Whether you sport a shock of flaming red hair, cascading blonde tresses, or no-nonsense black braids, the color of your mane is often a source of identity or a statement on social mores.
Hair culture is complex, but perhaps even more complex is the way our hair pigments are entangled within our DNA. Natural hair color is genetic, and a new report published this week in Nature Genetics shows that a surprisingly high number of genes may have a say in the process.
The new study, the largest to date, combed through genetic data of almost 300,000 European men and women who self-reported their hair color either with the U.K. BioBank or with the genetic profiling company, 23andMe. Using a genome-wide association study, or GWAS, researchers then unraveled how hair color correlates with genetic variations. Together they identified variants at 258 unique spots in the genome that span a total of 124 genes.
“When I was in medical school, we were taught there were about four genes influencing hair color,” says Timothy Spector, a geneticist and epidemiologist at King’s College in London and senior author of the study. “Now there are hundreds.”
A delicate balance between two pigments called eumelanin and pheomelanin dictates hair color: while pheomelanin adds a reddish hue to hair, more eumelanin means darker black or brown hair. It’s unclear how the majority of newly found genes act, but many may influence the way cells make, transport, or destroy melanin pigments. Because melanin also defines skin and eye color, the genes identified could shed light on pigmentation disorders and skin cancers too, Spector says.
The researchers put their new insights to work by building an algorithm to predict a person’s hair color by scanning their DNA alone. While black and red hair was easier to guess, predicting blond and brown hair proved challenging.
“We don’t fully understand why that is,” says Manfred Kayser, a forensic molecular biologist at the Erasmus University Medical Center in Rotterdam and senior co-author of the study. “But we do know there is blond to brown age-dependent hair color change in Europeans, which could add to the variability.”
The prediction test could be especially valuable in forensics and anthropology to add color to scenes after the fact, says Kayser. “If you have a DNA sample from a crime scene or from a bone, you can tell what hair color that person might’ve had,” he says. “It can be used to put appearance back to people who died a long time ago.”
Perhaps the most intriguing finding, however, was that women were more likely to report having blond hair than men, and three times less likely to say they had dark hair. The gene frequencies for blond hair between men and women themselves weren’t very different, but actually having blond hair was different, Spector says.
“We think the reason to that is the generally known psychology that fairer women prefer darker men, and men prefer fairer women,” he says. “This blonde business might be that blondes do have more fun and have more success and larger families. We don’t know the mechanism but it was so consistent that we believe it’s true.”
The issue with this finding, however, is that because participants reported their own hair color, the data could suffer from differences in human perception, says David Hunter, an epidemiologist at the University of Oxford, who was not part of the study. “Many of us find it difficult to describe hair color, and inevitably there will be subjectivity around if someone describes their hair as light brown or dark brown,” he says.
In addition, by limiting the study to people of European ancestry, the authors limited the possibility of comparing data with people from other continents to tell if the genetic variants they found are truly related to hair color or if they’re simply associated with being European and have nothing to do with hair color. “It makes sense to do this analysis with other populations and stratify genetic variants by continental ancestry,” Hunter says.
Even as scientists continue to probe how these myriad genes paint our hair, one thing is clear — the genetics of hair color is more complex than we thought, perhaps even more than the hair-dye aisle at the pharmacy.