It’s been theorized that transgenderism is caused by social influences, but there is no scientific evidence to support this claim. Scientific evidence does suggest that transgenderism is caused by a brain that is unusually masculinized or feminized due to a combination of genetic and pernatal hormonal factors. Let me list off some evidence for this:
They found significant differences between male and female brains in four regions of white matter – and the female-to-male transsexual people had white matter in these regions that resembled a male brain (Journal of Psychiatric Research, DOI: 10.1016/j.jpsychires.2010.05.006). “It’s the first time it has been shown that the brains of female-to-male transsexual people are masculinised,” Guillamon says.
Surprisingly, in each transsexual person’s brain the structure of the white matter in the four regions was halfway between that of the males and females
In female to males (FtMs) these regions matched the brain regions of men and in male to females (MtFs) they are halfway between male and female. Not just that, these regions are believed to be related to body perception.
“It connects the parietal lobe [involved in sensory processing] and frontal lobe [involved in planning movement] and may have implications in body perception.”
Here we show that the volume of the central subdivision of the bed nucleus of the stria terminals (BSTc), a brain area that is essential for sexual behaviour, is larger in men than in women. A female-sized BSTc was found in male-to-female transsexuals. The size of the BSTc was not influenced by sex hormones in adulthood and was independent of sexual orientation.
However, there are subtle deviations [in subjects with gender dysphoria] from the natal sex in sexually dimorphic structures, which can represent signs of a partial sex-atypical differentiation of the brain.
Another research group made a graph to show these differences:
Results: MtF transsexuals differed from both male and female controls bilaterally in the superior longitudinal fasciculus, the right anterior cingulum, the right forceps minor, and the right corticospinal tract.
Conclusion: Our results show that the white matter microstructure pattern in untreated MtF transsexuals falls halfway between the pattern of male and female controls. The nature of these differences suggests that some fasciculi do not complete the masculinization process in MtF transsexuals during brain development.
On top of that, trans women have less exposure to androgens, which are responsible for masculinization in the womb
“Comparison between right-handed individuals revealed that the right-hand 2D:4D in MFT is higher than in control males but similar to that observed in control females. In FMT we found no differences in 2D:4D relative to control females. Our findings support a biological etiology of male-to-female transsexualism, implicating decreased prenatal androgen exposure in MFT. “
The brains of transgender people are clearly different, and the fact that these regions resemble the brain of the oppoisite sex and that transgender women are less masculinized by prenatal hormones suggests that the brains of transgender individuals are uniquely feminized or masculinized.
Studies of identical twins and fraternal twins are used to determine if something has a genetic component. Identical twins have exactly the same DNA and share the womb, and fraternal twins have different DNA and share the womb. They are used elsewhere to prove that things like bipolar disorder, autism, and personality all have a genetic component. In sets of identical twins where at least one twin has the studied condition, having a higher rate of both identical twins having the same condition (the concordance rate) than fraternal twins indicates that the condition is at least partly genetic.
And in twin studies of transgenderism, they prove just that.
More specifically, within this combined data pool there is a 33.33% concordance among monozygotic male twins compared with a 4.76% concordance among dizygotic male twins. In addition, there is a 28.38% concordance among monozygotic male and female twins compared to a 0.34% concordance among dizygotic male and female twins.
So the concordance rate for transgenderism in male and female identical twins is 28.38% while the rate for male and female fraternal twins is .34%. That shows there is a large genetic component to transgenderism.
For more reading on twin studies:
Studies on mammals close to humans are very useful in understanding the human body. In fact these animals are used in drug testing because the drugs affect animals similarly to the way they affect humans. Studies on these animals are used elsewhere to study conditions like autism in humans. What these researchers did was the manipulated hormones to give a male rat feminine behavior:
“Male rats were prenatally (Day 10-19 of pregnancy) exposed to an antiestrogen, nitromifene citrate (CI628, 1 mg/rat), or an antiandrogen, cyproterone acetate (CA, 10 mg/rat), and in adulthood were examined for their exhibition of male-typical and female-typical behavior pattern. Treatment with CI628 abolished the capacity of the adult intact male to ejaculate, enhanced his potential to exhibit feminine sexual behavior, and decreased the intensity of the level of female-oriented behavior in a two-choice stimulus situation (estrous female vs active male)”
If feminine behavior in male rats is directly caused by manipulating hormones in mice, humans should be assumed to work the same way unless there is evidence to the contrary.
Transgenderism is also linked to homosexuality. 38% of trans women are bisexual, 27% are exclusively attracted to men, and only 35% are exclusively attracted to women. The majority of trans men are attracted primarily or exclusively to women. Compare that to only about 3.5% of people being homosexual or bisexual and it’s obviously very disproportional. Homosexuality a biological condition and what causes homosexuality also seems to cause transgenderism.
Because of the unique brain structures, the unique pre-natal hormone levels, the twin studies indicating the condition is heritable, the animal studies, and the relation of transgenderism to the biological condition of homosexuality it is easy to conclude that the condition is caused by biological factors.
As for the cause of social influences, there is currently not much evidence to support that social influences are the cause. However there are interesting cases of a non-transgender boys being raised as a girls.
The TL:DR of it is a psychologist convinced the family of a child named David Reimer to raise the him as female. They subject him to estrogen so his body develops as female. The boy attempts suicide multiple times and rejects being female in various ways throughout his life. He even rejects feminine toys. Later on he goes back to being male through testosterone injections. He tragically commits suicide when he is older.