Thursday, June 17, 2021

Getting the message


Gaps between perceived and actual crime rates, by immigrant group in the Netherlands. Dutch people underestimate the crime rate of immigrants from sub-Saharan Africa and the Caribbean while overestimating the crime rate of lighter-skinned immigrants, including Roma, Turks, and Chinese. The latter don’t benefit from the messaging of modern culture.



The crime news is unfair to Negroes, on the one hand, in that it emphasizes individual cases instead of statistical proportions [...] and, on the other hand, in that all other aspects of Negro life are neglected in the white press which gives the unfavorable crime news an undue weight. Sometimes the white press "creates" a Negro crime wave where none actually exists. (Myrdal 1944, pp. 655-656)


Gunnar Myrdal wrote An American Dilemma during the early years of the civil rights movement. He won over many young educated people, particularly when he argued that prejudice was making Black American criminality seem worse than it really was:


The popular belief that all Negroes are inherently criminal operates to increase arrests, and the Negro's lack of political power prevents a white policeman from worrying about how many Negro arrests he makes. Some white criminals have made use of these prejudices to divert suspicion away from themselves onto Negroes: for example, there are many documented cases of white robbers blackening their faces when committing crimes. (Myrdal 1944, p. 968)


The theme of the "framed Black man" would be central to a work of fiction, To Kill a Mockingbird. Since its publication in 1960 it has never been out of print. In 2006, it was the book most often mentioned when British librarians were asked: "Which book should every adult read before they die?" (Pauli 2006). Thus, for at least six decades, there has been a social norm of downplaying Black crime.


This norm has spread not only within the United States but also to all countries where English is widely used, particularly among the university-educated. In fact, it has spread to countries that never had black slavery or Jim Crow, or even a substantial African minority until recent times.


Perceptions and realities of crime in the Netherlands


One such country is the Netherlands. In a recent survey, 615 Dutch adults were given the following instructions:


There are many different immigrant groups in the Netherlands. For each of the groups, adjust the slider to your estimation of the crime rate relative to Dutch natives. This means you should adjust the slider to two (2) if you think the crime rate of this group is twice that of natives. (Kirkegaard and Gerritsen 2021, p. 4)


The actual crime rate of each immigrant group is known from public data published by the government. It was thus possible to measure how much the survey respondents overestimated or underestimated the criminality of each immigrant group. The respondents were chosen by two polling firms. A little over two-thirds of them came from a firm that tended to select younger and more university-educated people.


The findings are shown in the above graph. On the y-axis, the crime rate is overestimated at values higher than zero and underestimated at values lower than zero. The x-axis shows the percentage of Muslims in the immigrants' home country.


Kirkegaard and Gerritsen (2021, pp. 12-17) argue that the results show a pro-Muslim bias: the respondents tended to underestimate the crime rate of Muslim immigrants. But the bias was not favorable toward all Muslims. In fact, the crime rate was overestimated for immigrants from Indonesia, Syria, Turkey, Pakistan, and Afghanistan and more or less correctly estimated for those from Egypt, Iran, and Iraq. In addition, the respondents showed much larger gaps between perception and reality when estimating the crime rates of different non-Muslim groups.


For source countries less than 25% Muslim, the crime rate was greatly underestimated (by a factor of 1 or more) for people from Congo, Angola, Cape Verde, the Netherlands Antilles, and the Dominican Republic. Conversely, it was greatly overestimated for people from Hungary, Poland, Romania, and Mexico.


Do you see a pattern? The respondents were underestimating the crime rate of immigrants from sub-Saharan Africa and the Caribbean. Their pro-Black bias was much stronger than their supposed pro-Muslim bias. In fact, it was so strong that it affected their perceptions of different Muslim groups. The respondents perceived North Africans and Somalis as being better than they really are, while perceiving Turks as being worse than they really are.


It looks like people in the Netherlands, and probably throughout the West, are being conditioned to view the Black African phenotype positively and the White European phenotype negatively. This bias caused the respondents to overestimate the arrest rate not only of European immigrants but also of any group that deviates too far from the Black African phenotype, including Chinese, Mexicans and, apparently, Roma.(1)


What about the respondents who voted for Nationalist parties? You know, the “far right.” Although Nationalist voters were more inclined to overestimate the crime rate of Muslim immigrants, they were just as inclined to underestimate the crime rate of sub-Saharan African and Caribbean immigrants. The pro-Black bias seems very pervasive.





