Is Sex a Binary?

The ideological battle of sex as a binary versus sex as a spectrum (or range, variation, etc.) is a fiercely waged one. I guess I’ve decided to play out my inner Merry Brandybuck and jump in on it. And while I don’t intend to stab a witch-king, I do intend to correct a lot of scientific inaccuracies and misconceptions, including but not limited to the idea that human sex is a binary determined solely by chromosomes and that one’s sex is obvious and innate rather than often ambigious and assigned.

But first let’s just pause a second and ask why we’re engaging in this debate at all. Think about it, are you a doctor for whom defining sex is relevant to your practice? A different health care professional? A patient? Just someone with strong opinions? Personally I’m a science communicator with a gender studies major whose life is happily filled with many gender nonconforming individuals.

Consider why you are motivated to be interested in this question. There’s not a right or wrong reason, but your motivation for engaging in debates about sex influence how you will respond to and interpret data and facts. None of us are unbiased, and we do a diservice to each other to pretend that we are.

Now, onto the crux of my point.

In humans the genotypes associated with male or female have many phenotypes. Specifically there are more than 2 distinct phenotypes exhibited.

Let’s talk about sex.

When a baby is born, a sex is assigned to them, usually by doctors, according to 5 factors:

  1. Whether or not they have a Y chromosome.
  2. The gonads they have (testes or ovaries).
  3. The sex hormones they produce (testosterone or estrogen, and in what proportions).
  4. Their internal reproductive organs (uterus or no uterus).
  5. Their external genitalia (penis or clitoris).
    Source- (yes I’m citing Wikipedia, if you have an issue with that I highly suggest you check out or get involved with Guerilla Skeptics.)

Sometimes, these factors all agree, and a baby is simply assigned a sex. Other times one or more of these factors oppose each other. When this happens, sometimes a doctor will overlook disagreeing sex factor(s) and go with majority rules to assign the baby a sex. Sometimes the disagreeing factor(s) will be surgically corrected, sometimes they won’t. And sometimes the baby will not be assigned a sex, in which case they are referred to as being intersex.

Not all factors are weighted equally, however, as reproduction and penile/clitoral size are seen as mattering more in most cases. This means that a baby with reproductively functional gonads and internal reproductive organs may be assigned their sex according to these, even if the other 3 factors disagree, going against the majority rules.

This also means that in the absence of reproductive potential, babies with external genitalia that is larger than the average clitoris is likely to be assigned male, and vice-versa, even if it goes against the majority.

Once we move away from babies and into adults, we must also take into account secondary sex characteristics like amount of breast tissue (do they have boobs or not, do those boobs have developed mammary glands) or facial hair (how much or how little), but we can look chiefly at these 5 fundamental factors for now.

While scientists may think of sex in terms of chromosomes, many others do not. Ask random people on the internet what defines a female and you’ll hear every answer from XX to having a uterus to being fertile to having breasts. To talk only of chromosomes is to ignore the anatomical features and secondary sex characteristics many people base their conceptualizations of male and female on.

Never the less, since scientists seem to favour chromosomes, and I am a scientist (or so they tell me) let’s start with chromosomes. They’re often said to be the underlying and most important factor in all of this, and certainly, from a developmental standpoint, they hold the instructions for what sex features an individual will have. So, isn’t it just as simple as males are XY and females are XX?
Well, in truth it’s not so simple. For one thing, chromosomal abnormalities exist, which throws a wrench in that simple definition.

Turners Syndrome is a disorder of sex development (DSD) wherein an individual has less than 2 X chromosomes (for example only 1 X, or 1 and ¾ X).
Klinefelter’s Syndrome is a DSD wherein an individual is XXY, XXXY or XXXXY.
There is also Triple X syndrome (which can give someone XXX or XXXX or even XXXXX) and actually a rather huge number of conditions of this type.

You can argue that there are only 2 “proper” genotypes of human sex chromosomes, XX and XY, and that the variations I’m discussing are only accidents on the road to these true genotypes. However, the reality remains that these variations exist, whether they “should” or “should not”.

Whether you view variations from XX or XY as new sexes (as Fausto-Sterling does) or as unintended divergences from “normal” chromosomal division, they’re here, they’re clear, and they’re not going to disappear. As are individuals living with these divergences who are seeking to find an identity in a world that has traditionally ignored them.

Genotypes, however, are only part of the picture. The other part is phenotypes, the physical expressions of ones genes. For XX, XY and any other sex chromosome combination, there exist a wide range of phenotypes. There are XX individuals with testes, XY individuals who produce no testosterone, and almost any other configuration you could imagine.

Alright, factor-by-factor, let’s go.

Factor 2: Gonads. Gonads are the reproductive glands that produce gametes and sex hormones. Typically, in females, they are ovaries, which produce an ovum, estrogen, testosterone, inhibin, and progesterone. Typically, in males, they are testes, which produce testosterone and other androgens.

I say typically because, as you might expect if you’ve studied biology, there is another wrench.
Anorchia is a DSD in which a person with an XY genotype is born without testes. It’s related to Swyer syndrome, where an individual is born with external female features, but also streak gonads (typically nonfunctional testes).

