Why We Get Sick

by Randolph M. Nesse

  Technological advances later allowed our ancestors to invade other habitats and regions, such as deserts, jungles, and forests. Beginning about one hundred thousand years ago, our ancestors began to disperse from Africa to parts of Eurasia, including seasonally frigid regions made habitable by advances in clothing, habitation, and food acquisition and storage. Yet despite the geographic and climatic diversity, people still lived in small tribal groups with hunter-gatherer economies. Grainfield agriculture, with its revolutionary alteration of human diet and socioeconomic systems, was practiced first in southwest Asia about eight thousand years ago and shortly thereafter in Egypt, India, and China. It took another thousand years or more to spread to central and western Europe and tropical Africa and to begin independently in Latin America. Most of our ancestors of a few thousand years ago still lived in bands of hunter-gatherers. We are, in the words of some distinguished American anthropologists, “Stone Agers in the fast lane.”

  DEATH IN THE STONE AGE

  Imagine what it must have been like in that idyllic era. You were born into a nomadic band of forty to a hundred people. Whatever its size, it was a stable social group. You grew up in the care of various close relatives. Even if your local band consisted of a hundred or more people, many of them were distant cousins. You knew them all and knew their genetic and marital connections to yourself. Some you loved deeply and they loved you in return. If there were those you did not love, at least you knew what to expect from them, and you knew what everyone expected of you. If you occasionally saw strangers, it was probably at a trading site, and you knew what to expect of them too. In a sparsely peopled world the necessities of life—plant and animal foods uncontaminated by pesticides—were there for the taking. You breathed the pure air and drank the pure water of a preindustrial Eden.

  Having asked you to imagine an idyllic past, we now urge that you be more realistic. Like other Golden Age legends, such as the age of chivalry or that delightful antebellum world into which Scarlett O’Hara was born, it is a fabricated myth. Enjoy it in fantasy or fiction, but do not let it mislead serious thought on medicine or human evolution. The unpleasant fact is that our hunter-gatherer ancestors lived with enormous difficulty and hardship. Simple arithmetic on the rates of death and reproduction makes this conclusion inescapable. Death always balanced reproduction, even though people reproduced at something approaching the maximum feasible rate.

  In most primitive social systems, women start bearing children as soon as they are able to do so, which, because of nutritional limitations, is often delayed until about age nineteen. Pregnancy and childbirth are followed by two or three years of lactation, which inhibits ovulation. Then the mother is soon pregnant again, whether this is medically advisable or not. In the unlikely event that she remains fully fertile and survives to menopause, she will probably produce about five babies. Having more children would require shortened lactation periods, and this is unlikely given the limited foods available for babies in preagricultural societies.

  But even if hunter-gatherer women averaged only four children before succumbing to sterility or death, only half their babies could have survived to maturity. Otherwise the human population would have steadily increased, and this obviously did not happen. Even an increase of 1 percent per century would cause a population to become a thousand times as numerous in less than seventy thousand years, but populations remained extremely sparse until the invention of agriculture. The conclusion is thus quantitatively inescapable that deaths almost precisely kept up with births for nearly all of human history. The extraordinarily low death rates of the last few centuries, and especially in the last few decades in Western societies, show that we live in times of unprecedented safety and prosperity. It is no doubt difficult for most readers of this book to appreciate the harshness and insecurity of human life under natural conditions.

  Mortality rates in the Stone Age, like those of today, were highest in infancy and declined throughout childhood. Many early deaths in some groups were from infanticide, motivated by parents’ economic hardship or imposed by patriarchs. While fictional accounts of Stone Age conditions probably exaggerate the ravages of predation and other wild-animal attack, lions, hyenas, and venomous snakes were ever-present hazards and took a steady toll, with children especially vulnerable. Death rates from poisoning and accidents were far higher than they are now.

  The infectious diseases, which were probably the most important source of mortality for all age groups, were not the same bacterial and viral diseases that afflict us today. Most of today’s infections depend on rates of personal contact only possible in abnormally dense populations. Back then, vector-borne protozoa and worms were common causes of prolonged sickness and ultimate death. Many of these diseases are not merely lethal but most unpleasantly so. Some readers will know how unpleasant malaria can be, from personal experience or from knowing someone who has had the disease. It is a lark compared to other protozoan diseases such as kalaazar, which slowly destroys the liver and other viscera; parasites such as lungworms, which cause death by suffocation; hookworms, which are seldom fatal but can make children grow into physically and mentally defective adults; and filaria, which among other things cause elephantiasis. The name comes from the swelling of the limbs and scrotum to elephantine proportions because the parasites block the lymphatic vessels.

  Food was often abundant for hunter-gatherers, but memories of bounteous fruit harvests or an occasional big kill must have been a poor solace during the regularly recurring famines. Climatic variations induce fluctuation in resources. Even in the most stable climates, food abundance varies because of plant and animal diseases. Prior to the invention of reliable preservation techniques, temporarily abundant food could not be saved for leaner times. Even foods preserved by drying or smoking could be attacked by pests that could frustrate the most careful planning for future emergencies.

