Adapting to an environment of their making

The last 30,000 years of cognitive evolution in Europe

Kostel na kopci, Jindrich Štýrský (1921) - Wikicommons

We make culture and it remakes us — by favoring those who better fit in and exploit its possibilities. Humans and culture have thus been remaking each other along trajectories that differ from one population to another. This was the trajectory of ancestral Europeans.

Unlike other animals, humans have adapted much more to culture than to nature —things like climate, soil, and vegetation. Consider the rate of change to the human genome. This rate increased more than a hundred-fold some 10,000 years ago, when our ancestors had already spread from the Tropics to the Arctic and were no longer adapting to new natural environments. But they were adapting to new cultural environments. Hunting and gathering gave way to farming, which then brought many other changes:

• rapid growth of population

• shift to sedentary living in villages and towns

• emergence of the state and its monopoly on violence

• increase in peaceful interactions with non-kin

• resolution of disputes through codified law

• growth of trade, specialization of labor, literacy and numeracy, social stratification, and much more.

When farming replaced hunting and gathering, the rate of change to the human genome increased more than a hundred-fold (Hawks et al., 2007). Think of a logarithmic curve. More genetic change has occurred in our species over the past 10,000 years than over the previous 100,000.

This acceleration has been due to the quickening pace of cultural change over those 10,000 years. Like nature, culture can decide who will survive to pass on their genes. Unlike nature, it is a human creation, being in fact the human-made portion of our environment. We make culture, and it remakes us — by favoring those who better fit in and exploit its possibilities. Humans and culture have thus been remaking each other along trajectories that differ from one population to another.

But didn’t cultural evolution replace genetic evolution? Didn’t one make the other unnecessary? That used to be the accepted view, but the truth now seems to be the opposite. When humans gave up hunting and gathering, they had to adapt to a faster-changing cultural environment, and not simply a slow-changing natural one. So new adaptations appeared at a faster rate. Yes, many were nongenetic, but the sharp rise in adaptive change of any sort — whether learned behaviors or innate capabilities — necessarily spurred the pace of genetic change. Instead of slowing down, genetic evolution began to go even faster! (Cochran & Harpending, 2009; Hawks et al., 2007; Rinaldi, 2017).

What exactly was causing this acceleration? In part, humans were adapting to new diets, particularly grains instead of fruits, tubers, and vegetables. They were also adapting to infectious diseases — smallpox, typhus, cholera, bubonic plague — which could spread like wildfire through towns and cities.

Above all, our ancestors were adapting to new ways of using their minds. As society became more complex, they had to evaluate a larger number of people who were neither close kin nor close friends. They also had to decode a greater amount of encoded information — not only in speech but also on surfaces of clay, papyrus, and parchment. Finally, they had to make a wider range of objects from a wider range of materials, first wood and stone, then metal, glass, and gems.

All of this required an increase in the capacity to process information, recognize patterns, and solve problems — in other words, an increase in cognitive ability.

First cognitive advance: the peopling of northern Eurasia

We will focus here on ancestral Europeans, beginning with those modern humans who entered northern Eurasia some 30,000 years ago, long before farming and the cultural changes it caused.

At that time, cognitive ability still served to meet the challenges of hunting and gathering. Those challenges were especially great in cold environments, as shown by the inverse correlation between temperature and technological complexity in present-day hunter-gatherers.

Figure 1: Inverse correlation between technological complexity and temperature in present-day hunter-gatherer groups (Hoffecker, 2002, p. 10).

The most challenging environments were in northern Eurasia until the end of the last ice age some 10,000 years ago. Food was potentially abundant but almost wholly “meat on the hoof” — herds of wandering reindeer and other herbivores. That food was inaccessible unless one could:

• collect, process, and remember huge quantities of spatiotemporal data to track the herds, predict their movements, and find one’s way back to camp;

• monitor untended traps and snares to capture solitary animals, which were dispersed over a larger territory than in warmer environments and took too much time to hunt;

• make cold-resistant shelters and clothing;

• plan ahead to store fuel for winter and food for times of need.

Other cognitive challenges arose from a new sexual division of labor. Because women had few opportunities for food gathering, they specialized much more in higher-order tasks: weaving, needlework, leatherwork, garment making, pottery, kiln operation, shelter building, and food processing.

For all of the above reasons, northern Eurasians were selected for higher cognitive ability, as shown by the positive correlation between latitude and brain size. Indeed, brain size correlates with latitude not only in humans and other hominids but also in any animal that remains active during winter. As a general rule, cognitive demands are higher in colder, more seasonal environments (Beals et al., 1984; Frost, 2019a; Kirkegaard, 2022).

Northern Eurasians were thus “pre-adapted” for the cognitive demands of complex societies in the future — including many that would arise among humans native to the temperate and tropical zones. Such societies would be repeatedly taken over and replaced by northern Eurasians who, though less adapted climatically, could better exploit the possibilities being created.

Figure 2: Human variation in cranial capacity. Black, 1,450 cc and over; checkerboard, 1,400-1,449 cc; crosshatching, 1,350-1,399 cc; horizontal striping, 1,300-1,349 cc; diagonal striping, 1,250-1,299 cc; dots, 1,200-1,249 cc; white areas, under 1,200 cc (Beals et al., 1984).

Second cognitive advance: the rise of farming

Hunting persisted after the ice age, but the cognitive demands were no longer the same. The tundra was now boreal forest, where hunters pursued solitary animals over short distances, rather than large herds over longer distances. So the human mind had less need to store and process huge quantities of spatiotemporal data. Shorter hunting distances, followed by the shift to farming and sedentism, may explain why brain size decreased during post-glacial times, a trend that has been shown for European and Chinese populations but not for tropical ones, like the Nubians (Hawks, 2011). Did the decrease in brain size reflect a decrease in cognitive ability? Or was cognition simply reoriented toward tasks that consume less memory? Perhaps the excess mental capacity made new tasks easier to create and develop.

About 12,000 years ago, farming replaced hunting and gathering in the Middle East, followed by southeast Europe three thousand years later. Over the next thousand years, this new form of subsistence would spread north and west to a line stretching from the Netherlands to the Black Sea. After a pause, it resumed its advance and was still spreading into northern Europe on the eve of recorded history.

