How Social Norms Are Like Chili Peppers

Peter Turchin


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I grew up in Russia and for the first 20 years of my life I never tasted a chili pepper. I still remember my first encounter with this potent condiment in a Thai restaurant after moving to the United States: biting into an innocuous looking bit, burning sensation followed by intense pain in the mouth, copious tears flowing out of my eyes. Thai restaurants in Seattle, WA, when I did my postdoc there, had a numerical system allowing one to specify how hot you wanted your meal to be. I never graduated beyond 2 (or 3, if I felt particularly masochistic). It was incomprehensible to me that the Thai not only endured but actually enjoyed food with spiciness dialed up to its maximum level.

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I am happy to report that recently this great mystery has been solved to my satisfaction. Now I understand not only why this cultural practice evolved, but also why individual Thai people genuinely enjoy super-hot dishes. The source of this understanding was a truly excellent book by Joseph Henrich on Cultural Evolution (The Secret of Our Success: How Culture Is Driving Human Evolution, Domesticating Our Species, and Making Us Smarter; Princeton, 2016).

Cultural Evolution is a new interdisciplinary field whose intellectual roots go back only to the 1970s (unless, of course, you count Charles Darwin; but in a sense any new development in evolutionary science can be traced to Darwin). In this new field, “culture” is defined as information, which can affect human behavior, that is socially transmitted—through books and manuals, by teaching, or simply by observing and imitation. Cultural variants are information packages that cause people to behave in alternative ways. Cultural Evolution, then, studies how and why frequencies of cultural variants change with time, just as biological evolution focuses on the changing frequencies of genetic variants.

It was during the 1970s when evolutionary scientists started to ask whether the quantitative tools developed for the Modern Evolutionary Synthesis, which had become broadly accepted by that point, could also be useful for studying the evolution of human societies. These pioneers were largely working independently of one another.

Following the publication of Sociobiology: The New Synthesis (1975) and On Human Nature (1979) E. O. Wilson teamed up with Charles Lumsden to publish Genes, Mind and Culture: The Coevolutionary Process (1981). That book became one of the three foundational texts of Cultural Evolution. The second foundational work was written by the geneticist Luca Cavalli-Sforza and the theoretical biologist Marcus Feldman, Cultural Transmission and Evolution: A Quantitative Approach, also published in 1981. The third, and ultimately the most influential book, Culture and the Evolutionary Process (1985), was published by the anthropologist Robert Boyd and the ecologist Peter Richerson. This book summarized their papers, written in the 1970s, that developed a mathematical theory of what they called “dual inheritance,” a coevolutionary process between genes and culture.

As Joe Henrich relates in the Preface of The Secret of Our Success, his encounter with Cultural Evolution began after he started graduate school at the University of California at Los Angeles in 1993. While still a graduate student Joe became a leader in using experimental approaches to investigating cultural variation in how people cooperate (see the edited volume Foundations of Human Sociality: Economic Experiments and Ethnographic Evidence from Fifteen Small-Scale Societies; Oxford, 2004).

The Secret of Our Success is an account of the first twenty years of Joe’s encounter with Cultural Evolution. It’s engagingly written, is illustrated with fun examples, includes autobiographical reminiscences, and (important!) there is not a single equation in it. In this respect it’s part of a new trend in publishing, reflecting the invasion by formerly staid academic presses into the turf traditionally occupied by for-profit publishers of popular nonfiction (“trade books”).

