When Two Minds Think Alike - SBC Again - Sigh...........

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When Two Minds Think AlikeSimon Baron-Cohen discusses how a powerful new idea may give usvaluable insights into the cause of autism.by Simon Baron-Cohen • Posted November 10, 2006 12:45 AMOver the years I've been struck by a pattern among the parents ofchildren with autism. The mothers often say things like "my child is alot like my husband—just writ large. My husband has to watch theweather forecasts every night, and my son has to watch them everyhour." When I ask about their parents, the mothers comment, "Well, myfather was rather similar to my husband—he collected model trains andknew everything there was to know about each one."Such observations don't amount to evidence about the cause of autism,but they do give us clues about where to look. Autism is at rootgenetic, but new research from my lab at Cambridge Universityimplicates genes inherited from both parents. From this and otherobservations, we've formulated the "assortative mating theory." Itscentral idea is that both mothers and fathers of children with autism(or its milder variant, Asperger Syndrome) share a commoncharacteristic and have been attracted to each other because of theirpsychological similarity.Assortative mating is a term borrowed from the field of genetics thatrefers to a long-recognized aspect of animal behavior: the sim­pleidea that mate selection is not random. An­mals, including humananimals, do not mate with just anyone.Darwin theorized that two kinds of selection operate to ensure thatsome animals have better reproductive success than others: naturalselection and sexual selection. Deer with large antlers, for example,are more likely to reproduce—not just because they can defeat weakermales in contests over females (natural selection), but also becausethe females themselves tend to prefer males with the largest antlers(sexual selection). Animals are finely tuned to external indicators offitness, and these indicators influence whether or not they will matewith a potential partner.Assortative mating goes one step further by noting that two animals ofthe same species often end up mating when they have a common orsimilar trait. A clear example in humans is that taller men tend, onaverage, to have female partners who are also above average in height.Unconsciously, we seem to select partners who are similar to ourselvesin at least one respect. Other studies in humans have shownassortative mating for physical characteristics as subtle as eye colorand for psychological characteristics such as personality.So what has all of this got to do with autism? We know that autismruns in families, and that if a child with autism is a twin, thechances of the other twin also having autism is much higher if thetwins are identical. This tells us that genes are likely to be animportant part of the explanation, and that one should look at theparents of children withautism for clues. Furthermore, our studies have uncovered fourfindings that implicate assortative mating in autism. First, bothparents of children with autism are likely to be super-fast onattention tasks, in which the aim is to spot a detail as quickly aspossible. Second, both parents have an increased likelihood of havinghad a father who worked in the field of engineering. Third, bothparents are more likely to have elevated scores on subtle measures ofautistic traits. And fourth, both parents show a trend toward a moremale pattern of brain activity when measured using MRI.The chances of both parents displaying these similarities arevanishingly small. Something must be causing two such individuals tobe attracted to one another. I propose that "something" is strongsystemizing—the drive to analyze the details of a system in order tounderstand how it works.All human brains have a systemizing mechanism that is set at differentlevels. The extreme behavior of children with autism (whosesystemizing mechanism may be set too high) may seem like a far cryfrom the more moderate behavior seen in their parents andgrandparents, but this new theory proposes that across the generationsthese are only differences of degree. Think of a child with autism,who appears lost in his or her own world, totally focused on lining upLego bricks into colorful patterns for hours at a time. This ishypersystemizing. Then think of the parents we talked about at theoutset: a fascination with weather reports is one example ofsystemizing; a fascination with model trains is another, albeitmilder, example.Evidence from parents in the general population suggests there isassortative mating for systemizing, such that people who are attractedto systems are more likely to have a partner who shares thischaracteristic. Combined with the fact that both parents of childrenwith autism are likely to be very detail-oriented, highly analytic,and to have a father who worked in a field requiring good systemizingskills, this suggests that the genes involved in systemizing may belinked to the genes that cause autism.Although these genes remain to be identified, the assortative matingtheory throws up some testable predictions: First, autism should bemore common in families where both parents are strong systemizers. Forexample, some media reports have claimed that autism is more prevalentin areas like Silicon Valley, but we need well-controlled tests to seeif this is true. Second, since the drive to systemize is stronger inmales than in females, it should be the case that both mothers andfathers of children with autism are more likely to have strongly"male" interests and behaviors. Finally, if systemizing is linked inpart to prenatal testosterone levels (which studies from our labsuggest may be the case), then mothers of children with autism may bemore likely to have testosterone-linked medical conditions. Again, ahighly testable prediction.Autism has skyrocketed from a rare condition of only four in 10,000children in the 1970s to an astonishing 1 percent of children today.This massive change undoubtedly reflects improved recognition of thecondition and consequent growth in services. In addition, even the wayin which we conceptualize autism has changed, from being a discretecategory in the 1970s—you either had autism or you did not—to aspectrum condition that acknowledges degrees of autism. Therefore, theboundary between those who have the diagnosis and those who do not isa fuzzy one, leaving room for clinical interpretation.But could the apparent rise in the prevalence of autism also in partbe the result of assortative mating of two strong systemizers? Is itpossible that over and above the effects that social and clinicalfactors have had, assortative mating of two strong systemizers hasbecome more frequent?Consider that in the late 1950s, less than 2 percent of undergraduatesat MIT (a university that caters to people with good systemizingskills) were women. Today female enrollment has jumped to 50 percent.This microcosm is just one example of how society has changed in waysthat would bring strong systemizers into greater proximity. Over thesame period, air travel has also meant far greater opportunities forpeople from widely differing backgrounds to meet, possibly broughttogether by their common interest in systems. Finally, over this sametimeframe, individuals who are systemizers have enjoyed new employmentopportunities as the result of the digital revolution. Where 50 yearsago a strong systemizer might have found a job as an accountant, todayevery workplace needs computer-savvy employees, and the financialrewards for good systemizing skills can be immense.The contribution of assortative mating to the changing prevalence rateof autism is difficult to study. It is also controversial: the ideathat a child with autism is the result of the unique mixing of genesfrom parents who share a common feature sits uncomfortably with thosewho want to believe the cause of autism is purely environmental. But Ibelieve the preliminary evidence in support of the theory warrantsfurther research. We stand to gain valuable insight into the cause ofautism; and given the links between autism and the capacity tosystemize, a trait that has helped humans to dominate the planet, westand to gain a better understanding of human nature.—Simon Baron-Cohen is professor of developmental psychopathology anddirector of the Autism Research Centre at Cambridge University

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