Ashkenazi Jews and recent cognitive evolution

Distribution of Jews in central and eastern Europe, circa 1900 (Wikicommons)

For almost a millennium, Ashkenazi Jews saw their mean cognitive ability steadily increase from one generation to the next. That increase ended in the 20th century and has given way to a noticeable decline since the 1970s.

Trade selects for cognitive ability. The selection may act directly, through the cognitive demands of bargaining, calculating, writing, budgeting, and planning. It may also act indirectly, through a consequent increase in social complexity. For example, trade leads to use of written documents as a means to record transactions and contractual obligations, but the same skills of reading and writing also favor the development of literature in general.

I have already described this evolutionary trajectory with respect to the Igbos of Nigeria and the Parsis of India. I will now turn to the Jewish communities of central and eastern Europe, i.e., the Ashkenazi Jews. They have existed as a distinct group for about a millennium and a half, and for most of that time they were mainly traders of one sort or another. Those niches required certain mental abilities, particularly numeracy and literacy. Literacy also mattered for the minority who went into religious study and who, unlike their Christian counterparts, could marry and have families.

Today, they are renowned for achievement in a wide range of fields:

In the first half of the 20th century, despite pervasive and continuing social discrimination against Jews throughout the Western world, despite the retraction of legal rights, and despite the Holocaust, Jews won 14 percent of Nobel Prizes in literature, chemistry, physics, and medicine/physiology. In the second half of the 20th century, when Nobel Prizes began to be awarded to people from all over the world, that figure rose to 29 percent. So far, in the 21st century, it has been 32 percent. (Murray, 2007, p. 30)

Such a record of achievement is usually put down to Jewish culture and its emphasis on education (Botticini and Eckstein, 2012). That explanation, however, does not preclude a genetic one. A culture that favors learning will favor those who are better at learning. Such individuals will do well in life. They will more likely survive into adulthood, build a stable livelihood, get married, and have a large family. That kind of reproductive success fueled a population boom that took the Ashkenazim from an estimated 25,000 in 1300 to over eight and a half million by 1900 (DellaPergola, 2001, p. 12). Because the successful among them translated their economic success into reproductive success, certain mental abilities became more and more prevalent with each passing generation.

The above cognitive evolution is attested by two kinds of genetic evidence: polygenic scores and neurological disorders.

Polygenic score (PGS) - alleles associated with educational attainment

Researchers have identified a large number of genes whose alleles are associated with differences in educational attainment, which can serve as a proxy for differences in IQ. Taken together, these alleles can provide a measure of the genetic component of cognitive ability: the polygenic score (PGS) (Lee et al., 2018).

The Dunkel et al. PGS study

Dunkel et al. (2019) compared the PGS with performance on three measures of cognitive ability: IQ, educational attainment, and a similarities test (e.g., “In what way are air and water alike”). The data came from the Wisconsin Longitudinal Study (WLS), a longitudinal study of randomly sampled Wisconsin high school students that ran from 1957 to 2011. The students were asked about their religious affiliation in 1975 and genotyped in 2007-2010. There were three main groups: Jews (n=53), Catholics (n=2,603), and Lutherans (n=2,027).

The Jewish students outperformed their Catholic and Lutheran counterparts on all three scores. Moreover, their superior performance was significantly explained by their high frequencies of alleles associated with high educational attainment.

The study’s methodology has been criticized, particularly the small sample of 53 Jewish students, and the possible risk of it being unrepresentative. Although the Jewish students, like the non-Jewish ones, were selected at random from Wisconsin high schools, there were nonetheless significant differences between the two groups:

For example, even though graduates from over 400 high schools are included in WLS, most Jewish respondents in WLS graduated from just two high schools. The non-Jewish respondents from those two schools were also much more likely to attend college than the overall proportion in WLS (89% and 57% vs. 42%). Similarly, even though more than 20% of WLS respondents grew up on farms, virtually no 6 Jewish respondents did (0%). (Freese et al., 2019, pp. 5-6)

