The Gender Spectrum: A Scientist Explains Why Gender Isn’t Binary

The gender spectrum is an understanding that gender is not binary (female/male), 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 the belief that gender is composed of two distinct and opposite genders (female and male) in which there is not overlap.

Unfortunately for those who believe in a gender binary, it is not scientifically or medically correct.

Today, numerous scientific fields, including biology, endocrinology, physiology, genetics, neuroscience, and reproductive science, have confirmed that sex and gender exist as a spectrum, both for humans and across the animal kingdom.

Sex (and Gender) are Bimodal, Not Binary

For all too long, the government, the medical system, and even our parents have assumed that sex (and gender) are 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, men do have penises, and on average, women do have vaginas, which 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, men tend to have XY chromosomes and women 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, men also tend to have more facial and body hair than women (a secondary sex characteristic), but there are also women with coarse and dense body hair and men who can’t grow a full beard.

On average, men tend to be taller than women, but there are most certainly women that are taller than some men. If skeletal structure (a biological marker of sex) was binary, then all men would have to be taller than all women, which of course, they are not.

As explained by these examples, gender is not binary, because it cannot be grouped into two separate, non-overlapping groups.

However, bimodal sex characteristics are not uncommon. Bimodel 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,” but there are also clearly overlaps present between the peaks. This is is what makes sex (and gender) 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 word, it is a spectrum that has clusters.

The Difference Between Sex and Gender

In describing the terms sex and gender, it’s important to note that within Western culture the word “sex” describes biological differences between people (male, female, intersex, etc.), while the term “gender” is a broader term that reflects how a person lives within society (that is, gender identity).

Despite the binary options on most state and federal IDs, your biological sex can be variable. This is certainly true for people who are intersex and likely for others as well. Intersex means that a person was born with variations in their sex characteristics, including but not limited to internal and external genitalia, gonads, chromosomes, hormones, brain structure, and more.

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:

1. Not all doctors, parents, or individuals release this medical information.
2. While existing research has focused on the presence of atypical external genitalia, and to a lesser degree chromosomes, there are at least 10 medically accurate markers of sex (described below).
3. There are subtle forms of sex variations that do not show up until later in life which go undocumented.
4. Definitions of what intersex is have not reached consensus. The Intersex Society of North America uses the following examples: “How small does a penis have to be before it counts as intersex? Do you count sex chromosome variations as intersex if there’s no external sexual ambiguity?”

In short, it’s unfortunate that federal and state-issued documents often use external genitalia to make a male/female assignment, because for many people this is an inaccurate or incomplete description.

Sex and Gender

Even sex and gender are not fully separate from each other. Across many cultures, they 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

One of the people who has done a phenomenal job of deconstructing the concept that sex and gender are separate is Alok Vaid-Menon, a gender non-conforming performance artist, educator, and writer.

Alok describes the prevailing idea that gender is “cultural” and exterior and sex is “biological” as neglectful of the fact that biological sex is also cultural. In line with this, Alok explains that the sex/gender split relies on a particularly western historical conception of the body as individually enclosed by skin.

Alok explains that in contrast to the Western belief of “the body proper,” many other cosmologies (studies of the origin of the universe) do not perceive adornment as a supplement to the body. Instead, Alok says, it is foundational to its constitution. In other words, ‘this is not my costume, it is my being’.

Even from a scientific perspective, the skin does not do an accurate job of describing where our bodies end. This is because we are composed of atoms which have an incredibly small nucleus and even smaller electrons, which move around at a far a distance from the center. As a result, we are largely composed of space and only perceived to be solid, because of electron repulsion and patterns of absorbed and reflected light.

Why a Sex and Gender Spectrum?

As a nonbinary person, I have heard 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.”

However, as a scientist, I can tell you that both sex and gender are complex, and across all species, exist as a spectrum. (See author bio at end of article.)

Currently, sex gets assigned at birth based on external genitalia, but there are at least 10 important and medically accurate markers of sex (and likely more), as described below.