We have retrieved enough DNA from European remains to chart the evolution of cognitive ability since the advent of farming (Akbari et al., 2024; Kuijpers et al., 2022; Piffer et al., 2023). To be precise, we can chart changes in the population frequencies of alleles associated with intelligence, fluid intelligence, educational attainment, and household income — all of which are highly correlated with cognitive ability. Of course, these measures may also track other mental abilities, like proactiveness and rule following. If you show initiative and follow the rules, you will go farther at school and earn more money, independently of your cognitive ability.

Not much DNA is available from the Paleolithic or the Mesolithic, but the little we have indicates no change in mean cognitive ability during the long period of hunting and gathering. If more DNA becomes available, we should break it down by region. Did cognitive ability differ between the Arctic-adapted hunter-gatherers of northern Europe and those of central and southern Europe?

Around 9,000 years ago, Europeans became sufficiently numerous to provide enough DNA for study. Mean cognitive ability was now rising, apparently with the spread of farming into Europe, and the rise was especially steep until 7,000 years ago. Was this initial surge due to the cognitive demands of farming? Perhaps. But we should not rule out the consequences of admixture from indigenous hunter-gatherers. Admixture certainly occurred, for the earliest farmers looked distinctly more African than the later ones (Angel, 1972; Brace et al., 2006; Frost, 2015). As farmers spread into Europe, they must have mixed more and more with the indigenous hunter-gatherers, including northern groups that had previously adapted to Arctic environments.

This admixture is difficult to quantify. We could assume that Middle Eastern ancestry corresponds to the genetic difference between farmers and hunter-gatherers, but that assumption would be wrong. Some of the difference would also be due to founder effects, and some to natural selection. For instance, haplogroup U is often cited as a genetic marker of indigenous hunter-gatherers, yet it disappeared from Europe long after the transition to farming, probably because it was no longer needed (Melchior et al., 2010). This haplogroup shifts the energy balance toward production of body heat — an advantage for people who sleep in makeshift shelters and pursue game in all kinds of weather (Balloux et al., 2009).

In sum, we over-estimate Middle Eastern ancestry if we assume that all genetic change across the hunter-gatherer/farmer time boundary is due to the latter replacing the former. This change also includes “false positives”:

• alleles that may have originated among farmers but then steadily increased through natural selection in the farming population — regardless of its degree of hunter-gatherer ancestry.

• founder effects among those hunter-gatherers who joined farming communities. These effects were random but a certain number would be "false positives" and wrongly indicate farmer ancestry.

• convergent evolution, where similar selection pressures produced similar genetic adaptations in those hunter-gatherers who adopted farming.

The initial cognitive surge may thus reflect an ongoing inflow of ex-hunter-gatherers into farming communities — as spouses, as captives, or even as landowners with a right to settle there. Anthropologists have observed all three scenarios, and it is impossible to say which one applies here. Whatever the scenario, these ex-hunter-gatherers became much more present in DNA samples from archeological sites, which, in most cases, had been farming communities. It may therefore be no coincidence that the steep rise in mean cognitive ability began roughly when the advancing farmers first encountered the hunter-gatherers of northern and eastern Europe — who had adapted to the high cognitive demands of Arctic environments.

So the subsequently slower rise should not mislead us. Cognitive evolution did not slow down; rather, with no hunter-gatherers remaining to be assimilated, this evolution would be driven only by the cognitive demands of farming and the progressive increase in social complexity.

Social stratification

Subsequent evolution would also be driven by a stronger linkage between cognitive ability and reproductive success. Farming created a storable food surplus that fell under the control of powerful families, thereby increasing their power further (Harris, 1959; Testart et al., 1982). Society thus became stratified, and this stratification would determine the pace of cognitive evolution through a continual replacement of lower social classes by higher ones:

• Alleles associated with high cognitive ability became concentrated in the dominant class through the rise of more capable individuals and the fall of less capable ones.

• Because this class enjoyed higher fertility and lower mortality, it produced more offspring than could be supported by niches at the same social level.

• Surplus offspring moved down into niches left vacant by the lower classes, which had lower fertility and higher mortality.

• The lower classes were thus continually replaced by the higher ones, with the result that mean cognitive ability steadily rose from one generation to the next.

The same “rinse and repeat” cycle has been described by Gregory Clark in his work on English demography from the Middle Ages onward (Clark, 2007; 2009; 2023).

Pacification of social relations

Stratification would also assist cognitive evolution through a less direct chain of causation:

• Emergence of the State - Powerful families initially asserted their power through physical strength, charisma, and eloquence. This power gave them control over key resources, particularly the food supply, which enabled them to increase their power further — through a self-reinforcing feedback loop. In particular, they could hire young men for a personal guard and, eventually, an army. This was how the State came to be.

• Imposition of a State monopoly on violence - To eliminate potential rivals, the State reserved the use of violence to itself alone and maintained this monopoly by eliminating any man who used violence on his own initiative.

• Pacification of social relations - By eliminating such men, the State pacified not only social relations but also, over time, the gene pool: alleles associated with male violence were selected out, while those associated with deference and submission were selected in.

• Expansion of trade and other activities with high cognitive input - Peaceful interactions became the norm. Eventually, most men could live their entire lives without having to defend themselves or their families. They were free to devote themselves to other activities, including many that required specialized skills. Trade in particular benefited, both between and within communities. There thus arose a new kind of man who was not only less aggressive but also better able to handle the cognitive demands now possible (Frost, 2010; Frost & Harpending, 2015).

Figure 3: Changes in European DNA over the last 9,000 years for alleles associated with intelligence, household income, and years of schooling. Note the steep rise when farming replaced hunting and gathering. Also note the decline during the time of Imperial Rome (Akbari et al., 2024).

First cognitive retreat: the Imperial Era of Rome

Mean cognitive ability rose throughout the Neolithic and into historic times — a process eventually culminating in the civilizations of Greece and Rome. In this flowering of material and intellectual culture, the most intelligent individuals could go far beyond satisfying their basic needs and ask questions about the world, thus laying the groundwork for philosophy, mathematics, history, geography, astronomy, and other fields of enquiry.

