“Everything had to be neat and orderly. No mess.”
In 1968, Richard Plochman, a German forestry professor, called attention to forestry’s ugly secret. Two centuries after Johann Gottlieb Beckmann had been tidying up messy ancient woodlands into neat rows of Norwegian spruce, the German forests were dying.
In Forestry in the Federal Republic of Germany, Plochman wrote that the “pure stands” of Norway spruce, so profitable in the early years after Beckmann’s work, “grew excellently in the first generation but already showed an amazing retrogression in the second generation.” Yields were down by a quarter and the decline was continuing. The trouble had started as early as the second generation of Norway spruce, but trees live long enough that it had taken a century to be certain that something was amiss.
The Germans gave the malaise the name Waldsterben, or “forest death” syndrome; in 1986, West Germany produced a set of commemorative stamps with the message “Save our forests in the eleventh hour.”
What was happening? The single-minded focus of German foresters on timber was backfiring. According to the ecologist Chris Maser, merely removing fallen logs and dead trees would result in the loss of almost a third of non-bird wildlife species in a forest. These losses seemed irrelevant to scientific foresters, who targeted maximum “sustained yield” and, tellingly, “minimum diversity.” Yet over time they altered the ecology of the forest and exposed the trees to fungi and other invasive species. The new, tidy forest, with each tree the same size and the same species, was easily exploited, not just by foresters but by parasites.
Yes, the Norway spruce had been profitable at first, but that profit concealed the fragility of the situation. The first generation of spruce trees had lived off the fertile humus laid down by the messier deciduous old-growth forest, and their roots had pushed down into the deep channels freed up as the old roots rotted. Over time, the spruce laid down their own acidic humus, which was far harder for the already weakened forest ecosystem to decompose. The soil gradually compacted, the nutrients leached away, and the second- and third-growth Norway spruce trees grew shallow roots in malnourishing soil.
None of this was anticipated by the foresters of yesteryear. They were sure their new forests were a simple, well-understood, and highly ordered system. Georg Hartig, one of the generation of scientific foresters to follow in Beckmann’s footsteps, confidently produced tables forecasting the yield of the great Jagerthal forest for two centuries, through to 2019.
Such assured forecasting proved hubristic. The mess and diversity of the old German forests had to be painstakingly reconstructed, reintroducing dead logs—and leaving dead trees (“snags”) standing—a more varied set of trees, woodpeckers, even certain species of spider. It is too early to tell whether this artificially created mess will prove a successful replacement for the original. Yet what is perfectly clear is that the attempt to map, quantify, and ultimately tidy the German forests not only transformed them but nearly killed them. It turns out that what you need to keep a forest alive cannot easily be quantified and mapped.
In nature, mess often indicates health—and not only in the forest.
• • •
In 1982, a trainee Australian doctor carried out the most famous piece of self-experimentation since Benjamin Franklin (perhaps) flew a kite in a thunderstorm. Barry Marshall was frustrated by treating stomach ulcers, which were thought to be caused by stress. Ulcers weren’t curable, but managing their symptoms was a fantastically profitable business, producing the first blockbuster drugs, Tagamet and Zantac.1
Marshall and his colleague J. Robin Warren had a radically different view: ulcers weren’t caused by stress at all, but by a corkscrew-shaped bacteria, Helicobacter pylori. They could be cured promptly and completely by a course of inexpensive antibiotics. Nobody else took this view seriously, and there was a lot of money riding on it being untrue.
Irritated and determined to prove his point, Barry Marshall drank a flask full of H. pylori. He swiftly became ill, with an inflamed stomach full of incipient ulcers—and just as swiftly cured himself with a course of antibiotics. Finally Marshall and Warren had the attention of the medical profession. Eventually they shared the Nobel Prize in Medicine in 2005.
We could end the tale there as a triumph for careful observation, Aussie grit, and the wonders of antibiotics. There was even talk among gastroenterologists of trying to eradicate H. pylori entirely. But two years after Marshall and Warren’s Nobel was awarded, Martin Blaser, a microbiologist at the New York University School of Medicine, discovered a twist in the story: H. pylori might be doing us some good.
