Categories are usually fuzzy. That is, when humans use a category, there are usually some members of the category who have all the traits you associate with that category, some members that have many of the traits, and some members where you have to make a judgment call about whether it counts or not.

The Cluster Structure of Thingspace provides several excellent and uncontroversial examples. For instance, think about birds. Robins and sparrows are very typical birds. Eagles are less typical than robins, but still very typical. Penguins are really fucking weird birds. And you have to make a judgment call about bats: for purposes of biology, a bat is not a bird, whereas for purposes of trying to decide which animals are kosher, a bat is a bird. You make the decision based on whether the more important bird trait is “related to dinosaurs” or “flies.”

Or think about mothers. A typical mother gives birth to and raises a baby who is genetically related to her. Less typical mothers include birth mothers, adoptive mothers, surrogate mothers, genetic mothers, lesbian partners of the mother who gave birth, and so on. A baby’s egg donor is still her mother in some ways– for instance, you’d want to look at the egg donor rather than the adoptive mother to figure out what the baby’s risk of getting a rare disease is– but she’s missing some very common mother traits like being pregnant with the child or raising it.

Gender is a very politicized topic. So it makes sense that while some people agree that whether bats are birds depends on whether you’re doing biology or theology, and that while penguins are birds you shouldn’t assume that they’re able to fly, this common sense goes out the window when you’re talking about gender. I am going to address two issues where poor reasoning about more and less central members of categories makes people deeply confused: biological sex and gender differences.

Biological Sex

Biological sex is actually a remarkably good classification system: something like 98% of humanity can be easily and unambiguously placed into one of two discrete categories, which has to be some kind of record. Of course, not everyone is a metaphorical robin. Eagles are quite common: men with gynecomastia and noticeable hip fat; women who can grow beards; women who have had hysterectomies; men who have had their testicles removed.

However, it all runs into trouble when we’re talking about transgender people (as well as intersex people, but I’m mostly going to focus on transness). People really, really want to insist that there is a single biological sex that we really are. They usually pick chromosomes as the deciding factor, perhaps because medical science is not currently able to change a person’s chromosomes. (I have seen people attempt to be intersex-inclusive by declaring “males” to be the ones with at least one Y chromosome and “females” the ones with no Y chromosome.) They then point out that you have to know what a person’s biological sex is for medical reasons and therefore we trans people are running around being special snowflakes by putting down our identified genders on medical forms.

Except there are actually a very small number of medical problems that are affected by sex chromosomes: for instance, whether you are XX or XY affects your risk of hemophilia or colorblindness; if your sex chromosomes are something other than XX or XY, you may be at risk of various health problems, depending on what your sex chromosomes are. It is usually possible to infer many traits from the fact that a person has XX chromosomes (well, in reality, we usually infer the fact that a person has XX chromosomes from their traits, because most people are not karyotyped). But trans people get biomedical interventions all the time.

For instance, a doctor might be concerned about prescribing a teratogen to someone who might be pregnant. In that case, what matters is whether the person is capable of getting pregnant (many trans men and some cis women are not). A doctor may need to decide whether to screen someone for breast cancer, in which case what matters is whether a person has breasts. Testosterone increases a trans man’s risk of high cholesterol, heart disease, high blood pressure, and diabetes, although probably not to the level that cisgender men have. And, of course, our unusual sexes present unique health issues: for instance, testosterone is a teratogen, which means that trans men who take testosterone have to be particularly careful about birth control use.

These are not theoretical issues. Trans people have been routinely denied sex-specific medical care, because insurance companies believe that there are men and there are women, and therefore there don’t exist any people who need both a prostate screening and breast cancer screenings. Intersex people even today receive cosmetic genital surgery as infants so that people don’t have to be disturbed by a person who doesn’t fit the categories very well.

The obvious solution to this issue is to say that whether a trans person’s sex is male or female depends on what question you’re asking. A trans woman on estrogen is male for the purpose of whether she should get prostate cancer screenings and female for the purpose of whether she should get breast cancer screenings. When thinking about his risk of high cholesterol, a trans man is probably best considered neither male nor female. We are bats, and you don’t have to have a firm position on whether or not we are birds.

