Natural Causes: An Epidemic of Wellness, the Certainty of Dying, and Killing Ourselves to Live Longer

by Barbara Ehrenreich

This book cannot be summarized in a sentence or two, but here is a rough road map to what follows: The first half is devoted to describing the quest for control as it is acted out through medical care, “lifestyle” adjustments in the areas of exercise and diet, and a nebulous but ever-growing “wellness” industry that embraces both body and mind. All of these forms of intervention invite questions about the limits of human control, which leads us into the realm of biology—what lies within the body and whether its various parts and elements are even susceptible to conscious human control. Do they form a harmonious whole or are they engaged in perpetual conflict? I present the emerging scientific case for a dystopian view of the body—not as a well-ordered machine, but as a site of ongoing conflict at the cellular level, which ends, at least in all the cases we know of, in death. Finally, at the end of this book, if not at the end of our individual lives, we are left with the inevitable question of “What am I?”, or you, for that matter. What is the “self” if it is not rooted in a harmonious body, and what do we need it for anyway? Here you will find no “how-to” advice, no tips about how to extend your life, upgrade your diet and exercise regimen, or fine-tune your attitude in a more healthful direction. If anything, I hope this book will encourage you to rethink the project of personal control over your body and mind. We would all like to live longer and healthier lives; the qu...

The result was a diagnosis of “osteopenia,” or thinning of the bones, a condition that might have been alarming if I hadn’t found out that it is shared by nearly all women over the age of thirty-five. Osteopenia is, in other words, not a disease but a normal feature of aging. A little further research, all into readily available sources, revealed that routine bone scanning had been heavily promoted and even subsidized by the drug’s manufacturer.1 Worse, the favored medication at the time of my diagnosis has turned out to cause some of the very problems it was supposed to prevent—bone degeneration and fractures. A cynic might conclude that preventive medicine exists to transform people into raw material for a profit-hungry medical-industrial complex.

Dentists—and I have met a number of them in my moves around the country—always wanted a fresh set of X-rays, even if the only problem was a chip in the tip of a tooth. All I could think of was the X-ray machines every shoe store had offered in my youth, through which children were encouraged to peer at the bones of their feet while wiggling their toes. The fun ended in the 1970s, when these “fluoroscopes” were eventually banned as dangerous sources of radiation. So why should I routinely expose my mouth, which is much more cancer-prone than the feet, to high annual doses of roentgens? If there was some reason to suspect underlying structural problems, okay, but just to satisfy the dentist’s curiosity or meet some abstract “standard of care”—no.

It was my dentist, oddly enough, who suggested, during an ordinary filling, that I be tested for sleep apnea. How a dentist got involved in what is normally the domain of ear, nose, and throat specialists, I do not know, but she recommended that the screening be done at a “sleep center,” where I would attempt to sleep while heavily wired to monitoring devices, after which I could buy the treatment from her: a terrifying skull-shaped mask that would supposedly prevent sleep apnea and definitely extinguish any last possibility of sexual activity. But when I protested that there is no evidence I suffer from this disorder—no symptoms or detectable signs—the dentist said that I just might not be aware of it, adding that it could kill me in my sleep. This, I told her, is a prospect I can live with.

But if mammography seems like a refined sort of sadism, colonoscopies mimic an actual sexual assault. First the patient is sedated—often with what is popularly known as the “date rape drug,” Versed—then a long flexible tube, bearing a camera on one end, is inserted into the rectum and all the way up through the colon. What repelled me even more than this kinky procedure was the day of fasting and laxatives that was supposed to precede it, in order to ensure that the little camera encounters something other than feces. I put this off from year to year, until I finally felt safe in the knowledge that since colon cancer is usually slow-growing, any cancerous polyps I contain are unlikely to flourish until I am already close to death from other causes.

Rather than being fearful of not detecting disease, both patients and doctors should fear healthcare. The best way to avoid medical errors is to avoid medical care. The default should be: I am well. The way to stay that way is to keep making good choices—not to have my doctor look for problems.