Blaser found that Americans who had H. pylori in their guts were far less likely to suffer from asthma. A laboratory study of mice demonstrated that deliberately infecting them with H. pylori guaranteed that they would not develop asthmatic symptoms. Blaser and his colleagues also believe that H. pylori helps prevent obesity by regulating a stomach enzyme called ghrelin: again, this idea comes from observational studies of humans and controlled experiments in mice. When mice are dosed with antibiotics, H. pylori is scoured from the stomach system and the mice get fat. (The intensive farming industry has known for years that antibiotics help fatten up livestock, but not why.) It also turns out that if you transfer microbes from thin mice to the fat ones, the fat ones will lose weight.2
These discoveries hint at what might be possible as we begin to understand our microbiota (the microbes that live on and inside us) and their microbiome (their genes). The view used to be that the human body was under assault from bacteria, and that antibiotics were an unalloyed good, albeit one to be used with care lest bacteria evolve resistance. But recently medical researchers have realized that our relationship with bacteria is more complex than that. The average human is host to ten thousand bacterial species. These germs outnumber the cells of our own body, they weigh a total of about three pounds, and they play a crucial role in keeping our metabolism ticking. Some bacteria are dangerous, some are harmless passengers, and some are beneficial. Some, such as H. pylori, can be dangerous or beneficial depending on the situation.3
Martin Blaser has become one of the leading champions of the view that our bacterial guests are starting to become less diverse, and that this thinning of the microbiome is doing us harm.
Researchers at the University of Toronto found that it was easier to stay slim in the 1980s: looking at data about diet and exercise for tens of thousands of people since the early 1970s, they found that people today seem to be heavier than their forebears, even when they ate the same and were equally as active. One of the favored explanations for this is that young people today have denuded gut bacteria; a separate large study of European microbial genes has shown that a less diverse microbiome is correlated with a tendency to be obese.
Meanwhile a team at the University of California at San Francisco found that Lactobacillus sakei—another of the bacteria we have cluttering up our bodies—appears to prevent sinusitis, presumably by outcompeting the more harmful bacteria that might inflame our sinuses. A dose of antibiotics can wipe out the lactobacillus, and—paradoxically—invite a painful infection.4
The most disgusting example concerns the treatment of Clostridium difficile gut infections. Doctors have been facing an increasing struggle with this condition, which can cause severe and bloody diarrhea and crippling abdominal pain, and which kills almost thirty thousand Americans a year.5 The affliction often results from prolonged treatment with antibiotics, which scour the gut’s usual benign microbes and leave it open to an opportunistic takeover from the C. difficile bacteria. Perhaps unsurprisingly, given its origins, C. difficile itself is increasingly resistant to antibiotics.
But now a near-miraculous cure has been discovered—first there were anecdotes and occasional case reports, then a randomized trial that had to be abandoned because it was so dramatically effective that it would have been unethical to deny treatment to the control group. The treatment in question was fecal microbiota transplantation—which is a polite way to describe blending a healthy person’s excrement with a little salty water, and injecting the mixture into the patient via the obvious orifice. Recovery is rapid, nearly ubiquitous, and often requires just a single enema of salted poo.6
Doctors and researchers are now wondering what else can be treated with fecal bacteria. For example, neurosurgeons have been discussing the possibility that Enterobacter aerogenes, a common bacteria in feces, can be used to treat glioblastoma, a kind of deadly brain tumor. The thinking is that, if surgeons smear the bacteria in the brain itself, the body’s immune system will mount a ferocious response and attack the tumor. Doctors can then cure the infection. “A brain abscess can be treated, a glioblastoma cannot,” one surgeon told The New Yorker.7 It’s a desperate gamble, and an enormously controversial one. But the basic idea—that some of our microbes can do us a great deal of good—is now widely accepted.
Why, then, are our microbes going missing? The most obvious culprit is the routine use of antibiotics. These powerful lifesaving drugs should be saved for serious bacterial infections but are often used to treat minor ones, wrongly prescribed for viral infections where they cannot work, or used simply to fatten up the animals that we eat. A second factor is that our surroundings have become more sterile thanks to the frequent use of detergents, antiseptic hand washes, and other attempts at purification. Some of these sterilizing processes take place without our realizing; for example, one research team found that hospital air-conditioning systems seemed to be filtering out many harmless microbes, and that dangerous pathogens had taken their place.8
A third explanation is the rise of the cesarean section, which is now how almost a third of American babies come into the world. Babies collect a rich broth of microbes from their mothers, but this transfer does not occur in the womb as one might expect. Instead, they are smeared with bacteria as they pass through the birth canal—if they pass through the birth canal. This may explain the otherwise puzzling fact that babies born by cesarean section suffer more from asthma and allergies. It also explains the mysterious behavior of Rob Knight, a microbial ecologist whose baby daughter was born by emergency cesarean section in 2012. Concerned that the baby had bypassed the microbes of the birth canal, Professor Knight waited until the doctors and nurses were out of the room, then rubbed his baby with a swab coated in her mother’s vaginal fluids in an effort to colonize his daughter’s skin with those maternal microbes. That was speculative—Wild West science in the tradition of Barry Marshall. But Professor Knight is now running a controlled study of much the same technique with babies born by cesarean section in Puerto Rico.9
Finally there is the simple fact that our microbiome is partially heritable, passed from mothers to daughters. It follows that if one generation thins out the messy diversity of their microbiome through antibiotics and antiseptics, the following generation will start from a less diverse foundation.10
It is worth acknowledging that these ideas have already become a fad—a great deal of nonsense is now being talked by quacks and purveyors of probiotic yogurt aiming to promote a “healthy microbiome.” There is no such thing, or rather there is a vast range of healthy microbiomes. People can have very different microbiota, yet still be perfectly healthy; the biological makeup of the same person can also change rapidly, day by day. And of course, eating dirt can make you ill, and antibiotics save many lives. There is a balance to be struck here—a balance that we are still working hard to understand.11
Yet the early lessons of the new science of the microbiome chime strikingly with what we’ve already discovered: If you try to control a complex system, suppressing or tidying away the parts that seem unimportant, you are likely to discover that what seemed unimportant turns out to be very important indeed.
