I. 

Maciej Cegłowski’s essay Scott And Scurvy is one of the most interesting things we’ve ever read. We keep coming back to it — and we hope to write more about it in the future — but today we want to start with just how weird the whole thing is.

Scott and Scurvy tells the true history of scurvy, a horrible and dangerous disease. Scurvy is the result of a vitamin C deficiency — if you’re a sailor or something, eating preserved food for months on end, you eventually run out of vitamin C and many horrible things start happening to your body. If this continues long enough, you die. But at any point, consuming even a small amount of vitamin C, present in most fresh foods, will cure you almost immediately. 

We can’t do the full story justice (read the original essay, seriously), but just briefly: The cure was repeatedly discovered and lost by different crews of sailors at different points in time. Then in 1747, James Lind tried a bunch of treatments and found that citrus was more or less a miracle cure for the disease. Even so, it took until 1799, more than 50 years, for citrus juice to become a staple in the Royal Navy. 

Originally, the Royal Navy was given lemon juice, which works well because it contains a lot of vitamin C. But at some point between 1799 and 1870, someone switched out lemons for limes, which contain a lot less vitamin C. Worse, the lime juice was pumped through copper tubing as part of its processing, which destroyed the little vitamin C that it had to begin with. 

This ended up being fine, because ships were so much faster at this point that no one had time to develop scurvy. So everything was all right until 1875, when a British arctic expedition set out on an attempt to reach the North Pole. They had plenty of lime juice and thought they were prepared — but they all got scurvy. 

The same thing happened a few more times on other polar voyages, and this was enough to convince everyone that citrus juice doesn’t cure scurvy. The bacterial theory of disease was the hot new thing at the time, so from the 1870s on, people played around with a theory that a bacteria-produced substance called “ptomaine” in preserved meat was the cause of scurvy instead. 

This theory was wrong, so it didn’t work very well. Everyone kept getting scurvy on polar expeditions. This lasted decades, and could have lasted longer, except that two Norwegians happened to stumble on the answer entirely by accident: 

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) in pigeons, and when they decided to switch to a mammal model, they serendipitously chose guinea pigs, the one animal besides human beings and monkeys that requires vitamin C in its diet. Fed a diet of pure grain, the animals showed no signs of beriberi, but quickly sickened and died of something that closely resembled human scurvy.

No one had seen scurvy in animals before. With a simple animal model for the disease in hand, it became a matter of running the correct experiments, and it was quickly established that scurvy was a deficiency disease after all. Very quickly the compound that prevents the disease was identified as a small molecule present in cabbage, lemon juice, and many other foods, and in 1932 Szent-Györgyi definitively isolated ascorbic acid.

Even in retrospect, the story is pretty complicated. But we worry that it would have looked even messier from the inside.

II.

Holst and Frolich also ran a version of the study with dogs. But the dogs were fine. They never developed scurvy, because unlike humans and guinea pigs, they don’t need vitamin C in their diet. Almost any other animal would also have been fine — guinea pigs and a few species of primates just happen to be really weird about vitamin C. So what would this have looked like if Holst and Frolich just never got around to replicating their dog research on guinea pigs? What if the guinea pigs had gotten lost in the mail?

Let’s imagine a version of history where the guinea pigs did indeed get lost in the Norwegian mail, so Holst and Frolich only tested dogs, and found no sign of scurvy. Let’s further imagine that Frolich has been struck by inspiration, and through pure intuition has figured out exactly what is going on. 

—

Frolich: You know Holst, I think old James Lind was right. I think scurvy really is a disease of deficiency, that there’s something in citrus fruits and cabbages that the human body needs, and that you can’t go too long without. 

Holst: Frolich, what are you talking about? That doesn’t make any sense.

Frolich: No, I think it makes very good sense. People who have scurvy and eat citrus, or potatoes, or many other foods, are always cured.

Holst: Look, we know that can’t be right. George Nares had plenty of lime juice when he led his expedition to the North Pole, but they all got scurvy in a couple weeks. The same thing happened in the Expedition to Franz-Josef Land in 1894. They had high-quality lime juice, everyone took their doses, but everyone got scurvy. It can’t be citrus.

Frolich: Maybe some citrus fruits contain the antiscorbutic [scurvy-curing] property and others don’t. Maybe the British Royal Navy used one kind of lime back when Lind did his research but gave a different kind of lime to Nares and the others on their Arctic expeditions. Or maybe they did something to the lime juice that removed the antiscorbutic property. Maybe they boiled it, or ran it through copper piping or something, and that ruined it.

