What exactly is Sex?

Rebecca Gellman
8 min readJun 29, 2021

No, not like that. Purile teenagers — away with you.

Artistic image of X and Y chromosomes, which Gender Criticals seem to think is the be-all and end-all of sex.
Artistic image of X and Y chromosomes, which Gender Criticals seem to think is the be-all and end-all of sex.

One thing Gender Criticals LOOOOVE to bang on about, is the importance of sex, and more specifically the definition of sex.

There is a reason for this, and of course it’s transphobic. Though, like many things the transphobes haven’t thought it through at all. The basic principle, according to the Gender Criticals, is this:

Your sex is recorded at birth
Your sex is immutable
Your sex is derived from DNA (XX vs XY)
Your sex is based around reproduction
Your sex cannot change, and
Your sex is biological

On this basis, the transphobes will argue that “women’s spaces” are for “women”, rigidly defined as “females” according to the above criteria. But this presents a big problem. As soon as you try to make a definition to fit your ideology, nature has this tendency to get in the way.

Myth: Your Sex Is Recorded At Birth

This might seem counter-intuitive, but think about it. When you are born, nobody does a DNA test. You’re not x-rayed for the presence of ovaries. The doctor looks at what’s between your legs and says “boy” or “girl”. This is then written down as the official record.

So what’s wrong with that? Well, it skips over two problems. First is gender identity (which we’ll get more to in a moment), but more importantly it erases intersex people.

Now Gender Criticals get very, very mad when you talk about intersex people. They’ll bring in all sorts of intersex transphobes to tell you that you’re such a nasty evil nasty terrible horrible nasty horrible person for even daring to contemplate thinking about the word “intersex”.

But, there are plenty of intersex people who would tell those transphobes to do one, too. The fact is, intersex people rarely conform to what someone says their sex should be according to some arbitrary criteria of what genitals you have.

People are presumed a certain sex at birth, and to declare this gospel truth erases the lived experience of intersex people.

Myth: Your Sex is Derived From DNA

A classic argument is that “Men are XY, Women are XX. You can’t change that”. The problem with this argument is that it is a catastrophic failure to understand DNA.

DNA is not a description of the end result. You’re not male because you have a Y chromosome. DNA describes the target of development. Insofar as natural things can have an intent, DNA describes the instructions for development, it does not prescribe that those instructions have been followed to the letter.

A good analogy here is Lego: I can buy a Lego set. Let’s say a spaceship. But if I take those pieces and build a train out of it, and then point to the instructions and say “this is a spaceship, because that’s what I was meant to build”, you’d rightfully think I was a loony (or had some creative ideas on what a spaceship can look like).

So it is with DNA. People rarely have DNA that says “hole in the heart”, and yet many babies are born with such a defect. We don’t tell them “well your DNA says you have this, therefore you do”. That would be madness.

Myth: Your Sex is Derived from your Reproductive Role

Putting aside the elephant in the room of 1950s sexism re-enforcing gender stereotypes of women existing for the purpose of making babies, this also doesn’t work very well.

There are several problems with this argument. Firstly, what of those born with NO reproductive ability? “But they should have!” say the GCs, but then see the DNA problem above.

Then there’s intersex people again. What if you have ovaries AND testicles? Which one of those is the definitive answer as to what is your “biological sex”? It just doesn’t work as a definition.

The last problem with this argument is that humans are not two separate species. Those we typically call males can grow breasts. They can even lactate, but these are not typically male features. They are typically female.

Similarly, women can grow beards. Mustaches. These are not typically female, they are typically male. We’ll come back to these points in a moment.

So what IS sex?

“Sex” as a concept is a human classification. Historically, it has been based on reproductive ability, but only as a simplistic view towards animal behaviour. We can say “you need a male and female to reproduce”, and from that we can identify an example from any given sexually dimorphic species to explain what that would look like.

But what are we actually pointing at? Are we confirming an actual ability to reproduce of that example? Or are we just going “it’s got the right bits, this is the (fe)male” ? In animals, we use the latter, in all but the closest of examinations.

So here we have sex: it is a collection of traits that we can hold up an expectation and say “what fits closest?”. Male genitals? Male size gametes? Male chromosomes? Pretty good bet this is a male. But we’ve prescribed that onto our species sample. We’ve said “it has these things, therefore we classify it as a male”.

Sex is not immutable

We know that we can change sex characteristics. We’ve been doing it since Lily Elbe in 1930. So if we take someone presumed male at birth and change the penis to a vagina, removal all facial hair, supress the testosterone and supplement the estrogen, then we’ve basically changed someone’s sex, in terms of how we classify that person.

We’ve said “given the characteristics that we associated with male and female, this person is closer to female.” A similar process exists for female to male. This is what trans people call a transition. From possessing a set of majority male sex characteristics to possessing a majority female set.

