Well biology doesn't necessarily mean genetic - the same genes can express in different ways depending on a number of factors. Two children can be born with markers for type 1 diabetes with one losing pancreatic function almost immediately and the other never becoming insulin dependent. The womb is an environment that is also a biologic factor as the mother's body chemistry can affect the way in which an embryo develops.
If genetics were a very strong factor, one would expect identical twins to have a very strong correlation in sexual orientation - although it seems that if one twin is gay there is only a 70% chance that the other will be as well; remember, however, that they are both products of the same womb.
Honestly, I think there are just too many factors at play for a conclusive determination to ever be made. I think of this as being akin to the factors that determine who will be artistic, musically inclined, mathematically inclined, etc. There are so many variations in the human psyche that I feel that that variation itself is the evolutionary advantage that pulled us through.
Evolution isn't just about the individual organism surviving, it's about the species surviving. Remember Dawkins' selfish gene.
I know we're dealing with really important topics here like how to explain the existence of transgendered people from an evolutionary perspective, whether transgendered people should be "allowed" to have surgery, and on and on.
But, maybe we could all take a short break from these lofty discussions to consider another matter? Namely, what the fuck do YOU intend to do about this: Results of the National Transgender Discrimination Survey. Anything? No? Well, that's okay.
I'm sure all the transgendered people in the world will be happy to hear the outcome of this discussion. Maybe not the ones who are too busy being fired from a job, or brutally beaten, or murdered. Maybe not the 19% who reported that they have been denied medical care, or the 3% who were physically attacked while they were in a doctor's office or hospital emergency room. They might be a little preoccupied right now.
It's right for them... So who's to say differently...
I do not believe that it is wrong at all, and I guess my question would be why is it wrong? Unfortunately the Human creature is by no means perfect, and thus so, a lot of issues can happen before and during its lifespan. Science has proven that the brain can develop one way and the body another. Knowing this, why is it wrong to want to be happy with yourself and do what you can when science offers a solution, cuz god knows (teehee, sorry) that religion offers no help, aside from keeping it locked away deep in your head. You are only your sex because you were the fastest swimmer; nothing determined who you were before conception. Its chance, and it is also one of those things that one has no control over, just like race, country of origin and species. So if sex is chosen without the consent of the individual, and it ends up being wrong or mixed up, why leave it broken? cuz an ancient archaic text said so? Not a good reason.