Twin gender roles

Firstly, I love how as soon as Zach leaves the country this blog comes to a complete halt. Aren’t we doing anything interesting this summer???

Secondably, I was watching CNN earlier (while working out – YAY ME) and need to vent about a story I heard/watched. There’s apparently some study looking at twins where one is male and the other is female. They claim that the female twin ends up being more masculine than non-twin girls because (supposedly) she spent 10 months in the womb next to her twin brother and his male-making hormones.

Problems with this: 1) there’s no control for the masculine behaviors being due to how the twins were brought up, 2) this assumes gender is related to sex, 3) assumes that there are two genders, 4) assumes those two genders have specific behaviors associated with them. The news anchors described the “practical application” of this project as follows: girls with twin brothers are apparently less likely to suffer from an eating disorder, so (according to the anchors, not any scientists) perhaps they can use this knowledge to prevent non-twin girls from getting eating disorders. WHAT?! If the eating disorder thing is even true (since there were no facts like how many twin pairs were looked at and how many “most” is), and if it is due to being twins (i.e. stuff that happens in the womb) and not due to how they were raised, what are they going to do? Add more testosterone to the womb when they know it’s a girl?? That was like the WORST example of a practical application I’ve ever heard.

One interesting “fact” about this story: Apparently girls with twin brothers have more skeletally male skulls (big teeth is the thing mentioned by the news anchors). I would be interested to know the clinical results on this topic. Is there a significant difference between twins with brothers and other girls? Is this enough of a difference that we could tell if a girl had a twin brother based on skull? I’m guessing probably not – trends like this are rarely applicable, but that was the part of this story I found interesting.

My own personal understanding of sex and gender is that what a person does, what a person likes, is usually due more to environment than genes and hormones and such. Notice I said “due more” not “due entirely” – a very smart populations genetics professor once told me that nature and nurture are necessarily affected, and I believe him. But I think it’s crap to assign certain behaviors to males and others to females!

And this is part of why I try not to watch my news – I save TV for good stuff like Food Network!

6 thoughts on “Twin gender roles

  1. I'm a bit distressed by your conclusions. In other mammals (cows, pigs, rats, etc.) a masculinized female that results from in utero position near her brother is known as a freemartin. Degree of masculinization depends on the period of gestation at which exposure to testosterone (T) occurs, as well as the length and degree of exposure. Some females will exhibit male typical behavior (mounting), while others may even possess a penis! The other student in JCB's lab (in BioPsych) wrote her M.S. on artificial administration of T to pregnant sheep and its effect on behavior & physiology of genetically female offspring (XX). Is it such a far stretch to postulate that such a phenomenon occurs in other mammals, namely Homo sapiens?Culture doesn't erase our biological heritage. There are behaviors in humans that are more common in males than females, and vice versa. Likewise there are numerous conditions of varying degrees of masculinization/ feminization due to uterine effects of androgens. I agree with you that the way the story is framed presumes two genders. Instead of the dichotomy, they should have suggested a gender continuum from full masculine to full feminine. I also agree with you that the eating disorder conclusion is speculation at best, but other behaviors & physiological effects (e.g. the teeth issue) are possibly justified. This research is near impossible to conduct on humans for ethical reasons (can't give pregnant women T), but you could compare full-sibling, non-twin sisters to the fraternal twin female. Then again, you can't control for different maternal environments during the respective pregnancies. In short, you need to use the animal model.

  2. Ha, somehow I knew you’d have problems with this post. OK, I’ll admit the idea of extra T in the womb causing things like big teeth is a cool premise that could potentially be true.My problem is with the jump to extra T affecting the behavior of the twin girl. This assumes that we can assign behaviors as more masculine or feminine, which is simply not the case in humans. It’s one thing to say more male sheep do X than female sheep, but with all the cultural differences throughout human history and prehistory, it is simply impossible to make such generalizations for Homo sapiens. I should probably have mentioned that the crappy news segment kept showing one female twin playing sports and not wearing makeup, as though that proved the point, which is part of what got me all riled up. Even with a continuum, as you suggest, I don’t think this holds up very well. You also assume that there are more masculine and more feminine behaviors done by humans. I would like to know if that’s an assumption on your part or if there’s a basis for it. If the latter, what behaviors are more masculine and which are more feminine? Do these patterns hold up in all human cultures (throughout time) or just in certain ones?

  3. I think this story just made the news because it could be easily sensationalized. If there are significant effects of T on twin girls, it might be interesting to see how the ‘masculinization’ affects fitness. While this would be a daunting task to study with humans, I’m sure there’s something on it in other animals.Earlier this summer I read–in Nature, or Science, of all places–about a research team that claims to have found a “gay gene,” which as we all know is a bit preposterous. But it’s the kind of story that sells, and that’s why it’s making the news. And that’s probably what we’re seeing with this Boy Twin Girl story.

  4. P.S. Dave, did you grow a sweet beard while you were in the field? If so, do you still have it? And if you did, but no longer have it, do you have pictures?

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