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Ideology trumps biology: Three evolution societies again issue a misleading statement about the definition of sex (Post #30,000)
I wish I had a happier post for number 30,000, but you’re stuck with this one. However, it’s in line with the kind of stuff I’ve been writing about for a while, so it’s appropriate. Today we must deal with a letter from the Presidents of three organismal evolution and ecology societies (The Society for … Continue reading Ideology trumps biology: Three evolution societies again issue a misleading statement about the definition of sex (Post #30,000)
I wish I had a happier post for number 30,000, but you’re stuck with this one. However, it’s in line with the kind of stuff I’ve been writing about for a while, so it’s appropriate.
Today we must deal with a letter from the Presidents of three organismal evolution and ecology societies (The Society for the Study of Evolution, American Society of Naturalists, and the Society of Systematic Biologists), a Diktat declaring that biological sex is not binary, exactly as they did in 2018 (same societies, almost the same statement). Both letters were also responses to statements by the U.S. government headed by Trump, taking issue with the government’s position that sex is binary. HHS incorrectly used genitalia as an earlier criterion for what was binary, but Trump’s new Executive Order uses an accurate definition of sex, one based on whether an individual’s reproductive apparatus is set up to produce large immobile or small mobile gametes. (I guess I should make the requisite disclaimer that while I agree with much but not all of Trump’s statement, that doesn’t mean I endorse Trump!)
My critique of the 2018 statement is posted at this site. I took the position that scientific societies shouldn’t take ideological stands unless they are attacking an ideology that damages the mission of the society itself, and are making a statement that corrects an incorrect but widespread view. Well, this again applies here: these three societies are attacking a biological fact: the binary definition of biological sex, something well within the ambit of biology societies. The problem is that, as in 2018, the three societies are using misleading and false arguments to show that biological sex is a spectrum. Further, as in 2018, the motivation for this statement does not appear to be a scientifically-based attempt to correct government misinformation, but rather seems to be ideological. In fact, biologists have recognized sex as binary (with a few very rare exceptions) since the late nineteenth century, and have based the binary conclusion on the fact that all animals and plants produce two types of gametes, with no intermediates (see below for references).
The desperate attempt in this letter, and the one in 2018, to show that sex is a spectrum intends, I think, to buttress those people who either feel they don’t belong in one of the two sexes, are transsexual (a behavior that assumes two sexes) or feel that they are somewhere in between—or even members of neither sex. But the attempt is misguided, for, as I’ve said repeatedly, morality, as The Naturalistic Fallacy and The Appeal to Nature Fallacy argue, should not be strongly based on biological reality. Observing nature does not tell us what is right or wrong, or specify how we should behave towards others.
However, the 2018 and present letters, instantiate a third falacy—what Luana Maroja and I call the “reverse naturalistic fallacy” described in our Skeptical Inquirer paper (bolding is mine below):
Both fallacies lead to the same errors. First, if we condition our politics and ethics on what we know about nature, then our politics and ethics become malleable to changes in what we discover about nature later. For example, the observation that female bonobos rub each other’s genitals as a bonding behavior has been used to justify why human homosexuality is neither offensive nor immoral. Bonobo behavior is, after all, “natural.” (Similar same-sex behaviors have been reported in many species and have been used to the same end.) But what if no such behavior had been seen in any nonhuman species? Or what if the bonobo observation was shown to be wrong? Would this make homosexual behavior immoral or even criminal? Of course not, because enlightened views of homosexuality rest not on parallels with nature but on ethics, which tells us that there’s nothing immoral about consensual sex between adults.
Second, we must realize that many behaviors that are “natural” because they’re found in other species would be considered repugnant or immoral in our own. These include infanticide, robbery, and extra-pair copulation. As one of us wrote, “If the gay cause is somehow boosted by parallels from nature, then so are the causes of child-killers, thieves and adulterers.” But we don’t really derive our morality or ideology from nature. Instead, we pick and choose those behaviors in other species that happen to resemble a morality we already have. (People do exactly the same thing—ignoring the bad behaviors and lauding the good ones—when they pretend to derive morality from religious texts such as the Bible.)
