The Rational Optimist: How Prosperity Evolves

In truth, far from being unsustainable, the interdependence of the world through trade is the very thing that makes modern life as sustainable as it is. Suppose your local laptop manufacturer tells you that he already has three orders and then he is off on his holiday so he cannot make you one before the winter. You will have to wait. Or suppose your local wheat farmer tells you that last year’s rains means he will have to cut his flour delivery in half this year. You will have to go hungry. Instead, you benefit from a global laptop and wheat market in which somebody somewhere has something to sell you so there are rarely shortages, only modest price fluctuations.

For example, the price of wheat approximately trebled in 2006–8, just as it did in Europe in 1315–18 (#litres_trial_promo). At the earlier date, Europe was less densely populated, farming was entirely organic and food miles were short. Yet in 2008, nobody ate a baby or pulled a corpse from a gibbet for food. Right up until the railways came, it was cheaper for people to turn into refugees than to pay the exorbitant costs of importing food into a hungry district. Interdependence spreads risk.

The decline in agricultural employment caused consternation among early economists. François Quesnay and his fellow ‘physiocrats’ argued in eighteenth-century France that manufacturing produced no gain in wealth and that switching from agriculture to industry would decrease a country’s wealth: only farming was true wealth creation. Two centuries later the decline in industrial employment in the late twentieth century caused a similar consternation among economists, who saw services as a frivolous distraction from the important business of manufacturing. They were just as wrong. There is no such thing as unproductive employment, so long as people are prepared to buy the service you are offering. Today, 1 per cent works in agriculture and 24 per cent in industry (#litres_trial_promo), leaving 75 per cent to offer movies, restaurant meals, insurance broking and aromatherapy.

Arcadia redux

Yet, surely, long ago, before trade, technology and farming, human beings lived simple, organic lives in harmony with nature. That was not poverty: that was ‘the original affluent society (#litres_trial_promo)’. Take a snapshot of the life of hunter-gathering human beings in their heyday, say at 15,000 years ago well after the taming of the dog and the extermination of the woolly rhinoceros but just before the colonisation of the Americas. People had spear throwers, bows and arrows, boats, needles, adzes, nets. They painted exquisite art on rocks, decorated their bodies, traded foods, shells, raw materials and ideas. They sang songs, danced rituals, told stories, prepared herbal remedies for illnesses. They lived into old age far more frequently than their ancestors had done. (#litres_trial_promo)

They had a way of life that was sufficiently adaptable to work in almost any habitat or climate. Where every other species needed its niche, the hunter-gatherer could make a niche out of anything: seaside or desert, arctic or tropical, forest or steppe.

A Rousseauesque idyll? The hunter-gatherers certainly looked like noble savages: tall, fit, healthy, and (having replaced stabbing spears with thrown ones) with fewer broken bones than Neanderthals. They ate plenty of protein, not much fat and ample vitamins. In Europe, with the help of increasing cold, they had largely wiped out the lions and hyenas (#litres_trial_promo) that had both competed with and preyed upon their predecessors, so they had little to fear from wild animals. No wonder nostalgia for the Pleistocene runs through many of today’s polemics against consumerism. Geoffrey Miller, for example, in his excellent book Spent, asks his readers to imagine a Cro-Magnon mother of 30,000 years ago living ‘in a close-knit clan of family and friends…gathering organic fruits and vegetables…grooming, dancing, drumming and singing with people she knows, likes and trusts…the sun rising over the six thousand acres of verdant French Riviera coast that her clan holds.’

Life was good. Or was it? There was a serpent in the hunter-gatherer Eden – a savage in the noble savage. Maybe it was not a lifelong camping holiday after all. For violence was a chronic and ever-present threat. It had to be, because – in the absence of serious carnivore predation upon human beings – war kept the population density below the levels that brought on starvation. ‘Homo homini lupus’, said Plautus. ‘Man is a wolf to man.’ If hunter-gatherers appeared lithe and healthy it was because the fat and slow had all been shot in the back at dawn.

