Why life can be a letdown for girls with a twin brother

WOMEN with a twin brother are less likely to marry and have children than those with a twin sister, a study suggests.

What’s more, they will probably earn less and leave education earlier, it said.

Researchers claim this may be linked to the high level of testosterone that female twins are exposed to when they share the womb with a brother. In the largest study of its kind, scientists tracked 13,800 sets of twins born in Norway between 1967 and 1978 for 30 years.

They found women with a twin brother were 4 per cent less likely to graduate from university than those with a female twin, while their lifetime earnings were 8.6 per cent lower on average.

The results, published in Proceedings of the National Academy of Sciences, also showed the women were nearly 12 per cent less likely to get married – while fertility rates were 6 per cent lower.

Authors suggest the reason testosterone levels impact marriage and employment prospects could be because women with higher levels of the hormone can be more anti-social and aggressive, while increased exposure to it is known to reduce fertility.

The research by Northwestern University in Illinois looked at whether the effect could be caused by growing up with a brother. But female twins whose brother died at birth showed the same outcomes.