shaped blades and instruments, but also sculpted figures, ceremonial burials, musical instruments, and cave art.

The world is now a remarkably different place from what it was throughout the first 99.996 percent of its history. Almost everything around you in your bustling everyday lives is owed to the new evolutionary world in which ideas could accumulate on top of ideas, and most of those ideas were first thought up by someone distant to you in time and space. Having culture is why we watch 3D television and build soaring cathedrals while our close genetic relatives the chimpanzees sit in the forest as they have for millions of years cracking the same old nuts with the same old stones. Even so, having become the fi rst species to throw off the yoke of its genes, our life in the presence of culture would usher in an irony. It is that we have fallen in thrall to the new sets of instructions our cultures provide. This is because to take advantage of culture meant evolving a new kind of mind. It had to be a cultural blank slate or tabula rasa, a compliant or docile mind, designed to be programmed by and embrace the culture into which it happened to be born. A wolf brought up by sheep will remain a wolf and soon turn on its benefactors, but a newborn human must be ready to join any cultural group on Earth, and without knowing which. It might find itself living on the Arctic ice, the Russian steppes, or sailing across Polynesia; it might find itself in the Australian Outback, the deserts of Arabia, on the prairies of North America, or the African savannah, on an island in the Indian Ocean, or fishing along the rich tropical coasts of Papua New Guinea. And so we have had no choice but to evolve to allow our culture to occupy our minds, writing its language and story into our consciousness.

In nearly every other respect for which the great English philosopher John Locke proposed his doctrine of tabula rasa, the human brain has been shown to come into the world prepared, and not at all a blank slate. We are primed to learn language, to comprehend shapes and movement, to expect causation, to manipulate numerical quantities, to be afraid of heights, to mimic others, and to favor our relatives. But we are not primed to acquire any particular culture. The one we do inherit is an arbitrary story, an accident of birth, but it is one to which we show a surprising and sometimes alarming devotion. People will risk their health and well-being, their chances to have children, or even their lives for their culture. People will treat others well or badly merely as an accident of their cultural inheritance. If there is a humbling lesson of culture, it is that we do these things even though each of us might have been someone else, with a different internal voice, likes and dislikes, and allegiances. If there is a comparison, it is to ducklings whose parents have been lost and when they hatch from their shells adopt as their parent the first animal that wanders past—even a human. Animal ethologists call this imprinting; it is difficult to escape the feeling that we seem to imprint on our cultures, and in a way that is hard to shake off.

Genes are carefully shepherded into our bodies inside small vehicles known as gametes—sperm from fathers and eggs from mothers— which are designed to see to it that a body is made that carries a collection of its parents’ genes. Part of the imprint of culture is to get us later in life to act as its shepherds. Each of us who has children will have shepherded pieces of our culture into them, some of it from mothers, some of it from fathers, ensuring that they were French, Korean, English, Melanesian, or American, Italian, Russian, or Chinese, and that they were religious or atheist, but also that they spoke a particular language and held certain beliefs about their nation and the rest of the world. We should be aware that it is at least a curious, and surely a compelling, feature of our species that a child born into the world as nothing more than a “blank” human being might be labeled as a Christian or a Hindu, Jewish, Buddhist, Muslim, or Confucian, and that this label—or some other its culture provides— can influence the course of this child’s life, as if it were a trait inherited on some gene. There are places all over the world where a child born into one of these religions might peer across a fence at children from another whose parents are sworn enemies of its own, and only then because their parents labelled them.

The reason for this shepherding is clear. Human culture has been a development of revolutionary social and genetic effect, easily the most potent trait the world has ever known for converting new lands and resources into more humans. Our genes’ gamble at handing over control to the new sphere of evolving ideas paid off handsomely. Culture became our species’ strategy for survival, a biological strategy, not just some bit of fun and amusement on the side, and it would trump all the wonderful wings and feathers, shells, claws, poisons, acts of camouflage or deception, odors, feats of running speed, long necks or beaks, powerful jaws, and spectacular colors and displays of the rest of the animal kingdom. It didn’t have to be this way. Our newly liberated minds might have chosen aesthetic reverie, feckless indolence, jumping off cliffs, debilitating drug use, or mindless warfare. But, for the most part, we didn’t. We seem to have followed our ancient genetic instincts for survival, and culture has been remarkably able to oblige.

