If Biological Sex Matters, so must Our Perception of Sex

What is a woman? That once-simple but now-controversial question divided opinion in the 2024 Paris Olympics, where boxers Imane Khelif and Lin Yu-ting both won gold medals. The International Boxing Federation had previously excluded them from women’s boxing, reportedly because they have XY chromosomes, denoting them as males. But the International Olympic Committee saw things differently. IOC spokesman Mark Adams claimed that, “They are women in their passports and it’s stated that this is the case, that they are female.”

To be clear, this was not a transgender issue. Khelif and Lin are alleged to have an intersex condition — a difference of sexual development. The political stand-off was familiar enough, however. The defenders of biology clustered on one side of the ring, while those guarding the right to self-identify stood in the other. But amidst the emotion and the rhetoric, what are these groups trying to argue?

As a transsexual, I have a personal stake in the ongoing dispute. Though born male, I transitioned at age 44 in 2012 and, after gender reassignment surgery in 2016, there is no going back — certainly not to how things were. I’ve since come to realise that I was never a woman trapped in a man’s body. The truth that I discovered about myself is far more interesting, and it has helped me to understand and explain why neither “Team Biological Sex” nor “Team Gender Identity” can prevail alone. Biological sex does matter. But crucially, the perception of sex, which is just as much a product of our biology, also matters — and in many situations, it matters more.

Both sides make passionate statements about what the word “woman” (and “man”) ought to mean. In recent years, trans activists have persuaded governments and authorities that those words should denote self-declared “gender identity.” I think that’s a mistake, and when I pointed that out in 2017, I was branded a heretic and lost a lot of friends. Meanwhile, those on the other end of the issue in the “gender-critical” camp have made the case that “woman” and “man” should be carefully defined in terms of the reproductive process: chromosomes, gonads, and genitals. For a while, I agreed with them, but I’ve since come to think that they are also wrong and, following that, became a heretic for a second time. But the impact on my life was rather more profound than being ejected from Facebook groups and finding myself blocked on Twitter.

From the fall of 2017, trans activists found out where I worked and complained to my employer. As a teacher, they reasoned that by rejecting the concept of gender identity, I posed a “danger” to trans kids. When my school principal took no action against me, they contacted the city safeguarding officer. Meanwhile, according to tweets that tagged me and the school, we had both been reported to the Teaching Regulation Agency — a government organisation in the UK that has the power to remove us from the teaching profession. Thankfully, my principal stood by me — otherwise my career in teaching (and my livelihood) might have been over.

More recently, gender-critical activists have fired in complaints about me. Their concern is also the impact on children, but for different reasons. I have been accused of parading a “sexual fetish” in the classroom. In their minds, I am a man who derives specific sexual excitement from dressing as a woman. The reality is rather more mundane. Like most other people, I wear the clothes in which I feel comfortable and confident — in my case, usually those marketed at women. But what I happen to be wearing is incidental, as indeed is my transsexualism. What matters in teaching is my ability to teach well and facilitate the effective learning of my students.

The two groups that have taken issue with me both assert what the words “woman” and “man” should mean (in their opinion), but both miss the point because they overlook what goes on in our minds when we use those words.

We were using “man” and “woman” — quite successfully — to label the two types of adult human before gender identity was coined by Robert Stoller and Ralph Greenson in 1963. In fact, we have been using them and their linguistic equivalents since time immemorial, and long before Nettie Stevens discovered sex chromosomes in 1905 or Antonie van Leeuwenhoek first observed spermatozoa in 1677. Rishi Sunak — former British prime minister — came close when he told his party that, “A man is a man and a woman is a woman. That’s just common sense.” Indeed it is, but perhaps not as Sunak imagined. Common (i.e., shared) sense predates our knowledge of biology: it’s a gut feeling, though perhaps “evolved instinct” describes it more scientifically. In fact, species across the animal kingdom can differentiate between their males and females without scientific knowledge — presumably by the same evolved instinct — so why should human beings be any different?

Sex is crucial, but to understand the human condition, we must also consider the perception of sex. In many situations, perception is what really matters, and I do not think we will resolve this polarised and sometimes toxic dispute until that point is accepted and understood. Where the two Olympic boxers are concerned, campaigners who perceived them to be men felt a grave sense of injustice occurring in the boxing ring. When attempts were made to exclude these boxers, those who perceived them to be women responded with outrage. Through the lens of perception, we can appreciate why opinions are so strongly held on both sides.