However, the Secret of Our Success is much more than a popular book. It addresses the most fundamental questions about our societies. Why are humans so smart and cooperative, compared to other animals? How do we solve ubiquitous “cooperation dilemmas”?

~~~ *** ~~~

Let’s go back to the burning question (pun intended) of the chili peppers (I will also eventually get to social norms, I promise). Why do Thai love hot, spicy food and Russians don’t? It turns out that certain chemical compounds in spices, such as capsaicin in chili peppers, are potent antimicrobials. In hot climates food, and meat especially, spoils rapidly. Spices kill pathogens, and people in the tropics who eat highly spiced foods enjoy better health. So far, this looks like a classic case of natural selection. However, of all animal species only humans use spices to control pathogens. Other animals evolve biological adaptations to safely consume dangerous, toxic foods.

Humans, on the contrary, “devolved” in this respect. Over the last five million years, since our lineage diverged from other hominid primates, our digestive apparatus (mouth, teeth, stomach, intestines) became much smaller. We also largely lost our ability to detoxify wild foods. If you try to eat like a chimpanzee (something that the anthropologist Richard Wrangham actually attempted) you will starve to death, unless you get poisoned first.

What happened? “Culture stole our guts,” says Joe. Evolution sacrificed digestive apparatus so that our bodies could grow huge oversized brains, which made possible human cultural evolution. And sacrificing digestive and detoxification functions was possible, because in parallel with the evolution of large brains and devolution of guts, humans acquired a remarkable assortment of techniques for processing foods. The most important, of course, is treating food with heat—roasting, baking, boiling, stewing, frying in oil, sautéing, etc. But cooking in a more general sense also includes chopping, slicing, pounding, grinding, leaching, marinading, smoking, salting, drying—and seasoning. Processing food in this fashion “externalizes” digestion. It makes food much more digestible and, very important, removes dangerous toxins or pathogens.

Unlike detoxification adaptations in other animals, cooking techniques are traits that are transmitted not genetically, but culturally. Thus, the evolution of food processing becomes a subject for Cultural Evolution (recall the definition I gave at the beginning of this article). When a cooking technique spreads through a population, this is cultural evolution. In fact, the initial adoption of chili peppers in Thailand is also an example of cultural evolution, because these cultivars were brought to Southeast Asia by Europeans from the Americas during the Age of Discovery.

We now understand why people in hotter climates use more spices, and why people in cold climates tend to eat bland food.[1] Thus, one cultural variant (seasoning food with copious amounts of capsaicin) spread under a particular set of environmental conditions (hot climate), because there it conferred better health and survival for cultural groups practicing it. But it did not spread in another environment, where it does not result in better health. All pain, no gain.

But why do inhabitants of hot climates enjoy highly spiced food? After all, capsaicin literally causes pain (it activates a pain channel). Capsaicin is the active ingredient in Mace (the pepper spray)!


It turns out that as children grow up in cultures that value highly spiced foods, such as Mexico, they learn to reinterpret pain signals as pleasure. Their brains are “rewired.”

Now, perhaps chili-lover brains are rewired in a metaphorical, rather than literal sense. But there is another example, discussed in the book, in which cultural transmission literally rewires the brain. This is the case of London cab-drivers, who have to acquire the Knowledge, a memorized map of London’s central part, including some 25,000 streets and thousands of landmarks. Not everybody is capable of this feat, but in those taxi drivers who manage it, a part of the brain, known as hippocampus, becomes enlarged by adding a substantial amount of gray matter—the biological wiring of our brains.

Let’s step back for a moment. The expansion of human brain size during the last two millions of years and the expansion of hippocampus in London cab drivers are, of course, very different processes. One is a slow evolutionary change of a particular group of organisms, the other is a fast developmental response in one particular organism (well, not so fast—it takes four years to acquire the Knowledge). But there is also a shared feature. Both examples show that culture and biology (genetics, neurophysiology) are, really, not separate. This continuum between culture and biology is one of the most important threads in Henrich’s book. Far from being separate, culture and biology are actually parts of one interacting system, with feedbacks going both ways. This is why gene-culture coevolution is a central idea in Cultural Evolution. For convenience, a particular study might focus on culture or biology, but if we want to understand human behavior we need to synthesize the two.

