It has been noted for centuries that more boys are born after major wars, scientists have even confirmed it. But the phenomenon remains a major mystery, no one can actually tell you why it happens. First observed by researchers in 1945 after World War II in the United States, it has been replicated in every nation that took part in a major war.
As you may have guessed it has been called The Returning Soldier Effect, and it is not the strangest phenomenon that has been observed after times of war. For example, in Britain after World War I, it was proven that the men who survived & came back to their wives were on average 1 inch taller than those who lost their lives. Another statistic that does not really make much sense, but nevertheless was prominent enough to be significant.
Doctors have published reports before that taller people seem to have more boys than daughters so, this is one theory that is put forth. Taller soldiers survive conflicts and therefore when returning to their countries after the war more sons are born.
But not many agree with this view and the phenomenon has confused thinkers & scientists for generations. Some put forth the argument that is is simply theological: a divine intervention for more boys to be born. Another theory, however, pins the explanation on a gene that both men & women carry but is only active in men. It is the gene that decides how many of a man’s sperm carry the X chromosome and how many carry the Y chromosome. If you have more Y sperm then genetically speaking you have a higher chance of fathering a boy.
So how does this tie into the argument of world wars cause more boys to be born? It comes down to a family’s genetic tree, a man with more brothers always has a higher chance of fathering a boy as on average he has more Y sperm. Mathematically speaking if 3 brothers go to war, you have a higher chance of one of them returning. This could be another reason why we witness The Returning Soldier Effect.