Tripping over Chesterton's Fence
Tradition is definitely smarter than I am
Tradition is Smarter than You
I recently tripped over Chesterton’s Fence while on vacation in Tobago. I also found lots of interesting information about the cassava root, which, as I have discovered, is both deadly and tasty!
A while back, I read the excellent article Tradition is Smarter than You from Scholar’s Stage, which introduced me to the concept of Chesterton’s Fence, the evolutionary biologist Joseph Heinrich (good Dwarkesh podcast episode with him), and the cassava root. I’m going to follow the article fairly closely, so I would be remiss if I didn’t tell you to just go read it, but the basic thesis is as follows:
Humans individually are clever apes
Humans collectively are very clever apes
Human collectives accumulate traditions that are sometimes adaptive
The reasoning/adaptivity of traditions is not always obvious
Beware the temptation to overweight #1 (your own intelligence) and underweight #2 (traditions that have no obvious purpose)
The article illustrated its point with a fable and an extended anecdote. From G.K. Chesterton’s 1929 book, The Thing: Why I Am a Catholic, Chesterton writes:
In the matter of reforming things, as distinct from deforming them, there is one plain and simple principle; a principle which will probably be called a paradox. There exists in such a case a certain institution or law; let us say, for the sake of simplicity, a fence or gate erected across a road. The more modern type of reformer goes gaily up to it and says, "I don't see the use of this; let us clear it away." To which the more intelligent type of reformer will do well to answer: "If you don't see the use of it, I certainly won't let you clear it away. Go away and think. Then, when you can come back and tell me that you do see the use of it, I may allow you to destroy it."
Joseph Heinrich provides an illustration of this principle with an anecdote about the cassava root, also known as manioc or yuca. Let’s take an aside for a moment and learn about cassava.
Cassava Plant Uses and Toxicity
The cassava plant produces large, starchy roots, can grow in bad soil and hot weather, and is extremely drought resistant. It is a staple crop for much of the world, used to make, among other things, tapioca pearls, West African Fufu, and “Provisions” here in Tobago (along with other starchy foods). It has two drawbacks — it goes bad very quickly without proper storage methods, and is very poisonous.
Cassava contains two glycoside toxins, linamarin and its methylated relative lotaustralin, stored in the cell vacuole of the root. Linamarin is the primary toxin, and consists of a glucose molecule bonded to, essentially, acetone + cyanide (a glycoside generally is a sugar bonded to a not-sugar).
When the vacuoles inside the cells are broken (by chewing the plant, for example), the linamarin is hydrolyzed by an enzyme in the cell wall into glucose and acetone cyanohydrin, which quickly breaks down into acetone and cyanide. Cyanide is exceptionally poisonous to basically everything, because it interferes directly with cellular respiration/the electron transport chain. Cellular respiration is the term for the process of converting glucose and oxygen into energy, and is extremely fundamental to cell operation, hence cyanide’s extreme toxicity. Cyanide is also apparently a major component of interstellar gas clouds (in cyanogen form), and is used to measure the temperature of those clouds. That’s a new one to me, and a great fun fact at certain types of parties.
Tradition is Smarter than Cassava Roots
Now the poison can be effectively removed from the cassava, but as Joseph Heinrich explains, this is a time-consuming and seemingly pointless process. I’ll quote him at length here, because it’s a great anecdote. Remember manioc = cassava, and I’ve bolded an importance sentence.
In the Americas, where manioc [(cassava)] was first domesticated, societies who have relied on bitter varieties for thousands of years show no evidence of chronic cyanide poisoning. In the Colombian Amazon, for example, indigenous Tukanoans use a multistep, multiday processing technique that involves scraping, grating, and finally washing the roots in order to separate the fiber, starch, and liquid. Once separated, the liquid is boiled into a beverage, but the fiber and starch must then sit for two more days, when they can then be baked and eaten.
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However, despite their utility, one person would have a difficult time figuring out the detoxification technique. Consider the situation from the point of view of the children and adolescents who are learning the techniques. They would have rarely, if ever, seen anyone get cyanide poisoning, because the techniques work. And even if the processing was ineffective, such that cases of goiter (swollen necks) or neurological problems were common, it would still be hard to recognize the link between these chronic health issues and eating manioc. Most people would have eaten manioc for years with no apparent effects. Low cyanogenic varieties are typically boiled, but boiling alone is insufficient to prevent the chronic conditions for bitter varieties. Boiling does, however, remove or reduce the bitter taste and prevent the acute symptoms (e.g., diarrhea, stomach troubles, and vomiting).