None of that indicates that the sample was unrepresentative. The American Jewish community is more likely to live in urban areas and have postsecondary education. The methodology is, however, vulnerable to criticism on another point. The PGS over-predicts Jewish IQ and under-predicts Catholic/Lutheran IQ:

A naïve causal interpretation of the polygenic score difference might therefore lead one to anticipate that cognitive test scores for Jewish respondents would be not just above the mean for non-Jewish respondents, but routinely at genius levels. Instead, as noted, the average for Jewish respondents is only about two-thirds of an SD above the mean (or about 110 in the IQ metric), and even this shrinks to just below half an SD when we look at all respondents for whom we have 1975/7 survey data in WLS, as opposed to only those for whom we have genetic data. (Freese et al., 2019, p. 3)

Keep in mind that the PGS is based on those alleles that have been identified to date. Those that remain unidentified tend to be less frequent and more likely to escape the notice of researchers. The PGS is thus biased toward frequent alleles. Such alleles have contributed much more to cognitive evolution among the Ashkenazim, who began as a small founder group of perhaps 350 individuals (Carmi et al. 2014). They have thus had a narrower range of promising alleles than have Europeans in general.

The Piffer PGS study

When Piffer (2019) measured the PGS of several populations, he found that Ashkenazi Jews had the highest score of all the populations under study, with a predicted IQ of about 108. The sample size (n=145) was larger than that of Dunkel et al. (2019), and the sample data came from the Genome Aggregation Database—the largest publicly-available source of genomic information. Since this database receives data from many different studies (mainly relating to diseases or population genetics), it is difficult to say how the sample might be biased.

Neurological disorders

Ashkenazi Jews have higher 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 disorders affect the capacity of neural tissue to store sphingolipids, which are vital to the growth of neurons.

Nine mutations have thus arisen independently in the same metabolic pathway and have become unusually frequent in the same population over the same short time. That isn't chance. That's strong natural selection, most likely through heterozygote advantage. In other words, a disorder develops only if the same allele is inherited from both parents. If just one parent has it, as more often happens, the child will suffer no adverse effects; in fact, the child's brain will be better supplied with sphingolipids and better at processing information. Evidently, these alleles are a fraction of a much larger number of alleles that explain the Ashkenazi cognitive advantage. They are simply the most obvious ones (Cochran et al., 2006; Diamond, 1994).

Trajectory of Ashkenazi cognitive evolution

The various communities of the diaspora have probably enjoyed a cognitive advantage over their host societies. But the advantage has been much greater among those from central and eastern Europe (Ashkenazim) than among those from North Africa and the Middle East (Sephardim and Mizrahim). Cochran et al. (2006) attribute this difference to a greater concentration of Ashkenazim in occupations with high cognitive demands, notably sales, trade, and finance.

In my opinion, there are two additional reasons.

• From the fourteenth century onward, Europe offered a more dynamic economic environment than did North Africa and the Middle East. This is reflected in the higher rate of population growth of the Ashkenazi community during that period, in comparison to the Sephardic and Mizrahi communities. That growth was fueled by successful men translating their economic success into reproductive success, partly because they saw procreation as a desirable goal in and of itself, and partly because they relied primarily on a family workforce. Expanding that workforce was most easily done by having more children, both by marrying earlier and by helping one’s children to marry earlier. In less successful households, children would postpone marriage or never marry. Family formation was thus predicated on success at cognitive tasks that most non-Jews did not have to succeed at.

• The Ashkenazim ceased to practice polygyny circa 1000 AD, when a Jewish synod at Mainz, Germany, forbade men to take more than one wife (Dinonline, 2015).  That ruling had the effect of reducing female hypergamy and thereby increasing the reproductive importance of upper-class women. In particular, it prevented the typical case of a wealthy man taking a second wife who would be not only younger but also lower in social status, and less likely to possess the mental and behavioral characteristics that had made him successful and able to afford a second wife. The polygyny ban was not accepted by Sephardim and Mizrahim (Dinonlne, 2015).