1. Roma in Western Europe identify themselves to the authorities by their country of origin, not by their ethnicity. The Dutch respondents greatly overestimated the crime rate of immigrants from Romania, and the recent wave of Romanian migrants is widely perceived to be mostly Roma:


In these figures, the number relating to the Roma is indeterminate since the ethnicity of asylum seekers is not recorded. Nonetheless, the assumption is that the majority of these applications were made by Roma. Certainly, the press is of this view. Articles discussing Czech or Romanian asylum seekers refer frequently to the Roma. As a result, it is easy for the ordinary member of the public to assume that such groups of applicants are of Roma extraction (Stevens 2003, p. 440)





Kirkegaard, E.O.W., and A. Gerritsen. (2021). A study of stereotype accuracy in the Netherlands: immigrant crime, occupational sex distribution, and provincial income inequality. OpenPsych, June 14


Myrdal, G. (1944). An American Dilemma. The Negro Problem and Modern Democracy. New York: Harper and Row.


Pauli, M. (2006). Harper Lee tops librarians' must-read list. The Guardian, March 2  


Stevens, D.E. (2003). The Migration of the Romanian Roma to the UK: A Contextual Study. European Journal of Migration and Law 5(4): 439-461.  



Friday, May 14, 2021

Damunwha in South Korea


Graffiti in Ansan (Wikicommons – Piotrus)


I've published a paper on the Damunwha children of South Korea. In that country, foreign brides, mainly from Southeast Asia, produce almost 6% of births. These children do poorly at school, ostensibly because of discrimination and imperfect learning of spoken Korean from their mothers. Yet they actually do well in subjects that emphasize social interaction and spoken language. Their learning deficit is in subjects that require abstraction and memorization, such as mathematics.


This is the abstract:


In South Korea, over 10% of new couples involve a foreign bride. Most come from Southeast Asia (Vietnam, Philippines, Thailand, Cambodia, Indonesia), and others from East Asia (China, Japan). Such couples now produce almost 6% of births. Their children tend to do badly at school and many drop out, the commonly cited reason being the child's poor acquisition of language skills from a foreign mother. In reality, Damunwha ("multicultural children") have no trouble with spoken Korean. Their deficiency is in written Korean, particularly in literary and specialized vocabulary that is largely learned at school. They actually do well in subjects that emphasize the spoken language and social interaction, like music, painting, and physical education. They do badly only in those subjects that require abstraction and memorization, like mathematics and social studies. Damunwha children are also more prone to hyperactivity, impulsivity, and non-compliance with rules. These divergences in cognition and behavior seem confined to children of Southeast Asian mothers, since children of Chinese or Japanese mothers perform as well as those of unmixed Korean parentage. It looks as if the country's social norms, particularly those of Confucianism, favored the spread of certain cognitive and behavioral traits within the Korean population, and more broadly among East Asians. These traits include not only high cognitive ability but also a high capacity to obey rules, to defer gratification, and to control impulsive behavior.




Frost, P. (2021). Damunwha in South Korea: A case study of divergences in cognition and behavior. Advances in Anthropology 11(2): 153-162.




Tuesday, April 27, 2021

Polygenic scores and Black Americans


Sunday Morning in Virginia (1877), by Winslow Homer. 

The ability to acquire language may be the mental domain where people of sub-Saharan African descent have undergone the most cognitive evolution since their separation from other humans.




If we look at SNP alleles associated with educational attainment, we see differences between Europeans and sub-Saharan Africans. In a previous post I asked whether the cause was genetic drift or natural selection (Frost 2021).


That post brought a comment on Twitter:


Or maybe the fact that educational attainment is based on whiteness and familial wealth in the USA but not in Africa? And familial wealth tends to be concentrated in specific closed groupings of people who only breed with each other?


I don’t think so. First, the alleles were identified in subjects from the Netherlands Twin Registry, the Finnish Twin Cohort, the Swedish Twin Registry, the Avon Longitudinal Study of Parents and Children, the UK Biobank and 23andme. Of those sources, only 23andme had American subjects.


Second, let's suppose that those alleles are incidentally related to educational attainment. Maybe they are just something that wealthy Europeans share with each other through inbreeding, a bit like the Habsburg jaw. Those alleles should therefore be useless for predicting educational attainment in other populations. Are they?


Let me answer that question by discussing two recent studies:



The Guo et al. study


Guo et al. (2019) used the same alleles to predict success on a cognitive test (verbal ability) by 8,078 Americans of different ethnic backgrounds. Two polygenic scores were calculated: one based on alleles associated with educational attainment (education PGS) and the other based on alleles associated with IQ (IQ PGS).


The polygenic scores significantly correlated with test results for all major ethnic backgrounds, except one:


The education PGS was significantly predictive of verbal ability in all estimated models and its coefficients were similar in size except for the black sample in which the coefficient was much smaller. The IQ PGS significantly predicted verbal ability in all samples except the black sample. (Guo et al. 2019)


[...] The incremental R2 s or the R2 s of "pure" PGS effects were 1.8%, 0.1%, 1%, 1.8%, 1.7%, and 1% for whites, blacks, Asians, Hispanic whites, the combined sample and the overall sample, respectively.


