Men with more sisters are more likely to have daughters. Predicting Baby Gender Early
Researchers conducted a statistical survey of the histories of 927 families across Europe and North America, involving over 550,000 individuals. The findings revealed that men with more brothers were more likely to have sons, while those with more sisters were more likely to have daughters. This suggests that the ability to have sons or daughters may be inherited from the father.
Researchers suggest this finding may also help solve a historical puzzle: after World War I, the birth rate of male infants exceeded that of female infants by an average of two per 100 newborns.During wartime, fathers who were more likely to have sons had a lower probability of losing all their sons in combat, making it easier for the gene for producing sons to be passed down. Conversely, fathers who were more likely to have daughters had fewer sons to begin with; if their sons were killed in action, the ability to produce daughters could not be inherited.