Hair whorl: The myth
When viewed from above and behind the head, many people's hair whorls in either a clockwise (CW) or counterclockwise (CCW) direction. This is sometimes used to illustrate basic genetics; the myth is that whorl direction is controlled by a single gene with two alleles, and the allele for clockwise is dominant to the allele for counterclockwise. Several studies have data that fit this myth fairly well, but with enough exceptions that the myth can't be completely true.
While hair whorl is occasionally used to illustrate basic genetics, it gets more attention because some studies have suggested that counterclockwise whorls are more common in left-handed people than in right-handed, and other studies have suggested that counterclockwise whorls are more common in gay men than in straight men. Other studies have given conflicting results, and it is not clear yet whether there is any relationship between hair-whorl direction and either handedness or sexuality.
Hair whorl as a character
In people with short, straight hair, a single whorl is usually fairly obvious. 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.
The direction of the whorl can be difficult to determine. 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.
Bernstein (1925) compared parents and offspring, with the following results (omitting double whorls):
|Parents||CW offspring||CCW offspring||Percent CW|
|CW x CW||58||12||83%|
|CW x CCW||32||8||80%|
|CCW x 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 the myth were true, two parents with counterclockwise whorls could not have a child with a clockwise whorl, so the three CW children of CCW x CCW parents do not fit the myth.
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 x CW||385||56||87%|
|CW x CCW||140||57||71%|
|CCW x CCW||3||16||16%|
The data clearly indicate that there is a genetic influence on the direction of the hair whorl, because CW x CW parents have a much higher percentage of CW offspring than do CCW x CCW parents. However, the three CW offspring of CCW x 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 x CCW matings should be rr and therefore half the offspring of CCW x CCW matings should be CCW. Instead, the data in the table above show three CW and 16 CCW offspring from CCW x 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.
Rife (1933) looked at 13 pairs of monozygotic 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. The pairs of twins that differ in their whorl direction do not fit the simple model of the trait being completely determined by genetics.
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|
|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|
|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 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 there is an association between handedness and hair whorl direction. This could be an interesting class project, if enough care was taken to be unbiased in observing the direction of 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.
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. This result got a lot of attention in the popular press (France 2007) and is mentioned on a lot of web pages about "gaydar." 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 and 14 percent of straight men to have counterclockwise whorls, while Schwartz et al. (2010) found 19.7 percent 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 may be an important difference between these studies and that of Klar (2004).
It's hard to determine which way the hair whorls in people with long or curly hair, and the data do not fit the simple genetic model perfectly. So you should not use hair whorl direction to demonstrate basic genetics.
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This page was last revised December 8, 2011. Its address is http://udel.edu/~mcdonald/mythhairwhorl.html. It may be cited as pp. 40-45 in: McDonald, J.H. 2011. Myths of Human Genetics. Sparky House Publishing, Baltimore, Maryland.
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