For thousands of years, people thought the earth was flat. Then, around the 3rd century BC, Hellenistic astronomy determined the Earth to be “roughly spherical” and calculated the Earth’s circumference. Of course, humans then spent thousands of years thinking the stars orbited the earth. But in 1543, Nicolaus Copernicus introduced evidence that the Earth, along with the other planets, rotated around the sun.
Today, we have a new situation of in which some individuals are similarly clinging to a simple lie, when science has confirmed a new and more nuanced truth.
Although there are people who still think human sex is a binary (female/male), science has widely disproven it in recent years.
Intriguingly, a search of the research database PubMed.gov confirms that an astounding 53,000 scientific articles have been published to date about intersex conditions.
Today, numerous scientific fields, including biology, endocrinology, physiology, genetics, neuroscience, and reproductive science, have confirmed that both biological sex and gender exist as a spectrum.
Sex is a Constellation of Traits, None of Which Are 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 widely confirmed across multiple fields of study is that biological sex presents as a constellation of traits, none of which are binary—not even gametes or the presence of a Y chromosome.
What is true is that there are “clusters” of characteristics that tend to be associated with people that we call “female” or “male”—and what is also true is that there are exceptions, called “intersex” people.
To biologists, this is unsurprisingly, because diversity is a nearly ubiquitous characteristic of life.
With this understanding, let’s consider the most common markers that people try to use to create a sex binary—and explore why none of them are able to create separate and non-overlapping groups.
None of the Biological Sex Markers Are Binary
Since genitals are the current method of sexing babies in the United States and around the world, let’s start with that.
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.
Similarly, most men do have testes and produce sperm, while women do have ovaries and produce eggs. However, intersex people exist who have both male and female gonadal tissue, called an ovotestis. This tissue can present as a spectrum, with both testicular cells and ovarian cells present in the same organ, known as a streak gonad.
Additionally, there are females, males, and intersex people who do not produce gametes (egg/sperm/neither), which means gametes are not binary. In particular, people with duel or ambiguous gonadal tissue coupled with no gamete production eliminate the ability to use gametes to create a sex binary.
Similarly, males tend to have XY chromosomes and females tend to have XX chromosomes. However, sex chromosomes (another biological marker of sex) come in a wide variety as well, with at least 16 different naturally occurring variations (see below). This means that chromosomal presentation is not binary either.
On average, males do have higher testosterone levels than females, but there are females who have higher testosterone levels than some males (called hyperandrogenism). In males, low testosterone levels is called hypogonadism. For sex hormones to be binary, then males would have to have higher androgen levels than all females, which of course, they do not.
On a day-to-day basis, we tend to identify each other’s sex using what is called “secondary sex characteristics.” The most common secondary sex characteristics we notice are body and facial hair, as well as chest contour and development.
On average, males do have more facial and body hair than females, but there are also females with facial hair and males who can’t grow a full beard. Similarly, there are men who have substantial breast development (called gynecomastia) and women who have a nearly flat chest. Thus, the secondary sex characteristics aren’t binary either.
As explained by these examples, sex is not binary, because people cannot be grouped into two separate, non-overlapping groups.
Indeed, there is not a single marker of biological sex—not gametes, not chromosomes, and not genitals—that can be broken down into a binary.
Biological Sex Diversity Proliferates
The reason that some still people still believe in a sex binary is that they are noticing are averages, while carefully avoiding exceptions.
However, in science, is it critical and part of the scientific process to document both high and the low frequency events.
For example, it is common to have XX chromosomes, a vagina, and produce eggs as a gamete. This is an example of “female sex clustering”. Meaning, these biological markers of sex have a very high probability of appearing together in the same individual who would be labeled as “female”.
Similarly, “male sex clustering” is also very common. That would look like a person who has XY chromosomes, a penis, and produces sperm.
What is now being recognized is that there are clusters of traits that have a tendency to go together for “intersex” people as well.
Although there are a diverse range of intersex conditions, common one include mixed gonadal disgenesis, hypospadias, partial androgen insensitivity syndrome, 5-alpha reductase deficiency, gonadal plasia, and congenital adrenal hyperplasia.
For each of these conditions, there is a mix of biological sex traits that tend to appear together in most individuals.
For example, it is common for an intersex person with androgen insensitivity syndrome (AIS) to have a vagina and breasts, as well as undeveloped testes in their abdomen (“undescended”) that may or may not produce gametes.
If you tried to “sex” this person using a binary approach, it would look like this:
- External Genitals (Vagina) = “Female”
- Secondary Sex Markers (breasts) = “Female”
- Gonads (Testes) = “Male” but undescended and retained in the abdomen
- Gametes = “Undefined” or “Male” (depending on the person)
Instead of trying to force an person instead a binary, why not recognize that this individual has a natural blend of traits that are common for individuals with that intersex condition?
Indeed, many of the current “female” mid-distance runners at the Olympic level have this specific mosaic of biological sex traits.
Why the Olympic Committee Switched to a “Sex Classification”
To provide an interesting example, all three of the all three medalists at the 2016 Olympics in the women’s 800 meter event (Castor Semenya, Francine Niyonsaba, and Margaret Wambui) were barred from competition after the event, because of their naturally high testosterone levels.
As the WSJ wrote, “Since the Rio Olympics, track and field’s governing body tightened its hormone restrictions. As a result, all three medalists from 2016 are ineligible to compete in the event.”
Indeed, it is fascinating that the Olympic Committee—the body with the greatest incentive and the most resources—has not established a sex binary.
