I don’t want to see your genitals, and I really, really don’t want to see what fluids your genitals produce

Last night, I was listening to Katy Montgomerie’s latest TERF Wars video while I was supposedly puttering away at a lecture — it’s a nice entertaining mix of laughter and righteous anger — when she mentioned a name I hadn’t heard in a while, Andy Lewis. I banned him for his obnoxious TERFy bullshit way, way back in 2018, and I got a lot of cluck-clucking and tut-tutting from the British sceptic community for it. He’s such a rational fellow, don’t you know. Such an important figure in UK scepticism. He is still ranting away about Adult Human Females now in 2021, I guess, so I took a peek at his blog. He wrote about me just last year! Not just me, though, the main target of his ire was Rebecca Watson, who is still punching all the right buttons.

He was mad because she was using slurs and pointing out that the XX/XY dichotomy is “middle school science” and largely irrelevant in any discussion about human rights. He wants to discuss the True Science, which reveals that there are only males and females, and chortles dismissively at the idea that he and his fellow TERFs would use the XX/XY distinction.

The claim is that this is ‘middle school science’ and that if ‘the fervent believers’ are challenged they ‘will throw their hands in the air, claim it’s too complicated or the data is lying or whatever other excuse they can think of, and continue believing what they believe. And in a statement that we shall come back to, “They came to their belief first, for other reasons, and then attempted to build up science and reason in a way that makes it look like it supports their belief.”

This is a straw man argument because biologists do not define your sex by the chromosomes XX and XY. These chromosome combinations are part of a *sex determining mechanism* in organisms like humans. This mechanism is not universal in life. Birds, for example, have a different chromosomal sex determining mechanism – ZZ/ZW. Birds still have quite distinct males and females though.


In the XX/XY system found in humans, the actual determination mechanism is the SRY gene that is usually, but not always found on the Y chromosome. This gene switches between one of two evolved developmental pathways.

Almost, but not quite. He’s trying to reduce it even further, from a whole chromosome to just a single region on that one chromosome. If only he thought a little deeper about that phrase, “developmental pathways”, because that’s what really matters from a biological perspective — there’s a whole long chain of events that are usually, but not always, in concordance, and there’s a fair bit of wobble in the outcome. It’s not binary at all — as soon as you start dealing with multigenic processes, you open the door to a whole lot of variation.

(By the way, birds aren’t quite so binary, either. Gynandromorphs, anyone? Avian homosexuality? Birds don’t play by your rules, man.)

If not chromosomes, then what is the binary defining character? He plops down in favor of gametes.

Sex is not defined by these chromosomes. Sex arises from the fact that we are evolved sexually reproducing organisms. Sex evolved deep in life’s history and has remained remarkably conserved – although there are many *sex determination mechanisms* in organisms. [Yes? He keeps almost getting it — sex determination in different species is fluid!]

Sex is near universal in eukaryotes and is the ‘the mixing of genomes via meiosis and fusion of gametes’. In multicellular organisms it is almost always done through the joining of unequal size gametes (anisogamy).

It is this fundamental and ancient asymmetry in gametes and the joining together of one of each type that gives rise to the sexes. The small, mobile gamete we class as male and the larger, and immobile one we class as female.

In multicellular organisms like us where anisogamy rules, the *sex determining mechanism* (the SRY gene) is used to switch between two sets of genes that develop different phenotypes to support each gamete type – males and females.

To suggest that there are more than two sexes, or even more extreme, that somehow sex forms a continuum, a distribution or a spectrum is completely incompatible with this view of life and sexual reproduction. (The idea that ‘sex is a spectrum’ is a core part of the credo of gender ideology.)

As usual, he misses the point. He is correct that there are two functional classes of gametes in humans. Generally speaking, an individual can only form one or the other, or none at all. But so what? Am I going to have to provide a semen sample before I’m allowed to use a public restroom? From a policy and social interaction perspective, this is a non-starter.

