There seems to be repeated confusion, willful or otherwise, about the nature of sex (here I’m talking about biological sex, not gender, which is one’s perceived identity). I’m fine with anyone calling themselves whatever they want, except that it may not be so easy for sports divided into “men’s” and “women’s” events (but I’m glad I don’t have to adjudicate that issue).

But with sex, well, biological sex in our species, and most other sexually-reproducing animals, does fall into two classes, male and female. The Oxford English dictionary defines “male” in biological terms as

That which belongs to the sex which can produce offspring only by fertilization of the opposite sex (contrasted with female); characteristic of or relating to this sex.

or

Of the reproductive organs of an animal or plant: characteristic of the males of a species; producing gametes (such as spermatozoa) that can fertilize female gametes (ova). Also: designating such gametes, which are usually smaller and more motile than the corresponding female gametes.

“Female” is defined similarly with respect to fertilization and gamete size:

A person of the sex that can bear offspring; a woman or a girl.

or

Of the reproductive organs of an animal or plant: characteristic of the females of a species; producing gametes (ova) that can develop into a new individual, usually (but not always) after fertilization by a male gamete (as a spermatozoon). Also: designating such gametes, which are usually larger and less motile than the corresponding male gametes.

Now of course you can find some exceptions among some species. In seahorses, for instance, males can “bear offspring” because they raise the fertilized eggs in their pouch, but nevertheless they still produce sperm. But in humans it’s rarely doubtful whether an individual is a male or a female. Males have a chromosomal constitution XY, produce small gametes that fertilize the large eggs of females, and have male genitalia (penises). Females produce fewer but larger gametes, are XX in chromosomal constitution, and have female genitalia (vaginas).

Of course there are some exceptions to all of these. We have humans with chromosomal constitutions XXY and XO; we have developmental intersexes that have characteristics of both male and female, we have females and males with all the traits above but which are sterile and so can’t produce eggs or sperm, and so on.

The point is that these exceptions are rare. I don’t know the figures for males and females that fit neatly into the classes I’ve given above, but I’d guess it would be about 98% of humanity; the Intersex Society, lumping chromosomal and developmental exceptions together, gets a frequency of non-binaries of about 1-2% (Fausto-Sterling gave roughly the same figure in 2001). So yes, sex isn’t truly binary in that every individual can’t be unambiguously slotted into either male or female—but the vast majority can.

What this means is that if you do a plot of sex versus frequency in which you combine all traits that define “males” (above) at one end and those defining females at the other, and then plot the frequency on the Y-axis, you’ll get a plot with two distinct and widely-separated peaks, with a valley containing some intermediates (intersexes and the like) between them. This is what I mean by the bimodality of sex. And there’s a reason for it: having two sexes is the result of evolution in our ancestors. (I won’t go into why, nor do we fully understand the selective pressures). Let me add that I’m talking about biological sex here and not gay behavior, so that I am counting male homosexuals as males because they have the physiological and chromosomal features of males, even if they are sexually attracted to males, and the converse for lesbians.

Yet Anne Fausto-Sterling, an emeritus professor of biology and gender studies at Brown university, conflates the issues of sex and gender in her op-ed piece in the New York Times (below), implying that because sex is not “binary” (i.e., there are some exceptions), that it is not bimodal. Now she doesn’t use the word “bimodal”, but the implication here is that somehow science has decided that there are more than two biological sexes, and implying that there is just two is somehow damaging to those individuals who are intermediate. (Again, I’m not referring to transsexuals here, many of whom are born having one distinct biological sex but decide, as a matter of gender preference, that they’re members of the other, intermediate, or are members of some unusual gender.) Her article, as you’ll see from contrasting the title with the last paragraph, conflates sex and gender, and I think that’s deliberate. But it’s confusing and mistaken.

Click on the screenshot to read the article:

You can see by the subtitle that she is discussing biological “complexity”. And yes, there’s complexity if you look at the 1-2% of people who are not binary but intermediate between “male” and “female.” But throughout the article, Fausto-Sterling concentrates on these exceptions, managing to convey the message that they are so common that we really shouldn’t think that the human population falls nearly into two sexes—that biological sex isn’t even close to being binary. In fact, in the entire article, Fausto-Sterling doesn’t mention the frequency of these exceptions, which we need to consider if we want to know what we mean when we claim that “there aren’t two biological sexes in humans”.

Note that Fausto-Sterling’s piece is a biological response to a political decision: Trump’s Department of Health and Human Service’s desire to legally define sex as “a person’s status as male or female based on immutable biological traits identifiable by or before birth.” One can object to that definition on three grounds. The first is that not every single person will fall into these categories no matter which “immutable biological trait” you use.

The second is that it’s completely worthless because sex, like gender, is a social construct. Now the latter seems silly to those who know anything about biology, but the idea that sex itself is a social construct is increasingly common (see my critique of one such claim here).

The third is that the definition was made to disenfranchise, punish, or demonize transsexuals (many of whom were born fully male or female), and has no useful social value. I don’t see what social value it does have, so on first principles I’m not behind it.

But back to the biology. Fausto-Sterling does state the truth at the outset:

It has long been known that there is no single biological measure that unassailably places each and every human into one of two categories — male or female.