The literature is showing a consistent trend: polygenic scores have much less power to predict cognitive ability in people of sub-Saharan African descent than in people of European or Asian descent. In this case, the polygenic scores were ten to eighteen times worse at predicting verbal ability in Black Americans than they were at predicting verbal ability in White, Asian, and Hispanic White Americans.


Why? The reason may be that Eurasians and sub-Saharan Africans have different gene pools. Some alleles for higher cognitive ability are available in one gene pool but not in the other. There is undoubtedly overlap between the two, but not total overlap. Intelligent Nigerians, for instance, may owe their intelligence to alleles that exist only in sub-Saharan Africa.


To return to the Twitter comment, it seems clear that polygenic scores are predicting something that correlates with cognitive ability, and that "something" is not an artefact of wealthy people being related to each other and sharing the same genes. It's already a stretch to believe that close family ties are shared by high achievers throughout the United Kingdom, the Netherlands, Sweden, and Finland. Does the same family clique also include high achievers of Asian American origin? 



The Rabinowitz et al. study


Rabinowitz et al. (2019) used an education PGS to predict cognitive ability in Black American participants, specifically three cohorts from first grade to young adulthood (at which point their DNA was collected and analyzed).


The results? The PGS significantly correlated with pursuit of postsecondary education. The correlation was weak or insignificant, however, for performance on school tests. The PGS did not predict performance on a standardized reading test for any of the three cohorts, and it predicted performance on a standardized math test for only one of them. In addition, the PGS negatively correlated with having a criminal record (but only in the male subjects).


A problem here may be the young age of the participants. Cognitive ability seems to become less malleable and more hardwired with age. We can help children do better on IQ tests, but the improvement tends to disappear by adulthood (Frost 2008). Consequently, academic success in childhood may be too clouded by environmental factors to show a significant correlation with genetic factors.


On the other hand, the PGS did predict some things better than others. It predicted general academic success (pursuit of postsecondary education) and compliance with rules (absence of a criminal record). For actual school tests, it had some power to predict success on the math test but none at all on the reading test. The ability to acquire language may be the mental domain where people of sub-Saharan African descent have undergone the most cognitive evolution since their separation from other humans. The PGS cannot predict superior reading ability among Black Americans because too many of the relevant alleles are exclusive to the sub-Saharan African gene pool and remain to be identified by scientific studies.


The take-home message? At present, we can create polygenic scores that provide a rough idea of cognitive ability in people of sub-Saharan African descent. To get more than a rough idea, we need to identify the relevant alleles specific to that population.





Frost, P. (2008). IQ: Interaction between race and age. The Unz Review, May 20


Frost, P. (2021). The mismeasure of genetic differentiation. Evo and Proud, April 13


Guo, G., Lin, M.J., and K.M. Harris. (2019). Socioeconomic and Genomic Roots of Verbal Ability. bioRxiv, 544411.


Rabinowitz, J.A., S.I.C. Kuo, W. Felder, R.J. Musci, A. Bettencourt, K. Benke, ... and A. Kouzis. (2019). Associations between an educational attainment polygenic score with educational attainment in an African American sample. Genes, Brain and Behavior, e12558.

Tuesday, April 20, 2021

Selection for fair skin in Europeans and North Asians


Selection for fair skin in different human populations (Huang et al. 2021)

Selection for fair skin was about four times stronger among ancestral Europeans than it was among ancestral North Asians or the earlier shared ancestors of both groups. So says a recent genome study.


Huang et al. (2021) examined genes that influence skin pigmentation to calculate the strength of selection for lighter skin among the ancestors of today’s Europeans and North Asians. They concluded that selection for lighter skin was strongest among the unique ancestors of present-day Europeans, with a selection pressure of 25.9. It was about four times weaker among the unique ancestors of North Asians (5.61) and the earlier shared ancestors of both groups (6.5). East Asians actually became darker after they split from North Asians, with a negative selection pressure of -5.53.


Our estimate shows that the modern European lineage had the largest selective pressure (s4=0.0259/generation) on light pigmentation than the other branches, suggesting that recent natural selection favoured light pigmentation in Europeans. Recent studies using ancient DNA could support our observation of recent directional selection in Europeans (Huang et al. 2021, p. 3)


This finding supports earlier findings. Modern humans remained dark-skinned in Europe long after they had spread north into northern latitudes some 45,000 years ago. It was not until 20,000 years ago that alleles for white skin made their appearance (Beleza et al. 2013; Canfield et al. 2014; Norton and Hammer 2007). As a Science correspondent concluded: "The implication is that our European ancestors were brown-skinned for tens of thousands of years" (Gibbons 2007).


