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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: 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