Here’s a must-skim paper by Bernard Crespi about a paradox I myself noticed a long time ago. A lot of autistic people have all the signs of high IQ (intellectual interests, high IQ genetic variants, incredible talents, high social class, big heads, hyperlexia, photographic memory, calculating ability) yet are below average in IQ.
In an attempt to resolve the paradox, Crespi argues something like autism is unbalanced high intelligence. But unbalanced high IQ usually leads to a lot of subtest scatter around an overall high composite score, it doesn’t lead to the below average or even mentally retarded IQs often found in autism.
Of course as commenter Swank noted, autistics are often good at what they practice. So if you have the genetic potential to have an IQ of 170, but spend all your time thinking about toothpicks, you might end up with a took pick IQ of 250 and IQ of 60 in everything else, and since toothpicks aren’t on the IQ test, your overall IQ will appear to be impaired, even though it would actually be in the genius range if a high ceiling toothpick subtest could be added.
So perhaps autism isn’t so much a cognitive disability as an interest disability. Autistics are born not being interested in people or their culture, and thus don’t develop the parts of the brain that our valued by society. This assumes of course the neuro-plasticity model where cognitive abilities can be exercised like muscles which is true up to a point (though IQ tests try to include abilities no one’s had a chance to exercise because they’re so novel).
But why should autism be more common in high IQ or at least upper class families as some (though not all) studies suggest? Perhaps because iin our high tech society, it helps to have enough non-social interests and abilities to acquire a lucrative high-tech job, where you meet others with equally non-social interests. But when two non-socials mate, they risk having a baby that is pathologically non-social, to the point where it doesn’t even care to learn basic social skills and language, and thus is considered autistic.
And of course if you don’t learn the language, the autistic will fail even the IQ test items he’s brilliant at because he wont understand the instructions.