diff --git a/content/post/biological-sex.md b/content/post/biological-sex.md
new file mode 100644
index 0000000..ecac589
--- /dev/null
+++ b/content/post/biological-sex.md
@@ -0,0 +1,236 @@
++++
+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](https://en.wikipedia.org/wiki/Caster_Semenya) or
+[Dutee Chand](https://en.wikipedia.org/wiki/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](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2190741/)
+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"