The question is often asked, What makes us human? Quite apart from its interest to anthropologists and other scholars, it is a question that invades nearly every aspect of our lives, our psychology and behavior. Who are we, and why are we the way we are, so utterly different from other animals? What makes us kind and forgiving, generous and friendly, but also wicked, murderous, and vengeful? Why do we have morality? The usual answers to these questions are that we are made human by virtue of possessing consciousness, or that we have this or that gene, an opposable thumb, or an upright posture and bipedal gait, that we learned to control fi re, or that we have empathy, language, or our extraordinary intelligence. For others it is the belief we are made in God’s image and in possession of a soul. And it is true, these traits and beliefs set our species apart. But the argument of this book is that these usual answers are the wrong way around. They are the wrong way around because they fail to recognize that it is only because of culture that we have many of these traits. Here is something we will have to get used to: all of us carry around in our minds something akin to a software “operating system” installed without our consent by our parents and others in our societies. It defines who we are and is our internal voice. It frames our social and cultural identities, and fundamentally influences the course of our lives. No other species has such a system. Only when we understand this, and understand how the traits we acquired in response to this new way of life serve our interests, can we begin to grasp what it means to be human.

And here is why. Evolutionary biology teaches us that in a competitive world, if we know something about the environment an animal lives in, we can make some predictions about what it will be like. If an animal lived its life in trees or flying in the air, hunting for insects or swimming in the water, we could expect it to have acquired certain characteristics to promote its survival and well-being—long arms to swing in trees, wings for flight, an acute nose or hearing to detect insects, or a streamlined shape for swimming. Most animals are adapted to a physical environment such as one of these, and are confined to areas of the Earth where that environment is found. But for the last 160,000 to 200,000 years, humans have roamed the Earth conquering its many environments, chauffeured wherever we travelled by the inventive and cooperative tribal societies that are their cultures. And so, we are entitled to expect that, instead of adapting to the demands of any one physical environment, our genes have evolved to use the new social environment of human society to further their survival and reproduction. These are the adaptations that have wired our minds and bodies for culture.

It is a subject that touches the most fundamental aspects of our lives. We will see in the chapters of this book that our responses to culture have produced some of our best and our worst tendencies, creating a species brimming with contradictions. Our possession of culture is responsible for our art, music, and religion, our unmatched acts of charity, empathy, and cooperation, our sense of justice, fairness, altruism, and even self-sacrifice; but also for our undeniable self-interest, our tendency to favor people from our own ethnic or racial groups, wariness of strangers, xenophobia, and predilections to war. But it goes further than this. The nature of our culture will tell us why we alone as a species have language, why it is that we alone can show kindness to strangers, and even to other animals, but also why we can be callous and murderous. It is why we are the only species with morality, but also why we apply it capriciously to suit our needs. Culture equips us with envy, jealousy, and spite, indignation and contempt, but also with friendship, forgiveness and affection, and a conscience. It is why we, and probably we alone, have consciousness, and yet why our conscious mind is often divided between reason and passion, unsure or even in conflict with itself over how to behave. It is why we differ from each other, why we differ so from the other apes despite sharing so many of their genes, why we are shrewd and deceptive, and even why we deceive ourselves. We will see that our cultures can even get us to kill our own children—so called honor killings—and at the same time can get us to behave so selflessly that we would have to travel all the way to bees in a hive or to the cells in our body to see anything else like it in nature.

True, it would be wrong to suggest we are the only species with culture; it is just that only in humans has the handover been so great and the occupation of our minds so complete. New Zealand’s chaffinches, a songbird carried to those islands by homesick Europeans, learn their songs from their parents and thereby produce a surprising range of local dialects. Some chimpanzee troops have cultural traditions in the styles of tools they use to fish insects from the ground, or in the stones they use to crack nuts. Some meerkat colonies living side by side have persistent but arbitrary differences in the times they get up in the morning. There are idiosyncratic hunting styles among some dolphin pods and variety among the songs of some whales. In another dolphin species, females wear decorative sponges on their noses that they have gathered up from the seabed, and some groups of orang-utans make leaf-bundle “dolls.” Japanese macaques produce a wonderfully humanlike potato-washing behavior beloved of television documentaries. These cultural achievements are delightful, often entertaining, and sometimes even unexpected. But they bear about as much resemblance to human culture as a gorilla beating its chest or a chimpanzee drumming on a log does to a Bach cantata, scarcely deserving to be compared to the varieties, contrivances, complexities, and intricacies of human science, technologies, language, art, music, and literature.

