If you are a twin, it is possible that your brother may have infected you in the womb.
Scientists have long known that females in a male-female twin group get all kinds of fun effects from their male counterparts.
In cows, hormones passed to the female can make them sterile. In rodents, research shows that it makes them more aggressive.
But some scientists are beginning to identify a similar link in humans as well.
The effect is said to lie in testosterone, the male sex hormone, which floods the uterus during childbirth.
Sometimes it leaks from the male fetus to the female fetus and affects how it grows, according to research.
Studies show that women with male twins exhibit a variety of traditionally masculine behaviors, due to exposure to testosterone in utero.
“It’s really strange to think that something as random as who you develop with in the womb can absolutely change the trajectory of your development and therefore your physiology throughout your life,” Bryce Ryan, professor of biology at the University of Redlands . he told NPR.
Although twins have their own separate amniotic sacs, separating them from their sibling in the womb, hormones can sometimes flow between them, Professor Ryan explained.
During early development, female embryos do not produce much of the female sex hormone, called estrogen. But men start producing testosterone, the male sex hormone, early on, Ryan said.
By studying rodents, scientists determined that hormones can sometimes flow between developing twins. This has not been found to produce any strange results in male twins, but it has been seen to induce some differences in female twins.
A review from 2019 Of 60 studies on the subject by researchers from Denmark, the United States and South Korea concluded that this can affect the behavior and personality of twins. Specifically, it may increase the likelihood that they will develop traditionally masculine traits.
In utero, the male sex hormone testosterone has been shown to sometimes affect twins.
Twins were more likely to develop an alcohol use disorder than non-twins, according to psychologists at the University of Missouri found in a 2013 study.
They were also more likely to display risk-seeking behavior than identical twins, a trait traditionally associated with boys. 1993 investigation reported the University of Pennsylvania.
Women of a male twin were found to have opinions that are more common in men than women, according to 1994 investigation from the University of New Orleans and the Queensland Institute of Science.
Unfortunately, there is also evidence that hormonal leakage can have a negative impact on twins as they reach adulthood.
They are 15 percent less likely to graduate from high school, six percent less fertile and 12 percent less likely to marry than identical twins, according to one study. study 2019 from the Norwegian School of Economics, Emory University, and Northwestern University.
The 2019 study, which was published in the journal Proceedings of the National Academy of Sciences, analyzed 13,800 pairs of twins born between 1967 and 1978. The study “supports the hypothesis that being exposed to a male twin in utero may have effects lasting in women.
Developing in a womb shared with a man can mean that exposure to testosterone makes the twins less fertile, earn less and be at greater risk of dropping out of school.
But other researchers are less convinced of this pattern.
TO Danish Twin Registry study in 2000 found no physical differences between fraternal twins compared to identical twins.
“Although we found moderate effects at the national level, these results reflect average differences and not everyone will be affected in the same way,” said study co-author Krzyzstof Karbownik of Emory University.
“Some twins may not be affected at all.”
Furthermore, scientists are not sure that the male twin’s hormones are the only thing acting on his womb mate.
Research into the effect of sex hormones on the uterus is complicated by other environmental factors, such as whether or not a mother of twins drank plastic water bottles during pregnancy, Professor Ryan said.
In the early 2000s, researchers and public health officials identified that a chemical found in plastic water bottles, called bisphenol A (BPA), could affect the developing fetus.
BPA is similar in structure to estrogen, but has a number of effects on developing bodies, including brain growth, thyroid function and behavioral development, according to the Massachusetts Office of Climate and Environmental Health.
BPA is just one factor that could affect the development of the fetus and, later, the child, Ryan said. This is one reason it’s difficult to determine to what extent a twin’s characteristics are caused by her sibling, she said.