Here is the data. From the !Kung in the Kalahari to the Inuit in the Arctic, two-thirds of modern hunter-gatherers have proved to be in a state of almost constant tribal warfare, and 87 per cent to experience annual war. War is a big word for dawn raids, skirmishes and lots of posturing, but because these happen so often, death rates are high – usually around 30 per cent of adult males dying from homicide. The warfare death rate of 0.5 (#litres_trial_promo) per cent of the population per year that was typical of many hunter-gatherer societies would equate to two billion people dying during the twentieth century (instead of 100 million). At a cemetery uncovered at Jebel Sahaba (#litres_trial_promo), in Egypt, dating from 14,000 years ago, twenty-four of the fifty-nine bodies had died from unhealed wounds caused by spears, darts and arrows. Forty of these bodies were women or children. Women and children generally do not take part in warfare – but they are frequently the object of the fighting. To be abducted as a sexual prize and see your children killed was almost certainly not a rare female fate in hunter-gatherer society. After Jebel Sahaba, forget the Garden of Eden; think Mad Max.

It was not just warfare that limited population growth. Hunter-gatherers are often vulnerable to famines. Even when food is abundant, it might take so much travelling and trouble to collect enough food that women would not maintain a sufficient surplus to keep themselves fully fertile for more than a few prime years. Infanticide was a common resort in bad times. Nor was disease ever far away: gangrene, tetanus and many kinds of parasite would have been big killers. Did I mention slavery? Common in the Pacific north-west. Wife beating? Routine in Tierra del Fuego. The lack of soap, hot water, bread, books, films, metal, paper, cloth? When you meet one of those people who go so far as to say they would rather have lived in some supposedly more delightful past age, just remind them of the toilet facilities of the Pleistocene, the transport options of Roman emperors or the lice of Versailles.

The call of the new

None the less, you do not have to be starry-eyed about the Stone Age to find aspects of modern consumer society obscenely wasteful. Why, asks Geoffrey Miller (#litres_trial_promo), ‘would the world’s most intelligent primate buy a Hummer H1 Alpha sport-utility vehicle’, which seats four, gets ten miles to the gallon, takes 13.5 seconds to reach 60 mph, and sells for $139,771? Because, he answers, human beings evolved to strive to signal social status and sexual worth. What this implies is that far from being merely materialist, human consumption is already driven by a sort of pseudo-spiritualism that seeks love, heroism and admiration. Yet this thirst for status then encourages people to devise recipes that rearrange the atoms, electrons or photons of the world in such a way as to make useful combinations for other people. Ambition is transmuted into opportunity. It was allegedly a young Chinese imperial concubine in 2600 bc who thought up the following recipe for rearranging beta pleated sheets of glycine-rich polypeptides into fine fabrics: take a moth caterpillar, feed it mulberry leaves for a month, let it spin a cocoon, heat it to kill it, put the cocoon in water to unstick the silk threads, carefully draw out the single kilometre-long thread from which the cocoon is made by reeling it on to a wheel, spin the thread and weave a fabric. Then dye, cut and sew, advertise and sell for cash. Rough guide on quantities: it takes about ten pounds of mulberry leaves to make 100 silkworm cocoons to make one necktie.

The cumulative accretion of knowledge by specialists that allows us each to consume more and more different things by each producing fewer and fewer is, I submit, the central story of humanity. Innovation changes the world but only because it aids the elaboration of the division of labour and encourages the division of time. Forget wars, religions, famines and poems for the moment. This is history’s greatest theme: the metastasis of exchange, specialisation and the invention it has called forth, the ‘creation’ of time. The rational optimist invites you to stand back and look at your species differently, to see the grand enterprise of humanity that has progressed – with frequent setbacks – for 100,000 years. And then, when you have seen that, consider whether that enterprise is finished or if, as the optimist claims, it still has centuries and millennia to run. If, in fact, it might be about to accelerate to an unprecedented rate.

If prosperity is exchange and specialisation – more like the multiplication of labour than the division of labour – then when and how did that habit begin? Why is it such a peculiar attribute of the human species?

CHAPTER 2 The collective brain: exchange and specialisation after 200,000 years ago (#ulink_9bc453ef-7646-5383-9315-46fee91dc93c)

He steps under the shower, a forceful cascade pumped down from the third floor. (#litres_trial_promo) When this civilisation falls, when the Romans, whoever they are this time round, have finally left and the new dark ages begin, this will be one of the first luxuries to go. The old folk crouching by their peat fires will tell their disbelieving grandchildren of standing naked mid-winter under jet streams of hot clean water, of lozenges of scented soaps and of viscous amber and vermilion liquids they rubbed into their hair to make it glossy and more voluminous than it really was, and of thick white towels as big as togas, waiting on warming racks.

