Coin-tossing and the sex binary

June 7, 2023 • 9:30 am

Yesterday I posted about the sex binary once again, this time giving a letter I wrote to the San Francisco Chronicle explaining the male/female binary in humans (and all other animal species, as well as most plants). My letter is archived here.

In it, I said this about the standard biological definition of biological sex, which is based on gamete size and the apparatus used to produce gametes:

This standard definition applies not just to animals but also to nearly all plants, and is indeed binary: only about 1 human in 5,500 is an exception.

Well, that statement brought out the Pecksniffs: those gender activists who are determined to claim that sex is a spectrum. To them, if exceptions are only 0.018%, as they are, well, that means that sex isn’t really a binary trait. (That figure comes from this paper on the proportion of intersex people born; but even those intersex individuals aren’t regarded as members of a “third sex”!)  Only if there were NO sex-indeterminate humans would these people accept sex as a binary trait. (Again, even if intersex people were more common, they still wouldn’t be members of a third biological sex.) 0.018% exceptions is about as close as you can get to a binary.

I read somewhere else that the chances of a tossed coin landing on its edge—something I’ve never seen happen—is about 1 in 6,000, very close to the proportion of intersex individuals born. I checked out that coin-tossing figure, and it turns out to be true, at least if you’re tossing an American nickel.  Click on the screenshot below to go to the Physical Review E paper that comes up with that figure:

They did a complicated calculation and came up with an equation for coins of various weights and sizes landing on their edge when tossed. Then they actually did an experiment using hexagonal brass nuts of various sizes that were tossed in the air. After that, they extrapolated to an American 5¢ piece, and got this:

Since the agreement between the model and experiment shows no systematic deviation as p gets smaller, it is tempting to extrapolate the curve to thicknesses of familiar coins. One example will be considered here, which is the American nickel (five American cents, 5p). The diameter of this coin is 21.25 mm and the thickness is 1.96 mm at the rim. This gives an aspect angle of 0.092 rad. However when tip-over angles are measured, the results are 0.037 rad for tipping over with the President’s head up and 0.051 rad for tipping over with the President’s head down. In other words, a slight disturbance of a nickel which is set up on edge on a level table is more likely to result in the coin falling over “heads. ” The experiment to verify this is entertaining and easy to perform. The difference between tip-over angles between heads and tails is reproducible among several coins of this denomination. If p=0. 04 is selected as a representative tip-over angle, the extrapolation of the model leads to a probability of landing on edge of 1 in 6000 tosses. This has not been tested experimentally.

Note that they didn’t have the moxie to toss a nickel thousands of times, but I’m betting that at least one reader of this site has seen a tossed coin land on its edge. And if that happens only once, the “heads/tails” binary is violated. I was amused at this, for when we toss coins, people call either “heads” or “tails”; they never call “edge”!  Yet the chance of it landing on its edge appears to be about the same as the chance of an intersex individual being born.  For all practical purposes, then, just as the heads/tails dichotomy is an effective binary, so is biological sex, which becomes indeterminate at about the frequency that a coin lands on edge.

Thus, the calculated chance of a tossed nickel landing on its side is almost the same as the chance of a human being born as an “intersex”,  supposedly violating the sex binary by being neither male nor female.  Yet we don’t, when tossing coins, say, “Call it: heads, tails, or edge.” If you’re going to insist that there be NO production of humans that are neither male nor female—even in a trillion individuals—before you accept a binary, you are being obtuse—and denying the reality of how nature really works.

And again, I emphasize that intersex individuals, or those of indeterminate sex, are not considered members of another sex, and so don’t violate the binary nature of biological sex.  Further, I’ll note again that our concern and respect for individuals that become trans men or trans women has absolutely nothing with the frequency of intersex individuals in nature. Our treatment of gender-changing people is a question of civility and morality that should not be justified by referring to what we see in nature.

Finally, and I should have guessed this, there is indeed a video of two people tossing a nickel that lands on its edge. YouTube has it all! They don’t give the number of tries before the successes, though. And I think they’re tossing it in a way that maximizes the chance of the coin landing on its edge.

