Ecology Letters, which I thought was a reasonably respectable journal, has now accepted a “viewpoint” article arguing that there is no consensus on biological sex, and that a definition based on gamete size—a consensus if ever there was one—is just viable as “multivariate” definition that incorporates a combination of chromosomes, genetics, and morphology.
They’re wrong and misguided in many ways, but, as Colin Wright notes in a tweet at bottom, there are so many mistakes and misconceptions in this paper that it would take a full reply to the journal to correct them. I’ll just tender a few comments here, but you can read the paper for free by clicking the title below, or download the pdf at this site.
The authors give three definitions of sex: the classical one based on gamete size (males have small, mobile gametes, females large and immobile ones); a “multivariate” one, popular in some nescient quarters, that defines sex base on some combination of morphology, chromosomes, and “genetics,” and, finally something called “sex eliminativism,” which “eliminates the concept of sex altogether.” They graciously admit that they won’t discuss the last one because “rigorous research on sex-based variation remains vital.” True enough.
But they add that the “rigorous research” they propose be done “also challenges simplistic and harmful ideologies of the sex binary”. This is a red flag that their criticism of the sex binary is partly (if not wholly) based not on biology but on ideology, for the “sex binary” is described as “ideological” and “harmful”. (They are talking, of course, about how a binary may harm people who don’t see themselves as fitting into it.) They later add that there are “ethical and political implications of defining sex.” Only if they care to draw them; most real biologists don’t.
But sex was defined by gamete type long before the “gender” ideology began questioning the view that there are two sexes. And definition has been widely adopted, as I’ve said, not on ideology but on universality and utility. (See this discussion by Richard Dawkins.) All animals and vascular plants have only two sexes corresponding to gamete size, so the gametic definition holds across the animal kingdom. That leads to research questions about why this is so: why do animals, for instance, have only two sexes (some rare parthenogenetic species have only one sex: egg-producing females), but not three or more sexes. There are many papers discussing this question, and the answer seems to be that isogamous species evolve by natural selection to be anisogamous ones (two types of gametes), with that state now seen to be an evolutionarily stable to invasion by more sexes. This already shows that defining sex based on gametes is universal among animals and plants and, because it leads to research questions, also utilitarian. It becomes even more utilitarian when we see that the gametic sex dimorphism helps us understand many facts about biology, most notably the morphological and behavioral differences between males and females explained by sexual selection—an approach first suggested by Darwin in 1871.
What are the problems with a biological sex definition? The authors claim that in most cases biologists don’t look at gametes when discussing or enumerating sexes, and that is usually true. When I divided fruit flies into piles of males vs. females, I looked not at their gametes, but their genitals. This is not a problem because in virtually all species there are proxies for gametes: traits like chromosomes or morphology that are closely correlated with sex. They are not 100% correlated, but pretty close to it.
But that’s not a problem, for the authors don’t seem to realize that there’s a difference between defining sex and recognizing sex. The binary gamete-based definition is universal (and of course useful), while a definitions based on chromosomes, appearance, or genetics is not universal. (Many species have sex determined not by chromosome type or genetics but by rearing temperature, social milieu, haploidy, so on.) Still no matter how sex is determined, if you look at gamete types you always find two sexes. Further, the authors don’t tell us how one is to combine the other traits in a multivariate way to define sex in any species. Would they care to give us a multivariate definition of sex for humans (or any other animal)? They refrain—and for good reason: it would be a futile task.
Their other criticisms of gametic sex are that it doesn’t deal with those species like algae or fungi that don’t have morphologically distinct gametes but are isogamous, with gametes looking the same. These species can have dozens of “mating types” based on genes, each of which can fuse only with gametes of a different type. These have long been called “mating types” and not “sexes” by biologists, and are not a problem for most species we’re interested in—including, of course, humans. As Colin notes below:
But anisogamy (reproduction via the fusion of gametes of different sizes) isn’t meant to apply to isogamous organisms (organisms that reproduce via the fusion of same-sized gametes). Anisogamy and the sexes—male and female—are fully intertwined and inseparable. Isogamous organisms don’t have sexes; they have “mating types.” They’re different from sexes, and that’s why biologists aren’t “inclusive” of isogamous organisms when talking about males and females.
