That quote is from a good article in Nature on how sex is non-binary — my only quibble would be with that “now”. You’d have to define “now” as a window of time that encompasses the entirety of my training and work in developmental biology, and I’m getting to be kind of an old guy. Differences in sex development (DSDs) are common knowledge, and rather routine — and coincidentally, I’m giving an exam on sex chromosome anomalies today.
The article works through a lot of basic concepts: chimeric sex, genetic vs. cellular vs. organismal sex, and the development of sexual characters. I was so happy that they did not trigger one of my pet peeves, the claim that we all start out as female — we don’t, we start out sexually indifferent.
That the two sexes are physically different is obvious, but at the start of life, it is not. Five weeks into development, a human embryo has the potential to form both male and female anatomy. Next to the developing kidneys, two bulges known as the gonadal ridges emerge alongside two pairs of ducts, one of which can form the uterus and Fallopian tubes, and the other the male internal genital plumbing: the epididymes, vas deferentia and seminal vesicles. At six weeks, the gonad switches on the developmental pathway to become an ovary or a testis. If a testis develops, it secretes testosterone, which supports the development of the male ducts. It also makes other hormones that force the presumptive uterus and Fallopian tubes to shrink away. If the gonad becomes an ovary, it makes oestrogen, and the lack of testosterone causes the male plumbing to wither. The sex hormones also dictate the development of the external genitalia, and they come into play once more at puberty, triggering the development of secondary sexual characteristics such as breasts or facial hair.
That’s exactly right.
The major point of the article is something a lot of people deny: that sex is complicated, there’s more than two states of human existence, and most importantly, that biology verifies the existence of a continuum of sexual differentiation. Drag this article out next time someone tries to argue that biology supports their simplistic version of a discrete sexual dichotomy.
Yet if biologists continue to show that sex is a spectrum, then society and state will have to grapple with the consequences, and work out where and how to draw the line. Many transgender and intersex activists dream of a world where a person’s sex or gender is irrelevant. Although some governments are moving in this direction, Greenberg is pessimistic about the prospects of realizing this dream — in the United States, at least. “I think to get rid of gender markers altogether or to allow a third, indeterminate marker, is going to be difficult.”
So if the law requires that a person is male or female, should that sex be assigned by anatomy, hormones, cells or chromosomes, and what should be done if they clash? “My feeling is that since there is not one biological parameter that takes over every other parameter, at the end of the day, gender identity seems to be the most reasonable parameter,” says Vilain. In other words, if you want to know whether someone is male or female, it may be best just to ask.
I’ll also add that it’s not just biology that supports the idea that sex is a spectrum. It’s also the case of psychology and sociology — any science that has to address sex differences.