I see autism (Autistic Disorder, Aspergers, PDD-NOS) as genetically related within families since they often occur within the same families. Between families, there's probably some variation although still maybe some larger genetic markers in common. I think autism, "disorder" aside, makes up a solid portion of the population, leading up into a Broader Autistic Phenotype which I still consider autism although which may not win a diagnosis by a professional. Still, it's the same underlying issues. To me, I find little sense in trying to separate out the different labels used today from one another; I don't bother to take part in discussions these days as to whether Aspergers should be considered "autism" and "What are the differences between HFA and AS", etc. To me, these variations are no longer very relevant and not particularly integral in my view to understanding the whole of autism.
Instead, I prefer to look at the similarities and differences from person to person, rather than label to label. I think things are clearer that way. I like thinking of "autism" from brain to brain, body to body. Generalizing things too much I think runs the danger of ignoring the fact that evolution (unwittingly) designs each creature anew, albeit based on the genes it was given. But each creature is still a new attempt to beat the next one to reproduce, whether they're of the same species or not. And either they're successful or they're not.
That's my personal view.
I do see a huge number of traits where people can differ in any one or more of the traits from each other, both quantitatively and qualitatively.
The autism spectrum is a plane that transects the 3-D Bell curve, creating a 2-D Bell curve of the sort you see in all sorts of books.
On the left end are people with autism, and as it gets further and further to the left, the autistic traits become more pronounced.
On the right end are ultra-social people: Presidents, movie stars, the guy "everyone knows", the con artist who can talk anyone into anything.
In the middle are the NTs: People who use social skills competently, but aren't smashingly good at them, either.
There are other spectrums intersecting the autism Bell curve, at all sorts of angles--the ADHD spectrum, the sexuality spectrum... spectrums for personality traits and behaviors.... Those spectrums form the range of human behavior and mind. And, for each person (which is why you need the 4th dimension), you can place a dot on the curve to signify his traits.
The thing about Bell curves is that the "middle range" is always arbitrarily determined; and so "NT" is arbitrarily determined. Most people agree that the nonverbal person who spends most of the time stimming isn't NT; but what about me, with my verbal skills? What about the quirky engineer who prefers to socialize with other engineers? What about the shy kid who has a small circle of friends? Where does the "autism" part of the spectrum start, and the NT part end?
Fact is, nobody can say where it does. Autism blends smoothly into NT; and where you put the line depends on how you define autism--which is also completely arbitrary.
People are just people. Some people have more autistic traits than others; some have more social skills than others. That's all.
Even the most NT people I have ever known have acted in a way I could identify as autistic sometimes. and There are many NT behaviors that are like counterparts to autistic behaviors: we stim mostly by rocking, hand flapping, and the like; NTs tap pencils, twiddle thumbs, and such things. These activities serve similar (if not identical) purposes for NTs as for autistics. however, since the majority of the population is more NT than autistic, then the NT methods of stimming are more common, whereas autistic stimming stands out and looks weird. So, autistics stimming becomes categorized as pathological and NT behaviors that are nearly identical in form and function, save for the fact that it's usually less obvious in NTs (tapping a pen is usually less noticeable than a full-body rocking), are overlooked and considered normal.
After all, with autism being uncommon but also very genetic, it seems to follow as necessary, even without the experience of seeing autistic traits in NTs with no autistics in the near family, that there must be slightly autistic NTs around, with perhaps fewer of the genes expressed. Ever since I got diagnosed, we pretty much immediately assumed it was from my dad's side, since he seems very likely on the spectrum, and he has speculated that his father and grandfather likely were. Nevertheless, on my mom's side, while mostly very NT, among her siblings there is a talent for computers and some social awkwardness, suggesting maybe that there were some autistic genes on her side (and that would make sense, since I'm a girl and so have an extra X chromosome, that traits on both side would probably be needed for me to show as autistic as I am).
Anyway, that's my take.
I see autism (Autistic Disorder, Aspergers, PDD-NOS) as genetically related within families since they often occur within the same families. Between families, there's probably some variation although still maybe some larger genetic markers in common. I think autism, "disorder" aside, makes up a solid portion of the population, leading up into a Broader Autistic Phenotype which I still consider autism although which may not win a diagnosis by a professional. Still, it's the same underlying issues. To me, I find little sense in trying to separate out the different labels used today from one another; I don't bother to take part in discussions these days as to whether Aspergers should be considered "autism" and "What are the differences between HFA and AS", etc. To me, these variations are no longer very relevant and not particularly integral in my view to understanding the whole of autism.