• • •
If we are increasingly understanding that mess makes natural systems more healthy and resilient, then could the same be true for artificial systems, such as the neighborhoods, cities, and countries where we live?
Jane Jacobs, the urban writer and campaigner, made the case for neighborhood diversity in The Death and Life of Great American Cities. She wrote of “the daily ballet of Hudson Street” in Greenwich Village, New York, where she lived.
“We may fancifully call it the art form of the city and liken it to the dance,” she wrote. “Not to a simple-minded precision dance with everyone kicking up at the same time, twirling in unison and bowing off en masse, but to an intricate ballet in which the individual dancers and ensembles all have distinctive parts which miraculously reinforce each other.”12
Jacobs explained that it was the diversity of this urban ballet that made it work. In the morning, shopkeepers opened their stores and children walked to school. Smartly dressed professionals emerged from their homes, hailing the taxis that had earlier brought the investment bankers south from Midtown, and riding them north. After the morning rush hour, the street was kept busy with mothers and housewives, and with local workers out for a coffee or lunch. In the late afternoon, children played safely on the sidewalk, and as dusk fell, people gathered in the pools of light around the pizza stand and the bars. Because the neighborhood had such a mixture of residents and such a mixture of attractions, it was always busy but never overwhelmed with people. The diversity of activities made Hudson Street pleasant and safe and engaging, and that very diversity was itself an attraction.
Diversity at street level was made possible by a mix of offices and homes, stores and workshops. It was also made possible, Jacobs argued, by a mix of old and new buildings. She would not have been surprised by the story of Building 20, the low-status structure in the middle of high-status MIT that was home to so many intriguing experiments. It sounds not unlike a building she describes in The Death and Life of Great American Cities:
The floor of the building in which this book is being written is occupied also by a health club with a gym, a firm of ecclesiastical decorators, an insurgent Democratic party reform club, a Liberal party political club, a music society, an accordionists’ association, a retired importer who sells maté [sic] by mail, a man who sells paper and who also takes care of shipping the maté, a dental laboratory, a studio for watercolor lessons, and a maker of costume jewelry. Among the tenants who were here and gone shortly before I came in, were a man who rented out tuxedos, a union local and a Haitian dance troupe. There is no place for the likes of us in new construction . . . what we need, and a lot of others need, is old construction in a lively district, which some among us can help make livelier.13
Diverse streets and neighborhoods work better than monotonous ones, and Jacobs argued that the same is true for diverse cities. It is preferable, she argued, to have an inefficient hodgepodge of different industries than to specialize in a single industry, however efficient that might seem in the short term. One of her favorite examples was the unromantic mess of Birmingham, the second-largest city in England. Birmingham is famous for making nothing in particular, yet over the years has been a hub for steam engines, pneumatic tires, pen nibs, toys, jewelry, cars, chocolate, buckles, buttons, tanks, planes, banking, and electrical engineering. Stumped for a marketing slogan to sell this hodgepodge to a skeptical world, Birmingham’s elders have tended to go for “the city of a thousand trades.” It hasn’t really caught on.*14
When Jane Jacobs was admiring Birmingham in the early 1960s, her view seemed odd. Detroit, the quintessential one-industry town, was booming. The standard view was that cities could prosper by playing to their own strengths. But as deindustrialization ripped the life out of specialized cities from Detroit to Glasgow, it became clear that this view was shortsighted. Jacobs had been right that specialized cities were fragile. Diverse industries might seem untidy, and they might occasionally get in one another’s way. But the diversity gave a city a chance to respond to shocks. And while nobody ever gets very excited about Birmingham, it has adapted and endured for hundreds of years.
