In the Solomon Islands, just northeast of Australia, about 10 per cent of the dark-skinned indigenous population has blond hair. Globally, blond hair is rare, occurring with substantial frequency only in northern Europe and in Oceania. Most experts believed the gene for light hair had been passed on to dark-skinned people by European traders, colonisers or explorers.
“Up to now, most cases of blond hair among dark-skinned people have been thought to be the result of genetic mixing with Europeans,” says anthropologist Dr Nina Jablonski.
But in reality what has been theorised and in some cases assumed for centuries is not the case, according to a new study by Stanford University School of Medicine.
In fact, the gene that causes blond hair in Solomon Islanders is completely different and independent of the gene that causes blond hair in Europeans. And the frequency of blond hair on the islands is comparable to Europe.
“The results of this study challenge any simple notion that we may have about defining race,” says Dr Eimear Kenny, who led the study on blond hair in the Solomon Islands. A population geneticist and Stanford University postdoctoral fellow, Dr Kenny has been involved in the study of genetics in the South Pacific Ocean for more than seven years. She says “what we have found is just the tip of the iceberg”.
The study identifying the gene responsible for blond hair among the Melanesian people in the Solomon Islands was published in May’s issue of the journal Science. The researchers compared the DNA of more than 900 Solomon Islanders and discovered that a single gene known as TYRP1 was responsible for the hair-colour variance.
Then by examining whether the mutation existed among more than 900 other individuals from 52 different populations around the world, the scientists discovered that this gene was unique to the Oceanic region.
According to Dr Carlos D. Bustamante, co-senior author of the study and professor of Genetics at Stanford University, the rare case of a simple gene determining human appearance shows the importance of including understudied populations in gene mapping.
The way blond hair evolved in the Solomon Islands is quite different from the way blond hair evolved in Europe, says Dr Kenny. “In European blondes the trait is the effect of a combination of many genes and is a much more complex genetic model because of the history of the people in terms of travel. The isolation of the Solomon Islands might have had an impact on the simplicity of the genetic model in that part of the world,” she adds.
“The world of medical genomics research is rapidly changing,” Dr Kenny says. “These findings highlight the importance of studying the genetics of isolated populations.”
Up until five years ago genetic research was almost exclusively focused on European origins because of the large collection of research material from the past which serve as references in the present, and for technical reasons such as access to laboratories and equipment.
“A large amount of genetic variations around the world are being missed. If we broaden ethnic representation within biomedical genomics or biomedical research, we may uncover that susceptibility to disease or variations in eye colour and facial features differ from population to population,” Dr Kenny says.
The blond gene in Solomon Islanders is likely to have first appeared about 10,000 years ago. About 50 per cent of Solomon Islanders carry the mutation for TYRP1 in their genomes, but it is a recessive trait, which means an individual needs two copies — one from each parent — to be blonde.
This study further demonstrates that physical traits are poor characteristics for defining genetically distinct groups or races, says the head of Pennsylvania State University’s Anthropology department.
Dr Jablonski has been a published expert on variations in skin tone for more than 20 years. She says physical traits that appear to be the same can have different genetic origins.
“The ‘same’ trait doesn’t denote membership in the same group. Races have no validity as biological categories, but they continue to be widely used and faithfully inherited social categories that are ill-defined, historically and geographically contingent and culturally defined” says Dr. Jablonski. “We need to get used to the idea that many of the most visible human traits — such as skin colour, hair colour and hair texture — evolved independently in different populations.”
“It is certainly possible that blue eyes or variations in skin tone evolved independently [among dark-skinned populations] as well,” Dr Kenny says. “We haven’t investigated that yet, but further research would probably reveal that some cases were due to migration and some were because that human characteristics arose more than once among different groups of people.”
Dr Bustamante is seeking funding to analyse the rest of the data gathered from the Solomon Islands. The team’s next step is to further investigate the genetics of skin, hair and eyes in the Solomon Islands and Melanesia.
In an article by Stanford University’s School of Medicine, Dr Bustamante further stressed the importance of studying genetic models among various populations by warning against assuming that genetic findings from one population will translate to another.
“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, we could disproportionately benefit some populations and harm others,” Bustamante said.
Sarah Jones is a freelance journalist based in the US.