The Silicon Valley Phenomenon
One way to test the assortative mating theory is to compare couples in which both individuals are strong systemizers with couples who include only one strong systemizer—or none. Two-systemizer couples may be more likely to have a child with autism. My colleagues and I created a Web site where parents can report what they studied in college, their occupations, and whether or not their children have autism (www.cambridgepsychology.com/graduateparents).
Meanwhile we are exploring the theory from other angles. If genes for technical aptitude are linked to genes for autism, then autism should be more common in places around the world where many systemizers live, work and marry—places such as Silicon Valley in California, which some people claim has autism rates 10 times higher than the average for the general population.
In Bangalore, the Silicon Valley of India, local clinicians have made similar observations. Alumni of the Massachusetts Institute of Technology have also reported rates of autism 10 times higher than average among their children. Unfortunately, no one has yet conducted detailed and systematic studies in Silicon Valley, Bangalore or M.I.T., so these accounts remain anecdotal.
My colleagues and I, however, have investigated the rates of autism in Eindhoven, the Silicon Valley of the Netherlands. Royal Philips Electronics has been a major employer in Eindhoven since 1891, and IBM has a branch in the city. Indeed, some 30 percent of jobs in Eindhoven are in the IT sector. Eindhoven is also home to Eindhoven University of Technology and High Tech Campus Eindhoven, the Dutch equivalent of M.I.T. We compared rates of autism in Eindhoven with rates of autism in two similarly sized cities in the Netherlands: Utrecht and Haarlem.
In 2010 we asked every school in all three cities to count how many children among their pupils had a formal diagnosis of autism. A total of 369 schools took part, providing information on about 62,505 children. We found that the rate of autism in Eindhoven was almost three times higher (229 per 10,000) than in Haarlem (84 per 10,000) or Utrecht (57 per 10,000).
In parallel with testing the link between autism and systemizing, we have been examining why autism appears to be so much more common among boys than among girls. In classic autism, the sex ratio is about four boys to every girl. In Asperger's, the sex ratio may be as high as nine boys for every girl.
Likewise, strong systemizing is much more common in men than in women. In childhood, boys on average show a stronger interest in mechanical systems (such as toy vehicles) and constructional systems (such as Lego). In adulthood, men are overrepresented in STEM subjects (science, technology, engineering and math) but not in people-centered sciences such as clinical psychology or medicine. We have been investigating whether high levels of the hormone testosterone in the fetus, long known to play a role in “masculinizing” the developing brain in animals, correlate with strong systemizing and more traits associated with autism. A human male fetus produces at least twice as much testosterone as a female fetus does.
To test these ideas, my colleague Bonnie Auyeung of the Cambridge Autism Research Center and I studied 235 pregnant women undergoing amniocentesis—a procedure in which a long needle samples the amniotic fluid surrounding a fetus. We found that the more testosterone surrounding a fetus in the womb, the stronger the children's later interest in systems, the better their attention to detail and the higher their number of traits associated with autism. Researchers in Cambridge, England, and Denmark are now collaborating to test whether children who eventually develop autism were exposed to elevated levels of testosterone in the womb.