The rise in autism is extremely easy to explain. Basically, what we know as “autism” today has changed dramatically in the last 50 years or so. The easiest example of this is what used to be known as Asperger’s sydrome — this was a diagnosis very similar to autism, but less severe and with a couple of different symptoms. The diagnosis has now been eliminated completely, and kids who would be diagnosed with Asperger’s in the 80s and 90s are now considered low on the autism spectrum, meaning that more kids are diagnosed as “autistic” despite there being no change in the actual prevalence of the disease. Essentially, we have changed the label of “autism” to include more children, mostly because we have discovered that treatments for autism are effective for what used to be thought of as completely separate disorders.
In 2014, a group of researchers looked at all the studies on autism prevalence for the last 30 years, and tried to calculate exactly how many more people are autistic, taking into account the changing diagnostic criteria. After looking at hundreds of such studies, they found that there has been no clear increase in the number of people with autism, and that the apparent increase is mostly to do with changes in what we define as autism.
I am truly sorry, but you have been lied to.