Before too long, the planet’s human population will be more than fifty percent urban. Perhaps in a few decades, that figure will shoot up to eighty percent. At the time when Snow and Whitehead were alive, a mere ten percent of the population was urban. Human thought is still catching up to the urban revolution of the last 150 years—history books treat modern history as a series of interactions between nations, but the city is becoming the dominant unit of civilization.
In some ways, the growth of cities is the defining event of modernity, and yet it’s rarely an important part of history classes. The study of cities is still in many ways a vague discipline: Johnson argues persuasively that people should become more aware of the science and sophistication that go into building a successful metropolis.
Living in a city has big advantages. Studies suggest that urbanites live longer than those living in rural areas. Furthermore, health and air quality in American cities is as good as it’s been in two centuries. Perhaps most surprisingly, cities have become important forces of environmental health: urbanites consume less energy than their rural counterparts. Additionally, cities act as a form of population control—families in agrarian economies tend to have more children, for the simple reason that they need more hands to help. Cities, on the other hand, tend to offer more opportunities to women without children. In many urbanized countries, the birthrate has dropped below “replacement level” (i.e., the population is shrinking).
In many ways, the most popular stereotypes about cities—that they’re congested, unlivable, etc.—are a century behind the times. Cities are some of the healthiest and cleanest forms of human society; they also offer more opportunities to minorities and women. Thus there are good reasons to believe, and even to hope, that the future of humanity hinges on the future of cities.
To no small extent, Snow and Whitehead made the contemporary urban world possible. Thinkers no longer doubt that it’s possible to crowd tens of millions of people into a small radius—and in large part, that's because scientists learned how to control microbes. Since Victorian times, cities have become “great conquerors of disease,” centers of scientific research and public health measures.
Few if any thinkers would seriously dispute that it’s possible for a big city to survive indefinitely, provided that it’s run efficiently. But only 150 years ago, cities such as London were laboratories of public health and urban planning—the fate of urbanism in general rested on the survival of places like London, and therefore, the work of men like Whitehead and Snow.
It’s unclear what the future of cities will be. However, for the time being, “cities are where the action is.” They’re centers of “tolerance, wealth creation, social networking, health,” etc. While it’s been argued that the Internet will curb the growth of cities, since it reduces people’s incentive to move to cities, it seems that the Internet won’t be enough to prevent cities from expanding. It’s been argued that global warming will spell the end of urbanism—many big cities are within a few miles of the rising oceans. However, it seems likelier that global warming will damage some cities without challenging the premise of urbanism. Others have argued that the decline of available oil will prevent urbanism; however, the increased energy efficiency of cities would seem to refute such a claim. If anything, the decline of available energy will accelerate urbanization.
Urbanism has become the dominant paradigm for the human race—country by country, populations tend to be migrating out of rural communities and into large cities. Johnson acknowledges that global warming or the Internet might undo some of the growth of urbanism (since, if you have good Wi-Fi, you can get many of the same experiences you’d otherwise only be able to get in a metropolis). In a way, however, these challenges to urbanism resemble Snow’s challenges to miasma theory: even if they chip away at the feasibility of urbanism, people will continue moving to cities for a long time to come.
It would be wrong to claim that urbanization is inevitable—new, unpredictable problems are always threatening cities. The September 11 attacks on the World Trade Center illustrate one of the great weaknesses of cities: a densely packed area is a prime target for a terrorist attack. Another factor to consider is the threat of nuclear war: if a larger portion of the population is packed into cities, a nuclear blast could do far more damage than it would if the population were spread out into smaller towns. In a way, big cities are bull’s-eyes—it seems inevitable that, one day, a troubled soul will find a way to detonate a nuclear bomb in an urban center.
Perhaps the biggest downside to living in an urban center, Johnson argues, is that it’s a potential target for terrorist attacks. Terrorists looking to do harm to a great number of people have no better target than a city, where thousands of people might be packed into a single building. There have been many unforgettable attacks in cities—for example, the bombings of Hiroshima or Dresden, or the attack on the World Trade Center in New York City. But these disasters seem to have had no effect on the growth of cities, suggesting that urbanism is here to stay.
Perhaps the greatest danger of urban life is the heightened possibility of an epidemic. Ten people infected with Ebola in Manhattan could easily infect millions of others. However, it’s important to remember how far epidemiology has come since the 19th century. In the 2000s, there’s been a lot of debate over the possibility of an avian flu epidemic, which could claim tens of millions of victims. In 2004, Thai health officials began requiring poultry workers to receive conventional flu vaccines, in order to prevent an avian flu outbreak. In doing so, the officials decreased the probability that the H5N1 flu virus (for which conventional vaccines are useless) would come into contact with an ordinary flu virus and mutate into a stronger virus that could set off a human epidemic.
The possibility of a global avian flu epidemic is still an important research topic in the medical community. As Johnson characterizes it, medical research into avian flu is a constant process of anticipating what avian flu could do, and then preventing it from happening. For example, when officials ordered that poultry workers receive their flu vaccines, they were trying to “nip in the bud” the possibility that the avian flu could merge with an ordinary flu virus and form an incurable epidemic.