Factor 3: Hormones. Conditions concerning variations in sex hormone production are downright common. Hyper and hypo estrogenism and androgenism have a huge variety of causes, from tumours of the Leydig cells to liver cirrhosis.

Factor 4: Internal reproductive organs. We can examine conditions like Müllerian agenesis wherein an individual develops functional ovaries and fallopian tubes but has a small or absent uterus. Or you could look to case studies such as this, which describe a self-identified male, with male external genitalia, who also had an internal uterus and fallopian tubes.

Factor 5: External genitalia. I can probably leave this one with a cursory look at clitoromegaly or hypospadias. The varying degrees of severity these traits may exhibit can lead to snap decisions of sex assignment at birth that are often challenged later in life as the person grows and forges their own identity.

5 different factors multiplied by the many different configurations of each equals a huge variety of phenotypes and genotypes.

A question regarding medically necessary, or elective, changes to the reproductive bits in these 5 categories must also be raised. If sex is partially defined by one’s gonads or internal genitalia, or hormones, does their alteration change your sex? If a male has his testes removed, is he no longer male? Are post-menopausal women who no longer produce estrogen in quantities greater than males no longer female? What if you couple several of these conditions together? If I have an XXY karyotype, no ovaries, no uterus, but a vagina and enlarged breasts, am I a female?

“BUT” you may be screaming, “THESE DISORDERS ARE A TINY PERCENTAGE OF THE POPULATION” and whether you’re screaming or not, you are kind of right. Take a look at this cool chart, taken from here.

The commonly held population statistic, originating from the work of Anne Fausto-Sterling, is 1.7% for all intersex conditions (not just chromosomal abnormalities). If true, that makes intersex individuals about as common as red-haired individuals.

The problem is, this statistic itself is in question. It might be wildly inaccurate (too high or too low), because, as the Intersex Society of North America succinctly puts it, “How common is intersex? To answer this question in an uncontroversial way, you’d have to first get everyone to agree on what counts as intersex —and also to agree on what should count as strictly male or strictly female. That’s hard to do.”

Indeed, that’s why we’re all reading this post isn’t it, because we can’t agree on what counts as strictly male/female/intersex.

So, we cannot accurately know how common these genotypes and phenotypes are. But we do know that they exist. That there are a great number of genotypes ranging from XX to XXXXX, from XY to XXXY, with many in between, with an equally great number of phenotypes representing them.

If you’re tempted to ignore all genotypes and phenotypes that do not fit the “true female” and “true male” binary because they occur in such a small percentage of the population, consider that no one is discounting male calico cats from cat genetics, although this combination of traits only occurs in about 0.3% of calico cats.

Additionally, an estimated more than 100 million intersex people might be a small percentage of the population, but still represents a significant amount of people.

If someone asks me what my sex is, I’m usually going to follow it up with a why? Because most times they’re really asking about something in particular, not for the full range of where I fit across the gonadal, chromosomal, hormonal, genital and reproductive categories.

A store clerk is wondering whether to bring me boxers or panties to try on, or an ER doctor is wondering if she should also test my urine for pregnancy as well as a UTI. In these cases, it serves either of them no purpose to examine the intricacies of how I, and society, arrived at calling me male or female.

The doctor doesn’t want to know what genitals I have, she wants to know if I have a functioning uterus, fallopian tubes and ovaries. The store clerk doesn’t want to know what hormones I naturally produce (she doesn’t even really want to know what external genitalia I have) she just wants to know what type of underwear I want to try on.

My point is that nobody’s sex is your business unless they make it your business. You should never assume the genitals of a person based on their breast size, and you shouldn’t assume the hormone levels of a person based on their facial hair.

You should ask questions only when they matter, and leave people be when they don’t.

Humans have a variety of sex chromosome genotypes which are represented in a huge diversity of phenotypes across 5 main factors at birth, and more later in life. To ignore these variations is to ignore the realities upwards of 127 million people. To ignore these variations is simply ignorant. And more importantly, pointless.

I know we all want the world to be simple, but, like most things we observe in nature, human sex just isn’t.

Some good resources if you’d like to read more:

Anne Fausto‐Sterling – The Five Sexes (

Anne Fausto-Sterling – The Five Sexes, Revisited (

Susan Stryker – (De)Subjugated Knowledges: An Introduction to Transgender Studies (

Elizabeth Reis – Divergence or Disorder? : the politics of naming intersex (

Nicole Tartaglia et al. – A New Look at XXYY Syndrome: Medical and Psychological Features (

Justin Davies, Timothy Cheetham – Recognition and assessment of atypical and ambiguous genitalia in the newborn (

Council of Europe – Human Rights and Intersex People (

Writing Committee for the International Intersex Consensus Conference Participants – Summary of Consensus Statement on Intersex Disorders and Their Management (

World Health Organization – Eliminating forced, coercive and otherwise involuntary sterilization (

Gayle Rubin – Thinking Sex (

Judith Butler – Performative Acts and Gender Constitution: An Essay in Phenomenology and Feminist Theory (


One thought on “Is Sex a Binary?

  1. Pingback: So Your Kid is Trans and You Have Questions

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