58 thoughts on “Coin-tossing and the sex binary

  1. This is a great statistic to have. The popular press right now is full of people claiming that not only “intersex” but people with two fully functioning sets of genitals, is really quite common (“the average doctor in New York City will see two or three a month” or something similar was on Quora today).

    It’s becoming part of the “new normal knowledge” in the world of gender lunacy.

    1. I have never seen one case of a human with two fully functioning sets of genitals. As I’ve said, there are two cases of human hermaphrodites that were fertile, but one was fertile only as a male (producing only sperm) and the other as a female (producing only eggs).

        1. I sent Jerry the BBC version of that article a day or so again, so he’s probably seen it.

      1. I don’t see how it could even happen as both sexes require some fusion in the midline of initially bilateral structures…. and both sides are affected by the masculinizing effect (acting in trans) of the male gonad. Even to have one of each gonad would require the mosaic event to split down the midline. It doesn’t have to be “sided”.

        1. Related – slightly – is that I saw a claim by a certain odious ex-cagefighter neo-Nazi recently online that he had extraordinarily high, and not injection-assisted, “test” (presumably “testosterone”) levels. Which sounds to me like the exact sort of symptom you’d expect in a case of testicular cancer, where the cancer is producing testosterone and growing rapidly.
          Not that I’d want to worry a neo-Nazi needlessly.
          I don’t actually accept your “midline fusion” doubt on intersexuality though. There are enough cases of developmental abnormalities like “situs inversus” and (partly) duplicated organs that I wouldn’t rule out a duplication, then the two duplicate organs following different developmental paths. Your point about glands which distribute their effects to the whole body via the bloodstream (“endocrine” glands, IIRC) stands though. In either case, they’re developmental abnormalities, not an expression of “normal” anatomy.

  2. There are certain places in Terry Pratchett’s Discworld where it’s a good bet to call “edge” when one flips a coin, but EVEN THEN, it doesn’t change the heads/tails dichotomy…and, of course, it’s fictional. And, as you point out, the existence of rare individuals of indeterminate sex doesn’t constitute a third (or more) sex any more than having an occasional die accidentally stamped with two different “ones” and no “six” (for instance) would mean that there are anything other than six sides to a cube.

    1. I’ve never noticed that happen.
      But when £1 coins first came out, I got into the habit of trying to balance multiple “quidlets” edge-on-edge. Which isn’t as hard as it sounds – they’re relatively thick coins, and relatively small diameter. The milled edge helps too.
      I once got three stacked one atop the other two. But that was before phones had cameras, and only the barman witnessed it – before he kicked the bar and toppled them.
      I infer that the odds of a quidlet landing on edge are considerably better than for a “nickel”. At 23.03–23.43 diameter by 2.8 mm thickness, it’s got a fairly chunky aspect ratio. The newer design with the dodecahedral shape is probably easier to balance, but with less cash in my pocket, I don’t play balancing games any more.

  3. The 95% confidence interval (binomial distribution) for 1 out of 5500 is 0 – 0.1. Thus it is not distinguishable from 0 and hence, does not need its own category. Sex was, is, and will be binary.

    1. You’re making an error here. They observed many more than 5500 people; you’re giving the error limit as if they’d observed 5500 people. In fact, the number observed is much, much higher than that and the error limit is lower. I don’t think you understand how error limits are calculated.

  4. I was in college in the 70s. I was chatting with a physics professor and we decided to walk down to the department office where they always had coffee. I think it was 15 cents a cup, payment on the honor system. We both pulled change out, offering to pay for both. He said, “Let’s flip for it. You call.” Nickel went up, I called, it hit the table and spun around on its edge for a while and stopped. On its edge. We stood there in shock for a while and decided we would both pay for our own coffee. I said, “What do you suppose the chances are?” He said, “I don’t know. I suppose we could try to model it.” We never did, but it’s good to see that, 50 years later, somebody has.

