Tuesday, October 25, 2022

Eppur si muove


General intelligence (g) varies with ethnicity, as do genetic variants associated with educational attainment (Lasker et al. 2019, p. 445)



Bryan Pesta was fired from a tenured university position for a study he coauthored in a peer-reviewed journal. No one actually disputed his findings. It was simply taken for granted that they could not be true.



Three years ago I contributed a paper to a special issue of Psych. One of the other contributors, Bryan J. Pesta, coauthored a paper on “Global Ancestry and Cognitive Ability.” It was one of several recent studies that had used genetic data to understand how populations differ on average in their capacity for intelligence.


Pesta and his coauthors looked at data from an existing neurodevelopment study of 9,421 participants from Philadelphia. A little over half of them were European American, and a third were African American. They had all been genotyped and had all taken a battery of cognitive tests.


The study produced several findings:


·         Almost 15 IQ points separated the African American participants from the European American participants. About three quarters of the difference was due to general intelligence (g).

·         Among the African Americans, general intelligence correlated with the degree of European admixture.

·         The correlation was modestly reduced, but not eliminated, when controlled for parental education. Controlling for skin color had no effect. Although skin color does correlate with European admixture, it evidently has a less direct relationship to general intelligence. This finding therefore eliminates “colorism” (discrimination in favor of lighter-skinned African Americans) as a possible cause.

·         As much as 20-25% of the difference in general intelligence between the African Americans and the European Americans was explained by genetic variants associated with educational attainment. By comparison, the same variants explain only 11-13% of the variance in educational attainment among individuals.

·         Although these genetic variants predicted general intelligence in both groups, the predictive power for the African Americans was only 20% of the predictive power for the European Americans. This finding is consistent with a growing consensus that the genetic architecture of intelligence is different in the two groups. Because the genetic variants have been identified in Europeans or European Americans, they may contribute less to the capacity for intelligence in people of African descent. In addition, other variants may be found only in African populations and thus remain to be identified.


For the above findings, Bryan Pesta would be fired from his tenured position at Cleveland State University. The whole affair is described in The Chronicle of Higher Education. At no point did anyone actually dispute his findings. It was simply taken for granted that they could not be true. And that’s that.


Please don’t argue that Bryan Pesta unconsciously looked for data that would provide the findings he wanted. The data had already been collected by another research team for a completely different purpose. So put aside The Mismeasure of Man and tell Stephen Jay Gould to go back to sleep.


This story isn’t over. People are curious, and curiosity ends up finding a way—despite the barriers we erect. Below is a screen shot of the paper’s access statistics (Hint: The Chronicle’s article came out on October 13).





Lasker, J., B.J. Pesta, J.G.R. Fuerst, and E.O.W. Kirkegaard. (2019). Global Ancestry and Cognitive Ability. Psych 1(1):431-459. https://doi.org/10.3390/psych1010034  


Standifer, C. (2022). Racial Pseudoscience on the Faculty. A professor’s research flew under the radar for years. What finally got him fired? The Chronicle of Higher Education. October 13. https://www.chronicle.com/article/racial-pseudoscience-on-the-faculty?cid2=gen_login_refresh&cid=gen_sign_in

Tuesday, October 18, 2022

Sex differences in the whites of the eyes


Women have sclera (whites of the eyes) that are less yellow and less red. Although this sex difference is unknown to almost everyone, people nonetheless perceive a female face with redder and yellower sclera as less feminine.




A recent study has shown that men and women differ in the color of their sclera—the whites of their eyes (Kramer and Russell 2022). Sclera are less yellow and less red in women. In both sexes, they become yellower, redder, and slightly darker with age.


Although this sex difference is unknown to almost everyone, it does influence perceptions of masculinity and femininity. When subjects were shown pairs of androgynous young or middle-aged faces that differed only in sclera color, they perceived the one with redder and yellower sclera as being more masculine. When shown pairs of male or female faces, they perceived the female faces with redder and yellower sclera as being less feminine. Sclera color did not affect perceptions of male or elderly faces.


The authors concluded that “people have learned the natural image statistics associated with male and female sclera, thereby representing males as having redder and yellower sclera than females.” Such learning would presumably be unconscious. What about other factors? Could perception of sclera color be hardwired?


