Biological Womanhood

On April 16 2025, the UK supreme court ruled that according to existing UK law, the definition of a woman in equality legislation refers to “a biological woman and biological sex”. This, according to the court, categorically excludes trans women, who have been issued a gender recognition certificate.

This will lead to many problems, and terfs including JK Rowling are celebrating their victory against trans people, and immediately plotting their next moves to keep trans people out of public life. Setting aside the fact that the court refused to allow any transgender people or advocacy groups in to testify, and the danger this puts trans women in, I’d like to write about the way that trans people and researchers are actually talking about these categories.

Sex vs gender

A common way of understanding the transgender experience is to try to distinguish between sex and gender. One might say “sex is immutable, but you can change your gender identity” as a way of explaining what it means to be a woman. Gender as a social construct is an approachable thing to explain. You can explain that blue and pink had opposite gendered meanings back in the day. You can explain that a person’s clothes, hair, makeup, and way of carrying themselves make a difference in how they’re perceived, and that the categories of man and woman are simply societal shortcuts we use to quickly categorize each other. It makes sense that gender identity can be changed, and so it is how many people come to understand what it means to be transgender.

And to be fair, this is the way many trans people understand their own experiences and how they explain it. “I know my chromosomes will never change” is a thing that many will simply admit. Some people’s transition is purely social, with no HRT or surgical intervention. Personally, I identified as transgender and nonbinary for years before I started my hormonal transition. It is an important part of the trans identity, and isn’t to be discounted.

However, I don’t think it’s correct to simply write off “sex is immutable” as some indisputable truth. In reality, biological sex is a cluster of traits that we use to categorize. Sex is absolutely not a binary, and many of these traits are in fact modifiable through modern medicine. I don’t think it is at all unreasonable to say that transsexual women are biological women. Let’s explain why.

What is a woman?

I’ll be focusing on the profile of womanhood for the sake of this discussion, but there are of course corollaries for men. Medically speaking, the sexual characteristics of women consist of the following.

Primary sex characteristics

These are categorized as the female reproductive organs, the ovaries, fallopian tubes, uterus, and vagina. This also includes the rest of the structures of genitalia, such as the labia, the clitoris, and so on.

Secondary sex characteristics

These develop during puberty, such as breast development, wider hips, typically includes menstruation, distribution of body fat into the hips, thighs, and breasts, and typically less body hair.

Hormonal profile

Women typically have an estrogen and progesterone dominant hormone profile, with low (but still present) levels of testosterone.

Chromosomal patterns

Scientists have discovered that several patterns of chromosomes present in women, including XX, XO, XXX, and even XY.

However

Exceptions to all these categories exist. Primary sex characteristics are changeable. Due to health considerations or personal choice, a cisgender woman can modify any and all of her reproductive organs and genitalia without changing her status as a cisgender woman. Intersex people also exist, up to 1.7 percent of the population. They may have ambiguous genitalia, the presence of both testes and ovaries, and many more forms of variation. This is not always obvious at birth, but we still tragically have doctors intervening to “correct” sex traits that contradict our simplistic binary understanding of sex characteristics. And of course, trans women are able to have vaginas, genitalia, and will likely be able to receive uterus transplants as medicine advances.

Reducing women to their reproductive abilities is also harmful to women. There are many reasons that someone may be unable get pregnant. Some women are born without functioning uteruses or ovaries. Someone doesn’t stop being a woman post-menopause, nor are girls not girls until they start to have periods. We are human beings. Our value is intrinsic, whether you believe that is a mandate from god or because it is simply what we morally owe to each other. The logic of sorting humans according to their ability to carry children is deeply rooted in the oppression of women, but that is a conversation for another time.

When it comes to secondary sex characteristics and hormone profiles, these are patently changeable. Trans women grow breasts, our fat redistributes in feminine patterns. Our hair becomes softer and less coarse, and of course many of us pursue cosmetic hair removal like many women choose to in our society, through laser hair removal, IPL, or electrolysis. Not all women menstruate, and a woman who has had a hysterectomy or gone through menopause may cease to menstruate. My own lab results show that my body is now an estrogen dominant body, and my testosterone levels have fallen to those typical for a cisgender woman. These are changeable, and extremely perceptible changes to my sex. People didn’t start using she/her pronouns for me because I started asking them to - they started when I removed my facial hair and grew C cups.

As for chromosomal patterns, this is less mutable, but in general isn’t a level of scrutiny that most people will ever inspect. Chromosome testing involves inspecting 23 pairs of chromosomes visually under a microscope. Other tests involve DNA testing, where the technician will look for DNA expressions that are observed when the XY pair is typically present, which creates a circular reference. In fact, there is ongoing research that demonstrates that DNA expression of sex-based traits can be affected by hormonal transition: pubmed. Beyond that, chromosomes are by far the least accessible aspect of our bodies. Most people will have x-rays, blood work, MRIs or other types of medical tests done, but almost no one will get their chromosomes tested or their DNA sequenced, unless there are notable other symptoms that call for those tests specifically. If we started testing people’s chromosomes en masse, the main outcome is that many people would discover they have otherwise hidden intersex conditions, and would lead to needless identity distress for cisgender people.

Most aspects we can categorize as sex differences are hidden while someone is wearing clothes, and most are addressable through hormonal transition and hair removal. A woman who has undergone FFS, done voice training, and had bottom surgery is functionally indistinguishable from a cisgender woman. Transgender men have body hair and muscle growth, their voices drop, and they often struggle socially even in queer spaces when other queer people are unable to to tell they are trans. The socially relevant aspects of sex are changeable, and we should not allow anyone to pretend that these are immutable characteristics.

The short of it

Biology is not one thing and it is almost never binary. The phrase “biological sex” isn’t scientifically or socially useful, and the extent we continue to use it will only be a detriment to the conversation. It’s a politically correct way of glossing over what we precisely mean, and this will harm all women while allowing authoritarians to police the boundaries of womanhood. Do you never want to see a penis? You should have to say that. Do you not want to see someone with a strong jaw or “too much” facial hair? You should have to say that. Same with having short hair, a flat chest, too small hips, a pronounced adams apple, and so on. What are the specific remedies you’re seeking? How should the wrong women be kept out of women’s spaces?

The thing is, any attempt at excluding trans women will shrink the world of what is possible for cis women at the same time. The hypothetical harm of someone seeing a trans woman in a bathroom and feeling uncomfortable isn’t comparable to the threat of a man with a gun entering into that same safe space and dragging a woman out to be detained or god forbid forcibly inspecting her genitals. And the thing is, this is happening already. A cis woman was recently fired from her job at Walmart after someone called the cops on her for the crime of being too tall and using the bathroom at her own workplace. This starts with so called biology, but it ends with authoritarian dress codes and women being kept out of the workforce. To abandon trans rights is to abandon women’s rights.