An addendum to the above - as it turns out, this isn't entirely a psychological thing, but I could write forever on that. Feel free to learn something if you'd like, for example studies on twins found that identical twins are substantially more likely to either both have gender dysphoria or both not have gender dysphoria, than non-identical twins. Basically, there is strong support that there are genetic factors that determine gender dysphoria, and such support exists independent of the psychology of the individuals. I'm not an expert but I imagine that the real answer is a combination of the two, with psychology being a bigger one.
Other studies found that there are particular differences in some regions of the brains of trans***ual people, in the case of FtM tran***uals they saw things that much more closely resemble men than women. Aka, even though those FtM trans***uals had been born identified as women, their brains, in specific respects, developed in the way that you would expect the brain of a man to develop. (Though to be fair, MtF tran***uals when measured in the same way in a different study had developments that they would not have expected for either men or women) This shows that they might not just think they are men, but that they may actually be developing the brain of a man.
Other studies found that there are particular differences in some regions of the brains of trans***ual people, in the case of FtM tran***uals they saw things that much more closely resemble men than women. Aka, even though those FtM trans***uals had been born identified as women, their brains, in specific respects, developed in the way that you would expect the brain of a man to develop. (Though to be fair, MtF tran***uals when measured in the same way in a different study had developments that they would not have expected for either men or women) This shows that they might not just think they are men, but that they may actually be developing the brain of a man.
Our results show that the white matter microstructure pattern in untreated FtM trans***uals is closer to the pattern of subjects who share their gender identity (males) than those who share their biological *** (females).
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