But it was not to last. According to ancient DNA from central Italy, mean cognitive ability rose under the Roman Republic but then fell sharply under the Roman Empire. It would then rise again from Late Antiquity to post-medieval times (Piffer et al., 2023). The decline of the Imperial Era seems to have been confined to Roman territory, as it does not clearly show up in the first two studies of DNA from Europe as a whole (Kuijpers et al., 2022; Piffer & Kirkegaard, 2024), while appearing in the latest study, which used a larger dataset (Akbari et al., 2024).

Figure 4: Rise, fall, and renewed rise of mean cognitive ability in central Italy, as measured by alleles associated with educational attainment (EA4) (Piffer et al, 2023, Figure 1)

The cognitive decline of Imperial Rome likely had three causes:

• Decrease in fertility and family formation among the elite (Caldwell, 2004; Hopkins, 1965; Roetzel, 2000, p. 234; Sullivan, 2009, pp. 27-28, 35-38).

• Hypogamy between elite men and lowborn women, often in the form of polygyny with slave women or newly freed women. Elite women thus lost reproductive importance (Perry, 2013).

• Increase in the slave population, particularly foreign slaves (Harris, 1999. Previously, if elite offspring failed to find niches within their social level, they could move farther down the social ladder, but that option disappeared once those niches had been filled with slaves. Thus ended the “rinse and repeat” cycle of cognitive evolution.

This new social environment changed the life goals of the elite, causing them to value material wealth over family life. Sexual needs, though still important, could now be satisfied in less entangling ways, with slaves or prostitutes.

Some emperors challenged the new normal but ran into resistance from the very people whose lineages were dying out (Sullivan, 2009). In 27 BCE, Augustus Caesar condemned childlessness in a speech to Rome’s equestrian class:

For you are committing murder in not begetting in the first place those who ought to be your descendants; you are committing sacrilege in putting an end to the names and honours of your ancestors; and you are guilty of impiety in that you are abolishing your families, which were instituted by the gods, and destroying the greatest of offerings to them — human life. [Cassius Dio. Roman History, 56.5.2]

A related problem was the growing dependence on slavery, particularly for agriculture, which made the Empire ever more vulnerable to disturbances from within and without. Because slaves wished to grow only enough food for their own needs, they had to be coerced to meet the greater needs of the Empire (Harper, 2011, pp. 176, 250-254). Whenever coercion weakened during times of unrest or invasion, production fell and Romans starved. The slaves knew this. Everyone knew this.

But the benefits of slavery were difficult to ignore, and they were not simply economic. There were also the personal benefits for slaveowners, especially the access to young women without the restrictions and obligations of marriage. Slaves knew this weakness, as attested by a character in a 5th-century comedy: “We all steal and no one turns traitor, for we are all in it together. We watch out for the master and divert him, for slaves and slave-girls are in alliance” (Harper, 2011, p. 251).

One outcome was a growing number of alumni — offspring of masters and slave girls, or any slave children for whom the master had developed affection. If a master had no children by his wife, he could leave his property to such alumni (Rawson, 1986, 2014, pp. 173-179). Consequently, elite men were not just having fewer offspring by their wives; they were also having more by lowborn mistresses or simply adopting any the latter already had. Either way, Rome’s elite was no longer passing on its characteristics to future generations.

Rome needed a moral revolution. When Constantine the Great legalized Christianity, he saw it as a means to revitalize the Empire. Was he himself a Christian? Doubtful. His edicts were more consistent with a pagan mindset. One edict ordered the execution of any woman who had become involved with or married a slave, as well as the burning of her slave partner. Another authorized torture of slaves as a means to ascertain the truth (Thompson, 2008).

Third cognitive advance: the rise of Christianity

The cognitive decline of Imperial Rome reversed with the recognition of Christianity as a legal faith in 313 and as the State religion in 380. This reversal coincided with the growing power of the Church to intervene in many areas of life, especially marriage and procreation. In particular, the Church aggressively pushed monogamy and forced men to focus on procreation with a lawful wife, usually of similar status, rather than on sex with prostitutes or slave women. Successful men were now more likely to pass on the qualities of mind and behavior that had made them successful.

Did the new faith have that goal in mind? To some extent, yes. Early Christians understood that some lifestyles are more procreative than others. They also understood the basics of population genetics: 1) humans inherit not only physical traits but also mental and behavioral ones; 2) the latter vary not only among individuals but also among populations; and 3) selection for such traits will progressively change a population over successive generations.

This understanding of genetics was put into writing by Origen of Alexandria (c. 185–253 CE), a theologian who wrote over two thousand treatises on many subjects. Of course, the term “genetics” did not yet exist. He spoke instead of logoi spermatikoi, “the principles of the seed.” Logoi is difficult to translate; it conveys the idea of information that brings order out of disorder.

As Origen explained it, “the seed of someone has within itself — still immobile and placed in reserve — the procreator’s logoi” (Origen, Commentary on the Gospel of John, XX, 3).

This seed, which organizes both body and spirit, is passed down from one’s ancestors:

Just as among the seeds of the body there emerges sometimes, from a great number, a seed endowed with a greater capacity for action, so may we observe the same phenomenon with the seeds of the spirit. What I have said will become clear after what follows: since the procreator has within himself logoi from his ancestors and his collateral lines, it is sometimes his logos that prevails — and the child that comes into the world resembles its procreator — or sometimes the logos of his brother, his father or his uncle, sometimes even his grandfather. This is why those who come into the world resemble one or another [of that line]. We may equally see the wife’s logos prevail, or that of her father, her brother or her grandfather … (Origen, Commentary on the Gospel of John, XX, 35-36)

These logoi vary among humans:

It is evident that men have not all come into human life with absolutely identical logoi spermatikoi seeded into their souls. (Origen, Commentary on the Gospel of John, XX, 5)

Try to imagine whether it is not without reason that God destroys certain seeds in order to prevent the bad ones from multiplying on the earth, once there have been sown those [seeds] whose tendencies are not from the best, and to cultivate the products of superior seeds. This is why the Flood happened, to wipe out the seed of Cain … (Origen, Commentary on the Gospel of John, XX, 25)

