Let's talk about "biological" sex, baby
Sex is not binary. It's past time to stop pretending it is.
The “traditional” differentiation of sex and gender as two intertwined concepts came in the 1960s. Before that, gender was just a grammatical term.
Sex: biological and physiological characteristics that define male and female
Gender: Socially-constructed roles, behaviors, activities, and attributes that a society consideres appropriate for men vs women
For example, if I walk down the street, into a café, or give a lecture to strangers, everyone sees a man. I walk like a man, talk like a man, and live like a man. Society decides what “like a man” means, and that meaning fits into this concept of gender. No one actually knows what other people have in their pants!
This separation of sex and gender was useful in the (White) women’s movement. It allowed women to say, “Hey, we aren’t ‘stuck in the kitchen’ because of our biology (sex). No, it’s because of social norms. It’s culture (gender). And if it’s culture, we can change it.”
It’s been and still is an incredibly useful distinction in fighting for gender equality for women. It’s also useful to understand transgender people, when sex and gender are incongruent.
In January 2025, the federal government removed gender and denied that it exists. It said there is only sex and that there are only two sexes: female and male.
This is harmful to everyone. It is harmful to women’s bodily autonomy. It is harmful to all LGBTQI people.
Moreover, to claim that sex is binary is scientifically and biologically wrong.
Let’s look at how.
Sex, the biological aspect, is not one thing. Sex is made up of multiple dimensions that play out across time from fetal development through puberty.
I rely heavily on Anne Fausto-Sterling’s work here, especially her book Sexing the Body. She has a recent series of posts about this, so if you want in-depth info right from the source, check out her Substack!
In no particular order:
First, we have chromosomes, XX for females and XY for males, right? Yes, but we also have many other combinations. We have XO (Turner’s syndrome), XYY, XXXY (Klinefelter’s syndrome), and more. Moreover, some males have XX, but the SRY gene—the gene that turns on the development to maleness—just happened to be on the X gene instead of the Y gene. And some people have XY chromosomes, but can’t process testosterone (androgen insensitivity syndrome, AIS), so they are assigned female at birth.
Second, we have hormones, both in the womb (fetal development) and at puberty. Scientists named estrogen and testosterone as “sex hormones” when they thought women had only estrogen and men had only testosterone. But they were wrong! Everyone has both, just at different levels. Ovaries produce both estrogen and testosterone. Testes produce testosterone, which the body then converts into estrogen. Progestorone is also involved. If you measured everyone’s hormones and divided them up by commonality in hormone levels, you’d have two groups: pregnant people and everyone else! We specify clinically “normal” levels, but overlaps in men and women exist. Some women have higher testosterone levels than some men.
Third, we have internal reproductive organs such as the uterus, prostate, and gonads (ovaries and testes). But gonads can be half testes/half ovary, underdeveloped, or missing. Also, what’s on the inside doesn’t always match what’s on the outside.
Which brings us to external reproductive organs, our fourth dimension. In other words, our genitals. This is the one dimension of sex we use when a baby is born to determine “it’s a girl!” or “it’s a boy!” It’s the only one we can see at birth. But sometimes the organs can be ambiguous—you can’t determine clearly if it’s a girl or a boy. Also, external parts don’t always align with chromosomes, hormones, and internal organs.
As I mentioned above, a woman with AIS will be declared a girl at birth but have testes and no uterus inside. And at puberty, she won’t develop secondary sex characteristics, our fifth dimension. These are the things that show up in puberty, such as facial and body hair, menses, breasts, broad shoulders, wide hips, etc. Even here, though, we have overlap. Some women have facial hair; some men don’t. Some women have deep voices; some men have high voices. Lastly, men can develop breasts, a condition called gynecomastia. The most common gender-affirming surgery is breast reduction in cisgender men!
None of these dimensions is binary; they are all spectrums. Where along a spectrum we divide female from male is a societal choice. Sex can and does often differ from one dimension to the next. When it differs, as in all the dimensions, do not align as strictly female or male, we call that intersex.
There’s disagreement about how many of us are intersex, largely depending on what you count as intersex vs. not. An early definition restricted it only to people who have gonads that are half testes/half ovaries. That’s quite rare, and frankly, an arbitrary decision. I accept a broader definition of intersex that can include any of the various combinations of the five dimensions. With an inclusive definition, intersex people may be as common as 1.7% of the population—as common as people with red hair.