But most importantly, people are not gametes. Every person is the product of a fusion of two haploid gametes, one large immobile one and one small mobile one, so we start as a mixture of both. We then go through a complex developmental process with many steps that produce the messy diverse multicellular organism that may try to practice mating behavior of one sort or another, or contribute to the upbringing of more messy diploid multicellular organisms, or tries to shape the culture that we use to propagate ourselves. I, for one, do not consider myself a lumbering sperm delivery system, nor do I consider my wife an ambulatory incubator/ovum generator. I am also rather offended that a dilettante with only a superficial knowledge of evolution would think that evolutionary biology can be used to justify such an absurdly reductionist view of humanity.

Yes, I have gonads that produce sperm. It is categorically wrong to think that somehow tells you anything more about my nature, my sexual preferences, or whether I should be allowed to wear a skirt or not.

We see defenders of evolution such as @pzmyers reacting like the worst frothing mouth evangelical preacher when asked to defend the idea that women can have penises.

https://thoughtfreeblogs.com/pharyngula/2018/10/13/why-i-banned-andy-lewis-maria-maclachlan-and-alan-henness/ …

One would have thought that Myers would have taken the opportunity to use this as a quirky way to explain how evolution works and ends up with counterintuitive results. But no. Shouting and screaming instead.

I can only assume that Mr Lewis trusts that none of his readers will ever follow a link he gives, because there is no frothing mouth evangelical preacher or Shouting and screaming at that link. Go ahead, check.

There does seem to be a lot of shouting from TERFs over pragmatically useless distinctions between human individuals. I just don’t need to know about chromosomes or reproductive apparatuses in the people I interact with. As I said back then,

The presence or absence of a penis is possibly the worst gender signal ever, because we keep those hidden in almost all of our social interactions. I’d have to be really close, very intimate friends with a woman before she’d show me her penis.

I’d have to be even more intimate with her before I’d ask her to ejaculate for me.

Lewis also snipes at David Gorski.

And @oracknows screaming ‘TERF’ because I suggested the biggest sceptical issue that should be covered right now is the denial of the material reality of sex among gender ideologists. (now appears to be deleted.)

Tell me, has it ever been accurate to say David Gorski was screaming? It’d be fair to say I sometimes get worked up and rage loudly at the universe, but David is always careful and objective. I also can’t quite imagine him (or me, for that matter), denying the material reality of sex. Sex is most definitely real. It’s just not the simple phenomenon that Lewis thinks it is.


  1. AstrySol says

    People who don’t create any gametes throughout their lives exist. So even if what he argues is correct there will be at least three sexes, not two.

    Also I don’t think he even thought his position through: if gametes are the only thing that matters, does that mean 1) we cannot determine pre-puberty youths’ sex at all; and 2) puberty blockers, which essentially delay the gamete-producing business, can delay the determination of sex, and thus should be available to trans adolescents?

  2. birgerjohansson says

    To avoid having to provide a sperm sample for entering public bathrooms, he might advocate people having a bar code tattooed on the head…
    (sigh) Transphobes are so obsessed with labels one could dismiss it as OCD if they weren’t so goddamn dangerous.
    They are like weaponized characters from Monty Python.
    Distinctions: I am a bipedal SF-reading chordate that is also a pizzavore.
    I will demand Andy Lewis adress me as such.

  3. chrislawson says

    Let’s not be fooled by this. The only reason this argument even exists is that the TERFs and gender essentialists have been shown to be damned fools and liars with their use of the XX/XY argument. But this is still the same thing — a stupid and antiscientific form of gender essentialism that has merely shifted from using chromosomes to using SRY and gametogenesis as the defining feature of gender. And the only reason I can see for the shift is because it is more complex and therefore more likely to be useful in rhetoric.

    But it’s still wrong. Not just a matter of opinion wrong, but flat-out antiscientific bullshit wrong. SRY is NOT by any measure the defining feature of gender and what we’re seeing is not a more sophisticated argument, but the same stupid argument tacked onto a new version of the same fallacy.