We see a similar situation with the sex difference in skin color. Today, it’s largely unknown to people in the Western world, partly because many women have reduced it through deliberate tanning and partly because ethnic differences in skin color have become more visible in daily life. Yet several studies have shown that people associate women with light colors and men with dark colors. This was the case in three experiments with Dutch, Portuguese, and Turkish subjects:


·         The subjects identified personal names by gender faster when male names were presented in black and female names in white than when the gender/color combinations were reversed.

·         When asked to classify briefly appearing black and white blobs by gender, they usually classified the black blobs as male and the white ones as female.

·         In an eye-tracking experiment, their eyes showed longer observation and more frequent fixation when a dark object was associated with a male character and a light object with a female character (Semin et al. 2018).


Parallels with eye morphology and eye colors


Another recent study has shown that women have rounder eyes. This sex difference exists because the exposed sclera is more horizontally exposed in men. In addition, eye fissures are narrower and less rectangular in women than in men (Danel et al. 2020, see also Danel et al. 2018).


The same study also showed that this sex difference is confined to Europeans: women don’t have rounder eyes in other human populations. A similar situation exists with eye colors, which have diversified only in Europeans and more so in women than in men. Specifically, the range of eye colors is more evenly distributed among women: they have the less frequent colors more often and the more frequent ones less often (Frost 2022, pp. 9, 10, 13).


Is the sex difference in sclera color likewise confined to Europeans? For now, we don’t know. The sclera images were taken only from German faces (Kramer and Russell 2022).


Parallels with facial skin color


The natural colors of a woman’s face seem to interact with each other. The white of the eye serves to accentuate the color of the iris, and the lighter color of the facial skin serves to accentuate the darker colors of the eye and lip areas. If we consider the natural colors of the face in both sexes, a female face has a greater contrast in luminosity between the lighter-colored facial skin and the darker-colored lip and eye area (Russell 2003; Russell 2009; Russell 2010). A rating study has shown that faces with greater facial contrast are perceived as being more feminine:


Facial contrast was positively correlated with rated femininity of female faces but negatively correlated with rated masculinity of male faces. After controlling for skin luminance (which is also sexually dimorphic) and ethnicity (there were both Caucasian and East Asian faces), facial contrast was still positively correlated with rated femininity of female faces and negatively correlated with rated masculinity of male faces, though the relationship was very weak for male faces. In summary, greater facial contrast was considered more feminine in female faces and less masculine in male faces. (Russell 2010, p. 10).


In different cultures and geographic areas, women have developed cosmetics to accentuate the sex difference in facial contrast:


The received style of cosmetics involves darkening the eyes and lips while leaving the rest of the face largely unchanged. This is one of two patterns of cosmetic application that could increase facial contrast (the other being to significantly lighten the entire face, except for the eyes and lips). To confirm that cosmetic application increases facial contrast, we measured the facial contrast of the set of 12 Caucasian faces that were photographed with and without cosmetics (Russell 2009). On average, facial contrast was much larger with cosmetics than without cosmetics, and greater facial contrast was found in each of the 12 faces when they were wearing cosmetics than when they were not. Both eye contrast and mouth contrast were increased by cosmetics. The large and consistent increase in facial contrast achieved with cosmetics more clearly differentiates male and female faces. (Russell 2010, p. 13)




Europeans, and European women in particular, have followed an unusual evolutionary trajectory. Some kind of selection made their outward features more colorful, more accentuated, and more visually striking, particularly the features on or near the face.


Was it sexual selection? The authors of the eye morphology study considered that possibility but rejected it because female eye morphology does not correlate with two other aspects of female attractiveness: face shape and facial averageness (Danel et al. 2020). The lack of correlation, however, may simply mean that these three aspects impose different constraints on sexual selection. Making a face more average-looking is not at all the same process as increasing its visual contrast or adding bright colors.





