Getting straight about sex: A collection of useful videos about sex and sex differences, and some mishigas by a couple of scientists

December 4, 2022 • 9:15 am

A reader called my attention to a site that looks to be a gold mine of information on human sex, how sex evolved, why there are only two sexes, and on the various disorders of sex development, or DSDs (the term “DSD” isn’t much liked by the no-binary-sex crowd, but it’s ensconced in the literature).

The two dozen videos, mostly about biology rather than ideology, were made by the Paradox Institute, which states its mission this way (I’ve put in a link to the site’s founder):

Created in 2020 by Zachary Elliott, the Paradox Institute is an independent science education group focused on helping people learn about the biology of sex and the differences between males and females.

From cleanly illustrated animated videos to long form essays, the Paradox Institute aims to provide informative and entertaining content on some of the most fundamental and controversial research in the biology of sex differences.

And though the videos largely focus on biology, of course they have a quasi-ideological purpose: to dispel misconceptions about the binary nature of sex (yes, it’s binary), to explain why the sexes in animals are only two, to explain why traits like chromosome constitution are correlated with but not part of the definition of sex, and to explain the variety of DSDs.  This is important because the site uses science to correct widespread misconceptions about sex—misconceptions, like the view that “sex is a spectrum”, that arise from ideological commitments.

You can see the panoply of videos by clicking on the screenshot below:

I’ll post just three (all are on YouTube), and you can be the judge. I think watching these is a good way to inform yourself about the biology involved in the Sex and Gender Wars.

Below are the most important ones, which give you the biological definition of “sex” (i.e., what is a sex, not the act of sex!), and explain why there are two sexes. I’m interested in these because I’m writing a bit on the sex binary now.

The second video is longer and includes what’s in the first, so you may want to watch that one instead if you have time (the second is 17 minutes long). As far as I can judge, the videos are biologically truthful, which means they’ll offend those who want to claim that sex is a a continuous distribution—the “spectrum”.

In his influential book The Genetical Theory of Natural Selection, the famous but now canceled biologist R. A. Fisher extolled the virtue of theoretical biology in this way:

“No practical biologist interested in sexual reproduction would be led to work out the detailed consequences experienced by organisms having three or more sexes; yet what else should he do if he wishes to understand why the sexes are, in fact, always two?” (p. ix)

The video below gives an answer for the layperson that avoids mathematical messiness. Let me add that having two divergent types of gametes, one large and immotile and the other small and motile, is an “evolutionarily stable strategy” (ESS): once these two types have evolved, no other gamete type can evolve and invade the population. And that’s why the sexes—except for the “mating types” in some protists and fungi—are always two.

On the other side of the ring, wearing the blue trunks, is the Science-Based Medicine gang, which have lost their bearings over sex and gender after removing Harriet Hall’s laudatory review of Abigail Shrier’s book Irreversible Damage. Now they’re saying that sex isn’t binary but bimodal, and other such mishigas. This article by Andy Lewis from the site “Reality’s Last Stand” shows how far the nonsense has gone (click on screenshot):

An excerpt:

[Steven] Novella sums up his argument in a paragraph:

Biological sex is not binary

The notion that sex is not strictly binary is not even scientifically controversial. Among experts it is a given, an unavoidable conclusion derived from actually understanding the biology of sex. It is more accurate to describe biological sex in humans as bimodal, but not strictly binary. Bimodal means that there are essentially two dimensions to the continuum of biological sex. In order for sex to be binary there would need to be two non-overlapping and unambiguous ends to that continuum, but there clearly isn’t. There is every conceivable type of overlap in the middle – hence bimodal, but not binary.

This is quite an extraordinary claim for the simple reason that not a single peer reviewed biology paper, written by a biologist, has ever claimed that sex is best described as “bimodal.” There may be papers that characterise sex differences in various features (the amount of dimorphism, etc.) as being bimodal, but not sex itself. How can Novella be so confident in saying that the “bimodality” of sex is uncontroversial among experts when not a single expert has ever said it in their primary literature? This needs explaining.

Read the explanation for yourself. The end of the piece says this:

Steven Novella sets out with the explicit political intention of showing how people with trans identities fall in the middle of a “bimodal distribution of sex.” He claims this characterisation of sex is settled and non-controversial.

