Biological Sex is a social construct


I recently tweeted, as an aside, that biological sex is a social construct, and the backlash and attacks were swift, incredulous and heavily reliant upon very basic biology.

There is a common perception amongst those who have given it little thought, that gender is a social construct, whilst biological sex is solid and rigid and fixed and binary and scientific. Those who wish to attack and marginalise trans girls like my daughter, like to argue that her biological sex is male, as though that is a scientific fact.

They are wrong.

To unpick this we need to tackle several different issues.

Biological Sex

Biological sex is a term used to refer to a person’s sexually differentiated biology. It encompasses a range of sexually differentiated traits and processes including:

  • Sex determining genes (e.g. the SRY gene on a Y chromosome often promotes testosterone driven development, the presence of the WNT4 gene can promote ovarian development, the DMRT1 gene suppresses an oestrogen driven path)
  • Enhancers outside of genes (in junk DNA) that regulate the SOX9 gene
  • Sex chromosomes (e.g. XX or XY)
  • Sex hormones in a fetus in the first phase of fetal development (high oestrogen or high testosterone)
  • Sex hormones in a fetus in the second phase of fetal development (high oestrogen or high testosterone)
  • H-Y antigen
  • Functioning of sex hormone receptors (hormones can be present but not processed)
  • External primary sex characteristics (penis or vagina)
  • Gonads (ovaries or testes)
  • Type of gamete (egg or semen)
  • BSTc (sexually differentiated brain region)
  • Sex hormones at puberty (high oestrogen/progesterone or high testosterone)
  • Secondary sexual characteristics (oestrogen driven puberty or testosterone driven puberty)
  • Post puberty levels of sex hormones

The term biological sex often presumes that there are two biologically discrete types of people:

Type one is XX in every cell of their body, has raised levels of oestrogen as a tiny foetus, causing the development of ovaries and eggs, and the development of a uterus and vagina, has a second surge of oestrogen as a foetus (potentially contributing to development of a female gender identity), has ovaries that release a surge of oestrogen at puberty, causing oestrogen driven secondary sexual characteristics including periods, breast development, maturation of eggs and the ability to become pregnant and carry a foetus.

Type two is XY in every cell of their body, has raised levels of testosterone as a tiny foetus, causing the development of testes and semen, and the development of a penis, has a second surge of testosterone as a foetus (potentially contributing to development of a male gender identity), has testes that release a surge of testosterone at puberty, causing testosterone driven secondary sexual characteristics including Adam’s apple, hair growth, raised height and maturation of semen capable of fertilising an egg.

Social construct

A social construct is when we put artificial boundaries around groupings that are really more complex and messy. Biological sex is certainly a social construct.

In order to prove biological sex is a social construct we only need to find one example of a person who does not fit into the two neat biological boxes outlined above.

We know that up to 1.7% of people are born intersex/born with diverse sex traits.

These ‘exceptions’ exist because the idea of two binary biological sexes is just that – an idea – something we humans have come up with to explain and simplify our world – a social construct.

Biology is complex

There are many examples where individual biology lies outside of two clear cut binaries of sex differentiation.

Sex chromosomes come in more options than two. Although most people have XX or XY sex chromosomes, a small portion of the population have sex chromosomes outside of these two options. There are people whose sex chromosomes are XXY or XXYYY for example.

Sex chromosomes do not always align with other sexually differentiated biological features. For example:

A woman who for all purposes appeared as a typical cisgender woman, including typical internal and external genitalia, oestrogen driven primary and secondary sexual characteristics, getting pregnant and giving birth to a healthy baby, who upon testing in late adulthood, was shown to have XY sex chromosomes.

Individuals can even have different sex chromosomes in different parts of their body – For example a woman who has some cells with XX sex chromosomes and some cells with XY chromosomes

“new technologies in DNA sequencing and cell biology are revealing that almost everyone is, to varying degrees, a patchwork of genetically distinct cells, some with a sex that might not match that of the rest of their body.”

