It always surprises me that whilst many of us believe that transexuality is a brain thing i.e. mtfs have brain 'structure' very similar to other females, nobody really makes the link that if certain factors can cause your brain to develop in one way or another i.e. male or female, then why not various shades of in-between? It is logical when you consider the various shades and forms the human body can take. For example, men tend to be taller yet we have men shorter than women. If your brain can become masculanised from a female base, then it makes sense that it could get stuck half way.
We have regions of the brain that may account for gender identity, regions to do with sexuality, regions to do with behaviour, regions to do with body shape and so on. The factors which transgender brains (assuming this is what 'causes' ->-bleeped-<-) probably can affect all of these things. But there is no reason why they would impact on them equally. I guess what I am saying is they often seem to be linked i.e. a mtf is likely to want to look like a woman, behaves like a woman, desire a female body etc.. But sometimes they are not linked. We get people who are 'trans' in some aspects and not so much others - an example might be a cross dresser or a tomboy.
What does this mean? I guess this 'linkedness' accounts for why most people are either male or female and tend to dress and look and act like 'males' or 'females'. Because this linkedness may not be hard and fast it would also account for the huge range of gender queer people. Perhaps it even accounts for something like homosexuality where you often see gay male stereotype as being rather feminin (linkness aspect again). I guess it is a unifying theory.
It makes the existance of non-binaries not only plausable (we do exist so there is no doubt there anyway), but perhaps you could also predict our existance in absence of evidence and the range and forms we could take.
