Why sex is binary
In discussions about gender and sex, it’s very likely that sooner or later someone will claim that “biological sex is a spectrum”. Usually, they will point to intersex conditions as a way to argue that male and female aren’t clearly defined categories, or that there are multiple sexes that exist on a continuum. Here’s why this is not true:
An organism’s biological sex is defined by the type of gamete their reproductive anatomy is organized to produce: sperm or eggs. Males develop towards the production of small gametes, called sperm; and females develop towards the production of large gametes, called ova.
Since there are no intermediate gametes between sperm and eggs, and since there is no third kind of gamete, there are only two sexes: male or female. There are only two kind of sex cells, therefore, only two kinds of sexes.
Sex is binary: there are no additional sexes other than male or female, and sex does not fall on a spectrum of infinite possibilities. Your sex corresponds to one of two possible developmental pathways your body went down on to support the production of either sperm or eggs.
Human sexual dimorphism is so consistent, that more than 99.98% of births are unambiguously male or female. We rely on these clear differences between males and females to sexually reproduce, via the fusion of sperm and ova, in order to perpetuate the species.
Sex in humans is genetically determined at conception (when the sperm fertilizes the egg), specifically by the presence or absence of a functioning SRY gene, which typicallly finds itself on the Y chromosome provided by the father.
The present (and active) SRY gene differentiates the baby’s gonads into testes, and supports the production of small gametes (sperm). The fetus develops male.
The absent (or inactive) SRY gene differentiates the baby’s gonads into ovaries, and supports the production of large gametes (eggs). The fetus develops female.
Thanks to the SRY gene, sex determination in humans (and mammals in general) is completely dimorphic. This doesn’t mean, however, that variations don’t occur within this binary system. This is where intersex people come in.
Intersex people have rare conditions called Differences in Sex Development (DSDs for short). Intersex conditions are contingent on innate, physical bodily characteristics, not personal identity or expression. What defines intersex people is that their innate sex characteristics differ from medical norms. Intersex is not an identity or a feeling, but a biological reality.
Intersex people are neither an amorphous mixture of sex characteristics, nor a third sex, nor “hermaphrodites”. People with DSDs are still male or female like every single other human being, they simply have differences in how their bodies developed in anatomy and physiology towards being male or female.
Differences in Sex Development are congenital medical conditions of the reproductive system which affect males and females differently. DSDs are sex-specific. There are males who have intersex conditions and females who have intersex conditions.
To illustrate how DSDs are not exceptions to the binary system of sex, I’ll use three examples:
In very rare circumstances, a fetus may develop with a chormosome variation of XXY. Or even rarer, XXXY. Despite the extra X chromosome, these cases develop as male, thanks to the present and active SRY gene on the Y chromosome that triggers the developmental pathway that supports gonadal differentiation into testes and sperm production. These babies are male.
Sometimes, a fetus with an XX karyotype has a translocation of the SRY gene that results on the SRY being present on the X chromosome, instead of the Y. Thanks to the present and active SRY gene on the X chromosome, testicular tissue is developed and the baby develops towards the production of sperm. These babies are also male.
In some intersex cases, a fetus with an XY karyotype, but with an inactive, although present, SRY gene, develops as female. With this gene being inactive, the gonadal tissue differentiates into ovaries that support the production of eggs. These babies are female.
So, looking at sex determination and the role of the SRY gene in the development of reproductive anatomy, we can clearly see that sex is completely binary. The baby either supports sperm production, or egg production. There is no “in-between” or a third kind of development. In no way is sex a spectrum or an undefinable category.
There are plenty of sex differences between males and females: chromosomes, hormone levels, gonadal tissue, gene expression, genital anatomy, weight, height, muscle mass and bone density, for example. No matter the type of variation in characteristics, biological sex is and forever will be, defined by the type of gamete your body develops to produce. Males support small gamete production and females support large gamete production. Two gametes = two sexes.
Biologists do not support the claim that variation of chromosomes, gonads or hormones is equivalent to “new sexes”. Sex is the developmental pathway your body went on to produce sperm or eggs. Variation in development does not mean one becomes a different sex. Intersex conditions are anatomical variations within males and females, not “new sexes”. XXY males are still males, and XO females are still females.
Intersex people are tired of being used as pawns in anti-scientific arguments made by activists who use the complexity of DSD conditions as a way to muddle and confuse the discussion about biological sex. Sex is still binary, even when you consider intersex conditions.
Don’t let activists confuse you and convince you that your scientific knowledge is “outdated” or “bigoted”. Don’t let social justice activists persuade you by taking advantage of your likely unfamiliarity with intersex conditions and fool you into thinking science supports the existence of more than two sexes. Gender theorists are not scientists, and they lack severe understanding of biology and DSD conditions.
In these arguments, don’t let it slip your mind that sex is, always has been and always will be universally defined by the kind of gamete production your body supports; not by anatomical variations in sex development. When the definition of biological sex is clear to you, it will become much less likely that these con artists manage to confuse you into thinking “sex is a spectrum”, that there are “more than two sexes” or that it’s impossible to clearly define male and female categories.
Using intersex conditions as a “gotcha” in arguments about gender and sex serves trans activists and gender theorists no purpose: the fact that people with DSDs exist does not mean that human beings can switch sex, that sex is a spectrum or that unambiguously male and female people (99.98%+ of births) can become the opposite sex.
Social justice activists do not need to lie about science and erase the reality of the sex binary in order to advocate for acceptance and inclusion of people who express themselves in different ways in society. Sex IS still a binary.