Believe me, it has tried. The Olympic Committee started with genital analysis in the 1940s, but quickly ran into difficulties, because as described above, it is common for individuals with androgen insensitivity syndrome (AIS) to have female genitals but undescended testes that can produce moderate to high levels of androgens.
In addition to Castor Semenya, Francine Niyonsaba, and Margaret Wambui, this was the case in for Stanislawa Walasiewicz, who was an intersex athlete who competed in the 100m dash at the 1932 Olympic Games.
After realizing they couldn’t use genitals to create a sex binary, the Olympic governing body switched to chromosome testing, which was introduced by the International Olympic Committee in 1968. At that time, the committee tested for a Y-chromosome in an attempt to classify competitors. Unsurprisingly, this method of testing was ended in 1999 because it was shown to be “inconclusive” at sex determination.
Specifically, the committee ran into problems with using a Y chromosome for sex classification because:
- People can have XX chromosomes and a penis (called an “XX male”).
- People can have XX chromosomes and a vagina, but possess male internal organs, commonly an undescended testes. (This was the debate around 800m star, Caster Semenya, for example.)
- People can can have XX chromosomes and a vagina but “overproduce” testosterone, called hyperandrogenism. (This is common among mid-distance runners at the Olympic level.)
Given this, how should these individuals be “sexed”? As these examples illuminate, the presence of one (or more) “Y” chromosomes does not create a sex binary.
If you want to understand this even better, you can read about it in great detail here.
Why the Olympic Committee Switched to a “Sex Classification”
Because no marker of biological sex is binary, the Olympic Committee has stopped trying to assign “Sex” and instead has come up with a concept called a “Classification”. Specifically, it now assigns a “Female Classification” and a “Male Classification” to athletes.
Today, the Olympic Committee allows athletes to exhibit a “constellation of sex traits” while competing in the “Female Classification”, including:
- Any external genitals (vagina, penis, ambiguous, or both)
- Any set of internal genitals (ovaries, undescended testes, duel or ambiguous)
- Any chromosomes (XX, XY, XXY, XXX, etc.)
- Any secondary sex characteristics (high or low voice, facial hair, etc.)
Instead, it has chosen to use a single and continuously fluctuating sex trait: androgen levels. This is a fascinating decision, because as described above, there are women who naturally have higher testosterone levels than most men.
Testosterone presents as a spectrum and does not create a sex binary. In humans, testosterone naturally ranges from about 15 to 1,000 nanograms per deciliter (ng/dL), with overlap between female, intersex, and male individuals.
Although males do have higher testosterone levels than females on average, there are certainly some females who have higher testosterone levels than some males. For sex hormones to be binary, all males would have to have higher androgen levels than all females, which of course, they do not.
With a “Classification” system instead of a “Sex” system, the Olympic governing body has allowed itself to take a biological marker which presents along a spectrum—and create an arbitrary cut-off in order to establish two separate and distinct categories for competition.
A “classification” is the only way to take a spectrum and turn it into two non-overlapping categories for competition.
Although there is still great debate about what the testosterone cut-off should be for “Female Classification, the idea behind this approach is to acknowledge human sex is a spectrum, while creating two categories for competition.
Low Frequency Events Get Documented in the Scientific Process
In the case of human biological sex, it is critical to note that an estimated 1.7% of births are intersex.
Moreoever, this number is likely to be substantially underestimated because it primarily documents the occurrence of external genitals presenting as a different sex than an individual’s chromosomes.
Today, there are at least 10 known markers of biological sex, all of which can mix-and-match with each other. As described above, it is very common for “female” traits and “male” traits to cluster together.
However, science must document all data points in a set, even the ones that appear at lower frequencies, as occurs with the prevalence of intersex traits.
Exploring Biological Sex as a Spectrum
For all too long, the government, the medical system, and even our parents have tried to enforce a sex binary. As discussed above, this approach is not biologically or medically accurate.
Today, an increasing number of people are exploring their own constellation of biological sex traits and discovering an intriguing range of results. This exploration can involve:
- Sex chromosome testing
- MRI analysis of internal gonads (ovaries, undescended testes, duel or undefined)
- Bloodwork to identify sex hormone levels
- Genetic testing to determine if a person has an active or mutated SRY gene
- Testing for gamete production
- Analysis of skeletal structure
- Investigation of secondary sex characteristics
- Brains scans to determine grey-to-white matter ratios, as well as activation patterns
- And so much more
As this individual instigation gains momentum and these services come down in price, it is likely that more and more people will get identified as being along a female-intersex-male continuum.
Of course, the majority of people will still feat neatly into “female” and “male” sex categories—meaning, all of their biological sex traits will align as a single sex—but there will also be exceptions.
In a high school of 2000 kids like I attended growing up, an average of 34 youth would be likely to intersex. (2000 youth x 1.7% intersex = 34 individuals). At least that many more would be likely to be transgender too (another 34).
Of course, some of those children could be both intersex and transgender, because those identities refer to sex and gender, respectively. Gender is a personal identity and is socially constructed, while sex, which refers to one’s biological characteristics.
Biological Sex Diversity Will Persist
As mentioned above, U.S. government funded database PubMed.gov reveals that an incredible 53,000 scientific articles have been published to date about intersex conditions.
One-third (17,399 / 32.6%) of those have been published in the past 10 years, confirming that rates of research into intersex conditions are exploding.
As these numbers confirm, biological sex diversity is real, it is prevalent, and it is widely documented.
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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 they were 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 an expert on stem cells, Cade has been interviewed by the Wall Street Journal, Los Angeles Business Journal, Xconomy, and Vogue Magazine, as well as cited in Tony Robbin’s his best selling book, Life Force.