Thyroid cancer is particularly vulnerable to overdiagnosis. With the introduction of more high-powered imaging techniques, doctors were able to detect many more tiny lumps in people’s necks and surgically remove them, whether surgery was warranted or not. An estimated 70 to 80 percent of thyroid cancer surgeries performed on US, French, and Italian women in the first decade of the twenty-first century are now judged to have been unnecessary. In South Korea, where doctors were especially conscientious about thyroid screening, the number rose to 90 percent. (Men were also overdiagnosed, but in far lower numbers.) Patients pay a price for these surgeries, including a lifelong dependence on thyroid hormones, and since these are not always fully effective, the patient may be left chronically “depressed and sluggish.”

Increasingly, we read laments about the “medicalization of dying,” usually focused on a formerly frisky parent or grandparent who had made clear her request for a natural, nonmedical death, only to end up tethered by cables and tubes to an ICU bed. Physicians see this all the time—witty people silenced by ventilators, the fastidious rendered incontinent—and some are determined not to let the same thing happen to themselves. They may refuse care, knowing that it is more likely to lead to disability than health, like the orthopedist who upon receiving a diagnosis of pancreatic cancer immediately closed down his practice and went home to die in relative comfort and peace.9 A few physicians are more decisively proactive, and have themselves tattooed “NO CODE” or “DNR,” meaning “do not resuscitate.” They reject the same drastic end-of-life measures that they routinely inflict on their patients.

Most of us would readily recognize the Ihamba ceremony as a “ritual”—a designation we would not be so quick to apply to a mammogram or a biopsy. The word carries a pejorative weight that is not associated with, for example, the phrase “health care.” Early anthropologists could have called the healing practices of so-called primitive peoples “health care,” but they took pains to distinguish the native activities from the purposeful interventions of Euro-American physicians. The latter were thought to be rational and scientific, while the former were “mere” rituals, and the taint of imperialist arrogance has clung to the word ever since.

According to critical thinkers like Zola and Illich, one of the functions of medical ritual is social control. Medical encounters occur across what is often a profound gap in social status: Despite the last few decades’ surge in immigrant and female doctors, the physician is likely to be an educated and affluent white male, and the interaction requires the patient to exhibit submissive behavior—to undress, for example, and be open to penetration of his or her bodily cavities. These are the same sorts of procedures that are normally undertaken by the criminal justice system, with its compulsive strip searches, and they are not intended to bolster the recipient’s self-esteem. Whether consciously or not, the physician and patient are enacting a ritual of domination and submission, much like the kowtowing required in the presence of a Chinese emperor.

The Ihamba ritual may be the culturally appropriate way for the Ndembu people to express concern for an afflicted person; Westerners require the trappings of big science—imaging machines, centrifuges, and sterile, or at least blank, interior rooms. But to my knowledge no one has tested this proposition. Would it help to add cut flowers, soothing music, and friendlier faces to the conventional medical encounter? Does all the equipment have to be real, or would cardboard imitations do just as well? And if the real point of medical ritual is to demonstrate social support for the patient, surely we could do so in ways that are less grotesquely expensive, as well as less stressful and demeaning.

In 1974, a former physician turned mathematician, David M. Eddy, was asked to give a talk on medical decision making, and chose to focus on diagnostic mammography since Betty Ford’s and Happy Rockefeller’s breast cancers were very much in the news at the time. Years later, he wrote that he had “planned to write out the decision tree I presumed their physicians had used, fully expecting to find strong evidence, good numbers, and sound reasoning that I could describe to my audience. But to my amazement I found very few numbers, no formal rationale, and blatant errors in reasoning. How could that be?”

Most of the medical screenings that have been pressed on me by one health professional or another fail the evidence-based test. Mammograms, for example: The conventional wisdom, tirelessly repeated by the leading breast cancer advocacy group, the Susan G. Komen Foundation, was that early detection through annual mammography would significantly increase the five-year survival rate from breast cancer.4 But repeated, huge, often international studies showed no significant decline in breast cancer mortality that could be attributed to routine mammographic screening. True, any woman whose cancer had been detected through screening might claim to have been saved by the intervention, but the likelihood was that the spot in her mammogram would never have developed into full-blown cancer. What screening was finding, and doctors were treating, were often slow-growing or inactive tumor sites—or even noninvasive conditions like the wrongly named “ductal cancer in situ,” or DCIS. Treating pre-cancers and non-cancers may seem like a commendable excess of caution, except that the treatments themselves—surgery, chemotherapy, and radiation—entail their own considerable risks. Disturbingly enough, breast biopsies are themselves a risk factor for cancer and can “seed” adjacent tissue with cancer cells.

