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The gender spectrum is an understanding that gender is not binary, but rather a spectrum of biological, mental and emotional traits that exist along a continuum.
In contrast, the gender binary—also called gender binarism or genderism—is a belief that gender is composed of two distinct and opposite genders (women/men) in which there is not overlap.
Unfortunately for those who believe in a gender binary, it is not scientifically or medically correct. Gender can’t be binary, because it is a personal identity and is socially constructed.
Sex, which refers to one’s biological characteristics, also exists as a spectrum, because intersex people exist. A person’s sex can be female, male, or intersex—which can present as an infinite number of biological combinations.
Today, numerous scientific fields, including biology, endocrinology, physiology, genetics, neuroscience, and reproductive science, have confirmed that both sex and gender exist as a spectrum.
This is true for humans and across the animal kingdom.
Gender Spectrum vs. Sex Spectrum
When using the terms sex and gender, it is important to note that “sex” (female/male/intersex) describes biological traits. In contrast, “gender” is a broader term that reflects how a person lives within society. One’s gender identity could be woman, man, transgender, nonbinary, or an infinite number of other possibilities.
Because gender is a personal identity, is socially constructed, and has limitless possibilities, it takes no further explanation to explain why it is a spectrum.
Therefore, when people question the existence of a gender spectrum, what they are usually questioning is the existence of a sex spectrum.
Sex (and Gender) are Bimodal, Not Binary
For all too long, the government, the medical system, and even our parents have assumed that sex is binary. Based on science, this is not biologically or medically accurate.
What is true is that sex characteristics tend to be bimodal, meaning there are clusters of characteristics that tend to be associated with people that we call “female” or “male.”
On average, males do have penises, and on average, females do have vaginas. This is what allows for reproduction. However, there are many examples where this is not the case, such as intersex people. External genitals (a biological marker of sex) present across a spectrum from full-size penis to small penis to micro-penis to clitoromegaly to enlarged clitoris to standard-sized clitoris.
On average, males tend to have XY chromosomes and females tend to have XX chromosomes. However, sex chromosomes come in a wide variety as well, with at least 16 different naturally occurring variations (see details below). This means that chromosomal presentation is not binary either.
On average, males tend to have more facial and body hair than females (a secondary sex characteristic), but there are also females with coarse and dense body hair and males who can’t grow a full beard.
On average, males tend to be taller than females, but there are most certainly females that are taller than some males. If skeletal structure (a biological marker of sex) was binary, then all males would have to be taller than all females, which of course, they are not.
As explained by these examples, sex is not binary, because people cannot be grouped into two separate, non-overlapping groups.
However, bimodal sex characteristics are not uncommon.
Bimodal means the presence of two (“bi”) statistical modes, which can be seen as peaks in a graph. The two modes represent probability clusters.
With regard to human sex, this means that for some sex characteristics, there may be common norms among people whom we tend to assign as “male” and “female.” However, there are also clearly overlaps present between the peaks. This is what makes sex bimodal, and not binary.
Finally, at risk of getting too mathematical, a bimodal distribution is by definition, a continuous probability distribution with two different modes.
In other words, biological sex is a spectrum that has clusters.
If sex is a spectrum, then gender is unquestionably a spectrum, because gender includes aspects of biological sex, interwoven with how a person lives within society and self identifies.
Why Genitals Do Not Determine Sex
With regard to assigning sex to people by their external genitalia, it is an inaccurate system at best. There are several reasons for this, as described below.
1) External Genitalia Are Diverse
In newborn humans, genitals are extremely diverse in size and shape. Until about week 7 to week 8 of pregnancy, all fetuses have what’s known as a “genital ridge.”
This genital ridge is the tissue that eventually becomes the sex organs.
At the time of birth, a newborn’s genitals are usually labeled by a physician as male or female, even if the newborn presents with sex organs or characteristics that are intersex, ambiguous, or undefined. In a few places, such as Ontario (Canada), 19 U.S. states, and Washington, DC, “nonbinary” or “gender unspecified” options now exist, but this is not yet the norm.