What I have shown is how biology reveals sex to be a strict dichotomy of male and female based on anisogamy (two distinct gamete types). No peer reviewed biology paper has ever characterised sex itself as bimodal and shown how to create this statistical distribution from measurements of sex. At best the bimodal idea is a metaphor. At worst, it is handwaving nonsense. The idea has not come from biological science but from “gender studies” academics with explicit political agendas.

. . . In Part II, we will look at how Novella ups a gear and introduces new muddles and conflations between sex and sexuality, between sex and gendered expressions, how the controversy over brain dimorphism is exploited, and how incoherent concepts of “gender identity” muddy the waters.

Finally, I will address why this massive muddle exists. What is going on where so many people are now believing things found nowhere in the actual primary biological literature? How did Novella come to write such a tangled web of nonsense?

I couldn’t find part II of Lewis’s piece, but maybe I didn’t look hard enough. At any rate, Novella (a neurologist) and the Science-Based Medicine website are influential communicators of science, with many followers. But on this issue, at least, it’s gone off the rails.

Another person who’s wobbling on the rails appears to be Neil deGrasse Tyson, also a respected and wildly popular science communicator (and of course, an astrophysicist). Although in the past I’ve been mildly irritated by his waffling about being an atheist vs. an agnostic, I have no major beef with him and do enjoy his palpable enthusiasm for physics. But I have a small beef today (a filet mignon?): Tyson, like Novella, appears to reject the binary nature of biological sex.

Reader Luana sent me this tweet showing pages from a new book by Tyson, Starry Messenger: Cosmic Perspectives on Civilization. You can read what he wrote in three pages, and I have no big objection to most of what is shown, though it gets a bit weird when he says, “At last count, there were at least seventeen [gender] nonconforming designations. . . “. That’s a remarkably precise statement when there are at least 100! But he’s talking about “designations”, which means words, not clear-cut categories.  What really bothers me is what he says in the two excerpts below, particularly the second (I’ve added the red rectangles for emphasis:

Now that’s not egregious, though the world still remains “quite binary” when it comes to biological sex. But Tyson appears to be conflating sex with gender, as we can see from the truly bothersome bit below:

“The presumed binary of sex in nature is overrated and rife with exceptions. . . “?  “Presumed “binary? And “rife” with exceptions? The exceptions to the binary are 0.018% of the population, or about one person in 5600. If 5599 people are either male or female, and there’s one intersex person, that’s as close to a binary as you can get.

Here Tyson, like Novella and many others (see our old friends at Scientific American here and here), want to be on the side of the angels by asserting that sex, like gender, is a spectrum. Well, gender is more towards being a spectrum than sex, but gender is still bimodal rather than binary. That is, there are two frequency humps for gender roles (“male role” and “female role”), and many more individuals in between than the 1/5600 we see for sex.

This is my prime example of the distortion of science by ideology.  The purpose of pretending there are more than two sexes is to support those who have assumed non-traditional gender roles. In other words, those who question the binary nature of sex are doing so because they’re trying to make nature itself conform to an ideology that accepts the non-binary nature of gender. The conflation is deliberate, an example of what I call the “reverse appeal to nature”: “what is good must be what is natural.” But as Richard Feynman said about the Challenger space shuttle disaster, “reality must take precedence over public relations, for Nature cannot be fooled.”

And, in the end, there’s no reason to misrepresent science: people of different genders can be supported and respected without having to distort the nature of biological sex.

h/t: Allan, Christina

56 thoughts on “Getting straight about sex: A collection of useful videos about sex and sex differences, and some mishigas by a couple of scientists

  1. Perhaps an email to Dr. Tyson, giving him a basic lesson in biology, is necessary. Knowing about Venus and Mars doesn’t seem to have helped him much in this area of the pursuits of scientific knowledge.