Those ancestors were initially proto-Eurasians, and it was only later that they differentiated to become respectively Europeans and North Asians. Only then, and only in the European lineage, did skin color begin to lighten at a fast rate. This rapid evolution seems to have been confined to a relatively small area that stretched from the Baltic to central Siberia. Elsewhere, in western and southern Europe, people remained dark-skinned until almost the dawn of history, as shown by DNA dated to 11,000 years ago from England, 8,000 years ago from Luxembourg, and 7,000 years ago from Spain (Brace et al. 2019; Lazaridis et al. 2014; Olalde et al. 2014).


The fair skin phenotype, together with a variety of hair and eye colors, would later spread throughout all of Europe, while going extinct east of the Urals. In the latter region it would persist into historic times. At sites in south-central Siberia, dating from the third millennium BC to the fourth century AD, genetic analysis has shown that most of the buried individuals had blue or green eyes, light hair (blond, red, light brown), and light skin (Bouakaze et al. 2009). South Siberian peoples were, in fact, described as having "green eyes" and "red hair" in old Chinese records (Keane 1886, p. 703).


It seems that Europeans acquired their current appearance very fast, perhaps ten to twenty thousand years ago during the last ice age. Initially confined to northeastern Europe and parts of Siberia, the new phenotype would in time spread to the rest of the continent ... on the eve of recorded history. Only then did all Europeans come to look “European” (Frost 2014; Frost 2020).




Beleza, S., A.M. Santos, B. McEvoy, I. Alves, C. Martinho, E. Cameron, et al. (2013). The timing of pigmentation lightening in Europeans. Molecular Biology and Evolution 30(1): 24-35.


Bouakaze, C., C. Keyser, E. Crubézy, D. Montagnon, and B. Ludes. (2009). Pigment phenotype and biogeographical ancestry from ancient skeletal remains: inferences from multiplexed autosomal SNP analysis. International Journal of Legal Medicine 123(4): 315-325.


Brace, S., Y. Diekmann, T.J. Booth, Z. Faltyskova, N. Rohland, S. Mallick, et al. (2019). Ancient genomes indicate population replacement in Early Neolithic Britain. Nature Ecology & Evolution 3(5): 765-771.


Canfield, V.A., A. Berg, S. Peckins, S.M. Wentzel, K.C. Ang, S. Oppenheimer, and K.C. Cheng. (2014). Molecular phylogeography of a human autosomal skin color locus under natural selection. G3, 3(11): 2059-2067.


Frost, P. (2014). The puzzle of European hair, eye, and skin color. Advances in Anthropology 4(2): 78-88.


Frost, P. (2020). White Skin Privilege: Modern Myth, Forgotten Past. Evolutionary Studies in Imaginative Culture 4(2): 63-82.


Gibbons, A. (2007). American Association of Physical Anthropologists Meeting: European skin turned pale only recently, gene suggests. Science 20 April 2007, 316(5823): 364.


Huang, X., S. Wang, L. Jin, and Y. He. (2021). Dissecting dynamics and differences of selective pressures in the evolution of human pigmentation. Biology Open 15 February 2021; 10(2): bio056523.


Keane, A.H. (1886). Asia with Ethnological Appendix. London: Edward Stanford.


Lazaridis, I., N. Patterson, A. Mittnik, G. Renaud, S. Mallick, K. Kirsanow, et al. (2014). Ancient human genomes suggest three ancestral populations for present-day Europeans. Nature 513(7518): 409-413.


Norton, H.L., and M.F. Hammer. (2007). Sequence variation in the pigmentation candidate gene SLC24A5 and evidence for independent evolution of light skin in European and East Asian populations. Program of the 77th Annual Meeting of the American Association of Physical Anthropologists, p. 179.


Olalde, I., M.E. Allentoft, F. Sanchez-Quinto, G. Santpere, C.W.K. Chiang, M. DeGiorgio, et al. (2014). Derived immune and ancestral pigmentation alleles in a 7,000-year-old Mesolithic European. Nature 507 (7491): 225-228.


Tuesday, April 13, 2021

The mismeasure of genetic differentiation


Red Tree, Piet Mondrian (1908-10)

If we look at SNP alleles associated with educational attainment, we see differences between Europeans and sub-Saharan Africans. Is genetic drift the cause? Or natural selection?



IQ has long been the yardstick of cognitive ability. As such, it describes phenotype, not genotype: it measures how your inborn potential has developed in your environment. Genotype is the inborn component of IQ. It can be inferred from twin studies, family studies, and adoption studies, but those approaches are indirect and far from perfect.


