Girls who grow up with younger brothers are more likely to have sex for the first time almost two years later than girls with no younger brothers or sisters, according to a new study. And girls with just older brothers had their first period a year later than girls with no siblings or just older sisters.
The research suggests that girls often help their parents raise their younger brothers and sisters, therefore delaying their maturity, reports the Metro.
“Reports of daughters helping parents are common,” said Fritha Milne and Debra Judge, from the University of Western Australia.
“Associated with this is a delay in sexual activity and thus a delay in potential for starting their own family. We find brothers impose an early-life cost on their sisters’ sexual maturation.
“Having elder brothers delays physiological maturation, while presumably care-taking of younger brothers delays behavioural maturation,” added Fritha and Debra.
The study looked at only 273 people, aged 18 to 75, and appears in the journal Proceeding of the Royal Society B.