    But if the assertions that sex is binary were true, what, pray tell, would that look like? An egg with a flagellum that seeks out non-motive sperm? A spermatazoan with an enormous head and additional mitochondria that is fertilizes by a smaller spermatozoon? Two eggs that merge, or two spermatozoa? What is it that there people actually think happens during sexual intercourse and reproduction? And why must they assert that denying biological sex is anything but binary automatically leads to transphobia, as if one must always put a moral value on such things? Things can be different without necessarily being good vs bad, which is the binary thinking they promote but which they should be discarding.

    1. I think, Christopher, you meant to say “non-binary” where you say “binary”. Sex is binary. It is the trans ideologues who say it is non-binary.. it is they, not us, who deny that sex is anything but binary. Everything you say is factually true. You’ve just switched the non’s around in the way the terms are used by the two sides.

      Aside to Jerry: even the one person in 5600 who exhibits true hermaphroditism is still binary. If the person produces any gametes at al—many don’t—they will be recognizable sperm or recognizable ova, no “intermediate” or “spectral” gamete, like an imaginary “ovosperm”. The rare individual who produces both gametes is therefore still binary. S/he merely represents both binary gametic sexes in the same body…, of course, do regularly occurring hermaphrodites in tapeworms and some flukes, where if you are the only worm that grew inside the host and reached adulthood, you would have a lonely, childless existence if you couldn’t have sex with yourself. But these worms are still sexually binary.

      So in my view, you don’t have to concede that hermaphroditism requires you to say that 5599 out of 5600 is as close to binary as you can get. Even that one is still binary: 100%.

      1. Yes, you have a point, though there are many DSD’s lumped together in the 1/5600 frequency, not just hermaphrodites. Read the paper I linked to. If you were a hardass, I suppose you could make a case that all intersex individuals could be assigned to one sex or another, and that they’re certainly not members of a “third sex”! But I’m happy to let people say that some DSDs can’t be assigned to male or female categories, so long as we realize that they are vanishingly rare, and don’t affect the “sex binary”.

        1. This is just to acknowledge that I was wrong in my recollection of the Sax paper. (It rebuts the oft-made claim that 1.7% of the population is intersex.). It’s paywalled, but I agree the prevalence of true hermaphroditism is much less than 1 in 5600 live births.

          DSDs are not relevant to trans-gender ideology in any case, which is what I would say when any activist brings them up. That, and that they are rare.

      2. Yes, Leslie, good catch there. Fat thumbs or damn autocorrect, or perhaps my own a stupid brain. And I don’t usually get the chance to edit. My comments take an unusual amount of time to appear and rarely show the edit feature. Granted, the edit feature can’t make up for my being probably a good 20 IQ points or more below the average commenter here.

      3. Individuals with Turner syndrome or other relatively common DSDs often bristle at the idea they are not men or women, and that they somehow fall in between the two sexes.

  2. On the topic of sex differences, and since I use a pseudonym here, I’ll go ahead and share that I had dinner with a Nobel Laureate who won it for a discovery of RNA interference. The meeting was an excruciating experience. He claimed that biological sex was a continuum. Dear Ceiling Cat in the Sky of Diamonds, how, or how, could a biologist claim such idiocy? But he did. Notekin: He’s a fan of Stephen J. Gould. I left the meeting depressed. Wokeness destroys everything.

  3. Another good article from Andy Lewis on this topic is “On the Ontology and Epistemology of Sex”, which can be found on his Quackometer website. It points out how those who argue against two sexes will seamlessly but erroneously switch between the questions of “what is sex” and “how do you determine the sex of a particular individual” depending on which supports their argument.

    1. Yes, I learned about that essay from this website. The distinction between ontology and epistemology is key to understanding what’s going on in these discussions.

  4. I found the video about why there are two sexes to be fascinating.

    But it also made me think: isn’t there a second reason for why sexual reproduction would have evolved to involve two–and only two–parents? To wit: Having only two sexes enables the individual to simultaneously get the advantage of sexual recombination while maximizing its individual genetic contribution to offspring. That is, with two sexes, each parent contributes 50% of its genes to offspring. If you had three or more sexes, each parent’s contribution to offspring would plummet. In a way, that would also mean that its fitness would plummet, yes?

    1. Yes partly. The main reason not to deviate from 50-50 is that in an unequal mating one parent gets more genetic benefit from the union, and this would be evolutionarily unstable (a population like that could be invaded by a mutant that enforces a 50-50 sharing).