IAN MCEWAN

Saturday

One day a little less than 500,000 years ago, near what is now the village of Boxgrove (#litres_trial_promo) in southern England, six or seven two-legged creatures sat down around the carcass of a wild horse they had just killed, probably with wooden spears. Each took up a block of flint and began to fashion it into a hand axe, skilfully using hammers of stone, bone or antler to chip off flakes until all that remained was a symmetrical, sharp-edged, teardrop-shaped object in size and thickness somewhere between an i-phone and a computer mouse. The debris they left that day is still there, leaving eerie shadows of their own legs as they sat and worked. You can tell that they were right-handed. Notice: each person made his own tools.

The hand axes they made to butcher that horse are fine examples of ‘Acheulean bifaces’. They are thin, symmetrical and razor-sharp along the edge, ideal for slicing through thick hide, severing the ligaments of joints and scraping meat from bones. The Acheulean biface is the stereotype of the Stone Age tool, the iconic flattened teardrop of the Palaeolithic. Because the species that made it has long been extinct we may never quite know how it was used. But one thing we do know. The creatures that made this thing were very content with it. By the time of the Boxgrove horse butchers, their ancestors had been making it to roughly the same design – hand-sized, sharp, double-sided, rounded – for about a million years. Their descendants would continue to make it for hundreds of thousands more years. That’s the same technology for more than a thousand millennia, ten thousand centuries, thirty thousand generations – an almost unimaginable length of time.

Not only that; they made roughly the same tools in south and north Africa and everywhere in between. They took the design with them to the Near East and to the far north-west of Europe (though not to East Asia) and still it did not change. A million years across three continents making the same one tool. During those million years their brains grew in size by about one-third. Here’s the startling thing. The bodies and brains of the creatures that made Acheulean hand axes changed faster than their tools.

To us, this is an absurd state of affairs. How could people have been so unimaginative, so slavish, as to make the same technology for so long? How could there have been so little innovation, regional variation, progress, or even regress?

Actually, this is not quite true, but the detailed truth reinforces the problem rather than resolves it. There is a single twitch of progress in biface hand-axe history (#litres_trial_promo): around 600,000 years ago, the design suddenly becomes a little more symmetrical. This coincides with the appearance of a new species of hominid which replaces its ancestor throughout Eurasia and Africa. Called Homo heidelbergensis, this creature has a much bigger brain, possibly 25 per cent bigger than late Homo erectus.Its brain was almost as big as a modern person (#litres_trial_promo)’s. Yet not only did it go on making hand axes and very little else; the hand-axe design sank back into stagnation for another half a million years. We are used to thinking that technology and innovation go together, yet here is strong evidence that when human beings became tool makers, they did not experience anything remotely resembling cultural progress. They just did what they did very well. They did not change.

Bizarre as this may sound, in evolutionary terms it is quite normal. Most species do not change their habits during their few million years on earth or alter their lifestyle much in different parts of their range. Natural selection is a conservative force. It spends more of its time keeping species the same than changing them. Only towards the edge of its range, on an isolated island, or in a remote valley or on a lonely hill top, does natural selection occasionally cause part of a species to morph into something different. That different sport sometimes then spreads to conquer a broader ecological empire, perhaps even returning to replace the ancestral species – to topple the dynasty from which it sprang. There is constant ferment of change within the species’ genes as it adapts to its parasites and they to it. But there is little progressive alteration of the organism. Evolutionary change happens largely by the replacement of species by daughter species, not by the changing of habits in species. What is surprising about the human story is not the mind-bogglingly tedious stasis of the Acheulean hand axe, but that the stasis came to an end.

The Boxgrove hominids of 500,000 years ago (who were members of Homo heidelbergensis) had their ecological niche. They had a way of getting food and shelter in their preferred habitat, of seducing mates and rearing babies. They walked on two feet, had huge brains, made spears and hand axes, taught each other traditions, perhaps spoke or signalled to each other grammatically, almost certainly lit fires and cooked their food, and undoubtedly killed big animals. If the sun shone, the herds of game were plentiful, the spears were sharp and diseases kept at bay, they may have sometimes thrived and populated new land. At other times, when food was scarce, the local population just died out. They could not change their ways much; it was not in their natures. Once they had spread all across Africa and Eurasia, their populations never really grew. On average death rates matched birth rates. Starvation, hyenas, exposure, fights and accidents claimed most of their lives before they were elderly enough to get chronically ill. Crucially, they did not expand or shift their niche. They remained trapped within it. Nobody woke up one day and said ‘I’m going to make my living a different way.’