Another theologian, Augustine of Hippo (354–430 CE), likewise understood that people differ innately in body and spirit, particularly in the power to distinguish bad desires from good ones and the power to put the latter into effect. He initially believed that these powers could be lacking only in a non-Christian, but he later acknowledged that a Christian could lack them too, despite baptism (Pang-White, 2001). Thus, a sinful act may arise from a weakness of will, rather than from a will to do wrong:

Whatever these souls do, if they do it by nature, not by will, that is, if they lack a movement of the spirit [that is] free both to do and not to do, if finally, no power of abstaining from their action is given to them, we cannot consider the sin theirs. (Augustine, Retractationes 1,14, 6)

Although such people are not responsible for their weakness of will or their inability to understand rules, they should still be shunned and resisted:

… But they are an evil for us if we are enticed and led astray by them; if, however, we are on our guard against them and overcome them, it is an honorable and glorious thing. (Augustine, Retractationes 1,14, 7)

In sum, Christianity reversed the cognitive decline of Imperial Rome, thereby launching an upward trend that would last throughout the Christian Era. The reversal was achieved by increasing the reproductive importance of elite women, essentially by limiting polygyny between elite men and lowborn women. Polygyny was already forbidden by pagan Roman law, but that ban had been ignored and openly flouted. Thus, in this and other ways, the new faith changed the culture not so much by making new rules as by reviving old rules and enforcing them more effectively.

Indeed, Christianity was much more rules-based than paganism, particularly the watered-down version of the Imperial Era. Pagans were more interested in developing a transactional relationship with their favorite god: “do this for me, and I’ll do that in exchange.” Their “religion” was not one as we understand the term:

It might be less confusing to say that the pagans, before their competition with Christianity, had no religion at all in the sense in which that word is normally used today. They had no tradition of discourse about ritual or religious matters (apart from philosophical debate or antiquarian treatise), no organized system of beliefs to which they were asked to commit themselves, no authority-structure peculiar to the religious area, above all no commitment to a particular group of people or set of ideas other than their family and political context. (North, 2013)

Christianity may have therefore assisted cognitive evolution not only indirectly, by increasing the reproductive importance of elite women, but also directly — by rewarding those individuals who could better learn and follow rules, while punishing those who could not. Rule following requires cognitive ability, while soliciting other mental domains and their underlying genetic factors (O’Gorman et al., 2008; Sasaki et al., 2013).

Fourth cognitive advance: the rise of the middle class

In the late Middle Ages, northern and western Europe became consolidated into a few nation states that expanded outward, first within Europe and then beyond. Eventually, these states would dominate the world, as evidenced not only by their colonial empires but also by their ascendancy in trade, science, technology and almost any other field of activity.

Meanwhile, cognitive evolution accelerated among Europeans. Between the Middle Ages and the present, mean cognitive ability rose substantially — by one third to one half of a standard deviation (Frost, 2024; Piffer & Kirkegaard, 2024). The actual increase may have been even greater, since it is imperfectly measured by a comparison between medieval and contemporary genomes. At one end of the timeline, this increase had already begun before the end of the Middle Ages (Clark, 2007). At the other end, it likely leveled off in the late 19th century and was followed by a decline throughout the 20th (see last chapter of the present article).

Differences in timeline may explain why the cognitive increase seems smaller for England than for Europe as a whole, i.e., the increase began earlier and ended earlier in England. European genomes thus fit better into the medieval vs. contemporary comparison. On a side note, the cognitive increase is underestimated by alleles associated with socioeconomic status (SES), perhaps because such alleles favor aspects of mind and behavior that contribute much more today to social and economic success than they did in the past.

Figure 5: Size of the cognitive increase in S.D. (Cohen’s d) for England and for Europe as a whole, as measured by alleles associated with EA3, EA4, IQ, and SES (Piffer & Kirkegaard, 2024). EA3 is based on alleles identified by Lee et al. (2018). EA4 is based on alleles identified by Okbay et al. (2022).

This cognitive increase brought a corresponding growth of the “smart fraction” — the proportion of highly gifted people. No longer voices in the wilderness, they could now gather in salons or coffeehouses, come together in learned societies, and publish their ideas in academic journals. This intellectual ferment became known as “the Enlightenment” and would affect all domains of production — not only the sciences but also literature, music, and the arts (de Courson et al., 2023).

In addition, a growing share of the population was rising above a lower but equally crucial cognitive threshold. Previously, most people failed to develop beyond the stage of preoperational thinking. They could learn language and social norms but their ability to reason was hindered by cognitive egocentrism, anthropomorphism, finalism, and animism. From the 16th century onward, more and more people were capable of operational thinking. They could better understand probability, cause and effect, and another person’s perspective, whether real or hypothetical (Rinderman, 2018, pp. 49, 86-87; Oesterdiekhoff, 2012).

But cognitive ability was not the sole mental trait behind the rise of northwest Europeans to global dominance. Some human groups have never achieved the same dominance, while having comparable or even higher levels of cognitive ability. Think of the Parsis, the Igbo, the Ashkenazim, or even the Chinese. Something held them back while pushing northwest Europeans forward.

Was it colonialism? The slave trade? The printing press? The Reformation? All of them together?

Yet in the 14th century — well before any of the above — England and Holland were already surpassing the rest of the world in GDP per capita growth (Frost, 2022a; Greer, 2013a; Greer, 2013b). This trajectory can be traced back to the 7th century, when trade began to intensify among the North Sea peoples (Melleno, 2014). Their network of exchange steadily grew in scale and in scope — through the commercialization of land, labor, and capital that used to exist outside the market economy.

Those traders were able to transcend their ties of kinship and organize new and more flexible relationships with a potentially much larger population. In this, they were unlike other trading peoples for whom a “market” was merely a marketplace — a small island of exchange limited in time and space, beyond which a person would usually produce not for a market but for family, kin, and lord. The North Sea traders were the first to break free of this economic model. They and their descendants would extend the market principle to society as a whole, thereby making kinship obsolete.

A different mindset

Initially, this trajectory was not made possible by a high level of cognitive ability. Although IQ scores and PISA results tend to be higher in the north and west of Europe, and lower to the south and east, this gradient seems to be relatively recent — an outcome of cognitive evolution since the late Middle Ages (Frost, 2022b; Jensen & Kirkegaard, 2024; Piffer & Lynn, 2022). Selection for cognitive ability was a consequence of the rise of northwest Europe, rather than an initial cause.

