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Girls who share a womb with boys tend to make less money than those with twin sisters
Female twins who shared a womb with a brother tend to get less education, earn less money, and have fewer children than girls who shared a womb with another girl, according to an analysis of hundreds of thousands of births over more than a decade. Researchers suspect the cause is testosterone exposure during fetal development, though the exact mechanism remains a mystery.
"I think it's a really interesting look at how this really complicated system might impact females," says Talia Melber, a biological anthropologist at the University of Illinois in Urbana who wasn't involved in the study. Still, she cautions, a lot more work needs to be done to establish a causal link.
Fraternal twins, in which each of two eggs is fertilized by a different sperm cell, occur in about four of every 1000 births. About half of those result in male-female twin pairs. Typically, about 8 to 9 weeks into gestation, a male fetus begins to produce massive amounts of testosterone, which helps jump-start the development of male reproductive organs and brain architecture; female fetuses receive only modest amounts of the sex hormone. In male-female twins, though, small amounts of the male fetus's testosterone can seep into the female twin's separate amniotic sac. Scientists have known about this phenomenon for decades, and have been arguing for just as long over what effects, if any, it has on women later in life.
[...] Controlling for factors such as birth weight and maternal education, women who had a male twin were 15.2% less likely to graduate from high school, 3.9% less likely to finish college, and 11.7% less likely to be married—compared with women with a twin sister. They also had 5.8% fewer children and earned 8.6% less money, the team reports today in the Proceedings of the National Academy of Sciences.
Evidence that prenatal testosterone transfer from male twins reduces the fertility and socioeconomic success of their female co-twins (open, DOI: 10.1073/pnas.1812786116) (DX)
(Score: 1, Insightful) by Anonymous Coward on Tuesday March 19 2019, @03:40PM (8 children)
Because they controlled for that. Read the paper.
If you just read headline, articles and even paper titles you're not going to understand what a given paper is about. Media goes through published papers looking for anything that can spice up their science section. They'll take any excuse to write a story on something they can play off as interesting. You need to read the abstract at a minimum to get any idea of what the paper is really about, and usually the detailed methodology (i.e. the meat of the paper) has a huge impact on the meaning of the result.
If you find yourself asking "why did they conclude X?" that's _exactly_ what is in the paper. Half the time you'll find X didn't even mean what you initially thought it did.
(Score: 2) by kazzie on Tuesday March 19 2019, @05:14PM (5 children)
Did they, though?
I've had a brief read of the paper, and I can't find anything to say that they controlled for the social influence of having a twin brother (instead of sister):
Controlling for the mother's age and education catches the social influences of the family as a whole, but it doesn't address the newly arrived sibling.
Example hypothesis: Because there is a societal bias toward encouraging more males into high-paid jobs than females, a female with a male twin will see this attention and encouragement focused on their brother as they grow up. If both twins are female, then the attention and encouragement will be more equally divided between them, resulting in higher average earnings.
It might be interested to compare their results with a third group, namely pairs of male fraternal twins.
(Score: 3, Informative) by FatPhil on Wednesday March 20 2019, @11:50PM (4 children)
Great minds discuss ideas; average minds discuss events; small minds discuss people; the smallest discuss themselves
(Score: 2) by kazzie on Thursday March 21 2019, @10:24AM (3 children)
Right, I missed that. That'd add weight to their hypothesis.
(Score: 2) by FatPhil on Thursday March 21 2019, @11:22AM (2 children)
Great minds discuss ideas; average minds discuss events; small minds discuss people; the smallest discuss themselves
(Score: 2) by kazzie on Thursday March 21 2019, @05:26PM (1 child)
I suspect a lot of that would be caught by controlling for the mother's years in education.
(Score: 3, Touché) by FatPhil on Thursday March 21 2019, @08:53PM
Great minds discuss ideas; average minds discuss events; small minds discuss people; the smallest discuss themselves
(Score: 2) by Osamabobama on Tuesday March 19 2019, @06:02PM (1 child)
I see you are leading with your strongest material.
Okay, that's amusing, but you should have used it as a build-up to the punchline that you delivered at the beginning. I'm not sure you understand your own comedy.
There is longstanding tradition on this site and those like it not to read the articles (let alone academic papers!). There will generally be a few people, though, who do read it and explain how the clickbait headline has it all wrong, or whatever. I guess you're not the person for that role, but few of us are. Just try to keep the overall dynamic of social news in mind to avoid future etiquette breaches. Thanks.
Appended to the end of comments you post. Max: 120 chars.
(Score: 2) by FatPhil on Wednesday March 20 2019, @11:58PM
https://www.pnas.org/content/pnas/early/2019/03/14/1812786116/F1.medium.gif
Look at the error bars. A claim of A > B where A's error bar descends lower than B's error bar is, erm, not hugely convincing.
If you read more, you might notice phrases like "on the margins of significance".
In science-speak, that means "not significant" with a /soto voce/ "shit we didn't get the result our confirmation bias promised us" (read the first sentence - they were definitely striving to confirm the conclusion).
Also note that this was multivariate regression, which is a fancy way of trying to get away with p-hacking - if you throw enough parameters in there, some will correlate with each other.
It looks like they did put in enough leg-work, it was a big study. But if the effect was so insignificant, then this is simply not an issue worth wasting any time/money/effort over.
So there's no point banning green jelly beans because of this.
Great minds discuss ideas; average minds discuss events; small minds discuss people; the smallest discuss themselves