Why Are “Gender Critical” Activists So Fond of Gametes?

plus my new video “Trans People and Biological Sex: What the Science Says”

Julia Serano
11 min readFeb 12, 2024
an image (cartoon or painting) of several dozen sperm converging on an ovum/egg
image by Nadezhda Moryak from Pexels

One of the most common ways in which anti-trans activists attempt to delegitimize trans people is by playing the “biological sex” card. As both a biologist and author of several trans-themed books, I have written extensively about the many problems inherent in such “biological sex” arguments. Those writings are collected in Biology, Sex, and Transgender People: A Resource Page. Adding to that body of work, I just released a YouTube video entitled Trans People and Biological Sex: What the Science Says. It is my most thorough critique yet, and it addresses nearly every concern and claim that I could find along these lines — I encourage you to check it out!

But there was one point that I couldn’t quite fit into the video without it becoming far too long of a digression: the recent gender-critical fascination with gametes. This is a rather new development, as infamous trans-exclusionary-feminist books like Janice Raymond’s The Transsexual Empire and Sheila Jeffreys’s Gender Hurts never once mention the word “gametes” or raise the issue of “gamete size.” Indeed, reducing all people down to the status of being either “egg producers” or “sperm producers” appears to be a rather reductive and tenuous foundation upon which to build a feminist movement. For more on this point, see Grace Lavery’s excellent essay Gender Criticism Versus Gender Abolition: On Three Recent Books About Gender.

And, as I discuss in my Trans People and Biological Sex video, gametes suffer from the same problem that genitals, sex chromosomes, and other imperceptible sex characteristics have, namely, we do not rely on them at all in everyday life. Every single day, we call people “he” or “she,” and relate to them as women or men, without ever knowing what gametes they may or may not possess.

Of course, as with all “biological sex” arguments, gender-critical activists are not attempting to appeal to logic or common sense here. Rather, they are making an appeal to authority. In effect, they are saying, “trans activists may insist that sex is a spectrum, but scientists have determined that sex is a strict binary based on gametes.” In this essay, I will interrogate such claims.

Why Gametes?

There seems to be two main reasons why gender-critical activists have gravitated toward gametes. The first is that most other sex characteristics — whether they be chromosomes, genitals, other reproductive organs, and so-called secondary sex characteristics (e.g., facial hair, breasts, muscle/fat distribution) — do not fall into a strict dichotomy. There are XX people who exhibit certain male sex characteristics and XY people who exhibit certain female ones. Some intersex people have chromosome combinations that fall outside of XX and XY, and/or sex characteristics that fall “in between” what is considered “standard” for male and female. In addition to this, trans people often change our sex characteristics via gender-affirming hormones (which alter our secondary sex characteristics) and surgeries (which may reconfigure our genitals and other reproductive organs).

From an anti-trans perspective, the appeal of gametes is that they only come in two flavors: egg and sperm. Indeed, I have seen gender-critical activists assert that there is “no third gamete” or “no gamete in between sperm and egg.” But of course, this isn’t truly a binary outcome, as a significant number of people do not make any gametes, either due to infertility or because they’ve had their testes or ovaries removed. Are such people “sexless” according to this gamete-centric scheme?

In apparent recognition of this giant hole in their logic, some gender-critical activists have taken to adding qualifiers to their claims, for instance, saying that females are “the sex that all going well produces large immobile gametes (eggs),” or who “do or did or will or would, but for developmental or genetic anomalies, produce eggs.” Those links will take you to critiques of such qualifying language and their unforeseen ramifications.

Frankly, this is the same circular reasoning and goalpost shifting that gender-critical activists constantly engage in. Their starting premise (and desired conclusion) is: There must be a strict binary because that would define trans people out of existence. When we discuss how gender identity and gender expression vary in the population, they claim that “gender” is somehow completely divorced from “biological sex” (it isn’t, see video). When they insist that genitals are the primary determinant of sex, we point to trans and intersex people who fall outside of those expectations. When they shift from genitals to sex chromosomes, or the SRY gene, we point to even more exceptions there. So now they’re championing gametes, but once again, there are always exceptions. Because human beings, like all animals, display some degree of sexual variation.

Speaking of all animals, the second reason why gender-critical activists have embraced gametes is that they believe they have stumbled upon a universal definition of sex that overrides all other conceptualizations (and we know how much they love their definitions). Their argument goes something like this: “In organisms that sexually reproduce, scientists categorize the sex that makes the larger gametes as ‘female’ and the sex that makes the smaller gametes as ‘male.’ Therefore, we must use this same standard when [checks notes] deciding which human beings can use which restrooms or play in which chess tournaments. Because science!”