    1. Did you check the time and date? It was probably when the Tevatron, or an ancestor of the LHC had a “glitch”. Or George Lucas came up with the idea of “The Force”. Or something.
      Maybe another supernova going off in the Milky Way, whose ejecta still haven’t peeked out from behind it’s obscuring dust clouds?

  5. I think this is a great way to look at the overall question of when the (in)frequency of a particular outcome means that we have to modify our entire approach to a situation. In this way, it is a sort of thought experiment that tests our mindsets by avoiding the emotionally charged aspect of the issue.

  6. The idea that “sex is a spectrum” has for various reasons come to be the way of asserting that transgender is physically real. Declarations of respecting civility or morality do not address the issue there. Indeed, regardless of intent, it can come off as patronizing by appearing to dodge the matter of fundamental physical reality.
    I do not know how to change the way this cycles around.

      1. No, what you reference is exactly the issue – is being anatomically unambiguous all there is? The idea is that there is something physical involved in transgender which is more than simple gamete biology, hence all the gesturing to the edge cases of sexual anatomy development. A view that anatomy is destiny goes down a path of arguing transgender isn’t physically real, which is again the driver of all this.

        1. No one is claiming that being anatomically unambiguous is all there is (not those acting in good faith anyway). You are conflating the acknowledgement of reality (i.e. the sex binary) with what someone thinks they are.

          Gesturing at the edge cases doesn’t make the notion of transgenderism true. Who knows, there might well be a physical driver behind transgenderism. But that does not mean that the edge cases are the reason for it. Perhaps we might come to find evidence for a “sexed brain” one day. Or perhaps we might come to find evidence that transgenderism is a specific instantiation of believing something you’re not, i.e. anorexia. Whatever the belief is, until evidence is presented and subjected to scientific scrutiny, it’s fine to acknowledge that we don’t know, as opposed to contorting and corrupting the scientific literature. In the mean time, we can still be respectful and honor their rights as much as reasonably possible.

          1. I would say the claim that being anatomically unambiguous is all there is, is very frequently made in various forms, including comments on this very post. Mike discusses it extensively: “From that pov, trans is not physically real”. Jon Gallant, contra “(1) It is possible to be “born in the wrong body””. That’s why all the stuff of sex is a spectrum thrives in opposing this. I keep saying, I have no idea how make this any better. It doesn’t work to lecture people about how you think they should frame their argument, even if objectively their argument has problems.

            1. It may not work to lecture TRAs about how they should frame their arguments. As with many previous discussions on this site about religion and atheism in public life, one is probably not going to convince true believers to change their minds. But it’s possible (maybe common) to reach those who are sitting on the fence, haven’t committed to a position, and can be convinced to choose the rational one if presented with a sensible rational argument (like “sex is binary, humans can’t be born in the wrong body, and here is the evidence”). This is a worthwhile project.

      2. Almost everybody

        For values of “almost” of around 5499 in 5500.
        Actually, that’s assuming that transgender people are randomly distributed in the population. But I wouldn’t be astonished to find that the presence of ambiguous or non-standard genitals is correlated to some degree with self-identification as transgender. But that’s a hypothesis that is definitely amenable to testing, and certainly should be tested before use.

    1. One way to change that is to ask for clarity about the claim that trans is physically real. The weak form of the claim is that males (females) exist who say they feel like women (men). This is of course true. The strong form is that humans have a gendered soul that’s present from birth, immutable, and knowable by introspection, but that’s also discovered gradually over time, may be fluid or changeable, and can be in conflict with a person’s sex. This is of course false: humans don’t have souls, the mind and brain are parts of the body and can’t be born in the wrong body, and it’s not possible for a male to have an inborn sense of what it’s like to be a woman (or a man). From that pov, trans is not physically real: one has to first experience being female (or male) to know what it’s like to be a woman (or a man). Trans people (especially trans men) get little glimpses of this when they take cross-sex hormones — see the many reports about changes in the sexual experiences of trans men on testosterone. Ironically, this contradicts the claim that trans people know *before* cross-sex hormones that they belong to the other sex.

