1. Manioc poisoning in Africa vs. indigenous Amazonian cultures: a biological explanation?

Note that while Josef Henrich, the author of TSOOS, correctly points out that cassava poisoning remains a serious public health concern in Africa, he doesn't supply any evidence that it wasn't also a public health issue in Amazonia. One author notes that "none of the disorders which have been associated with high cassava diets in Africa have been found in Tukanoans or other indigenous groups on cassava-based diets in Amazonia."

Is this because Tukanoans have superior processing methods, or is it perhaps because Tukanoan metabolism has co-evolved through conventional natural selection to eliminate cyanide from the body? I don't know, but it doesn't seem impossible.

2. It's not that hard to tell that manioc causes health issues.

Last year, the CDC published a report about an outbreak of cassava (manioc) poisoning including symptoms of "dizziness, vomiting, tachypnea, syncope, and tachycardia." These symptoms began to develop 4-6 hours after the meal. They reference another such outbreak from 2017. It certainly doesn't take "20 years," as Scott claims, to notice the effects.

There's a difference between sweet and bitter cassava. Peeling and thorough cooking is enough for sweet cassava, while extensive treatments are needed for bitter cassava. The latter gives better protection against insects, animals, and thieves, so farmers sometimes like it better.

Another analysis says that "A short soak (4 h) has no effect, but if prolonged (18 to 24 h), the amounts of cyanide can be halved or even reduced by more than six times when soaked for several days." Even if the level is cut by 1/6, is this merely slowing, or actually preventing the damage?

Wikipedia says that "Spaniards in their early occupation of Caribbean islands did not want to eat cassava or maize, which they considered insubstantial, dangerous, and not nutritious."

If you didn't know the difference between sweet and bitter cassava, it sounds like you'd discover your error the first time you happened to make flour from bitter cassava root in dramatic fashion. You could distinguish them by seeing their effect on insects and animals.

Moreover, sweet cassava is the product of thousands of years of selective breeding, though "bitter cultivars appear to have been more important than sweet." How could indigenous Amazonian cultures have run a selective breeding program for thousands of years, unless they knew what qualities they were breeding for?

3. Cultural selection might still be relevant, but maybe not for manioc/cassava

It's far from obvious to me that Amazonian manioc processing is best described as a result of blind cultural evolution. It seems far more likely that it's the result of careful observation, cause-and-effect reasoning, and traditions that pass down conscious knowledge from generation to generation.

In addition to Benquo's objections, I'd add that the persistence of African cassava poisoning may be due partly to the (purely conjectural) idea that Amazonian indigenous people may have developed a more cyanide-resistant metabolism over the course of their ancient relationship with the plant.

Cultural evolution might still be relevant to explain why Tukanoan and other indigenous cultures seem to have a "healthier relationship" with the plant. They've had thousands of years to develop cultural forms that work to consistently process manioc root, and to avoid famine situations in their local environment that might cause them to trade convenience for safety.

Anthropologists of modern cultures look at blue zones to see what people are eating and how they're living in the places where life expectancy is longest. This is a correlational waggling of the eyebrows. A culture that's found a way to consistently eat a healthy diet might be an object for our admiration, as opposed to a culture that is consistently trading food safety for convenience. It’s a “nice place to live.”

Ancient cultures have found complex systems that work for their local context through millennia of tinkering that you could never invent through rational thought. These systems are not just complicated. Each new development depends on pre-existing social dynamics. But we don’t therefore need to appeal to a blind force of cultural selection to explain how they develop.

Bring in an external shock, such as modernity, or bring a single practice to a culture in a different environment, and you risk changing the context in which that culture is a good adaptation for its members' wellbeing. It can’t adjust instantly to make itself a “nice place to live” again.

I've only read Scott's book review of TSOOS. It's possible that Scott, or Benquo, is missing the point, and that Henrich was just trying to illustrate this aspect of cultural evolution.

4. Quick takes on other examples

Arrow making: Why do we need to posit a blind force of cultural evolution to explain complex procedures for Fuegan arrow-making? They could have just made arrows in an obvious, easy way, then experimented with refinements slowly over time, keeping what worked and throwing out the rest. The end result is an arrow that works better than anything even a brilliant tinkerer could come up with on their own.

Fire making: It seems totally implausible to me that fire-making was discovered "maybe once." Lightning strikes would have been a source of fire around the world, just for starters. There was always an opportunity to get more fire, even if it was lost. Perhaps the reason aboriginal Tasmanians "lost the ability to make fire" is because they simply didn't want it anymore, for reasons that are peculiar to their culture.

Even if we take it as fact that fire-making was discovered a few times, or even once, this isn't clear evidence that fire-making is particularly hard to discover. It just means that it may have been so important to most cultures (except the Tasmanians), that they took pains to ensure that methods for fire-making were passed down generation to generation. If they failed, they either died out, or were taught by somebody else. Fire-making wasn't invented so few times because it's hard, but because it was unnecessary.

