Quick and cheap explanation many use, but not the case. Severe autism is also on the rise, and that doesn't need special telescopes, it's just evident.

It's entirely possible that the ability of doctors to diagnose even severe autism has improved, for example a family doctor who sees a young child with very low IQ may not be surprised by undeveloped language skills and may not recognize that as autism specifically. It's also possible that the increasing destigmatizing of mental/developmental disorders and increased awareness of autism in general could result in more parents and doctors seeking proper assessments. The sad reality is that there are still places where autism is likely to be seen a spiritual condition, a witch's curse, or demonic possession.

Well we used to just let those people die. You know how the medieval family had like 15 children and 4 survived to adulthood? Some of those 11 were severely autistic.

That would be relevant if we compared to the 10th century. We're comparing to the 1960s and 1980s.

>but not the case

like all things in life, it's not the only variable. but better recognition is absolutely a factor.

What is the incidence per million over the last couple of decades?

I have twin cousins who have severe autism, one of which is institutionalized. When they were very young we (their caregivers, family, and doctors) understood their diagnosis to be "mental retardation." Nowadays they are known as autistic. They didn't change, but the world around them changed so their diagnosis shifted.

Before there were government services families still had children with profound disabilities that required lifelong care, they just didn't usually have any formal diagnosis. Everyone still understood that they need help with everyday activities and can't live on their own but sending them to specialist for a diagnosis didn't seem like something that was needed or even available if desired. The diagnosis is needed if you're applying for services, so more services that exist means more formal diagnosis will happen.

A) There are more autistic people because something noxious causes autism.

B) Nope. There are more autistic people because tests improved.

This common discourse annoys me a little, frankly. The problem is that "B" does not imply "not A". Both explanations can be true at the same time.

But people people will automatically discard "A" because "A is problematic". It implies a cause, and we may not like it, so is removed from the discussion ASAP.

The same kind of "problematic" that was to observe in 1960's that "smokers develop lung cancer frequently, maybe tobacco causes cancer". Companies will fight teeth and nails to dismiss it and say "look at the cute squirrel over there".

But is true that we started to notice much more autistic people after the use of some particular pesticide became widespread in the entire planet. May be related. May be not. May be a common result triggered by many causes, but we should not jump to bring home the "nice" B just because is nice (and politically convenient)