Colin Wright debunks a dreadful paper claiming that sex is “multimodal”

Colin Wright has made one of his missions the explanation of biological sex and why those who claim it’s a spectrum—or simply bimodal rather than binary—are misguided. This is important because the “no-binary” crowd is infecting biology with ideology that confuses people. Wright also deals with gender issues, and hosts guest posts on his Substack site, “Reality’s Last Stand”

Colin writes well and clearly, and although I’ve referred you to a number of papers on biological sex in humans and other animals in the last few weeks, this is one of the best. It originated when Wright came across the paper below on bioarχiv—a paper written (largely from ideological motives) to show that sex isn’t binary, nor even bimodal, but multimodal.  What that means is that if you look at different characteristics of organisms instead of just gamete size, you can come up with any number of sexes.

Click to read it, if you must:

Wright found the paper abysmal, because it is. It’s dire and apparently hasn’t yet been accepted for publication anywhere.  In the piece below, which is long but comprehensive, Wright simply dismantles the authors’ claims one by one, leaving them with. . . well, no thesis at all. Their main issue is that the authors apparently don’t understand the biological definition of sex, and so try to pretend that other characteristics associated with sex, including both morphology and behavior, are variable, in turn implying that there are many dimensions of biological sex. In fact there’s only one: gamete size, and if you read their paper and Wright’s refutation, you’ll see that the authors are deeply muddled. The alternative view is that they’re scientifically duplicitous, motivated by ideology to muddle biology. But I’ll be charitable and say that they’re muddled thinkers rather than sneaky ones.

As one example, McLaughlin et al (henceforth “MEA”) think they make a huge dent in the definition of sex by stating that female hyenas have pseudopenises through which they give birth.  The response is easy: “How do you know they’re female hyenas?” Because they make eggs, Jake! Many of the examples in the McLaughlin paper are of this nature, conflating sex with sex-related characteristics.

Click below to read Wright’s critique:

I can’t begin to summarize all the many points of this paper, but let me give a few quotes. (Colin’s own words are indented, except where he quotes MEA, when it gets doubly indented. My own words are flush left.)

The ideological motivation for McLaughlin et al.

Because the sex binary has been deemed “oppressive” and invalidating of transgender identities and experiences—cardinal sins of our age—this has started an arms race among activist scientists to come up with a model of sex that is the least binary thing imaginable. Since the “bimodal spectrum” concept still entails two of something, this must be abandoned as it may be seen as problematically implying a fundamentally binary underlying property that’s producing the bimodal distribution of sex-related traits—and they’d be right!

In pursuit of this goal, a “Multimodal Sex literature survey team” composed of researchers from UC Berkeley and Loyola University Chicago has been assembled to “re-imagine a more inclusive framework for biological sex.” On January 27, 2023, the team produced their first pre-print titled “Multimodal models of animal sex: breaking binaries leads to a better understanding of ecology and evolution.” The paper argues that sex is best viewed as “a constructed category operating at multiple biological levels” (C) rather than binary (A) or bimodal (B).

At the end Colin’s paper notes even more ideological impetus:

The paper ends with a discussion about “the interplay of science and society” that reveal the authors’ true motivations. They assert that “uncritically applying a simple binary without considering the mechanisms shaping sex-specific effects can confound inferences and completely erases the biological realities of TGNC and intersex people.” Further, the authors state:

The historical legacies of sexism, racism, queerphobia, and ableism have deeply influenced the frameworks we use to study nature. Challenging these foundations is difficult but vital to both increasing inclusion in biology and dismantling assumptions that interfere with our ability to observe the natural world on its own terms.

It is undoubtedly true that sexism and racism has historically interfered with producing good science, but we cannot allow new passions and political ideologies to do the same.

The authors make their political motivations explicit:

There is pressure for scientists to avoid making the politics of our work explicit, especially those of us who do not directly study social issues. However, especially in the United States, legislation targeting TGNC people is increasingly undergirded with simplistic binary language purportedly rooted in biology.

Because they believe “binary language” is fueling “legislation targeting [transgender and gender nonconforming] people,” all binary language must be abandoned. As scientists, the authors say we are “best situated to communicate how nature is a rich tapestry of diversity that affirms, rather than invalidates, human experience.”

As biologists we should not be engaged in erasing, invalidating, or affirming people’s identities or experiences. Our job is simple: describe and explain the natural world as accurately as possible.

Those last two sentences are about as clear as you can get.

I haven’t read a single paper claiming that sex isn’t binary in animals (and most plants) that isn’t at bottom motivated by ideology. You might like the ideology, which is often to validate people who feel that their sex isn’t “male” or “female”, but what you want to see in nature needn’t correspond to what we do see in nature. And that’s a sex binary.

Why do I go on about this? Because this is one example of a trend in which people impose onto nature the ideologies they hold, often distorting biology in the process and confusing lay readers. It’s an offense to science, and one that’s the subject of the paper I’ve written with a co-author that will be out in two months. Stay tuned.

But I digress and self aggrandize. Let’s proceed:

Why hermaphrodites are not a third sex. 

The authors [of MEA] then go on to present supposed challenges to the “common assumption” of two sexes. The first challenge they posit is the existence of hermaphroditic species, which they believe violates the binary sex model because individuals produce both sperm and ova and “do not have separate sexes.”

