alt Hacker News> If I were to include additional biological possibilities, I'd include: a) birth control -> waiting to have children until a later age, more de novo mutations due to age.
Surely it should be easy to collect the data to plot such a hypothesis: incidence rate vs age of father and vs age of mother at conception, and at birth.
Be careful of reverse causation. Being autistic makes you more likely to have children later (if at all) and we know it's at least partially heritable.