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I don't think the second of Robert McNeil's Autism Now reports on the PBS NewsHour is especially informative or enlightening, but it at least it is not mean-spirited and destructive in the way that the first one was.  Unlike his own grandson, MacNeil presents most of the autistic children in this segment as having strengths as well as weaknesses. I will probably nitpick some of the language used here and in the first segment in another post later, but here I want to focus on why I think MacNeil's discussion of why the prevalence of autism has increased so dramatically was incomplete.

Autism used to be very uncommon.  Now about 1% of the population is considered to have some form of autism.  Why the dramatic change?

One of of the two factors discussed here is an increasingly broad definition and improving understanding of autism.  MacNeil's guest Richard Grinker points out that more kinds of kids are being identified as autistic and we are doing a better job of identifying them.  Research indicates that that may account for as much as one-third of the increase. 

The other factor they discuss is environmental toxins, which are also a likely cause.  Researcher Irva Hertz-Picciotto names several possibilities:

I have a lot of candidate factors, actually. And they include nutritional factors, infectious agents, chemicals in our environment, including chemicals in the household products that we use every day. There are a variety of factors that could be influencing development, and they may play a role at different points in development.

But I wish they went beyond toxins to other likely environmental factors.

In a previous piece, I described my belief that understanding autism requires us to understand that the brain physically changes when we learn something.  We literally connect new learning to other pieces of information that our brains have chosen to store.  I believe that autism is the tendency of some brains to make some kinds of connections too strong and others too weak.

There are two kinds of factors that make our brains similar to those around us.  One is the self-regulation of the brain, which causes us to make strong connections to learning that affects our safety (things like what causes pain).  That self-regulating capacity is weaker in people with autism, and our brains tend to grow in ways that make them unique.  

The other set of factors come from the culture in which we live.  We are reinforced to learn the same things as the people around us when there are few choices.  People used to do things like sing together and play musical instruments- things that encourage learning a small number of songs very well.  They used to go to church and learn to use one book to interpret the world.  Our brains did not have the stimulation of computers, videogames, or even telephones and television just a couple of generations ago.

We live in a world of increased choice, and in most ways that's a good thing.  But the increase in disabling autism is, I think, in part the result of a world where if there are five people in one house, they are likely to each be watching their own television rather than than talking together about one thing they can all understand.  Think about the increasingly fragmented ways people are using media.  We don't even listen to albums or watch whole TV shows any more-- we download songs and watch clips on YouTube.

I don't see how living in such an increasingly fragmented world, one where our brains are presented with infinite ways of processing information and an amount of information to process for which nothing in human history has prepared us, could not result in more autism.  We have removed most of the things that used to reinforce the brain's own tendency to make connections similar to those of the people around us.  For someone whose brain has a tendency to develop in unusual ways already, that sort of change has got to make a profound difference.

And then there is the matter of what happened two hundred years ago when the sun went down: it was dark and quiet.  Before electricity was commonly used, our brains were pretty much guaranteed a few hours daily with very minimal input. The fact that we can now exposed to light and noise 24 hours a day is a huge change to the environment that it seems like researchers want to ignore.

We are familiar with the idea that chemicals we put into the environment can cause unexpected negative results, thanks to people like Rachel Carson who changed the world in 1962 with her book Silent Spring.  But we tend to think that toxic chemicals are the only things in the environment we need to worry about.  With autism, I think you also need to consider light, noise, and the quality of data.  

But we don't.  When a study indicated that mothers living near California freeways were much more likely to have children with autism than those that didn't, people made the mistake that MacNeil does:  they assumed the reason had to air pollution.  It could be.  It could also be light, noise, or  vibration.

We ignore environmental factors that we cannot equate in our minds with poison.  Take the vaccine controversy-- please.  I personally believe that the most likely reason that children seem to become autistic after being vaccinated is coincidence: regression happens to happen in many cases at about the same time kids get vaccinated.  But maybe both the people who think it's a terrible chemical in the vaccine and people like me who think it's a coincidence are both wrong.  Maybe the physical trauma of vaccination causes a reaction in some extremely sensitive kids that causes them to withdraw into themselves.

We don't know.  And nobody's really looking.