IT REALLY is brains not brawn that women look for in a man. An exhaustive study of people from primary school to middle age has proved that clever men are much more likely to marry than those with lesser intelligence.

But for female high-flyers, the reverse is true. Their chances of walking up the aisle are considerably lower than those of classmates who left school at 16.

When Nicola Horlick, the City investment manager nicknamed Superwoman for juggling her job and family of six, wrote her book on career and domestic bliss, its title posed the question: Can You Have It All? The answer, it appears, is yes ? but only if you are a man.

The study, based on 900 men and women, measured their IQ at the age of 11 then revisited them 40 years later to find out whether they had ever married.

Academics at the four British universities who carried out the survey said the schoolgirls with high IQs later witnessed a dramatic decline in their marriage prospects. But the brighter schoolboys found it easier to find a bride.

The results are borne out by evidence from psychologists that successful career women are struggling to find "interesting men" who are interested in them.

Relationship experts say professional men prefer to marry women "like their mum" who will provide the domestic support while they go out to work.

Women achievers, however, find it difficult to find men willing to sacrifice their careers to become house husbands.

"The finding that IQ in early life appears to be associated with the likelihood to marry is important because factors in childhood may determine a person's marital status in adulthood, which may in turn influence future health and mortality," says the study, to appear in the Journal of Personality and Individual Differences.

For boys, there is a 35% increase in the likelihood of marriage for each 16-point rise in IQ. For girls, there is a 40% drop for each 16-point increase.

The results may explain why a sharp-witted man like Vic Reeves, 45, the comedian, appears to have found wedded bliss with Nancy Sorrell, 30 ? perhaps she is highly intelligent, but her jobs as underwear model and lap dancer have certainly enabled her to hide the fact.

Conversely, Horlick, 44, has separated from her husband Tim. "Maybe you can't necessarily have a happy marriage if you end up being a very high-powered woman," she said. "It may be that men find it difficult living with a woman who's forging ahead.

"But would I have wanted to sit around at home just doing the school run? I don't think I could take that."

Similarly, the actress Renée Zellweger, 35, has men fighting over her when she plays Bridget Jones but her real life is littered with failed relationships. Zellweger, who studied English at the University of Texas, parted last month from Jack White, the White Stripes singer, after a two-year romance.

The academics at Aberdeen, Bristol, Edinburgh and Glasgow universities have double- checked their research in a separate analysis based on earnings.

They found 88% of 40-year-old men in the top socioeconomic class were married, compared with 80% in the lowest class. Among women aged 40 the trend is reversed. The researchers found that 82% of the top class were wed, compared with 86% in the lowest class.

Marriage experts say the results reflect changes in society. Christine Northam, a senior counsellor at Relate, the relationship guidance organisation, said: "IQ measurements are frightfully judgmental, but it is true that men do not want women more intelligent than themselves. It bolsters their position if their partner is not too challenging."

She added: "Today more and more women are questioning marriage. But in the past, professional men have been more desirable as husbands, while for women with low IQs the only prospect of gaining some recognition and power was to be married."

Dr Paul Brown, visiting professor of psychology at Nottingham Law School and an expert on relationships, said: "What we are finding is that women in their late 30s who have gone for careers after the first flush of university and who are among the brightest of their generation are finding that men are just not interesting enough.

"It is a really difficult issue. Women want independence but we are all hard-wired into wanting to be into relationships. The paradox of the post-feminist position is how we create a social system in which both independence and inter-dependency can flourish."

Claire Rayner, the writer and broadcaster, has been married for 47 years to Desmond Rayner, a former actor who gave up the theatre when they wed.

She said: "A chap with a high IQ is going to get a demanding job that is going to take up a lot of his energy and time. In many ways he wants a woman who is an old-fashioned wife and looks after the home, a copy of his mum in a way.

"The bright girl, on the other hand, remembers that old saying that at first she sinks into his arms only to spend the rest of her life with her arms in his sink."