The other criticism of gametic sex are just dumb: we can’t tell the sex of an individual before it produces gametes (like young men [in humans, newborn girls already have eggs!]) or after reproduction has stopped and gametes are no longer produced. From the paper:
. . . this narrow [gametic] definition is not inclusive of reproductive approaches beyond anisogamy (e.g., isogamy) and does not classify organisms before sexual maturity or after reproductive cessation as having a sex.
According to these authors, then, newborn boys do not have a sex (newborn girls do) nor do postmenopausal women or some old men who don’t produce sperm. That is crazy because the gametic definition of sex involves having the biological apparatus to produce large or small gametes; it does not have to be operational. To quote Colin again:
And the notion that a gamete-based definition doesn’t apply to sexually immature individuals or individuals who have ceased producing gametes ignores that the sexes are defined by having the biological FUNCTION to produce small or large gametes—and things still have a function even when it’s not being currently realized.
Below is a table from the paper comparing the gametic versus “multivariate” definitions of sex (the latter broken down into chromosomes, genetics, and morphology), seeing how useful each of the types is in defining sex in nine species (click to enlarge). Note that only one species, the New Mexico whiptail lizard (Aspidoscelis neomexicanus) is said to defy definition by gametes. Yet it is called, in the footnoes, a “female only species”. It is parthenogenetic, formed by the hybridization of two regular species having two gametic sexes, and the hybrids cannot produce males but produce females from unfertilized eggs that are diploid and genetic clones of the mother. So if it’s hard to define organisms in this species as male or female, why do the authors call it a “FEMALE ONLY SPECIES.” Because it produces eggs, Jake! It does not defy the binary at all, and you can put a “yes” in the first column where there’s a “no”.
Note that no other form of classification has “yes” all the way down: not chromosomal definitions, not genetic definitions, not morphological definitions (they again make the ludicrous claim that immature individuals don’t have sexes). And when you combine each of the three univariate non-gametic definitions in some multivariate way, you get a mess. Only the first column, the operational definition using gametes, holds in all organisms. But we already knew that.
There’s another table that’s even more ludicrous. This one points out (as they do in the text, so the table is superfluous) that in some species of hummingbirds, some (not all) females have male-like coloration, even though they have large gametes. There is thus a disparity between the gametic definition of sex and a morphological one. But note that the morphology is used as a species-recognition trait here, not as a way to define sexes. This is one case where a proxy trait for sex doesn’t jibe with the gametes.
Are the females with male-like coloration really males? No biologist would say that, and if you look at the references for the table, you see papers like this (my bolding):
1992. “Widespread Polychromatism in Female Sunangel Hummingbirds (Heliangelus: Trochilidae).” Biological Journal of the Linnean Society of London 45: 291–314.
, , and . 2021. “Male-Like Female Morphs in Hummingbirds: The Evolution of a Widespread Sex-Limited Plumage Polymorphism.” Proceedings of the Royal Society B: Biological Sciences 288: 20203004.
, , , and . 2022. “Intersexual Social Dominance Mimicry Drives Female Hummingbird Polymorphism.” Proceedings of the Royal Society B: Biological Sciences 289: 20220332.
, , and . 2021. “Male-Like Ornamentation in Female Hummingbirds Results From Social Harassment Rather Than Sexual Selection.” Current Biology 31: 4381–4387.e6.
