By Maggie Fox
WASHINGTON (Reuters) - Women who have a male twin are less likely to marry and have children, perhaps because of being exposed to their brother's testosterone for nine months in the womb, researchers reported on Monday.
A study of Finnish twins showed that women were 25 percent less likely to have children if their twin was a male. Those who did have children gave birth to an average of two fewer babies than women who had a twin sister.
Based on an analysis of 18th and 19th century data, researchers found women who had a male twin also were 15 percent less likely to get married, Virpi Lummaa of the University of Sheffield in Britain and Finland's University of Turku and colleagues reported.
"We show that daughters born with a male co-twin have reduced lifetime reproductive success compared to those born with a female co-twin," they wrote in their report, published in the Proceedings of the National Academy of Sciences. "This reduction arises because such daughters have decreased probabilities of marrying as well as reduced fecundity."
The data used in this study was from the years 1734 to 1888. So, we’ll keep our stunned surprise to ourselves. Back then, we think, people were probably a little fearful of twins. And twins in which one was a boy and one a girl probably really freaked people out. The researchers speculate that some of this has to do with testosterone absorbed by girls in the womb. This could have resulted in some masculine features and reproductive problems. We’ve heard that fraternal twins (which boy-girl twins have to be) are genetic. It would seem that if this were the case that twins would become steadily less abundant. Thinking back to the 1700s – 1800s, that encompassed a lot of the Victorian era. Maybe those Fops just preferred their women and men to be a little more feminine.