All the biological misconceptions we’ve discussed involve forcing preconceived beliefs onto nature. This inverts an old fallacy into a new one, which we call the reverse appeal to nature. Instead of assuming that what is natural must be good, this fallacy holds that “what is good must be natural.” It demands that you must see the natural world through lenses prescribed by your ideology. If you are a gender activist, you must see more than two biological sexes. If you’re a strict egalitarian, all groups must be behaviorally identical and their ways of knowing equally valid. And if you’re an anti-hereditarian—a blank slater who sees genetic differences as promoting eugenics and racism—then you must find that genes can have only trivial and inconsequential effects on the behavior of groups and individuals. This kind of bias violates the most important rule of science, famously expressed by Richard Feynman: “The first principle is that you must not fool yourself—and you are the easiest person to fool.”
Thus the latest letter, like the earlier one, is apparently written to try to convince people that in reality sex is not binary in nature, thereby buttressing gender-activist ideology. It is not meant to clarify mistaken biological views. In fact, the letters muddy the waters by presenting a misguided view of sex and giving it the imprimatur of biological societies. As we’ve learned so often recently, though, what scientific societies and journals say often flouts the truth, intended to be ideological rather than scientific.
The problem, then, is not that the societies are making a political statement about biology. The problem is twofold. First, the societies’ attempt to buttress their biological argument is wrong, involving a lot of misleading assertions—all in three short paragraphs.
Second, the Presidents of the Society say they are speaking not only for the 3500 scientists who belong to their organizations, but also for the majority of biologists, saying that their conception of sex represents a scientific “consensus”. It does not, nor do they know this. They did not poll their members before issuing their statement, and they buttress their argument by citing just two papers, one a very short Scientific American op-ed showing that the development of biological sex is complex and can be derailed by a number of mutations, the other a Nature paper by a freelance science journalist who uses a similar argument: the process of sex determination is “complex.” Indeed it is, but development is always complex, and yet, remarkably, evolution has channeled it into two pathways with similar destinations in all animals and vascular plants, producing, by a variety of developmental processes, two types of individuals in these species, one producing sperm and the other eggs. And that journalist, as you see below, doesn’t support the statement at all! Did they even bother to check that? (h/t: a reader below):
No, not at all. Two sexes, with a continuum of variation in anatomy/physiology.
— Claire Ainsworth (@ClaireAinsworth) July 21, 2017
The best refutation of the letter below is actually Richard Dawkins’s Substack piece on the binary nature of sex (excerpted from a forthcoming essay), “Is the male female divide a social construct or a scientific reality?” I recommend that you read it after you read the letter below. But I’ll give one quote from the piece first, showing Dawkins presenting the “Universal Biological Definition” (UBD) of sex:
It is no idle whim, no mere personal preference, that leads biologists to define the sexes by the UBD. It is rooted deep in evolutionary history. The instability of isogamy [the condition in which all individuals have gametes of the same size], leading to extreme anisogamy [the condition in which individuals have gametes of different sizes, meaning two], is what brought males and females into the world in the first place. Anisogamy has dominated reproduction, mating systems, social systems, for probably two billion years. All other ways to define the sexes fall afoul of numerous exceptions. Sex chromosomes come and go through evolutionary time. Profligate gamete-spewing into the sea gives over to paired-off copulation and vice versa. Sex organs grow and shrink and grow again as the aeons go by, or as we jump from phylum to phylum across the animal kingdom. Sometimes one sex exclusively cares for the young, seldom the other, often both, often neither. Harem systems change places with faithful monogamy or rampant promiscuity. Psychological concomitants of sexuality change like the wind. Amid a rainbow of sexual habits, parental practices, and role reversals, the one thing that remains steadfastly constant is anisogamy. One sex produces gametes that are much smaller, and much more numerous, than the other. That is all ye know of sex differences and all ye need to know, as Keats might have only slightly exaggerated if he’d been an evolutionary biologist.
On to the letter, and I’ll try to be brief since Richard’s piece shows the fallacies inherent in their defense of a “spectrum” of biological sexes. The letter is indented, and you can see the original by clicking the title below:
Policy: Letter to the US President and Congress on the Scientific Understanding of Sex and Gender
President Donald J Trump
Washington, DCMembers of the US Congress
Washington, DCFebruary 5, 2025
RE: Scientific Understanding of Sex and Gender
Dear President Trump and Members of the US Congress,
As scientists, we write to express our concerns about the Executive Order “Defending Women From Gender Ideology Extremism And Restoring Biological Truth To The Federal Government”. That Order states first, that “there are two sexes…[which] are not changeable”. The Order goes on to state that sex is determined at conception and is based on the size of the gamete that the resulting individual will produce. These statements are contradicted by extensive scientific evidence.
