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

Though the study included only children who are not autistic, it provides 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 fall into the first group and men into the second, while autistic people are extreme systemisers whose social problems emerge from a fundamental difficulty with empathy.

The model fits with the way in which autism is four times more common among boys than girls and 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.

Testosterone in the womb is produced primarily by the foetus and is more abundant for males. Individual genetic differences, can lead to wide variations, the highest levels measured in the Cambridge study were more than 20 times higher than the lowest ones.Both environmental factors and the mother's physiology are also thought to play a role. There is some evidence, for example, that mothers who have previously conceived several sons expose subsequent foetuses to higher levels of male hormones.

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

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’s latest study, conducted with his graduate student, Bonnie Auyeung, suggests that this may indeed be the case. Prenatal testosterone levels were first measured for 235 foetuses whose mothers had amniocentesis - a prenatal test usually used to check for genetic abnormalities such as Down’s syndrome - between the 16th and 21st weeks of pregnancy. .

When the children were born, they were followed up to assess their psychological development. They have already been examined at ages of 12 months, 18 months and four years and the latest data, from questionnaires given to mothers when the children were eight, were presented yesterday at the BA Festival of Science in York.

While all the children were developmentally normal and none was autistic, both boys and girls who had higher levels of foetal testosterone were significantly more likely to have a large number of autistic traits. Such children were more likely, for example, to prefer playing alone to joining in at birthday parties and to be good at remembering numerical patterns, such as car number plates and telephone numbers.

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