why do ASD's persist?

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I'm wondering if anyone else here is interested in how the ASD's (autism spectrum disorders) merge into neurotypicals, and why ASD's persist in the population.

Given the strong genetic component(s) and the number of people with ASD's who have trouble finding a mate, I would expect ASD's to disappear if there were not some fitness advantage... maybe to people who have some Asperger's traits but not strongly enough to cause them major problems? Or if the genes most responsible for ASD's have other advantages that outweigh their tendency to cause ASDs?

I've noticed that there are a lot of people I know who show at least slight tendencies towards ASDs. Now granted, I know a lot of unusual people, but still. One has to wonder how common these tendencies are.

I live in a fairly rual area, where mostley everyone goes about thier business.
i really dont people watch, as much i gaze at the beautiful scenery around me

(edit)

Because two NTs can give birth to someone on the spectrum and because lots of people on the spectrum do indeed find mates.

Here's my theory, from a blog post I wrote a while back:
Bob the Autistic Cave-Man

Hi Callista, from what I read on your blog there are two basic arguments you are using in partially overlapping ways, one based on group selection and one based on kin selection. Kin selection is well-accepted in behavioural biology, group selection not so much. Your hypothesis makes sense in the situation you are giving because a tribe is small enough that many of the people benefitting are Bob the caveman's relatives who are therefore passing on his genes. In larger societies (ie. for example a modern country with millions of people) I think the effect of Bob discovering fire would get swamped because all the unrelated NTs would have the benefit too while being better at finding mates.

That said, I suspect you are right that kin selection is at least part of the answer as to why the spectrum persists. It might be possible to test kin selection by checking the reproductive rate of those closely related to those on the spectrum and seeing if it is higher or lower than the general population.

I'm wondering what other reasons there might be. For example, do people who are on the less severe (to the point of never being diagnosable) end of the spectrum produce more offspring rather than less? Or those who have just one or two isolated Autistic traits? Has this ever been tested?

It is true that many people on the spectrum do reproduce, but it is less common than for NTs, and even a small disadvantage tends to add up over generations. We don't really have reliable diagnosis for a long enough period to be able to say whether the percentage of the population who is on the spectrum is increasing, decreasing or stable but it is certainly here now. There must be a reason.

Thanks for the ideas; this is really interesting.

Even though people with ASD's have less chance of reproduction, there are still some people with ASD's who do manage to find mates and reproduce. Also, you need to consider the fact that some people may carry the autism genes but may not have any ASD's themselves. These are people belonging to a group called BAP (Broader Autistic Phenotype).

I've just been reading that there are many, many genetic alterations linked to Autism, so there might be many answers to the question I posed depending on which genetic change it is and what else that particular change actually does. I don't think the question I asked is answerable as I posed it. Sorry.

A more interesting question IMO is why are they apparently increasing in frequency?