At CSICON this year I gave talk about topics over which skeptics have and continue to disagree with each other. My core theme was that these are the topics we absolutely should be discussing with each other, especially at skeptical conferences. Nothing should be taboo or too controversial. We are an intellectual community dedicated to science and reason, and have spent decades talking about how to find common ground and resolve differences, when it comes to empirical claims about reality. But the fact is we sometimes disagree, and this is a great learning opportunity. It’s also humbling, reminding ourselves that the journey toward critical thinking and reason never ends. On several topics self-identified skeptics disagree largely along political grounds, which is a pretty sure sign we are not immune to ideology and partisanship.

I spent most of the talk, however, discussing the issue of biological sex in humans, which I perceive as the currently most controversial topic within skepticism. My goal was to explore where it is we actually disagree. Generally speaking skeptics don’t disagree about the facts or about the proper role of science in determining what is likely to be true. We tend to disagree for more subtle reasons, although often the reason does come down to a lack of specific topic expertise on questions that are highly technical. The most important thing is that we actually engage with each-other’s arguments and positions, to make sure we truly understand what those who disagree with us are saying so that we can properly explore premises and logic.

Jerry Coyne, author of the book and blog Why Evolution is True, was also at CSICON and gave a talk essentially taking the opposing position to my own. His position is that biological sex in humans is binary, that this is the only scientific position, and anything else is simply ideology trumping science. His talk was after mine so I was very interesting in how he would respond to my position. He essentially didn’t – he just gave the talk he was going to give and then included a single slide with his “responses” to my talk. Except, they weren’t responses at all, just a list of standard talking points that really had nothing to do with my talk.

Now he has written a blog post discussing my talk. Here is his opening paragraph:

“I’ve been busy at the CSICon conference, which included giving my own 30-minute presentation this morning. I had to modify it to take into account the misguided views of Steve Novella, who gave a talk yesterday about “When Skeptics Disagree.” It turned out to be largely a diatribe about how sex in humans is not binary, and in fact isn’t even to be defined by morphology or physiology. As far as I can see, Novella’s view of sex is that one is born with a “brain module” (which of course is biological) that determines which sex you are. No, not gender, but actual biological sex. You can have a “female” module or a “male module”, and regardless of gametes, hormones, genitalia, and so on, you are whatever sex your module dictates to your self-identification.”

It’s difficult to convey how disappointing this response is, from someone I previously admired for his science communication about evolution and creationism. His summary of my position is completely and utterly wrong. Calling it a strawman does not do justice to how off it is. He sat through my talk (as I sat through his), and yet I have to wonder if he actually listened to it. We do agree on one thing – CSI will be making the recorded talks available and people can watch and decide for themselves – please do.

Here is my actual position, as articulated (quite clearly, if the overwhelming feedback I got was any indication) in the talk. Biological sex in humans is multifactorial and complicated, pretty much like all of biology. While there are two pathways of sexual development (we are a sexually dimorphic species), humanity is not “strictly” binary because not everyone fits cleanly or unambiguously into one of two sexes. Pretty much every aspect of biological sex has variations, or “differences in sexual development”, or ambiguous features in some individuals. These are the facts, and you cannot meaningfully disagree about this. So how do skeptics disagree? Largely due to semantics (or I guess making the other side into a one-dimensional strawman).

As an example I used archaeopteryx – a “transitional” species with morphological features that are pretty much half modern bird and half theropod dinosaur (the non-avian branch, if you are using cladistics, which of course is just another tradition of categorization). Creationist Duane Gish famously said that archaeopteryx is simply a bird. It had feathers and it flew, so it was a bird. When confronted about the fact that it also had teeth he say – well, some birds had teeth. He also, interestingly, said that you could look at archaeopteryx as a dinosaur with feathers. He was apparently blissfully unaware of the fact that he was just arbitrarily choosing a subset of morphological features as the “defining characteristics”. You could say feathers and flying equals bird, or teeth, claws, bony tail (and other features) equals dinosaur. Or – you could look at all the features and say it was transitional between these two groups. But that, of course, is exactly what he was trying to avoid and deny.