For most of human history, those perceptions would have arisen from our five senses at close range — when we first meet someone, we identify their sex based on how they look, sound, and, in the most intimate settings, even how they smell and feel. We might not consciously know exactly how we do it, but we all do it.

However, we evolved to do this in person and at close quarters. We have since invented communication at a distance, but our instincts hardly shifted. Evidence can now be second-hand, patchy, and unreliable, but our minds nonetheless wish to call a binary decision — is this a woman or a man? Once that dichotomy is broken, our thoughts become hostage to our feelings.

So, when people use the word “woman”, it’s important to distinguish between “adult human female” and the perception of an adult human female. Almost all the time, those two categories are the same, but the distinction is crucial to understanding the rows like the one over the intersex boxers and passionate debate over what it means to be trans and how trans people should be accommodated in society.

To help explain why perception matters so much, let’s consider something that doesn’t tend to raise strong feelings — the colour yellow. As a physicist, I think that yellow light ought to refer to electromagnetic waves with wavelengths between about 570 and 580 nanometres. We might dispute the precise boundaries, but we can agree that yellow is not blue, red, or green. Those words have meaning — colours cannot choose to identify as another colour. Yet, if you’re reading this on an electronic device, anything on the screen that you perceive to be yellow is actually a mixture of red and green light — modern LCD screens are an array of red, green, and blue subpixels. When those photons of light strike your retinas, your red-, green-, and blue-sensitive cones send the same signals to your brain as they would if they were hit by monochromatic light somewhere around 575 nm.

What we convey when we describe an object as yellow is literally a common sense — a feeling in our heads. And no matter how much I cling to my scientific definition of yellow, any campaign to redefine the word strictly in terms of wavelength is unlikely to succeed. Granted, there are situations where wavelength matters most: for example, growing plants under artificial light. But we can be specific with our language in those situations without redefining the word in others.

This is what many gender-critical or “strictly biology” campaigners miss. Just as with “yellow”, when people use the words “woman” and “man”, they are very often not referring to a biological fact, but to that built-in perception of sex we all share. Acknowledging it might remove some heat from the debate. For example, with the dispute over the boxers — and sports categories in general — we could look beyond the words “man” and “woman.” Those terms refer to how Khelif and Lin are perceived by others. Sports are not divided because of perception, but because one sex has an objective advantage over the other, and sex arises in our chromosomes. Most of us are either XX or XY, and, where sports are concerned, that’s what really matters.

Intersex people can be assessed according to their specific and diagnosable difference of sexual development. It might be that women with CAIS, whose bodies are insensitive to the testosterone produced by their internal testes, could be eligible for women’s sports, while males born with rare genetic conditions like 5-alpha reductase deficiency that may make them appear to be women are not. That latter group — reported to include the runner Caster Semenya — can also be perceived to be female at birth and brought up as girls, but crucially, their bodies respond to testosterone during puberty, and they can therefore develop male advantages. There are a limited number of intersex conditions. Each one can be assessed in turn without depending on who our perceptions might tell us is a woman.

The one group that certainly should be excluded from women’s sports are typical males, and that includes trans women. The reason I transitioned was rather less to do with some ethereal gendered soul, and more to do with my sexuality, my self-image, and how I wanted to be perceived by others. I think that is rather more typical than many male transitioners would care to admit.

Sexuality is usually understood to be attraction to one sex or the other, or both in the case of bisexuality. But sexual attraction is also rooted in perception. People don’t directly sense chromosomes or gametes, nor can they detect anyone else’s internal sense of self. Straight men, for example, might have different preferences, but they are all attracted to the perceptual cues of the female form. That need not be an actual woman. The success of the porn industry is testament to that — computer generated images can produce the excitement of flesh and blood. But generally, the focus of their sexual interest is external to themselves.

If, however, that sexual focus is turned inwards in such a way that a heterosexual man is attracted to the thought of himself as a woman, it’s known as autogynephilia, or AGP. This isn’t as strange as it seems at first glance: sexuality and self-image are related. I’ve experienced AGP firsthand. The problem was that while I am heterosexual and attracted to women, my body was lamentably male. The urge to “transition” into something that better matched my mental image of an attractive female body overwhelmed me. At the same age at which other men’s midlife sex drives lead to extramarital affairs, I transitioned. Perhaps I had my affair with myself?