To measure genotype directly, we need to identify the alleles that affect the development of cognitive ability. We also need to measure the size of each allele’s effect. Recently, much progress has been made. By using genome-wide association studies (GWAS), researchers have identified many alleles that are associated with educational attainment (EA). EA is not quite the same as IQ—it also includes things like sitting still in class and brownnosing the teacher—but it's a good approximation.


In the most recent study of this sort, Lee et al. (2018) identified 1,271 single-nucleotide polymorphisms (SNPs) that are significantly associated with high EA in a sample of over one million people of European ancestry. Together, the SNPs can explain 11-13% of the variance in EA among individuals. This new yardstick is called the "polygenic score."


The polygenic score is more accurate for populations than for individuals. If we compare the mean polygenic score of a population and its mean IQ, the correlation is 90% (Piffer 2019). This high correlation is due to the logic of sampling: to estimate the mean cognitive ability of a population, we don't have to identify all of the relevant SNPs, just a large enough sample.


Like mean IQ, the mean polygenic score differs among human populations. It seems to have increased during the northward spread of modern humans out of Africa and into the temperate zone of Europe and Asia, with East Asians having the highest scores. This geographic pattern is in line with IQ data. The mean polygenic score is also very high among Ashkenazi Jews and Finns, again in line with IQ data (Piffer 2019).



Kevin Bird’s paper


The above findings have been disputed by the American researcher Kevin Bird in a recent paper. Although Europeans and sub-Saharan Africans have different alleles at genes associated with educational attainment, he argues that these differences correspond to small differences in cognitive ability. In fact, they are more consistent with genetic drift than with natural selection.


To prove his argument, he performed two analyses of the data: an Fst and a test for polygenic selection. In my opinion, both analyses have serious problems.


The Fst


This is the most common measure of genetic differentiation. If the Fst is low, differentiation is trivial and consistent with genetic drift. If it is high, differentiation is significant and consistent with natural selection.


For SNPs associated with EA, Kevin Bird reports an Fst of 0.111. Is that low or high? When Sewall Wright (1978, pp. 82-85) created this measure, he defined four categories of differentiation:


0 to 0.05 - little genetic differentiation

0.05 to 0.15 - moderate genetic differentiation

0.15 to 0.25 - great genetic differentiation

0.25 to 1 - very great genetic differentiation


Those categories are widely cited in the literature. A search in Google Scholar for "moderate genetic differentiation" and "0.05 - 0.15" shows over two hundred papers.


So does an Fst of 0.111 mean moderate genetic differentiation? Not according to Kevin Bird, who sees nothing at all below a benchmark of 0.118. That benchmark may be valid, but it cannot be easily verified and does not appear elsewhere in the literature. Nor does Kevin explain why it is better than the ones put forward by Sewall Wright. In fact, he makes no reference to them.


One may also question the Fst of 0.111. For the data source, the reader is referred to Lee et al. (2018), but that study was done only with European subjects. Moreover, Kevin Bird used 1,259 SNPs to calculate that Fst, even though he found only 685 SNPs that had data on both Africans and Europeans.


The Fst of 0.111 seems to be the diversification of those SNPs in Europeans. That value is what would be expected, but it says nothing about diversification between Europeans and sub-Saharan Africans.


The polygenic selection analysis


The other analysis is more on subject. Kevin Bird compared European data with African data as follows:


1. First, he looked through the 1000 Genomes Project for SNP data on Europeans and sub-Saharan Africans. He found data on five European-descended populations (Utah residents, Tuscans, Finns, British, Iberians) and five African populations (Yoruba, Luhya, Gambians, Mende, Esan). The two datasets had information on 685 of the 1,271 SNPs associated with educational attainment.


2. For each SNP, he noted the allele frequencies in Europeans and the allele frequencies in sub-Saharan Africans.


3. He calculated the differences in allele frequencies between the two groups. He then weighted the differences for the allele's effect size (its estimated positive or negative effect on educational attainment). For each allele, he used two different estimates of effect size: one from between-family data and the other from within-family data.


4. Alongside this list of weighted alleles, he created a second list to simulate genetic drift by randomly flipping the sign of effect size for 10,000 permutations.


5. When effect size was calculated from between-family data, the two lists clearly differed from each other. When it was calculated from within-family data, the overall difference was much smaller and easily explained by genetic drift.


Bird (2021) prefers the second dataset to the first, whereas Piffer (2019) prefers the first. Who is right? All things being equal, data should come from within families. There is less statistical noise because siblings have similar upbringings. With less noise, group differences can more easily be identified.


Yet, here, we have the opposite. We see a significant difference between Europeans and Africans in the between-family data, but not in the within-family data. Why? The reason is that the between-family data came from over a million subjects whereas the within-family data came from 20,000 sibling pairs. Being smaller, the second dataset had a lot more noise. Sure, there should have been less noise, all things being equal. But some things weren't.



