the rise in the incidence of autism is far more likely to be a growth in the diagnosis of autism.

I agree with this take. I started school in the 80s and we had a lot of mentally challenged kids in our school. Some were more proficient than others, but they all were in the same classes up until graduation. Yet, there was no talk of autism. They’ve always been here. It’s just that instead of medicine diagnosing them with a named disorder, they were called condescending names that I shall not repeat here.