Interviews & Essays
Q. This is your first historical narrative. What attracted you to the story of London's 1854 cholera epidemic?
I've always been fascinated by this period, because in many ways Londoners were living through something that had genuinely never been experienced before in human history - a true metropolis with close to three million people sharing 90 square miles. So there's great novelty and turbulence to the setting, but at the same time, it's an experience that would become increasingly commonplace in the next century. I'd been thinking about London in the 1850s from a cultural perspective for a while (my grad school focus, many years ago, was on the British and French metropolitan novels of the 19th-century). But the Broad Street outbreak added a whole new element, in that it made it a book about science and prejudice and the battle for new ideas. But more importantly, it gave me a story that I could wrap all these ideas around.
Q. What type of epidemic was this? When and where did it start? How many people died in it? Why was it unique?
It was an outbreak of cholera, transmitted originally via a contaminated well that was popular with the residents of Soho in London. More than five hundred people died in about a week; on the streets directly next to the pump, ten percent of the neighborhood perished. Earlier epidemics of cholera in London had killed more people, but they generally took much longer to do their
damage. The Broad Street outbreak was unusually deadly because the neighborhood was so densely settled, and because this particular pump was very popular with the residents.
Q. Dr. John Snow was the first person to prove that cholera is a water-borne disease. How did he manage to link the microscopic bacterial cause of the disease with the macroscopic causes at the level of city planning and the everyday patterns of urban life?
Snow did a number of different studies to prove his theory, but his investigation into the Broad Street outbreak turned out to be the most influential, largely because there was a single, identifiable culprit in the form of the contaminated well. With the help of Henry Whitehead, he was able to personally interview hundreds of residents - or their surviving next of kin - and prove that there was a massively disproportionate number of deaths among people who had drunk from the Broad Street well. It was ultimately that detective work that solved the mystery of cholera: if you had consumed water from the Broad Street pump, you were seven times more likely to contract cholera that week than non-pump-water drinkers were.
Q. What special qualities did Dr. Snow have that allowed him to go against the conventional medical wisdom?
I think the crucial element was that he was a "consilient" thinker, which means that he analyzed the disease on multiple scales of experience, and built connective chains of cause and effect between those scales. He never actually was able to see the cholera bacterium directly, but he used the available technologies of microscopy to analyze the water supply to look for signs of contamination; he was an immensely talented physician, and his understanding of the human body's response to cholera pointed him towards an infectious agent that was ingested not inhaled; and at the same time, he was a kind of amateur sociologist, thinking about broad patterns of activity on the scale of the city itself. To "see" the cholera bacterium, you need to think on all those scales simultaneously.
Q. What role did Reverend Henry Whitehead play in the investigation?
The local curate Whitehead was absolutely crucial to the investigation, and his role has been historically ignored in favor of the "rogue visionary scientist" story that emphasizes Snow over everyone else. In fact, it was a true collaboration, because Snow needed Whitehead's social intelligence, his local knowledge of all the residents, to build the case against the Broad Street pump. And in fact, in the end, Whitehead ultimately discovered the crucial link between the pump and the origins of the outbreak. Without Whitehead's contribution, it's entirely possible that the Broad Street case wouldn't have established the primacy of the waterborne theory, and it might have taken decades longer for Western cities to defeat cholera, costing thousands of lives in the process.
Q. Why was there such resistance to the idea that cholera was a water-borne disease?
There are many reasons, but I think the most important one is that London was just incredibly smelly. It was entirely common for people to have cesspools in their basements that were filled with several feet of human excrement. When you add all the industrial fumes and the amount of
livestock in the city (cows were frequently kept it attics as a ready-made supply of milk), the overall effect was a city that was literally overwhelmed by odor. And because the human nose is much more sensitive to smell than our eyes are to the presence of tiny bacteria, it just seemed overwhelmingly obvious to people that the smell must be responsible for disease.
Q. How long did it take before Snow and Whitehead's findings were completely accepted? What does this delay say about the nature of scientific progress?
The tide began to turn in the first few years after the Broad Street outbreak subsided, and within a decade the waterborne theory was widely acknowledged as the correct one. I think it shows that the battle for new ideas is rarely a matter of a clean, eureka moment where some genius comes up with a great breakthrough and the world is changed in an instant. Instead, it's a slower, almost evolutionary process where good ideas take time to win out over lesser ones, depending on the historical conditions that surround them.