Think of it this way. You don’t expect to get better and better at walking in each successive generation – or breathing, or laughing, or chewing. For Palaeolithic hominids, hand-axe making was like walking, something you grew good at through practice and never thought about again. It was almost a bodily function. It was no doubt passed on partly by imitation and learning, but unlike modern cultural traditions it showed little regional and local variation. It was part of what Richard Dawkins called ‘the extended phenotype’ of the erectus hominid species (#litres_trial_promo), the external expression of its genes. It was instinct, as inherent to the human behavioural repertoire as a certain design of nest is to a certain species of bird. A song thrush lines its nest with mud, a European robin lines its nest with hair and a chaffinch lines its nest with feathers – they always have and they always will. It’s innate for them to do so. Making a teardrop-shaped sharp-edged stone tool takes no more skill than making a bird’s nest and was probably just as instinctive: it was a natural expression of human development (#litres_trial_promo).

Indeed, the analogy with a bodily function is quite appropriate. There is now little doubt that hominids spent much of those million and a half years eating a lot of fresh meat. Some time after two million years ago, ape-men had become more carnivorous. With their feeble teeth and with finger nails where they should have had claws, they needed sharp tools to cut the skins of their kills. Because of their sharp tools they could tackle even the pachydermatous rhinos and elephants. Biface axes were like external canine teeth. The rich meat diet also enabled erectus hominids to grow a larger brain, an organ that burns energy at nine times the rate of the rest of the body. Meat enabled them to cut down on the huge gut (#litres_trial_promo) that their ancestors had found necessary to digest raw vegetation and raw meat, and thus to grow a bigger brain instead. Fire and cooking in turn then released the brain to grow bigger still by making food more digestible with an even smaller gut – once cooked, starch gelatinises and protein denatures, releasing far more calories for less input of energy. As a result, whereas other primates have guts weighing four times their brains, the human brain weighs more than the human intestine. Cooking enabled hominids to trade gut size for brain size.

Erectus hominids, in other words, had almost everything we might call human: two legs, two hands, a big brain, opposable thumbs, fire, cooking, tools, technology, cooperation, long childhoods, kindly demeanour. And yet there was no sign of cultural take-off, little progress in technology, little expansion of range or niche.

Homo dynamicus

Then there appeared upon the earth a new kind of hominid, which refused to play by the rules. Without any changes in its body, and without any succession of species, it just kept changing its habits. For the first time its technology changed faster than its anatomy. This was an evolutionary novelty, and you are it.

When this new animal appeared is hard to discern, and its entrance was low-key. Some anthropologists argue that in east Africa and Ethiopia the toolkit was showing signs of change as early as 285,000 years ago (#litres_trial_promo). Certainly, by at least 160,000 years ago (#litres_trial_promo) a new, small-faced ‘sapiens’ skull was being worn on the top of the spine in Ethiopia. Around the same time at Pinnacle Point in South Africa (#litres_trial_promo), people – yes, I shall call them people for the first time – were cooking mussels and other shellfish in a cave close to the sea as well as making primitive ‘bladelets’, small flakes of sharp stone, probably for hafting on to spears. They were also using red ochre, perhaps for decoration, implying thoroughly modern symbolic minds.

This was during the ice age before last, when Africa was mostly a desert. And yet apparently nothing much came of this experiment. Consistent evidence of smart behaviour and a fancy toolkit peters out again. Genetic evidence suggests human beings were still rare even in Africa, eking out a precarious existence in pockets of savannah woodland when it was dry, or possibly on the margins of lakes and seas. In the Eemian interglacial period of 130,000–115,000 years ago, the climate grew warmer and much wetter and sea level rose. Some skulls from what is now Israel suggest that a few slender-headed Africans did begin to colonise the Middle East (#litres_trial_promo) towards the end of the Eemian, before a combination of cold weather and Neanderthals drove them back again. It was during this mild spell that a fancy new toolkit first appeared in caves in what is now Morocco: flakes, toothed scrapers and retouched points. One of the most extraordinary clues comes in the form of a simple estuarine snail shell called Nassarius. This little winkle keeps popping up in archaeological sites, with unnatural holes in its shells. The oldest certain Nassarius find is at Grottes des Pigeons near Taforalt in Morocco (#litres_trial_promo), where forty-seven perforated shells, some smeared with red ochre, date from certainly more than 82,000 years ago and perhaps as much as 120,000 years ago. Similar shells, harder to date, have been found at Oued Djebanna in Algeria and Skhul in Israel, and perforated shells of the same genus but a different species are found at Blombos cave in South Africa from about 72,000 years ago along with the earliest bone awls. These shells were surely beads, probably worn on a string. Not only do they hint at a very modern attitude to personal ornament, symbolism or perhaps even money; they also speak eloquently of trade. Taforalt is 25 miles and Oued Djebanna 125 miles from the nearest coast. The beads probably travelled hand to hand by exchange. Likewise, there are hints from east Africa and Ethiopia that the volcanic glass known as obsidian may have begun to move over long distances (#litres_trial_promo) around this time too, or even earlier, presumably by trade, but the dates and sources are still uncertain.