These all say that the male-appearing hummers are females that have evolved a male-like coloration (they apparently have done to avoid harassment and get more food). These are cases of polymorphism: some of the females look like males, while others look like regular females. The important question is this: why do all the authors call these male-looking birds “females”? It’s not hard to see: they produce large gametes and lay eggs (the authors used other traits associated with female-ness, like body shape in non-mimetic females, to suss out the male-like females). The females that look like males also show territorial behavior characteristic of males, and that’s because biological males have to acquire territories to attract females. Why do only the males do this? Because of the disparity in gamete size—the male mating strategy is to mate with as many females as they can, while females are more selective. (This is a classic behavioral difference due to sexual selection.)
In sum. the authors only buttress the gamete-based definition of sex in their tables. They do show argue that, in cases where you can be deceived about gametes by other traits, biologists like ones studying hummingbirds should describe the criteria they use for assessing sex. That seems okay to me and in fact that’s what’s done in the paper. But sure enough, the authors use color as a proxy for gamete size, not the other way around! Gamete size is fundamental. This is one case, where, as Colin says:
. . . every non-gametic view of sex is logically incoherent and self-refuting because they all rely on gametes as the conceptual anchor.
Here the color serves as a clue to what the conceptual anchor is and, sure enough, it’s gamete size.
In the end, this paper is deeply misguided and, I suspect, driven by ideology rather than biology. What else but ideology would cause four biologists to make such incoherent and misleading arguments? I could think of other reasons, but ideology is the most parsimonious (and the most au courant) given that the authors call the sex binary a “simplistic and harmful ideology” (it’s not an ideology, but an observation) as well as claiming that the definition of sex has ethical and political implications. No, it doesn’t—unless you are an ideologue.
Colin says in his tweet below, “I have reached out to the editors of Ecology Letters asking if they would consider publishing a counter-Viewpoint.” I hope they do. If they don’t, then they are suppressing valid scientific dissent in the name of maintaining a “progressive” ideology. I would like to think that Ecology Letters would do that. Stay tuned.
Here’s Colin’s tweet, which should be expanded to see his take:
🚨ALERT: Top-ranking ecology journal Ecology Letters has published a “Viewpoint” paper titled “There is No Consensus on Biological Sex.”
The authors call the “sex binary” a “simplistic and harmful ideolog[y].”
Yet they then claim that no view of sex (gamete-based, multivariate,… pic.twitter.com/3V7ksTgA9h
— Colin Wright (@SwipeWright) March 10, 2026
h/t: Michael
“Consensus is the business of politics. Science, on the contrary, requires only one investigator who happens to be right, which means that he or she has results that are verifiable by reference to the real world. In science consensus is irrelevant. What is relevant is reproducible results.”
-Michael Crichton
LIKELY to be from:
Lecture, California Institute of Technology in Pasadena, CA
January 17, 2003
(Have not 100.0% verified)
See https://pmc.ncbi.nlm.nih.gov/articles/PMC2719747/
And obligatory Feynman (100000.000% verified 😁 – I bolded the part that dispels the IMHO mystification from complexity suggestion I get from the article ):
“It does not make any difference how beautiful your guess is. It does not make any difference how smart you are, who made the guess, or what his name is – if it disagrees with experiment it is wrong. That is all there is to it.”
-R. P. Feynman
The Character of Physical Law
1965
Chapter 7, “Seeking New Laws”, p.150 (Modern Library edition, 1994)
ISBN 0-679-60127-9
Truth does not require consensus.
Same failure to recognize the distinction between the definition of something and what it takes to recognize the something. The sex binary based on gamete size defines male and female, but it may (sometimes, but rarely in humans) require a multivariate analysis to recognize male and female if gametes aren’t readily available. Surely the distinction between definition and recognition is widely appreciated in science. Why is that distinction not being recognized here? Proposing multivariate analysis to recognize male and female (if it’s really needed at all in practice) doesn’t reflect on the sex binary definition at all.
There’s little doubt that this paper is contorting its analysis of sex in order to support transgender identification — “if I look, feel, and act like a sex, then I am a legitimate member of that sex.” Definition and recognition therefore HAVE to be conflated with each other. Throw as many things into the pot as you can. The authors don’t have a choice once they’ve made an emotion-based moral commitment for inclusion.
