#GenderWeek: Biological sex is not binary

By Malin Ah-King

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Biological sex is often assumed to be binary, but it is not. Among animals there are a range of species that change sex on a regular basis, for example shrimps that hatch as males and turn female at a certain body size, and some fish that change sex depending on social circumstances. Sex is not always decided when an egg and a sperm fuse – as in crocodiles and most turtles, whose eggs are unsexed at first and it is the temperature during incubation that leads to the development of a certain sex. There is even a lizard species in which both sex chromosomes and temperature simultaneously influence which sex develops.

Neither is there a strict dichotomy between human male and female bodies. Having XX chromosomes does not always mean having a female body and having XY chromosomes does not always mean having a male body; sometimes an individual with XY chromosomes is insensitive to the influence of testosterone, resulting in a female body. There are also other combinations of sex chromosomes, such as X0, XXX, XXY, XXYY, XXXY, XXXXY and XYY, and exposure of external hormones as a fetus may also influence sexual characteristics.

There is a range of variation in anatomical and reproductive characteristics – chromosomes, ovaries/testes, genitals, bodily appearance – that do not fit typical definitions of male or female. That is the definition of intersex (in medical terms, Disorders of Sexual Development). Some intersex organisations reject the term DSD because it is not necessarily a disorder, but simply part of the variability of human bodies. This variability means that sex is much more complicated than the commonly assumed binary; there simply is no true boundary between female and male bodies, we are all part of a continuum or a mosaic of sexual characteristics.

How would it influence your identify if you realized tomorrow that your biological sex – your sex chromosomes, your ovaries/testes, your hormone levels, or your body – are not what you were brought up to think they were? Would that change your whole perception of your identity, your behaviour, appearance and relations – or would it not matter at all?

What is the connection between biological sex and gender identity? This is a contested area of research for psychologists, sexologists and medical scientists, and intersex individuals have often been the means by which to test and prove various theories. Psychologist John Money, who became very influential for the treatment of intersex children from the 1950s and onward, considered gender identity to be only dependent on the social circumstances and that there was no innate basis for it. Successful treatment would lead the child to psychologically developing into an unambiguous gender, and as part of this it was essential that both the parents and the child believed that the child had a true sex that only needed medical intervention to get it right.

The assumption of the all over-shadowing social influence, however, has not been without critics. This is especially true following Money’s showcase example of John/Joan, a boy who accidently lost his penis and was brought up as a girl, who turned out to reject his assigned sex, transition to male and later take his own life. In 1965, Milton Diamond suggested a competing hypothesis, namely that the influence of hormones provides a predisposition for gender identity and behavior that sets limits to the social influences. Later, evidence accumulated of intersex individuals rejecting their medical sex assignment and, as more and more intersex individuals give their stories and interpretations, the still controversial debate has become more nuanced. Yet intersex children are still regularly treated to conform to current binary gender norms, despite there being no medical reason to do so in most cases.

The idea that prenatal hormone levels determine gender and sexual identity in turn has become the dominant theoretical framework within the neurosciences, but brain scientist Rebecca Jordan-Young has criticised this research tradition on the basis of questionable assumptions, methodological inconsistencies and overly grand conclusions given the conflicting results. She suggests that brain scientists are too focused on nailing down sex differences and would be better off studying the dynamic processes of the interaction between environment and internal factors.

Hence there are both cultural and biological deterministic essentialist positions when it comes to sex and gender. The biological sciences have a high status among the general public and what is considered biological or ”natural” has a material affect on people’s lives. Several gender researchers have problematised the distinctions between gender/sex and nature/culture, notably Judith Butler, saying that conceptions about biological sex are already culturally influenced. In the structure which Butler calls the heterosexual matrix, norms about sex/gender are inextricably intertwined with norms of sexuality: the only positions available are male or female.

