Once again: Why sex is binary

December 11, 2018 • 12:30 pm

Over at Medium, Alex Byrne, who happens to be a professor of philosophy, and chair of the Department of Linguistics and Philosophy at the Massachusetts Institute of Technology (MIT) has written an article criticizing Anne-Fausto Sterling’s NYT Op-Ed, “Why Sex is not binary.” Click on the screenshot below to see Byrne’s take, which is pretty sensible.

I also criticized the NYT article, as did psychologist Debra Soh.  My own criticism concluded that sex—defined as either “male” or “female”, each of which has a correlated suite of primary and secondary sexual traits connected with (and the evolutionary result of) the production of large or small gametes—is pretty much binary, and certainly strongly bimodal, with only a very small fraction of people who don’t fit neatly in the slots. For all practical purposes, sex is a binary, and it should be, since evolution produced (in most animals) two sexes that must mate to produce offspring. If you’re neither, or an intermediate, you don’t leave offspring and you don’t leave your genes.

Gender, on the other hand, is perhaps a bit less binary, as there are more people who identify as either an intermediate, something else, or a sex that wasn’t their birth sex. But gender, too, is bimodal.

The shameful part of all this is that the scientific journal Nature, as well as three evolutionary biology/ecology societies, who should know better, made statements or editorials that neither sex nor gender are binary. That’s a flat-out abnegation of both their responsibility and of science itself. Evolution itself produces a binary of sex! To be anthropomorphic, evolution wants a binary of sex.

Why, then, do people harp on the non-binary nature of sex? It’s clear: because if they see sex as a spectrum, then that supposed continuum will help eliminate discrimination against transgender people (who still, I should add, adhere to one biological sex or another) or against those rare intermediate folks who don’t fall into the sex binary. But, as Byrne points out, you don’t need to twist biology to construct a caring and inclusive morality. But have a read:

Byrne’s definition of “sex,” which leads to his binary, is that of Simone de Beauvoir herself in The Second Sex, one of the founding documents of modern feminism:  the sexes “are basically defined by the gametes they produce.” Big gametes = female, small gametes = male; these are, in our species, eggs and sperm, respectively.

But what about those who produce no gametes? Well, Byrne, being a philosopher, has already thought of that:

There is a complication. Females and males might not produce gametes for a variety of reasons. A baby boy is male, despite the fact that sperm production is far in his future (or even if he dies in infancy), and a post-menopausal woman does not cease to be female simply because she no longer produces viable eggs. Female worker honeybees are usually incapable of producing eggs because their ovarian development has been inhibited by chemicals secreted by the queen. (In one species of bee, the female workers are all permanently sterile, even in queenless colonies.)

In the light of these examples, it is more accurate (albeit not completely accurate) to say that females are the ones who have advanced some distance down the developmental pathway that results in the production of large gametes — ovarian differentiation has occurred, at least to some extent. Similarly, males are the ones who have advanced some distance down the developmental pathway that results in the production of small gametes. Definitions in biology are never perfectly precise, and these are no exception. Still, they give us some traction in examining whether there are any humans who are neither female nor male.

He concludes that yes, there are some intersex conditions, but also that, arguably, “there are no clear and uncontroversial examples of humans who are neither male nor female”. By that that he also means that there are no humans who are both male and female, though I’d think that if there are true hermaphrodites and intersexes—which there appear to be—those would qualify.

But it doesn’t matter. If you adhere to the gamete-based definition used by most biologists, sex is effectively binary. In his footnote #2, Byrne argues that intersex individuals have a frequency of 0.015%, or about 1 individual in 6700. That would be the number of individuals falling in the “valley” between the male and female frequency peaks, making sex almost a pure binary.  And that frequency, or even the 1% touted by Fausto-Sterling, neither effaces the binary nor should have any bearing on how we treat transgender or intersex individuals.

That’s the main point here, and one that Byrne emphasizes. I can’t say this too often: you should not base human rights on biological facts, for then those rights become susceptible to changes in scientific thinking. Of course some morality must be informed by biology (abortion is one example), but whether or not a class of people should be afforded equal treatment and equal opportunities should have nothing to do with biological differences. If you think otherwise—if you think that sexes and ethnic groups must be equal in all respects, genetically, behaviorally, in brain structure, and so on, because otherwise we succumb to sexism and bigotry—then you’re leaving yourself wide open to the finding of differences that would undermine your scientific claims, and hence your biologically-based morality.