      But the main reason that 2 parents are required and each has to contribute half of the genes to the zygote is because gametes are formed by dividing the genome in half (and here we’re ignoring sex chromosomes, which are a derived way to organize your sex-linked genes, and are not found in all organisms). If the genome was divided into thirds in the gonad to make gametes, then 3 gametes and 3 parents would be needed to form an offspring with a genome similar to the parents (and this is the whole point of reproduction).

      Organisms could have sex this way but they don’t. Why is the genome divided in half always? Because meiosis and gamete formation is evolutionarily derived from a much older and simpler process – mitosis or simple cell division – and meiosis reuses a lot of the same cellular machinery (microtubules for the chromosomes to ride on, molecular motors to push the chromosomes to different parts of the dividing cell, etc.) used for mitotic cell division. Meiosis is not the only way for organisms to have sex and recombination (bacteria do it just fine), but for diploid organisms it’s the only way to fly.

  5. I’ve never paid attention to the use of “gender” vs. “sex” before when I read biology. Are they actually synonyms and interchangeable? It seems to me that at this date gender is the social construct, meant to side-step the more precise and obvious nature of the sexes.

    1. The terms were used synonymously for decades in the literature, but recently–the last 10 years or so–I think pretty much everybody understands it as you say. There were holdouts, and may still be.

      1. If on a questionnaire or so they ask ‘Gender: M or F ‘, I often take the absolutely useless trouble to strike through the ‘Gender’ and write-in ‘Sex’. Such is my pettiness (on occasion).
        I have not yet seen (praise the Lord!): ‘M, F, other’

  6. According to these videos, sex is defined by whether or not an individual produces small gametes or large gametes, so sex is essentially binary- or at least a bimodal distribution with very small variance around the modes.

    In contrast, gender is a bimodal distribution with large variance around the modes.

    According to this definition of sex, is a man still a man after he gets his testicles (small gamete-generating organs) removed?

    1. I’ve discussed this issue before. Yes, he’s still a man because he was born with the apparatus for making sperm. That also goes if he’s sterile or hasn’t produced sperm yet. And a postmenopausal woman is a biological woman.

        1. People go by whether you have testes, sperm-making tissue, an so on. When a baby is born, virtually every time you can predict from its reproductive tract what kind of gametes it’s going to produce (female babies are born already carrying eggs).

    2. Obviously after castration he still is a man, it is not as if a male eunuch will start producing eggs or intermediate gametes.

  7. If sex is defined by gamete production, and there are two size-and-mobility types of gametes, that makes four logically possible sex-characteristics for an organism, by my count: hermaphroditic, male, female, and sexless. Sure enough, two of those categories are going to be very thinly populated in many species – an important fact which evolution obviously predicts. But I still call it a misnomer to say that sex is a binary. It’s two binaries.

    1. A hermaphrodite human has both male and female gametes. Everyone else has one or the other or none.

      Where is the third gamete?

      1. Actually, I’ve found only one case of a hermaphrodite that made both sperm and eggs that functioned. Most are either partly or completely sterile, or make only one viable gamete. But, as you say, they are not a third sex–any more than dioecious plants.

        1. I’ve seen you refer to this case before, Dr. Coyne. I wonder, would this individual have been able to fertilize him/herself and create a new human being? If so, would it essentially have been a clone?

          1. No these individual humans are not self-fertile and can’t successfully make and gestate a fetus. Also that fetus wouldn’t be a clone because genetic recombination shuffles the complement of parental genes in each gamete: when two gametes from the same individual fuse, the genome is virtually guaranteed to differ from the parent.

          2. Mike, if they were able to create both a sperm and egg, why couldn’t they fertilize themselves – with a bit of laboratory help? Obviously, the offspring wouldn’t be a clone, thanks to recombination.

            I do think that in vitro gametogensis, the creation of new gametes outside the body, is a fascinating topic.

      2. Is a gamete a sex? I thought sex was defined by gamete-production ability. Since there are two types, and an organism can have the ability to produce both, exactly one, or neither – well, I could repeat myself, but why bother.

