What we once called autism is now called Autism Spectrum Disorder. Many different syndromes have been lumped into this disorder and because of that we have an increase in autism.
http://healthland.time.com/2012/03/29/autism-rises-more-u-s-children-than-ever-have-autism-is-the-increase-real/
Autism was “discovered” in 1943 as Sowell says. In 1944, Hans Asperger published his study on “Asperger’s Syndrome”, the mildest form of Autism on the Autistic Spectrum. Therefore, the Autistic Spectrum has been defined since 1944. There are more specific diagnoses now, but the worst case to least bad case of autism has been defined for 70 years. There is a certain amount of greater awareness of autism leading to more diagnoses, but it does not come close to explaining away increase rate of autism in the population from 1 in 2500(1985) to 1 in 68(2010. “researchers from Columbia University reported[2] that approximately 26% of the rise in autism caseload between 1992 and 2005 could be directly attributed to changes in diagnostic criteria,” That leaves the other 74% unaccounted for.