Thus, beginning around the year 1000, and even more so from 1300 onward, Ashkenazi Jews embarked on an upward cognitive trajectory. In theory, we can reconstruct that trajectory by retrieving DNA from human remains and identifying the alleles of genes associated with educational attainment. 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.

We still lack such longitudinal data for Ashkenazi Jews, but we do have a proxy: alleles for neurological disorders that are unusually frequent among them and which seem to be associated with their cognitive evolution. 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 fourteenth century (Waldman et al., 2022, p. 16).  Those individuals were not directly ancestral to Ashkenazi Jews; instead, both groups seem to descend from an ancestral population of the eleventh 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 is thought to have first appeared between the eleventh and thirteenth centuries (Colombo, 2000).

An Ashkenazi origin in the eleventh 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 10th century. The biographies of St. Adalbert tell us that they trafficked in slaves. There was also in the early 11th 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 10th 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 trade with eastern Europe is also shown by the many 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 the Ashkenazim entered a better economic environment during the eleventh century. This was when Church and State joined forces to pacify the social environment of Western Europe (Frost and Harpending, 2015; Head, 1992; Wikipedia, 2022b). Trade thus became safer. In particular, merchants were able to establish long trade routes 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 a stop on a route from Bohemia to Spain (Skirda, 2010, p. 115). The new social and economic environment coincided with the acceleration of cognitive evolution among Ashkenazi Jews.

The following centuries saw the slave trade lose importance. As the Slavs converted to Christianity, it became morally difficult to enslave them for export to the Muslim world. Such trade was also made difficult by the Reconquista in Spain and the Crusades in the Middle East (Skirda, 2010, pp. 104-105). Ashkenazi Jews thus turned toward other activities. At first, they looked 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 more opportunities. The result was a sustained demographic expansion of their community until the late nineteenth century (DellaPergola, 2001, p. 12).

 “A strange collapse”

The early to mid-twentieth century seems to have marked the peak of Ashkenazi achievement in science, the arts, entertainment, industry, and academia. A decline then set in. Ron Unz presents several lines of evidence for what he calls "the strange collapse of Jewish achievement":

• U.S. Math Olympiad – Over 40% of the top students were Jewish in the 1970s. During the 1980s and 1990s, the percentage averaged about one-third. From 2000 to 2012, it was 2.5%.

• Putnam Exam (a mathematics competition for American college students) – Over 40% of the winners were Jewish before 1950. Between then and the 1990s, the percentage was 22-31%. It has been under 10% since 2000, without a single likely Jewish name between 2005 and 2012.

• Science Talent Search – Of the national finalists, 22-23% were Jewish from the 1950s to the 1980s. The percentage was 17% in the 1990s, 15% in the 2000s, and 7% from 2010 to 2012.

• Physics Olympiad – Jews were over one-quarter of the top students from 1986 to 1997. During the 2000s the percentage was 5%.

• Biology Olympiad – From 2000 to 2012, only 8% of the top students were Jewish, and none from 2010 to 2012.

• Computing Olympiad – Between 1992 and 2012, only 11% of the winners had Jewish names.

• Siemens AP Award – Between 1992 and 2012, only 8% of the winners had Jewish names.

• Chemistry Olympiad – From 2010 to 2012, none of the winners had a probable Jewish name. (Unz, 2012)

The post-1970s decline has also been described by Chad and Brym (2020):

[…] the proportion of Jewish recipients of the Fields Medal, awarded to mathematicians under the age of 40, is 65.3% lower thus far in the twenty-first century than in the twentieth century. Prior to 2000, Jews won the majority of world chess championships. Since then, not a single world chess champion has been of Jewish origin. The number of American Ph.D. recipients with distinctive Jewish names has been falling since the 1970s. The declining rate of Jewish winners of middle school spelling bees and high school science olympiads in the United States leads us to anticipate a continuation of the trend into the next generation

Among students at the University of Toronto Medical School, Jewish representation reached a high point of 26% between 1958 and 1978. It then fell to 18% in 1988, 17% in 1998, 14% in 2008 and 11% in 2018. If one adjusts for the size of the Jewish population in the Toronto region, the decline seems to have begun during the 1970s (Chad and Brym, 2020).

