Human development at the edge of sexual ambiguity


This is a fascinating column, and I’ll be revisiting it as the ideas seem so fundamental to a lot of conversations I’ve had / would like to have. However, my biggest take-away is that I should possibly be thinking differently about, which I see most often tossed out as the go-to example for content farms. I usually blush at the point that it is, because I do actually use it quite a bit for introductory information, but this has been my general impression of the place…


Hah, the usual BoingBoing transphobes are gonna flip their shit.

Fascinating stuff. Here’s hoping this research brings us closer to the day that “you’re either male or female, period” goes the same way that “it’s just not right for different races to live together” is going.


Love this article. Everytime someone with a voice discusses these issues, it chips away at the bigotry that trans folks deal with.

So… “the gene responsible for the development of testes is surprisingly unreliable” = “evolution has favored a broad range of social competencies” I feel like I’m maybe missing some key piece of information. I absolutely buy into the idea of a gender spectrum, but I’m not at all clear on how the activity of this SRY gene would be a mechanism that helps create that spectrum (except in cases of “human sex reversal” like the one cited). Especially because this study has no bearing on people with XX chromosomes, right?
It’s a super interesting finding, tho.

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Hey Whim,
You’re not missing anything, this finding has no direct connection to gender at all (since it’s only looking at one part of sex assignment, the chromosome part).

But what it suggests (or what I’m going to argue it points to, since I have no idea if the authors would agree with this) is that the categories of male/female, as defined by a body with cells with XY or XX chromosomes, are not actually as stable as we think.

So evolutionary biologists might claim that our bodies are fixed because we’ve evolved in ways that mean we’ll survive (so we are born with hearts that can sustain us, and skulls that can (barely) fit out brains, etc… And some say that sex is this way too. That chromosomal sex is fixed and that’s because it’s an evolutionary advantage.

And this research is simply pointing out that in fact, what some call “chromosomal abnormalities” (which by the way described people I call “friend”) isn’t an abnormality at all, it’s an expected and useful evolutionary adaptation.

Basically this fits into a whole shift that’s happening which is that where diversity used to be understood as weird or bad, now it’s slowly being constructed as good. Whether or not this filters down to those of us who don’t fit into boxes being treated any better, having more access to basic rights, etc… is any one’s guess. But I was excited about the work and also, particularly impressed with the press release that led me to it, so I wrote it up.

Hope that makes a bit of sense. Cory


You’re not alone, most of my friends are shocked when they find out I write for and that, in fact, it’s not a content farm. Thanks for reading!


So this is saying Klinefelter Syndrome isn’t an abnormality? Even thought it affects 1-2 in 1000 males, and the wikipedia article indicates there are health effects (granted not severe, and can be treated: but infertility is common apparently)

I also wonder how a prehistoric community could benefit from diversity provided by a very rare genomic effect. A small community might never have sufficient cases for the difference to make a difference.

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One way of looking at it - maleness and femaleness have some pretty severe health effects too.


As does fertility. I hear it puts you at pretty high risk for having a parasitic human develop inside the female that can take up to 18 years to be completely rid of! (26 years under the right conditions*).

*post-2008 economy…


So, I like this finding because it punches a hole in the binarist, biological-essentialist claim that there are hard and fast boundaries between “men” and “women” and that is natural and good.
But to say the “ambiguity” of this gene is an evolved adaption is just as silly. If this aspect of the gene’s expression isn’t even affecting most people (or even most early human groups, since the incidence of sex reversal is like 1/20,000), then I don’t see how it could be selected for, and I think it’d be better to say it wasn’t selected against and didn’t provide an evolutionary disadvantage.
I have a special dislike for the “appeal to nature” fallacy when discussing people. Biology is not steady ground on which to build your ethics, and treating people with respect because they are an example of a “useful evolutionary adaptation” isn’t good ethics anyway. On the other hand, you’re right that playing on that misconception might be very important for basic rights, etc… *complicated feelings*


So there are the direct findings reported in the paper, and then there’s speculation/hooks for further research based on them.

The direct findings are basically this: the gap between a functional female->male development switch and a non-functional one is surprisingly narrow, and this appears to be “deliberate” and selected for.

The speculation part is that with a narrow gap, any natural variation of the efficiency of the switch will produce notable differences in the development of sex and gender. In the words of the researchers:

No part of biological development is purely binary - there are always elements of chance (will the switch work in each cell?) and time (when will a cell reach the threshold for the switch? how long will it take for the cell to differentiate and assume new function? etc). In this case, the efficiency of the SRY switch determines how quickly and how much testosterone will be produced at a critical early stage of development. Fetal testosterone affects the development of the brain, which in turn goes into the development of gender identity and sexuality.

Not really. The authors of the paper point out that traits which are selected to be robust and unvarying exhibit canalisation - that is, there are mechanisms that cancel out outside influences and the development is always channeled towards a singular “normal” state. As shown here, this is not the case for the development of (male) sex in mammals, which suggests that variation and ambiguity is indeed an evolved state.


Yes, ok, this was the gap in my thinking. Thank you; that all makes a lot of sense.

Kinda dumb. First off, where is the evidence that this is exclusive to humans? It seemed like that was a big part of his argument. Second, nature is lazy, good enough is usually enough cheaper than perfect that good enough usually wins, so I’m thinking that is far more likely what is going on.

Um, no. The original paper draws comparison with mice which also exhibit similar ambiguity, and the hypothesis is that this is common for all mammals. Not sure where you’re getting the human-only angle.

Well, even if that were the case, it still means that “good enough” for sex/gender determination is “a nebulously defined range with a couple of more prominent focal points” rather than “strict binary separation”. It still undercuts the argument that naturally there are only two sexes and two genders.

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