Photo: Hanne Gaby Odiele, supermodel. Credit: Inez & Vinoodh
We’ve heard it all so many times before: humans with an XY pair of sex chromosomes are male and those with an XX pair are female. Sexual Characters is a series of brief articles on how things are slightly more complicated.
The making of a man
One of the key steps in becoming a male is that androgens have to hook up with an androgen receptor and enter the cell’s nucleus. Androgens are a class of hormones, featuring testosterone as their best known member.
You can picture the whole process as a covert military operation.
Testosterone and its fellow androgens are on a mission. They must infiltrate the cell’s nucleus and turn on other genes needed for Peak Maleness. To access the nucleus, they must meet the androgen receptor (code name: AR) and perform the Secret Handshake.
Androgen Insensitivity Syndrome and the case of bad intel
Androgen insensitivity syndrome, or AIS, occurs when Strike Force Androgen receives bad intel. They show up at the right place and the right time, but armed with the wrong secret handshake. Mission fails.
The sex spectrum
At this point, things get interesting. An entire spectrum of androgen insensitivity exists, with complete insensitivity alongside a host of partial and mild degrees.
Complete androgen insensitivity is exactly what it sounds like. No androgens enter the nucleus. AR holds the door.
In this case, a person develops external female sex features, such as breasts and vagina, but not the internal features such as a uterus and fallopian tubes. An uncomfortably close inspection will also reveal undescended testes, which carry a small risk of developing cancer. Because what in our bodies doesn’t develop cancer, amiright?
Partial forms of AIS occur when – you guessed it – cells only partially resistant androgen infiltration. Partial insensitivity also goes by the name of Reifenstein Syndrome.
Depending on the amount of resistance, partial insensitivity results in a variety of sexual characteristics: typically female genitalia, typically male genitalia or even a bit of both. This may be where the word “hermaphrodite” comes from, although this is difficult to really prove.
Fun Fact
People with AIS and a number of similar conditions generally fall under the term “intersex“. Intersex individuals are estimated to comprise about 1.7% of the overall population, which, as it turns out, is nearly equal to the worldwide proportion of redheads.
Sex and gender
For what it’s worth, reports detailing AIS describe those with the spectrum of syndromes as identifying as female. The textbook “The Sexed and Gendered Brain” (2010) mentions that “The literature does not contain any reports of affected individuals changing to a male gender identity.”
I won’t delve into that topic much here, partly because the focus of these articles is on the genetics of sex determination and partly because the dissonance between one’s chromosomal sex and the sexual characteristics of their brain will be the topic of a later post.
Parting thoughts
For now, I think it’s enough to contemplate the idea that what we think of as one’s “sex”, as determined by our chromosomes, does not always align with mainstream concepts of “male” and “female”. It’s as though we try to force biological facts to fit a predetermined language of sex, rather than allowing data to guide our language.
A really fun aspect of intersex biology is the havoc it wrecks on evolutionary theory. Evolutionary theory has long offered up the idea that straight men are drawn to characteristics like slim waists, curvy hips and full breasts for the supposed reproductive advantages that they signal.
As Jenna Pincott, author of “Do Gentlemen Really Prefer Blondes?” writes on her blog, regarding the beauty-signals-fertility hypothesis: “AIS is the ultimate deception. As gorgeous as an AIS woman is, there’s no chance of conception. But this ultimately doesn’t matter. It’s the 21st century, and an important lesson must be learned: Femininity is about more than reproduction.”
Well said, Jenna.
I’m always interested in hearing readers’ thoughts. Feel free to write yours in the comments!