Prof Rushton believes the differences are directly linked to brain size, with other studies showing men having slightly bigger brains than women.

'We know that men have larger brains, even when you take into account larger body size,' said the researcher. 'That means there are more neurons. The question is what these neurons are doing in a man - and they probably have an advantage in processing information.'

It is thought the difference may date back to the Stone Age, with women seeking out men who are more intelligent than them in a bid to pass on the best genes to their children.

'Some people have suggested it evolved because women prefer men who are more intelligent than they are for husbands,' said the professor.

'Just as they prefer men who are taller than them, they also prefer a male who is a little ahead of them in IQ.'

Critics claim Prof Rushton's results could have been skewed by the inclusion of more test results from females than form males.

Prof Rushton, who four years ago triggered a scientific row by claiming intelligence and behaviour are influenced by race, with blacks being more likely to be involved in crime and Asians having a greater chance of high IQs, however, stands by his results.

'These are unpopular conclusions,' he said. 'People should not be made to feel afraid to study controversial issues.

'We have the right to find the truth. One should really look at the facts.'

His work appears to confirm British research which showed men have bigger brains and higher IQs than women, which may explain why chess grandmasters and geniuses are more likely to be male.

The analyses of more than 20,000 verbal reasoning tests taken by university students from around the world revealed that women's IQs are up to five points lower than men's .

Women needn't feel despondent, however, as the scientists believe women can achieve just as much as men - as long as they work harder.

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