    Just for everyone’s information, this is the story as told by the new gender essentialists: XX males account for around 1 in 9,000 – 20,000 people (depending on the study). These males form from XX embryos, but with the SRY gene attached to one of the X chromosomes by recombination error in the paternal gamete. Usually the X chromosome with the SRY gene becomes the dominant chromosome and the non-SRY chromosome gets deactivated. This leads to the development of the male phenotype.

    We can see why this would appeal to someone who likes the idea that that XX/XY defines gender but has got sick of being knocked about in arguments by the many, many counter-examples to simple XX/XY-based gender definitions.

    But the problem is still the same. Many XX males have no SRY gene. And in fact, about 25% of XX males have zero Y-chromosome material at all. The mechanism here is not understood. But critically, we can say with confidence that in these individuals the SRY gene is ABSOLUTELY IRRELEVANT TO THEIR MASCULINITY. So, just like the old XX/XY gender essentialism, the new SRY gender essentialism is the same old bullshit based on ignorance.

    And the worst of it all? This has absolutely zero to do with transgender identity anyway. Transgender people do NOT have atypical XX/XY chromosomes or SRY crossovers any more than the rest of the population. Despite numerous studies looking for genetic or neuroanatomical causes of transgender identity, we’ve never found anything more than the occasional weak correlation here and there, and without much in the way of explanatory power. In other words, all this gender essentialism malarkey is nothing more than dressing up bad science to argue that trans women aren’t women and trans men aren’t men.

  4. garnetstar says

    First, everyone knows that biology is a mess, notoriously gooey, and that there is NO rule or law that doesn’t have exceptions. There are always variations and spectrums, that’s what is a law. Biology is just a bunch of chemical reactions, which are required to have multiple products.

    Then, the last time there was a TERF fuss about this, I recall a tweet from a human geneticist that there are actually six common sex chromosone combinations in humans–like XXY, and all the variants like that–and four uncommon ones. So, Lewis assumes that he is XY, but he doesn’t actually know. Very, very few people ever get around to having their actual sex chromosones identified, and everyone else in the world gets along in life just fine without themselves or anyone else ever knowing what their chromosones are. Could not be a better highlight of the almost complete irrelevance to anyone’s life of knowing your own or anyone else’s chromosone set.

    Then, what has sex got to do with gender? Really, could we quit talking about sex? If you want to be bigoted and hateful on the basis of gender, just say so, and quit talking about sex, which is irrelevant.

    And, I recall from my days of keeping freshwater aquaria a phenomenon that fish breeders occasionally encountered (with what particular species, or all species, I do not know.) Those fish find mates by releasing sex-specific hormones into the water, and scenting the male or female one, and moving towards it.

    But, if you happen to get a tank full of fish of all one sex–let’s say females–who couldn’t detect any opposite-sex hormone in their enclosed space, some of the fish would actually change to the other sex–in this example, males–so that they could breed. I have no idea what that requires, and it’s not something that humans still can do, but if we are pulling up examples from “evolutionary biology”, like birds and lobsters, let us consider aquarium fish. I don’t know if they have gender, but they can change their “sex”, whatever that is, when needed.

  5. says

    I still don’t care what bathroom anyone uses as long as they don’t pee on the seat.

    These people are entirely too concerned with what is, fundamentally, not their business. I find that creepy and concerning. I am more concerned that some gender-policing creep may want to have a look at my penis than that one of my fellow pissers might and I’m damned if I can figure out if having a woman, a man, or my girlfriend’s cat look at my penis makes some kind of difference. Maybe someone could set up a forum where TERFs could police eachothers’ genitals and they could leave everyone else alone? They’re just busybodies – they don’t deserve a fancy acronym.

