Here we are dealing with sex again. But quite a few readers have written me asking me about the new paper below, which appeared in Biology Letters of the Proceedings of the Royal Society of London. (Click on the title below to read, or find the pdf here.
. . . and there is also a News and Views in Science.
The upshot of the paper is that researchers from Australia looked at 480 Australian birds across five species (rainbow lorikeet, scaly breasted lorikeet, laughing kookaburra, crested pigeon, and Australian magpie); their goal was to see how often a bird’s sex chromosomes (ZW in females, ZZ in males; in birds females are the heterogemetic sex), were discordant with that bird’s gonadal makeup (what we call “biological sex” as well as other aspects of its morphology. (Since these birds are sexually monomorphic for color and pattern, the authors looked at wing, bill, and tarsus size, which presumably do vary among the sexes on average.)
But the main object of study was whether the chromosomes—identified using two sets of DNA primers for genes that were chromosome-specific—were dicordant with the gonads. If everything’s concordant, all ZW birds should have ovaries and all ZZ birds should have had testes.
The surprising result was that there was a fair amount of discordance between sex traits (gonads) and the chromosomes, ranging between 3% and 6% of individuals depending on the species. (These individuals are called “sex reversed”, which I think is a bit confusing.) But it’s still high. Moreover, most, but not all of those “sex-reversed” (henceforth “SR”) individuals seemed to have gonads that appeared normal, though testes in SR ZZ males were generally smaller than normal. We don’t know what percentage of the SR birds were fertile, though at least one female showed signs that she produced an egg.
The authors also found that more than a third of the SR individuals had both male and female gonadal tissue, though most of these were all likely sterile or fertile as only one sex (the authors dissected dead or injured birds sent to wildlife hospitals and thus don’t know their reproductive history). From the paper:
. . . . . 20% of sex-discordant individuals in our study presented with some gonadal enlargement, indicative of reproductive readiness [67–69], while 36% had atypical gonadal make-up (i.e. ovotestes, both an ovary and a testis or ambiguous gonads.
My conclusion:
Since I’ll take 5% as the general proportion of SR birds, 36% of that is about 1.8%, meaning that 1.8% of the sample—if you consider these birds a random sample—had a mismatch between gonads and chromosomes, either having fairly normal gonads that were different from those predicted by the chromosomes, or having ovotestes and were true intersexes. That is unexpectedly high. The authors do say that birds can get screwed up this way because they’re susceptible to environmental toxins, but we don’t know about these individuals.
Now before these data are scarfed up and distorted by gender activists, I have to make a few points:
1.) Humans do not have anything like this kind of discordance. How do we know? Because by now thousands of human genomes have been sequenced, both randomly by the NIH and the “thousand genome project” (now much more than 1000), as well as gene-sequencing companies like 23andMe, and if there were this kind of discordance, we would know: fertile women who submitted their DNA, for example, would hear that they had a Y chromosome. So you can’t extrapolate these bird data to humans, who are very different in both chromosomal constitution and lability to disorders of sex determination (see Emma Hilton’s tweets below).
2.) The prevalence of “intersex” individuals in humans is much lower than these authors observed in birds. Although “intersex” has been estimated in different ways by different people, decent estimates range around one in 5,600 people (0.018%) or, close to that, about 1 individual in 6700 (0.015%). That is much lower than 1.8%, which is nearly 2 birds in a hundred. Extrapolations to humans are again unwarranted.
3.) These data do not tell us that the sex binary is wrong, in birds or any other animal. Even the SR birds, produced either testes, ovaries, or tissues from both: two types of reproductive tissue evolved to produce the two types of gametes that constitute the sex binary. There was no tissue that could have produced any other type of gamete, nor do we know of any such thing in birds.
4.) These data say nothing about the prevalence of gender-nonconforming or transsexual individuals in other species, including humans. It is folly, of course, to use this kind of data from nature to address these gender-ish phenomena in humans. What these authors have an “is” (discordance) in birds, but gender-nonconforming and transsexual people in humans still conform to the sex binary, but feel their gender is different from that of their natal sex. And of course discussing the problems with extrapolating these data to humans is not in any way “transphobic.”
So that’s my caveat, but Emma Hilton from the University of Manchester, who knows a lot more than I do, has produced a thread of tweets about the paper with her usual wit. The tweet thread starts here, and I’ve posted them all below.
Emma’s last couple of tweets were added in response to my importuning her to say something that I could understand, because, with her knowledge, she wrote tweets I found hard to fathom. She also wrote me an email in response to my own question, which as I recall was something like, “Emma, does this mean that the proportion of true intersex birds is much higher than found in humans?” Her response [“DSD” means either “disorders of sex determination” or its more euphemistic “differences of sex determination”].