~~~ *** ~~~

What about social norms, and why are they like chili peppers? “Norms” are socially transmitted rules of behavior. Like cooking techniques, they are elements of culture (again, using the special definition I gave at the beginning). Cooking with chili peppers and enjoying highly spicy foods is also socially transmitted, so both social norms and food processing techniques are cultural traits. But the similarity between social norms and spicy foods goes deeper than that.

Let’s talk specifically about “prosocial” norms that induce people to behave in more cooperative ways. Social cooperation is the all-important glue that enables societies to produce public goods, things like public roads, clean air, and low crime. Public goods benefit all members of a community, or the whole society, but are costly to produce. As is well known, cooperation is highly problematic from the theoretical point of view, because selfish agents gladly benefit from public goods, but refuse to contribute to them (“defect”). How humans evolved the capacity to overcome this “Cooperation Dilemma” is a big question, which doesn’t yet have a universally accepted answer. But most researchers agree that prosocial norms play a very important role in whatever theory that we will eventually develop to solve this puzzle.

As an example of cooperation, consider meat-sharing, which is the norm in most foraging societies. Meat-sharing has numerous benefits for the group within which it is practiced. First, any particular hunter, no matter how skilled, is not always successful in bringing home game. Sharing ensures that everybody has a moderate amount of meat every day. Not sharing results in long spells of famine, interspersed with feasts (with a portion of the kill spoiling, or being wasted in other ways).

Second, put yourself in the moccasins of a hunter. You have an interest in the well-being of others in your tribe. There is that old-timer who is not as spry as he used to be, and can’t chase the game in the bush. But he is an amazing repository of knowledge that can save the whole tribe when a drought strikes (read the story about an old man Paralji in The Secret of Our Success). Or that pregnant woman, whose husband was killed in a hunting accident. When her son grows up, he will stand together with your children against the tribe’s enemies.

Thus, the whole tribe, including you and your descendants, benefits from meat sharing. But when you bring that yummy warthog from a successful hunt, there is a terrible temptation not to share it with others. It’s the Cooperative Dilemma all over again. The benefits of meat sharing are spread thinly over all. Its consequences are often deferred into distant future. Meanwhile, pigging out on the juicy warthog steak is here and now.

This is why you need social norms to help you stick to the straight and narrow. Such “cultural-institutional technologies” make sharing psychologically easier and prevent free-riding. One kind of such a social technology is meat taboos. Among some Kalahari foragers, for example, “the hunter himself could only eat the ribs and a shoulder blade; the rest of the animal was taboo for him. The hunter’s wife received the meat and fat around the animal’s hindquarters, which she had to cook openly and share with other women (only). Taboos prohibited young males from eating anything except abdominal walls, kidneys, and genitals.” These taboos essentially guaranteed that a large carcass would be widely distributed across the whole band.

Mbendjele meat sharing

I don’t know how deeply internalized are these food taboos in the !Kung. But food taboos in general can be very powerful because they plug into one of the most basic emotions: disgust. Many years ago, while touring Paris, I experimentally ate a sandwich with horse meat. Now Russians never eat horse meat, but I hadn’t realized how deeply this taboo was ingrained. I had an upset stomach that evening. Meanwhile the French, or the Mongols, eat horse without any ill effects. Culture.

