How Monogamy and Incest Taboos Made the West

A review of The WEIRDest People in the World by Joseph Henrich

I struggled for a while over whether to read Joseph Henrich’s The WEIRDest People in the World. Ten years ago, I would’ve jumped at the chance, given my interest in the big questions surrounding humanity and how we got here, and in consuming any work that took our evolutionary past seriously in exploring them.

In the intervening years, however, I have received a PhD in political science and grown cynical about academic research, to the point where an author being a Harvard professor signals to me that, while he may be extremely intelligent, his work, whatever merit it has, will in the end be forced to pay homage to political correctness and rely on shoddy experimental and statistical methods. Almost every time I’ve looked closely at a quantitative literature in the social sciences, I’ve ended up remarkably unimpressed. That makes “big theory” kinds of books unlikely to be useful, since they’ll have to draw on diverse kinds of literature, and most of the literature in most fields is awful. Thus, I expected Henrich’s book to maybe make some interesting points, but otherwise show the flaws that are the hallmarks of our era.

The other reason I resisted reading it is that I wasn’t sure there was that much to explain. Is the West really that special? Works like Hive Mind by Garett Jones show how remarkably well national IQ predicts wealth. This connection is clear and robust in a way that puts it on a different level than most social science, but it’s ignored, again, because modern social science is mostly a joke. East Asia has been catching up to the West, and by some metrics like rates of violent crime and social stability has surpassed it, so why do we need to know anything specific about European history?

That was my thinking. And then covid hit. While East Asians at first looked much more capable at preventing infections and deaths, eventually vaccines were developed, and strong precautions to protect against the disease came to look more and more self-destructive and absurd. China still has regular lockdowns, but in many ways what has happened in South Korea, Taiwan, and Japan is even more disturbing given continuing quarantines and mask mandates, and even voluntary masking, in the context of democratic governance. In other regions of the world, covering an individual’s face is used to prevent socializing and eventual sexual contact. Taiwan and South Korea are setting record lows in fertility – another sign of something deeply pathological in East Asian culture – and so this seems like the worst possible time to adopt a custom that is not only inherently degrading but in other contexts designed to keep unrelated men and women apart. China destroying its economic growth and blowing its opportunity to overtake the US in order to maintain Zero Covid has echoes of the emperor burning the royal fleet after it reached Africa three quarters of a century before Columbus discovered America.

My personal background also made me naturally inclined to think that there was something distinct about Westerners. My family came to the United States from the Middle East, and I grew up around Arab Christians. While religious similarity with the majority population made assimilation relatively frictionless, for the first generation there was always a sense that the white people around them were psychologically different. One particular moment that sticks out for me is when a relative was talking about someone he knew who made an excuse as to why he couldn’t be somewhere at a certain time. This was followed by the statement, said in passing, that “he wouldn’t lie, you know, he’s an American.” The implication was that when an Arab gives you an excuse for why he can’t be somewhere, you can start with the premise that he’s probably just saying whatever is most convenient for him in the moment. As someone who is hardwired to be pathologically honest and disagreeable, it was always the casual lying and how taken for granted it was that alienated me most from the culture I grew up in, and allowed me to fit in among the WEIRD, to the extent that I could fit in anywhere.

Recent events made me see such memories in a new light, and led me to believe that we don’t only need a theory to explain why the Industrial Revolution took off in Western Europe, but why the same people of the region and their institutions still seem the best adapted to modernity today. In that context, and being allergic to modern books written by professors, I first decided to pick up Max Weber’s The Protestant Work Ethic and the Spirit of Capitalism. Coming away impressed, I decided to give Henrich a chance. In the end, I’m glad I did. While some of my fears regarding political correctness and flawed research methods were confirmed, the book is a theoretical breakthrough explaining some of the most important questions regarding the history of our species. Namely, what makes for successful human societies? And what was so special about the Western edge of the Eurasian landmass?

The Importance of Not Marrying Your Cousin

Biology is complicated, but Darwinism is at its heart based on a remarkably simple principle. Various organisms exist. Mutations occur during the process of genes being passed on to offspring. Some of them are beneficial towards the ends of survival and reproduction, while others are harmful. Those that are beneficial spread, and populations change. One doesn’t have to know anything about the specifics of, say, how cells work or the structure of the brains of mammals to understand the basic concept.

