You may have come across the idea that more boys are born after a war. It’s an effect that could be interpreted as divine intervention – a karmic response to men being lost in combat.
This shift in the sex ratio, however, isn’t limited to wars. Any significant stressful time in a nation’s history – such as earthquakes, famine or even a time of public mourning – can alter the rate at which boys are born.
In 2015, for example, research by Maltese paediatrician Prof Victor Grech indicated that the number of boys born in the UK took a temporary dip after the death of Princess Diana.
Some of these changes can be explained by the long-held association between stress and the rate of miscarriages. New research has found that miscarriage affects female foetuses slightly more often than male foetuses.
Why? It’s not completely clear.
But females appear to be more susceptible in the womb, especially during the first trimester and when recurrent miscarriages have taken place.
So, when miscarriages become more frequent due to longstanding stress – such as wartime – the sex ratio skews towards boys.
But there’s another reason why boy births may rise post-war: the overall birth rate tends to rise as soldiers return home. This can be crudely explained by partners having more sex.
But why more boys? Well, there’s a theory that boys are slightly more likely to be conceived at the start and end of the menstrual cycle, whereas girls are slightly more likely to be conceived in the middle.
And if couples are having sex more frequently, they’re marginally more likely to conceive at the start of the cycle (in the ‘boy’ phase), meaning by the middle of the month (the ‘girl’ phase), a pregnancy has already begun.
More sex, then, means slightly more boys.
The difference isn’t large enough to help those hoping to conceive a child of a particular sex, but across hundreds of thousands of births, it can nudge the overall sex ratio.
This article is an answer to the question (asked by Nicole Porter, via email) 'What is the returning soldier effect? Is it real?'
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