Forgetting what we know when we don't know what we don't
A story about the dangers of induction and assumption
Many times, we have learned, and then forgotten, the cure for scurvy. How was that knowledge continuously discovered, forgotten, then rediscovered, then reforgotten - over hundreds of years?
Well, here’s the story, the details of which come from an essay by @baconmeteor, who I asked for permission to paraphrase for a lecture years ago. I highly recommend reading the whole thing. It’s a tale that has stuck with me for a long while, and one I often re-tell when the concept of knowledge enters a conversation as if it is something that, once acquired, remains a permanent fixture in the lives of those who acquired it.
What follows is a very brief and incomplete summary. Ok here we go:
Scurvy takes a few months to become a problem, and a little vitamin C prevents it. Why did we often figure this out only to forget it and then figure it out again? Two reasons: scurvy takes a few months to become a problem, and a little vitamin C prevents it.
The body can't make its own vitamin C. We didn't need to worry about that for millennia because most of the plants and animals we ate had plenty. But then we developed the ability to sail for long stretches of time, and those vitamin-C-rich foods would spoil early into the trip. Sailors on long journeys often got scurvy. Sometimes more than 90 percent of the crew would die from it. But since it takes a long time to set in, it was difficult to A/B test different solutions.
Since antiquity, many cultures knew that fruit would help, yet it wasn't until 1747, thanks to the experiments of James Lind, that we discovered the power and convenience of using the juice of citrus fruits to prevent the disease. Problem solved, for a moment. Once they added a squirt of lemon juice to daily rations, some navies began to conquer the globe. Ships could go out for years at a time. Navies that didn't adopt lemon juice rations fell behind those that did.
Then steam power comes along, and those long voyages became short voyages. Scurvy was now no longer a problem, and so the massive, expensive orchards of lemons and the system for distributing the juice were retired for something easier to grow in smaller quantities – limes.
The science of vitamin C wasn't known at the time, just the curative power of citrus, and since lemons and limes seemed interchangeable, and since British colonialism offered new places to grow lots of limes using (terrible) plantation labor, that's what they switched to. The problem for sailors was that limes are far less potent a source of vitamin C than lemons, and the methods they used for storing lime juice further reduced its potency to almost zero. It would take many decades for science to discover this, so on they went, not getting scurvy all the while thinking it was the lime juice (which didn't work) that was preventing the illness when it was actually the speed of travel.
Then they started going on arctic expeditions, and with the return of long journeys the problem of scurvy mysteriously returned as well, despite all their efforts to produce, carry and drink lime juice. At times, half of the snow-stalled crews attempting to reach the North Pole would fall ill. “Hmmm,” they thought, “maybe we were wrong about citrus.” (not a direct quote)
They began to blame food poisoning. If it wasn’t the lack of fruit then it must be something else, they assumed, and since arctic explorers favored tinned and salted meat which sometimes went bad along the way, then maybe that was the source of scurvy. They started making extra sure the meat was cooked, but they didn’t know that boiling the meat they carried also destroyed the vitamin C. Since they didn't know what they didn't know, but believed they did know something that they didn't, even though lemon juice would have worked – they didn't use it, and scurvy reclaimed its position as a medical mystery.
“They had a theory of the disease that made sense, fit the evidence, but was utterly wrong...In one sense, the additional leap required for a correct understanding was very small. In another sense, it would have required a kind of Copernican revolution in their thinking,” writes Cegłowski.
“It was pure luck that led to the actual discovery of vitamin C. Axel Holst and Theodor Frolich had been studying beriberi (another deficiency disease)...they serendipitously chose guinea pigs, the one animal besides human beings and monkeys that requires vitamin C in its diet."
Finally, in the 1930s, we accumulated enough evidence to bust up our old assumptions, the ones that had fit the evidence available at the time and therefore didn’t seem questionable.
Before then, as Cegłowski writes, “The evidence on its own did not point clearly at any solution. It was not clear which results were the anomalous ones that needed explaining away." He concludes, "the villain here is just good old human ignorance, that master of disguise. We tend to think that knowledge, once acquired, is something permanent. Instead, even holding on to it requires constant, careful effort."
Here’s a link to my new book, How Minds Change