Danel, D.P., S. Wacewicz, Z. Lewandowski, P. Zywiczynski, and J.O. Perea-Garcia. (2018). Humans do not perceive conspecifics with a greater exposed sclera as more trustworthy: a preliminary cross-ethnic study of the function of the overexposed human sclera. Acta Ethologica 21: 203-208. https://doi.org/10.1007/s10211-018-0296-5  


Danel, D.P., S. Wacewicz, K. Kleisner, Z. Lewandowski, M.E. Kret, P. Zywiczynski, and J.O. Perea-Garcia. (2020). Sex differences in ocular morphology in Caucasian people: a dubious role of sexual selection in the evolution of sexual dimorphism of the human eye. Behavioral Ecology and Sociobiology 74(115) https://doi.org/10.1007/s00265-020-02894-1


Frost, P. (2022). European Hair, Eye, and Skin Color: Solving the Puzzle. Washington: Academica Press. ISBN 9781680538724


Kramer, S.S., and R. Russell. (2022). A Novel Human Sex Difference: Male Sclera Are Redder and Yellower than Female Sclera. Archives of Sexual Behavior 51, 2733–2740. https://doi.org/10.1007/s10508-022-02304-9


Russell, R. (2003). Sex, beauty, and the relative luminance of facial features. Perception 32(9): 1093-1107. http://dx.doi.org/10.1068/p5101


Russell, R. (2009). A sex difference in facial pigmentation and its exaggeration by cosmetics. Perception 38(8): 1211-1219. https://doi.org/10.1068/p6331


Russell, R. (2010). Why cosmetics work. In R.B. Adams Jr., N. Ambady, K. Nakayama, and S. Shimojo (Eds.) The Science of Social Vision, (pp. 186-203). New York: Oxford.


Semin, G.R., T. Palma, C. Acartürk, and A. Dziuba. (2018). Gender is not simply a matter of black and white, or is it? Philosophical Transactions of the Royal Society B Biological Sciences 373(1752):20170126. https://doi.org/10.1098/rstb.2017.0126

Tuesday, October 11, 2022

How some populations adapt to vitamin D scarcity


Vitamin D metabolism varies from one human population to another, as do most heritable traits. This is the subject of a review article I’ve recently published in the journal Nutrients. Here is the abstract:



Vitamin D metabolism differs among human populations because our species has adapted to different natural and cultural environments. Two environments are particularly difficult for the production of vitamin D by the skin: the Arctic, where the skin receives little solar UVB over the year; and the Tropics, where the skin is highly melanized and blocks UVB. In both cases, natural selection has favored the survival of those individuals who use vitamin D more efficiently or have some kind of workaround that ensures sufficient uptake of calcium and other essential minerals from food passing through the intestines. Vitamin D scarcity has either cultural or genetic solutions. Cultural solutions include consumption of meat in a raw or boiled state and extended breastfeeding of children. Genetic solutions include higher uptake of calcium from the intestines, higher rate of conversion of vitamin D to its most active form, stronger binding of vitamin D to carrier proteins in the bloodstream, and greater use of alternative metabolic pathways for calcium uptake. Because their bodies use vitamin D more sparingly, indigenous Arctic and Tropical peoples can be misdiagnosed with vitamin D deficiency and wrongly prescribed dietary supplements that may push their vitamin D level over the threshold of toxicity.





Frost P. (2022) The Problem of Vitamin D Scarcity: Cultural and Genetic Solutions by Indigenous Arctic and Tropical Peoples. Nutrients 14(19):4071. https://doi.org/10.3390/nu14194071


Monday, October 3, 2022

European Hair, Eye, and Skin Color: Solving the Puzzle


The distinguishing physical features of Europeans began as female features.


I’ve published a book through Academica Press. It’s titled: European Hair, Eye, and Skin Color: Solving the Puzzle. It can be ordered at: https://www.academicapress.com/node/549  


Here is a summary:



Europeans are strangely colored, particularly in the north and east. Hair is not only black but also brown, flaxen, golden, or red. Eyes are not only brown but also blue, gray, hazel, or green. Finally, skin is white, almost like that of an albino.


That color scheme is strange for several reasons:


·        It arose through new alleles at unrelated genes: hair color diversified through a proliferation of new alleles at MC1R, and eye color through a proliferation of new alleles in the HERC2-OCA2 region. Skin color became fair through new alleles at SLC45A2, SLC24A5, and TYRP1. All three changes occurred in parallel at different loci on the genome.


