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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: 5, Insightful) by Immerman on Tuesday March 19 2019, @01:21PM (10 children)
Agreed. Going from "the girls in mixed-gender twin pairs suffer a disadvantage" to "prenatal testosterone is the suspected cause" is a rather huge leap, especially when they don't even have a suggested mechanism for their assumption.
Given the social and evolutionary value placed on boys (males can spread their genetic material across the population much faster than females - higher risk of low fan-out, but potentially much higher reward), it would not surprise me at all to find that in having to split attention and resources between two age-synchronized children, the boy would tend to get preferential treatment.
And that's before we even get into the different biological and/or socialized behaviors expected from children of different genders - which would likely tend to bias things even more strongly in favor of a boy. Not to mention the social backlash against a girl who picks up "male" behaviors from her twin.
(Score: 2, Insightful) by Anonymous Coward on Tuesday March 19 2019, @02:10PM (2 children)
Feminine males are routinely assaulted and harassed not only by their peers but by the grownups in their life. At school, they are subject to institutional harassment and humiliation. Some of this centers around gym class, but it is pervasive.
So whatever it is that we do to masculine girls must be worse, right?
(Score: 0) by Anonymous Coward on Wednesday March 20 2019, @05:50AM (1 child)
Yes, they are.
From what I've seen, up until age 30 or so girls like the bad boys with gushing adrenaline oozing testosterone
After hitting 30 they start looking for a male who has money and or is friendly
Although by that time it's possible that those males have learned that paying for sex is cheaper and easier
(Score: 0) by Anonymous Coward on Sunday March 24 2019, @08:58PM
Chose to be V-Safe, because fuck why would I want to pass my genes on?
I'm now in my late 30s without many female successes, I've started pulling the 18 crowd with daddy issues. Unfortunately they pretty much all want you to treat them as a slut and help them get gangbanged. Which isn't really my thing. But I'm at girl 6 or so, which is making it hard to refute that at least this demographic has a stereotype (and this is a random sampling of girls from all over, white, asian and black.)
(Score: 2) by HiThere on Tuesday March 19 2019, @04:52PM (1 child)
Actually, there are reasons why that should be suspected. Look up freemartin. https://www.google.com/search?q=freemartin [google.com]
Whether this applies to humans is a decent question, and there are lots of reasons to think that one would expect such an effect from social causes. (Boys tend to be more invested in than girls by the parents.) But to suspect a biological cause is also not unreasonable.
Javascript is what you use to allow unknown third parties to run software you have no idea about on your computer.
(Score: 2) by Immerman on Tuesday March 19 2019, @06:19PM
Freemartins are chimeras though, whose bodies contain both male and female cells, so there's a lot more than just placental hormones involved: https://en.wikipedia.org/wiki/Freemartin [wikipedia.org]
And even with freemartins I see no suggestion of any handicap that would interfere with education or earning potential.
If they were talking about *physical* symptoms, I would certainly be inclined assume a physical source - but since the symptoms appear to be social, I think assuming a physical source is grossly premature.
(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.