Some babies are born with genitalia that does not fit a simplistic binary. These babies were, and in many place still are, operated on, having their bodies surgically altered without consent, by a world that couldn’t bear to acknowledge that sex has never been a simple binary.

Even gonads do not fit a simple binary – there are XX people with an ovotestis—a gonad with areas of both ovarian and testicular development.

A 70-year-old cisgender man, a father of four, was found during surgery to have a womb.

Genes are more influential in sex differentiation than perhaps we imagine – researchers found that activating a gene in mice changed gonads from egg producing to sperm producing post-natally (in grown mice). Inactivating a different gene turned adult testicular cells into adult ovarian ones.

Hormones are hugely influential on sex differentiation, and hormone levels fluctuate – and are not binary. Cisgender women usually have both testosterone and oestrogen in their bodies. Cisgender men usually have both testosterone and oestrogen in their bodies. Hormone ratios and levels fluctuate from individual to individual (and from day to day and month to month and year to year).

Complete androgen insensitivity syndrome (CAIS) occurs when a person’s cells are unresponsive to testosterone, usually because hormone receptors are not working. People with CAIS have Y chromosomes and internal testes, with external genitalia developing along an oestrogen driven path, and secondary sexual characteristics at puberty also developing on an oestrogen driven path (breast development, wider hips etc).

There are people whose testosterone was suppressed as a fetus, who develop oestrogen driven primary sex characteristics (characteristics typically associated with cisgender women), and who have a surge in testosterone at puberty, developing testosterone driven secondary sexual characteristics (secondary sexual characteristics typical of a cisgender male eg low voice and adam’s apple).

Biology is complex and there are multiple intersex variations outside of a sex binary.

There is a biological underpinning to gender identity

The Endocrine Society has concluded there is a durable biological underpinning to gender identity. See here and here

“Considerable scientific evidence has emerged demonstrating a durable biological element underlying gender identity”

There is likely a role of genetics and genes. There is likely a role of hormone levels whilst in the womb. Hormones and genes are both biological processes. Complex non-binary biological processes.

Given the biological underpinning to gender identity, it is bad science to separate out gender identity from being part of biological sex.

Endocrine Society

A simplistic binary model of biological sex always has been a social construct, glossing over the complexity and messiness of natural human diversity. The Endocrine society (2017), well versed on the complexity of the human endocrine system, is very clear:

“Biological sex, biological male or female: These terms refer to physical aspects of maleness and femaleness. As these may not be in line with each other (e.g., a person with XY chromosomes may have female-appearing genitalia), the terms biological sex and biological male or female are imprecise and should be avoided.”

The term biological sex is imprecise and should be avoided. In place of the term biological sex we can use the term ‘sex traits’, acknowledging that sex traits are not binary, acknowledging that complex variations in sex traits are part of natural human diversity.

Trumpian Approach to Science, Trumpian Approach to Minorities

Sex traits are extremely complex. Not binary.

I’ve read some articles recently that argue as follows. They state that the majority of people do neatly fit into a sex binary. They point out that people who do not fit into a neat sex binary are a minority. They argue that we should not care about minorities. They really do betray their Trumpian urges.

They argue that because intersex or transgender people do not fit within a socially constructed sex binary, we should ignore (or erase) their existence.

That is not how science works.

You can make a political decision to ignore and disenfranchise and abuse minorities like intersex or transgender people. But you do not get to claim that your political decision is underpinned by science.

One article focused on a specific variation and claimed it was irrelevant as it only affects 0.1% of people. In the world that would make for the whole population of Switzerland!

Population estimates of intersex people are 1.7 %. Recent population estimates of trans people range from 0.5 to 6%. Combined (though of course there are people who are intersex and trans) that’s up to approximately 52 million people – equivalent to the population of South Korea!

A world that ignores and marginalises and disenfranchises people just because they are different, just because they are a minority, is an unjust world.

The idea of a rigid sex binary (biological sex) is flawed science. It is wrong. It is a simplification.

Are we saying that biology doesn’t matter?

No! Biology of course matters. No one is denying that there are important biological differences between humans that impact on our lives and on how society treats us.

