>>733844There is no single cause of gender identity or gender dysphoria.
But we do have a consistent body of evidence showing that biological factors contribute to gender identity development in a subset of people. Below is a short summary of peer-reviewed findings with direct quotes where possible.
1. Twin studies
Monozygotic twins show much higher concordance rates for gender dysphoria compared to dizygotic twins, which strongly suggests a genetic component.
“The data suggest a strong heritable component to gender identity.”
(Diamond & Hawk, 2013)
https://www.tandfonline.com/doi/abs/10.1080/15532739.2013.750222Twin studies don’t mean “biology determines everything.”
They simply show that biology matters.
2. Genetic polymorphisms (AR, CYP17, etc.)
These studies do not claim “a trans gene,” but they do show statistically significant associations between certain polymorphisms and MtF/FtM populations.
Androgen receptor repeat length associated with MtF transsexualism:
“MtF transsexuals had significantly longer AR repeat lengths compared to controls.”
(Hare et al., 2009)
CYP17 variant associated with FtM transsexualism:
“A significant association was found in FtM but not MtF transsexuals.”
(Bentz et al., 2008)
These are correlations — not deterministic causes.
3. Neuroanatomy (BSTc, INAH, BNST, gray/white matter)
Multiple independent groups have replicated findings of structural brain differences.
“The BSTc of MtF transsexuals was of female size and neuron number.”
(Zhou et al., 1995)
“MtF transsexuals have female-typical neuron numbers in a limbic nucleus.”
(Kruijver et al., 2000)
Structural MRI studies show similar trends:
“Regional gray matter variation in MtF individuals resembles that of cis females.”
(Rametti et al., 2011)
“White matter microstructure in FtM individuals is shifted toward the male pattern even before hormones.”
(Rametti et al., 2010)
Again, these do not prove causation — they show that gender identity correlates with specific brain phenotypes.
4. Psychosexual differentiation reviews
Major reviews emphasize that the mechanisms are complex and multifactorial.
“Human psychosexual differentiation is influenced by genes, prenatal hormones, and social factors, none of which alone can explain all cases.”
(Gooren, 2006)
“Gender identity appears to be related to sexually dimorphic brain structures that may be influenced by atypical hormone effects.”
(García-Falgueras & Swaab, 2008)
This is the actual scientific consensus: complex, multi-layered, not reducible to a single mechanism.
5. Hormone exposure & brain development
Research on animals and humans shows that both prenatal and pubertal hormones play roles, but neither explains gender identity fully.
A review notes:
“In children who persist in gender dysphoria past puberty, hormone activation does not seem to alter gender identity.”
(Guillamon et al., 2016)
This directly contradicts the argument that gender identity is “just hormones” — identity remains stable despite hormonal changes.
6. Intersex cases
David Reimer’s case is not unique.
Many intersex individuals assigned to a gender surgically in infancy later experience gender dysphoria.
This shows that gender identity cannot be created through socialization alone.
7. Regarding autogynephilia
The most widely cited study shows:
“93% of cisgender women reported autogynephilic arousal in at least one scenario.”
(Bailey, 2009)
https://doi.org/10.1080/00918360903005212Thus AGP is not a uniquely “trans” phenomenon and cannot explain gender identity.
Conclusion
No current research supports a single deterministic biological cause for trans identity.
But multiple lines of evidence — genetics, neuroanatomy, twin studies, intersex cases — strongly demonstrate that gender identity is real, enduring, and affected by biological factors in ways incompatible with the idea that it is “delusion” or “social contagion.”
This is not about reducing people to hormones — it’s about recognizing that human identity emerges from the interaction of biology and lived experience.