[newzjunkey]

if these random mutations are the only or primary cause of autism, it does not make sense that the incidence of autism has increased so much in the last twenty-five years.

All manner of things may effect fertility. There are different medications, diets, additives, lifestyles, pollutants, household products than 25 years ago. Some of the higher incidence may be a change in diagnoses.

If something was causing a greater number of mutations, we would be seeing an increase in all kinds of birth defects and cancers.

That doesn't necessarily follow.

[Explorer89]

Interesting that you mention fertility. What else is different in the past 25 years is the treatment of infertility. I’m sure someone has done the studies trying to correlate: maternal age, paternal age, fertility treatments used/not used with the incidence of autism.