The World Until Yesterday

Questions about religion

“In the beginning, all people lived around a great ironwood tree in the jungle, speaking the same language. One man whose testes were enormously swollen from infection with a parasitic worm spent his time sitting on a branch of the tree, so that he could rest his heavy testes on the ground. Out of curiosity, animals of the jungle came up and sniffed at his testes. Hunters then found the animals easy to kill, and everyone had plenty of food and was happy.

“Then, one day, a bad man killed a beautiful woman’s husband, in order to get the woman for himself. Relatives of the dead husband attacked the murderer, who was defended in turn by his own relatives, until the murderer and his relatives climbed into the ironwood tree to save themselves. The attackers tugged on the lianas hanging from one side of the tree, in order to pull the tree’s crown down towards the ground and get at their enemies.

“Finally, the lianas snapped in half, causing the tree to spring back with tremendous force. The murderer and his relatives were hurled out of the tree in many directions. They landed so far away, in so many places, that they never found each other again. With time, their languages became more and more different. That is why people today speak so many separate languages and cannot understand each other, and why it is hard work for hunters to catch animals for food.”

That story is told by a tribal people in northern New Guinea. The story exemplifies a widespread class of myths called origin myths, familiar to us through accounts of the Garden of Eden and the Tower of Babel in the Bible’s book of Genesis. Despite those parallels with Judeo-Christian religions, traditional New Guinea societies, like other small-scale societies, lacked churches, priests, and sacred books. Why is that tribal belief system so reminiscent of Judeo-Christian religions in its origin myth, yet so different in other respects?

Virtually all known human societies have had “religion,” or something like it. That suggests that religion fulfills some universal human need, or at least springs from some part of human nature common to all of us. If so, what is that need, or that part of human nature? And what really defines “religion”? Scholars have been debating these and related questions for centuries. For a belief system to constitute a religion, must it include belief in a god or gods or some supernatural forces, and does it necessarily include anything else? When, in human evolutionary history, did religion appear? Human ancestors diverged from the ancestors of chimpanzees around 6,000,000 years ago. Whatever religion is, we can agree that chimps don’t have it, but was there already religion among our Cro-Magnon ancestors and our Neanderthal relatives of 40,000 years ago? Were there different historical stages in the development of religions, with creeds like Christianity and Buddhism representing a more recent stage than tribal belief systems? We tend to associate religion with humanity’s noble side, not with its evil side: why, then, does religion sometimes preach murder and suicide?

These questions posed by religion are especially interesting in the context of this book, devoted to exploring the whole spectrum of human societies, from small-scale or ancient to populous or modern. Religion is an area where traditional institutions still thrive within otherwise modern societies: the world’s major religions today arose between 1,400 and over 3,000 years ago, in societies much smaller and more traditional than the ones that still espouse those religions today. Religions nevertheless vary with the scale of society, and that variation cries out for explanation. In addition, most readers of this book, and I, question our personal religious beliefs (or lack thereof) at some point in our lives. When we do, understanding of the different things that religion has meant to different people may help us find answers that fit us as individuals.

For individuals and for societies, religion often involves a huge investment of time and resources. To mention just a few examples, Mormons are expected to contribute 10% of their income to their church. It’s estimated that traditional Hopi Indians devote an average of one out of three days to religious ceremonies, and that one-quarter of the population of traditional Tibet consisted of monks. The fraction of resources in medieval Christian Europe devoted to building and staffing churches and cathedrals, supporting the many orders of monasteries and nunneries, and underwriting crusades must have been large. To borrow a phrase from economists, religion thus incurs “opportunity costs”: those investments of time and resources in religion that could have been devoted instead to obviously profitable activities, such as planting more crops, building dams, and feeding larger armies of conquest. If religion didn’t bring some big real benefits to offset those opportunity costs, any atheistic society that by chance arose would be likely to outcompete religious societies and take over the world. So why hasn’t the world become atheistic, and what are those benefits that religion evidently brings? What are the “functions” of religion?

To a believer, such questions about religion’s functions may seem nonsensical or even offensive. A believer might respond that religion is nearly universal among human societies simply because there really is a God, and that the ubiquity of religion no more requires discovering its supposed functions and benefits than does the ubiquity of rocks. If you are such a believer, let me invite you to imagine, just for a moment, an advanced living creature from the Andromeda galaxy, who races around the universe at a velocity far exceeding the speed of light (considered impossible by us humans), visits the universe’s trillions of stars and planets, and studies the diversity of life in the universe, with metabolisms variously powered by light, other forms of electromagnetic radiation, heat, wind, nuclear reactions, and inorganic or organic chemical reactions. Periodically, our Andromedan visits Planet Earth, where life evolved to utilize energy only from light and from inorganic and organic chemical reactions. For a brief period between about 11,000 BC and September 11, AD 2051, Earth was dominated by a life form that called itself humans and that clung to some curious ideas. Among those ideas: that there is an all-powerful being, called God, which has a special interest in the human species rather than in the millions of trillions of other species in the universe, and which created the universe, and which humans often picture as similar to a human except for being omnipotent. Of course the Andromedan recognized those beliefs to be delusions worthy of study rather than of credence, because the Andromedan and many other living creatures had already figured out how the universe really had been created, and it was absurd to imagine that any all-powerful being would be especially interested in or similar to the human species, which was much less interesting and advanced than billions of other life forms existing elsewhere in the universe. The Andromedan also observed that there were thousands of different human religions, most of whose adherents believed their own religion to be true and all the other religions to be false, and that suggested to the Andromedan that all were false.

But this belief in such a god was widespread among human societies. The Andromedan understood the principles of universal sociology, which had to provide an explanation for why human societies persisted despite the huge drain of time and resources that religion imposed on individuals and societies, and despite religion’s motivating individuals to inflict on themselves painful or suicidal behaviors. Obviously, the Andromedan reasoned, religion must bring some compensating benefits; otherwise, atheistic societies not burdened by those time and resource drains and those suicidal impulses would have replaced religious societies. Hence if you, my readers, find it offensive to inquire about the functions of your own religion, perhaps you would be willing for a moment to step back and inquire about the functions of New Guinea tribal religions, or to place yourself in the frame of mind of the Andromedan visitor and inquire about human religions in general.

Definitions of religion

Let’s begin by defining religion, so that we can at least agree about what phenomenon we are discussing. Which features are shared by all religions, including Christianity and tribal religions along with the polytheism of classical Greece and Rome, and are necessary and sufficient to identify a phenomenon as a religion rather than as some related but different phenomenon (such as magic, patriotism, or a philosophy of life)?

Table 9.1. Some proposed definitions of religion

Table 9.1 lists 16 different definitions proposed by scholars of religion. Definitions numbers 11 and 13, by Émile Durkheim and Clifford Geertz respectively, are the ones most frequently quoted by other scholars. It will be obvious that we are not even close to agreement on a definition. Many of these definitions are written in a convoluted style similar to the language used by lawyers in drafting a contract, and that warns us that we are treading on hotly contested ground.

As a fallback position, could we skirt the problem of defining religion in the same way that we often skirt the problem of defining pornography, by saying, “I can’t define pornography, but I nevertheless know it when I see it!”? No, unfortunately even that fallback position won’t work; scholars don’t agree about whether to recognize some widespread and well-known movements as religions. For instance, there have been long-standing debates among scholars of religion about whether Buddhism, Confucianism, and Shintoism should be counted as religions; the current trend is to count Buddhism but not Confucianism, although Confucianism was usually counted a decade or two ago; Confucianism is now instead usually termed a way of life or a secular philosophy.

These difficulties in defining religion are instructive. They warn us that the phenomena that we lump together as religions contain several different components, which are variously strong, weak, or virtually absent in different religions, different societies, and different stages of the evolution of religions. Religion shades into other phenomena, which possess some but not all of the attributes usually associated with religion. That’s why there is disagreement over whether Buddhism, usually counted as one of the world’s four biggest religions, really is a religion at all or is “just” a philosophy of life. The components commonly attributed to religions fall into five sets: belief in the supernatural, shared membership in a social movement, costly and visible proofs of commitment, practical rules for one’s behavior (i.e., “morality”), and belief that supernatural beings and forces can be induced (e.g., by prayer) to intervene in worldly life. As we shall see, though, it would not make sense to define religion by the combination of all five of those attributes, nor to label as non-religion a phenomenon lacking one or more of them, because one would thereby exclude some branches of movements widely recognized as religions.

The first of these five attributes is the basis of the definition of religion that I offered to my University of California undergraduate students when I first taught a course in cultural geography. I proposed, “Religion is the belief in a postulated supernatural agent for whose existence our senses can’t give us evidence, but which is invoked to explain things of which our senses do give us evidence.” This definition has two virtues: belief in supernatural agents is indeed one of the most widespread characteristics of religion; and explanation, as we shall discuss later, was among the main origins and early functions of religions. Most religions do postulate the existence of gods, spirits, and other agents that we term “supernatural” because they or their provable consequences can’t be perceived directly in the natural world. (Throughout this chapter, I shall repeatedly use the word “supernatural” in that neutral sense, without any of the pejorative connotations sometimes associated with the word.) Many religions go further and postulate the existence of an entire parallel supernatural world—often, a heaven, a hell, or another afterlife to which we ourselves shall be transferred after our death in this natural world. Some believers are so convinced of the existence of supernatural agents that they insist that they have seen, heard, or felt spirits or ghosts.

But I soon realized that my definition was inadequate, for reasons that are also instructive. Belief in supernatural agents characterizes not only religions but also phenomena that no one would consider religious—such as belief in fairies, ghosts, leprechauns, and aliens in UFOs. Why is it religious to believe in gods, but not necessarily religious to believe in fairies? (Hint: believers in fairies don’t meet on a specified day each week to perform certain rituals, don’t identify themselves as a community of fairy-believers separate from fairy-skeptics, and don’t offer to die in defense of their belief in fairies.) Conversely, some movements that everyone considers to be religions don’t require belief in supernatural agents. Numerous Jews (including rabbis), Unitarians, Japanese people, and others are agnostics or atheists but still consider themselves, and are considered by others, to belong to a religion. The Buddha did not associate himself with any gods and claimed that he was “merely” teaching a path to enlightenment that he had discovered.

A big failing in my definition was that it omitted a second attribute of religions: they are also social movements of people who identify themselves as sharing deeply held beliefs. Someone who believes in a god and in a long list of other doctrines that he invented, and who devotes part of every Sabbath to sitting in a room by himself, praying to that god, and reading a book that he has written himself but shown to no one else, doesn’t qualify as practising a religion. The closest actual equivalent to such a person is hermits who live in isolation and devote themselves to prayer. But those hermits arose from a community of believers who provided the hermits’ beliefs, and who may continue to support and visit the hermits. I’m not aware of hermits who devised their own religion from scratch, went off into the desert to live alone, and refused food offerings and discouraged visitors. If someone should show me such a hermit, I would define him as a non-religious hermit or else as a misanthrope, while others might consider him to be a typical religious hermit except for failing the test of sociality.

A third attribute of many religions is that their adherents make costly or painful sacrifices that convincingly display to others the adherents’ commitment to the group. The sacrifice may be of time: e.g., interrupting other activities five times per day to face towards Mecca and pray, or spending part of every Sunday in church, or spending years memorizing a complex ritual, prayers, and songs (possibly requiring learning another language), or devoting two years to missionary activities as a young adult (expected of Mormons), or joining a crusade or a pilgrimage or visiting Mecca at one’s own expense. The sacrifice may be of money or property donated to the church. One may offer a valuable domestic animal: one sacrifices to God one’s own lamb, not some captured wild animal that cost nothing. Or the sacrifice may be of one’s bodily comfort or integrity, by fasting, chopping off a finger joint, circumcising or subincising (splitting lengthwise) the penis, or spilling one’s blood by cutting one’s nose or tongue or penis or inside the throat or other body part. All of those costly public or painful displays serve to convince other believers that one is serious in one’s commitment to their religion and will even sacrifice one’s life if necessary. Otherwise, if I merely shouted “I’m a Christian!,” I might be lying for personal advantage (as some prisoners do in the hopes of gaining parole), or to save my life. While the second and third attributes (i.e., a social movement and costly sacrifices) seem to me necessary conditions for a movement to count as a religion, they’re not sufficient conditions by themselves. There are also non-religious social movements sharing deeply held beliefs and demanding costly sacrifices of their adherents, such as patriotism.

The next-to-last attribute of religions is that belief in gods and other postulated supernatural agents has practical consequences for how people should behave. Those rules of behavior may variously take the form of laws, moral codes, taboos, or obligations, depending on the type of society. While virtually all religions have such rules of behavior, it is not the case that rules of behavior stem only from religion: modern secular state governments, countless non-religious groups, and atheistic or agnostic citizens also have their own rules.

Finally, many religions teach that supernatural agents not only reward virtuous rule-obeying people and punish evil-doers and rule-breakers, but also can be induced by prayers, donations, and sacrifices to intervene on behalf of mortal petitioners.

Thus, religion involves a constellation of five sets of attributes, which vary in strength among the world’s religions (including traditional religions). We may use this constellation to understand the differences between religion and several related phenomena that share some but not all of the attributes of religion. Patriotism and ethnic pride resemble religion in being social movements distinguishing their adherents from outsiders, demanding sacrifice (even of one’s life) as a display of one’s commitment, and celebrated in rituals and ceremonies such as (for Americans) Independence Day, Thanksgiving Day, and Memorial Day. Unlike religion, patriotism and ethnic pride do not teach belief in supernatural agents. Sports fans, like religious believers, form social groups of adherents (e.g., Boston Red Sox fans) distinct from adherents of other social groups (e.g., New York Yankee fans) but don’t espouse supernatural agents, don’t demand great sacrifices as proof of affiliation, and don’t regulate a broad range of moral behavior. Marxism, socialism, and other political movements do attract committed groups of adherents (like religions), motivate adherents to die for their ideals, and may have broad moral codes, but don’t rely on the supernatural. Magic, sorcery, superstition, and water-witching (the belief that underground water can be located by a divining rod) do involve belief in supernatural agents with consequences for everyday behavior. However, magic, superstition, and related phenomena do not serve as defining attributes of committed social groups akin to believers: there are not groups of believers in the dangers of black cats who meet every Sunday to re-affirm their separateness from non-believers in the dangers of black cats. Perhaps the grayest borderline area involves movements such as Buddhism, Confucianism, and Shintoism, about which there are varying degrees of uncertainty whether they constitute religions or else philosophies of life.

Functions and electric eels

Religion is nearly universal in humans, but nothing even remotely resembling it has been described in animals. Nevertheless, we can inquire about—indeed, we have to wonder about—the origins of religion, just as we wonder about the origins of other uniquely human traits such as art and spoken language. Six million years ago, our ancestors were apes that surely lacked religion; by the time that the first written documents appeared around 5,000 years ago, there was already religion. What happened in the intervening 5,995,000 years? What were religion’s antecedents in animals and in human ancestors, and when and why did it arise?

A method termed the functional approach has been the commonest framework adopted by scholars of religion since they began studying it scientifically almost 150 years ago. They ask: what functions does religion fulfill? They note that religion often imposes heavy costs on individuals and societies, such as impelling many people to live celibate lives and to forgo having children, to go to the effort and expense of building huge pyramids, to kill one’s valuable domestic animals and occasionally even one’s own child and oneself, and to spend much time repeating the same words over and over again. Religion must have functions and bring benefits to offset those heavy costs; otherwise, it wouldn’t have come into being and couldn’t be maintained. What human problems did the invention of religion solve? A brief summary of the functional approach might be to assert something like this: religion was invented in order to carry out certain functions and solve certain problems, such as maintaining social order, comforting anxious people, and teaching political obedience.

Another approach, emerging more recently from the field of evolutionary psychology, objects: religion surely didn’t evolve and wasn’t consciously invented for any specific purpose or to solve any specific problem. It wasn’t the case that some budding chief got a brilliant idea one day and invented religion from scratch, foreseeing that he could more easily hold his subjects in sway if he convinced them of religious reasons to build a pyramid. Nor is it likely that a psychologically attuned hunter-gatherer, concerned that his fellow tribesmen had become too depressed by a recent death to go hunting, made up a story about the afterlife in order to console them and give them new hope. Religion instead probably arose as a by-product of some other capacities of our ancestors and of their own animal ancestors, and those capacities had unforeseen consequences and gradually acquired new functions as they developed.

To an evolutionary biologist like myself, there is no contradiction between these two different approaches to the origin of religion, in effect postulating two stages. Biological evolution itself similarly proceeds in two stages. First, variation between individuals is generated by mutations and recombinations of genes. Second, because of natural selection and sexual selection there are differences among the resulting variant individuals in how they survive, reproduce, and pass on their genes to the next generation. That is, some of those variant individuals turn out to perform functions and to solve life’s problems better than do other variant individuals. A functional problem (e.g., surviving in a colder climate) isn’t solved by an animal realizing that it needs thicker fur, nor by cold climates stimulating mutations for a thicker fur. Instead, something (in the case of biological evolution, the mechanisms of molecular genetics) creates something else (in this case, an animal with thicker or thinner fur), and some life conditions or environmental problems (in this case, cold temperatures) endow some but not others of those variant animals with a useful function. Thus, gene mutations and recombinations provide the origins of biological diversity, while natural selection and sexual selection sieve that starting material by the criterion of function.

Similarly, evolutionary psychologists assert that religion is a by-product of features of the human brain that arose for reasons other than building pyramids or comforting bereaved relatives. To an evolutionary biologist, that’s plausible and unsurprising. Evolutionary history is chock-full of by-products and mutations that were initially selected for one function and then developed further and became selected to fulfill another function. For example, creationists skeptical of the reality of evolution used to point to electric eels that electrocute their prey with 600-volt shocks, and then argued that a 600-volt eel could never have arisen from a normal no-volt eel by natural selection, because the necessary intermediate stages of low-voltage eels couldn’t electrocute any prey and wouldn’t be good for anything. In fact, it turns out that 600-volt eels evolved through changes of function, as a by-product of electric field detection and electricity generation in normal fish.

Many fish have skin sense organs sensitive to electric fields in the environment. Those fields can be either of physical origin (e.g., from ocean currents or from the mixing of waters of different salinities), or else of biological origin (from the electrical triggering of animals’ muscle contractions). Fish possessing such electric-sensitive sense organs can employ them for two functions: to detect prey, and to navigate through the environment, especially in muddy water and under nighttime conditions where eyes are of little use. The prey reveal themselves to the animals’ electric field detector by having a much higher electrical conductivity than does fresh water. That detection of environmental electric fields may be termed passive electrodetection; it does not require any specialized electricity-generating organs.

But some fish species go further and generate their own low-voltage electric fields, which let them detect objects not only by an object’s own electric field, but also by its modification of the electric field set up by the fish. Organs specialized to generate electricity evolved independently in at least six separate lineages of fish. Most electrical organs are derived from the electricity-generating membranes of muscles, but one fish species develops its electric organs from nerves. The zoologist Hans Lissmann furnished the first compelling proof of such active electrodetection, after much inconclusive speculation by others. Lissmann conditioned electric fish, by food rewards, to distinguish an electrically conducting object from a non-conducting object of identical appearance, such as a conducting metal disk versus an identical-looking non-conducting plastic or glass disk. While I was working in a Cambridge University laboratory near the building in which Lissmann was doing his studies, a friend of Lissmann told me a story illustrating the sensitivity of electrodetection by electric fishes. Lissmann noticed that a captive electric fish that he was maintaining in his laboratory got excited around the same time in the late afternoon of every weekday. He eventually realized that it was because his female technician was getting ready to go home at that hour, stepped behind a screen, and combed her hair, which set up an electric field that the fish could detect.

Low-voltage fish use their electricity-generating organs and their skin electrodetectors for improved efficiency of two different functions, both shared with the many fish possessing electrodetectors but lacking electricity-generating organs: prey detection and navigation. Low-voltage fish also use each other’s electric impulses for a third function, that of communicating with each other. Depending on the pattern of the electric impulses, which varies among species and individuals, a fish can extract information and thereby recognize the species, sex, size, and individual (strange or familiar) of fish generating the impulses. A low-voltage fish also communicates social messages to other fish of its species: in effect, it can electrically say, “This is my territory, you get out,” or “Me Tarzan, you Jane, you turn me on, it’s time for sex.”

Fish generating a few volts could not only detect prey but could also use their shocks for a fourth function: to kill small prey, like minnows. More and more volts let one kill bigger and bigger prey, until one arrives at a 600-volt eel six feet long that can stun a horse in the river. (I remember this evolutionary history all too vividly, because I started to do my Ph.D. thesis on electricity generation by electric eels. I got so absorbed in the molecular details of electricity generation that I forgot the end results, and I impulsively grabbed my first eel to start my first experiment—with a shocking outcome.) High-volt fish can also use their powerful discharges for two more functions: to defend themselves against would-be predators, by blasting the attacker; and to hunt by “electrofishing,” i.e., attracting prey to the electrically positive end of the fish (the anode), a technique also used by commercial fishermen who however have to generate electricity with batteries or generators rather than with their own bodies.

Now, let’s go back to those skeptical creationists who object that natural selection could never have produced a 600-volt eel from a normal no-volt eel, supposedly because all the necessary intermediate stages of low-volt electric organs would have been useless and wouldn’t have helped their owners survive. The answer to the creationist is that killing prey with a 600-volt shock wasn’t the original function of electric organs, but arose as a by-product of an organ initially selected for other functions. We’ve seen that electrical organs acquired six successive functions as natural selection ramped up their output from nothing to 600 volts. A no-volt fish can do passive electrodetection of prey and can navigate; a low-volt fish can perform those same two functions more efficiently, and can also electrocommunicate; and a high-volt fish can electrocute prey, defend itself, and carry out electrofishing. We shall see that human religion topped electric eels by traversing seven rather than just six functions.

The search for causal explanations

From which human attributes might religion similarly have arisen as a by-product? A plausible view is that it was a by-product of our brain’s increasingly sophisticated ability to deduce cause, agency, and intent, to anticipate dangers, and thereby to formulate causal explanations of predictive value that helped us survive. Of course animals also have brains and can thereby deduce some intent. For instance, a Barn Owl detecting a mouse by sound in complete darkness can hear the mouse’s footsteps, calculate the mouse’s direction and speed, thereby deduce the mouse’s intent to continue running in that direction at that speed, and pounce at just the correct time and place to intersect the mouse’s path and capture the mouse. But animals, even our closest relatives, have far less reasoning ability than do humans. For example, to the African monkeys known as vervet monkeys, ground-dwelling pythons are major predators. The monkeys have a special alarm call that they give at the sight of a python, and they know enough to jump up into a tree if warned by the python alarm call of another monkey nearby. Astonishingly to us, though, those smart monkeys don’t associate the sight of the python’s track in the grass with the danger that a python may be nearby. Contrast those weak reasoning abilities of monkeys with the abilities of us humans: we have been honed by natural selection for our brains to extract maximum information from trivial cues, and for our language to convey that information precisely, even at the inevitable risk of frequent wrong inferences.

For instance, we routinely attribute agency to other people besides ourselves. We understand that other people have intentions like ourselves, and that individuals vary. Hence we devote much of our daily brain activity to understanding other individual people and to monitoring signs from them (such as their facial expressions, tone of voice, and what they do or don’t say or do), in order to predict what some particular individual may do next, and to figure out how we can influence her to behave in a way that we want. We similarly attribute agency to animals: !Kung hunters approaching a prey carcass on which lions are already feeding look at the lions’ bellies and behavior to deduce whether the lions are sated and will let themselves be driven off, or whether they are still hungry and will stand their ground. We attribute agency to ourselves: we notice that our own actions have consequences, and if we see that behaving in one way brings success and another doesn’t, we learn to repeat the action associated with success. Our brain’s ability to discover such causal explanations is the major reason for our success as a species. That’s why, by 12,000 years ago, before we had agriculture or metal or writing and were still hunter-gatherers, we already had by far the widest distribution of any mammal species, spread from the Arctic to the equator over all of the continents except Antarctica.

We keep trying out causal explanations. Some of our traditional explanations made the right predictions for reasons that later proved to be scientifically correct; some made the right predictions for the wrong reason (e.g., “avoid eating that particular fish species because of a taboo,” without understanding the role of poisonous chemicals in the fish); and some explanations made wrong predictions. For example, hunter-gatherers overgeneralize agency and extend it to other things that can move besides humans and animals, such as rivers and the sun and moon. Traditional peoples often believe those moving inanimate objects to be, or to be propelled by, living beings. They may also attribute agency to non-moving things, such as flowers, a mountain, or a rock. Today we label that as belief in the supernatural, distinct from the natural, but traditional peoples often don’t make that distinction. Instead, they come up with causal explanations whose predictive value they observe: their theory that the sun (or a god carrying the sun in his chariot) marches daily across the sky fits the observed facts. They don’t have independent knowledge of astronomy to convince them that belief in the sun as an animate agent is a supernatural error. That isn’t silly thinking on their part: it’s a logical extension of their thinking about undoubtedly natural things.

Thus, one form in which our search for causal explanations overgeneralizes and leads straightforwardly to what today we would term supernatural beliefs consists of attributing agency to plants and non-living things. Another form is our search for consequences of our own behavior. A farmer wonders what he did differently this time to cause a formerly high-yielding field to have a poor yield this year, and Kaulong hunters wonder what a particular hunter did to cause him to fall into a hidden sinkhole in the forest. Like other traditional peoples, the farmers and the hunters rack their brains for explanations. Some of their explanations we now know to be scientifically correct, while others we now consider to be unscientific taboos. For instance, Andean peasant farmers who don’t understand coefficients of variation nevertheless scatter their crops among 8 to 22 fields (Chapter 8); they may traditionally have prayed to the rain gods; and Kaulong hunters are careful not to call out the names of cave bats while hunting bats in areas with sinkholes. We have now become convinced that field scattering is a scientifically valid method to ensure yields above some minimum value, and that prayers to rain gods and taboos on calling bat names are scientifically invalid religious superstitions, but that’s the wisdom of hindsight. To the farmers and hunters themselves, there isn’t a distinction between valid science and religious superstition.

Another arena for over-pursuit of causal explanations is theories of illness. If someone gets sick, the victim and her friends and relatives search for an explanation of the illness just as they would for any other important happening. Was it due to something that the sick person did (e.g., drinking from a certain water source), or neglected to do (e.g., washing her hands before eating, or asking a spirit for help)? Was it because of something that someone else did (e.g., another sick person sneezing on her, or a sorcerer working magic on her)? Like traditional people, we First World citizens in the era of scientific medicine continue to seek satisfying explanations for illness. We have come to believe that drinking from a certain water source or not washing one’s hands before eating does provide a valid explanation for illness, and that not asking a spirit for help doesn’t. It’s not enough to be told that you got stomach cancer because you inherited variant 211 of the PX2R gene; that’s unsatisfying and leaves you helpless; maybe instead it was because of your diet. Traditional people seek cures for illness, just as we do today when doctors’ cures fail. Often those traditional cures do appear to be beneficial for many possible reasons: most illnesses cure themselves anyway; many traditional plant remedies do prove to have pharmacological value; the shaman’s bedside manner relieves the patient’s fear and may provide a placebo-based cure; assigning a cause to an illness, even if it’s not the right cause, makes the patient feel better by letting him adopt some action rather than waiting helplessly; and if the victim does die, it may mean that he sinned by violating a taboo, or that a powerful sorcerer was responsible who must be identified and killed.

Still another form of our search for causal explanations is to seek explanations for events about which modern science just gives us the unsatisfying answer “It has no explanation, stop trying to find an explanation.” For instance, a central problem in most organized religions is the problem of theodicy, the theme of the book of Job: if a good and omnipotent god exists, then why does evil happen in the world? Traditional peoples, ready to discuss for an hour the explanation of a broken stick in the ground, will surely not fail to discuss why a good person apparently obeying the society’s rules nevertheless became injured, defeated, or killed. Did he break a taboo, or do evil spirits exist, or were the gods angry? People will also surely not fail to try to explain why someone who an hour ago was breathing, moving, and warm is now cold and not breathing or moving, like a stone: is there a part of the person, called a spirit, that has escaped and entered a bird or is now living somewhere else? Today, you might object that those are searches for “meaning” rather than for explanations, and that science provides only explanations, and that you should either turn to religion for meaning or else acknowledge that your thirst for meaning is meaningless. But everybody in the past, and still most people today, want their demand for “meaning” answered.

