Is it true that as many girls as boys are born on earth?
The spontaneous assumption that a pregnant woman is just as likely to give birth to a girl as she is to give birth to a boy. In reality, the probability of having a boy is slightly higher: on average, 105 boys are born for every 100 girls. We have no explanation for this fact.
In some societies, notably in Asia and Central Europe, the sex ratio at birth exceeds that 105 boys (for 100 girls) biological threshold, rising to approximately 120. This is due to a socio-cultural preference for boys.
However, excess male mortality over the course of life reverses the overrepresentation of boys at birth, leading generally to a overrepresentation of women in the upper age brackets.