The process of sexing bodies, which makes them conform to a sex binary, is already regulated by culture because it does not allow for ambiguity. This sexual binary, unquestioned and assumed to be natural, becomes the basis for constructing gender as a natural binary, and the naturalisation of a gender binary leads to oppression of those who do not conform to it. Questioning both binaries of biological sex and gender gives room for more variable concepts of both sex and gender.

I think that these variations in biological sex and the lived experiences of intersex individuals unsettle many taken-for-granted assumptions about gender. Irrespective of different feminists’ views on transgender identities (personally, I respect each person’s gender identity), gender is clearly not a direct effect of biological sex, and there is not a perfect overlap between biological sex and gender identity. These findings problematise both biologically essentialist notions about sex and the culturally essentialist notion of gender identity as a purely social construction. So, what are the consequences for liberal vs radical feminists’ debates about gender?

Malin Ah-King is an evolutionary biologist and gender researcher at Humboldt University Berlin, Germany.

Suggested readings: Anne Fausto-Sterling Sexing the body 2000, multiple works by Alice Domurat Dreger.

Intersex organizations:

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5 thoughts on “#GenderWeek: Biological sex is not binary

  1. Emma Goldman

    Did you interview any intersex people for this article, asking how they feel having THEIR lived experience appropriated for trans to score points in a debate?

    Re: “How would it influence your identify if you realized tomorrow that your biological sex – your sex chromosomes, your ovaries/testes, your hormone levels, or your body – are not what you were brought up to think they were? Would that change your whole perception of your identity, your behaviour, appearance and relations – or would it not matter at all?”

    Humans are a sexually reproducing species. The way humans reproduce is egg and sperm. As with all species, our bodies are merely sheaths around our gametes. Sheaths, husks, coverings, shelters built around our gametes. Which are either eggs…or sperm. There are no eggerms and there are no sperggs. You have two choices. This is called a binary. All the rest of it is irrelevant, from the biological point of view.

    Please, do revolutionize biology, and prove the existence of a human being capable of producing viable gametes, which are not either eggs or sperm.

  2. Concerned Mother

    Intersex people are not trans, though trans keep trying to appropriate their experiences.

    There is nothing here, nor in any scientific knowledge or complaints of trans violence from other men, which challenges the sober radfem analysis that trans are men who, as such, perpetuate the oppression of women as a class.

  3. Woman

    Congenital defects can take place in every system of the human body such that the structures affected “do not fit typical definitions.” It is unsurprising that defects would sometimes occur in the genital and reproductive systems. Are we to consider Gardner syndrome and anorectal malformations evidence of a “range of variation” that takes place in the digestive system? Why should DSDs be regarded differently?

  4. Antiplondon

    This is such a disappointing article, especially coming from a ‘real’ scientist.

    Yes, there are lots of species that ‘do’ biological sex differently to humans, and they prove exactly nothing about human beings, as the variations in fish and reptiles serve the purpose of continuing the species.

    ‘Intersex’ covers a whole range of conditions, all of which are, essentially, developmental abnormalities, which result in lowered fertility or sterility; they don’t disprove the fact that human beings reproduce through biological sex, through the existence of males and females, any more than a person born blind disproves the fact that we are a sighted species.

    Does anybody really believe that an XX individual (a woman) whose uterus does not develop properly is a whole new sex, and in need of a whole new ‘gender identity’ and a new set of pronouns? How about an XY individual (a man) whose urethra exits his body at the base of his penis rather than the tip?

    This is pure appropriation of Intersex experience by trans activists, and a blatant misuse of science. World class scientist say that brain sex is a myth (see, for example, here: ).

    Sex and gender are linked, in that the sex one is assigned at birth (and that ‘assigned at birth’ bit is key here, most intersex people will be assigned male or female at birth), will determine which gender role one is conditioned/raised into. Gender roles are oppressive, they oppress men and women in different ways, but it is always women who come out worse.