Right. This is a politically motivated effort.
And a rather sad one, in that these chaps have just decided now to show themselves to be “on the right side of history” when it is no longer brave, nor even necessarily the right side anymore. Racing to show your bona fides after everyone else is embarrassing and awkward. They should probably have rejected the paper as being nothing to do with ecology.
I often encourage students to avoid using binary definitions or outcomes and wherever possible take measurements instead. Binary outcomes from an experiment or survey have embarrassingly wide error bars unless n is very large.
I’ve often argued that treating something as univariate binary is usually a mistake, and most things are multivariate measurements or counts.
And then I often finished the rant by commenting that pretty much the only thing that really is binary is biological sex.
I don’t add that last bit any more, but given that my university is somewhat atypical, I doubt I’d get any pushback.
Ever buy a product with a decent to strong reputation for quality only to discover that new corporate owners hollowed out the product while they profit off remaining reputation among the uninformed or those stuck in their habits? Think about those 1960s and 1970s Florsheim shoes that your father or grandfather so loved, and then you regrettably bought a pair in the 1990s. Landscaping equipment, hand tools, household appliances—we can all name our “favorite” examples.
I long ago began to view the peer-reviewed journal process in the same light. The NYT: just slower, more obscure, and leaning even harder on free labor. Sure, I accept there is still great work out there, particularly if it doesn’t touch on the political or anything else addressing the “human.” But how would I know outside of my own domain or the limits of my own time, curiosity, and intelligence?
This sort of thing is why the public is losing trust in science and scientists.
Sadly, you’re completely right.
It’s absolutely insane that in 2026 it needs to be explained that “sex” is a reproductive classification, not an anatomical (etc.) classification… It’s right in the name! Sex!
It’s honestly really sad to see “biologists” who are so confused that they can produce and publish a table that clearly shows the only consistently applicable definition of sex across the entire tree of life is the traditional gamete-based definition, and then they “well ackshually” themselves into arguing against it. What a failure of education and common sense.
Ecology Letters is only a small step up from Reddit or tumblr at this point.
As per Joan Roughgarden:
“To a biologist, ‘male’ means making small gametes, and ‘female’ means making large gametes. Period!”
And even if you redefine “sex”, “male”, and “female” to mean something else, there are still sperm-producers and egg-producers, and we need terms to refer to them.
And yet this is also Joan (formerly John) Roughgarden, “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.” (Evolution’s Rainbow). S/he is well known for straw-manning arguments about sex and gender in order to work out a space in which “trans”women are women.
I’m not sure if you provided that additional quote to agree with it or disagree with it, but what is said in that quote is obviously true.
The two quotes together summarize Jerry’s entire point: some sexually dimorphic traits overlap, but the gametic definition of sex remains binary.
And there are indeed people who make the mistake of thinking that a gamete binary implies non-overlapping distributions of traits. That’s one of the primary misconceptions of people who are opposed to a binary definition of sex. There’s nothing wrong with correcting that misconception.
You’re strawmanning Roughgarden by saying Roughgarden created a strawman in this case.
Sorry I didn’t mean to be cryptic. Our host has asked for shorter comments (and sometimes I go on and on).
I agree with you! But I think Joan Roughgarden is not an honest narrator. “[I]n biology today…” is the straw man: no biologist really thinks that the gamete binary implies that other sex differences should also be binary. Not even Ally Swank (they/them) believes that. In both cases, the claim is just a means to an ideological end.
Swank pretends to believe this in order to justify transgenderism, and her own privileged ranking in the Oppression Olympics that will inevitably lead to a sweet, sweet tenure-track faculty job if she continues to pump out polemics like this Ecology Letters drivel.
