Monday, April 1, 2019

They really are smart ... and other surprises

Rachela - Maurycy Gottlieb (1856-1879) (Wikicommons). Ashkenazi Jews have a higher incidence of genetic variants associated with high educational attainment.

Intelligence varies from one individual to the next, and most of this variance has genetic causes. But what, exactly, are these causes? Lots and lots of genes, it seems. To be precise, if we look at the genes that influence human intelligence, we find two things:

1. They are very numerous, numbering in the thousands.

2. In general, their variants differ slightly in their effects.

This shouldn't be surprising. Evolution proceeds by tinkering, i.e., by making little changes. Big changes tend to produce big side-effects, and most side-effects are deleterious. So the genetic capacity for intelligence differs among humans through small differences at thousands upon thousands of genes. Does it follow, then, that we cannot understand these differences by looking only at a few genes? Not necessarily. Each gene is like a weathervane. If you can get enough subjects from a human population, even a few genes will tell you the direction and strength of natural selection for intelligence. 

Davide Piffer began looking at these “weathervanes” six years ago. He gathered data from different human populations on ten SNPs (single nucleotide polymorphisms) whose genetic variants are associated with differences in intelligence, specifically differences in educational attainment. Then, for each population, he estimated its genetic capacity for intelligence by calculating a "polygenic score"—the number of genetic variants associated with higher educational attainment, out of a maximum of ten.

This score correlated with population IQ (r=0.90) and with PISA scores (r=0.84). It was highest in East Asians:

East Asians have the highest frequencies of alleles beneficial to educational attainment (39%) and consistently outperform other racial groups both within the US and around the world, in terms of educational variables such as completion of college degree or results on standardized tests of scholastic achievement. Europeans have slightly lower frequencies of educational attainment alleles (35.5%) and perform slightly worse in terms of educational attainment, compared to East Asians. On the other hand, Africans seem to be disadvantaged both with regards to their level of educational attainment in the US and around the world. Indeed, Africans have the lowest frequencies of alleles associated with educational attainment (16%). (Piffer 2013)

These results were considered preliminary. Thousands upon thousands of genes influence intelligence, and here we have only ten! Perhaps chance alone produced this geographic pattern. Over the next few years, as other researchers discovered more SNPs associated with educational attainment, Davide Piffer repeated his study with more of these weathervanes.

His latest study has just come out. It uses data on 2,411 SNPs, and the polygenic score correlates even higher with population IQ (r=0.98). The geographic pattern is the same, with East Asians scoring higher than Europeans, and with Africans scoring lower.

Yes, Jews really are smart

This time, however, the highest score was obtained for Ashkenazi Jews: 

This dataset included a sample of 145 Ashkenazi Jewish individuals. The IQ of Ashkenazi Jews has been estimated to be around 110 [34]. Remarkably, their EDU polygenic score was the highest in our sample, corresponding to a predicted score of about 108, mirroring preliminary results from a smaller (N = 53) sample (Dunkel et al., 2019) [34]. (Piffer 2019)

This finding vindicates the authors of a paper written more than a decade ago. Gregory Cochran, Jason Hardy, and Henry Harpending presented evidence that the mean IQ of Ashkenazi Jews exceeds not only that of non-Jewish Europeans but also that of other Jewish groups. The most striking piece of evidence is the high incidence among Ashkenazim of four genetic disorders: Tay-Sachs, Gaucher, Niemann-Pick, and mucolipidosis type IV (MLIV). All four affect the capacity to store sphingolipid compounds that promote the growth and branching of axons in the brain. These disorders are caused by alleles that are harmful in the homozygote state and beneficial in the much more common heterozygote state, i.e., the brain receives higher levels of sphingolipids without the adverse health effects.

Ironically, these facts are coming to light at a time when Ashkenazi Jews are disappearing through low fertility and high out-marriage. Meanwhile, and not coincidentally, they are disappearing from the ranks of top winners at the U.S. Math Olympiad, the Putnam Exam, the Computing Olympiad, and other academic competitions. This decline became noticeable in the 1980s and has accelerated since the turn of the millennium (Unz 2012; Frost 2018). Jews are still present in intellectual and cultural life, but this presence is losing its dynamism and becoming a mere legacy.

African American IQ is higher than predicted

The polygenic score seems to underpredict the IQ of African Americans:

Indeed, the IQ of African Americans appears to be higher than what is predicted by the PGS (Figure 2), which suggests this cannot be explained by European admixture alone, but it could be the result of enjoying better nutrition or education infrastructure compared to native Africans. Another explanation is heterosis ("hybrid vigor"), that is the increase in fitness observed in hybrid offspring thanks to the reduced expression of homozygous deleterious recessive alleles. (Piffer 2019)

I’d propose another possible explanation: higher intelligence in African Americans may be associated with a somewhat different basket of genetic variants. Some of these variants may come from our friends the Igbos, who seem to have followed their own evolutionary path toward higher intelligence (Frost 2015). Many notable African Americans are in fact of Igbo descent, including Forest Whitaker, Paul Robeson, and Blair Underwood (Wikipedia 2019).

Davide is skeptical about this explanation, pointing out that population IQ is in line with the polygenic score he calculated for sub-Saharan African groups (Esan, Gambians, Luhya, Mende, Yoruba). None of those groups, however, are Igbo, and it's really the Igbo who stand out among West Africans in measures of intellectual and educational attainment. If only for the sake of curiosity, we should find out their polygenic score. This score may underpredict their genetic capacity for intelligence, which to some degree would be boosted by genetic variants that exist only in sub-Saharan Africa, but it should still exceed what we see for other West Africans.


This latest study brings to 2,411 the number of SNPs that can inform us about the genetic capacity for intelligence in different human populations. This information was more dubious when only ten SNPs were available, and the geographic pattern could be put down to chance. That argument now seems weak. If chance is causing this pattern, why do we keep getting the same one?

Sure, we can wait until we get even more relevant SNPs, but the overall picture will probably remain the same. We will get finer geographic detail. In France, for example, we will probably understand why educational attainment is so much higher in Brittany (see:  H/T to Philippe Gouillou). There are probably several European regions and subregions where the genetic capacity for intelligence is on a par with what we see in Ashkenazi Jews and East Asians.

In sum, these findings deserve to be better known ... and more widely discussed.


Initially, I wrote that Davide Piffer used 127 SNPs. In fact, 127 is the number of SNPs found in the HGDP (low coverage) dataset. In the other two datasets (1000 Genomes and GnomAd), those that the main analysis was based on, there were actually 2,411 SNPs.

Hiatus alert ****

I'll be unable to post for the near future, probably the next three months. 


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

Frost, P. (2018). The end of Jewish achievement? Evo and Proud, May 21

Frost, P. (2015). The Jews of West Africa, Evo and Proud, July 4

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(1): 55-75

Piffer, D. (2013). Factor analysis of population allele frequencies as a simple, novel method of detecting signals of recent polygenic selection: The example of educational attainment and IQ, Mankind Quarterly 54(2): 168-200 

Unz, R. (2012). The myth of American meritocracy. The American Conservative, November 28   

Wikipedia (2019). Igbo people.