The initial cause was a pre-existing mindset that expressed itself in a behavioral pattern of greater individualism and weaker kinship. This pattern has prevailed, and still does, north and west of a line running from Trieste to St. Petersburg, the so-called “Hajnal Line.” It is characterized by:

• solitary living for at least part of adulthood, with many individuals remaining single their entire lives;

• departure from home on reaching adulthood, either to form a new household or to circulate among unrelated households, typically as servants;

• greater individualism, less loyalty to kin, and more willingness to trust strangers;

• impersonal pro-sociality, i.e., social interaction that is less emotionally intense while encompassing more people (Schulz et al., 2019; see also Frost, 2017; Frost, 2020; Hajnal, 1965; Hartman, 2004; hbd*chick, 2014; ICA, 2020; MacDonald, 2019; Seccombe, 1992, pp. 94-95, 150-153, 184-190).

The underlying mindset may be summarized as follows:

Moral universalism and moral absolutism. Rules are followed more willingly if framed in universal and absolute terms, as opposed to the situational and relativistic framing of kinship.

Moralized perception of non-kin. Help is provided to non-kin if they belong to the same community of rule followers. Continual rule breaking leads to expulsion from the community. Insiders are thus separated from outsiders by a line dividing the morally worthy from the morally worthless. Xenophobia is thus much more a moral judgment than a simple rejection of the “Other.”

Proneness to guilt. Rule breaking is punished much more by guilt than by shame. A rule breaker feels guilt even when no one else has witnessed the rule breaking. Shame is felt only when others have witnessed it. Guilt is thus internally generated, whereas shame is socially imposed (Benedict, 1946).

Broader range of targets for affective empathy. Affective empathy is extended from the mother-child relationship to all social relationships. Through this involuntary transfer of another person’s feelings to oneself, rule breaking is thus emotionally experienced as harm not only to the other person but also to oneself. Affective empathy and guilt may be two aspects of the same mental mechanism (Frost, 2017; Frost, 2020).

Christian or pre-Christian origin?

The “northwest European mindset” is attributed by some to Western Christianity and by others to earlier causes. The first scenario is situated in the early Middle Ages when the Western Church severely limited cousin marriages and thereby encouraged individualism through weaker kinship ties. Previously, only first-cousin marriages had been banned. That ban was initially extended two degrees further in the 7th century, when the Church adopted the anti-incest prohibitions of the Visigothic Code. Then, in the early 9th century, the Church began to calculate degrees of kinship through the so-called “Germanic system,” thus doubling the number of forbidden marriage partners. This extreme ban on cousin marriages may have therefore come from norms that had already existed among northwest Europeans, particularly the Germanic tribes (Frost, 2020; McCann, 2010, pp. 57-58; Policy Tensor, 2021; Schulz et al., 2019).

Those norms were certainly enforced more effectively by the Church, but their actual origin seems to be pre-Christian. In the 9th century, when the extreme ban on cousin marriages was introduced, French households were already small and nuclear, with 12% to 16% of adults being unmarried and with adults usually marrying in their mid to late twenties (Hallam, 1985, p. 56; Seccombe, 1992, p. 94). This pattern of delayed marriage seems to have been present even further back in time, as suggested by the writings of Julius Caesar and Tacitus on the Germanic tribes of Antiquity:

Those who have remained chaste for the longest time, receive the greatest commendation among their people: they think that by this the growth is promoted, by this the physical powers are increased and the sinews are strengthened. And to have had knowledge of a woman before the twentieth year they reckon among the most disgraceful acts. Caesar, De Bello Gallico 6: 21

Late comes love to the young men, and their first manhood is not enfeebled; nor for the girls is there any hot-house forcing; they pass their youth in the same way as the boys. Tacitus, Germania 20

We now come to the second scenario, which is situated before Christianity, specifically in post-glacial times among the fishing peoples of the North Sea and the Baltic. Unlike other hunter-gatherers, they lived in large semi-sedentary communities thanks to an abundance of fish, seals, and shellfish (Price, 1991). They thus had to solve the “large society problem” at an early date, and not necessarily as later peoples would. Perhaps they reduced clannishness by discouraging cousin marriages and by imposing the same universal rules on all community members. Kin-based morality would thus give way to moral universalism and moral absolutism. This cultural evolution could have then acted as a template for genetic evolution (Frost, 2020).

Whatever its origin, this mindset would enable northwest Europeans to organize themselves into ever-larger entities, to a degree that would be impossible elsewhere because of kinship rivalries and loyalties. Such entities included not only the market economy, but also the nation state and the Church as a parallel state.

Rise of the State, the Church, and the market economy

The rise of these larger entities — the State, the Church, and the market economy — would trigger the cognitive advance of late medieval and post-medieval times, first in England and then, increasingly, across the whole continent.

The High Middle Ages (1000 - 1300 CE) saw the rise of the modern Western State, particularly its power to subdue local strongmen and enforce the rule of law. Meanwhile, the Church came to accept the need to execute violent males so that good men and women could live in peace. There thus emerged a State-Church consensus in favor of capital punishment. Courts imposed it more and more often and, by the late Middle Ages, were condemning to death between 0.5 and 1.0% of all men of each generation, with perhaps just as many offenders dying at the scene of the crime or in prison while awaiting trial. As a result, the homicide rate fell from between 20 and 40 homicides per 100,000 in the late Middle Ages to between 0.5 and 1 per 100,000 in the mid-twentieth century. The pool of violent men dried up until most murders occurred under conditions of jealousy, intoxication, or extreme stress. (Frost & Harpending, 2015).

The outcome was an ever-larger space for peaceful production and exchange. This space offered niches for individuals with the requisite cognitive skills, notably literacy, numeracy, and planning, as well as a desire to advance peacefully in life through trade and work, rather than theft and plunder.

Their descendants — the future middle class — would grow in number with the expansion of the market economy, eventually representing, in the case of England, the majority of lineages in the population. The historical economist Gregory Clark has argued that this demographic change brought a behavioral change: "Thrift, prudence, negotiation, and hard work were becoming values for communities that previously had been spendthrift, impulsive, violent, and leisure loving” (Clark, 2007, p. 166; Clark, 2009; Clark, 2023; Frost, 2022b).