Admitting, describing, and explaining that truth provoked a frenzied response from erstwhile friends who I suspect fitted the AGP mould. I was accosted in person and cancelled online, which, while unfortunate, was understandable. It’s easy to seek sympathy if your claim is that you’re a woman trapped in a man’s body — saying you transitioned because you were a man who fancied a female image of himself is a much harder sell. Which trans woman wants to admit that? My explanations were therefore unwelcome and furiously denied.

Gender-critical campaigners can be wary of AGP for different reasons. Firstly, when the interactions are purely online, there is no reason for them to perceive me as anything but a man. But then, the thought of men in dresses (which I do wear occasionally) can generate negative emotions. Secondly, autogynephilic males can become parodies of the female form, as evidenced by too many egregious social media posts of AGP males with short skirts, high heels, and way too much makeup.

Whatever the reason that drives an individual to transition, it doesn’t change their sex. But we don’t need to change sex to change the way that we are perceived by other people. Gender transition is therefore a meaningful process. That can be controversial on both sides of the dispute. Trans activists fearful of medical gatekeeping might claim that you don’t need to transition to be trans. Some gender-critical campaigners, on the other hand, dismiss the concept altogether — “you were a man, Debbie, and you are still a man” — and posit that nothing changed. But perceptions — at least in real life — did change, and the repercussions are felt more widely than in the narrow area of sports. Society also divides for toilets and changing rooms. We would not be human if we did not feel differently in the company of women than we do in the company of men. Or more precisely, people whom we perceive to be women and men.

Personally, I don’t use spaces reserved for women because it wouldn’t feel right; however, using men’s spaces would introduce discomfort of another kind. My body really doesn’t look like a man’s these days, so demanding that men accept me as another guy in their spaces misses the point. Our minds evolved to perceive the two different types of bodies humans inhabit, and we react differently to them. Millions of years of evolutionary history have seen to that. The humane case is for (private) third spaces for anyone who prefers not to share communal facilities with their own sex. Trans activists might have been wiser to adopt that campaign from the beginning.

The current trans debate is nasty and sometimes brutal. That’s not surprising when both sides fear their opponents might succeed in redefining woman and man, and consequently the way we relate to each other. The stakes appear to be enormous, but everyone should relax. Reality is not constructed from words. Words might convey our feelings, but those feelings cannot be easily changed — we are stuck with our perception of sex just like we are stuck with our perception of yellow. Attempts from both camps to deny our perception of sex will not succeed.

However, the debate over what it means to be a woman or a man has perhaps served as a good preparation for what might well come next: the debate over what it means to be human. Humanoid robots have long featured in science fiction, and just like C-3PO from Star Wars (1977) was a “man” and T-X from Terminator 3 (2003) was a “woman”, there may one day be androids (“man” robots) and gynoids (“woman” robots) who walk amongst us. This is not a difficult prophecy — men will build them if only to have sex with them. Besides, we already use those words to convey intelligible meanings independently of biological life forms with chromosomes and gametes, like “the woman in my satnav.”

In the present dispute, both sides make unfalsifiable claims about the definition of the words “woman”and “man”, and merely assert what they think those words ought to mean. My claim about perception, on the other hand, will be testable — and falsifiable — by analogy. How will society treat humanoid robots who are widely perceived as male or female?

Robots might never need to use the toilet, but they could need to change their clothes. Would they do that in the street? They are, after all, merely ambulating computers. Or would they use a more private space? It might not bother the robot — that would depend on their programming — but it would probably bother the human beings watching, and that will matter. Further, despite having neither chromosomes nor gender identities, these machines will be referred to consistently by the appropriate pronoun, “he” or “she”, because common sense dictates that a woman is someone whom we perceive to be a woman. That’s what our instincts tell us, and those instincts are beyond ancient and resistant to change.

My argument about why sex and perception of sex both matter will not please either side in the current debate, and that may be all the more reason why it’s needed. Evolution has moulded our minds as well as our bodies. While the charge of denying biological science has rightly been levelled at the more extreme trans activists, those who ignore evolved human psychology in arguments around trans issues might be guilty of a second form of biology denialism. Are they brave enough to consider that they might also be wrong?

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By Debbie Hayton

* This article was first published by Queer Majority on 16 June 2025: If Biological Sex Matters, so must Our Perception of Sex.