There is an inherent problem with cancer screening: It has been based on the assumption that a tumor is like a living creature, growing from small to large and, at the same time, from innocent to malignant. Hence the emphasis on “staging” tumors, from zero to four, based on their size and whether there is evidence of any metastasis throughout the body. As it turns out, though, size is not a reliable indicator of the threat level. A small tumor may be highly aggressive, just as a large one may be “indolent,” meaning that a lot of people are being treated for tumors that will likely never pose any problem. One recent study found that almost half the men over sixty-six being treated for prostate cancer are unlikely to live long enough to die from the disease anyway.10 They will, however, live long enough to suffer from the adverse consequences of their treatment.

As of 2008, 22 percent of Fortune 500 companies provided “executive exams” to their top personnel,18 both as a perk and as a way to avoid having a trusted leader die of a heart attack at his or her desk. But an article in the Harvard Business Review entitled “Executive Physicals: What’s the ROI [Return on Investment]?” answers its own question with what amounts to a firm “not much”—and for all the reasons I have given here: the frequency of false positives, the dangers of the tests themselves (such as radiation), and the unlikelihood of finding a problem in a still-treatable stage.

Predictably enough, the medical reforms of the early twentieth century narrowed the demographic base of the medical profession. The requirement that medical schools possess laboratories eliminated most schools that had admitted women and African-Americans. Furthermore, at a time when only 5 percent of the population had a college degree, the requirement of at least some college limited medical school admissions to the upper and upper middle classes. No longer could any “crude boy or…jaded clerk,” as one of the leading reformers described the run-of-the-mill doctors of his time,24 expect to gain medical training. Doctors would be recruited from the class of “gentlemen,” which was why even female patients could now entrust them with intimate access to their bodies. For most people, throughout most of the twentieth century, medical care necessarily involved an encounter with a social superior—a white male from a relatively privileged background.

Many physicians and social scientists have questioned the pedagogical value of cadaver dissection. After all, the cadaver is dead and artificially preserved; it is smelly, leathery, and utterly lacking in the “flux” that constitutes life. Some prestigious medical schools have abandoned it altogether, instead teaching anatomy on plastic “prosections” of body parts. But for the most part, American medical schools (though not Italian ones) still insist on cadaver dissection, going so far as to defend it as a “rite of passage,” in which even the trauma that some medical students experience can be justified as a vital part of their transformation from initiate into full-fledged physician. Medical schools often attempt to “humanize” the process with little rituals of gratitude to the cadavers’ donors, but dissection remains a violent and transgressive undertaking.

Of course most of the young, educated people who started jogging and gym-going in the 1970s and ’80s had never expected, much less worked to bring about, a political and cultural revolution. But they had hoped for stable employment, preferably in jobs they found meaningful and creative, and in an age when the entire sociological map was being redrawn, there was little chance of that. First, the traditional blue-collar working class gave way to “deindustrialization,” meaning plant closings and layoffs. As the downsizing fervor spread to the nonprofit sector, whole sections of the professional middle class crumbled off like calves from a melting iceberg. Human service agencies began to shed their social workers, psychologists, and public-interest lawyers. Universities shuttered departments, like philosophy and foreign languages, that were failing to generate sufficient revenue. An alarming new phenomenon appeared—the taxi-driving PhD, predecessor of today’s avatar of educational disutility, the PhD on food stamps.4 In the face of so much class turmoil, young people rapidly rolled back their expectations to fit the narrowing career possibilities. UCLA’s annual survey of undergraduate attitudes found a sharp decline in “altruism and social concerns,” with a record 73 percent in 1987 reporting that their top goal was “being very well-off financially,” compared with 39 percent in 1970.5 I met them all the time on campuses, students who had started out with an interest in social ...

But if women are in a way “masculinized” by the fitness culture, one might equally well say that men are “feminized” by it. Before the 1970s, only women were obsessed with their bodies, although in a morbid, anorectic way. But in the brightly lit gyms, where walls are typically lined by mirrors, both sexes are invited to inspect their body images for any unwanted bulges or loose bits of flesh and plan their workouts accordingly. Gay men flocked to the gyms, creating a highly chiseled standard of male beauty. The big change, though, was that heterosexual men were also “objectified” by the fitness culture, encouraged to see themselves as the objects of other people’s appreciation—or, as the case may be, scorn. For both sexes in the endangered white-collar middle class, the body became an essential element of self-presentation, not just its size and general shape but the squareness of shoulders, the flatness of tummy, and, when sleeves were rolled up, the carefully sculpted contours of muscle.

