Thursday, June 23, 2022

Ancestral East Asians and adaptation to coronaviruses


Early farming village in China (Wikicommons – Xinyang City Museum, Gary Todd)


Respiratory viruses began to propagate more easily when hunting and gathering gave way to farming and as settlements grew larger. Humans may have then evolved to use coronaviruses as a natural vaccine against deadlier respiratory diseases, like tuberculosis and pneumonia.



A new genomic study has found that East Asians had to adapt to epidemics of coronaviruses some 25,000 years ago. The authors looked at gene variants for proteins that interact with coronaviruses in five East Asian populations: Han Chinese (Beijing); Han Chinese (South China); Dai (Yunnan, China); Japanese; and Vietnamese. There were three main findings:


·         Ancestral East Asians had to adapt to coronavirus epidemics around 25,000 years ago

·         They adapted by acquiring mutations that are close to genes that regulate the development of lung tissue and other tissues affected by COVID-19

·         Those mutations either promote or block infection by coronaviruses (Souilmi et al. 2021, p. 3505).


The last finding is puzzling. Did those ancestral East Asians become more vulnerable or less vulnerable to coronaviruses? The authors simply say that half of those mutations from 25,000 years ago have “anti- or proviral effects” versus 29% of all proteins that interact with coronaviruses (Souilmi et al. 2021, p. 3509). Fine. But how many of those mutations were antiviral and how many proviral?


It might seem strange that natural selection would actually make people more susceptible to coronavirus infections. Yet such susceptibility could be beneficial. A viral infection can boost immunity to other viruses, including deadly viruses that cause tuberculosis, pneumonia, or pneumonic plague. Until recently, coronaviruses were typically mild in their effects, producing what we call the “common cold.” They may thus act as a natural vaccine against deadlier respiratory viruses (Frost 2020).


Respiratory viruses are believed to have become serious for humans when hunting and gathering gave way to farming. People became sedentary and their settlements grew larger with time, thus providing respiratory viruses with better conditions for propagation (Comas et al. 2013). This theoretical model is in conflict, however, with the above finding that ancestral East Asians began adapting to coronaviruses some 25,000 years ago, long before they adopted farming and became sedentary. We’re thus left with the unlikely conclusion that coronavirus epidemics began among scattered bands of hunter-gatherers.


The estimate of 25,000 years ago is probably wrong. The authors arrived at that figure by calculating the latest date when the ancestors of the four East Asian groups were still a single population. But East Asians are not descended from a single population. Their origins are best described by the "Two-Layer" (TL) hypothesis:


·         Modern humans spread into East Asia through a northern route and a southern route.

·         The southerners were then replaced to varying degrees by northerners who spread out of northeast Asia and successively occupied northern China, southern China, and Southeast Asia (Oxenham and Buckley 2016; Xu et al. 2006).

·         Thus, as you go farther south in East Asia, the population has a greater admixture from the earlier southern “layer”—from hunter-gatherers who closely resemble the relic groups that still exist in parts of Southeast Asia, i.e., the Andaman Islanders, the Aeta of the Philippines and the Maniq and Semang of the Malayan Peninsula.


Admixture from that older southern substrate pushes back in time the latest common ancestors, who never existed. Adaptation to coronaviruses therefore happened at a later date, probably when the “northerners” pushed into what is now northern China and adopted farming. They then grew in population, pushed farther south, and intermixed with the hunter-gatherers who lived there. 





Comas, I., M. Coscolla, T. Luo, et al. (2013). Out-of-Africa migration and Neolithic coexpansion of Mycobacterium tuberculosis with modern humans. Nature Genetics 45: 1176–1182.


Frost, P. (2020). Does a commensal relationship exist between coronaviruses and some human populations? Journal of Molecular Genetics 3(2): 1-2.


Frost, P. (2022). A natural vaccine. Evo and Proud, February 21


Oxenham, M., and H.R. Buckley. (2016). The population history of mainland and island Southeast Asia, in M. Oxenham and H.R. Buckley (eds) The Routledge Handbook of Bioarchaeology in Southeast Asia and the Pacific Islands. Routledge.


Souilmi, Y., M.E. Lauterbur, R. Tobler, C.D. Huber, A.S. Johar, S.V. Moradi, W.A. Johnston, N.J. Krogan, K. Alexandrov, and D. Enard. (2021). An ancient viral epidemic involving host coronavirus interacting genes more than 20,000 years ago in East Asia. Current Biology 31(16), 3504–3514.e9.