People with a uterus can face real biological risks and opportunities (e.g. pregnancy and child birth) that people without a uterus do not face (this includes some trans masculine people as well as many but not all cis women). Let’s build a world that is fairer to all people with a uterus.

People presumed to have a uterus face social and cultural discrimination including in employment, (and this discrimination impacts on trans girls as well as cis girls).

Biology does matter. Cis people’s biology matters. And trans people’s biology matters too.

Trans people are as biologically real, biologically valid, as cis people. Just there are fewer trans people, and most of our science and laws and assumptions are written about cisgender people.

Outdated basic biology is not an acceptable basis upon which to inflict harm on my trans daughter. We need to develop a more sophisticated understanding of biology.

We need to understand that much of our conversations around biology are cisnormative, assuming everyone is cisgender. We can widen our horizons and make space for conversations about trans people within our understanding of human biology.

The starting point for this is an acknowledgement that our traditional ideas of binary biological sex is a social construct that works and can even be helpful (in simplifying a complex world) most of the time – but that it specifically does not work, and causes harm, when applied to transgender and intersex people.

In the latter part of last century, in some places, we reached a point where the social construct of rigid gender roles, gender norms and gender stereotypes were found to be unhelpful (and harmful) to enough people to be challenged and discarded.

This century we have reached a point where the social construct of rigid binary biological sex is unhelpful (and harmful) enough to be challenged and discarded.

Bigotry not biology

Given that there is a biological underpinning to gender identity, my daughter’s gender identity is part of her biology.

Saying a trans girl is biologically male is not science. It is bigotry. It is simplifying complex reality to fit an anti-trans agenda. To other and marginalise and stigmatise trans girls.

My daughter is a girl. Her gender identity is female. Her biology is the same as many other trans girls.

Her biological existence as a transgender person is as valid as the biological existence of any cisgender person.

Her GP registration says female. Her passport says female. Her birth certificate may currently say male (due to an inadequate legal system in the UK), but will at some point in the future be corrected to say female.

There are those who purposefully call my daughter a boy and a male. They deny the lived reality of trans people, and deny decades of scientific literature on trans identities. They don’t care a jot for my daughter’s wellbeing.

There are those who call my daughter a girl, but at the same time say she is a ‘biological male’. This makes no sense whatsoever. Calling my daughter ‘biologically male’ is just as rude as calling her a boy. It is also biologically incorrect, ignoring the biological underpinning of gender identity and the current and future biological differences between a trans girl and a cis boy.

Biological terminology shifts and evolves along with our understanding of the world. There is no situation in which it is acceptable, or scientifically correct, to call my daughter biologically male. It is akin to calling her a cisgender boy or a cisgender male.

Of course my daughter has some biological differences to the average cisgender girl. Trans girls are in some ways biologically different to cis girls. No one is denying that or would ever want to deny that.

If you want to talk about sexually differentiated organs, of course most trans girls have a penis and do not have a uterus (but don’t spend your time thinking about my child’s genitals, it is seriously weird and inappropriate).

The term ‘biological male’ denies the known biological underpinnings of gender identity.

It denies the physiological differences between trans people and cis people, with likely influence of genes and pre-natal hormones, including impacts on brain development.

It denies the reality that trans girls like my daughter will likely never go through a testosterone driven puberty but instead an oestrogen driven puberty, meaning they will never develop secondary sexual characteristics like an adam’s apple or facial hair, instead developing breasts and wider hips.

It denies the biological reality that very many trans women have less testosterone in their bodies than cisgender women.

It denies the biological reality that many trans women have more oestrogen in their bodies than cisgender women.

It denies biological complexity just so that you can impose the word ‘male’ on my daughter to control her, to other her, to misgender her and to cause her harm.

It is an imposition of cisgender power onto the bodies of trans people. It is not good enough.

The people clinging to ‘biological sex’ have the understanding of and respect for science of President Trump. They have similar levels of respect for minorities.

