Cognitive evolution in eastern Eurasia
We make culture, and it remakes us.
Written by Peter Frost.
Beginning some 10,000 years ago, hunting and gathering gave way to farming. This in turn gave way to ever more cultural change: population growth, year-round living in villages and towns, trade and specialization of labor, numeracy and literacy, the formation of states, the development of religion, the standardization of law and so on.
Humans were thus entering an ever-wider range of cultural environments, which, to varying degrees, placed new demands on the capacity to process information, recognize patterns and solve problems — in other words, cognitive ability.
The new demands varied from one region to another and from one time period to another, with the result that cognitive ability followed different trajectories of evolution in different populations. We can now chart this evolution by looking at DNA from human remains, specifically the various alleles associated with educational attainment (EA) and their population frequencies.
Several recent studies have revealed how cognitive ability has evolved in Europeans:
No change during the long period of hunting and gathering.
With the emergence of farming, a steep rise between 9,000 and 7,000 years ago, possibly due to the cognitive demands of farming and also admixture from northern hunter-gatherers.
A slower rise through the Neolithic and into recorded history, possibly due to the cognitive demands of increasing social complexity. With the stratification of society into classes, cognitive evolution was increasingly driven by higher fertility within the upper classes.
A decline during the Imperial Era of Rome, possibly due to a decline in family formation and fertility among the upper classes.
A renewed upward trend beginning in Late Antiquity, possibly due to the rise of Christianity and an increase in family formation among the upper classes.
An especially rapid rise in late medieval and post-medieval Western Europe, possibly due to the demographic expansion of the middle class through higher fertility and lower mortality (Akbari et al., 2024; Frost, 2024; Kuijpers et al., 2022; Piffer et al., 2023; Piffer & Kirkegaard, 2024).
The other end of Eurasia
Europe is one of two large regions where mean cognitive ability has risen the most. How has cognitive ability evolved at the other end of Eurasia?
This question has been addressed by Davide Piffer in his recent study of 1,245 ancient genomes from eastern Eurasia over the last 12,000 years. (For earlier periods, we have too few samples to draw worthwhile conclusions, as is also true for western Eurasia.)
He found that mean cognitive ability has risen over time in eastern Eurasia. The increase was largest in southern China, followed by Mongolia and Southeast Asia. The size of the increase in southern China probably reflects not only cognitive evolution in situ but also the replacement of hunter-gatherers and simple farming societies by Han immigrants from northern China (Yang et al., 2020). Similarly, the increase in Mongolia may partly reflect gene flow from Han Chinese (10-51% of current Mongolian ancestry) and Europeans (6-40%) (Zhao et al., 2020). Southeast Asia has likewise seen extensive replacement of hunter-gatherers by Austronesian or Sino-Tibetan farmers (Lipson et al., 2018).
Increases in cognitive ability have been smaller elsewhere in eastern Eurasia. This may reflect persistence of low social complexity (Arctic, North Siberia), failure to develop beyond a certain level (Central Asia and Tibet) or a complicated trajectory of positive and negative evolution (Northeast China).
A closer look
By pooling these regional results, Piffer was able to track the cognitive evolution of eastern Eurasia in greater detail. His second analysis shows stagnation during the hunter-gatherer period, followed by a sustained upward trend beginning around 9,000 to 8,000 years ago, apparently with the advent of farming. This upward trend ended a little less than 1,500 years ago, near the beginning of the Tang Dynasty (618-907 CE).
The last finding may seem surprising because the Tang Dynasty was a time of great advances in art, literature and technology. Did this golden age have a darker side? Did the upper classes suffer a decline in fertility as they did in Imperial Rome?
This explanation has some support from historical sources.
During the Tang Dynasty, the poet Wang Fanzhi affirmed that having one son was enough. During the Song Dynasty (960–1279 CE), according to a number of scholars, people wanted to have only two sons or just one. (Zhao, 2002, p. 756). Abortive drugs were sold during the Tang Dynasty and became even more available during the Song and Yuan (1206–1368 CE) dynasties. Such drugs were produced on a large scale in certain areas during the reign of Kang Xi (1662–1722 CE). They were widely used by the population, from members of the imperial family to ordinary citizens (Zhao, 2006, p. 17). When describing certain places in one of his poems, Wang Fan Zhi (c. 590–c. 660 CE) noted that the rich had few children while the poor had many (Zhao, 2006, p. 22).
