A conscious basis for gender identification?
There is currently no evidence to suggest that conscious experiences are a factor in leading a transgender person to identify with the opposite sex. Additionally, there is mounting evidence that transgender children are statistically indistinguishable from children of the gender with which they identify, meaning the process is set as early as five years old in humans (Olson, Key and Eaton, 2015). This suggests a predominantly biological basis. Because we cannot, for good reasons, conduct the appropriate experiments on humans, it is difficult to collect direct experimental evidence for any biological hypothesis, however.
Mammalian gender and sexual behavior
Rather than resulting from experience, the direction in which any mammal's sexual behavior will develop generally appears to be set sometime during the prenatal period, long before humans start having or remembering conscious experiences. In some sense, it appears that gender may be more biological and less psychological than traditionally believed.
The subject was covered in a recent Nature article, where researchers concluded that DNA methylation plays a primary role in the determination of gender and sexual behavior (Nugent et al., 2015). In their experiment, the researchers manipulated developing rats' exposure to gonadal steroids by gene manipulation and pharmacological means, and thereby induced or inhibited masculinized sexual behavior.
Pharmacological inhibition of Dnmts mimicked gonadal steroids, resulting in masculinized neuronal markers and male sexual behavior in female rats. Conditional knockout of the de novo Dnmt isoform, Dnmt3a, also masculinized sexual behavior in female mice. RNA sequencing revealed gene and isoform variants modulated by methylation that may underlie the divergent reproductive behaviors of males versus females. Our data show that brain feminization is maintained by the active suppression of masculinization via DNA methylation.
One should be careful to generalize from rats to humans, but the proposed developmental dynamic of gender is highly consistent with the way mammalian sex is believed to be determined, and the ability to induce and inhibit masculinized sexual behavior at will provides substantial evidence for the DNA methylation dynamics hypothesis.
We ultimately do not yet fully understand the basis for human sexual behavior. What we can say is that we have no evidence for the idea that conscious experiences are in any way a factor in the development of gender or sexual behavior, and that already by five years old, the direction of sexual behavior development has been set for long enough to render the transgender child statistically indistinguishable from a cisgender child of the gender they identify with. A possible candidate theory for an underlying biological mechanism is prenatal DNA methylation dynamics.
- Nugent, B. M., Wright, C. L., Shetty, A. C., Hodes, G. E., Lenz, K. M., Mahurkar, A., ... & McCarthy, M. M. (2015). Brain feminization requires active repression of masculinization via DNA methylation. Nature neuroscience.
- Olson, K. R., Key, A. C., & Eaton, N. R. (2015). Gender Cognition in Transgender Children. Psychological science, 0956797614568156.