Doing the comparison again but better


I suspect Kevin Bird still prefers within-family data. Fine. Let's repeat the comparison with a much larger sample of sibling pairs. There would then be less noise and probably a significant difference between African and European alleles in their effect on educational attainment. Kevin seems to anticipate this eventuality:


While the results presented here are more consistent with neutral evolution rather than divergent natural selection, it is not possible to rule out that data sets with more power could present different results. Additionally, although within-family effect sizes are recommended over between-family effect sizes, if the within-family effect sizes are re-estimated for SNPs ascertained by a between-family GWAS, there is still likely to be some level of confounding from population structure. (Bird 2021, p. 7)


He elaborates on the last point:


[...] the [polygenic] scores might be biased by a variety of factors, including the nonrandom ways that society is geographically structured [...]. For instance, Black people in the US, for reasons unrelated to genetics, live in areas with poorer air quality and more exposure to environmental toxins (Bird 2021, p. 8)


Yet, as he notes further on, these SNP alleles were identified only in European subjects, and their effects on educational attainment were estimated only from European data. So how could different alleles among Europeans be spuriously associated with differences in educational attainment among Europeans because of socioeconomic deprivation among Black Americans? Where and when do the latter come into this presumably spurious association?


Kevin Bird is right to point out that the allele effects were calculated from European data and may be less applicable to people of other origins. In fact, there is growing evidence that the genetic architecture of cognition is different in sub-Saharan Africans (Frost 2019). By ignoring that factor, however, we introduce even more noise into the data and muddle even more any differences that may exist between Africans and Europeans. The data may indeed be of low quality, but that shortcoming would, if anything, obscure group differences. Again, Kevin is making a coherent point within an incoherent argument.



Other ways?


There are other ways to distinguish between genetic drift and natural selection. One way is to measure the ratio of nonsynonymous alleles to synonymous alleles. If a trait has little functional value and is thus vulnerable to genetic drift, nonsynonymous alleles will tend to proliferate and become as numerous as synonymous alleles (Tomoko 1995). Of course, if nonsynonymous alleles greatly outnumber synonymous alleles, there may be natural selection for diversity (Rana et al. 1999).


An SNP, by its very nature, has alleles that differ from each other by only one base substitution, and this fact limits our ability to distinguish between genetic drift and natural selection. It would thus be interesting to identify genetic polymorphisms that are associated with educational attainment but have several nucleotides.


If such a polymorphism is undergoing genetic drift, the most frequent alleles will be the ancestral allele and those that differ from it by one base substitution. The less frequent ones will be those that differ by two or more base substitutions. In short, the frequency of an allele will be inversely related to the number of base substitutions that separate it from the ancestral allele.


The picture is different with natural selection. The most frequent alleles will not necessarily be the ones that differ the least from the ancestral allele. If allele frequency is graphed as a function of base substitutions, the result will not be a smoothly decreasing exponential curve. The most successful allele may differ from the ancestral one by several base substitutions.





Bird, K.A. (2021). No support for the hereditarian hypothesis of the Black-White achievement gap using polygenic scores and tests for divergent selection. American Journal of Physical Anthropology. Feb. 1-12, DOI: 10.1002/ajpa.24216.


Frost, P. (2019). Differences in the genetic architecture of cognition? Evo and Proud, September 25


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.  


Tomoko, O. (1995). Synonymous and nonsynonymous substitutions in mammalian genes and the nearly neutral theory. Journal of Molecular Evolution 40 (1): 56-63


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.   


Rana, B.K., D. Hewett-Emmett, L. Jin, B.H.J. Chang, N. Sambuughin, M. Lin, et al. (1999). High polymorphism at the human melanocortin 1 receptor locus. Genetics 151(4): 1547-1557.


Wright S. (1978). Evolution and Genetics of Populations, Volume 4. University of Chicago, Chicago, IL.

Tuesday, March 30, 2021

Recent cognitive evolution in West Africa


If we look at alleles associated with higher educational attainment, we find more of them among the Yoruba of Nigeria than among the Mende of Sierra Leone. The reason may be differences in social evolution over the past 1,000 years, particularly in trade, urban settlement, State formation, and other forms of social complexity. 

Ife king's head (14th or early 15th century) (Wikicommons - Vassil)



How can we measure the genetic component of cognitive ability? We have long used IQ tests to get a rough idea, but they are not an ideal yardstick. Twin studies have shown that genetic factors explain about two thirds of the variance in IQ results, perhaps even less for comparisons between people of different cultural backgrounds.


In recent years we've found a new yardstick: the polygenic score. It's a more direct genetic measurement, being a summation of alleles that have been linked to higher educational attainment. As a method for estimating the mean cognitive ability of a population, it seems to be as good as IQ tests. Piffer (2019) found a 90% correlation between the two methods. In his latest study, he has again found the same correlation (Piffer 2021, see Figure 8).


