More than once, people have suggested that I cover biological sex in the Science of Sex feature. I have shied away from it because it seemed controversial. However, the more I know, the more I understand that some science isn’t at all controversial. In fact, understanding it can lend to our understanding of sex and gender and why it’s never been black-and-white.

One of the transphobic arguments often made is that two pairs of chromosomes determine if a person has the biological sex of a male or female: XY and XX, respectively.  Each cell contains each of these chromosomes, which each come from one of our parents. Most of us learned this in a science class, and many of us haven’t learned anything more since then.

However, there are actually more than two chromosomal possibilities, including

• XX
• XY
• X
• XXY and XXXY
• XXX, XXXX, XXXXX
• XYY
• XX with translocation (XX male)
• XY with deletion (Swyer syndrome)

With this in mind, sex seems much more of a spectrum than a binary.

Some of these variations have their own names. For example, a single X chromosome is Turner Syndrome, which is accompanied by several abnormal growth patterns. On the other hand, having three or more X chromosomes is labeled Triple-X syndrome or trisomy X, and these people have the nickname “super-female”. A “super-male,” on the other hand,  has an extra Y chromosome and will tend to be quite tall with extra testosterone. A person with Triple-X syndrome may be slightly taller and thinner than the typical XX woman, but may not be noticeably different. An assumed male who inherits an extra X chromosome or two has Klinefelter syndrome and may have stereotypically female traits and be unable to reproduce.

The latter two examples represent instances in which person’s sexual organs do not align with their karyotype. For example, a person may have the “male” sex chromosomes with female reproductive organs, which are typically not functional. This is known as Swyer syndrome/XY gonadal dysgenesis. These people are usually raised and treated as women while the counterpart is an XX “male,” who is viewed by the world as a boy. Those with this syndrome may not have a detectable SRY gene, which is responsible for an embryo turning male.

Discrepancies between chromosomes and genitals is sometimes known as being “intersex.” This term can also refer more broadly to anyone whose sexual anatomy doesn’t align with the binary (male or female) or whose internal and external genitals do not match. In the past, this has been confused hermaphroditism; however, many prefer the term “intersex” as a less offensive alternative. The World Health Organization explains how true hermaphroditism occurs when a person has mature testicle and ovary tissues. The term “intersex” is not accepted by everyone, however, because of the implication that something is wrong with someone who has these chromosomal differences.

Surgical interventions can be used on young children to “correct” these things, and those children may never realize that they do not conform to the binary. However, these surgeries. which are intended to allow a person to live normally and prevent or reduce psychosocial outcomes may not work as intended. Many surgeries were performed to feminize an intersex person, but this can affect adult sexual function. Furthermore, people may continue to develop with more typical male patterns.

And sometimes that discrepancy can exist but a person with XX chromosomes can have functional sperm while a person with XY chromosomes may have functional ovaries. So it’s possible for a person not to realize that there is a discrepancy if their sex organs are functional — to be “invisibly” intersex. While current estimates vary — some put the intersex population at about 1 out of 100 people in the US and others at 1 in 2000 — the real number could be higher because of these people.

The final nail in the coffin about chromosomes defining sex and, by association, gender, as binary might be the fact that it doesn’t take into consideration at all the role of hormones, which may not respond as expected, either. A person with XY chromosomes who has androgen sensitivity syndrome will develop female-typical sex organs because their body doesn’t respond to androgens, for instance.

There are cases of female-typical bodies and chromosomes responding in male-typical ways in limited situations. And people with similar chromosomes or bodies can still respond uniquely to different hormones and systems. Understanding these very specific differences has revealed the myriad ways that the sex binary fails us and the important things we must note to provide adequate medical care.

This messiness indicates why viewing male and female as the only two sex options is limiting and confusing. While simplifying these ideas has been helpful in some instances, it has been harmful in others. It’s not scientifically sound and can lead to social stigma for those people who do not fit within the binary.

This is all pretty basic stuff that has been researched, even if the general public hasn’t learned about it. When contrasted with gender identities, which have been conflated with sex and similarly viewed as binary, we see that there should be a lot more room for expression. It may very well be that there is overlap with people whose biology falls more toward the middle and those who identify as nonbinary or transgender (at least one study finds that the brains of trans kids match their gender identity). But these things aren’t mutually inclusive.

Further Reading

• Sex Chromosome Abnormalities
• Swyer syndrome
• Turner syndrome
• Klinefelter syndrome
• Gender and Genetics
• Androgen insensitivity syndrome
• ScienceVet’s twitter thread
• What’s intersex?
• How common is intersex?
• Transgender brains are more like their desired gender from an early age
• XX Male Syndrome

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Categories: Science of Sex