In 2016, a controversial bill was signed in Georgia, banning transgender individuals from using restrooms designated for the sex with which they identify. In the wake of this legislation, Between the (Gender) Lines: The Science of Transgender Identity explored what was known at the time about transgender identity, discussing scientific evidence for its biological bases, as well as the social and psychological ramifications of binary gender classifications. Regrettably, both the text and the figures in this article were being abused by those seeking to support their own beliefs. As such, we decided to remove this article in 2021 to prevent its further misappropriation by individuals and groups seeking to oversimplify this complex subject and promote views that lack a scientific basis.

We still believe in the value of rigorous scientific research about transgender identity and encourage you to read the published, peer-reviewed studies that we cited in the original article if you are interested in learning more about this topic (linked below):

  1. Transsexuality among twins: Identity concordance, transition, rearing, and orientation
  2. A sex difference in the human brain and its relation to transsexuality 
  3. Male-to-female transsexuals have female neuron numbers in a limbic nucleus
  4. A sex difference in the hypothalamic uncinate nucleus: relationship to gender identity 
  5. Changing your sex changes your brain: influence of testosterone and estrogen on adult human brain structure 
  6. Regional gray matter variation in male-to-female transsexualism
  7. White matter microstructure in female to male transsexuals before cross-sex hormone treatment: A diffusion tensor imaging study 
  8. The (CA)n polymorphism of ERβ gene is associated with FtM Transsexualism 
  9. Should transvestic fetishism be classified in DSM 5? Recommendations from the WPATH consensus process for revision of the diagnosis of transvestic fetishism

We also encourage you to explore additional resources on this topic:

  1. For a SITN blog article discussing sex determination, check out “I’m XY and I Know It”: Sex determination systems 101
  2. For a quantitative view of transgenderism in the US, take a look at this analysis from Times Union
  3. For a review of discrimination against transgender persons, see this report from the National Center for Transgender Equality 
  4. For a more complete discussion on queer acronyms, see this description from BBC news
  5. For an in-depth look at how disagreements over restroom usage has shaped policy, check out this Politico article

The SITN editorial team






809 thoughts on “Between the (Gender) Lines: the Science of Transgender Identity

  1. More total nonsense.
    What matters are X and Y chromosomes. Other genetic commentary had NO scientific basis. The LGBQTZ people are trying to remake science, just like they are trying to remake grammar with their pronoun nonsense.

    1. ” just like they are trying to remake grammar with their pronoun nonsense.” Say that again, but slowly. “They” and “Their”. No one is trying to remake grammar, just call them what they want to be called. It’s not that hard. Also,
      Also, it’s LGBTQIA+, please at least learn the very basics of what you are arguing against.
      “What matters are X and Y chromosomes.”.
      Do you have a source? Come on, stop overcompensating, we all know you want to be a girl 🙂

    2. X and Y chromosomes definitely play a park in determining sex, however the result is hardly ever binary. There are too many genetic factors that go into the development of gender which result in an incredibly wide variation of physical development. I believe that you believe in the basic science of X & Y chromosomes, but please take some time to actually research the biology further. The LGBTQIA+ community is not at all trying to remake science, nor grammar. They simply want to feel validated and respected by those they interact with, which the same can be said for most anyone – including you, I’m sure.

    3. You are not anything near a scientist. You are a contrarianist, and someone who seeks to use “science” to prove yourself right rather than engage in actual science to discover truth.

      This behavior is neither brave nor intelligent, and definitely not noble. Do better.

    4. But this is part of science? brain structure and psychology is part of science too. Science cannot be bent or changed because science uses, you know, science, logic and testing, not people’s opinions. If other psychological anomalies cause brain structure to be abnormal, why would something like this be excluded? It is something literally going wrong with someone’s head.
      And yeah, chromosomes matter, but psychology and biology is also science and matters too. And chromosomes can still be messed up just like the brain, men can sometimes be born as xx an women as xy, and sometimes there’s other things like xxx and xxy. Gender dysphoria is just another one of those gender-factor anomalies.

    5. Hey! So everyone has pronouns. You have pronouns. “You”, “I”, “We”, “Us”, and many more are ALL pronouns! Hope this helps, and I hope you realised that you’re wrong. <3

  2. I now consider Pope Francis’s encyclical “Dignitas Infinita” to be the authority on gender identity.

    1. Then you don’t care about science or reality and will simply adopt any “authority” who happens to support your position.

    2. You are literally going against a Harvard blog page, how do you not realise your insane delusion. Also, L-G-B-T-Q, it‘s not that tricky to get right

  3. Your referenced Hawaiian article, “Transsexuality Among Twins”, manipulatively misuses terms, applying a different definition than the accepted definition.

    They refer to “Transsexuality Identity”. There’s no such thing:

    – Transsexuality means: Born ANATOMICALLY with both male and female sex characteristics. It’s not an “identity”, it’s pure biology.

    – Transgenderism means: Born anatomically with the biological sex characteristics of JUST ONE biological sex, but FEELING as if they are the opposite sex.