      1. “The strong form is that humans have a gendered soul that’s present from birth, immutable, and knowable by introspection, but that’s also discovered gradually over time, may be fluid or changeable, and can be in conflict with a person’s sex.”

        Lindsay discusses parallels if gender ideology with Gnosticism and Hermeticism. In particular the “gnosis” part.

        Make of it what you will – I never paid attention to Gnosticism or Hermeticism until now – but it makes me wonder if the fascination is a part of human nature.

  7. This is great! A detail I always wanted to know!

    And I have to comment – perhaps only on one philosophical element in PCC(E)’s statement :

    “Thus, the calculated chance of a tossed nickel landing on its side is almost the same as the chance of a human being born as an “intersex”, supposedly violating the sex binary by being neither male nor female. ”

    I think I understand – if the remarkable coincidence of this observation is left as a remarkable coincidence (among possibly other remarkable coincidences) – and as I think we are doing here, then that is settled.

    However, if there is an appeal of some sort made, would it be an appeal to Nature? A coin is a manufactured object. It is of course not “unnatural”, but can it be part of an “appeal to Nature” (or the naturalistic fallacy)?

      1. I think I know why that is.

        Real coins aren’t fair, as the article shows. But even if they were, a bookie wouldn’t offer a bet on a coin with a 1:1 payoff because even if he got to keep all the bets if the coin landed on its edge, (analogous to the zeros in roulette, or when an unbacked horse wins), this wouldn’t happen often enough for him to make much money off it. He’d rather take bets on horse races or run a roulette wheel where he gets to keep more of the action. (He also manipulates the quoted odds or point spreads to protect his downside.). In more casual bets, the probability that a coin will land on its edge is too small to worry people “calling it” as to who kicks off. Besides, if it did land on its edge, everyone would laugh and the referee would just toss it again. The edge outcome either counts so little that no one will make book on it or it can be literally ignored (because the edge outcome prompts a repeat toss.). In real games, this would be like not letting the casino take the chips if the ball landed in a zero, or running the horse race again if an unbacked horse won. The operators of the games would not agree to that curtailment of their edge.

        In sex, all people count. A baby born (or discovered later) with a DSD is not conjured away and the parents told to try again. The affected child has to be raised and cared for and she has to figure out her sexuality (even if her decision is to have no sexuality.). So I think that’s why the activists won’t let you off the hook about an event as rare as a coin landing on its edge (or four of a kind in poker). Such people really do exist, even if, in a sense, edge tosses don’t exist because in real life we would ignore them and toss again. It’s not the rareness of the outcome as much as the fact that you can’t call for a do-over.

        The logic the trans activists are using is all wrong: DSDs are still binary at whatever frequency they occur. But I can see why they aren’t silenced by the comparison to a coin toss. They think they are that edge outcome, dammit, and they do damn well count.

      2. The obvious experiment is to ask all subscribers to flip a coin, once, and report if they got an “edge”. (Seeing my comments up-thread about chunky quidlets versus slender nickels.)
        With 30,181 (at this time) subscribers, the expectation would be 5 or 6 “edges”. Significantly different results would indicate that the theorist’s prediction is wrong, or there is a mismatch between their definition of a “coin” and reality. Specifically, a “nickel’s” dimensions, mass distribution (president’s head “up” or “down”), or (my beer-worth favourite) edge damage leaving a relatively flat-wide spot. Or possibly a reporting problem – “self reporting” is not very reliable.

  8. And somehow this attempt to re-write a century old definition of biological sex is supposed to accomplish … what? One scarcely understands what the point of all this is, although plain as day its supposed to somehow connect to instilling acceptance of LGBTQ people.

    1. Thomas Khun’s Structure of Scientific Revolutions discusses the “paradigm shift”. I wonder if it sits in many post modernism scholars’ piles.

      It’s all I can imagine to be a scientific explanation … or rather, expectation of the scientific process to fulfill … even though it’s not how it would work anyway….

