Mick Hartley

In which Nathan Williams destroys the absurd claims of PZ Myers:

A scientist with 150,000 twitter followers and a well-read blog has, I believe, the responsibility not to spread scientific misinformation. One such scientist is biologist PZ Myers, who styles himself as a purveyor of science and rationality on his blog Pharyngula. It’s therefore disappointing to see him spread obvious untruths such as that biological sex is a social construct or that there are an unknown number of sexes. As I’ve written before, sex is a biological reality, not a social construct and mammals have only two sexes. As an evolutionary biologist, PZ Myers must know that sex evolved at least a billion years ago and therefore seems unlikely to be a construct of human (or even ape) society. Which makes me wonder why he would spread such obviously false information.

Recently, Myers has started breeding spiders, a project which he is documenting in great detail on twitter. What I found intriguing is that in his spider updates, any uncertainty about the reality of sex or how many sexes there are, seems to be forgotten. When he charted the growth of his arachnoid pets, he used two colours: yellow for spider-girls and blue for spider-boys with no need for intermediate hues. His blog is full of references to his female spiders producing eggs — never the males, whose function is to provide the sperm ideally without getting eaten by their mates. Quite how his spiders know about sex, given that it is (according to Myers) a social construct, is never explained.

I noted this fascinating discrepancy on twitter and hoped he would clarify exactly what he does believe. He replied that I was wrong and that “sex is bimodal”. This is a phrase often used by Myers and others, which adds confusion rather than clarity to the issue. Many of the debates in this topic come down to disagreements over definitions. Whether sex is “binary” or “a spectrum” depends on how you define those terms — they have precise definitions in mathematics or physics but are rather less clear when applied metaphorically to biology. I therefore try to stay out of arguments about whether sex is or is not binary. However, “bimodal” has a very clear definition so that we can say with confidence that sex is not bimodal….

Finding out whether a particular variable is bimodal is easy — you just plot it on a graph. I asked Myers if he could share an example of a graph based on real data showing that sex is bimodal. His response was characteristically blunt: “You want a ‘graph of sex’? You really think it can be plotted in two dimensions? What the fuck is wrong with you?”

Therein lies the problem. Sex can’t be plotted on a graph because it is a category, not a number. I’m male, but I don’t have a maleness score. Whilst I fall well short of the platonic ideal of a stereotyped hunky six-packed alpha-male, I don’t think that makes me only 85 per cent male. For all my faults, and regardless of my gender identity, I am fully and entirely male. Since sex isn’t a value that can be quantified, the description “bimodal” is nonsense.

Given that PZ Myers agrees that any kind of graph of sex is impossible, you might think he would admit that it isn’t in fact bimodal or alternatively provide evidence that it is. Sadly, no. Instead he called me a “dishonest debater” and a “lying ass” and then blocked me. Then from behind his block he called me a nitwit — which is definitely the kind of behaviour you expect from an honest debater.

He also published a blog attacking me where he lied about me and threw further insults (“dim & bigoted fanatic”). He did, however, attempt some kind of a defence for his “sex is bimodal” claim. He admits he can’t plot a single value for sex. The problem, he says, is that he can provide so many: “receptivity, courtship initiation, web twanging frequency, successful insemination frequency, dancing intensity, abdomen size, interval since last courtship, metabolism levels”.

What he has done here is change his claim entirely. He’s now saying, not that sex itself is bimodal, but that some characteristics linked to sex are bimodal. This is obviously true, and no one denies it. Some traits are indeed bimodal (for instance, testosterone levels in humans) though others are not (interestingly, height isn’t bimodal in humans despite being sex-linked, since the overlap between males and females is so great you get a single mode). Other measures may even have more than two modes….

Sex isn’t bimodal, because it’s a category, not a value.

Myers is confusing sex itself, a category, with secondary sexual characteristics and gender presentation. Maybe he's doing it deliberately in the hope that all this talk of bimodal sex sounds kind of sciencey and will fool people, or maybe he really believes it. Who knows?