Food taboos is just a special case. More generally, what deeply internalized social norms do to most of us is rewire our brains to feel inappropriate pleasure as pain (just like chili peppers, although in that case pain is rewired as pleasure).  It’s interesting that norm-breaking often evokes disgust (“what he did made me sick to my stomach”). Cultural groups whose members internalize prosocial norms will sustain higher degree of within-group cooperation—and will win and spread at the expense of other, less cooperative groups. And so will the prosocial norm.

~~~ *** ~~~

In the Preface, Joe Henrich writes, “Intellectually, I was also keenly interested in the evolution of human societies, particularly in the basic question of how humans went from living in relatively small-scale societies to complex nation-states over the last ten millennia.” He doesn’t really sink his teeth into this question, as the bulk of The Secret of Our Success is devoted to human evolution preceding the great transition of the last 10,000 years. This is where my own Ultrasociety: How 10,000 Years of War Made Humans the Greatest Cooperators on Earth picks up the story of human history. Interestingly,, very appropriately, often pairs our two books as “frequently bought together.”

I also “converted” to Cultural Evolution in the mid-1990s, but whereas Joe moved from the bottom up, running behavioral experiments that probed why people in small-scale societies cooperate, I approached the subject from the opposite direction. I was interested (still am) in throwing the scientific method, in all its awful majesty, at the age-old question of why empires rise and fall. Very quickly I realized that Cultural Evolution provides us with an invaluable set of conceptual and mathematical tools to build, and test theories about the evolution and dynamics of large-scale complex societies. Ultrasociety is more work-in-progress than The Secret of Our Success. But it’s becoming increasingly more clear how Cultural Evolution will help us solve age-old questions about human societies.

Evolution of prosocial norms is a big subject in The Secret of Our Success. It is, indeed, one of the major contributions from Cultural Evolution to the question of how complex societies are organized and function. Of course, the study of social norms and institutions is a well-developed subfield of social sciences (for example, the New Institutional Economics). But institutionalists in social sciences tend to focus more on the “institutions as rules of the game” aspects. Yet, no matter how well an institution is designed, it will not ensure cooperation if people don’t internalize prosocial norms. What is needed for rules to work is that conforming to the norm becomes a preference that has intrinsic, rather than instrumental value. In other words, people need to feel good about doing right. To put it crudely, their brains need to be rewired to experience pleasure while sacrificing time, effort, food, money, etc. for the common good. Biology (genetic influences on behavior, physiological and neurophysiological mechanisms, and so on) plays a very important role in this. We leave in exciting times, as science makes great strides in understanding such social and biological influences on human behavior, and what makes our wonderful complex societies work (or not). And Cultural Evolution provides us with an indispensable set of tools to untangle the interactions between the social and biological factors.

My review of has barely scratched the surface of the great variety of topics covered in the book. I didn’t even talk about the Lost European Explorer Files. It goes without saying that my strong recommendation is to read the book. I’ll say more: The Secret of Our Success is going to be a field-defining book for Cultural Evolution in the next decade.



[1] I should point out that Joe’s example of a northern country with bland food is Norway. It’s a better example than my native country, because Russians are quite fond of mustard and horseradish. As a result, our traditional dishes are not quite as bland as Nordic food. Unfortunately, high level of resistance to allyl isothiocyanate, the active ingredient in mustards and horseradish, does not increase your ability to handle capsaicin without bursting out in tears.


A shortened version of this review was published in Vol. 1.1 of Evolutionary Studies in Imaginative Culture. Reprint

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Tom Hite

The book CATCHING FIRE is a revolutionary book. Many in academia don’t except the disruptive conclusions. But after reading the book you can glance at a primate skeleton and determine whether that individual used fire. I’ll put the these other books on my reading list. Thanks for the suggestions.

Another mind bogglingly good book along these same lines is:

The 10,000 Year Explosion: How Civilization Accelerated Human Evolution -Cochran/Harpening

The observations in that book are so incisive that many of my long held cherished beliefs became quacking canards.

Joost Douma

Thoroughly enjoyed reading this. Your review also reminded me of Nobert Elias’, “Über den Prozeß der Zivilisation”. .

Ross Hartshorn

Having read both “Catching Fire” and “The 10,000 Year Explosion”, I can say both provided a lot of fuel for thought. I’m adding “The Secret Of Our Success” to my “to buy” list, as well.