Just across the strait of Gibraltar from where these bead-wearing, flake-making people lived were the ancestors of Neanderthals, whose brains were just as big but who showed no signs of making beads or flake tools, let alone doing long-distance trade. There was clearly something different about the Africans. Over the next few tens of millennia there were sporadic improvements, but no great explosion. There may have been a collapse of human populations. The African continent was plagued by ‘megadroughts’ at this time, during which desiccating winds blew the dust of extensive deserts into Lake Malawi, whose level dropped 600 metres (#litres_trial_promo). Only well after 80,000 years ago, so genetic evidence attests, does something big start to happen again. This time the evidence comes from genomes, not artefacts. According to DNA scripture, it was then that one quite small group of people began to populate the entire African continent, starting either in East or South Africa and spreading north and rather more slowly west. Their genes, marked by the L3 mitochondrial type, suddenly expanded and displaced most others in Africa (#litres_trial_promo), except the ancestors of the Khoisan and pygmy people. Yet even now there was no hint of what was to come, no clue that this was anything but another evolutionary avatar of a precariously successful predatory ape. The new African form, with its fancy tools, ochre paint and shell-bead ornaments, might have displaced its neighbours, but it would now settle down to enjoy its million years in the sun before gracefully giving way to something new. This time, however, some of the L3 people promptly spilled out of Africa and exploded into global dominion. The rest, as they say, is history.

Starting to barter

Anthropologists advance two theories to explain the appearance in Africa of these new technologies and people. The first is that it was driven by climate. The volatility of the African weather, sucking human beings into deserts in wet decades and pushing them out again in dry ones, would have placed a premium on adaptability, which in turn selected for new capabilities. The trouble with this theory is first that climate had been volatile for a very long time without producing a technologically adept ape, and second that it applies to lots of other African species too: if human beings, why not elephants and hyenas? There is no evidence from the whole of the rest of biology that desperate survival during unpredictable weather selects intelligence or cultural flexibility. Rather the reverse: living in large social groups on a plentiful diet both encourages and allows brain growth (#litres_trial_promo).

The second theory is that a fortuitous genetic mutation triggered a change in human behaviour (#litres_trial_promo) by subtly altering the way human brains were built. This made people fully capable of imagination, planning, or some other higher function for the first time, which in turn gave them the capacity to make better tools and devise better ways of making a living. For a while, it even looked as if two candidate mutations of the right age had appeared – in the gene called FOXP2, which is essential to speech and language in both people and songbirds (#litres_trial_promo). Adding these two mutations to mice does indeed seem to change the flexibility of wiring in their brain in a way that may be necessary for the rapid flicker of tongue and lung that is called speech, and perhaps coincidentally the mutations even change the way mice pups squeak (#litres_trial_promo) without changing almost anything else about them. But recent evidence confirms that Neanderthals share the very same two mutations (#litres_trial_promo), which suggests that the common ancestor of Neanderthals and modern people, living about 400,000 years ago, may have already been using pretty sophisticated language. If language is the key to cultural evolution, and Neanderthals had language, then why did the Neanderthal toolkit show so little cultural change?

Moreover, genes would undoubtedly have changed during the human revolution after 200,000 years ago, but more in response to new habits than as causes of them. At an earlier date, cooking selected mutations for smaller guts and mouths, rather than vice versa. At a later date, milk drinking selected for mutations for retaining lactose digestion into adulthood in people of western European and East African descent. The cultural horse comes before the genetic cart. The appeal to a genetic change driving evolution gets gene-culture co-evolution backwards: it is a top-down explanation for a bottom-up process.

