/sci/ - Science & Math

Many variables are at play...

better diagnosis: people recognize autism and Aspergers more easily.
over diagnosis: some people tend to lable children for being a little odd, or socially awkward, when they don't need to be treated any different.

PDD (Pervasive Developmental Disorders) are genetic. And individuals can be born with PDD when no one else in their family clearly has autism or asperger's. An earlier generation may only have a few Asperger tendencies (say a heavy talker) but otherwise is fairly normal in social situations.

Environment can have effect on the degree that the PDD develops. A child may be born and have the genetics for high-functioning Asperger's, but then an outside variable flips a switch and leaves the kid with lower-functioning Autism. The outside variable can be anything from a vaccine, certain diseases, artificial contaminate, etc. I've even seen it mentioned that aspirin could have an affect.