In 1994, over three decades after Jane Jacobs set out this idea, AnnaLee Saxenian, an economist and political scientist, published a study comparing two famous technology clusters, Silicon Valley and Boston’s Route 128. I say “famous,” but Route 128, once regarded as the leading technology hub in the world, was so comprehensively overshadowed by Silicon Valley that it is now just the name of a strip of tarmac around Boston.15
Saxenian found that the technology companies of Route 128—companies such as Wang, Raytheon, and Sun—kept themselves in tidy silos, specializing in narrow fields of excellence. The fledgling companies of Silicon Valley sprawled into one another, engineers constantly gossiping with each other or moving in informal networks that had little to do with the corporate structures that employed them. Initially, like Detroit or a German forest, the focused structure of Route 128 companies was hugely successful. But as technology continued to leap forward, the specialized Route 128 companies proved unable to adapt; many of them went out of business, or stagnated in the shadow of the Silicon Valley titans.
New data are adding further support to the view that economic diversity is integral to economic health. Cesar Hidalgo, a physicist at the MIT Media Lab, has produced innovative maps showing the underlying structure of different economies. (Unfortunately, city-level data aren’t available in enough detail, so these maps describe national economies.) Hidalgo’s structural maps look like fine cobwebs linking different types of product clusters and subclusters. They allow us to distinguish between products that require closely related capabilities (for example, handbags and shoes) and those that seem to require very different expertise (for example, clocks and medical devices).16
Hidalgo has discovered that there is a strong correlation between being a diversified economy, a complex economy, and a rich economy. It is unusual for a country that exports highly sophisticated products to do only that; they will also tend to export a wide variety of much simpler things. It is also unusual for a country to make lots of different kinds of simple products, yet no sophisticated products. And if a country exports only a small number of products, it’s a safe bet that they will be simple, not complex. Variety and sophistication go hand in hand. For example: the Netherlands, a complex economy, exports almost everything that Argentina exports—94 percent of Argentine exports have equivalents that can be bought from the Netherlands, according to Hidalgo’s latest data, from refined petroleum to engine parts and cut flowers. But the Netherlands also exports many products that Argentina does not, such as computers.
These highly diversified economies also tend to be rich. There are examples of rich yet specialized economies—the petro-states of the Middle East today, or, in the past, the agriculturally based prosperity of Uruguay and Argentina. But they are few. And Hidalgo finds that such prosperity is extremely fragile. Over time, rich but specialized economies usually lose ground to economies that enjoy more diversity.
Diverse economies, like diverse German forests, are more resilient. On first principles it is far from obvious that this should be true: forests are not cities and the organisms in a forest, like the organisms camping out in our bodies, have evolved together for thousands upon thousands of generations. While that long evolution is no guarantee of resilience, it is a process that is likely to have hidden depths. In contrast, an artificial system such as a city or a neighborhood will have developed over a time scale measured over years or decades rather than millennia. Perhaps we should not be surprised that classical economic theory has emphasized specialization, rather than following nature’s lead and being wary of monoculture: cities or countries are advised to get very good at producing a few products, and then trade those products for everything else they need.
In recent decades, economists have started to realize that this theory doesn’t capture what matters in reality. The old proverb “Jack of all trades, master of none” captures our intuition that we limit what we can achieve by targeting wide-ranging competence rather than choosing one domain in which to specialize. Perhaps that is true of an individual; it’s not true of a city or a country. The economies that do lots of things tend to do most of those things very well. That is the road to prosperity—and in an unpredictable world, it is the road to resilience, too.
• • •
Jane Jacobs has deservedly attracted an army of admirers, and the intellectual battle in favor of diverse cities seems to have been won. But as Jacobs understood, two powerful forces stand in the way.