And so Byrne, as a philosopher, points out the obvious (my emphasis below to make it even more obvious):

That sex is not binary is evidently something that many progressives dearly wish to believe, but a philosophically sound case for treating everyone with dignity and respect has absolutely no need of it. People with intersex conditions have historically been subject to ethically dubious genital surgery as children, or deceived about their medical status by (usually well-meaning) doctors. It would be a huge mistake to think that such surgery is unjustified because the patients fall outside the binary, and so should not be surgically fashioned to appear to be within it. The main arguments against surgery (there are risks with little compensating benefit, and patients are too young to consent) have nothing to do with whether the patients are female, male, both, or neither.

Further, the issue of whether sex is binary, although of academic interest, is of no relevance to current debates about transsexuality and the changing models for treating gender dysphoria. To those struggling with gender identity issues, it might seem liberating and uplifting to be told that biological sex in humans is a glorious rainbow, rather than a square conservatively divided into pink and blue halves. But this feel-good approach is little better than deceiving intersex patients: respect for autonomy demands honesty. And finally, if those advocating for transgender people (or anyone else) rest their case on shaky interpretations of biology, this will ultimately only give succor to their enemies.

As a (former) scientist, it’s distressing to me to see my fellow progressive scientists twist and deform biology out of all recognition so that it buttresses their ideology. We don’t need to do that. Our ideology is a good one—much preferable to discriminating against groups based on (supposed) biological differences—but we should ground it in reason, not biology. And the reason is simple, recognized long before biology became a discipline: we should, in a good and caring society, treat all people as we would wish to be treated were we in their position. (This reciprocity is embodied in the ethical philosophy of John Rawls.)

Of course the Authoritarian Left will demonize people like Byrne (I can already anticipate him being called a “transphobe”), and it’s not pleasant for me to criticize the Society for the Study of Evolution, of which I was once President, for distorting biology in the interest of social justice. I share their goals, but as a biologist I don’t share the “scientific” assertions cooked up to buttress those goals.

Wary of all this, Byrne put this on his MIT webpage:

h/t: Cesar

44 thoughts on “Once again: Why sex is binary

    1. WordPress has also banned ‘deadnaming’ which means even here it would be risking the existence of the site by discussing one of the most notorious child killers in recent British history.

      At least WordPress only bans blasphemy in Pakistan.

      This new religion is global.

      1. There was a good article in The Spectator about the sex offender who pretended to be trans so that he could get transferred to a woman’s prison in order to molest more women.

        Far leftists have created quite a mess with all of this bs, so instead of admitting fault (that they lied when they said that sex offenders would never ever ever pretend to be trans in order to prey on vulnerable women) they go on the attack, accusing the victims of various crimes against trans people, such as ‘deadnaming’.

        Oh, and I can’t find it now, but apparently one of the prison officials who had a hand in helping trans sex offenders get into women’s only prisons was in fact a sex offender himself.

    2. Or, that could just be an exaggeration or a distortion based on some isolated incident. Banning just for the reason stated in that tweet? – I doubt it.

      Given the reputed shitfight between various flavors of feminists and trans and all the other acronymic alphabet soup, I expect Twitter has been getting squawks about users, phony or otherwise.


  1. The awkward truth is that nobody is really arguing about intersex because of the rights of intersex people. There hasn’t been a sudden increase in the numbers of intersex people, nor have intersex people become more politicised or radicalised.

    There aren’t clusters of intersex children appearing among school children, there aren’t YouTube channels pushing intersex ideology onto vulnerable children, and there aren’t publicly funded charities claiming that intersex conditions are the cure for autism or eating disorders.

    There aren’t intersex thugs punching 60 year old women, denying gender-critical feminists a platform, shutting down meetings by making bomb threats or setting off fire alarms.

    We don’t have large numbers of intersex category A prisoners in the UK demanding to be housed in the female estate, nor have we got intersex murderers and rapists demanding hormone treatment that would be denied to natal menopausal women.

    The whole damn argument is a proxy for transgenderism. It has nothing to do with intersex. Intersex is just the smoke transgender rights activists are blowing up our arses.

  2. Humans are bipeds.

    Some humans are born without legs. They are still human, but their existence does not mean that humans are not bipeds. Those humans are apedal bipeds.

    And then there are a few quadraped humans. They are also human, and their existence does not mean that humans are not bipedal.

    Outside of a shoe store, these distinctions are meaningless.

  3. It’s very similar to the biological arguments for same-sex attraction. Gay rights activists would rely on biology as a means to defuse objections to gay rights, as if the people opposed to gay rights really cared whether it was biological (you could argue it had a beneficial effect with fence sitters).