Q. What was the "ghost map"? Who created it, and why was it such an influential document?
It's a map that John Snow made of the outbreak, which showed all the deaths from the disease marked as black bars at each address in the neighborhood. The power of the map is that you can see in a glance the deaths radiating out from the pump on the map; the map is dense with black bars right around the pump, but the bars steadily disappear as you get further away from it. It was a pioneering document both in the field of information design and public health, because it made the cause of an outbreak immediately visible to a layperson, in a way that a long table of statistics never would have.
Q. Why do you write that this is a story not only about the triumph of science but also about the triumph of urban life?
It's a triumph of urban life in two senses of the phrase. First, winning the battle over cholera was crucial to creating sustainable metropolitan life. We weren't going to keep building cities with two million people if ten percent of your neighborhood could just suddenly die in a week. But it was also a triumph of urban life in that the detective work involved in solving the case was very much dependent on the local knowledge of dense urban living, and on the cross-disciplinary sharing of expertise that so often flourishes in urban environments.
Q. You maintain that Snow and Whitehead developed a model for managing and sharing information with implications that extend far beyond epidemiology. Can you give some examples of their ideas at work in contemporary life?
The best example is the wonderful 311 service in New York City, which taps the local knowledge of all the city's residents, by allowing them to call into a centralized number to report potholes, or homeless people, or ask questions about park activities, or a thousand other things. The city that takes in all that information and plugs it into databases and maps that give the government a much more nuanced sense of what's happening on the ground in the city, just as Snow and Whitehead's investigation and map made the path of the cholera much more
intelligible. This is also happening on the web right now in a million interesting ways, as
"amateur" experts use their powers of observation and local knowledge to map their own neighborhoods, via blogs and Google map "mashups."
Q. The possibility of a terrorist attack by biological means has been in the forefront of every city dweller's mind since 9/11. What are the chances that a new epidemic - whether natural or engineered by humans - could once again threaten our great cities and the whole idea of urban civilization?
The chance is quite high that we'll be hit by some kind of serious pandemic - bird flu, perhaps, or ebola, or some engineered species - in the coming decades, though I think it will be unlikely to turn us away from the great migration to the city that has enveloped the world since the 19th-century. But in the long-term, I'm a bit more optimistic about our chances, because we have so much technology at our disposal now for tracking, identifying, and neutralizing biological agents. In the most basic sense, our understanding of DNA is evolving much more quickly than bacterial or viral DNA is. That's a very encouraging trend-line, in a field where most of the stories are apocalyptic ones.
Q. What about the likelihood of a nuclear attack by terrorists? Could any of the techniques developed to fight epidemics be useful against it?
No, not really, and that's the problem. I'm more worried about the threat to metropolitan living posed by rogue nuclear weapons detonated by suicide bombers than I am the threat posed by viruses. Because there are no vaccines for nuclear weapons, and no quarantine strategies once one goes off. And the death toll would be staggering: a million people could die in an instant, if the weapon were large enough and planted in a densely populated city center.
Q. Are the problems we face today - like the world's apparently inexhaustible demand for resources and goods, or environmental crises like global warming - inherently worse than the ones faced by our Victorian ancestors?
Clearly the scale of the problems is bigger. The Victorians had to deal with the pollution problems involved in contaminating the water supply of the Thames, not altering the temperature of the entire planet. They had to deal with the problem of getting three million people to share a relatively small amount of land, while today's mega-cities are dealing with populations of more than twenty million. But of course, our expertise and our data-collection tools have grown just as fast over that period, if not faster. Snow and Whitehead had to generate the map because they couldn't isolate the cholera bacterium itself to prove that it was in the water. Today we have amazingly in depth maps created instantly whenever unusual diseases erupt anywhere on earth - and at the same time, we can not only see the cholera bacterium, we can decode its DNA. So the problems are real ones today, and they are serious, but they're also solvable, if we commit ourselves to finding those solutions, and steer clear of orthodoxy and superstition, as Snow and Whitehead did a hundred and fifty years ago.
Q. Tell us a little about your approach in writing The Ghost Map.
I tried very consciously to model the book's technique on Snow's consilient way of thinking about cholera and the Broad Street outbreak. In the preface, I describe it as a book with four protagonists: two men, a bacterium, and a city. Conventional history is too often limited to the scale of individual human lives. Snow and Whitehead were no doubt crucial to the story of the Broad Street epidemic, but the evolutionary history of the bacteria was just as crucial, as was the macro, collective development of the city itself. So I tried in The Ghost Map to write a history of this fascinating week that would do justice to those different scales.
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