The Origins of Transgender - Science - Transgender Universe

The Origins of Transgender: Hormones and Gender Identity

Are hormones the determining factor in what makes us transgender? We previously gave you a primer on the subject in “The Origins of the Transgender Condition“. Now we are going to go into further detail while providing you with the best known information from some of the leading scientists and authorities on the subject.

Did you know that everyone is born with the neurological pathways to become both male and female? Did you also know that many of the parts for each sex are still inside us all? To further understand, we need to first take a look at some basic biology and chromosomes.

For this section we will refer to the research of Eric Kandel. He is a professor of Biophysics and Biochemistry at Columbia University’s College of Physicians and Surgeons. He is also a Nobel Prize Winner for his research in Neuroscience.

We are all born with an undifferentiated gonad which is not yet male or female.

The Undifferentiated Gonad

We are aware there is a male gonad (testis) and a female gonad (ovaries). However we are all born with an undifferentiated gonad which is not yet male or female. This is where the chromosomes come in. If you have “XX” chromosomes, your undifferentiated gonad will develop into female ovaries. If you have “XY” chromosomes, your undifferentiated gonad will develop into male testis. In the interest of keeping things simple for the moment we are going to stay in a binary perspective and hold off on getting into the various intersex combinations of chromosomes at this time.

Undifferentiated Gonads - The Origins of Transgender - Sciance - Transgender Universe

Male Development

With “XY” chromosomes, male development (the formation of the testis) is triggered after 7 weeks in utero. At this point the testis send a massive blast of testosterone equal to that of puberty. This testosterone blast masculinizes the brain and causes the body to develop with male characteristics.

Female Development

With “XX” chromosomes, female development (the formation of the ovaries) is also triggered after 7 weeks. The ovaries develop and begin to secrete both estrogen and progesterone. These hormones feminize the brain and cause the female body to develop.

Male and Female Development - The Origins of Transgender - Transgender Universe

At this point things get interesting. We will reference the work of Norman Spack, MD. He is the Assistant Professor of Pediatrics at Harvard Medical School and the Clinical Director of the Endocrine Division at Children’s Hospital, Boston, MA.

Spack shows us that at birth, the male receives a second blast of testosterone which the female does not. After this phase there is no more hormone induced development until puberty. What is fascinating is that we do not yet know why the males get this second testosterone blast just after birth. The challenge is that we cannot measure the hormones without harming the patient. We also cannot measure the ability of the body’s hormone receptors to receive these hormones without also harming the patient.

Sex Hormones During Human Lifespan - The Origins of Transgender: Hormones and Gender Identity - Transgender Universe

So we are now able to establish the fact that though the chromosomes play the role of of the blueprint for the body, it is hormones that begins the development and effects of gender. At puberty, the hormone process starts up again. The hormone system works like a relay. You have the hypothalamus in the brain, which sends signals to your pituitary, which then sends a hormone to your gonads (ovaries or testes) which then secrete sex hormones (Estrogen or Testosterone).

Professor Hines found that the presence of testosterone plays a major role in the development of gender identity.

Gender Development

Professor Melissa Hines of Cambridge University researches gender development and the prenatal influences that affect it. Her research shows that both genetic factors and hormones during early development affect gender identity. She also found that social encouragement and self-socialization based on gender identity affects later development. Professor Hines found that the presence of testosterone plays a major role in the development of gender identity. She discerns that gender identity is affected by the hormone blasts that occur prenatally and immediately after birth. Her research also found this exposure affects behaviors during childhood.

Professor Hines studied female children with congenital adrenal hyperplasia (CAH); a genetic disease where the girls have a high exposure to androgens (testosterone), and compared them to children who do not have the condition. She found that girls with CAH were just as likely to choose toys made for boys as a male control group. She also found in a study of 9000 children that in girls who displayed more masculine tendencies, their mothers had higher levels of testosterone. Most importantly her study found that girls that were exposed to more testosterone in development had a reduced female identity.

Gender Expression

Catherine Dulac is a professor of Molecular and Cellular Biology at Harvard University. Her work has shown that the neural pathways to be both male and female exist in the brain. She only found a few parts in the brain that differ between men and women. In studies on mice, she found neurons in the brain that control maternal behavior that exist in both females and males. Her research also found that females are spontaneously paternal while the males are not. She discovered that if you activate these neurons in a specific way, males can also become spontaneously paternal just as the females.

Dulac also experimented with hormones. She discovered that hormones can determine the development potential for male or female behavior at an early age. She also found that hormones will determine expression of that behavior later in life. Her research determined 3 things:

  1. Development of male sexual behavior requires that the brain of a newborn mouse is exposed to testosterone, but development of female behavior does not require estrogen.
  2. Testosterone masculinizes the nervous systems of both genetic males and genetic females.
  3. Exposure to sex steroid hormones in adulthood is necessary for the expression of sexual behavior, but testosterone produces male behavior only in adult mice whose brains were masculinized when they were newborns, and estrogen produces female sexual behavior only in adult mice whose brains were not masculinized when they were newborns.

The study concluded that the sex steroid hormones that are present at the time of birth determine which pattern of behavior develops and the sex steroids that are present in adulthood determine which pattern is expressed.


We can conclude that prenatal hormones have a profound effect on gender identity. However we do need to further understand what happens during the second hormone blast at childbirth and it’s affect on the masculine identity. Below is a video from Charlie Rose and his Brain Series which includes the scientists and the studies mentioned in this article.

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  • Terri Ellen

    I very much agree. Just from my on reading of articles and such it’s clear that while chormosomes set the stage it’s the hormones that produce and direct the show.

  • Emily Wells

    OK, not being a scientist I’ve obviously missed something somewhere along the way. Keeping things simple, if you have “XY” chromosomes after the formation of the testis, post 7 weeks in utero, a massive amount of testosterone is released that masculinises the brain and causes the body to develop with male characteristics. Right? Now, more testosterone is again released again just after birth and more masculinity of the brain and body occurs. Right?

    So, if all this testosterone masculinises the brain, why do I have a gender identity set in my brain that is not masculine though rather feminine (i.e. Gender Dysphoria)?

    • Renee Wal

      I agree Emily this Article Doesn’t explain WHY?? I’m Trans it’s just basic Biology!!

    • BrookeWyvers

      What I got out of the story is that perhaps; some brains were not masculinized when they were newborns. And thus that baby was not “locked-into” the classic masculine behavior which the burst of newborn testosterone provides.

      In addition, the story reports that “estrogen produces female sexual behavior only in adult mice whose brains were not masculinized”. While at the same time we read that “development of female behavior does not require estrogen”.

      So it would seem that if my newborn body did not produce that “testosterone burst” I would then be (biologically at least) free to develop/exhibit either (or both) classical gender expressions.

      Extrapolating now; Then later in life I might choose HRT to better present the outer me, that I feel better matches the inner me. In other words, HRT won’t feminize the already feminine inner me, but will change the visual presentation of the outer masculine me… Wow, I just love having been given the choice!

      • Emily Wells

        Thankyou Brooke. That does make sense; however I am not sure how some brains of those with XY chromosomes were not masculinised in the first instance – unless the testis didn’t develop.

        • BrookeWyvers

          Thank you Emily. here’s my theory:

          My XY chromosomes pulled the trigger on the “testosterone gun” twice.

          The first time it fired was after 7 weeks in utero, BOOM! I have testicals (outwardly masculinised).

          The second time my XY chromosomes pulled the testosterone trigger after birth, nothing happened. Or as I would rather think… I dodged the bullet 🙂