All sex organs come from the same genital ridge, with the testes in men being equivalent to labia and ovaries in women and the penis being equivalent to the clitoris.
This is why the penis and vagina do not exist as a binary, but rather, as a spectrum that includes the following:
- Full-size penis
- Small penis
- Micro-penis
- Clitoromegaly, also called a “Pseudopenis”
- Enlarged clitoris
- Standard-sized clitoris
2) Intersex People Exist
Intersex means that a person was born with variations in their sex characteristics, such as the biological markers described above. These can include: internal genitals, external genitals, gonads, chromosomes, gene expression, hormone levels, receptor sensitivity, and brain structure.
Current research estimates that intersex people compose 1.7% of the population, which makes being intersex about as common as having red hair.
However, this metric is understated for the following reasons:
- Most doctors, parents, or individuals don’t release this confidential medical information.
- There are subtle forms of sex variations that do not show up until later in life which go undocumented.
- Definitions of what intersex is have not reached consensus.
- There are at least 10 biologically relevant markers of sex (described below), and all but one (external genitals) are not routinely assessed.
The following examples explain this lack of consensus:
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- How small does a penis have to be before it counts as intersex?
- Do you count sex chromosome variations if there’s no external sexual ambiguity?
- Do unusually high or low sex hormone levels (estrogen, progesterone, testosterone) make someone intersex?
- If so, how high or low must these hormones levels be and where is the “cut-off?” (The Olympic Committee has struggled mightily with this question.)
- How do you classify someone whose secondary sex characteristics (body hair, facial hair, or muscle mass, for example) don’t match their genitals?
As these questions illuminate, sex may present as a spectrum for people who have not been classified as intersex, as well as those who have.
What about Chromosomes?
While chromosomes are another biological trait that some people try to use to explain the sex binary (male/female), chromosomes are also varied and diverse across the human species. On average, most people assigned male at birth have XY chromosomes, while most people assigned female at birth have XX chromosomes.
However, other sex chromosomal variations frequently exist as a result of the loss, damage, or addition of one or both of the sex chromosomes.
In humans, the following sex chromosome variations are naturally occurring:
- 45, X, also called Turner syndrome
- 45,X/46, also called XY mosaicism
- 46, XX/XY
- 47, XXX, also called Trisomy X
- 47, XXY, also called Klinefelter syndrome
- 47, XYY with normal phenotype
- 48, XXXX
- 48, XXXY
- 48, XXYY
- 49, XXXXY
- 49, XXXXX
- XX Male Syndrome
- XX Gonadal Dysgenesis
- XY Gonadal Dysgenesis
Where Gonadal Dysgenesis is listed above, it refers to reproductive tissue (gonads) being replaced by non-reproductive fibrous tissue during prenatal development.
Furthermore, even a newborn born with “binary” sex chromosomes (XY or XX) can present with intersex characteristics.
For example, either the fetus or the mother’s adrenal glands can produce elevated levels of androgens. When this happens, an XX (“female”) child can be born with a phallus (small penis). In some cases, these newborns may will appear to have a scrotum, due to the labia fusing together.
Similarly, an XY (“male”) child can be born with an enzyme deficiency, such as 5-alpha deficiency and 17-beta dehydrogenase deficiency. When this happens, that “male” infant can be born without a penis and labelled “female” at birth.
Other biological conditions can create similar incongruities between chromosomes and genitals. This is why it’s unfortunate that federal and state-issued documents use external genitalia to make a sex assignments.
The 10 Biological Markers of Sex
Often, you will hear people say things like, “Gender is determined by what is in your pants. If you have a penis you are a man. If you have a vagina, you are a woman.”
As we’ve already addressed, gender incorporates personal identity, so it is unquestionably a spectrum. Biological sex is also complex, and across all species, exists as a spectrum. With regard to this specific statement, external genitals are highly variable, may be ambiguous, and both male and female sex organs can be present.
