The scientists found that biological fathers play a major role in the girls’ sexual maturity. It has to do with hormones and pheromones, chemicals that scientists were so uncertain about. For a long time, scientists have debated whether humans have these chemicals like animals do and use to attract the opposite sex.
A study that included 1,983 college girls showed that girls who lived with their biological fathers and brothers had later onset of menstrual periods and that their sexual maturity was slightly delayed. Girls who lived at homes or with their step-fathers started menstruating on average 3 months that the girls who lived with their real fathers.
Brothers seem to have the same influence because girls who lived with their step or half brother also had an early onset of menstruation and so did the girls in big cities regardless whether they lived with their biological fathers and brothers. Girls who lived in rural areas became sexually mature a bit later.
Pheromones were found to influence periods of girls who lived or hanged a lot together making them often menstruate together.
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