Through decades of data collection, scientists have observed a puzzling phenomenon known as the ‘returning soldier effect,’ where a greater number of male children are born during or immediately after a war. This trend was first identified in 1954, in the aftermath of World War II, when researchers noticed an unusual spike in the number of male children born to white parents in the United States. Ever since, the same pattern has been observed in other countries that have experienced wars.
Not Just a Coincidence
This gender imbalance, with approximately 104 boys born for every 100 girls, isn’t just a random occurrence. Countries such as France, Germany, Austria, Belgium, and Denmark have all seen this trend, particularly after the world wars. In fact, in 1920, soldiers returning from World War I fathered a record 1.1 million children, the highest number of births for that century, with a noticeable increase in the number of boys. But despite this well-documented phenomenon, there’s no globally accepted explanation for why it occurs.
A Theory as Old as Time
Interestingly, this effect was noticed long before the world wars. Pastor JP Süssmilch, back in the 1700s, observed from parish records that more boys were born during times of conflict. Süssmilch attributed this to divine intervention, suggesting that God was balancing the male population to compensate for war casualties. Although intriguing, this theory didn’t hold up under scientific scrutiny.
The Height Connection
One modern theory comes from psychologist Satoshi Kanazawa, who found that surviving soldiers from wars were, on average, taller than those who died in battle. According to Kanazawa’s hypothesis, taller men are more likely to have male offspring than shorter men. This could explain why more boys were born following the wars—surviving, taller soldiers returned home and fathered more male children.
Time of Conception Theory
Statistician Bill James proposes another theory based on conception timing. Research indicates that women who conceive earlier in their menstrual cycles have a slightly higher chance of giving birth to boys. When soldiers return from war, there may be a surge in sexual activity, leading to more pregnancies occurring earlier in the cycle. Though the variation is small on an individual basis, it could have a significant impact when looking at large-scale birth data.
No Definitive Answer Yet
While these theories are compelling, they remain speculative. The ‘returning soldier effect’ continues to be a mysterious phenomenon. More research is needed to pinpoint the biological or social factors driving this trend, but it certainly raises fascinating questions about human reproduction during times of conflict.
