The Ghost Map: Epilogue Summary & Analysis

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.

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).

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.

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.

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 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.

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.

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.

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.

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.

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.

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.