But then she goes into the many layers of complexity, to wit:

Chromosomal: some individuals are XXY, XXY, XO, and so on.

Developmental issues that produce non-“binary morphological individuals based on hormones or other non-genetic factors.

The perception of “genital sex” by adults affects how adults socialize the children. That, however, is a social issue that is the outcome of “nonbinary” biological factors, and doesn’t belong on Fausto-Sterling’s list.

“Brain sex”: Brain cells, stimulated themselves by fetal hormones, can also produce intermediate sexual morphology in the body. But this is also a developmental issue, falling under the second point above.

And yes, these exceptions make unambiguous classification of some individuals based on biological traits a dicey affair. But not often: it works, I’d guess, at least 98% of the time. So I think Fausto-Sterling is exaggerating a bit when she says this:

By birth, then, a baby has five layers of sex. But as with chromosomal sex, each subsequent layer does not always become strictly binary. Furthermore, the layers can conflict with one another, with one being binary and another not: An XX baby can be born with a penis, an XY person may have a vagina, and so on. These kinds of inconsistencies throw a monkey wrench into any plan to assign sex as male or female, categorically and in perpetuity, just by looking at a newborn’s private parts.

The question is how much damage that monkey wrench really does. Not much, I’d say. And for most purposes, including sports, the exceptions are few. Where we run into problems, by and large, is where “non-binary” people want to compete in sports as females, though having the upper-body strength of males. Many people, including women athletes, see that as unfair. I won’t enter that controversy, as I don’t know how to resolve it. (I’ve suggested a third category in addition to “male” and “female”, but I’m not wedded to that solution.)

And the bit below is a tad exaggerated, because the “wide” variation isn’t all that wide. The disputes arise because the problems in sports come precisely from those few individuals whose sex is ambiguous:

Dr. Money called these layers pubertal hormonal sex and pubertal morphological sex. But these, too, may vary widely beyond a two-category classification. This fact is the source of continuing disputes about how to decide who can legitimately compete in all-female international sports events.

Fausto-Sterling’s purpose is ideological, and adding information about how sex is determined doesn’t change the strong bimodality of sex, so this bit is obfuscation:

There has been a lot of new scientific research on this topic since the 1950s. But those looking to biology for an easy-to-administer definition of sex and gender can derive little comfort from the most important of these findings. For example, we now know that rather than developing under the direction of a single gene, the fetal embryonic testes or ovaries develop under the direction of opposing gene networks, one of which represses male development while stimulating female differentiation and the other of which does the opposite. What matters, then, is not the presence or absence of a particular gene but the balance of power among gene networks acting together or in a particular sequence. This undermines the possibility of using a simple genetic test to determine “true” sex.

In fact, what matters is how often the outcome of these opposing networks yields a binary result: male or female. Whether the network is the presence or absence of a particular gene or of several genes is completely irrelevant. And the answer to how often the process yields a binary result is this: almost all of the time. Whatever “undermining” there is, it’s not a serious undermining.

Let me reiterate what I’m trying to say here, because I think Fausto-Sterling’s essay is motivated by good will and is not blatantly wrong, just misleading.

1.) Human sex is not absolutely binary because there are exceptions no matter how you define “male” and “female”.

2.) Those exceptions, however, are rare, so considering most individuals, sex is binary. And for the population of humans, sex is strongly bimodal: most people, no matter whether you define sex using chromosomes or morphology or gamete structure, fit into the classes of either “male” or “female.”

3.) I agree with Fausto-Sterling that it’s unwise to try to impose an absolute binary system on all human beings. That’s hurtful to intermediate or non-binary individuals, who, as I’ve always maintained, should be treated with respect, dignity, and as much accommodation as is compatible with social well-being. But we simply cannot maintain that sex is a social construct like gender. And Fausto-Sterling’s last paragraph, despite the title of her piece, conflates sex and gender (my emphasis below):

The policy change proposed by the Department of Health and Human Services marches backward in time. It flies in the face of scientific consensus about sex and gender, and it imperils the freedom of people to live their lives in a way that fits their sex and gender as these develop throughout each individual life cycle.

I haven’t pondered the HHS definition, but I suspect it is aimed at transsexuals, and if it is then it’s likely nefarious. But we shouldn’t pretend that sex is a continuum or not bimodal simply to justify social conclusions. Fausto-Sterling walks a fine line between sex and gender, and crosses it at the end.

We can still say that someone who has surgery to convert from a male to a female gender was born a biological male, and what does it matter, except to either officials of the Olympics (who do face a big issue) or Republicans who are bigoted? We should take our stand on gender from a liberal morality, but we should not pretend that sex itself is a continuum, for that depends on a distortion of biological data. And I’m not saying that Fausto-Sterling pretends that sex is a continuum, but neither does she emphasize the strong nature of its bimodality: a bimodality that is of no consequence when it comes to gender issues. Gender may be a social construct, but sex is not.

4.) To reiterate: we shouldn’t get social “oughts” from biological “is”s, nor inappropriately wrangle science into supporting claims about morality and ethics. There are sufficient reasons to oppose the Trump regime’s proposal without obfuscating or spinning the facts to try to prop up your position.