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Sex Chromosome Variants Are Not Their Own Unique Sexes

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Sex Chromosome Variants Are Not Their Own Unique Sexes

Colin Wright
Dec 2, 2020

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The list of bad arguments forwarded by activists designed to undermine the reality of there being two and only two sexes is very long and constantly growing. I dealt with some of these common arguments for Quillette in 2020. However, I came across a tweet by Dr. Shay-Akil McLean responding to Zach Elliott claiming “there are precisely two sexes (no more, no less).”

Twitter avatar for @Hood_Biologist
Dr. Shay-Akil McLean, BA, BA, MA, MA, Ph.D. @Hood_Biologist
Hi, I’m a transgender biologist, specifically an evolutionary geneticist who studies humans. In humans there are 6 common sex karyotypes: XX, XY, XXY, XXXY, & XYYY. & there are 4 rare sex karyotypes: XO, XO/XX mosaicism, XY/XXY mosacism, XXY/XXXY/XXXXY mosaicism.
Twitter avatar for @zaelefty
Zach Elliott @zaelefty
The biological sciences overwhelmingly support the claim that there are precisely two sexes (no more, no less) in almost all complex multicellular life. Here are 40 peer-reviewed journal articles from biologists on the evolution of sex and why there are only two sexes. https://t.co/j02seUIdXh
2:01 PM ∙ Nov 30, 2020
15,512Likes4,233Retweets

McLean, who prominently lists five degrees after his name and claims to be a human evolutionary geneticist, took issue with that claim and forwarded a very common—and very wrong—portrayal of biological sex: that different sex chromosome compositions beyond the standard XX and XY each represent their own unique sex. In fact, Dr. McLean appears to suggest in his tweet that there may be as many as 10 biological sexes!

Such extreme misinformation would be concerning coming from anyone, but especially so coming from someone with a PhD in human evolutionary genetics who. The 4000+ retweets his tweet received demonstrate just how fast misinformation can spread. However, a glance at his Google Scholar reveals he has authored several papers on racism and only one paper that discusses some topics in genetics yet contains no actual genetic analyses whatsoever. His claim to being a geneticist (of any kind) is therefore dubious. But credentials don’t determine whether someone is right or wrong, and I am sure it wouldn’t be hard to find a real geneticist making the same argument, so let’s look at the argument itself.

The argument that individuals with sex chromosomes that deviate from the typical (46, XX and 46, XY) arrangements, such as those with Klinefelter syndrome (47, XXY) or Turner syndrome (45, X0), is common and usually used to argue that there are 6 sexes, though other numbers are frequently thrown around as well. Searching Twitter for the term “6 sexes” returns countless tweets similar to the one below.

Twitter avatar for @iamyourmother22
Ace #JUSTICEFORREIDGIBSON @iamyourmother22
@AndrewsFive @ManMilk2 @RoxyThe12th There are more than 6 sexes, which I have listed already, but shall list again X XX XXY XY XYY XXXY I have my sources that prove I am right if you'd like to see them. (2/2)
8:59 PM ∙ Nov 17, 2020
26Likes1Retweet

This argument results from a fundamental misunderstanding about what distinguishes males and females biologically, which is the size of the gametes (sex cells) they produce. Males produce small gametes (sperm) and females produce large gametes (ova). But on an individual level (since not all individuals may be able to produce gametes) an organism’s sex corresponds to the type of primary sex organs (testes vs ovaries) and individual has developed.

In mammals, which includes humans, the Y chromosome carries a gene (SRY) that encodes a testes-determining factor. If an individual has a Y chromosome with a functional SRY gene, they will develop testes and therefore will be biologically male. Absent a Y chromosome and functional SRY gene (unless the SRY gene has been transposed to an X chromosome), an embryo will develop ovaries and will therefore be biologically female. What’s important to note is that the presence of a Y chromosome, or two, or three, etc., all result in the development of testes and therefore these individuals are biologically male. Likewise, individuals with additional or fewer X chromosomes, in the absence of a Y, all develop ovaries and are therefore biologically female.

With this in mind, the chart in the above tweet can more accurately be rewritten as:

  • X – Female

  • XX – Female

  • XXY – Male

  • XY – Male

  • XYY – Male

  • XXXY – Male

So no, these different chromosomal compositions are not new sexes, but rather represent natural variation within males and females. To illustrate by way of analogy, a person with Klinefelter syndrome (47, XXY) isn't a new sex in the same way that a person with Down's syndrome (who have 3 instead of 2 copies of chromosome 21) isn't a new species.

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Organizations to Support

  • Sex Matters

  • Parents Defending Education

  • Transgender Trend

  • Genspect

  • Foundation for Individual Rights and Expression (FIRE)

  • Women’s Liberation Front (WoLF)

  • LGB Alliance

  • Fair Play for Women

  • Society for Evidence-Based Gender Medicine

  • Counterweight

  • The Free Speech Union

  • Heterodox Academy

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Sex Chromosome Variants Are Not Their Own Unique Sexes

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20 Comments
Jennifer Lahl
Dec 2, 2020Liked by Colin Wright

Thank you for explaining this so others can understand. And argh, the misinformation and retweeting is maddening! Did people miss bio 101?

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James Hammerton
Dec 5, 2020Liked by Colin Wright

Thanks for a clear explanation. Regarding the SRY gene and it appearing on X chromosomes, wikipedia's article about XX male syndrome (https://en.wikipedia.org/wiki/XX_male_syndrome) claims that about 10% of XX males do not have SRY, but that having an extra copy of a gene called SOX9 or the absence of a gene called DOX1 can also cause XX male syndrome. Furthermore, 2 other genes, SF1, WNT4 are claimed to be being investigated for roles in XX male syndrome. So it seems the genetics of XX males aren't straightforward.

I also have a question: Do people ever have both (or some mix of) testes & ovaries or is it always the case you have one or the other but not both?

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