Biological markers of sex include:

1. Chromosomes – Types of chromosomal expression.
2. Gonads – Organs that produce gametes (testis or ovaries).
3. Hormones –Types and level of hormone secretion, which vary within and across the sexes.
4. Secondary Sex Characteristics – Features that appear during puberty, but are not involved with reproduction.
5. External Genitalia – Genitals visible outside the body.
6. Internal Genitalia – Genitals present within the body.
7. Skeletal Structure – Sex differences may be seen in the pelvis, jaw bone, brow, and limb length and thickness.
8. 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.
9. Brain Structure – Both brain structure characteristics (including the ratio of white matter to grey matter) and brain activation patterns vary by sex.
10. Personal Identity – How a person self-identifies. It is often a result of the other factors interacting, making it a valuable marker.

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), 11 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) Existence of Intersex People

Intersex means that a person was born with variations in their sex characteristics, such as the biological markers described above, including but not limited to internal and external genitalia, gonads, chromosomes, hormone levels, and brain structure.

Intersex people are biological proof that sex is not binary.

What about Chromosomes?

While chromosomes are another biological trait that some people try to use to explain the gender binary, 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.

Gender and the Brain

The brain is another biological marker of sex that presents with great diversity, further supporting the concept of a 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, 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.

Because brain structure and activation patterns vary across the human species, the brain is a biological marker of sex that confirms we exist along a spectrum.

The mind, on the other hand, is the conscious product of that biological activity that creates emotions, ideas, memories, interpretations, and creative thought. It determines your personality, plays a role in how you prefer to present, and impacts how you interact with the world. The mind plays a central role in your gender identity.

There is an enormous amount of psychological research confirming the role of the mind in creating a variety of genders.

Sex Identification at Birth

When sexing babies by their external genitalia, an Ob/Gyn has no idea as to the baby’s internal genitals or gonads or chromosomes or gene expression or brain structure or personal identity or how the child will want to 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:

1. The requirement that parents select a sex for their child. For a wide variety of reasons, parents should be allowed not to indicate a sex for their child if this is their preference.
2. That sex being glued to a child for the rest of their life when it may (or may not) be the right fit.
3. Binary options for sex, when it is clear that sex exists along a spectrum. At the very least, there should be the option to choose Female (F), Male (M), or (X) for all other genders.

In short, I would strongly prefer to see children encouraged to explore their personal identity and self-expression as they come of age.

Gender Neutral Birth Certificates

In recent years, it has become increasingly recognized that it is difficult to assess a newborn’s sex in a meaningful or medically accurate way.

As described above, external genitals are not an accurate marker of sex, because they are one of at least 10 different biological markers of sex. They are also highly variable across our species, may be ambiguous, and/or can have both male and female sex organs or  characteristics present.

Importantly, performing sex assignment based on external genitals does not recognize the critical role of a newborn’s mind on what will ultimately become their gender identity.

For this reason, Ontario, Canada’s most populous province, began allowing Canadian born-citizen’s (including adults) to choose one of the following options on their birth certificate in October of 2018:

• Female
• Male
• Nonbinary / Unspecified

Alternatively, Ontario citizens can remove a sex assignment from their birth certificate in entirety.

Joshua Ferguson, a nonbinary filmmaker born in Ontario who uses gender-neutral pronouns (they/them), was issued the province’s first known nonbinary birth certificate on May 4, 2018, with an “X” instead of an “M” or “F.”

U.S. States Allowing Gender-Neutral IDs

Within the United States, there are now 11 states that grant identity documents with nonbinary options, as well as our nation’s capital of Washington, DC.

These policies of these states and district are described below:

While it will take time, I am confident that other states and countries will also acknowledge a sex and gender spectrum, because science (and society) are progressing.

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 7.7 billion strong!

---

AUTHOR BIO: Cade Hildreth attended Dartmouth College & Smith College for Undergraduate Studies in Biology and subsequently acquired a Master’s Degree in Biochemistry and Molecular Biology with Specialization in Biotechnology from Georgetown University, where they were Valedictorian. Cade is the Founder and 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, Goldman Sachs, PerkinElmer, and Merck. Cade has authored over one-thousand articles about the stem cell industry and interviewed hundreds of executives from across the industry. As a media expert on stem cells, Cade has been interviewed by the Wall Street Journal, Los Angeles Business Journal, Xconomy, & Vogue Magazine. As a professional real estate investor, Cade owns a portfolio of residential and commercial properties. Learn more here.

---

Do you have questions about either the sex or gender spectrum? Ask them in the comments below or contact me here.

Up Next: Gender Neutral Pronouns: The Rise of They/Them/Their