Gender Differences

Men are more likely to use an ethic of justice, which emphasizes universal standards and impartiality. Women are more likely to use an ethic of care, which emphasizes a specific obligation to those you have interpersonal relationships with or those who are vulnerable to the consequences of your choices. The Cohen’s d of this difference (which is a measure of how different the two groups are from each other) is about 0.2.

This is a picture of a Cohen’s d of 0.2. (Picture comes from this excellent website.) It is genuinely difficult to tell that this is a picture of two bell curves instead of one. If you know someone is a man or a woman, it doesn’t tell you much of anything about whether they use an ethic of justice or an ethic of care.

Has that stopped anyone? No, it has not.

For instance, look at the Stanford Encyclopedia of Philosophy page on feminist ethics, which includes an entire section on care-focused ethics which includes paragraphs like this:

Gilligan believes that Kohlberg’s methodology is male-biased. Its ears are tuned to male, not female, moral voices. Thus, it fails to register the different voice Gilligan claims to have heard in her study of twenty-nine women reflecting on their abortion decisions. This distinctive moral voice, says Gilligan, speaks a language of care that emphasizes relationships and responsibilities. Seemingly, this language is largely unintelligible to Kohlbergian researchers who speak the dominant moral language of traditional ethics—namely, a language of justice that stresses rights and rules.

Ah, yes, the distinctive moral voice of women. The one that sounds almost fucking exactly like the voice of men. That distinctive moral voice of women?

Putting known gender differences into the Cohen’s d chart generator is an instructive experience. For instance, here’s gender differences in masturbation and casual sex, respectively:

And here’s neuroticism, agreeableness, and conscientiousness/extroversion (the latter two have the same effect size), again in the order I listed:

Now, there are in fact some effect size charts that look like Men Are From Mars, Women Are From Venus. Here’s an example:

This is a picture of the difference in toy preferences at age three. I am not sure how useful this is for anyone who isn’t a toy marketer, but there you go. (Note that one-year-olds and five-year-olds both have less stark gendered toy preferences. Presumably male toddlers are from Mars, female toddlers are from Venus, and everyone else is from Earth.)

So what’s the takeaway here? (Besides “Ozy is fascinated with their new stats discovery,” of course.) The answer is that people are bad at categories. We learn facts about the typical man: for instance, he uses an ethic of justice, masturbates more, is okay with casual sex, is more introverted, is less neurotic, is more disagreeable, is less conscientious, and played with trucks but not dolls as a child. We then conclude from this that everyone we stick in the category “man” uses an ethic of justice and therefore we are perfectly justified in creating an entire subfield of ethics complaining about how the ethics of care is excluded because of sexism.

But that isn’t true! It is possible that people in a category are more likely to have a particular trait, but the size of this effect is not actually large enough for this to be useful information. In fact, in studies of gender differences, this is quite common!

While I’ve been picking on Carol Gilligan (and god is she an easy target to pick on), I think this kind of thought is actually more common among anti-feminists than it is among feminists.

Think about gender differences in permissive attitudes about casual sex. This is actually a fairly striking difference: about four-fifths of men have a more permissive attitude towards casual sex than the average woman does. (Of course, this might be caused by inborn tendencies, by cultural influence, or by a combination of both; you shouldn’t assume that a difference existing means it is biological.) You can see the effects of this difference clearly: for instance, it is generally easier for heterosexual women to have casual sex than it is for heterosexual men to have casual sex; gay men are more likely to have casual sex than lesbians are; there are essentially no full-service sex workers who target a solely female audience, presumably because women who want no-strings-attached casual sex rarely have to pay for it.

But there’s also a considerable amount of overlap: about seven-tenths of the two groups overlap. And that matters too! For instance, many people assume that casual sex must be a rapacious man taking advantage of an innocent woman who just wants love. But there are lots of women who like casual sex. Perhaps the women who have casual sex disproportionately come from the 20% of the female population who have more permissive attitudes about casual sex than the average man. In that case, we don’t have to be worried that hookup culture is harming women; it is merely catering to the desires of women who are a little unusual (eagles, not robins).

And I’m using a relatively stark gender difference, which would bias my case. Looking at something like neuroticism– where 65% of men are above the female mean, and there’s an 84% overlap– it’s hard to see much justification for an “essential masculine nature” or an “essential feminine nature.” Such reason is merely looking at robins and then assuming, in defiance of all the evidence, that they are the only kind of bird.