Miasma and the persistent power of bad ideas

PUBHLTH 405
Social Epidemiology of Infectious Disease
University of Michigan School of Public Health

Jon Zelner
[email protected]
epibayes.io

Today’s Theme

Chronicling the life-cycle of bad ideas

Agenda

  • Wrapping up your contamination dossiers

  • Understanding the strong hold of Miasma theory

  • Miasmas of the Covid era and beyond

“All Smell is Disease” and the consequences of bad ideas

Sir Edwin Chadwick

Miasmatist PPE

Where are we?

More than 500 residents of Golden Square had died in the 5 days leading up to September 5th

An eternal question 🕯️

“Why was the miasma theory so persuasive? Why did so many brilliant minds cling to it, despite the mounting evidence that suggested it was false? This kind of question leads one to a kind of mirror-image version of intellectual history: not the history of breakthroughs and eureka moments, but instead the history of canards and false leads, the history of being wrong.” (Johnson 2007, 126)

What’s old is new…

[B]oth the long delays in replacing flawed, miasma-driven approaches to cholera prevention in the nineteenth century and long delays in replacing an exclusively contact-and-droplet model of SARS-CoV-2 prevention with one that includes airborne transmission in the twenty-first had a philosophical explanation in terms of which mental models of reality prevailed and the extent to which scientists and policymakers favoured data over theory. (Greenhalgh 2021)

Understanding the persistence of a bad idea

With a partner:

  1. What aspects of human biology and psychology made miasma a difficult idea to dispense with?

  2. Which one of Rosenberg’s types of explanation did the miasmatists draw on to deal with the gaping logical holes 🧀 in miasma theory?

  3. Which social prejudices were reinforced by miasma theory? Did these skew in one political direction or another?

Persusasive mental models require abstraction

“The miasma theory drew on other sources for its power as well. It was as much a crisis of imagination as it was pure optics. To build a case for waterborne cholera,the mind had to travel across scales of human experience, from the impossibly small—the invisible kingdom of microbes—to the anatomy of the digestive tract, to the routine daily patterns of drinking wells or paying the water-company bills, all the way up to the grand cycles of life and death recorded in the Weekly Returns.” (Johnson 2007, 131)

Consilience Is Not Easy!

“Miasma was so much less complicated [than contagion]. You didn’t need to build a consilient chain of argument to make the case for miasma. You just needed to point to the air and say: Do you smell that?” (Johnson 2007, 132)

Overdetermination: Consilience’s evil twin?

Miasma turns out to be a classic case of what Freud, in another context, called “overdetermination.” It was a theory that drew its persuasive power not from any single fact but rather from its location at the intersection of so many separate but compatible elements, like a network of isolated streams that suddenly converges to form a river. (Johnson 2007, 134)

The ability to deny individual responsibility for the death caused by a firing squad is a common example of the dangers of overdetermination

Mental models and data are complementary tools

As Sir Peter Medawar observed in his essay Induction and intuition in scientific thought, for example, scientists need to do more than ‘browse over the field of nature like cows at pasture’. This is because scientific reasoning is not merely the apprehension of facts but ‘an exploratory dialogue that can always be resolved into two voices: imaginative and critical’, hence ‘the initiative for scientific action comes not from the apprehension of facts but from an imaginative preconception of what might be true’. (Greenhalgh 2021)

One without the other 💑 can lead us astray

In Medawar’s view, mental models and empirical data keep each other in check — he described them respectively as the ‘bride’ and ‘groom’ of science — and scientific progress in any discipline occurs by the back-and-forth dialogue between their two ‘voices’. (Greenhalgh 2021)

Persuasive mental models often come in the form of intuition pumps

As described by the philosopher Daniel Dennett:

Intuition pumps are cunningly designed [thought experiments, which] focus the reader’s attention on “the important” features, and…deflect the reader from bogging down in hard-to-follow details. (Dennett and Crawford 2014)

A less metaphorical intuition pump

This concept is easier to understand if we consider its opposite

Too much detail distracts from the mechanisms you are trying to highlight

Greenhalgh points out two additional issues with the failure to embrace contagionism over miasma theory

  1. It wasn’t really consistent with the available evidence, anyway.

  2. Theories are underdetermined by data because many theories can explain the same dataset. So, consistency with one theory is not sufficient grounds to reject another.

How have more recent, faulty mental models led us astray?

  • What is evidence-based medicine, and what is Greenhalgh’s critique of its role in the COVID-19 pandemic?

  • What weaknesses does she highlight in the Danamask RCT?

  • What alternative sources of evidence does Greenhalgh argue should have been considered sooner in the SARS-CoV-2 pandemic?

  • What historical experiences might have accounted for the different response to SARS-CoV-2 in China as compared to the U.S.? Does this connect to John Snow’s experienced in any way?

  • Are there similar fallacies you can identify from having worked on your contamination dossiers?

Small scale data provided compelling evidence for the droplet theory of SARS-CoV-2 transmission

Does this bias against certain types of evidence echo anything from The Ghost Map?

Why didn’t mechanistic evidence dislodge the droplet-only perspective on SARS-CoV-2 transmission?

Relationship between voice volume and aerosol production (From Asadi et al. 2019)

EBM’s hierarchy of evidence

  • What is meant by ‘risk of bias’?

  • Quality of evidence?

  • Where would Snow’s explorations fit in this hierarchy?

  • How could you re-draw this hierarchy to allow for more consilient explanations?

A version of the ‘evidence pyramid’ central to the philosophy of evidence-based medicine

Why is this kind of diagram inevitably controversial?

Two ways of aggregating evidence

Brick Wall: Collecting similar forms of evidence to test the strength of a hypothesis

Stone Wall: Collecting heterogeneous evidence to develop a robust and comprehensive explanation

Next Time: The Road to Removing the Pump Handle

Who will win???

References

Dennett, Daniel C., and Jeff Crawford. 2014. Intuition Pumps and Other Tools for Thinking. Unabridged edition. Brilliance Audio.
Greenhalgh, Trisha. 2021. “Miasmas, Mental Models and Preventive Public Health: Some Philosophical Reflections on Science in the COVID-19 Pandemic.” Interface Focus 11 (6): 20210017. https://doi.org/10.1098/rsfs.2021.0017.
Johnson, Steven. 2007. The Ghost Map: The Story of London’s Most Terrifying Epidemic–and How It Changed Science, Cities, and the Modern World. Reprint edition. London: Riverhead Books.