The first is hard to do anything about, as it seems deeply ingrained in human nature. It’s a regrettable fact that neighborhoods have a tendency to segregate themselves, like oil and vinegar. If people prefer to live near similar people—perhaps people of the same race, class, ethnicity, or income—then even quite mild preferences can lead to marked social segregation.17 (This is the same tendency we observed on university campuses: students seek out friendships with similar people.) The political implications of this tendency were parsed by Bill Bishop and Robert Cushing in their book The Big Sort, which showed that American neighborhoods were becoming more polarized. When Jimmy Carter won the U.S. presidency in 1976, just over a quarter of Americans lived in “landslide counties,” where Carter had either won or lost by 20 percentage points. By the 2012 election, more than half of Americans lived in landslide counties.18
The second is more avoidable—a bureaucratic desire for tidy, segregated cities is expressed in zoning and planning laws that are designed to prevent different aspects of city life from getting tangled up with one another. The planner’s vision, reasonable enough, is a world where smokestacks and brothels are kept far away from playgrounds and family homes. There is a question of balance here, but the problem is that what seems like the right balance on a planner’s map will look very different at street level. Zoning restrictions seem pleasing in theory; in practice, they can produce dull city neighborhoods. Recall how Jane Jacobs’s ballet of Hudson Street relied on the fact that the street was always active at any time of day, because so many different kinds of people used it. In contrast, thoroughly zoned neighborhoods are unbalanced. They are too busy at certain times, deathly quiet at others; they are unable to support local shops and businesses. They encourage a dependency on cars, because people tend to work far from where they live. They reinforce social divisions, too: Jonathan Rothwell of the Brookings Institution has shown that by preventing the development of new affordable housing, zoning restrictions often amplify existing racial and social inequalities.19
This, by now, should be a familiar story: the people who make the rules find themselves hypnotized by a tidy aesthetic that looks good on a map, graph, or screen—but which is a disaster for the people who have to live and work in a world defined by those tidy rules. Successful cities are a glorious mess of old and new, of houses and shops and workplaces, and where the richer residents and the poorer ones mingle together. And it is that diverse mess that makes them safe, innovative—and perhaps above all, resilient.
• • •
There are some forms of urban mess that nobody wants to live with. In the spring of 2010, cleaners at Utrecht railway station in the Netherlands went on strike. The station is a busy place, and in the absence of the cleaning staff it rapidly became the most appalling mess, the ground littered with newspapers, food cartons, and other trash. If this variety of mess has any positive effects on city living, then it’s not clear what they are. But what’s interesting in this context is how we instinctively seem to overestimate the benefits of tidying up.
Two Dutch psychologists, Diederik Stapel and Siegwart Lindenberg, decided to take advantage of the disruption to conduct a clever experiment. They asked commuters using the station to sit on a bench and fill in a questionnaire in exchange for a small reward. The questionnaire tested their tendency to stereotype others. The researchers also placed an actor on the bench: sometimes the actor was black, sometimes white. Would the experimental subjects sit near the stranger or far away? Stapel and Lindenberg repeated the experiment when the strike was over and the station was clean and tidy.
The experiment was a smash hit, reported around the world. Here’s Diederik Stapel’s recollection of the immediate response:
I was in the paper—in fact I was in all the papers. I had published a study which showed that messy streets lead to greater intolerance. In a messy environment, people are more likely to resort to stereotypes of others because trash makes you want to clear it up, and the use of stereotypes lets you feel like you’re clearing things up. Stereotypes bring clarity to a messy world. Women are emotional, men are aggressive, New Yorkers are in a hurry, Southerners are hospitable. Stereotypes make the world predictable, and we like that, especially if the world currently looks dirty and unkempt. The publication of this study caused a sensation. It was published in the most prestigious journal of them all, Science, and it made headlines around the world.20
Not only did people use more stereotypes when answering the questionnaire in the messy environment, they sat farther from the actor on the bench—but only if the actor was of a different race from their own. Stapel and Lindenberg theorized that stereotyping was an attempt to compensate for a messy environment: “a way to cope with chaos, a mental cleaning device.” Mess invites us to impose our own oversimplified order on the universe: it makes us racists. And Stapel and Lindenberg had a clear policy recommendation:
One way to fight unwanted stereotyping and discrimination is to diagnose environmental disorder early and to intervene immediately by cleaning up and creating physical order.21
What Stapel and Lindenberg had found seemed intriguing, surprising, yet strangely plausible. It seems to make sense that mess is bad for us, making us suspicious. We have a curious faith in the idea that if only we could live in a tidy world we’d be better people.
But within a few months of publication, social psychologists received some unsettling news: Diederik Stapel was a fraud. In paper after paper, he had fudged the data or even invented it completely, fooling the journals, his peers, and even his coauthors. (Stapel’s colleague Siegwart Lindenberg was unaware of the deception.) Here, in Stapel’s own words, is what really happened in Utrecht station:
The empirical tests were completely imaginary. The lab research hadn’t been carried out. The field studies never happened.22
The driving force, the bait that lured Stapel into a life of academic deceit, was simple: journal editors wanted to publish tidy results, too. And that is what Stapel kept providing for them. Stapel, it appears, was not only a fraud but something of a neat-freak himself.
