- Silicon Valley and other tech-savvy communities report exceptionally high rates of autism. These trends might reflect a link between genes that contribute to autism and genes behind technical aptitude.
- When two technical-minded individuals pair up, their children may inherit genes for useful cognitive skills, as well as genes involved in the development of autism.
- Furthermore, high levels of testosterone in the womb may play a role in the development of both technical and autistic minds.
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In 1997 my colleague Sally Wheelwright and I conducted a study involving nearly 2,000 families in the U.K. We included about half these families because they had at least one child with autism, a developmental condition in which individuals have difficulty communicating and interacting with others and display obsessive behaviors. The other families had children with a diagnosis of Tourette's syndrome, Down syndrome or language delays but not autism. We asked parents in each family a simple question: What was their job? Many mothers had not worked outside the home, so we could not use their data, but the results from fathers were intriguing: 12.5 percent of fathers of children with autism were engineers, compared with only 5 percent of fathers of children without autism.
Likewise, 21.2 percent of grandfathers of children with autism had been engineers, compared with only 2.5 percent of grandfathers of children without autism. The pattern appeared on both sides of the family. Women who had a child with autism were more likely to have a father who had been an engineer—and they were more likely to have married someone whose father had been an engineer.
Coincidence? I think not.
A possible explanation involves a phenomenon known as assortative mating, which usually means “like pairs with like.” I first encountered the concept in an undergraduate statistics tutorial at the University of Oxford in 1978, when my tutor told me (perhaps to make statistics a little more lively) that whom you have sex with is not random. When I asked her to elaborate, she gave me the example of height: tall people tend to mate with tall people, and short people tend to mate with short people. Height is not the only characteristic that consciously and subconsciously influences partner selection—age is another example, as are personality types. Now, more than 30 years later, my colleagues and I are testing whether assortative mating explains why autism persists in the general population. When people with technical minds—such as engineers, scientists, computer programmers and mathematicians—marry other technical-minded individuals, or their sons and daughters do, do they pass down linked groups of genes that not only endow their progeny with useful cognitive talents but also increase their children's chances of developing autism?
I began studying autism in the 1980s. By then, the psychogenic theory of autism—which argued that emotionally disinterested mothers caused their children's autism—had been soundly refuted. Michael Rutter, now at King's College London, and others had begun to study autism in twins and had shown that autism was highly heritable. Genetics, not parenting, was at work.
Today researchers know that an identical twin of someone with autism is around 70 times more likely to develop autism, too, compared with an unrelated individual. Although researchers have uncovered associations between specific genes and autism, no one has identified a group of genes that reliably predicts who will develop the condition. The genetics of autism are far more complex than that. What I have been interested in understanding, however, is how genes for autism survive in the first place. After all, autism limits one's abilities to read others' emotions and to form relationships, which in turn may reduce one's chances of having children and passing on one's genes.
One possibility is that the genes responsible for autism persist, generation after generation, because they are co-inherited with genes underlying certain cognitive talents common to both people with autism and technical-minded people whom some might call geeks. In essence, some geeks may be carriers of genes for autism: in their own life, they do not demonstrate any signs of severe autism, but when they pair up and have kids, their children may get a double dose of autism genes and traits. In this way, assortative mating between technical-minded people might spread autism genes.