5. Overall thoughts on cultural evolution

It seems obviously true to me that cultural transmission of knowledge is the secret of our success. it's just that this isn't a mysterious process by which some indigenous cultures blindly stumbled their way into particular technologies, such as fire-making, arrow-making, or manioc processing. Indigenous cultures observe, experiment, and transmit acquired knowledge from generation to generation. Outsiders cannot re-invent that total body of knowledge and accumulated physical technology at the drop of a hat.

So we don't need "evolution" to explain the accumulation and transmission of this body of knowledge, or the difficulty of replicating it. Indigenous technology didn't develop through blind stumbling akin to genetic mutation.

It develops through deliberate tinkering and conscious observation of cause and effect. To participate in it depends on having enough accumulated knowledge, cooperation across a whole culture, and having enough physical artifacts to carry out the processes you've invented, and teaching these things to extremely plastic children's brains.

What's interesting here is that indigenous people do eventually sometimes seem to lose the ability to explain the technologies of their culture. Scott gives the example of Fijian women who are prohibited from eating sharks. Sharks happen to contain birth-defect-causing chemicals. But the women don't seem to have conscious awareness of that fact.

Is this because they don't understand why they don't eat shark, or are they just engaging in the time-honored tradition of messing with anthropologists just for the fun of it? What if some of the materially incorrect explanations are just stories that "overlay" the actual material understanding that shark meat isn't good for you?

Fijian girls telling anthropologists that eating shark meat makes children be born with shark skin reminds me of parents telling children that they shouldn't make funny faces because they'll get stuck that way. Parents know that the real reason is that it's socially obnoxious, and Fijian women might know that the real reason for not eating shark meat while pregnant is that it's not good for the baby.

These objections aside, it does seem possible that an oral tradition might be enough to transmit a huge number of useful technologies and processes, but not high-bandwidth enough to transmit all the reasons for them. Fuegans understand that they should generally stick with traditional arrow-making practices those practices represent an enormous amount of ancestral tinkering, but perhaps haven't passed down an oral history of the 17 different types of wood their greatX20-grandfather tried before hitting on the best choice.

If those causal stories are lost, it seems implausible that cultural transmission is so reliable that indigenous people never, ever tinker with tradition. Even if they develop the optimal method of making arrows, perhaps they occasionally experiment with other methods, observe that they do indeed work worse, and go back to the old ways. Maybe sometimes it works better, and they keep the modification.

But that's not how evolution works. Mutations accumulate by mechanisms that are actually blind and random, and the optimal methods are found by actually killing off the least-successful and rewarding the most successful with better reproductive success.

Cultures develop by tinkering, seeing what works, and keeping it. It's the rational minds of a culture's people, not random mutations and natural selection, that optimize the culture itself.

It does seem to me that a certain amount of cultural stability and smallness is helpful to optimize a culture. You have to see what effect a certain change has on your relationships, your material outcomes, or your society as a whole. In a modern context where our individual relationships are changing more often as we move, change jobs, and explore our self-actualization more frequently, perhaps the instability makes it more difficult to understand the role that any one thing plays?

But then again, maybe we'll just continue finding cultural and technological solutions for that faster rate of change. Maybe people will recognize the optimal rate of change for themselves personally, and seek to align their life choices with it. They won't move too often unless they can clearly recognize the benefits in moving. They won't change their religion or their job too often unless they have a good causal story as to why it will help them.

6. What does this mean for "rationalism?"

Well, score one for Elizabeth's epistemic spot checks.

To be autocontrarian, I wonder if our subculture's embrace of a misleading interpretation of TSOOS is in fact an example of the phenomenon itself. Through blind "rational" thought and failures to reason correctly, we arrive at a story that's superficially compelling yet wrong. Because there's so little bandwidth to pin down the exact theoretical claims and subject them to rigorous empirical study, and because Henrich has a sort of authorial "ownership" over the concept, there's a possibility that, like Intelligent Design and Marxism, it's somewhat unfalsifiable. There are interested parties in finding new equivocations to salvage the argument.

Unlike arrow-making, manioc processing, hunting practices, and fire-making, macro explanations for culture don't make limited, material claims that lend themselves to easy falsification. So they hang around. It's hard to say the effect they have on individual people or on societies. I'm not confident that Marxist ideology was a necessary condition for the 20th century deaths in countries that identified themselves as Stalinist/Maoist.

We don't want to create a rationalist culture that's unfriendly to new ideas. But we do want one that recognizes how extremely limited our bandwidth is for testing them.

My sense is that one original rationalist impulse was to borrow well-established ideas in scientific, mathematical, and humanities literature and create a lifestyle based on them. It's low-hanging fruit. Examples include Bayesian statistics, the efficient market hypothesis, understanding how an exponential graph works, and political liberalism.

The replication crisis showed us the danger of using new scientific ideas as we go about it. The "cultural evolution" hypothesis is even more poorly vetted.

It seems like it would be good to adopt a sort of "developmental approach" to ideas.

If an idea is brand new and from outside the academic literature, treat it with kid gloves. It may not be in its most compelling form. But don't adopt it as a lifestyle. Play with it and put it down.
If an idea is a new and trendy idea that has been published in scientific literature, treat it with deep skepticism, but not toxic rejection out of hand.
Old ideas with a strong body of scientific literature behind them are the prime examples of concepts we should try to understand and adopt.