The Root of Your Hair Color Lies in Your DNA

Over 100 newly discovered genes appear to explain why Irish people might have red hair, Swedes are often blonde, and Italians tend to be dark.

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Police detectives might soon be able to determine a suspect’s hair color with a sample of their DNA without needing to compare that evidence to a criminal database, according to researchers.

Publishing their findings in the journal Nature Genetics, the researchers found the genes that determined red hair almost 35 percent of the time, black hair more than 26 percent of the time, and blonde hair almost 25 percent of the time.

That means scientists might be able to reconstruct the hair color of anyone who leaves behind body fluids or skin cells. Currently, to determine a suspect’s hair color they would need to cross reference the DNA from those clues with mugshots and other images.

“This is relevant for forensics because it allows describing the appearance of an unknown perpetrator from crime scene DNA,” Manfred Kayser, a study co-author and professor of forensic molecular biology at the Erasmus MC University Medical Center in Rotterdam, Netherlands, told Seeker. “Unknown perpetrators cannot be identified via standard forensic DNA profiling. In anthropology this is useful to bring back the appearance to a person who passed away hundreds or thousands of years ago.”

The research might also help develop therapies related to ailments connected to hair color or melanin, the pigmentation that determines the color of one’s eyes and skin.

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Kayser and his colleagues looked at genes from 300,000 Europeans with black, blonde, dark brown, light brown, and red hair. They obtained that data from UK Biobank, a health charity and research organization, the Silicon Valley genome-testing company 23andMe, and the Visible Trait Genetics Consortium, an academic group. They tested Europeans because Africans, Asians, and others have less variability in their hair colors.

They identified 111 new genes that appear to be key to determining why the Irish might have red hair, Swedes are often blonde, and Italians tend to be dark.

Studies of twins show that genes determine their hair color 97 percent of the time, said Kayser. But the secrets of how that works are still being revealed. He noted that the hair of many blonde children, for example, turns brown as they grow older. As a result, it was much easier to determine red or black hair colors, while blonde and brown were trickier.

Male ancestors may have preferred blonds.

But geneticists don’t know why some hair colors are more easily predicted than others. The findings show that more research is necessary, said Kayser. “We assume that they’re either more genes that need to be discovered, or this missing heritability is explained by other phenomena,” he said.

Interestingly, women were around 25 percent more likely to report having blond hair than men. Because survey participants were self-reporting their hair color, women might have been fibbing when they said they had golden locks. But Kayser believed there was a biological reason, including maybe that humankind’s male ancestors preferred blondes.

“One explanation would be sexual selecting acting differently via males and females,” he said. “A naive interpretation is that men preferred light hair women as mates over dark hair women.”