Xue, Y., T. Zerjal, W. Bao, S. Zhu, Q. Shu, J. Xu, R. Du, S. Fu., P. Li, M.E. Hurles, H. Yang, C. Tyler-Smith. (2006). Male demography in East Asia: A north-south contrast in human population expansion times. Genetics 172: 2431-2439,

Monday, June 13, 2022

Humans and the olfactory environment


Perfume burner, Egypt, c. 700-900 (Wikicommons, Musée du Louvre, Marie-Lan Nguyen)


We have sought to remake our environment in ever more appealing ways, including its smell. But the change hasn’t been one-way. By remaking our olfactory environment, we’ve ended up remaking ourselves.



I’ve published a new paper in Psych. When I wrote it, I had three aims:


·         Explain the concept of gene-culture coevolution

·         Provide a concrete example, i.e., how we have coevolved with the odors around us, not only in our ability to emit and sense them but also in our ability to represent them mentally

·         Develop the theoretical basis of gene-culture coevolution


Please feel free to comment. The following is the abstract:



As hunter-gatherers, humans used their sense of smell to identify plants and animals, to find their way within a foraging area, or to distinguish each other by gender, age, kinship, or social dominance. Because women gathered while men hunted, the sexes evolved different sensitivities to plant and animal odors. They also ended up emitting different odors. Male odors served to intimidate rival males or assert dominance. With the rise of farming and sedentism, humans no longer needed their sense of smell to find elusive food sources or to orient themselves within a large area. Odors now came from a narrower range of plants and animals. Meanwhile, body odor was removed through bathing to facilitate interactions in enclosed spaces. This new phenotype became the template for the evolution of a new genotype: less sensitivity to odors of wild plants and animals, lower emissions of male odors, and a more negative response to them. Further change came with the development of fragrances to reodorize the body and the home. This new olfactory environment coevolved with the ability to represent odors in the mind, notably for storage in memory, for vicarious re-experiencing, or for sharing with other people through speech and writing.





Frost, P. (2022). Humans and the olfactory environment: a case of gene-culture coevolution? Psych 4(2): 301-317.  


Monday, June 6, 2022

Recent cognitive evolution in Europe: a new study of ancient DNA


Polygenic scores for alleles associated with educational attainment - Europeans of different time periods (Kuijpers et al. 2022)


According to a new study of ancient European DNA, cognitive evolution stagnated after the last ice age and then speeded up with the rise of farming. It stagnated again during Antiquity and then speeded up again sometime between then and now.



In my last post, I mentioned an ancient DNA study of 99 genomes from sites across Europe and Central Asia. It showed an apparent increase in mean cognitive ability between 4,560 and 1,210 years ago, as measured by alleles associated with educational attainment (Woodley et al. 2017).


That finding has been partially replicated by a new study of 827 genomes from ancient European remains and 250 genomes from modern Europeans. It looks like cognitive evolution stagnated after the last ice age and then speeded up with the rise of farming. It stagnated again during Antiquity and then speeded up again sometime between then and now:


Interestingly, while the period between the Early Upper Paleolithic and the Neolithic is characterized by stagnation or slight decrease in PRS related to intelligence, the genetic data show a clear increase in the scores for educational attainment, intelligence, and fluid intelligence from the Neolithic onwards, while the traits related with unipolar depression tend to decrease from that era on. The most significant differences can be observed comparing the pre-Neolithic and Neolithic groups, as well as the post-Neolithic and modern groups, whereas the period between the Neolithic and post-Neolithic shows a very constant distribution of PRS scores. (Kuijpers et al. 2022).


The authors define the time periods as follows:


Early Upper Paleolithic era – before 28,000 years BC

Late Upper Paleolithic era – 28,000 to 11,000 BC

Mesolithic - 11,000 to 5500 BC

Neolithic - 8,500 to 3900 BC

Post-Neolithic - 5000 BC and more recent ages (no end date given)

Modern – circa 1950 AD


The Mesolithic, the Neolithic, and the Post-Neolithic overlap a lot with each other. This is because their boundaries are defined by cultural changes that came to different parts of Europe at different times. The Neolithic began when hunting and gathering gave way to farming, which came later to northern Europe. Similarly, the post-Neolithic began with the advent of metallurgy, which likewise came later to northern Europe.


Such overlap is problematic for three reasons:


·         In some cases, there is uncertainty as to whether the ancient DNA came from the remains of hunter-gatherers or those of farmers.

·         “Hunter-gatherer” is not a homogeneous category. It includes not only small nomadic groups but also the hunter-fisher-gatherers of the Baltic and North Sea, who attained a degree of sedentism, population growth, and social complexity that we normally associate with farmers (Price 1991).

·         The Post-Neolithic is too long to be meaningful. It covers all of recorded history, and then some.


The study’s authors could have divided the Post-Neolithic into smaller time periods to give us a better look at changes during historical times. In particular, did cognitive evolution regress during Classical Antiquity? That was the preliminary finding of a team led by Michael Woodley of Menie (2019) in a study of ancient DNA from Greece. They found that mean cognitive ability increased from the Neolithic to the Mycenaean period and then decreased sometime between the latter and the present day. That study was never published, perhaps because the geographic area and the time periods were too small to provide robust results.


