We find out the real reason why more boys are born than girls - and it's pretty interesting

Mathematician Hannah Fry has explained why more baby boys are born, and why the levels of baby boys born peak immediately after a war or crisis

newborn baby next to mother
(Image credit: Getty Images)

More baby boys are born than baby girls, and mathematician Hannah Fry has explained just why that is. 

You’d be forgiven for thinking that the numbers of baby boys and baby girls born are basically equal. After all, we consider there to be a 50/50 chance of each when we’re expecting new arrivals – we can try to predict with this Chinese birth chart or the Nub Theory, but the gender itself is really just down to chance. 

However, mathematician Hannah Fry, who you might recognise from the BBC, has explained in a recent Instagram post that more baby boys are born than baby girls, and why. 

She says that a biologist told her – slightly morbidly – that slightly more boys being born was “evolution’s correction” for boys being more likely to get into accidents. 

However, the ratio can change dramatically over time, and peak in some interesting places. For example, at the end of a war, there’s an increase in the number of baby boys born. This isn’t something that’s unique to Britain, either – it happens all around the world. 

The most notable peaks in the UK over the last century or so occurred around 1919, 1945, and 1973. The First World War ended in 1918 and the Second ended in 1945, so this stands to reason. There was no such war around 1973, but it was a turbulent time for the country with an energy crisis and the three-day week. 

There are a number of theories that could explain this phenomenon. Fry’s personal favourite is that “God must be trying to replenish the male stock in the country,” but the actual reason, she says, is that “it turns out that the chances of a woman conceiving a male or female child actually very subtly change depending on when in her cycle she conceives.”

So if a woman conceives slightly earlier in her cycle, she’s very slightly more likely to have a baby boy. And, at the end of a war (or when there’s a three-day week, apparently) people have more sex than usual. Women get pregnant slightly earlier in their cycles, and consequently, more baby boys are born. 

In other fertility and conception news, here are 21 of the best foods for getting pregnant, and here’s our ovulation calculator to find out when you’re most fertile.

Freelance writer

Adam is an experienced writer who regularly covers the royal family and celebrity news for the likes of Goodto, The List, The Metro, and Entertainment Daily. However, you can also find Adam covering relationships, mental health, pet care, and contributing to titles such as Creative Bloq.