Hmm..
I don't think its as rare as has previously thought - and I do think some of what we're describing as ND is in fact perfectly normal for humans.
What I think is happening:
- We live in a world that is extremely busy and overstimulating
- ND people will gravitate toward other ND people and of course, reproduce with them
- Higher rate of DX and higher awareness of the differences
- Change in classification of ND conditions
40 years ago, 'autism' was really used for the non-verbal, apparent inability to learn anything, extremely high care needs folks only.
I strongly believe that is a very different thing, I don't think we know what causes that level of disability in every case nor do we actually know what to look for AND theres a long history of just slapping an 'autistic' label on that and not looking any further. I suspect there are a wide range of genetic fubars that cause such symptoms and most have absolutely fuck all to do with what people commonly refer to as 'ASD'.
I think what most people are being dx with or self dx'ing with, called 'ASD' or ND... is well within the range of 'normal' for humans - but where our natural environment meant that was an advantage (or at least not a disadvantage), our environment has now changed to the point where it is often a huge disadvantage.
The people who find an overly stimulating, 'always on', bright, loud, busy, heavily populated environment perfectly ok and easy to navigate would not have been the norm at one point (but how would we know.. mm) ... I don't actually think they are the norm now, but we haven't really got any choice!
I suspect we've always had two types of people (very very broadly speaking) - those we currently call ND and those we currently call NT, and the environment favoured one kind in the past, and now favours the other kind.