Americans reduced their fat intake from 40 percent of calories ingested in 1970 to 34 percent in 2000,10 with the result, which makes sense retrospectively, that we had an “obesity epidemic” as people gave up fat for “healthy” treats like fat-free cookies.

But stay around a little longer—thirty years of attending various gyms around the country in my case—and the picture looks a little less idyllic. Despite the pulsing pop music and comfortable clothes, gyms are not sites of spontaneity and play. There are rules beamed out from video monitors, mostly innocuous ones, like no cursing, “staring” at others, or expressing effort in audible form such as grunts or panting. Once, in a Key West gym, which you might imagine to be a somewhat permissive environment, I saw the manager chastise a young woman for moving too freely and rhythmically. “No dancing in the gym,” he announced, nonsensically, as if to underscore the seriousness of our undertaking. A regimented dancelike experience, as in aerobics or Zumba, is fine, but unsupervised dance moves reek of hedonism, and working out is supposed to be a form of work. Most people come with a plan like “legs and shoulders today” or “45 minutes of cardio and 15 minutes of abs,” usually preceded by a warm-up and topped off with several minutes of stretching on a mat. Working out very much resembles work, or a curious blend of physical labor and office work. Members not only lift weights, for example, they often carry clipboards on which to record the number of reps and sets and the amount of weight lifted for each workout, like a supervisor monitoring a factory worker’s performance.

We learn from coaches and fitness class instructors that, like any other beast of burden, the body is always inclined to take the path of least resistance unless we can “trick” it with a sudden variation in the workout routine. Western philosophy has long separated body from mind; fitness culture takes this dualism further—to an adversarial relationship in which mind struggles for control over the lazy, recalcitrant body. I plan to work out today, but I will not tell you exactly what I’ll do, lest my body find out.

The South African runner Oscar Pistorius, who is now serving a sentence for the 2013 murder of his girlfriend, had more to overcome than most athletes: His legs had been amputated below the knees when he was a toddler. But he managed to become both a Paralympic and Olympic champion. Tattooed on his back is a modified verse from Corinthians: I do not run like a man running aimlessly I do not fight like a man beating the air; I execute each stride with intent; I beat my body and make it my slave I bring it under my complete subjection…

Many of the people who got caught up in the health “craze” of the late twentieth century—people who exercised, watched what they ate, abstained from smoking and heavy drinking—have nevertheless died. Lucille Roberts, owner of the chain of women’s gyms that introduced me to the fitness culture, died incongruously from lung cancer at the age of fifty-nine, even though she was a “self-described exercise nut” who, the New York Times reported, “wouldn’t touch a French fry, much less smoke a cigarette.”1 Jerry Rubin, who devoted his later years to trying every supposedly health-promoting diet fad, therapy, and meditation system he could find, jaywalked into Wilshire Boulevard at the age of fifty-six and died of his injuries two weeks later.

Jerome Rodale, the founder of Prevention magazine and an early promoter of organic food, died of a heart attack at age seventy-two, while taping The Dick Cavett Show—a death made particularly memorable by Rodale’s off-camera statement that he had “decided to live to be a hundred.”2 Jim Fixx, author of the bestselling The Complete Book of Running, believed he could outwit the cardiac problems that had carried his father off to an early death by running at least ten miles a day and restricting himself to a diet consisting mostly of pasta, salads, and fruit. But he was found dead on the side of a Vermont road in 1984, at the age of only fifty-two. In 2017, Henry S. Lodge, coauthor of the bestselling Younger Next Year: Live Strong, Fit, and Sexy—Until You’re 80 and Beyond, died of pancreatic cancer at the still-youthful age of fifty-eight.