Interestingly, that study shows differences in mean cognitive ability within West Africa: the Mende of Sierra Leone score much lower than the Yoruba of Nigeria. In fact, the Yoruba have almost the same polygenic score as do African Americans, even though the latter have about 20% European admixture. Unfortunately, we have no data on the Igbo of Nigeria, who are known to be high achievers at school and in other areas of life (Frost 2015).


These differences within West Africa support the argument that mean cognitive ability has continued to increase in some human populations, even in relatively recent times. With respect to the Yoruba, their cognitive ability may have increased in tandem with their advances in trade, urban settlement, and State formation from the tenth century onward (Akintoye 2014; McIntosh and McIntosh 1988). Meanwhile, the Mende remained at a lower level of social complexity.


There is one problem with using polygenic scores for West Africans, or for any non-European population. To identify alleles associated with higher educational attainment, researchers have used genomes of European origin. There is evidence, however, that the architecture of cognitive ability may differ in different human populations. The same alleles might not explain high cognitive ability in West Africans and Europeans. Indeed, Lasker et al. (2019) found a lower correlation between polygenic scores and cognitive ability in African Americans than in European Americans.




Akintoye, S.A. (2014). A History of the Yoruba People. Dakar: Amalion.


Frost, P. (2015). The Jews of West Africa. The Unz Review, July 4


Lasker, J., B.J. Pesta, J.G.R. Fuerst, and E.O.W. Kirkegaard. (2019). Global ancestry and cognitive ability. Psych 1(1)  


McIntosh, S.K., and McIntosh, R.J. (1988). From stone to metal: New perspectives on the later prehistory of West Africa. Journal of World Prehistory 2: 89-133.  


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. (2021). Divergent selection on height and cognitive ability: evidence from Fst and polygenic scores. OpenPsych  

Monday, March 22, 2021

The big bird that takes away water


The constellation of the Southern Cross has inspired similar myths among indigenous peoples as far apart as Australia and South America. Why?

Southern Cross (Wikipedia – Yulanlu97). 



Did people cross the Pacific in pre-Columbian times? This question has aroused renewed interest with the discovery of sweet potato remains at Polynesian sites dated to A.D. 1000. There also seem to be loan-words of Polynesian origin in some Amerindian languages (Jones et al. 2011). Finally, we have strong evidence that Polynesians introduced chickens to the west coast of South America in prehistoric times, probably A.D. 1300-1420 (Fitzpatrick and Callaghan 2009).


A new piece of evidence is the similarity between a myth told by Aboriginal Australians, particularly those of southeast Australia, and a myth told by indigenous peoples in Argentina and central Brazil. In both cases, one finds the same two elements:


- A large flightless bird that can cause the land to dry up.

- The constellation of the Southern Cross and two adjacent regions of the sky: the Southern Pointers (Alpha and Beta Centauri) and the Coalsack Nebula


These similarities are mentioned by Gullberg et al. (2020) in a cross-cultural study of beliefs about the 'Dark Constellations':


Wiradjuri, Kamilaroi, Euahlayi, and others (Australia)


The Emu in the Sky is perhaps the best-known Aboriginal dark constellation (Figure 2). It is the silhouette of an emu traced out by the dark nebulae within the plane of the Milky Way and is featured in the traditions of Aboriginal people across Australia. The Coalsack Nebula, near the Southern Cross, forms the head, and the body extends along the dust lanes through Centaurus in the Milky Way, to the body as outlined by the galactic bulge in Scorpius and Sagittarius (Gullberg et al. 2020, p. 392)


When the celestial emu swings to where it is low on the horizon in October and November, the galactic bulge is now seen as the backside of an emu sitting in a waterhole, displacing the water and causing the land to dry up as the hot summer months approach. (Gullberg et al. 2020, p. 393)


Moqoit (Argentina)


Due to this crucial role of the Milky Way and the fact that it is a huge area of diffuse brightness interrupted by dark spots, it is not surprising that the Moqoit pay attention to dark patterns on it. The most important of all of them is the Mañic, the master of the South American rheas, a large flightless bird similar to an emu or ostrich shown in (Figure 5)


[…] We know many Moqoit stories mention that in the time of the origins, the master of Mañic used to shelter in a number of burrows, under the roots of an ombú (a very big tree, seen as the world tree—the Milky Way), and eat humans. Lapilalaxachi, a powerful human ancestor of the Moqoit people identified with the Pleiades, decided to face the Mañic. He chased the Mañic throughout the world and the cornered Mañic climbed up the ombú trunk to the sky.


