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Deconstructing the Biological Gender Binary

Updated: Apr 21, 2021

This week we’re tackling the transphobia toolbox’s favorite catchphrase: “you can’t argue with science.” But we’re here to lay it all out, deconstruct the idea of a biological gender binary, and translate some of the newer scientific research. Basically, The “you can’t argue with science” people would be trembling if they, you know, understood the science.

Many of us have heard this statement: Gender is a social construct, but sex is biologically determined.

This was considered pretty radical at one point. It concedes that gender is not determined at birth, but rather constructed as someone grows up and interacts with their cultural environments. But, this statement is still not fully correct.

Here’s a statement that shouldn’t be seen as radical, considering the vast amount of scientific and sociological research supporting it: sex is not biologically determined.

It’s an idea that might piss off a lot of angry Facebook mutual friends. It might shock some of our health and sexuality teachers. It shocked me when I learned it because I realized I was fully buying into the first statement, which I had been taught repeatedly.

So let’s start at the biological basics: our genes. We are taught that sex is determined by our “sex chromosomes” that is, the X and the Y chromosome. The myth goes that if you have XX chromosomes then you will be female, and if you have XY chromosomes then you will be male. Unfortunately, this isn’t true (a, d).

First of all, the X and Y chromosomes control over 1,400 genes, and only a few of them have anything to do with sex. Basically, “sex chromosomes” is a misnomer.

Second, people can be born with any combination of X and Y chromosomes: People can be born with a single X chromosome, or possibly and XXY. and they may not correlate to physical sex characteristics at all.

Third, it is not the presence of XY chromosomes that leads to “male sex characteristics” but rather the presence of the SRY gene, which leads to the development of testes in utero (a, d). This means people with XX chromosomes and the SRY gene can develop as male.

Finally, none of these genes control the development of secondary sex characteristics: that is, genitalia, behavior, etc. Those arise later in life and are affected by hormone production.

Next up is hormones. We are taught that if you are male, your body produces testosterone, and if you are female, your body produces estrogen. Guess what? Not true! Everyone’s body produces both estrogen and testosterone (d).

Before puberty, most people have no significant difference in estrogen and testosterone levels in their bodies.

In adulthood, both “males” and “females” have about equal amounts of estrogen and progesterone. There is a significant difference in testosterone levels in “men,” but studies suggest that genetics (that is, your chromosomes) only influence about 56% of testosterone production. That means that something other than biology is affecting hormone levels in men.

Finally, there is evidence suggesting that social factors affect hormone levels. Activities like competitive sports, hanging out with friends, and even raising a child affect both estrogen and testosterone levels (d).

So let’s tackle a pretty widespread myth about non-binary biological sex. The myth goes that intersex, meaning having physical or biological sex characteristics that fall outside of the male/female binary, is a rare medical “condition.” (Guess what? Note true.)

First, being intersex isn’t a medical condition: it’s just a variation of the human body.

Second, intersex traits are so common! Research suggests as many as 1 in 100 people are born with some type of intersex trait (a, c).

The scientific community is slowly but thoroughly debunking the myth that biological sex is binary. So why hasn’t society caught up yet?

One possible explanation is that the idea of a biological binary is fundamental to many aspects of our life, such as policies, science, and behavior. In fact, the social concept of gender may have impacted science and policy to such an extent that we created and naturalized the idea of a biological binary.

The social construct of gender created the idea of biological sex.

Let’s walk through this a bit: We are taught that scientific knowledge is unbiased, objective, and not situated in any singular culture. Guess what? Not true. Cultural ideas (such as the gender binary) affect every step of the scientific process. They affect what questions are asked, how experiments are designed, how data is analyzed, and how results are interpreted.

This suggests that we quite literally created the idea of biological sex to support and reinforce our social hierarchy of gender. This also makes sense when we look at what identities were doing most of the research into human biology in the 1800-1900’s when the idea of biological sex became substantiated -> that is, white men.

All in all, the idea of a biological binary is too simplistic to encompass the vastness of human sex and gender. Sun (2019) captures this idea well: “Transgender humans represent the complexity and diversity that are fundamental features of life, evolution and nature itself.” (d)


A. Ainsworth, C. (2018, October 22). Sex Redefined: The Idea of 2 Sexes Is Overly Simplistic. Retrieved from

B. M. E., Says (. (2020, December 28). Sociology of Gender. Retrieved from

C. Mikkola, M. (2017, October 25). Feminist Perspectives on Sex and Gender. Retrieved from

D. Sun, S. D. (2019, June 13). Stop Using Phony Science to Justify Transphobia. Retrieved from

E. US proposal for defining gender has no basis in science. (2018, October 30). Retrieved from

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