      1. I wonder if it sits in many post modernism scholars’ piles.

        Did you edit “unread” out of your original posting?

  9. I don’t understand the logic of saying a classification is binary while simultaneously acknowledging exceptions. Call me a Pecksniff, but if a classification truly is binary, there can be no exceptions. Would it be fair to characterize the sex binary as a useful model in biology which is, ultimately, wrong? I’m alluding to George Box’s saying that “all models are wrong, but some are useful”.

    Perhaps the exceptions to the sex binary have never been explanatory in any biological hypothesis, especially at a population genetics level. This is unlike the exceptions to, say, Newtonian mechanics that gave us modern computers (quantum mechanics) and GPS (general relativity). So, it may be tempting to assert that sex is truly binary because acknowledging otherwise has never been useful; however, I still think it is intellectually worthwhile to keep track of all the assumptions that undergird a model.

    1. Sexual reproduction among Earth species takes two sexes. One that produces large immobile gametes, and one that produces small mobile gametes. One or the other by themselves can not sexually reproduce. There is no third, or fourth, or any other type that is necessary or that has every been observed to be involved in a successful sexual reproduction event. Intersex people either produce viable copies of one of the two types of gametes, in which case they may be able to successfully participate in sexual reproduction, or they don’t, in which case they can’t. That’s what makes sex, in the biological sense, binary.

      It takes two different kinds of gametes for successful sexual reproduction. There aren’t any exceptions that I’m aware of. It seems like no one wants to say it, but intersex individuals, and similar, are not a different sex, they are individuals that are born with a defect compared to the general population. I hope it goes without saying that no one should be stigmatized in any way for being born with a defect of their sexual apparatus, or any other kind of defect.

      I’d think it would be clear to most that it isn’t biologists that are making a naturalistic fallacy in this debate. Scientists like Jerry are not arguing that because biological sex is binary that Trans-peoples’ self image, or lived experience, are invalid. Or that it’s okay to treat them poorly or limit their rights. They are not committing the naturalistic fallacy here, that’s what the more fervent anti-Trans and Trans proponents do. Scientist like Jerry are simply defending the truth of biological sex.

    2. In mammals (perhaps other species as well) only types of gametes have ever been found with zero exceptions. A true binary.

  10. Sadly, there will for a long time to come be people whose ideology compels them to seek to validate their positions on a hairsbreadth of hope. The best we can do—and should continue to do—is to provide factual rejoinders each time this hydra sprouts a new tentacle. The goal is not to convince the unconvinceable, but to provide facts for those who really want to know the truth. You’re doing a good job of it!

  11. Well, consider the sheer number of individuals who believe propositions like the following. (1) It is possible to be “born in the wrong body”. (2) Dominion voting machines mysteriously changed millions of Trump votes into Biden votes. (3) Systemic white supremacy is deeply embedded in the subjects of Ecology, Chemistry, Human Genetics, and musical notation. (4) Hilary Clinton, Nancy Pelosi, and George Soros ran a white slavery ring from the basement of a pizza place in Washington D.C. (5) African-Americans will be attracted to science if the names of some birds are changed. (6) Indigenous (Maori, Native American, etc.) concepts in astronomy will be helpful in space exploration. (7) Two of every kind of animal rode out the flood in Noah’s ark.

    Given the ubiquity of these beliefs and similar ones, one has to wonder how the human species survived as long as it has. But it hasn’t been such a long run, come to think of it.

    1. In all the eons that life has been possible here and the earth is consumed by the expanding sun, humans are likely to be the only species whose success was due to their intelligence but whose extinction was due to their stupidity.

  12. I wonder how (say) trinary sex would work in practice. If parents contributed an X, or Y, or Z chromosome how would the children gain their triploid chromosomes and how would their sex be decided? Perhaps parents would form triples rather than couples? But this seems rather fragile.

