Science now knows whether having boys or girls 'run in the family'

Photo: iStock
Photo: iStock 

We've all heard of families who've had many boy or girl babies through the generations, which has led to the common perception that it's possible that having one particular sex can 'run in families.'

We hate to burst your bubble but science now has evidence that it's simply untrue.

A study just published in scientific journal Proceedings of the Royal Society, has nixed the notion that a skew towards a particular sex of children in a family is genetic.

Researchers studied the sex statistics of all babies born in Sweden since 1932 — which equates to more than 4.7 million children born to 3.5 million parents — which revealed that having a boy or girl is "essentially random," and there is no genetic link between a person and how many girls or boys they will have.

All family members were 'linked' and researchers examined whether "the sex of a person's children was associated with the sex of their brother or sister's children."

While there "are slightly more male births in general," Dr Brendan Zietsch from the University of Queensland's School of Psychology said in a statement, "We found individuals don't have an innate tendency to have offspring of one or the other gender."

"The chances are more like 51 to 49 of having a boy, but the genes of the mother and father don't play any role. These findings have crucial implications for biological and evolutionary theories of offspring sex ratios."

Things that were previously thought to be true about what influenced high concentrations of boys or girls in a family have been disproved by the large body of evidence.

Dr Zietsch said, "It was thought that rich or tall parents should have more boys and beautiful parents should have more girls. It was also thought that parents' hormone levels at the time of conception were important."

He suggested further research into "offspring sex ratio theory" was necessary in order to ascertain why variations occur.

"Our results rule out all these possibilities and suggest a rethink of offspring sex ratio theory is necessary to properly understand why offspring sex ratios appear to vary, for example, across countries."