More importantly, this statement is incomplete from a biological perspective.
While sex has traditionally been assigned based on external genitalia, this approach neglects that there are at least 10 biologically relevant markers of sex (and likely more).
Biological markers of sex include:
- Chromosomes – Types of chromosomal expression.
- Gonads – Organs that produce gametes (testes or ovaries).
- Hormones –Types and level of hormone secretion, which vary within and across the sexes.
- Secondary Sex Characteristics – Features that appear during puberty, but are not involved with reproduction.
- External Genitalia – Genitals visible outside the body.
- Internal Genitalia – Genitals present within the body.
- Skeletal Structure – Sex differences may be seen in the pelvis, jaw bone, brow, and limb length and thickness.
- Gene Expression –Levels and types of gene expression. Genes dictate the proteins made by the body. Known genes that impact sex include DMRT1, SRY (produces Testis-Determining Factor), and Foxl 2.
- Brain Structure – Brain structure characteristics (including the ratio of white matter to grey matter) and brain activation patterns vary by sex.
- Hormone Receptor Sensitivity – The response to sex hormones can vary, depending on receptor sensitivity. Some individuals may be partially or completely insensitive to hormones, negating their effect.
Given that there are 10 biologically relevant markers of human sex, using external genitalia is at best, a partial assessment. In some cases, it is wholly incorrect.
For example, it would be easy to identify a person with a vagina as female, but this person could also present with “male” gene expression or androgen insensitivity or an intersex brain structure. The same is true for someone who presents with a penis.
If you want to assess gender instead of sex, then you also have to add an 11th marker, which is personal identity. Personal identity is how a person self-identifies. This is often a result of many of the other factors interacting, making it a valuable scientific marker as well.
Gender and the Brain
The brain is another biological marker of both sex and gender that presents with great diversity, further supporting the concept of a sex (and gender) spectrum.
In a fascinating study published May 2018 by the European Society of Endocrinology researchers discovered, “Brain activity and structure in transgender adolescents more closely resembles the typical activation patterns of their desired gender.”
When MRI scans of 160 transgender youths were analyzed using a technique called diffusion tensor imaging, the brains of transgender boys’ resembled that of cisgender boys’, while the brains of transgender girls’ brains resembled the brains of cisgender girls’.
Put simply, transgender kids’ brains resemble their gender identity and not their biological sex.
Cisgender means that a person’s gender identity aligns with the sex assigned to them at birth, while transgender means a person’s gender identity does not align with the sex assigned to them at birth.
As stated by Julie Bakker, lead researcher from the University of Liege, “We now have evidence that sexual differentiation of the brain differs in young people with [gender dysphoria], as they show functional brain characteristics that are typical of their desired gender.”
This study explored the brains of cis girls, cis boys, trans girls and trans boys. The next step is for more sexes and genders to become integrated within this neuroscience research.
The Role of the Mind versus the Brain
Of course, the brain and the mind are also two different things.
The brain is the physical structure in your head that is composed of grey and white matter. It has neurons firing within it and uses neurotransmitters as chemicals messengers.
The brain can be thought of as your central processor, because it integrates and facilitates all of the functions within your body.
As noted by Julie Bakker (lead researcher in the MRI study above) and others, brain structure and activation patterns present along a spectrum.
The mind, on the other hand, is the conscious product of that biological activity that creates emotions, ideas, memories, and creative thought. It determines your personality and impacts how you interact with the world.
The mind plays a central role in your gender identity.
Sex and Gender Identification at Birth
As described above, external genitals are not an accurate marker of sex to use at birth, because they are one of at least 10 biologically relevant markers of sex. External genitals are also highly variable, may be ambiguous, and can have both male and female sex organs present.
Furthermore, performing this gender assignment at birth based on external genitals does allow a physician to integrate information about the child’s internal genitals, gonads, chromosomes, gene expression, skeletal structure, brain structure, hormone receptivity, and most importantly, how the child will grow up and express themselves within society.