To get more robust results, we could look at ancient DNA from the entire Greco-Roman world, perhaps divided into three time periods: 5000 to 1000 BC; 1000 to 0 BC; and 0 to 500 AD. Was there a large increase in mean cognitive ability followed by an equally large decrease? Or was there simply a long period of stagnant evolution?


In a previous post, I argued that the culture of Classical Antiquity, particularly in its later stages, caused cognitive evolution to regress (Frost 2022). There were several reasons:


·         A decline in fertility and family formation, particularly among the upper classes;

·         A corresponding increase in female hypergamy, often by freed slaves, which reduced the reproductive importance of upper-class women;

·         An increase in the foreign slave population, which disrupted cognitive evolution within the local population. Even if there had been demographic overflow from the upper classes, that overflow could not have replaced the lower classes, since those classes were being replaced from external sources.


We need a clearer picture. According to the current data, it looks like cognitive evolution simply stagnated during the Post-Neolithic, but I suspect that time period is so broadly defined that it conceals a regression during the centuries before the fifth century collapse and the centuries immediately after.




Frost, P. (2022). When did Europe pull ahead? Evo and Proud, May 16.


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


Price, T.D. (1991). The Mesolithic of Northern Europe. Annual Review of Anthropology, 20, 211-233. Price, T. D. (1983). The European Mesolithic. American Antiquity 48(4), 761–778.  


Woodley, M.A., S. Younuskunju, B. Balan, and D. Piffer. (2017). Holocene selection for variants associated with general cognitive ability: comparing ancient and modern genomes. Twin Research and Human Genetics 20: 271-280.


Woodley of Menie, M.A., J. Delhez, M. Peñaherrera-Aguirre, and E.O.W. Kirkegaard. (2019). Cognitive archeogenetics of ancient and modern Greeks. London Conference on Intelligence  

Monday, May 30, 2022

Recent cognitive evolution: The case of Ashkenazi Jews


Old Jewish cemetery in Prague (Wikicommons - Uoaei)

The 11th century seems to be the time when cognitive evolution began to accelerate among Ashkenazi Jews. In terms of mean cognitive ability, they would end up surpassing not only Christian Europeans but also other Jewish populations. 



In a previous post, I described how Christianity restarted cognitive evolution after a decline during Classical Antiquity, specifically by supporting the formation of monogamous families, by discouraging slavery, at least during the long period from 500 to 1500 AD, and eventually by creating the peace, order, and stability that allowed the middle class to expand and become dominant (Frost 2022).


I will now describe a parallel evolution that occurred under Judaism, particularly within its Ashkenazi branch, i.e., the Jewish communities of Central and Eastern Europe. This cognitive evolution is indicated by four lines of evidence:


·         A high polygenic score for alleles associated with educational attainment (Dunkel et al. 2019; Piffer 2019).

·         High incidences of nine neurological disorders of genetic origin: Tay-Sachs (two unrelated alleles), Gaucher's (five unrelated alleles), Niemann-Pick, and Mucolipidosis Type IV. These mutations affect the capacity of neural tissue to store sphingolipids, which are vital to the growth of neurons in the brain. All nine of them have arisen independently in the same metabolic pathway and have become unusually common in the same population over a relatively short time, perhaps a thousand years (Cochran et al. 2006; Diamond 1994).

·         A mean IQ that exceeds not only that of non-Jewish Europeans but also that of other Jewish groups. This cognitive advantage seems to be relatively recent, originating probably in the Middle Ages (Cochran et al. 2006).

·         A high proportion of Nobel Prize winners: 14% in the first half of the 20th century, 29% in the second half of the 20th century and, so far, 32% in the 21st century (Murray 2007, p. 30).


Within the Ashkenazi community, cognitive evolution was driven largely by specialization in trade, particularly in family-run businesses that operated in the increasingly dynamic economic environment of post-medieval Europe. This class of people, though proportionately smaller, would also contribute to the cognitive evolution of Christian Europeans. "They were not specialized craftsmen in life-trades with skills developed through long years of apprenticeship; they were semi-skilled family labour teams which set up in a line of business very quickly, adapting to shifts in market demand" (Seccombe, 1992, p. 182). The workforce was the household. In more successful households, the parents would have as many children as possible, and the children would marry earlier and start their own households earlier. In less successful ones, the children would postpone marriage or never marry.


This demographic model explains not only the cognitive evolution of Ashkenazi Jews but also their impressive population growth between the 16th and 19th centuries (Frost 2007). It is also the same model that Gregory Clark (2007) used to describe the mental and behavioral shift of the English population during medieval and post-medieval times: demographic success was closely linked to economic success, which in turn was linked to possession of cognitive ability and “middle-class” traits (low time preference, high impulse control, thrift, etc.).


