So is Asperger's by the way. Mild forms of autism, it seems, is an adaptation of a brain to cope with overwhelming cognitive overload of certain types, usually related to other people and unfamiliar places, which could be compared to too loud noise or an attacks of height-sickness.
And there is no single cause, of course. The symptoms are results of some genetic predisposition (slight differences in brain structure, perhaps, or higher levels of some neurotransmitters) and environmental and social factors, which conditioned the resulting habits and behavioral patterns.
One of the simplest and less wrong theories about mild forms of autism is that of so-called mind blindness. The children who have difficulty with maintaining eye contact and are looking to a mouth area instead of eyes area, could not learn to properly read accompanying emotions form faces of other people, so they constantly confused about interpreting the intentions and behavior of others and easily fooled by fake "Pan Am" smiles, so they learn to avoid confusing society and develop what we call introvert or nerdy mentality, with typical social awkwardness and eventually lack of interest in all these clowns, which clowns label sociopaths.)