A recent article in Nature claims that biologists ‘now think’ that sex is not a binary feature for human beings – rather than being simply male or female, there are various kinds of sex, such as chromosomal sex or hormonal sex, and all of us exist across several spectrums of sexual identity.

Two sex; five sex; nine sex models



The claim that we are non-binary is well evidenced, but the claim that this is what biologists ‘now think’ seems to ignore much of the history of sex and gender research. This is made clear by the very first comment on the article, signed ‘Anne Fausto-Sterling’. Fausto-Sterling is a pioneering researcher into sex and gender identities, and published controversial work in the early 1990s suggesting that there were at least five different ways of measuring sex – a publication which is not mentioned at all in the Nature article.

The scientific scepticism of ‘binary’ sex – that is the idea that there are men and women and they can be clearly distinguished – started even earlier. In 1968 the Journal of the American Medical Association carried an article by biologist Keith L Moore, listing nine different components of someone’s sexual identity: external genital appearance, internal reproductive organs, structure of the gonads, endocrinologic sex, genetic sex, nuclear sex, chromosomal sex, psychological sex and social sex.

It’s possible to design tests for many of these kinds of sex, but none of them provide a convenient ‘male or female’ binary answer. Results will always depend on averages, on statistical norms, or on arbitrary cut-off points, and there will always be people who appear both male or female (or neither) when all nine kinds of sex are considered. Further, what science cannot do is tell us which of these tests is the best measure of sex, or which gives us our ‘true’ identity – that entirely depends on what we want to do with the results, why we’re testing, and our cultural attitudes towards sex and gender (gender being the psychological and social aspects of sexual identity).

(Barr) Bodies of Evidence

Moore wrote his article in 1968 specifically to criticise one form of sex testing: the tests that were being used in international sport to decide whether athletes were eligible to compete as women. Sport is often an arena that absolutely insists that human beings come in only two forms, male or female, and has spent around 80 years trying to find an objective scientific test that will prove that this is the case. So far it has failed.

This failure came as no surprise to many of the scientists working in genetics, or endocrinology, or other areas of the study of sex and gender. At least as early as the 1930s it was scientifically understood that some aspects of biological sex and gender identity might not match in individuals, and surgery and hormonal treatments were used to help people create stable identities. There were several high-profile cases of transgendered athletes in the 1930s and ‘40s, so the idea that sexual and gender identity might be fluid rather than fixed was discussed in the popular press as well as in scientific journals. These stories were part of the reason international sports organisations began to introduce stricter eligibility rules for women’s sports in the 1940s.



Tests for Barr bodies can easily be performed on cheek cells taken by a simple oral swab - the simplicity of the test is probably part of the reason it lasted for so long in international sport. Photograph: Guardian

Moore was intimately familiar with these tests, as he was a co-developer of the one the International Olympic Committee (IOC) used for nearly 25 years. Moore was the PhD student of Canadian scientist Murray Barr, who in 1949 published (in Nature as it happens) the discovery of the ‘Barr body’. This is a chromosomal artefact caused by the inactivation of the second X chromosome in a cell; as it is relatively easy to visualise it is sometimes used as a rough and ready indicator of ‘femaleness’ in mammals.

The Barr body test was the first standardized scientific test for sex used in international sport, replacing the unpopular ‘naked parades’ in 1968. But by the time the IOC introduced the Barr body test, it was already being condemned as unreliable as a proxy for sex by Barr and his fellow researchers, including Moore, who said

Females have been declared ineligible for athletic competition for no other apparent reason than the presence of an extra chromosome…[these tests] cannot be used as indicators of ‘true sex’

Why do we need the binary?

I’ve pointed out elsewhere that the problem with sex testing for sports is that none of the ‘kinds’ of sex correlate perfectly with sporting ability, so any test will exclude competitors with no physical advantage. Meanwhile lots of other genetic and physiological variations - such as height - confer advantages on some lucky competitors, and yet we make no effort at all to segregate these athletes in the name of ‘fairness’. Scientists always understood the limitations of sex tests, even if sports administrators struggled to accept them: in particular there was Finnish geneticist Albert de la Chappelle, who fought against the IOC’s sex testing regime of the 1980s, promoting a more complicated way of determining eligibility that would consider hormonal, physiological and psychological sexual identity.

Although attitudes towards people who identify as transgender or intersex, or simply ‘non-binary’, have not always been sympathetic, there has never been scientific (or philosophical, or sociological) consensus that there are simply two human sexes, that they are easily (and objectively) distinguished, and that there is no overlap between the two groups. Nor have they agreed that all of us are ‘really’ one sex or the other even if bits of our bodies or our identities don’t entirely match that sex. You can examine someone’s genitals, their blood, their genes, their taste in movies, the length of their hair, and make a judgement, but none of these constitute a universal or objective test for sex, let alone for gender.

When groups, whether in sport or elsewhere, turn to scientific definitions to try to exclude some people from the category of ‘woman’, it is worth remembering this fact: scientists have never agreed on which kind of sex really matters to our identities, or to our right to call ourselves men, or women, or neither, or both.

If you want to read more about the conflict between science and sex testing, @hps_vanessa has recently published a chapter in the Routledge Handbook of Sport, Gender and Sexuality that covers the topics in this post, and more.