Everyone has the same genitals for roughly the first two months in the womb, a small bud, two outer folds, two inner folds and a groove. Hormones then steer those structures in one direction or another. Breasts and faces follow the same pattern, so gender-affirming care works with tissue that could always develop either way.
I am starting a new series on how gender-affirming surgeries work, and I wanted to begin at the very beginning, before any surgery, before puberty and before birth. The first thing to know is that human bodies are far more alike than they are different. It is also the idea I come back to most when I am explaining this subject, because it makes so much of it simpler.
What do all bodies have in common in the womb?
For roughly the first two months of life in the womb, every single one of us has exactly the same genitals. There is a small bud called the genital tubercle. On either side of it sit two outer folds of tissue, then two inner folds, and a little groove runs underneath.
That is the whole starting kit, and it is the same for everyone. Nobody begins with a penis and nobody begins with a vulva. Everybody begins with the same few structures, waiting to see what happens next.
How do hormones shape the genitals?
Then hormones arrive in the womb, and those same structures develop in one direction or the other. Sometimes, where the hormones are not doing their usual work, they develop in neither, which I will come back to below.
The tubercle becomes either the head of the penis or the clitoris. The outer folds become either the scrotum or the labia majora. The inner folds either close over the urethra, the tube that carries urine, to form the underside of the penis, or they stay open as the labia minora.
So the clitoris and the head of the penis are the same tissue, and so are the scrotum and the labia majora. Each pairing is one structure that took a different route. Once you have seen it laid out like that, it is hard to unsee.
Are breasts the same story?
They are. Everyone has breast tissue. Everyone has nipples, milk ducts and a little glandular tissue behind them. What happens at puberty depends on which hormones are in charge: oestrogen drives the tissue to grow into breasts, and in the presence of testosterone it mostly does not.
This is why the answer to "can this tissue respond?" is so often yes. Many cis men develop some breast tissue at some point, and many trans women develop breasts on oestrogen. The tissue was always there and always capable.
What about faces, voices and the rest of the body?
Faces work in much the same way. Every face is built from the same set of bones. Testosterone and oestrogen simply tell those bones, along with the voice box, the muscles and the fat, to grow in different ways during puberty.
That gives us the familiar differences: how the brow and jaw develop, how deep the voice becomes, where fat is stored, how much muscle is built. These are different instructions given to the same underlying parts. It also explains something I hear from many trans people, which is that a puberty driven by the wrong hormones leaves changes that hormone treatment later cannot fully undo. A deepened voice does not rise again on oestrogen, for example, and bones that have finished growing stay as they are. That is a big part of why this series covers voices and facial surgery as well as the more obvious topics.
What happens when hormones do not follow the usual pattern?
Not everyone develops along one of two clean lines. Some people have bodies that develop in between, or differently from what you would expect, because the hormones in the womb were different or the tissue responded differently. These are often called intersex variations, and they are a natural part of human variety, not a mistake to be corrected.
They are also a very good reminder of how flexible the original tissue is. If the same structures can take more than two shapes before birth, then it is hardly surprising that people have such different relationships with the bodies they end up with.
Does anatomy decide who somebody is?
No. Genitals, chromosomes, breasts and hormones do not determine gender. A trans woman is a woman and a trans man is a man, and non-binary people exist, whatever their bodies look like. Some women have a penis and some men can become pregnant. This series is about bodies, and what we know about bodies, but it is not an argument about identity. Nobody needs a particular body to be who they are.
What the shared starting point does tell us is that there is nothing unnatural about wanting your body to develop differently from the way it did, or about medicine helping it do so.
Why does this matter for gender-affirming surgery and hormones?
This is why I find gender-affirming surgery and hormone treatment so exciting. Surgeons and doctors are not creating something from nothing. They are working with tissue that was always capable of developing either way.
I think that changes how the whole subject feels. It is easy to hear gender-affirming care described as dramatic or extreme, as though it were a departure from nature. It is not: it is skilled, careful work that builds on how bodies already develop, using the same hormones and the same tissues that every body uses anyway. That does not make surgery simple, and it takes real expertise. But it does mean that the foundations are common to all of us.
If you are trans and thinking about surgery, I hope that is reassuring in a practical way. What you are asking for is not exotic, and the body you have is not somehow too far from the one you want. If you are supporting someone who is, I hope it helps you see why their wish makes sense.
What is coming in this series?
Over the series I want to take you through the really clever bits: top surgery, facial surgery, voices, genital surgery, breasts, waists, muscles and fat. Each one starts from the same place as this piece, with what the tissue is, where it comes from and what it can do.
By the end, I hope you will see what I see, which is that human bodies are far more alike than they are different. If any part of this raises questions for you, Sammy is here to talk them through.
If there is a topic that you would like me to cover, just let Sammy know.
Dr Helen Webberley is a Gender Specialist, Medical Educator, writer and advocate.
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