Even more disturbing, to those who knew about it, was the untimely demise of John H. Knowles, director of the Rockefeller Foundation and promulgator of what became known as the “doctrine of personal responsibility” for one’s health. Most illnesses are self-inflicted, he argued—the result of “gluttony, alcoholic intemperance, reckless driving, sexual frenzy, and smoking,”4 as well as other bad choices. The “idea of a ‘right’ to health,” he wrote, “should be replaced by the idea of an individual moral obligation to preserve one’s own health.” But he died of pancreatic cancer at the age of fifty-two, prompting one physician commentator to observe that “clearly we can’t always be held responsible for our health.”

Apple cofounder Steve Jobs’s 2011 death from pancreatic cancer continues to spark debate. He was a food faddist, specifically a consumer only of raw vegan foods, especially fruit, refusing to deviate from that plan even when doctors recommended a diet high in protein and fat to help compensate for his failing pancreas.

Defenders of veganism argue that his cancer could be attributed to his occasional forays into protein-eating (a meal of eel sushi has been reported), or perhaps to exposures to toxic metals as a young man tinkering with computers. A case could be made, however, that it was the fruitarian diet that killed him: Metabolically speaking, a diet of fruit is equivalent to a diet of candy, only with fructose instead of glucose, with the effect that the pancreas is strained to constantly produce more insulin.

Nothing has happened to ease the pressures on low-wage workers. On the contrary, if the old paradigm of a blue-collar job was forty hours a week, an annual two-week vacation, and benefits such as a pension and health insurance, the new expectation is that one will work on demand, as needed, without benefits or guarantees of any kind. Some surveys now find a majority of US retail workers working without regular schedules19—on call for when the employer wants them to come and unable to predict how much they will earn from week to week or even day to day. With the rise in “just in time” scheduling, it becomes impossible to plan ahead: Will you have enough money to pay the rent? Who will take care of the children? The consequences of employee “flexibility” can be just as damaging as a program of random electric shocks applied to caged laboratory animals.

In late 2015, the British economist Angus Deaton won the Nobel Prize for work he had done with fellow economist Anne Case, showing that the mortality gap between wealthy white men and poor ones was widening at a rate of one year each year, and slightly less for women. A couple of months later, “economists at the Brookings Institution found that for men born in 1920, there was a six-year difference in life expectancy between the top 10 percent of earners and the bottom 10 percent. For men born in 1950, that difference more than doubled, to 14 years.”22 Smoking could account for only one-fifth to one-third of the excess deaths. The rest were apparently attributable to alcoholism, opioid addiction, and actual suicide—as opposed to metaphorically killing oneself through unwise lifestyle choices.

Poor whites had always had the comfort of knowing that someone was worse off and more despised than they were; racial subjugation was the ground under their feet, the rock they stood upon, even when their own situation was deteriorating. That slender reassurance is shrinking.

There are some practical reasons too why whites are likely to be more efficient than blacks at killing themselves. For one thing, they are more likely to be gun owners, and white men favor gunshots as a means of suicide. For another, doctors, undoubtedly acting in part on stereotypes of nonwhites as drug addicts, are more likely to prescribe powerful opioid painkillers to whites than to people of color. Pain is endemic among the blue-collar working class, from waitresses to construction workers, and few people make it past fifty without palpable damage to their knees, back, or rotator cuffs.

Or, for a more global and somber analogy, we could reach back to the deadly consequences of European expansionism in the sixteenth through the twentieth centuries, and still ongoing. The number of indigenous people killed in this “single, multi-century, planet-wide exterminatory pulse,”25 whether by bullets, disease, or mass deportations, has been estimated at fifty million.26 But when the shooting stopped, the survivors were often left suffering from what could be a fatal malaise, characterized by alcoholism, depression, and suicide. This was the background for anthropologist Claude Lévi-Strauss’s 1955 Tristes Tropiques: decimated native cultures, stripped of customs, rituals, or traditional means of subsistence, left listless and dispirited by their encounter with the West.

This is an underestimate by at least a factor of two. China and India alone are 100 million+.

These are terms drawn from psychology or philosophy; they are “nebulous,” as philosopher of science Alfred I. Tauber has pointed out, adding that “the self can hardly be viewed as a scientific concept.”11 In fact, it was barely even a concept at all until about the seventeenth century, when languages such as English and German began to use the word “self” as something other than an intensifier (as in “I did it myself”). Then, as we shall see in a later chapter, the “self” began to replace the “soul” as a special kind of kernel within each individual, walled off in part from everyone else. Attention turned inward, as people were encouraged to know themselves through, for example, the widespread use of mirrors, the writing of journals and autobiographies, and the painting of portraits, often self-portraits. “Western individualism” was born, along, eventually, with psychoanalysis and any number of afflictions of the self.

