Though the indigenous people of the Solomon Islands all have dark skin, about 5% to 10% also have naturally blond hair – and a new study finds that the genetic quirk responsible for this is different from the one that produces blond hair in people of European ancestry.

Researchers from Stanford University and colleagues collected spit samples from 43 Solomon Islanders with blond hair and 42 with the darkest hair. They scanned the DNA in all of the samples and looked for telltale differences that were linked with hair color. Sure enough, they found that on chromosome 9, there was one spot where blonds usually had a “T” (short for the DNA chemical thymine) and dark-haired people typically had “C” (the DNA chemical cytosine), they report in Friday’s edition of the journal Science.

That small change results in a significant change in a gene called TYRP1, which was already known to play a role in pigmentation in mammals. This single mutation explains 50% of the variability in the islanders’ hair color, the researchers found.

Many Westerners had assumed that encounters with European explorers and traders over the years had introduced a blond gene into the Melanesian gene pool. Among the residents of the Solomon Islands, conventional wisdom holds that sun exposure or heavy fish consumption could be responsible, said co-senior author Sean Myles, a former Stanford postdoc who is now a professor at Nova Scotia Agricultural College, in a statement.

Naturally blond hair is rare on Earth, limited mainly to northern Europe and the collection of South Pacific islands that includes the Solomon Islands. The researchers checked to see whether the C-to-T change on chromosome 9 was also present in Europeans. It wasn’t. That means blond hair evolved not once but twice.

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By Karen Kaplan, Los Angeles Times/For the Booster