Zinnia Jones has written:

“calling trans women “male” is often an intentional choice meant to promote public fear and advance discriminatory laws”.

“Many people don’t like it when trans women call ourselves female because it undermines the forms of transphobia that rely on thinking of us as men”.

Science calls bullshit on your outdated bigotry.

Biological sex is complex, messy, overlapping. There is a ton of evidence of this, and only someone with Trumpian levels of ignorance can attempt to deny this.

The term ‘biological sex’ is outdated and needs to be thrown out, along with other outdated concepts that we as a society have ditched. There have been numerous historical parallels, where other areas of complex variation were overly simplified and fixed, usually to enable those with more power to use rigid categories as a way of policing and controlling those with less power (rigid class and race categorisations spring to mind).

A binary understanding of biological sex is a simplification that causes harm to those for whom the multiple components and processes contributing to sex differentiation do not all neatly align. This includes people who are intersex and trans people.

Being trans is not a choice, there is a biological underpinning of being transgender.

We can find a way to live within a complex messy world of biological diversity whilst providing dignity and respect to those who are in a minority.

Specialists agree

Dr Joshua Safer, Endocrinologist and President of US Professional Association for Transgender Health has recently stated:

“The idea that a person’s sex is determined by their anatomy at birth is not true, and we’ve known that it’s not true for decades,” said Dr. Joshua D. Safer, an endocrinologist and executive director of the Center for Transgender Medicine and Surgery at Mount Sinai Health System in New York. He is also president of the United States Professional Association of Transgender Health.

“We know that there is a significant, durable biological underpinning to gender identity,” Dr. Safer said. “What we don’t know are all of the biological factors at play that explain gender identity. As far as we in the mainstream biological-medical community understand it in 2018, it is hard-wired, it is biological, it is not entirely hormonal, and we do not have identified genes, so we cannot specifically say it is genetic.”

Genetics does play a role, though. In studies of twins, if one is transgender, the other is far more likely to also be transgender if they are identical, rather than fraternal twins. Identical twins are near matches, genetically; fraternal ones are not. The findings are similar for twins who have Type 1 diabetes, which is known to have a strong genetic component.


The World Professional Association for Transgender Health (WPATH) board recently released a statement in response to Trump’s plans to enforce a narrow binary of biological sex upon transgender and intersex Americans (abridged below):

The WPATH Board of Directors expresses its strongest disagreement with the intention of the Trump administration to define human gender as the sex recorded at birth based on visible genital formation and to restrict changes, all via regulation. It has been known for decades that sex and gender cannot be determined solely by birth anatomy or chromosomes. More recently, the durable biological underpinnings for gender identity have become better understood within the mainstream medical and scientific communities.

The Trump administration’s past efforts to erase transgender people from American society indicate that its officials believe that XX or XY chromosomal testing to be definitive and definitional. However, this testing is insufficient to measure the known factors that affect the actual sex or gender of a sentient human being.

To acknowledge the diversity of sex and/or gender present in all human beings gives life and potential to those millions of people whose characteristics are not simply defined by sex chromosomes.

WPATH member physicians and researchers stand ready to testify before Congress to protect and defend the health and well-being of all transgender and gender-nonconforming people.

Here’s Dr Vilain, director of the Center for Gender-Based Biology at the University of California

“So if the law requires that a person is male or female, should that sex be assigned by anatomy, hormones, cells or chromosomes, and what should be done if they clash? “My feeling is that since there is not one biological parameter that takes over every other parameter, at the end of the day, gender identity seems to be the most reasonable parameter,” says Vilain. In other words, if you want to know whether someone is male or female, it may be best just to ask.”

#ProtectTransKids #ScienceIsComplex #BiologicalSexIsNotBinary

#TransgenderPeopleAreBiologicalToo #BiologicalNotMythological #MinorityRights

For support on Intersex issues in the UK please contact IntersexUK:

Email- | Twitter-  | Facebook- IntersexUK

One thought on “Biological Sex is a social construct

  1. Pingback: Caster Semenya, and what it means to be a woman in sports – Pragya Bhagat

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