Gametes Are Not an ‘Arbitrary Definition’ of Biological Sex

PZ Myers is wrong about biological sex. Here’s why.

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The month of May is off to a rocky start. On May 1st, two essays denying the empirical scientific basis of the sex binary were published in major media outlets. The first piece, titled “Here’s Why Human Sex Is Not Binary,” was written by Agustin Fuentes, a Princeton anthropology professor, and was featured in Scientific American. The essay was a comically bad attempt to refute the binary nature of sex by arguing, in part, that gametes are not “the entirety of biology.”

Producing ova or sperm does not tell us everything (or even most things) biologically or socially, about an individual’s childcare capacity, homemaking tendencies, sexual attractions, interest in literature, engineering and math capabilities or tendencies towards gossip, violence, compassion, sense of identity, or love of, and competence for, sports.

Dealing with just one bad article of this magnitude would have been more than enough to keep busy, but to make matters worse, the Washington Post published a nonsensical article by Jennifer Finney Boylan, an English professor, who argued in favor of the pseudoscientific notion of “brain sex” while also denying the sex binary rooted in gametes. Not good.

In the wake of these essays and the large critical response to them on social media, several academics decided to come out and publicly express their own ignorance of basic biology. One was Dr. Holly Dunsworth, a biological anthropologist at the University of Rhode Island, who took to Twitter to call those who understand the gametic basis of male and female “a$$hole[s].”

Are you beginning to understand why I left academia?

The cherry on top of all this virtue signaling and intellectual seppuku in the name of appeasing gender ideologues is a post by biologist PZ Myers on his blog Pharyngula titled “Let’s pretend humans are single-celled organisms.” In this post, PZ claims that sex being “defined by the size of your gametes” is “a strange new dogma” that is “stupid” and “arbitrary.” He says that this gametic definition is being used “to replace the Y chromosome excuse but “all the failings of any attempt to reduce a complex biological process to a single phrase.”

To call Myer’s framing “wrong” would be a gross understatement.

For one, the idea that males and females are defined by the size of their gametes is far from new. It dates back to the mid-19th century, when scientists first began to unravel the technical complexities of sexual reproduction involving sperm and ova. Furthermore, the gamete size definition is far from arbitrary; it reflects two fundamentally distinct reproductive strategies with enormous downstream consequences for the evolution of bodies, behavior, and physiology. If, as the geneticist Theodosius Dobzhansky once observed, “Nothing in biology makes sense except in the light of evolution,” it may also be said that nothing—or at least very little—about animals makes sense except in the light of anisogamy (sexual reproduction involving gametes of two different sizes).

Secondly, PZ’s claim that the focus on gametes represents an abandonment of appealing to chromosomes as a way of rooting sex in something binary is not just incorrect, but underscores PZ’s ignorance about the fundamental and universal definition of males and females.

While it is true that some individuals mistakenly equate the sex binary with chromosomes (XX for females and XY for males), they, like PZ, are unaware of what male and female actually refer to. I have written previously about this, and it boils down to a confusion between what determines an individual’s sex and what defines it. “Sex determination” refers to the processes that set an embryo on the developmental pathway that results in becoming male or female, but the mechanisms responsible for triggering male and female development are not the same as males and females themselves. Humans and other mammals use genes on chromosomes to trigger sex development, but some animals, like many reptiles, use temperature. But just as a mammal's sex is not defined by chromosomes, an alligator's sex is not defined by temperature. If it were, we would have to accept that alligators have an infinite number of sexes that correspond to every possible temperature at which an egg could be incubated. In reality, we only see male and female alligators, which are defined by their primary reproductive anatomy, indicating the type of gametes they can or would produce.

Just because some people wrongly believe that chromosomes define the sex binary in humans doesn’t mean that every other trait people might point to is equally arbitrary and rooted in ignorance. The size of the gamete an individual has the function to produce really is the fundamental and universal definition of male and female that unites all anisogamous species. This is what the sex binary refers to.

Lastly, I want to highlight a common fallacy deployed by people like PZ Myers and Agustin Fuentes, which is to falsely equate what people are with who they are. Fuentes, in his essay in Scientific American, argued that “Gametes and gamete production physiology, by themselves, are only a part of the entirety of human lives.” However, no one has ever claimed that gametes represent “the entirety of human lives,” only that they define whether someone is male or female. PZ commits the same fallacy in the title of his blog post, “Let’s pretend humans are single-celled organisms.” Who has ever claimed that? To my knowledge, no one. Later in his post, PZ says that “It’s embarrassing that there are actual scientists, biologists even, who dismiss all the complexity of post-zygotic development to shrink people down to nothing more than their gametes.” However, once again, I am unaware of anyone who has ever denied “the complexity of post-zygotic development” or claimed that people are “nothing more than their gametes.”

Literally no one has said this or believes this.

What we are correctly pointing out is that all the diversity of morphology and behavior observed in nature in anisogamous species is completely irrelevant when asking a very simple question: “What is this individual’s sex?”

Despite the flailing and complaints of PZ and his ilk, the immutable truth remains unchanged. Accusations of transphobia or “idiotic biases” only serve as a feeble attempt to obscure the inescapable fact that the gametic foundation of sex is fundamental and unassailable. The future belongs to those of us who stand firm in the face of delusion and deceit. Reality can only be stretched so far before inevitably snapping back with a force that cannot be denied. I believe we are at the brink.