Still, is the 160,000 to 200,000 years we have been around long enough for traits to have evolved in response to living in the social environment of our cultures? Has there been time enough to become wired for culture? The simple way to answer this question is to look around you. For instance, sometime around 25,000 years ago, people began living above 12,000 feet in the high Tibetan plateau, and they acquired physiological adaptations that allow them to cope with the reduced oxygen at these altitudes. One of these was so advantageous that it might have spread to 90 percent of all Tibetans in just four thousand years. The Dinka tribespeople of Sudan are tall and slim and have unusually dark skin. The Inuit people of northern North America are shorter, of stocky build, and have lighter skin. The Dinkas’ spaghetti-like body shape gives them a large surface area for shedding heat, while the Inuits’ more spheroid shape reduces their surface area to conserve it. The Dinkas’ dark skin protects them from the sun, but the melanin needed to produce it isn’t needed in the Arctic, so the Inuit make less of it.

These are all genetic adaptations acquired, in the case of the Tibetans and the Inuits, since our species walked out of Africa: a Dinka raised in the Arctic will not look like an Inuit, and vice versa, and the Tibetan capacity to live with reduced oxygen levels doesn’t evolve at low altitudes. If this kind of rewiring of our genes and physiology can take place over such short periods of time, this tells us that other features of our nature, including our psychology and social behaviors, have had plenty of time to evolve since we acquired culture. Even so, many people hold the view that humans fall outside the grip of Darwinian evolution by natural selection. We are intelligent beyond comparison to other animals, we use language creatively, we have art, music, dance, and religion, and, above all, a free will. But we must be careful. The standard philosophical objection to free will is that we aren’t as free to do what we “want” as we would like to think we are, because our current “wants” will always be influenced by our previous wants. And these previous wants form a chain leading all the way back to our birth and early upbringing when we were unable to make free choices. The first of these events over which we had little control might have been the accident of being born into a particular culture.

And to an evolutionist free will isn’t even all it’s cracked up to be anyway: good judgment should trump free will in most circumstances. Throughout our evolutionary history those of us who behaved in ways that promoted our survival and reproduction, rather than merely doing what we “wanted” to do, will have left the most descendants—descendants who will have inherited these same tendencies. If even just one of your ancestors had decided to give up having children for his or her art, the consequences for you would be no different than had that ancestor been killed—you would not be here today reading this book. Indeed, it is an underappreciated fact of biology that throughout history the overwhelming majority of individuals ever born, hatched, or budded off died long before adulthood. So the world is populated today by a select group of survivors whose ancestors had the dispositions and the wherewithal to survive and reproduce, and this alone tells us there is no particular reason to believe that free will per se has been positively favored throughout our evolution. Survival is a rare thing, far too valuable to be entrusted to what could be a capricious free will.

Many people believe that to allow natural selection a role in defining who we are consigns us to having a selfish agenda, one in which our genes single-mindedly promote their existence. Our genes do that, but it is a misunderstanding of evolution to think that natural selection always favors a nasty and ruthless nature. It is far more creative than that, and nowhere more it seems than in our species. In fact, if the history of biological evolution teaches us anything, it is that natural selection can often achieve the most for its genes by building cooperation among actors or even among genes that avoids debilitating conflict, returning greater gains than could be achieved by competition or a solitary existence. Among the triumphs of modern evolutionary biology is the demonstration that many of the outlines of culture and of our behaviors can be explained as strategies for promoting our survival and reproduction. The influential evolutionary theorist William Hamilton anticipated this some years ago, saying:

to come to our notice cultures, too, have to survive and will hardly do so when by their nature they undermine the viability of the bearers. Thus we would expect the genetic system to have various inbuilt safeguards and to provide not a blank sheet for individual cultural development but a sheet at least lightly scrawled with certain tentative outlines. . . .

It is those “tentative outlines” we seek to understand.

A Conversation with Mark Pagel, Author of WIRED FOR CULTURE: The Natural History of Human Cooperation

In your book “culture” doesn’t just mean art, literature or music – what is your definition of “culture”, in a nutshell?

Yes, the arts, music and religion are what most people have in mind when they refer to “culture.” This is so-called high culture, there to move, uplift, entertain, or console us. But we can define ‘culture’ more generally as knowledge, beliefs, and practices acquired from watching and learning from others.