For Ashkenazi Jews during the same time period, cognitive evolution was also assisted by a ban on polygyny. Around 1000 AD, a Jewish synod at Mainz, Germany forbade men to take more than one wife. The ruling was made for several reasons: (1) to reduce “quarreling” within the family; (2) to deter men from abusing their wives; (3) to prevent de facto divorce (i.e., abandonment of the first wife in her own household); and (4) to prevent the husband’s financial resources from being spread too thinly over several wives (Dinonline 2015). The ban on polygyny strengthened the reproductive importance of upper-class women by reducing female hypergamy. In particular, it prevented the classic case of a wealthy man taking a second wife who would be younger than the first but lower in social status … and thus less likely to have the mental and behavioral characteristics that had made him economically successful and able to afford polygyny.


The polygyny ban was accepted by Ashkenazi Jews but not by Sephardic Jews (Dinonlne 2015). This may explain why cognitive evolution was weaker among the latter than among the former. In addition, the Sephardim were operating within a much less dynamic economic environment, particularly during the period from the 16th to 19th centuries that saw so much population growth among the Ashkenazim. 


Reconstructing cognitive evolution


Until recently, it was possible to reconstruct cognitive evolution only by looking at present-day genomes and making inferences about the past. We can now look directly at past cognitive evolution by examining DNA from human remains. For example, when Woodley et al. (2017) compared DNA from sites across Europe and central Asia, they found a net increase between 4,560 and 1,210 years ago in the frequency of alleles associated with high educational attainment.


Unfortunately, that kind of longitudinal data is not yet available for Ashkenazi Jews. But we have a proxy: alleles that affect sphingolipid storage, specifically those for Tay-Sachs, Gaucher’s, Niemann-Pick and Mucolipidosis Type IV. An allele for Gaucher’s disease, and specific to Ashkenazi Jews, has been retrieved from the remains of 33 Jewish individuals who had lived in Erfurt, Germany during the 14th century (Waldman et al. 2022, p. 16).  Those individuals were not directly ancestral to modern Ashkenazi Jews; instead, both groups seem to descend from a common ancestral population that probably existed in the 11th century, when Jewish merchants first became established in Erfurt (Waldman et al. 2022; Wikipedia 2022a). That date is consistent with the estimated time of origin of the allele for Gaucher’s disease, which has been dated to a period between the 11th and 13th centuries (Colombo 2000).


A time of origin in the 11th century is also consistent with the founding of Jewish communities in what is now the Czech Republic and Poland:


We have already mentioned the existence of Jewish traders in Prague in the late tenth century. The biographies of St. Adalbert tell us that they trafficked in slaves. There was also in the early eleventh century, we will discuss further, a Jewish establishment at Przemysl, a town at the crossroads of two trading routes: Prague-Krakow-Kiev and Hungary-Kiev. The importance of this center is confirmed by the discovery, in the mid nineteenth century, of a great treasure of dirhams [Arab silver money] from the Iranian dynasty of the Samanids, dating from the first half of the tenth century. We will see that certain Hebrew documents from the 11th and 12th centuries also report the trade of Rhineland Jewish merchants with Poland. Gallus Anonymus, the famous Polish chronicler of the 11th century, relates that Queen Judith repurchased slaves in Poland from Jewish traders—which also proves the existence of this trade. A final confirmation of this phenomenon: the discoveries of Polish “treasures of silver” [hoards] from the 10th and 11th centuries, which have very many coins from the Rhineland towns of Western Europe. (Lewicki 1960, p. 232)


The importance of that trade is also indicated by the large number of Slavic words that appear in the works of contemporary Jewish authors from the Rhineland and even northern France (Lewicki 1960, pp. 236-237).


It looks like Ashkenazi communities entered an upward economic trend not long before the 11th century. This was a time when both the State and the Church began pacifying the social environment of Western Europe (Frost and Harpending 2015; Head 1992; Wikipedia 2022b). Trade thus became safer. In particular, slave merchants were able to establish long trade routes that ran from the lands of the pagan Slavs, across Western Europe, and into the Islamic world via Muslim Spain (Blumenkranz 1960; Korn 1971; Skirda 2010, pp. 83-120). Erfurt itself was one of several stops on a route from Bohemia to Spain (Skirda 2010, p. 115). It is likely, then, that the 11th century coincides with the time when cognitive evolution began to accelerate among Ashkenazi Jews.


After the 11th century, the slave trade began to lose importance, and other activities gradually took their place. There were a number of reasons. Trade with the Muslim world was disrupted by the Reconquista of Spain and by the Crusades in general. Throughout Western Europe, Jewish communities were accused of having Muslim sympathies and suffered persecution (Skirda 2010, pp. 104-105). Above all else, the Slavs were converting to Christianity, and their enslavement was becoming harder to justify.


