A lot of people crusade on the idea that autism is an epidemic caused by pollution of some type, whether from the air, ground, water, vaccines, medicines, etc. It's a thought many parents seem to cling to. Why? Because they think of their beautiful children as defective.
Guess what? They're not defective. You are. You're the one that gave them the genes that made them more sensitive to the pollution you created.
I wish I could find the reference, but a man (who, with his son, is ASD) said that ASDs are society's "canaries in the coalmine." He was speaking of the health issues ASDs suffer from at a higher level than NTs. And it's true. And the studies that have shown higher diagnosed occurences of ASD in areas with greater pollution levels, give me a small basis for a personal theory.
ASD is genetic. It's there, lurking in the chromosomes of many people. A lot of people have grown up and led decently successful lives with no diagnosis (of course, part of this is because there would not have been an overwhelming reason to test them, but also because they wouldn't have met the earlier criteria anyway) of ASD.
There is no epidemic, but there is better diagnosis. There is no epidemic, but there are more noticeable symptoms. What's my personal theory? The number of ASDs has not grown, but pollution and other outside factors are causing an increase in obvious symptoms, making an appearance of an increase in ASD individuals.
All those people throughout history who were reclusives (including the religious who lived in silent meditation), hermits, non-social geniuses, and such were the more obvious ASDs. The social introverts, non-partiers, putterers, quiet individuals were the non-obvious ASDs. Now, the non-obvious are becoming more obvious, partially due to paranoid parents who worry over everything, but also because some are displaying more obvious behaviors due to outside pollutants.
Additionally, the modern world, especially our computer-supported society and the Internet, have allowed people who would previously have been social outcasts, to build lives and relationships. These people are now more likely to get married and have children, children who are more likely to be ASD themselves.
Maybe we're the future. We probably should be.