Since time immemorial, a very specific community of organisms — microbes, parasites, some viruses — has aggregated to form the human superorganism. Mounds of evidence suggest that our immune system anticipates these inputs and that, when they go missing, the organism comes unhinged.The idea is that autism is one of a whole slew of disorders that have been increasing at a galloping rate, all tied to autoimmune problems, and the problem is a too-clean environment is leading to poorly calibrated immune systems. I have a special interest in this because my father (an otherwise quite healthy guy in good shape) was diagnosed with Type I diabetes awhile back. That kind (which has little to do with your diet) has also been on the increase, and some have postulated a similar hypothesis there.
This theory has been around for awhile (check out this Radiolab towards the end for some hilarious background), but it seems to be gaining steam. I'll be keeping on the beat—I'd gladly take some minor parasite infections if it would prevent my own Type 1 diagnosis.