Steve H.

It’s oversimplifying to provide a binary interaction between genetics and culture. There’s a baseline of DNA, but then epigenetic effects interact with environmental conditions, which we glimpse in outcomes like lactose intolerance. We can’t jump straight to an abstract reward system without taking into account varieties of gut bacteria, which like mitochondria act like an ‘extended phenotype’ of a much greater pool of DNA which interacts with our own symbiotically. This includes bacterial effects on serotonin, which affects the reward structures. Learning piggybacks on at least these different scales.

It’s not true that ‘of all animal species only humans use spices to control pathogens.’ Chimps are known to ingest toxic plants versus gut parasites. Chimps also have cultural variations in meat sharing which seem to correlate with environmental conditions, as investigated in ‘The New Chimpanzee’ (an older National Geographic documentary).

Tom Hite

Perhaps you are referring to lactose tolerance (not lactose INtolerance as you mentioned). These recent mutations which allow you to tolerate milk beyond childhood are fully genetic mutations, not epigenetic.

There are six currently known genetic mutations, the one most common in Europe is the −13,910 C/T mutation. See “lactase persistence” in Wikipedia.

al loomis

the ‘interesting’ part of this is whether cultural evolution processes will enable us to cope with the threats emerging from technological development.
unlikely, but we live in hope.

Bryan Atkins

Agree with Thee. Almost always more complex; and saw a bit about chimps using plant “meds.”

Bryan Atkins

Apologies, the above was supposed to be a response to a comment by Steve H.

Bryan Atkins

Re RULES: Maybe not wholly transferable, but I see rules as code.
Code is physics generated and physics efficacious Relationship Infrastructure in bio, cultural & tech networks: genetic language math moral religious legal monetary etiquette software, etc.
“The story of human intelligence starts with a universe that is capable of encoding information.” — Ray Kurzweil — “How To Create A Mind”
Think the dominant phenomenon of our era is Exponentially Accelerating Complexity.
We don’t have to adequate coding – relationship infrastructure – to navigate the alien and unprecedented environs we’ve created.
We’re literally doing multilevel selection with world culture’s dominant information processing mechanism: humans using monetary code.
That mechanism lacks information processing reach, speed, accuracy & power, qualities necessary to continue passing natural selection tests.
Verily, if your culture’s relationships with the sky and ocean are deadly, your cultural genome sucks.
Currently, humans aren’t sufficiently coded — genetically, culturally or technologically — to pass natural selection tests in environs undergoing exponentially accelerating complexity for X number of years. Year X approaches.
For more, please see: The Price Is Wrong:

Peter van den Engel

Very interesting. Yes, the energy connections create information that is understood by the brain, basicly because it’s a parallel living energy connection itself, that however responds to observations of the outside world in the first place, as far as the outer layers are concerned.
So, therefore I believe gene selection by coincidence as an evolutionairy tool is far less relevant than behavioral connection synchronizing with the outside world, like for animals food and temperature are most important. After this, it creates synchrone genes to its behavior.

As far as the growth of the human brain compared to animals goes, I have a very different theory, than food.
Using cooking to neutralize bacteria needs humans to have discovered fire, so their brains already had grown before that.

As I stated earlier I use a time/ energy equation, because the energy connections always are related to time.
The main reason for humans to develop brains, is because they have hands and fingers, splitting time in much smaller fractions. This creates a very different economy of time sharing. As you can also relatively see with ape communities in their behavior. Why apes however did not evolve further like humans did is a different story I will save for my book.

The very reason why humans react to the energy connection of their environmental culture, also creates a parallel with how their financial system is designed. When this is not a most parallel concept; like it is!; it wil create asynchronicies in societies cultural behavior.

The example you mentioned of building roads, while commercial economic activity does not feel much like it, I can explain very well. It is as an effect created by the money system itself.

Because it only rewards economic time sharing, that trades inmediately and not in a delayed fashion, as goes for education as well.
That is way this kind of labor is not perceived as productive/ but as a cost. Finally creating a fiscal system in counter reaction to that, which has not understood its own cultural functioning, because the financial did not understand it either.

Graeme Bushell

Hi All,
Another great book that sheds light on how humans evolved big brains and small guts in the first place is “The Story of the Human Body: Evolution, Health, and Disease” by Daniel Lieberman.

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