Building on the work of Robert Boyd, Peter Richerson, and others, Henrich’s big idea is to apply a similar principle to human culture. Groups differ on a countless number of dimensions, from the foods they eat to how they raise children. Yet the ones that adopt the cultural preferences that are most successful will see them spread, through some combination of the direct conquest of other groups, outbreeding them, immigration to more successful territories, and imitation by less successful communities. Henrich’s book goes through the steps from hunter-gatherers to agriculture and the rise of chiefdoms, and finally to cities, industrialization, and the modern world. Every step in the process is convincing and seemingly backed up by various streams of research. What’s particularly impressive is the ways in which he connects political developments to biochemical processes at the level of individual psychology. For example, he explains the potency of synchronous movements during rituals to our brains having evolved to use our own movements to predict the movements of those around us, which can create the illusion that others are more similar to, if not extensions of, ourselves.

Charlemagne (747-814 AD), the “Father of Europe,” who put his authority behind a synod creating a wait time before marriage during which local communities could investigate whether the couple had any blood ties. He personally had 10 known wives and at least 18 children, so it took a while for church norms to bind kings. Source.

Ultimately, Henrich traces the success of the West back to the sex and marriage taboos of early Christianity. The book highlights how obsessed early Christian leaders were with preventing incest, and just how rare this concern has been historically. An appendix to the book lists milestones in the process, beginning with the Synod of Elvira in 305-306 AD decreeing that a man could not take communion if he married his dead wife’s sister, to bans on marrying family members that started with close relatives like first cousins and nieces and expanded to include sixth cousins by the eleventh century in a system that covered not only blood relations, but affines (i.e., in-laws, step-children, etc.) and spiritual kin (godmothers, etc.). The first documented communication between a Frankish king and a pope is a letter from 538 AD about the incest issue. In the eleventh century, the Duke of Normandy, who would later be known as William the Conqueror, was excommunicated for marrying a distant cousin. While church leaders always had to be cognizant of political realities, European history shows that they did exercise power in their own right, even over the lives and behavior of some of the most powerful figures of late antiquity and the Middle Ages.

A fascinating line of evidence documenting the development of changing family norms can be found in the linguistic record. Earlier in their history, European languages had terms for things like “mother’s sister” or “male cousin on my dad’s side” instead of just saying “aunt” or “cousin.” Such distinctions matter in societies in which clans and extended family relations are important and descent is traced through either the male or female line alone, and so these kinds of words are still used in modern languages such as Arabic. They would disappear across Europe, first in the Romance languages like French and Italian around 700, and then German and English by around 1100. Usually, it takes languages a few centuries to catch up to cultural changes that have taken place in people’s daily lives, so the timeline is consistent with the decrees of the Catholic Church having had a major effect on society. Yiddish, however, which split from German in the Middle Ages, would continue to use highly specific terms to refer to extended family members, thus reflecting different marriage and reproduction norms among Jews.

What Henrich calls the Church’s “Marriage and Family Plan” (MFP), which included features like monogamy in addition to an obsession with preventing broadly-defined incest, had important downstream consequences in practically every aspect of life. Young men would be more likely to find marriage partners since a few high-status leaders could not claim a disproportionate share of women, creating incentives for individuals to be more hard-working and less violent. The power of elders was further reduced by an inability to arrange marriages in ways that would keep wealth and resources within the same family, unlike in Muslim societies where the son of one brother would often be wedded to the daughter of another. When incest taboos extended to sixth cousins, Henrich estimates that an individual may have had 10,000 total relatives that were off limits in the marriage market. This wouldn’t be a big deal in a modern city, but when most people lived in small villages it would have created major difficulties for anyone trying to find a spouse. This led to a population that was more mobile, less embedded in kinship networks, and ultimately more individualistic.

For most of those unfamiliar with the anthropological literature, what is sure to be one of the most surprising findings discussed in the book relates to how rare the individual components of the MFP have been throughout history. According to one database looking at 1,200 societies before industrialization, only 5% had newlywed couples start their own households, 8% organized domestic life around nuclear families, 15% had only monogamous marriages, 25% had little or no cousin marriage, and 28% had bilateral descent, meaning that lineages are traced through both the mother and father. Christian Europe under the MFP had all five, which wasn’t true for over 99% of other societies. Today, after the rest of the world has been heavily influenced by Western culture, given its success, it’s easy to lose sight of how unique its mating and familial practices have been in the larger historical context.

People prone to individualism would go on to achieve high rates of urbanization and form guilds, universities, marketplaces, and other voluntary institutions that were based on principles of mutual self-interest and competed with one another. Ultimately, Western Europe would conquer the world on the back of the strengths of these institutions, with democracy and capitalism being arguably the most important among them.

Near the end of the book, Henrich presents a flowchart that explains how this all works.

