When Biology Isn’t Black and White

The federal government now defines sex as only male or female; there is no federal recognition of gender identity, including on passports; and there are new restrictions on gender-affirming care for federal employees. And more than 600 anti-LGBTQ bills were introduced in state legislatures in the past few years, with at least 27 states enacting major restrictions or outright bans on gender-affirming care for minors.

Some say this protects children, particularly from transition surgeries. However, these surgeries are incredibly rare, and transition surgeries on genitals are not even allowed for minors in the U.S. Another concern is that transgender women competing in sports are given an unfair advantage. But transgender participation in sports is also incredibly rare. The NCAA has roughly 510,000 college athletes, and NCAA President Charlie Baker claims that he knows fewer than 10 of those athletes who are transgender—0.002 percent.

Regardless of how you feel about policy, when you ask the science community whether gender is binary, the answer is “no, not necessarily,” and any argument for gender as binary falls apart quickly when you look at biology.

Source: Katie Rainbow/Pexels

Gender and Biology

Most people like to think of gender as part of our biology. Each cell in our body has 46 chromosomes. A father’s sperm and a mother’s egg each have only half—23 each. At conception, the chromosomes of the sperm and the egg match up into 22 identical pairs, with the 23rd pair being the sex chromosome. In most cases, a person with an XX chromosome will be female, and a person with an XY chromosome will be male.

Sex is what is written in the chromosomes, or what is dictated by our biology—another word for this is genotype. Gender is what actually gets expressed—how we look, how we act, and how we feel. This is called phenotype, which is the interaction between the genes (genotype) and the environment. Sex doesn’t necessarily map perfectly to gender, and the environment plays a role in determining the gender of each person. Most of the time, a person’s sex and gender are the same, but this is not necessarily the case. And sometimes not even sex is determined by sex chromosomes.

The sex of many species is determined entirely by environmental circumstances and not by their chromosomes. For example, several species of coral reef fish like the clownfish (yup, we’re talking about Nemo) don’t have sex chromosomes at all and can actually switch genders if their schools require it. Likewise, alligators, crocodiles, turtles, and some lizards don’t have sex chromosomes; their sex is determined by nest temperature during incubation.

Physical Anatomy and Sex Chromosomes

The boys have a penis and girls have a vagina argument falls apart even more when we think about the relationship between our sex chromosomes and our external genitalia. Going back to human sex chromosomes, all fetuses start undifferentiated. At some point during prenatal development, genes on the Y chromosome cause the fetus to develop testes; these testes begin producing androgen, which is then what causes the development of the rest of the male anatomy.

However, there are cases when the fetus is not receptive to the androgen that is being produced. In these cases, the fetus will have testes, but the rest of the male genitals will not fully develop. When the baby is born, it will appear like a girl with female external genitalia, but no actual uterus or fallopian tubes. In most cases, the baby will be raised as a girl and will not know that she has an XY chromosome until puberty, when she never gets her period. This condition is called androgen insensitivity syndrome. The opposite can also occur, when a fetus with an XX chromosome produces too much androgen and develops ambiguous or partial male genitalia. This condition is called congenital adrenal hyperplasia.

This suggests that even sex characteristics are not all-or-none: the amount of androgen produced by the fetus determines whether a fetus develops male or female sex organs, when it’s produced, and how sensitive the fetus is to that androgen. There is a clear biological reason that there is more variation in both sex and gender than can be explained by a simple dichotomy of male-female, boy-girl, man-woman, or even penis-vagina.

When Not to Trust Your Gut

If scientists support the idea that gender is not necessarily binary, why don’t people believe it? One possibility is that it goes against many people’s basic intuition, or their gut. But unfortunately, intuition isn’t always right, and we shouldn’t always believe what our gut tells us. There are a ton of biases that are common in humans and very hard to shake, like the idea that coincidences are meaningful, that first impressions are most important, or that if you flip a coin five times and heads keeps coming up, tails is due to come up next (the odds are still 50/50). We also prefer explanations that are easy to understand. Explanations that favor gender as binary are simple and appeal to our own intuitions, and for many of us, to our own gender identities. We prefer black and white, and we resist the gray area in between. But in reality, most things aren’t just one thing or another; instead, they fall on a spectrum. Indeed, life is much more colorful than just black or white; it’s beautiful and complicated, just like gender.