I’d been having trouble with my experiments for some time. Even with my various “gray” methods for improving the data, I wasn’t able to get the results the way I wanted them. I couldn’t resist the temptation to go a step further. I wanted it so badly . . . I was alone in my tastefully furnished office at the University of Groningen. I’d taken extra care when closing the door, and made my desk extra tidy. Everything had to be neat and orderly. No mess.23
Fortified by his scrupulously tidy environment, Diederik Stapel began to fabricate the data underpinning fifty-five research papers. And Stapel himself later told The New York Times that he was motivated by a desire for neatness, and by a desire to please the editors of academic journals who didn’t like messy results any more than Stapel did.
Stapel, the newspaper reported, “had been frustrated by the messiness of experimental data, which rarely led to clear conclusions.” His lifelong obsession with elegance and order, he said, led him to concoct sexy results that journals found attractive. “It was a quest for aesthetics, for beauty—instead of the truth.”24
Diederik Stapel’s fraud is a morality tale on two levels. His yearning for neatness led to his fraud. But more pertinent, it was our eagerness to believe what his fraudulent study was telling us—to overestimate the ill effects of mess, to imagine that tidying up would have profoundly transformative effects on our moral selves, rather than just make our morning commute more pleasant—that led to its generating so much publicity.
Not all messes have redeeming features: a train station that isn’t strewn with litter is more pleasant than one that is. It’s worth sweeping the platforms. But tidying up isn’t going to turn us into better people.
• • •
The story of the “broken windows” theory of urban decay is another example of how we instinctively overestimate the benefits of tidying up certain kinds of urban mess. The theory was proposed in an influential article in The Atlantic Monthly in 1982 by criminologist George Kelling and political scientist James Q. Wilson. Kelling and Wilson argued that small signs of disorder led to the breakdown of community norms and, eventually, to serious criminality. Here’s a taste of their argument:
A stable neighborhood of families who care for their homes, mind each other’s children, and confidently frown on unwanted intruders can change, in a few years or even a few months, to an inhospitable and frightening jungle. A piece of property is abandoned, weeds grow up, a window is smashed. Adults stop scolding rowdy children; the children, emboldened, become more rowdy. Families move out, unattached adults move in. Teenagers gather in front of the corner store. The merchant asks them to move; they refuse. Fights occur. Litter accumulates. People start drinking in front of the grocery; in time, an inebriate slumps to the sidewalk and is allowed to sleep it off. Pedestrians are approached by panhandlers.
At this point it is not inevitable that serious crime will flourish or violent attacks on strangers will occur. But many residents will think that crime, especially violent crime, is on the rise, and they will modify their behavior accordingly. They will use the streets less often, and when on the streets will stay apart from their fellows, moving with averted eyes, silent lips, and hurried steps. “Don’t get involved.” . . . Such an area is vulnerable to criminal invasion. Though it is not inevitable, it is more likely that here, rather than in places where people are confident they can regulate public behavior by informal controls, drugs will change hands, prostitutes will solicit, and cars will be stripped. That the drunks will be robbed by boys who do it as a lark, and the prostitutes’ customers will be robbed by men who do it purposefully and perhaps violently. That muggings will occur.25
This is a plausible idea, and its plausibility was greatly strengthened when it was embraced by New York City’s police department, which began to focus on disorderly behavior in public spaces in the 1990s. Serious crime fell sharply.26
But just because the theory is plausible does not mean it is true. In Kelling and Wilson’s breathless narrative, why exactly is a property abandoned in the first place? Properties are much more likely to be left derelict in poor areas than in prosperous ones. So did the abandoned property trigger the decline of this imagined neighborhood? Or was the neighborhood already in trouble when someone abandoned their property? The story that Kelling and Wilson spin tries to make cause and effect seem clear, but in reality they are hopelessly tangled.
Indeed, as one looks into the evidence base for the broken windows idea, it starts to look very thin. The psychologist Philip Zimbardo is mentioned by Kelling and Wilson:
He arranged to have an automobile without license plates parked with its hood up on a street in the Bronx and a comparable automobile on a street in Palo Alto, California . . . The car in Palo Alto sat untouched for more than a week. Then Zimbardo smashed part of it with a sledgehammer. Soon, passersby were joining in. Within a few hours, the car had been turned upside down and utterly destroyed.27
Interesting, but it is a stretch to build a theory of urban decay on what happens after one psychologist takes one sledgehammer to one car in one California city.
The truth is that social science has not been able to muster much support for the broken windows theory of policing, nor for the idea that it deserves credit for breaking New York City’s crime wave in the 1990s. There is no shortage of explanations for the decline in crime, and any plausible explanation must deal with the fact that crime fell across the United States, not just in New York. Steve Levitt, the economist now famous for the Freakonomics books, surveyed the evidence in 2004. He began by looking at newspaper accounts of the trend, and found that broken windows policing usually got the credit for the fall in crime.
