Looking at a newborn baby is such a powerful moment for parents—the huge, overwhelming swell of love, the first feelings of fierce protectiveness, the onset of the terrifying responsibility. They feel such a sense of awe, of wonder at tiny fingers and tiny toes and little ears. And hair that grows in swirls clockwise; or counterclockwise.
Okay, maybe not those last two. Unless you are Marjolaine Willems, a clinical geneticist at the University Hospital of Montpellier in France. When her identical twin daughters were born, “I noticed that they had the same orientation of the hair whorl, so that is clockwise,” she says, referring to what are sometimes known as cowlicks, those patches of hair that grow in a different direction than the rest of what’s on our heads. But one twin had their hair whorl on the right side of her head, and the other had it on the left side. Not so identical after all. A few years later, her sister also had twins—and they had the same whorl placements as their older cousins.
Being a clinical geneticist, Willems found herself unable to let it go. And now, after 13 years of staring at the heads of twin and singleton babies, her team’s paper on the association between global hemisphere and hair whorl formation has won the 2024 IgNobel prize in anatomy. The prize is for science that makes you laugh and then makes you think. Is it somewhat silly to study whether people in the Southern Hemisphere have hair that swirls counterclockwise more often than in the Northern Hemisphere? Sure. But it’s also a demonstration of how much humans can vary—from tiny changes in our genes to the visible marks they can leave on our appearances.
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If there is hair on your head, that hair has at least one whorl in it—a patch of hair that grows out of the scalp in a spiral direction. It makes good sense. Hair set in lines on a sphere simply can’t be brushed flat, Willems explains. There will always be a cowlick somewhere.
Obviously, human heads are not spherical, but they are round on top, and so we all have hair whorls. Most humans—98.5 percent—will have only one, while a lucky 1.5 percent will have two (perhaps not so lucky for the people who cut their hair). They can be in the center of the scalp, towards the right or towards the left, and can twist clockwise or counterclockwise. You can try to feel around and find yours, but Willems notes it’s a whole lot easier if you have a friend look instead.
But what causes our hair to grow like that? “We have no idea how it began,” Willems says. Scientists do know that it probably has some genetic basis; other hairy mammals exhibit whorls where they have rounded parts, from the forehead of cows to the heads, legs or buttocks of dogs or horses. People with rare genetic conditions may be more likely to have double whorls, or whorls that are in the front instead of on the crown of the head.
To try to find out if hair whorls are the result of genetics or environment, Willems and her colleagues decided to study identical twins, and compare them with nontwins in the Northern and Southern hemispheres. While twin studies could determine a genetic component, a difference between the hemispheres might indicate the environment played a part in how hair swirls.
Willems started by getting the consent of new parents to ogle the scalps of their newborns. “The gynecologist ask[ed] them first if they would be interested in a special study,” she says. And when they found out the study was on how hair grows in whorls, most of the parents were laughing. Babies were her preferred subjects, since they don’t have much hair, and the whorls are easier to see. In older children or adults with longer hair it can be a process.
The scientists compared 37 pairs of French twins, 50 singleton French children in the Northern Hemisphere and 50 Chilean singletons in the Southern Hemisphere (They did not stare at Chilean twins, and sadly, I couldn’t get an answer about why). The vast majority of hair whorls were clockwise. In twins 70 percent had hair whorls going the same direction—and 86 percent of all twins had clockwise whorls. In the nontwin French kids, only about 4 percent of kids had a counterclockwise whorl. But in Chile 28 percent of kids had a counterclockwise whorl. Genetics are definitely involved, the scientists concluded, but environment can play a role too.
Willems and her colleagues joked that maybe hair whorled based on the Coriolis effect. This is a pattern of deflection that affects very large objects not attached to the Earth. Since the Earth is roughly a sphere, as it rotates the equator moves faster than the poles. Things going very long distances from the equator to the north or south will shift, because the north and south are moving more slowly. In the Northern Hemisphere, things shift to the right. In the Southern Hemisphere, they shift to the left.
The Coriolis effect is why hurricanes and cyclones spin one way in the Northern Hemisphere, and the other way in the Southern Hemisphere. Over the vast distances of these storms, the Coriolis effect pushes wind and rain counterclockwise in the North, and clockwise in the South—to equally deadly effect. The Coriolis effect is also the origin of the myth that toilets spin the opposite way in Australia. In a toilet, the water volume and distance are too small to be subject to the Coriolis effect—a relief for anyone flushing the toilet at the equator.
If toilets aren’t subject to Coriolis forces, hair certainly isn’t either, Willems says. “That was like a little joke of a hypothesis,” she notes. Willems and her colleagues did try to be serious about their paper, “but as all our colleagues were laughing, we knew it was quite funny.”
Yet the prospect of genetics and environment acting together raises more scientific questions. It means learning more about how hair twists on the head could teach people about how we develop—how our genes and environment translate into the reality of our faces and heads. It’s a small difference. But a small difference could provide a lot of clues about how cells divide, form and migrate—and how to deal with them when the process goes wrong. So the whorl is a source of wonder. Just as wonderful as fingers, toes or tiny little noses. It’s a sign that cells divided, migrated, organized—and made something wonderful and new.
This is an opinion and analysis article, and the views expressed by the author or authors are not necessarily those of Scientific American.
