Was the rise of European cognitive ability part of a broader mental and behavioral shift?

A shift toward middle-class values?

Portrait of Ekaterina Ivanovich Novosiltsev with children, c. 1830.

Before the late 19th century, middle-class families had more children on average, particularly children surviving to adulthood. This difference in fertility drove a rise in mean cognitive ability that began in late medieval times with the emergence of the market economy.

By examining DNA from human remains, specifically alleles associated with cognitive ability, we can reconstruct not only how people looked in the past but also their capacity for thinking and reasoning. This is the case with a recent study of English DNA, which has revealed a post-medieval rise in mean cognitive ability (Piffer & Kirkegaard, 2024).

This increase may actually be understated because the study compared medieval genomes with contemporary genomes, whereas this cognitive evolution probably began in late medieval times and ended in the late 19th century (Frost, 2022). It would therefore be better to measure the cognitive evolution between the late medieval period and the Victorian Era, rather than between the entire Middle Ages and the present.

This rise in cognitive ability is consistent with work by Gregory Clark (2007; 2009; 2023) on England’s demographic history. As the middle class grew from the 12th century onward, its lineages contributed more and more to the country’s gene pool. The result was a shift toward “middle class” qualities of mind and behavior — not only higher cognitive ability but also lower time preference, greater impulse control, and less willingness to settle disputes through violence. “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).

A similar late medieval / post-medieval shift is posited by Georg Oesterdiekhoff (2023) for the whole of Western Europe. He describes it in terms of Jean Piaget’s stages of cognitive development, i.e., a growing proportion of the population could go beyond preoperational thinking (egocentrism, anthropomorphism, finalism, animism) and achieve operational thinking (ability to understand probability, cause and effect, and another person’s perspective). 

The rise in cognitive ability thus seems to have caused a cascade of mental and behavioral changes. Is this because cognitive ability is genetically linked to other mental and behavioral traits? Or is this because selection for “middle-class-ness” tends to select for a number of qualities, and not just cognitive ability?

In a new book, Philippe Gouillou argues that an increase in cognitive ability makes it easier to perform other mental tasks: people see the world in more abstract terms and are better able to decouple information from its context. Thus, as mean IQ rises, inanimate objects do not seem animate anymore, things are perceived as happening in predictable ways, and fate is no longer to be feared or bargained with. This change in perception eventually changes the culture:

The higher a person's IQ, the more they tend to abstract and intellectualize the world around them, constructing their Umwelt—their perceived environment—primarily through abstract reasoning. This intellectualized approach shapes how they experience and interact with the world.

… A higher IQ also helps to "decouple" information from its context. Information cannot be fully understood without integrating all the complexity of its context. But in some cases, it is much more effective to isolate it and study it in itself, to "decouple" it from its context and in particular from its emotional charge. For example, a sentence can be true whoever says it, it does not lose all validity if we disagree with its author on other points. (Gouillou, 2024, pp. 111-115)

From the late medieval period onward, this Umwelt became the perceived reality of more and more Western Europeans, in line with the growth of the middle class and its growing contribution to the gene pool. In particular, it became the perceived reality of those who increasingly came together to talk in salons, coffeehouses, and learned societies. This was the Enlightenment, and it would have been impossible with the gene pool of a few centuries earlier.

Can we learn more?

We can learn more about the past by examining ancient DNA through the lens of different sets of alleles, such as those associated with educational attainment, socioeconomic status, or household income. They all produce similar but somewhat different results, probably because some of them measure not only cognitive ability but also other mental traits, like rule-following and proactiveness.

On this point, Philippe’s new book sounds a note of caution: the same mental trait may have different consequences in different historical settings. Perhaps we gain today from being pro-active and entrepreneurial, but the same was not necessarily so in medieval times. You really had to know your place back then, and act accordingly.

Status can be based on dominance (fear-based) or prestige (admiration-based). Leadership through prestige is a voluntary exchange of services and influence, but it can easily shift into dominance-based hierarchies. Prestige is more closely tied to IQ than dominance.

… In modern societies, resource accumulation changes the dynamics of status acquisition, with wealth becoming a powerful determinant of status.

… Culture, which coevolves with genes, further influences status rules. For example, dominance criteria affect IQ across generations by determining who will pass on their genes. (Gouillou, 2024, p. 121)

The late medieval period saw a shift in the nature of high status. Getting ahead no longer meant theft and plunder. It meant using peaceful means to accumulate wealth in the emerging market economy. Instead of favoring physical strength and verbal bombast, selection now rewarded certain skills, like numeracy, literacy, and planning.

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Philippe’s new book is a fascinating summary of what we currently know about IQ. I thought I was on top of the literature, but he apparently knows more than I do. He also puts into crisp prose a number of ideas that previously seemed vague and woolly to me.

I only have a few minor criticisms:

• The first third of the book is a discussion of terminology. How do we define intelligence? What are the components of intelligence? What is the bell curve? I’ve seen this approach used by other authors, and I understand the reasons. Nonetheless, there is a risk that some readers may lose interest and go no farther than this part of the book.

• There is very little on polygenic scores, either from present-day populations or from those of the past. This research tool will probably replace IQ tests as the best means to estimate cognitive ability, since an IQ test measures not only the heritable component of intelligence but also the environmental component — learning, family environment, accidents during pregnancy or childhood, etc. At present, the main problem with polygenic studies is that they are good only for measuring the mean IQ of a population. They are not very good for estimating the IQ of an individual.

• Some conclusions by other authors are taken at face value. For instance,

  Pascali (2016) found that southern Italian cities that expelled Jewish populations in the Middle Ages continued to experience economic repercussions five centuries later. (Gouillou, 2024, p. 162)

  When Jews were expelled from southern Italy in 1541, there was already a deep divide between the south and the north. Southern Italy had an economy dominated by large farms that produced food for export. In contrast, Northern Italy had a much more diverse economy: small farms, textiles, small-scale manufacturing, finance, and trade with the Middle and Far East.

  Not long after the discovery of the Americas, and the establishment of plantations in the West Indies and Brazil, the entire Mediterranean basin fell into economic decline, including those areas where a Jewish presence would continue and even grow, i.e., the Ottoman territories. It was now cheaper to buy food products from North and South America, rather than from Valencia and Sicily. In addition, the geo-center of economic activity was moving away from the Mediterranean and toward Western Europe and the New World. This decline affected all of Italy, but it was more severe and longer-lasting in the South than in the North. Northern Italy was closer to the geo-economic center of Western Europe — being, in fact, a part of that region — and its economy was more diversified. The South was too dependent on export agriculture. When that sector collapsed, there was nothing to pick up the slack.

In sum, this book is a good read and, even if you think you know the terminology, you may still benefit from reading the first third of the book.

References

Clark, G. (2007). A Farewell to Alms. A Brief Economic History of the World. Princeton University Press: Princeton.

Clark, G. (2009). The domestication of man: the social implications of Darwin. ArtefaCToS, 2, 64-80. https://www.researchgate.net/publication/277275046_The_Domestication_of_Man_The_Social_Implications_of_Darwin  

Clark, G. (2023). The inheritance of social status: England, 1600 to 2022. Proceedings of the National Academy of Sciences, 120(27), e2300926120 https://doi.org/10.1073/pnas.2300926120

Frost, P. (2022). The Great Decline. Regressive cognitive evolution in the West. Peter Frost’s Newsletter, December 20. https://peterfrost.substack.com/p/the-great-decline

Gouillou, P. (2024). IQ: From Causes to Consequences. From genetics to cognitive capitalism. Gouillou.com. https://www.amazon.ca/IQ-Consequences-Genetics-Cognitive-Capitalism/dp/295939853X

Oesterdiekhoff, G.W. (2023). Was pre-modern man a child? The quintessence of the psychometric and developmental approaches. Intelligence, 40, 470-478. https://doi.org/10.1016/j.intell.2012.05.005

Pascali, L. (2016). Banks and Development: Jewish Communities in the Italian Renaissance and Current Economic Performance. Review of Economics and Statistics, 98(1), 140–158. https://doi.org/10.1162/REST_a_00481

Piffer, D., & Kirkegaard, E.O.W. (2024). Evolutionary Trends of Polygenic Scores in European Populations from the Paleolithic to Modern Times. Twin Research and Human Genetics, 1, 30-49. https://doi.org/10.1017/thg.2024.8