Levitt himself, armed with a rich set of data, disagreed with the newspapers. He concluded that four factors seemed to explain the timing, extent, and geographical pattern of the fall in crime: more police; a larger prison population (this may deter crime, and will also prevent crimes because would-be criminals are locked up); the waning of an epidemic of crack use; and the legalization of abortion in the 1970s, which reduced the number of unwanted children.* Levitt considered and dismissed several other explanations, including broken windows policing: “My reading of the limited data that are available leads me to the conclusion that the impact of policing strategies on New York City crime are exaggerated, and that the impact on national crime is likely to be minor.”28
Levitt is not the only social scientist to be skeptical. Consider a fascinating debate in 2005 in the pages of Legal Affairs between two experts in the field, Bernard E. Harcourt and David Thacher. Each man cited the best available evidence based on various statistical studies. Harcourt was skeptical of broken windows policing. Thacher was supposed to be writing in support of a broken windows policing strategy. Yet even he was agnostic about the idea that disorder breeds serious crime. Instead, he made the much more defensible claim that police should deal with disorder because that’s worth doing in its own right:
Somehow the question of whether police should take order maintenance more seriously got equated with the question of whether doing that would reduce crime. I think that’s an interesting and a little dispiriting comment on our culture . . . As if there were no reason for a cop walking by to do something about a guy urinating in the middle of the street in a commercial district [unless this] would prevent a statistically-significant number of burglaries next month.29
Thacher is right—certain kinds of mess are worth tidying up for their own sake. But it’s striking how easily we fall for the old-fashioned idea that “cleanliness is next to godliness”—that a mess is not just a mess, but the precursor to some dreadful evil.
There’s another problem with piling too many hopes on broken windows policing. It turns out that when we perceive our neighborhoods as messy, we may not be quite as objective as we’d like to think. In 2004, two social psychologists, Robert Sampson of Harvard and Stephen Raudenbush of the University of Michigan, asked a basic but revealing question: When residents call their streets “disordered,” what’s really on their minds?30
Sampson and Raudenbush drove cars up and down the streets of Chicago, taking videos of over 23,000 segments of street frontage. Then they used a team of research assistants to rate the levels of disorder witnessed in those videos. They included physical disorder (graffiti, abandoned cars, litter, broken glass, beer bottles, discarded condoms), social disorder (loiterers, street prostitutes, drugs being sold, street drinking, gangs of teenagers), and structural disorder (vacant houses, boarded-up commercial buildings). The team members cross-checked one another’s work to ensure consistency, leaving Sampson and Raudenbush with a neutral observer’s rating of the visual level of disorder on each street.
Then Sampson and Raudenbush conducted a survey of thousands of Chicago residents, asking them about their own perceptions of disorder. How big a problem was graffiti in their neighborhood? What about litter? What about public drunkenness? Drug dealing? Teenagers causing a disturbance? Then they compared the subjective perceptions of the people who lived in these blocks with the objective observations of the external observers who had rated the street-level videos.
The answer is disturbing. There was, of course, a correlation between the perceptions of the residents and that of the external observers. But there was a stronger correlation: what really seemed to drive people’s sense that they lived in a disordered neighborhood wasn’t the visible manifestations of disorder on the street. It was whether the neighborhood was poor, and whether it was black. Neighborhoods with many poor families, or with a high proportion of African American residents, or both, were perceived as being more disordered by the people who lived there, relative to richer, whiter neighborhoods with the same levels of trash, graffiti, or panhandlers.
If we want to predict whether a city block’s residents think that it’s a mess, we would learn more from looking at data on race and poverty than we would learn from looking at videos of what the neighborhood actually looks like. People feel that richer white neighborhoods look neat and poorer black neighborhoods look disorderly, regardless of what is really happening on the street. So when people demand that police tidy up their neighborhood, to some extent they might actually be giving voice to a subconscious wish that they lived somewhere a little bit richer, and a little bit whiter.
• • •
A century ago, the greatest mathematician alive was the German David Hilbert. He was a man whose research program inspired a generation of younger mathematicians, and whose achievements include developing a more rigorous version of the theory of special relativity at around the time Einstein himself was discovering the idea. Hilbert was the beating heart of Göttingen University’s stellar mathematics department.
Yet Hilbert had a long retirement, during which he saw many of his former colleagues forced out under Nazi rule, sometimes because of a single Jewish grandparent.31 In 1934, Hilbert found himself sitting next to Bernhard Rust, Hitler’s minister for education, at a banquet.
