One way to unravel the riddle of autism
TWO big scientific debates have attracted a lot of attention over the past year. One concerns the causes of autism, while the other addresses differences in scientific aptitude between the sexes.
At the risk of adding fuel to both fires, I submit that these two lines of inquiry have a great deal in common. By studying the differences between male and female brains, we can generate significant insights into the mystery of autism.
On average, males have a stronger drive to systemise, and females to empathise. Systemising involves identifying the laws that govern how a system works. Once you know the laws, you can control the system or predict its behaviour. Empathising, on the other hand, involves recognising what another person may be feeling or thinking, and responding appropriately.
Our research team in Cambridge, after questioning men and women, found three types of people: one for whom empathy is stronger than systemising (Type E brains); another for whom systemising is stronger (Type S brains); and a third for whom empathy and systemising are equally strong (Type B brains). More women (44 per cent) have Type E brains than men (17 per cent), while more men have Type S brains (54 per cent) than women (17 per cent).
What of the claim that such sex differences are innate? We know that culture plays a role in the divergence of the sexes, but so does biology. For example, on average, at 24 hours old, male infants are more likely to look at a mechanical mobile suspended above them, whereas more female infants will look at a human face.
It has also been found that the amount of prenatal testosterone, produced by the foetus, predicts how sociable a child will be. The higher the level of prenatal testosterone, the less eye contact the child will make as a toddler, and the slower the child will develop language.
Males obviously produce far more prenatal testosterone than females do, but levels vary considerably even across members of the same sex. In fact, it may not be your sex per se that determines what kind of brain you have, but your prenatal hormone levels.
From there it's a short leap to the intriguing idea that a male can have a typically female brain (if his testosterone levels are low), while a female can have a typically male brain (if her testosterone levels are high).
That notion fits with the evidence that girls born with congenital adrenal hyperplasia, who for genetic reasons produce too much testosterone, are more likely to exhibit "tomboy" behaviour.
What does all this have to do with autism? According to what I have called the "extreme male brain" theory of autism, people with autism simply match an extreme of the male profile, with a particularly intense drive to systemise and an unusually low drive to empathise. When adults with Asperger's syndrome (a subgroup on the autistic spectrum) took the same questionnaires we gave to non-autistic adults, they exhibited extreme Type S brains. Psychological tests reveal a similar pattern.
And this helps explain the social disability in autism, because empathy difficulties make it harder to make and maintain relationships. It also explains the "islets of ability" that people with autism display in subjects like maths or music - all skills that benefit from systemising.
People with autism often develop obsessions, which may be nothing other than very intense systemising at work.
One needs to be extremely careful in advancing a cause for autism, because this field is rife with theories that have collapsed. Nonetheless, my hypothesis is that autism is the genetic result of "assortative mating" between parents who are both strong systemisers. Assortative mating is the term we use when like is attracted to like, and there are four significant reasons to believe it is happening here.
First, mothers and fathers of children with autism complete the embedded figures test faster than the general population.
Second, both mothers and fathers of children with autism are more likely to have fathers who are talented systemisers (engineers, for example).
Third, when we look at brain activity, males and females on average show different patterns while performing empathising or systemising tasks. But both mothers and fathers of children with autism show strong male patterns of brain activity.
Fourth, mothers and fathers of children with autism score above average on a questionnaire that measures how many autistic traits an individual has. These results suggest a genetic cause of autism.
In order to fully test this theory, we still need to do a lot of work. The specific genes involved must be identified. It is a theory that may be controversial and perhaps unpopular among those who believe the cause of autism is largely or totally environmental. But controversy is not a reason not to test it - systematically, as we might say.
Simon Baron-Cohen is director of the Autism Research Centre in Cambridge
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