Is there a biological component in gender identity?

Introduction: Gender identity is each person's internal sense of being a woman, a man, both, neither, or anywhere along the gender spectrum, which may (cisgender) or may not (transgender) coincide with the sex assigned at birth. The multiple difficulties experienced by transgender individuals constitutes a risk factor for mood disorders and self-harming behaviors. However, knowledge about biological influences on gender identity development has the potential to reduce the stigmatization of gender minorities.

Materials and methods: We conducted a literature review of the available literature on the biological basis of gender identity, summarizing the main scientific evidence in the field in addition to its limitations.

Results: A growing body of research supports that the broad spectrum that characterizes gender identity constitutes a multifactorial trait with a heritable component. At the neuroanatomical level, this model translates to the high variability observed in the degree of masculinization/feminization of different features within a single brain, with considerable overlap between different gender identities at the individual level. Hence, neither genetic variants nor neuroanatomic measures can be used to identify or predict an individual's gender identity.

Conclusion: The evolutionary advantage of sexual reproduction lies in the huge increase in variation produced among individuals. The continuous distribution of gender identities in the population appears to be just one more aspect of sexual reproduction as a source of variability.