Is "assortative mating" to blame for the rise of autism?

There's no shortage of theories about what causes infants to develop autism: At various points, researchers have blamed medication, the age of the child's parents, pesticide exposure, and the now-debunked vaccine link. Another theory, known as "assortative mating," proposes that parents who share certain tendencies — an expertise in math and science, for example — may produce children with a higher risk of developing autism. Here, a concise guide:

What does this theory propose?

According to the leading proponent of assortative mating, Simon Baron-Cohen, director of Cambridge University's Autism Research Center (and cousin to the comedian Sasha Baron-Cohen), autism tends to run in families. While that’s not news — it's been estimated that a family with one autistic child has a 1 in 20 risk of having a second autistic child — Baron-Cohen has expanded upon that theory to posit entire communities of people with some tendency toward autism or Asperger’s syndrome, a related disorder.

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What kinds of communities?

Places that attract people with a "common cognitive profile" that includes autism or Asperger’s. Take Silicon Valley, for instance. It's populated with lots of men — and an increasing number of women — who are drawn to science and technology, but are deficient in areas like empathy and relating to others. When these people start raising families, Baron-Cohen argues, it's more likely that their kids will develop the same tendencies to even more pronounced degrees.

Is there evidence for this theory?

Not much. Most of what supports the theory of assortative mating is just anecdotal hearsay, and "Baron-Cohen is the first to caution that his results are preliminary," says Meredith Melnick in TIME. There is, however, one study that found kids living in Eindhoven — the Dutch Silicon Valley — were two to four times more likely to be diagnosed with autism than kids in similar but less tech-centric areas. More research is needed before any definite conclusions can be drawn.

Sources: Babble.com, TIME, WebMD