One popular hypothesis, proposed in 1989, is that the relatively hygienic environments of affluent societies do not give immune cells enough practice in facing their “real” enemies from the microbial world. They grow up, in other words, soft and pampered. But today there is increasing acknowledgment that the link between lack of childhood exposure is not one of cause and effect. One possibility is that highly hygienic environments may simply allow more children to live long enough to develop an autoimmune disease.

In the “positive” view, menstruation has a serious biological function. Every month, at least in humans, the lining of the uterus grows thick, supposedly to provide a soft cushion for any fertilized eggs that find their way into it. If no embryo implants, the uterus sheds this lining, if only because it would be costly, in a caloric sense, to maintain it—hence the mess of blood and tissue fragments that make up the menstrual discharge. But repeated monthly over decades, the shedding of the uterine lining is itself very costly; women typically lose a pint of blood a year and sometimes several more, creating the risk of anemia.

Not only did he find deadly competition between the sexes even in their most intimate moments, but he proposed that our genomes contain many stretches of DNA (often subsumed under the label “junk DNA”) that are truly “selfish” in the sense that they have discovered ways to spread and persist without contributing to organismal fitness. At times, this means encoding actions that are diametrically opposed to those of the majority of genes. As a consequence, most organisms are not completely harmonious wholes and the individual is, in fact, divisible.

Menstruation, for example, is not the gentle, autumnal-sounding process of “shedding” an endometrial lining that it is usually described as. When no embryo implants, the uterus releases chemical signals summoning immune cells to come in from the bloodstream and devour its thick endometrial lining, which quickly becomes a killing field, with the debris pouring out of the vagina. Fortunately, during most of human existence, thanks to frequent pregnancies and lengthy periods of lactation, human females probably endured very few menstrual periods during their lifetimes.

Autoimmune diseases involve an apparently spontaneous attack by immune cells on other body cells; cancer is a mad pursuit of lebensraum originating in a single cell or a small group of cells. Fortunately, from the point of view of the organism as a whole, there are plenty of mechanisms to keep adventurous cells in place. Tissue cells are bound to each other by “intercellular glue” as well as by “junctions,” some of them so tight as to be almost unbreakable. As an additional precaution, organs are often enclosed in membranes that may be difficult or impossible for a cell to breach. Then there is the steady hail of chemical signals that one cell receives from others, some of them sent from considerable distances. We can translate very few of these signals, and they appear to say things like “Danger!” or “Come here right away!” And—who knows?—some of the messages may be propagandistic, urging cells to carry on stalwartly with their appointed tasks. Then there is the final sanction for a recalcitrant cell: death. Signals come in saying “Die!” and, in a process called apoptosis, the cell obligingly shuts down its metabolism, folds neatly into its membrane, and awaits disposal.

Macrophages had been known since the nineteenth century to gather at tumor sites, leading Virchow and others to speculate that cancer is caused by inflammation, meaning a gathering of leucocytes at some site of injury or infection. Or, more optimistically, one might imagine that the macrophages were massing for an assault on the tumor. Instead, it turned out that they spent their time in the neighborhood of tumors encouraging the cancer cells to continue on their reproductive rampage. They are cheerleaders on the side of death. Frances Balkwill, one of the cell biologists who contributed to the recognition of treasonous macrophage behavior, described her colleagues in the field as being “horrified.”

In 2012 the distinguished physician and science writer Jerome Groopman wrote an entire article in the New Yorker on scientific attempts to enlist the immune system in fighting cancer without once mentioning that certain immune cells—macrophages—have a tendency to go over to the other side.7 The omission is made all the stranger by the fact that Groopman introduces his essay with a story about a young woman in 1890 whose hand injury led to a long and painful inflammation, which was followed by a fatal metastatic sarcoma. In the article, he assures us, without explanation, that the sarcoma was “unrelated to her initial injury.” By 2012, though, there had already been reports about the role of macrophages in injury-induced sarcomas.

