Monday, March 9, 2015

Rogue Science and the Ghost Map



Because my wife loves audio books, we usually have a selection of books to listen to as we drive all over the midwest during the holidays.  The 25 hours we usually spend in the car during our average Christmas visiting is a good time to catch up on interesting books.  This Christmas, we listened to Steven Johnson's 2007 book The Ghost Map: The Story of London's Most Terrifying Epidemic--and How It Changed Science, Cities, and the Modern World.  I quite enjoyed it, even though it had some frustrating bits.  The frustrating bits are what I really want to focus on.

For those who haven't read the book, it tells the story of the 1854 Broad Street cholera outbreak in London, and the quest of Dr. John Snow to figure out what caused it.  Today, Dr. Snow is remembered chiefly among microbiologists and epidemiologists for seminal research that established that cholera is spread through water.  At the time, the London medical establishment still held to the idea of miasma - diseases were caused by bad air.  Cholera outbreaks were therefore the result of the stench produced by the poorly managed sewage in poor London neighborhoods, and the cure was "fresh air."

The thing about miasma that bothered Snow was how discriminating the air seemed to be.  Individuals living on the same block would only sporadically contract cholera, even though they were all breathing the same air.  How could bad air infect one person in one house, but leave the very next house completely untouched?  And how could bad air pick and choose between members of the same household?  A husband dies from cholera, leaving his widow and children to carry on, even though they breathe the same air.  How could this be?

Miasmatists would reply that whether or not one was susceptible to cholera depended on vaguely defined factors of personal constitution: "strength," "health," and the like.  Thus, miasma could explain disease outbreaks of any kind.  We even have leftover tidbits of miasma theory in modern medicine - the name malaria comes from the Latin for "bad air."

As I said, Snow was skeptical of miasma and began his own investigation of the outbreak.  One common thread he noted was that many of the victims seemed to have consumed water from the Broad Street pump, and that was the subject the titular "Ghost Map."  By timing himself as he walked the streets of London, he showed that for every victim, the closest water pump by walking was the Broad Street pump.  He and local reverend Henry Whitehead even found "patient zero" who lived next to the Broad Street pump and used a cesspool that basically leaked directly into the pump.

He managed to convince officials to remove the handle from the Broad Street pump early in the outbreak, presumably preventing an even bigger disaster.  Despite that small victory, though, the official report was against him: The medical establishment of London declared miasma to be the most likely explanation.  Further, they rejected Snow's careful work and conclusions as speculative and without evidence.

It staggers the imagination how anyone could look at the careful work done by Snow and Whitehead and conclude that it was just wrong, and it's even more chilling to think that this was the official government position on water-transmitted cholera.  In the 1854 outbreak, 616 people died of cholera, and there would be more outbreaks before the medical establishment finally conceded to Snow's conclusion.  How many lives were snuffed out prematurely because the government was devoted to the faulty miasma theory?

Johnson sees in this tale a triumph of what he calls "rogue science."  On the one hand, we have the careful research of Snow that led to what we now know was a correct conclusion: cholera is transmitted through contaminated water.  On the other hand, we have the ignorant government rejecting the best research and instead endorsing what was essentially dogma and speculation.  Snow worked outside of and even against the mainstream conclusions of his medical contemporaries, thus making him a rogue.  But he was still doing what we recognize as legitimate research and so it's real science.  If only the establishment had listened to this rogue science, how many lives might have been saved?  From this, Johnson concludes that we ought to put our trust in science because it will help us solve major problems facing us today.  He concludes the book with a long section on modern ecological crises, and what we might do about them based on science.

As I listened to the story of Dr. Snow, I drew a very different conclusion, and I was surprised and bothered as the book wrapped up.  I found myself concerned mostly about tribalism, as I mentioned last week, and I didn't share Johnson's almost religiously optimistic perspective on science.

The problem as I see it is that Snow did not actually demonstrate how cholera was transmitted.  His map was definitely suggestive, but questions still remained.  In fact, some questions neither miasma nor water transmission could explain.  Why would a single household lose only one member, when they breathed the same air and drank the same water?  Even more baffling: How could some people survive cholera by drinking huge amounts of water from the Broad Street pump?

Don't get me wrong: Snow's map is fantastic, and he did extremely important pioneering research in epidemiology.  But judged by the standards of the day, what would you do with his work?  His map definitely implicated the Broad Street pump, but he provided no better understanding of how cholera could be transmitted than did the miasma theory.  Why did the pump suddenly become infectious?  People all over the city regularly drank water contaminated with sewage; this was common practice.  What made the Broad Street pump different?  With the scientific tribe of the day dominated by the miasma paradigm, what were they supposed to think about Snow's idea?  I don't find it remotely shocking that they decided that he had not proven his case.  He hadn't.

It's easy for us to look back and look down on Snow's contemporaries that dismissed his research.  We know that cholera is caused by Vibrio cholerae and that Vibrio is transmitted through contaminated water.  We know that people only contract cholera when Vibrio reaches a threshold density.  Too little Vibrio will not infect you.  We also know that outbreaks from contaminated water can go away when the source of contamination is removed.  So when patient zero died, their sewage no longer contaminated the pump, making it relatively safe to drink again.

Knowing that, we look at Snow's experience with great frustration, knowing that he was on the right track and knowing that the official report endorsing miasma would probably cost human lives.  But the evidence Snow gathered at that point was ambiguous.  It left a lot of unanswered questions, and "everyone knew" that miasma caused disease.

Last week, I concluded by asking a simple question: Is it realistic that scientific consensus could be completely wrong?  How could so many scientists be so wrong?  Well, there you go.  Miasma.  I think the answer to how is that we're human.  We get things wrong all the time.  I think there's a far more important question:  What is my tribe getting wrong, and what can I do about it?

Johnson sees science as the solution, as if it could somehow break out of human bias and tribalism, but science is a human activity.  It suffers from the same foibles as the rest of us do.  True, it does have a good track record of breaking out of bias, as many scientists scrutinize the same data.  The systematic rigor of science also contributes to it's success.  Scientists are not generally satisfied with ideas; they constantly test them against data.  If necessary, they get more data.

But I think we're fooling ourselves if we think that the modern scientific culture is incapable of running down a dead end.  Science is great, but we're still human.

My solution to this conundrum?  Keep searching.  Keep watching the rogue science.   Don't dismiss anything just because it's not what your tribe thinks.  Keep thinking for yourself.  Don't let the tribe do it for you.

Feedback? Email me at toddcharleswood [at] gmail [dot] com.