While I am not opposed to the option to note sex on a child’s birth certificate, I am opposed to:
- The requirement that parents select a sex for their child. Parents should be allowed not to indicate a sex for their child if this is their preference.
- Binary options for sex, when it is clear that sex exists along a spectrum and intersex people exist. At the very least, there should be the option to choose Female (F), Male (M), or Other (X).
- That sex being a permanent identification marker, when that child’s other biological markers of sex (described above) are yet unknown.
Sex versus Gender
Although it has been useful to consider sex and gender separately for the sake of this analysis, it should be mentioned that they are not fully separate from each other. This is because a physical organ (the brain) directly impact gender identity, a phenomenon which is culturally experienced.
Across many cultures, both biological sex and gender are intertwined. Examples of this include:
- Two-Spirited People for Native American/First Nations people
- Hijra for South Asian people (also known as Kinnar or Kinner)
- Māhū for Kanaka Maoli (Hawaiian) and Maohi (Tahitian) cultures
- Fakaleiti for Tongans
- Ffa’afafine for Samoans
- And many others
Gender diversity has existed across all time periods and cultures, with evidence of it being documented as long as 4,500 – 9,000 years ago across Sumerian, Mediterranean, Greece, Phrygia, and Roman cultures. Hijras within Indian and kathoeys in Thailand have existed since ancient times, with the presence of trans male individuals also described within texts that are thousands of years old. Today, it is estimated that more than a half a million hijras live in India and another half million live in Bangladesh, legally recognized as a third gender.
Given that gender is personally and societally expressed, every culture has gender diverse individuals represented within its population.
Gender Diversity Across the Animal Kingdom
Finally, gender diversity is widely present across the animal kingdom. For example, seahorses, pipefish, and sea dragons all have pregnancy as a male reproductive process. In these species, the male fertilizes eggs that are deposited within a pouch in his belly and then he carries his developing embryos until they are ready to be birthed.
In another example, female spotted hyenas have a pseudo-penis that is capable of erection and can be as much as 90% the size of a male hyena’s penis. They have two fleshy masses at the base of their pseudopenis that contain fat and connective tissue which appear analogous to a scrotum. Where you’d expect there to be a vagina, spotted hyena females have fused labia. Female spotted hyenas also dominate males behaviorally.
Chickens can also naturally undergo gender changes. This is because female chickens only use one functional ovary on their left side. However, they have two sex organs that are present from their embryonic stage onward through their lifespan. If the left ovary shrinks within a hen, then its right gonad may start secreting androgens, turning the hen into a rooster.
In short, sex and gender exist as a spectrum for humans and animals (and in fact, plants too). We might as well embrace it, because after all, natural variation has caused the rise of our species to 7.8 billion strong!
Do you have questions about the gender spectrum? Ask them in the comments below. View the Portuguese translation here.
Interested to learn more? Join nearly two million other readers who are learning from Cade.
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*This article is part of a Biological Sex and Gender Diversity Series published by Cade Hildreth, B.A., M.S. You can read the other articles here:
AUTHOR BIO: Cade Hildreth attended Dartmouth College & Smith College for Undergraduate Studies in Biology and then acquired a Master’s Degree in Biochemistry and Molecular Biology with Specialization in Biotechnology & Bioinformatics from Georgetown University, where Cade was Valedictorian. Cade is the Founder/President of BioInformant.com, the world’s largest stem cell industry news site that attracts nearly one million views per year and serves all-star clients that include GE Healthcare, Pfizer, and Goldman Sachs. Cade has authored over one-thousand articles about the stem cells, interviewed hundreds of executives from across the industry, and presented at stem cell conferences worldwide. As a media expert on stem cells, Cade has been interviewed by the Wall Street Journal, Los Angeles Business Journal, Xconomy, and Vogue Magazine, as well as quoted in Tony Robbin’s his best selling book, Life Force.
