Chapter 4
Clans, States, and Why You Can't Get Here from There
To understand how WEIRD psychology emerged, we must examine how human societies scaled up from egalitarian hunter-gatherer bands to vast modern nations. The crucial difference came with food production, which intensified intergroup competition and its effects on cultural evolution, institutions, and psychology. This agricultural revolution created population pressures and resource competition that fundamentally transformed social organization.
As societies shifted from mobile networks to sedentary communities, cultural evolution retrofitted existing kin-based institutions to create tighter, more cooperative groups. One key innovation was the shift from bilateral descent (tracking relatedness through both parents) to unilineal descent systems (patrilineal or matrilineal clans). This transition was particularly evident in agricultural societies where land inheritance and resource management became critical concerns.
Clans evolved to foster greater cooperation by mitigating conflicts of interest that arise in bilateral kinship systems. By elevating one line of descent and focusing kinship around shared ancestors, clans created clearer relationships where everyone from the same generation is equally related. In patrilineal systems, your father's brothers become "fathers" and their children become your "brothers" and "sisters." This system reduced inheritance disputes and strengthened group solidarity through shared property rights and collective responsibility.
The clan system proved remarkably effective at organizing groups of up to several thousand people. Archaeological evidence from early agricultural settlements shows how residential patterns often reflected clan-based organization, with distinct neighborhoods or sectors housing extended patrilineal families. These arrangements facilitated collective action for defense, resource management, and ritual activities.
While clans created internal cooperation, they hit a ceiling when trying to scale up further. Cultural evolution fashioned higher-level institutions to integrate these kin-groups into larger communities. Segmentary lineages provided one mechanism, creating nested structures of alliances that could mobilize hundreds of thousands of people. The Nuer of Sudan demonstrated this power when they assembled fighting forces of over 10,000 warriors to drive out the Dinka, who despite large populations could never mobilize more than a few thousand fighters at once. This system worked through a principle of "opposition at every level" - groups united against common enemies while maintaining internal divisions.
The legacy of these institutions persists into modern times. Even in the 21st century, tribal populations with segmentary lineages experience higher rates of violence and civil war, and report less trust in outsiders. The culture of honor associated with these institutions persists-counties in the U.S. South with higher percentages of Scottish or Scotch-Irish settlers in 1790 still have higher murder rates today. Modern studies have shown these areas maintain distinctive attitudes toward violence, particularly regarding self-defense and personal reputation.
These historical patterns help explain why simply imposing modern state institutions on clan-based societies often fails. The deep cultural and psychological adaptations associated with clan organization can persist for generations, influencing everything from political participation to economic development and social trust. Understanding these dynamics is crucial for appreciating both the emergence of WEIRD psychology and the challenges of institutional change in many parts of the world today.
Chapter 5
The Gods Are Watching. Behave!
Religious beliefs powerfully influence human behavior, particularly regarding cooperation and fairness. In laboratory experiments, participants unconsciously reminded of God-related concepts became significantly more generous in economic games. While control participants gave strangers only $2.60 on average from $10, those primed with God-related words gave $4.60 on average.
This effect isn't just about associating religion with charity. When researchers analyzed 26 studies, they found that God-primes only influenced believers, having no effect on atheists. However, secular primes involving concepts like "police" and "courts" increased generosity in both believers and non-believers, suggesting that both supernatural and secular monitoring systems can promote prosocial behavior.
Early hunter-gatherer gods were typically weak, whimsical, and not particularly moral. They could be bribed or tricked, punished people based on arbitrary pet peeves rather than moral violations, and rarely connected proper behavior with afterlife quality. The Ju/'hoansi's creator god =Gao!na, for example, might punish someone for burning bees but wasn't concerned with how people treated each other.
Through intergroup competition, communities with gods who punished antisocial behaviors gained advantages. This evolutionary process gradually assembled cultural packages of gods, rituals, and institutions that expanded trust, motivated sacrifice in war, and reduced internal conflict. To scale beyond the face-to-face interactions of communal rituals, cultural evolution needed to fashion "imagined communities"-networks of strangers connected by shared supernatural beliefs.