This definition can make culture sound bland and uninteresting but our ability to exchange information by copying and imitating others is unique among animals and means that our species invented and then launched an entirely new sphere of evolution – the sphere of ideas. And, it was an invention that would alter the course of evolution. Now, ideas could accumulate in the form of knowledge, skills, beliefs and technologies, and without having to wait for the much slower pace of genetic evolution. As a result, our species became the only one on Earth that acquires the rules of its daily living from the accumulated knowledge of our ancestors rather than from the genes they pass to us.

Culture is why our species spread around the world adapting to its many environments while all other species are limited to places on Earth their genes adapt them to. Today, the accumulation of ideas we call culture is responsible for nearly everything around us in our bustling everyday lives – our mobile telephones and hammers, our trains and wooden chairs, our microscopes and space shuttles and our Large Hadron Colliders. All of these evolved by the gradual accumulation of ideas, one on top of the another, in a manner analogous to the way genes evolved, it is just that the pace is millions of times faster.

What are the key aspects of human behaviour which separate us from other species in the use of culture as a survival tool?

All other species have instincts for survival that are hard-wired into their genes, and those instincts are suited to the environment their species is adapted to. Thus, a gorilla, or an elephant or a chimpanzee can be plucked from its group and put down anywhere else in the world where its species is found and it will know what to do and how to communicate.

But we are different. What is hard-wired into our genes is an instinct to adopt and then embrace the culture of our birth. Our minds are cultural ‘blank slates’ – each of us could have been born into a different culture and be someone else, with a different internal voice, language customs and beliefs. A human plucked from one corner of the earth often cannot even communicate with a human from another corner, or often even from next door! And someone from, say, a Polynesian culture would have no idea how to survive in, for example, a traditional Inuit society.

This tells us that we have evolved to use culture – any culture – as our strategy for survival and prosperity. We are programmed to acquire the knowledge, skills, and beliefs and learn the rules of the culture of our birth because that culture is adapted to its particular environment. Our minds are full of the culture of our birth and we carry that information and pass it onto our children in a manner not so different from the way we carry and then pass on genetic information to our children.

You could say we are ‘cultural zombies’ and so much so that we cannot imagine our lives any other way.

You mention in the book the idea of altruism and cooperation being key aspects of human’s success – yet humans go to war, murder, are xenophobic and racist. How do the two aspects of human nature sit side by side?

Our species left Africa around 60,000 years ago and then spread around the world in small cooperative tribal societies. These tribal groups have been the fundamental social unit of our survival and reproduction throughout our species’ history. As a result we have developed a set of social rules for sharing and cooperating within our social groups.

But the success of our species in occupying the world has meant that these tribal societies will have been in constant competition with other tribal groups seeking to occupy the same territories and use the same resources. This competition has been such a continual feature of our history that some anthropologists and archaeologists describe that history as one of ‘constant battles’.

These two forces – cooperation within our groups but competition with other groups – have produced a species that is brimming with contradictions. We have morality but we apply it shrewdly and conveniently. We are kind and generous, but our history shows we are also capable of throwing a switch in our minds that makes us capable of treating members of other societies as something less than human in moral terms.

Sadly, these tendencies reside to a greater or lesser extent in all of us – just contrast your feelings at hearing of one of your country’s soldiers being captured and tortured with those you feel about the same events happening to someone from another country. Our altruism and generosity on the one hand, and our tendency to xenophobia on the other are both part of our evolved psychology for making our cultural groups work to serve our interests. This is not to say we should approve or condone the behaviours this psychology promotes, but these tendencies do lurk in our nature and so should be something we are aware of.

Can any of the arguments you put forward in your book find equivalents in the news at the moment?

Yes, there are a number of contemporary events that have links to our evolved tribal psychology.

Our in-built wariness of strangers, often shading into xenophobia, will be one of the most overworked features of our psychology as we enter increasingly into a modern globalised world characterized by the mass movement of people from poorer to richer areas. The contemporary news, sadly, is dominated by sectarian and ethnic strife fueled by the tensions that so naturally arise between people simply because they represent different cultures.

Happily, we can see one way to overcome some of our wariness of others in the financial difficulties that are facing nations like Italy and Greece. The small tribal societies of our past have worked in part by linking people’s fates. As soon as the success and survival of your group depends upon everyone pulling together – perhaps it is in battle with another group – the psychology and emotions that promote group cohesion will evolve. One of the most reassuring long-term tendencies of our species has been to recognize that formerly competing groups can often do better by cooperating than by engaging in endless cycles of betrayal and revenge. So, our history has been to build larger and larger cooperative groups – chiefdoms, city-states, nation states, and even collections of nations such as the E.U.

