Girls with big brothers go through puberty later, while those with little brothers wait longer before having a sexual relationship…

Researchers questioned almost 300 men and women about their families and lives.

The women with older brothers had started their periods almost a year later than those with younger brothers or with sisters of any age.

It is thought this is because carrying a boy through a pregnancy uses up so much of a woman’s reserves that there is less to nourish the next child, whose health suffers as a result.

If the next child is a girl, that could lead to a delay in starting her periods.