Ashkenazi Jews thus shifted toward other activities. At first, they turned to trade with Central Asia via Kiev and the Black Sea (Skirda 2010, p. 105). In time, their interest focused on Europe, which was developing economically and offering many more opportunities. The result was a demographic expansion. From an estimated 25,000 in 1300, the Jewish population of Eastern Europe would grow to 50,000 by 1490, 250,000 after the mid-1600s, 910,000 by 1765, two and a quarter million by 1825, over five and a half million by 1880, and over eight and a half million by 1900 (DellaPergola 2001, p. 12).




Blumenkranz, B. (1960). Juifs et Chrétiens dans le monde occidental. Paris: Imprimerie nationale


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


Cochran, G., J. Hardy, and H. Harpending. (2006). Natural history of Ashkenazi intelligence. Journal of Biosocial Science 38(5): 659-693.


Colombo, R. (2000). Age estimate of the N370S mutation causing Gaucher disease in Ashkenazi Jews and European populations: A reappraisal of haplotype data. American Journal of Human Genetics 66(2):692-697.


DellaPergola, S. (2001). Some fundamentals of Jewish Demographic History. In: S.DellaPergola, and J.Even (eds.) Papers in Jewish Demography 1997, (pp. 11-33), Jerusalem: The Hebrew University.


Diamond, J.M. (1994). Jewish Lysosomes. Nature 368: 291-292.


Dinonline. (2015). Marrying more than one wife: The decree of Rabbeinu Gershom — Then and today. November 18.


Dunkel, C.S, M.A. Woodley of Menie, J. Pallesen, and E.O.W. Kirkegaard. (2019). Polygenic scores mediate the Jewish phenotypic advantage in educational attainment and cognitive ability compared with Catholics and Lutherans. Evolutionary Behavioral Sciences 13(4): 366-375.


Frost, P. (2007). Natural selection in proto-industrial Europe. Evo and Proud, November 16


Frost, P. (2022). When did Europe pull ahead? Evo and Proud, May 16


Frost, P. and H. Harpending. (2015). Western Europe, state formation, and genetic pacification. Evolutionary Psychology 13(1): 230-243.


Head, T.F. (1992). The Peace of God: Social Violence and Religious Response in France around the Year 1000. Cornell University Press.


Korn, B.W. (1971). Slave Trade. Encyclopaedia Judaica 14: 1660-64. Jerusalem: MacMillan.


Lewicki, T. (1961). Les sources hébraïques consacrées a l'histoire de l'Europe centrale et Orientale et particulièrement a celle des pays slaves de la fin du IXe au milieu du XIIIe siècle. Cahiers du Monde russe et soviétique 2(2): 228-41.


Murray, C. (2007). Jewish Genius. Commentary. April: 29-35


Piffer, D. (2019). Evidence for recent polygenic selection on educational attainment and intelligence inferred from Gwas hits: A replication of previous findings using recent data. Psych 1: 55–75.


Seccombe, W. (1992). A Millennium of Family Change. Feudalism to Capitalism in Northwestern Europe. London: Verso.


Skirda, A. (2010). La traite des Slaves. L’esclavage des Blancs du VIIIe au XVIIIe siècle. Paris: Les Éditions de Paris Max Chaleil.


Waldman, S., D. Backenroth, É. Harney, S. Flohr, N.C. Neff, G.M. Buckley, et al. (2022). Genome-wide data from medieval German Jews show that the Ashkenazi founder event pre-dated the 14th century. bioRxiv 2022.05.13.491805.


Wikipedia. (2022a). Erfurt.


Wikipedia. (2022b). Peace and Truce of God.


Woodley, M.A., S. Younuskunju, B. Balan, and D. Piffer. (2017). Holocene selection for variants associated with general cognitive ability: comparing ancient and modern genomes. Twin Research and Human Genetics 20: 271-280.   


Monday, May 23, 2022

A virus that increases intelligence, and what else?


Caterpillar infected by baculovirus, before liquefaction (Wikicommons, Williams et al. 2017)


Higher IQ is associated with antibodies to cytomegalovirus, but only in adults whose IQ is already above a certain level. Which is the cause, and which is the effect?