Determining who is “really” female and male is fraught, and I’m not even talking about trans people here. If you divide people up into two groups by one of these dimensions, it won’t match the division if done by any other dimension. No single dimension can accurately determine binary sex—because it doesn’t exist. The Olympics stopped doing chromosome testing to determine sex because it unfairly excluded some women and caused distress to some people who newly learned they were intersex. (A colleague made this tongue-in-cheek “pissport” to satirize how inaccurate the claim about only two sexes is. )
This isn’t just a biology lesson. This is about bodily autonomy, gender equality, women’s rights, and trans and intersex rights. The federal government knows this. The EOs are aimed at hurting us. Having accurate information is just the first step in fighting back.
This is the most exceptionally sophisticated, and thoroughly written, article on this topic that I have ever read to date. 💯 Thank you trillions of times over for your meticulously beautiful explanation. I hope the right people read, and more importantly understand your words. 💓💓💓
This is a fascinating subject. Yes I'm glad you showed how there are 6 basic chromosomal patterns which they generally start with (not just XY and XX). And that is really only the beginning of discussion. And of course men and women both have sex hormones. Males and females both have estrogen and testosterone. However the levels are going to vary depending on the individual. The way the government is characterizing and limiting variation in sex and gender identity is harmful and ignorant. It is easy to see that Trump and his people want to structure society where anyone deviating from the "normal" pattern of male and female is excluded. They have already structured how we characterize male and female with the intention of denying any variation in sex. Gender identity is offered as only two strict narrow choices.
When I first started seeing my current transgender doctor, she asked me if I had an orchiectomy done (which is a surgical procedure removing the testicles). Because my testosterone level was very low and just about non-existent. I told her no and it was just the use of the medicines I was on which gave this result. And she explained that even cisgender women will normally have some testosterone. And in my case the level was too low even for a cisgender woman. She also explained that when my testosterone level was so extremely low I could actually be tired and not function well. Which was probably the case. So she cut back one of my anti-androgens to rebalance things. But the point I'm making is that although I was born a biological male, I am hormonally and neurochemically no longer one. While all the changes from puberty have not been reversed, I am biologically no longer male. This also does not account for changes in my brain which I'm sure have happened. The human brain is capable of neuroplasticity. And they are finding out even late in life change is possible. This has been documented in all kinds of ways from research on people who have had brain injuries into adulthood (studies on topics including phantom limb, aphasia, and other speech-related impediments from brain injury, for example). Situations where the human brain needs time to recover and will essentially rewire itself back to baseline levels.
Whatever the government decides to say, I know that I'm female. And my lab work bears that out. And my transitioning is a matter of having my body catch up with that fact. But our bodies and brains do change if we begin a medical transition involving the use of hormones. Transgender men will use testosterone, and that has a profound effect on their bodies. I have seen transgender men with beards and a beautiful gym rat buff body. They look nothing like the girls they were born as. And as a society we need to accept them. Denying science and trying to prescriptively relegate sexual variation down to strictly two sexes (from birth) is to deny and ignore the experience of some people in our populations (both myself and the writer of this post).
This is a fascinating topic. Not just for people that are transgender. But anyone trying to understand the human experience and how our bodies work. And how anomalies and aberrations occur in science and the natural world. I don't identify as intersex because I was born with genitals that appear in line and normal for a biological male. But I truly believe that we transgender people are essentially intersex in that we start out with built-in differences in our brains. And then problems start for us because our bodies do not match our sense of self and so on.
Both men and women have hormonal regulation which can sometimes show differences but still share similarities. Even hormones generally discussed as part of women's functioning have a role in men's health. The lines can be blurred depending on the function of the specific hormone and neurochemical process. For example, both men and women produce oxytocin. Oxytocin is normally discussed in regard to childbirth and women's uterine contractions. But there are all kinds of details to learn just for this one hormone alone. Men release oxytocin during sexual activity. Then there are other hormones such as prolactin, which has a role in women's lactating and breast function. And there are medicines that will affect the level of prolactin even in males (and may affect breast growth resulting in gynomastia). Such is the case with some antipsychotic or mood regulating psychiatric medicines.
Thanks for a great article.