What has been driving that decline? For Unz (2012), the cause was loss of immigrant values: "today's overwhelmingly affluent Jewish students may be far less diligent in their work habits or driven in their studies than were their parents or grandparents, who lived much closer to the bracing challenges of the immigrant experience." This is also the explanation favored by Chad and Brym (2020). If the cause is indeed loss of immigrant values, it should correlate with use of the Yiddish language, which began to decline during the 1930s among foreign-born American Jews (Wikipedia, 2022d). Yet academic achievement would not begin to decline until four decades later.

In support of his argument, Unz (2012) points to the Jewish winners of the Math Olympiad during the 1990s and 2000s, up to half of whom were recent immigrants from the former Soviet Union. During the same period, however, almost a million Soviet Jews moved to Israel, and yet that country’s mean IQ has fallen from 101 in the 1960s to 95 today (Rindermann 2018, p. 148).

Perhaps the Soviet Jews who left for Israel were different from those who left for the United States. About half of the latter arrived under the Lautenberg amendment (1990), which authorizes the entry of religious minorities "with a credible, but not necessarily individual, fear of persecution." In Israel, they arrived under the Law of Return, which lets in anyone with at least one Jewish grandparent or a Jewish spouse.

Israel is thus more open to immigrants from the former Soviet Union, as long as they have some sort of Jewish affiliation. The affiliation is often weak:

In 1988, a year before the immigration wave began, 58% of married Jewish men and 47% of married Jewish women in the Soviet Union had a non-Jewish spouse. Some 26%, or 240,000, of the immigrants had no Jewish mother (Wikipedia, 2022c)

Intermarriage has increased considerably in the source countries of Israel’s immigrants, not only the former Soviet Union but also the United States, Canada, and France. If Jews are becoming less and less Jewish by ancestry, it should be no surprise that anything specific to them genetically is likewise becoming less and less, whether they live in Israel or in the United States.

Conclusion

The decline in Jewish achievement since the 1970s may either support or refute a genetic cause. Ron Unz argues that "the innate potential of a group is unlikely to drop so suddenly." But that is true only when the group has a closed membership. According to a 2013 American survey, the intermarriage rate is now 58% among all Jews and 71% among non-Orthodox Jews. Yet 81% of all Jews still raise their children as Jewish (Goodstein, 2013). "Jewishness" is increasingly self-defined and self-ascribed.

A secondary cause is the sharp decline in fertility among the most intelligent women of Western societies (Kanazawa 2014). This may explain the recent slowing down and reversal of the Flynn Effect and the increase in reaction time since 1980 (Flynn, 2007, pp. 143; Frost, 2014; Madison, 2014; Teasdale and Owen, 2005). The same differential fertility probably affects Jewish Americans.

In sum, mean cognitive ability has been declining in successive generations of Jewish Americans for two reasons: (1) intermarriage; and (2) lower fertility of those with higher cognitive ability. When the baby-boom generation dies off, we may see an end to the remarkable Jewish presence in American life.

References

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

Botticini, M. and Z. Eckstein. (2012). The Chosen Few. How Education Shaped Jewish History, 70-1492. The Princeton Economic History of the Western World, vol. 42. Princeton University Press. https://doi.org/10.1515/9781400842483

Carmi, S., K. Hui, E. Kochav, X. Liu, J. Xue, F. Grady, S. Guha, K. Upadhyay, D. Ben-Avraham, S. Mukherjee, et al. (2014). Sequencing an Ashkenazi reference panel supports population-targeted personal genomics and illuminates Jewish and European origins. Nature Communications 5: 4835. https://doi.org/10.1038/ncomms5835

Chad, J.A., Brym, R. (2020). Jewish Intellectual Exceptionalism? Ethnic Representation at the University of Toronto Medical School. Contemporary Jewry 40, 387–402 (2020). https://doi.org/10.1007/s12397-020-09344-0

