Comment by yummyfajitas | Hacker News Reader

Comment by yummyfajitas | Hacker News Reader

But in the second half of the nineteenth century, the cure for scurvy was lost. The story of how this happened is a striking demonstration of the problem of induction, and how progress in one field of study can lead to unintended steps backward in another.

This isn't the only time progress in one field leads to steps backward in another.

Once upon a time, the Romans knew the cause of plague: evil spirits. Evil spirits lived in the bodies of the living and the dead, but would occasionally jump from a sick person to a healthy person The health person would become sick, and further spread evil spirits.

The Romans knew how to prevent the spread of evil spirits: isolate the sick and the dead, and even burn the bodies. They even weaponized it, using the bodies of those that died of plague as a biological weapon.

Once we learned that evil spirits don't exist, we threw away this theory of disease. Instead, we believed that plague (much like flies, mold and other such unpleasantness) was spontaneously generated in matter. It wasn't until much Pasteur that we discovered the Romans were 90% correct.

Is it correct to say that the English understanding of scurvy really went backward?

They started with an incorrect theory (acidic fruit stops scurvy) which was later falsified (so does fresh meat). Their progress towards the truth is quite direct, a testament to good record-keeping and communication.

In contrast, the remedies lurch wildly around in effectiveness -- because they weren't properly tested, in isolation from other factors. Nor were they ever retested, even when they changed to the limes. That seems to be where the real failures occurred.

If their record keeping had actually been so good they would have remembered that citrus (by whatever means, and not to the exclusion of other remedies) cures scurvy and would not have wandered off into the weeds chasing spoiled meat (which, if the navies were at sea for years at a time could not possibly have been the case).

I don't see the 'direct progress' you mention, then again maybe my sarcasm detector is miss-calibrated.

No, I didn't mean that sarcastically. Their theories go like this, at least in my reading.

1 - Something about citrus fruits cures scurvy. Correct.

2 - Something about living on a diet of preserved foods causes scurvy. This is even more correct, since now we're getting at the cause.

But I agree we're seeing some interesting cognitive biases here.

Once their original theory is disproved, they focus on explaining the latest results, and seem to forget that they still have to explain why citrus fruit ever seemed to cure scurvy. (Or perhaps the story is more complex than we suppose, and they had some other explanation).

What's certain is that they don't test their ideas with enough experimentation. There seems to be a bias towards formulating theories, and trusting in the expert's judgment, without any empirical verification.

2 is more like "toxins in improperly canned meat cause scurvy".

Did you actually read the article? It isn't so simple.

They transitioned from lemons to limes without realizing that they had gone from a kind of citrus that protected from scurvy to one that didn't. Their interest in meat was due to expeditions which unambiguously demonstrated that lime juice did not protect against scurvy while polar bear meat did. And no simple categorization would have explained to them why you don't want to use copper in preparing food.

The only thing shown unambiguously was that "that juice did not prevent scurvy". Taking this to reason inductively that "no citrus juice prevents scurvy" is the real problem. They discarded documented evidence and grasped at other straws instead of stepping back and investigating history.

The problem is that they had no mental frame of reference from which to understand the importance of avoiding heat, light, and copper. Therefore even if they performed experiments and discovered the truth, they would have no theory to tell them that taking the obvious next step was a bad idea.

Witness for example Scott's ability to demonstrate that seal meat prevented scurvy, and his inability to realize that trying to preserve it by boiling it wouldn't work.

The original theory was that a shortage of some nutrient carried by acidic fruits prevents scurvy. This theory is correct.

It did go backward. The 18th century concept of the disease was as a dietary deficiency, while the 20th century concept was chronic food poisoning.

One point I was trying to stress is that "properly tested, in isolation from other factors" depends a great deal on your mental model of the thing you're testing.

I originally thought you were wrong about this, because a lot of the other articles seemed to suggest they only understood the citrus connection as a cure for some mysterious disease. Which would have made it the wrong theory, but coincidentally the right practice.

But at least according to Wikipedia, there were plenty of people who understood scurvy as a dietary deficiency, even in the 1600s. They thought it was more about acidity, but that's close enough. So, I was wrong and you are right.

http://en.wikipedia.org/wiki/Scurvy

The wikipedia article is kind of iffy, I would recommend this great overview instead:

http://idlewords.com/sailors_scurvy.pdf

Or 'The History of Scurvy and Vitamin C' by Kenneth Carpenter if you want to really dig in.

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