website/content/post/biological-sex.md

+++ title = "Biological sex" date = "2019-12-23" tags = ["biology"] +++

DRAFT

"Biological Sex"

This is a term I've been bumping up against on various online communities recently - usually in discussions about (or, more accurately, against) trans people, but it shows up in other contexts too.

Being a (lapsed) biologist, I have Opinions about this term. Rather than repeat the same case over and over again in these discussions, I'm laying it out here for easy linking, and to act as a sort of persistent memory of my conversations on this topic. If I've linked you to this page, you've probably used the term where I could hear you, and I am now grumpy at you. This is easily resolved - read the page, think carefully about its implications for what you are saying, and act or respond accordingly. If you think the positions or ideas on this page - either my own, or those I'm representing on behalf of others - need changes, let me know. We can talk about it.

Anyway, what is "biological sex"?

The people using it seem to want a static label for people - "male" or "female" (sometimes "hermaphrodite" is recognised, sometimes not). The categories and their immutability are asserted because "sex is biological". As a (very sad, purely coincidental, honest guv) consequence, trans men aren't, and neither are trans women. Gender theory is entirely bypassed - you are your biological sex (curiously, this is usually identical to the gender you were assigned at birth), and you will be that forever. There is no point to reassignment surgery, and your pronouns absolutely must be determined from this datum, as must the bathroom you use, the sports competitions you take part in, and the systemic biases or privileges you suffer or benefit from.

This position is upsetting to various people, and I don't like it myself, but as a biologist, I have a very specific question - which definition of "biological sex" are we using here?

That animals (and, by extension, humans) have multiple sexes is definitely not in doubt, but for biologists, the term means different things in different contexts . Even when restricting the discussion to just humans, we can talk about sex as a genotypical, phenotypical, or even neurotypical attribute. Biologists may assign one person to different categories for each definition, depending on circumstances.

Which definition were you thinking of when you said "biological sex" to me? Maybe jump straight to that section. If you weren't thinking of one at all, maybe you've got a problem - start at the top. If you were thinking of one that I've not listed, maybe I've got a problem - tell me about it.

Genotype

In this model of biological sex, men are XY, women are XX, and you can work out which sex you are by karyotyping. Anyone can do it - all you need is a swab, a light microscope, and a bit of stain. It's irrefutable. Sorry, trans people - if your karyotype disagrees with your feelings, that's just reality come to call. This is probably what most people implicitly think of when talking about biological sex.

The biggest question I have about this model is why we would use it in the first place. Fundamentally - why does it matter what karyotype people are? How does this characteristic feed into decisions people make about other people when, even though it's so easy and simple to do, karyotyping is almost never done, and plays almost no role in human social interaction? Why do we pick this attribute? To me, it looks like it's just a fairly good proxy for things that people care about, rather than being the cared-about thing itself.

Note that there are other possible sets of sex chromosomes in humans. There are, in fact, six reasonably-common permutations:

• XX - Female
• XY - Male
• X - Turner's syndrome
• XXY - Klinefelter's syndrome
• XYY - XYY syndrome
• XXYY - XXYY syndrome

Approaches to managing this extra complexity vary - you could declare there are more than two biological sexes, for instance, or that being biologically male is all about having at-least-one Y chromosome. The former is very uncommon, but if karyotype itself matters, rather than being a proxy for something, I'd expect people to take it.

Some examples of outliers may be instructive here. Yes, outliers. Theories are tested against anomalous data - Einstein's model of gravity works where Newton's doesn't, and we'll all be much happier when we find something that works where both fail. If biological sex is a biological concept, it needs to run the same gauntlet.

To pick on sports performance for a moment - we don't actually know which karyotypes Caster Semenya or Dutee Chand have, but measures against them have focused on other attributes, like testosterone levels. Being uncharitable to the IAAF, this suggests to me that they have an XX karyotype, but the governing body still isn't happy with them competing. In any case, we can certainly imagine athletes like them existing with an XX karyotype.

Why don't we karyotype all athletes and use that as the sole basis of sex here? Would that solve all these issues, in your view?

Another example: if a person who is a mosaic of X and XY cells has given birth to a child, what is the biological sex of the parent, and are they a mother, or a father?

Yup, people can be several different karyotypes at the same time. Does this mean that they're multiple sexes at the same time? Do we take the most prevalent karyotype? Are different parts of them different sexes? How does this feed into policy?

This person is almost entirely XY-karyotype. Does this mean they're male, and should be treated as such? If not, why not?

For some reason, despite the fact that a simple karyotype would have returned XY, this person was assigned female at birth. They grew up as a woman, and had a baby in due course via the usual mechanisms. I don't know if they were into sport or not, though.