  6. chrislawson says

    For two examples of the strength of genetic studies on transgenderism:

    The Use of Whole Exome Sequencing in a Cohort of Transgender Individuals to Identify Rare Genetic Variants: “Whole exome sequencing revealed 120,582 genetic variants. After filtering, 441 variants in 421 genes remained for further consideration, including 21 nonsense, 28 frameshift, 13 splice-region, and 225 missense variants. Of these, 21 variants in 19 genes were found to have associations with previously described estrogen receptor activated pathways of sexually dimorphic brain development.” So after generating over 120K sequence variations, they found that a whopping 21 were associated with transgender identity. This was drawn from a sample size of 30 transgender people, btw, and the decision of what was an “association” was finding a genetic variation that was not found in a control group of 88 cis-gender individuals. Most of those variants were called “associations” when they turned up as a heterozygous allele in one person in the transgender group. Yes, you read that right. One person with heterozygosity = an association!

    The CYP17 MspA1 Polymorphism and the Gender Dysphoria: “We analyzed 151 male-to-female (MtF), 142 female-to-male (FtM), 167 control male, and 168 control female individuals.” And found: “A2 frequency was higher in the FtM (0.45) than the female control (0.38) and male control (0.39) groups, or the MtF group (0.36). This FtM > MtF pattern reached statistical significance (P = 0.041)…”

    When you hear people talking about the genetic associations with transgender identity, remember that this is the sort of insipid correlation they’re actually referring to.

    There is strong evidence of a genetic component to transgenderism from twin studies, where a transgender person’s identical twin is around 30-40% likely to be transgender themselves — far, far higher than in non-identical twins. But even here it is important to note that two people who are almost 100% genetically identical still have a less than even chance of sharing transgender identity. Which means there’s a lot more going on than simple genetics. It’s not like blood types.

  7. specialffrog says

    Aren’t there organisms with more than two sexes where any non-like pair can reproduce as well?

  8. eliza422 says

    So what’s the big deal for these folks if someone doesn’t fit their model of male / female anyway? I mean, there’s just about 8 billion people in the world – it certainly can’t be population dwindling fears (unless this is also combined with “white genocide” crapola).
    It just boggles my mind that they can’t just live and let live.

  9. jillianemergent says

    Yeah, the transphobes have decided “gametes” is their devastating refutation of “trans men are men, trans women are women”. This has been going on for ages – they’ve been trying to find an “objective” definition that classifies people the way they want. No false positives, no false negatives, no exclusions. Even with “gametes” there’s a degree of subjectivity – it’s currently “bodies designed* around the production of…”

    So, PZ, if you don’t fancy giving a sperm sample before you pee, an MRI will probably suffice.

    Yeah, I know.

  10. rrhain says

    An XY individual is born with testosterone resistance. This results in differentiated testicles that are internal to the body. No penis is formed. Instead, a vagina with vulva and clitoris develop but no cervix or uterus develops and the vagina ends blindly.

    This is a real person from my biology text that is used as an example showing how complicated the development of sex is and how there is no “either/or.”

    What “sex” is this person?

    And for those about to respond, “But that’s intersex, not trans,” I say: Yes. But if the morphological development of a person can exist on a spectrum, what makes you think that the psychological development of a person can’t also exist on a spectrum? Shouldn’t our comprehension of how the body is complicated and can’t be locked into two and only two choices inform our comprehension of how the mind is also complicated and can’t be locked into two and only two choices? And since the psychology of a person will be affected by their morphology (even if only indirectly), is it really so odd to think that there might be people whose morphology and psychology are not pointing in the same direction?

  11. jillianemergent says

    @14 rrhain: Yes, exactly. Science is messy. And it’s not just the biological sciences. Define “planet”.

    All this nonsense is driven by transphobes wanting something more objective-sounding than “eww, trans people”. Having a bathroom door labelled “Women who, in our opinion, aren’t icky” isn’t a good look.

  12. John Harshman says

    @garnetstar #6

    And, I recall from my days of keeping freshwater aquaria a phenomenon that fish breeders occasionally encountered (with what particular species, or all species, I do not know.)

    I was going to bring this up, but I see you have already. What you describe is common in reef fish, notably parrotfish. There’s usually only one male on the reef. If he’s removed, the biggest female has a sex change and becomes the new male. I don’t think the change is reversible, but the obvious advantage is that you become a parent of all the new babies on the reef (who are of course all born female), whoever the eggs belong to. Pretty sure humans can’t do that. But I do wonder what Republicans think of parrotfish.