As someone who has a Ph.D. in biology, I have to say that I had never come across this definition before — neither in my biology classes nor in the countless sex determination and differentiation research papers I’ve read over the years — until I read Joan Roughgarden during the 2000s (Roughgarden, 2004, 2009). In fact, outside of the recent spurt in gender-critical writings on this topic, the only people I’ve ever observed making such statements are biologists who specifically study the evolution of sexual reproduction.

I point this out because saying “scientists define sex as…” makes it sound as though we all got together at a meeting and unanimously decided this, when in reality, it seems more like a definition that has taken hold in this one particular subfield. In fact, even within this subfield, some researchers treat this more as a claim than a definitive fact. For instance, Gorelick et al. (2017) say, “The production of eggs vs. sperm is often cited as a way of distinguishing between the sexes,” and Henshaw et al. (2023) state, “Anisogamy is often taken as the defining difference between ‘male’ and ‘female’ sexual strategies” [emphasis mine].

Over the last six months, I have read scores of research articles and reviews on the evolution of sex and anisogamy (more on that word in a minute), yet I have not been able to figure out who first proposed the idea that sex should be defined based on gamete size. On the rare occasion that researchers bother to provide a reference for this definition, they typically cite Charles Darwin’s 1871 book, The Descent of Man, and Selection in Relation to Sex.

If you search The Descent of Man for the word “gamete,” you won’t find anything, because apparently that word wasn’t introduced until 1886; the book was also written before genes, sex chromosomes, and sex hormones had been discovered (Carlson, 2013; Kubiak et al. 2020). There’s also no mention of “sperm” other than one passage about sperm-whales. Darwin does discuss female “ova” and male “fertilising elements,” although I couldn’t find any consideration of their relative sizes (other than a brief mention in Part II, p.274). But what Darwin does assert (at great length) is that females and their ova are “coy” and passive, while males and their fertilising elements are “eager” and active — I will return to this shortly. Also, The Descent of Man is almost entirely focused on sexual selection and sex differences in animals, whereas the universal gamete-size definition of sex that gender-critical activists now embrace applies to plants, fungi, and unicellular organisms as well. Thus, Darwin’s book does not appear to be the true source of this definition.

Aside from the articles that cite Darwin, the only other reference for the origin of this definition that I could find appears in Michael Ghiselin’s 1974 book, The Economy of Nature and the Evolution of Sex. In it, he describes the gamete-size definition of sex as “a convention of terminology” (p. 103) rather than an unassailable fact. So perhaps we should ask how and why this convention arose?

Warning! Gory Biological Details Ahead!

Gamete Size as an Attempt to Construct Universal Maleness and Femaleness Where None Actually Exists

Organisms can reproduce in one of two ways. Asexual reproduction occurs when organisms make a genetically identical copy of themselves. In contrast, sexual reproduction occurs when individuals within a particular species produce gametes that are haploid (i.e., they have half the complement of chromosomes) that can fuse with another individual’s gametes, thereby generating offspring that have a combination of DNA from both parents. There are theoretical explanations for why sexual reproduction is more prevalent in nature, often centered on its ability to generate far more genetic variation (read: variation is a good thing!).

With regards to organisms that sexually reproduce, some make gametes that are all the same size (isogamy), while others make gametes of different relative sizes (anisogamy; occasionally called “heterogamy”). There are theoretical explanations for why anisogamy is more widespread than isogamy, often centered on large gametes being better able to provide resources for developing offspring coupled with smaller gametes being better able to seek out the former.

Over the course of the twentieth century, some researchers within this subfield argued that there was a direct connection between anisogamy and Darwin’s passive/coy females and active/eager males. Often this is called the Darwin-Bateman Paradigm and it’s sometimes associated with Robert Trivers’ “parental investment” theory. Here, I will refer to it more generally as the “gamete size leads to universal sex differences” theory. In my research for this essay, the earliest claims I could find explicitly stating that sex is defined based on gamete size occurred during the 1970s, just as this theory was garnering momentum — so it seems as though this convention stems largely from this theory. While the “gamete size leads to universal sex differences” theory has many proponents, other researchers have pointed out its many exceptions and contradictions (reviewed in Ah-King, 2013; Ah-King & Ahnesjö, 2013; Ah-King & Gowaty, 2016; Gorelick et al., 2013, 2017; Gowaty, 2003; Mokos et al., 2021; Roughgarden, 2004, 2009; Tang-Martínez, 2016).