The middle class grew especially through a population boom among “proto-industrial” artisans — semi-rural cottagers who produced on contract for urban merchants. This boom was due to a combination of low mortality and high fertility. Mortality was low because these artisans lived away from urban areas, where population growth was held in check by disease and malnutrition. Fertility was high because they employed their own family members, and thus had only one means to expand their workforce:

The family economy of cottage proto-industrialists was fundamentally different from that of either urban artisans or self-sufficient peasant agriculturalists. … The labour team of proto-industrial households was normally comprised exclusively of family members. Parents could not afford to retain live-in servants or hire others … (Seccombe, 1992, p. 183)

Because these artisans operated in elastic, competitive markets, some of them did much better than others. And because of the tight linkage between economic and reproductive success, some of them had many more children than others — generally by marrying earlier and by helping their offspring do likewise.

This type of cottage industry emerged in the 15th century and reached its peak in the 17th, 18th, and early 19th centuries. It existed across most of Europe but was especially concentrated in the semi-rural areas of Westphalia, Saxony, the Zurich uplands, Piedmont, Lombardy, Alsace, Flanders, Brittany, Lancashire, Yorkshire, and Ulster (Seccombe, 1992, pp. 205, 217). These regions would contribute disproportionately to the gene pool of modern Europe, thereby creating a cognitive gradient between Western Europe and those regions where cottage industry appeared later and to a lesser extent (Frost, 2022c; Jensen & Kirkegaard, 2024; Piffer & Lynn, 2022).

Beyond Western Europe, this gradient tends to coincide with cultural boundaries, since some cultures were more inclined than others to participate in the emerging market economy. Ashkenazi Jews, in particular, benefited from the more dynamic economic environment that prevailed from the late Middle Ages onward. Their numbers grew in Eastern Europe from a little over 7 thousand in the 12th century to over 8 million by 1900. The population boom seems to have been driven by successful traders and artisans translating their economic success into demographic success, partly because they saw procreation as a desirable goal in itself, and partly because they relied primarily on a family workforce (Cochran et al., 2006; DellaPergola, 2001; Frost, 2022b; Murray, 2007).

This rapid population growth thus caused equally rapid cognitive evolution. Of all human populations, Ashkenazim today have the highest frequencies of alleles associated with educational attainment, and this genetic profile corresponds closely to their IQ scores (Dunkel et al., 2019; Piffer, 2019).

One result was an increase in alleles associated with nine neurological disorders: Tay-Sachs (two unrelated alleles); Gaucher's (five unrelated alleles); Niemann-Pick; and Mucolipidosis Type IV. These disorders affect the capacity of neurons to store sphingolipids, which are vital to neuronal growth. Thus, nine mutations have independently reached high frequencies in the same metabolic pathway, in the same population, and in the same time period. The proximate cause seems to be unusually strong natural selection operating through heterozygote advantage: if just one parent has the mutation, as more often happens, the child suffers no adverse effects; in fact, the child's neurons are better supplied with sphingolipids (Cochran et al., 2006; Diamond, 1994). Evidently, these alleles are a fraction of a much larger number of alleles that explain the higher cognitive ability of Ashkenazi Jews.

Figure 6: Distribution of IQ scores and alleles associated with educational attainment (PGS), Wisconsin Longitudinal Study (Dunkel et al., 2019, Figure 1)

The same late medieval/post-medieval cognitive surge seems responsible for a cognitive gradient on the Italian peninsula. Students from the north consistently outperform those from the south on the INVALSI, an annual exam in Italian schools. Academic performance differs on average by a little over half a standard deviation (Piffer & Lynn, 2022).

This difference is paralleled by a difference in alleles associated with educational attainment, as shown by a study of 1,076 individuals whose grandparents were born in the same Italian region. The data revealed “a clear north-south gradient, with central Italians occupying an intermediate position” (Piffer & Lynn, 2022). The cause is likely a post-medieval divergence: the south participated much less in the emerging market economy and, by the 18th century, was lagging far behind the north; its middle class was still small and economic relationships were still structured by paternalism and familialism (De Rosa, 1979).

Figure 7: Distribution of alleles associated with northern and southern Italians (Piffer & Lynn, 2022, Figure 2)

In sum, it was the tight linkage between economic and reproductive success in an expanding market economy that drove the fast cognitive advance of late medieval and post-medieval times. One could imagine a positive feedback loop: 1) as the market economy expanded, it created niches that could be filled only by individuals with a certain level of cognitive ability; 2) such individuals translated their economic success into reproductive success, thus raising mean cognitive ability; 3) as mean cognitive ability rose, the smart fraction could come up with better products and better ways of doing things, thus spurring further expansion of the market economy.

Second cognitive retreat: the Era of Industrial Capitalism

The middle-class baby boom began to run out of steam in the late 19th century. Household workshops, where family members did the work, gave way to factories, where it was done by employees. A successful entrepreneur could simply hire more workers, instead of marrying earlier and having more children. Children thus became a net economic cost, rather than a net economic benefit — all the more so because this cost came on top of the many others now needed to maintain a middle-class lifestyle: a big home, a summer cottage, a luxury car, a college education for the kids, and so on.

For all these reasons, the middle class had fewer and fewer children. The result would be a decline not only in fertility but also in mean cognitive ability, as shown by several lines of evidence.

Alleles associated with educational attainment

We have already seen this measure. It is constructed from the human genome, specifically from alleles associated with differences in educational attainment (EA) — a good proxy for cognitive ability. In an initial study, such alleles were identified at 1,271 loci in over one million people. Using them, we can calculate an "EA polygenic score" that explains 11-13% of the differences in educational attainment among individuals (Lee et al., 2018). In a more recent study, EA-associated alleles were identified at 3,952 loci in about three million people. The resulting EA polygenic score explains 12-16% of the differences in educational attainment among individuals (Okbay et al., 2022). Although this score is still unreliable for measuring the IQ of any one individual, it is a much better measure of mean population IQ — the correlation being 90% between the two (Piffer, 2019).

The following studies concern successive age cohorts within a single population. In all three cases, the mean polygenic score fell during the 20th century from one cohort to the next.