    I do not ‘identify’ as female, I am female. I do not ‘identify’ as feminine, I have had that role forced upon me, and I am socially penalised when I do not conform. Women who do conform to femininity are also penalised, because gender is a hierarchy, that came about to reinforce male supremacy, the only people who really benefit from ‘gender roles’ are masculine men.

    That the author asks “So, what are the consequences for liberal vs radical feminists’ debates about gender?” shows that she has no real understanding of radical feminists’ views on gender in the first place; we’re not being big ol’ meanies over ‘gender identity’ for the fun of it, gender harms all women (and many men as well).

  5. Zoe Brain

    Let me guess… the number of Intersex people commenting on the “misappropriation” of Intersex by Trans here is… zero.

    Because those who are not Intersex know what we think better than we do, right?

    Yes, there’s a difference, but the boundaries are more blurry than those biologically misinformed realise. If we define Intersex as “neither anatomically stereotypically male nor female” – a definition used by many Intersex organisations, as well as researchers, then there’s an unimpeachable case for saying that technically Transsexuality is just one of the many and varied Intersex situations

    See A sex difference in the human brain and its relation to transsexuality by Zhou et al Nature (1995) 378:68–70.

    Our study is the first to show a female brain structure in genetically male transsexuals and supports the hypothesis that gender identity develops as a result of an interaction between the developing brain and sex hormones.

    But that is a purely technical issue – it’s not terribly useful, as most Intersex people have completely different issues and concerns from most Trans people. Partly because of the longstanding but debunked idea that Transsexuality is a mental illness, It’s more convenient for everyone to treat the two concepts as distinct. The last thing Intersex people need is for their very real endocrinal and physical issues to remain unexamined because they’re dismissed as “delusional” by psychs who don’t bother to check that their bodies really do differ from the norm. It’s happened, too, many people still aren’t aware that Intersex people can exist, let alone do.

    On the other hand, a 46,XX woman with CAH has different concerns from a 47,XXY man, and both differ from a 46,XY woman with Swyer syndrome, or a 46,XX man with CAH for that matter. Biologically, Intersex is anything but monolithic and heterogenous. Some identify as men, others women, but a minority identify as neither or both, and have the biology to back that up.

    The one thing we all have in common is that non-Intersex – Intrasex – people claim to know more about what we think than we do. Sometimes from a “christian perspective”, sometimes from a “radical feminist perspective”, but always arrogantly denying Intersex people their own agency. In actuality, there’s as much variety of opinion amongst Intersex people as there is in Intrasex people.

    Apart from that, there are a few Intersex situations which really blur the Intersex/Trans line. Not just the minority of Intersex people who reject the sex arbitrarily assigned to them at birth – and Transition, just like Transsexuals – but those who get an apparent “natural sex change” due to 5ARD, 17BHSD, the 3BHSD form of CAH, 45,X/46,XY MGD, or other syndromes. Technically it’s from “mostly female” to”mostly male” with the change more complete in 5ARD than 17BHSD, or the reverse for 3BHSD or MGD, but close enough.

    See The ‘Guevedoces’ of the Dominican Republic for a pictorial showing the effects of 5ARD. As I said, close enough.

    Depending on the sexing of the neurology – and it’s multidimensional and continuous, anything but a single dimension binary – this involuntary Transition can either induce or cure the symptoms of “Gender Dysphoria” – the symptoms Trans people exhibit. Often though, in perhaps one third of cases, it’s just an interesting life experience, the brain is not strongly sexed either way.

    People who transition like this – or have treatment to prevent and reverse the natural process – have far more in common with Trans people than they do with many other Intersex situations.

    So enough with the You have two choices. This is called a binary. stuff. It doesn’t apply. Biological Sex is not a single dimension, and has more than 2 values. It’s like size – insisting everyone is “large” or “small” and then arguing if someone 2 meters tall weighing 50kg is larger or smaller than someone 1.5 meters tall and weighing 100kg, and which category to put someone 1.75m tall and 75kg in weight.


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