Implicit in the discourse of gender identity is the understanding that the mind, or inner feelings produced by the mind, is who we “really are” – the body is at worst an irrelevance, at best a malleable vessel or tool for the expression or performance of the true person within, a person who has a distinct and stable “identity” irrespective of the physical conditions imposed on it by the incidental body. This view is called dualism, specifically Cartesian Dualism, after the philosopher René Descartes. There is a hierarchy built in to dualism: the mind is the real human being, the seat of reason and conscience. The body is just so much dead meat. To alter the mind is a violation; to alter the body, a trifle.
But it turns out the body and mind don’t work like that. The former is not some inert Golem for which the latter is the magic, animating scroll. To the best of our current understanding, the mind is an emergent property of complex interactions within the brain that are entirely and completely physical. No special substance, no stuff of thought, is circulating around your scull cavity, “being” you. Your mind is not something that is, it is something that your brain does. A process is a better way of thinking about it; or even, according to some philosophers, a mostly illusory effect.
Brains, as we all know, are not independent agents knocking about in the world. Your brain lives inside your body, is an inseparable part of the complex system of interactions and symbioses that make up the entire animated, sentient entity that is you. Your brain eats the same food as you, it breathes the same air as you. It gets sick when you are sick. It goes through puberty when you go through puberty – worse, in fact, the whole damn thing is its fault, because it kicks it off to begin with. Your brain “hears” everything that is said to you. It is a full participant in the process of conditioning, education, learning, trauma, memory, preference building and socialisation that you undergo. The brain does not “store” who you are – it becomes who you become.