I think we probably are born this way, whether its genes or hormone imbalance in the womb etc etc.
My only proof of this is
firstly: Children, a lot of kids know at a young age and havent been influenced by media or parents etc.
Secondly: History, Transgender is not a 20th/21st Century thing like some idiots believe, transgendered souls have been upon this earth for centuries. The Western world just refused to acknowledge these people. Asia, Native America & Africa all have works/pictures etc showing that Trans people were around. As trans existed centuries ago, that rules out any pollution, modern tech and electromagnetic radiation theories, GMC crops, pesticides, nuclear emmissions etc etc.
Thirdly: Brain, Because the brain knows it and the body doesnt. They used to shock trans people to "correct" their brains, yet it cannot be corrected in that way. The body has to alter to change the mind. I'm not sure at what stage the brain develops BUT it is ingrained into the brain or at least the potential to be transgender lies there. The best study I have seen (although not fully reliable due to the lack of trans people involved) showed that MtFs have pituatry glands (they start your puberty and control hormones/development) have the same size as a cis-female. FtMs have the same sized one as a cis-male.
Fourth: We know that consciously most of us would NOT choose to be transgender and would rather live a normal cis life. Its human nature to not want to stick out all the time. We and only we know that something doesnt feel right. The world thinks we are attention seekers and are deliberately trying to change the status quo, but its normal human instinct to coincide with the status quo, so long as it isnt against any instinctual morals.
Fifth: If we developed it in life, if it were for instance a flu. Then we would be cured of it, it would simply only pass. We would have grown out of it. It would have been a phase and yet it becomes a way of life - for most.
Sixth: Because the human body is adaptable. We do not know the human body very well. We still have to figure out what and how the brain properly functions, how it stores things. How the rest of your body stores memories -yes you read that right! The body stores memories just like the brain. In recent transplants people have reported the same suicidal feelings after taking someone elses heart (without knowing he was depressed). Having anothers face and suddenly twitching the same as they used to (again without knowing). The adaptation comes from animals being able to switch sexes, something that can be done on human gonads (only in labs ATM). If fishes/toads etc can change sex to save their species then why wouldnt the same be in mammals/humans - which we have now found proof of!
I personally like to think its a switch, moreso a dimmer switch. I think its built into many of us, some have it on really low and they never know its even on, its only a little sliver of light at the back of their minds. Some have it on full and no matter what they do they cant turn the damn thing off. And some have it switched off. It lies dormant until they turn 36 and then they are dazzled by its brightness.
I honestly dont think its an external force that made us like this. We all dont live in the same place, therefore we cant have all been exposed to the same external forces - unless there is one particular thing we all have in common (par the trans-ness) that cis-people and LGB persons dont have in common with us.
Gentle