Beyond XX & XY—Human Sex And Gender Were Never A Simple Binary
Humans are more complicated than most online experts think.
Without fail, whenever there's an article about a transgender person, the comments have at least one person who boldly declares:
“There’s only two genders! XX and XY!”
But “is” there only two?
The autistic in me must add kudos to these ill-informed commenters for at least picking “There’s” instead of “Theirs”—even though “There are" still eluded them. But don't get me started on “your” and “you're” in that last one…
These online experts’ linguistic skills aside, are they doing any better with science? Do chromosomes have anything to do with gender? Or is biology only related to sex? What's the difference between sex and gender?
Let's take a dive into the science and culture behind both and find out.
Sex ≠ Gender
First, we need to understand that sex and gender—as defined in a scientific, medical, sociological, and anthropological context—aren't the same thing.
On April 11, 2025, Republicans in the Texas House of Representatives struggled to understand this basic concept.
Texas MAGA state Representative Andy Hopper—who was trying to get an anti-LGBTQ+, anti-DEI amendment added to an appropriations bill—revealed his profound ignorance on the topic of sex and gender, an ignorance shared by many of his Republican cohorts in federal, state, and local government, as well as in online forums.
But luckily, Texas Democratic state Representative Lauren Ashley Simmons was there to dumb it down for them.
Unfortunately, cognitive dissonance exists.
In the age of information, ignorance is a choice. But sometimes that choice is driven by an inability to grasp or understand information.
So let's see if we can make this clear.
Sex
Sex refers to the biological characteristics—such as chromosomes and reproductive organs—that differentiate individuals from one another.
Humans can then be grouped and categorized by these biological characteristics, with the two largest categories labeled male and female.
An individual may be born fully female—meaning all of their biological characteristics align fully with those associated with a female—or fully male. But they can also be a combination of or variation of male or female due to a single variant or multiple variants.
In sex-determining chromosomes—X and Y—alone, a wide spectrum of variations occur in humans.
In 2017, I wrote a piece introducing the research of Amanda Hobbs—under expert review by Amy Wisniewski of the University of Oklahoma Health Sciences Center. Hobbs's research identified five factors that determine sex: chromosomes, genes, hormones, reproductive organs, and secondary sex characteristics.
And those five factors are not static.
Chromosomes and genes exist at conception. Hormones are present by birth, but will fluctuate throughout life—especially during puberty.
Reproductive organs (both internal and external) are present at birth, but will develop throughout childhood until adulthood. Those developmental changes can sometimes change the biological sex of the person.
During puberty, most of our secondary sex characteristics—like body hair and breasts—develop.
Hobbs's research was mapped in this graphic by Amanda Montañez for Scientific American. It displays just a fraction of the pathways of sex determination.
But every human is either XX or XY, right?
Hardly. Even the number of chromosomes varies from person to person.
Some of the karyotype (number) and phenotype (appearance) variations related to sex chromosomes are as follows (with the sex most often assigned at birth and syndrome related to the variant where available):
45, X, Turner syndrome—assigned female born with only 1 X chromosome
45,X/46,XY, mosaicism—also known as X0/XY and often intersex
46, XX/XY, chimerism—intersex
47, XXX, trisomy X or triple X syndrome
47, XXY, Klinefelter syndrome
47, XYY, Jacobs syndrome
48, XXXX, tetrasomy X
48, XXXY, assigned male with an extra X chromosome
48, XXYY, assigned male with range of developmental, cognitive, behavioral, & physical abnormalities
48, XYYY, assigned male—exceptionally rare to reach viable birth
49, XXXXY, Fraccaro syndrome
49, XYYYY, assigned male
49, XXXXX, also known as pentasomy X
46, XX gonadal dysgenesis—internal female genitals fail to fully develop
46, XY gonadal dysgenesis, Swyer syndrome—male chromosomes, female genitals and secondary sex characteristics
46, XX, XX male syndrome or de la Chapelle syndrome phenotypic variance—female chromosomes with male genitals and secondary sex characteristics
In some of the cases above, individuals will appear female but have only male chromosomes or vice versa. In some of the cases, individuals will have a difference between reproductive organs and secondary sexual characteristics.
In some cases, individuals will be intersex and have a combination of internal and external reproductive organs associated with males and females. In some cases, chromosomes and reproductive organs indicate one sex, while the body produces an excess of hormones related to another.
SciShow broke down the information to make it a little easier to understand.
As of 2025, there are over 40 intersex variants—or Differences of Sexual Development (DSD)—identified in humans.