  Shortages of vital necessities were not only directly stressful, they also encouraged strife. Imagine that people from a hill tribe were suffering from a protein shortage, while people in the valley were feasting on the abundant fish from their lake. The people from the hills would no doubt insist that their leaders take them to that lake, no matter how loudly the valley people asserted their exclusive fishing rights. If catching the fish means killing the fishermen and appropriating their fishing gear, that is what the hill people might decide to do. Even in the absence of economic necessity, human nature often finds excuses for armed robbery and attendant taking of life. Fortunately for early tribal societies, they lacked the technology of transport and communication that permitted banditry on the scale practiced by Genghis Khan or Alexander of Macedon.

  Human nature has, of course, its nobler aspects. There are such things as love and charity and honesty. Unfortunately, the evolutionary origins of such qualities are rooted in their utility in parochial tribal settings. Natural selection clearly favors being kind to close relatives because of their shared genes. It also favors being known to keep one’s promises and not cheating members of one’s local group or habitual trading partners in other groups. There was, however, never any individual advantage from altruism beyond these local associations. Global human rights is a new idea never favored by evolution during the Stone Age. When Plato urged that one ought to be considerate of all Greeks, not merely all Athenians, it was a controversial idea. Today, humanistic sentiments still face formidable opposition from parochialism and bigotry. In fact, these destructive tendencies are aggravated by what we just now called the “nobler” aspects of human nature. As Michigan biologist Richard Alexander so neatly put it, today’s central ethical problem is “within-group amity serving between-group enmity.”

  LIFE IN THE STONE AGE

  Human nature was formed in what anthropologists have recently termed (following a 1966 suggestion by psychiatrist John Bowlby) the environment of evolutionary adaptedness, or EEA. Despite their frequent reference to the EEA, anthropologists differ widely about what it was like. They can
not directly observe the ways of our ancestors of tens of thousands of years ago or the effects of environmental conditions on the human genetic makeup. They must base their conclusions on indirect evidence: skeletal remains, stone tools, cave paintings, and information about modern groups with seemingly primitive economies and social conditions.

  The shortage of information is serious. What are the historically normal conditions of human childbirth? This is just one of many basic questions for which there is no assured answer. We suspect that the correct answer to many such questions is, it was highly variable. Attitudes toward childbirth differ enormously among different cultures today, and there is no reason to believe they were any less variable a hundred thousand years ago. They must also have been quite variable within social groups. The solicitude offered to a chiefs wife no doubt differed from that proffered a concubine captured from a hostile tribe. Giving birth during times of plenty in a settled camp might have been rather different from giving birth in leaner times or during travel to a new location.

  We also suggest that the correct answer to other important questions is, it varied. What sorts of rewards went to gifted poets, artists, or others of high intellectual attainment, compared to those who were good hunters or warriors? How stratified, by family connections or merit, were the socioeconomic conditions? Was inheritance matrilineal or patrilineal? What were the child-rearing customs? What were the religious doctrines and constraints, and how strong a factor was religion? These questions would have vastly different answers in different societies in the EEA. There is no one “natural” way of human life.

  Despite great variation in the human adaptations to a variety of EEA conditions, the available evidence does support some generalizations. Social systems were constrained by economics and demography. No elaborately stratified societies with hereditary class structures were possible in the Stone Age, because groups that had to gather their food from within walking distance necessarily remained small. Likewise, no chief of a nomadic band can have dozens of wives when the band only includes a few dozen people. Prior to the development of agriculture, no chief could control enough land, wealth, and people to build cathedrals or pyramids.

  Social systems were also constrained by the physiological and structural differences between the sexes. The physiological costs of reproduction involved in pregnancy and lactation are borne entirely by women. By what rules were the economic costs of reproduction apportioned? Again, we suggest, they varied. On the basis of what we know about current human groups, husbands no doubt contributed significantly in most cultures, but in others a mother’s brothers and other relatives made a greater contribution. Likewise, the gross physical differences between the sexes imply behavioral differences. The greater size and strength of men suggest that these attributes provided important competitive advantages, especially in the competition for mates. We discuss this and related matters in Chapter 13.

  Economic necessity often demanded that adults and older children of both sexes spend much of their time searching for and preparing food. It is usually assumed that men did the hunting and women the gathering in hunter-gatherer societies, although the antiquity and importance of big-game hunting have been exaggerated in fictional accounts of Stone Age life. Archery and other weapons effective against such animals as deer were in fact not invented until late in the Stone Age. Dogs, which can play crucial roles in many hunting techniques, were not common human associates before about fifteen thousand years ago. Meat or hides from large animals may often have been procured not by hunting but by scavenging or stealing from other predators.

  The mainstay foods in the Stone Age would seem to us inedible or too demanding of time and effort. We would find most of the game strong-tasting and extremely tough. Most of us have little appreciation of the tedious skinning and butchering it takes to turn a wild animal carcass into a serving of meat. Many wild fruits, even when fully ripe, are sour to our tastes, and other plant products are bitter or have strong odors. We find them unpleasant thanks to our adaptations that make us avoid toxins, as discussed in Chapter 6. Most natural human foods require a far greater labor of preparation and chewing than the foods we eat now. Domesticated animals and plants have been artificially selected to be tender, nontoxic, and easily processed.