Our cross-cultural study examined how belief in supernatural monitoring and punishment affects fairness toward strangers. Using the Random Allocation Game, we found that people who believed in more punishing Big Gods showed less bias against distant coreligionists. Those with strong beliefs in divine punishment allocated nearly 15 coins (out of 30) to strangers, while those who viewed their god as "an all-loving softy" allocated only about 13.
Chapter 6
WEIRD Families: The Church's Radical Experiment
WEIRD families are truly peculiar from a global and historical perspective. Unlike most societies, WEIRD people lack extensive lineages or large kindreds that entangle individuals in webs of familial responsibilities. Their identity, legal existence, and personal security aren't tied to membership in a house or clan. They practice strict monogamy, avoid marrying relatives (including cousins), and form marriages based on mutual affection rather than arrangement.
Anthropological data reveals just how unusual these patterns are: 50.2% of pre-industrial societies possessed none of these WEIRD kinship traits, while only 0.7% possessed all five. Even today, cousin marriage remains common globally-approximately 1 in 10 marriages worldwide is between relatives, with rates exceeding 50% in parts of the Middle East and Africa.
The roots of WEIRD families lie in the Western Church's marriage and family policies that gradually dismantled Europe's intensive kin-based institutions between 400-1200 CE. While many assume WEIRD kinship emerged from industrialization and modernization, in Europe the historical order was reversed-first traditional kinship systems were demolished by the Church, then voluntary associations based on shared interests rather than blood ties emerged from these ruins.
The Church's systematic dismantling of traditional kinship began in earnest around 597 CE when Pope Gregory I sent missionaries to Anglo-Saxon England with strict marriage instructions. Pope Gregory prohibited marriages between first cousins (and closer relatives), stepfamilies, and dead brothers' wives. Two centuries later in 786, papal commissioners still found widespread "incest" (cousin marriage) and polygyny among the Anglo-Saxons.
By the 11th century, these taboos included even sixth cousins-covering blood relatives, in-laws (affines), and spiritual kin (godrelatives). The penalties for violating these incest prohibitions grew increasingly severe, evolving from simple suspension from Communion to excommunication and anathema-a ritual that formally handed the soul to Satan.
The Church systematically blocked traditional strategies for maintaining lineages. Adoption, common in pre-Christian Europe, was effectively banned. Polygynous marriage, which allowed men to take additional wives to produce heirs, was prohibited. Even divorce and remarriage were forbidden. Without adoption, polygamy, or remarriage as options, European dynasties frequently died out for lack of heirs-an outcome that benefited the Church by weakening kin networks and generating wealth through the sale of annulments.
Chapter 7
Psychological Differences, Families, and the Church
To measure kinship intensity across populations, researchers developed two key metrics: the Kinship Intensity Index (KII), which combines anthropological data on cousin marriage, family structures, inheritance patterns, and residence norms; and actual rates of cousin marriage. These measures reveal striking global patterns-darker regions on the world map indicate more intensive kin-based institutions, with much of the Americas showing European-derived patterns except for indigenous populations.
Intensive kinship fundamentally shapes how people think about themselves and their relationships. In societies with dense, interdependent kinship networks, people develop psychological adaptations favoring conformity, deference to authority, sensitivity to shame, and collective orientation. By contrast, societies with weaker kinship bonds foster independence, less deference, more guilt, and greater concern with personal achievement.
The data confirms this pattern: societies with higher kinship intensity have "tighter" social norms that are numerous, contextually sensitive, and strictly enforced. Experimental evidence from Asch's conformity studies shows people from societies with weaker kin-based institutions are 20-30% less likely to conform to incorrect group judgments than those from high-kinship societies.
Intensive kin-based institutions cultivate moral standards rooted more in in-group loyalty than impartial principles. When comparing universal moral dimensions (fairness and care/harm) against tribal dimensions (in-group loyalty and authority deference), those from intensive kinship societies prioritize tribal values while downplaying universal principles.
The Public Goods Game reveals how kinship intensity affects cooperation with strangers. When given $20 and the opportunity to contribute to a group project that benefits everyone, people from societies with intensive kinship contribute significantly less (40% of their endowment) compared to those from weak-kinship societies (57%).
