Cognitive evolution in Europe: two new studies

It happened faster than you may think

Farm at Duivendrecht, Piet Mondrian, 1905. The shift from hunting and gathering to farming led to a new cultural environment that selected against sensation seeking and monotony avoidance

Europeans became a high-IQ population through an evolutionary trajectory that began with the adoption of farming and continued because of the cognitive demands of social complexity. Much of the upward trend in cognitive ability has occurred since medieval times.

Human evolution did not end in the Paleolithic. It continued and even accelerated along different trajectories in different populations and for different traits (Cochran and Harpending, 2009; Hawks et al., 2007; Rinaldi, 2017).

One trait is cognitive ability — the ability to process information, recognize patterns, and solve problems. Among those humans who entered Europe, mean cognitive ability would increase to such a degree that the continent is today one of the world’s two “IQ plateaus.” When did that increase happen? During the last ice age? Or more recently?

A recent increase is postulated by Gregory Clark (2007; 2009; 2023), who has studied the demographic history of England. As the English middle class grew in size from the twelfth century onward, its lineages contributed more and more to the country’s gene pool. The result was a mental and behavioral 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.

Georg Oesterdiekhoff (2023) has argued for a similar evolution across Western Europe during the same period. He interprets this evolution 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). 

First study of European cognitive evolution - Kuijpers et al. (2022)

To test the hypothesis of recent cognitive evolution, a team led by Yunus Kuijpers compared the DNA of 250 present-day Europeans with the DNA of 827 Europeans from different stages of cultural development: the Upper Paleolithic (before 11,000 years ago), the Mesolithic (11,000 to 5,500 years ago), the Neolithic (8,500 to 3,900 years ago), and the post-Neolithic (5,000 to “more recent ages”). The researchers looked at changes over time in mean cognitive ability, as measured by alleles associated with intelligence, fluid intelligence, and educational attainment.

All three measures of cognitive ability showed the same pattern of cognitive evolution:

• no change during the long period of hunting and gathering

• with the emergence of farming, a sustained upward trend until the dawn of history

• stagnation during the classical era of civilization

• a renewed upward trend during the last few centuries (Kuijpers et al., 2022).

These results are in line with Clark’s hypothesis of an increase in mean cognitive ability from the twelfth century onward. They may also be in line with the findings of a team led by Davide Piffer on the genetic history of central Italy. That sub-region seems to have gone through three stages of cognitive evolution:

• an upward trend in mean cognitive ability from the Neolithic to the time of the Roman Republic

• a downward trend during the Imperial Era

• a renewed upward trend from Late Antiquity to the Middle Ages (Piffer et al., 2023; see also Frost, 2023).

These ups and downs are absent from the Kuijpers et al. study because they are subsumed within a broader temporal frame (“post-Neolithic”) and a broader spatial frame (Europe).

All three measures of cognitive ability show the same pattern over time (Kuijpers et al., 2022).

Second study of European cognitive evolution - Piffer and Kirkegaard (2024)

The above findings prompted Davide Piffer and Emil Kirkegaard to do the same kind of study with a larger number of European genomes (n=2625) and with measures of cognitive ability based on larger samples. In particular, the alleles associated with educational attainment were identified by other research teams from two large samples, one having over a million individuals (EA3) and the other three million individuals (EA4).

The two researchers found essentially two stages of cognitive evolution:

• no change between approximately 35,000 and 15,000 years ago.

• an upward trend beginning near the end of the last ice age and lasting to the present (Piffer and Kirkegaard, 2024)

In this study, the upward trend is more continuous and consequently less steep, perhaps because more of the samples came from non-Romanized regions that were less affected by the cognitive decline of the Imperial Era.

As with the other study, we see a close alignment of all three measures of cognitive ability. The evolutionary change has clearly been in that trait, and not in some non-cognitive aspect of educational attainment.

All three measures of cognitive ability show the same pattern over time. In this study, the upward trend is more continuous and consequently less steep (Piffer and Kirkegaard, 2024).

Regional trends

Because the regional subsamples were often too small, it was difficult to analyze shorter-term trends within any one European region, such as the cognitive decline of Imperial Rome or the cognitive takeoff of late-medieval/post-medieval Western Europe. Among the subsamples, Bronze Age Greeks showed the highest level of cognitive ability as measured by alleles associated with IQ, but this result was not replicated by alleles associated with EA.

The English subsample had enough individuals to test Clark’s hypothesis of an upward trend in mean cognitive ability from the twelfth century onward. When medieval genomes were compared with those of contemporary England, all three cognitive measures showed a significant increase.

This increase may, in fact, be understated. First, mean cognitive ability seems to have fallen in England, and more generally within the Western world, since the turn of the twentieth century (Frost, 2022). Second, the “cognitive takeoff” hypothesized by Clark began in late medieval times. The comparison should therefore be made between the start and end points of this cognitive evolution, i.e., between the early medieval period and the Victorian Age, and not between the medieval period as a whole and the present.

Finally, a comparison was also made between England and the rest of Europe with respect to this recent upward trend in mean cognitive ability. No significant difference was found. Clark’s hypothesis seems to apply not only to England but also to other parts of Europe, certainly Western Europe. For future research, a more appropriate model would be one where this cognitive increase is seen as beginning initially in Western Europe and then spreading outward in line with the growth of the middle class. 

Alleles associated with socioeconomic status

The researchers also looked at changes over time in alleles associated with socioeconomic status, as ascertained in contemporary British individuals. Alleles associated with higher status became more frequent from the end of the ice age to around 2500 years ago, after which there was no further change.  There was likewise no change between medieval and contemporary English genomes.

This is not what Clark would predict. He argued that the late-medieval/post-medieval growth of the middle class favored not only alleles associated with higher cognitive ability but also those associated with “middle class values,” like lower time preference and greater impulse control. Perhaps higher socioeconomic status is today determined by a different package of mental and behavioral traits.

Alleles associated with autism, schizophrenia, and depression

In addition to alleles for cognitive ability, the two authors also looked at alleles for certain mental illnesses. Autism has become more common since the last ice age. Is this upward trend a side-effect of selection for cognitive ability? Or has it been directly favored by something in our cultural environment?

Meanwhile, schizophrenia has become less common. Schizophrenics have lower cognitive ability, (i.e.., a reduction from 100 to 70-85 IQ), particularly a reduced ability to attach meaning to words, to see through visual illusions, and to understand the self in relation to others. This finding may support Oesterdiekhoff’s argument for a shift away from pre-operational thinking in modern European adults.

Finally, depression has become less common. Perhaps sedentism has selected against sensation seeking and monotony avoidance. These traits are highly heritable and key to the behavioral repertoire of hunters and gatherers (Zuckerman, 2008). In the case of farmers, the same traits would be maladaptive and selected out of the gene pool. One consequence may thus be a higher threshold for depression.

Remaining questions

Cognitive evolution and the transition to farming

Were native Europeans selected for higher cognitive ability when hunting and gathering gave way to farming? Or were they simply replaced by Middle Eastern farmers moving into Europe from Anatolia? Piffer and Kirkegaard argue for the latter scenario:

Hunter-gatherer ancestry (particularly V2 or WHG) was negatively associated with EA3, EA4 and IQ in the regression models (Supplementary Tables S1-S3) even after accounting for Years BP (β=-0.314, -0.4, -0.249), suggesting that the increase in cognitive capacity was not solely driven by the Neolithic revolution but was partly mediated by admixture with the immigrants that accompanied it. Anatolian Neolithic farmers who intermixed with native HGs contributed between approximately 40% and 98% of Neolithic European ancestry (Piffer and Kirkegaard, 2024)

The estimate of 40 to 98% replacement of European hunter-gatherers by Anatolian farmers should be viewed with caution. It is based on the assumption that demographic replacement explains all of the genetic change across the time boundary between hunter-gatherers and farmers. In reality, some of it was due to:

• Founder effects - Hunter-gatherers who adopted farming were a tiny percentage of all hunter-gatherers, hence the founder effects were considerable. These genetic changes were random, but a certain percentage of them would have matched the genetic profile of Anatolian farmers.

• Selection effects - Hunter-gatherers who adopted farming were now adapting to the same regime of natural selection as that of Anatolian farmers. Hence there was some convergent evolution. Such evolution may, for instance, explain why Europeans lost haplogroup U, which is associated with greater production of body heat — a useful cold adaptation for hunter-gatherers, who slept in makeshift shelters and pursued game in all kinds of weather. In contrast, farmers slept in a warmer environment and could more easily plan their outdoor activities (Balloux et al., 2009; Montiel-Sosa et al., 2006). Farmers likewise had less need for odor recognition, monotony avoidance, and sensation seeking. In sum, even if there were no population replacement at all, we would still expect to see genetic change across the time boundary between hunter-gatherers and farmers.

There is thus an inevitable confound between farmer ancestry and natural selection due to farming. If we look at alleles that seem to indicate native hunter-gatherer ancestry, we are excluding the alleles of hunter-gatherers who successfully adapted to farming and who thus acquired a genetic profile that converges, to some extent, on that of Anatolian farmers. A certain amount of “Anatolian admixture” is actually pseudo-admixture.

We cannot avoid this methodological problem by using only noncoding loci, as is often done, since such loci can still regulate how alleles at other loci behave. Noncoding loci have, in fact, contributed disproportionately to recent evolution. Comparison of our genome with other primate genomes has shown that almost all human-specific deletions are in noncoding regions. Furthermore, DNA is mostly noncoding in human accelerated regions (HARs), which have been well conserved throughout vertebrate evolution but are strikingly different in humans (Bae et al., 2015).

Reduction in brain size after the last ice age

Cranial capacity, and hence brain size, decreased among Europeans after the last ice age (see Hawks, 2011 for a review of the literature). Yet, during the same period, mean cognitive ability held steady or increased among Europeans. How do we explain this apparent contradiction?