  Despite the abundance of foods available in the EEA much of the time, the village elders would have been able to remember times of severe famine. Actual starvation may have been rare, but deaths from the combined stresses of disease, malnutrition, and poisoning by the excessive consumption of marginally edible plants were probably common. These same stresses also would have caused abortion of fetuses, curtailment of lactation, reduced fertility, and actions such as infanticide and the abandonment of the old or impaired.

  In addition to xenophobic conflict with other groups, social strife within groups, famines, and toxic diets, there were many other environmental stresses. Our ability to tolerate the atmospheric pollution of modern cities may owe much to our many thousands of years of exposure to smoke toxins from woods and other fuels. Imagine living in a hut with a fire on the floor and only a small hole in the roof. Atmospheric pollution was different in the EEA, but it was substantial and real. We would find the odors of a Stone Age settlement most unpleasant. There were no soaps or deodorants, no flush toilets, or readily cleanable chamber pots, or any installations worthy of the term latrine. Wastes of various kinds were taken away to some customary distance and no further. Other wastes simply accumulated where they were produced. The average Stone Ager lived in a dump and moved away when conditions got really bad.

  Children grew up, and adults lived out their lives, in the constant awareness, and sooner or later the personal experience, of woeful illness, painful injury, physical handicaps, debilitation, and death. There were no antibiotics, tetanus shots, or anesthetics, no plaster casts, corrective lenses, or prosthetic devices, no sterile surgery or false teeth. Our remote ancestors had few cavities, but they had many other dental problems. Teeth could be injured or lost in accidents, and they could literally wear out before what we call middle age. Abrasive plant products can wear molars down to gum level, as seen in some fossil skulls and even in some contemporary groups.

  Lest it seem that our account of the EEA is merely a selection of items for a catalog of horrors, we should emphasize that we are discussing our fully human ancestors, with a fully human capacity for pleasure as well as pain and a fully human intellect. The bonds of kinship and friendship could be strong and a source of great pleasure and security. In seasons of plenty there would be abundant time for play: games, music and dancing, storytelling and poetry recitals, intellectual and theological disputes, and the creation of ornamental artwork. The cave paintings at Lascaux, France, created perhaps 25,000 years ago, have been described by anthropologist Melvin Konnor as “a Paleolithic Sistine Chapel” that impresses a sensitive observer “whether religious or not—whether expert or not—with a strong sense of the holy.” And our ancestors also had the ability to look on the bright side in times of adversity and to find reasons for laughter. Mark Twain’s hero Sir Boss in A Connecticut Yankee in King Arthur’s Court lamented having to listen, at a sixth-century campfire, to the same jokes he had already found tiresome in the nineteenth. We suspect that if he had gone back to the Stone Age he would have groaned at many of the same jokes.

  10

  DISEASES OF CIVILIZATION

  You have now spent several hours reading this book. Do you realize how much thoroughly abnormal use of your eyes this feat required? Was the light source the sun, with its normal spectrum? Probably not, at least not entirely. How much muscular exertion did you expend during those hours of reading? How could you be so inactive for that much time without jeopardizing your well-being, perhaps your life, by having spent inadequate time and effort in vigilance against enemies and in foraging for food? But you are in fact well fed? How long did it take to pick or dig or hunt or fish for your last meal? How much shelling and grinding and butchering? If
the food was cooked, how long did it take you to gather the fuel and kindle the fire? How much sweating and shivering have you done in the last twenty-four hours? What’s that about thermostatically controlled heating and air conditioning? How bizarre! And what are the long-term consequences of such meager challenge to your body’s built-in temperature controls?

  As the last chapter (we hope) made clear, only the grossly uninformed or irrationally romantic would think we were ever better off than we are now. Rousseau’s noble savage and the Flintstones’ merry capers are delightful in escapist fiction, but the reality was painful and sad compared to our lives today or even to when farming first replaced nomadic scrounging. Agriculture led to urban civilization, with its durable architecture and associated fine arts, and the nautical and other technological advances that permitted exploration of distant lands. The domestication of hoofed animals enabled one worker to do jobs that would previously have required several. It also contributed to revolutionary advances in transportation. Continuing technological advances have led to ever greater freedom from want and freedom of movement for ever larger numbers of people.

  The long-term consequences of the soft and gratifying lives we now enjoy are mostly beneficial or harmless, but many of the advantages we enjoy today are mixed blessings. Benefits have costs, and even the most worthwhile benefits can be costly to our health. For a good example we need look no further than the effects of lower mortality rates in early life. Because fewer people die young from smallpox, appendicitis, childbirth complications, and hunting accidents, the death rates from old-age afflictions like cancer and heart failure are much higher now than they were a couple of generations ago. This is largely because a higher proportion of people live to the ages at which the body becomes especially vulnerable to these illnesses. The price of not being eaten by a lion at age ten or thirty may be a heart attack at eighty. Modern practices of food production, medicine, public health, and industrial and household safety have drastically improved the prospects of surviving to old age. Unfortunately, the increased effects of aging are not the only bad aspects of the good life.