In short, what we now term religion may have arisen as a by-product of the human brain’s increasing sophistication at identifying causal explanations and at making predictions. For a long time there wouldn’t have been a recognized distinction between the natural and the supernatural, or between religion and the rest of life. As for when “religion” arose in the course of human evolution, I would guess: very gradually, as our brain became more sophisticated. Over 15,000 years ago, Cro-Magnons were already sewing tailored clothing, inventing new tools, and creating superb paintings of polychrome animals and humans on the walls of the Lascaux, Altamira, and Chauvet caves, in deep chambers where the paintings would have been visible only by candlelight, and which fill many modern visitors with religious awe (Plate 25). Whether or not arousing awe was the actual intent of the prehistoric painters, they surely had sufficiently modern brains to be capable of holding beliefs qualifying as religious. As for our Neanderthal relatives, for whom there is evidence that they decorated with ocher pigments and buried their dead—maybe. It seems to me safe to assume that our ancestors have had religious beliefs for at least the 60,000-year-plus history of behaviorally modern Homo sapiens, and perhaps for much longer.

Table 9.2. Examples of supernatural beliefs confined to particular religions

Supernatural beliefs

Virtually all religions hold some supernatural beliefs specific to that religion. That is, a religion’s adherents firmly hold beliefs that conflict with and cannot be confirmed by our experience of the natural world, and that appear implausible to people other than the adherents of that particular religion. Table 9.2 offers a sample of such beliefs, to which innumerable other examples could be added. No other feature of religion creates a bigger divide between religious believers and modern secular people, to whom it staggers the imagination that anyone could entertain such beliefs. No other feature creates a bigger divide between believers in two different religions, each of whom firmly believes its own beliefs but considers it absurd that the other religion’s believers believe those other beliefs. Why, nevertheless, are supernatural beliefs such universal features of religions?

One suggested answer is that supernatural religious beliefs are just ignorant superstitions similar to supernatural non-religious beliefs, illustrating only that the human brain is capable of deceiving itself into believing anything. We can all think of supernatural non-religious beliefs whose implausibility should be obvious. Many Europeans believe that the sight of a black cat heralds misfortune, but black cats are actually rather common. By repeatedly tallying whether or not a one-hour period following or not following your observation of a black cat in an area with high cat density did or did not bring you some specified level of misfortune, and by applying the statistician’s chi-square test, you can quickly convince yourself that the black-cat hypothesis has a probability of less than 1 out of 1,000 of being true. Some groups of New Guinea lowlanders believe that hearing the beautiful whistled song of the little bird known as the Lowland Mouse-Babbler warns us that someone has recently died, but this bird is among the commonest species and most frequent singers in New Guinea lowland forests. If the belief about it were true, the local human population would be dead within a few days, yet my New Guinea friends are as convinced of the babbler’s ill omens as Europeans are afraid of black cats.

A more striking non-religious superstition, because people today still invest money in their mistaken belief, is water-witching, also variously known as dowsing, divining, or rhabdomancy. Already established in Europe over 400 years ago and possibly also reported before the time of Christ, this belief maintains that rotation of a forked twig carried by a practitioner called a dowser, walking over terrain whose owner wants to know where to dig a well, indicates the location and sometimes the depth of an invisible underground water supply (Plate 46). Control tests show that dowsers’ success at locating underground water is no better than random, but many land-owners in areas where geologists also have difficulty at predicting the location of underground water nevertheless pay dowsers for their search, then spend even more money to dig a well unlikely to yield water. The psychology behind such beliefs is that we remember the hits and forget the misses, so that whatever superstitious beliefs we hold become confirmed by even the flimsiest of evidence through the remembered hits. Such anecdotal thinking comes naturally; controlled experiments and scientific methods to distinguish between random and non-random phenomena are counterintuitive and unnatural, and thus not found in traditional societies.

Perhaps, then, religious superstitions are just further evidence of human fallibility, like belief in black cats and other non-religious superstitions. But it’s suspicious that costly commitments to belief in implausible-to-others religious superstitions are such a consistent feature of religions. The investments that the 10 groups of adherents listed in Table 9.2 make or made to their beliefs are far more burdensome, time-consuming, and heavy in consequences to them than are the actions of black-cat-phobics in occasionally avoiding black cats. This suggests that religious superstitions aren’t just an accidental by-product of human reasoning powers but possess some deeper meaning. What might that be?

A recent interpretation among some scholars of religion is that belief in religious superstitions serves to display one’s commitment to one’s religion. All long-lasting human groups—Boston Red Sox fans (like me), devoted Catholics, patriotic Japanese, and others—face the same basic problem of identifying who can be trusted to remain as a group member. The more of one’s life is wrapped up with one’s group, the more crucial it is to be able to identify group members correctly, and not to be deceived by someone who seeks temporary advantage by claiming to share your ideals but really doesn’t. If that man carrying a Boston Red Sox banner, whom you had accepted as a fellow Red Sox fan, suddenly cheers when the New York Yankees hit a home run, you’ll find it humiliating but not life-threatening. But if he’s a soldier next to you in the front line and he drops his gun (or turns it on you) when the enemy attacks, your misreading of him may cost you your life.

That’s why religious affiliation involves so many costly displays to demonstrate the sincerity of your commitment: sacrifices of time and resources, enduring of hardships, and other costly displays that I’ll discuss later. One such display might be to espouse some irrational belief that contradicts the evidence of our senses, and that people outside our religion would never believe. If you claim that the founder of your church had been conceived by normal sexual intercourse between his mother and father, anyone else would believe that too, and you’ve done nothing to demonstrate your commitment to your church. But if you insist, despite all evidence to the contrary, that he was born of a virgin birth, and nobody has been able to shake you of that irrational belief after many decades of your life, then your fellow believers will feel much more confident that you’ll persist in your belief and can be trusted not to abandon your group.

Nevertheless, it’s not the case that there are no limits to what can be accepted as a religious supernatural belief. Scott Atran and Pascal Boyer have independently pointed out that actual religious superstitions over the whole world constitute a narrow subset of all the arbitrary random superstitions that one could theoretically invent. To quote Pascal Boyer, there is no religion proclaiming anything like the following tenet: “There is only one God! He is omnipotent. But he exists only on Wednesdays.” Instead, the religious supernatural beings in which we believe are surprisingly similar to humans, animals, or other natural objects, except for having superior powers. They are more far-sighted, longer-lived, and stronger, travel faster, can predict the future, can change shape, can pass through walls, and so on. In other respects, gods and ghosts behave like people. The god of the Old Testament got angry, while Greek gods and goddesses became jealous, ate, drank, and had sex. Their powers surpassing human powers are projections of our own personal power fantasies; they can do what we wish we could do ourselves. I do have fantasies of hurling thunderbolts that destroy evil people, and probably many other people share those fantasies of mine, but I have never fantasized existing only on Wednesdays. Hence it doesn’t surprise me that gods in many religions are pictured as smiting evil-doers, but that no religion holds out the dream of existing just on Wednesdays. Thus, religious supernatural beliefs are irrational, but emotionally plausible and satisfying. That’s why they’re so believable, despite at the same time being rationally implausible.

Religion’s function of explanation

Religion has changed its functions with time over the course of the history of human societies. Two of its oldest functions have variously decreased or almost disappeared among citizens of Westernized societies today. Conversely, several of its major modern functions scarcely existed in small-scale hunter-gatherer and farming societies. Four functions that were formerly weak or non-existent rose to peak importance and have now been declining again. These changes of religion’s functions during its evolution are similar to the changes of function of many biological structures (such as fish electric organs) and forms of social organization during biological evolution.

I shall now discuss what are proposed by various scholars as seven major functions of religion, to conclude by asking whether religion is becoming obsolete or is likely to survive and, if the latter, which functions will sustain its persistence. I’ll consider these seven functions roughly in the inferred sequence of their appearance and disappearance during the history of societal evolution, starting with functions prominent early in human history but less so now, and ending with functions originally absent but prominent recently or now.

An original function of religion was explanation. Pre-scientific traditional peoples offer explanations for everything they encounter, of course without the prophetic ability to distinguish between those explanations that scientists today consider natural and scientific, and those others that scientists now consider supernatural and religious. To traditional peoples, they are all explanations, and those explanations that subsequently became viewed as religious aren’t something separate. For instance, the New Guinea societies in which I have lived offer many explanations for bird behavior that modern ornithologists consider perceptive and still accurate (e.g., the multiple functions of bird calls), along with other explanations that ornithologists no longer accept and now dismiss as supernatural (e.g., that songs of certain bird species are voices of former people who became transformed into birds). Origin myths, like those of tribal people and of the book of Genesis, are widespread to explain the existence of the universe, people, and language diversity. The ancient Greeks, who identified correct scientific explanations for many phenomena, incorrectly invoked gods as supernatural agents to explain sunrises, sunsets, tides, winds, and rain. Creationists, and the majority of Americans today, still invoke God as a “First Cause” who created the universe and its laws and thus accounts for their existence, and who also created every plant and animal species, including the human species. But I’m not aware of creationists continuing to evoke God to explain every sunrise, tide, and wind. Many secular people today, while attributing to God the universe’s origin and its laws, accept that the universe, once thus created, has thereafter run with little or no divine interference.

In modern Western society, religion’s original explanatory role has increasingly become usurped by science. The origins of the universe as we know it are now attributed to the Big Bang and the subsequent operation of the laws of physics. Modern language diversity is no longer explained by origin myths, such as the Tower of Babel or the snapping of the lianas holding the New Guinea ironwood tree, but is instead considered as adequately explained by observed historical processes of language change, as I shall discuss in Chapter 10. Explanations of sunrises, sunsets, and tides are now left to astronomers, and explanations of winds and rain are left to meteorologists. Bird songs are explained by ethology, and the origin of each plant and animal species, including the human species, is left to evolutionary biologists to interpret.

For many modern scientists, the last bastion of religious explanation is God-as-First-Cause: science seemingly can have nothing to say about why the universe exists at all. From my freshman year at Harvard College in 1955, I recall the great theologian Paul Tillich defying his class of hyper-rational undergraduates to come up with a scientific answer to his simple question: “Why is there something, when there could have been nothing?” None of my classmates majoring in the sciences could give Tillich any answer. But they in turn would have objected that Tillich’s own answer “God” consisted merely of putting a name on his lack of an answer. In fact, scientists are working now on Tillich’s question and have proposed answers.

Defusing anxiety

The next function of religion that I’ll discuss is another one that was probably strongest in early societies: religion’s role in defusing our anxiety over problems and dangers beyond our control. When people have done everything realistically within their power, that’s when they are most likely to resort to prayers, rituals, ceremonies, donations to the gods, consulting oracles and shamans, reading omens, observing taboos, and performing magic. All of those measures are scientifically ineffective at producing the desired result. However, by preserving the fiction and convincing ourselves that we are still doing something, aren’t helpless, and haven’t given up, we at least feel in charge, less anxious, and able to go on to make our best effort.

Our craving for relief from feeling helpless is illustrated by a study of religious Israeli women, carried out by anthropologists Richard Sosis and W. Penn Handwerker. During the 2006 Lebanon War the Hizbollah launched Katyusha rockets against the Galilee region of northern Israel, and the town of Tzfat and its environs in particular were hit by dozens of rockets daily. Although siren warnings while rockets were en route alerted Tzfat residents to protect their own lives by taking refuge in bomb shelters, they could do nothing to protect their houses. Realistically, that threat from the rockets was unpredictable and uncontrollable. Nevertheless, about two-thirds of the women interviewed by Sosis and Handwerker recited psalms every day to cope with the stress of the rocket attacks. When they were asked why they did so, a common reply was that they felt compelled “to do something” as opposed to doing nothing at all. Although reciting psalms does not actually deflect rockets, it did provide the chanters with a sense of control as they went through the semblance of taking action. (Of course, they themselves did not give that explanation; they did believe that reciting psalms can protect one’s house from destruction by a rocket.) Compared to women in the same community who did not recite psalms, the psalm reciters had less difficulty falling asleep, had less difficulty concentrating, were less inclined to bursts of anger, and felt less anxious, nervous, tense, and depressed. Thus, they really did benefit, by reducing the risk that natural anxiety over uncontrollable danger would cause them to endanger themselves in a different way by doing something foolish. As all of us who have been in situations of unpredictable and uncontrollable danger know, we do become prone to multiply our problems by thoughtlessness if we can’t master our anxiety.

This function of religion, at its peak already in early religious societies, would have decreased as societies increased their control over life’s course, through state government growing stronger and decreasing the frequency of violence and other dangers, states becoming increasingly able to avert famines by distributing stored food, and (in the last two centuries) the development of science and technology. But it’s hardly the case that traditional people were largely helpless. Instead, they impress us with their ability to use their observations and their experience so as to leave as little room for chance as possible. For instance, New Guineans and other traditional farmers know dozens of varieties of sweet potatoes or other crops, where and how best to grow each one, and how to weed, fertilize, mulch, drain, and irrigate. When !Kung men and other hunters go hunting, they study and interpret animal tracks, thereby estimate the number and distance and speed and direction of movement of their prey, and observe the behavior of other animal species that provide clues to prey presence. Fishermen and sailors without compasses or other instruments can still navigate by understanding movements of the sun and stars, winds, ocean currents, reflections on clouds, seabirds, ocean bioluminescence, and other indicators of position. All peoples post defenses and remain alert against enemy attacks, and form alliances and plan ambushes to attack the enemy first.

But for traditional peoples, even more than for us moderns, there are limits to their effectiveness, and large areas beyond their control. Crop yields are affected by unpredictable droughts, rainfall, hail, wind storms, cold temperatures, and insect pests. There is a large role of chance in the movements of individual animals. Most illnesses lie beyond traditional control because of the limits of traditional medical knowledge. Like the Israeli women who recited psalms but couldn’t control the paths of the rockets, much also remains beyond the control of traditional peoples after they have done their best. They, and we, rebel against remaining inactive and doing nothing. That makes them and us anxious, feeling helpless, prone to make mistakes, and unable to put out our best efforts. That’s where traditional peoples, and still often we today, resort to prayer, rituals, omens, magic, taboos, superstitions, and shamans. Believing that those measures are effective, they and we become less anxious, calmer, and more focused.

One example, studied by the ethnographer Bronislaw Malinowski, comes from the Trobriand Islands near New Guinea, where villagers catch fish in two types of locations requiring different fishing methods: in the sheltered, calm inner lagoon, where one dumps poison into a patch of water and then just picks up the stunned or dead fish; and in the open sea, spearing or netting fish while paddling a canoe through waves and surf. Lagoon fishing is safe, easy, and offers predictable yields; open-sea fishing is dangerous and unpredictable, with large bonanzas if a shoal of fish happens to be running at that particular time and place, but with little profit and much personal risk if one doesn’t happen to encounter a shoal that day. The islanders perform elaborate magical rituals before embarking on open-sea fishing in order to secure safety and success, because much doubt remains even after they have laid the best plans based on experience. But no magic is associated with lagoon fishing: one merely sets out and does it, without uncertainty or anxiety about the predictable result.

Another example is provided by !Kung hunters, whose expertise seems to leave nothing to chance. Little !Kung boys start playing with tiny bows and arrows from the time that they can walk, and begin hunting with their fathers when they reach adolescence. At evening campfires men recount over and over their previous hunts, listen to each other’s stories about who saw what animals where in recent days, and plan the next hunt accordingly. During the hunt itself they remain attuned to sights and sounds of animals and of birds whose behavior may betray the presence of animals, as well as scrutinizing tracks to learn what animal passed by, and where it is likely to be found and to be heading now. One might imagine that these masters of desert hunting skills would have no need for magic. In fact, though, when hunters set out in the morning, there is always a big element of anxiety-provoking uncertainty about where prey will happen to be on that particular morning.

Some !Kung men deal with their anxiety by consulting oracle disks supposed to prophesy what direction will be most promising, and what prey they should be prepared for. Those disks are sets of five or six thin circles of antelope leather graded in diameter from two to three inches, each with its own name and with a recognizable top and bottom. Each man owns a set. A man stacks the disks on the palm of his left hand with the largest disk on top, shakes and blows on the disks, asks a question in a loud ritualized voice, then throws the disks on a garment spread on the ground. A diviner interprets the pattern of disks on the ground according to features that include whether or not they overlap, and which disks land top up or bottom up. The interpretation of the pattern seems to follow few fixed rules, except that disks 1 through 4 landing upside down predict the successful killing of a game animal.

Of course the disks don’t tell the !Kung anything that they don’t already know. !Kung men understand so much about animal behavior that their hunting plan has a good chance of proving successful, whatever the pattern of the disks. Instead, the disk pattern seems to be interpreted imaginatively like a Rorschach test, and serves to psych men up for a day of hunting. The disk ritual is useful in helping them reach agreement about pursuing one direction; choosing one direction, any direction, and sticking to it are preferable to becoming distracted by arguments.

For us today, prayer and ritual and magic are less widespread, because science and knowledge play a larger role in the success of our endeavors. But there remains much that we still can’t control, and many endeavors and dangers where science and technology don’t guarantee success. That’s where we, too, resort to prayers, offerings, and rituals. Prime examples in the recent past have been prayers for safe completion of sea voyages, bountiful harvests, success in war, and especially healing from disease. When doctors can’t predict a patient’s outcome with high probability, and especially when doctors admit that they are helpless, that’s when people are especially likely to pray.

Two specific examples illustrate for us the association between rituals or prayers on the one hand, and uncertain outcome on the other hand. Gamblers in a game of chance often follow their own personal rituals before throwing the dice, but chess-players don’t have such rituals before moving a piece. That’s because dice games are known to be games of chance, but there is no role of chance in chess: if your move costs you the game, you have no excuses, it was entirely your own fault for not foreseeing your opponent’s response. Similarly, farmers wanting to drill a well to find underground water often consult dowsers in western New Mexico, where the area’s local geological complexity results in big unpredictable variation in the depth and quantity of underground water, such that not even professional geologists can predict accurately from surface features the location and depth of underground water. In the Texas Panhandle, though, where the water table lies at a uniform depth of 125 feet, farmers merely drill a well to that depth at a site nearest to where the water is needed; no one uses dowsers, although people are familiar with the method. That is, New Mexico farmers and dice players deal with unpredictability by resorting to rituals just as do Trobriand ocean fishermen and !Kung hunters, while Texas Panhandle farmers and chess-players dispense with rituals just as do Trobriand lagoon fishermen.

In short, religious (and also non-religious) rituals are still with us to help us deal with anxiety in the face of uncertainty and danger. However, this function of religion was much more important in traditional societies facing greater uncertainty and danger than do modern Westernized societies.

Providing comfort

Let’s now turn to a function of religion that must have expanded over the last 10,000 years: to provide comfort, hope, and meaning when life is hard. A specific example is to comfort us at the prospect of our own death and at the death of a loved one. Some mammals—elephants are a striking example—appear to recognize and mourn the death of a close companion. But we have no reason to suspect that any animal except us humans understands that, one day, it too will die. We would inevitably have realized that that fate lay in store for us as we acquired self-consciousness and better reasoning power, and began to generalize from watching our fellow band members die. Almost all observed and archaeologically attested human groups demonstrate their understanding of death’s significance by not just discarding their dead but somehow providing for them by burial, cremation, wrapping, mummification, cooking, or other means.

It’s frightening to see someone who was recently warm, moving, talking, and capable of self-defense now cold, motionless, silent, and helpless. It’s frightening to imagine that happening to us, too. Most religions provide comfort by in effect denying death’s reality, and by postulating some sort of afterlife for a soul postulated as associated with the body. One’s soul together with a replica of one’s body may go to a supernatural place called heaven or some other name; or one’s soul may become transformed into a bird or another person here on Earth. Religions that proclaim an afterlife often go further and use it not just to deny death but also to hold out hope for something even better awaiting us after death, such as eternal life, reunion with one’s loved ones, freedom from care, nectar, and beautiful virgins.

In addition to our pain at the prospect of death, there are many other pains of life for which religion offers comfort in various ways. One way is to “explain” a suffering by declaring it not to be a meaningless random event but to possess some deeper meaning: e.g., it was to test you for your worthiness for the afterlife, or it was to punish you for your sins, or it was an evil done to you by some bad person whom you should hire a sorcerer to identify and kill. Another way is to promise that amends will be made to you in the afterlife for your suffering: yes, you suffered here, but never fear, you will be rewarded after your death. Still a third way is to promise not only that will your suffering be offset in a happy afterlife, but also that those who did you evil will have a miserable afterlife. While punishing your enemies on Earth gives you only finite revenge and satisfaction, the eternal exquisite tortures that they will suffer after death in Dante’s Inferno will guarantee you all the revenge and satisfaction that you could ever long for. Hell has a double function: to comfort you by smiting your enemies whom you were unable to smite yourself here on Earth; and to motivate you to obey your religion’s moral commands, by threatening to send you too there if you misbehave. Thus, the postulated afterlife resolves the paradox of theodicy (the co-existence of evil and a good God) by assuring you not to worry; all scores will be settled later.

This comforting function of religion must have emerged early in our evolutionary history, as soon as we were smart enough to realize that we’d die, and to wonder why life was often painful. Hunter-gatherers do often believe in survival after death as spirits. But this function expanded greatly later with the rise of so-called world-rejecting religions, which assert not only that there is an afterlife, but that it’s even more important and long-lasting than this earthly life, and that the overriding goal of earthly life is to obtain salvation and prepare you for the afterlife. While world rejection is strong in Christianity, Islam, and some forms of Buddhism, it also characterizes some secular (i.e., non-religious) philosophies such as Plato’s. Such beliefs can be so compelling that some religious people actually reject the worldly life. Monks and nuns in residential orders do so insofar as they live, sleep, and eat separately from the secular world, although they may go out into it daily in order to minister, teach, and preach. But there are other orders that isolate themselves as completely as possible from the secular world. Among them were the Cistercian order, whose great monasteries at Rievaulx, Fountains Abbey, and Jerveaulx in England remain England’s best-preserved monastic ruins because they were erected far from towns and hence were less subject to plunder and re-use after they were abandoned. Even more extreme was the world rejection practiced by a few Irish monks who settled as hermits in otherwise uninhabited Iceland.

Small-scale societies place much less emphasis on world rejection, salvation, and the afterlife than do large-scale, more complex and recent societies. There are at least three reasons for this trend. First, social stratification and inequality have increased, from egalitarian small-scale societies to large complex societies with their kings, nobles, elite, rich, and members of highly ranked clans contrasting with their mass of poor peasants and laborers. If everybody else around you is suffering as much as you are, then there is no unfairness to be explained, and no visible example of the good life to which to aspire. But the observation that some people have much more comfortable lives and can dominate you takes a lot of explaining and comforting, which religion offers.

A second reason why large, complex societies emphasize comforting and the afterlife more than do small-scale societies is that archaeological and ethnographic evidence shows that life really did become harder as hunter-gatherers became farmers and assembled in larger societies. With the transition to agriculture, the average daily number of work hours increased, nutrition deteriorated, infectious disease and body wear increased, and lifespan shortened. Conditions deteriorated even further for urban proletariats during the Industrial Revolution, as work days lengthened, and as hygiene, health, and pleasures diminished. Finally, as we shall discuss below, complex populous societies have more formalized moral codes, more black-and-white emphasis on good and evil, and bigger resulting problems of theodicy: why, if you yourself are behaving virtuously and obeying the laws, do law-breakers and the rest of the world get away with being cruel to you?

All three of these reasons suggest why the comforting function of religion has increased in more populous and recent societies: it’s simply that those societies inflict on us more bad things for which we crave comfort. This comforting role of religion helps explain the frequent observation that misfortune tends to make people more religious, and that poorer social strata, regions, and countries tend to be more religious than richer ones: they need more comforting. Among the world’s nations today, the percentage of citizens who say that religion is an important part of their daily lives is 80%–99% for most nations with per-capita gross domestic products (GDP) under $10,000, but only 17%–43% for most nations with per-capita GDP over $30,000. (That doesn’t account for high religious commitment in the rich U.S., which I’ll mention in the next paragraph.) Even within just the U.S., there appear to be more churches and more church attendance in poorer areas than in richer areas, despite the greater resources and leisure time available to build and attend churches in richer areas. Within American society, the highest religious commitment and the most radical Christian branches are found among the most marginalized, underprivileged social groups.

It may initially seem surprising that religion has been maintaining itself or even growing in the modern world, despite the rise in two factors already mentioned as undermining religion: science’s recent usurpation of religion’s original explanatory role; and our increased technology and societal effectiveness reducing dangers that lie beyond our control and thus inviting prayer. That religion nevertheless shows no signs of dying out may be due to our persistent quest for “meaning.” We humans have always sought meaning in our lives that can otherwise seem meaningless, purposeless, and evanescent, and in a world full of unpredictable unfortunate events. Now along comes science, seeming to say that “meaning” isn’t meaningful, and that our individual lives really are meaningless, purposeless, and evanescent except as packages of genes for which the measure of success is just self-propagation. Some atheists would maintain that the problem of theodicy doesn’t exist; good and evil are just human definitions; if cancer or a car crash kills X and Y but not A and B, that’s just a random catastrophe; there isn’t any afterlife; and if you’ve suffered or been abused here on Earth, it won’t be fixed for you in the afterlife. If you respond to those atheists, “I don’t like to hear that, tell me it’s not true, show me some way in which science has its own way of providing meaning,” those atheists’ response would be “Your request is in vain, get over it, stop looking for meaning, there isn’t any meaning—it’s just that, as Donald Rumsfeld said of looting during the war in Iraq, ‘Stuff happens!’” But we still have our same old brains that crave meaning. We have several million years of evolutionary history telling us, “Even if that’s true, I don’t like it and I’m not going to believe it: if science won’t give me meaning, I’ll look to religion for it.” That’s probably a significant factor in the persistence and even growth of religion in this century of growth in science and technology. It may contribute part—surely not all, but perhaps part—of the explanation for why the United States, the country with the most highly developed scientific and technological establishment, is also the most religious among wealthy First World countries. The greater gulf between rich and poor people in the U.S. than in Europe may be another part of the explanation.

Organization and obedience

The remaining four features of religion that I’ll discuss—standardized organization, preaching political obedience, regulating behavior towards strangers by means of formal moral codes, and justifying wars—were absent in small-scale societies, appeared with the rise of chiefdoms and states, and have declined again in modern secular states. A defining feature of modern religions that we take for granted is standardized organization. Most modern religions have full-time priests, alias rabbis, ministers, imams, or whatever else they may be called, who receive either a salary or else life’s necessities. Modern religions also have churches (alias temples, synagogues, mosques, etc.). Within any given sect, all of its churches use a standardized sacred book (Bible, Torah, Koran, etc.), rituals, art, music, architecture, and clothing. A practising Catholic who has grown up in Los Angeles and visits New York City can celebrate Sunday mass in a New York Catholic church and find all those features familiar. In religions of small-scale societies, on the other hand, all of those features either aren’t standardized (rituals, art, music, clothing) or don’t exist at all (full-time priests, dedicated churches, sacred books). While small-scale societies may have their shamans, and some of those shamans may receive fees or gifts, the shamans are not full-time professionals: they have to hunt, gather, and grow crops like every other able-bodied adult in their band or tribe.

Historically, those organizational features of religion arose to solve a new problem emerging as ancient human societies became richer, more populous, and both obliged and enabled to become more centralized. Band and tribal societies are too small and unproductive to generate food surpluses that could feed full-time priests, chiefs, tax collectors, potters, shamans, or specialists of any sort. Instead, every adult has to acquire his or her own food by hunting, gathering, or farming himself or herself. Only larger and more productive societies generate surpluses that can be used to feed chiefs and other leaders or craft specialists, none of whom grow or hunt food.