Americans

This study used data taken from Americans shortly before and during retirement, specifically 11,822 Americans of European ancestry born between 1931 and 1953 (Beauchamp, 2016).

From 1931 to 1953, each successive age cohort had, on average, fewer alleles associated with educational attainment. The decline seemed to be due to lower fertility among those participants who had pursued higher education. The mean EA polygenic score was thus significantly higher among the childless than among individuals with one or more children.

This study, like the next two, may suffer from survivorship bias — if you manage to live to an old age, you are probably smarter than average (Gottfredson & Deary, 2004). The bias must be small, however, since 85% of the original participants were still alive in 2008, the last year of genotyping.

Figure 8: Mean EA polygenic score as a function of lifetime reproductive success (LRS) (Beauchamp, 2016, Fig. 2)

British

This study used UK Biobank data, specifically 409,629 British individuals of European origin from two successive generations. The median birth year was 1950 for the second generation and unknown for the first (Hugh-Jones & Abdellaoui, 2022).

The second generation had fewer alleles associated with educational attainment, particularly at lower incomes. Conversely, there were increases in the frequencies of alleles associated with obesity, attention deficit hyperactivity disorder, depressive disorder, schizophrenia, neuroticism, and male extraversion.

This generational change may be underestimated because the childless individuals of the first generation were necessarily excluded.

Icelanders

This study used data from a genealogical database (deCODE genetics), specifically 129,808 Icelanders born between 1910 and 1990 (Kong et al., 2017).

The mean EA polygenic score fell at a rate of about 0.010 standard deviation per decade, with one pause in the 1950s and another in the 1970s. The first pause coincided with the post-war boom and a corresponding improvement in the ability of middle-class couples to start a family early in life. The second pause might reflect a law passed in 1975 to liberalize access to abortion in cases of rape, mental disability of the mother, and “difficult family situation” (Wikipedia, 2025a)

This cognitive decline was due only in part to the more intelligent staying in school longer and postponing marriage. Some of it was independent of higher education, perhaps because smarter people — irrespective of whether they go to university — tend to plan ahead and postpone family formation until they are financially ready. Survivorship bias was not a major factor in this study, being low for the last five cohorts born since 1940 and especially low for those born in the 1970s and the 1980s.

Figure 9: Mean polygenic score of Icelanders by year of birth for alleles associated with educational attainment (Kong et al., 2017, Fig. 2)

Brain size

This measure correlates moderately with IQ (r = 0.2 to 0.4) and is obtained through MRIs, autopsies, and anthropometry (Lee et al., 2019).

Americans (Framingham Heart Study)

In Framingham, Massachusetts, three generations have been examined since 1948 to understand the causes of heart disease. In particular, brain MRIs were done each year between 1999 and 2019 on 4,506 individuals born between 1902 and 1985. For each successive decade of birth, brain volume increased by 1.7 cc for men and 1.2 cc for women (DeCarli et al., 2023).

This seems to be evidence for an increase in cognitive ability. However, the cohorts are not comparable: the older ones were mill and factory workers, while the younger ones tended to be college-educated nurses and doctors:

Requirements for entry [into the Framingham Heart Study] were an age between 30 and 62 years at the time of first examination, with no history of heart attack or stroke. Due to lukewarm interest at first, doctors, nurses and healthcare workers volunteered for the study to set an example for patients. (Wikipedia, 2025b).

The presence of these younger, better educated volunteers likely explains the correlation between brain size and decade of birth. Indeed, the proportion of college-educated participants rose by decade of birth, reaching a peak of nearly 92% for women born in 1970 (DeCarli et al., 2023).

Americans (Forensic Anthropology Data Bank)

According to data from the Forensic Anthropology Data Bank, mean brain size increased among Americans between 1820 and 1920 with no further improvement during the time of the Flynn effect (Jantz & Jantz, 2016). Was this increase due to better nutrition or less childhood disease? Infant mortality is a good proxy for both, and it did not begin to fall until the turn of the 20th century. Since we have no data from before 1820, the increase in brain size may be the tail-end of a longer-term increase that began in late medieval times with the growing contribution of the middle class to the gene pool.

British and Germans (autopsies)

Three autopsy datasets, one from the UK and two from Germany, show a rise in brain weight by year of birth from the mid-19th century to the mid-20th. In the British dataset, male brains increased by 52 grams and female brains by 23 grams. In the German dataset, male brains increased by 73 grams and female brains by 52 grams (Haug, 1984; Kretschmann et al., 1979; Miller & Corsellis, 1977; Woodley of Menie et al., 2016).

Again, this seems to be evidence for an increase in cognitive ability. Unfortunately, the age cohorts suffer from collection bias, particularly the earlier ones. During the 19th century, autopsies were done largely on charity cases and condemned criminals because of the stigma attached to cutting up a dead body: “dissection was considered a ‘degrading and sacrilegious practice’ and was something reserved as a form of extra punishment for executed criminals” (Nystrom, 2011).

Attitudes changed during the 20th century, and autopsies became more socially acceptable. The increase in brain size may therefore be due to a more representative sampling of the population.

Estonians (anthropometry)

In Soviet Estonia, cranial volume was measured for an anthropometric survey of students born between 1937 and 1962 (7,123 boys and 9,866 girls). Volunteer bias was nonexistent because the measurements were mandatory, and mortality bias was minimal because the participants were all younger than 20 (Hõrak & Valge, 2015; Valge et al., 2021; Valge et al., 2022).

Girls with larger crania were more likely to pursue higher education. They thus married later and had fewer children. Throughout the 20th century, Estonian women with only primary education bore 0.5 to 0.75 more children on average than women with tertiary education. In contrast, higher education had no effect on male fertility. The most fertile men had average-sized crania.

Reaction time

This measure is the speed at which the brain processes information. It has a moderate to high correlation with IQ (Der & Deary, 2017).

We seem to be taking longer to process the same amount of information. This is the conclusion that emerged when 14 studies, published since 1941, were compared with a study by Francis Galton from the late 19th century. With one exception, the post-1941 studies showed a lengthening of reaction time since Galton’s study (Silverman, 2010). The corresponding decline in IQ is estimated at 1.23 points per decade, for a total loss of 14 points since the Victorian era (Woodley et al., 2013).

