Let’s Talk About Sex

Well. That’s a headline that catches the eye, isn’t it?

Sexual orientation and gender identity are all over the news right now, and have been for… well, since ever. It’s a politically charged topic, and everyone—everyone—has an opinion on the subject. Sexuality is a powerful current running through questions of ethics and morality, religious belief and cultural expectations, and survival and propagation of the species. “Everything in the world is about sex except sex,” as Oscar Wilde is reputed to have said. “Sex is about power.”

Despite this—or, perhaps, because of this—there are a lot of misconceptions about the subject. A whole lot of misconceptions. As skeptics, it’s important that we try to step outside our own biases and preconceptions and look at the actual evidence for a topic, even one so important and integral to our species as sexuality. Or, perhaps, especially one so important.

So, Salt-N-Pepa? Take it away:

Let’s talk about sex, baby
Let’s talk about you and me
Let’s talk about all the good things
And the bad things that may be
Let’s talk about sex
Let’s talk about sex
Let’s talk about sex
Let’s talk about sex

Ideas people have

Things people think. But what does science say?

Currently, there are two cultural debates going on in the United States. Well, there’s more than two—there’s always more than two—but there are two that are relevant to this article. The first is superficially about bathrooms but deeply about questions of gender identity, with one side saying that sex is a binary structure (exclusively male or exclusively female) and the other that it is a spectrum (ranging from male to female, with shades and variations between the two poles). The second is about sexual attraction, questioning whether attraction to the same gender is “natural” or “unnatural.”

Here at Skeptoid, we do not take a political stance. We believe in science, and in following the evidence. The decisions you make should then be based on the evidence. With that in mind, let’s look at the evidence.

But surely, “male” and “female” is simple enough?

Gender identity is one of those things that looks simple and easy to resolve. If you have a penis, you have an XY chromosome and you’re male. If you have a vagina, you have an XX chromosome and you’re female. Biology carries the day, and we can get on with our lives. Right?

Not so fast. Human beings are complicated.

As reported by the World Health Organization, “most women are 46XX and most men are 46XY,” meaning they have 46 chromosomes in 23 pairs with an XX chromosome pair indicating “female” and an XY chromosome indicating “male.” But, well, that’s not always true. The WHO continues:

Research suggests, however, that in a few births per thousand some individuals will be born with a single sex chromosome (45X or 45Y) (sex monosomies) and some with three or more sex chromosomes (47XXX, 47XYY or 47XXY, etc.) (sex polysomies). In addition, some males are born 46XX due to the translocation of a tiny section of the sex determining region of the Y chromosome. Similarly some females are also born 46XY due to mutations in the Y chromosome. Clearly, there are not only females who are XX and males who are XY, but rather, there is a range of chromosome complements, hormone balances, and phenotypic variations that determine sex.

Roughly 5% of all pregnancies result in fetuses with aneuploidy, a condition in which the fetus is either monosomic (possessing only one of a specific set of chromosomes) or polysomic (possessing more than two of a specific chromosome). The most common form of this is sex chromosome aneuploidy (SCA), accounting for nearly half of all aneuploidies and occurring in 1 out of every 1,400 human beings. SCA can result in a number of conditions (including the following):

  • Turner syndrome (monosomy X or 45X). This condition is found in 1 out of 3,000 live births, and results in a “phenotypically female” human lacking prominent female secondary sexual characteristics. These people are generally sterile.
  • 47XXX Females. Approximatly 1 in 1,000 women is a 47XXX. They tend to be taller than average and have slender builds.
  • 47XXY Males (also known as Klinefelter syndrome). Approximately 1 in 1,600 males is a 47XXY. They are generally tall, sterile, and have incompletely developed secondary sexual characteristics because they produce relatively small amounts of testosterone.
  • 47XYY Males. Approximately 1 in 1,000 males is a 47XYY. They tend to be taller than average and produce more testosterone and, like 47XXX women, are only rarely aware that they have a chromosomal abnormality.

SCA is not the only reason that an individual may not fit neatly into the perceived biological binary, though. There is also a condition known as “intersex” (once known as “hermaphroditism”), in which the individual cannot be neatly fit into a specific category because of the absence or presence of specific hormones, or enzymes, or for reasons we don’t clearly understand yet. This can include:

  • XX Intersex, in which the individual has XX chromosomes and ovaries, but has external genitals that appear male. At times, XX Intersex individuals may be raised as girls, only to take on male characteristics at puberty.
  • XY Intersex, in which the individual has XY chromosomes but the external genitals are either ambiguous or appear female.
  • True Gonadal Intersex, in which the individual (who can have XX, XY, or aneuploid sex chromosomes) has both ovarian and testicular tissue. Individuals with true gonadal intersex may appear externally male, female, or ambiguous.

“Complicated” doesn’t quite do it justice, does it?

Nope. Biology is messy.

Now, let’s be clear here: I’m not saying that every transgender individual has a chromosomal abnormality or an intersex condition. That’s a crude—and rude—oversimplification. My point here is that “sex” is not the simple black and white that it appears to be on the surface. And that doesn’t even begin to address what happens when we toss our brains into the equation, because psychology is every bit as important (perhaps even more so) than genetics and hormones when it comes to the expression of gender identity.