·        The new hair and eye color alleles are too numerous and too recent to be due to anything but strong selection. Among Europeans, the various hair colors are produced by new alleles at over 200 loci (SNPs), and the various eye colors by new alleles at over 124. Those alleles arose over a relatively short span of time, certainly less than the 50,000 years that modern humans have been in Europe. Only some kind of selection, and very strong selection at that, could have caused such a proliferation of new alleles over such a short time.


·        The selection was aimed primarily at women. Even today, women naturally have a higher incidence of red hair, blonde hair, and green eyes. Hair and eye colors are more evenly distributed among women: the less frequent colors are more common, and the more frequent ones less common. Skin is also fairer in women.


·        The new colors are mostly on or near the face, the focus of visual attention. When compared with the original black and brown, they are brighter and “purer” (they occupy thinner slices of the visible spectrum). Brightness and purity are characteristic of colors favored by sexual selection. A third characteristic is novelty: the relative rarity of a color. Novelty improves mating success by attracting attention and interest, but that success is eventually its undoing. As each generation passes, it becomes more common and less novel. Other colors attract more interest, particularly new ones that arise through mutation, with the result that a growing number of color variants accumulate in the gene pool. Such color polymorphisms are a frequent outcome of sexual selection.


·        Unlike the hair and the eyes, the skin did not develop a color polymorphism among Europeans, instead becoming unusually pale. The reason may be that sexual selection was guided by a pre-existing dimorphism. In all populations, men are browner and ruddier than women, who by comparison are fairer. Fairer-skinned women were seen as more feminine in traditional cultures and preferred as mates. Sexual selection, if sufficiently strong, would have drained the European gene pool of alleles for dark skin.


Sexual selection is not the preferred explanation among writers on this subject. Most lean toward one of two scenarios that involve natural selection:


·        Relaxation of selection for dark skin: when modern humans entered Europe, natural selection stopped favoring dark skin because UV protection was less necessary at northern latitudes. Defective alleles for skin pigmentation began to accumulate in the gene pool, and some of them had effects on hair and eye color.


That scenario has two weak points:


o   Relaxation of selection would take more than a million years to produce the current diversity of hair and eye colors. Yet modern humans have been in Europe for only 50,000 years. In fact, it was only around 20,000 years ago that some Europeans began to acquire pale skin and diverse hair and eye colors, and that phenotype would not become fully established throughout Europe until 10,000 to 5,000 years ago.

o   Skin color is weakly linked to hair color and eye color. Light skin often coexists with dark hair and dark eyes.


·        Selection for light skin: natural selection reduced skin pigmentation in order to maintain sufficient production of vitamin D. The hair and the eyes underwent a similar reduction in pigmentation because a change to one pigmentary trait presumably affects the others.


That scenario has two weak points:


o   Again, skin color is weakly linked to hair color and eye color. Yet the changes to the latter have been as profound as those to skin color. Moreover, the changes to hair and eye color have not been so much a reduction in pigmentation as a non-random creation of new hues that emit more light within narrower slices of the spectrum.

o   Analysis of ancient DNA and present-day DNA indicates that modern humans were dark-skinned for tens of thousands of years after their entry into Europe. Why wasn’t vitamin D a problem then? If we consider the indigenous inhabitants of North and South America, we see that natural selection has created very little latitudinal variation in their skin color, even though they have lived in the Americas for some 12,000 years. Natural selection, by itself, appears to change skin color rather slowly.


The current physical features of Europeans seem to have arisen on the steppe-tundra of eastern Europe and western Siberia during the last ice age, between 10,000 and 20,000 years ago, when nomadic humans subsisted almost entirely on meat from reindeer and other migratory game. Long-distance hunting increased the death rate among men and decreased the polygyny rate—only the ablest hunters could provide for more than one woman and her children because women had almost no food autonomy. 

The result: a surplus of women on the mate market; intense rivalry among them for male attention; and strong selection for eye-catching female features. Such features became more frequent with succeeding generations, eventually forming what is now seen as the “European” phenotype.



Frost, P. (2022). European Hair, Eye, and Skin Color: Solving the Puzzle. Washington: Academica Press, 169 pp., hardcover, ISBN 9781680538724


If you wish to buy a less expensive paperback edition, please make your preference known to Academica Press by emailing to: