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Genetics of hair whorl
Summary
Summary
You probably aren't familiar with the back of your own head, but you might have hair that whorls in a clockwise or counterclockwise direction. Some people have claimed that clockwise whorls are a dominant genetic trait, but that's not true. Don't worry if your family includes two counterclockwise parents and clockwise child, and if you're a teacher, don't use hair whorl as an example of a simple genetic trait.
Some studies have found that counterclockwise whorls are more common in left-handed people than in right-handed, and other studies have found that counterclockwise whorls are more common in gay men than in straight men. Other studies have not found these results, and it is not clear yet whether there is any relationship between hair-whorl direction and either handedness or sexuality.
Does everyone have a clockwise or counterclockwise whorl?
If you look at someone with short, straight hair, you can usually see a whorl near the crown of their head. If you start at the center of the whorl and follow the hairs out, they either bend clockwise around the center, or counterclockwise. Clockwise whorls are most common; estimates of the frequency of clockwise whorls range from 51 percent in Japan (Klar 2009) to 65 percent of undergraduate psychology students in the United Kingdom (Annett 1985), 69 percent of Nigerians (Ucheya and Igweh 2005), 74 percent of German schoolboys (Bernstein 1925), 81 percent of students in the United States (Lauterbach and Knight 1927), 92 percent of the "general population" in Maryland (Klar 2003), and 94 percent of newborns in the United States (Wunderlick and Heerema 1975). Some people have two or more whorls; Lauterbach and Knight (1927) found 5 percent of white Massachusetts schoolchildren to have double whorls, while Schwarzburg (1927) found 5.4 percent of Germans to have double whorls. Wunderlich and Heerema (1975) found double whorls in 1.5 percent of white newborns, while Ucheya and Igweh (2005) found double whorls in 2 percent of Nigerian men.
Sometimes it's not clear which direction the whorl goes. Rahman et al. (2009) had two people independently judge photographs of whorls, and for about 4 percent of subjects, one observer called the whorl clockwise while the other called it counterclockwise. The whorl can be particularly hard to see in people with long or curly hair. Lauterbach (1925) says "frequently the hair requires considerable combing in order to discover the natural whorl... Long, fine hair sometimes assumes a false whorl but the true whorl can always be located close to the scalp." Ziering and Krenitsky (2003) reported that 78 percent of women had what they called a "diffuse" pattern instead of a whorl. Wunderlich and Heerema (1975) could see a hair whorl in only 10 percent of Black newborns, and Ziering and Krenitsky (2003) reported that 80 percent of African-American men had a diffuse pattern instead of a whorl. Ucheya and Igweh (2005), however, identified a whorl in all 500 of their sample of Nigerian men.
It is clear that with double whorls, straight hair with ambiguous or "diffuse" whorls, and curly hair with no apparent whorls, there are a lot of people who don't have a clear clockwise or counterclockwise whorl.
Family studies
Bernstein (1925) compared parents and offspring, with the following results (omitting double whorls):
| Parents | CW offspring | CCW offspring | Percent CW |
|---|---|---|---|
| CW×CW | 58 | 12 | 83% |
| CW×CCW | 32 | 8 | 80% |
| CCW×CCW | 3 | 8 | 27% |
He concluded that hair whorl was a simple Mendelian trait, with the allele for clockwise whorl dominant to the allele for counterclockwise whorl. However, if this were true, two parents with counterclockwise whorls could not have a child with a clockwise whorl, so the three CW children of CCW×CCW parents do not fit Bernstein's interpretation.
Schwarzburg (1927), Kloepfer (1946), Beckman et al. (1960), and Sharma (1985) collected similar data. Adding all of their numbers to those of Bernstein (1925) yields the following:
| Parents | CW offspring | CCW offspring | Percent CW |
|---|---|---|---|
| CW×CW | 385 | 56 | 87% |
| CW×CCW | 140 | 57 | 71% |
| CCW×CCW | 3 | 16 | 16% |
The data clearly indicate that there is a genetic influence on the direction of the hair whorl, because CW×CW parents have a much higher percentage of CW offspring than do CCW×CCW parents. However, the three CW offspring of CCW×CCW matings, which all come from Bernstein (1925), do not fit the simple model that CW is completely dominant. Because other researchers have shown that it can be difficult to determine the direction of whorl (Rahman et al. 2009), it is possible that the 3 people who do not fit the model really had CCW whorls but were observed incorrectly (or one of their parents was incorrectly called CCW).
Klar (2003) proposed a "random recessive" model for the inheritance of hair whorl, in which there are two alleles, R for clockwise whorl and r for random whorl direction. In this model, RR and Rr individuals have clockwise hair whorls, while half of rr individuals have clockwise whorls and half have counterclockwise whorls. Klar (2005) reanalyzed the data of Schwarzburg (1927) and concluded that the data fit the random-recessive model better than the model in which CW is dominant. However, Klar's random-recessive model predicts that all CCW individuals have the rr genotype, so all of the offspring of CCW×CCW matings should be rr and therefore half the offspring of CCW×CCW matings should be CCW. Instead, the data in the table above show three CW and 16 CCW offspring from CCW×CCW matings. This is significantly different from the prediction of Klar's random-recessive model (exact binomial test, P=0.004). So the data don't fit Klar's random-recessive model very well, either.
Twin studies
Rife (1933) looked at 13 pairs of identical twins. Seven of the pairs had opposite whorls: clockwise in one twin, counterclockwise in the other. Sharma (1985) looked at the hair whorls of 27 pairs of identical twins and found one pair with opposite whorls. If hair whorl was determined by genetics, identical twins should have identical hair whorls, so something else is influencing them.
Genome studies
Luo et al. (2023) did a genome-wide association study in Chinese adults. After excluding people with double whorls and diffuse patterns, they had 4,099 people with single whorls. They found four regions in the genome that were associated with hair whorl direction. This is evidence that hair whorl direction is at least partially determined by genetics, but that it is not a single-gene trait.
Hair whorl and handedness
Klar (2003) surreptitiously observed people in Maryland shopping malls, most of whom would be right-handed; of the 500 people with clearly visible, single whorls, 8.4% had counterclockwise whorls. He also surveyed 49 non-righthanded people (this includes left-handed and ambidextrous individuals) and found that 44.9% had counterclockwise whorls. Klar (2003) concluded that the much higher proportion of counterclockwise whorls in left-handed people fit a random recessive model. In this model, a person with an RR or Rr genotype is right-handed and has a clockwise whorl. A person with an rr genotype has a 50 percent chance of being left-handed and a 50 percent chance of having a counterclockwise whorl; therefore half of all left-handed people would have a counterclockwise whorl, and half of all people with a counterclockwise whorl would be left-handed.
Klar's work received a lot of media attention, and led to several followup studies and renewed attention to some earlier work. In all of these, the hair whorl was observed at close range with the permission of the subject, rather than being observed surreptitiously from a distance the way Klar did. I summarize the data below; "CCW" is counterclockwise whorl, "RH" is right-handed, "NRH" is non-right-handed, "N" is the number of RH or NRH individuals. "Sig" is whether the difference in CCW percentage between RH and NRH is statistically significant. I omitted people with double whorls from the percentages.
| reference | Subjects | CCW percentage in RH | N | CCW percentage in NRH | N | sig? |
|---|---|---|---|---|---|---|
| Lauterbach and Knight (1927) | white children | 19.3 | 877 | 20.6 | 63 | No |
| Newman (1934) | American | 15 | ? | 21 | ? | No |
| Annett (1985) | British adults | 34.9 | 209 | 38.0 | 38 | No |
| Scott et al. (2005) | Pennsylvania whites | 13.8 | 123 | 11.1 | 36 | No |
| Beaton and Mellor (2007) | Welsh men | 12.8 | 125 | 54.2 | 48 | Yes |
| Jansen et al. (2007) | German soldiers | 18.3 | 981 | 19.7 | 127 | No |
| Schmidt et al. (2008) | German children | 10.2 | 177 | 32.5 | 40 | Yes |
| Perelle et al. (2009) | New York general population | 15.6 | 179 | 22.7 | 66 | No |
| Barron (2009) | California men | 19.8 | 470 | 20.8 | 77 | No |
| Schwartz et al. (2010) | North American men | 18.7 | 1168 | 16.0 | 206 | No |
If Klar's random recessive model were correct, you'd expect to see a very low frequency of counterclockwise whorls in righthanded people, while about half of non-righthanded people would have counterclockwise whorls. The results of Beaton and Mellor (2007) and Schmidt et al. (2008) support Klar's model, but the other studies do not.
The results from the different studies are puzzling; there is no obvious difference in the way the studies were conducted, or the populations studied, that would explain why some studies find a difference and other studies do not. For now, it is not clear whether handedness and hair whorl direction are related.
Hair whorl and male sexuality
Klar (2004) surreptitiously recorded the direction of hair whorl at a beach near Rehoboth Beach, Delaware that is popular among gay men. Out of 272 men with single whorls, 29.8 percent had counterclockwise whorls. This was a higher proportion than the 9.1 percent counterclockwise he counted in 328 men from malls, stores, and the beach at Atlantic City, most of whom would be straight. He concluded that the genetic basis for hair whorl was related to the genetic basis for male homosexuality. This study should be in textbooks, as an example of how not to do science. The direction of hair whorl can be difficult to determine, even from close up, so it would be very easy to subconsciously interpret ambiguous hair whorls in a way that yielded the most interesting result.
Despite the glaring flaws in Klar (2004), the paper got a lot of attention in the popular press (France 2007) and is mentioned on a lot of web pages about "gaydar," the ability to identify gay people based on subtle physical and behavioral characteristics. However, two more rigorous studies did not find a significant difference between gay and straight men in the proportion of counterclockwise whorls. Rahman et al. (2009) and Schwartz et al. (2010) separated gay and straight men based on a questionnaire, not which beach they went to, and determined their whorl type based on close examination, not from a distance. Rahman et al. (2009) found 18 percent of gay men and 14 percent of straight men to have counterclockwise whorls, while Schwartz et al. (2010) found 19.7 percent counterclockwise in gay men and 17.2 percent in straight men. In both studies, the observer determined whether the whorl was clockwise or counterclockwise without knowing whether the subject was gay or straight, which is a critically important difference between these studies and that of Klar (2004).
Further research
The genetics and developmental biology of left-right asymmetrical traits are a fascinating puzzle, so it would be great if someone did more research on the four genes identified by Luo et al. (2023) that influence hair whorl direction.
The data on hair whorl and handedness are confusing; some studies find more lefthanded people are CCW, and some studies don't. This could be an interesting class project, but it would be important to be unbiased: the people observing hair whorl shouldn't know who is right or left handed, and the people observing handedness shouldn't know the direction of hair whorl. Rahman et al. (2009) are a good example of how to do this; they took a photograph of each person's whorl, then had two people who were unaware of the purpose of the study independently judge whether it was clockwise or counterclockwise. It would also be important to only include people with a single whorl in a clear direction, and not use data from a lot of people, rather than trying to force everyone into the CW or CCW category.
It's clear to me that if there's any difference in proportion of CCW between gay and straight men, it's very, very small (Rahman et al. 2009, Schwartz et al. 2010). I don't think the subject needs further research.
References
Annett, M. 1985. Left, right, hand and brain: The right shift theory. London, UK: Erlbaum.
Barron, J. 2009. The relation of men's hair whorl patterns to handedness in heterosexual men and gay and bisexual men. M.S. thesis, California State University Fullerton.
Beaton, A.A., and G. Mellor. 2007. Direction of hair whorl and handedness. Laterality 12: 295-301.
Beckman, L., J.A. Böök, and E. Lander. 1960. An evaluation of some anthropological traits used in paternity tests. Hereditas 46: 543-569.
Bernstein, F. 1925. Beiträge zur Mendelistischen Anthropologie. II. Quantitative Rassenanalyse auf Grund von statistischen Beobachtungen über den Derhsinn des Kopfhaarwirbels. Sitzungsberichte der Prüssischen Akademie der Wissenschaften. 71-82.
France, D. 2007. The science of gaydar. New York June 25, 2007.
Jansen, A., H. Lohman, S. Scharfe, C. Sehlmeyer, M. Deppe, and S. Knecht. 2007. The association between scalp hair-whorl direction, handedness and hemispheric language dominance: Is there a common genetic basis of lateralization? NeuroImage 35: 853-861.
Klar, A.J.S. 2003. Human handedness and scalp hair-whorl direction develop from a common genetic mechanism. Genetics 165: 269-276.
Klar, A.J.S. 2004. Excess of counterclockwise scalp hair-whorl rotation in homosexual men. Journal of Genetics 170: 2027-2030.
Klar, A.J.S. 2005. A 1927 study supports a current genetic model for inheritance of human scalp hair-whorl orientation and hand-use preference traits. Genetics 170: 2027-2030.
Klar, A.J.S. 2009. Scalp hair-whorl orientation of Japanese individuals is random; hence, the trait's distribution is not genetically determined. Seminars in Cell and Developmental Biology 20: 510-513.
Kloepfer, H.W. 1947. An investigation of 171 possible linkage relationships in man. Annals of Human Genetics. 32-70.
Lauterbach, C.E. 1925. Studies in twin resemblance. Genetics 10: 525-568.
Lauterbach, C.E., and J.B. Knight. 1927. Variation in whorl of the head hair. Journal of Heredity 18: 107-115.
Luo, J., et al. (12 co-authors. 2023. GWASs identify genetic loci associated with human scalp hair whorl direction. Journal of Investigative Dermatology 143: 2065-2068.
Newman, H.H. 1934. Dermatoglyphics and the problem of handedness. American Journal of Anatomy 55: 277-322.
Perelle, I.B., Ehrman, L., and Chanza, M. 2009. Human handedness and scalp hair whorl direction: no evidence for a common cause. Laterality 14: 95-101.
Rahman, Q., Clarke, K., and Morera, T. 2009. Hair whorl direction and sexual orientation in human males. Behavioral Neuroscience 123: 252-256.
Rife, D.C. 1933. Genetic studies of monozygotic twins. III. Mirror imaging. Journal of Heredity 24: 443-446.
Schmidt, H., Depner, M., and Kabesch, M. 2008. Medial position and counterclockwise rotation of the parietal scalp hair-whorl as a possible indicator for non-right-handedness. Scientific World Journal 8: 848-854.
Schwartz, G., Kim, R.M., Kolundzija, A.B., Rieger, G., and Sanders, A.R. 2010. Biodemographic and physical correlates of sexual orientation in men. Archives of Sexual Behavior: 39: 93-109.
Schwarzburg, V. W. 1927. Statistische untersuchungen uber den menschlichen scheitelwirbel und seine vererbung. Zeitsch. F. Morphol. U. Anthropol. 26: 195-223.
Scott, N.M., S.M. Weinberg, K. Neiswanger, C.A. Brandon, and M.L. Marazita. 2005. Hair whorls and handedness: informative phenotypic markers in nonsyndromic cleft lip with or without cleft palate (NS CL/P) cases and their unaffected relatives. American Journal of Medical Genetics 136A: 158-161.
Sharma, K. 1985. Inheritance of occipital hair whorls in man: a twin and family study. Indian Journal of Physical Anthropology and Human Genetics 11: 17-23.
Ucheya, R.E., and J.C. Igweh. 2005. Hair whorl patterns on the posterior aspect of the scalp among Nigerians. J. Exp. Clin. Anat. 4: 21-24.
Wunderlich, R.C., and N.A. Heerema. 1975. Hair crown patterns of human newborns: Studies on parietal hair whorl locations and their directions. Clin. Pediatr. 14: 1045-1049.
Ziering, C., and G. Krenitsky. 2003. The Ziering whorl classification of scalp hair. Dermatologic Surgery 29: 817-821.
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