Perhaps the brain was starting to do more with less, specifically be relying more on recursive thinking (Corballis, 2014; Cutler, 2024). Alternatively, the decrease in brain size may simply reflect a decrease in mental storage of spatiotemporal data, due to the abandonment of hunting over large expanses of territory. This decrease is much less apparent in tropical humans, who hunted over smaller expanses (Frost, 2019b; Hawks, 2011).

Cold winter theory

Neither of the above two studies supports the theory that higher cognitive ability was favored by Europe’s cold climate — especially during the last ice age. The theory is that the harshness of a cold climate, specifically its occurrence over a predictable yearly cycle, selects for the ability to plan ahead and prepare accordingly (Frost, 2019a). Perhaps cognitive ability did increase when modern humans initially entered Europe, but this increase does not show up in the genetic data because the Upper Paleolithic timeframe is too broad and has too few data points, especially from northern Europe. For later periods, selection for cognitive ability would be determined much more by other factors, particularly the increase in social complexity from the late Mesolithic onward.

References

Bae, B-I., Jayaraman, D., and Walsh, C.A. (2015). Genetic changes shaping the human brain. Developmental Cell 32: 423-434. https://doi.org/10.1016/j.devcel.2015.01.035

Balloux F., Handley, L.J., Jombart, T., Liu, H., and Manica, A. (2009). Climate shaped the worldwide distribution of human mitochondrial DNA sequence variation. Proceedings of the Royal Society B. Biological Sciences 276: 3447-3455.  https://doi.org/10.1098/rspb.2009.0752

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

Cochran, G. and Harpending, H. (2009). The 10,000 Year Explosion: How Civilization Accelerated Human Evolution. Basic Books: New York. https://www.hachettebookgroup.com/titles/gregory-cochran/the-10000-year-explosion/9780465020423/

Corballis, M.C. (2014). The Recursive Mind: The Origins of Human Language, Thought and Civilization, Princeton University Press. https://press.princeton.edu/books/hardcover/9780691145471/the-recursive-mind

Cutler, A. (2024). Eve Theory of Consciousness v3.0. Vectors of Mind, February 27.

Frost, P. (2019a). The Original Industrial Revolution. Did Cold Winters Select for Cognitive Ability? Psych 1(1): 166-181. https://doi.org/10.3390/psych1010012   

Frost, P. (2019b). Why did brain size decrease after the Ice Age? Evo and Proud, July 6. https://evoandproud.blogspot.com/2019/07/why-did-brain-size-decrease-after-ice.html

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

Frost, P. (2023). Was the Roman Empire eugenic? Peter Frost’s Newsletter, December 11. https://peterfrost.substack.com/p/was-the-roman-empire-eugenic

Hawks, J., Wang, E. T., Cochran, G. M., Harpending, H. C., and Moyzis, R. K. (2007). Recent acceleration of human adaptive evolution. Proceedings of the National Academy of Sciences (USA), 104, 20753-20758. https://doi.org/10.1073/pnas.0707650104  

Hawks, J. (2011). Selection for smaller brains in Holocene human evolution. arXiv:1102.5604 [q-bio.PE] https://arxiv.org/abs/1102.5604

Kirkegaard, E.O. (2024). What do ancient genomes show about recent human evolution? Just Emil Kirkegaard Things, March 7.

Kuijpers, Y., Domínguez-Andrés, J., Bakker, O.B., Gupta, M.K., Grasshoff, M., Xu, C.J., Joosten, L.A.B., Bertranpetit, J., Netea, M.G., and Li, Y. (2022). Evolutionary Trajectories of Complex Traits in European Populations of Modern Humans. Frontiers in Genetics 13: 833190. https://doi.org/10.3389/fgene.2022.833190

Montiel-Sosa, F., Ruiz-Pesini, E., Enriquez, J.A., Marcuello, A., Diez-Sanchez, C., Montoya, J., Wallace, D.J., and López-Pérez, M.J. (2006). Differences of sperm motility in mitochondrial DNA haplogroup U sublineages. Gene 368: 21-27. https://doi.org/10.1016/j.gene.2005.09.015

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

Piffer D, Dutton, E., and Kirkegaard, E.O.W. (2023). Intelligence Trends in Ancient Rome: The Rise and Fall of Roman Polygenic Scores. OpenPsych. Published online July 21, 2023. https://doi.org/10.26775/OP.2023.07.21

Piffer, D., and Kirkegaard, E.O.W. (2024). Evolutionary Trends of Polygenic Scores in European Populations from the Paleolithic to Modern Times. Twin Research and Human Genetics. Published online:1-20. https://doi.org/10.1017/thg.2024.8

Rinaldi, A. (2017). We're on a road to nowhere. Culture and adaptation to the environment are driving human evolution, but the destination of this journey is unpredictable. EMBO reports 18: 2094-2100. https://doi.org/10.15252/embr.201745399

Zuckerman, M. (2008). Genetics of Sensation Seeking. In J. Benjamin, R.P. Ebstein, and R.H. Belmaker (Eds) Molecular Genetics and the Human Personality, (pp. 193-210). Washington D.C.: American Psychiatric Publishing Inc.