Holst: Two different kinds of limes? Frolich, you gotta get a hold of yourself. Besides, the polar explorers found that fresh meat also cures scurvy. They would kill a polar bear or some seals, have the meat for dinner, and then they would be fine. You expect me to believe that this antiscorbutic property is found in both polar bear meat AND some kinds of citrus fruits, but not in other kinds of citrus?

Frolich: You have to agree that it’s possible. Why can’t the property be in some foods and not others? 

Holst: It’s possible, but it seems really unlikely. Different varieties of limes are way more similar to one another than they are to polar bear meat. I guess what you describe fits the evidence, but it really sounds like you made it up just to save your favorite theory. 

Frolich: Look, it’s still consistent with what we know. It would also explain why Lind says that citrus cures scurvy, even though it clearly didn’t cure scurvy in the polar expeditions. All you need is different kinds of citrus, or something in the preparation that ruined it — or both! 

Holst: What about our research? We fed those dogs nothing but grain for weeks. They didn’t like it, but they didn’t get scurvy. We know that grain isn’t enough to keep sailors from getting scurvy, so if scurvy is about not getting enough of something in your diet, those dogs should have gotten scurvy too.

Frolich: Maybe only a few kinds of animals need the antiscorbutic property in their food. Maybe humans need it, but dogs don’t. I bet if those guinea pigs hadn’t gotten lost in the mail, and we had run our study on guinea pigs instead of dogs, the guinea pigs would have developed scurvy.

Holst: Let me get this straight, you think there’s this magical ingredient, totally essential to human life, but other animals don’t need it at all? That we would have seen something entirely different if we had used guinea pigs or rats or squirrels or bats or beavers?

Frolich: Yeah basically. I bet most animals don’t need this “ingredient”, but humans do, and maybe a few others. So we won’t see scurvy in our studies unless we happen to choose the right animal, and we just picked the wrong animal when we decided to study dogs. If we had gotten those guinea pigs, things would have turned out different.

III.

Frolich is entirely right on every point. He also sounds totally insane. 

Maybe there are different kinds of citrus. Maybe some animals need this mystery ingredient and others don’t. Maybe polar bear meat is, medically speaking, more like citrus fruit from Sicily than like citrus fruit from the West Indies. Really???

This looks a lot like special pleading, but in this case, the apparent double standard is correct. All of these weird exceptions he suggests were actually weird exceptions. And while our hypothetical version of Frolich wouldn’t have any way of knowing, these were the right distinctions to make. 

Reality is very weird, and you need to be prepared for that. Like the hypothetical Holst, most of us would be tempted to discard this argument entirely out of hand. But this weird argument is correct, because reality is itself very weird. Looking at this “contradictory” evidence and responding with these weird bespoke splitting arguments turns out to be the right move, at least in this case. 

Real explanations will sometimes sound weird, crazy, or too complicated because reality itself is often weird, crazy, or too complicated. 

It’s unfortunate, but scurvy is really the BEST CASE SCENARIO. The answer ended up being almost comically simple: it’s just a disease of deficiency, eat one of these foods containing this vitamin and be instantly cured. But the path to get to that answer was confusing and complicated. Think about all the things in the world that have a more complicated answer than scurvy, i.e. almost everything. Those things will have even weirder and more confusing stories to untangle.

This story has a couple of lessons for us. The first is just, don’t discard an explanation just because it’s weird or complicated. 

Focus on explanations that are consistent with all the evidence. Frolich’s harebrained different-citrus different-animals explanation from above does sound crazy, but at least it’s consistent with everything they knew at the time. If some kinds of citrus cured scurvy and other kinds didn’t, that would explain why it worked for Lind and for early sailors, but it didn’t work for the polar explorers after 1870. And in fact, that does explain it.  

It’s also testable, at least in principle. If you think there might be differences between different kinds of citrus fruits, you could go back and try to figure out the original source used by James Lind and the Royal Navy, and try to re-create those conditions as closely as possible.

We’re taught to see splitting  — coming up with weird special cases or new distinctions between categories — as a tactic that people use to save their pet theories from contradictory evidence. You can salvage any theory just by saying that it only works sometimes and not others — it only happens at night, you need to use a special kind of wire, the vitamin D supplements from one supplier aren’t the same as from a different supplier, etc. Splitting has gotten a reputation as the sort of thing scientific cheats do to draw out the con as long as possible.

