Ah, so is anatomy the answer? You have a penis and testes, and you’re a boy. You have a vagina, uterus, and ovaries, and you’re a girl. Ah, if only it were that simple.

Consider the story of a boy who accidentally had his penis cut off due to a freak accident during circumcision. The parents and doctor decided to just go with it and raise this child as a girl, complete with surgeries to make girl-ish anatomy and hormone replacement therapy. It wasn’t until puberty that this biological boy and socially constructed girl found out the truth about him-her-self. He went off the hormones and resumed life as the boy he was genetically destined to be, but he did not have a penis or testes. So who does he get to marry?

Okay, then. Now you probably think that the answer simply lies in our sex chromosomes. Those two letters that determine so much of our identity, X and Y. XX is a girly whirly, and XY is a boy toy. Right?

Not always.

For starters, not everyone gets 2 sex chromosomes. Some people wind up with extra ones, or are missing one. You can have XXY, XYY, XXX, or just X.

So what about them? They don’t match your cute definition of XX-female and XY-male. Some states define a man as someone with a Y chromosome, so someone without a Y is then a woman. That sounds relatively simple.

Now let’s get really complicated. Even if you are XX or XY, sex doesn’t always manifest based on which 2 chromosomes you have. It’s about hormones, a complicated balance of hormones. And this can get tricky.

A person can be XY and appear female or be XX and appear male.

A person with XY chromosomes can appear female with a condition called androgen insensitivity syndrome. The Y chromosome has the gene for testosterone, which gets produced just like in many other guys, but the receptors for testosterone don’t work. So even though testosterone is present, it can’t do what it normally does: make a penis, put hair on the chest, etc. So someone who has this condition grows up appearing female, and often only finds out at puberty when no menstruation happens that she actually doesn’t have a uterus or ovaries.

A person can be XX but appear to be a male because of congenital adrenal hyperplasia, where hormones in overdrive during development masculinize the body even though there is no Y chromosome. In an extreme case, a baby boy could be born and mature normally, having a fully functioning penis (and sex life), only to find later that not only does he have a penis and testes, but internally, a uterus and ovaries as well.

And finally, there is an issue of gene cross over. A female, XX, can still have a gene from the Y chromosome, such as the one to produce testosterone, because during meiosis in sperm formation, the X and Y chromosomes are near each other, and genes can be swapped. Does this make the woman who is XX and has female body parts less of a woman just because she has a gene to produce testosterone? The Olympics thinks so.

Sex is not the binary system we think it is, and we can’t go around making rules about what people can and can’t do based on what anatomy happens to be between their legs. So on top of the fact that gay marriage bans are unconstitutional, unnecessary, and downright petty, they are also terribly unscientific. And Beatrice will have none of that.

Edit: I continue this discussion with a follow-up post: Clarification, Sex Determination, and Cheesecake

(For more about anatomy and identity, watch this great TED talk by Alice Dreger, “Is Anatomy Destiny?” http://www.ted.com/talks/alice_dreger_is_anatomy_destiny.html)