Besides, there is a more fundamental objection. If a genetic change triggered novel human habits, why do its effects appear gradually and erratically in different places at different times but then accelerate once established? How could the new gene have a slower effect in Australia than in Europe? Whatever the explanation for the modernisation of human technology after 200,000 years ago, it must be something that gathers pace by feeding upon itself, something that is auto-catalytic.

As you can tell, I like neither theory. I am going to argue that the answer lies not in climate, nor genetics, nor in archaeology, nor even entirely in ‘culture’, but in economics. Human beings had started to do something to and with each other that in effect began to build a collective intelligence. They had started, for the very first time, to exchange things between unrelated, unmarried individuals; to share, swap, barter and trade. Hence the Nassarius shells moving inland from the Mediterranean. The effect of this was to cause specialisation, which in turn caused technological innovation, which in turn encouraged more specialisation, which led to more exchange – and ‘progress’ was born, by which I mean technology and habits changing faster than anatomy. They had stumbled on what Friedrich Hayek called the catallaxy: the ever-expanding possibility generated by a growing division of labour. This is something that amplifies itself once begun.

Exchange needed to be invented. It does not come naturally to most animals. There is strikingly little use of barter in any other animal species. There is sharing within families, and there is food-for-sex exchange in many animals including insects and apes, but there are no cases in which one animal gives an unrelated animal one thing in exchange for a different thing. ‘No man ever saw a dog make fair and deliberate exchange of a bone with another dog,’ said Adam Smith.

I need to digress here: bear with me. I am not talking about swapping favours – any old primate can do that. There is plenty of ‘reciprocity’ in monkeys and apes: you scratch my back and I scratch yours. Or, as Leda Cosmides and John Tooby put it (#litres_trial_promo), ‘One party helps another at one point in time, in order to increase the probability that when their situations are reversed at some (usually) unspecified time in the future, the act will be reciprocated.’ Such reciprocity is an important human social glue, a source of cooperation and a habit inherited from the animal past that undoubtedly prepared human beings for exchange. But it is not the same thing as exchange. Reciprocity means giving each other the same thing (usually) at different times. Exchange – call it barter or trade if you like – means giving each other different things (usually) at the same time: simultaneously swapping two different objects. In Adam Smith (#litres_trial_promo)’s words, ‘Give me that which I want, and you shall have this which you want.’

Barter is a lot more portentous than reciprocity. After all, delousing aside, how many activities are there in life where it pays to do the same thing to each other in turn? ‘If I sew you a hide tunic today, you can sew me one tomorrow’ brings limited rewards and diminishing returns. ‘If I make the clothes, you catch the food’ brings increasing returns. Indeed, it has the beautiful property that it does not even need to be fair. For barter to work, two individuals do not need to offer things of equal value. Trade is often unequal, but still benefits both sides. This is a point that nearly everybody seems to miss. In the grasslands of Cameroon (#litres_trial_promo), for example, in past centuries the palm-oil producers, who lived on the periphery of the region on the poorest soils, worked hard to produce a low-value product that they exchanged for cereal, livestock and iron with their neighbours. On average it took them thirty days to afford the price of an iron hoe that had cost its makers just seven person-days of work. Yet palm oil was still the most profitable product they could make on their own land and with their own resources. The cheapest way for them to get an iron hoe was to make more palm oil. Or imagine a Trobriand island tribe on the coast that has ample fish and an inland tribe that has ample fruit: as long as two people are living in different habitats, they will value what each other has more than what they have themselves, and trade will pay them both. And the more they trade, the more it will pay them to specialise.

Evolutionary psychologists have assumed that it is rare for conditions to exist in which two people simultaneously have value to offer to each other. But this is just not true, because people can value highly what they do not have access to. And the more they rely on exchange, the more they specialise, which makes exchange still more attractive. Exchange is therefore a thing of explosive possibility, a thing that breeds, explodes, grows, auto-catalyses. It may have built upon an older animal instinct of reciprocity, and it may have been greatly and uniquely facilitated by language – I am not arguing that these were not vital ingredients of human nature that allowed the habit to get started. But I am saying that barter – the simultaneous exchange of different objects – was itself a human breakthrough, perhaps even the chief thing that led to the ecological dominance and burgeoning material prosperity of the species. Fundamentally, other animals do not do barter.

