After major wars, more boys are born than girls. This pattern is called the Returning Soldier Effect, and it has been recorded in many countries after World War I, World War II, and other large conflicts. The shift is small, often less than one extra boy per 1,000 births, but it's consistent across large populations. After World War II in the US, male births rose from 51.4% to 51.48%, a subtle but statistically real increase. Why More Boys Are Born After War: Biological Changes. Some scientists believe the stress of war affects hormones in both men and women, which might increase the chances of conceiving boys. Population Rebalancing. One theory is that nature attempts to restore balance by producing more males to replace those lost in battle. Survivor Traits. Returning soldiers tend to be taller and healthier than average, and those traits are linked with a slightly higher chance of fathering boys. Marriage Boom. After war, birth rates surge as soldiers reunite with partners. Th...