Scientific consensus defines sex in humans as a biological construct that relies on a combination of chromosomes, hormonal balances, and the resulting expression of gonads, external genitalia and secondary sex characteristics. There is variation in all these biological attributes that make up sex. Accordingly, sex (and gendered expression) is not a binary trait. While some aspects of sex are bimodal, variation along the continuum of male to female is well documented in humans through hundreds of scientific articles. Such variation is observed at both the genetic level and at the individual level (including hormone levels, secondary sexual characteristics, as well as genital morphology). Beyond the incorrect claim that science backs up a simple binary definition of sex, the lived experience of people clearly demonstrates that the genetic composition at conception does not define one’s identity. Rather, sex and gender result from the interplay of genetics and environment. Such diversity is a hallmark of biological species, including humans.
We note that you state that “Basing Federal policy on truth is critical to scientific inquiry, public safety, morale and trust in the government itself”. We agree with this statement. However, the claim that the definition of sex and the exclusion of gender identity is based on the best available science is false. Our three scientific societies represent over 3500 scientists, many of whom are experts on the variability that is found in sexual expression throughout the plant and animal kingdoms. More information explaining why sex lies along a continuum can be found here, under the Education and Outreach tab. If you wish to speak to one of our scientists, please contact any of the societies listed below.
Carol Boggs, PhD
President
Society for the Study of Evolution
president@evolutionsociety.orgDaniel Bolnick, PhD
President
American Society of NaturalistsJessica Ware, PhD
President
Society of Systematic Biologists
president@systematicbiologists.org
Oh dear; what a thicket of misguided argumentation we must make our way through here! Let’s take it paragraph by paragraph.
The first paragraph simply denies that there are two sexes, with sex is defined by gamete size. These contentions, they say are contradicted by “extensive scientific evidence”. But they cite only two papers supporting that, throwing out a number of traits connected with sex but not part of the UBD, a definition that goes at least as far back back as Robert Payne Bigelow in 1894. For a list of gamete-based definitions from different eras, see this paper by Carlos Y. Fuentes (pdf here); the article is in Spanish but should self-translate into English. To check a more recent book, I just pulled the second edition of Doug Futuyma’s textbook Evolution on my shelf, whose various editions I taught from at Chicago. Sure enough, on p. 389 I find this:
Most sexually reproducing species have distinct male or female sexes, which are defined by a difference in the size of their gametes (ANISOGAMY). In ISOGAMOUS organisms, such as Chlamydomonas and many other algae, the uniting cells are the same size; such species have mating types but not distinct sexes.
I’ve pointed out before that the sex binary applies to all animals (including of course us) and all vascular plants, but not to protists, algae, and some fungi. But the UBD of course centers on humans, not algae or fungi, for humans are the object of the letter below. (They do note that the trait diversity that produces a sex spectrum applies to all biological species!)
The second paragraph can be addressed by Dawkins’s excerpt above: it mentions a lot of traits associated with biological sex that show variation, but these are not part of the UBD itself. Let me repeat his words again:
All other ways to define the sexes fall afoul of numerous exceptions. Sex chromosomes come and go through evolutionary time. Profligate gamete-spewing into the sea gives over to paired-off copulation and vice versa. Sex organs grow and shrink and grow again as the aeons go by, or as we jump from phylum to phylum across the animal kingdom. Sometimes one sex exclusively cares for the young, seldom the other, often both, often neither. Harem systems change places with faithful monogamy or rampant promiscuity. Psychological concomitants of sexuality change like the wind. Amid a rainbow of sexual habits, parental practices, and role reversals, the one thing that remains steadfastly constant is anisogamy. One sex produces gametes that are much smaller, and much more numerous, than the other. That is all ye know of sex differences and all ye need to know, as Keats might have only slightly exaggerated if he’d been an evolutionary biologist.
