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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: 4, Informative) by slinches on Tuesday March 19 2019, @05:42PM (4 children)
I scanned the study and they attempted to control for the nurture side of things by looking at the differences between twins of same and differing gender where one of the twins died soon after birth. The sample size was too low for very early deaths, but the trend held with sufficient statistical significance for those whose twin died before they were 1yr old. It's hard to tell if there might be some other confounding factors, but it does tend to point to some sort of prenatal effect.
It would be interesting to look at this in the context of single births with varying levels of testosterone in the mothers to see if there are similar differences in outcomes for girls. That could help determine whether the fetal testosterone exposure hypothesis is worth pursuing or it could point to something else.
(Score: 3, Interesting) by Azuma Hazuki on Tuesday March 19 2019, @06:33PM (2 children)
I do wonder sometimes about the effects of fetal testosterone. Specifically, I wonder if I might be a "freemartin," which itself was a slang term for lesbians for a long time, and if my mother just had higher than normal T in her bloodstream as she was carrying me. I've read gay women do have slightly masculinized brains, and I always did have an interest in science and computers and suchlike from a very young age...
I am "that girl" your mother warned you about...
(Score: 0) by Anonymous Coward on Sunday March 24 2019, @09:02PM (1 child)
nurture.
When I was a kid the tomboyish girls were mostly into guys, although out of my age range. Sadly once I reached my teens or so, the tomboyish girls all seemed to be either lesbians, bisexual domme types, or the rare straight one was married.
Having said that, there was this SUPER nerdy, SUPER HOT girl when I was in college who was such a big nerd that she reject me with the fact that I was both too young and not nerdy enough for her, because she had run an 8 line BBS from home off her after-school job before I had purchased my first 2400 baud modem.
I would have married that girl :)
(Score: 2) by Azuma Hazuki on Monday March 25 2019, @04:41AM
I was never a tomboy though. I'm still way into the femme side, though not lipstick, and if anything even nerdier than ever.
I am "that girl" your mother warned you about...
(Score: 0) by Anonymous Coward on Wednesday March 20 2019, @05:53AM
So one twin dies. Do they control for the depression in the parents?
Because I can totally see losing a kid making for a pretty dour household where the surviving kid(s) are not as engaged in play and learning.