    2. Hermaphrodites are simultaneously male and female. They are not themselves a sex because they can mate with either males or females. And they make either male or female gametes, not a third type.

      Sexless is not a sex because to be a sex you have to have the potential to reproduce. Sequential hermaphrodites, like clownfish, are first one sex and not the other; they’re almost never both sexes in the same body.

      1. Regarding “Sexless is not a sex because to be a sex you have to have the potential to reproduce”, would an individual born with the apparatus for making sperm (testes, etc.), but who is nonetheless unable to produce viable sperm that could potentially lead to reproduction still be considered male? Or sexless?

          1. But, per the scenario described, if the person is unable to produce reproductively viable sperm, then the person has no potential for sexual reproduction. Hence, according to the definition “without any means or potential for sexual reproduction”, the person should be regarded as ‘sexless’.

            Even if the person has other reproductive equipment that is typical of males, the person still lacks reproductive capacity- so is sexless (per the definition).

            Sorry if I’m being obtuse. I’m just trying to gain clarity on the definitions that are being used for ‘sex’, ‘male’, ‘female’, ‘sexless’.

          2. Yes, you are being obtuse. I said, as I believe, the apparatus for making sperm or ova, regardless of whether it’s working. Do you think a postmenopausal woman is “sexless”?

            Give us your own definition instead of “just asking questions.” On second thought, never mind

      1. As I understand what Jerry (and the biologist in the video) said, sex of an organism is determined by what gametes it *produces* (or did produce before e.g. menopause). One that produced none and never could, would be sexless.

        1. No, I said sex is ascertained by “what gametes its reproductive system is ‘designed’ to produce.
          If you want to proffer your own definition and then tell us how many sexes it leads to, be my guest.

          1. Sorry for getting that wrong. So, if an organism has a chromosomal abnormality leading to lack of any gamete producing tissues, can it always nevertheless be said to be *designed* to be male or female? If not, wouldn’t that mean it has neither sex, according to the definition? What about a chimera that had the misfortune to fail to develop any gamete producing organs, because its female-typical chromosome bearing cells and its male-typical chromosomal cells were all in the wrong places?

          2. I don’t think you can use any kind of disordered sexual development to probe the value of a classification system that is organized around normal developmental outcomes. There are two normal sexes based on gametes and the tissues/organs that produce and conduct them toward fertilization. No matter what abnormalities arise, none has ever produced a third type of gamete, not even a non-functional one, which shows how rigidly conserved the whole sexual process is.

            I can’t see how it matters whether you define a person with no gonadal development as an embryo sexless or not. Since such babies appear to be female at birth, regardless of Y chromosome or not, they are going to grow up regarding themselves as girls. The diagnosis won’t be made until menstruation fails to start. Common sense says we will call them women without ovaries. We won’t tell them to go back to Vital Statistics and change their birth certificates to X or, worse, to M.

            I commented elsewhere today.

          3. I’ve said a lot on this thread already, which is discouraged by The Roolz, so, last quick point. It’s not about the value of birth certificate classifications – it’s about spelling out the logic of the biological definition, which contains two binaries. Namely, (1) designed to produce small gametes (yes/no); (2) designed to produce large ones (yes/no). Precise formulations enhance rational discussion, and I’m a big fan of boolean logic.

  8. > If 5599 people are either male or female, and there’s one intersex person, that’s as close to a binary as you can get.

    It’s certainly close enough for most people, most of the time. Not all people all the time, but most.

    1. Really, do you have to barge in here with fatuous remarks like that? I presume you’re the one who doesn’t buy it as a binary.

      What point are you trying to make? That a tiny number of people don’t see that as effectively a binary?

  9. All of this mess seems to stem from the failure by the ‘more than 2’ side to grasp, or refusal to acknowledge, the very sharp literalness and black-and-white specificity of science and scientific terms, and that many attacking the ‘more than 2’ side do so for completely non-scientific, even antiscience reasons, That’s what I said on twitter. The ‘more than 2’ side’s position is at least somewhat understandable considering the history of what those not falling within accepted ‘norms’ of behavior have suffered, they will fight against anything that justifies the treatment they’ve endured. What’s far more disturbing in my mind is the most vehement of those on the ‘right’ side aren’t on the right side for valid reasons, they no more understand the actual science than the ‘wrong’ side, they see non-traditional gender behavior as an attack on their religion, that it means their god made a mistake in some way, that their dogma is wrong, even immoral, and they can’t have that.