    But they painted themselves into a corner when it came to bisexuality, because it becomes harder to imagine a bioligical reality that would cause one to be attracted to both sexes. As a result, you have somewhat of a schism in the LGBT community, with bisexuals having to defend their orientation from attacks from both the hetero and gay communities.

    I’ve always preferred the libertarian argument: I don’t care if it’s biology or a personal choice, you be you, and everyone should be treated with respect and have the same basic rights, regardless.

    1. “I’ve always preferred the libertarian argument: I don’t care if it’s biology or a personal choice, you be you, and everyone should be treated with respect and have the same basic rights, regardless.”

      Couldn’t agree more!

      1. I too prefer the libertarian argument because, as Alice Dreger pointed out, the issue with ‘born that way’ is that, in people’s minds, certain behaviours are only justifiable if there is a biological reason.

        If a natal male wants to put on a dress and lipstick I have no problem with that, he should not have to be ‘born that way’ to justify his lifestyle choice.

    2. It is important to continue research to determine how it develops. That is the rise of science, to research explore and discover things. Applications of basic research comes later.

    3. I think most enlightened and reasonable people should be willing to accept that other people’s sexuality or dress is pretty much none of our business.

      I sort of draw the line at the point where I am expected to support those choices and beliefs, and persecuted if I do not. Especially where science is concerned. The data is what it is. And as soon as we are willing to modify the facts to fit trendy political beliefs, we lose all credibility.

    4. Gay rights activists would rely on biology as a means to defuse objections to gay rights, as if the people opposed to gay rights really cared whether it was biological

      This really requires emphasis. “Being gay is unnatural” is just one of many rationalizations for their position.


    5. But they painted themselves into a corner when it came to bisexuality, because it becomes harder to imagine a bioligical reality that would cause one to be attracted to both sexes.

      I don’t see how. Hair color is biological but it comes in all sorts of shades. Saying sexual preference is (primarily) genetic does not commit one to the fallacy of the excluded middle.

  4. It never ceases to amaze me how blithely trans radicals can cite Dr. John Money. It’s on par with ‘studies conducted by Dr. Josef Mengele found ….’

  5. <blockquote"… we now know that rather than developing under the direction of a single gene…"

    Like little Jack Horners, the anti-science Left continually amazes itself with the plum of discovering the existence of polygenic traits, thus destroying their strawmanned ‘genetic determinist’ foes, Q.E.D.

    “… the fetal embryonic testes or ovaries develop under the direction of opposing gene networks, one of which represses male development while stimulating female differentiation and the other of which does the opposite.”

    Only someone as delusional as Anne Fausto-Sterling could imagine sex determination as a tug-of-war between competing genes, with every individual popping out somewhere in the middle.

    1. That’s a good piece, though he gets it quite wrong when he says:

      “After all, unlike a person’s sex, one’s ethnic identity is obviously, demonstrably socially constructed, and race, (beyond the human) is an outright fiction constructed out of superficial differences in material appearances, like skin color or eye shape, …”

      1. What seems to elude Kaufman is that race can be and is defined by those ‘superficial’ differences. Racial discrimination uses those as markers for substantive differences.

        Sam Harris has noted the risk of arguing for social equality based on (asserted) natural equality: if new data appear that contract your assertion, your argument is turned around against you. Which is why the regressive left is so vehemently opposed to any research into race & intelligence.

    2. That blogpost is quite tendentious. One example:

      “The material fact that women bear children and men do not was used to justify the belief that they, as a group, suffer diminished rationality and lack emotional discipline, which provided the grounds for men’s control of their reproductive cycles and ultimately, their lives.”

      Asserting no tangible differences exist between groups because you believe in equality (committing the moralistic fallacy), traps one in the naturalistic fallacy.

      We now know that women tend to be much higher in the Big 5 trait of Neuroticism. Per Kaufman’s formula, this ‘material fact’ justifies men controlling woman.

  6. I continue to be worried by these posts about the so-called sex binary. I think this is quite misguided. For the love of pie, please just talk to some nonbinary folks and try to understand what it is like to be them. They’re not denying biology; their existence is evidence that while biology and biological knowledge can tell us a lot, they sometimes reinforce social values and ideas–two main options (female;male), three at most (intersex)–as much as they accurately describe the world as it is. Of course you and Byrne are right that the moral argument for treating trans and/or nonbinary folks with dignity and respect does not depend on what biology says. But likewise what so many continue to say on this topic seems completely devoid of the actual experiences of anyone but cisgender binary folks, which is just confirmation bias, isn’t it? Until you’ve actually grappled with what it is like to be someone who does not identify as either male or female, these takes get more tired and tired. I hope you can see how frustrating and disappointing such takes might be to people whose identity you are basically saying doesn’t exist.