To assess the Church's impact on kinship intensity, researchers tracked the expansion of bishoprics across Europe from 500-1500 CE, calculating "church dosage" measures for both Western and Orthodox Churches. The results were striking: Church exposure explains about 40% of global differences in kinship intensity and 62% of variation in cousin marriage rates. The Western Church's effects were stronger than the Orthodox Church's, with each century of Western Church exposure cutting cousin marriage rates by nearly 60%.
Chapter 8
WEIRD Monogamy: Taming Male Competition
Monogamous marriage represents one of the most distinctive yet underappreciated aspects of WEIRD psychology. When Spanish conquistadors encountered the Aztec Empire in 1521, both societies had developed as complex agricultural states with hereditary rulers and powerful religions, despite 15 millennia of separation. Yet their marriage systems differed dramatically. While Aztec elites practiced extensive polygyny, Europeans had adopted strict monogamy through the Church's influence.
This contrast highlights a fundamental truth: WEIRD monogamy is the peculiar outlier from both evolutionary and global-historical perspectives. No group-living primates practice monogamous pair-bonding naturally, and our evolved psychology actually biases us toward polygynous arrangements.
Polygynous marriage creates a fundamental mathematical problem: a large pool of low-status unmarried men with few prospects for marriage or reproduction. In a society with equal numbers of men and women, when high-status men take multiple wives, many low-status men are left with none.
Consider two hypothetical communities of 20 men and 20 women each. In the monogamous community, every man can find a wife and gain a stake in the future. In the polygynous community, if just the top 20% of men marry polygynously (with the highest having four wives), the bottom 40% of men become involuntary lifelong bachelors-evolutionary zeros.
This creates dramatically different incentive structures. Low-status men in polygynous societies face much steeper competition. They must make enormous status leaps to enter the marriage market, making them more likely to engage in risky, violent, or criminal behavior.
Testosterone plays a crucial role in male competition. In monogamous bird species like song sparrows, testosterone levels rise during mating season for territory establishment but drop once eggs arrive as males prepare to care for hatchlings. By contrast, in polygynous species like red-winged blackbirds, testosterone remains elevated throughout breeding season as males continue seeking additional mates.
Similarly in humans, marriage and fatherhood lower men's testosterone levels in WEIRD societies. A study in Cebu, Philippines showed men's testosterone plummeted among those who married and had children, while declining least in those who remained single. WEIRD monogamy norms suppress testosterone at a societal level by ensuring more men marry and experience the resulting hormonal changes.
Chapter 9
Market Mentalities: The Psychology of Commerce
The spread of mechanical clocks across European cities in the 13th century marks the emergence of WEIRD time psychology. Unlike people in many non-Western societies who view time fluidly, Westerners obsess over "saving" and "making" time. Research shows urbanites in individualistic countries walk 30% faster and complete transactions more quickly than those in less individualistic societies.
Europeans began working longer and harder during what historians call the Industrious Revolution, traceable to at least 1650. Court records from London's Old Bailey reveal that between 1748 and 1803, the workweek lengthened by 40% as people worked 30 minutes more per day, abandoned "Saint Mondays," and worked through traditional holy days-adding about 1,000 extra working hours annually.
Market integration appears to foster greater patience and self-control. Among BaYaka hunter-gatherers in the Congo Basin, those living in market towns were significantly more patient than their forest-dwelling counterparts-54% versus 18% were willing to wait one day for five soup stock cubes rather than taking one immediately. This difference partly stems from wage labor, which trains people to work now for delayed rewards.
Historical evidence suggests Europeans became increasingly patient over centuries. Interest rates in England dropped from 10-12% in the Middle Ages to below 4% by 1750, continuing to fall during the Industrial Revolution. While European interest rates fell below 5% before the Industrial Revolution, rates elsewhere remained much higher-50% in China's Yangtze delta, 25-50% in Korea, and 12-15% in Osaka.
The personality patterns observed among WEIRD populations aren't universal human traits but rather culturally evolved adaptations. When anthropologist Mike Gurven studied personality among the Tsimane', Bolivian farmer-foragers with minimal market integration, he found only two personality dimensions rather than the WEIRD-5. These dimensions-"interpersonal prosociality" and "industriousness"-represent the two primary routes to social success in their society.