Melissa Murphy says
Internally, in the deepest pit of my gut, I have ALWAYS believed this to be true. To read a scientifically-backed, beautifully-written article that validates what I’ve always somehow known, will allow me to share with as many people as I can in a way I may not have been able to articulate before reading this. This has been an enormous reinforcement of my support of my 9-yr old grandson in his journey of navigating this world with so many who simply do not understand. Thank you, Cade. You are amazing:)
Gina Logan says
My understanding is that at birth, the newborn’s having a very large clitoris or a very small (micro) penis might impact how the infant’s gender is assigned. The former might be incorrectly assigned as male; the latter might be incorrectly assigned as female. There are cases in medical literature that illustrate this potential problem, including cases of babies whose genitalia were surgically altered to coincide with what the medical folks THOUGHT was the correct choice, only to discover later that the baby with the micro penis had ovaries and a uterus, for one example.
Joanne says
What an amazing article. As an Intersex person with Klinefelters Syndrome (XXY chromosomes) I have so many traits that are female and many that are male, with a brain with sits somewhere in the middle toward the female side. I hope that one day, everyone will understand the non-binary natural of sex and gender and we can all just be accepted.
Donna says
Thank you Cade for this very informative article! It’s now part of the course reading in my class, Women’s Health and Global Issues, where I emphasize the importance of recognizing that bimodal sex variation is the biologically accurate descriptor. We’re already having meaningful, thoughtful, and scientifically accurate discussions around the topic of bimodal sex and gender…we’re starting the year off well and wanted to you to know you’ve helped make that happen.
Kris says
There is a blood test than can check your chromosomes. I found that I am mosaic turner’s by complete accident while looking for something else all together at the age of 29. It made so much of my existence make sense. So I have an incomplete x and several pieces of Y. This article touches on my chromosome abnormality and so much more, and I felt seen and understood reading this.
Thank you, Cade.
Helen Silvis says
Thank you Cade I now feel confident about explaining why bio sex is a spectrum and my feelings about self ID have changed
Adam says
I followed everything besides how the size of a penis or an enlarged clit is relevant. Only part I didn’t quite understand, but I would love to hear why.
Holly says
Holy crap this article is amazing!! Thank you for writing it so I could learn this! I came in with the private opinion that your genitals “make you” one sex or the other and that people that become trans must do so as a response to some kind of trauma in their lives to emotionally survive. But wow this is such compelling information to the contrary! I can see there are many biological (not environmental) reasons why someone could be trans now. And the existence of 10 sex indicators and the intersex spectrum completely (and rightly) dissolves that inner theory of mine. So thank you for teaching me. I’m so glad I was directed to look up the existence of other sexes besides male and female and found your article. Thanks for taking the time to write it so people with opinions like mine can learn this information and update their understanding accordingly. 🙏🏼 Sorry I held the view I did before.
Tj Gundling says
I teach an Introduction to Transgender Studies course at my university, and as an anthropologist I take an approach that is intentionally and intensively biocultural. This is to say that it is a fool’s errand to try and tease out the biological from the cultural, and vice-versa, especially as pertains to Homo sapiens.
The distinction of bimodal vs. binary is very useful, and I will incorporate this into my Unit on Intersex/DSD. If students can be persuaded, BY THE EVIDENCE, that biosex exists in clusters yet along a continuum, resistance to conceptualizing gender in an analogous manner will be greatly reduced.
Thanks!
Natalie Baker says
This article is excellent.
Roman says
Extremely helpful! I’m writing an essay for school about gender identity, and this helped me a lot! Also, as a non-binary person, it was very validating and enlightening. Thank you for writing this!
Sean says
Absolutely best and most helpful explanation I have ever read. Thank you.
Brian says
Wonderful article, Cade! This is a fascinating and important topic which needs to be thoroughly examined – as you are doing – in order for society to evolve and find ways to help all people feel welcome and accepted.
I have long believed gender and sex are on a continuum and I was pleased to see your explanation of the bimodal reality of both these attributes.