In the 1990s, two Harvard scientists discovered that the cholera bacterium had evolved to be lethal to human beings by acquiring genes from a virus called the CTX phage. In other words, cholera “is not a born killer”—rather, it acquires a genetic code that allows it to infect a human host. In the 21st century, doctors fear a similar “merging” of the H5N1 virus and the conventional flu viruses that cause millions of people to become mildly sick every year. Health officials regularly launch “preemptive strikes” against the global flu epidemic.
Johnson explains why it’s so important to vaccinate poultry workers against ordinary forms of flu: if poultry workers don’t receive this vaccination, there’s a possibility that their flu viruses could merge with the H5N1—in more or less the same way that the CTX phage merged with the ancestors of the modern cholera bacterium. The medical community faces the constant possibility that a new virus or deadly bacterium will emerge—and must ensure that these possibilities don’t evolve into realities.
Some have argued that a global flu epidemic is inevitable, especially with so much of the world’s population crowded into cities. But if such an epidemic occurs, it’s unlikely that urbanization will reverse itself. Again and again, after a major urban disaster, the city’s population continues to grow. However, if a virus killed half a million New Yorkers, other New Yorkers would probably move somewhere else.
At this point in the history of urbanization, it’s unclear how much danger urban dwellers will be willing to put up with before they move out of cities and back to rural communities. In the last hundred years, cities have been bombed, ravaged by war and disease, etc.—and yet people have continued moving to cities.
Perhaps humanity’s greatest weapon in fighting a global epidemic is biology. Scientists’ knowledge of DNA code might one day enable them to rewrite the code of viruses and bacteria in order to render them safe for human beings. In the twenty-first century, humans are locked in an arms race with microbes—scientists are developing ever-more complicated tools for fighting disease, while most viruses and bacteria possess no more than a few genes. It’s been suggested that terrorists will one day give up using bombs and instead use viruses to kill millions of people. The difference is that viruses have vaccines—bombs don’t. It seems likely that defensive tools, such as vaccines, will prove more powerful than the viruses themselves. And one of the most powerful defensive tools humans have is mapping, of the kind pioneered by John Snow. It’s not enough to research new vaccines in response to outbreaks of disease—urban planners must also make maps that anticipate how an epidemic will spread.
Microbiologists have developed a formidable arsenal of tools for fighting diseases. In many ways, they’re winning the war with disease: they’re getting closer and closer to being able to “reprogram” viruses and bacteria so that they pose no significant harm to homo sapiens. And even if microbiologists don’t succeed in doing so, they can construct ingenious maps, the descendants of the maps designed by John Snow, that can be used to predict the spread of disease and then minimize the damage.
But even if humanity should be optimistic about the threat of a virus, there’s less reason to be optimistic about nuclear weapons. Nobody is working on a way to “neutralize a nuclear explosion”—explosions can be anticipated, and the effects of radiation poisoning can be curbed, but the explosions themselves can’t really be prevented. Perhaps “urban nuclear explosions will turn out to be like hundred-year storms”—catastrophes that kill millions without threatening the survival of the human race itself.
Nuclear war is a big, complicated topic for Johnson to introduce in the final pages of his book. However, it illustrates an important principle that Johnson has alluded to throughout: there may be some problems for which human beings will never have perfect solutions. Perhaps humans will learn to live with the threat of nuclear war, much as generations of Victorians learned to live with the constant threat of an epidemic.
In all, urbanization is far from inevitable—viruses and bombs could easily turn cities into centers of danger and death, incentivizing people to move back to smaller communities. But there are two things human beings can do to sustain urbanism. First, they can embrace science—in particular, genetics, Darwinism, and environmental science. Doing so will allow us to predict what viruses and bacteria will do in the future. The second thing people can do to sustain urban life is to support strong public health systems.
Even if humans can’t avert nuclear destruction, they can immerse themselves in science and public health projects. In doing so, they maximize the likelihood that the scientific community will be able to develop cures for new, deadly diseases.
There have been many challenges to urbanism, science, and public health in the last few years. Intelligent design theorists spend millions attacking the theory of evolution, even as the United States spends millions on nuclear weapons. But humanity would do well to remember Henry Whitehead and John Snow. Instead of despairing in the face of what seemed an unsolvable problem, Whitehead and Snow used ingenuity and hard work to save lives. Humanity has confronted appalling crises before, and emerged victorious. Hopefully, in the 21st century, it will emerge victorious once again.
In the 21st century, humanity faces some serious challenges, some of which seem not to have a solution of any kind. Science has made people healthier and lengthened lifespans, but it’s also led to the creation of weapons like nuclear warheads that have made the world dangerous in ways the Victorians couldn’t comprehend. Furthermore, there’s a limit to human beings’ ability to predict the future—some dangers can’t be anticipated, and therefore can’t be prevented. However, Johnson offers a cautiously optimistic conclusion: the future of the human race seems pretty dire, but no more so than it did to Snow and Whitehead. Perhaps science and research will prove to be humanity’s salvation, just as it was in Victorian England.