To confirm the cognitive stagnation of the Tang Dynasty and later periods, as shown by alleles associated with EA, Piffer repeated his analysis but now used alleles associated with IQ. This method has the advantage of homing in on cognitive ability itself, rather than other traits that may assist success at school. But it also has the disadvantage of being based on far fewer alleles (only 434 independent SNPs, as compared to almost 4,000 for EA).
These results differ from those of his previous analysis in two ways:
Instead of remaining unchanged during the hunter-gatherer period, mean cognitive ability fell and continued to fall into the farming period, bottoming out only 6,000 years ago. This decline seems to mirror a decline in brain size that began in Eurasian populations after the last ice age, perhaps because their brains no longer had to store huge amounts of spatiotemporal data for hunting over large expanses of territory (Frost, 2019; Hawks, 2011). This loss of spatiotemporal ability may be better measured by IQ than by EA.
Instead of remaining unchanged during the last 1,500 years, mean cognitive ability fell somewhat. This decline may be better measured by IQ because EA captures not only cognitive ability but also certain propensities – rule following, submissiveness, resistance to boredom – that were somehow maintained in the entire population despite the fertility decline of the upper classes.
Conclusion
The “archeology of the mind” is shedding new light on the historical process. In particular, we’re learning that history is a reciprocal relationship between the human mind and the culture it creates. 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.
Culture especially favors those individuals who have certain properties of mind and behavior, such as cognitive ability. This “cultural selection” has gone farther in some parts of the world than in others, and it has gone especially far in two regions: Europe and East Asia. Their trajectories of cognitive evolution have certain points in common, notably:
An upward trend initiated by the advent of farming and sustained by a parallel rise of social complexity.
A halt and even reversal at a fairly high stage of social complexity – Imperial Rome and Tang China – perhaps due to a fertility decline among the upper classes.
But this reversal would play out differently in the two regions. In the Roman Empire, mean cognitive ability fell and then rose again a few centuries later. This “reboot” was associated with an ideological change, i.e., the rise of Christianity and its preeminent role in enforcing morality, particularly with respect to sexual behavior and family formation. The new ideology would survive the collapse of Rome and define what would be called “Christendom” (Frost, 2024).
In China, the ensuing trajectory is less clear-cut. Whereas alleles associated with EA suggest a flat-lining of cognitive evolution, those associated with IQ suggest a decline. Perhaps the decline in upper class fertility was partially offset by the growing importance of the Imperial Examination for social and economic advancement (Frost, 2011; Wen et al., 2024). This examination favored not only high cognitive ability but certain other mental traits: rule following, submissiveness and resistance to boredom — in short, the ability to sit still at a desk and do tedious mental work.
Like Imperial Rome, Tang China experienced a movement for social and moral reform. This movement was based on the teachings of Kong Qiu (Confucius) and gained ground during the Tang Dynasty through the work of pronatalist scholars who condemned abortion and advocated control of sexual desires (Hsiung, 2011). Their work led to the emergence of neo-Confucianism, which resembled Christianity in some respects, particularly in its desire to regulate sexual behavior and family formation. However, unlike Christianity, it did not create an organizational network to impose its norms on the population.
In sum, East Asia failed to develop a regulator of public morality that could act independently of the elites and make them conform to certain sexual and reproductive norms. This point is broadly made by Francis Fukuyama in his work The Origins of Political Order.
Hopefully, we will see more studies of this kind, especially on the last 1,500 years of cognitive evolution. In particular, we need to resolve an apparent contradiction between Davide Piffer’s findings and Ron Unz’s argument that mean cognitive ability continued to rise in China until the 20th century, as a result of higher fertility among the wealthy (Unz, 2013).
Peter Frost has a PhD in anthropology from Université Laval. His main research interest is the role of sexual selection in shaping highly visible human traits, notably skin color, hair color and eye color. Other research interests include gene-culture coevolution. Find his newsletter here.
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References
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Very interesting article. This kind of research is finally revealing the origins of group differences in cognitive ability today. It seems to have something to do with experience with agriculture and centralized civilization. This created greater selection pressures for cognitive ability and educational attainment. But this probably not the whole story. For example, the area around the Fertile Crescent has the longest record of agriculture and civilization, but these regions do not exhibit high cognitive ability now. There must something more to the story.
Makes you wonder if industrial society, for all its apparent might, has the capacity to successfully craft and then more important- consistently impose, positive selective pressure on its population for centuries. I would say no. The risk of unintended consequences for such plans seems high as well, with the results on society and culture unknown until many generations later. Or maybe there are other approaches that are less obvious...