My larger point was that, in the end our labels are ultimately meaningless. They do not determine reality. Archaeopteryx is what it is regardless of what box we put it in. Saying that some birds have teeth or some dinosaurs have feathers are both equally correct, equally misleading, and equally just non sequiturs.

I then gave as an example of biological sex in humans those with CAIS (complete androgen insensitivity syndrome). These are people who are XY, produce male levels of testosterone, have undescended testes, produce sperm, and do not develop a uterus, but they do not respond to testosterone so they develop otherwise along the female body plan. They have vaginas, a complete (and often even more so than average) suite of female secondary sexual characteristics, and typical female neurological development. So they have male genetics, hormones, and gametes, but female genitalia, body and brain. So – are they male or female? Do some men have vaginas, or do some women have XY chromosomes?  You see the parallel?

There is no necessarily right or wrong answer. Categorization is ultimately arbitrary and context dependent. You  have to ask – why are we dividing humanity up into two categories of biological sex in the first place? Is this just an exercise in abstract biological science, is this for social reasons, medical purposes, designing public bathrooms, or making rules for competitive sports? The answer may differ depending on the context. Also, CAIS is just one example. There are differences in every feature of biological sex, and often those features are ambiguous (there are conditions that are literally referred to as ambiguous genitalia, for example).

To me it is an unavoidable and simple fact that biological sex in humans is not strictly binary. I always use the modifier “strictly” to be as clear as possible. Even critics of this position admit humans are only “mostly” binary when it comes to sex. But they say – “mostly” binary equals binary. But this is nonsensical – it is a purely semantic argument.

What they are saying (pretty directly) is that biological sex in humans is binary, and anyone who does not fit into this binary simply doesn’t count. They also say that some features of sexual dimorphism in humans don’t count. Coyne’s position is that we should categorize biological sex by gametes and gametes only. Why? He only said during his talk that this is how it is done, so an appeal to tradition, I guess. He seems to be engaged in a bit of circular logic – biological sex is binary because of gametes, and we use gametes to define biological sex because they are essentially binary (with rare exceptions). I have also seen him make the justification (which I find ironic coming from an evolutionary biologist) that biological sex is about reproduction, and reproduction is all about gametes. But biological features, even if they evolved mainly for a specific purpose, often take on other purposes and aspects. I would argue that people are more than their gametes. Again – context matters. Should we have sperm and egg leagues in competitive sports? Should we just have pictures of sperms and eggs on signs outside public bathrooms?

Coyne argued that the percentage of people with differences of sexual development is too small to count. He used the very low end of estimates (without disclosing or discussing this fact), but even with this estimate we are talking about millions of people. And also where you draw the line is yet another arbitrary choice of categorization.

He also explicitly argues that the brain does not count. He ridicules this notion in his response, again creating a shallow strawman, and uses quotation marks inappropriately. I never said, for example, “male module” and yet his use of quotes made it seem as if I did. He states that it is my position that only the brain counts – which is pretty close to the exact opposite of my position, which is that everything counts. All sexual dimorphism, from genes to neurological development, are part of biological sex. It is a complex, dynamic, and multifactorial system, with lots of variation. There is no one “correct” way to categorize male and female. Sure, you can make rules that are true for most people. There are typical schemes of development. But whatever system you come up with, there will be people who do not fit. And yet all people count, and not just because they are actual people. Even in the abstract – all data counts.

My final point was that I don’t think we would even be having this discussion were it not for the political controversy around the trans issue. The point, in my opinion, of saying that only gametes count is to argue that the brain specifically does not count. But the brain is a biological organ, and brain development is absolutely influenced by sex genes and hormones. The brain is a sexual organ, and part of sexual dimorphism. Why wouldn’t it count as part of biological sex? I specifically said that at this time we have not identified the specific neuroanatomic correlates of gender identity (which are likely to be complex). But the early research so far is pointing in the direction that gender identity is both real and a neurological trait. It has the features of other neurological traits – like core personality features, and sexual orientation. Most people who identify as trans knew their gender identity from a very young age, and their identity is remarkably persistent over their lives. They are likely not a homogenous group, which is to be expected for a complex phenomenon like gender identity. But again, most show clear signs of gender identity being a persistent neurological trait (something Coyne dismisses as mere “feelings”).

