WHEN men meet fair-haired women they really do have a “blonde moment”. Scientists have found that their mental performance drops, apparently because they believe they are dealing with someone less intelligent.

Researchers discovered what might be called the “bimbo delusion” by studying men’s ability to complete general knowledge tests after exposure to different women. The academics found that men’s scores fell after they were shown pictures of blondes.

Further analysis convinced the team that, rather than simply being distracted by the flaxen hair, those who performed poorly had been unconsciously driven by social stereotypes to “think blonde”.

“This proves that people confronted with stereotypes generally behave in line with them,” said Thierry Meyer, joint author of the study and professor of social psychology at the University of Paris X-Nanterre. “In this case blondes have the potential to make people act in a dumber way, because they mimic the unconscious stereotype of the dumb blonde.”

The research adds to a body of evidence that people’s behaviour is powerfully influenced by stereotypes. Previously scientists have found that people walk and talk more slowly in front of the elderly, while other studies have revealed that unconscious racial assumptions and prejudices emerge in written tests.

Researchers believe that blondes have been particularly vulnerable to stereotyping over the past century.

The image of the dizzy blonde came to prominence in the 1925 Anita Loos novel Gentlemen Prefer Blondes. Film stars including Marilyn Monroe, Suzanne Somers and Goldie Hawn further popularised the “dumb blonde”.

The persona has more recently been boosted by celebrities such as Paris Hilton, the member of the hotel family nicknamed the “heirhead”, and Jessica Simpson, the singer.

Others believe its origins go far deeper. According to researchers at St Andrews University, north European women evolved blonde hair and blue eyes at the end of the Ice Age to make them stand out from their rivals at a time of fierce competition for scarce males.

Psychologists have suggested that because white babies are often born blond, there is a primal association between blondness and childhood, encouraging people to admire and fawn over the pale-haired.

The new peer-reviewed study, published in the Journal of Experimental Psychology, was based on two trials.

In all cases those participants exposed to images of blondes recorded the lowest scores.

Real-life blondes were sceptical about the findings. Laura Bailey, the Marks & Spencer model, said: “I’ve always been taken very seriously. I have always been blonde and I have never had an issue with the way I am. If I’m being insulted, then I’m blissfully unaware.”

Michelle Collins, the blonde-haired former EastEnders actress, suspected the results were more to do with men’s approach to sex than intelligence. “I don’t think it’s to do with hair at all; it’s all about the breasts,” she said.

“But if someone walks round with extensions down to their bottom, even I would treat them differently.”

Light-headed

Exactly why and when humans developed blond hair is a mystery. It appears to have emerged late in evolution after humans had first travelled out of Africa.

Up to a third of women in Britain may look blonde, but only about 3% are naturally so.

How blondes developed a reputation for dizziness is also unclear, though the likes of Marilyn Monroe may have helped the process along. Certainly “blonde jokes” have become a popular genre.

For example: Q: What do you call a blonde with two brain cells?

A: Pregnant.

Some blondes are of course highly intelligent. Susan Greenfield is an Oxford professor of pharmacology and director of the Royal Institution. The actress Joanna Lumley is a noted environmentalist and a fellow of the Royal Geographical Society.

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