I've had a lot of exposure to learning disabilities, social impairments and general developmental disorders and since it just so happened that I was having a debate with someone about autism and the recent prevalence of diagnoses recently, I thought I add my tuppence.
Apologies if this goes on..
As most people have said, the main reason we're seeing more autistic people is because more people are being diagnosed. Due to the world getting smarter, and ideas being spread more, a greater number of doctors are able to diagnose the condition. Similarly, due to the reducing nature of the stigma previously associated with mental conditions, more people have been willing to get checked out. Particularly adults aware they may never have received diagnosis as a child.
That's the simple answer, but there are concerns going forward.
Something I've heard a few times, is that autism is very Hollywood. For one, there's a certain charm about a seemingly competent adult who struggles a bit in doing regular adult stuff. The obvious is socialising in general, but then there's the lack of eye contact, the lack of empathy (I think that one is a myth by the way), the idiosyncratic mannerisms, the hand flailing (my favourite), the general social unintelligence, the obsessive habits etc. Some autistic people can't lie,which is in itself a very childlike trait (Children under 4 usually can't comprehend sophistry).
But more-so, as is the major issue with understanding the condition, the disorder is a very large spanning one. This means that from an industry perspective, there's a lot more room for both creativity and error in the portrayal of a character with Autism. In fact, I believe there is indeed a thing called Hollywood autism if someone can be bothered to google that for me.
What this has lead to is autism becoming a fad. But unlike previous fads (ADHD, OCD), an autistic spectrum disorder is easier to be diagnosed for. Whilst the more traditional form of autism is very easy to see in someone (like ADHD and OCD), Asperger Syndrome can be very difficult to detect in certain people, and often doesn't present itself too differently (on the outside) to a typical/neurotypical person who might just have certain specific anti-social traits. And as it turns out, in an age where technology is taking over, anti-social behaviours have tended to be on the up too.
When someone says, 'Oh I'm so OCD/ADHD lol!' it's normally quite easy for anyone who understands the conditions to be dismissive. But it's not with Asperger's. Many people who possess certain anti-social qualities (lack of eye contact and empathy particularly) claim to be somewhat autistic too. But where I'm going with that idea; is that combining this with the extremely varying nature of autism, as well as the fact that people with the condition often only present specific disorders (eg they struggle with socialising, but they don't present anything physical) has meant that there's probably been an increase in misdiagnoses (self or otherwise), primarily because it's just as difficult to say someone doesn't have some form of the condition, especially when there are people out there who claim that everyone is on the spectrum somehow. I imagine several personality disorders are incorrectly categorised under autism.
I think the major result of all this is a huge misunderstanding of the condition in both the media and public opinion. As such, any discussion on the subject is always going to be difficult (Just look at this vaccines bullshit). As with anything, people without any direct experience of the condition will always be at risk to not truly appreciating the condition. In fact someone with said experience might resent us using terms like autism, as opposed to the newly trendy neurotypical and atypical.
The conclusion of this is even though it seems autism is on the up, it's too hard to really know what's going on for sure because autism is both an incredibly widespanning and misinterpreted condition in itself.
Now, as to what specifically causes it, I don't know. But there has been research suggesting that autism has been around a long time, and it had it's advantages back in the early human days. This would suggest there's a genetic cause that we've 'evolved' to have.
But I don't imagine there's a specific autistic gene. I'd assume there's a very large combination of certain genomes that leads to an ASD development, hence the huge variety in individual cases. There's bound to be some environmental and epigenetic actions too.
