The theory that autism is caused by an extreme version of the “male brain” has won strong support from new research showing that male hormones in the womb are linked to social and emotional skills in childhood.

Scientists at the University of Cambridge found that both boys and girls who are exposed to high levels of testosterone before they are born are more likely than usual to develop traits typical of autism, such as a preference for solitary activities and strong numerical and pattern-recognition skills.

The study included only children who are not autistic, but it gives some of the firmest biological evidence yet that the social impairments that characterise the condition may be affected by prenatal hormone exposure.

This in turn backs the theory that autistic people are best understood as having extreme versions of a brain type that is common in the population at large, particularly among men.

The idea advanced by Professor Simon Baron-Cohen, who leads the Cambridge team, is that human brains are predominantly attuned either to empathising with others, or to understanding how systems work. Women are more likely to be in the first group and men in the second, while autistic people are extreme systemisers whose social problems emerge from a fundamental difficulty with empathy.

The model fits with the observation that autism is four times more common among boys. One possible explanation is that male hormones in the womb could promote systemising at the expense of empathy. Very high exposures may thus trigger autism.

Professor Baron-Cohen’s study, conducted with his graduate student, Bonnie Auyeung, looked at prenatal testosterone levels in 235 foetuses whose mothers had had amniocentesis.

When the children were born, they were followed up to assess their psychological development. The latest data, from questionnaires given to mothers when the children were eight, were presented yesterday at the British Association Festival of Science in York.

While all the children were developmentally normal, boys and girls who had higher levels of foetal testosterone were significantly more likely to have a large number of autistic traits such as preferring playing alone to joining in at birthday parties, and being good at remembering numerical patterns, such as car numberplates.

About 20 per cent of the variation between children’s autistic traits appeared to match foetal testosterone levels, with the remainder likely to be caused by genetic and environmental factors.

Previous research with the same group of children has shown that at 12 months, children with high foetal testosterone make less eye contact with their parents and look at others’ faces less frequently. At 18 months, they have a smaller vocabulary than children exposed to lower concentrations of the male hormone.

Professor Baron-Cohen said that the results did not prove that the link between male hormones and autistic traits was causal: both could be the result of something else. He also said that his team had not yet examined autistic children, only autistic traits in the normal population.

Even so, he said, the work added strong biological evidence to his extreme male brain theory. “The hypothesis was based on observed sex differences,” he said. “Simply put, girls tend to show better empathy, and boys tend to have a stronger interest in systems. Children with autism seem to have an exaggerated version of typical male preferences. They have a strong interest in systems, and difficulty empathising.

“We are now moving from a psychological level down to a biological level. It is an exciting development.”

Professor Baron-Cohen has won funding from the Medical Research Council to conduct a study using two large databases in Denmark, an archive of 90,000 amniocentesis samples, and a national register of people with psychological or developmental disorders. He said: “We are going to look at who has a diagnosis of autism and then pick out their amniocentesis sample and look at testosterone.”

Professor Baron-Cohen said it was unlikely that it would be possible to prevent autism by controlling foetal testosterone, not least because doing so might adversely affect other aspects of foetal development.

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