What does the science say about gender identity?

Reproductive Health

A: Differences in brain structure and/or function, hormone levels during different phases of development, and even genetics seem to shape our internal sense of gender identity.

We all have a gender identity, or an internal sense of self as belonging somewhere on a gender spectrum. For most people, their gender identity aligns with what is stereotypically expected for their body anatomy (biological sex). In some folks, however, it does not. These individuals may identify as transgender, non-binary, or gender fluid. We now have data that helps to explain why and how this might happen.

Brain Differences 🧠

There are both structural and functional differences that can be seen in certain brain regions for the different sexes. There really do seem to be “male” and “female” brain types. Studies of the brains of transgender people show that they are different from what would typically be expected based on their other body parts. In some cases, their brains look like the gender with which they identify. In other cases, their brains seem to be “in-between” what is typically seen for a cisgender man or woman. These differences in brain structure and function may be due to a combination of genetic and hormonal factors.

Impact of Hormones 🩸

Exposure to certain hormones while in the womb and during early infancy seem very important in “wiring” the brain along male or female lines. This has been shown extensively in animal studies as well as in some studies of humans. Interestingly, the hormonal signals that cause the body anatomy to develop a certain way occur early in pregnancy, during the first trimester, and the hormonal wiring of the brain seems to occur later, during the second and third trimesters. Therefore, it makes sense that the body anatomy could develop one way and that gender identity in the brain could develop another way as a result of different hormonal conditions present at those different times.

Twin Studies & Genetics 🧬

While most individuals with XX chromosomes grow up to identify as women and most individuals with XY chromosomes identify as men, there seem to be many genes, located on OTHER chromosomes, that play a role in the development of gender identity. Alterations in such genes have been found to be associated with a transgender identity. Additionally, studies have found that identical twins (who share 100% of their DNA) are more likely to both be transgender than fraternal twins (who only share 50% of their DNA), also suggesting a strong genetic influence. This evidence suggests that genes may play a very large role in gender identity.

Failures of Gender Assignment in Intersex Kids 👨🏽‍⚕️

Some infants are born intersex, which means that their body anatomy (internal reproductive organs and external sex organs) isn’t entirely all female or all male but either a mix of both or somewhere in between. Historically, such infants were often treated surgically to make their external sexual organs look female (as it’s a technically simpler surgery) and then were raised as girls. (Note: significant efforts have been made and are ongoing to prevent unnecessary surgeries on intersex infants – see resources below for more information.) Studies have found that, despite these interventions, which often included feminizing hormone treatments and never telling the children about their history, many of these children grew up to identify as boys. This suggests that gender identity is not something that can be changed or molded once formed, but may be a fixed and integral part of someone’s wiring.

Failure of Conversion Therapy 🙏

Society does not make it easy to be transgender or non-binary, and so MANY people have tried, often desperately, to change their gender identity through counseling, prayer, or other interventions designed to “correct” the disconnect they feel between their sex assigned at birth and their gender identity. This is often referred to as conversion therapy. Studies of this approach have shown it to be ineffective – it doesn’t work. Even worse, it’s harmful. Conversion therapy is associated with increased ⚠️ rates of mental health distress and suicide. (Stay tuned for a future post about what does seem to be effective for gender-questioning youth.) Despite potential good intentions, there is no evidence to support the idea that someone can change their gender identity through therapy or prayer – it truly doesn’t seem to work. This further suggests that gender identity may be inherent to someone’s wiring, even when it doesn’t “match” their body anatomy.

Bottom line: The current evidence suggests that brain, genetic, and hormonal factors are key influences on the formation of one’s sense of gender identity. Sometimes these “line up” with the factors determining body anatomy, and sometimes they do not. Gender identity seems to be “hard wired” into the brain. There is no evidence to support the idea that gender identity can be changed through counseling or therapy, and such attempts have actually been shown to be harmful.

Stay safe, stay well.

Those Nerdy Girls

Jennifer Finney Boylan on the brain’s role in gender identity

Scientific American on brain’s role in gender identity

Evidence supporting the biologic nature of gender identity

Genetic variants (not on X or Y chromosomes) associated with transgender identity

Effects of conversion therapy on transgender youth

SAMHSA publication on evidence of harm from conversion therapy and effective alternatives

American Psychological Association on Understanding Transgender People

Scientific American on the results of gender affirming care for kids

TNG post on the difference between sex and gender identity

TNG post on intersex conditions

Unnecessary surgeries on intersex infants

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