    1. Transsexuality is, by your definition, an extremely rare anomaly.
      Transgenderism is, by your definition, nothing more than confusion-a mental health problem, not a physical problem requiring surgical intervention.

      1. This assertion is incorrect. If you bothered to do any research, you would have learned that gender dysphoria (the mental health condition associated with being transgender) is reduced only through transition, which may be social, medical or legal. ‘Transgenderism’, as you put it, is not classified as a mental health problem by any reputable psychological organisation. Attempts to change a person’s gender identity into a cisgender one (aka conversion therapy) worsens gender dysphoria and psychological distress, not decreases.
        There have been ample studies showing that transition leads to better mental health outcomes and conversion therapy to worse, however some people still choose to believe that a normative sexual and gender identity is the desired outcome rather than happiness and peace for the patient.

    2. John, you have confused the terms ‘transsexual’ and ‘intersex’. The definition of “transsexual” is as follows: a transgender person, especially one whose bodily characteristics have been altered through surgery or hormone treatment to bring them into alignment with their gender identity.
      The definition of intersex is this: people who are born with genetic, hormonal or physical sex characteristics that are not typically ‘male’ or ‘female’
      The term transsexual was the word used to refer to transgender people before the word transgender was invented.
      I see you have corrected yourself, I will leave these definitions here for future reference.

  4. Your referenced Hawaiian article, “Transsexuality Among Twins”, contradicts itself.

    Their data shows “20% of all male and female monozygotic twin pairs were found concordant for transsexual identity.” That data unambiguously indicates a NON-genetic influence for transsexuality.

    Yet they contradict their own data, by proclaiming transsexuality is “more influenced by their genetics than their rearing.”

    1. You are incorrect. That sentence by itself doesn’t show anything. Just because someone has the genes for something does not mean that those genes will be active. The way to show that something is likely to be a result of genetics is to compare the rate of incidence between the monozygotic and dizygotic twins. If there is a significantly higher incidence in the monozygotic twins, then the trait is likely to be a genetic trait, as the monozygotic twins share the same genes.

      1. On checking the article again, i think you’re correct. Their data suggests that the feeling of being the wrong gender is, in 20% of the cases, genetic, and in 80% of the cases, environment. It doesn’t prove that the persons actually ARE the wrong gender, only that their FEELING has, in 20% of cases, a genetic component, and in 80% of cases, a purely environmental one.

        By analogy, schizophrenia has a strong genetic component. Schizophrenics exhibit hallucinations. The strong genetic influence doesn’t indicate that their hallucinations are real; it only indicates that their hallucinations have a biological component.

        So this Hawaii study doesn’t indicate that people truly are the wrong gender — it only indicates that the FEELING of being the wrong gender has a genetic component in some cases, but not most.

        1. May I recommend that you go speak to some biological researchers to further your understanding of how twin studies actually work, as you clearly either are not understanding the material or are intentionally misrepresenting it (and I’m choosing to give you the benefit of doubt on this one).

  5. How does orientation factor in?
    “As reported by Dr Julie Bakker, from the University of Liège, Belgium, the research team found evidence that transgender teenagers with gender dysphoria show functional brain characteristics that are typical of their desired gender.”
    For example, is this also true of boys who doubt their masculinity and consider themselves more aligned with girls, yet eventually conclude that it is not they but society which must change to accept alternative ways of being “a man.” My story, my partner’s story, happily in our same-sex relationship for 30yrs.

    Seeing the same potential in our (toddler) grandson but not concluding anything : time will tell, the child will evolve naturally to present as best fits given a generally supportive society.
    However, his parents with recent psych degrees in child development steadfastly deny their sons evident biological sex for fear of being discriminatory, just in case. The child is confused as to whether his male bosy parts can be female, and this is exacerbated as his folks now do not cut his hair and dress him such that he appears more feminine than toddler boys already often do. Their “affirmation” is actually guidance.

    Ultimately, as exploration through science brings more learning, the cases remain individual, real life stories. I fear the maxim: the road to hell is paved with good intentions. In our case, we have not seen our grandchild for years becuase neutrality is not acceptable to his parents. Ripple effects abound.

    1. erm you can be trans and gay btw. sexual orientation has nothing do with gender identity. so nope being trans is not erasing gay people or what not some people think it’s doing. you seem to be implying this. “happily in a same-sex relationship for 30 years”. there is a pervasive idea that people transition to like the same gender. the fact that only 15-19% of transgender people are exclusively heterosexual disputes this claim. i’ve seem several ‘progressive’ people (those who have no issues with gay and lesbian rights) who rally against trans identities due to this reason. obviously, there are conservatives and religious people who disagree for other reasons. that being said, i do apologise if i’ve misconstrued your comment. also, gender identity and gender expression do not correlate necessarily. you seem to be conflating the two. gender identity is your internal sense of self. for example, your partner has a male gender identity but may express feminine traits (expression). a transwoman has a female gender identity. do you see it? a cis can be feminine but it does not make them trans. say a man wearing a skirt. it’s simply a gender expression not identity.

    2. Hello! Could you please find the source? I am researching this topic and I find your comment to be very supporting to my hypothesis. Thank you, have a great day!

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