One can synthesize Weber and Henrich by understanding that while Protestantism was important for the Industrial Revolution, it was the MFP that created the psychological conditions for a faith that emphasized the individual’s relationship with God to conquer much of Europe. Henrich goes as far as in effect arguing that if Martin Luther had never existed, larger trends ensured that movements with many of the same characteristics of what became Protestantism would have gained adherents, even if they never officially broke with Rome.

It is important to note that the Church did not have any idea about what the long-term consequences would be when it began enforcing the MFP, any more than a hunter-gatherer tribe in the Australian outback understands that its traditional cooking methods are what make a particular seed digestible. Henrich argues that breaking down kinship ties was potentially a great way for the Church to seize large estates upon the deaths of individuals, and it therefore ended up as the largest landholder in Europe. So while individuals and institutions found certain aspects of the MFP appealing for reasons related to their own interests, no one could foresee the ways in which monogamy, incest taboos, and other Christian familial practices would eventually create the modern world.

The Best and Worst of Social Science

Practically every major part of the process described in the book is convincing, and it appears that Henrich has achieved the highest calling of a scholar, which is to take a simple cause and use it to explain an important phenomenon. The fact that the impact of the MFP was felt centuries before the West conquered the rest of the world argues against a reverse causation story, or the idea that it is primarily a matter of wealth causing new kinds of familial patterns and social arrangements, rather than the other way around.

There are two things that trouble me about the book, however. The first is superficial, and doesn’t really matter for its conclusions, while the second is more substantive.

First, Henrich is too willing to cite data that supports whatever he happens to be arguing for at the moment, and in doing so it appears that a lot of the social science relied upon is open to multiple interpretations, has not been replicated, or is otherwise flawed. The weak parts of the book take away from the more important arguments that seem to be on much more solid ground. For example, in making the case that cultural evolution selected for gods that reward or punish individuals based on their actions, Henrich notes that “statistical analyses indicate that the higher the percentage of people in a country who believe in hell and heaven (not just heaven), the faster the rate of economic growth in the subsequent decade.” Well, ok, but what if you only look within the US, at the state or county level? What if we compared ethnic groups in the US or most European countries? I googled belief in hell by American state, and the relationships between practically all forms of religiosity and wealth seem to go in the opposite direction (which I would’ve guessed based on my pre-existing knowledge). In the replication crisis, scholars have noticed the tendency to cherry-pick variables within the context of an individual study. When you’re looking at data comparing various jurisdictions and the researcher is allowed to pick and choose the parameters of an analysis across temporal and spatial dimensions, in addition to which dependent and independent variables to measure, it’s easy to support almost any narrative. Thus, not only is some of the research of this type relied upon questionable, but the absence of other studies is also suggestive.

The following are just a series of examples that made my eyes roll, all interspersed throughout a book whose main ideas changed the way I view the world.

For every 1,000 km (621 mi) closer a region is to the core of an earthquake zone, an active volcano, or a storm center, the percentage of people affirming these supernatural beliefs increases by about 10 percentile points.

For each crusader who mobilized an army and went to war, the number of urban residents in his polity increased by between 1,500 and 3,000 people relative to a similar city without that military mobilization – this represents faster economic growth in urban areas that were more engaged in the Crusades.

For every 10 percent increase in those killed by the Allied bombing campaign in a German city during World War II, there is a 6 percentile increase in the number of people who believe in God today.

The results show that the higher the density of Cistercian monasteries in a region during the Middle Ages, the more likely a person from that region today is to say that ‘hard work’ is important for children to learn.

The analysis shows that people from Swiss communities with a longer history of participatory governance are more conditionally cooperative with strangers today. In fact, for each additional century of exposure to democratic government, a contemporary person’s inclination for conditional cooperation increases by nearly nine points.

While Christianity has traditionally condemned homosexuality, the earlier a region in central Europe was exposed to Protestantism, the higher is the percentage in that area that supports gay marriage today. This holds even when controlling for income, age, the foreign-born share of the population, and other potential confounders.

These experimental patterns were mirrored in the soccer games: those least affected by the war received zero foul cards (for rule violations), while those most affected had nearly a 50 percent chance of getting at least one foul card.

I made two of the above passages up (try to guess which ones¹), but the rest are real, and I could’ve come up with countless others that were similarly questionable. With regards to laboratory and other experiments, some of the findings seem custom made to eventually wind up as cautionary tales in a future history of the replication crisis. For example, kids and young adults in a soccer league in Sierra Leone were more egalitarian with their own teammates and more competitive with players from other teams, but this pattern was only observed among those most directly affected by the recent civil war. I doubt this has been replicated, the results are ambiguous and only somewhat consistent with other research from the same country cited alongside it, and frankly, I doubt that any academic who puts the time and resources into doing studies in one of the poorest and least-governed countries in the world is going to dare come back with a null result. If there hadn’t been a result that depended on who was influenced by the war – which is self-reported, by the way – one could have made a different distinction between Westerners and Africans that fit the theory of WEIRD in some other way.