The best analogy here is sexual orientation, which also behaves like a stable neurological trait. People cannot be “turned” gay, nor converted from being gay. Sexual orientation is basically a brain phenomenon, influenced by biological sex, including genetics and the hormonal environment of the womb. And yet, all the same arguments against the claim that gender identity is real and neurological were used against sexual orientation being a neurological trait, including the lack of a “gay gene” (analogous so saying their is no “gender module” in the brain).

This is the basic science, and we should be able to find common ground here. We can have meaningful discussions about what all this means for sports, bathrooms, and medical care for those identifying as trans. That is the social, medical, and political debate we should be having, because this is a complex topic. The claim that biological sex is simply binary, and any other thought is (as Coyne writes) “full-out progressive woke” is just not true. It strikes me as a rhetorical strategy to win the debate by semantic fiat. Biological sex is binary (because gametes) therefore all other discussions about sports and medical care is merely an exercise is delusion.

The position is one giant non-sequitur. What do we do in this specific context with people who do not unambiguously fit into a biological sex binary? Well, the answers seems to be, they don’t count because biological sex is binary because gametes. And they are a small percentage of humanity. But they exist and we still need to decide how best to accommodate them. Insisting sex is strictly binary is not only wrong, it doesn’t even address the issue.

Coyne makes some other claims (as if they are a rebuttal to my position) that are not based in reality (but are suspiciously similar to right-wing talking points and propaganda). He says, for example,

“And what about those people—yes, they exist—who think they really are in the wrong body, and should be a member of another species, like a horse or a cat? Does that actually make them a cat or horse? Of course not.”

First, reports of this phenomenon (called therians) is greatly exaggerated. They are often conflated with other groups (like furries). This is pretty clearly a social and psychological phenomenon, not a neurological trait, and having nothing to do with a system of neurological development (influenced by hormones, for example). He is making some sort of slippery slope argument, which does not hold up to examination. Some people have a strong psychological identity with an animal archetype, just like some people think they are aliens, or that they were reincarnated. This has literally nothing to do with gender identity and is not the same kind of phenomenon.

He also writes:

“One more example. There are people who are nonbinary, but are that way on a temporal basis: they change from feeling male to feeling female on a daily or even hourly basis.”

There are some people who are “gender fluid”. So what? What does that say about people who are not fluid, but remarkably stable in their gender identity (ie, most people)? Nothing. It’s irrelevant. It’s similar to arguing that we cannot treat people with MS because a subset of people with MS have a type that does not respond to treatment.

I think this statement by Coyne highlights his misunderstanding:

“Does a full biological man, with the right genitalia, hormones and chromosomes, but who feels that he’s a woman, actually become a woman (or vice versa for women)? Of course not, unless you think that words mean whatever you want them to. This is why I believe that people can claim to be of any gender, but they can’t actually change their biological sex.”

This is a non sequitur, and has nothing to do with my actual position. It shows that he completely does not get it. Notice that he thinks there is a “right” genitalia. This is a strangely essentialist formulation for an evolutionary biologist. Notice also that he dismisses how someone “feels” as if this is not, in some cases, a function of developmental neurology. But the core fallacy here is the straw man that gender identity changes biological reality. Rather, it is just part of biological reality. The entire point of the “trans” identity is that gender identity (which behaves in most people like a neurological trait) does not align with aspects of sexual morphology. They are not delusional about their genitalia – otherwise they would not identify as trans. Every aspect of biological sex may line up or not line up in some people. That is just reality. Coyne’s entire framing, however, is as a conflict between subjective feelings (which are not real) and anatomy (which is real). And in people where the more tangible anatomy does not line up (like in CAIS)? Well, they don’t count. Only gametes count.

I don’t expect we will agree on the broader issues here. But at the very least we should be able to agree on the basic science. This means getting past pointless semantic arguments and confidently mischaracterizing the “other side”. If I have misstated his position in any way I will happily make corrections, but I tried to fairly and with the principle of charity reflect what he has written. You can read it for yourself and see. My summary here is pretty much exactly what I said during my CISCON talk and have written elsewhere.