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.
"Our results show that females who had a male cotwin have reduced fitness compared to those who had a female cotwin, but the success of males is unaffected by the sex of their cotwin," the researcher wrote.Perhaps the female twins had more masculine attitudes and behaviours that affected their decision to get married, the researchers speculated. Male features could have made the women less attractive to mates, they added.Other studies have shown, for instance, that exposure to testosterone in the womb affects facial features and even finger lengths.