  13. says

    I’m surprised PZ and others haven’t homed in more on this:

    To suggest that there are more than two sexes, or even more extreme, that somehow sex forms a continuum, a distribution or a spectrum is completely incompatible with this view of life and sexual reproduction.

    Precisely. It’s incompatible with your philosophy, with your view, but it’s not incompatible with the facts. This here is a (likely unknowing) admission that they reject facts about sexual and gender development because they have committed, a priori, to to a binary view of sex. His view is that this binary is with respect to gametes. Other anti trans reactionaries construct their binary based on something else.

    But the inescapable truth is that they reject facts when they are incompatible with their view. We sometimes imagine that they don’t realize this, but at least some of them clearly do.

  14. edmond says

    I can treat people with love, acceptance, kindness, empathy and compassion without giving two shits about their gametes.

  15. lochaber says

    One thing I find curious – a lot of the people that are trying to argue that sex is binary, and gender is binary and adamantly defined by sex, also seem to be really big on gender roles, often claiming they are “natural” or some such bullshit.

    So, the very thing they are arguing against (little human babies with a penis, growing up to be women and wear dresses, or whatever), seems to me to be a blatant example of how at least one of their views are factually wrong? Like, if all human babies born with a penis will grow up to be “men”, and “men” don’t wear dresses…

    The sooner society relegates these jackasses and bigots unworthy of attention, the better…

  16. KG says

    it’s currently “bodies designed* around the production of… – jillianemergent@13

    Ah! So they’re creationists!

  17. Allison says

    I can see it is fun to debate this stuff, and the mere fact that most of it has already been rather solidly resolved by biologists (and is probably already in the syllabus of one or another of PZ’s introductory biology courses) isn’t allowed to spoil the fun.

    I can also see that it has little or nothing to do with transphobia, TERF-ism, homophobia, etc. Even if you could convince the haters of the truth about … well, all of this — it wouldn’t make them stop hating who they hate. From everything I’ve seen, the need to hate comes first, then they latch on to some group or other to hate, preferrably one which society has already defined and designated as hate-worthy so you can more easily find people who share your choice of hate-object. The rationalizations come later and tend to mutate and shift as the pseudo-intellectual winds shift. But the hate stays constant.

    I mean, really, how does other people’s sex (however defined) being binary or not affect most people’s lives? Most of us are just trying to get through the day, and whether the check-out clerk at the local Shop & Drop is XX or XY or something else or even chimeric, or what they have in their pants, is utterly irrelevant to that. The amount you have to pay is the same. You have to have a need to hate to put out all the effort to find out what characteristics that check-out clerk has and then the extra effort to run around trying to make their life miserable.

  18. jillianemergent says

    @25 Allison.

    You are correct, of course. It’s the opposite of following the evidence: start with the conclusion, then scramble around looking for something which can be used for support. (See also creation science / ID).

  19. says

    The small, mobile gamete we class as male and the larger, and immobile one we class as female.

    Teetering on the brink of an epiphany is one of my favourite phrases in the English language and terfs provide ample opportunity for me to use it.

  20. Frederic Bourgault-Christie says

    @21: That’s the point.

    What finally clicked for me recently is that this has nothing to do with sex or even gender. It has to do with what kind of identity claims conservatives are willing to respect.

    Because of their low ambiguity tolerance, and all sorts of other psychological and ideological aspects of the conservative worldview and mind, they need to have who you are allowed to be strictly policed. (Even when they pretend to themselves to be libertarians, who if consistent would say that it’s no one’s business, especially not the government’s; and, of course, remember that some of the same people trying to police sex and gender also think we should get rid of census identification for race, because, well, the government shouldn’t care, because it risks being racist).

    To those who are intellectually left-wing, it doesn’t matter. We are not so invested into policing who has power and respect based on identity. Say what you are about yourself; who cares?