Rust asked Hilbert, “How is mathematics in Göttingen now that it has been freed of Jewish influence?”
Hilbert’s reply: “Mathematics in Göttingen? There is really none any more.”32
We all know the grotesque project of the extermination camps during the Second World War. But in the prewar buildup, the persecution was of a different kind: Jews were hounded and humiliated. Academics with Jewish ancestry found their careers in ruins. The best of them left, seeking less intolerant cultures in Britain and the United States. A torment for those that fled, this policy was also a self-inflicted wound. German science was crippled. Despite a formidable industrial base and engineering tradition, Germany was unable to keep pace with the innovations that emerged from Britain and the United States—often from the very people who had been driven out. Racial and ideological purity is not a recipe for scientific success.
The economist Fabian Waldinger has recently examined the impact of the purge and found something striking. Waldinger’s research strategy was based on the fact that different subjects suffered very different rates of dismissal. At Hilbert’s beloved Göttingen, for example, 60 percent of the mathematicians were forced to leave, but the chemistry department lost nobody. Using such random variations across Germany, Waldinger was able to show how serious the impact was of losing, say, 10 percent of the scientists at a department. Then he compared it with the impact of bombing raids on university departments during the war. He found the damage from losing Jewish or dissident scientists was far greater and longer-lasting than the damage to offices or laboratory facilities. Insisting on a racially pure scientific establishment inflicted permanent harm both to research output and to the productivity of young PhD students who lost some of their best mentors. Stripped of their diversity, the German universities could not bounce back.*33
Adolf Hitler’s insouciant remark that “we’ll have to do without science for a few years” was as self-destructive in his day as it would be in ours. Few people nowadays would publicly embrace the Nazi enthusiasm for racial purges from the intellectual professions, but in other ways fear of social diversity still runs deep. During the Republican primary campaign for the 2016 U.S. presidential election, for example, Donald Trump’s artful courting of controversy to keep within his rivals’ OODA loops often involved taking tough stances on immigration. He began his rise to frontrunner status by promising to build a wall along the U.S.–Mexico border, having linked Mexican immigrants with drugs, crime, and rape. It was when he later called for “a total and complete shutdown of Muslims entering the United States” that media commentators seemed confident he had finally overstepped the mark. Evidently not: his poll ratings climbed higher.34
Modern societies continue to flirt with subtler versions of the same desire for homogeneity that underpinned the Nazi purges, and which research shows is self-defeating. Consider the work of two economists, Gianmarco Ottaviano and Giovanni Peri, who asked what impact a stream of immigrants from across the world might have on American cities. In particular they wanted to look at cities with a large number of foreign-born residents, from a range of countries. One might expect that such melting pots might struggle with social cohesion, gangs, and classrooms overstretched by language barriers. Instead, Ottaviano and Peri found that cities that hosted a complex patchwork of nationalities prospered as a result. U.S.-born residents enjoyed higher wages and, if they were landlords, could charge higher rents. If they were tenants, they paid extra for the privilege of living in such vibrant, productive cities.35
To many modern ears, some of the stories in this chapter about how diversity builds resilience may not seem surprising. Most of us know that monoculture is a risky idea, and would scoff at the hubris of replacing an entire ecosystem with a single species and expecting everything to go well. We’ve all read about the importance of “good bacteria.” But it seems hard for us to take these warnings to heart. When a doctor tells us we have a minor bacterial infection and prescribes antibiotics, few of us say that we’d really rather not take them unless absolutely necessary. Indeed, many patients demand to be prescribed antibiotics for viral infections, a situation where antibiotics are useless. We grumble at the city planners when they reject our application for a house extension, but few of us who live in leafy residential areas are clamoring to have more shops, restaurants, offices, and light industrial units intermingled with our homes.
And we still fear outsiders. Most of us living in rich countries seem content with immigration policies that exclude people from our own societies simply because of where they were born. The idea that immigration is excessive, out of control, and damaging is not just acceptable but the majority view in many countries. That view may be popular, but it is a mistake. Recall that Katherine Phillips and her colleagues found that small student groups disliked having a stranger in their midst, even as the stranger was helping them solve the murder-mystery problem they faced. We suffer the same problem at a societal level: we find it easy to overlook the contributions that immigrants make, and are acutely aware of our own discomfort. Somehow we must get over that: every society needs its outsiders to bring new attitudes, ideas, and perspectives.
These stories are not just about particular examples of diversity. They are about our reaction to diversity, again and again. In our organizations, politics, marketplaces, and personal lives, we continue to enjoy the apparent convenience, neatness, and short-term profits of imposing order, and fail to notice when it is sowing the seeds of fragility.