And while some variants will be assigned male or female at birth, each variation is actually its own biological sex. Making the number of sexes in humans far greater than two.
But this is just the tip of the biological sex iceberg.
We haven't even touched on the other genetic material, hormones, reproductive organs, or secondary sex characteristics that factor into determining biological sex.
Nor have we addressed the relatively recent research being performed on how brain structure and function relate to biological sex and gender.
As one such brain imaging study found:
“...there is a biological basis for being transgender and thus, destigmatizes transgender individuals.”
And from another comparative study of the brains of cisgender and transgender individuals:
“These findings add support to the notion that the underlying brain anatomy in transgender people is shifted away from their biological sex towards their gender identity.”
Psychiatry and psychology are exploring these findings as explanations for trans people “feeling” or “knowing” they’re not aligned with the biological sex that was assigned to them at birth as early as their beginning of cognizance—between 2-4 years of age.
Those who would deny needed healthcare to trans children argue—without evidence—that children can't know they're trans until adulthood. But this research disputes those unsupported assertions with scientific data.
So while an easily identified binary in biological sex would make things simple for people who desperately need simple…
…it's not the reality of human existence.
As the editors of Scientific American wrote in 2017:
“To varying extents, many of us are biological hybrids on a male-female continuum. Researchers have found XY cells in a 94-year-old woman, and surgeons discovered a womb in a 70-year-old man, a father of four.”
Gender
In her piece for Scientific American, Montañez wrote:
“In an additional layer of complexity, the gender with which a person identifies does not always align with the sex they are assigned at birth, and they may not be wholly male or female.”
Anthropology and psychology define gender as a social construct, wholly distinct from biological sex. Gender emphasizes culturally shaped expectations, behaviors, and roles.
While sex refers to only biological characteristics, gender encompasses psychological, behavioral, social, and cultural aspects of the gender identities within a culture.
Some cultures inseparably tied observed biological sex with gender, leading to the limited understanding of both and ignoring the existence of intersex people. In other words, visible penis = male, no visible penis = female, and unidentifiable genitals = immediate surgical intervention.
Despite knowing that observable genitalia doesn't indicate even biological sex, this simplistic worldview was embraced by major religions and colonizing cultures, whose violent takeover of much of the world has led to modern humans now spouting misinformation like “There’s only two genders!”
But throughout recorded and oral history, for many millennia, thriving cultures recognized and revered more than two genders.
Most of the terms used in popular culture related to gender, sex, and sexuality—transgender, female, bisexual—are strictly colonizer constructs that assume three things: there are only two sexes (male/female), only two genders (man/woman), and therefore only three sexualities (heterosexual/homosexual/bisexual).
But in cultures that tied gender to traits, behaviors, and preferences—instead of looking at a person's genitalia at birth—a spectrum of genders and sexualities developed.
But being transgender or nonbinary is a fad and an invention of Millennials and Gen Z, right?
Hardly. Within Jewish culture and law, as many as eight genders have been recognized since ancient times.
According to “The Seven Genders in the Talmud” by Rachel Scheinerman, within that “authoritative compendium of Jewish legal traditions” were references to:
Zachar, male
Nekevah, female
Androgynos, having both male and female characteristics
Tumtum, lacking sexual characteristics
Aylonit, identified female at birth without developing secondary female sexual characteristics at puberty
Saris hamah, identified male at birth without developing secondary male sexual characteristics at puberty
Saris adam, identified male at birth without developing secondary male sexual characteristics because of castration
Scheinerman pointed out that the seven genders the Rabbis describe in The Talmud are distinguished physically and biologically, not culturally. And in addition to the seven recognized genders, Jewish tradition recognized the first human as being both male and female.
According to PBS's Independent Lens:
“Even after the end of the modern era and as the colonial period wanes, hundreds of distinct Indigenous societies around the globe still retain their own long-established traditions for third, fourth, fifth, or more genders.”
In the United States, even biased Eurocentric anthropological research documented over 100 instances of diverse gender expression in the Indigenous American tribes at the time of early European contact.
At the point of contact, almost all Indigenous societies acknowledged three to five gender roles: female, male, fluid/nonconforming female, fluid/nonconforming male and transgender. While fluid genders might change their gender expression, transgender individuals lived fully as a gender different than their sex or as neither male nor female.
In some tribes, children wore gender-neutral clothing until they reached an age where they decided which path they would walk. After that, the appropriate naming and adulthood ceremonies followed.
