Is there more to life than XX and XY? Getting past the sexual binary

Transgender, nonbinary, intersex, and other queer individuals have more visibility today than ever. While many people have learned a lot about these communities and have accepted their identities, many people remain confused, or are hostile toward the idea of a person feeling that they were assigned the wrong sex at birth, or feeling they don’t belong to either sex. How can a person be assigned the wrong sex? How can there be anything other than male and female sexes?

Most of us learned in school that there are two biological sexes, and they are controlled by two chromosomes X and Y. If a person has XX they will be female, and XY will be male. You may have even learned that it is the presence of the Y chromosome that makes someone male, so someone with an extra sex chromosome XXY would still be male. Unfortunately, like so many other things you learned in school, it turns out that your teachers did not tell you the whole story. Biological sex is actually a really complex subject, there are many mechanisms that play into how a person’s sex is determined and that means that the simplified version taught in schools is leaving out some important stuff.

When an embryo is growing you cannot distinguish its sex until after the fifth week of developement. Prior to that time the embryo could develop into either a male or female. It is in the sixth week that either testosterone begins to be produced, which leads to a male embryo, or estrogen, leading to a female. So what determines which hormone will be made? It’s a gene usually found on the Y chromosome called SRY - if it is activated at a specific time during development then the embryo will develop as a male.

If the SRY gene is not activated at the usual time, the person may end up with female gonads or the individual may be intersex. “Intersex people are born with sex characteristics (including genitals, gonads and chromosome patterns) that do not fit typical binary notions of male or female bodies.” About 1.7% of the population is intersex, which is about the same percentage of people in the world who have red hair. Many of these individuals are assigned one sex or the other at birth, and are raised as such, and may experience a mismatch between the sex they were assigned and their gender identity or expression.

There are other ways that sex determination can vary. It is possible for the segment of the Y chromosome that contains the SRY gene to break off when sperm are being created and it can attach itself to an X chromosome. This can result in an embryo developing as a male even though it has XX chromosomes. If the SRY gene segment breaks off the Y chromosome in a sperm, and that sperm fertilizes an egg you can also have a female who has the chromosomes XY.

Aside from chromosomes and genes determining sex, hormones can also determine sex in different ways. For example, some people are born with cells that are unable to respond to androgens, which is a condition called androgen insensitivity syndrome. Androgens are steroid hormones like testosterone that contribute to male sexual development. If a person has the chromosomes XY and is insensitive to androgens, they will develop externally as female.

On top of the mechanisms mentioned here, there are also genes, like DMRT1, that are involved in maintaining sex characteristics that can come into play. There is also chimaerism, where a person can have both male cells and female cells in one body. These are just some of the known complications of the biological sex binary. As with all science, there is more to be discovered.

There is so much nuance to biological sex that scientists have begun referring to it as a spectrum, with typical biological male on one end, typical biological female on the other, and lots of situations in between. If people continue to think that sex is binary, rather than a spectrum, we erase the experiences of all the individuals who fall in the middle.

One important way in which people who do not identify as male or female are seeking recognition is in their identification documents. Eighteen states now allow people to select gender X on their driver’s license or state ID, including Maryland, Pennsylvania and New Jersey. Delaware has not made gender X an option, but the DMV has said they are considering it. If you would like to see a non-binary gender option added to Delaware licenses and state IDs you can email DELDOT at dotpublic@delaware.gov.