Sex is biological and real

This is the one thing that trans people and Gender Criticals agree on. Nobody trans (at least not with a modicum of knowledge) is trying to claim that sex doesn’t exist or isn’t biological. But the arguments of defining it by DNA, reproductive ability or gamete size are asinine.

But there is one aspect I haven’t covered here, that is the bane of the Gender Critical:

Where does Gender Identity fit into this?

It would be far too easy to read all the above, and just slide gender identity out of the way. And if we were simpler mammals without the ability to communicate thoughts and ideas, this might be viable.

The problem is that as an intelligent species, we have the ability to communicate how we feel.

Before I elaborate on that, I need to remind you of how I define Gender Identity, because this is very often lost on the Gender Criticals:

Gender Identity is the innate knowledge of one’s sex, even if that identity might seem to be in conflict with one’s presumed sex at birth or one’s genetic sex.

Gender Identity itself is not a feeling. But it can cause feelings: If a trans woman is told “you’re a man”, this provokes a feeling of incorrectness: “Are you sure? That doesn’t seem right somehow. It seems like that statement is false.”

Nor is Gender Identity simply putting on a dress, or some idea of a gender role. It’s another product of the development not following the DNA plan.

When nature goes wrong

The brain is a very complicated organ. I think we can all agree on that. While it’s been conclusively proven there is no difference in overall brain structure between men and women, it has been similarly proved that brain neurology, that is the way neurons connect within the brain, does differ.

Gender Dysphoria occurs when the body is instructed to develop one way, and the the brain another. This is not a mental disorder because everybody has the ability to develop one way or the other. When the two match, that person is cisgender. When they don’t, they are transgender.

The treatment for this is transition. This is not some wishy-washy idea that’s only be around for a few years. Medical professionals (in questionable fields) have tried persuading the mind to conform to the body, but when gender identity isn’t a mental disorder, there’s no way to “cure” it.

After decades of conversion therapy, medical professionals finally learned the way forward is to make the body match the mind, insofar as is possible with current medical technology.

When does sex A become sex B?

This leads to a problematic question for Gender Criticals: If we accept that sex is a classification, then we accept that a transitioned trans woman is a woman. This leads to a problem: If we accept that, why, as an intelligence species with compassion, do we not accept them as a woman before that point?

This is why in a modern society, we do accept self-id, because we place the value of sentience above physical characteristics. We may say that when a trans woman begins her transition she is closer in sex to a man, but we compassionately agree that her gender, that is her autonomous gender identity is of more value.

But it is all binary, right?

Nope. While sex as a classification is a little fuzzy in terms of classifying people to one side or another (mostly for historical reasons), intersex people do exist and do bring this “binary” paradigm crashing down.

When we factor in gender identity, which can develop some parts of the brain one way, others another (non-binary). Or develop the brain neurology in such a way that it is not static (genderfluid), or in a way that has no similarity to any established gender neurological pattern (agender), or sometimes such an intermingled mesh of developments that both gender identities assert themselves (bigender), or even more (pangender).

The idea that humans can be classified as “binary” according to sex or gender is ludicrous. Sorry Gender Criticals, but nature just isn’t playing your game here.

So why do Gender Criticals even care?

As always, the base reason is about exclusion. If Gender Criticals can define sex, gender or any other classification they feel is useful, in such as way as to exclude trans women, then they feel they have a bargaining chip.

Don’t want trans women in “women’s spaces”? No problem.. just define “woman” in such as way as to exclude them, then protest when it happens anyway.

This is another reason why the “safety” argument doesn’t work. What do we define as the unsafe factor?

If it’s the presence of male genitals, then you’re excluding intersex people who have lived all their life as women.

If it’s the presence of testosterone then you’re excluding anyone with a high testosterone level, even if they are a cis woman.

If it’s presumed sex at birth, then you’re prejudicially saying all cis women are safe and all trans women are dangerous (which is a preposterous proposition at the best of times).

Plus, the safety argument is already null and void: The UK has had self-id for access since 2010, with no effect on women’s safety. This doesn’t mean every single trans person is an angel, just that there has been no statistically significant change in levels of sexual assault as a result. This has been proven empirically.

Additionally, other countries that have self-id, and even the GRA reforms that trans people are calling for, including our nearest neighbour Ireland (5 years and counting) have also had no issues.

The safety argument is simply a non-starter.


There is no definition of sex that conveniently excludes trans women and includes cis women without unfairly excluding some other group.

There is no way to factor in “transsexuals” in a way that doesn’t dehumanise the person by reducing their sex to whether they’ve had Gender Confirmation Surgery or not.

We define sex as having specific sex characteristics, and we compassionately accept gender identity because we are human beings. To do otherwise is to reject humanity.

Perhaps in a future world, we may not even care about sex, except for reproduction.

Perhaps in a further future world we may not even care for that purpose.



Rebecca Gellman

A nerd, software engineer and trans woman, fed up with the lies pushed by the so-called Gender Critical movement. Also on Mastodon: @GellmanRebecca@home.social