Although, to be clear, there is some evidence that transsexuality has some genetic basis. At least one study has shown that, among twins, if one monozygotic twin is transsexual it is likely that the other will be as well (roughly 33.35 of XY twins are concordant, and 22.8% of XX twins are concordant). The reason for believing that it has some genetic basis is the sharply reduced concordance in dizygotic twins (who are not genetically identical)—concordance for both XX and XY dizygotic twins runs about 2.6%.

The slope gets even more slippery when we consider how much of our perceived gender identity is based in cultural norms instead of anything to do with biology. Is an XX who wears pants, keeps her hair short, hunts and fishes, is good at math and is attracted to other women a transman who hasn’t transitioned, or a lesbian with stereotypically masculine interests?  Is an XY who listens to rap, works on cars, watches football, and is attracted to women a transwoman who hasn’t transitioned, or a heterosexual man with stereotypically masculine interests? Is an XYY who wears skirts, likes to cook and work with children and watch romcoms and who is attracted to men and women both a transwoman who hasn’t transitioned, or a bisexual man with stereotypically feminine interests? The answer is simple: ask them. Or, better yet, don’t ask them. Treat them like human beings, and let them tell you if they think it’s important.

You’d think that wouldn’t be controversial.


Oh, and speaking of controversy? Next time, we’ll look at the other question: is attraction to your own gender “natural”?

About Richard Gant

Richard Gant is a husband, a father, and a huge nerd with a deep love of science, science fiction, and fantasy. He works for a brokerage firm he won't name here in order to keep his Compliance department happy, and frequently talks to inanimate objects as if they can understand him. He also has a difficult time writing seriously about himself in the third person.
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7 Responses to Let’s Talk About Sex

  1. Durinn McFurren says:

    Biologically, males produce the small gametes and females produce the large gametes (Dusenbery, David B. (2009). Living at Micro Scale.). The type of gamete produced is determined differently in different species. In humans, it is determined by chromosomes, but that is not universally the case in sexually reproducing species. Some species can switch the type of gamete they produce partway through their lives. However, it remains the case that there are really only four sex possibilities, biologically, for species with two distinct sexes:

    1. Female: Produce the large gametes.
    2. Male: Produce the small gametes.
    3. Hermaphroditic: produce both large and small gametes.
    4. Drone(?): produce no gametes.

    Note that some species have similar gametes, which is called isogamy, but this is not the case for humans or most advanced animals.

    A human’s chromosomal identity allows for other combinations, but that’s not exactly the same thing as their biological sex.

  2. Pete Strange says:

    Thanks for that story.
    Enjoyed having a quick read whilst having a coffee and learning something.
    The day I stop learning is the day I`m no longer here.

  3. Deon says:

    Thanks for a great article. As usual well researched and based on science rather than prejudice.

    In your quote from the WHO you mentioned men with XX chromosomes and women with XY both with translocation of a small section of the Y chromosome. Is this correct as the men have only XX?

  4. Isaac says:

    Wow…this post is clearly a,failure in skepticism and really a post in fully engaged political nonsense. 1 in 1600? So 99.999375% of the population doesn’t adhere to the description. You describe outliers to define the norm. If that is the case you need to rethink your opposition to antivacciners and climate change deniers. You are picking facts only when they suit your political leanings.

    • Richard Gant says:

      Based on the tenor of your comment, I strongly suspect that nothing I say will make an impact on your opinions. But, on the off chance, I’ll take a crack at it anyway.

      Current estimates put the percentage of transgender people in the Inited States at 0.6% (http://www.npr.org/sections/thetwo-way/2016/06/30/484253324/1-4-million-adults-identify-as-transgender-in-america-study-says). Now, it is true that only 1 in 1,600 persons in the United States are biologically intersex or transgender, which works out to about 200,000 people. So, yes, that means we have (roughly) seven times as many people identifying as transgender as would be expected from a purely biological definition.

      The point, and perhaps I should have spelled this out more clearly, is that sexuality and gender identity are both complicated and culturally-defined. 200,000 people in the United States (statistically) don’t fit into our simplistic binary assumptions of sex just because of biology. Add in to that psychology – because the brain is complicated – and we have no reason to suspect that it gets any clearer.

      Yes, the binary definition works for most people. 1,599 in 1,600 people are XX or XY genetically. 994 out of 1,000 people identify with the culturally-defined assumptions and expectations of their biological gender. But the outliers still need to be accounted for – not ignored, belittled, or condemned.

      To use your labored vaccination analogy, nobody denies that a tiny percentage of individuals can have adverse reactions vaccines. Allergies, for example, exist. Side effects can happen. Medical exemptions to even the strictest vaccination schedule requirements are permitted. And there is a specialized court system to investigate alleged harm caused by vaccinations. In other words, we take care of the minority, even while working for the benefit of the majority.

      Perhaps we should do the same in other arenas as well?

  5. Simon says:

    While I had a rough overview of the possibilities you listed here, the detail was appreciated, along with the lack of polito-religious ‘interpretation’. If only some of the politically or religiously bigoted folk actually took the time to understand the background… and realise the world is not ‘right OR wrong, black OR white’.

    Thanks for making the time and taking the effort in such a Sisyphean task: we can only hope to educate folks who are actually interested in finding out the truth, convoluted as that may be.

    Keep up the good work.

  6. WorkingInACopShop says:


    Does anybody remember the time back when the only question was: Am I getting any tonight? And that’s as complicated as it got.

    I think I was 19.

    Thanks for the detail. I don’t know what I am going to do with it, but thanks anyway.

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