How did such a diversion of food come about? A dilemma results from the confluence of three self-evident facts: populous societies are likely to defeat small societies; populous societies require full-time leaders and bureaucrats, because 20 people can sit around a campfire and reach a consensus but 20,000,000 people cannot; and full-time leaders and bureaucrats must be fed. But how does the chief or king get the peasants to tolerate what is basically the theft of their food by classes of social parasites? This problem is familiar to the citizens of any democracy, who ask themselves the same question at each election: what have the incumbents done since the last election to justify the fat salaries that they pay themselves out of the public coffers?

The solution devised by every well-understood chiefdom and early state society—from ancient Egypt and Mesopotamia, through Polynesian Hawaii, to the Inca Empire—was to proclaim an organized religion with the following tenets: the chief or king is related to the gods, or even is a god; and he or she can intercede with the gods on behalf of the peasants, e.g., to send rain or to ensure a good harvest. The chief or king also renders valuable services by organizing the peasants to construct public works, such as roads, irrigation systems, and storehouses that benefit everybody. In return for those services, the peasants should feed the chief and his priests and tax collectors. Standardized rituals, carried out at standardized temples, serve to teach those religious tenets to the peasants so that they will obey the chief and his lackeys. Also fed by food collected from the peasants are armies obedient to the chief or king, with which the chief can conquer neighboring lands and thereby acquire more territory for the benefit of his peasants. Those armies bring two further advantages to the chief: wars against neighbors may enlist the energy of ambitious young nobles who might otherwise scheme to overthrow the chief; and the armies are ready to put down revolts by the peasants themselves. As early theocratic states evolved into the empires of ancient Babylon and Rome and commandeered more and more food and labor, the architectural trappings of state religions became more elaborate. That’s why Karl Marx viewed religion as the opium of the people (Table 9.1), and an instrument of class oppression.

Of course, within recent centuries in the Judeo-Christian world, this trend has been reversed, and religion is much less than before the handmaiden of the state. Politicians and the upper classes now rely on means other than assertions of divinity to persuade or coerce all of us peasants. But the fusion of religion and state persists in some Muslim countries, Israel, and (until recently) Japan and Italy. Even the United States government invokes God on its currency and places official chaplains in Congress and in the armed forces, and every American president (whether Democrat or Republican) intones “God bless America” at the close of speeches.

Codes of behavior towards strangers

Yet another attribute of religion that became important in state societies but that didn’t exist in the smallest societies was to dictate moral concepts of behavior towards strangers. All major world religions teach what is right, what is wrong, and how one should behave. But this link between religion and morality is weaker or absent, especially as regards behavior towards strangers, in the New Guinea societies of which I have experience. Instead, social obligations there depend heavily on relationships. Because a band or tribe contains only a few dozen or a few hundred individuals respectively, everyone knows everyone else and their relationships. One owes different obligations to different blood relatives, to relatives by marriage, to members of one’s own clan, and to fellow villagers belonging to a different clan.

Those relationships determine, for example, whether you may refer to people by their names, marry them, or demand that they share their food and house with you. If you get into a fight with another tribe member, everyone else in the tribe is related to or knows both of you and pulls you apart. The problem of behaving peacefully towards unfamiliar individuals doesn’t arise, because the only unfamiliar individuals are members of enemy tribes. Should you happen to meet an unfamiliar person in the forest, of course you try to kill him or else to run away; our modern custom of just saying hello and starting a friendly chat would be suicidal.

Thus, a new problem arose by around 7,500 years ago, when some tribal societies evolved into chiefdoms comprising thousands of individuals—a far greater number than any single person can know by name and relationship. Emergent chiefdoms and states faced big problems of potential instability, because the old tribal rules of behavior no longer sufficed. If you encountered an unfamiliar member of your chiefdom and fought with him according to tribal rules of behavior, a brawl would result as your relatives jumped in on your side and his relatives jumped in on his side. A death in such a brawl would spark efforts by the victim’s relatives to kill one of the murderer’s relatives in revenge. What’s to save the society from collapsing in an incessant orgy of brawls and revenge murders?

The solution to this dilemma of large societies is the one used in our own society, and documented in all chiefdoms and early states for which we have information. Rules of peaceful behavior apply between all members of the society, regardless of whether some individual whom you encounter is familiar to you or a stranger. The rules are enforced by the political leaders (chiefs or kings) and their agents, who justify the rules by a new function of religion. The gods or supernatural agents are presumed to be the authors of the rules, codified in formal codes of morality. People are taught from childhood onward to obey the rules, and to expect severe punishment for breaking them (because now an attack on another person is also an offense against the gods). Prime examples familiar to Jews and Christians are the Ten Commandments.

In recent secularized societies, such rules of moral behavior within society have moved beyond their religious origins. The reasons why atheists, as well as many believers, now don’t kill their enemies derive from values instilled by society, and from fear of the potent hand of the law rather than fear of the wrath of God. But from the rise of chiefdoms until the recent rise of secular states, religion justified codes of behavior and thereby enabled people to live harmoniously in large societies where one encounters strangers frequently. Religion’s function in permitting strangers to live peacefully together, and its function in teaching the masses to obey their political leaders, constitute the twin aspects of the often-discussed roles of religion in maintaining social order. As Voltaire remarked cynically, “If God did not exist, he would have to be invented.” Depending on one’s perspective, these roles of religion have been regarded as either positive (promoting social harmony) or negative (promoting exploitation of the masses by oppressive elites).

Justifying war

Another new problem faced by emergent chiefdoms and states, but not by the bands and tribes of previous history, involved wars. Because tribes primarily use relationship by blood or marriage, not religion, to justify rules of conduct, tribesmen face no moral dilemmas in killing members of other tribes with whom they have no relationship. But once a state invokes religion to require peaceful behavior toward fellow citizens with whom one has no relationship, how can a state convince its citizens to ignore those same precepts during wartime? States permit, indeed they command, their citizens to steal from and kill citizens of other states against which war has been declared. After a state has spent 18 years teaching a boy “Thou shalt not kill,” how can the state turn around and say “Thou must kill, under the following circumstances,” without getting its soldiers hopelessly confused and prone to kill the wrong people (e.g., fellow citizens)?

Again, in recent as well as in ancient history, religion comes to the rescue with a new function. The Ten Commandments apply only to one’s behavior toward fellow citizens within the chiefdom or state. Most religions claim that they have a monopoly on the truth, and that all other religions are wrong. Commonly in the past, and all too often today as well, citizens are taught that they are not merely permitted, but actually obliged, to kill and steal from believers in those wrong religions. That’s the dark side of all those noble patriotic appeals: for God and country, por Dios y por España, Gott mit uns, etc. It in no way diminishes the guilt of the current crop of murderous religious fanatics to acknowledge that they are heirs to a long, widespread, vile tradition.

The Bible’s Old Testament is full of exhortations to be cruel to heathens. Deuteronomy 20:10–18, for example, explains the obligation of the Israelites to practice genocide: when your army approaches a distant city, you should enslave all its inhabitants if it surrenders, and kill all its men and enslave its women and children and steal their cattle and everything else if it doesn’t surrender. But if it’s a city of the Canaanites or Hittites or any of those other abominable believers in false gods, then the true God commands you to kill everything that breathes in the city. The book of Joshua describes approvingly how Joshua became a hero by carrying out those instructions, slaughtering all the inhabitants of over 400 cities. The book of rabbinical commentaries known as the Talmud analyzes the potential ambiguities arising from conflicts between those two principles of “Thou shalt not kill [believers in thine own God]” and “Thou must kill [believers in another god].” For instance, according to some Talmudic commentators, an Israelite is guilty of murder if he intentionally kills a fellow Israelite; is innocent if he intentionally kills a non-Israelite; and is also innocent if he kills an Israelite while throwing a stone into a group consisting of nine Israelites plus one heathen (because he might have been aiming at the one heathen).

In fairness, this outlook is more characteristic of the Old Testament than of the New Testament, whose moral principles have moved far in the direction of defining one’s dealings with anyone—at least in theory. But in practice, of course, some of history’s most extensive genocides were committed by European Christian colonialists against non-Europeans, relying for moral justification on the New as well as the Old Testament.

Interestingly, among New Guineans, religion is never invoked to justify killing or fighting with members of an out-group. Many of my New Guinea friends have described to me their participation in genocidal attacks on neighboring tribes. In all those accounts, I have never heard the slightest hint of any religious motive, of dying for God or the true religion, or of sacrificing oneself for any idealistic reason whatsoever. In contrast, the religion-supported ideologies that accompanied the rise of states instilled into their citizens the obligation to obey the ruler ordained by God, to obey moral precepts like the Ten Commandments only with respect to fellow citizens, and to be prepared to sacrifice their lives while fighting against other states (i.e., heathens). That’s what makes societies of religious fanatics so dangerous: a tiny minority of their adherents (e.g., 19 of them on September 11, 2001) die for the cause, and the whole society of fanatics thereby succeeds at killing far more of its perceived enemies (e.g., 2,996 of them on September 11, 2001). Rules of bad behavior toward out-groups reached their high point in the last 1,500 years, as fanatical Christians and Muslims inflicted death, slavery, or forced conversion on each other and on the heathen. In the 20th century, European states added secular grounds to justify killing millions of citizens of other European states, but religious fanaticism is still strong in some other societies.

Badges of commitment

Secular people remain puzzled and troubled by several features of religion. Foremost among those are its regular association with irrational supernatural beliefs, such that each religion has a different set of such beliefs and adheres firmly to them but dismisses most such beliefs of other religions; its frequent promotion of costly, even self-mutilating or suicidal behaviors that would seem to make people less rather than more disposed to be religious; and its apparent basic hypocrisy of preaching a moral code and often claiming universality, while at the same time excluding many or most people from application of that code and urging the killing of them. How can these troubling paradoxes be explained? There are two solutions that I have found useful.

One solution is to recognize the need for adherents of a particular religion to display some reliable “badge” of commitment to that religion. Believers spend their lives with each other and constantly count on each other for support, in a world where many or most other people adhere to other religions, may be hostile to your own religion, or may be skeptical about all religions. Your safety, prosperity, and life will depend on your identifying correctly your fellow believers, and on your convincing them that they can trust you just as you trust them. What proofs of your and their commitment are believable?

To be believable, the proofs must be visible things that no one would or could fake for treacherous gain of temporary advantage. That’s why religious “badges” are always costly: high commitments of time to learn and regularly practise rituals, prayers, and songs and to undertake pilgrimages; high commitments of resources, including money, gifts, and sacrificed animals; publicly espousing rationally implausible beliefs that others will ridicule as silly; and publicly undergoing or displaying signs of painful permanent body mutilation, including cutting and bleeding sensitive parts of one’s body, disfiguring operations on one’s genitals, and self-amputation of finger joints. If you see that someone has made those expensive commitments with lifelong consequences, then they’ve convinced you much more effectively than if they merely told you, “Trust me, I’m with you, I’m wearing the right sort of hat (but I might have bought it cheaply yesterday and might discard it tomorrow).” For essentially the same reason, evolutionary biologists recognize that many animal signals as well (such as a peacock’s tail) have evolved to be costly, precisely because that makes them believable. When a female peahen sees a male peacock with a big tail displaying to her, she can be sure that such a male, capable of growing and surviving with such a big tail, really must have better genes and be better nourished than a male pretending to be superior but with just a small tail.

An interesting example of how religion fosters group cooperation and commitment comes from survival rates of American communes. Throughout the history of the United States continuing into modern times, people have experimented with forming communes where people can live together with other people chosen as sharing their ideals. Some of those communes share religious ideals, and others are non-religiously motivated; many non-religious communes were formed in the U.S. in the 1960s and 1970s. But all communes are subject to financial, practical, social, sexual, and other pressures, and to competition from the attractions of the outside world. The vast majority of communes disband, whether gradually or explosively, within the lifetimes of their founders. For example, in the 1960s one friend of mine was a co-founder of a commune in a beautiful, peaceful, but remote area of Northern California. Gradually, though, the other founder members drifted away because of the isolation, boredom, social tensions, and other reasons, until my friend was the last person left. She still lives there, but now just as a single person, no longer a member of a commune.

Richard Sosis compared the fates of several hundred religious and secular American communes founded in the 19th and early 20th centuries. Almost all eventually dissolved, except for the extremely successful colonies of the religious group known as Hutterites: all 20 Hutterite colonies that were in Sosis’s sample survived. Leaving aside those Hutterite colonies, 199 sampled colonies eventually disbanded or died out, always preceded by a loss of faith in the group’s ideology, and sometimes also by natural disasters, death of a charismatic leader, or hostility of outsiders. However, the annual probability of dissolution was four times higher for the secular communes than for the religious communes. Evidently, religious ideologies are more effective than secular ideologies at persuading members to maintain a possibly irrational commitment, to refrain from deserting even when it would make rational sense to do so, and to deal with the constant challenges of living in a community that holds property in common and that is at high risk of being abused by free-riding members. In Israel as well, where for many decades there have been both religious kibbutzim and a much greater number of secular kibbutzim, the religious kibbutzim have been more successful than the secular ones in every year, despite the high costs imposed on religious kibbutzim by their religious practices (e.g., abstaining from all labor one day a week).

Measures of religious success

The other solution that I have found useful for resolving religion’s paradoxes is the approach of evolutionary biologist David Sloan Wilson. He notes that a religion serves to define a human group competing with other human groups espousing different religions. The most straightforward measure of a religion’s relative success is its number of adherents. Why does the world today hold over a billion Catholics, about 14,000,000 Jews, and no Albigensian Manichaeans (members of a formerly numerous Christian sect believing in the dual existence of evil and good supernatural forces locked in eternal struggle)?

Wilson proceeds by recognizing that a religion’s number of adherents depends on the balance between several processes tending to increase the number of adherents and several processes tending to decrease that number. The number of adherents is increased by believers giving birth to children and successfully raising their children in that faith, and by conversions of adherents of other religions or previously non-religious people. The number is decreased by deaths of adherents, and by losses of adherents to conversion to other religions. One might pause at this point and say, “Of course, that’s obvious, so what?—how does that help me understand why Catholics believing in Christ’s resurrection outnumber Jews who don’t?” The power of Wilson’s approach is that it provides a framework for examining separate effects of a religion’s beliefs or practices on those various processes increasing or decreasing the number of adherents. Some of the results are straightforward, while others are subtle. It turns out that religions practise widely different strategies for achieving success.

For example, the American religion known as the Shaker movement was for a period in the 19th century very successful, despite demanding celibacy of its believers and thus lacking completely the commonest method by which religions propagate themselves (by having children). The Shakers achieved their success entirely by winning converts for many decades. At the opposite extreme, Judaism has persisted for several thousand years despite not seeking converts. Not surprisingly, Christianity and Islam, which do proselytize, have far more adherents than does Judaism, but Judaism has nevertheless persisted because of other factors contributing to its demographic growth: relatively high birth rates, low death rates except at times of persecution, emphasis on education to generate economic opportunities, strong mutual help, and low losses by conversion of Jews to other religions. As for Albigensian Manichaeans, their disappearance was only indirectly due to their belief that the forces of evil and of good are locked in eternal struggle. It wasn’t the case that that belief discouraged Albigensians from having children, or that it was so implausible as to prevent their winning converts. Instead, that belief was anathema to mainstream Catholics, who declared a holy war against the Albigensians, eventually besieged and captured their stronghold, and burned all remaining Albigensians there to death.

More subtle reasons emerge from Wilson’s framework for answering one of the biggest questions of Western religious history. Why, among the innumerable tiny Jewish sects competing with each other and with non-Jewish groups within the Roman Empire in the first century AD, did the one of them that became Christianity emerge as the dominant religion three centuries later? In late Roman times Christianity’s distinctive features contributing to this outcome included its active proselytizing (unlike mainstream Judaism), its practices promoting having more babies and enabling more of them to survive (unlike contemporary Roman society), its opportunities for women (in contrast to Judaism and Roman paganism at that time, and to later Christianity), its social institutions resulting in lower death rates of Christians than of Romans from plagues, and the Christian doctrine of forgiveness. That doctrine, which is often misunderstood as the simplistic notion of indiscriminately turning the other cheek, actually proves to be part of a complex, context-dependent system of responses ranging from forgiveness to retaliation. Under certain circumstances, experimental tests carried out by playing simulation games show that forgiving someone who has done you one wrong may really be the response most likely to gain you advantages in the future.

Another example of the use of Wilson’s framework involves the success of Mormonism, which has been among the most rapidly growing religions of the last two centuries. Non-Mormons tend to doubt the claim I cited earlier, by Mormonism’s founder Joseph Smith, that the angel Moroni appeared to him on September 21, 1823, to reveal golden plates buried on a hilltop near Manchester village in western New York State and awaiting translation (Table 9.2). Non-Mormons also doubt the sworn statements of 11 witnesses (Oliver Cowdery, Christian Whitmer, Hiram Page, and 8 others) who claimed to have seen and handled the plates. Hence non-Mormons may wonder: how have those apparently implausible claims led to the explosive growth of Mormonism?

Wilson’s approach involves realizing that a religion’s success in increasing its number of adherents does not depend on whether its tenets happen to be true, but instead on whether those tenets and associated practices motivate the religion’s adherents to conceive and successfully rear children, win converts, constitute a smoothly functioning society, or do all of those things. In Wilson’s words, “Even massively fictitious beliefs can be adaptive, as long as they motivate behaviors that are adaptive in the real world…. Factual knowledge is not always sufficient by itself to motivate an adaptive behavior. At times a symbolic belief system that departs from factual reality fares better.”

In the case of Mormonism, its tenets and practices have been outstandingly successful at promoting demographic growth. Mormons tend to have many children. They form a strongly supportive and interdependent society offering a full and satisfying social life and incentives to work. They emphasize proselytizing; young Mormons are expected to devote up to two years of their lives to winning converts, either overseas or else near home. Mormons are expected to pay to their church an annual tithe equaling 10% of their income (in addition to paying the usual U.S. federal, state, and local taxes). These high demands for commitment of time and resources guarantee that those who choose to become or remain Mormons take their faith seriously. As for the supposed implausibility of the statements of Joseph Smith and his 11 witnesses about divine revelations via the golden plates—what, really, is the difference between those statements and the biblical accounts of divine revelations to Jesus and to Moses, except for millennia of elapsed time and our differing skepticisms derived from our different upbringings?

What does Wilson have to say about the basic hypocrisy common among religions, in preaching noble moral principles while urging the killing of believers in other religions? Wilson’s response is that a religion’s success (or its “fitness,” to use the language of evolutionary biology) is relative and can be defined only by comparison with the successes of other religions. Whether one likes it or not, religions can increase, and often have increased, their “success” (defined as the number of their adherents) by killing or forcibly converting adherents of other religions. As Wilson writes, “Whenever I strike up a conversation about religion, I am likely to receive a litany of evils perpetrated in God’s name. In most cases, these are horrors committed by religious groups against other groups. How can I call religion adaptive in the face of such evidence? The answer is ‘easily,’ as long as we understand fitness in relative terms. It is important to stress that a behavior can be explained from an evolutionary perspective without being morally condoned.”

Changes in religion’s functions

Let’s finally return to my initial question about the functions and definition of religion. We now see why religion is so difficult to define: because it has changed its functions as it has evolved, just as have electric organs. In fact, it has changed functions even more than have electric organs, which have adopted only six functions, compared with the seven functions variously characterizing religions (Figure 9.1). Of those seven functions, four were entirely absent at one stage of religion’s history, and five were still present but in decline at another stage. Two functions had already appeared and were at their peak by the time of the emergence of intelligent questioning humans before 50,000 BC, and have been in steady decline in recent millennia: supernatural explanation (in steeper decline), and defusing anxiety about uncontrollable dangers through ritual (in gentler decline). The other five functions were absent (four of them) or weak (the fifth) in early intelligent humans, rose to a peak in chiefdoms and early states (three of them) or late Renaissance states (two of them), and have declined somewhat or sharply since that peak.

Figure 9.1 Religion’s functions changing through time

Those shifts of function make it harder to define religion than to define electric organs, because electric organs at least all share the trait of setting up detectable electric fields in the surrounding medium, whereas there is no single characteristic shared by all religions. At the risk of coming up with yet another definition to add to those of Table 9.1, I’d now propose: “Religion is a set of traits distinguishing a human social group sharing those traits from other groups not sharing those traits in identical form. Included among those shared traits is always one or more, often all three, out of three traits: supernatural explanation, defusing anxiety about uncontrollable dangers through ritual, and offering comfort for life’s pains and the prospect of death. Religions other than early ones became co-opted to promote standardized organization, political obedience, tolerance of strangers belonging to one’s own religion, and justification of wars against groups holding other religions.” That definition of mine is at least as tortured as the most tortured definitions already in Table 9.1, but I think that it corresponds to reality.

What about religion’s future? That depends on what shape the world will be in 30 years from now. If living standards rise all around the world, then religion’s functions numbers 1 and 4–7 of Figure 9.1 will continue to decline, but functions 2 and 3 seem to me likely to persist. Religion is especially likely to continue to be espoused for claiming to offer meaning to individual lives and deaths whose meaning may seem insignificant from a scientific perspective. Even if science’s answer to the search for meaning is true, and if religion’s meaning is an illusion, many people will continue not to like science’s answer. If, on the other hand, much of the world remains mired in poverty, or if (worse yet) the world’s economy and living standards and peace deteriorate, then all functions of religion, perhaps even supernatural explanation, may undergo a resurgence. My children’s generation will experience the answers to these questions.

Multilingualism

One evening, while I was spending a week at a mountain forest campsite with 20 New Guinea Highlanders, conversation around the campfire was going on simultaneously in several different local languages plus two lingua francas of Tok Pisin and Motu, as commonly happens when a group of New Guineans from different tribes happens to be gathered. I had already become accustomed to encountering a new language approximately every 10 or 20 miles as I walked or drove through the New Guinea Highlands. I had just come from the lowlands, where a New Guinea friend had told me how five different local languages were spoken within a few miles of his village, how he had picked up those five languages as a child just by playing with other children, and how he had learned three more languages after he began school. And so, out of curiosity that evening, I went around the campfire circle and asked each man to name each language that he “spoke,” i.e., knew well enough to converse in.

Among those 20 New Guineans, the smallest number of languages that anyone spoke was 5. Several men spoke from 8 to 12 languages, and the champion was a man who spoke 15. Except for English, which New Guineans often learn at school by studying books, everyone had acquired all of his other languages socially without books. Just to anticipate your likely question—yes, those local languages enumerated that evening really were mutually unintelligible languages, not mere dialects. Some were tonal like Chinese, others were non-tonal, and they belonged to several different language families.

In the United States, on the other hand, most native-born Americans are monolingual. Educated Europeans commonly know two or three languages, sometimes more, having learned in school the languages other than their mother tongue. The linguistic contrast between that New Guinea campfire and modern American or European experience illustrates widespread differences between language use in small-scale societies and in modern state societies—differences that will increase in coming decades. In our traditional past, as is still true in modern New Guinea, each language had far fewer speakers than do the languages of modern states; probably a higher proportion of the population was multilingual; and second languages were learned socially beginning in childhood, rather than by formal study later in schools.

Sadly, languages are now vanishing more rapidly than at any previous time in human history. If current trends continue, 95% of the languages handed down to us from the tens of thousands of years of history of behaviorally modern humans will be extinct or moribund by the year 2100. Half of our languages will actually have become extinct by then, most of the remainder will be dying languages spoken only by old people, and only a small minority will be “live” languages still being transmitted from parents to children. Languages are disappearing so rapidly (about one every nine days), and there are so few linguists studying them, that time is running out even to describe and record most languages before they disappear. Linguists face a race against time similar to that faced by biologists, now aware that most of the world’s plant and animal species are in danger of extinction and of disappearing even before they can be described. We do hear much anguished discussion about the accelerating disappearance of birds and frogs and other living species, as our Coca-Cola civilization spreads over the world. Much less attention has been paid to the disappearance of our languages, and to their essential role in the survival of those indigenous cultures. Each language is the vehicle for a unique way of thinking and talking, a unique literature, and a unique view of the world. Hence looming over us today is the tragedy of the impending loss of most of our cultural heritage, linked with the loss of most of our languages.

Why are languages vanishing at such a catastrophic rate? Does it really matter? Is our current plethora of languages good or bad for the world as a whole, and for all those traditional societies still speaking languages now at risk of vanishing? Many of you readers may presently disagree with what I just said, about language loss being a tragedy. Perhaps you instead think that diverse languages promote civil war and impede education, that the world would be better off with far fewer languages, and that high language diversity is one of those features of the world of yesterday that we should be glad to be rid of—like chronic tribal warfare, infanticide, abandonment of the elderly, and frequent starvation.

For each of us as individuals, does it do us good or harm to learn multiple languages? It certainly takes much time and effort to learn a language and become fluent in it; would we be better off devoting all that time and effort to learning more obviously useful skills? I think that the answers emerging to these questions about the value of traditional multilingualism, both to societies and to individuals, will intrigue you readers, as they intrigued me. Will this chapter convince you to bring up your next child to be bilingual, or will it instead convince you that the whole world should switch to speaking English as quickly as possible?

The world’s language total

Before we can tackle those big questions, let’s start with some preamble about how many languages still exist today, how they developed, and where in the world they are spoken. The known number of distinct languages still spoken or recently spoken in the modern world is around 7,000. That huge total may astonish many readers, because most of us could name only a few dozen languages, and the vast majority of languages are unfamiliar to us. Most languages are unwritten, spoken by few people, and spoken far from the industrial world. For example, all of Europe west of Russia has fewer than 100 native languages, but the African continent and the Indian subcontinent have over 1,000 native languages each, the African countries of Nigeria and Cameroon 527 and 286 languages respectively, and the small Pacific island nation of Vanuatu (area less than 5,000 square miles) 110 languages. The world’s highest language diversity is on the island of New Guinea, with about 1,000 languages and an unknown but apparently large number of distinct language families crammed into an area only slightly larger than Texas.

Of those 7,000 languages, 9 “giants,” each the primary language of 100 million or more people, account for over one-third of the world’s population. In undoubted first place is Mandarin, the primary language of at least 700 million Chinese, followed by Spanish, English, Arabic, Hindi, Bengali, Portuguese, Russian, and Japanese in approximately that sequence. If we relax our definition of “big languages” to mean the top 70 languages—i.e., the top 1% of all languages—then we have encompassed the primary languages of almost 80% of the world’s people.

But most of the world’s languages are “little” languages with few speakers. If we divide the world’s nearly 7 billion people by 7,000 languages, we obtain 1 million people as the average number of speakers of a language. Because that average is distorted by the 100-million-plus speakers of just 9 giant languages, a better measure of a “typical” language is to talk about the “median” number of speakers—i.e., a language such that half of the world’s languages have more speakers, and the other half have fewer speakers. That median number is only a few thousand speakers. Hence half of the world’s languages have under a few thousand speakers, and lots of them have between only 60 and 200 speakers.

But such discussions of numbers of languages, and numbers of language speakers, force us to confront the question that I anticipated in describing my New Guinea campfire language poll at the beginning of this chapter. What’s the difference between a distinct language and a mere dialect of another language? Speech differences between neighboring populations intergrade completely; neighbors may understand 100%, or 92%, or 75%, or 42%, or nothing at all of what each other says. The cut-off between language and dialect is often arbitrarily taken at 70% mutual intelligibility: if neighboring populations with different ways of speaking can understand over 70% of each other’s speech, then (by that definition) they’re considered just to speak different dialects of the same language, while they are considered as speaking different languages if they understand less than 70%.

But even that simple, arbitrary, strictly linguistic definition of dialects and languages may encounter ambiguities when we try to apply it in practice. One practical difficulty is posed by dialect chains: in a string of neighboring villages ABCDEFGH, each village may understand both villages on either side, but villages A and H at opposite ends of the chain may not be able to understand each other at all. Another difficulty is that some pairs of speech communities are asymmetrical in their intelligibility: A can understand most of what B says, but B has difficulty understanding A. For instance, my Portuguese-speaking friends tell me that they can understand Spanish-speakers well, but my Spanish-speaking friends have more difficulty understanding Portuguese.