Cytomegalovirus (CMV) belongs to the herpes family and is spread by contact with bodily fluids. Around 45 to 100% of the population may be infected, although most hosts are unaware that they are infected. It has one of the largest genomes among human viruses, a sign perhaps of its ability to manipulate its host:


With millions of years of coevolution within their hosts, CMVs, like other herpesviruses, encode numerous proteins that can broadly influence the magnitude and quality of both innate and adaptive immune responses. These viral proteins include both homologues of host proteins, such as MHC class I or chemokine homologues, and proteins with little similarity to any other known proteins, such as the chemokine binding protein. Although a strong immune response is launched against CMV, these virally encoded proteins can interfere with the host's ability to efficiently recognize and clear virus, while others induce or alter specific immune responses to benefit viral replication or spread within the host. (Miller-Kittreall and Sparer 2009)


CMV infection at birth leads to mental retardation (Andreou et al. 2021). Recently, however, it has been shown that infection later in life can lead to higher IQ. This is one of three findings from a Norwegian study on IQ and antibodies to CMV in adults. The study showed that CMV seropositivity was significantly associated with higher IQ in men who suffered from bipolar spectrum disorders and with lower IQ in women who suffered from schizophrenia spectrum disorders. CMV seropositivity was not associated with IQ in healthy controls (Andreou et al. 2021). The study’s authors were at a loss to explain the association between CMV seropositivity and higher IQ in bipolar men, all the more so because the number of bipolar men was small, only 35.


An association between CMV and IQ has now been found in healthy individuals. A Czech study has shown that IQ, especially verbal IQ, is higher in people with antibodies to CMV. Moreover, the IQ advantage decreases with decreasing levels of CMV antibodies, i.e., with increasing time since the CMV infection (Chvatálova et al. 2022).


Why do healthy Czechs show this association but not healthy Norwegians? It’s not because the Czechs were a larger sample. In fact, the Czech sample had 283 healthy individuals, and the Norwegian sample 474. The two samples did differ, however, in educational attainment. The Czechs were biology students at a university in Prague, whereas the Norwegians were randomly recruited from the Norwegian population register. The latter were also described as “Caucasians” living in Oslo. Oslo’s population is almost one third of immigrant origin, with Pakistanis forming the largest immigrant group. There are also large numbers of people from Sri Lanka, Turkey, Morocco, and Iraq (Wikipedia 2022). 


The last point would not be problematic if cognitive evolution had ended long ago among the common ancestors of Europeans, Middle Easterners, and South Asians. There is mounting evidence, however, for cognitive evolution in recent times. Ashkenazi Jews seem to have gained their cognitive advantage during the past 1,000 or so years, and the same seems to be true for the Parsis (Cochran et al. 2006; Dunkel et al. 2019; Frost 2021). There is even evidence for significant cognitive evolution in communities that are not normally thought of as ethnic groups, such as French Canadians in regions where British and American traders were historically few in number (Frost 2012).


Why does CMV seropositivity correlate with higher IQ?


The authors of the Czech study suggest that more intelligent people have more social contacts and are thus more likely to catch the virus: “we suggest that more intelligent subjects who have more social and sexual contacts—CMV is transmitted by close contacts, e.g. by kissing—might have a higher risk of encountering a CMV infection.” Yet there is no evidence that smarter people are more extraverted. In fact, they tend to be loners, if only because they have fewer people of their intellectual level to hang out with. The academic consensus seems to be that neither introversion nor extraversion correlates with intelligence (Saklofske and Kostura 1990).


Could the arrow of causality run in the other direction? Is it possible that CMV makes its host smarter? The authors reject that explanation because congenital CMV infection reduces intelligence. But maybe the effect is different in adults.


If CMV does increase the intelligence of adult hosts, the effect would be confined to those whose IQ is already above a certain level. The above two studies showed a significant increase only among university students, and not in a more mixed population with varying levels of educational attainment. But why did the latter study show significantly higher IQ in men with bipolar disorders and significantly lower IQ in women with schizophrenia? For the answer, we can turn to the results of a recent genome-wide association study: most of the alleles for schizophrenia are associated with lower intelligence, and most of the alleles for bipolar disorder are associated with higher intelligence (Smeland et al. 2020). Those results are partially confirmed by the findings of a prospective cohort study: “at least in men, high intelligence may indeed be a risk factor for bipolar disorder, but only in the minority of cases who have the disorder in a pure form with no psychiatric comorbidity” (Gale et al. 2013).


Behavior alteration?


Why would a virus try to make its host smarter? What would it gain? Perhaps the increase in intelligence is a side-effect. Perhaps the virus is trying to improve its chances of spreading to new hosts by altering the behavior of its current host (Cochran et al. 2000; Frost 2020).


Although behavior is more often altered by larger and more complex pathogens, particularly fungi, there are many viruses that engage in behavior alteration. For example, viruses from the baculoviridae family will infect a caterpillar and make it hyperactive to spread their viral progeny over a wider area. Or the caterpillar will be made to climb to the top of a plant and dissolve itself through overproduction of enzymes, thus becoming a mass of tasty goo for ingestion by potential hosts (Han et al. 2015; Williams et al. 2017). Rabies is another behavior-altering virus: it makes its host more aggressive and thus more likely to bite potential hosts.


Although CMV infects a wide range of people, it seems to target a smaller subgroup for behavior alteration, i.e., individuals with intelligence above a certain threshold, and men more than women. If we look at the epidemiological data, we see that male homosexuals are especially susceptible. A study at a venereal disease clinic found that antibodies to CMV were present in 94% of the male homosexual patients and 54% of the male heterosexual patients. “The data suggest that sexual transmission is an important mode of spread of CMV among adults and that homosexual men are at greater risk for CMV infections than are heterosexual men” (Drew et al. 1981). Another study has identified passive anal sex as the most effective means of transmission: “Of seven sexual practices investigated, only passive anal-genital intercourse correlated with the acquisition of cytomegalovirus infection (p =0.008)” (Mintz et al. 1983).


Which is the cause and which is the effect? Does passive anal sex facilitate CMV infection? Or does CMV infection facilitate the desire for passive anal sex? The answer may be ‘yes’ to both questions. Sometimes ‘the cause’ and ‘the effect’ are two sides of the same coin.


This virus may indeed be the ‘gay germ’ that Greg Cochran has written about. Or one of them. Male homosexuality probably has several causes, and the microbial cause probably involves more than one pathogen.





Andreou, D., K.N. Jørgensen, L.A. Wortinger, K. Engen, A. Vaskinn, T. Ueland, R.H. Yolken, O.A. Andreassen, and I. Agartz. (2021). Cytomegalovirus infection and IQ in patients with severe mental illness and healthy individuals. Psychiatry Research 300:113929.  


Chvatálová, V., B. Šebánková, H. Hrbáčková, P. Tureček, L. Příplatová, and J. Flegr. (2022). Differences in cognitive performance between cytomegalovirus-infected and cytomegalovirus-free students. PsyArXiv, 5 May 2022.  


Cochran, G.M., P.W. Ewald, and K.D. Cochran. (2000). Infectious Causation of Disease: An Evolutionary Perspective. Perspectives in Biology and Medicine 43 (3): 406-48.  


Cochran, G., J. Hardy, and H. Harpending. (2006). Natural history of Ashkenazi intelligence. Journal of Biosocial Science 38: 659-693,  


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Wikipedia (2022). Oslo – Demographics.

Monday, May 16, 2022

When did Europe pull ahead?


Medieval market – Nicole Oresme (15th century) (Wikicommons)


In terms of GDP per capita growth, northwest Europe began to surpass the rest of the world during the 14th century: before the conquest of the Americas, the invention of printing, the Atlantic slave trade, and the Protestant Reformation.



In a recent post, Steve Sailer asks why the European world pulled ahead of the non-European world between 1000 and 1500 AD:


[…] much of the non-European world entered a sort of cultural recession well before Europeans directly interfered with them. If you look at, say, Charles Murray’s 2003 book Human Achievement, several major non-European civilizations appear to have lost momentum in making progress in the arts and sciences over roughly the time period of 1000 or maybe 1250 to 1500. (Sailer 2022)


For Steve, the reason was the collapse of the Mongol Empire during the 14th century. That century was indeed a turning point for Europe, particularly for England and Holland:


These North Sea economies experienced sustained GDP per capita growth for six straight centuries. The North Sea begins to diverge from the rest of Europe long before the 'West' begins its more famous split from 'the rest.'


[...] we can pin point the beginning of this 'little divergence' with greater detail. In 1348 Holland's GDP per capita was $876. England's was $777. In less than 60 years time Holland's jumps to $1,245 and England's to 1090. The North Sea's revolutionary divergence started at this time. (Greer 2013b)


This process began before the European conquest of the Americas, the invention of printing, the creation of modern finance institutions, the Atlantic slave trade, or the Protestant Reformation. None of these can be proper explanations for this "little divergence." (Greer 2013a; see also Thompson 2012 and Hbd *chick 2013).


The divergence began within a part of Europe that was much less affected by the rise and fall of the Mongol Empire. Moreover, if we compare southern Europe with North Africa during the same period, we see the same divergence that we see more generally between Christian Europe and the rest of the world. Yet North Africa was never conquered by the Mongols.


It looks like internal causes were responsible for the divergence between Christian Europe and the rest of the world. Those causes seem to have their point of origin in northwest Europe during the long period from 500 to 1500 AD. In that region, the Western Church consolidated a pre-existing pattern of small, nuclear households, weak family ties, and residential mobility, thus strengthening a mindset of individualism and impersonal sociality (Frost 2020; Schulz et al. 2019). Then, from 1000 AD onward, the Western Church strove to pacify social relations (Frost and Harpending 2015). Those two factors—an individualistic mindset operating in a pacified social environment—allowed the market economy to expand into all areas of life and eventually replace kinship as the main organizing principle of society (Frost 2020; Macfarlane 1978; Weber 1930).