I’m not resistant to “true intersex”, although I could introduce a resolution not often talked about – the left-right resolution 😀 [JAC: see below about developmental asymmetry]OT-DSD (ovotestis-DSD) in humans is “true intersex”, at least when the amounts of each tissue generate meaningful conflict in downstream development, which, for the most part, they don’t. Most OT-DSD is discovered in XX individuals with residual testicular tissue that doesn’t interfere with healthy ovarian tissue function and downstream development i.e., they are uncomplicated females and furthermore, natural mothers!(On the above, there is brilliantly-crazy paper that you might like to see, where a group of medics in Turkey – IIRC – present a panel of female OT-DSD and babies [all good info], and the whole discussion is about Jesus and the possibility of virgin births).So birds are more plastic than humans for various reasons – the specifics of their genetic determination, the common asymmetry of development in females (that might hint at the possibility of sequential hermaphroditism), the ensuing susceptibility of the undifferentiated gonad to a “make male” trigger.So I’d be happy to stand by the premise that OT-DSD is often “genuinely intersex” at the individual level (typically arising from a left-right conflict) and the birds are more susceptible to this particular type of conflict.
I’ll reread the genetics here later – I’m a big time Emma fan of many years.
An aside, everybody goes on about the charismatic and deadly fauna of Australia, but what makes a bigger impression (living there ..once) are the birds and the weird sounds they make. You won’t encounter many blue ringed octopus or bunyips on the Melbourne busses, but you’ll hear those weird assed birds from the first morning you wake up!
D.A.
NYC (formerly Melbourne)
Ah, well you see, this again simply shows the hard limit of a mere reductionist model which will never capture the fundamental socially constructed nature of sex – and the forces which created society itself.
#DoYourBestSokalImpression
Well, since the gender discussion was brought up again, even though the post was largely about birds, …
There’s an interesting case here in Germany, in which Sven Liebich, a neo-Nazi and anti-trans activist who has been sentenced to some prison time for various offences, has changed his gender to female and his name to Marla Svenja Liebich. All are agreed he has done so in order to lampoon gender/trans ideology.
He recently lost a lawsuit against a journalist who insisted on calling him a man, but he will be incarcerated, in accordance with German law, in a women’s prison. So the legal system is currently quite conflicted.
Someone asked a few days ago on another thread here on WEIT what people could possibly see in the nutcase Candace Owens. Well, it occurred to me that some might see that loonies like Liebich and Owens are (at least for the most part) right about the trans issue and might therefore ask themselves, “well, what else might they be right about!?”
Yes, I have this in tomorrow’s Nooz, along with a picture of “Maria”, complete with a big mustache. It’s bizarre that Germany is putting an obvious man in a woman’s prison (find his photo!).
Yes, I’ve seen the photo, a look which is a rather recent development.
I saw that tweet thread and loved it because I had no idea that sex determination in birds was based on amount of gene expression (DMRT1) rather than a presence-absence difference in gene expression (SRY in mammals). Cool.
Are people really saying this has something to do with “trans” individuals?
Not yet, but I’m pretty sure they will. The paper just came out. What I am sure of is that activists like Agustin Fuentes are going to use it.
Of course they are. On the plus side, they make fewer references to clownfish these days, thankfully.
I’m so sick of the damn clown fish Jezgrove.
Sashimi nemo I say. 🙂
D.A.
NYC
😆
Before damning clownfish, I’d recommend diving down to see them in their natural habitat. They’ve certainly given me some great memories, and I’d love it if I were capable of doing so again.
Probably but they will completely ignore the fact that not one of these birds has to take cross sex hormones or have surgery and embrace sexist regressive stereotypes. Of course humans are not birds but that too will be ignored.
Completely wild thought is I wonder if this is how dinosaurs reproductive systems functioned in a more abstract way and this is a hangover from those days.
The point I tried to make to the Science journalist was that with a PCR test like the one used in this paper, it is not really possible to know whether these “sex reversed” individuals are truly ZW females. The PCR primers amplify Z and W fragments of the CHD gene, and so it is also possible that there has been some other process, such as W -> Z gene conversion or duplication of all or part of the CHD gene, that has resulted in a Z chromosome which contains the PCR fragment from the W. Why this would happen repeatedly across several species is not clear, though karyotyping or whole genome sequencing could help differentiate these alternate scenarios. The journalist wasn’t terribly interested in the technical side of it, so I didn’t get very far with them on this.
Judith thanks for trying with the journalist. Like Marlene Zuk yesterday, I hope it’s worth the effort. Sometimes people don’t know what they’re wrong about, and I hope folks like you & Marlene trying to set them straight will be useful.
Emma Hilton’s admirably clear and informative thread called to mind an incidental feature of contemporary academia: Gender Studies concentrations typically do not include any requirement for Biology course-work. Of course not, it is just a matter of “ways of knowing”. If we also enjoyed departments of Critical Astrological Studies, these redoubts of scholarship would see no need to require any courses in Astronomy.
This is in extremely interesting topic to me, although I’m not a biologist, because humans/mammals and birds are so different.
It’s fascinating that “everyone” doesn’t use X and Y chromosomes. The fact that some reptiles have sex determined by incubation conditions is interesting, and I will reread the blog post and other comments (which are often very well informed) to better understand how this works.
If there is a book or journal article explaining how the common ancestor of mammals birds and reptiles led to this variety I’d be interested. Amazing world.
Thanks for the blog post!
Well that is still pretty wild! So this should be repeated in other species as well.