Those are two types of problems in drawing a line between dialects and languages on strictly linguistic grounds. A bigger problem is that languages are defined as separate not just by linguistic differences, but also by political and self-defined ethnic differences. This fact is expressed in a joke that one often hears among linguists: “A language is a dialect backed up by its own army and navy.” For instance, Spanish and Italian might not pass the 70% test for being ranked as different languages rather than mere dialects: my Spanish and Italian friends tell me that they can understand most of what each other says, especially after a little practice. But, regardless of what a linguist applying this 70% test might say, every Spaniard and Italian, and everybody else, will unhesitatingly proclaim Spanish and Italian to be different languages—because they have had their own armies and navies, plus largely separate governments and school systems, for over a thousand years.

Conversely, many European languages have strongly differentiated regional forms that the governments of their country emphatically consider mere dialects, even though speakers from the different regions can’t understand each other at all. My north German friends can’t make heads or tails of the talk of rural Bavarians, and my north Italian friends are equally at a loss in Sicily. But their national governments are adamant that those different regions should not have separate armies and navies, and so their speech forms are labeled as dialects and don’t you dare mention a criterion of mutual intelligibility.

Those regional differences within European countries were even greater 60 years ago, before television and internal migration began breaking down long-established “dialect” differences. For example, on my first visit to Britain in the year 1950, my parents took my sister Susan and me to visit family friends called the Grantham-Hills in their home in the small town of Beccles in East Anglia. While my parents and their friends were talking, my sister and I became bored with the adult conversation and went outside to walk around the charming old town center. After turning at several right angles that we neglected to count, we realized that we were lost, and we asked a man on the street for directions back to our friends’ house. It became obvious that the man didn’t understand our American accents, even when we spoke slowly and (we thought) distinctly. But he did recognize that we were children and lost, and he perked up when we repeated the words “Grantham-Hill, Grantham-Hill.” He responded with many sentences of directions, of which Susan and I couldn’t decipher a single word; we wouldn’t have guessed that he considered himself to be speaking English. Fortunately for us, he pointed in one direction, and we set off that way until we recognized a building near the Grantham-Hills’ house. Those former local “dialects” of Beccles and other English districts have been undergoing homogenization and shifts towards BBC English, as access to television has become universal in Britain in recent decades.

By a strictly linguistic definition of 70% intelligibility—the definition that one has to use in New Guinea, where no tribe has its own army or navy—quite a few Italian “dialects” would rate as languages. That redefinition of some Italian dialects as languages would close the gap in linguistic diversity between Italy and New Guinea slightly, but not by much. If the average number of speakers of an Italian “dialect” had equaled the 4,000 speakers of an average New Guinea language, Italy would have 10,000 languages. Aficionados of the separateness of Italian dialects might credit Italy with dozens of languages, but no one would claim there to be 10,000 different languages in Italy. It really is true that New Guinea is linguistically far more diverse than is Italy.

How languages evolve

How did the world end up with 7,000 languages, instead of our all sharing the same language? Already for tens of thousands of years before language spread by the Internet and Facebook, there has been ample opportunity for language differences to disappear, because most traditional peoples have had contact with neighboring peoples, with whom they intermarry and trade, and from whom they borrow words and ideas and behaviors. Something must have caused languages, even in the past and under traditional conditions, to diverge and to remain separate, in the face of all that contact.

Here’s how it happens. Any of us over the age of 40 has observed that languages change even over the course of just a few decades, with some words dropping out of use, new words being coined, and pronunciation shifting. For instance, whenever I revisit Germany, where I lived in 1961, young Germans notice that they have to explain to me some new German words (e.g., the new word Händi for cell phones, which didn’t exist in 1961), and that I still use some old-fashioned German words that have been going out of use since 1961 (e.g., jener/jene for “that/those”). But young Germans and I can still mostly understand each other well. Similarly, you American readers under the age of 40 may not recognize some formerly popular English words like “ballyhoo,” but in compensation you daily use the verb “to Google” and the participle “Googling,” which didn’t exist in my childhood.

After a few centuries of such independent changes in two geographically separate speech communities derived from the same original speech community, the communities develop dialects that may pose difficulties for each other to understand: e.g., the modest differences between American and British English, the bigger differences between the French of Quebec and of metropolitan France, and the still bigger differences between Afrikaans and Dutch. After 2,000 years of divergence, the speech communities have diverged so much as to be no longer mutually intelligible, although to linguists they are still obviously related—such as the French and Spanish and Romanian languages derived from Latin, or the English and German and other Germanic languages derived from proto-Germanic. Finally, after about 10,000 years, the differences are so great that most linguists would assign the languages to unrelated language families without any detectable relationships.

Thus, languages evolve differences because different groups of people independently develop different words and different pronunciations over the course of time. But the question remains why those diverged languages don’t merge again when formerly separated people spread out and re-contact each other at speech boundaries. For instance, at the modern boundary between Germany and Poland, there are Polish villages near German villages, but the villagers still speak a local variety of either German or of Polish, rather than a German-Polish mish-mash. Why is that so?

Probably the main disadvantage of speaking a mish-mash involves a basic function of human language: as soon as you start to speak to someone else, your language serves as an instantly recognizable badge of your group identity. It’s much easier for wartime spies to don the enemy’s uniform than to imitate convincingly the enemy’s language and pronunciation. People who speak your language are your people: they’ll recognize you as a compatriot, and they’ll support you or at least not be immediately suspicious of you, whereas someone speaking a different language is apt to be regarded as a potentially dangerous stranger. That instant distinction between friends and strangers still operates today: just see how you (my American readers) react the next time that you’re in Uzbekistan, and you finally to your relief hear someone behind you speaking English with an American accent. The distinction between friends and strangers was even more important in the past (Chapter 1), often a matter of life and death. It’s important to speak the language of at least some community, so that there will be some group that considers you as “our own.” If you instead speak a mish-mash near a speech boundary, both groups may understand much of what you say, but neither group will consider you “one of our own,” and you can’t count on either group to welcome and protect you. That may be why the world’s speech communities have tended to remain thousands of separate languages, instead of the whole world speaking one language or forming one dialect chain.

Geography of language diversity

Languages are distributed unevenly around the world: about 10% of the world’s area contains half of its languages. For instance, at the low-end extreme of language diversity, the world’s three largest countries—Russia, Canada, and China, each with an area of millions of square miles—have only about 100, 80, and 300 native languages respectively. But at the high-end extreme of language diversity, New Guinea and Vanuatu, with areas of only 300,000 and 4,700 square miles respectively, have about 1,000 and 110 native languages. That means that one language is spoken over an average area of about 66,000, 49,000, and 12,000 square miles in Russia, Canada, and China respectively, but only over 300 and 42 square miles respectively in New Guinea and Vanuatu. Why is there such enormous geographic variation in language diversity?

Linguists recognize ecological, socio-economic, and historical factors apparently contributing to the answer. Language diversity—e.g., the number of native languages per 1,000 square miles of area—correlates with numerous potentially explanatory factors, but these factors are in turn correlated with each other. Hence one has to resort to statistical methods, such as multiple regression analysis, to tease out which factors have primary effects actually causing language diversity to be high or low, and which other factors have just apparent effects mediated by their correlations with those primary factors. For example, there is a positive correlation between Rolls-Royce car ownership and lifespan: Rolls-Royce owners live on the average longer than do people who don’t own Rolls-Royces. That’s not because Rolls-Royce ownership directly improves survival, but because Rolls-Royce owners tend to have lots of money, which enables them to pay for the best health care, which is the actual cause of their long lifespans. When it comes, though, to correlates of linguistic diversity, there isn’t yet a corresponding agreement about the actual underlying causes.

The four closest ecological correlations of language diversity are with latitude, climate variability, biological productivity, and local ecological diversity. First, language diversity decreases from the equator towards the poles: all other things being equal, tropical areas hold more languages than do equivalent areas at higher latitudes. Second, at a given latitude language diversity decreases with climate variability, whether the variability consists of regular within-year seasonal variation or of unpredictable between-year variation. For instance, language diversity is higher in tropical rainforests that are wet all year round than in adjacent more seasonal tropical savannahs. (This factor of seasonality could account at least in part, through the correlation between latitude and seasonality, for the higher language diversities in the less seasonal tropics than in strongly seasonal high latitudes.) Third, language diversity tends to be higher in more productive environments (e.g., higher in rainforests than in deserts), though again at least some of that effect could be because of a tendency for deserts and many other unproductive environments to be strongly seasonal. Finally, language diversity is high in ecologically diverse areas and tends especially to be higher in rugged mountainous areas than in flat areas.

These four ecological relationships are just correlations, not explanations. Suggested underlying explanations involve human population size, mobility, and economic strategies. First, a speech community’s viability increases with its number of people: a language spoken by only 50 people is more likely to disappear, due to its speakers all dying or abandoning their language, than is a language spoken by 5,000 people. Hence regions with a lower biological productivity (supporting fewer people) tend to support fewer languages, and to require more area for the speakers of each language. A viable population in Arctic or desert regions needs tens of thousands of square miles to support itself, while a few hundred square miles would be ample in productive landscapes. Second, the more constant is the environment between seasons and between years, the more self-sufficient and sedentary can a speech community be within a small area, without much need to move periodically or to trade for necessities with other peoples. Finally, an ecologically diverse area can support many different language communities, each with its own specific subsistence economy adapted to a different local ecology: for instance, a mountainous area can support mountain herders, hill farmers, lowland river fishermen, and lowland savannah pastoralists at different elevations and in different habitats.

Ecological factors thus already tell us several reasons why small New Guinea has 5–10 times more languages than does huge Russia, Canada, or China. New Guinea lies within a few degrees of the equator, so its people experience only slight variations in climate. The New Guinea landscape is wet, fertile, and productive. New Guineans don’t move much or at all with seasons or from year to year; they can meet all of their subsistence needs within a small area; and they don’t have to trade except for salt, stone for tools, and luxuries like shells and feathers. New Guinea is rugged and ecologically diverse, with mountains up to 16,500 feet, rivers, lakes, seacoasts, savannahs, and forests. One could object that China and Canada have even higher mountains and offer a larger range of elevations than does New Guinea. But New Guinea’s tropical location means that New Guineans can live year-round and farm at high population densities up to elevations of 8,000 feet, while high elevations in China and Canada are seasonally freezing and support only low human population densities (in Tibet) or no people at all.

In addition to those ecological factors, there are also socio-economic and historical factors contributing to differences in language diversity around the world. One such factor is that hunter-gatherer speech communities consist of fewer individuals but may cover larger areas than farmer speech communities. For instance, Aboriginal Australia was traditionally inhabited entirely by hunter-gatherers occupying an average of 12,000 square miles per language, while neighboring New Guinea supported mostly farmers occupying only 300 square miles per language. Within Indonesian New Guinea, I worked in areas supporting nearby both farmers (in the Central Highlands) and hunter-gatherers (in the Lakes Plains), with about two dozen languages for each lifestyle. The average hunter-gatherer language there had only 388 speakers, while the average farmer language had 18,241 speakers. The main reason for the small speech communities of hunter-gatherers is low food availability, hence low human population densities. Within the same environment, population densities of hunter-gatherers are 10 to 100 times lower than those of farmers, because much less food is available to hunter-gatherers, able to eat only that tiny fraction of wild plant species that is edible, than to farmers, who convert the landscape into gardens and orchards of edible plants.

A second socio-economic factor related to language diversity is political organization: language diversity decreases, and language communities increase in population and in area, with increasing political complexity from bands to states. For instance, the United States today, a large state with a single dominant coast-to-coast language, has a population about 30 times what was the population of the entire world at a time when the world still consisted entirely of hunter-gatherer bands and tribes with thousands of languages. The dominant U.S. language of English has largely replaced the hundreds of different local languages formerly spoken five centuries ago in what is now the national territory of the U.S. when it was divided among Native American bands, tribes, and chiefdoms. Underlying this trend is the fact, discussed in the Prologue, that increasing political complexity becomes necessary as a society increases in population—because a society of a few dozen people can make decisions in a group meeting without a leader, but a society of millions requires leaders and bureaucrats to operate. States expand their own languages at the expense of the languages of conquered and incorporated groups. That language expansion is partly a matter of state policy for the purposes of administration and national unity, and partly a spontaneous matter of individual citizens adopting the national language in order to obtain economic and social opportunities for themselves.

The remaining factor is a historical one whose various outcomes include the just-mentioned decrease in language diversity with increasing political complexity. World regions have repeatedly been swept by “language steamrollers,” in which one group enjoying some advantage of population numbers, food base, or technology exploits that advantage to expand at the expense of neighboring groups, imposing its own language on the region and replacing previous local languages by driving out or killing their speakers or converting them to speaking the invader’s language. The most familiar steamrollers are those associated with expansions of powerful states over stateless peoples. Recent examples have included European expansions replacing native languages of the Americas, the British conquest of Australia replacing Aboriginal Australian languages, and the Russian expansion over the Ural Mountains to the Pacific Ocean replacing native Siberian languages. In the past, as well, there have been historically documented state-driven steamrollers. The Roman Empire’s expansion over the Mediterranean basin and most of Western Europe extinguished Etruscan, Continental Celtic languages, and many other languages. The expansion of the Inca Empire and its predecessors similarly spread the Quechua and Aymara languages over the Andes.

Less familiar to non-linguists are the steamrollers driven by expansions of pre-literate farmers over the lands of hunter-gatherers, and inferred from linguistic and archaeological rather than historical evidence. Well understood ones include the expansions of Bantu and Austronesian farmers, which largely replaced the former languages of hunter-gatherers in subequatorial Africa and Island Southeast Asia respectively. There were also steamrollers in which hunter-gatherers overran other hunter-gatherers, driven by improved technology: e.g., the expansion of the Inuit 1,000 years ago eastwards across the Canadian Arctic, based on technological advances such as dog sleds and kayaks.

A consequence of these several types of historical expansions is that some world regions containing few geographic barriers have repeatedly been overrun by linguistic steamrollers. The immediate result is very low linguistic diversity, because an invading language sweeps away pre-existing linguistic diversity. With time, the invading language differentiates into local dialects and then into separate languages, but all of them still closely related to each other. An early stage in this process is illustrated by the Inuit expansion of 1,000 years ago; all eastern Inuit people from Alaska to Greenland still speak mutually intelligible dialects of a single language. The Roman and Bantu expansions of 2,000 years ago represent a slightly later stage: the various Italic languages (such as French, Spanish, and Romanian) are very similar but no longer mutually intelligible, as is also true of the hundreds of closely related Bantu languages. At a still later stage, the Austronesian expansion that began around 6,000 years ago has by now generated a thousand languages falling into eight branches, but still sufficiently similar that there is no doubt about their relationship.

Contrasting with those easily overrun areas that Johanna Nichols terms “language spread zones” are what she terms “residual zones” or refugia: mountainous and other areas that are difficult for states and other outsiders to overrun, where languages survive and diffentiate for long times, and hence where unique language groups survive. Famous examples are the Caucasus Mountains, with 3 unique language families plus a few recently invaded languages belonging to three other widespread families; northern Australia, to which 26 of Aboriginal Australia’s 27 language families are confined; Indian California, with about 80 languages variously classified into somewhere between 6 and 22 families; and, of course, New Guinea, with its 1,000 languages classified in dozens of families.

We thus have several more reasons why New Guinea leads the world in number of languages and of language families. In addition to the ecological reasons previously mentioned—little seasonal variation, sedentary populations, a productive environment supporting high human population densities, and great ecological diversity supporting many co-existing human groups with different subsistence strategies—we now have some socio-economic and historical factors as well. Those include the facts that traditional New Guinea never developed state government, so there was never a state steamroller to homogenize linguistic diversity; and that, as a result of New Guinea’s highly dissected mountainous terrain, the steamroller probably caused by the spread of Highlands farming (that associated with the so-called Trans–New Guinea language phylum) was unable to eliminate dozens of older New Guinea language phyla.

Traditional multilingualism

Those are the reasons why the modern world inherited 7,000 languages from the traditional world until yesterday, and why language communities of hunter-gatherers and small-scale farmers without state government contained many fewer speakers than do modern state societies. What about bilingualism and multilingualism? Are traditional societies more, less, or equally often bilingual compared to modern state societies?

The distinction between bilingualism (or multilingualism) and monolingualism proves even more difficult to define and more arbitrary than is the distinction between a language and a dialect. Should you count yourself as bilingual only if you can converse fluently in a second language besides your mother tongue? Should you count languages in which you can converse clumsily? What about languages that you can read but not speak—e.g., Latin and classical Greek for those of us who learned those languages at school? And what about languages that you can’t speak, but that you can understand when spoken by others? American-born children of immigrant parents often can understand but not speak their parents’ language, and New Guineans often distinguish between languages that they can both speak and understand, and languages that they say that they can only “hear” but not speak. Partly because of this lack of agreement on a definition of bilingualism, we lack comparative data on the frequency of bilingualism around the world.

Nevertheless, we don’t have to throw up our hands in despair and ignore the subject, because there is much anecdotal information about bilingualism. Most native-born Americans with English-speaking parents are effectively monolingual for obvious reasons: in the United States there is little need, and for most Americans little regular opportunity, to speak a second language; most immigrants to the U.S. learn English; and most English-speaking Americans marry English-speaking spouses. Most European countries have only a single official national language, and most native-born Europeans with native-born parents learn only that national language as pre-school children. However, because European countries are all much smaller in area and (today) much less self-sufficient economically, politically, and culturally than is the United States, most educated Europeans now learn additional languages in school by formal instruction and often achieve fluency. Shop assistants in many Scandinavian department stores wear pins on their jackets showing the flags of the various languages in which they are competent to help foreign customers. Nevertheless, this widespread multilingualism in Europe is a recent phenomenon that has resulted from mass higher education, post–World War II economic and political integration, and the spread of English-language mass media. Formerly, monolingualism was widespread in European nation-states, as in other state societies. The reasons are clear: state speech communities are huge, often millions of speakers; state societies favor the state’s own language for use in government, education, commerce, the army, and entertainment; and (as I’ll discuss below) states have potent intentional and unintentional means of spreading their state language at the expense of other languages.

In contrast, multilingualism is widespread or routine in traditional small-scale non-state societies. The reasons are again simple. We have seen that traditional language communities are small (a few thousand speakers or less) and occupy small areas. Immediately neighboring communities often speak different languages. People regularly encounter and have to deal with speakers of other languages. To trade, to negotiate alliances and access to resources, and (for many traditional people) even to obtain a spouse and to communicate with that spouse requires being not merely bilingual but multilingual. Second and further languages are learned in childhood and in the home or socially, not through formal instruction. In my experience, fluency in five or more languages is the rule among traditional New Guineans. I shall now supplement those New Guinea impressions of mine with brief accounts from two continents: Aboriginal Australia and tropical South America.

Aboriginal Australia was occupied by about 250 different language groups, all of them subsisting by hunting-gathering, with an average of about a thousand speakers per language. All reliable reports describe most traditional Aboriginals as being at least bilingual, and most as knowing many languages. One such study was carried out by anthropologist Peter Sutton in the Cape Keerweer area of the Cape York Peninsula, where the local population of 683 people was divided into 21 clans, each with a different form of speech and averaging 33 people per clan. Those speech forms are classified into five languages plus about seven dialects, so that the average number of speakers is about 53 per speech form, or 140 per language. Traditional Aborigines in the area spoke or understood at least five different languages or dialects. In part because speech communities are so tiny, and in part because of a preference for linguistic exogamy (marrying someone whose primary language is not one’s own), 60% of marriages are between partners speaking different languages, another 16% are between speakers of different dialects of the same language, and only 24% are within the same dialect. That is despite the fact that neighboring clans tend to be linguistically similar, so that mere propinquity would lead to marriages being made within the same dialect if it were not for that preference for seeking geographically and linguistically more remote partners.

Because many social groups at Cape Keerweer involve speakers of different languages, conversations are often multilingual. It is customary to begin a conversation in the language or dialect of the person whom you are addressing, or (if you are a visitor) in the language of the host camp. You may then switch back to your own language, while your partners reply in their own languages, or you may address each person in his/her own language, your choice of language thereby indicating whom you are addressing at the moment. You may also switch languages depending on the implicit message that you wish to convey: e.g., one choice of language means “You and I have no quarrel,” another means “You and I do have a quarrel but I wish to cool it,” still another means “I am a good and socially proper person,” and yet another means “I will insult you by talking to you disrespectfully.” It is likely that such multilingualism was routine in our hunter-gatherer past, just as it still is today in traditional areas of New Guinea, and for the same underlying reasons: tiny speech communities, hence frequent linguistic exogamy, and daily encounters and conversations with speakers of other languages.

The other pair of studies, by Arthur Sorensen and Jean Jackson, is from the Vaupés River area on the border between Colombia and Brazil in the northwest Amazon Basin. About 10,000 Indians, speaking about 21 different languages of four different language families, are culturally similar in gaining their livelihood by farming, fishing, and hunting along rivers in tropical rainforests. Like Cape Keerweer Aborigines, Vaupés River Indians are linguistically exogamous but much more strictly so: in over a thousand marriages studied by Jackson, only one may possibly have been within a language group. While boys remain as adults in their parents’ longhouse in which they grew up, girls from other longhouses and language groups move to their husband’s longhouse at the time of marriage. A given longhouse contains women marrying in from several different language groups: three, in the case of a longhouse studied intensively by Sorensen. All children learn both their father’s and their mother’s languages already from infancy, then learn the languages of the other women of the longhouse. Hence everyone in the longhouse knows the four longhouse languages (that of the men, and those of the three language groups of the women), and most also learn some other languages from visitors.

Only after Vaupés River Indians have come to know a language well by hearing and passively acquiring vocabulary and pronunciation do they start speaking it. They carefully keep languages separate and work hard to pronounce each language correctly. They told Sorensen that it took them one or two years to learn a new language fluently. High value is placed on speaking correctly, and letting words from other languages creep into one’s conversation is considered shameful.

These anecdotes from small-scale societies on two continents and on New Guinea suggest that socially acquired multilingualism was routine in our past, and that the monolingualism or school-based multilingualism of modern state societies is a new phenomenon. But this generalization is only tentative and subject to limitations. Monolingualism may have characterized small-scale societies in some areas of low language diversity or recent language expansions, as at high latitudes or among the Inuit east of Alaska. The generalization remains based on anecdotes and on expectations derived from traditionally small language communities. Systematic surveys employing some standard definition of multilingualism are needed to place this conclusion on a firmer foot.

Benefits of bilingualism

Let’s now ask whether that traditional multilingualism or bilingualism brings net benefit, net harm, or neither to bilingual individuals compared with monolingual individuals. I’ll describe some fascinating and recently discovered practical advantages of bilingualism that may impress you more than the usual claim that learning a foreign language enriches your life. I’ll discuss here only the effects of bilingualism for individuals: I’ll defer to a later section the corresponding question about whether bilingualism is good or bad for a society as a whole.

Among modern industrial countries, bilingualism is a subject of debate especially in the United States, which has been incorporating a large fraction of non-English-speaking immigrants into its population for over 250 years. A frequently expressed view in the U.S. is that bilingualism is harmful, especially for children of immigrants, who are thereby hindered in negotiating the prevalently English-speaking culture of the U.S. and will be better off not learning their parents’ language. This view is widely held not only by native-born Americans but also by first-generation immigrant parents: e.g., by my grandparents and by my wife’s parents, who diligently avoided speaking together in Yiddish and Polish respectively in the presence of their children, in order to make sure that my parents and my wife would learn only English. Additional bases for this view on the part of native-born Americans include fear and suspicion of things foreign, including foreign languages; and a concern on the part of both native-born and immigrant parents that it may be confusing for children to be exposed simultaneously to two languages, and that their mastery of language would be faster if they were exposed to just one language. That reasoning is a legitimate concern: a child learning two languages must learn twice as many speech sounds, words, and grammatical structures as a monolingual child; the bilingual child has only half as much time to devote to each language; and so the bilingual child (it is feared) may end up speaking two languages poorly, instead of speaking one language well.

In fact, studies carried out in the U.S., Ireland, and Wales until the 1960s did report that bilingual children were significantly disadvantaged linguistically compared to monolingual children, learned command of language more slowly, and ended up with smaller vocabularies in each language. But it was eventually realized that that interpretation was confounded by other variables correlated with bilingualism in those studies. In the U.S. more than in other countries, bilingualism is associated with poverty. When American bilingual children were compared with American monolingual English-speaking children, the latter tended to be from more affluent communities, to be attending better schools, and to have more educated and wealthy parents working at higher occupational levels and with larger vocabularies. Those correlates of bilingualism alone might have accounted for the lower language skills of the bilingual children.

More recent studies in the U.S., Canada, and Europe control for those other variables, by comparing bilingual and monolingual children attending the same school and matched for parental socio-economic status. It turns out that bilingual children and monolingual children matched in other respects pass milestones of language acquisition (e.g., age to say first word, first sentence, or to acquire a 50-word vocabulary) at the same age. Depending on the study, either bilingual and monolingual children end up as adults with essentially the same vocabulary size and word-retrieval rate, or else the monolingual children end up with a slight advantage (vocabulary up to 10% larger in their sole language). However, it would be misleading to summarize this result by saying, “Monolingual children end up with a slightly larger vocabulary: 3,300 versus only 3,000 words.” Instead, the result is, “Bilingual children end up with a much larger vocabulary: a total of 6,000 words, consisting of 3,000 English words plus 3,000 Chinese words, instead of 3,300 English words and no Chinese words.”

Studies to date have not demonstrated generalized cognitive differences between bilingual and monolingual people. It is not the case that one group is on the average smarter or thinks more quickly than the other group. Instead, there appear to be specific differences, such as (perhaps) slightly faster word retrieval and ability to name objects on the part of monolinguals (because they don’t have the problem of selecting among different names, all correct but in different languages familiar to them). Among these specific differences, the most consistently established to date involves what cognitive scientists term “executive function,” and that difference is in favor of bilinguals.

To understand the meaning of executive function, picture a person doing anything at all, e.g., crossing a street. Reflect that we are constantly bombarded by sensory information in many modalities, including sight, sound, smell, touch, and taste, plus our own thoughts. Into the pedestrian’s senses flood the sight of billboards and of clouds overhead, the sounds of people talking and birds singing, the smells of the city, the touch sensation of the pedestrian’s feet on the pavement and of his arms swinging at his sides, and thoughts of what his wife said to him at breakfast that morning. If he were not crossing a street, the pedestrian would concentrate on the words of people or on the sight of billboards or on his wife’s most recent words. When crossing a street, though, his survival requires that he concentrate on the sights and sounds of cars approaching at different speeds from both directions, and on the feeling of his feet stepping off the curb. That is, to do anything at all in life requires inhibiting 99% of one’s sensory input and thoughts at any moment, and paying attention to the 1% of input relevant to the task currently at hand. That brain process of executive function, also known as cognitive control, is believed to reside in the brain area known as the pre-frontal cortex. It’s what permits you to pay selective attention, to avoid being distracted, to concentrate on solving a problem, to shift between tasks, and to call up and use the word or bit of information needed at the moment out of your huge stockpile of words and information. That is, executive control is a big deal: it’s crucial to our functioning competently. In children, executive control develops especially over the course of the first five or so years of life.

Bilingual people have a special issue of executive control. Monolingual people hearing a word compare it with their single stock of words, and when uttering a word they draw it from their single stock. But bilingual people must and do keep their languages separate. Every time they hear a word pronounced, they must instantly know according to which set of arbitrary rules to interpret the meaning of those sounds: for instance, a Spanish/Italian bilingual has learned that the sounds b-u-rr-o mean “donkey” in Spanish but “butter” in Italian. Every time bilinguals wish to say something, they must call up the words from the language being used in the current conversation, and not from their other language. Multilingual people participating in a group bilingual conversation, or Scandinavian shop assistants, must switch those arbitrary rules every few minutes or even more often.