    They need to think that gender is natural because they want some way of demonizing those men who wear dresses.

    It comes down to them being scared that, without some kind of authority telling you what you can and can’t be, society will crumble. Or, worse, that choice will be revealed as one that isn’t automatic, and you have to think about.

  21. John Morales says


    To those who are intellectually left-wing, it doesn’t matter.

    Wings, two. Left wing, right wing. A binary, right?

    (No centre wing. No up wing. No down wing. No non-wing)

  22. Silentbob says

    @ ^

    Oh good catch, Morales, because no one ever used the term “centrist” before, it’s unheard of. *rollseyes*

    (No centre wing. No up wing. No down wing. No non-wing)

    Well, one thing’s for sure, you ain’t charm wing.

  23. John Morales says

    Silentbob, I think you missed the joke, which is in the context of binary classifications.

    Frederic suggests that there are two kinds of people: those who are intellectually left-wing, and there are those who are not.

  24. vucodlak says

    @ John Morales, #31
    Some species of insects have four wings. Seraphim* typically have six, although I’ve read stories of those with five or seven. I seem to recall that elder things have five. My high school had three.

    As to political spectrum, there’s definitely more than two “wings,” even if they aren’t always called wings. For example, it’s common to talk about “liberal,” “moderate,” and “conservative” wings of parties which are themselves considered mostly “left” or “right” wing. So, right there that works out to up to six wings. That’s… sextary or whatever. I’m too lazy to look up the proper term, and I’m not putting “sextary” into a search engine.

    *While “left wing” and “right wing” may have begun as physical descriptors, they now refer to non-literal concepts. As such, it seems reasonable to bring mythical beings into the discussion.

  25. John Morales says

    vucodlak, sure. BTW, good use of the general rule, but in English it would properly be ‘sextuple’.

  26. vucodlak says

    @ John Morales, #35

    BTW, good use of the general rule, but in English it would properly be ‘sextuple’.

    I thought of that, but I’m not sure that’s right. If you count backwards from sextuple, you get quintuple, quadruple, triple, and then double, right? Not binary. If you count up from “binary,” you get ternary, and then? Is “sextuplary” a word? Ah fuck it, I’ll just look it up…

    It’s “senary,” apparently.

  27. chrislawson says


    The fungus Schizophyllum complex has two sex-selection loci with 288 alleles at one and 81 alleles at the other, meaning it has 288 x 81 = 23,328 different sexes. Gametes can only fuse to form a new individual if they are dissimilar. That is, if they share the same alleles at either locus A or locus B, then no embryo will form.

    The current evolutionary explanation is that this system evolved to reduce inbreeding. The more closely related the gametes are, the more likely they will share the same allele at both loci. If sibling gametes meet, there is a 1 in 2 chance that they will be unable to produce offspring. If random, unrelated gametes meet then that chance is 1 in 22,960. Quite a neat system for a planet-wide species (the one species has large populations on every continent except Antarctica).

    This is an interesting organism and I recommend Tom Volk’s blog post about it (although he does get some numbers wrong in his genetics explanation) if you want to read the horror story about the child whose soft palate became so colonised that she was growing fruiting bodies in her sinuses!

  28. Siobhan says

    I gather there’s relatively minimal appetite among trans people to have a philosophical debate about what makes a man or a woman, because our principle concerns are usually more urgent than a thought experiment. What TERFs need to do is show that any of their arguments about gender etiology have the slightest relevance to things like healthcare access, public accommodations, or employment discrimination. Whether one personally considers me a man or a woman, I’m getting catcalled when I leave my apartment, so the debate starts to just strike me as, pardon my French, a little fucking silly.

  29. garnetstar says

    @39, yes, entirely. I have pissed off many TERFs by telling them that they need to find something more urgent and pressing than theoretical definitions to fret about.

    If full civil rights and social acceptance for trans people is too much for them, I have suggested “When will the sun explode?” as more relevant to humanity than crazed attempts to define specious categories.