    1. People have thought about this a lot. One obstacle to evolving three sexes is that, to maintain the same genome size in offspring and parents, each parent would have to divide the genome into thirds, with three of those genome copies joining together when the three gametes fuse at fertilization. But the molecular biology of cell division (including gamete formation in meiosis) is fundamentally binary – the dividing cell duplicates its genome to make two genomes (not three), then the cell divides into two descendant cells (not three).

      Another obstacle is that sex evolved specifically to facilitate genetic recombination: to create gametes with many different combinations of variable parts within the parent genome, then add those different combinations together from two parents in each offspring. There are lots of evolutionary benefits to creating that kind of genetic variation within and among offspring via sex (compared to making genetically identical offspring using asexual reproduction – lots of organisms do this).

      The cost of sex for each parent is that only half of his (or her) genome goes into each offspring, and for each offspring the rest of its genome comes from the other parent. That’s a big loss for each parent. This is what evolutionary biologists call the two-fold cost of sex.

      Dividing the genome in half to make gametes is as small as that evolutionary cost can be. Dividing the genome into thirds or quarters (in a hypothetical organism that has 3 sexes or 4 sexes) makes the genetic cost of sex much greater to each parent (not to mention other costs & problems such as having to find 2 mates or 3 mates for sex). So evolving sex and recombination with just 2 sexes is probably evolutionarily stable – to add a third sex (setting aside the molecular biology obstacles) would require some additional evolutionary benefit to make up for the greater genetic cost to each parent.

      1. So, the problem is the binary nature of cell division. On the other hand, multiple fissions of specialized kinds occur in slime molds and sponges, so we can soon expect a Scientific American polemic explaining that cell division is on a spectrum. On the other hand, slime molds and sponges also have binary sex (with just two kinds of gametes), so the Sci Am article after that will denounce invertebrate Biology for its systemic heteronormativism. [Worse yet, Biology sometimes refers to colonial growth of this or that organism, and we know what that means.]

        1. Slime moulds, some sponge tissues, and a number of other species and tissues (I’m looking at your muscle hells here) also complicate school-level biology by being poly-nucleic. Or syncitial. Each cell membrane can contain many (hundreds, thousands even) of nuclei. Which would make cell division either very complex, or very simple. Or a Poisson (?) distribution in nucleus number with minimum of 1 and a high (unbounded?) maximum.

        2. Just to blow your mind: in some animals most of the tissues are cellular but the *gonad* is a syncytium, and gametes are formed by cellularizing nuclei after meiosis occurs. This blows the lid off the “cell division is binary” limitation on the sex binary. So as Jon noted we can now look forward to Scientific American polemics on how rotifers are trans. /s

      2. If I recall correctly, the “Origin(s) Of Life” people have manufactured triple-stranded polymers analogous to DNA (and RNA) with a peptide backbone (hence, PNA), which would have the potential to interact in a genuinely triploid genetic and sexual system. Not that they’ve found examples in the real world – it’s largely a paper + chemistry set exercise.
        Your point about such systems involving more parts coming together than a binary system stands – and probably always will stand.
        (I should point out that two-stranded PNA’s have also been made. “Peptide” can cover a multitude of sins of structure, possibly more so than the “sugar-phosphate” molecular backbones we all have in our DNA and RNA. Some people have proposed a “PNA world” precursor to the “RNA world” which probably was partly replaced by DNA in our extant biological system.)

    2. If you’re into SF, Larry Niven proposed a trinary-gendered alien species (also, possibly not un-related, they were tripedal, symmetry axis perpendicular to the ground) in the late 1960s. But he only elaborated on the gory details (not quite a spoiler) in his late 90s-00s retconning of that universe. When it turned out that genetically, they were actually binary.
      Even SF authors can’t make it work, and they’re allowed to be unreasonable.

  13. There is nothing non-binary about people with disorders (or differences) in sexual development, no matter how rare or common they are. There is no need to open the chink in the armour: “close enough for me”. No one ever produces a third type of gamete, nor does anyone ever produce a gamete on a spectrum between ovum and sperm. Two gamete types, that’s it. If a person with ovotestis did produce both gametes, — none has — that would not make him/her non-binary any more than petunias and tapeworms are non-binary. But because no one has produced both eggs and sperm, we can include in our definition of binary in humans the further statement: either of two gametes but never both.