  10. Whatever happened to “extraordinary claims require extraordinary evidence?” Now a bearded male says to skeptic Steve Novella, “I’m a woman,” and Novella replies, “Yes ma’am, this way to the women’s locker room.”

    1. I concur. In fact, I tried to email former Atheist Experience host Matt Dillahunty, who describes himself primarily as a skeptic, to ask the following:

      Isn’t the properly skeptical approach to question the assertions of a person who is morphologically one sex but claims to be the other? There are multiple ways to sort this out, primary and secondary sex characteristics, skeletal characteristics (this is a thing, I learned while working in the field for a few years with archaeologists recovering remains from World War II; they can also determine, broadly, race, with a high degree of confidence) genes, gamete-producing setup, and so on.

      It seems passing strange that the assertions of how someone “feels inside” should be the governing factor, here.

  11. What you called the “reverse appeal to nature” was named the Moralistic Fallacy by Bernard Davis. I suspect that virtually all attempts to deny sex differences is motivated by either the moralistic fallacy or the appeal to nature fallacy, because people don’t realize you can believe men and women are different and still care about their wellbeing. It’s called utilitarianism and it cares only about maximizing human wellbeing no matter what their traits are.

  12. On the Paradox Institute website, Zachary Elliott introduces himself as an architecture student. He graduated from High School in 2016 and does not have formal training in biology. Nevertheless, he was able to create accurate and truthful videos that clearly communicate misconceptions about the biology of sex.

    On the Quackometer website, Andy Lewis introduces himself as the inventor of the quackometer, “an experiment to see if it is easy to spot quack web sites just from the language they use.” His article was originally published here and then republished on Colin Wright’s site, “Reality’s Last Stand.” As far as I can tell, Andy has no training in biology. He says, “A common response to my posts has been to question my qualifications for writing. This is known as an ad hominem attack and I will always try not to engage…I want to see who is presenting good arguments for their claims and who is talking gobbledegook. For this reason, I do not want to offer chances for my critics to start fights about my education. I want to stick to the arguments.”

    As best I can tell, Part II of Andy Lewis’s analysis of Steven Novella’s posts on Science Based Medicine has not yet been published. I will keep my eye out for it.

    I’m impressed that these two people were able to produce high-quality arguments on a complex topic without formal training in biology. They have demonstrated that evidence and rational arguments are more important than credentials.

    I also appreciate the fact that they are talented communicators. Zachary Elliott is on Twitter and explained how he is able to change people’s minds in this thread ( Responding to a young activist that thought atypical chromosomes were additional sexes, he asked, ““How do we know the sex of crocodiles? They don’t have sex chromosomes at all.” He goes on to introduce one of his videos and elaborates, “The database mentioned is called the Tree of Sex (, which catalogues all the different sex determination mechanisms across tens of thousands of species of plants, vertebrates, and invertebrates.” You can read the thread to find out how he changed the mind of this activist, but I find it impressive that he found a constructive way to engage.

    I have been reluctant to speak of the biology of sex for fear of being viewed as a guy with a tin-foil hat on my head by people with a “Believe Science” sign in their front yard. Colin Write speaks to this point while being interviewed by Meghan Daum on her podcast “The Unspeakable” ( This episode is about youth gender surgery is causing real harm to young people. Future generations may look back on this practice the way we look back at lobotomies (I acknowledge that in both cases the advocates were well intentioned).

    Bad science get corrected only by the minority standing up to the establishment with good evidence and arguments. Thanks to Jerry, Zachary and Andy for leading the way.

  13. What I miss in the explanation of this overwhelming trend towards the dichotomy between large slow eggs and nimble small sperm, is the role of mitochondria. Nick Lane is quite good at explaining this in his “Power, Sex, Suicide: Mitochondria and the Meaning of Life”. A must read. He also explains ‘why Eukaryotes have a nucleus’ in his stride (spoiler: it is due mitochondria).

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