The importance of executive control for multilingual people was brought home to me by a disconcerting failure of it on my part. When I went to work in Indonesia in 1979 and began learning the Indonesian language, I had already lived for extended periods in Germany, Peru, and Papua New Guinea, and I had become comfortable at speaking German, Spanish, or Tok Pisin without confusing those languages with each other or with English. I had also learned some other languages (especially Russian) but had never lived in their countries long enough to gain experience of speaking them continually. When I was initially talking with Indonesian friends, I was astonished to discover that my intention of pronouncing an Indonesian word often resulted in my uttering the Russian word with the same meaning, despite the Indonesian and Russian languages being completely unrelated! I had evidently learned to separate English, German, Spanish, and Tok Pisin into four well-controlled pigeonholes, but I was still left with an undifferentiated fifth pigeonhole equivalent to “language other than English, Spanish, German, and Tok Pisin.” Only after more time in Indonesia was I able to inhibit the stock of Russian words lurking out of control in my mind and ready to creep into my Indonesian conversations.

In short, bilingual or multilingual people have constant unconscious practice in using executive control. They are forced to practise it whenever they speak, think, or listen to other people talking—i.e., constantly throughout their waking hours. In sports, art performance, and other arenas of life, we know that skills improve with practice. But: which are the skills that practice of bilingualism improves? Does bilingualism merely develop bilinguals’ specific skill at switching between languages, or is bilingualism more generally useful to them?

Recent studies have devised tests to explore this question by comparing problem-solving by bilingual and monolingual people ranging from 3-year-old children to 80-year-old adults. The overall conclusion is that bilinguals of all those ages have an advantage at solving only a specific type of problem. But it is a broad specific problem: solving tasks that are confusing because the rules of the task change unpredictably, or because there are misleading and irrelevant but glaringly obvious cues that must be ignored. For instance, children are shown a series of cards depicting either a rabbit or a boat that is either red or blue, and that does or doesn’t have a gold star. If a gold star is present, children must remember to sort the cards by color; if a gold star is absent, they must remember to sort the cards by the object depicted. Monolingual and bilingual subjects are equally successful at such games as long as the rule remains the same from trial to trial (e.g., “sort by color”), but monolinguals have much more difficulty than bilinguals at accommodating to a switch in rules.

As another example of a test, children sit in front of a computer screen on which either a red square suddenly flashes on the left of the screen or else a blue square flashes on the right of the screen. The keyboard below the screen includes a red key and also a blue key, and the child must push the key with the same color as the flashing square. If the red key is on the left of the keyboard and the blue key is on the right—i.e., in the same relative position as the flashing square of the same color on the screen—then bilinguals and monolinguals perform equally well. But if the positions of the red and blue keys are reversed to create confusion—i.e., if the red key is on the left side of the keyboard but the blue flashing square is the one on the left side of the screen—then bilinguals perform better than monolinguals.

It was initially expected that this advantage of bilinguals at tests involving rule changes or confusing information would apply only to tasks involving verbal cues. However, the advantage proves to be broader, and to apply also to non-verbal cues of space, color, and quantity (as in the two examples that I just described). But this hardly means that bilinguals are better than monolinguals at everything: the two groups tend to perform equally well at tasks without rule changes to be attended to, and without misleading cues to be ignored. Nevertheless, life is full of misleading information and changing rules. If bilinguals’ advantage over monolinguals in these trivial games also applies to the abundance of confusing or shifting real-life situations, that would mean a significant advantage for bilinguals.

One interesting recent extension of these comparative tests is to infants. One might imagine that it would be meaningless or impossible to test “bilingual infants”: infants can’t speak at all, they can’t be described as bilingual or monolingual, and they can’t be asked to perform tests by sorting cards and pushing keys. In fact, infants develop the ability to discriminate speech that they hear long before they can speak themselves. One can test their powers of discrimination by watching whether they can learn to orient differently to two different sounds. It turns out that newborn infants, who have had no exposure to any of the world’s languages, can discriminate between many consonant and vowel distinctions used in one or another of the world’s languages, whether or not it happens to be their “native” language (which they haven’t heard except from inside the womb). Over the course of their first year of life, as they hear speech around them, they lose that initial ability of theirs to discriminate non-native distinctions that they aren’t hearing around them, and they sharpen their ability to discriminate native distinctions. For instance, the English language discriminates between the two liquid consonants l and r, while the Japanese language doesn’t; that’s why native Japanese people speaking English sound to native English-speakers as if they are mispronouncing “lots of luck” as “rots of ruck.” Conversely, the Japanese language discriminates between short and long vowels, while the English language doesn’t. However, newborn Japanese infants can discriminate between l and r, and newborn English infants can discriminate between short and long vowels, but each loses that ability over the first year of life because the distinction carries no meaning.

Recent studies have concerned so-called crib bilinguals: i.e., infants whose mother and father differ from each other in native language, but whose mother and father have both decided to speak her or his own language to the infant already from day 1, so that the infant grows up hearing two languages rather than just one language. Do crib bilinguals already gain over monolinguals the advantage in executive function, enabling them to deal better with rule switches and confusing information, that is apparent after the child can actually speak? And how does one test executive function in a pre-verbal infant?

A recent ingenious study by the scientists Ágnes Kovács and Jacques Mehler, carried out in the Italian city of Trieste, compared seven-month “monolingual” infants with infants “bilingual” in Italian plus either Slovenian, Spanish, English, Arabic, Danish, French, or Russian (i.e., hearing one language from their mother and the other language from their father). The infants were trained, conditioned, and rewarded for correct behavior by being shown a cute picture of a puppet popping up on the left side of a computer screen; the infants learned to look in the direction of the puppet and evidently enjoyed it. The test consisted of pronouncing to the infant a nonsense trisyllable with the structure AAB, ABA, or ABB (e.g., lo-lo-vu, lo-vu-lo, lo-vu-vu). For only one of the three structures (e.g., lo-lo-vu) did the puppet appear on the screen. Within 6 trials, on hearing lo-lo-vu both “monolingual” and “bilingual” infants learned to look towards the left side of the screen to anticipate the appearance of the cute puppet. Then the experimenter changed the rules and made the puppet appear on the right side (not on the left side) of the screen, in response not to the nonsense word lo-lo-vu but to lo-vu-lo. Within 6 trials, the “bilingual” infants had unlearned their previous lesson and had learned the new correct response, but the “monolingual” infants even after 10 trials were still looking at the now-wrong side of the screen on hearing the now-wrong nonsense word.

Alzheimer’s disease

One can extrapolate from these results, and speculate that bilingual people may have an advantage over monolingual people in negotiating our confusing world of changing rules, and not merely in the trivial tasks of discriminating lo-lo-vu from lo-vu-lo. However, you readers will probably require evidence of more tangible benefits before you make the commitment to babble consistently in two different languages to your infant children and grandchildren. Hence you will be much more interested to learn about reported advantages of bilingualism at the opposite end of the lifespan: old age, when the devastating tragedy of Alzheimer’s disease and other senile dementias lies in store for so many of us.

Alzheimer’s disease is the commonest form of dementia of old age, affecting about 5% of people over the age of 75, and 17% of those over the age of 85. It begins with forgetfulness and a decline of short-term memory, and it proceeds irreversibly and incurably to death within about 5 to 10 years. The disease is associated with brain lesions, detectable by autopsy or (in life) by brain-imaging methods, including brain shrinkage and accumulation of specific proteins. All drug and vaccine treatments to date have failed. People with mentally and physically stimulating lives—more education, more complex jobs, stimulating social and leisure activities, and more physical exercise—suffer lower rates of dementia. However, the long latency period of up to 20 years between the beginning of protein build-up and the later appearance of Alzheimer’s symptoms raises questions of cause and effect about the interpretation of these findings concerning stimulating lives: does stimulation itself really decrease Alzheimer’s symptoms, or were those individuals instead able to lead stimulating lives precisely because they were not suffering from early stages of protein build-up, or because of genetic advantages that also protected them against Alzheimer’s disease? In the hope that stimulating lives might be a cause rather than a result of reduced disease processes, older people afraid of developing Alzheimer’s disease are sometimes urged to play bridge, play challenging online games, or solve Sudoku puzzles.

Intriguing results of the last few years suggest a protective effect of life-long bilingualism against Alzheimer’s symptoms. Among 400 patients studied at clinics in Toronto, Canada, mostly in their 70s, and with a probable diagnosis of Alzheimer’s disease (or other dementias in a few cases), bilingual patients showed their first symptoms at an age 4 or 5 years older than did monolingual patients. Life expectancy in Canada is 79, hence a delay of 4–5 years for people in their 70s translates into a 47% decrease of probability that they will develop Alzheimer’s symptoms at all before they die. The bilingual and monolingual patients were matched in occupational status, but the bilingual patients had received on the average lower (not higher) levels of education. Because education is associated with lower incidence of Alzheimer’s symptoms, this means that differences in education could not explain the lower incidence of symptoms in the bilingual patients: their lower incidence was despite their having received less education. A further intriguing finding was that, for a given level of cognitive impairment, bilingual patients had more brain atrophy revealed by brain-imaging methods than did monolingual patients. Expressing this differently, bilingual patients suffer less cognitive impairment than do monolingual patients with the same degree of brain atrophy: bilingualism offers partial protection against the consequences of brain atrophy.

The protection afforded by bilingualism does not raise the same uncertainties of interpretation about cause versus effect raised by the apparent protection offered by education and stimulating social activities. The latter might be results rather than causes of early stages of Alzheimer’s lesions; and genetic factors predisposing one to seek education and social activities might also protect one against Alzheimer’s disease. But whether one becomes bilingual is determined in early childhood, decades before the earliest Alzheimer’s brain lesions develop, and regardless of one’s genes. Most bilingual people become bilingual not through any decision or genes of their own, but through the accident of growing up in a bilingual society, or of their parents emigrating from their native land to a land with a different language. Hence the reduced Alzheimer’s symptoms of bilinguals suggest that bilingualism itself protects against Alzheimer’s symptoms.

How might this be? A short answer is the aphorism “Use it or lose it.” Exercising most body systems improves their function; failing to exercise them lets their function deteriorate. This is the reason why athletes and artists practise. It’s also the reason why Alzheimer’s patients are encouraged to play bridge or online games, or to solve Sudoku puzzles. But bilingualism is the most constant practice possible for the brain. Whereas even a bridge or Sudoku fanatic can play bridge or solve Sudoku puzzles for only a fraction of a day, bilingual people impose extra exercise on their brain every second of their waking hours. Consciously or unconsciously, their brain is constantly having to decide, “Shall I speak, think, or interpret sounds spoken to me according to the arbitrary rules of language A, or of language B?”

Readers will share my personal interest in some unanswered but obvious further questions. If one extra language offers some protection, do two extra languages offer more protection? If so, does the protection increase in direct proportion to the number of languages, or else more steeply or less steeply? For instance, if bilingual people get four years of protection from their one extra language, does a New Guinean, an Aboriginal Australian, a Vaupés River Indian, or a Scandinavian shopkeeper speaking five languages (four beyond her first language) still get just 4 years of protection, or does she get 4 × 4 = 16 years of protection, or (if juggling four extra languages is much more than four times more taxing than juggling just one extra language) does she even get 50 years of protection? If you had the misfortune that your parents didn’t raise you as a crib bilingual, and that you didn’t learn a second language until you began high school at age 14, can you ever catch up to crib bilinguals in the benefits obtained? Both of these questions will be of theoretical interest to linguists, and of practical interest to parents wondering how best to raise their children. All of this suggests that bilingualism or multilingualism may bring big practical advantages to bilingual individuals, beyond the less practical advantages of a culturally enriched life, and regardless of whether language diversity is good or bad for the world as a whole.

Vanishing languages

The world’s 7,000 languages are enormously diverse in a wide range of respects. For instance, one day while I was surveying birds in jungle around Rotokas village in the mountains of the Pacific island of Bougainville, the villager guiding me and naming local birds for me in the Rotokas language suddenly exclaimed “Kópipi!” as he pointed out the most beautiful bird song that I had ever heard. It consisted of silver-clear whistled tones and trills, grouped in slowly rising phrases of two or three notes, each phrase different from the previous one, and producing an effect like one of Franz Schubert’s deceptively simple songs. The singer proved to be a species of long-legged short-winged warbler previously unknown to Western science.

As I talked with my guide, I gradually realized that the music of Bougainville’s mountains included not only the kópipi’s song but also the sound of the Rotokas language. My guide named one bird for me after another: kópipi, kurupi, vokupi, kopikau, kororo, keravo, kurue, vikuroi…. The only consonant sounds from those names are k, p, r, and v. Later, I learned that the Rotokas language has only 6 consonant sounds, the fewest of any known language in the world. English, by comparison, has 24, while the now-extinct Ubykh language of Turkey had about 80. Somehow, the people of Rotokas, living in a tropical rainforest on the highest mountain of the Southwest Pacific Ocean east of New Guinea, have managed to build a rich vocabulary and communicate clearly while relying on fewer basic sounds than any other people in the world.

But the music of their language is now disappearing from Bougainville’s mountains, and from the world. The Rotokas language is just 1 of 18 languages spoken on an island roughly three-quarters the size of the American state of Connecticut. At last count it was spoken by only 4,320 people, and that number is declining. With its vanishing, a 30,000-year experiment in human communication and cultural development will come to an end. That vanishing exemplifies the impending tragedy of the loss not just of the Rotokas language, but of most of the world’s other languages. Only now are linguists starting seriously to estimate the world rate of language loss, and to debate what to do about it. If the present rate of language disappearance continues, then by the year 2100 most of the world’s current languages will either already be extinct, or else will be moribund languages spoken only by old people and no longer being transmitted from parents to children.

Of course, language extinction isn’t a new phenomenon that began only 70 years ago. We know from ancient written records, and we infer from distributions of languages and peoples, that languages have been going extinct for thousands of years. From Roman authors and from scraps of writing on ancient monuments and coins in the territory of the former Roman Empire, we know that Latin replaced Celtic languages formerly spoken in France and Spain, and replaced Etruscan, Umbrian, Oscan, Faliscan, and other languages within Italy itself. Preserved ancient texts in Sumerian, Hurrian, and Hittite attest to now-vanished languages spoken several thousand years ago in the Fertile Crescent. The spread of the Indo-European language family into western Europe, beginning within the last 9,000 years, eliminated all the original languages of Europe except for the Basque language of the Pyrenees. We infer that African Pygmies, Philippine and Indonesian hunter-gatherers, and ancient Japanese people spoke now-vanished languages replaced by Bantu languages, Austronesian languages, and the modern Japanese language respectively. Far more languages must have vanished without a trace.

Despite all that evidence for past extinctions of languages, modern language extinctions are different because of their greatly increased rate. Extinctions of the last 10,000 years left us with 7,000 languages today, but extinctions of the next century or so will leave us with only a few hundred. That record-high rate of language extinction is due to the homogenizing influences of the spreads of globalization and of state government over the whole world.

As an illustration of the fates of most languages, consider Alaska’s 20 native Inuit and Indian languages. The Eyak language, formerly spoken by a few hundred Indians on Alaska’s south coast, had declined by 1982 to two native speakers, Marie Smith Jones and her sister Sophie Borodkin (Plate 47). Their children speak only English. With Sophie’s death in 1992 at the age of 80, and Marie’s death in 2008 at the age of 93, the language world of the Eyak people reached its final silence. Seventeen other native Alaskan languages are moribund, in the sense that not a single child is learning them. Although they are still spoken by older people, they too will meet the fate of Eyak when the last of those speakers dies, and almost all of them have fewer than a thousand speakers each. That leaves only two native Alaskan languages still being learned by children and thus not yet doomed: Siberian Yupik, with 1,000 speakers, and Central Yupik, with a grand total of 10,000 speakers.

In monographs summarizing the current status of languages, one encounters the same types of phrases monotonously repeated. “Ubykh [that Turkish language with 80 consonants]…the last fully competent speaker, Tevfik Esen, of Haci Osman, died in Istanbul 10/92. A century ago there were 50,000 speakers in the Caucasus valleys east of the Black Sea.” “Cupeño [an Indian language of southern California]… nine speakers out of a total population of 150… all over 50 years old… nearly extinct.” “Yamana [an Indian language formerly spoken in southern Chile and Argentina]… three women speakers [in Chile], who are married to Spanish men and raised their children as Spanish speakers… extinct in Argentina.”

The degree of language endangerment varies around the world. The continent in most desperate straits linguistically is Aboriginal Australia, where originally about 250 languages were spoken, all with under 5,000 speakers. Today, half of those Australian languages are already extinct; most of the survivors have under 100 speakers; fewer than 20 are still being passed on to children; and at most a few are likely still to be spoken by the end of the 21st century. Nearly as desperate is the plight of the native languages of the Americas. Of the hundreds of former Native American languages of North America, one-third are already extinct, another third have only a few old speakers, and only two (Navajo and Yupik Eskimo) are still being used for broadcast on local radio stations—a sure sign of trouble in this world of mass communications. Among the thousand or so native languages originally spoken in Central and South America, the only one with a secure future is Guarani, which along with Spanish is the national language of Paraguay. The sole continent with hundreds of native languages not already in dire straits is Africa, where most surviving native languages have tens of thousands or even millions of speakers, and where populations of small sedentary farmers currently seem to being holding on to their languages.

How languages disappear

How do languages go extinct? Just as there are different ways of killing people—by a quick blow to the head, by slow strangulation, or by prolonged neglect—so too are there different ways of eradicating a language. The most direct way is to kill almost all of its speakers. That was how white Californians eliminated the language of the last “wild” Indian of the United States, a man named Ishi (Plate 29) belonging to the Yahi tribe of about 400 people, living near Mount Lassen. In a series of massacres between 1853 and 1870 after the California gold rush had brought hordes of European settlers into California, settlers killed most Yahi, leaving Ishi and his family, then Ishi alone, to survive in hiding until 1911. British colonists eliminated all the native languages of Tasmania in the early 1800s by killing or capturing most Tasmanians, motivated by a bounty of five pounds for each Tasmanian adult and two pounds for each child. Less violent means of death produce similar results. For example, there used to be thousands of Native Americans of the Mandan tribe on the Great Plains of the United States, but by 1992 the number of fluent Mandan speakers was reduced to six old people, especially as a result of cholera and smallpox epidemics between 1750 and 1837.

The next most direct way to eradicate a language is not to kill its speakers, but instead to forbid them to use their language, and to punish them if they are caught doing so. In case you wondered why most North American Indian languages are now extinct or moribund, just consider the policy practised until recently by the United States government regarding those languages. For several centuries we insisted that Indians could be “civilized” and taught English only by removing Indian children from the “barbarous” atmosphere of their parents’ homes to English-language-only boarding schools, where use of Indian languages was absolutely forbidden and punished with physical abuse and humiliation. To justify that policy, J. D. C. Atkins, the U.S. commissioner for Indian affairs from 1885 to 1888, explained, “The instruction of Indians in the vernacular [that is, in an Indian language] is not only of no use to them, but is detrimental to the cause of their education and civilization, and it will not be permitted in any Indian school over which the Government has any control…. This [English] language, which is good enough for a white man and a black man, ought to be good enough for the red man. It is also believed that teaching an Indian youth in his own barbarous dialect is a positive detriment to him. The first step to be taken toward civilization, toward teaching the Indians the mischief and folly of continuing in their barbarous practices, is to teach them the English language.”

After Japan annexed Okinawa in 1879, the Japanese government adopted a solution described as “one nation, one people, one language.” That meant educating Okinawan children to speak Japanese and no longer letting them speak any of the dozen native Okinawan languages. Similarly, when Japan annexed Korea in 1910, it banned the Korean language from Korean schools in favor of Japanese. When Russia re-annexed the Baltic republics in 1939, it replaced the Estonian, Latvian, and Lithuanian languages in schools with Russian, but those Baltic languages continued to be spoken in homes and resumed their status as national languages when the republics regained independence in 1991. The sole surviving Celtic language on the European mainland is Breton, which is still the primary language of half a million French citizens. However, the French government’s official policy is in effect to exclude the Breton language from primary and secondary schools, and Breton’s use is declining.

But in most cases language loss proceeds by the more insidious process now under way at Rotokas. With political unification of an area formerly occupied by sedentary warring tribes come peace, mobility, and increasing intermarriage. Young people in search of economic opportunity abandon their native-speaking villages and move to urban centers, where speakers of their own tribal language are greatly outnumbered by people from other tribal backgrounds, and where people needing to communicate with each other have no option except to speak the majority language. Increasing numbers of couples from different language groups marry and must resort to using the majority language to speak to each other; hence they transmit the majority language to their children. Even if the children do also learn a parental language, they must use the majority language in schools. Those people remaining in their natal village learn the majority language for its access to prestige, power, commerce, and the outside world. Jobs, newspapers, radio, and television overwhelmingly use the majority language shared by most workers, consumers, advertisers, and subscribers.

The usual result is that minority young adults tend to become bilingual, and then their children become monolingual, in the majority language. Transmission of minority languages from parents to children breaks down for either or both of two reasons: parents want their children to learn the majority language, not the parents’ tribal language, so that their children can thrive in school and in jobs; and children don’t want to learn their parents’ language and only want to learn the majority language, in order to understand television, schools, and their playmates. I have seen these processes happening in the United States to immigrant families from Poland, Korea, Ethiopia, Mexico, and many other countries, with the shared result that the children learn English and don’t learn their parents’ language. Eventually, minority languages are spoken only by older people, until the last of them dies. Long before that end is reached, the minority language has degenerated through loss of its grammatical complexities, loss of forgotten native words, and incorporation of foreign vocabulary and grammatical features.

Of the world’s 7,000 languages, some are in much more danger than are others. Crucial in determining the degree of language endangerment is whether a language is still being transmitted at home from parents to children: when that transmission ceases, a language is doomed, even if 90 more years will pass before the last child still fluent in the language, and with him or her the language itself, dies. Among the factors making it likely that parent-to-child transmission will continue are: a large number of speakers of the language; a high proportion of the population speaking the language; government recognition of the language as an official national or provincial language; speakers’ attitude towards their own language (pride or scorn); and the absence of many immigrants speaking other languages and swamping native languages (as happened with the Russian influx into Siberia, the Nepali influx into Sikkim, and the Indonesian influx into Indonesian New Guinea).

Presumably among the languages with the most secure futures are the official national languages of the world’s sovereign states, which now number about 192. However, most states have officially adopted English, Spanish, Arabic, Portuguese, or French, leaving only about 70 states to opt for other languages. Even if one counts regional languages, such as the 22 specified in India’s constitution, that yields at best a few hundred languages officially protected anywhere in the world. Alternatively, one might consider languages with over a million speakers as secure, regardless of their official status, but that definition also yields only 200 or so secure languages, many of which duplicate the list of official languages. Some small languages are safe because of governmental support, such as Faroese, spoken by the 50,000 inhabitants of Denmark’s self-governing Faroe Islands, and Icelandic, spoken as the official language of 300,000 Icelanders. Conversely, some languages with over a million speakers but no or until recently limited state support are threatened, such as Nahuatl (over 1,400,000 speakers in Mexico) and Quechua (about 9,000,000 speakers in the Andes). But state support doesn’t guarantee a language’s safety, as illustrated by the fading of the Irish language and the rise in the English language in Ireland, despite strong Irish governmental support for Irish and the teaching of Irish as an official language in Irish schools. It’s on these bases that linguists estimate that all except a few hundred of the world’s current 7,000 languages will be extinct or moribund by the end of this century—if current trends continue.

Are minority languages harmful?

Those are the overwhelming facts of worldwide language extinction. But now let’s ask, as do many or most people: so what? Is language loss really a bad thing? Isn’t the existence of thousands of languages positively harmful, because they impede communication and promote strife? Perhaps we should actually encourage language loss. This view was expressed by a deluge of listener comments sent into the British Broadcasting Corporation after it broadcast a program trying to defend the value of disappearing languages. Here is a sample of the quotes:

“What an extraordinary amount of sentimental rubbish! The reason that languages died out was that they were the expression of moribund societies incapable of communicating the intellectual, cultural, and social dynamics required for sustained longevity and evolution.”

“How ridiculous. The purpose of language is to communicate. If nobody speaks a language, it has no purpose. You might as well learn Klingon.”

“The only people that 7,000 languages are useful to are linguists. Different languages separate people, whereas a common language unites. The fewer living languages, the better.”

“Humanity needs to be united, that’s how we go forwards, not in small-knit tribes unable to communicate with one another. What good is there in even having five languages? Document them by all means, learn what we can from them, but consign them to history where they belong. One world, one people, one common language, one common goal, perhaps then we can all just get along.”

“7,000 languages is 6,990 too many if you ask me. Let them go.”

There are two main reasons that people like those who wrote to the BBC give in order to justify getting rid of most of the world’s languages. One objection can be summarized in the one-liner “We need a common language in order to communicate with each other.” Yes, of course that’s true; different people do need some common language in order to communicate with each other. But that doesn’t require eliminating minority languages; it just requires that speakers of minority languages become bilingual themselves in a majority language. For example, Denmark is the seventh-richest country in the world, although virtually the only people who speak the Danish language are the 5,000,000 Danes. That’s because almost all Danes also fluently speak English and some other European languages, which they use to do business. Danes are rich and happily Danish, because they speak Danish. If Danes want to go to the effort of becoming bilingual in Danish and English, that’s their own business. Similarly, if Navajo Indians want to go to the effort of becoming bilingual in Navajo and English, that’s their business. The Navajos aren’t asking and don’t even want other Americans to learn Navajo.

The other main reason that people such as those who wrote to the BBC give to justify getting rid of languages is the belief that multiple languages cause civil wars and ethnic strife, by encouraging people to view other peoples as different. The civil wars tearing apart so many countries today are determined by linguistic lines—so it is claimed. Whatever the value of multiple languages, getting rid of them may supposedly be the price we have to pay if we are to halt the killing around the globe. Wouldn’t the world be a much more peaceful place if the Kurds would just switch to speaking Turkish or Arabic, if Sri Lanka’s Tamils would consent to speak Sinhalese, and if Quebec’s French and the U.S. Hispanics would just switch to English?

That seems like a strong argument. But its implicit assumption of a monolingual utopia is wrong: language differences aren’t the most important cause of strife. Prejudiced people will seize on any difference to dislike others, including differences of religion, politics, ethnicity, and dress. The worst mass killings in Europe since the end of World War II involved Eastern Orthodox Serbs and Montenegrans (who later split from each other), Catholic Croats, and Muslim Bosnians in the former Yugoslavia slaughtering each other, even though all of them speak the same language, Serbo-Croat. The worst mass killings in Africa since the end of World War II were in Rwanda in 1994, when Hutu people killed nearly a million Tutsi and most of Rwanda’s Twa people, all of them speaking the Rwanda language. The worst mass killings anywhere in the world since the end of World War II were in Cambodia, where Khmer-speaking Cambodians under their dictator Pol Pot killed about two million other Khmer-speaking Cambodians. The worst mass killings anywhere in the world, anytime in history, were in Russia under Stalin, when Russians killed tens of millions of people, most of whom also spoke Russian, over supposed political differences.

If you believe that minorities should give up their languages and adopt the majority language in order to promote peace, ask yourself whether you also believe that minorities should promote peace by giving up their religions, their ethnicities, and their political views. If you believe that freedom of religion, ethnicity, and political view but not of language is an inalienable human right, how would you explain your inconsistency to a Kurd or a French Canadian? Innumerable examples besides those of Stalin, Pol Pot, Rwanda, and the former Yugoslavia warn us that monolingualism is no safeguard of peace.

Given that people do differ in language, religion, ethnicity, and political view, the only alternative to tyranny or mass killing is for people to live together in mutual tolerance. That’s not an idle hope. Despite all the past wars over religion, people of different religions do co-exist peacefully in the United States, Germany, Indonesia, and many other countries. Similarly, many countries that practise linguistic tolerance find that they can accommodate people of different languages in harmony: for example, 2 native languages in the Netherlands (Dutch and Frisian), 2 in New Zealand (English and Maori), 3 in Finland (Finnish, Swedish, and Lapp), 4 in Switzerland (German, French, Italian, and Romansh), 43 in Zambia, 85 in Ethiopia, 128 in Tanzania, and 286 in Cameroon. On a trip to Zambia when I visited a high school classroom, I recall one student asking me, “Which tribe in the United States do you belong to?” Then each student told me, with a smile, his or her tribal language. Seven languages were represented in that small classroom, and no one seemed ashamed, afraid, or intent on killing each other.

Why preserve languages?