Unfortunately, relying on mountains of bad research is almost a requirement for writing a book in the human sciences today. We fetishize data – the more granular and exotic, the better, as long as you throw in enough “controls,” even when they do nothing to correct for possible selection effects or other kinds of bias. It’s not that all the priming, historical, and cross-national studies that Henrich relies on are worthless. Rather, there is such wide variation in quality between them that the book has the feeling of throwing whatever it can against the wall and seeing what sticks. Cross-national surveys on values, for example, often involve large sample sizes and have seen roughly the same results replicated in various ways. They roughly match up with what we understand about how people in different cultures think. Such studies are therefore much more believable than priming experiments conducted among hunter-gatherer tribes, which are hard to do, and potentially subject to every kind of research bias one can think of. There’s a reason that medical science conducts double-blind tests, not even allowing the doctor administering a treatment to know who received a placebo and who got the real thing. A similar method is impossible in cross-national experiments, or ones that involve explaining the rules of complicated games to hunter-gatherers. And such studies aren’t easily replicable either, given that they require anthropological fieldwork. Henrich is more judicious with questionable data than most, being honest with the reader when he speculates about some supposed causal effect being based on one or two studies. Yet there’s a tendency to retreat into acting as if the quantity of questionable data has a quality of its own.

Academics do this of course, because they are supposed to build on the publications of others. In the Kindle version of WEIRDest, footnotes and the bibliography take up about a third of the book. A scholar working within the peer review system has to pay homage to the work of other researchers, even if that work is flawed. And since physics envy has led to an overreliance on experiments and data analysis, any successful book is going to have to take such methods seriously. Max Weber could simply provide a detailed history of the ideas of various branches of Protestantism, and connect them to a few big facts in the world related to broad patterns of social organization and economic development. Henrich’s book would probably have been better if he could have followed a similar path.

The tragedy here is that most of the questionable studies that are cited are not all that important to the main arguments of the book. But they do take away from my enjoyment of it. I wanted to love and be inspired by it in toto the way I loved Weber. But I was forced into a more complicated relationship in which the book changed the way I looked at the world while a large portion of it made me recoil by standing as a reminder of what has gone wrong in the human sciences.

Gene-Culture Coevolution Minus the Genes

While reading WEIRDest, I could brush aside the bad studies and simply benefit from the main arguments without losing much other than my aesthetic appreciation for the work. The second problem of the book, however, is more substantive and provides an opportunity for future scholars to build upon it. While the author has previously written about gene-culture coevolution, the possibility that cultural evolution could have had genetic influences is not addressed until the last chapter of the book, and even then treated in a very unsatisfactory way. Henrich brings up the point that cities were demographic shredders, so it’s possible that WEIRD populations were getting less WEIRD genotypically while their phenotypes moved in the opposite direction. Plausible. But the author makes such a strong case for the MFP penetrating practically all aspects of European society that it doesn’t seem believable that this effect wouldn’t cause selection pressures in the WEIRD direction even in the countryside. As Henrich points out, the new social arrangements of the West were unique in a historical perspective. Are we to conclude that a millennium or more of adhering to a completely new mating system with practically no precedent in human history did not meaningfully change the genetic characteristics of a population? Henrich asserts that large genetic changes within populations tend to happen over the course of millennia, yet research by Henry Harpending, Gregory Cochran, and David Reich provides strong evidence that mere centuries can make a difference. Reich’s groundbreaking 2018 book Who We Are and How We Got Here is cited only once in passing, its arguments left unaddressed.

A particularly shocking omission from the book is the lack of any substantive discussion of whether bans on cousin marriage would have led to improved health and cognitive ability. It seems beyond doubt that they would have, but admitting this would raise uncomfortable questions regarding certain modern populations.