My paternal nation—Očhéthi Šakówiŋ—and my maternal nation—Haudenosaunee—both recognized five genders, although modern teachings often try to match colonizer constructs, especially among the tribes of the Haudenosaunee Confederacy.
Contact with colonizers and the adoption of European culture began in the 1600s for the Haudenosaunee. It wasn't until the late 1800s that the Očhéthi Šakówiŋ had sustained contact with settlers and their culture.
By the early 1900s, it was claimed there were no alternative genders among the Six Nations of the Haudenosaunee, despite documentation and oral histories proving otherwise. Tribes were rewarded for compliance—and punished for noncompliance—with Christian homophobia and transphobia.
The Indigenous gender traditions were formally targeted by religious missionaries, the Bureau of Indian Affairs, and Indian boarding schools in the United States, along with all the rest of Indigenous culture.
The LGBTQ+ rights movement that began with a riot at the Stonewall Inn coincided with the Indigenous rights movement. Since the 1970s, Indigenous Americans have been revitalizing their traditional roles and teachings about gender.
At the Third Annual Intertribal Native American, First Nations, Gay and Lesbian American Conference in Winnipeg, Manitoba, Canada in 1990, the organization adopted a pan-Indigenous term that could be used and recognized across NDN Country—Two-Spirit.
The intent was to create a term that differentiated Indigenous concepts of gender and sexuality from those of non-Native communities. The term is for use by only Indigenous peoples who wish to identify as Two-Spirit.
Indigenous activist, basket artist, and model Geo Neptune explained Two-Spirit for them magazine in 2019.
The Indigenous peoples of southern North America and South America also had a history of recognizing genders beyond just the binary, but the invading Spanish and Portuguese labeled these people sodomites and heretics, killing or imprisoning them.
But some endured, like the Muxes of the Zapotec people of Mexico.
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Throughout Pacific Islander cultures, many genders beyond the binary continue to be recognized and given the respect they deserve.
The Kanaka Maoli of Hawai'i have the Mahu…
…the Samoans have the Fa'afafine and Fa’afatama, the Tongans recognize the Fakaleiti, and the Māori historically had the Whakawahine, the Whakatāne, the Tangata ira tāne, and the Tangata ira wahine.
As with Indigenous American peoples, modern Te Reo Māori terms have also been adopted in Aotearoa (New Zealand).
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Asia also has cultures that still embrace a gender spectrum.
The Bugi people of southern Sulawesi, Indonesia, recognize five genders (and three sexes—male, female, intersex). Their genders are oroani, makkunrai, calabai, calalai, and bissu.
As far as third genders, Indonesia also has the Waria, Thailand has the Kathoeys, Myanmar the Acault, the Philippines the Bakla, Nepal the Metis, the Indian state of Tamil Nadu celebrate the Aravani, while throughout South Asia there are the Hijra.
Unfortunately, throughout Africa and Europe such gender expressions were wiped out—mostly by Christianity—by the early 1900s.
A few remain, like the Mashoga of Kenya and Tanzania and the Burrnesha of Albania, but their numbers are dwindling due to the lack of traditional community support.
No Binaries Here
As we're finding with almost all aspects of humanity, sex and gender—like sexuality—is more of a spectrum than two singular homogeneous opposites.
For example, in the United States, the Republican Party has spent the last several years asking people, “What is a woman?” because they don’t seem to know.
According to the GOP, a woman is someone identified as female on their birth certificate.
Unless they don't look like the Republican stereotype of a woman. In which case their genitalia determines if they're a woman.
Unless they really don't match the GOP stereotypes, have skin darker than a pumpkin spice latte, and are successful in sports. Then their birth certificate and genitals don't matter—it's all about their testosterone levels.
Unless they're post-op trans. In which case it's all about the birth certificate.
Again.
But life is way more complicated than that.
Take it from biology teacher Grace Ann Pokela who went viral in 2017 with her takedown of a transphobic, scientifically illiterate meme.
So, the next time you encounter someone spouting, “There’s only two genders! XX and XY!” in the comments—or in Congress—please give them an education.
~~~~~~~~~~
I had already read in high school about intersex individuals. Then I got to Urology in medical school and saw all the pictures of genital differences. The professor showed one pic of a guy with 2 perfectly formed penises (peni?). Jealous, guys? The point is not that some people have developmental differences. It is simply that some people are so very intolerant of the differences.
What a FABULOUS piece! And thank you so much for a trip around the world! I watched with envy a lovely film on the multi-gendered of Oaxaca and their inclusion in society. Only in the Christian world are there shame-based obsessions--blanket denials of the beauty of life itself.