I must say I am not an expert on biology or philosophy for that matter.
First, to answer the nature or nurture debate from a radical point of view: it is always nurture, no matter what. What is called "human nature", is the result of something else, because humans did not exist 10 millions years ago. Their existence comes from preexisting law of physics that were "left to work", creating new "pseudo laws of nature" from their interaction. Problem: how to reconcile this with quantum physics and the existence of random happenstances, meaning some pseudo laws would emerge at random, meaning you couldn't really deduce them from preexisting laws?
The answer I found: If you had infinite calculating capabilities, even if there are random happenstances, this randomness is still bound to some rules. You would be able to calculate every way fundamental laws could interact with one another, even if they could interact at random, you should be able to know when they can act at random. You could make the list of every possibility, and whatever happens in reality already exists in this list of possibilities.
We must take into account that "nature" is a spectrum, that "freedom" is a spectrum, etc. So, "Are humans programmed to have some behaviour at birth?"
Therefore raising the question: are you born autistic, or do you become autistic? You can replace autism with anything: are you born mentally ill, or do you become mentally ill? Are you not born mentally ill, but with a predisposition to it? Are you born with no predisposition, but become autistic because of environment?
I could say "You obey rules of physics, you're a result of rules of physics. Your behaviour is a result of rules of physics, you have no choice in the matter. "
The prevalence of behaviour in time is a mere matter of stability based on physical constraints.
Mind is software. When you're born, your brain is not empty.
If we had empty brains at birth, we would not be able to learn anything. It is the result of a particular structure of matter, our neural cells, who are computing thanks to the input given by the other cells. In the act of learning, your cells are told how to store information (by changing the structure of your brain), and what information to store. So, to some extent, yes you are programmed at birth, otherwise you'd be like pebble.
In that mindset, three ways for autism (or any mental illness) to emerge.
First : You are born with a particular brain structure that will make you think autistic, and when you will develop your behaviour (remember it is algorithmic), you will only consider autistic solutions to issues, like how to behave socially. Being autistic is a way to look at reality pre-determined by the code you were born with at birth that survived, and how the hell can autism exist if it's a handicap, it can be for various reasons : randomness (there are some "defects of evolution"), advantages of autism that compensate its disadvantages or the genes coding for autism also coding for something such as higher resistance to illness or whatever other explanation evolution theory can come up with.
Second : You aren't born autistic. By pure happenstance (environment), your brain will pick up "autistic solutions" to problems. Such as, "When around people, avoid them." (Having to deal with them consumes resources, you need to think on it, which can be considered as a burden). Or, it can be taught, by imitating others and it will "crystallize" into your sense of self.
Third: You are born with a bias towards autism, and it will be crystallized into your sense of self and behaviour with decrease in brain's plasticity. Environment can make you develop it faster. If brought up in the right environment, you could be normal, and only extreme environmental changes or a shattering of your sense of self can change it.
Quantifying the link between autism and genes is hard. We would have to find a few hundreds children of autistic parents who were raised by non-autistic parents. Could be interesting...
I wrote enough for now. I would like some insight from people who suffer from autism: what do you think caused autism for you? Edit :
When did you understand you were autistic? Can you remember times you didn't have any issues with it ?
And, if somebody finds faults in my reasoning, I'd like them pointed out, thanks.