Another way in which Henrich pacifies the God of PC – again, this is a modern book after all – is by ignoring research on cognitive ability more generally, which has been highlighted by Garett Jones and others. As already mentioned, WEIRDest is not all that selective with regards to what kinds of data it relies on. If there’s any study showing a difference between Westerners and everyone else, even if it’s rates of nose picking, he’ll take the relevant data and put it on a y-axis to show the cross-national correlation with the prevalence of cousin marriage or strength of kinship ties. But sources like IQ tests and PISA scores are completely ignored. While the former field of research as used to make cross-national comparisons has been roundly criticized and debated, PISA provides a rich database that seeks to be representative of each country’s student body. Neither measure is perfect, but the results of both IQ and PISA tests are more comprehensive, unambiguous, and replicable than the vast majority of research that Henrich relies on, particularly when he highlights survey data and priming studies. Rates of numeracy and other data match more comprehensive measures of cognitive ability. Of course, such research shows that East Asians have higher levels of performance than Westerners, which complicates Henrich’s story a bit, particularly given that he uses his own measure of “analytic thinking” that is divorced from anything resembling IQ and shows those of European descent ahead of everyone else. Remarkably low East Asian crime rates represent another important statistical reality that Henrich ignores, despite a discussion in which he argues that the MFP restrains violence between males. If this is correct, then the fact that Japan, South Korea, and China – which only adopted aspects of the MFP over the course of the last century and a half and have not had time for it to fully penetrate more traditional ways of thinking – have nearly non-existent levels of interpersonal violence relative to the West is another one of those anomalies that go ignored.

Of course, general intelligence is nowhere near the entire story in explaining how and why institutions differ across the world. Henrich is right that there is something unique about the West. But the fact that East Asians are higher on the trait that is easily the best predictor of wealth is a fact that any broad theory of human difference needs to grapple with. Westerners might have had the right combination of psychological traits to create democracy and set off the Industrial Revolution, but East Asians have also shown themselves to be quite unique, and any story of humanity that simply breaks the world down into the “West” and “other” is missing something very important.

The hesitancy to talk about genetic differences or cognitive ability is somewhat ironic given that Henrich seems to make a strong case for Western moral superiority. While denouncing any suggestion that he is passing judgment on any particular culture, he in effect argues that people in Europe ended up becoming more likely to be honest, willing to treat strangers fairly, cooperate for the sake of the common good, and apply moral standards objectively. Unlike people from other countries, European diplomats pay their parking tickets, even when they don’t have to. One finding that I found particularly shocking was that people in more traditional cultures often place little emphasis on the intentions of an actor when judging his conduct and whether he should be punished for it. Sure, we can pretend that all this makes more primitive societies morally no better or worse than we are, but doing so strikes me as adopting an extreme form of moral relativism. The fact that one can make a strong case for Westerners being more ethical than the rest of the world while discussing IQ is out of bounds, even though East Asians come out on top, supports the idea that people at the deepest level consider intelligence to be the most important trait in determining the value of an individual or group.

This is Still an Amazing Book

I realize that this review sounds quite critical. But it is the excellence of WEIRDest that makes its flaws so glaring. And pointing out shortcomings in a work is much more worthwhile than simply repeating its arguments and singing the author’s praises.

I hope that the criticisms made in this review don’t discourage anyone from reading the book. Henrich makes a convincing case that the Christian Marriage and Family Plan led to Western exceptionalism. If correct, and I believe it is, his discovery belongs in the top tier of theories that best explain the broad sweep of human history, in the same league with Smith’s division of labor, Darwinian natural selection, and Ricardo’s idea of comparative advantage. Drudging through some flawed data and sacrifices to the God of PC to gain deep insight into the causes of human progress is a trade worth making.

Henrich touches a bit on the policy and social implications of his work in the conclusion. In what appears to be a jab at the Bush-era wars, he doubts we can easily transfer institutions from the West and graft them onto a different psychological substrate without causing major problems. Immigration goes unmentioned, but there are bound to be implications here, as Garett Jones and others have written about. Unfortunately, any attempts to draw political or social conclusions from WEIRDest will be subject to the same flaws found in the book itself. And I fail to see many policy recommendations that are straightforward. One could make the argument, for example, that history suggests that the MFP is portable, given the extent to which much of the world has followed the West by adopting its restrictions on polygamy and broadly-defined incest. This means that perhaps Bush’s mistake wasn’t that he tried to change Iraq, but that he focused on the method the population used to pick its leaders rather than forcing them to stop marrying their cousins and waiting a few hundred years.

It would therefore be a mistake to read Henrich and simply try to extract a few talking points to argue for immigration restrictionism and a non-interventionist foreign policy. Of course, WEIRDest should influence your reading of history, understanding of human nature, and yes, ultimately your politics in deep ways. But the implications of Henrich’s big ideas are far from obvious or easy to discern.

Even if there were no broad applications of the lessons of the book, and it would be absurd to believe that there aren’t, knowledge is worthwhile for its own sake. And Henrich has moved us forward in the journey to understand why humanity has been so successful. I hope his work inspires others to be clear-sighted and brave enough to continue building on his accomplishment.

1. Numbers 3 and 6.