These larger entities link people’s fates and thereby promote cooperation even if that cooperation is purely pragmatic. Thus, our willingness to bail our Greece and Italy, among others, is a recognition that our economies are now interdependent. You could say that we have been trapped by our own cooperative mentality.

Our tendency towards altruism and generosity give rise to some of the more peculiar behaviours of our species. We routinely help others, give up our seats on trains, hold doors for people, contribute to charities and we might even risk our health and well being or our lives by pulling someone from a burning building or fighting in a war.

These altruistic acts all evolved to promote the cooperative tribal societies of our evolutionary past, and they are based on a deep-seated notion of ‘fairness’ in our dealings with others. This notion of fairness acts like a psychological police force: we expect others to behave in ways that benefit those around them, and we know they expect the same of us. It is the social glue that makes our cooperative societies possible. We take it for granted but no other animal has such a feeling.

It is this ancient evolutionary trait that gets aroused in public debates about bankers and other people in business receiving huge bonuses. Their rewards somehow seem ‘unfair’. But what do we mean by this? In many cases these people have not broken any laws. Still, we feel this peculiar and yet powerful emotion even though in most cases stopping one of these people from receiving their award will not help us in any way – a banker turning down a bonus doesn’t put more money in your pocket, and most of us would have to concede that if offered such a bonus ourselves we would want to take it.

So, why do we feel this emotion so strongly and vividly? Fairness can be seen as an emotion that gets us to behave in ways that invest in the future, and this is what we expect of emotions designed to police and maintain our social groups. When we publicly ridicule and criticize ‘fat cats’ it is a way of sending a message to others that we are not the sort of people to be trifled with. We might not benefit in any way now, but our actions are explained by what they might return in the future. Protestations about fairness tell others they won’t get way with the same sorts of things.

You mention that the only other organism to use this “shared cultural knowledge” is lowly bacteria. If it’s such a successful survival technique, why don’t more species use it?

Culture means our species can share knowledge, technology and skills and this makes available a vast shared stored of information – each of us can draw on things discovered by someone else at a far different time and place and this has allowed us to adapt to every environment on the planet.

Curiously, the bacteria, simple one-celled organisms, have evolved an ability to exchange genes between individuals and even between species, rather than solely by passing them on to their offspring. This has made available to the bacteria a vast shared store of genetic information, and perhaps in this light it is not surprising that they too have occupied nearly every environment on earth, from deep sea ‘smokers’ (small volcanic chimneys that spew out super-heated water) to the glacial ice, and extremes of salt and acidity.

Other animals haven’t been able to do this because they cannot exchange genes in the ways that bacteria can, and because they don’t have ‘culture’. It seems that human culture requires an ability to understand what others are thinking and why they do the things they do. No other animal seems to have this capability, or at least not beyond the capability of a typical human 2-3 year old. Our very large brains might have at least in part evolved to be able to represent both what is going on in our own minds and what we think is going on in others’ minds – this takes lots of processing power, like a big computer.

Are there any real-world applications people can take from your book? If they learn to be more altruistic on a personal level will they reap any benefits, or does it take a whole society?

Two things really stand out for human interactions: generosity and reputation, and these two are linked. Human societies are built on trust and cooperation. Our altruism is risky because any time you help someone else, chances are that they can benefit from you, but at your expense. So, our societies place a great emphasis on people demonstrating that they are the sort of people who can be trusted not to take advantage of others.

Our many ongoing acts of altruism – our holding doors, giving up seats on trains – are ways we show others we are that sort of people. This is why generosity and forgiveness are so valuable. It shows people you are willing to make sacrifices to be part of a larger cooperative social group, and people will therefore wish to associate with you. Studies show that generous people often do better in cooperative experiments that do selfish people. The selfish people might do well in the short term, but not over the long run because they do not attract allies.

Reputation is the currency we use to buy other people’s trust and because we have language, word of our reputation can travel far and wide. The value of a good reputation cannot be overstated, it can even be as valuable as one of your own children. The terrible practice of so-called honour-killings is a way that families try to claw back what they perceive to be damage to their reputations – here is a grotesque demonstration of the value of ‘reputation’: it is worth a human life.

At a more mundane level it is also why parents worry so about how their children behave and dress, and who they associate with.