Wow, great question!
I agree with most of the people who have already answered: no, it's pretty much an evolutionary dead end. And I'm so pleased to see that so many of us are on the spectrum, as people like to say. I am, too. And I recognize several names on here who are people who have helped me in the past, people I have taken a liking to. Interesting, no? Like calls to like, I guess.
I was self diagnosed with Asperger's, and got an official diagnosis about 15 years ago. And yeah, it did make me feel better about myself. That, and finding out that i have Ehlers-Danlos Syndrome. Oddly enough, the 2 seem to go together quite often.
I'm super smart, 134 IQ, which is close to genius. I did well in school, because I liked taking tests and was good at it. And yet, I never did well in life. I live at poverty level on disability due to severe panic attacks and depression, which took me out of the game in my mid 30's. Even before that, I was never able to work a full time, "real" job. Never been able to support myself. I'll be 64 in April.
Even tho I'm so "smart", my memory is shit, and always has been. I'm never gonna be able to tell if I'm senile because I already can't remember anything. I guess I'll know when I start putting my shoes in the fridge. It's why I always had trouble spelling. Memorization was always very difficult for me. The reason I had straight A's was because I actually understood what I was learning, rather than just using rote memory. I'm like a computer with super processing and speed, and 50 KB of memory.
I can remember feeling different at a very early age, in first grade. I could tell the other kids just didn't see or feel things like I did. I knew I was smarter. I went to Catholic school in the early 60's, and it was very rigid. I had problems with that. I distinctly remember praying every night to god to make me normal and stupid like everyone else. I suffered from terrible anxiety, to the point where I couldn't eat breakfast until I was in high school. I just wanted to be normal.
I found out in my 40's that I was also faceblind, which apparently goes along with autism a lot. It was a real ah-ha! moment. I finally understood a major cause of why I was so anxious at school. I couldn't tell people apart! And Catholic school with the nuns all wearing veils and habits? It was a nightmare. I was terrified when my mother would leave me off at school. I never went on school trips until 4th or 5th grade, because I was terrified of getting lost. By "lost", I mean not being able to recognize my teacher or chaperone. Growing up smoothed thing out a bit, but it's still tough. Of all my handicaps, I would say the faceblindness is probably the worst. Imagine living in world of strangers, all the time. The sad thing is, I never knew this was abnormal, so I blamed myself. I thought I wasn't trying hard enough to memorize faces. I didn't know that normal people don't HAVE to memorize faces. It just come naturally.
Same with the EDS and Asperger's. I was always down on myself for being a jerk, for being lazy. I was always getting reprimanded for it, for not working hard enough. Now I know I was working twice as hard as everyone else just to survive, to just stay upright. EDS causes laxness in ligaments and tendons. Connective tissue is weak. In normal people, exercise is partially passive. You move a muscle by your will, and it snaps back with the help of tendons. Mine are like stretched out rubber bands, so my muscles have to work much harder, essentially doing all the work. No wonder I was always exhausted. Add to that all the psychological stuff, and, well...
So no, I don't think it's a step in evolution. It's too exhausting. And severe autism would have been a death sentence in prior times. I have a theory that autism is nothing new. I think that all those legends of babies being taken by the fairies was really autism rearing it's ugly head at a certain age. And being "taken by the fairies" was a pretty good justification for leaving your substitute, weird fairy child out in the woods to be exposed.
My mother was 40 when I was born, which was quite old back in 1960 to have a baby. She was also sick at the time with gallbladder, and didn't know it. She said she threw up through the whole pregnancy, which would tie in with what someone else here said about it being caused by nutritional deficiency in the mother.
It's not something I would wish on anyone. At least, anyone I like. And oh yeah, no kids here. I'm so glad I had the inner knowledge to know raising kids was not something I was capable of.