All right, so there’s nothing inevitably harmful or burdensome about preserving languages except the effort of bilingualism for the minority speakers themselves, and they can decide for themselves whether they’re willing to put up with that effort. Are there any positive advantages of preserving linguistic diversity? Why shouldn’t we just let the world converge on its five top languages of Mandarin, Spanish, English, Arabic, and Hindi? Or let’s push that argument one step further, before my English-speaking readers enthusiastically answer, “Yes!” If you think that small languages should give way to big languages, a logical conclusion is that we should all adopt the world’s biggest language, Mandarin, and let English die out. What’s the use of preserving the English language? Among many answers, I’ll mention three.

First, with two or more languages, we as individuals can be bilingual or multilingual. I discussed earlier in this chapter the evidence for cognitive advantages of bilingual individuals. Even if you’re skeptical about bilingualism’s reported protection against symptoms of Alzheimer’s disease, everyone fluent in more than one language knows that knowledge of different languages enriches one’s life, just as a large vocabulary in one’s first language permits a richer life than does a small vocabulary. Different languages have different advantages, such that it’s easier to express some things, or to feel in certain ways, in one language than in another. If the much-debated Sapir-Whorf hypothesis is correct, a language’s structure molds the way in which that language’s speakers think, with the result that one views the world and thinks differently when one switches languages. Hence language loss doesn’t only curtail freedom of minorities; it also curtails the options of majorities.

Second, languages are the most complex product of the human mind, each differing in its sounds, structure, and pattern of thought. But a language itself isn’t the only thing lost when a language goes extinct. Literature, culture, and much knowledge are encoded in languages: lose the language, and you lose much of the literature, culture, and knowledge. Different languages have different number systems, mnemonic devices, and systems of spatial orientation: for instance, it’s easier to count in Welsh or Mandarin than in English. Traditional peoples have local-language names for hundreds of animal and plant species around them: those encyclopedias of ethnobiological information vanish when their languages vanish. While Shakespeare can be translated into Mandarin, we English-speakers would regard it as a loss to humanity if Hamlet’s speech “To be or not to be, that is the question” were available only in Mandarin translation. Tribal peoples also have their own oral literatures, and losses of those literatures also represent losses to humanity.

But perhaps you’re still thinking, “Enough of all this vague talk about linguistic freedom, unique cultural inheritance, and different options for thinking and expressing. Those are luxuries that rate low priority amid the crises of the modern world. Until we solve the world’s desperate socio-economic problems, we can’t waste our time on bagatelles like obscure Native American languages.”

Then please think again about the socio-economic problems of the people speaking all those obscure Native American languages (and thousands of other obscure languages around the world). They are the poorest segment of American society. Their problems are not just narrow ones of jobs, but broad ones of cultural disintegration. Groups whose language and culture disintegrate tend to lose their pride and mutual self-support, and to descend into socio-economic problems. They’ve been told for so long that their language and everything else about their culture are worthless that they believe it. The resulting costs to national governments of welfare benefits, healthcare expenses, alcohol-related and drug-related problems, and drain on rather than contribution to the national economy are enormous. At the same time, other minorities with strong intact cultures and language retention—like some recent groups of immigrants to the U.S.—are already contributing strongly to the economy rather than taking from it. Among native minorities as well, those with intact cultures and languages tend to be stronger economically and to place fewer demands on social services. Cherokee Indians who complete Cherokee language school and remain bilingual in Cherokee and English are more likely to pursue their education, obtain jobs, and earn higher salaries than Cherokees who can’t speak Cherokee. Aboriginal Australians who learn their traditional tribal language and culture are less prone to substance abuse than are culturally disconnected Aborigines.

Programs to reverse Native American cultural disintegration would be more effective and cheaper than welfare payments, for Native American minorities and for majority taxpayers alike. Such programs aim at long-term solutions; welfare payments don’t. Similarly, those countries now racked by civil wars along linguistic lines would have found it cheaper to emulate countries (like Switzerland, Tanzania, and many others) based on partnerships between proud intact groups than to seek to crush minority languages and cultures.

Language as a focus of national identity can mean the difference between group survival and disappearance not only to minorities within a country but to whole nations as well. Consider the situation in Britain early in World War II, in May and June of 1940, when French resistance to the invading Nazi armies was collapsing, when Hitler had already occupied Austria and Czechoslovakia and Poland and Norway and Denmark and the Low Countries, when Italy and Japan and Russia had signed alliances or pacts with Hitler, and when the United States was still determined to remain neutral. Britain’s prospects of prevailing against the impending German invasion appeared bleak. Voices within the British government argued that Britain should seek to make some deal with Hitler, rather than to attempt a hopeless resistance.

Winston Churchill responded in the House of Commons on May 13 and June 4, 1940, with the two most quoted and most effective 20th-century speeches in the English language. Among other things, he said, “I have nothing to offer but blood, toil, tears and sweat…. You ask, what is our policy? I will say. It is to wage war, by sea, land, and air, with all our might and with all the strength that God can give us: to wage war against a monstrous tyranny, never surpassed in the dark, lamentable catalog of human crime…. We shall not flag or fail. We shall go on to the end, we shall fight in France, we shall fight in the seas and ocean, we shall fight with growing confidence and growing strength in the air, we shall defend our island, whatever the cost may be, we shall fight on the beaches, we shall fight on the landing-grounds, we shall fight in the fields and in the streets, we shall fight in the hills; we shall never surrender.”

We know now that Britain never did surrender, did not seek a settlement with Hitler, continued to fight, after a year gained Russia and then the United States as allies, and after five years defeated Hitler. But that outcome was not predestined. Suppose that the absorption of small European languages by large languages had reached the point in 1940 at which the British and all other Western Europeans had adopted Western Europe’s largest language, namely, German. What would have happened in June 1940 if Churchill had been addressing the House of Commons in the German language, rather than in English?

My point is not that Churchill’s words were untranslatable; they ring as powerful in German as in English. (“Anbieten kann ich nur Blut, Müh, Schweiss, und Träne….”) My point is instead that the English language is a proxy for everything that made the British keep fighting against seemingly hopeless odds. Speaking English means being heir to a thousand years of independent culture, history, increasing democracy, and island identity. It means being heir to Chaucer, Shakespeare, Tennyson, and other monuments of literature in the English language. It means having different political ideals from Germans and other continental Europeans. In June 1940, speaking English meant having something worth fighting and dying for. While no one can prove it, I doubt that Britain would have resisted Hitler in June 1940 if the British had already been speaking German. Preservation of one’s linguistic identity is not a bagatelle. It keeps Danes rich and happy, and some native and immigrant minorities prosperous, and it kept Britain free.

How can we protect languages?

If you now at last agree that linguistic diversity isn’t harmful and might even be good, what can be done to slow the present trend of dwindling linguistic diversity? Are we helpless in the face of the seemingly overwhelming forces tending to eradicate all but a few big languages from the modern world?

No, we’re not helpless. First, professional linguists themselves could do a lot more than most of them are now doing. The great majority of linguists assign low priority to the study of vanishing languages. Only recently have more linguists been calling attention to our impending loss. It’s ironic that so many linguists have remained uninvolved at a time when languages, the subject of their discipline, are disappearing. Governments and society could train and support more linguists to study and tape-record the last speakers of dying languages, so as to preserve the option that surviving members of the population can revive the language even after the last aged speaker dies—as happened with the Cornish language in Britain, and as may now be happening with the Eyak language in Alaska. A notable success story of language revival is the modern reestablishment of Hebrew as a vernacular language, now spoken by 5,000,000 people.

Second, governments can support minority languages by policies and by allotting money. Examples include the support that the Dutch government gives to the Frisian language (spoken by about 5% of the Netherlands’ population), and that the New Zealand government gives to the Maori language (spoken by under 2% of New Zealand’s population). After two centuries of opposing Native American languages, the U.S. government in 1990 passed an act to encourage their use, and then allocated a small amount of money (about $2,000,000 per year) to Native American language studies. As that number illustrates, though, governmental support for endangered languages has a long way to go. The money that the U.S. government spends to preserve endangered animal and plant species dwarfs its expenditures to preserve endangered languages, and the money spent on one bird species alone (the California condor) exceeds that spent on all of our 100-plus endangered Native American languages combined. As a passionate ornithologist, I’m all in favor of spending money for condors, and I wouldn’t want to see money transferred from condor programs to Eyak language programs. Instead, I mention this comparison to illustrate what seems to me a gross inconsistency in our priorities. If we value endangered birds, why don’t we assign at least as much value to endangered languages, whose importance one might think would be easier for us humans to understand?

Third, there’s a lot that minority speakers themselves can do to promote their languages, as the Welsh, Quebec French, and various Native American groups have been doing recently with some success. They are the living custodians of their language—the people in by far the best position to pass the language on to their children and to other members of the group, and to lobby their government for support.

But such minority efforts will continue to face an uphill struggle if strongly opposed by the majority, as has happened all too often. Those of us majority-speakers and our governmental representatives who don’t choose actively to promote minority languages can at least remain neutral and avoid crushing them. Our motives for doing so include ultimately selfish motives as well as the interests of minority groups themselves: to pass on a rich and strong world, rather than a drastically impoverished and chronically sapped world, to our children.

Non-communicable diseases

When I began working in Papua New Guinea in 1964, the vast majority of New Guineans still lived largely traditional lifestyles in their villages, growing their own food and consuming a low-salt, low-sugar diet. The dietary staples in the Highlands were root crops (sweet potato, taro, and yams) providing about 90% of Highlanders’ caloric intake, while the lowland staple was starch grains from the heart of sago palm trees. People with some cash bought small quantities of trade store foods as luxury items: crackers, tinned fish, and a little salt and sugar.

Among the many things that impressed me about New Guineans was their physical condition: lean, muscular, physically active, all of them resembling slim Western body-builders. When not carrying loads, they ran along steep mountain trails at a trot, and when carrying heavy loads they walked all day at my own unencumbered walking pace. I recall a small woman who appeared to weigh no more than 100 pounds, carrying a 70-pound rice bag resting on her back and suspended by a strap around her forehead, up boulder-strewn river beds and mountains. During those early years in New Guinea I never saw a single obese or even overweight New Guinean.

New Guinea hospital records, and medical examinations of New Guineans by physicians, confirmed this appearance of good health—at least in part. The non-communicable diseases that kill most First World citizens today—diabetes, hypertension, stroke, heart attacks, atherosclerosis, cardiovascular diseases in general, and cancers—were rare or unknown among traditional New Guineans living in rural areas. The absence of those diseases wasn’t just because of a short average lifespan: they still didn’t appear even among those New Guineans who did live into their 60s, 70s, and 80s. An early-1960s review of 2,000 admissions to the medical ward of the general hospital of Port Moresby (the capital and largest city) detected not a single case of coronary artery disease, and only four cases of hypertension, all four in patients of mixed racial origins rather than unmixed New Guineans.

But that’s not to say that traditional New Guineans enjoyed a carefree health utopia: far from it. The lifespans of most of them were, and still are, shorter than in the West. The diseases that killed them, along with accidents and interpersonal violence, were ones that have by now been largely eliminated as causes of death in the First World: gastrointestinal infections producing diarrhea, respiratory infections, malaria, parasites, malnutrition, and secondary conditions preying on people weakened by those primary conditions. That is, we Westerners, despite having traded our set of traditional human illnesses for a new set of modern illnesses, enjoy on the average better health and longer lives.

Already in 1964, the new killers of First World citizens were beginning to make their appearance in New Guinea, among those populations that had had the longest contact with Europeans and had begun to adopt Western diets and lifestyles. Today, that Westernization of New Guinea diets, lifestyles, and health problems is in a phase of explosive growth. Tens of thousands, perhaps hundreds of thousands, of New Guineans now work as businesspeople, politicians, airline pilots, and computer programmers, obtain their food in supermarkets and restaurants, and get little exercise. In cities, towns, and Westernized environments one commonly sees overweight or obese New Guineans. One of the highest prevalences of diabetes in the world (estimated at 37%) is among the Wanigela people, who were the first New Guinea population to become extensively Westernized. Heart attacks are now reported among city-dwellers. Since 1998 I have been working in a New Guinea oil field whose employees eat all three daily meals in a buffet-style cafeteria where one helps oneself to food, and where each dining table has a salt-shaker and sugar-shaker. New Guineans who grew up in traditional village lifestyles with limited and unpredictable food availability react to these predictable daily food bonanzas by piling their plates as high as possible at every meal, and inverting the salt and sugar dispensers over their steaks and salads. Hence the oil company hired trained New Guinean health workers to educate staff on the importance of healthy eating. But even some of those health workers soon develop Western health problems.

These changes that I have been watching unfold in New Guinea are just one example of the wave of epidemics of non-communicable diseases (NCDs) associated with the Western lifestyle and now sweeping the world. Such diseases differ from infectious (communicable) and parasitic diseases, which are caused by an infectious agent (such as a bacterium or virus) or a parasite, and which are transmitted (“communicate” themselves) from person to person through spread of the agent. Many infectious diseases develop quickly in a person after infection by the agent, such that within a few weeks the victim is either dead or recovering. In contrast, all of the major NCDs (as well as parasitic diseases and some infectious diseases, such as AIDS and malaria and tuberculosis) develop slowly and persist for years or decades until they either reach a fatal end or are cured or halted, or until the victim dies of something else first. Major NCDs in the current wave include various cardiovascular diseases (heart attacks, strokes, and peripheral vascular diseases), the common form of diabetes, some forms of kidney disease, and some cancers such as stomach, breast, and lung cancers. The vast majority of you readers of this book—e.g., almost 90% of all Europeans and Americans and Japanese—will die of one of these NCDs, while the majority of people in low-income countries die of communicable diseases.

All of these NCDs are rare or absent among small-scale societies with traditional lifestyles. While the existence of some of these diseases is attested already in ancient texts, they became common in the West only within recent centuries. Their association with the current explosive spread of the modern Western lifestyle around the world becomes obvious from their epidemics among four types of population. In the cases of some countries that became rich recently and suddenly, and most of whose inhabitants now “enjoy” the Western lifestyle—Saudi Arabia and the other Arab oil-producing nations, plus several suddenly affluent island nations including Nauru and Mauritius—the entire national population is at risk. (For instance, of the world’s eight countries with national diabetes prevalences above 15%, every one is either an Arab oil-producer or an affluent island nation.) Other epidemics are striking citizens of developing nations who emigrated to the First World, suddenly exchanged their formerly spartan lifestyle for a Western lifestyle, and are thereby developing NCD prevalences higher either than those of their countrymen who stayed home and continued their traditional lifestyle, or than those of long-term residents of their new host countries. (Examples include Chinese and Indians emigrating overseas [to Britain, the U.S., Mauritius, and other destinations more affluent than China or India], and Yemenite and Ethiopian Jews emigrating to Israel.) Urban epidemics are being recorded in many developing countries, such as Papua New Guinea, China, and numerous African nations, among people who migrate from rural areas to cities and thereby adopt a sedentary lifestyle and consume more store-bought food. Finally, still other epidemics involve specific non-European groups that have adopted a Western lifestyle without migrating, and that have thereby sadly become famous for some of the world’s highest prevalences of diabetes and other NCDs. Often-cited textbook examples include the Pima Indians of the U.S., New Guinea’s Wanigela people, and numerous groups of Aboriginal Australians.

These four sets of natural experiments illustrate how the adoption of a Western lifestyle, no matter what leads to it, by people previously with a traditional lifestyle results in NCD epidemics. What these natural experiments don’t tell us, without further analysis, is which particular component or components of the Western lifestyle trigger the epidemic. That lifestyle includes many components occurring together: low physical activity, high calorie intake, weight gain or obesity, smoking, high alcohol consumption, and high salt consumption. Diet composition usually shifts to low intake of fiber and high intakes of simple sugars (especially fructose), saturated fats, and trans-unsaturated fats. Most or all of these changes happen simultaneously when a population Westernizes, and that makes it difficult to identify the relative importance of individual ones of these changes in causing an NCD epidemic. For a few diseases the evidence is clear: smoking is especially important as a cause of lung cancer, and salt intake is especially important as a cause of hypertension and stroke. But for the other diseases, including diabetes and several cardiovascular diseases, we still don’t know which of these co-occurring risk factors are most relevant.

Our understanding of this field has been stimulated especially by the pioneering work of S. Boyd Eaton, Melvin Konner, and Marjorie Shostak. Those authors assembled information on our “Paleolithic diet”—i.e., the diet and lifestyle of our hunter-gatherer ancestors and of modern surviving hunter-gatherers—and on the differences between the principal diseases affecting our ancestors and modern Westernized populations. They reasoned that our non-communicable diseases of civilization arise from a mismatch between our bodies’ genetic constitution, still largely adapted to our Paleolithic diet and lifestyle, and our current diet and lifestyle. They proposed tests of their hypothesis and offered recommendations about diet and lifestyle to reduce our exposure to our new diseases of civilization. References to their original articles and book will be found under the Further Readings for this chapter.

Non-communicable diseases associated with the Western lifestyle offer perhaps this book’s most immediately practical example of the lessons that can be extracted from traditional lifestyles. By and large, traditional people don’t develop the set of the NCDs that I’ve discussed, while by and large most Westernized people will die of these NCDs. Of course, I’m not suggesting that we adopt a traditional lifestyle wholesale, overthrow state governments, and resume killing each other, infanticide, religious wars, and periodic starvation. Instead, our goal is to identify and adopt those particular components of the traditional lifestyle that protect us against NCDs. While a full answer will have to wait for more research, it’s a safe bet that the answer will include traditional low salt intake and won’t include traditional lack of state government. Tens of millions of people around the world already consciously use our current understanding of risk factors in order to lead healthier lives. In the remainder of this chapter I shall discuss two NCD epidemics in more detail: the consequences of high salt intake and of diabetes.

Our salt intake

While there are many different chemicals falling into the category termed “salts” by chemists, to laypeople “salt” means sodium chloride. That’s the salt that we crave, season our food with, consume too much of, and get sick from. Today, salt comes from a salt-shaker on every dining table and ultimately from a supermarket, is cheap, and is available in essentially unlimited quantities. Our bodies’ main problem with salt is to get rid of it, which we do copiously in our urine and in our sweat. The average daily salt consumption around the world is about 9 to 12 grams, with a range mostly between 6 and 20 grams (higher in Asia than elsewhere).

Traditionally, though, salt didn’t come from salt-shakers but had somehow to be extracted from the environment. Imagine what the world used to be like before salt-shakers became ubiquitous. Our main problem with salt then was to acquire it rather than to get rid of it. That’s because most plants contain very little sodium, yet animals require sodium at high concentrations in all their extracellular fluids. As a result, while carnivores readily obtain their needed sodium by eating herbivores full of extracellular sodium, herbivores themselves face problems in obtaining that sodium. That’s why the animals that you see coming to salt licks are deer and antelope, not lions and tigers. Human hunter-gatherers who consumed much meat, such as the Inuit and San, thus met their salt requirement readily, though even their total salt intake was only 1 or 2 grams per day because much of their prey’s sodium-rich blood and other extracellular fluids became lost in the course of butchering and cooking. Among traditional hunter-gatherers and farmers consuming a diet high in plant food and with limited meat, those living on the seacoast or near inland salt deposits also have easy access to salt. For instance, average daily salt consumption is around 10 grams among the Lau people of the Solomon Islands, who live on the coast and use salt water for cooking, and also among Iran’s Qashqa’i nomadic herders, whose homeland has natural salt deposits on the surface.

However, for dozens of other traditional hunter-gatherers and farmers whose daily salt intake has been calculated, it falls below 3 grams. The lowest recorded value is for Brazil’s Yanomamo Indians, whose staple food is low-sodium bananas, and who excrete on the average only 50 milligrams of salt daily: about 1/200 of the salt excretion of the typical American. A single Big Mac hamburger analyzed by Consumer Reports contained 1.5 grams (1,500 milligrams) of salt, representing one month’s salt intake for a Yanomamo, while one can of chicken noodle soup (containing 2.8 grams of salt) represents nearly two months of Yanomamo salt consumption. A possible record was set by a Chinese-American restaurant near my home in Los Angeles. Its double pan-fried noodles combo dish was reportedly analyzed as containing one year and three days’ worth of Yanomamo salt intake: 18.4 grams.

Hence traditional peoples crave salt and go to great lengths to obtain it. (We, too, crave salt: just try eating nothing but fresh, unprocessed, unsalted food for one day, and then see how wonderful salt tastes when you finally sprinkle some on your food.) New Guinea Eastern Highlanders with whom I have worked, and whose diet consists up to 90% of low-sodium sweet potatoes, told me of the efforts to which they used to go to make salt a few decades ago, before Europeans brought it as trade goods. They gathered leaves of certain plant species, burned them, scraped up the ash, percolated water through it to dissolve the solids, and finally evaporated the water to obtain small amounts of bitter salt. The Dugum Dani people of the Western New Guinea Highlands made salt from the only two natural brine pools in their valley, by plunging a spongy piece of banana trunk into a pool to soak up brine, removing the piece and drying it in the sun, burning it to ash, and then sprinkling water on the ash and kneading the moist mass into cakes to be consumed or traded. After all that traditional effort to obtain small quantities of impure bitter-tasting salt, it’s no wonder that New Guineans eating in Western-style cafeterias can’t resist grabbing the salt-shaker on the dining table and letting the stream of pure salt run out onto their steaks and salads at every meal.

With the rise of state governments, salt became widely available and produced on an industrial scale (as it still is today) from salt-water drying pans, salt mines, or surface deposits. To its use as a seasoning was added its use, reportedly discovered in China around 5,000 years ago, to preserve food for storage over the winter. Salt cod and salt herring became fixtures of the European diet, and salt became the most traded and most taxed commodity in the world. Roman soldiers were paid in salt, so that our word “salary” for pay is derived not from the Latin root for “money” or “coins” but from the Latin root for “salt” (sal). Wars were fought over salt; revolutions broke out over salt taxes; and Mahatma Gandhi rallied Indians against the perceived injustice of British colonial rule by walking for one month to the ocean, violating British laws by illegally making salt for himself on the beach from the freely available salt water, and refusing to pay the British salt tax.

As a result of the relatively recent adoption of a high-salt diet by our still largely traditional bodies adapted to a low-salt diet, high salt intake is a risk factor for almost all of our modern non-communicable diseases. Many of these damaging effects of salt are mediated by its role in raising blood pressure, which I’ll discuss below. High blood pressure (alias hypertension) is among the major risk factors for cardiovascular diseases in general, and for strokes, congestive heart disease, coronary artery disease, and myocardial infarcts in particular, as well as for Type-2 diabetes and kidney disease. Salt intake also has unhealthy effects independent of its role in raising blood pressure, by thickening and stiffening our arteries, increasing platelet aggregation, and increasing the mass of the heart’s left ventricle, all of which contribute to the risk of cardiovascular diseases. Still other effects of salt intake independent of blood pressure are on the risks of stroke and stomach cancer. Finally, salt intake contributes indirectly but significantly to obesity (in turn a further risk factor for many non-communicable diseases) by increasing our thirst, which many people satisfy in part by consuming sugary high-calorie soft drinks.

Salt and blood pressure

Let’s now pause for a quick crash course on blood pressure and hypertension, to help you understand what those numbers mean when your doctor inflates a rubber cuff about your arm, listens, deflates the cuff, and finally pronounces, “Your blood pressure is 120 over 80.” Blood pressure is expressed in units of millimeters of mercury: the height to which your blood pressure would force up a column of mercury in case, God forbid, your artery were suddenly connected to a vertical mercury column. Naturally, your blood pressure changes throughout each heart stroke cycle: it rises as the heart squeezes, and it falls as the heart relaxes. Hence your physician measures a first number and then a second number (e.g., 120 and 80 millimeters of mercury), referring respectively to the peak pressure at each heartbeat (called systolic pressure) and to the minimum pressure between beats (termed diastolic pressure). Blood pressure varies somewhat with your position, activity, and anxiety level, so the measurement is usually made while you are resting flat on your back and supposedly calm. Under those conditions, 120 over 80 is an average reading for Americans. There is no magic cut-off between normal blood pressure and high blood pressure. Instead, the higher your blood pressure, the more likely you are to die of a heart attack, a stroke, kidney failure, or a ruptured aorta. Usually, a pressure reading higher than 140 over 90 is arbitrarily defined as constituting hypertension, but some people with lower readings will die of a stroke at age 50, while others with higher readings will die of a car accident in otherwise good health at age 90.

In the short run, your blood pressure increases with your anxiety level and with vigorous exercise. In the long run, though, it increases with other factors, especially with salt intake (for reasons discussed below) and (in us Westernized moderns but not in traditional peoples) with age. The relationship between salt intake and blood pressure was noted more than 2,000 years ago in the Chinese medical text Huangdi neijing suwen, which says, “Therefore if large amounts of salt are taken, the pulse will stiffen and harden.” In recent experiments on captive chimpanzees, our closest animal relatives, their blood pressure while consuming a Purina Monkey Chow diet providing 6 to 12 grams of salt per day (like most modern humans eating a Western diet) was a pleasingly healthy 120 over 50, but it increased with age (also like modern humans on a Western diet). After a year and seven months on a high-salt diet of up to about 25 grams per day, the chimps’ blood pressure rose to about 155 over 60, qualifying them to be called hypertensive by human standards, at least as judged by their systolic blood pressure.

For us humans it’s clear that salt intake does influence blood pressure, at least at the opposite extremes of very low and very high salt intake. The international INTERSALT project of the 1980s used a uniform methodology to measure salt intake and blood pressure in 52 populations around the world. The population that I already mentioned as having the world’s lowest recorded salt intake, Brazil’s Yanomamo Indians, also had the world’s lowest average blood pressure, an astonishingly low 96 over 61. The two populations with the next two lowest salt intakes, Brazil’s Xingu Indians and Papua New Guinea Highlanders of the Asaro Valley, had the next two lowest blood pressures (100 over 62, and 108 over 63). These three populations, and several dozen other populations around the world with traditional lifestyles and low salt intakes, showed no increase in blood pressure with age, in contrast to the rise with age in Americans and all other Westernized populations.

At the opposite extreme, doctors regard Japan as the “land of apoplexy” because of the high frequency of fatal strokes (Japan’s leading cause of death, five times more frequent than in the United States), linked to high blood pressure and notoriously salty food. Within Japan these factors reach their extremes in northern Japan’s Akita Prefecture, famous for its tasty rice, which Akita farmers flavor with salt, wash down with salty miso soup, and alternate with salt pickles between meals. Of 300 Akita adults studied, not one consumed less than 5 grams of salt daily (three months of consumption for a Yanomamo Indian), the average Akita consumption was 27 grams, and the most salt-loving individual consumed an incredible 61 grams—enough to devour the contents of the usual 26-ounce supermarket salt container in a mere 12 days. That record-breaking Akita man consumed daily as much salt as an average Yanomamo Indian in three years and three months. The average blood pressure in Akita by age 50 was 151 over 93, making hypertension the norm. Not surprisingly, Akita’s frequency of death by stroke was more than double even the Japanese average, and in some Akita villages 99% of the population died before 70.

The evidence is thus striking that extreme variations in salt intake have big effects on blood pressure: very low salt intake results in very low blood pressure, and very high salt intake results in very high blood pressure. However, most of us will never follow a diet as extreme as that of a Yanomamo Indian or an Akita farmer. Instead, we would like to know whether more modest variations in salt intake, within the middle of the range of world salt intakes, have at least some modest effects on blood pressure. For several reasons, it really isn’t surprising that there is still some controversy about effects of variation within this middle range. The middle range encompasses only a narrow spread of salt intake: for instance, 48 of the 52 populations in the INTERSALT study (all populations except the Yanomamo and the three other low-salt outliers) had mean salt intakes falling between 6 and 14 grams per day. Individual variation in salt intake and blood pressure within most populations is large and tends to obscure average differences between populations. Salt intake itself is notoriously difficult to measure consistently unless one confines people in a hospital metabolic ward for a week and measures salt levels in all of their foods consumed and urine produced. That’s completely impossible to do for Yanomamo Indians in the jungle, as well as for most of us city-dwellers wanting to lead normal lives outside metabolic wards. Instead, salt intake is commonly estimated from 24-hour urine collections, but those values are subject to huge variation from day to day, depending on whether one happens to eat a Big Mac or a can of chicken noodle soup on some particular day.