The expansion of the market economy went hand in hand with the expansion of the middle class. In England, this class began to expand in the twelfth century and would gradually replace the lower classes through downward mobility. By the 1800s, its lineages accounted for most of the English population. English society thus became more middle class in its values: "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). The same process took place elsewhere in Western Europe and more generally throughout Europe to varying degrees and over different timescales (Frost 2019, p. 176).


In sum, between 500 and 1500 AD the Western Church created a system of social reproduction that would have far-reaching demographic, behavioral, and economic consequences. To understand that system, one must understand not only the Bible but also the writings of early and medieval Christianity, as well as the pagan Germanic elements it incorporated (Russell 1994). Finally, one must understand the preceding system, and its failings.


The pre-Christian world: demographic and cognitive decline


Ancient DNA from Greece suggests that mean cognitive ability began to decline at some point during Classical Antiquity (Woodley of Menie et al. 2019). A similar decline probably happened throughout the Mediterranean basin and the Middle East of that time.

There were three main causes:


·         A decline in fertility and family formation, particularly among the upper classes (Caldwell 2004; Hopkins 1965; Roetzel 2000, p. 234);

·         A corresponding increase in female hypergamy, often by freed slaves, which reduced the reproductive importance of upper-class women (Perry 2013);

·         An increase in the slave population, particularly foreign slaves (Harris 1999). This ongoing influx disrupted the process of local cognitive evolution. Even if there had been demographic overflow from the upper classes, that overflow could not have replaced the lower classes, since those classes were being replaced from external sources.


Christianity and Islam both tried to correct the ruinous demographic state of the ancient world. Islam succeeded in reversing negative population growth but failed to restart cognitive evolution. In some ways, it made such evolution more difficult. Islam increased female hypergamy by permitting male polygamy, thus further reducing the reproductive importance of upper-class women (van den Berghe 1960). Foreign slaves were also imported on a larger-scale than in antiquity, thus further disrupting local cognitive evolution (Lewis 1990). Finally, the upper classes tended to congregate in urban areas, where the death rate was higher.


Before the 20th century, population growth had been sluggish in the Muslim world. Wherever Muslims coexisted with Christians, the latter community was often the one that grew at a faster pace. This was the case in the Balkans:


By the end of the eighteenth century the Muslim population had entered a period of comparative economic and moral decline. Several explanations have been offered for this development. Certainly the fact that the Muslim population provided the soldiers contributed to its ultimate weakening. Their concentration in towns also made them more susceptible to the ravages of plague and other diseases. Turkish customs, particularly the practice of polygamy, played a part. This process of decay was clearly illustrated in the eighteenth century in the changing demography of the Balkan towns where Christian and national elements formed an increasingly larger proportion of the population (Jelavich and Jelavich, 1977, pp. 6-7)


Christianity, especially Western Christianity, succeeded not only in promoting population growth but also in restarting cognitive evolution, specifically by supporting the formation of monogamous families, by discouraging slavery, at least during the long period from 500 to 1500 AD, and eventually by creating the peace, order, and stability that allowed the middle class to expand and become dominant. The rise of Christian Europe actually began before its expansion into the Americas and Asia. The latter was, in fact, a consequence of the former.




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Frost, P. and H. Harpending. (2015). Western Europe, state formation, and genetic pacification. Evolutionary Psychology 13(1): 230-243.


Greer, T. (2013a). The Rise of the West: Asking the Right Questions. July 7, The Scholar's Stage.  


Greer, T. (2013b). Another look at the 'Rise of the West' - but with better numbers. November 20, The Scholar's Stage.    


Harris, W. (1999). Demography, Geography and the Sources of Roman Slaves. Journal of Roman Studies 89, 62-75.  


Hbd *chick (2013). Going Dutch, November 29.


Hopkins, K. (1965). Contraception in the Roman Empire. Comparative Studies in Society and History 8(1): 124-151.  


Jelavich, C. and B. Jelavich. (1977). The Establishment of the Balkan National States, 1804-1920. Seattle: University of Washington Press.


Lewis, B. (1990). Race and Slavery in the Middle East. New York: Oxford University Press.


Macfarlane, A. (1978). The Origins of English Individualism: The Family, Property and Social Transition. Oxford: Blackwell.


Perry, M.J. (2013). Gender, Manumission, and the Roman Freedwoman. Cambridge University Press.


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Russell, J.C. (1994). The Germanization of Early Medieval Christianity: A Sociohistorical Approach to Religious Transformation. New York; Oxford: Oxford University Press.


Sailer, S. (2022). Why was much of the non-European world stagnating well before 1492? The Unz Review, May 10  


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