Uta Frith is one of the most notable names in what we might call the autism research 'establishment'. She has recently stated  that autism in earlier decades was usually of the classic, severe variety, whereas nowadays most or many cases are of the mild to moderate or high-functioning variety. Putting that in the context of my view that there has been a major global increase due to a certain identified environmental factor, her observation poses the question of why that environmental factor should have produced generally less extreme autism than the preceding "genetic" form did.
And that is a question that is very happily answered by my explanation of the increase. Because the cause I invoke accumulates postnatally, it only impacts at a later age, whereas the classic genetic causation would impact from long before birth. And so one would indeed expect the new causation to commonly be less severe than the earlier variety.
1. Uta Frith, Autism: A very short introduction, OUP 2008