A team of anthropologists at Borås College, central Sweden, published the breakthrough discovery on Tuesday morning following a comprehensive four-year study of over 30,000 Swedes.
"It might be time to put an end to the dumb blonde jokes," researcher Sofia Håkansson told The Local with a chuckle.
The idea for the study was born after she had noticed during a team-building weekend away that several of the admin staff outfoxed the academics in problem-solving tasks.
"At first I thought it was a gendered observation, with ideas of looking into women multi-tasking at home as more of a basis for a working hypothesis," said Håkansson. She set to work enrolling students in IQ tests and noting a huge array of other factors - from age and gender to which courses the students were taking on campus.
At that point, hair colour was not a parameter.
"One day, there was this tiny little blonde who kept staring at her test while twirling her blonde hair. At first my own reaction was that she was slow and dumb, then with a minute to go she filled out every single answer, and to my amazement she had one of the highest scores yet," Håkansson said.
"That's when I had the very un-PC thought of writing down the participants' hair colour, because I'd discarded her as a dumb blonde."
Håkansson admitted that she kept the new research method to herself for fear of incurring at best sceptical glances, at worst an official racism probe by the faculty's diversity ombudsman.
"But in the end our research shows that people with blonde hair, on average, are smarter. But not by much, mind you," said. "And it holds true for fake blondes too, regardless of ethnicity."
She ran a smaller sample of 2,000 participants through a spatial awareness test in the lab and found the same pattern. And blonde women received an average test score that was 1.3 percent higher than the men's.
Håkansson then further narrowed her sample, asking the top scorers whether or not their hair colour was genuine. In many cases it was straight out of a bleach bottle, leading Håkansson to breathe a sigh of relief.
"We're not talking of a 'smart gene'; there seems just to be a correlation here between fair locks and IQ test scoring and I have no idea why," said Håkansson, who is incidentally a blonde herself.
Regardless, her research sent shock waves around social and national media.
"Ha! In your face brunettes. Finally an end to the blonde jokes," Greta Persson tweeted, while Heronymous, another blonde, tweeted "Science, bitch!"
Story continues below…
Within hours of publishing the study, however, Sweden's academic research oversight committee, based in Gröngölingsköping, said it would subject research leader Håkansson to an investigation.
The committee members said in a joint statement that they had serious doubts as to whether the Borås-based scientist had "willfully formulated a hypothesis to stoke a media wildfire rather than advance the cause of science".
Håkansson herself quickly rebutted accusations of foul play, but admitted personal trauma had played into how she had chosen her line of research, adding that one too many blonde jokes had plagued her during "a troublesome recent holiday in Greece".
"I have heard every blonde joke in the world and I've never laughed once," Håkansson said. "And it's much funnier to pick on Norwegians anyway... though they're mostly blonde too."