I still don’t quite know why, but I have a lot of trouble getting this point across to both economists and biologists. Economists see barter as just one example of a bigger human habit of general reciprocity. Biologists talk about the role that reciprocity played in social evolution, meaning ‘do unto others as they do unto you’. Neither seems to be interested in the distinction that I think is vital, so let me repeat it here once more: at some point, after millions of years of indulging in reciprocal back-scratching of gradually increasing intensity, one species, and one alone, stumbled upon an entirely different trick. Adam gave Oz an object in exchange for a different object. This is not the same as Adam scratching Oz’s back now and Oz scratching Adam’s back later, or Adam giving Oz some spare food now and Oz giving Adam some spare food tomorrow. The extraordinary promise of this event was that Adam potentially now had access to objects he did not know how to make or find; and so did Oz. And the more they did it, the more valuable it became. For whatever reason, no other animal species ever stumbled upon this trick – at least between unrelated individuals.

Do not take my word for it. The primatologist Sarah Brosnan tried to teach two different groups of chimpanzees about barter (#litres_trial_promo) and found it very problematic. Her chimps preferred grapes to apples to cucumbers to carrots (which they liked least of all). They were prepared sometimes to give up carrots for grapes, but they almost never bartered apples for grapes (or vice versa), however advantageous the bargain. They could not see the point of giving up food they liked for food they liked even more. Chimpanzees and monkeys can be taught to exchange tokens for food (#litres_trial_promo), but this is a long way from spontaneously exchanging one thing for another: the tokens have no value to the chimpanzees, so they are happy to give them up. True barter requires that you give up something you value in exchange for something else you value slightly more.

This is reflected in the ecology of wild chimpanzees. Whereas in human beings, each sex eats ‘not only from the food items they have collected themselves, but from their partners’ finds,’ says Richard Wrangham, ‘not even a hint of this complementarity is found among nonhuman primates. (#litres_trial_promo)’ It is true that male chimps hunt monkeys more than females do and that having killed a monkey, a male sometimes allows others to share it if they beg to, especially a fertile female or a close partner to whom he owes a favour. But the one thing you do not see is trade of one food for another. There is never barter of meat for nuts. The contrast with human beings, who show an almost obsessive interest not just in sharing food with each other from an early age, but in swapping one item for another, is striking. Birute Galdikas reared a young orang-utan in her home alongside her daughter Binti, and was struck by the contrasting attitudes to food sharing of the two infants. ‘Sharing food seemed to give Binti great pleasure,’ she wrote. ‘In contrast, Princess, like any orang-utan would beg, steal and gobble food at every opportunity’.

My argument is that this habit of exchanging, this appetite for barter, had somehow appeared in our African ancestors some time before 100,000 years ago. Why did human beings acquire a taste for barter as other animals did not? Perhaps it has something to do with cooking. Richard Wrangham makes a persuasive case that control of fire had a far-reaching effect on human evolution. Beyond making it safe to live on the ground, beyond liberating human ancestors to grow big brains on high-energy diets, cooking also predisposed human beings to swapping different kinds of food. And that maybe got them bartering.

Hunting for gathering

As the economist Haim Ofek has argued, fire itself is hard to start, but easy to share (#litres_trial_promo); likewise cooked food is hard to make but easy to share. The time spent in cooking is subtracted from the time spent in chewing: wild chimpanzees spend six hours or more each day just masticating their food. Carnivores might not chew their meat (they are often in a hurry to eat before it is stolen), but they spend hours grinding it in muscular stomachs, which comes to much the same thing. So cooking adds value: the great advantage of cooked food is that though it takes longer to prepare than raw food, it takes just minutes to eat, and this means that somebody else can eat as well as the person who prepares it. A mother can feed her children for many years. Or a woman can feed a man.

In most hunter-gatherers, women spend long hours gathering, preparing and cooking staple foods while men are out hunting for delicacies. There is, incidentally, no hunter-gatherer society that dispenses with cooking. Cooking is the most female-biased of all activities, the only exceptions being when men prepare some ritual feasts or grill a few snacks while out on the hunt. (Does this ring any modern bells? Fancy chefs and barbecuing are the two most masculine forms of cooking today.) On average, across the world, each sex contributes similar quantities of calories, though the pattern varies from tribe to tribe: in Inuits, for example, most food is obtained by men, whereas in the Kalahari Khoisan people, most is gathered by women. But – and here is the crucial point – throughout the human race, males and females specialise and then share food (#litres_trial_promo).