I mean, yeah there is? There are 7 billion people on this planet. If you could create some score of peoples intelligence, how they react/respond to people, their normal physical movements and put that into a distribution the autistic people would definitely be on the tail end of the curves.
Sure everyone is different in various ways- but a lot of those differences are very small compared to the differences exhibited by autistic people.
I can give you a direct example- my oldest son has.. something. We had him tested for autism when he was younger and were basically told that yeah there is 'something'. He's not technically autistic, or at least not the level where he needs extreme special stuff, but he does exhibit some of the traits of autistic children, just in a more minor way. So for lack of any better term he is "very slightly autistic". At 7 years old he has an insane memory (closest to "photographic" that I've ever encountered) and seems highly intelligent in some areas (but definitely not in others! it's quite incredible actually to see sometimes..). He has some of the physical traits where he can't really sit still, needs weighted blankets, has some of those unique arm movements of autistic people.. but again fairly subtle. A lot of things to him can be more black/white than gray, because he seems to need to fit everything into a very specific bucket in his mind.
Every teacher he has had, including some which work with the more special ed kids, has said "yeah there is... something different about him".
Now conversely, my younger child I would classify as "normal". Why do I say that? Well.. I worked at co-op preschools with both of my boys for years. I saw lots of kids. And when you see a ton of kids and play/interact with them... I mean yeah there is a normal. Normal is how you would expect someone to behave and interact with. There is a relatively normal way you would expect a 7 year old to respond in various situations, etc.
Anyway- sorry for writing a book. I guess I'm putting off work.. I just found it a bit strange to not accept that, well, most people are actually pretty darn similar while a minority of people are very different. I see it every day in my house!