However, the binary classification of gametic sex breaks down when we consider the broader diversity of gametic phenotypes. For instance, hermaphroditic species possess both gamete types required for reproduction, and do not have separate sexes (Jarne and Auld 2006).

The sex binary, however, does not require that the two sexes exist in separate bodies. The authors are simply conflating the sex binary with a phenomenon called gonochorism or dioecy, which is “the condition of individual organisms within a species existing as one of two possible sexes, specifically male or female.” The existence of hermaphroditic and gonochoric species just represent different ways a species can utilize male and female reproductive strategies. Regardless of whether an organism is only male, only female, or both male and female, there are still only two fundamental functions—the production of sperm and/or ova.

I’ll add here that I’ve looked at the literature on human hermaphrodites, and found only two cases in which fertile gametes are produced: one had viable sperm and the other viable eggs. No hermaphrodite has both viable sperm and eggs, as some animal hermaphrodites do. But there are still only two sexes.

The sex binary involves gamete size and the reproductive systems that produce sperm vs. eggs, not other traits.  This is one of the biggest errors that people make when debunking the sex binary; you can see it, for instance frequently espoused by P. Z. Myers and his acolytes. Wright:

To make their strawman argument even more explicit, the authors quote the biologist Joan Roughgarden saying that “the biggest error in biology today is uncritically assuming that the gamete size binary implies a corresponding binary in body type, behavior, and life history.”

Now let me make my point more explicit: biologists do not claim that “the gamete size binary implies a corresponding binary in body type, behavior, and life history,” because such a claim is absurd, unnecessary, and easily refuted by the most cursory glance at reality. [Emphasis is Wright’s, and Myers badly needs to absorb this.]

The final strawman the authors construct is to incorrectly assert that “sex” is a term “used to encompass a broad collection of gametic, genetic, hormonal, anatomic, and behavioral traits.” They claim that semantically flattening all of these traits into “a binary model, for which individuals are classified as either ‘female’ or ‘male’” is “an oversimplification, since ‘sex’ comprises multiple traits, with variable distributions.”

While this portrayal of sex as a combination of many traits is a common belief among those who lack a fundamental understanding of what it means to be male or female, this does not track reality. Rather, these traits are upstream mechanisms that guide sex development and downstream consequences of one’s sex. They do not describe sex itself which, again, refers only to the function of producing a certain type of gamete.

As I’ve mentioned before, the recognition of the gamete size binary—the so-called “flattening”, has in fact been enormously productive in biology, for it’s given us not only an explanatory basis for sexual selection (which itself explains a ton of biological phenomena), but also enables us to make predictions about how parental investment affects behavior (e.g., why female seahorsea rather than males are members of the sex with colorful adornments).

The authors of the MEA paper actually recognize that sex is binary when making arguments against it. For example, they mention the damn penis in the female hyena without realizing how they know she’s a female, and somehow think that variation within a sex effaces the sex binary. I’ll give just one example:

The second case study claims to investigate “the evolutionary consequences of more than two sexes.” Perhaps here we will finally be told what these new sexes are! But the first sentence moves the goalpost from “sexes” to “operative sexes,” which they never define.

The example they give of a species “with more than two sexes” is the white-throated sparrow (Zonotrichia albicollis). This species has two color morphs, males and females with either white or tan stripes. The more aggressive white stripe morph has a large inversion on chromosome 2, and the species mates disassortatively by color more, meaning that white stripe morphs tend to mate with tan striped morphs. This chromosome inversion coupled with the disassortative mating by morph has led to a situation where chromosome 2 “behaves like” another sex chromosome.

But having more than two sex chromosomes is not the same as having more than two sexes. While this species may be an interesting case study for how sex chromosomes have have evolved, it certainly isn’t an example of a species with “four sexes,” which would require four distinct gamete types.

Any competent reviewer of this paper would see immediately that this is a case of sex-related variation in coloration that causes assortative mating, but in the end a male sparrow still produces sperm and a female produces ova, regardless of their color. This interesting case of evolution doesn’t do jack about dispelling the sex binary.

Finally, Wright doesn’t pull any punches about the scientific value of the MEA paper:

In the end, the authors have failed to demonstrate anything other than the existence of two sexes. In fact, their language throughout reveals the fundamentally binary nature at the root of every phenomena they claim debunks it. They have done nothing but demonstrate their complete ignorance of a field they are claiming to be advancing, and have made their political motivations for doing so explicit.

Because this paper is currently a pre-print, that means it has not yet completed peer review. It may be under review somewhere right now. Let me be clear: this paper does not deserve a review; it deserves an immediate rejection without comment. However, given current political trends, I do not trust the review process to filter out papers of such poor quality drenched fashionable DEI rhetoric.

Yes, the paper is dire and full of errors, and surely shouldn’t be published in this form. But regardless, in the course of taking it apart, Wright demonstrates many of the fallacies that plague the “no-sex-binary” crowd, and does so clearly. If you’re interested in this topic, you should have a look at his article. Among those people who keep their eyes on the prize, Colin Wright and Emma Hilton are, in my view, the people most worth following.