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Now consider what might result if a self-reliant Tukanoan mother decided to drop any seemingly unnecessary steps from the processing of her bitter manioc. She might critically examine the procedure handed down to her from earlier generations and conclude that the goal of the procedure is to remove the bitter taste. She might then experiment with alternative procedures by dropping some of the more labor-intensive or time-consuming steps. She’d find that with a shorter and much less labor-intensive process, she could remove the bitter taste. Adopting this easier protocol, she would have more time for other activities, like caring for her children. Of course, years or decades later her family would begin to develop the symptoms of chronic cyanide poisoning.
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Thus, the unwillingness of this mother to take on faith the practices handed down to her from earlier generations would result in sickness and early death for members of her family. Individual learning does not pay here, and intuitions are misleading. The problem is that the steps in this procedure are causally opaque—an individual cannot readily infer their functions, interrelationships, or importance.
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Perhaps it’s actually rather easy to individually figure out the detoxification steps for manioc? Fortunately, history has provided a test case. At the beginning of the seventeenth century, the Portuguese transported manioc from South America to West Africa for the first time. They did not, however, transport the age-old indigenous processing protocols or the underlying commitment to using those techniques. Because it is easy to plant and provides high yields in infertile or drought-prone areas, manioc spread rapidly across Africa and became a staple food for many populations. The processing techniques, however, were not readily or consistently regenerated. Even after hundreds of years, chronic cyanide poisoning remains a serious health problem in Africa. Detailed studies of local preparation techniques show that high levels of cyanide often remain and that many individuals carry low levels of cyanide in their blood or urine, which haven’t yet manifested in symptoms. In some places, there’s no processing at all, or sometimes the processing actually increases the cyanogenic content. On the positive side, some African groups have in fact culturally evolved effective processing techniques, but these techniques are spreading only slowly.
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The point here is that cultural evolution is often much smarter than we are. Operating over generations as individuals unconsciously attend to and learn from more successful, prestigious, and healthier members of their communities, this evolutionary process generates cultural adaptations. Though these complex repertoires appear well designed to meet local challenges, they are not primarily the products of individuals applying causal models, rational thinking, or cost-benefit analyses. Often, most or all of the people skilled in deploying such adaptive practices do not understand how or why they work, or even that they “do” anything at all. Such complex adaptations can emerge precisely because natural selection has favored individuals who often place their faith in cultural inheritance—in the accumulated wisdom implicit in the practices and beliefs derived from their forbearers—over their own intuitions and personal experiences.1
Tradition is Smarter than My Family?
Now Heinrich is burying the lede here a little. Taste is actually a pretty reliable indicator of glycoside content in the raw plant.2 Karlton et al. in the linked study showed that among Malawian farmers with a history of cassava cultivation, their ability to predict cyanogenic content correlated strongly with their classification into “cool” (sweet) and “bitter,” and that tasting the tip of the root improved the toxicity prediction. The farmers achieved an r^2 of 0.67 when graphing subjective bitterness on a five-point scale vs. measured cyanogen content, a strong, but not perfect correlation. HOWEVER, cyanide is not a glycoside but a derivative, and it is the glycosides themselves, linamarin, etc. that are actually bitter, not the poisonous cyanide. So taste cannot be a perfect indicator.
All of this brings me to my vacation to Tobago, my wife’s home island, and hanging out (or “ limin’ ” in the local slang) with her family. Well, they served me a lot of cassava, which was very tasty.
While I was eating the cassava (which I noted was not in the form of a mash, grate, or any other product of extensive processing), I asked them about the cassava preparation. Do you have to extensively process the cassava root you eat? Is it poisonous if you don’t, and thus poisonous… right now?
Nope! they said. That’s mostly a myth, all you have to do is peel the cassava, wash it and boil it, and it’s completely fine! Don’t worry about it.
Well, that was a bit concerning. That’s not what the Scholar’s Stage article said at all! In fact, the article warned against more-or-less exactly this failure mode when preparing cassava! A Trinibagonian article I found called Boil Your Cassava Well actually falls exactly into the failure mode described by Heinrich, they:
Reference having two types of cassava,
Mention the need for careful processing of the bitter type, and
Get the processing wrong, suggesting that all you must do is thoroughly boil it!
“It is essential to clean and boil cassava thoroughly before consuming to remove all traces of cyanide.”
According to my reading of the Joseph Heinrich passage, this is absolutely not the case, the intense multiday processes are necessary to reduce the cyanide level below the chronic toxicity level, not just the acute level where the bitter taste is probably a decent indicator.
Have we removed a critical Chesterton Fence? Is my family going to get chronic cyanide poisoning? To my slight embarrassment, I did look around for any signs of goiters (a swollen thyroid gland, a classic symptom of chronic cyanide poisoning) at the dinner table. I found none.
Tradition is Smarter than Me
As it turns out tradition is still smarter than me. Despite having just tried to defer to a very respectable tradition, I deferred to the wrong one.
According to the Trinidad and Tobago Ministry of Agriculture, Land & Fisheries,3 all cassava varietals grown in T&T (for the fresh market) are of the sweet variety. They are in fact completely safe to consume by just peeling and boiling.