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. https://doi.org/10.1017/S0021932005027069  

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. https://doi.org/10.1086/302757  

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. https://doi.org/10.1038/368291a0  

Dinonline. (2015). Marrying more than one wife: The decree of Rabbeinu Gershom — Then and today. November 18. https://dinonline.org/2015/11/18/marrying-more-than-one-wife-the-decree-of-rabbeinu-gershom-then-and-today/  

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. https://psycnet.apa.org/doi/10.1037/ebs0000158  

Flynn, J.R. (2007). What is Intelligence? Beyond the Flynn Effect. Cambridge University Press.

Freese, J., B. Domingue, S. Trejo, K. Sicinski, and P. Herd. (2019). Problems with a Causal Interpretation of Polygenic Score Differences between Jewish and non-Jewish Respondents in the Wisconsin Longitudinal Study. SocArXiv, 10 July https://doi.org/10.31235/osf.io/eh9tq  

Frost, P. (2014). What happened in the 1980s to reaction time? Evo and Proud, May 3. http://evoandproud.blogspot.ca/2014/05/what-happened-in-1980s-to-reaction-time.html  

Frost, P. and H. Harpending. (2015). Western Europe, state formation, and genetic pacification. Evolutionary Psychology 13(1): 230-243. https://doi.org/10.1177%2F147470491501300114  

Goodstein, L. (2013). Poll shows major shift in identity of U.S. Jews. The New York Times, October 1. https://www.nytimes.com/2013/10/01/us/poll-shows-major-shift-in-identity-of-us-jews.html   

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

Kanazawa, S. (2014). Intelligence and childlessness. Social Science Research 48: 157-170. https://doi.org/10.1016/j.ssresearch.2014.06.003  

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

Lee, J. J., Wedow, R., Okbay, A., Kong, E., Maghzian, O., Zacher, et al. (2018). Gene discovery and polygenic prediction from a genome-wide association study of educational attainment in 1.1 million individuals. Nature Genetics 50(8): 1112-1121. https://doi.org/10.1038/s41588-018-0147-3   

Lewicki, T. (1961). Les sources hébraïques consacrées à l'histoire de l'Europe centrale et Orientale et particulièrement à celle des pays slaves de la fin du IXe au milieu du XIIIe siècle. Cahiers du Monde russe et soviétique 2(2): 228-41. https://doi.org/10.3406/cmr.1961.1466  

Madison, G. (2014). Increasing simple reaction times demonstrate decreasing genetic intelligence in Scotland and Sweden, London Conference on Intelligence, Psychological comments, April 25, #LCI14 Conference proceedings. http://www.unz.com/jthompson/lci14-questions-on-intelligence/

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. https://doi.org/10.3390/psych1010005  

Rindermann, H. (2018). Cognitive Capitalism. Human Capital and the Wellbeing of Nations. Cambridge University Press.

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

Teasdale, T.W., and D.R. Owen. (2005). A long-term rise and recent decline in intelligence test performance: The Flynn Effect in reverse. Personality and Individual Differences 39(4): 837-843. https://doi.org/10.1016/j.paid.2005.01.029  

Unz, R. (2012). The myth of American meritocracy. The American Conservative, November 28. http://www.theamericanconservative.com/articles/the-myth-of-american-meritocracy/

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. Cell online 30 November. https://doi.org/10.1016/j.cell.2022.11.002  

Wikipedia. (2022a). Erfurt. https://en.wikipedia.org/wiki/Erfurt#Middle_Age  

Wikipedia. (2022b). Peace and Truce of God. https://en.wikipedia.org/wiki/Peace_and_Truce_of_God  

Wikipedia (2022c). 1990s Post-Soviet Aliyah. https://en.wikipedia.org/wiki/1990s_Post-Soviet_aliyah

Wikipedia (2022d). American Jews – Demographics. https://en.wikipedia.org/wiki/American_Jews#Demographics

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. https://doi.org/10.1017/thg.2017.37    

Updated December 6, 2022