Roughgarden uses this critique as a means to her claim that sex means gametes but all other sexually selected traits should be redefined as “gender”. Thus other animals also have gender just like in humans, and gender is a natural and normal part of the rainbow. Jerry wrote about this view, which Roughgarden has unsuccessfully promoted to other biologists for a long time more or less this way:
“In matters of law and policy, ‘sex’ actually refers to elements of gender because the criteria that have historically determined one’s “legal sex” (typically genitals, chromosomes, appearance and/or behavior) are properties of gender and not sex. As such, the courts should recognize that legal sex encompasses gender diversity.”
https://whyevolutionistrue.com/2025/11/20/joan-roughgarden-and-jaimie-veale-on-sex-and-gender/
And that’s Roughgarden’s goal: to make laws and policies focused on sex differences instead focused on “gender”, specifically the claim by male transexuals like Roughgarden to be women in law.
I would argue that parthenogenetic species don’t have a sex category and don’t have sexual reproduction.
I’m not a biologist, but that is my gut reaction as well. Absent a binary (or certainly an n-ary) opposition, there are, by definition, no categories to be distinguished.
In parthenogenetic species their sex cell still undergo meiosis, a necessary step in sexual reproduction
I guess I’m confused. Thanks.
It’s true that parthenogenetic species don’t reproduce sexually, but individuals of those species produce eggs, from which offspring develop (without male input). Since they produce eggs then under the gametic definition of sex they can be regarded as female.
As said in the follow-up comments. But there are species that reproduce asexually without gametes of any kind. They reproduce by budding, or by rhizomes and so on. They would be sex-less.
But of course that makes no dent in the rebuttal to this mis-guided article.
Like Richard Carrier often says, when you put back in the evidence that they deliberately left out, their argument collapses. Of course he’s usually talking about apologists for that other religion, Christianity.
This isn’t the first time I’ve heard the “multivariate” approach being touted as a useful form of hand-waving to cover the assertion that sex is non-binary. It’s convenient because, without abandoning a pretence to be dealing in scientific reality, it insists that sex is a combination of factors whose precise makeup and interrelationships are never specified, essentially creating a sort of Schroedinger’s box whose contents are unknowable. The advantage of this approach is that proponents are never required to specify the contents, while always giving them the option, if someone else tries (and fails) to specify a concrete hypothesis, of saying “obviously that’s not the combination that I meant”.
The mode of argument is essentially theological, like believers unable to articulate what they think god is but who will respond to any characterization of the idea by atheists by saying “obviously that’s not the God that I’m talking about”.
Needless to say, we in the furry community object to the simplistic and harmful ideologies of defining species in terms of genome, or in terms of hybrid infertility (which reflects genomic determinants). We propose, instead, a more inclusive, multivariate definition of species which includes psychology, self-presentation, and persona (or fursona, as we of the furry community prefer to say).
Jon your furrynormative comment is not inclusive of therians and the theriosexual community and is highly offensive. /s
You probably learned in 7th grade biology that “species” is defined as a population whose members can mate and produce viable offspring. But guess what? Some big cat hybrids can produce non-sterile cubs!
And that’s why my cat Delilah, who identifies as a jaguar, is a jaguar. QED.
/s
Thank goodness for Colin and the boss here, and people like that for holding the sane line.
I note “harm” as a motivator/reason YET AGAIN. This word’s mission creep over the past few decades has been startling, wrong, and deeply stupid. Now anything is “harm” – like “trauma”. Which just mean “Stuff I don’t like.”
D.A.
NYC
This subject makes me so tired.
Not the fact that Jerry and others post about the topic—I think that it is a civic duty to point out what is happening. But the fact that scientific publications have subjected science to political folderol- whatever is fashionable among “journalists”, politicians, influencers—whatever —weighs heavily on me.
I suppose it was inevitable; after all, it happened in the humanities and social sciences, so it was bound to get to the sciences as well. But like many of us, I always felt, and continue to feel, that science is something apart. It is a search for truth, and should be independent of ideology. And truth, as we know it, is based on empirical evidence, not ideology, politics, or anything else.