Today, the shadow-soul (la 'al) of the Mañic can be seen in the Milky Way's dark clouds, with its head in what we know as the Coalsack (around -59° 50' galactic longitude). Alpha and Beta Centauri are the dogs of the man chasing the Mañic and bite at its neck (López and Giménez-Benítez, 2008). The Mañic's head is the Coalsack.

(Gullberg et al. 2020, p. 396)


Tupi (central Brazil)


In a similar view, the Tupi people of central Brazil also perceive a rhea in the sky, making essentially the same shape as the Aboriginal emu. The rhea and the emu are both large, flightless birds with a similar appearance and breeding cycle. Just as in Moqoit traditions, the head of the rhea is the Coalsack, and the body is traced out by dust lanes in Centaurus and Scorpius. The Tupi associate the rhea with the end of the world. The stars of Crux are holding the head of this animal. If it escapes, it will drink all the water of the world (Alencar, 2011)

(Gullberg et al. 2020, p. 397)



Why is this myth found only in Australia and South America? Why is it absent in-between? Actually, a version does exist on the Polynesian island of Tonga, except that the large flightless bird is a giant duck and it simply keeps people from getting access to water:


Tongans (Polynesia)


Polynesians of the Pacific recognise dark spaces in the Milky Way, focusing on the Coalsack Nebula and relating it to fish or fishing. Polynesian traditions of Tonga describe it as Humu (a giant triggerfish). In their traditions (Gifford, 1924), a Tongan chief named Ma'afu took a lizard wife and had twin sons, which they wanted gone as the chief's subjects were afraid of the pair. Ma'afu sneakily instructed the brothers to collect water from a waterhole containing a giant duck that would kill and consume anyone who came too close. The boys were attacked by the duck but grabbed it by the neck and killed it. When the boys returned unharmed, the father instructed them to obtain water from a more distant waterhole, inhabited by Humu, a triggerfish (these are large aggressive animals with powerful teeth designed for crushing shellfish). The boys killed the triggerfish and in anger at this, the father blurted out his secret to have the boys killed. The boys walked away and ascended to the stars, each carrying one of the two animals they killed. The twins became the Magellanic Clouds, the duck became the Southern Cross (with the duck's bill as γ Crucis), and Humu became the Coalsack Nebula

(Gullberg et al. 2020, p. 398)



My thoughts


This myth seems to have begun in one of three areas (Australia, Polynesia, South America) and then spread to the other two. If it began among Aboriginal Australians, the myth could be very old, going back perhaps 65,000 years. If it began among the Amerindian peoples of South America, it may go back 10,000 years. Finally, if it began among the Polynesians, the time depth would be no more than 3,500 years. The first and last scenarios seem most likely, given that oceanic travel was much easier from Polynesia to South America than the reverse (Fitzpatrick and Callaghan 2009).


Nonetheless, all of the scenarios run into a big problem: the myth is known to South American groups on the east side of the continent but not to those on the west side (which would be more consistent with trans-Pacific contact). I can think of only one other scenario. Given that the Americas were once inhabited by a population related to Aboriginal Australians and similar groups in Southeast Asia (Frost 2015), the myth may have originated in Asia more than 65,000 years ago and then spread in two directions: to Australia via Southeast Asia and to the Americas via the Bering Strait. But could a myth survive intact for that long?


Two other things leave me wondering. Why would the sky around the Southern Cross be seen as a large flightless bird? Gullberg et al. (2020) provide several pictures of that part of the sky and trace the outline of a bird on them. To my eyes, one could just as easily trace the outline of many other animals.


Finally, is this evidence, à la Von Däniken, of extraterrestrial contact? Keep in mind that the region of the Southern Cross includes the closest star system to ours. And if that system does have intelligent life, should we be reaching out to them and inviting them over? The last time around they didn’t leave a good impression.


Enough! I shouldn’t let myself get carried away. Extraordinary claims require extraordinary evidence, and a single myth hardly qualifies as extraordinary.





Fitzpatrick, S.M. and R. Callaghan. (2009). Examining dispersal mechanisms for the translocation of chicken (Gallus gallus) from Polynesia to South America. Journal of Archaeological Science 36(2): 214-223.


Frost, P. (2015). Guess who first came to America? Evo and Proud. August 1


Gullberg, S.R., D.W. Hamacher, A. Martin-Lopez, J. Mejuto, A.M. Munro, and W. Orchiston. (2020). A Cultural Comparison of the 'Dark Constellations' in the Milky Way. Journal of Astronomical History and Heritage 23(2): 390-404.


Jones, T.L., A.A. Storey, E.A. Matisoo-Smith, and J.M. Ramirez-Altamira (eds). (2011). Polynesians in America: Pre-Columbian Contacts with the New World. Rowman Altamira.