And of course we do see variation in sex organs, chromosomes, behavior, and so on, as well as “the lived experience of people”, which has nothing to do with any biological definition of sex. (What is the “lived experience” of sea urchins, foxes, or gingko trees, that would affect the binary nature of sex in those species?) In humans, the frequency of exceptions to the sex binary lies between 1/5600 individuals and 1/20,000 individuals. As I’ve said, that’s as close to a binary as you can get.
The authors also say this:
Scientific consensus defines sex in humans as a biological construct that relies on a combination of chromosomes, hormonal balances, and the resulting expression of gonads, external genitalia and secondary sex characteristics. There is variation in all these biological attributes that make up sex.
I have no idea what a “biological construct” is! What is the consensus about the meaning of that term?
The argument proceeds to cite a number of factors associated with sex in some but not all species, but, as Dawkins notes, these traits do not partake in the UBD noted by biologists well before we learned about chromosomes or hormones.
The authors fail to address this important question: if sex is defined by where an organism is positioned along dozens of variable axes, like hormone titer, lived experience, external genitalia, sex chromosomes (many species don’t have these), and other secondary sex traits (there’s a reason they’re called “secondary”!), then how do we determine what sex an individual is? It would have to be some kind of combinatorial, multifactoral analysis that takes all these factors into account. And of course it would result in the delineation of a gazillion sexes within many species—perhaps an infinite number in humans! Is that what the authors really believe. If they say they are “male,” for example, how do they know that?
And yet I’m sure that all of the authors of this letter, if they work on animals or plants, would use the terms “male” and “female” without defining them. For example, ASN President Daniel Bolnick, who works on stickleback fish, also sells them from his lab’s “stickleback stock center”. Below are the going prices. Note that they sell ony two sexes of stickleback: male and female. Why aren’t there more? Aren’t there sticklebacks with a lived experience that aren’t either male or female? How does Bolnick define these sexes and why aren’t there more of them?
I see this is running long, so I’ll make just two more points.
First, the spectrum of sex and the denial of the UBD is said not just to apply to humans, but to all species! From paragraph two of the letter (my bolding):
Beyond the incorrect claim that science backs up a simple binary definition of sex, the lived experience of people clearly demonstrates that the genetic composition at conception does not define one’s identity. Rather, sex and gender result from the interplay of genetics and environment. Such diversity is a hallmark of biological species, including humans.
What? All biological species have the kind of diversity that effaces the sex binary, so they must not participate in the UBD, either? Did the authors realize what they were saying? Is sex a spectrum in elephants, possums, aardvarks, cougars, and so on?
Finally, note that the paper repeatedly emphasizes the authority of their societies, as if they were speaking for all their members. But their members were not polled on this (I’ve asked some), and so the statements must have come from the Presidents themselves or more likely the small board of officers of the societies. It is a Diktat from on high, and the implied unanimity is false. Some members I’ve talked to in the last few days absolutely disagree with the statement and are even offended that they are implicitly characterized as agreeing that sex is non-binary. Nor do several people I’ve talked to observed a “scientific consensus” that sex is somehow defined by combining a number of traits in a multifactoral way.
The statement below should and will offend the many members of these societies who do see sex as binary:
However, the claim that the definition of sex and the exclusion of gender identity is based on the best available science is false. Our three scientific societies represent over 3500 scientists, many of whom are experts on the variability that is found in sexual expression throughout the plant and animal kingdoms. More information explaining why sex lies along a continuum can be found here, under the Education and Outreach tab. If you wish to speak to one of our scientists, please contact any of the societies listed below.
Well, I could produce a long list of members of these three societies who do not endorse the letter above. (I was once President of the SSE and don’t endorse it, and I have considerable expertise examining the variability of sex expression in fruit flies.)
In the end, what we see here is three prominent organismal-biology societies having been ideologically captured to the point where they will twist and misrepresent scientific fact to buttress an ideologically-based view that sex is a spectrum. These societies and their Presidents should be ashamed of themselves. Scientific truth is not determined by pronouncements of the presidents of scientific societies, however notable these presidents may be. The UBD is one of the great (and few) generalizations in evolutionary biology, a definition that’s been immensely fruitful in understanding things like sexual selection. It’s a great pity that these societies are trying to scupper the UBD simply to buttress an evanescent form of gender ideology.