The Communists know you are tired. They are counting on you to get more tired. They do not get tired. They have many miles of institutions to march through before they sleep.
Well, being woken up by missile attacks a few times every night doesn’t help.
One thing that does help my tiredness is a good cigar. My favorites these days are from the Dominican Republic. But I do have to admit that those commies in Cuba make a very good cigar.
I know you were speaking metaphorically, as I was with the “you” pronoun.
Thinking of you every time I imagine the sirens wailing.
Thank you.
The four authors of the article are members of the LGBTQIA+ community (two of whom use the pronoun “they”) or actively support it. Is it therefore a coincidence that they speak out so vehemently against the accepted definition of biological sex? I do not think so.
The authors have also submitted an article to Ecology and Evolution with the following title: “Where we go from here: harnessing Queer perspectives to advance pedagogy and practice in ecology and evolutionary biology.” If the article is accepted, we can look forward to yet another “masterpiece.”
https://www.madeline-eppley.com/publications.html
PS: Madeline Eppley’s homepage includes a land acknowledgment. You cannot get much more “woke” than that.
Gee whiz, I wonder how they feel about Palestine.
I bet I don’t need multivariate statistics to predict the answer.
Good digging. Yes, pretty sad when looking at some bios and one can predict everything in an article. All part on an innumeracy trend in academia in which most evidence excluded or ignored and a laser focus on exceptions (and personal advocacy). True in the Humanities and increasingly true in Science…. it’s really part of the narcissistic me-too movement.
Very well argued here, Jerry. I was going to suggest an alternative Viewpoint article be sent in, but I see the effort is planned. If the editors refuse, then that will be a scandal if ever there was one.
Do let your babies grow up to be bacteriologists, where this shit doesn’t even come into play. Although, if you’re old enough, you may remember when F+ was considered male (they had this long thing…never mind) and where, by George, if you were F-, you could become male in an instant. 🙂
Just occurred to me :
Cooking is sort of, and sometimes exactly, like chemistry or biochemistry.
Now, imagine writing up the recipes for a dish and getting it published (at some level, maybe opinion) in Journal of the American Chemical Society or similar.
The papers’ publication in Ecology Letters strikes me as very much like that.
Sigh….
I was really hoping that gender-mania was on a downward trend. Unfortunately, if these budding PhDs are going to be the educators and researchers of the future, I think we are in for a prolonged battle.
Will they personally ever change their minds? I don’t care if they are gay or lesbian. But whenever I see an obvious female proclaim pronouns “they/ them” I want to say, “I’m not like other girls either”.
Thank you, PCC, for staying on top of this issue (and a million others).
Can someone please explain what is the exact definition of multivariate sex? I have never seen a coherent definition. If it is true that “These traits can be primary sex characters (e.g., gonads, reproductive organs) or phenotypes that often (though not always) differ between the sexes (e.g., morphology or behaviour), and may have considerable within-sex variation”, then how exactly do you know if an individual is male, for example?
Yeah, who knows.
A “multivariate definition” seems like it could allow for the sperm producers in some species to be classified as male and the sperm producers in other species to be classified as female.
I mean, if that’s not true, then under a multivariate definition, sperm-producers are always considered male and egg-producers are always considered female in every species, so what good are any of the other variables besides gamete size in defining sex?
As an operational definition for recognizing sex (allowing for some errors), a multivariate definition may be fine or even necesssary. But not as an underlying definition for what sex actually is.
The only way I could see an operational multivariate definition working is if a bespoke multivariate definition is created for each species. And it would have to be created by first finding the sperm-producers and the egg-producers and determining how the gamete-defined sexes of the species tend to differ on multiple variables. So using a multivariate definition of sex seems to be contingent on first identifying sexually dimorphic characteristics using the gametic definition of sex.
(P.S. “sexually dimorphic” implies “only two sexes”.)