Chapter 10
Escape Velocity: How Europe Broke Free
In the late 18th century, the Industrial Revolution erupted from England's Midlands, triggering an economic transformation that continues today. This revolution propelled British incomes from $3,430 in 1800 (equivalent to modern Kenya) to $32,543 by 2000, while life expectancy rose from 39 to 78 years.
Innovation emerges not from individual genius but from collective cultural evolution. The rate of innovation depends primarily on two factors: the size of the population of engaged minds and their interconnectedness. While kin-based institutions like clans provide multiple teachers for young learners, they also foster conformity and discourage novelty. Nuclear families, though limited in teaching resources, can potentially connect to broader networks of expertise without kinship constraints.
Europe's unique social structures accelerated innovation. Young people often worked as "life-cycle servants" in successful households before marriage, exposing them to better practices. When couples established independent households in their mid-20s (encouraged by Church neolocal residence norms), they could implement and experiment with these techniques earlier than in societies where younger generations remained subordinate to elders.
Monasteries functioned as transnational innovation networks, spreading advanced techniques throughout Europe. The Cistercian Order created a network of monastery-factories deploying cutting-edge methods for grinding wheat, casting iron, tanning hides, and other industries. At mandatory annual meetings, hundreds of Cistercian abbots shared their best practices, effectively threading Europe's collective brain with nerves that transmitted innovations to even remote regions.
Unlike in China and India, where craft skills remained within families, European masters trained primarily non-relatives (72-93% of apprentices in 17th-century London). This broader diffusion of expertise accelerated innovation through several mechanisms: journeymen traveled between masters and cities, skilled masters were recruited between competing cities, and mobile artisans clustered in urban centers, creating competitive innovation hubs.
Cities dramatically expanded Europe's collective brain by bringing people, ideas, and technologies together. Between 800 CE and 1800, Europe's urban population (in cities over 10,000) grew 20-fold to nearly 16 million, while the Islamic world's didn't even double and China's remained flat. The relationship between city size and innovation is superlinear: contemporary data shows that for each 10-fold increase in population, there's a 13-fold increase in patent applications.
Chapter 11
The Dark Matter of History: Culture, Genes, and Modern Prosperity
Humans are fundamentally cultural beings. For over a million years, cumulative cultural evolution has shaped not just our bodies but our brains and psychology. Each generation must adapt to an ever-shifting landscape of norms, taboos, roles, and conventions. Cultural evolution has favored mind-shaping mechanisms-rituals, socialization practices, and games-that help people navigate their culturally-constructed worlds.
Diamond's "Guns, Germs, and Steel" explains why Eurasia developed complex societies first-it had the best crops, domesticable animals, and an east-west orientation facilitating technological diffusion. This accounts for global inequality around 1000 CE, when the most prosperous societies were in the Middle East, India, and China.
However, Diamond's explanation weakens after 1200 CE when European regions that experienced neither early agriculture nor precocious states-like England, Scotland, and the Netherlands-began unprecedented economic growth. My account picks up where Diamond's falls off, placing the coevolution of institutions and psychology at center stage.
East Asian societies like Japan, South Korea, and China adapted rapidly to Western economic models because: (1) their long histories of agriculture and statehood had already fostered cultural values around education, industriousness, and delayed gratification; and (2) their top-down governance allowed rapid adoption of Western institutions. Meanwhile, societies with particularly intensive kinship systems, especially in the Islamic world, have struggled to integrate with modern institutions.
Many WEIRD people assume psychological differences between populations stem from economic differences-and there's some truth to this. However, rising wealth didn't spark the modern world. In European Christendom, changes in kinship long preceded rising affluence, and psychological shifts toward individualism and independence arose before substantial wealth increases.
While natural selection may have responded to religious beliefs, institutions, and economic changes, genes likely contribute little to contemporary variation. Cultural evolution is faster and more powerful than genetic evolution over centuries. The power of cultural over genetic evolution is evident in research on educational attainment. While natural selection has reduced gene frequencies associated with schooling (decreasing educational attainment by 1.5 months per generation), cultural evolution has simultaneously increased education by 25.5 months per generation.
The psychological differences across populations profoundly matter for understanding our most cherished institutions and values. These differences create policy challenges, as WEIRD policymakers, politicians, and military strategists tend to assume others share their perceptions and judgments. The same policies can have radically different effects in London versus Baghdad because the people in these places are psychologically distinct.