Macrophages supply cancer cells with chemical growth factors and help build the new blood vessels required by a growing tumor. So intimately are they involved with the deadly progress of cancer that they can account for up to 50 percent of a tumor’s mass. Macrophages also appear to be necessary if the cancer is to progress to its deadliest phase, metastasis, and if a cancerous mouse is treated to eliminate all its macrophages, the tumor stops metastasizing.

Any reasonably genteel meeting of two cells begins with an exchange of chemical messages, more or less like an exchange of business cards between two professionals, only in the cellular case the transaction can quickly get out of hand. As a 2014 article on breast cancer in the journal Cancer Cell suggests, the macrophages release a growth factor that encourages the cancer cells to elongate themselves into a mobile, invasive form poised for metastasis. These elongated cancer cells, in turn, release a chemical that further activates the macrophages—leading to the release of more growth factor, and so on. A positive feedback loop is established.

A kind of “intravital” microscopy, developed at John Condeelis’s lab at the Albert Einstein College of Medicine, reveals that macrophages from within the tumor pair off with cancer cells to enter a blood vessel that would otherwise be impenetrable to the cancer cells. The macrophage has the chops, so to speak, to pry apart two adjacent blood vessel cells and make a hole through which the cancer cell can escape to colonize other parts of the body.12 And the cancer cells are desperate to escape, since their own reproductive success creates a suffocatingly crowded environment within the tumor, dangerously short of oxygen. So it doesn’t take just one rogue cell to create a metastatic cancer; it takes two—a cancer cell plus a normal, healthy, and all-too-helpful macrophage.

It is no longer enough to eliminate fats and cholesterol from one’s diet; an “anti-inflammatory diet” excludes processed foods, dairy products, and, commonly, meat. While such a diet may lead to weight loss, which can be a good thing, there is no hard evidence that it curbs inflammatory disorders or does anything else to tame the behavior of macrophages.

The question was how the macrophages knew what to attack and what to leave alone, which cells or particles were “normal” and which were deserving of destruction. Metchnikoff’s answer was essentially that macrophages, enjoying the “most independence” of any body cells, could decide this on their own2—protecting cells they recognized as belonging to the “self” and devouring anything else. This explanation was instantly rejected by most of Metchnikoff’s contemporaries. As philosopher Alfred Tauber writes, “The phagocyte [macrophage] as possessor of its own destiny and mediator of the organism’s selfhood was received as too vitalistic a conception,”3 meaning that it was almost mystical. How could a microscopic cell make decisions?

Perhaps one of the examples best known to biologists is the phage lambda, a virus that preys on that familiar resident of our guts—the bacterium E. coli. A virus is a strand or two of nucleic acid, usually DNA, coated with protein, visible only through an electron microscope, yet in the course of their development phage have a crucial choice to make: When one of them penetrates an E. coli cell, it can either remain there in a state of dormancy, passively reproducing its nucleic acid when the cell divides, or it can immediately lyse the cell—splitting it open and releasing a swarm of progeny to invade other E. coli. Acres of paper have been filled with differential equations in an effort to predict which way an encounter between phage and E. coli will go, with the result that the outcome seems to depend on decision making by individual phage.

As the renowned physicist Freeman Dyson has put it, “There is a certain kind of freedom that atoms have to jump around, and they seem to choose entirely on their own without any input from the outside, so in a certain sense atoms have free will.”

According to the latest from the field of cognitive science, humans have an innate tendency to see agency, whether in the form of gods or spirits, where it does not exist because there was once a survival advantage in doing so. A prehistoric person or hominid would be wise to imagine that every stirring in the tall grass meant that a leopard—or some such potentially hazardous life form—was closing in for an attack. If you decide the stirring is a leopard, you can run away, and if you were wrong, nothing is lost except perhaps some temporary peace of mind. But if you decide that it is just a breeze and it turns out to be a leopard, you become a leopard’s lunch. So our brains evolved to favor the scarier alternative and the choice of running. We have become what the cognitive scientists call “hyperactive agency detection devices”: We see faces in clouds, hear denunciations in thunder, and sense conscious beings all around us even when there is nothing there.

The hypothesized transition from suspected predators to the morally ambiguous “spirits” believed in by early humans makes more sense when we recall that, before humans could hunt for themselves, they seem to have relied on the bones and scraps of meat left by nonhuman predators. That is, the predator was also a provider, more or less like the gods that came later.