This startling theory has been put forward by Cambridge scientists who have discovered that the hormone - which is primarily found in men, but also in low levels in women - is linked to children's abilities to communicate and empathise with others.

As a result, scientists at the Cambridge Autism Research Centre are now preparing to launch a major study involving more than 3,000 children to establish testosterone's links to autism or, in less extreme cases, to inabilities to socialise.

Their results may also provide crucial insights into the causes of autism's recent dramatic rise in Britain.

'The condition may simply be one end of a continuum,' said project leader Professor Simon Baron-Cohen. 'In other words, social skills may be like height. Some people are smaller than others. Then you get a cut-off point where you start to talk about dwarfism. The same may true of autism.'

If this is true, autism may represent one end of a continuum that separates different people's ability to socialise, and that these differences are influenced by amounts of testosterone in their mothers' wombs. The theory would also explain why boys tend to be worse than girls at socialising and why males are more than twice as likely as females to suffer from autism.

Around one child in 200 is now thought to be affected by the condition or a milder version known as Asperger's syndrome. Victims have difficulties communicating ideas, in socialising, and with controlling their imaginations.

As part of their investigation of the condition's roots, the scientists - Baron-Cohen and Dr Svetlanka Lutchmaya, of the autism centre, and Dr Peter Raggatt, of Addenbrookes Hospital, Cambridge - used sophisticated new techniques to measure testosterone in samples of amniotic fluid taken from mothers during standard prenatal tests of babies.

'All foetuses produce a surge of testosterone around eight weeks after conception,' said Raggatt. 'Much more is produced in boys, and this triggers the development of male sexual organs. However, some testosterone is also produced in female foetuses.'

In fact, the team found that some boy babies have relatively low levels of testosterone - below the average for girls - while some girl babies have relatively high levels, around average for boys.

But what effects did these differences have later in life? To find out, the team tested each child using a series of different psychological tests - and discovered that a baby's ability to maintain eye contact with a parent was linked to testosterone.

Those who had experienced high testosterone in the womb tended to be poor at maintaining eye contact, a failing that typifies poor socialisers and communicators, and in severe cases, sufferers of autism.

In addition, the team found that elevated testosterone tended to produce children with the smallest vocabularies. By contrast, low testosterone babies were those who knew the greatest number of words. In between these extremes, there was a steady gradient in ability: as testosterone fell, social and communication skills increased. Papers on their findings are to be published shortly in the Journal of Infant Behaviour.

The Cambridge team point out that the hormone is known to stimulate the growth of the right-hand side of the brain. This may occur, they argue, at the expense of growth of the left-hand side - the brain hemisphere in which most of our language and social skills are thought to be stored.

Establishing such a connection will need further research, however, and the team is preparing to study a far larger sample of children: 3,000 as opposed to the 80 that have taken part in their studies so far.

'I don't think high testosterone on its own is the cause of autism,' said Raggatt. 'Other factors must be involved, otherwise virtually every male would suffer from the condition.

'However, once we understand the hormone's involvement, we will be able to unravel the other causes, and discover which of those may be responsible for the condition's increasing prevalence. Then we will be able to think about ways of alleviating the lives of sufferers.'