Despite those causes of uncertainty, many natural experiments as well as manipulative experiments indicate to me that variations of salt intake within the normal range do affect blood pressure. Regional variation, migration, and individual variation provide natural experiments. Salt intake is higher for coastal people than for interior people in Newfoundland and in the Solomon Islands, and it’s higher for rural Nigerians living near a salt lake than for nearby rural Nigerians not living near a salt lake; in each case the higher-salt population has higher average blood pressure. When rural Kenyans or Chinese move to cities, their salt intake often rises, and so does their blood pressure. Salt intake in Japan nearly doubles from south to north to reach its maximum in the already-mentioned Akita Prefecture in the north, and that salt trend is paralleled by a trend in hypertension and in deaths from stroke. Among individual Japanese in a single city (Takayama), hypertension and stroke deaths increase with salt intake.

As for manipulative experiments, Americans on a (mildly) low-salt diet for 30 days, New Guineans on a (mildly) high-salt diet for 10 days, and Chinese on a (mildly) low-salt or high-salt diet for 7 days all experienced a rise or fall in blood pressure paralleling the experimental rise or fall in salt intake. Epidemiologists in a suburb of the Dutch city of The Hague, with the cooperation of the mothers of 476 newborn infants, randomly assigned the infants (most of them breast-fed) for six months to either of two diets of food supplements differing by a factor of 2.6 in salt content. The blood pressure of the slightly high-salt babies increased progressively above the blood pressure of the slightly low-salt babies over the course of the six months, when the experimental intervention ended and the babies proceeded to eat whatever they wanted for the next 15 years. Interestingly, the effects of those six months of salt intake in infancy proved to be permanent: as teen-agers, the former slightly high-salt babies still had blood pressures above those of the slightly low-salt babies (perhaps because they had become permanently conditioned to choose salty food). Finally, in at least four countries notorious for high average levels of salt consumption and resulting stroke deaths—China, Finland, Japan, and Portugal—government public health campaigns that lasted years or decades achieved local or national reductions in blood pressure and in stroke mortality. For instance, a 20-year campaign in Finland to reduce salt intake succeeded in lowering average blood pressure, and thereby cut 75% or 80% off of deaths from stroke and coronary heart disease and added 5 or 6 years to Finnish life expectancies.

Causes of hypertension

For us to be able to deal with the problem of high blood pressure, we have to understand what else besides high salt intake can cause it, and why high salt intake can cause it in some individuals but not in others. Why is it that some of us have much higher blood pressure than do others of us? In 5% of hypertensive patients there proves to be a clearly identifiable single cause, such as hormonal imbalance or use of oral contraceptives. In 95% of patients, though, there is no such obvious cause. The clinical euphemism for our ignorance in such cases is “essential hypertension.”

We can assess the role of genetic factors in essential hypertension by comparing how closely blood pressure agrees between closer or more distant relatives. Among people living in the same household, identical twins, who share all of their genes, have quite similar blood pressure; the similarity is lower but still significant for fraternal twins, ordinary siblings, or a parent and biological child, who share about half of their genes. The similarity is still lower for adopted siblings or a parent and adopted child, who have no direct genetic connection but share the same household environment. (For those of you familiar with statistics and correlation coefficients, the correlation coefficient for blood pressure is 0.63 between identical twins, 0.25 between fraternal twins or parent and biological child, and 0.05 between adopted siblings or parent and adopted child. A coefficient of 1.00 between identical twins would mean that blood pressure is almost completely determined by genes, and that nothing you do [after being conceived] has any effect on your blood pressure.) Evidently, our genes do have a big effect on our blood pressure, but environmental factors also play a role, because identical twins have very similar but not identical blood pressures.

To place these results in perspective, let’s contrast hypertension with a simple genetic disease like Tay-Sachs disease. Tay-Sachs disease is due to a defect in a single gene; every Tay-Sachs patient has a defect in that same gene. Everybody in whom that gene is defective is certain to die of Tay-Sachs disease, regardless of the victim’s lifestyle or environment. In contrast, hypertension usually involves many different genes, each of which individually has a small effect on blood pressure. Hence different hypertensive patients are likely to owe their condition to different gene combinations. Furthermore, whether someone genetically predisposed to hypertension actually develops symptoms depends a lot on lifestyle. Thus, hypertension is not one of those uncommon, homogeneous, and intellectually elegant diseases that geneticists prefer to study. Instead, like diabetes and ulcers, hypertension is a shared set of symptoms produced by heterogeneous causes, all involving an interaction between environmental agents and a susceptible genetic background.

Many environmental or lifestyle factors contributing to the risk of hypertension have been identified by studies that compare hypertension’s frequency in groups of people living under different conditions. It turns out that, besides salt intake, other significant risk factors include obesity, exercise, high intake of alcohol or saturated fats, and low calcium intake. The proof of this approach is that hypertensive patients who modify their lifestyles so as to minimize these putative risk factors often succeed in reducing their blood pressure. We’ve all heard the familiar mantra of our doctor: reduce salt intake and stress, reduce intake of cholesterol and saturated fats and alcohol, lose weight, cut out smoking, and exercise regularly.

So, how does the link between salt and blood pressure work? That is, by what physiological mechanisms does increased salt intake lead to a rise in blood pressure, in many but not all people? Much of the explanation involves an expansion of the body’s extracellular fluid volume. For normal people, if we increase our salt intake, the extra salt is excreted by our kidneys into our urine. But in individuals whose kidney salt excretion mechanisms are impaired, excretion can’t keep pace with increased salt intake. The resulting excess of retained salt in those people triggers a sensation of thirst and makes them drink water, which leads to an increase in blood volume. In response, the heart pumps more, and blood pressure rises, causing the kidney to filter and excrete more salt and water under that increased pressure. The result is a new steady state, in which salt and water excretion again equals intake, but more salt and water are stored in the body and blood pressure is raised.

But why does a rise in blood pressure with increased salt intake show itself in some people but not in most people? After all, most people manage to retain a “normal” blood pressure despite consuming over 6 grams of salt per day. (At least Western physicians consider their blood pressure normal, although a Yanomamo physician wouldn’t.) Hence high salt intake by itself doesn’t automatically lead to hypertension in everybody; it happens in only some individuals. What’s different about them?

Physicians apply a name to such individuals in whom blood pressure responds to a change in salt intake: they’re termed “salt-sensitive.” Relatively twice as many hypertensive individuals as normotensive individuals (people with normal blood pressure) turn out to be salt-sensitive. Nevertheless, most deaths due to elevated blood pressure are not among hypertensives, defined as people having greatly elevated blood pressure (140 over 90), but among normotensive individuals with only moderately elevated blood pressure—because normotensive people far outnumber hypertensives, and the greater individual risk of death in hypertensives isn’t by a sufficiently large factor to offset the larger factor by which normotensives outnumber hypertensives. As for the specific physiological difference between hypertensive and normotensive people, there is much evidence that the primary problem of hypertensive people lies somewhere in their kidneys. If one transplants a kidney from a normotensive rat to a hypertensive rat as an experiment, or from a normotensive human kidney donor to a seriously ill hypertensive human in order to help the hypertensive person, the recipient’s blood pressure falls. Conversely, if one transplants a kidney from a hypertensive rat to a normotensive rat, the latter’s blood pressure rises.

Other evidence pointing to a hypertensive person’s kidneys as the site of origin of the hypertension is that most of the many human genes known to affect blood pressure turn out to code for proteins involved in kidney sodium processing. (Remember that salt is sodium chloride.) Our kidneys actually excrete sodium in two stages: first, a filter called the glomerulus at the beginning of each kidney tubule filters blood plasma (containing salt) into the tubule; and second, most of that filtered sodium is then re-absorbed back into the blood by the rest of the tubule beyond the glomerulus; the filtered sodium that isn’t re-absorbed ends up excreted into the urine. Changes in either of those two steps can lead to high blood pressure: older people tend towards high blood pressure because they have lower glomerular filtration, and hypertensives tend to it because they have more tubular re-absorption of sodium. The result in either case—less sodium filtration, or more sodium re-absorption—is more sodium and water retention and higher blood pressure.

Physicians commonly refer to the postulated high tubular sodium re-absorption of hypertensive people as a “defect”: for example, physicians say, “Kidneys of hypertensives have a genetic defect in excreting sodium.” As an evolutionary biologist, though, I hear warning bells going off inside me whenever a seemingly harmful trait that occurs frequently in a long-established and large human population is dismissed as a “defect.” Given enough generations, genes that greatly impede survival are very unlikely to spread, unless their net effect is somehow to increase survival and reproductive success. Human medicine has furnished the best example of seemingly defective genes being propelled to high frequency by counter-balancing benefits. For example, sickle-cell hemoglobin is a mutant gene that tends to cause anemia, which is undoubtedly harmful. But the gene also offers some protection against malaria, and so the gene’s net effect in malarious areas of Africa and the Mediterranean is beneficial. Thus, to understand why untreated hypertensives are prone to die today as a result of their kidneys’ retaining salt, we need to ask under what conditions people might have benefited from kidneys good at retaining salt.

The answer is simple. Under the conditions of low salt availability experienced by most humans throughout most of human history until the recent rise of salt-shakers, those of us with efficient salt-retaining kidneys were better able to survive our inevitable episodes of salt loss from sweating or from an attack of diarrhea. Those kidneys became a detriment only when salt became routinely available, leading to excessive salt retention and hypertension with its fatal consequences. That’s why blood pressure and the prevalence of hypertension have shot up recently in so many populations around the world, now that they have made the transition from traditional lifestyles with limited salt availability to being patrons of supermarkets. Note the evolutionary irony: those of us whose ancestors best coped with salt-deficiency problems on Africa’s savannahs tens of thousands of years ago are now the ones at highest risk of dying from salt-excess problems today on the streets of Los Angeles.

Dietary sources of salt

If by now you’re convinced that it would be healthy for you to decrease your salt intake, how can you go about it? I used to think that I had already done it, and that my own salt habits were virtuous, because I never, ever, sprinkle salt on my food. While I’ve never measured my salt intake or output, I naively assumed it to be low. Alas, I now realize that, if I did measure it, I would find it to be far above Yanomamo levels, and not so far below the levels of Americans who use salt-shakers.

The reason for this sad realization has to do with the sources from which we actually ingest our dietary salt. In North America and Europe only about 12% of our salt intake is added in the home and with our knowledge, either by whoever is cooking or by the individual consumer at the table. It’s only that 12% that I virtuously eliminated. The next 12% is salt naturally present in the food when it’s fresh. Unfortunately, the remaining 75% of our salt intake is “hidden”: it comes already added by others to food that we buy, either processed food or else restaurant food to which the manufacturer or the restaurant cook respectively added the salt. As a result, Americans and Europeans (including me) have no idea how high is their daily salt intake unless they subject themselves to 24-hour urine collections. Abstaining from the use of salt-shakers doesn’t suffice to lower drastically your salt intake: you also have to be informed about selecting the foods that you buy, and the restaurants in which you eat.

Processed foods contain quantities of salt impressively greater than the quantities in the corresponding unprocessed foods. For instance, compared to fresh unsalted steamed salmon, tinned salmon contains 5 times more salt per pound, and store-bought smoked salmon contains 12 times more. That quintessential fast-food meal of one take-away cheeseburger and fried potatoes contains about 3 grams of salt (one-third of a day’s total average salt intake for an American), 13 times the salt content of an otherwise similar home-made unsalted steak and fried potatoes. Some other processed foods with especially high salt content are canned corned beef, processed cheese, and roast peanuts. Surprisingly to me, the biggest source of dietary salt in the U.S. and UK is cereal products—bread, other baked goods, and breakfast cereals—which we usually don’t think of as being salty.

Why do manufacturers of processed foods add so much salt? One reason is that it’s a nearly costless way to make cheap unpalatable foods edible. Another reason is that increasing the salt content of meat increases the weight of water bound in meat, so the final product weight can cheaply be increased 20% by bound water. In effect, the manufacturer provides less meat itself and still gets the same price for a “pound” of meat, which actually now consists of only 83% original meat plus 17% bound water. Yet another reason is that salt is a major determinant of thirst: the more salt you consume, the more fluid you drink, but much of what Americans or Europeans drink is soft drinks and bottled waters, some of them sold by the same companies selling you the salty snacks and processed foods that made you thirsty. Finally, the public has become addicted to salt and now prefers salted to unsalted foods.

A different picture for the breakdown of the sources of consumed salt emerges in East and South Asia and most of the developing world, where most ingested salt doesn’t come from processed or restaurant foods but from salt added in the consumer’s own house. For instance, in China 72% of ingested salt is added during cooking or at the table, and another 8% is in salty soy sauce. In Japan the main sources of ingested salt are soy sauce (20%), salty miso soup (10%), salted vegetables and fruits (10%), fresh and salted fish (10%), and salt added in restaurants, in fast-food outlets, and at home (10%). That’s why salt intake in many Asian countries exceeds 12 grams per day. In developing countries, salt in sauces, seasonings, and pickled foods contributes along with salt added during cooking.

The high national health costs that hypertension, stroke, and other salt-related diseases inflict in the form of medical and hospital expenses and lost work lives have now motivated some governments to mount long-lasting national campaigns to help their citizens decrease their salt intake. But the governments quickly realized that they couldn’t achieve that goal without enlisting the cooperation of the food industry to reduce the amounts of salt added by the industry to processed foods. The reductions have been gradual ones of just 10% or 20% less salt added to foods every year or two—a reduction too small for the public to notice. The UK, Japan, Finland, and Portugal have operated such campaigns for between two and four decades, resulting in the decreases in salt intake and consequent reductions in national medical costs and improvements in national health statistics that I already mentioned.

Are we citizens of industrial nations thus helpless pawns in the hands of food manufacturers, and is there little that we can do to lower our salt intake and blood pressure except to pray for an effective government anti-salt campaign? Actually, there is a big step that you can take besides avoiding use of salt-shakers: you can eat a healthy diet high in fresh foods and low in processed foods—specifically, a diet high in vegetables, fruits, fiber, complex carbohydrates, low-dairy products including cheeses, whole grains, poultry, fish (yes, you can eat fatty fish), vegetable oils, and nuts, but low in red meat, sweets, sugar-containing beverages, butter, cream, cholesterol, and saturated fats. In controlled experiments on volunteers, such a diet, termed a DASH diet—Dietary Approaches to Stop Hypertension—markedly lowers blood pressure.

Perhaps you’re already thinking: “There’s no way that I’ll subject myself to a tasteless low-fat diet and destroy my pleasure in food, just in order to live 10 more years! I’d rather enjoy 70 years filled with great food and wine than 80 years of tasteless low-salt crackers and water.” In fact, the DASH diet is modeled on the so-called Mediterranean diet, with a luscious fat content of 38%, getting its name from the fact that that’s what Italians, Spaniards, Greeks, and many French people actually eat traditionally. (That fat of the DASH and Mediterranean diets is high in so-called mono-unsaturated fat, the type of fat that is good for us.) Those people aren’t eating crackers and water: they’re enjoying the greatest cuisines of Western civilization. Italians, who spend hours every day consuming their glorious pastas, breads, cheeses, olive oils, and other triumphs of Italian kitchens and farms, are still on the average among the slimmest people in the Western world. At the same time, we Americans, whose diet is anything but Mediterranean, have on the average the biggest waistlines in the Western world. One-third of adult Americans are obese, and another one-third of us are “merely” overweight, but we don’t even have the consolation of knowing that it’s the price we pay for the pleasures of Italian cuisine. You, too, can enjoy great food and be healthy.

Diabetes

Western diets that are high in sugar and in sugar-yielding carbohydrates are to diabetes as salt is to hypertension. When my twin sons were still too young to have learned healthy eating habits, taking them to a supermarket meant for my wife and me traversing a gauntlet of sweet dangers. Among breakfast foods, my kids were tempted by the choice between Apple Cinnamon Cheerios and Fruit Loops, respectively 85% and 89% carbohydrate according to their manufacturers, with about half of that carbohydrate in the form of sugar. Boxes picturing the famous turtles with Ninja powers seduced children to ask for Teenage Mutant Ninja Turtles Cheese Pasta Dinner, 81% carbohydrate. Snack choices included Fruit Bears (92% carbohydrate, no protein) and Teddy Graham’s Bearwich chocolate cookies with vanilla cream (71% carbohydrate); both listed corn syrup, as well as sugar, among their ingredients.

All of these foods contained little or no fiber. Compared with the diet to which our evolutionary history adapted us, they differed in their much higher content of sugar and other carbohydrates (71% to 95% instead of about 15% to 55%) and much lower protein and fiber content. I mention these particular brands, not because they are unusual, but precisely because their content was typical of what was available. Around the year 1700 sugar intake was only about 4 pounds per year per person in England and the U.S. (then still a colony), but it is over 150 pounds per year per person today. One-quarter of the modern U.S. population eats over 200 pounds of sugar per year. A study of U.S. eighth-graders showed that 40% of their diet consisted of sugar and sugar-yielding carbohydrates. With foods like the ones I just mentioned lurking in supermarkets to tempt kids and their parents, it’s no wonder that consequences of diabetes, the commonest disease of carbohydrate metabolism, will be the cause of death for many readers of this book. It’s also no wonder that we readers suffer from tooth decay and cavities, which are very rare in the !Kung. While living in the 1970s in Scotland, where consumption of pastries and sweets was prodigious, I was told that some Scottish people had already as teen-agers lost most of their teeth due to tooth decay.

The ultimate cause of the many types of damage that diabetes wreaks on our bodies is high blood concentrations of the sugar glucose. They cause the spilling-over of glucose into the urine: a manifestation from which stems the disease’s full name, diabetes mellitus, meaning “running-through of honey.” Diabetes isn’t infectious or rapidly fatal, so it doesn’t command press headlines, as does AIDS. Nevertheless, the world epidemic of diabetes today far eclipses the AIDS epidemic in its toll of death and suffering. Diabetes disables its victims slowly and reduces their quality of life. Because all cells in our body become exposed to sugar from the bloodstream, diabetes can affect almost any organ system. Among its secondary consequences, it is the leading cause of adult blindness in the U.S.; the second leading cause of non-traumatic foot amputations; the cause of one-third of our cases of kidney failure; a major risk factor for stroke, heart attacks, peripheral vascular disease, and nerve degeneration; and the cause of over $100 billion of American health costs annually (15% of our costs due to all diseases combined). To quote Wilfrid Oakley, “Man may be the captain of his fate, but he is also the victim of his blood sugar.”

As of the year 2010, the number of diabetics in the world was estimated at around 300 million. This value may be an underestimate, because there were likely to be other undiagnosed cases, especially in medically undersurveyed countries of the developing world. The growth rate in the number of diabetics is about 2.2% per year, or nearly twice the growth rate of the world’s adult population: i.e., the percentage of the population that is diabetic is increasing. If nothing else changes in the world except that the world’s population continues to grow, to age, and to move to cities (associated with a more sedentary lifestyle and hence increased prevalence of diabetes), then the number of cases predicted for the year 2030 is around 500 million, which would make diabetes one of the world’s commonest diseases and biggest public health problems. But the prognosis is even worse than that, because other risk factors for diabetes (especially affluence and rural obesity) are also increasing, so that the number of cases in 2030 will probably be even higher. The current explosion in diabetes’ prevalence is occurring especially in the Third World, where the epidemic is still in its early stages in India and China, the world’s two most populous countries. Formerly considered a disease mainly of rich Europeans and North Americans, diabetes passed two milestones by the year 2010: more than half of the world’s diabetics are now Asians, and the two countries with the largest number of diabetics are now India and China.

Types of diabetes

What normally happens when we consume some glucose (or other glucose-containing carbohydrates)? As the sugar is absorbed from our intestine, its concentration in our blood rises, signaling the pancreas to release the hormone insulin. That hormone in turn signals the liver to decrease glucose production, and signals muscle and fat cells to take up the glucose (thereby halting the rise in blood glucose concentration) and to store it as glycogen or as fat, to be used for energy between meals. Other nutrients, such as amino acids, also trigger the release of insulin, and insulin has effects on food components other than sugar (such as preventing the breakdown of fat).

Many different things can go wrong in that normal course of events, and so the term “diabetes mellitus” covers a wide variety of underlying problems linked by shared symptoms arising from high levels of blood sugar. That diversity can be crudely partitioned into two groups of diseases: so-called Type-2 or non-insulin-dependent diabetes mellitus (also known as “adult-onset diabetes”), and the much less common Type-1 or insulin-dependent diabetes mellitus (also known as “juvenile-onset diabetes”). The latter is an autoimmune disease in which a person’s antibodies destroy the person’s own pancreatic cells that secrete insulin. Type-1 diabetics tend to be thin, to produce no insulin, and to require multiple daily injections of insulin. Many of them carry certain genes (certain so-called HLA alleles) that code for elements of the immune system. Type-2 diabetes instead involves increased resistance of body cells to the person’s own insulin, so that cells fail to take up glucose at normal rates. As long as the pancreas can respond by releasing more insulin, the cells’ resistance can be overcome, and blood glucose remains within a normal range. But eventually the pancreas becomes exhausted, it may no longer be able to produce enough insulin to overcome that resistance, blood glucose levels rise, and the patient develops diabetes. Type-2 diabetes patients tend to be obese. In early stages of the disease they can often control their symptoms by dieting, exercising, and losing weight, without requiring tablets or insulin injections.

However, distinguishing Type-2 and Type-1 diabetes can be difficult, because Type-2 diabetes is now increasingly appearing already in teen-agers, while Type-1 diabetes may not first appear until in adulthood. Even Type-2 diabetes (as defined by insulin resistance) is associated with many different genes and manifests itself by varied symptoms. All of my subsequent discussion in this chapter will concern the much more common (about 10 times commoner) Type-2 diabetes, which I shall henceforth refer to simply as “diabetes.”

Genes, environment, and diabetes

More than 2,000 years ago, Hindu physicians noting cases of “honey urine” commented that such cases “passed from generation to generation in the seed” and also were influenced by “injudicious diet.” Physicians today have rediscovered those deadly insights, which we now rephrase by saying that diabetes involves both genetic and environmental factors, and possibly also intra-uterine factors affecting the fetus during pregnancy. Evidence for a role of genes includes the 10-times-higher risk of getting diabetes if you have a diabetic first-degree relative (a parent or a sibling) than if you don’t. But diabetes, like hypertension, is not one of those simple genetic diseases (as is sickle-cell anemia) in which a mutation in the same gene is responsible for the disease in every patient. Instead, dozens and dozens of different genetic susceptibility factors for diabetes have been identified, many of them united only by their common feature that a mutation in any of those genes may result in high blood-glucose levels due to insulin resistance. (I mention again that these comments apply to Type-2 diabetes; Type-1 diabetes involves its own separate set of genetic susceptibility factors.)

In addition to those genetic factors in diabetes, diabetes also depends upon environmental and lifestyle factors. Even if you are genetically predisposed to diabetes, you won’t necessarily get the disease, as would be the case if you carried a pair of genes for muscular dystrophy or Tay-Sachs disease. The risk of developing diabetes increases with age, and with having diabetic first-degree relatives, and with being born of a diabetic mother, which you yourself can’t do anything about. But other risk factors that predict diabetes are factors under our control, including especially being overweight, not exercising, eating a high-calorie diet, and consuming much sugar and fat. Most diabetics (I emphasize again, most Type-2 diabetics) can reduce their symptoms by reducing those risk factors. For example, the prevalence of diabetes is 5 to 10 times higher in obese people than in those of normal weight, so that diabetes patients can often regain health by dieting, exercising, and losing weight, and those same measures can protect people predisposed to diabetes against getting the disease.

Many types of natural experiments, including ones that I mentioned at the beginning of this chapter as demonstrating the relation between the Western lifestyle and non-communicable diseases in general, specifically illustrate the role of environmental factors in diabetes. The worldwide rise in those factors underlies the current worldwide diabetes epidemic. One such type of natural experiment involves the rise and fall of diabetes prevalences accompanying the rise and fall of Western lifestyle and affluence in the same population. In Japan, graphs against time of diabetes prevalence and economic indicators are parallel, down to details of year-to-year wiggles. That’s because people eat more, hence they risk developing more diabetes symptoms, when they have more money. Diabetes and its symptoms decline or disappear in populations under starvation conditions, such as French diabetes patients under the severe food rationing imposed during the 1870–1871 siege of Paris. Groups of Aboriginal Australians who temporarily abandoned their acquired sedentary Western lifestyle and resumed their traditional vigorous foraging reversed their symptoms of diabetes; one such group lost an average of 18 pounds of body weight within seven weeks. (Remember that obesity is one of the leading risk factors for diabetes.) Decreases in diabetes symptoms and in waist circumference were also noted for Swedes who for three months abandoned their very un-Mediterranean Swedish diet (over 70% of calories from sugar, margarine, dairy products, alcohol, oil, and cereals) and adopted instead a Mediterranean diet typical of slim Italians. Swedes who adopted a “Paleolithic diet” designed to resemble that of hunter-gatherers became even healthier and developed even slimmer waists.

Another natural experiment is provided by the sky-high explosions of diabetes among groups that emigrated and thereby gave up a vigorous Spartan lifestyle to adopt sedentary high-calorie low-exercise living based on abundant supermarket food. A dramatic example involved the Yemenite Jews who were airlifted to Israel by Operation Magic Carpet in 1949 and 1950, and were thereby plunged abruptly into the 20th century from formerly medieval conditions. Although Yemenite Jews were almost free of diabetes upon reaching Israel, 13% of them then became diabetic within two decades. Other migrants who sought opportunity and instead found diabetes included Ethiopian Jews moving to Israel, Mexicans and Japanese moving to the U.S., Polynesians moving to New Zealand, Chinese moving to Mauritius and Singapore, and Asian Indians moving to Mauritius, Singapore, Fiji, South Africa, the U.S., and Britain.

Developing countries that have recently been growing more affluent and Westernized have correspondingly been growing more diabetic. In first place stand the eight Arab oil-producers and newly affluent island nations that now lead the world in national diabetes prevalences (all of them above 15%). All Latin American and Caribbean countries now have prevalences above 5%. All East and South Asian countries have prevalences above 4% except for five of the poorest countries, where prevalences remain as low as 1.6%. The high prevalences of the more rapidly developing countries are a recent phenomenon: India’s prevalence was still below 1% as recently as 1959 but is now 8%. Conversely, most sub-Saharan African countries are still poor and still have prevalences below 5%.

Those national averages conceal large internal differences that constitute further natural experiments. Around the world, urbanization results in less exercise and more supermarket food, obesity, and diabetes. Individual urban populations that thereby achieved notably high diabetes prevalences include the already mentioned Wanigela people of Papua New Guinea’s capital city (37% prevalence) and several groups of urban Aboriginal Australians (up to 33%). Both of those cases are all the more striking because diabetes was unknown among New Guineans and Australians under traditional conditions.

Thus, the Western lifestyle somehow increases the risk that those enjoying it will become diabetic. But the Western lifestyle consists of many interlinked components: which components contribute most to the risk of diabetes? While it isn’t easy to tease apart the effects of correlated influences, it appears that the three strongest risk factors are obesity and sedentary lifestyle (which you can do something about) and family history of diabetes (which you can’t do anything about). Other risk factors that you can’t control are either high or low birth weight. While diet composition surely acts at least in part by its relation to obesity, it also seems to have some independent influence: among people matched for obesity, those consuming a Mediterranean diet appear to be at lower risk than those with high intakes of sugar, saturated fatty acids, cholesterol, and triglycerides. Not exercising may create risks mainly through predisposing towards obesity, while smoking, inflammation, and high alcohol consumption appear to be independent risk factors. In short, Type-2 diabetes originates with genetic factors and possibly intra-uterine factors, which may become unmasked later in life by lifestyle factors resulting in disease symptoms.