Admittedly, the decline may be due to a more representative sampling of the population by later studies (hbd*chick, 2013). On the other hand, a similar lengthening of reaction time has been shown by controlled studies of Swedish, Scottish, and American participants, especially for cohorts born since 1980. The corresponding decline in IQ is likewise estimated at 1.3 to 1.7 points per decade (Madison, 2014; Madison et al., 2016).

Figure 10: Lengthening of reaction time of Swedish participants. The red squares are adjusted for participant age (Madison et al., 2016)

Piagetian testing

This measure is highly correlated with IQ (r=0.51). Both are measures of speed, working memory, and complex reasoning (Rindermann & Ackermann, 2020).

When a research team examined the results of Piagetian tests in England and Wales from 1975-1976 to 2006-2007, they found that test scores began to fall after 1993, at a time when conventional IQ test scores were still rising. Moreover, the smart fraction was shrinking faster than the proportion of students who were simply above average:

The Piagetian results are particularly ominous … the pool of those who reach the top level of cognitive performance is being decimated: fewer and fewer people attain the formal level at which they can think in terms of abstractions and develop their capacity for deductive logic and systematic planning. (Flynn & Shayer, 2018)

And yet IQ scores were rising!

Mean IQ nonetheless rose throughout the 20th century. This upward trend was pointed out by intelligence researcher James Flynn (1984), who calculated a rise of 13.8 points between 1932 and 1978 among European Americans. Named the Flynn effect in his honor, it was charted from 1909 to 2013 by Pietschnig and Voracek (2015), who found a total rise of 35 points. It can be broken down into five periods:

• a small increase between 1909 and 1919 (0.80 points/decade)

• a surge during the 1920s and early 1930s (7.2 points/decade)

• a slower pace of growth between 1935 and 1947 (2.1 points/decade)

• a faster one between 1948 and 1976 (3.0 points/decade)

• a slower pace thereafter (2.3 points/decade)

The Flynn effect is now ending throughout the Western world. In fact, it has ended altogether in Norway and Sweden and has begun to reverse in Denmark and Finland (Pietschnig & Voracek, 2015).

How real was this increase? As a child, I knew people who had gone to school before IQ scores began to rise and who, presumably, were more than a standard deviation less intelligent than my generation. I also knew the textbooks they had read, which our elementary school kept in a storeroom. How could they have understood those books if they had been so lacking in intelligence? How could they have handled the dense subject matter, the vocabulary, the detailed charts and figures, and the long, complex sentences?

The Flynn effect is more likely an increase in familiarity with standardized written tests, due to students staying in school longer and teachers abandoning other methods of evaluation, like essays and orally administered tests. Remember, almost a third of the total Flynn effect occurred during the 1920s and early 1930s. This was when IQ testing, and standardized written tests in general, became much more widespread in American schools:

World War I, in effect, set in motion the process that would result — in an incredibly short time — in national intelligence testing for American school children. By the end of the first decade after the war, standardized educational testing was becoming a fixture in the schools. (U.S. Congress, 1992, pp. 121-122)

After World War II, standardized written tests became even more widely used as more students went to college and university. This rise in postsecondary enrolment levelled off not long after the turn of the millennium — at about the same time that the Flynn effect levelled off.

Thoughts on the Great Decline

The end of the Flynn effect is showing us the real long-term trend of the 20th century: a decline in the genetic capacity for intelligence. This is most clearly shown by the genome studies from the United States, the United Kingdom, and Iceland, all of which show a decline in alleles associated with educational attainment.

The main cause seems to be the tendency of the more intelligent to pursue higher education and thus postpone marriage and childbearing: “In all countries [Australia, United States, Norway, Sweden], however, education is negatively associated with childbearing across partnerships, and the differentials increased from the 1970s to the 2000s” (Thomson et al., 2014). Yet that is not the whole story. The Icelandic genome study found lower fertility among the more intelligent even after controlling for higher education.

The resulting cognitive decline would become measurable by IQ tests only after the population had become fully familiar with such tests. But it had been happening all along.

This view is not shared by everyone. In a study of Norwegian siblings, Bratsberg and Rogeberg (2018) found that the recent reversal of the Flynn effect in Norway can be explained by “within-family variation.” In other words, IQ is declining more in younger siblings than in older ones. Since siblings share the same genetic background, the cause must be environmental.

But siblings in Norway are increasingly half-siblings. Among Norwegian women with only two children, 13.4% have had them by more than one man. The figure rises to 24.9% among those with three children, 36.2% among those with four children, and 41.2% among those with five children (Thomson et al., 2014). If siblings have different fathers, they cannot share the same genetic background. Keep in mind that the Bratsberg and Rogeberg study was limited, by its very nature, to families with at least two children and was skewed toward those with even more.

With what sort of men do Norwegian single mothers have more children? The sort of polygynous, low-IQ men that single mothers often end up with: “At the lowest educational level, 19.3 percent of those [Norwegian men] who had become fathers had children with more than one woman, compared to 6.1 percent of those at the highest educational level” (Lappegård et al., 2011).

Thus ends a trajectory that took northwest Europeans from relative unimportance to global dominance. It began in late medieval times with an emerging middle class that catered to an emerging market economy. These entrepreneurs relied on a family workforce and, if successful, would expand it by having more children. As their lineages became more numerous with each generation, the population shifted toward higher cognitive ability, stronger impulse control, and greater foresight. In this way, the West remade itself in the image of its growing middle class (Clark, 2007, 2009, 2023; Frost, 2022a; Frost, 2024; Piffer & Kirkegaard, 2024).

That evolution began to stall in the late 19th century, as middle-class couples ceased to translate their economic success into reproductive success. “Ma and pa” shops gave way to modern businesses, which could more readily increase or reduce their workforce by hiring or firing as needed. Fertility thus fell into a decline that would momentarily reverse during the post-war baby boom, when the fruits of economic growth were widely distributed and when cultural messaging was much more pro-family than it is today (Frost, 2019b; Frost, 2022b).

The baby boom then gave way to a baby bust and then a “family bust.” Today, the family unit is less concerned with perpetuating a lineage, and more with serving the interests of its current members.

Overview of European cognitive evolution

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