I think that increasing rates of autism is a real phenomenon. Some of the increase may be due to improved diagnosis, but even if that effect were excluded, I think a real increase remains.
I do not think that vaccines are causing the increase in rates. When mercury preservatives were discontinued in the vaccines, the rates did not go down. When the MMR was given separately, the rates did not go down.
Clearly in extreme autism cases, something is wrong even prenatally, and children at high risk of autism have unusually large heads even before they receive any vaccines.
If the effect is real, what then could be causing it? I can think of three possible causes that would be so far removed from the effect that it is very difficult to determine the relationship between the cause(s) and the effect.
1. Low vitamin D levels. Serum vitamin D levels have plummeted for generations now that children spend more time indoors and their parents do not work outdoors the way nearly everyone did a century ago.
2. Imprinting. Effects of diet and other environmental factors can cause genes to be turned or off, particularly at the time the sperm and eggs are made. This gene tagging is known to extend as far as three generations.
3. Increasing rates of assortive mating.
I think the rates of assortive mating have increased dramatically because a century ago, only a small percentage of people went to college, and the colleges were often all-male.
Now, about 50% in the US go to college, and about 25% finish college.
Many people meet their spouses in college.
If a man with an IQ of 130 and a woman with an IQ of 130 marry, it is possible that the risk of the offspring being homozygous for one or more genes relating to autism would increase dramatically. The risk might be even higher if they both have IQs of 150.
This would explain this.
