Residents of the Solomon Islands in the Pacific have some of the darkest skin seen outside of Africa. They also have the highest occurrence of blond hair seen in any population outside of Europe. Now, researchers have found the single gene that explains these fair tresses.
A single mutation is responsible for almost half of the variation in Solomon Islanders' hair color, the scientists reported Thursday (May 3, 2012) in the journal Science. Most strikingly, this gene mutation seems to have arisen in the Pacific, not been brought in by fair-haired Europeans intermarrying with islanders.
"[T]he human characteristic of blond hair arose independently in equatorial Oceania," study researcher Eimear Kenny, a postodoctoral scholar at the Stanford University School of Medicine, said in a statement. "That's quite unexpected and fascinating."
Kenny and her colleagues traveled to the remote Solomon islands, where study co-author Sean Myles, now a professor at Nova Scotia Agricultural College, had previously noted a surprising number of blonds.
When the local chief gave the OK, the researchers recruited participants and assessed hair and skin color using a light reflectance meter, took blood pressure readings and measured heights and weights.
"They have this very dark skin and bright blond hair. It was mind-blowing," Myles said in a statement. "As a geneticist on the beach watching the kids playing, you count up the frequency of kids with blond hair, and say, 'Wow, it's 5 to 10 percent.'"
That's not very far off from the proportion of blond-haired people in Europe, Kenny said. The researchers gathered saliva from 43 blond and 42 dark-haired Solomon Islanders to analyze for clues to the genes behind their hair color.
A genome-wide analysis turned up a shockingly clear result, rare in the world of genetics where a single trait can be influenced by dozens or more genes. A gene called TYRP1, which resides on the ninth chromosome of human's 23 pairs of chromosomes, explained 46.4 percent of the variation in the islanders' hair color. (Chromosomes are coiled packets of DNA.) A mutation in this gene affects an enzyme known to be involved in human pigmentation, the researchers found.
This mutation doesn't appear in European genomes, an analysis of genomes from 52 human populations around the world revealed. Rather, it seems to have arisen independently and persisted in the Melanesian population.
That makes the gene different from the one responsible for blue eyes, which arose from a single common ancestor between 6,000 and 10,000 years ago. Before then, there were no blue eyes, they said.
The find solves a nifty genetic mystery, but it also highlights the dangers of assuming that genome findings from one population will translate to another, said study author Carlos Bustamante, a professor of genetics at Stanford.
"If we're going to be designing the next generation of medical treatments using genetic information and we don't have a really broad spectrum of populations included, you could disproportionately benefit some populations and harm others," Bustamante said.
Globally, blond hair is rare, occurring with substantial frequency only in northern Europe and in Oceania, which includes the Solomon Islands and its neighbors. Many assumed the blond hair of Melanesia was the result of gene flow — a trait passed on by European explorers, traders and others who visited in the preceding centuries.
The islanders themselves give several possible explanations for its presence - they generally chalked it up to sun exposure, or a diet rich in fish, say the researchers.
‘Within a week we had our initial result. It was such a striking signal pointing to a single gene — a result you could hang your hat on. That rarely happens in science,’ said Kenny‘It was one of the best experiences of my career.’ In terms of genetic studies, the analysis was straightforward, said Eimear Kenny, a study author, PhD, who was born in Ireland.