Instead, I prefer to look at the similarities and differences from person to person, rather than label to label. I think things are clearer that way. I like thinking of "autism" from brain to brain, body to body. Generalizing things too much I think runs the danger of ignoring the fact that evolution (unwittingly) designs each creature anew, albeit based on the genes it was given. But each creature is still a new attempt to beat the next one to reproduce, whether they're of the same species or not. And either they're successful or they're not.
I look at behavior and mental processes and genes the same way!
Like the article Max referenced (shadow syndromes), the number of "disordered" or "pathological" diagnoses in the DVM has jumped to over 400 now (from 80), which makes the terminology nearly passe at this point! What is "disordered" when nearly every behavior IS disordered?
I see autism (Autistic Disorder, Aspergers, PDD-NOS) as genetically related within families since they often occur within the same families. Between families, there's probably some variation although still maybe some larger genetic markers in common. I think autism, "disorder" aside, makes up a solid portion of the population, leading up into a Broader Autistic Phenotype which I still consider autism although which may not win a diagnosis by a professional.
I agree totally with the above, that if you could capture the "autistic" (primarily thinking vs. feeling; solipsistic vs. emphathetic, etc.) tendencies in the greater population, the one not yet diagnosed, you would find that it DOES "make up a solid portion of the population". Maybe someday it will be seen as comprising a near majority even (40 or more percent).
To me, the final, and only truly important distinction is one's spiritual status, which varies from soul to soul, and which will never be quantified by science. All other distinctions- gender, social status, the intelligence quotient, etc. - are meaningless and should never be subject to categorization like "good, better, best" because they merely reflect the shell, the "costume", the role, the soul has elected to take on to learn certain worldly lessons, to grow spiritually. For example, most Perfect Masters work in obscurity, but if you are ever lucky enough to come into their orbit you will find they appear often like madmen, oblivious to their clothes, hair, appearance. They mostly live in the East 'cause they would be institutionalized (or people would try anyway) in the West. 
To get back to genes, since AS was originally a N. European gene, it will probably just manifest itself in a big way where racial/cultural (Jews AND Christians; Buddhist AND Christians, etc.) inter-marriage is possible/condoned (and also where there are many more personal freedoms) and so will be most concentrated in developed countries probably and slower to manifest in Africa, China, the Middle East.
It may also be faster to manifest in 1st world countries because of medical intervention. Many of us had complications during birth and in days of yore, we might not actually be alive today. Not to mention early childhood infections, like inner ear infections, which could put our survival into adulthood in jeopardy.
Also, there's travel. People with more money tend to travel more, meet more people, marry from out of their communities. And many times like attracts like, so there's an increase, naturally, in the probability a person with autistic genes will be drawn to another with autistic genes, and transport makes it easier to get to those people and met more of them.
I'm sure there's other factors too. But those are two bigs ones I've noticed. I for one, without the aid of medical intervention, wouldn't likely be here.
But that's capabilities plural that appear in the diagnostic criteria. Not capability singular. Hence, no autism spectrum in my eyes, because that would imply that all of those different capabilities are all going to be at the same "level", which they're obviously (this can be told just by observing a number of autistic people) not.
Do I detect the "hard birth/brain damage" theory again?
No, not at all. I for one definitely feel the underlying traits are developmental. But prenancy/obstetric complications do seem to occur more in our ranks and I suspect it's because whatever may make these more probable are genetically linked to our developmental profiles (i.e., linked causes). The brain and body are connected and despite phrenology's ugly past, there may be some medical conditions and/or physical conditions which may occur more often with autism. And with this increased risk of complications, brain damage is more likely to occur, adding another layer to the autism.
All the same, I'm not really convinced that damage at birth CAUSES autism but it would certainly make it more likely that they would have other problems such as lowered intelligence.
Because autism in various forms is so prevalent within particular families, there is an excellent chance that it is mostly genetically determined.
"Bigger heads, bigger brains"
But a norwegian expression is:
"Er du tjukk i huet?"
Which means in its direct translation:
"Do you have a thick head?"
But really means:
"Are you stupid?"
But then again, monkeys aren't really that smart even though they have smaller heads than us. (monkeys... and cats! Fetched the double meaning?)