Are they, then, a woman? If not, why not?

If you're thinking something along the lines of "congratulations, he's a new father, but I really think he should stop entering women's bathrooms and sports competitions" - well, you're consistent, at least, but please do tell me why you think karyotype should determine this, because I can't think of a good reason for it.

Most people either already knew, or are perhaps now in the process of realising, that this version of biological sex doesn't encapsulate their beliefs at all. Which leads us on to...

Phenotype

Genotype plus interaction with environment equals phenotype. This is a very broad statement, but out of it falls all of developmental biology, morphology, etc. Typically, but not always, XX people will have no penis, but breasts, vagina and womb; cyclical oestrogen; and low testosterone. XY people will typically have a penis but no breasts, vagina, or womb; fairly stable oestrogen; and higher levels of testosterone. I submit that this is the kind of thing people generally mean when they talk about biological sex, even though they're thinking about genotype.

In support of this submission, note that this tidies up the outlier we found earlier - now an XY person who is "phenotypically female" can give birth and enter women's bathrooms without contradiction - and this is what people actually use, instead of karyotyping, to assign gender most of the time.

However, we need to let go of something very important here. Unlike genotype, phenotype can - and invariably does - change over time. By moving away from "genotype", we have lost the part of "biological sex" that was initially most attractive about it in the context of this discussion - immutability. Suddenly, one's "biological sex" is mutable, and it can change - or be changed - over time.

Hopefully the implications of that are clear, but there are a few angles that should be specifically addressed.

"Only your phenotype at birth matters"

Why? I was born with two legs, but if one comes off somehow, my phenotype is now "one-legged". This is not negotiable. Treating me as if I have two legs, just because I was born with two, is not going to be good for me, and you're going to look like a right prick at airport security when you take my crutch away.

"Reproduction is the key part of the phenotype"

Is it? Is it really? How do we account for people who are capable of reproducing, but choose not to? Or infertile people? Do women stop being women at menopause? Do men stop being men post-vasectomy? What do they become, if so?

What elevates this one aspect of human experience into the determinative one, anyway? On whose authority? Note that evolutionary teleology is not an answer.

"Trans women phenotypes are not identical to cis women phenotypes"

Certainly true. In other, entirely unrelated news, rich women phenotypes are not identical to poor women phenotypes.

This objection is often a repetition of "Reproduction is the key part of the phenotype", so you might want to read that as well.

"You're making it far too complicated, biological sex is just common sense"

Appeals to common sense are a particularly pernicious form of conservatism that I have no truck with. There is truthiness to the term "biological sex", but it falls apart upon careful examination. So kindly stop using it.

If you must persist with the general idea, consider using the term "genotypical sex", "phenotypical sex", or some other, more accurate, qualifier, so we can at least start this conversation from a different point in the future.

What attributes determine phenotypical sex anyway?

It's easy to put most people into one sex category or another, phenotypically - as I noted above, penises and vaginas are how assignments are usually made at birth. However, as with genotype, there are instructive outliers here. How do we decide when it's not obvious at first glance, and what does this tell us about "phenotypical sex"?

The obvious first bite is hermaphrodism, or people who have some form of sexual indeterminacy at birth. What we do here is variable - but sometimes includes surgical intervention to make one's phenotype "unambiguous". Often this is a matter of judgement by the surgeon. What happens if they get it wrong? What does it mean to get it wrong?

With adults, the phenotypical cues we use in the street to determine which category we put people into vary - and we quite often get it wrong. For many years, I had long hair. This often caused people to identify me as a woman, leading to embarrassment, confusion, and not a few cases of violence, when they realised their mistake.

Is long hair a biological trait of women, or does culture determine whether long hair connotates one sex or another? I think you know the answer.

Do you now agree that cultural has at least some part in determining what it means to be phenotypically male, or female? If not, why not?

Neurotype

Just as a brief coda - biologists have other definitions of sex, too. One of those is neurotype - the idea that a person's brain may be morphologically male or female (with the same caveats as above). This is mostly a specialism of phenotype, and nobody's resorted to it yet. Maybe I'll get to fill it out in the future.

tl;dr

• Biologists do not have a single concept of sex
• The term "biological sex" elides attributes of genotype and phenotype
• Genotypical sex is only a proxy for phenotypical sex
• The categories of sex found in phenotype are at least partly socially determined
• Although genotypes are fairly immutable, phenotypes are very mutable
• Some people changing their phenotype are trans people
• You cannot short-circuit gender theory by appeal to "biological sex"