I sometimes wonder if autism isn't more common partly because society has changed in ways that make autistic people more likely to be employed successfully. Historically, most work was physical and relied on strength and dexterity, and traditional social skills. Autistic people are far more likely than average to be hypermobile and dyspraxic. The hyper focus and pattern recognition strengths also more common with autistic people aren't as helpful for someone who has to do manual work - and monotropism, the inability to stay focused and diligent on things that bore you, isn't ideal in that labour market, either. But switch them to a world where IT skills and engineering are open to anyone who can learn, and you have high functioning autistic people who manage to survive (albeit with suffering and with a lot of anti-depressants) the horrors of school, find their niche at university, and then go on to work in specialised fields that value their skills. They then meet people who share their interests and values, double their earning capacity, and go on to have families - and autism is genetic, so two autistic people with more subtle presentations will more than likely have kids whose traits are clearer. It's also possible that non-autistic people with 'soft traits' are having kids together, and the genetics will combine to mean their kids are diagnosable.
I went to Cambridge. My husband was at Cambridge, too. Neither of us were diagnosed, though clearly both autistic. The same goes for many peers there - many of whom married contemporaries they started dating in those years. Of our college friends, I know of seven families who have autistic kids, and another my husband and I are quietly certain will have their kids diagnosed shortly. All of us have kids whose needs are markedly greater than our own, and impossible to miss. They aren't going under any radars. Given the number who married college contemporaries, that makes 12 people who were at university with us whose kids are at EHCP level autism. And those are just the ones with whom we're still in touch, whose kids are diagnosed already. There will, clearly, be many more.
In the past, a lot of autistic people would have been seen as weird and awkward and not marriageable. Some still are, of course. But you're a lot more likely to be seen as quirky and oddball but still able to find a partner in a world where your interests and skills carry a financial bonus, and that means you're likelier to have kids, too. The internet has also made it easier to meet those who share your interests, and also legitimised special interests and geek culture in a way that is new in its universality. And by definition, you're likelier to marry someone who shares your outlook and your interests, and/or your employer. So if we are indeed finding more and more couples with both parties autistic... is it really amazing that we are also finding more autistic people being born? And now diagnostic criteria are being honed, is it surprising that the greater numbers are also being accurately identified, too?
Autism is both strength and deficit. It's a disability, no question. My kids have a lot of associated physical and neurodevelopmental problems, and my son was supported too late and has the PTSD diagnosis to show for that. But they also have extraordinary IQs. My daughter's is 99.9th centile. Her NHS paediatrics reports list "extremely gifted" alongside her other, less positive key factors at the start of any reports. She was assessed as having a reading age of 19 yrs 11 months at 6, after being found in the reading tent at preschool polishing off The Enchanted Wood in her head - nobody had taught her to read, and that was how everyone found out she could. She's Matilda - also hyperlexic, and, for the record, 90% of hyperlexic kids are also autistic. And while most autistic kids aren't gifted, I know enough who are to believe that the overlap is undeniable. There's a (very brief) brilliant discussion on this by Andrew Solomon Autism is abnormality, but it persists in our gene pool because autistic people offer a different way of viewing the world that can, in some contexts, carry massive strengths and advantages. And in a world where those strengths are now monetised, I am not surprised that it is increasing. We're employable. We have value to capitalism. And we're marrying one another. As I joked to a friend, we're breeding a new master race of autistic kids.* You're welcome! Admittedly, my son can barely leave the house due to anxiety, but he's going great guns with the quadratic equation research while he's home.
*Probably worth contextualising this: my husband is Jewish, and the friend I was joking to is Muslim, of Iranian/Bangladeshi descent. We both have autistic kids and are both in EHCP appeals. Dark humour is a survival strategy.