It appears to be very common these days in fashionable circles to say that sex is not a binary and that sex is indeed a spectrum. Indeed, the idea that we can pigeonhole people into two classes — male and female — is presented as some sort of old fashioned bigotry.

But what could it mean for sex to be a spectrum? When we say ‘My sex is X’ what does that mean and what is a sex? The fashionable idea is that X can be a fluid choice between some sort of range. What sort of things can take the place of X in that statement? Is it just ‘male’ and ‘female’ or is there more to it than that?

The concept of a spectrum comes from physics. Physicists study spectra in order to determine the properties of things that emit light or sound or some other wave. Spectra are used to describe certain wave-like phenomena. We can describe the phenomena of light and sound as being wavelike and can exist on a spectrum of possible states described by a single parameter — wavelength, or frequency.

The note of a sound can be objectively described by its wavelength. Middle C has a wavelength of 1.311 meters and a frequency of 261,626 Hz. Red light has a wavelength of between 700–635 nm. When we observe a spectrum from stars, the intensity of light at each wavelength can tell us a great deal about the physical properties of the star. Spectra are useful concepts that help us describe and quantify wave-like phenomena. The title image is the spectrum emitted by our Sun. The black lines are absorption lines and tells us the composition of the Sun’s atmosphere.

The term ‘spectrum’ has been adopted into other areas of science and society. For example, we might talk of political views existing on a spectrum between left and right. This has some utility but, as we can see in today’s politics, this quickly breaks down as a useful metaphor. How can we define any particular scale that allows us to place people along a line of political views? That would not allow us to discriminate between the various political groupings that exist. People may be socially liberal but have very different views on financial and taxation policy. Political views do not have a ‘single’ spectrum associated with them. Politics is massively multi-dimensional and views tend to cluster into multiple related sets of opinions and values.

Medicine borrows the term spectrum too. We have all heard of the Autism Spectrum. But again it is only a metaphor as autism is not characterised by a single scale of intensity of any particular symptom. It is a series of neuro-developmental disorders with distinct characteristics.

So, it’s fairly common to see the concept of a spectrum used as a metaphor, but also to see that this metaphor can be more unhelpful at times than it is helpful. It is misleading to see politics as a spectrum of views. It is wrong to think of autism as just being a spectrum.

So, what about sex as a spectrum? Clearly there is nothing in the concept of sex that we could measure as a continuous function of wavelength etc. At best, we might be dealing with another metaphor.

It’s probably worth noting that sex describes reproductive roles. Any description of sex that does not take into account reproduction at some level is clearly unanchored and absurd. Specifically, when someone says their sex is X, a coherent and material explanation is that they are saying their bodies have developed along one of two pathways towards the production of specific gonads that produce specific gametes associated with each sex.

For many people, succesful production of gametes and reproduction does not occur — this is contingent on environmental and historical factors — a boy child may die at five before sperm are produced — they are still male — their development is still clearly along the male pathway. And of course, like any biological pathway, problems can occur and atypical development can occur due to chromosomal/genetic issues. Sometimes misleadingly called intersex conditions, these disorders of sex development are still variations on the development of one of two sexes.

So, where does the idea of a spectrum come from? Firstly, whilst sex is described by function, there is still a wide variation in the distribution of form. In short, and not to put too fine a point on it, sizes can vary.

Yes, height can vary enormously between sexes on average. And each sex, can see wide distributions in height. Men tend to be taller than women. But there is no height where males become females or vice versa. This goes for other characteristics too, like hormone levels etc. If we were to plot a spectrum of heights of people we would see a bimodal distribution of those heights. We are not seeing a bimodal distribution of sex though — a common misconception — as the x-axis would still be height. Sex might be the underlying cause of the bimodal distribution precisely because there are two discrete values that sex can have with distributions around an average for each of the two possible sexes. Such arguments do not show sex is a spectrum but quite the reverse: they are very strong evidence that humans are sexually dimorphic.

Perhaps the most misleading representation of ‘sex as a spectrum’ uses intersex conditions to suggest somehow that such conditions ‘move the line’ on what someone’s sex is. This diagram is most egregious…

It shows a series of different intersex conditions but lays them out as if they can be characterised along a spectrum. To force the point, a rainbow light spectrum is shown above. This is thoroughly misleading. What is being shown here are two sexes, male and female, and the different conditions that can occur with each. There is no natural distribution that could represent the x-axis here. It is artificially arranged. I suspect deliberately so, for ideological reasons.

And it is these ideological ‘gender’ ideas that are pushing ‘sex as a spectrum’. The idea is to undermine our understanding of what sex is & how humans can have a sex. It prevents proper descriptions and allows the subjective idea of gender to take prominence over objective sex.

There are winners and losers in this ideological stance. If sex is a subjective idea with artificial lines drawn on a spectrum, just as ‘red’ is a rather arbitrary range on the colour spectrum, then we should not pay too much attention to it. Rather, we should privilege the self-declared concept of gender that allow people to be ‘what they truly are’ — whatever that means. Females — women — no longer really exist. Their rights and spaces are just unimportant artefacts of ‘old science’.

This needs to be resisted and challenged by all those who care about the truth and by all those who seek justice. Sex is not a spectrum. It is the material reality of male and female for us all, and has material consequences for us all.

Fashionable nonsense is no substitute.