Note that my family told me that the necessity of extensive processing was mostly a myth. This is not true in general, but it is true on Tobago, where only sweet varieties are grown for market. Tradition, even in the absence of a correct explanation, is nevertheless correct.4
It turns out that most of the cyanogens in cassava are contained in the skin. For the bitter varieties, enough of the cyanogens penetrate into the flesh of the tuber that simple peeling and boiling isn’t adequate, hence the intensive grating/mashing to expose all of the cyanide derivatives to water. Cyanide, being water soluble, can then be extracted by soaking. But for the lower-cyanogen-concentration sweet varieties, peeling really does remove most of the cyanogens, and for Tobagonian cuisine, that’s all you need!
This brings me to my second question I asked my family — do you have to discard the water? Cyanide is water soluble, and, logically speaking, if boiling in water solubilizes and thus removes the cyanide from the cassava, it must necessarily then poison the water…
Also no. Apparently in Tobago it’s used to make punch creamier. I went back and reread the Joseph Heinrich passage after learning this, and guess what? The indigenous societies studied by Heinrich do this too. I guess the hot water boils off all the cyanide gas? My intuition has served me very poorly indeed.
Tradition is Hard to Defer To
In my ever-expanding quest to avoid writing like an LLM, I will not end this essay with a profound moral lesson or a tight, just-so story. I confess I would love to, but the lovely Tobago beaches have turned my brain into boiled cassava, and I honestly have no idea what conclusions to draw from this, other than that deferring to tradition is a tricky and granular process.
Perhaps the most relevant question, however, is how do you know when to defer to tradition? How do you avoid tearing down the “good” Chesterton Fences, while removing the “bad” ones?
My guess is that most of the time, when tearing down a Fence, the first-order, obvious, immediate consequences dominate. But not always! Opaque chains of causality are the bane of accurate theory.
I had a few unstructured thoughts that I’ll write down for possible future investigation, related to the question “When are Chesterton Fences likely?”
Context change — Traditions are highly local, and imported traditions from a different context are less likely to be authentically adaptive. This is pretty much my error in this cassava saga.
Interaction effects — Chesterton’s Fences are often causally opaque because they rely on second-order consequences of actions. Complex ecologies and biological systems in general are strongly subject to interaction effects, where changing one part of the system in isolation is impossible.
Long time horizons — Your ability to predict consequences of your actions decays rapidly (exponentially? factorially?) as time goes to infinity, and your first-order, local, linear intuitions or calculations may not serve you very well. I associate this failure mode with the “longtermism” school of effective altruism. I’m not just taking potshots at EA for fun, I actually like them quite a bit, but they exemplify this failure mode better than any others I can think of.
Since Substack added Latex, and this is my blog, I feel obligated to formalize statement 3. by deriving a Fence Ratio F. Be warned, this is not especially useful.
Let the jth consequence of your actions be c_j(t) over time t, let the validity horizon of your modeling have time constant τ, then c is described by a series expansion where each coefficient a_i represents your intuition or model about the “direction” of the consequence, and let us specialize to a single axis of consequence by dropping the j index:
\(c(t) = \sum_i a_i \left(\frac{t}{\tau}\right)^i = a_0 + a_1 \frac{t}{\tau} + a_2 \left(\frac{t}{\tau}\right)^2 + ...\)Your error in predicting the consequences of your actions \Delta c is given by standard error propagation of your modeling errors \Delta a_i:
\((\Delta c)^2 \approx \sum_{i=0}^{n} \left( \frac{\partial c}{\partial a_i} \Delta a_i \right)^2 \\ \)Thus, your Fence Ratio F is given by \Delta c / c:
\(F = \frac{\Delta c}{|c|} \approx \frac{\sqrt{\sum_i (\Delta a_i)^2 \left(\frac{t}{\tau}\right)^{2i}}}{\left|\sum_i a_i \left(\frac{t}{\tau}\right)^i\right|}\)When the Fence Ratio exceeds 1, your prediction error exceeds your prediction, and that’s when we should be wary of Chesterton’s Fence. I think that’s sufficient Moral Profundity for a conclusion, though it’s not a very good formalization. Future work, perhaps.
No post about tradition is complete without Tradition (from Fiddler on the Roof).
Joseph Henrich, The Secret of Our Success: How Culture Is Driving Human Evolution, Domesticating Our Species, and Making Us Smarter (Princeton: Princeton University Press, 2016)
Linley Chiwona Karlton et al., Bitter taste in cassava correlates with cyanogenic glucoside levels (2004)
Trinidad and Tobago Ministry of Agriculture, Land and Fisheries, Cassava Production (2016)
It’s also entirely possible they were just oversimplifying the full explanation for me, but I didn't get that impression.