    If a human is born with no gonads at all, one can say from a reproductive point of view the person is sexless, but this is also true of normal fertile people who decide not to have children or who are not successful in attracting mates. Humans born without gonads will look enough like baby girls that they can be regarded as being females, indeed they may never suspect anything is wrong until puberty doesn’t happen. Since they look like girls on the outside and not at all like boys, there is no ambiguity in their presentation as girls -> infertile women. So even “sexless” doesn’t violate the binary.

    Just for interest, I looked up the probabilities of poker hands. The one closest to the coin-on-edge outcome is four of a kind in a 5-card deal. This has the advantage of being able to be calculated explicitly but doesn’t address the binary question as nicely as the coin toss.

    Four of a kind in 5-card poker: 1 in ~4000 hands

    1. My guess is that such persons viewed themselves as unlucky women in a bygone era. This is of course, before DNA tests, ultrasounds, and X-rays.

  14. Okay, silly question time. If a child is born without a foot, does that mean that humans are not bipedal?

    1. Of course. It means that feet are on a spectrum.

      Seriously, I wonder how much simple word magic enters into these things. Progressive verbiage often includes the word “rainbow”, so maybe that is why “spectrum” has reached such popularity. Ditto for “affirmative” this or that. Notice also that the DEI clerisy is beginning to add the word “Belonging”, with its positive vibes, to its labels. We can presumably look forward to “puppies” being added next.

  15. I think it’s not best to make a quantitatively grounded argument here. It already concedes too much. People can disagree about whether 1/6000 is a small number or a big number. Sometimes it is, and sometimes it isn’t. If in some alternative universe the 1/6000 intersex people had a role in human reproduction, then no one would dismiss that.

    The real point is that we understand how human/mammalian/… reproduction works, and it has nothing to do with intersex organisms. It is a developmental error, from the point of view of evolution, like many others.

    This is not news to anyone at this blog (much less our host!). My point is only that I think it’s a tactical misstep to make a quantitative argument.

    Thank you so much for the blog, and all you do here!

  16. “only about 1 human in 5,500 is an exception”. In some sense, that number is both too low and too high. Apparently, the probability that a baby will be born with ambiguous genitalia is more like 1:1000. However, genital ambiguity does not mean sexual ambiguity. Almost all of 1:1000 are either male or female (although you might need a DNA test or ultrasound to figure it out). Note that real ambiguity does exist, although it is very, very rare. For example, some humans have both 46,XX and 46,XY cells in the same body. This condition is known as mosaicism. Some humans are 46,XY but have a defective SRY gene. This condition is called CAIS. Are such persons male or female? If you met such a person, you would say female. However, such persons have no uterus or ovaries. Even considering these very, very rare conditions, only two sexes exist. However, very, very rare cases assigning a person as male or female may be difficult or impossible.

  17. In the occasional debates I’ve had on this, the usual issue is that most folks have heard the term “intersex” and take that literally, so I always point out that “intersex” is a misnomer, the preferred term is “DSD” or “Differences in Sexual Development” (it can also be “Disorder of Sexual Development” but that often raises a side debate about supposedly introducing negatively into the discussion) and I point out that DSDs follow a female or male developmental path though there are sometimes ambiguous secondary sexual characteristics.

    The problem with that is that there are many seemingly authoritative sites that use the term “intersex,” don’t mention “DSD” and describe it simplistically and poorly. For instance, here is Planned Parenthood’s description:

    “Intersex means you’re born with biological traits that are outside the strict male/female gender binary, whether it’s your anatomy, chromosomes, and/or hormones. Being intersex is not the same thing as being transgender.”

    . . . which on the surface supports the “sex is a spectrum” argument (and notice they say “gender” instead of “sex” which makes it even more confusing). I’ve learned to always have my own references ready to present but it’s an uphill battle with the confusing material and blatant misinformation on the internet.

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