For all our technological cleverness, we live in an age of profound stupidity. It is indeed a ‘post-truth’ age – and the least truthful are the most passionately convinced that everyone else is wrong. Like ‘misinformation’, the ‘post-truth’ slur is most commonly wielded by those who are its most guilty proponents.
How often, after all, have you been finger-wagged on social media that, ‘I have doctorate in biology, and I’m telling you that the sex binary doesn’t exist. So, there.’
Well, Colin M Wright has a doctorate in biology, too (evolutionary biology, specifically). He’s also been a research fellow at Penn State and a prolific author, including the following peer-reviewed academic paper: Why There Are Exactly Two Sexes.
Here I synthesize evolutionary and developmental evidence to demonstrate that sex is binary (i.e., there are only two sexes) in all anisogamous* species and that males and females are defined universally by the type of gamete they have the biological function to produce – not by karyotypes, secondary sexual characteristics, or other correlates.
*Meaning “sexual reproduction that involves the union of two gametes that differ in size and/or form, such as egg and sperm cells”.
In other words, the sex binary is not a social construct, a spectrum or a vibes-based feeling. It is the direct consequence of anisogamy: the fusion of two differently sized gametes. Small, numerous, motile ones (sperm) and large, nutrient-rich ones (ova). Males produce the former. Females produce the latter. That is the definition. Full stop.
Everything else – chromosomes, hormones, genitals, secondary characteristics – is downstream of that functional distinction. They are how sex is determined (that is, not by doctors making an arbitrary judgement when a baby is born) or how it is expressed (which has nothing to do with fright wigs and bad makeup). They are not what sex is.
The paper methodically dismantles the usual objections. Claims of “hundreds of sexes” in fungi or slime moulds confuse mating types (compatibility classes in isogamous species) with actual sexes. Mating types are not sexes. Where reproduction is anisogamous, as it is in human beings, the number remains two.
A common line of argumentation used to undermine the binary nature of sex does so by misrepresenting the sex binary as a binary of human karyotypes (XX = female; XY = male) and then citing sex chromosome aneuploidies (e.g., XXY in Klinefelter syndrome; X0 in Turner syndrome) or rare XX males and XY females to claim there must be “more than two sexes”. How could sex be binary and determined by sex chromosomes, they argue, if there are more viable sex chromosome karyotypes in humans beyond XX and XY?
The fundamental flaw is conflating how sex is determined with how it is defined […]
Yet, regardless of the mechanism by which sex is determined, an individual’s sex – male or female – is universally defined by the type of gamete (sperm or ova) their reproductive system has the biological function to produce. Sex chromosome aneuploidies therefore represent variations within the two sexes, not additional sexes.
The spectrum model fares no better. Disorders of sex development produce developmental ambiguity, not new gamete types. Ambiguous genitalia do not create a third sex any more than a deformed limb creates a new limb type.
Sexual ambiguity is not a third or intermediate sex because developmental variation does not correspond to producing new gamete types.
And aping the outward signals associated with the opposite sex cannot make an individual produce opposite-sex gametes. A man who cuts his genitals off will never produce ova. A woman who cuts off her breasts and gobbles testosterone will never produce sperm. ‘Transwoman’ are not women, and vice-versa.
Polythetic and multilevel models, those that treat sex as a fuzzy bundle of chromosomes, gonads, hormones, behaviour and ‘identity’ are circular and self-contradictory. They label traits ‘male-typical’ or ‘female-typical’ only because those traits already correlate with organisms identified as male or female by their gametes. Remove the gametic anchor and the whole argument collapses into incoherence. Well, more incoherent than it already is.
Across anisogamous taxa, males and females are defined by gametic dimorphism. Proposals to redefine sex in terms of karyotypes, secondary sexual characteristics, behavior, or other correlates are incoherent and invariably presuppose this foundation, because the categories “male” and “female” are intelligible only by reference to sperm and ova.
The stakes are not merely academic. When medicine, law and public policy start treating the binary as optional, the results are predictable: compromised clinical protocols, muddled epidemiology, eroded sex-based protections and a steady erosion of public trust in the institutions that once claimed to follow the evidence.
This is not mere ideology: it is the hard facts of evolutionary biology stating the bleeding obvious. The only people who find it controversial are those for whom the bleeding obvious has become politically inconvenient. In a post-truth age, that is increasingly the entire point.