Some of the articles I just cited make the case that there are no universal sex differences. For instance, many species that sexually reproduce don’t even make differently sized gametes (i.e., they are isogametic). Furthermore, anisogamy appears to have evolved from isogamy independently numerous times (Gorelick et al., 2017; Henshaw et al., 2023), which means that all females and all males across species do not share a common origin. Furthermore, there is evidence that anisogamy may have first evolved in hermaphroditic species who produce both eggs and sperm, rather than in dioecious species that have separate female and male sexes (Henshaw et al., 2023; Iyer & Roughgarden, 2008). Or as we say in evolutionary biology, dioecy (two separate sexes) may be the derived state, at least in some species, which would render the notion of universal maleness and femaleness even less tenable.

In their article, “No universal differences between female and male eukaryotes: anisogamy and asymmetrical female meiosis,” Gorelick et al. (2017) chronicle how gametes are extremely diverse across species, and that there are exceptions to every commonly cited distinction between eggs and sperm (e.g., large versus small, immobile versus motile). Gorelick and colleagues conclude: “Therefore, currently, there are no universal criteria for distinguishing females from males across all animals, across all plants or across all stramenopiles, let alone across all eukaryotes.”

In other words, much to gender-critical activists’ chagrin, gametes are actually a part of natural variation and sex diversity, rather than the antithesis of it.

On top of all this, it is widely accepted that sex determination pathways are far more plastic and rapidly evolving than most other biological systems (reviewed in Ah-King & Nylin, 2010; Capel, 2017; Herpin & Schartl, 2015; Nagahama et al., 2021; Yadav et al., 2023). For instance, some organisms have XX/XY sex chromosomes, while others have ZW/ZZ chromosomes, and still others rely on environmental cues like temperature to determine sex. There’s also “sequential hermaphrodites” who can change their sex mid-life. And so on.

While anisogamy may be the most efficient way to sexually reproduce (hence the convergent evolution toward it), the way those gametes are “packaged” (to borrow a phrase from Roughgarden, 2009) into bodies differs significantly from species to species.

Seeing Sex

In my most recent book Sexed Up: How Society Sexualizes Us, and How We Can Fight Back, I analyze the largely unconscious mindsets that shape how we see and interpret sex. These include the “Two Filing Cabinets” mindset that we learn as children and which leads us to compulsively categorize everyone we meet as female or male, thus making it difficult for us to contemplate trans, intersex, and nonbinary people (pp. 19–39). Then there’s the “Predator/Prey” mindset, which leads us to imagine men as active “sexual aggressors” and women as passive “sexual objects” — this creates numerous sexual double standards that feminists have long challenged (pp. 85–107). Despite the fact that these mindsets do not accurately depict human sex and sexuality, many of us rely on them in order to make sense of the world.

The tendency to project “passive/coy” and “active/eager” stereotypes onto females and males (respectively) of other species seems driven by a combination of anthropomorphism and the Predator/Prey mindset, which explains why many researchers persist in doing this despite the countless documented exceptions that disprove the “rule” (see Ah-King & Ahnesjö, 2013; Roughgarden, 2009, pp. 23–60). And the desire to find a singular universal sex difference that applies to all human beings, or even all species, seems like a desperate attempt to rationalize our Two Filing Cabinets mindset.

As I detail in my Trans People and Biological Sex: What the Science Says video, sex is multifaceted, variable, and somewhat malleable. It’s multifaceted in that we have numerous sex characteristics that may develop somewhat independently of one another. It’s variable in that these sex characteristics are complex traits influenced by many factors and which give rise to bell-curve-shaped outcomes rather than strict dichotomies. And it’s malleable in that sex characteristics exhibit bipotentiality: As embryos, we all had the capacity to develop male or female anatomies had we been exposed to the right signals, and as adults, we may develop female or male sex characteristics depending upon the hormones in our system.

Trans people are a pancultural and transhistorical phenomenon, indicating that we arise as a part of natural variation rather than being mere products of any specific culture. Or to put it differently, we are the inevitable outliers that exist in every complex biological system. If you detest us for some reason, I suppose that’s your prerogative, but please don’t feign concern about “gametes” or “biology,” as it’s clear that you couldn’t care less about such things. If you truly understood or cared about biology, then you would embrace the reality of biological diversity rather than wielding dumbed-down caricatures of biological concepts in an attempt to further marginalize trans people.

This essay was made possible by my Patreon supporters — if you appreciate it, please consider supporting me there. A non-paywalled version of the same essay can also be found on Substack.



Julia Serano

writes about gender, sexuality, social justice, & science. author of Whipping Girl, Excluded, 99 Erics, & her latest: SEXED UP! more at juliaserano.com