But as we see from the history of scurvy, sometimes splitting is the right answer! In fact, there were meaningful differences in different kinds of citrus, and meaningful differences in different animals. Making a splitting argument to save a theory — “maybe our supplier switched to a different kind of citrus, we should check that out” — is a reasonable thing to do, especially if the theory was relatively successful up to that point. 

Splitting is perfectly fair game, at least to an extent — doing it a few times is just prudent, though if you have gone down a dozen rabbitholes with no luck, then maybe it is time to start digging elsewhere.

Scurvy isn’t the only case where splitting was the right call. Maybe there’s more than one kind of fat. Maybe there are different kinds of air. Maybe there are different types of blood. It turns out, there are! So give splitting a chance.

Be more forgiving of contradictory evidence. These days people like to put a lot of focus on the idea of decisive experiments. While it’s true that some experiments are more decisive than others, no experiment can be entirely decisive either for or against a theory. We need to stop expecting knock-down studies that solve things forever.

Contradictory evidence can be wrong! The person making the observations might have been confused. They might have done the analysis wrong. The equipment may have malfunctioned. They might have used dogs instead of guinea pigs, or they might have used the wrong kind of hamster. The data might even be fabricated! Shit happens. 

Things change as contradictory evidence piles up, but even then, it doesn’t mean you should scrap the theory you started out with. Everyone back in the 1870s made a big mistake throwing out their perfectly good “disease of deficiency” theory as soon as there were a few contradictory stories from polar explorers.

Their mistake was thinking “maybe the theory is wrong”, instead of “maybe the real theory is more complicated”. When you see evidence that goes against a theory, it could mean that you’ve been barking up the wrong tree. Or it could just mean that there’s a small wrinkle you aren’t aware of.

If you have a theory that’s been working pretty well for a while — it made good predictions, it solved real problems, it explained a lot of mysteries — you should stick with it in the face of apparent contradictions, at least for a while. When you hit a snag with a reliable theory, think “maybe it’s complicated” instead of “oh it’s wrong”. It may still be wrong, but it’s good to check!

Be careful of purely verbal, syllogistic reasoning. We make these arguments in conversation all the time. They seem plain, convincing, and commonsensical, but in reality they’re pretty weak. It’s hard to get away from commonsensical, verbal arguments since that’s how we naturally think, but don’t take them too seriously. They’re ok as starting points, but keep in mind that they’re not actually evidence.

“Different kinds of citrus fruits are more like one another than they are like polar bear meat” sounds very reasonable, but in this case it was wrong. Sicilian lemons really ARE more like polar bear meat than they are like West Indian limes, at least for the purposes of treating scurvy.

“Dogs are about as similar to humans as guinea pigs are” also sounds very reasonable. The three species are all the same class (Mammalia) but different orders (Carnivora, Primates, and Rodentia, respectively), so there seems to be some taxonomic evidence as well. But humans really are a lot more like guinea pigs than they are like dogs, or most other animals, at least for the purposes of getting scurvy.

IV.

We were tickled to see this paragraph near the end of Scott and Scurvy, for obvious reasons: 

…one of the simplest of diseases managed to utterly confound us for so long, at the cost of millions of lives, even after we had stumbled across an unequivocal cure. It makes you wonder how many incurable ailments of the modern world—depression, autism, hypertension, obesity—will turn out to have equally simple solutions, once we are able to see them in the correct light. What will we be slapping our foreheads about sixty years from now, wondering how we missed something so obvious?

This is really good, and we think it’s reason to be optimistic. We might be closer than we think to cures for depression, hypertension, and yes, even obesity. 

The answer to scurvy was just one thing, plus a few wrinkles — mostly “not all citrus has the antiscorbutic property” and “most animals can’t get scurvy”. This was only difficult because people weren’t prepared to deal with basic wrinkles, but we can do better by learning from their mistakes.

This means don’t give up easily. It suggests that there is lots of low-hanging fruit, because even simple explanations are easily missed.

Lots of theories have been tried, and lots of them have been given up because of something that looks like contradictory evidence. But the evidence might not actually be a contradiction — the real explanation might just be slightly more complicated than people realized. Go back and revisit scientific near-misses, maybe there’s a wrinkle they didn’t know how to iron out.