      1. I agree. I consider ‘cis’ a pejorative that erases my existence — identity as ‘sexed’. Please desist from using that hurtful & unwelcome term.

    1. The ‘nonbinary’ individuals you cite may or may not be denying biology, but Fausto-Sterling definitely is. Why shouldn’t she be called out on it?

      “what so many continue to say on this topic seems completely devoid of the actual experiences of anyone but cisgender binary folks”
      That could be because the majority of commenters are cisgender binary folks, don’t you think?

      99%+ of people are either male or female, and they are going to continue thinking of gender in those terms. Advertisers and songwriters are going to continue to cater to the majority, as they always do. Persuading people to be tolerant of the tiny minority who are ‘different’ might be possible, though somewhat hampered by ‘women’ with dicks who want to use the female rest room. Persuading the great majority that their mainstream gender identity is a myth (which seems to be what Fausto_Sterling is aiming at) is not only pointless but futile.


    2. PCC(E) never said anything about gender in these posts apart from saying that it may be more of a spectrum than sex. He is addressing those who say sex is a spectrum, who are definitely denying biology.

      Now I haven’t asked my nonbinary friend about their views on biological sex, but that should be irrelevant, as those who don’t assert sex is a spectrum aren’t exactly the target of these posts.


    3. How do these non-binary people “know” they’re non-binary? How do they know how “binary” people feel so that they know that they don’t fit into either? How CAN they know ANY of this?

      As a “cis-gender” man, I have no idea how any other man feels about their gender or maleness, much less how women do. I also don’t see any way I could, even in theory, know.

    4. I hope you can see how frustrating and disappointing such takes might be to people whose identity you are basically saying doesn’t exist.

      Perhaps you could write a post on what you think *needs* to be said that either (a) JAC is getting incorrect, or (b) JAC is omitting by focusing on the science errors commonly floating around in discussion space? Because I’m seriously at a loss to see how his posts say or even imply “[nonbinary folks] don’t exist.”

      He’s saying they’re rare in the human population, but that’s not a denial of their existence any more than pointing out that only about 10% of the human population is left-handed or that only about 2-5% of the human population is gay.

      Yes some traits are rare. This is a fact. If you know of a better way to communicate this fact without ‘denying the existence of’ the people who have it, please, help us do that. But the option of pretending, implying, or allowing ‘ignorance by omission’ that a rare trait is not rare is off the table…just as pretending, implying, or implying-by-omission that that rare trait doesn’t exist, as conservatives sometimes do, is off the table.

      I’m not trying to push back. I’m sincerely asking: please help me understand where the communication is going wrong. Please help us improve communication. Because as far as I can tell, JAC is communicating accurate science in an area where there are a lot of mistaken notions, which is a good thing.

    5. If gender exists on a spectrum, this is only because some biological males are shifted towards the feminine and some biological females are shifted towards the masculine.

      And in the end, aren’t we all non-binary to a degree, with varied interests and behaviours. The problem with ‘gender identity’ is it is based on cultural constructs. Was King Louis XIV a woman because he dressed in high heels, silk satins and kept his hair long and lustrous? When women started wearing pants in the 1930s did they all become men?

    6. But seriously,

      1) Our ‘take’ also sometimes goes by the name ‘the science of Biology’;

      2) You wrongly assume that the ‘actual experiences’ of ‘nonbinaries’ have not been taken into account;

      3) In no way are we saying trangenders don’t exist. They obviously do. So do anorexics, but refusing to acknowledge they are obese is not ‘erasing’ their existence;

      4) Transgenderism is a dysphoria. If you consider that ‘gaslighting’, TFB. For one can still be compassionate & empathetic toward the sufferer, seek to provide the best treatment protocol, and continue to defend their right to equal treatment under the law;

      5) What you demand, however, is that we conform objective science to those subjective feelings & experiences. That is a non-starter. Dysphoria by definition conflict with reality;

      6) Oh, and also seriously — ‘cis’ really is pejorative.

  7. Excellent post.
    “you should not base human rights on biological facts,” that can’t be repeated often enough indeed.
    Reminds me of the dangers of describing these ‘primitive tribes’ as “noble” and “peaceful”, (as Pinker pointed out) what when they turn out not to be so noble and peaceful, after all? Exterminate them?

  8. I don’t think you should refer to his article as “from Medium” any more than I should refer to this one as “from WordPress”. Medium is a blog/website-hosting site, not an online magazine or anything like that.


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