A point of confusion arose for me when you mentioned you are non-binary. How can this be possible if there isn’t a binary? Shouldn’t one say non-bimodal or intersex…or intergender? I feel the non-binary term assumes a binary which, as you point out, doesn’t exist. How can one be non-binary if there isn’t a binary? And, in a sense, those who don’t wish to be known as non-binary but also don’t identify as “typical male” or “typical female” – but believe in the continuum – are a bit “imprisoned” by a term that assumes a binary.
I would love your thoughts here if you have the chance to respond.
Many thanks for your thoughtfully written and super informative article.
marlene says
non-binary is a necessary term for a society that widely believes in a binary gender system / functions with a binary gender system, even if that system doesnt make sense. so as long as this is the dominant perception of gender, people who dont identify as men or women have the non-binary label to describe that
Gerardo Heredia says
Fascinating article. What I don’t have clear now is about those who identify as nongender. Is it possible no to have a gender? Does that mean they have not developed their identity?. I also was reading about the brain plasticity and how it is not a proof that gender is binary as it evolves according to our experiences and what we learn that happens to be determined by boys do this and girls do that. So that would also mean that the brain differences and changes would be irrelevant for gender identity as well if boys or girls start having experiences out of the social role assigned to their sex. I’d like to know your point of view on this.
Nana says
I like that this article takes a more neutral approach than other LGBTQ+ claims supposed to be “based on scientific facts” (or is it just because the article itself is too vague and thus does not touch the bottom of the sex =/= gender issue?).
This article shows that non-binary+trans genders exist naturally (as opposed to artificially).
However, this leads to the ever-debated question of “Do parents have to let their child take hormonal treatment/surgery if their child identify more to a certain gender? And if yes, starting at what age?”, which is basically one of the two core gender issues of society today, the other one being the recognition of sex/gender differentiation by governements + “normal” population + LGBTQ+ population (yes, even the LGBTQ+ population has issues identifying and separating both!).
Unfortunately, these issues are sociological and not biological, so they can only be solved by the continuing effort of communication to the “normal” population and governments by the LGBTQ+ population, in order to make society evolve toward a model where they will be recognized and accepted.
However, this is truly a good and short enough article to refute all the ever-so-present arguments about non-binary genders being mind constructs!
Jordan Lundenburg says
Hello! It’s important to be mindful of what a child says. If your kid’s sex is female and they begin to experiment with the idea of being more of something else, then acknowledge that. Personally, If my kid were to be having these thoughts around 5, I’d brush it off and see where it goes. If they’re still having these thoughts a year or two later, I would take them out to the store and get them clothes they’d be more comfortable in, start using the pronouns they want. See how they feel. If it ends up not being for them, that’s fine. If it is then I’d wait till puberty to get hormone blockers. If they want surgery, It would be at a time where I feel they’re mature enough to make the decision. Like 16. They can always do it themself at 18 anyway.
Simon B says
A very well written piece on sex and gender, which I intend to share with all my friends. I’m just a cishet guy, and my mum gave me this observation way back in the 1960s. She said, “Everybody’s different, but we are all human beings”, she really was an intelligent woman.
Finn says
well done! thank you!
Erica Pelz says
Thank you for an exceptionally well written piece on the spectrums of gender and sex. I’ll add this to my list of reference material, and look up the studies you referenced. By chance would you be willing to share the bibliography? I’m sure I can find it but would save me some digging. Thabks again!
Allison Kasper says
Hey, please let me know if you found that bibliography! I am a student at the University of Illinois at Chicago and I would love to read more into this. Thanks!
Ali Su says
How does one find out their sex genes? Is there somewhere to get tested. I identify as gender queer not transgender. Born female but always felt neutral about gender. Was wondering if maybe I have more than two X
JK says
Great breakdown of a topic that comes up a lot with some religious/transphobic people in my life. I find this info extremely helpful!
Jason Masters says
Excellent summary