Is it your fate to raise a son? Let's delve into the scientific findings.

In a groundbreaking study published in Science Advances, researchers led by Siwen Wang have delved into the intricate factors that contribute to the gender of offspring. The study, which analysed data from the Nurses' Health Study II and III, has shed light on various factors beyond biology that can influence the likelihood of having exclusively boys or girls.

The research involved 58,007 women who gave birth to 146,064 children, resulting in an average of 2.5 births per woman. The study found that factors such as the mother's age and genetics, the timing of conception, and the reproductive environment within the mother's body can all play a role in determining the gender of a child.

For instance, older maternal age at first birth increases the probability of having exclusively boys or girls in subsequent births. Additionally, a shorter follicular stage is linked to a higher chance of conceiving boys, while a longer stage is associated with conceiving girls. However, the mechanism behind these associations is not yet fully understood.

Interestingly, the study also found evidence for the "returning soldier effect," a well-documented phenomenon where there is an increase in the number of boys born after major wars. This suggests that external factors, such as stress levels and environmental conditions, may also have an impact on the gender of offspring.

However, the evidence for a biological predisposition for giving birth to one gender versus another is minimal due to the complexities of conducting research on human reproduction. For example, the father's influence was less clear or not accounted for in these studies. Some studies suggest that men who are taller, wealthier, or exhibit higher levels of aggression may be more likely to father sons, but the evidence is limited and controversial.

In a follow-up analysis, gender preference was shown to be a major driving force behind the trends observed in the original study. The preference for "one of each" isn't new and has been a factor in family planning decisions for a long time. In the 1800s, families were approximately 2 percent more likely to have a third child if their first two children were the same gender. In more recent years, this figure has increased to 6-7 percent.

Despite attempts to control for gender preference in the study, it was not quite enough to correct for this preference. This suggests that family patterns may not be entirely accidental and could hold clues to the complex interplay between biology, behavior, and reproduction.

Marcos Huerta, a data scientist and astrophysicist, conducted a separate analysis of the data and explained everything in it just with the preferences of when parents choose to stop. He believes that the data suggests that human reproduction may be more influenced by behavior and preferences than previously thought.

The study also found that elevated levels of cortisol in mothers, a marker of stress, have been tentatively associated with producing more daughters. However, this finding is still being researched and the evidence is not yet conclusive.

Worldwide, about 105 boys are born for every 100 girls, indicating a slight statistical edge for boys in birth ratios. This study provides valuable insights into the complex factors that contribute to this ratio and could potentially lead to a better understanding of human reproduction.