Pima Indians and Nauru Islanders

These proofs of an environmental role in diabetes are illustrated by the tragedies of the two peoples with the highest rates of diabetes in the world: Pima Indians and Nauru Islanders. To consider the Pimas first, they survived for more than 2,000 years in the deserts of southern Arizona, using agricultural methods based on elaborate irrigation systems, supplemented by hunting and gathering. Because rainfall in the desert varies greatly from year to year, crops failed about one year in every five, forcing the Pimas then to subsist entirely on wild foods, especially wild jackrabbits and mesquite beans. Many of their preferred wild plants were high in fiber, low in fat, and released glucose only slowly, thereby constituting an ideal antidiabetic diet. After this long history of periodic but brief bouts of starvation, the Pimas experienced a more prolonged bout of starvation in the late 19th century, when white settlers diverted the headwaters of the rivers on which the Pimas depended for irrigation water. The result was crop failures and widespread starvation. Today the Pimas eat store-bought food. Observers who visited the Pimas in the early 1900s reported obesity to be rare and diabetes almost non-existent. Since the 1960s, obesity has become widespread among the Pimas, some of whom now weigh more than 300 pounds. Half of them exceed the U.S. 90th percentile for weight in relation to height. Pima women consume about 3,160 calories per day (50% over the U.S. average), 40% of which is fat. Associated with this obesity, Pimas have achieved notoriety in the diabetes literature by now having the highest frequency of diabetes in the world. Half of all Pimas over age 35, and 70% of those at ages 55 to 64, are diabetic, leading to tragically high occurrences of blindness, limb amputations, and kidney failure.

My second example is Nauru Island, a small remote tropical Pacific island colonized by Micronesians in prehistoric times. Nauru was annexed by Germany in 1888, was occupied by Australia in 1914, and eventually achieved independence in 1968 as the world’s smallest republic. However, Nauru also has a less welcome distinction as the grimly instructive site of a rarely documented phenomenon: an epidemic of a genetic disease. Our familiar epidemics of infectious diseases flare up when transmission of the infectious agent increases, and then wane when the number of susceptible potential victims falls, due both to acquired immunity of the survivors and to differential mortality of those who are genetically susceptible. An epidemic of a genetic disease flares up instead because of a rise in environmental risk factors, and then wanes when the number of susceptible potential victims falls (but only because of the preferential deaths of those who are genetically more susceptible, not because of acquired immunity; one doesn’t acquire immunity to diabetes).

The traditional lifestyle of Nauruans was based on agriculture and fishing and involved frequent episodes of starvation because of droughts and the island’s poor soils. Early European visitors nevertheless noted that Nauruans were plump, and that they admired big fat people and put girls on a diet to fatten them and so make them more attractive in their eyes. In 1906 it was discovered that most of Nauru underlying those poor soils consists of rock with the world’s highest concentration of phosphate, an essential ingredient of fertilizer. In 1922 the mining company extracting the rock finally began to pay royalties to the islanders. As a result of this new wealth, average sugar consumption by Nauruans reached a pound per day in 1927, and laborers were imported because Nauruans disliked working as miners.

During the Second World War Nauru was occupied by Japanese military forces, who imposed forced labor, reduced food rations to half a pound of pumpkin per day, and then deported most of the population to Truk, where half of them died of starvation. When the survivors returned to Nauru after the war, they regained their phosphate royalties, abandoned agriculture almost completely, and resumed shopping in supermarkets, heaping their shopping carts with big bags of sugar and eating double their recommended calorie intake. They became sedentary and came to rely on motor vehicles to travel around their little island (averaging one and a half miles in radius). Following independence in 1968, per-capita annual phosphate royalties rose to $23,000, making Nauruans among the world’s richest people. Today they are the most obese Pacific Island population, and the one with the highest average blood pressure. Their average body weight is 50% greater than that of white Australians of the same height.

Although colonial European physicians on Nauru knew how to recognize diabetes and diagnosed it there in non-Nauruan laborers, the first case in a Nauruan was not noted until 1925. The second case was recorded in 1934. After 1954, however, the disease’s prevalence rose steeply, and it became the commonest cause of non-accidental death. One-third of all Nauruans over the age of 20, two-thirds of those over age 55, and 70% of those few who survive to the age of 70 are diabetics. Within the past decade the disease’s prevalence has begun to fall, not because of mitigation of environmental risk factors (obesity and the sedentary lifestyle are as common as ever), but presumably because those who are genetically most susceptible have died. If this interpretation should prove correct, then Nauru would provide the most rapid case known to me of natural selection in a human population: an occurrence of detectable population-wide selection within less than 40 years.

Diabetes in India

Table 11.1 summarizes for comparison some prevalences of diabetes around the world. It’s obvious that there are big differences among countries in their national average prevalences, ranging from low values of 1.6% in Mongolia and Rwanda up to high values of 19% in the United Arab Emirates and 31% in Nauru. But Table 11.1 also illustrates that these national averages conceal equally big differences within any given country related to differences in lifestyle: at least in developing countries, wealthy or Westernized or urban populations tend to have much higher prevalences than do poor or traditional or rural populations.

India provides excellent examples of those subnational differences. (For this information I am grateful to Professor V. Mohan, of the Madras Diabetes Research Foundation.) The average prevalence in India as of the year 2010 was 8%. But there was little diabetes in India until just a few decades ago. Surveys in 1938 and 1959, in large cities (Calcutta and Mumbai) that are today strongholds of diabetes, yielded prevalences of only 1% or less. Only in the 1980s did those numbers start to rise, first slowly and now explosively, to the point where India today harbors more diabetics (over 40,000,000) than any other nation. The reasons are essentially the same as those behind the diabetes epidemic around the world: urbanization, rise in standard of living, the spread of calorie-rich sweet and fatty fast foods cheaply available in cities to rich and poor people alike, and increased sedentariness associated with replacement of manual labor by service jobs, and with video games and television and computers that keep children (and adults) seated lethargically watching screens for hours every day. Although the specific role of TV has not been quantified in India, a study in Australia found that each hour per day spent watching TV is associated with an 18% increase in cardiovascular mortality (much of it related to diabetes), even after controlling for other risk factors such as waist circumference, smoking, alcohol intake, and diet. But those factors notoriously increase with TV watching time, so the true figure must be even larger than that 18% estimate.

Table 11.1. Prevalences of Type-2 diabetes around the world

The numbers in the right-hand column are prevalences of diabetes in percent: i.e., the percent of the population suffering from Type-2 diabetes. These values are so-called age-standardized prevalences, which have the following meaning. Because Type-2 prevalence in a given population increases with age, it would be misleading to compare raw values of prevalence between two populations that differ in their age distributions: the raw values would be expected to differ merely as a result of the different age distributions (prevalence would be higher in the older population), even if prevalences at a given age were identical between the two populations. Hence one measures the prevalence in a population as a function of age, then calculates what the prevalence would be for that whole population if it had a certain standardized age distribution.

Note the higher prevalences in wealthy, Westernized, or urban populations than in poor, traditional, or rural populations of the same people. Note also that those lifestyle differences give rise to contrasting low-prevalence and high-prevalence (over 12%) populations in every human group examined except Western Europeans, among whom there is no high-prevalence population by world standards, for reasons to be discussed. The table also illustrates the rise and subsequent fall of prevalence on Nauru Island, caused by rapid Westernization and then by the operation of natural selection against victims of diabetes.

Buried within that national average prevalence of 8% is a wide range of outcomes for different groups of Indians. At the low extreme, prevalence is only 0.7% for non-obese, physically active, rural Indians. It reaches 11% for obese, sedentary, urban Indians and peaks at 20% in the Ernakulam district of southwest India’s Kerala state, one of the most urbanized states. An even higher value is the world’s second-highest national prevalence of diabetes, 24%, on the Indian Ocean island of Mauritius, where a predominantly Indian immigrant community has been approaching Western living standards faster than any population within India itself.

Among the lifestyle factors predictive of diabetes in India, some are also familiar as predictors in the West, while other factors turn Western expectations upside down. Just as in the West, diabetes in India is associated with obesity, high blood pressure, and sedentariness. But European and American diabetologists will be astonished to learn that diabetes’ prevalence is higher among affluent, educated, urban Indians than among poor, uneducated, rural people: exactly the opposite of trends in the West, although similar to trends noted in other developing countries including China, Bangladesh, and Malaysia. For instance, Indian diabetes patients are more likely to have received graduate and higher education, and are less likely to be illiterate, than non-diabetics. In 2004 the prevalence of diabetes averaged 16% in urban India and only 3% in rural India; that’s the reverse of Western trends. The likely explanation for these paradoxes invokes two respects in which the Western lifestyle has spread further through the population and been practised for more years in the West than in India. First, Western societies are much wealthier than Indian society, so poor rural people are much better able to afford fast foods inclining their consumers towards diabetes in the West than in India. Second, educated Westerners with access to fast foods and sedentary jobs have by now often heard that fast foods are unhealthy and that one should exercise, whereas that advice has not yet made wide inroads among educated Indians. Nearly 25% of Indian city-dwellers (the subpopulation most at risk) haven’t even heard of diabetes.

In India as in the West, diabetes is due ultimately to chronically high blood glucose levels, and some of the clinical consequences are similar. But in other respects—whether because lifestyle factors or people’s genes differ between India and the West—diabetes in India differs from the disease as we know it in the West. While Westerners think of Type-2 diabetes as an adult-onset disease appearing especially over the age of 50, Indian diabetics exhibit symptoms at an age one or two decades younger than do Europeans, and that age of onset in India (as in many other populations as well) has been shifting towards ever-younger people even within the last decade. Already among Indians in their late teens, “adult-onset” (Type-2 or non-insulin-dependent) diabetes manifests itself more often than does “juvenile-onset” (Type-1 or insulin-dependent) diabetes. While obesity is a risk factor for diabetes both in India and in the West, diabetes appears at a lower threshold value of obesity in India and in other Asian countries. Symptoms also differ between Indian and Western diabetes patients: Indians are less likely to develop blindness and kidney disease, but are much more likely to suffer coronary artery disease at a relatively young age.

Although poor Indians are currently at lower risk than are affluent Indians, the rapid spread of fast food exposes even urban slum-dwellers in India’s capital city of New Delhi to the risk of diabetes. Dr. S. Sandeep, Mr. A. Ganesan, and Professor Mohan of the Madras Diabetes Research Foundation summarized the current situation as follows: “This suggests that diabetes [in India] is no longer a disease of the affluent or a rich man’s disease. It is becoming a problem even among the middle income and poorer sections of the society. Studies have shown that poor diabetic subjects are more prone to complications as they have less access to quality healthcare.”

Benefits of genes for diabetes

The evidence for a strong genetic component to diabetes poses an evolutionary puzzle. Why is such a debilitating disease so common among so many human populations, when one might have expected the disease to disappear gradually as those people genetically susceptible to it were removed by natural selection and didn’t produce children carrying their genes?

Two explanations applicable to some other genetic diseases—recurrent mutations and lack of selective consequences—can quickly be eliminated in the case of diabetes. First, if prevalences of diabetes were as low as those of muscular dystrophy (about 1 in 10,000), the genes’ prevalence could be explained as nothing more than the product of recurring mutations: that is, babies with a new mutation being born at the same rate as older bearers of such mutations die of the disease. However, no mutation occurs so frequently as to appear anew in 3% to 50% of all babies, the actual frequency range for diabetes in Westernized societies.

Second, geneticists regularly respond to the evolutionary puzzle by claiming that diabetes kills only older individuals whose child-bearing or child-rearing years are behind them, so the deaths of old diabetics supposedly impose no selective disadvantage on diabetes-predisposing genes. Despite its popularity, this claim is wrong for two obvious reasons. While Type-2 diabetes does appear mainly after age 50 in Europeans, in Nauruans and Indians and other non-Europeans it affects people of reproductive age in their 20s and 30s, especially pregnant women, whose fetuses and newborn babies are also at increased risk. For instance, in Japan today more children suffer from Type-2 than Type-1 diabetes, despite the latter’s name of juvenile-onset diabetes. Moreover (as discussed in Chapter 6), in traditional human societies, unlike modern First World societies, no old person is truly “post-reproductive” and selectively unimportant, because grandparents contribute crucially to the food supply, social status, and survival of their children and grandchildren.

We must therefore instead assume that the genes now predisposing to diabetes were actually favored by natural selection before our sudden shift to a Westernized lifestyle. In fact, such genes must have been favored and preserved independently dozens of times by natural selection, because there are dozens of different identified genetic disorders resulting in (Type-2) diabetes. What good did diabetes-linked genes formerly do for us, and why do they get us into trouble now?

Recall that the net effect of the hormone insulin is to permit us to store as fat the food that we ingest at meals, and to spare us the breakdown of our already accumulated fat reserves. Thirty years ago, these facts inspired the geneticist James Neel to speculate that diabetes stems from a “thrifty genotype” making its bearers especially efficient at storing dietary glucose as fat. For example, perhaps some of us have an especially hair-triggered release of insulin in rapid response to a small rise in blood glucose concentration. That genetically determined quick release would enable those of us with such a gene to sequester dietary glucose as fat, without the blood concentration of glucose rising high enough for it to spill over into our urine. At occasional times of food abundance, bearers of such genes would utilize food more efficiently, deposit fat, and gain weight rapidly, thereby becoming better able to survive a subsequent famine. Such genes would be advantageous under the conditions of unpredictably alternating feast and famine that characterized the traditional human lifestyle (Plate 26), but they would lead to obesity and diabetes in the modern world, when the same individuals stop exercising, begin foraging for food only in supermarkets, and consume high-calorie meals day in and day out (Plate 27). Today, when many of us regularly ingest high-sugar meals and rarely exercise, a thrifty gene is a blueprint for disaster. We thereby become fat; we never experience famines that burn up the fat; our pancreas releases insulin constantly until the pancreas loses its ability to keep up, or until our muscle and fat cells become resistant; and we end up with diabetes. Following Arthur Koestler, Paul Zimmet refers to the spread of this diabetes-promoting First World lifestyle to the Third World as “coca-colonization.”

So accustomed are we in the First World to predictable amounts of food at predictable times each day that we find it hard to imagine the often-unpredictable fluctuations between frequent food shortages and infrequent gluts that constituted the pattern of life for almost all people throughout human evolution until recently, and that remain so in many parts of the world today. I’ve often encountered such fluctuations during my fieldwork among New Guineans still subsisting by farming and hunting. For example, in one memorable incident I hired a dozen men to carry heavy equipment all day over a steep trail up to a mountain campsite. We arrived at the camp just before sunset, expecting to meet there another group of porters carrying food, and instead found that they had not arrived because of a misunderstanding. Faced with hungry, exhausted men and no food, I expected to be lynched. Instead, my carriers just laughed and said, “Orait, i nogat kaikai, i samting nating, yumi slip nating, enap yumi kaikai tumora” (“OK, so there’s no food, it’s no big deal, we’ll just sleep on empty stomachs tonight and wait until tomorrow to eat”). Conversely, on other occasions at which pigs are slaughtered, my New Guinea friends have a gluttonous feast lasting several days, when food consumption shocks even me (formerly rated by my friends as a bottomless pit) and some people become seriously ill from overeating.

Table 11.2. Examples of gluttony when food is abundantly available

These anecdotes illustrate how people accommodate to the pendulum of feast and famine that swung often but irregularly through our evolutionary history. In Chapter 8 I summarized the reasons for the frequency of famine under traditional living conditions: food shortages associated with day-to-day variation in hunting success, short bouts of inclement weather, predictable seasonal variation in food abundance through the year, and unpredictable year-to-year variation in weather; in many societies, little or no ability to accumulate and store surplus food; and lack of state governments or other means to organize and integrate food storage, transport, and exchanges over large areas. Conversely, Table 11.2 collects some anecdotes of gluttony around the world at times when food becomes available in abundance to traditional societies.

Under these traditional conditions of starve-and-gorge existence, those individuals with a thrifty genotype would be at an advantage, because they could store more fat in surplus times, burn fewer calories in spartan times, and hence better survive starvation. To most humans until recently, our modern Western fear of obesity and our diet clinics would have seemed ludicrous, as the exact reverse of traditional good sense. The genes that today predispose us to diabetes may formerly have helped us to survive famine. Similarly, our “taste” for sweet or fatty foods, like our taste for salt, predisposes us to diabetes and hypertension now that those tastes can be satisfied so easily, but formerly guided us to seek valuable rare nutrients. Note again, just as we saw for hypertension, the evolutionary irony. Those of us whose ancestors best survived starvation on Africa’s savannahs tens of thousands of years ago are now the ones at highest risk of dying from diabetes linked to food abundance.

Thus, the starve-and-gorge lifestyle traditionally shared by all human populations resulted in natural selection of genes for a thrifty genotype that served us well under those starve-and-gorge conditions, but that has then caused virtually all populations to end up with a propensity for diabetes under modern Western conditions of unremitting food abundance. But why, by this reasoning, are Pima Indians and Nauruans unusual in their world-record diabetes prevalences? I think that’s because they were subjected in the recent past to world-record strengths of selection for a thrifty genotype. The Pimas started out sharing with other Native Americans their exposure to periodic starvation. They then experienced a further prolonged bout of starvation and selection in the late 19th century, when white settlers ruined their crops by cutting off their sources of irrigation water. Those Pimas who survived were individuals who were genetically even better adapted than other Native Americans to survive starvation by storing fat whenever food had become available. As for Nauruans, they suffered two extreme bouts of natural selection for thrifty genes, followed by an extreme bout of coca-colonization. First, like other Pacific Islanders, but unlike the inhabitants of continental regions, their population was founded by people who undertook inter-island canoe voyages lasting several weeks. In numerous attested examples of such lengthy voyages, many or most of the canoe occupants died of starvation, and only those who were originally the fattest survived. That is why Pacific Islanders in general tend to be heavy people. Second, the Nauruans were then set apart even from most other Pacific Islanders by their extreme starvation and mortality during the Second World War, leaving the population presumably even more enriched in diabetes susceptibility genes. After the war, their newfound wealth based on phosphate royalties, their superabundant food, and their diminished need for physical activity led to exceptional obesity.

Three lines of human evidence and two animal models support the plausibility of Neel’s thrifty-gene hypothesis. Non-diabetic Nauruans, Pima Indians, African Americans, and Aboriginal Australians have postprandial levels of plasma insulin (in response to an oral glucose load) several times those of Europeans. New Guinea Highlanders, Aboriginal Australians, Maasai tribespeople of Kenya, and other peoples with traditional lifestyles have blood glucose levels far below those of white Americans. Given ample food, diabetes-prone populations of Pacific Islanders, Native Americans, and Aboriginal Australians do exhibit more propensity to obesity than do Europeans: first they gain weight, then they develop diabetes. As for animal models, laboratory rats carrying genes predisposing them to diabetes and obesity survive starvation better than do normal rats, illustrating the advantage of those genes under occasional conditions of famine. The Israeli sand rat, which is adapted to a desert environment with frequent scarcities of food, develops high insulin levels, insulin resistance, obesity, and diabetes when maintained in the laboratory on a “Westernized rat diet” with abundant food. But those symptoms reverse when the sand rat’s food is restricted. Hence diabetes-prone laboratory rats and Israeli sand rats serve as models both of the benefits of thrifty genes and of hair-triggered insulin release under “traditional rat conditions” of starve-and-gorge, and of the costs of those genes under “supermarket rat conditions.”

Why is diabetes low in Europeans?

Diabetologists used to point to Pimas and Nauruans as the glaring exceptions of high diabetes prevalence, standing out from a world in which the relatively low diabetes prevalence of Europeans was taken as the norm. But the information that has become available in recent decades shows that, instead, Europeans are the exception in their low prevalence, contrasting with the high prevalence reached by Westernized populations of everyone else. Pimas and Nauruans are “merely” the highest of that normal high prevalence, already approached closely by some Aboriginal Australians and New Guinean groups. For every well-studied large non-European population grouping, we now know of some Westernized subgroup with a prevalence above 11%, usually above 15%: Native Americans, North Africans, sub-Saharan Black Africans, Middle Easterners, Indians, East Asians, New Guineans, Aboriginal Australians, Micronesians, and Polynesians. Compared to that norm, Europeans, and overseas Europeans in Australia, Canada, New Zealand, and the U.S., are unique among the modern world’s populations in their relatively low prevalence. All 41 national European values for the prevalence of diabetes (Table 11.1, first row) fall between 2% and 10%, with a mean value of only 6%.

That’s astonishing when one reflects that Europeans in Europe itself and overseas are the world’s richest and best-fed people, and the originators of the Western lifestyle. We refer to our indolent, obese, supermarket way of life as Western precisely because it arose first among Europeans and white Americans and is only now spreading to other peoples. How can we account for this paradox? Why don’t Europeans now have the highest, rather than the lowest, prevalence of diabetes?

Several experts in the study of diabetes have suggested to me informally that perhaps Europeans traditionally had little exposure to famine, so that they would have undergone little selection for a thrifty genotype. Actually, though, history provides abundant documentation of famines that caused widespread severe mortality in medieval and Renaissance Europe and earlier. Those repeated famines should have selected for thrifty genes in Europe, just as everywhere else. Instead, a more promising hypothesis is based on Europe’s recent food history since the Renaissance. The periodic widespread and prolonged famines that used to rack Europe, like the rest of the world, disappeared between about 1650 and 1900 at different times in different parts of Europe, beginning in the late 1600s in Britain and the Netherlands, and continuing into the late 1800s in southern France and southern Italy. With one famous exception, Europe’s famines were ended by a combination of four factors: increasingly efficient state intervention that rapidly redistributed surplus grain to famine areas; increasingly efficient food transport by land and especially by sea; increasingly diversified European agriculture after Columbus’s voyage of AD 1492, thanks to European voyagers bringing back many New World crops (such as potatoes and corn); and, finally, Europe’s reliance not on irrigation agriculture (as in many populous areas of the world outside Europe) but instead on rain agriculture, which reduced the risk of a crop failure too widespread to be solved by food transport within Europe.

The famous exception to the end of Europe’s famines was of course the Irish potato famine of the 1840s. Actually, that was the exception that proved the rule, by illustrating what happened even in Europe when the first three above-mentioned factors ending famines elsewhere in Europe didn’t operate. The Irish potato famine was due to a disease of a single strain of potato in an agricultural economy that was unusual in Europe in its reliance on that single crop. The famine occurred on an island (Ireland) governed by an ethnically different state centered on another island (Britain) and notorious for the inefficiency or lack of motivation of its response to the Irish famine.

These facts of Europe’s food history lead me to offer the following speculation. Several centuries before the advent of modern medicine, Europeans, like modern Nauruans, may have undergone an epidemic of diabetes that resulted from the new reliability of adequate food supplies, and that eliminated most diabetes-prone bearers of the thrifty genotype, leaving Europe with its low prevalence of diabetes today. Those gene-bearers may have been undergoing elimination in Europe for centuries, as a result of many infants of diabetic mothers dying at birth, diabetic adults dying younger than other adults, and children and grandchildren of those diabetic adults dying of neglect or reduced material support. However, there would have been big differences between that postulated cryptic earlier European epidemic and the well-documented modern epidemics among Nauruans and so many other peoples today. In the modern epidemics, abundant and continually reliable food arrived suddenly—within a decade for Nauruans, and within just a month for Yemenite Jews. The results were sharply peaked surges in diabetes’s prevalence to 20%–50% that have been occurring right under the eyes of modern diabetologists. Those increases will probably wane quickly (as already observed among Nauruans), as individuals with a thrifty genotype become eliminated by natural selection within a mere generation or two. In contrast, Europe’s food abundance increased gradually over the course of several centuries. The result would have been an imperceptibly slow rise in diabetes prevalence in Europe, between the 1400s and the 1700s, long before there were any diabetologists to take note. In effect, Pimas, Nauruans, Wanigelas, educated urban Indians, and citizens of wealthy oil-producing Arab nations are telescoping into a single generation the lifestyle changes and consequent rise and fall of diabetes that unfolded over the course of many centuries in Europe.

A possible victim of this cryptic epidemic of diabetes that I postulate in Europe was the composer Johann Sebastian Bach (born in 1685, died in 1750). While Bach’s medical history is too poorly documented to permit certainty as to the cause of his death, the corpulence of his face and hands in the sole authenticated portrait of him (Plate 28), the accounts of deteriorating vision in his later years, and the obvious deterioration of his handwriting possibly secondary to his failing vision and/or nerve damage are consistent with a diagnosis of diabetes. The disease certainly occurred in Germany during Bach’s lifetime, being known there as honigsüsse Harnruhr (“honey-sweet urine disease”).

The future of non-communicable diseases

In this chapter I’ve discussed just two among the many currently exploding non-communicable diseases (NCDs) linked to the Western lifestyle: hypertension and its consequences, and Type-2 diabetes. Other major NCDs that I haven’t had space to discuss, but that S. Boyd Eaton, Melvin Konner, and Marjorie Shostak do discuss, include coronary artery disease and other heart diseases, arteriosclerosis, peripheral vascular diseases, many kidney diseases, gout, and many cancers including lung, stomach, breast, and prostate cancer. Within the Western lifestyle I’ve discussed only some risk factors—especially salt, sugar, high calorie intake, obesity, and sedentariness. Other important risk factors that I have mentioned only briefly include smoking, high alcohol consumption, cholesterol, triglycerides, saturated fats, and trans fats.

We’ve seen that NCDs are overwhelmingly the leading causes of death in Westernized societies, to which most readers of this book belong. Nor is it the case that you’ll have a wonderful carefree healthy life until you suddenly drop dead of an NCD at age 78 to 81 (the average lifespan in long-lived Western societies): NCDs are also major causes of declining health and decreased quality of life for years or decades before they eventually kill you. But the same NCDs are virtually non-existent in traditional societies. What clearer proof could there be that we have much to learn, of life-and-death value, from traditional societies? However, what they have to teach us is not a simple matter of just “live traditionally.” There are many aspects of traditional life that we emphatically don’t want to emulate, such as cycles of violence, frequent risk of starvation, and short lifespans resulting from infectious diseases. We need to figure out which specific components of traditional lifestyles are the ones protecting those living them against NCDs. Some of those desirable components are already obvious (e.g., exercise repeatedly, reduce your sugar intake), while others are not obvious and are still being debated (e.g., optimal levels of dietary fat).

The current epidemic of NCDs will get much worse before it gets better. Sadly, it has already reached its peak in Pimas and Nauruans. Of special concern now are populous countries with rapidly rising standards of living. The epidemic may be closest to reaching its peak in wealthy Arab oil countries, further short of its peak in North Africa, and under way but still due to become much worse in China and India. Other populous countries in which the epidemic is well launched include Bangladesh, Brazil, Egypt, Indonesia, Iran, Mexico, Pakistan, the Philippines, Russia, South Africa, and Turkey. Countries with lower populations in which the epidemic is also under way include all countries of Latin America and Southeast Asia. It is just beginning among the not-quite 1 billion people of sub-Saharan Africa. When one contemplates those prospects, it’s easy to become depressed.

But we’re not inevitably the losers in our struggles with NCDs. We ourselves are the only ones who created our new lifestyles, so it’s completely in our power to change them. Some help will come from molecular biological research, aimed at linking particular risks to particular genes, and hence at identifying for each of us the particular dangers to which our particular genes predispose us. However, society as a whole doesn’t have to wait for such research, or for a magic pill, or for the invention of low-calorie potato chips. It’s already clear which changes will minimize many (though not all) risks for most of us. Those changes include: not smoking; exercising regularly; limiting our intake of total calories, alcohol, salt and salty foods, sugar and sugared soft drinks, saturated and trans fats, processed foods, butter, cream, and red meat; and increasing our intake of fiber, fruits and vegetables, calcium, and complex carbohydrates. Another simple change is to eat more slowly. Paradoxically, the faster you wolf down your food, the more you end up eating and hence gaining weight, because eating rapidly doesn’t allow enough time for release of hormones that inhibit appetite. Italians are slim not only because of their diet composition but also because they linger talking over their meals. All of those changes could spare billions of people around the world the fates that have already befallen the Pimas and the Nauruans.

This advice is so banally familiar that it’s embarrassing to repeat it. But it’s worth repeating the truth: we already know enough to warrant our being hopeful, not depressed. Repetition merely re-emphasizes that hypertension, the sweet death of diabetes, and other leading 20th-century killers kill us only with our own permission.