May 3, 2023 - 1:00pm

Scientific American has a proud history as one of the world’s most distinguished magazines, predating Darwin’s On The Origin of Species and inspiring countless science enthusiasts over the centuries. What a shame, then, to see it recently fall down the rabbit hole of a pseudoscientific ideology claiming that there are more than two biological sexes, both in general and in humans specifically.

Let’s be clear: sex is binary. There are only two routes for a sexually reproducing individual’s genes to flow from one generation to the next: via either small gametes or large. There is no spectrum from sperm to egg. Individuals of any species who are shaped by evolution to reproduce via sperm are called males; those equipped to reproduce via the egg route are females.

Increasingly, however, it has become fashionable to argue that it’s all much more complicated than that. You fool — didn’t you know that clownfish can change sex? Did you know that a mole’s vagina seals shut outside the breeding season? Were you aware that one in 500 men has abnormal sex chromosomes?

These “gotchas” do not change the fact that there are only two types of gamete, or that humans produce at most one of them. A man is male by virtue of reproducing via sperm, irrespective of his chromosomes; the very fact that we are able to say that a clownfish has “changed sex” betrays the fact that we understand what makes the fish either one sex or the other.

In 2019, Scientific American released a graphic purporting to explain why a range of developmental conditions affecting people’s sexual organs are in fact proof that sex is a spectrum. No, we won’t elaborate what it means when we say one woman is “more female” than another. But look at all these criss-crossing arrows! Look at the colour-coding! It’s all very complicated, you see. This diagram is not intended to inform or explain: its purpose is to impress people into silence.

This week’s opinion piece in SciAm titled “Here’s Why Human Sex Is Not Binary”, written by anthropologist Agustín Fuentes, continues on this theme. Fuentes freely admits that there are only two kinds of gamete, but adds that “they are not the entirety of biology and don’t tell us all we need to know about sex, especially human sex”. But who ever said that sperm and eggs were “the entirety of biology”? And why would the fact that they aren’t mean that sex is not binary?

In his recent articleThe marketplace of rationalizations, philosopher Dan Williams argues that people want to believe not necessarily what is true but, instead, whatever aligns with their tribal allegiances and self-perception. Yet, often, we need to justify our beliefs to ourselves and others, which means there is a “marketplace” for arguments in favour of socially desirable positions. In this marketplace, Williams writes, “agents compete to produce justifications of widely desired beliefs in exchange for money and social rewards such as attention and status.”

Many people currently wish to believe, to put it crudely, that a man is a woman if he says he is; this belief is socially sanctioned, is endorsed by our institutions, and will often lead to peers seeing us as good, kind, right-thinking people. The fact that sex is observably a fixed, binary trait in humans is an impediment that would-be adherents must explain away, one way or another.

Fuentes and Scientific American are therefore filling a niche in the market that is created by trans ideology. I don’t believe Fuentes really thinks “human sex is not binary”, as his article states. He will be aware that he presumably, like the rest of us, has two biological parents, one of each sex; he will know that if he wants to reproduce, he will need to do so with an individual of the opposite sex to himself. But his ability to construct clever-sounding arguments obscuring this fact, backed up by his position of academic authority, is worth good money in the marketplace of rationalisations.

Ellen Pasternack is a PhD student in evolutionary biology at Oxford University.